CA1262556A - Process for oxydehydrogenation of ethane to ethylene - Google Patents
Process for oxydehydrogenation of ethane to ethyleneInfo
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- CA1262556A CA1262556A CA000519021A CA519021A CA1262556A CA 1262556 A CA1262556 A CA 1262556A CA 000519021 A CA000519021 A CA 000519021A CA 519021 A CA519021 A CA 519021A CA 1262556 A CA1262556 A CA 1262556A
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Abstract
PROCESS FOR OXYDEHYDROGENATION OF ETHANE TO ETHYLENE
Abstract A process for the oxydehydrogenation of ethane to ethylene in a reation system of open series connected stages, includes changing the total water and acetic acid content in the output gaseous stream after at least one stage other than the last stage of the series.
D-14,080
Abstract A process for the oxydehydrogenation of ethane to ethylene in a reation system of open series connected stages, includes changing the total water and acetic acid content in the output gaseous stream after at least one stage other than the last stage of the series.
D-14,080
Description
5~
PROCESS FOR OXYDEHYDRO~ENATION OF EI'HANE TO ETHYLENE
~ield of the Invention The invention relates tb R process for the oxydehydrogena~ion of ethane to ethylene, and particulerly t~ a process which uses a series arrangement of st~ges.
ck~round of the Invention The pr~or art discloses processes for the oxydehydrogenation of eth~ne ~o e~hylene, but the processes disrlosed use a single fixed bed of catalyst.
In particular, the prlor ~rt discloses the oxydehydrogen~tion of ethane to ethylene uslng low temperature catalysts which catalytlcally act on mixture oE ethane and oxygen to produce ~n output g~seous stream comprlsing ethylene, acetic acid, unreacted eth~ne, unre~cted oxygen, snd other gsses such as CO ~nd CO2. Such c~talysts ~nd processes are disclosed ln the article entitled, "The Ox~dative Dehydrogenatlon of Ethane Ovier Catalysts Containi.n~ Mixed Oxides of Molybdenum and Vanadium"
by E~Mo Thorsteinson, T.P. Wilson, F.G. Young~ and P.H. Kasai, in _urn~l of Cstalysis, 52, p.p.
116-132 (1978). In addition, U.S. P~tent Number 4,250,346 discloses processes for low tempersture catalytic oxydehydrogen~tion of eth~ne ~o ethy:lene and dlscloses m~ny sultable catslysts.
Summarg of the Invention The present inventlon relates to a process for convertlng ethane to ethylene, in a re~ction D-14,080 ., : . . ..
..
5~
system comprlsing ~t le~st two stages oonnected in open continuDus series rel~tionship wlth eaoh other;
each st~ge comprising an oxydehydrogen~ting catalyst system malntained at conditlons for catalyticRlly oonvert~ng an input g~seous stre~m comprising ethane ~nd oxygen to ~n output gsseous stream having temperature greater than 250C and oomprising ethylene, ~cetic acid, w~ter, ethane, and oxygen;
and the process comprising oooling the output g~seous stream of each stR~e oth~r th,Qn the output gaseous stream of the last st~ge to a temperature less th~n about 250Cc for the introduotion ~f oxygen; ch2nging the total water ~nd ~cetlo acid content in the input gsseous stre~m of ~t least one stage with respect to the total water and acetic acld content in the output gsseous stream lmmediately preceding thRt stage; and supplyln~
oxygen to the input gRseous stream of e~ch st~lge when the input gaseous stre~m is at ~ temper~ture less thsn about 250~C ~nd ln ~n smount such thllt the total oxygen oontent of the input gaseous stre~m of each st~ge is less than ~bo~t 6 mole percent wLth : respect to ~he total input gaseous stream of that stsge.
In one preferred embodiment, a portion of both water ~nd acetle aold ~re removed from the outpu~ gaseous stream of ~t least one stage other than the last st~ge of the series. In Rnother preferred embodiment, w~ter in the form of ste~lm ls ~dded to the input gaseous stre~m of at le~st one stage other than the first stage of the series.
Brle DescriPtion of the Dr~win~s D-14,080 :, ~
Fig. 1 shows a typical graph of selectivity to both ethylene plus ~cetic scid versus conversion of eth~ne for oxydehydrogenaticn ~f ethane;
Flgs. 2A ~nd 2B show parsllel and series ~rr~ngements ~f st~ges or c~t~lytic beds;
Fi~. ~ shows a block dlsgram o a portion of a system which uses one embodiment of the ; inven~ion~
Fig. 4 shows 8 block di~gram of a portion of a system which u~es another embodiment o~ the invention;
Fig. 5 shows a block diagr~m of ~
commerci~1 system uslng the invention; and Fig. 6 shows ~ block di~ram of a pllot plant system used to obtain data relating to the invention.
Discussion of the Inventlon The inventlon en~bles ~he economical commercl~l productlon o~ ethylene and/or scetic acid. The process accordin~ to the invention utilizes ~ prior ~rt catalyst system such th~t ~n input gaseous stream comprising ethane and oxygen under re~ctlon conditions results ln an output g~seous stream comprising ethylene, ~cetic ~cid, ethane, oxygen, as well as other gases. For such cat~lysts or c~talyst systems, some of the stolchiometric equ~tions for the re~ctlons are as ~oll~ws:
C2~ + 1/2 ~2 -~ C2H4 ~ H20 C2H6 + 3/~ 2 ~~ CH3COOH ~ H20 ~2H6 ~ ~3/2 + X)02 ~~ 2CO~ + 3H20 D-14,08b x c 1 or 2 The ide~ s heats of reActions (600K) indlc~te the hlghly exothermic char~cter of the process:
Hc~h4 -24.59 kcal/g-mole C2H4 CH ~ H - -116 54 Xcal/g-mole a H~o ' -90.13 koal/g-mole C0 ~ HC02 ~ -157.92 kcal/g-mole C02 The measure of the usefulness of a catalyst is conveniently char~cterized by selectivity (eth~ne efficiency) to ethylene plus ~cetic acid~ and conversion of ethane. The flrst term provides the mole percent of ethylene plus &cetic acid produced wlth respect to the input stream of ethane while the second term provides the mole percent of carbon containing products produced by the c~talyst (excluding the ethane in the output gaseous stream~
with respect to the ethane in input gaseous stream.
In c~rrying out the labor~tory me~surements, measurements were made ln the ex~mples for the mole content of ethane, ethylene, ~ce~lc ~cid, C0, ~nd C2 in the output g~seous stream. These five components constitute ~he primary ca~bon containing products.
B~sed on this, the following equ~tions h~ve ~ 25 been used for c~lcul~t~ons ln the ex&mples:
: D-~4,080 ' .:: .
,.
Selectlvity ~ethane efficiency) to ethylene plusacetic scld ~-~C2H~] + tcH3cOOH]
~ ~2 3 / ~ ~ [ C2H4 ] + Z cH3coo Conversion of ethane ~
~ ]_ ~2~/2 + [C2H4} + [CH3COOH]
10~ x ---- ---- --- -- ---] [CO2]/2 + [~2H4] ~ [CH3COOH~ ~ [C2H6]
[ ] = moles ~C2H6] - moles of unconverted ethane Generally, the selectivity to ethylene plus acetlc ~cid ls approxim~tely linearly rel~ted to the conversion of ethane over the preferred operatln~
rallge. Fig. 1 shows ~ typical curve relating selectivity to ethylene plus ~cetlc acid to conversion of ethane for a single st~ge containing a single fixed bed of c~tslyst. From this curYe, it c~n be seen that selectivity to ethylene plus ~cetic acid declines wlth increasing ethane conversion from about 100 percent for about zero conversion of ethane.
The mole ratlo of ethylene to ~cetlc ~cid defines the relative yield of these products. It will be described herein, process steps for chl~nging this r~tio for use in 8 commercisl viable process ~cccrding to the lnventlon~ Thus, a commercisl process can be carried out to ~avor the production of ethylene ~t the expense of acetic ~cid or to f~vor the production of ~cetic acid ~t the exp~nse of ethylene.
D-14,080 It has now been deteirmined that ~
commercial vi~ble process for the oxydehydrogenat~on of ethane to ethylene would require more than one catalytic bed to achieve economical operations. In this connection, some definitions used in the ~rt will be considered. It c~n be seen that comblnation of stages or c~talytic beds can be generally a parallel ~rrangement or a series arrangement as shown in Figs. 2A and 2B, respect~vely.
A parallel arrangement as used hereln described an ~rrangement of stages or c~talytic beds in which the lnput gaseous stream of each stage or catalytic bed is ~ portion of a common input gaseous stream.
As used herein, a series arrangement of stages or catAlytic beds is ~n arrangement of stages or catalytic beds in which a portion of the output gaseous stream of the first st~ge or catslytic bed forms ~ psrt of the input gaseous stream of the second stage or catalytic bed ~nd each successive stage or catalytic bed is interconnected with the preceding st~ge or catalytic bed slmilarly; however, the portion of the output gaseous stream forming a part of the input gaseous stream of the success,ive ~$ stages or catalytic beds need not be identical.
The following is some b~ck~round informRtion with respect to a commercial process in general and partlcularly some of the par~meters which urge certain process steps according to the lnvention~
~-14,080 ,,~"
~ ;, 5~i . .
From an an~lysis of processes for ~onverting ethane to ethylene ~nd ~cetic ~c~d ~y c~talytic oxydehydrogenation, it h~s been detelrmined that ~ system prefer~bly shGuld hRve ~ conversion of eth~ne from sbout 10 peroent to ~bou~ 50 perce~ nd more prefer~bly ~bout 20 pPrcent to about 30 percent.
In order to opPrate such ~ process, consider~tion must be given to certa~n s~fety factors. It is known that the ~mount of oxygen in a gaseous stream cont~ining hydrocÆrbong ~nd at An elev~ted temperAture must be limited in order to avoid ignition. ~he "limiting oxygen value" is defined hereln 8S the oxygen mole concentrstion in gaseous mixture for which there is ~ 50 percent probabllit~ of h~ving combustion or burning re~lction in the gaseous mlxture under speciflc test conditions fifter exposlng the g~s mlxture to a positlve ignltlon source.
It has been determined from experiment~
; 20 designed to correlate to the lnstant proces~ that the oxygen content in ~n input gsseou~ stre&m cont~inin~ ethAne should be less than about 6 mole percent of the input g~seous stream.
The temper~ture at which oxygen is introduced intc the g~seous stream containing hydrocarbons must be less th&n the temperature for which ~utoignition can occur.
The "~utoignition temper~ture" of ~ g~s mixture, ~s defined hereln, is the temperature ~t which the g~s will ignite und ~ust~in the combustion in the absence Qf ~n external ignition sour e.
Autoignition i~ ~ complex thermel phenomenon which D-14,080 depends both Dn the propertles of the gas mixture ~nd on the characteristics of the system to which the gas ~s exposed. Auto1gnition can occur at the temperature for whlch there ls ~ thermal instabllity in the bal~nce between heat generated in the system by chemical re~ctions ~nd the hest transferred across the system boundaries. Thus, the autoignit~on temperature is dependent on the system and is not ~n inherent property of the gRS stream.
It has been determined from studies that there sre two necessary ~nd sufficient conditions for the ~utoignition tempereture. One condition is that the rste of heat gener~ted by the reactlon ~' equals the rate o~ heat tr~nsferred. The other is that the change in the rate of heat generated by the reaction wlth respect to the ch~nge in the oper~ting temperature of the re~ction is equAl to the ch~nge in the rate of heat transfer wlth respect to ch~nge in the temper~ture. These condit1Ons ~o constitute an lnstability because Any increase ln the tempersture in the reactlon will result in a corresponding incresse in the temper~ture of the gases so that the gas temperatures c~n increase exponentislly. This implies ~ potentiel runaw~y re~ction and potentially explosive situation.
As ~ result of experiment~tions ~nd evaluRtlons, it wss determined ~hat oxygen introduced lnto a g~seous stream oontain~ng eth~ne and possibly ethylene should be cArried out when the temperature of ~he gaseous stream is less th~n about 250~C.
D-14,0B0 ., ~
- 9 - ~
A s1ngle stage h~ving ~ conversion of ethane of gre~ter th~n about lO percent would be considered unsae due to the requlred mol@
concent~etion of oxygen. Furthermore, ~ parallel arr~ngement of stages cannok provide a conversion of ethane ln this range becauce the conversion o ethane is not ~dditive for a parallel ~rrangement.
A series ~rr~ngement of stages does, however, provide fl cumu~ative increase in the conversion of eth ne, The unreacted ethane from ~ny ~tage can be further converted in ~ubsequent stages. The oxygen for the conYersion can be supplled to each st~ge. Thus, the serles ~rrangement of stages enables the safe ~chlevement of the conversion o ethane for all levels.
Broadly, lf eAch st~ge provi~ed ~
conversion of eth~ne of flbout 8 percent or more, then three stages ~ould provide a conversion of ethane of about ~4 percent. There ~re, however, number of fsctors which must be considered wi~h respect to a series arrangement of stages. Some of the ~mportant factors will be considered herein.
It is prefereable to oper~te e~ch stage so that all of the oxygen in the input g~seous streRm is not consumed because if all of the oxygen is consumed in a stage~ the ethane can ~ct 8S a reduclng agent to the c~tslyst in th~t st~ge, thereby irreversibly dam~ging the cstalyst.
Preferably, the output gsseous stre~m of any stage contalns about 0.2 mole percent of oxygen.
; .
D-14,080 - 10 - `
Except for the first stage, the lnput g~seous streRm of e~ch stage comprlses eth~ne~
ethylene, ~cetic ~cid, CO, G02, water, snd g~ses which might be found in commercially av~ilable ethane. The effect of such an input gaseous stre~m on the perform~nce and lifetime of ~ c:at~lyst bed sui~able for carrying out the invention must be consldered in order to provide a commercial process which ls economicslly adv~ntageous. Commerci~l ethsne typically contains methane, prop~ne, snd tr~ce qusntitles of hydrogen sulfide, C02t and nitrogen. The methane h~s been found ~o be essentially unreact~ve in the presence of eth~ne, but propane has been found to be more reactive than ethane with most of lt goin~ to CO and C02 ~long wlth some amounts of propylene, ace~lc ~cid ~nd other oxygenates.
Propane consumes oxygen to ~ greater extent than ~ simil~r amount of moles of ethane. Thus, thE
Amount of prop~ne ln the feed must be considered with respect to the smount of oxygen required ~s well 8S the he~t release and g~s processing out of the last st~ge~ Any hydro~en sulfide present does not poison the cat~lyst but oxldlzes over the catRlyst and cont~minates the condensate in the g~s processing ~fter the lsst stage.
Experlment~ ~nd ~nalyses were carried out to establish r~te models for the rsactions which occur for the instsnt process.
The following important conclusions were determined as ~ resul~ of extenslve work:
tl) Ethylene lnhib~ts ethylene formstivn.
D 14,0BO
~, ,
PROCESS FOR OXYDEHYDRO~ENATION OF EI'HANE TO ETHYLENE
~ield of the Invention The invention relates tb R process for the oxydehydrogena~ion of ethane to ethylene, and particulerly t~ a process which uses a series arrangement of st~ges.
ck~round of the Invention The pr~or art discloses processes for the oxydehydrogenation of eth~ne ~o e~hylene, but the processes disrlosed use a single fixed bed of catalyst.
In particular, the prlor ~rt discloses the oxydehydrogen~tion of ethane to ethylene uslng low temperature catalysts which catalytlcally act on mixture oE ethane and oxygen to produce ~n output g~seous stream comprlsing ethylene, acetic acid, unreacted eth~ne, unre~cted oxygen, snd other gsses such as CO ~nd CO2. Such c~talysts ~nd processes are disclosed ln the article entitled, "The Ox~dative Dehydrogenatlon of Ethane Ovier Catalysts Containi.n~ Mixed Oxides of Molybdenum and Vanadium"
by E~Mo Thorsteinson, T.P. Wilson, F.G. Young~ and P.H. Kasai, in _urn~l of Cstalysis, 52, p.p.
116-132 (1978). In addition, U.S. P~tent Number 4,250,346 discloses processes for low tempersture catalytic oxydehydrogen~tion of eth~ne ~o ethy:lene and dlscloses m~ny sultable catslysts.
Summarg of the Invention The present inventlon relates to a process for convertlng ethane to ethylene, in a re~ction D-14,080 ., : . . ..
..
5~
system comprlsing ~t le~st two stages oonnected in open continuDus series rel~tionship wlth eaoh other;
each st~ge comprising an oxydehydrogen~ting catalyst system malntained at conditlons for catalyticRlly oonvert~ng an input g~seous stre~m comprising ethane ~nd oxygen to ~n output gsseous stream having temperature greater than 250C and oomprising ethylene, ~cetic acid, w~ter, ethane, and oxygen;
and the process comprising oooling the output g~seous stream of each stR~e oth~r th,Qn the output gaseous stream of the last st~ge to a temperature less th~n about 250Cc for the introduotion ~f oxygen; ch2nging the total water ~nd ~cetlo acid content in the input gsseous stre~m of ~t least one stage with respect to the total water and acetic acld content in the output gsseous stream lmmediately preceding thRt stage; and supplyln~
oxygen to the input gRseous stream of e~ch st~lge when the input gaseous stre~m is at ~ temper~ture less thsn about 250~C ~nd ln ~n smount such thllt the total oxygen oontent of the input gaseous stre~m of each st~ge is less than ~bo~t 6 mole percent wLth : respect to ~he total input gaseous stream of that stsge.
In one preferred embodiment, a portion of both water ~nd acetle aold ~re removed from the outpu~ gaseous stream of ~t least one stage other than the last st~ge of the series. In Rnother preferred embodiment, w~ter in the form of ste~lm ls ~dded to the input gaseous stre~m of at le~st one stage other than the first stage of the series.
Brle DescriPtion of the Dr~win~s D-14,080 :, ~
Fig. 1 shows a typical graph of selectivity to both ethylene plus ~cetic scid versus conversion of eth~ne for oxydehydrogenaticn ~f ethane;
Flgs. 2A ~nd 2B show parsllel and series ~rr~ngements ~f st~ges or c~t~lytic beds;
Fi~. ~ shows a block dlsgram o a portion of a system which uses one embodiment of the ; inven~ion~
Fig. 4 shows 8 block di~gram of a portion of a system which u~es another embodiment o~ the invention;
Fig. 5 shows a block diagr~m of ~
commerci~1 system uslng the invention; and Fig. 6 shows ~ block di~ram of a pllot plant system used to obtain data relating to the invention.
Discussion of the Inventlon The inventlon en~bles ~he economical commercl~l productlon o~ ethylene and/or scetic acid. The process accordin~ to the invention utilizes ~ prior ~rt catalyst system such th~t ~n input gaseous stream comprising ethane and oxygen under re~ctlon conditions results ln an output g~seous stream comprising ethylene, ~cetic ~cid, ethane, oxygen, as well as other gases. For such cat~lysts or c~talyst systems, some of the stolchiometric equ~tions for the re~ctlons are as ~oll~ws:
C2~ + 1/2 ~2 -~ C2H4 ~ H20 C2H6 + 3/~ 2 ~~ CH3COOH ~ H20 ~2H6 ~ ~3/2 + X)02 ~~ 2CO~ + 3H20 D-14,08b x c 1 or 2 The ide~ s heats of reActions (600K) indlc~te the hlghly exothermic char~cter of the process:
Hc~h4 -24.59 kcal/g-mole C2H4 CH ~ H - -116 54 Xcal/g-mole a H~o ' -90.13 koal/g-mole C0 ~ HC02 ~ -157.92 kcal/g-mole C02 The measure of the usefulness of a catalyst is conveniently char~cterized by selectivity (eth~ne efficiency) to ethylene plus ~cetic acid~ and conversion of ethane. The flrst term provides the mole percent of ethylene plus &cetic acid produced wlth respect to the input stream of ethane while the second term provides the mole percent of carbon containing products produced by the c~talyst (excluding the ethane in the output gaseous stream~
with respect to the ethane in input gaseous stream.
In c~rrying out the labor~tory me~surements, measurements were made ln the ex~mples for the mole content of ethane, ethylene, ~ce~lc ~cid, C0, ~nd C2 in the output g~seous stream. These five components constitute ~he primary ca~bon containing products.
B~sed on this, the following equ~tions h~ve ~ 25 been used for c~lcul~t~ons ln the ex&mples:
: D-~4,080 ' .:: .
,.
Selectlvity ~ethane efficiency) to ethylene plusacetic scld ~-~C2H~] + tcH3cOOH]
~ ~2 3 / ~ ~ [ C2H4 ] + Z cH3coo Conversion of ethane ~
~ ]_ ~2~/2 + [C2H4} + [CH3COOH]
10~ x ---- ---- --- -- ---] [CO2]/2 + [~2H4] ~ [CH3COOH~ ~ [C2H6]
[ ] = moles ~C2H6] - moles of unconverted ethane Generally, the selectivity to ethylene plus acetlc ~cid ls approxim~tely linearly rel~ted to the conversion of ethane over the preferred operatln~
rallge. Fig. 1 shows ~ typical curve relating selectivity to ethylene plus ~cetlc acid to conversion of ethane for a single st~ge containing a single fixed bed of c~tslyst. From this curYe, it c~n be seen that selectivity to ethylene plus ~cetic acid declines wlth increasing ethane conversion from about 100 percent for about zero conversion of ethane.
The mole ratlo of ethylene to ~cetlc ~cid defines the relative yield of these products. It will be described herein, process steps for chl~nging this r~tio for use in 8 commercisl viable process ~cccrding to the lnventlon~ Thus, a commercisl process can be carried out to ~avor the production of ethylene ~t the expense of acetic ~cid or to f~vor the production of ~cetic acid ~t the exp~nse of ethylene.
D-14,080 It has now been deteirmined that ~
commercial vi~ble process for the oxydehydrogenat~on of ethane to ethylene would require more than one catalytic bed to achieve economical operations. In this connection, some definitions used in the ~rt will be considered. It c~n be seen that comblnation of stages or c~talytic beds can be generally a parallel ~rrangement or a series arrangement as shown in Figs. 2A and 2B, respect~vely.
A parallel arrangement as used hereln described an ~rrangement of stages or c~talytic beds in which the lnput gaseous stream of each stage or catalytic bed is ~ portion of a common input gaseous stream.
As used herein, a series arrangement of stages or catAlytic beds is ~n arrangement of stages or catalytic beds in which a portion of the output gaseous stream of the first st~ge or catslytic bed forms ~ psrt of the input gaseous stream of the second stage or catalytic bed ~nd each successive stage or catalytic bed is interconnected with the preceding st~ge or catalytic bed slmilarly; however, the portion of the output gaseous stream forming a part of the input gaseous stream of the success,ive ~$ stages or catalytic beds need not be identical.
The following is some b~ck~round informRtion with respect to a commercial process in general and partlcularly some of the par~meters which urge certain process steps according to the lnvention~
~-14,080 ,,~"
~ ;, 5~i . .
From an an~lysis of processes for ~onverting ethane to ethylene ~nd ~cetic ~c~d ~y c~talytic oxydehydrogenation, it h~s been detelrmined that ~ system prefer~bly shGuld hRve ~ conversion of eth~ne from sbout 10 peroent to ~bou~ 50 perce~ nd more prefer~bly ~bout 20 pPrcent to about 30 percent.
In order to opPrate such ~ process, consider~tion must be given to certa~n s~fety factors. It is known that the ~mount of oxygen in a gaseous stream cont~ining hydrocÆrbong ~nd at An elev~ted temperAture must be limited in order to avoid ignition. ~he "limiting oxygen value" is defined hereln 8S the oxygen mole concentrstion in gaseous mixture for which there is ~ 50 percent probabllit~ of h~ving combustion or burning re~lction in the gaseous mlxture under speciflc test conditions fifter exposlng the g~s mlxture to a positlve ignltlon source.
It has been determined from experiment~
; 20 designed to correlate to the lnstant proces~ that the oxygen content in ~n input gsseou~ stre&m cont~inin~ ethAne should be less than about 6 mole percent of the input g~seous stream.
The temper~ture at which oxygen is introduced intc the g~seous stream containing hydrocarbons must be less th&n the temperature for which ~utoignition can occur.
The "~utoignition temper~ture" of ~ g~s mixture, ~s defined hereln, is the temperature ~t which the g~s will ignite und ~ust~in the combustion in the absence Qf ~n external ignition sour e.
Autoignition i~ ~ complex thermel phenomenon which D-14,080 depends both Dn the propertles of the gas mixture ~nd on the characteristics of the system to which the gas ~s exposed. Auto1gnition can occur at the temperature for whlch there ls ~ thermal instabllity in the bal~nce between heat generated in the system by chemical re~ctions ~nd the hest transferred across the system boundaries. Thus, the autoignit~on temperature is dependent on the system and is not ~n inherent property of the gRS stream.
It has been determined from studies that there sre two necessary ~nd sufficient conditions for the ~utoignition tempereture. One condition is that the rste of heat gener~ted by the reactlon ~' equals the rate o~ heat tr~nsferred. The other is that the change in the rate of heat generated by the reaction wlth respect to the ch~nge in the oper~ting temperature of the re~ction is equAl to the ch~nge in the rate of heat transfer wlth respect to ch~nge in the temper~ture. These condit1Ons ~o constitute an lnstability because Any increase ln the tempersture in the reactlon will result in a corresponding incresse in the temper~ture of the gases so that the gas temperatures c~n increase exponentislly. This implies ~ potentiel runaw~y re~ction and potentially explosive situation.
As ~ result of experiment~tions ~nd evaluRtlons, it wss determined ~hat oxygen introduced lnto a g~seous stream oontain~ng eth~ne and possibly ethylene should be cArried out when the temperature of ~he gaseous stream is less th~n about 250~C.
D-14,0B0 ., ~
- 9 - ~
A s1ngle stage h~ving ~ conversion of ethane of gre~ter th~n about lO percent would be considered unsae due to the requlred mol@
concent~etion of oxygen. Furthermore, ~ parallel arr~ngement of stages cannok provide a conversion of ethane ln this range becauce the conversion o ethane is not ~dditive for a parallel ~rrangement.
A series ~rr~ngement of stages does, however, provide fl cumu~ative increase in the conversion of eth ne, The unreacted ethane from ~ny ~tage can be further converted in ~ubsequent stages. The oxygen for the conYersion can be supplled to each st~ge. Thus, the serles ~rrangement of stages enables the safe ~chlevement of the conversion o ethane for all levels.
Broadly, lf eAch st~ge provi~ed ~
conversion of eth~ne of flbout 8 percent or more, then three stages ~ould provide a conversion of ethane of about ~4 percent. There ~re, however, number of fsctors which must be considered wi~h respect to a series arrangement of stages. Some of the ~mportant factors will be considered herein.
It is prefereable to oper~te e~ch stage so that all of the oxygen in the input g~seous streRm is not consumed because if all of the oxygen is consumed in a stage~ the ethane can ~ct 8S a reduclng agent to the c~tslyst in th~t st~ge, thereby irreversibly dam~ging the cstalyst.
Preferably, the output gsseous stre~m of any stage contalns about 0.2 mole percent of oxygen.
; .
D-14,080 - 10 - `
Except for the first stage, the lnput g~seous streRm of e~ch stage comprlses eth~ne~
ethylene, ~cetic ~cid, CO, G02, water, snd g~ses which might be found in commercially av~ilable ethane. The effect of such an input gaseous stre~m on the perform~nce and lifetime of ~ c:at~lyst bed sui~able for carrying out the invention must be consldered in order to provide a commercial process which ls economicslly adv~ntageous. Commerci~l ethsne typically contains methane, prop~ne, snd tr~ce qusntitles of hydrogen sulfide, C02t and nitrogen. The methane h~s been found ~o be essentially unreact~ve in the presence of eth~ne, but propane has been found to be more reactive than ethane with most of lt goin~ to CO and C02 ~long wlth some amounts of propylene, ace~lc ~cid ~nd other oxygenates.
Propane consumes oxygen to ~ greater extent than ~ simil~r amount of moles of ethane. Thus, thE
Amount of prop~ne ln the feed must be considered with respect to the smount of oxygen required ~s well 8S the he~t release and g~s processing out of the last st~ge~ Any hydro~en sulfide present does not poison the cat~lyst but oxldlzes over the catRlyst and cont~minates the condensate in the g~s processing ~fter the lsst stage.
Experlment~ ~nd ~nalyses were carried out to establish r~te models for the rsactions which occur for the instsnt process.
The following important conclusions were determined as ~ resul~ of extenslve work:
tl) Ethylene lnhib~ts ethylene formstivn.
D 14,0BO
~, ,
(2) Eth~ne promotes ethylene form~tlon.
(3) Temper~ure is ~ slgnlflcant $~ctor in each o~ the r~tes, an lncreRse in temperature increases the r~te o~
production of`e~hylene to a greater extent than the increasle in the rate of production of acetic ~cid.
~4) Both ethane and ethylenle prop~l the form~tlon of CO ~nd CO2.
(5~ Oxy~en is signlfic~nt in sll of ~he r~tes.
(6~ Water promotes the formation of scetic ~cid Rnd lnhibits the formation of ethylene.
(7) E~h~ne ~nd ethylene h~ve ~ slgnific~nt lmpact on the rate at which acetic acid ls ~ormed.
(8) C~t~lyst ~ge h~s ~ slgnific~nt effect on each of the rates; the rates decllne with increaslng c~t~lyst ~ge.
The experimentfltion and analysis establlshed th~t the output gaseous stream fro~ one st&ge can be used to form p~rt of the input g~seous stream o~ ~nother st~ge. Of course, oxygen must be ~dded ~s part of the input gQseous stream $or a stage subsequent to ~he ~lrst st~e~
The c~alyst bed oper~tes at e temperRture greater than about 250C 80 that the output gaseous stre~m is at ~ temper~ture gre~ter than ~bout 250C. Accordingly~ it ls essenti~l to cool the output gase~us stream to A temper~ture below 250~C
before introduclng oxygen to form the input gaseous stream of the subsequent st~ge in ~he ~eries connected st2ges.
D-14,080 , , .
"
...
.,' ,-, ~ ~
s~
Pure oxygen or sir can be used for the process. Oxygen c~n be supplled from an ~ir separ~tion unit. The use of ~r results in the necessity of separ~ting nltrogen from the output g~seous stream of the l~st stage during the recovery of the ethylenev Such 8 sepBration requires ~dditional costs over the cost of n ~ir sepsration unit.
~~ The interst~ge cooling of the gaseous stream provides ~n opportunity to carry ou~ one of several critical process steps According to the invention. Water in the form of steam can be introduced into the lnterstage system to incre~se the Rmount of water ln the input gaseous stream.
The addltion of w~ter into the input gflseous stresm lncreases the ~mount o oxygen which c~n be s~fely ~dded to the lnput gsseous stream because the s~fe limit of the oxygen is relAtlve to the entire mole content of the input gaseous stre~m, Furthermore, the addition of water lnGresses the y~eld of ~ce~ic acid wlth respect to ethylene because water promotes the r~te of formatlon o~ ~cet~c acid while inhibitin~ the rate of formation of ethylene.
rhe water in the form of steam ls preferably lntroduced into the output gfiseous streflm of 8 stage prior to introducing oxygen to form p~rt of the lnput g~seous stre~m of ~ subsequent s~ge.
Gener~lly, the ~mount of water introduced is between ~bout zero mole percent to about 10 mole percent ~nd prefer~bly from about 2 mole percent to ~bout 6 mole peroent of the input g~seou~ stream.
D-l~,OflO
.. .
Another broad embodiment of the invention festures the rem~v~l of water and ecetic acid from the output gaseous stream between st~pes. Although i~ ls only the w~ter which need be removed, invari~bly acetlc ~cid is removed. The remov~l of w~er ls accomplished by cooling the output gaseous stream until the water cond~nses. When the water condenses, the acetic ~cid wlll also condense bec~use of the acetic acid has ~ higher bollin~
point th~n w~ter.
~he remov~l of the water ~ends to change the distributlon of the productlon of products ln favor of ethylene at the expense of the ~cetic acid. That is, reducing the amount of w~ter in the input g~seous stream results in the ratio of ethylene to acetlc ~cld increAslng with respect to the situation in which the wAter ln the lnput gaseous stre~m is not reduced.
The implementation of the equipment to c~rry out the cooling of the ~utput gaseous stream is straightforward technolo~y. The use of ~ he~t exch~nger is common in the prior Rrt for cooling a gaseous stream. Some consider~tion should be ~iven to the extreme corrosive property of aqueous acetic acid ~t elevated temperatures. For thls reason, lt would be desir~ble to use pipes made of a material such as tit~nlum in the equlpment for whlch the condens&t~on of the acetic ~cid will t~Xe place.
Another sultable msterial is sold under the tr~demark of HASTELLOY C. Portions of the pipin~
for whioh only eQol~ng of ~he gaseous streams occurs can be made out of st~inless steel.
D-14,Q80 5~
The catalyst used in carrying out the instant process ~akes an input gaseous stream comprising ethane and oxygen and produces an output gaseous stream comprising ethylene, water, acetic acid, CO, CO2, ethane and oxygen. The ethane and oxygen are generally unreacted gases from the input gaseous stream. For the stages contemplated in carrying out the invention, the amount of unreacted oxygen in the output gaseous stream is about 0.2 mole percent.
Preferably, the process is operated at the pressures from about 1 to about 40 atmospheres, and more preferably from about 10 to about 25 atmospheres.
Preferably, the gas hourly space velocity (GHSV) per stage is from about 500 to about 6000 h 1, and more preferably from about 2000 to about 5000 h 1, Some references have already been cited herein for disclosures on suitable catalysts. In addition, U.S. Patent No. 4,524,236 (issued June 18, 1985) discloses a process for oxydehydrogenating ethane to ethylene in a single stage and includes a description of a class of catalysts suitable for the instant invention and, moreover, the catalysts described in that patent application are the catalysts preferable for carrying out the instant invention.
The patent application discloses a calcined catalyst having the following composition:
MoaVbNbcSbdxe X = at least one of the following:
D-14,080 ,, ~, s~
Li, Sc, Na, Be, Mg, ~, Sr, Ba, TiD
Zr, H~, Y, Ta, Cr, Fe, Co, Ni, Ce~
L~, Zn, Cd, Hg, Al, Ti, Pb, ~s, B~, Te, U, Mn, a~d W; ~nd ~ ~ 0.05 to ~.9 b ~ ~.1 to 0.4 c ~ 0.001 to 0.2 d - 0.001 to 0.1 e = 0.001 to 1.0 The vslues of R, b~ c, d, ~nd e constitute rei~tive gram-atoms of the elements Mo, V, Nb, Sb, and X, ~espectively. The elements ~re present ln combination with oxygen in the form of various oxides.
Generally, e solution is prepared of compounds o~ the metals selected ~or the cat~lyst, and either ~ particul~te catslyst is formed or ~
supported catslyst is formed. The most preferred cat~lyst hAs the following formul~tion:
Mol~V6 ~Nbl,gSbl~0C~1.0 ~he following is a description of the prepar~tion of the catRlysts prefersbly for use in CArrying out the instant lnvention.
A precursor solu~ion of the compounds of the met~ls selected is prepared.
Preferably, the molybdenum is introduced into the solution in the orm of ammonium salts ~uch ~s emmonium par~molybdste, or organic acld sal~s of molybdenum such as acetates, oxalstes, mandel~tes, ~nd glycol~tes. Other parti~lly wster ~oluble molybdenum compounds whlch m~y be used inelude D-14,080 , " ~:
molybdenum o~ldes, molybdic ~cid, ~nd chlvrides of molybden~m.
. Pre~er~bly, the vsnadium is 1ntroduced into thls solution ~n the form of ~mmonium salts such ~s ammonlum meta-van~d~te ~nd ammonlum dec~vanad,Qte, or or~nlc ~cid s~lts of v~nadium such ~s acet~tes, ox~lstes snd t~rtrates. P~rti~lly water soluble vanadium compounds such as vansdium oxides, ~nd sulf~tes of vanadium can be used.
Prefer~bly, the niobium and tantalum~ when used are in the form o$ ox~l~tes. Qther sources o:F
these metsls ~n soluble form include compounds in which the metal is coordinated, bonded or complexed to ~ beta-dlketonate, carboxylic acid, ~n ~mine, ~n alcohol, or/and ~lkanolamlne.
Preferably, the Qntimony is introduced into solution ln the ~orm of antlmony oxelate. Other soluble and insoluble compounds of antimony cAn be used such ~s sntlmony oxide and ~ntimony chloride.
The X component of the eat~lyst can be soluble or insoluble compoundsl prefersbly soluble.
Compounds which are strongly reducing may Rdversely affect the oxidation states of the metals.
The following are some preferable compounds for the X components. One is tit~nium in the form o~ ~ wster soluble chel~te coordin~ted with ammonium lactate, and others ~re titanium compounds in which the metal is coordlnsted, or complexed in ~
beta-diketonate, a c~rboxyllc acid, an ~mlne, an ~lcohol ~nd/or slk~nolamine. Generally, nitr~tes fire desirable ~lon~ with w~ter soluble c~loride~ snd organie acid s~lts such ~s acetates, oxal~tes, ~ 80 ,. ~
~ 3~
t~rtr~tes, l~ct~tes, s~llcyl~tes, formates, and carbon~tes. Preferred compounds for tungsten are ln the form of smmonlum salts such ~s ~mmonium parstungstste or other water soluble compounds suoh ~s tungstic ~clds.
The precursor solutlon is dried r~pidly ~nd the ~olids are he~ted ~n sir for about 5 hours ~t a temper~ture of ~bout 350~C to ~tiv~te the c~t~lystO
Prefer~bly, a supported cat~lyst is used.
It is prepared by the following general procedure.
The vanadium compound is mixed with water to form first mixture; the niobium compound and anti~ony compound ~re mlxed with wster to form a second mixture; and the molybdenum compound ls mixed with w~ter to form ~ third mixture. Any X compounds which ~re ammonium ~lts ~re mixed with the flrst mlxture. Otherwise, X compounds ~re mixed into the second mixture. The first ~nd second mixtures are heated and mixed sepsr~tely for ~bout fifteen ~o minutes; and then comb1ned ~nd mixed with he~tlng : for ~bout Eifteen minutes. The third mixture ls heated ~nd mlxed, ~nd then added to the comblned first ~nd second mixtures to form a precursor mixture. A~ter mixing ~nd heating of the precursor mixture for about fifteen minutes, the precursor mixture ls r2~dy for the next step, sep~ration ~f the water ~oluble portion of the mixture.
The sep~r~tlon c~n be csrried out slmply by decantlng the soluble portion or by filtering. The filtering c~n be csrried out using sintered glass~
or ~ p2per fllter with or without suction. Th~
soluble portion ls used to impregnate the support.
D-14,0~0 3~56 ~he support is dried rapidly ~n ~ir usually, but the drylng can be carrled out in ~n inert atmosphere.
The suitable supports includ~e sllic~, ~lumlnum oxide, silicon carbide, æ~rconia, titani~, and mlxtures thereof.
Preferably, the support has relatively low surf~ce ~re~, less th~n ~bout 1~ 0 square meter per grsm, and relstiYely large pores, med:L~n pore di~meter greater thsn i3bout 10 microns. Table I
shows ~ v~riety of commerci~lly Mvsilable suppor~s suit~ble for carrying out the lnvention.
D- 14, 080 ~ ~ ~ ";
5~
~D
~_ 'D` ~ ~ N
Z ~ O ~ O
~ O
~ ! ~
~ ~ ~ ~ o o c~ o c~ o 'D O
E ~ o ~ r~ o O O ~ ~ o 1~ C~ O
~:1 _~
~n ~ 08æ ~3 ææ8~08g o W
o _ t ~ ~ 8 ~ ~ ~ N ~.'~ ~1 ~ æ æ ~
~ ~ I Ir~ z N
U~ o 8 ~ ~ 8 ~
r ~
~ ~ ~ J ~ J ~ J J ~
~ ~ .^Q u ~ ~ O --- N ~ ~
t:~ _ = = = ~ 8 0~ ~ V O U~
~_ ~ ~ U~
~ O U~ O
_/ 9_ t~,~3 It is known that the catalyst undergoes ~n ~ging process during its use and this reaults ~n a decline ln the reactlon rates. C~talyst re~enerstion can be carried out to maint~ln the perEorm~nee of the cataly~t. The catalyst can be regenerated by oxidation wlth dilute oxygen such ~s S volume pereent oxygen and n~trogen ln situ ~t ~
temper~ture of ~rom about 350C to ~bout 400~C for from about one to about 24 hours, preEerably about 10 hours.
Fig. 3 shows a block di~gram of a portion of a proces sys~em incorpor~tlng one embodiment of the invention~
Fig. 3 ~how~ A system comprlsing thr~e reActors wlth interst~ge cooling to remove water and ~cetic ~cid. Ethane and oxygen comprlse the lnput gaseous stream to reactor 20. As used herein, 8 reactor comprlses at le~st one catalytic bed ~or the oxydehydrogenation o~ ethane to ethylene. A
plur~lity ~f c~talytic beds ~ithin a ~ingle reactor would be ~rranged pre~erabIy ~n parallel but could : be in series or ~ combination thereof. The reactor 20 ls pre~erably ~n ~rrangement o~ tubes each containing ~ catalyst bed w~th the tubes enclosed in a shell to provide temperature control. 5uch an arrangement in ~he art i8 re~erred to a~ a "shell and tube geome~ry~'. Typically, ~he tube can h~ve sn inside di~meter of sbout 2.5 to about 4.0 centlmeters and a length o~ from sbout 6 to ~bout 12 meters. Each ~hell would cont~in ~s msny tubes as needed for the deslred production c8pacit~ . The tubes sre in 8 par~llel arr~ngemen~ with each t~
other. The l~se of sep~rste tubes within th shell is advantageous for temperature control in the tubes. The lnput g~seous ~trQam is dlvided into the tubes ~nd a 11quid such ~s the tr~demark DOWTH~RM A
sold by Dow Chemical Comp~ny circulstes ~round the tubes and within the shell to maintain the oper~ting temper~ture. The prim~ry component of DOWTHERM A is diphenyl ether. Another suit~ble liquid for maintaining the temperature ls ~ mixture of isomer~c dibenzyl benzenes ~uch as a product sold under the trademarX MAR~OTHERM S by Chemische Werke Huls AG.
Other llquids which ~ppear to be suitable bssed on their bo~ling temperatures at stmospheric pressure include tetr&cont~ne and pent~tricontane. In Qdd~tion, molten s~lts can be used.
Typically, the gas hourly space velocity (GHSV) for the reactor 20 ls from about 2000 to _l ~bout 5000 h . The pressure is from about 10 to ~bout 20 atmospheres with ~n lnpu~ oxy~en content of about 6 mole percent of the entire input gaseous s~ream. The output gaseous stre~m 21 contalns unre~cted ethane, unreacted oxygen, ethylene, ~cetic acid, and other gases such ~s ~ases which were present in the eommerci~l eth~ne and gsses produced by the reactlon such ~s CO ~nd CO2. The output gaseous streAm 21 eommunieates to cooling means 22 which simply cools the output g~seous stream 21 so that the weter and acetic acid in output g~seous stre~m 21 condense. As pointed out, the condens~te c~n be extremely corrosive so th~t the m~ter~ls used should be ~elec~ed to reslst the c~rroslon.
Portions of the equipment exposed to hot condens~ng D-14,0B0 , ,.
~ce~ic ~cld ~vapors can be f~bricated ~rom ti~nlum or HASTELLOY C. Portions ~f the equi.pment ln contact with cool 801ution8 of ~cetic ~cid can be m~de out of t~inless ~teel. Equipment whlch will be exposed to ~cetic acid vapors at high temperatures such ~s the reRctor tubes can be abrlcAted from c~rbon steel.
The choice of material~ used should be selected to avoid catalyst poisons. For example, metcls such as iron and nickel csn react with CO
under cert~in conditions to produce volstlle met~l csrbonyls. The metsl carbonyls c~n be decomposed over the c~tfllyst to deposit metal oxides on ~he c&talyst surface ~nd thereby alter the activity and perform~nce of the catalyst.
The cooling means 22 c~n be a he~t exchsnger or any other well known prior art equlpment for cooling the water snd acetic ~cid ~o that they condense. The water ~nd ~cetic acid ~re removed fr~m cooling mean~ 22 ~nd the remainlng gas is combined wlth ox~gen to ~orm the lnput g~se~us stream 23 whlch enters react~r 24. Re~ctor 24 ls essentially the same as re~ctor 20.
The reactor 24 produces ~n output gaseous stream 25 which enters c~oling me&ns 26 which is simllar to cooling means 22. After the water and Qcetic acid h~ve been removed the remaining g~s in coollng me~ns 26 is combined with oxygen to form input g~seous stream 27 into reactor 28. Reactor 28 is similar to re~ctor 23. The reactor 28 produces ~n output g~seous stre~m 29.
~-14,08~
5~ ~
- ~3 - -The OUtpllt g~seous stream 29 includes ethylene, ethRnei oxygen, ~cetic ~cld, w~er, ~nd some other ~ases 8S indicsted above.
For convenience, ~s used herein the term "stage" comprises ~ reactor for catalytic~lly oxydehydrogen~lng eth~ne to ethylene. The "l~st sta~e" referred ~o herein ls the "outpu~ st~ge1' in accord~nce with common pr~ctlce in the process art.
Also, system components such as the cooling means 22 is lnterstage equipment in ~ccordance with comm3n practice in the process ~rt.
Another impnrt~nt embodiment is sho~n in ~ig. 4. Eth~ne, oxygen ~nd weter in the form of steam enter re~ctor 30 to produce ~n output gaseous stre~m 31 whlch enters coollng me~ns 32. Coollng me~ns 3~ reduces the temper~ture of the output g~seous stream 21 to a temp0rature below about 2504C
so th6t oxygen of less then about 6 mole percent c~n be introd~ced s~fely. The input g~seous stream 33 including ~dded oxygen ~nd water in the form of ste~m enters re~c~or 34 to produce ~n output gas~ous stre~m 35. The output gaseous stream 35 enters the cooling means 36 which i~ similar to cooling means 32. The output gaseous s~re~m 35 ls cooled to less than ~bout 250C and oxygen and water in ~he form of steAm are lntroduced to produce ~n input g~seous stre~m 37 which enters ~eActor 38 to produce an output g~seous streRm 39~
The sys~ems shown ln Flgs. 3 and 4 in rel~tionship to ~n over~ll commercisl system is hown ln simplified form in Fig. 5. In Fig. 5p the EO~H re~ct~on system ~0 corresponds to essenti~lly D-1~,080 5~ ~
- 2~ - -all of the b~locks shown in elther Figo 3 or Fig. 4.
Oxygen is supplied to the EODH reactlon system 40 from ~n ~ir sep~r&tion unit 41. The eth~ne into the EODH re~ction system 40 comprises recycled ethane from unit 46 ~nd eth~ne from the dlstill~tion column 42 wh~ch separ~tes ou~ propane which m~y be present in the commercial eth~ne. The output of the EODH
reaction system 40 goes to a æcrubber 43 which sep~r~tes out the aqueous ficetic acid. The g~ses from the scrubber 43 go to a compressor 44 ~nd ~hen to U71i L 45 which sep&rates out CO2. Unit 45 is ~
prior art unit whlch could comprise a portlon which ~bsorbs CO2 with ~ solven~ such as ~lk~nol~mine ~ollowed by a stripper whlch removes the ~bsorbed CO2. The gases then pRSS to unit 46 whlch contains distilletion columns for separ~ting Ollt ethylene~ eth~ne, And v~rious i'llghts" such ~s 2' N2, CO and CH4. The ethane from unit 46 ls recycled to the EODH re~ction system 40. The ~qu~ous ~cetic ~cid from the scrubber 43 goes through ~n ~cetic acid refining unit 4~ which separates out water ~nd ~cetlc acid.
~ 2-stage pllo~ pl~nt was ~ullt ~nd operated. E~ch re~ction st~ge is a tube hsving dimenslons contemplated ~s being suit~ble for comm~rcisl oper~tions. The capability to feed gases such as steam, ace~ic 8cid, ethylene, CO, and CO2 together with eth~ne ~nd oxygen enabled the simulstion of any two series connected stages in a multlst~ge open series ~rrAngement.
Fig. 6 shows ~ block di~gram of the pilot pl~nt used.
D-14,080 ~ 5 Each re~ctor 60 and 61 comprised a tube ~bout 7.62 meters long having ~n ~nside diameter oE
about 2.6 em~ The bottom 1.8 meters of t~e tube w~s packed wlth gla~s be~d~ hsv~ng ~n ~versge diameter of about .6 cm. The g~ass beads served ~s a secondary prehç~ting ~ect~on for rslsing the Eeed gases to the reaction temperature. The tube ~as packed with about 4.6 meters o~ a catslyst ~nd the remainlng portion of the tube was packed with gl~s,s besds of the ~ype used in the bottom portion. The reaction temperature was controlled by circulating a heat transfer ~luid through a ~acket around the tube. The transEer fluld used was MARLOTHERM S.
The c~talyst used had the Eollowing gram-atom rfltios:
lS Mol6 V6 8 Nbl.g ~bl~o Cal.0 Support 12 of T~ble 1 was u~ed. The gases 2' N2- G2H6~ C2H4. CO, ~nd CO2 w supplied through respective m~ss ~lowmeters 62~
These gases were preheated ln heating unit 63 pr~or to belng supplied to the re~ctor 60. Any wster or aqueous ~cetic 8cid belng supplied to a reactor 60 was vaporized in a heating un~t 64. The hot heat transfer Eluid was circulated through the re~ctors 60 snd 61 with unit 65 which also controlled the temperature wlthin ~ preset range.
The output gaseous stream ~rom the reactorx 60 ~nd 61 were cooled in ~he respective coolin~
me~ns 66. The respective output gaseous streams were then p~ssed to a separator unit 67 which was used to separate ~nd accumulate ~queous ~cet~c ~cid from the gas stre~m. Oxygen was in~ected between the st~ge,s ln sccordance with the lnven~ion.
D-14,080 ,, - ~6 -The input ~nd output gaseous stre~ms of the reactors 60 ~nd 61 were an~lyzed us~ng g8S
chromatographs.
The pilot plant ~hown in Fig. 6 had only two stages; howeverg the d~ta were collected to simulate more ~hsn ~wo ~t~ges and enabled a oomputer simulation of systems having more th~n two st~ges.
EXAMPLES
The Ex~mples were e~rrled ou~ to compRre operations with and without the invention.
EX~MPLE 1 A 2-st~ge series connected system ~a~ -~
evaluated in the pilot pl~nt for operation wi~.h ~nd without inter~tage remov~l o~ water ~nd acetic ~cld (aqueous scetic ~cid). For e~ch case> ~bout 6 mole percent of oxygen w~s used For e~ch stage. T~bles 2 snd 3 correspond respectively to the operation of the 2-st~ge ~ystem wlth and without ~he inter~t~ge removal of water snd ~cetic ~cid. For ~ble 2, ~he total output ~ncludes the g~seous output stre~m ~f stage 2 ~nd ~lsv the H2O and C~13COOH removed before stage 2. The CH3COOH system selectivlty is for the total CH3COOH ~rom both the interst~ge removal and the outpu~ o~ st~ge 2 D-14, 08û
- 2~ -INTERSTAGE REMOVAL OF IdATE:R
AND: ACET l C P~C I 1) FOR 2 - ';TAGES
_COMPOSITIOII IN MOLE PERCENT
, I NPUT STAGE 1TOTAL O~ITPUT
~2~6 ~3.83 7~.63 2 5.93 1.44 ~,O~ 0.~5 0.5 ~2H4 O 7 . 66 CH3COOH 0 l. 5 H20 0 11. 25 CO, ~ Q.~8 About 987~ of H20 removed interst~ge.
SYSTEM ETHANE CONVERSION ~ 11. 41 C2H~ SYSTEM SELECTIVITY = 78 . 3 CH3COOH SYSTEM SELE~TIVITY = 15. 8 : ~ D-~4,0B0 . ....
:
. .
. , TABLE: 3 NO INTERSTAGE: REMoVAL OE' WATER
AND ACETIC ACID ~ FOP~ 2-STAGES
. COMPOSITION IIJ l~llOLE lPERCl~:NT
~INPUT STAGE: lOUTPUT STAGE 2 C2~i~;, 93.~7 76.8~
2 So~B 1~28 ~0 0~25 ~i7 . 2 C2H4 0 7 ~ 37 GH3~00H O 1. 6 2 H20 0 ll o 24 ~0 0 O.g8 SYSTEM ETHANE CONVERSION = 11. 27, C2H~ SYSTEM SELECTIVITY = 76 . 0 CH3COOH SYSTE?I SELECTIVITY = 16 . 6 From Tables 2 and 3, i~ can be ~pprec~a~ed that the 2-~tRge system wlth ~nterstage removal of water ~nd ~cetlc ~cid had a lhigher ethylene sys~em selectiv~ ty ~nd ~ lower ~cetic acld sy~tem selectivity ~s comp~red to the 2-ætage system which d~ d not hsve inters~ge remov~l o~ ws~er ~nd ~ce~ic ~c id .
thls Example, ~ 4-stage series c~nneeted sy~tem w~ ulated. The simu~t~n w~s c~rried out w~th ~nd wi'chou'c the removal of w~er ~nd ~ce~ic ~cid in the lnterst~ges . For ~eh run ~ f ixed D O ~B O
:
5~3~
eth~ne input to the first stagc was assumed and the oxygen input to each st~ge was taken AS sbout 5 mole percent of the lnput g~seous stream of that sthge.
The temper~ture of ~he inpu~ ~aS20US streaM of e~ch s~age was ad~usted to produre an opera~lng temperature for which the output gaseous stream includ~d ~bou~ a . ~ mole percent oxygenO
Removing water and acetic acid from the output g~seous stream of a st~ge reduces the flow rate of the inpu~ gaseous stream ~o the subsequen~
sta~s~ Th~s results in the subsequent stages having relatively lower oper~ting temperatur~s ~s compared to ~ system wlthout the removal of wflter.
The lower temperatures would tend to reduce the rate of productlon of ethylene relatlve to the rflte of production of ~cetlc acid. Nevertheless, a higher system selectivl~y to ethylene is obtained for process for which there is interstage removal of ~ater.
For such a system, Table 4 shows the system outpu~ composlt~on with ~nd wlthout the remov~l of water ~nd acetic acld ~f~er each of the intermediate stagesO For the interstage removal of water ~nd acetic ~cid, Table 4 shows cRlculations based on ~otal water ~nd acetlc acid out of all of the stsges.
D-14,080 TA~L 4
production of`e~hylene to a greater extent than the increasle in the rate of production of acetic ~cid.
~4) Both ethane and ethylenle prop~l the form~tlon of CO ~nd CO2.
(5~ Oxy~en is signlfic~nt in sll of ~he r~tes.
(6~ Water promotes the formation of scetic ~cid Rnd lnhibits the formation of ethylene.
(7) E~h~ne ~nd ethylene h~ve ~ slgnific~nt lmpact on the rate at which acetic acid ls ~ormed.
(8) C~t~lyst ~ge h~s ~ slgnific~nt effect on each of the rates; the rates decllne with increaslng c~t~lyst ~ge.
The experimentfltion and analysis establlshed th~t the output gaseous stream fro~ one st&ge can be used to form p~rt of the input g~seous stream o~ ~nother st~ge. Of course, oxygen must be ~dded ~s part of the input gQseous stream $or a stage subsequent to ~he ~lrst st~e~
The c~alyst bed oper~tes at e temperRture greater than about 250C 80 that the output gaseous stre~m is at ~ temper~ture gre~ter than ~bout 250C. Accordingly~ it ls essenti~l to cool the output gase~us stream to A temper~ture below 250~C
before introduclng oxygen to form the input gaseous stream of the subsequent st~ge in ~he ~eries connected st2ges.
D-14,080 , , .
"
...
.,' ,-, ~ ~
s~
Pure oxygen or sir can be used for the process. Oxygen c~n be supplled from an ~ir separ~tion unit. The use of ~r results in the necessity of separ~ting nltrogen from the output g~seous stream of the l~st stage during the recovery of the ethylenev Such 8 sepBration requires ~dditional costs over the cost of n ~ir sepsration unit.
~~ The interst~ge cooling of the gaseous stream provides ~n opportunity to carry ou~ one of several critical process steps According to the invention. Water in the form of steam can be introduced into the lnterstage system to incre~se the Rmount of water ln the input gaseous stream.
The addltion of w~ter into the input gflseous stresm lncreases the ~mount o oxygen which c~n be s~fely ~dded to the lnput gsseous stream because the s~fe limit of the oxygen is relAtlve to the entire mole content of the input gaseous stre~m, Furthermore, the addition of water lnGresses the y~eld of ~ce~ic acid wlth respect to ethylene because water promotes the r~te of formatlon o~ ~cet~c acid while inhibitin~ the rate of formation of ethylene.
rhe water in the form of steam ls preferably lntroduced into the output gfiseous streflm of 8 stage prior to introducing oxygen to form p~rt of the lnput g~seous stre~m of ~ subsequent s~ge.
Gener~lly, the ~mount of water introduced is between ~bout zero mole percent to about 10 mole percent ~nd prefer~bly from about 2 mole percent to ~bout 6 mole peroent of the input g~seou~ stream.
D-l~,OflO
.. .
Another broad embodiment of the invention festures the rem~v~l of water and ecetic acid from the output gaseous stream between st~pes. Although i~ ls only the w~ter which need be removed, invari~bly acetlc ~cid is removed. The remov~l of w~er ls accomplished by cooling the output gaseous stream until the water cond~nses. When the water condenses, the acetic ~cid wlll also condense bec~use of the acetic acid has ~ higher bollin~
point th~n w~ter.
~he remov~l of the water ~ends to change the distributlon of the productlon of products ln favor of ethylene at the expense of the ~cetic acid. That is, reducing the amount of w~ter in the input g~seous stream results in the ratio of ethylene to acetlc ~cld increAslng with respect to the situation in which the wAter ln the lnput gaseous stre~m is not reduced.
The implementation of the equipment to c~rry out the cooling of the ~utput gaseous stream is straightforward technolo~y. The use of ~ he~t exch~nger is common in the prior Rrt for cooling a gaseous stream. Some consider~tion should be ~iven to the extreme corrosive property of aqueous acetic acid ~t elevated temperatures. For thls reason, lt would be desir~ble to use pipes made of a material such as tit~nlum in the equlpment for whlch the condens&t~on of the acetic ~cid will t~Xe place.
Another sultable msterial is sold under the tr~demark of HASTELLOY C. Portions of the pipin~
for whioh only eQol~ng of ~he gaseous streams occurs can be made out of st~inless steel.
D-14,Q80 5~
The catalyst used in carrying out the instant process ~akes an input gaseous stream comprising ethane and oxygen and produces an output gaseous stream comprising ethylene, water, acetic acid, CO, CO2, ethane and oxygen. The ethane and oxygen are generally unreacted gases from the input gaseous stream. For the stages contemplated in carrying out the invention, the amount of unreacted oxygen in the output gaseous stream is about 0.2 mole percent.
Preferably, the process is operated at the pressures from about 1 to about 40 atmospheres, and more preferably from about 10 to about 25 atmospheres.
Preferably, the gas hourly space velocity (GHSV) per stage is from about 500 to about 6000 h 1, and more preferably from about 2000 to about 5000 h 1, Some references have already been cited herein for disclosures on suitable catalysts. In addition, U.S. Patent No. 4,524,236 (issued June 18, 1985) discloses a process for oxydehydrogenating ethane to ethylene in a single stage and includes a description of a class of catalysts suitable for the instant invention and, moreover, the catalysts described in that patent application are the catalysts preferable for carrying out the instant invention.
The patent application discloses a calcined catalyst having the following composition:
MoaVbNbcSbdxe X = at least one of the following:
D-14,080 ,, ~, s~
Li, Sc, Na, Be, Mg, ~, Sr, Ba, TiD
Zr, H~, Y, Ta, Cr, Fe, Co, Ni, Ce~
L~, Zn, Cd, Hg, Al, Ti, Pb, ~s, B~, Te, U, Mn, a~d W; ~nd ~ ~ 0.05 to ~.9 b ~ ~.1 to 0.4 c ~ 0.001 to 0.2 d - 0.001 to 0.1 e = 0.001 to 1.0 The vslues of R, b~ c, d, ~nd e constitute rei~tive gram-atoms of the elements Mo, V, Nb, Sb, and X, ~espectively. The elements ~re present ln combination with oxygen in the form of various oxides.
Generally, e solution is prepared of compounds o~ the metals selected ~or the cat~lyst, and either ~ particul~te catslyst is formed or ~
supported catslyst is formed. The most preferred cat~lyst hAs the following formul~tion:
Mol~V6 ~Nbl,gSbl~0C~1.0 ~he following is a description of the prepar~tion of the catRlysts prefersbly for use in CArrying out the instant lnvention.
A precursor solu~ion of the compounds of the met~ls selected is prepared.
Preferably, the molybdenum is introduced into the solution in the orm of ammonium salts ~uch ~s emmonium par~molybdste, or organic acld sal~s of molybdenum such as acetates, oxalstes, mandel~tes, ~nd glycol~tes. Other parti~lly wster ~oluble molybdenum compounds whlch m~y be used inelude D-14,080 , " ~:
molybdenum o~ldes, molybdic ~cid, ~nd chlvrides of molybden~m.
. Pre~er~bly, the vsnadium is 1ntroduced into thls solution ~n the form of ~mmonium salts such ~s ammonlum meta-van~d~te ~nd ammonlum dec~vanad,Qte, or or~nlc ~cid s~lts of v~nadium such ~s acet~tes, ox~lstes snd t~rtrates. P~rti~lly water soluble vanadium compounds such as vansdium oxides, ~nd sulf~tes of vanadium can be used.
Prefer~bly, the niobium and tantalum~ when used are in the form o$ ox~l~tes. Qther sources o:F
these metsls ~n soluble form include compounds in which the metal is coordinated, bonded or complexed to ~ beta-dlketonate, carboxylic acid, ~n ~mine, ~n alcohol, or/and ~lkanolamlne.
Preferably, the Qntimony is introduced into solution ln the ~orm of antlmony oxelate. Other soluble and insoluble compounds of antimony cAn be used such ~s sntlmony oxide and ~ntimony chloride.
The X component of the eat~lyst can be soluble or insoluble compoundsl prefersbly soluble.
Compounds which are strongly reducing may Rdversely affect the oxidation states of the metals.
The following are some preferable compounds for the X components. One is tit~nium in the form o~ ~ wster soluble chel~te coordin~ted with ammonium lactate, and others ~re titanium compounds in which the metal is coordlnsted, or complexed in ~
beta-diketonate, a c~rboxyllc acid, an ~mlne, an ~lcohol ~nd/or slk~nolamine. Generally, nitr~tes fire desirable ~lon~ with w~ter soluble c~loride~ snd organie acid s~lts such ~s acetates, oxal~tes, ~ 80 ,. ~
~ 3~
t~rtr~tes, l~ct~tes, s~llcyl~tes, formates, and carbon~tes. Preferred compounds for tungsten are ln the form of smmonlum salts such ~s ~mmonium parstungstste or other water soluble compounds suoh ~s tungstic ~clds.
The precursor solutlon is dried r~pidly ~nd the ~olids are he~ted ~n sir for about 5 hours ~t a temper~ture of ~bout 350~C to ~tiv~te the c~t~lystO
Prefer~bly, a supported cat~lyst is used.
It is prepared by the following general procedure.
The vanadium compound is mixed with water to form first mixture; the niobium compound and anti~ony compound ~re mlxed with wster to form a second mixture; and the molybdenum compound ls mixed with w~ter to form ~ third mixture. Any X compounds which ~re ammonium ~lts ~re mixed with the flrst mlxture. Otherwise, X compounds ~re mixed into the second mixture. The first ~nd second mixtures are heated and mixed sepsr~tely for ~bout fifteen ~o minutes; and then comb1ned ~nd mixed with he~tlng : for ~bout Eifteen minutes. The third mixture ls heated ~nd mlxed, ~nd then added to the comblned first ~nd second mixtures to form a precursor mixture. A~ter mixing ~nd heating of the precursor mixture for about fifteen minutes, the precursor mixture ls r2~dy for the next step, sep~ration ~f the water ~oluble portion of the mixture.
The sep~r~tlon c~n be csrried out slmply by decantlng the soluble portion or by filtering. The filtering c~n be csrried out using sintered glass~
or ~ p2per fllter with or without suction. Th~
soluble portion ls used to impregnate the support.
D-14,0~0 3~56 ~he support is dried rapidly ~n ~ir usually, but the drylng can be carrled out in ~n inert atmosphere.
The suitable supports includ~e sllic~, ~lumlnum oxide, silicon carbide, æ~rconia, titani~, and mlxtures thereof.
Preferably, the support has relatively low surf~ce ~re~, less th~n ~bout 1~ 0 square meter per grsm, and relstiYely large pores, med:L~n pore di~meter greater thsn i3bout 10 microns. Table I
shows ~ v~riety of commerci~lly Mvsilable suppor~s suit~ble for carrying out the lnvention.
D- 14, 080 ~ ~ ~ ";
5~
~D
~_ 'D` ~ ~ N
Z ~ O ~ O
~ O
~ ! ~
~ ~ ~ ~ o o c~ o c~ o 'D O
E ~ o ~ r~ o O O ~ ~ o 1~ C~ O
~:1 _~
~n ~ 08æ ~3 ææ8~08g o W
o _ t ~ ~ 8 ~ ~ ~ N ~.'~ ~1 ~ æ æ ~
~ ~ I Ir~ z N
U~ o 8 ~ ~ 8 ~
r ~
~ ~ ~ J ~ J ~ J J ~
~ ~ .^Q u ~ ~ O --- N ~ ~
t:~ _ = = = ~ 8 0~ ~ V O U~
~_ ~ ~ U~
~ O U~ O
_/ 9_ t~,~3 It is known that the catalyst undergoes ~n ~ging process during its use and this reaults ~n a decline ln the reactlon rates. C~talyst re~enerstion can be carried out to maint~ln the perEorm~nee of the cataly~t. The catalyst can be regenerated by oxidation wlth dilute oxygen such ~s S volume pereent oxygen and n~trogen ln situ ~t ~
temper~ture of ~rom about 350C to ~bout 400~C for from about one to about 24 hours, preEerably about 10 hours.
Fig. 3 shows a block di~gram of a portion of a proces sys~em incorpor~tlng one embodiment of the invention~
Fig. 3 ~how~ A system comprlsing thr~e reActors wlth interst~ge cooling to remove water and ~cetic ~cid. Ethane and oxygen comprlse the lnput gaseous stream to reactor 20. As used herein, 8 reactor comprlses at le~st one catalytic bed ~or the oxydehydrogenation o~ ethane to ethylene. A
plur~lity ~f c~talytic beds ~ithin a ~ingle reactor would be ~rranged pre~erabIy ~n parallel but could : be in series or ~ combination thereof. The reactor 20 ls pre~erably ~n ~rrangement o~ tubes each containing ~ catalyst bed w~th the tubes enclosed in a shell to provide temperature control. 5uch an arrangement in ~he art i8 re~erred to a~ a "shell and tube geome~ry~'. Typically, ~he tube can h~ve sn inside di~meter of sbout 2.5 to about 4.0 centlmeters and a length o~ from sbout 6 to ~bout 12 meters. Each ~hell would cont~in ~s msny tubes as needed for the deslred production c8pacit~ . The tubes sre in 8 par~llel arr~ngemen~ with each t~
other. The l~se of sep~rste tubes within th shell is advantageous for temperature control in the tubes. The lnput g~seous ~trQam is dlvided into the tubes ~nd a 11quid such ~s the tr~demark DOWTH~RM A
sold by Dow Chemical Comp~ny circulstes ~round the tubes and within the shell to maintain the oper~ting temper~ture. The prim~ry component of DOWTHERM A is diphenyl ether. Another suit~ble liquid for maintaining the temperature ls ~ mixture of isomer~c dibenzyl benzenes ~uch as a product sold under the trademarX MAR~OTHERM S by Chemische Werke Huls AG.
Other llquids which ~ppear to be suitable bssed on their bo~ling temperatures at stmospheric pressure include tetr&cont~ne and pent~tricontane. In Qdd~tion, molten s~lts can be used.
Typically, the gas hourly space velocity (GHSV) for the reactor 20 ls from about 2000 to _l ~bout 5000 h . The pressure is from about 10 to ~bout 20 atmospheres with ~n lnpu~ oxy~en content of about 6 mole percent of the entire input gaseous s~ream. The output gaseous stre~m 21 contalns unre~cted ethane, unreacted oxygen, ethylene, ~cetic acid, and other gases such ~s ~ases which were present in the eommerci~l eth~ne and gsses produced by the reactlon such ~s CO ~nd CO2. The output gaseous streAm 21 eommunieates to cooling means 22 which simply cools the output g~seous stream 21 so that the weter and acetic acid in output g~seous stre~m 21 condense. As pointed out, the condens~te c~n be extremely corrosive so th~t the m~ter~ls used should be ~elec~ed to reslst the c~rroslon.
Portions of the equipment exposed to hot condens~ng D-14,0B0 , ,.
~ce~ic ~cld ~vapors can be f~bricated ~rom ti~nlum or HASTELLOY C. Portions ~f the equi.pment ln contact with cool 801ution8 of ~cetic ~cid can be m~de out of t~inless ~teel. Equipment whlch will be exposed to ~cetic acid vapors at high temperatures such ~s the reRctor tubes can be abrlcAted from c~rbon steel.
The choice of material~ used should be selected to avoid catalyst poisons. For example, metcls such as iron and nickel csn react with CO
under cert~in conditions to produce volstlle met~l csrbonyls. The metsl carbonyls c~n be decomposed over the c~tfllyst to deposit metal oxides on ~he c&talyst surface ~nd thereby alter the activity and perform~nce of the catalyst.
The cooling means 22 c~n be a he~t exchsnger or any other well known prior art equlpment for cooling the water snd acetic ~cid ~o that they condense. The water ~nd ~cetic acid ~re removed fr~m cooling mean~ 22 ~nd the remainlng gas is combined wlth ox~gen to ~orm the lnput g~se~us stream 23 whlch enters react~r 24. Re~ctor 24 ls essentially the same as re~ctor 20.
The reactor 24 produces ~n output gaseous stream 25 which enters c~oling me&ns 26 which is simllar to cooling means 22. After the water and Qcetic acid h~ve been removed the remaining g~s in coollng me~ns 26 is combined with oxygen to form input g~seous stream 27 into reactor 28. Reactor 28 is similar to re~ctor 23. The reactor 28 produces ~n output g~seous stre~m 29.
~-14,08~
5~ ~
- ~3 - -The OUtpllt g~seous stream 29 includes ethylene, ethRnei oxygen, ~cetic ~cld, w~er, ~nd some other ~ases 8S indicsted above.
For convenience, ~s used herein the term "stage" comprises ~ reactor for catalytic~lly oxydehydrogen~lng eth~ne to ethylene. The "l~st sta~e" referred ~o herein ls the "outpu~ st~ge1' in accord~nce with common pr~ctlce in the process art.
Also, system components such as the cooling means 22 is lnterstage equipment in ~ccordance with comm3n practice in the process ~rt.
Another impnrt~nt embodiment is sho~n in ~ig. 4. Eth~ne, oxygen ~nd weter in the form of steam enter re~ctor 30 to produce ~n output gaseous stre~m 31 whlch enters coollng me~ns 32. Coollng me~ns 3~ reduces the temper~ture of the output g~seous stream 21 to a temp0rature below about 2504C
so th6t oxygen of less then about 6 mole percent c~n be introd~ced s~fely. The input g~seous stream 33 including ~dded oxygen ~nd water in the form of ste~m enters re~c~or 34 to produce ~n output gas~ous stre~m 35. The output gaseous stream 35 enters the cooling means 36 which i~ similar to cooling means 32. The output gaseous s~re~m 35 ls cooled to less than ~bout 250C and oxygen and water in ~he form of steAm are lntroduced to produce ~n input g~seous stre~m 37 which enters ~eActor 38 to produce an output g~seous streRm 39~
The sys~ems shown ln Flgs. 3 and 4 in rel~tionship to ~n over~ll commercisl system is hown ln simplified form in Fig. 5. In Fig. 5p the EO~H re~ct~on system ~0 corresponds to essenti~lly D-1~,080 5~ ~
- 2~ - -all of the b~locks shown in elther Figo 3 or Fig. 4.
Oxygen is supplied to the EODH reactlon system 40 from ~n ~ir sep~r&tion unit 41. The eth~ne into the EODH re~ction system 40 comprises recycled ethane from unit 46 ~nd eth~ne from the dlstill~tion column 42 wh~ch separ~tes ou~ propane which m~y be present in the commercial eth~ne. The output of the EODH
reaction system 40 goes to a æcrubber 43 which sep~r~tes out the aqueous ficetic acid. The g~ses from the scrubber 43 go to a compressor 44 ~nd ~hen to U71i L 45 which sep&rates out CO2. Unit 45 is ~
prior art unit whlch could comprise a portlon which ~bsorbs CO2 with ~ solven~ such as ~lk~nol~mine ~ollowed by a stripper whlch removes the ~bsorbed CO2. The gases then pRSS to unit 46 whlch contains distilletion columns for separ~ting Ollt ethylene~ eth~ne, And v~rious i'llghts" such ~s 2' N2, CO and CH4. The ethane from unit 46 ls recycled to the EODH re~ction system 40. The ~qu~ous ~cetic ~cid from the scrubber 43 goes through ~n ~cetic acid refining unit 4~ which separates out water ~nd ~cetlc acid.
~ 2-stage pllo~ pl~nt was ~ullt ~nd operated. E~ch re~ction st~ge is a tube hsving dimenslons contemplated ~s being suit~ble for comm~rcisl oper~tions. The capability to feed gases such as steam, ace~ic 8cid, ethylene, CO, and CO2 together with eth~ne ~nd oxygen enabled the simulstion of any two series connected stages in a multlst~ge open series ~rrAngement.
Fig. 6 shows ~ block di~gram of the pilot pl~nt used.
D-14,080 ~ 5 Each re~ctor 60 and 61 comprised a tube ~bout 7.62 meters long having ~n ~nside diameter oE
about 2.6 em~ The bottom 1.8 meters of t~e tube w~s packed wlth gla~s be~d~ hsv~ng ~n ~versge diameter of about .6 cm. The g~ass beads served ~s a secondary prehç~ting ~ect~on for rslsing the Eeed gases to the reaction temperature. The tube ~as packed with about 4.6 meters o~ a catslyst ~nd the remainlng portion of the tube was packed with gl~s,s besds of the ~ype used in the bottom portion. The reaction temperature was controlled by circulating a heat transfer ~luid through a ~acket around the tube. The transEer fluld used was MARLOTHERM S.
The c~talyst used had the Eollowing gram-atom rfltios:
lS Mol6 V6 8 Nbl.g ~bl~o Cal.0 Support 12 of T~ble 1 was u~ed. The gases 2' N2- G2H6~ C2H4. CO, ~nd CO2 w supplied through respective m~ss ~lowmeters 62~
These gases were preheated ln heating unit 63 pr~or to belng supplied to the re~ctor 60. Any wster or aqueous ~cetic 8cid belng supplied to a reactor 60 was vaporized in a heating un~t 64. The hot heat transfer Eluid was circulated through the re~ctors 60 snd 61 with unit 65 which also controlled the temperature wlthin ~ preset range.
The output gaseous stream ~rom the reactorx 60 ~nd 61 were cooled in ~he respective coolin~
me~ns 66. The respective output gaseous streams were then p~ssed to a separator unit 67 which was used to separate ~nd accumulate ~queous ~cet~c ~cid from the gas stre~m. Oxygen was in~ected between the st~ge,s ln sccordance with the lnven~ion.
D-14,080 ,, - ~6 -The input ~nd output gaseous stre~ms of the reactors 60 ~nd 61 were an~lyzed us~ng g8S
chromatographs.
The pilot plant ~hown in Fig. 6 had only two stages; howeverg the d~ta were collected to simulate more ~hsn ~wo ~t~ges and enabled a oomputer simulation of systems having more th~n two st~ges.
EXAMPLES
The Ex~mples were e~rrled ou~ to compRre operations with and without the invention.
EX~MPLE 1 A 2-st~ge series connected system ~a~ -~
evaluated in the pilot pl~nt for operation wi~.h ~nd without inter~tage remov~l o~ water ~nd acetic ~cld (aqueous scetic ~cid). For e~ch case> ~bout 6 mole percent of oxygen w~s used For e~ch stage. T~bles 2 snd 3 correspond respectively to the operation of the 2-st~ge ~ystem wlth and without ~he inter~t~ge removal of water snd ~cetic ~cid. For ~ble 2, ~he total output ~ncludes the g~seous output stre~m ~f stage 2 ~nd ~lsv the H2O and C~13COOH removed before stage 2. The CH3COOH system selectivlty is for the total CH3COOH ~rom both the interst~ge removal and the outpu~ o~ st~ge 2 D-14, 08û
- 2~ -INTERSTAGE REMOVAL OF IdATE:R
AND: ACET l C P~C I 1) FOR 2 - ';TAGES
_COMPOSITIOII IN MOLE PERCENT
, I NPUT STAGE 1TOTAL O~ITPUT
~2~6 ~3.83 7~.63 2 5.93 1.44 ~,O~ 0.~5 0.5 ~2H4 O 7 . 66 CH3COOH 0 l. 5 H20 0 11. 25 CO, ~ Q.~8 About 987~ of H20 removed interst~ge.
SYSTEM ETHANE CONVERSION ~ 11. 41 C2H~ SYSTEM SELECTIVITY = 78 . 3 CH3COOH SYSTEM SELE~TIVITY = 15. 8 : ~ D-~4,0B0 . ....
:
. .
. , TABLE: 3 NO INTERSTAGE: REMoVAL OE' WATER
AND ACETIC ACID ~ FOP~ 2-STAGES
. COMPOSITION IIJ l~llOLE lPERCl~:NT
~INPUT STAGE: lOUTPUT STAGE 2 C2~i~;, 93.~7 76.8~
2 So~B 1~28 ~0 0~25 ~i7 . 2 C2H4 0 7 ~ 37 GH3~00H O 1. 6 2 H20 0 ll o 24 ~0 0 O.g8 SYSTEM ETHANE CONVERSION = 11. 27, C2H~ SYSTEM SELECTIVITY = 76 . 0 CH3COOH SYSTE?I SELECTIVITY = 16 . 6 From Tables 2 and 3, i~ can be ~pprec~a~ed that the 2-~tRge system wlth ~nterstage removal of water ~nd ~cetlc ~cid had a lhigher ethylene sys~em selectiv~ ty ~nd ~ lower ~cetic acld sy~tem selectivity ~s comp~red to the 2-ætage system which d~ d not hsve inters~ge remov~l o~ ws~er ~nd ~ce~ic ~c id .
thls Example, ~ 4-stage series c~nneeted sy~tem w~ ulated. The simu~t~n w~s c~rried out w~th ~nd wi'chou'c the removal of w~er ~nd ~ce~ic ~cid in the lnterst~ges . For ~eh run ~ f ixed D O ~B O
:
5~3~
eth~ne input to the first stagc was assumed and the oxygen input to each st~ge was taken AS sbout 5 mole percent of the lnput g~seous stream of that sthge.
The temper~ture of ~he inpu~ ~aS20US streaM of e~ch s~age was ad~usted to produre an opera~lng temperature for which the output gaseous stream includ~d ~bou~ a . ~ mole percent oxygenO
Removing water and acetic acid from the output g~seous stream of a st~ge reduces the flow rate of the inpu~ gaseous stream ~o the subsequen~
sta~s~ Th~s results in the subsequent stages having relatively lower oper~ting temperatur~s ~s compared to ~ system wlthout the removal of wflter.
The lower temperatures would tend to reduce the rate of productlon of ethylene relatlve to the rflte of production of ~cetlc acid. Nevertheless, a higher system selectivl~y to ethylene is obtained for process for which there is interstage removal of ~ater.
For such a system, Table 4 shows the system outpu~ composlt~on with ~nd wlthout the remov~l of water ~nd acetic acld ~f~er each of the intermediate stagesO For the interstage removal of water ~nd acetic ~cid, Table 4 shows cRlculations based on ~otal water ~nd acetlc acid out of all of the stsges.
D-14,080 TA~L 4
4-STAGE SYSTEM WITH AND WITHOUT
REMOVAL OF WATER AN~ ACETIC ACID
_ COMPOSITION IIN ~OLE: PERCElldT
TOTAL OUTPUT WlTH OllTPUT WlTl~Ol)T
'REMOVAL REMOV~L
C2H6 58 . 49 58 . ~0 Oi! ~.17 ~.16 ~2 1 . 06 1 . 2 7 C2H4 13 . 60 12 .11 CH3COOH 2 . 67 4 . ~0 H2O 21. 43 21. 77 CO ~.58 ~.69 SYSTEM ETHANE CONVERSION (WITH REMOVAL) = 23.39l'J
SYSTEM ETHANE CONVERSION ~WITHOUT REMOVAL) ~ 23 . 57 C2H4 SYSTEM SELECTIVITY (WITII REMOVAL) - 74 . ~
C2H4 SYSTEM SELECTIVlTY (WITHOUT REMOVAL) = 66 . 4%
CH3COOH SYSTEM SELECTIVIlY ~ lTH REPIOVAL) = 15 . 0 CH3COOH SYSTEM SELECTIVITY ~WITHOUT RlEMOVAL) = 22.
Table 5 shows the ~verage temperature of each of l~he stages Eor the two runs.
TP~Bl.E 5 St~ge l St~F.e 2 St~e 3 Sta~e 4 With ~emov~l 358.8~C 365~6G 371.4C 374.6C
Without Remov~1 358.gC 369.4~C 376~3C 3~3.2 D-14,080 , ~rom T~ble ~ c~n be seen that ~he in~erst~ge removal of w~er ~nd ~cetir ~cld re~ul~s ln ~ hlgher e~hylene sys~em selectivity ~nd ~ lower acetic ~cid system selectl~ity ~s compsred to the system without lnterstAge removal of water ~nd ~cetic ~cid.
This Ex~mple is simil~r ~o Ex~mple 2 except th~t the 4-stage simul~tlon was used to compare system with ~nd withou~ the addition of w~ter to each st~ge. It was ~ssumed that 2-1/2 mole percent of water w~s ~dded to the input g~seous ~tream of.
the first sts~e and thst e~ch s~ge thereafter h~d an identical m~ss ~mount of w~ter Rdded tv the respective input ~sseous stream.
Adding w~ter to A ~t~ge would requlre ~
higher operating temper~ture for ~he st~ge snd ~his would tend ~o decre~se the r~te of productlon of acetlc ~cid rel~tive to the r~te of production of ethylene. It is found, however, that the ~ystem in which wa~er is ~dded to the stages has ~ greater selectivity to acetic ~cid.
Table 6 summ~rlzes the resu1ts of the two runs.
D-14,080
REMOVAL OF WATER AN~ ACETIC ACID
_ COMPOSITION IIN ~OLE: PERCElldT
TOTAL OUTPUT WlTH OllTPUT WlTl~Ol)T
'REMOVAL REMOV~L
C2H6 58 . 49 58 . ~0 Oi! ~.17 ~.16 ~2 1 . 06 1 . 2 7 C2H4 13 . 60 12 .11 CH3COOH 2 . 67 4 . ~0 H2O 21. 43 21. 77 CO ~.58 ~.69 SYSTEM ETHANE CONVERSION (WITH REMOVAL) = 23.39l'J
SYSTEM ETHANE CONVERSION ~WITHOUT REMOVAL) ~ 23 . 57 C2H4 SYSTEM SELECTIVITY (WITII REMOVAL) - 74 . ~
C2H4 SYSTEM SELECTIVlTY (WITHOUT REMOVAL) = 66 . 4%
CH3COOH SYSTEM SELECTIVIlY ~ lTH REPIOVAL) = 15 . 0 CH3COOH SYSTEM SELECTIVITY ~WITHOUT RlEMOVAL) = 22.
Table 5 shows the ~verage temperature of each of l~he stages Eor the two runs.
TP~Bl.E 5 St~ge l St~F.e 2 St~e 3 Sta~e 4 With ~emov~l 358.8~C 365~6G 371.4C 374.6C
Without Remov~1 358.gC 369.4~C 376~3C 3~3.2 D-14,080 , ~rom T~ble ~ c~n be seen that ~he in~erst~ge removal of w~er ~nd ~cetir ~cld re~ul~s ln ~ hlgher e~hylene sys~em selectivity ~nd ~ lower acetic ~cid system selectl~ity ~s compsred to the system without lnterstAge removal of water ~nd ~cetic ~cid.
This Ex~mple is simil~r ~o Ex~mple 2 except th~t the 4-stage simul~tlon was used to compare system with ~nd withou~ the addition of w~ter to each st~ge. It was ~ssumed that 2-1/2 mole percent of water w~s ~dded to the input g~seous ~tream of.
the first sts~e and thst e~ch s~ge thereafter h~d an identical m~ss ~mount of w~ter Rdded tv the respective input ~sseous stream.
Adding w~ter to A ~t~ge would requlre ~
higher operating temper~ture for ~he st~ge snd ~his would tend ~o decre~se the r~te of productlon of acetlc ~cid rel~tive to the r~te of production of ethylene. It is found, however, that the ~ystem in which wa~er is ~dded to the stages has ~ greater selectivity to acetic ~cid.
Table 6 summ~rlzes the resu1ts of the two runs.
D-14,080
5~3 TABLE S
~t-STAGE SYSTEM WITH AND
WITHOUT THE ADDITION OF WATElR
COMPOSITIOIJ IN MOLE PERCE:NT
OUTPUT WITH OUTPIJT WlTHOUT
DDED WATER Al:lDE:D WATEP~
C~H653 .13 58 . 00 2 O.22 0 ~6 ~2 1.32 ~.27 C2H410.54 12.ll CH3COOH4. 23 4. 30 H2028 . 01 21. 7 7 ~02 . 55 2 . ~9 . ..
SYSTEM ETHANE CONVERSION (WITH ADDED) = 23.6qo :~ 15 SYSTE:M ETHANE CONVERSlON ~WITHOUT ADI)ED) = ;~3,. 5S
C2H4 SYSTEM SELECTlLVlTY (WITH ADDED) = 62. 5~1L
C2H4 SYSTEM SEI.ECTIVITY (WITHOUT ADDED~ = 66 . 4%
~: CH3COVH 5YSTE~:M SELECTIVITY (WITH ADDED~ = 25. 7%
CH3COOH SYSTEM SELECTlVITY (WITHOUT ADDED~ = 22 . 5 Tsble 7 shows the ~ver~ge tcmperature o~
e~ch of the st~ges ~or the t3ro runs.
St~e 1 ~2. Sts~e 3 Sta~e 4 With Added 360,3C 372.7C 379.7C 386.~C
Wlthout Added 358.8~C 369.4C 376.3~C 383.2C
~:
~: D-149080 ..
'; ' 3L~ 3~i ~rom Table 6, lt c~n be seen 'C21~t tlle ~dditlon o~ w~ter to the input g ~seous stre~m c)f each stsge result~ in ~ higher scetic ~cid system selectlvlty ~nd ~ lower ethylene sys,tem selectlv~ty comp~red to the s~stem wlthol~t any inter~t~g,e ~dditlon o~ w~t:er.
D- 14, 080
~t-STAGE SYSTEM WITH AND
WITHOUT THE ADDITION OF WATElR
COMPOSITIOIJ IN MOLE PERCE:NT
OUTPUT WITH OUTPIJT WlTHOUT
DDED WATER Al:lDE:D WATEP~
C~H653 .13 58 . 00 2 O.22 0 ~6 ~2 1.32 ~.27 C2H410.54 12.ll CH3COOH4. 23 4. 30 H2028 . 01 21. 7 7 ~02 . 55 2 . ~9 . ..
SYSTEM ETHANE CONVERSION (WITH ADDED) = 23.6qo :~ 15 SYSTE:M ETHANE CONVERSlON ~WITHOUT ADI)ED) = ;~3,. 5S
C2H4 SYSTEM SELECTlLVlTY (WITH ADDED) = 62. 5~1L
C2H4 SYSTEM SEI.ECTIVITY (WITHOUT ADDED~ = 66 . 4%
~: CH3COVH 5YSTE~:M SELECTIVITY (WITH ADDED~ = 25. 7%
CH3COOH SYSTEM SELECTlVITY (WITHOUT ADDED~ = 22 . 5 Tsble 7 shows the ~ver~ge tcmperature o~
e~ch of the st~ges ~or the t3ro runs.
St~e 1 ~2. Sts~e 3 Sta~e 4 With Added 360,3C 372.7C 379.7C 386.~C
Wlthout Added 358.8~C 369.4C 376.3~C 383.2C
~:
~: D-149080 ..
'; ' 3L~ 3~i ~rom Table 6, lt c~n be seen 'C21~t tlle ~dditlon o~ w~ter to the input g ~seous stre~m c)f each stsge result~ in ~ higher scetic ~cid system selectlvlty ~nd ~ lower ethylene sys,tem selectlv~ty comp~red to the s~stem wlthol~t any inter~t~g,e ~dditlon o~ w~t:er.
D- 14, 080
Claims (20)
1. A process for converting ethane to ethylene, in a reaction system comprising:
at least two stages connected in open contiuous series relationship with each other;
each stage comprising an oxydehydrogenating catalyst system maintained at conditions for catalytically converting an input gaseous stream comprising ethane and oxygen to an output gaseous stream having a temperature greater than 250°C and comprising ethylene, acetic acid, water, ethane, and oxygen;
comprising the steps of:
cooling the output gaseous stream of each stage other than the output gaseous stream of the last stage to a temperature less than about 250°C for the introduction of oxygen;
changing the total water and acetic acid content in the input gaseous stream of at least one stage with respect to the total water and acetic acid content in the output gaseous stream immediately preceding that stage; and supplying oxygen to the input gaseous stream of each stage when the input gaseous stream is at a temperature less than about 250°C and in an amount such that the total oxygen content of the input gaseous stream of each stage is less than about 6 mole percent with respect to the total input gaseous stream of that stage.
at least two stages connected in open contiuous series relationship with each other;
each stage comprising an oxydehydrogenating catalyst system maintained at conditions for catalytically converting an input gaseous stream comprising ethane and oxygen to an output gaseous stream having a temperature greater than 250°C and comprising ethylene, acetic acid, water, ethane, and oxygen;
comprising the steps of:
cooling the output gaseous stream of each stage other than the output gaseous stream of the last stage to a temperature less than about 250°C for the introduction of oxygen;
changing the total water and acetic acid content in the input gaseous stream of at least one stage with respect to the total water and acetic acid content in the output gaseous stream immediately preceding that stage; and supplying oxygen to the input gaseous stream of each stage when the input gaseous stream is at a temperature less than about 250°C and in an amount such that the total oxygen content of the input gaseous stream of each stage is less than about 6 mole percent with respect to the total input gaseous stream of that stage.
2. The process of claim 1, wherein at least a portion of the water and acetic acid are D-14,080 removed from the output gaseous stream of at least one stage other than the last stage of the series.
3. The process of claim 1, wherein water in the form of steam is added to the input gaseous stream of at least one stage.
4. The process of claim 1, wherein there are three stages in series connection with each other.
5. The process of claim 1, wherein there are four stages in series connection with each other.
6. The process of claim 1, wherein there are at least three intermediate stages, and water and acetic acid are removed from the output gaseous stream of each of the stages other than the last stage of the series.
7. The process of claim 1, wherein the gases through each stage has a gas hourly space velocity of from about 500 to about 6000 h-1.
8. The process of claim 7, wherein the gases through each stage has a gas hourly space velocity of from about 2000 to about 5000 h-1.
9. The process of claim 1, wherein each stage is at a pressure of from about 1 to about 40 atmospheres.
10. The process of claim 9, wherein each stage is at a pressure of from about 10 to about 25 atmospheres.
D-14,080
D-14,080
11. The process of claim 1, wherein each catalyst system comprises a supported catalyst.
12. The process of claim 11, wherein said support has a surface area less than about 1.0 m2/g and a median pore diameter greater than about 10 microns.
13. The process of claim 1, wherein the output gaseous stream of each stage comprises oxygen.
14. The process of claim 13, wherein the output gaseous stream of each stage comprises about 0.2 mole percent oxygen.
15. The process of claim 14, wherein the input gaseous stream of each stage comprises about 5 mole percent oxygen.
16. The process of claim 1, wherein the overall conversion of ethane of all the stages is from about 10 percent to about 50 percent.
17. The process of claim 16, wherein the overall conversion of ethane of all the stages is from about 20 percent to about 30 percent.
18. The process of claim 1, further comprising separating most of the ethylene from the output gaseous stream of the last stage of the series.
19. The process of claim 1, further comprising separating most of the ethane from the output gaseous stream of the output stage and using D-14,080 at least a portion of the separated ethane as part of the input gaseous stream of the first stage of the series.
20. The process of claim 1, further comprising separating the acetic acid from the output gaseous stream of the last stage of the series.
D-14,080
D-14,080
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000519021A CA1262556A (en) | 1986-09-24 | 1986-09-24 | Process for oxydehydrogenation of ethane to ethylene |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000519021A CA1262556A (en) | 1986-09-24 | 1986-09-24 | Process for oxydehydrogenation of ethane to ethylene |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1262556A true CA1262556A (en) | 1989-10-31 |
Family
ID=4134011
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000519021A Expired CA1262556A (en) | 1986-09-24 | 1986-09-24 | Process for oxydehydrogenation of ethane to ethylene |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1262556A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017072086A1 (en) | 2015-10-26 | 2017-05-04 | Shell Internationale Research Maatschappij B.V. | Ethane oxidative dehydrogenation and acetic acid recovery |
| EP3354634A1 (en) | 2017-01-30 | 2018-08-01 | Shell International Research Maatschappij B.V. | Ethane oxidative dehydrogenation |
| WO2019025900A1 (en) | 2017-08-03 | 2019-02-07 | Nova Chemicals (International) S.A. | Agglomerated odh catalyst |
| WO2019025981A1 (en) | 2017-08-03 | 2019-02-07 | Nova Chemicals (International) S.A. | Agglomerated odh catalyst |
| US11319265B2 (en) | 2018-11-02 | 2022-05-03 | Shell Usa, Inc. | Separation of ethane oxidative dehydrogenation effluent |
-
1986
- 1986-09-24 CA CA000519021A patent/CA1262556A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017072086A1 (en) | 2015-10-26 | 2017-05-04 | Shell Internationale Research Maatschappij B.V. | Ethane oxidative dehydrogenation and acetic acid recovery |
| US10427992B2 (en) | 2015-10-26 | 2019-10-01 | Shell Oil Company | Ethane oxidative dehydrogenation and acetic acid recovery |
| EP3354634A1 (en) | 2017-01-30 | 2018-08-01 | Shell International Research Maatschappij B.V. | Ethane oxidative dehydrogenation |
| WO2019025900A1 (en) | 2017-08-03 | 2019-02-07 | Nova Chemicals (International) S.A. | Agglomerated odh catalyst |
| WO2019025981A1 (en) | 2017-08-03 | 2019-02-07 | Nova Chemicals (International) S.A. | Agglomerated odh catalyst |
| US11052380B2 (en) | 2017-08-03 | 2021-07-06 | Nova Chemicals (International) S.A. | Agglomerated ODH catalyst |
| US11772073B2 (en) | 2017-08-03 | 2023-10-03 | Nova Chemicals (International) S.A. | Agglomerated ODH catalyst |
| US11319265B2 (en) | 2018-11-02 | 2022-05-03 | Shell Usa, Inc. | Separation of ethane oxidative dehydrogenation effluent |
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