CA1055876A - Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock - Google Patents
Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstockInfo
- Publication number
- CA1055876A CA1055876A CA218,599A CA218599A CA1055876A CA 1055876 A CA1055876 A CA 1055876A CA 218599 A CA218599 A CA 218599A CA 1055876 A CA1055876 A CA 1055876A
- Authority
- CA
- Canada
- Prior art keywords
- water
- phase
- percent
- hydrocarbons
- solvent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G21/00—Refining of hydrocarbon oils, in the absence of hydrogen, by extraction with selective solvents
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C7/00—Purification; Separation; Use of additives
- C07C7/10—Purification; Separation; Use of additives by extraction, i.e. purification or separation of liquid hydrocarbons with the aid of liquids
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Water Supply & Treatment (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Extraction Or Liquid Replacement (AREA)
Abstract
IMPROVEMENT IN A PROCESS FOR THE
SEPARATION OF AROMATIC HYDROCARBONS
FROM A MIXED HYDROCARBON FEEDSTOCK
ABSTRACT OF THE DISCLOSURE
A process for the recovery of aromatic hydrocarbons having boiling points in the range of about 80°C to about 175°C from mixtures with aliphatic hydrocarbons comprising the following steps:
(a) contacting the feed-stock in an extraction zone with a mixture of water and a water-miscible organic solvent, said solvent having a boiling point of at least about 200°C, and with reflux hydrocarbons at a temperature between about 100°C and about 200°C and a pressure of about 6 to about 14.5 atmospheres to provide an extract comprising aromatic hydro-carbons, solvent and water as well as a raffinate comprising aliphatic hydrocarbons;
(b) separating the extract in a distillation zone with flash and fractionation, the fractionation utilizing steam, into an overhead distillate comprising a hydrocarbons phase and a water phase and furthermore bottoms comprising a mixture of solvent and water;
(c) recycling the hydrocarbons phase of the overhead distillate and the bottoms of step (b) to the extraction zone;
(d) washing all or part of the water phase of the overhead distillate with a slip stream of aromatic compounds, which comprises at least 95 percent by weight of aromatic hydrocarbons, the amount of the slip stream being about 0.1 to 5 percent by weight, based on the total weight of the aromatic hydro-carbons in the feedstock, to provide an aromatic hydrocarbons phase and a water phase; and (e) washing the aromatics phase of the side stream of aromatics compounds with the water phase produced in step (d), characterized in that the raffinate is washed with process water to provide a raffinate aliphatic hydrocarbons phase and one or more solvent containing raffinate water phases, and the raffinate water phases are recycled to the extrac-tion zone at about the midpoint thereof.
S P E C I F I C A T I O N
1(a)
SEPARATION OF AROMATIC HYDROCARBONS
FROM A MIXED HYDROCARBON FEEDSTOCK
ABSTRACT OF THE DISCLOSURE
A process for the recovery of aromatic hydrocarbons having boiling points in the range of about 80°C to about 175°C from mixtures with aliphatic hydrocarbons comprising the following steps:
(a) contacting the feed-stock in an extraction zone with a mixture of water and a water-miscible organic solvent, said solvent having a boiling point of at least about 200°C, and with reflux hydrocarbons at a temperature between about 100°C and about 200°C and a pressure of about 6 to about 14.5 atmospheres to provide an extract comprising aromatic hydro-carbons, solvent and water as well as a raffinate comprising aliphatic hydrocarbons;
(b) separating the extract in a distillation zone with flash and fractionation, the fractionation utilizing steam, into an overhead distillate comprising a hydrocarbons phase and a water phase and furthermore bottoms comprising a mixture of solvent and water;
(c) recycling the hydrocarbons phase of the overhead distillate and the bottoms of step (b) to the extraction zone;
(d) washing all or part of the water phase of the overhead distillate with a slip stream of aromatic compounds, which comprises at least 95 percent by weight of aromatic hydrocarbons, the amount of the slip stream being about 0.1 to 5 percent by weight, based on the total weight of the aromatic hydro-carbons in the feedstock, to provide an aromatic hydrocarbons phase and a water phase; and (e) washing the aromatics phase of the side stream of aromatics compounds with the water phase produced in step (d), characterized in that the raffinate is washed with process water to provide a raffinate aliphatic hydrocarbons phase and one or more solvent containing raffinate water phases, and the raffinate water phases are recycled to the extrac-tion zone at about the midpoint thereof.
S P E C I F I C A T I O N
1(a)
Description
~5S~76 This inv~ntion r¢l~te~ to an improvement ln ~ proces~ for the ~par~lon o~ sromatie hydrocarbon~
from ~ mlxed hytrocarbon ~e~d~tock and~ mor~ particularly~
to the recovery of high puri~y ~romatic hydrocarbon~ in hi8h yields while making efficient use of process compon-ent~.
Descrl~ n of the Prior Ar~E
With thQ advent of the benzene-toluene~CB
aromatic~ fraction ~kn~wn and herein~ter re~erred ~o ; as BTX) as the prlncipal r8w m~terial in the manufacture of petroch~mic~ls, o~tripp~ng ethylono in this rogard, and the increased domand or aromatics as a compon~nt in gasol~ne to increa~e its octan~ r~ting and ~hu~ r~duce or ellminate the need for lead, which has been unter ire ~s a pollutant, aromatics separation process~ availed of ln the past have come under close ~crutiny with an e~e towsrd improving proce~s eco~omic~.
Improved proces~ economics can be tra~lated ~0 lnto, among other thlngs, the use of less flpparatus, the lowering o heat~ng r~quirements, and the more e~fective use of proce~s co~ponents a~ aid~ in the ~epar~tion proces~.
Variou proees~es h~ve been used for aromat~c~
separ~tion~, e.g., (1) a process u~ing an extraction column which ~ends a glycol 801ven~/w~t0r solutio~, BTX
~nd r~1u~ to a two ~t~p di3tillation column. Th~ re~ulting
from ~ mlxed hytrocarbon ~e~d~tock and~ mor~ particularly~
to the recovery of high puri~y ~romatic hydrocarbon~ in hi8h yields while making efficient use of process compon-ent~.
Descrl~ n of the Prior Ar~E
With thQ advent of the benzene-toluene~CB
aromatic~ fraction ~kn~wn and herein~ter re~erred ~o ; as BTX) as the prlncipal r8w m~terial in the manufacture of petroch~mic~ls, o~tripp~ng ethylono in this rogard, and the increased domand or aromatics as a compon~nt in gasol~ne to increa~e its octan~ r~ting and ~hu~ r~duce or ellminate the need for lead, which has been unter ire ~s a pollutant, aromatics separation process~ availed of ln the past have come under close ~crutiny with an e~e towsrd improving proce~s eco~omic~.
Improved proces~ economics can be tra~lated ~0 lnto, among other thlngs, the use of less flpparatus, the lowering o heat~ng r~quirements, and the more e~fective use of proce~s co~ponents a~ aid~ in the ~epar~tion proces~.
Variou proees~es h~ve been used for aromat~c~
separ~tion~, e.g., (1) a process u~ing an extraction column which ~ends a glycol 801ven~/w~t0r solutio~, BTX
~nd r~1u~ to a two ~t~p di3tillation column. Th~ re~ulting
- 2 '-, ., , . .
lV5C ~ g506 BTX 18 then redistill~d to remov~ wat~r ~nd entrai~ed ~lycol; (2) a similar process using ~wo distillation columns, BTX and w~er belng dlstlll~d Ln th~ aecond column; (3) anoth~r simil~r proc~3~ UlBi~g two distlllation column~, in the ~ccond column of which ]3TX and glycol are distilledO
Generally, these proce~ses use two ~eparate wa er circuits. One circuit i8 the ~tripping w~ter circuit for removing arom~tics from the glycol in the ~tripper and thè oth~r i~ ~ water wash circuit. Both water stre~ms are revaporized in these processe~. The mak~-up o~ ~he w~ter wa~h circuit is such ~hflt the water ~rst washe~ raffinst~ and then ls distilled. Unfort-unately, distillation does not remove ~11 dissolved ~nd entrained ~liph~t~cs from the w~ter and yet lt is then used to wash glycol from the aromatics product ~esulting in decre~ed product purity. In the stripping water circuit, 8tripping water from the reflux d~canter ~l~o contains some aliph~tics. Finally, the use o~ two or more di~tillation columns i8 the rule rath~r than the exceptlon ln this type of 8y8tem.
In one ~provement over the foregoing, revaporiz-ation i~ avo~ded in the water wash circuit; however~ a water rectifier i8 nece~sary ~n the stripping water ; circuit and in another improveme~t, the water recti~i2r is avoided, but v~rious ~ntreflted w~ter 3treams are ~ combined to r~cover the glycol. Although an ~ttempt i~
;',
lV5C ~ g506 BTX 18 then redistill~d to remov~ wat~r ~nd entrai~ed ~lycol; (2) a similar process using ~wo distillation columns, BTX and w~er belng dlstlll~d Ln th~ aecond column; (3) anoth~r simil~r proc~3~ UlBi~g two distlllation column~, in the ~ccond column of which ]3TX and glycol are distilledO
Generally, these proce~ses use two ~eparate wa er circuits. One circuit i8 the ~tripping w~ter circuit for removing arom~tics from the glycol in the ~tripper and thè oth~r i~ ~ water wash circuit. Both water stre~ms are revaporized in these processe~. The mak~-up o~ ~he w~ter wa~h circuit is such ~hflt the water ~rst washe~ raffinst~ and then ls distilled. Unfort-unately, distillation does not remove ~11 dissolved ~nd entrained ~liph~t~cs from the w~ter and yet lt is then used to wash glycol from the aromatics product ~esulting in decre~ed product purity. In the stripping water circuit, 8tripping water from the reflux d~canter ~l~o contains some aliph~tics. Finally, the use o~ two or more di~tillation columns i8 the rule rath~r than the exceptlon ln this type of 8y8tem.
In one ~provement over the foregoing, revaporiz-ation i~ avo~ded in the water wash circuit; however~ a water rectifier i8 nece~sary ~n the stripping water ; circuit and in another improveme~t, the water recti~i2r is avoided, but v~rious ~ntreflted w~ter 3treams are ~ combined to r~cover the glycol. Although an ~ttempt i~
;',
- 3 -~o~s~7~ 9506 m~de ln bo~h improvements to displaee aliphatlcR with aromatics in the proc~s~ wa~er, i~ i~ apparent tha~
aliphAtic~ are necessarily prese~t in the fin~l product thu3 reduclng purity.
In sum, a~l of the proces~es men,tioned heretoore, while viable ccmmerci~lly, have not succeeded in optimizing process economics together with purity.
Great strides hav~ bsen made in such optimi~ation ~nd in obtaining hlgh purity benzene; a~, or example, :
in Uhited Sta~e~ pat~nt 3,714,033; however, processes which improve process economicsJ obtain high purit~ benz~ne, and, further, achieve hlgher toluene and xylene puritie~
are still being sought ater.
Summa~y of the Invention An ob3ect of this lnvention, therefore, 1~ to provide an improvQment in a process for the ~eparation of aroma~ic hydrocarbon~ from a mixed hydroc~rbon feedstock ln which a ~olvent-w~ter composition 1~ utilized wh~reby aromatic~ are recovered in high purity u~ing a mlnimum o spparatus and heat and making more effective u~e o~
. , .
process componen~s.
O~her objects and atvantagas will beca~e apparent , herein~fter.
According to the pres~nt invention) high p~rity aromatic hydrocarbons are effect~vely recover~d u~ing min~mal 8ppar~tu8 and heat by a oontinuou~ ~01~2n~
.- 4 . , . . ...................... . - .. . - . . . . .
. , .
~ ~ 5 ~8 7 6 9506 extr~ction - ~te~m dl~Z~illation proc~s~ ~or theZ recovery of sromatic hydrocflrbons ha~ing boiling polnts in the range of about 80C. to about 175C. from ~ fe~datock containing ~liphatlc hydrocarbo~ ant said aromatic hydro-carbons ccmpri~ing the following ~tep~:
~a) introducing the ~eed~tock into ~n e~x~raction - zone at about the midpoint Zthereof;
(b) introduc1ng a mixturc o~ water and 301ve,nt into the extraction zone ~t about the top of ~aid extraction zone, ssld ~olvent being a water-misc~,le organic liquid having a bolling point o~ at least about 200C. and having a decomposition teZ~perature of at least about 225C,;
(c) inZ~roducing re1ux hydro¢~rbons into th~
extraction zone at about the bo~ttom thereof;
: (d) contact~ng ~e f~Zedatock in the eZxtraction one with the mixture of w~ter and a solvent, the water phase of stsp (J), and ~he reflux hydro~arbons ~o provide an extract compris~ng aromatic hytrocarbons, reflux ali-phatic hydrocarbons, solvent, and water and a ra~inate co,~prising e~s2ntially aliphatic hydrocarbons;
~) contacting the ex~ract with steam in a di~,Ztillation zone ~o provide an overhead distillate compri~ng a reflux hydrocarbon~ phas~ and a water phase, B a ~ide cut di~tillate co~ rising ~n aromatic~ hydrocarbo~s pha3e and a w~ter ph~e~ and bo~t~oms comprising a mixture o~ solvenZ~ ~nd w~r;
_ 5 .
, .......................... . . .
. . . .
: . . , . . ~ .
~Sj~37~
: ~ .
(f~ contacting the ra~finate with the water phase of step (g~ to provide a raffinate aliphatic :
hydrocarbons phase and a water phase;
~ (g) contacting the raffinate aliphatic hydro-- carbons of step (f) with the water phase of (f) to the side cut distillate to provide a raffinate aliphatic . hydrocarbons phase and a water phase;
(h) contacting ~he water phase of the overhead `~
distillate with an aromatic hydrocarbons stream containing at least 95 percent aromatic hydrocarbons, the amount of said stream being in the range of akout 0.1 percent to -:
about 5 percent by weight of ~he total aromatic hyclrocarbons : ~
, in the eedstock to form an aromatic hydrocarbons phase .
and a water phase;
(i) contactlng the aromatic hydrocarbons phase . ;
`.^f of the side-cut distillate with the water phase of (h) ~ ~
j to form an aromatic hydrocarbons phase and a water phase; `~
(j) recycling the water phase of step (f) to .' the extraction zo~e.at about the midpoint thereof;
~: 20 (k) recycling the water phase of step (i) to the . ~ ,.. .
~. distillation zone where said water phase is essentially ~ :
,::
converted to steam; ~ .
. .. . ..
(1) recycling the reflux hydrocarbons phase of the overhead distillate and the bottoms of step (e) to J the extraction zone to provide, respectively, reflux :~
3 hydrocarbons for step (c) and mixture of water and solvent ~ .. , for step (b); and (m) recovering the aromatic hydrocarbons phase of step 6 - :
...
, 'l ~
. ..
"!
,;''~ :
''' P~ , ' ~
... .
' ;.. ' , . ' ' . '.,. . ' ' . ' '' . '. "' ' . ' '. " . ' I . ' .
~05 ~7 ~ 9506 ~i) and the raffinate ~liphatic hydrocarbon~ phase o s~p (g)~
~I e~ 9~l~5¦9~___ __ __ _.win~
The ~ole flgure is a schemat~c flow diagram of fln illustrative embodiment of the pr~sent inv~ntion~ :
1~5lJ~95L~5 ~____ __ __ d~ E~
A~ noted aboveS there i8 ~n indu~trlal need ~or BTX, whlch i~ available in hi~h propo~ti,on9 e.g.~ greater ~han 30 percent by weight, ln a wide varlety o~ hydro-carbon feed8tocks ~uch as re~onmed ga~oline8; coke oven light oila; cracked ga301ine~; and dripol2ne~ which, ater hydrogenztion, can contain as much a~ 70 to 98 percent BTX. These feedstocks also contain both ~liphatic and cycloaliphatic hydrocarbon~ (herein reerred to collect-ively a8 aliphatic h~droearbon~). Since the individual hydrocsrbon compounts which make up the3e feedstocks are ~: well known, they w~ll not be discuss~d extensively; how-. ever, ~t can be pointed out that the ma~or components o :. the ~eed~tocks u8ed herein are hydrocarbon8 with boiling points ranging from 25C. to 175C~ including straight-chain and branched-chain pa~affln~ and naphthenes, such as n-heptane, i~ooctane, and methyl cyclohexane9 a~d ar3matics such 89 BTX.
The BTX fr~ction c~n include benzene, tolue~e, the~Cg aromatics including ortho-xylens, meta~xylene, pars-xylffne, ~nd ethyl benz~ne, and Cg aromaticfi which9 i~ pre~ent at all~ a~pear ln the gmall~3~ proportion in relation to the other co~ponent~.
The 801ve~t~ used in ~ub~ect proce~ are, a8 . 7 , . :' ;; , .
: .
.. .. . . . :
7 ~
described above, wa~er-miscible organi~ liquids (at process temperatures) having a boillng point of at least about 200C. and having a decomposition temperature of at least about 225C. The term "water-miscible" includes those solvents which are complete miscible over a wide range of temperatures and th~ e solvents which have a high partial miscibility at room temperature since the latter are usually completely miscible at process temperatures.
The solvents are also polar and are generally comprised of car~on, hydrogen and oxygen with some exceptions.
Examples of solvents which may be used in the process ~-of this invention are dipropylene glycol, tripropylene glycol, diethylene glycol, N-methyl-2-pyrrolidonc, triethylene glycol, tetraethylene glycol, acetamide~
diethylenetriamine, triethylenetetramine, diethanolamine~
para-cresol and meta-cresol, and mixtures thereof. The preferred group of solvents is the polyalkylene glycols and the preferred solvent is tetraethylene glycol.
, : , The apparatus used in the process both for the main extraction and the distillation is conventional, e.g., an ,i :
extraction column of the multistage reciprocating type containing a plurality o~ perforated plates centrally mounted on a vertical shaft driven by a motor in an oscillatory manner can be used as well as columns containing ,1 pumps w~ h settling zones, sieve trays with upcomers, or even a hollow tube while the distillation can be conducted in a packed or bubble plate fractionating column. Counter-current flows are utilized in both extraction and ` distillation columns.
` .:
~8--.,.... ~,`, ' " ' . ~' ~ ''.
'. ' , . , . ~. , ' ' ' ' ' ' . .. , " ' ,'~ ' ' ' ' '' ', , " :,', '',.'. . ' .' " , ' ' ` , '' ' ' ' ' ~ , ' ' .. . .. . ..
.
~55~'7~;
Heat exchangers, decanters, reservoir and solvent regenerator are also conventional as well as various extractors other than the main extrac~or~ These oth~r extractors are preferably single stage miixer settlers, but can be any of the well known types.
The solvent is used as an aqueous solution thereof and in the case, e.g. of tetraethylene g;Lycol, it usually contains about 4 percent to about 6 percent by weight of wa~er based on the combined weight of the solvent and water ; 10 and preferably contains water in an amoune of about 4.5 percent to about 5 percent by weight. Generally, however, the aqueous solutions contain about 1 to about 8 percent .; .
' ' ': ,.
.. ` , ,, .
` ' ~
.'.' ,.
"
~, .
,. . _g_ (3S~ 7 ~ 9~06 water and preerably about 2 to ~bout 5 percen~.
Thi~ aqueous ~olution 18 r~f~rred to h~re~ft~r ~n some lng~nce8 ~8 a solvent~water mixture. In thl~ psrticular prQcess, the foregoing amounts of water ~re thoHe used initi-ally and those that will ~ppear in ths ~t:Lll bottoms and the upper portion of the extractor, i.e., ~bove the mid~
point or feed-polnt. It ~g well known that these amount~
of water c~n be ad~usted by ad~usting the ~emperature ~nd pressure at the bottom of the ~till ~shown in the drawing as stripper 23). The amounts of water in the lGwer portion of the extractor, i.e" below the midpoint, will b~
discussed hereina~ter.
GeneraLly, to ~ccomplish th~ extr~ction, the ratio of solvent (exclusive of water) to ~eedstock in the extractor i3 in the range of about 4 to about 8 parts by weight of ~olvent to one part by weight of feedstock. Thi~
broad range can be expanded upon whera nonpreferred ~olvents are u~ed. A broad r~nge of abou~ 3 to about 12 parts by weigh~ of solvqnt t~ one part by welght o ~eedstock ~nd a p~e~erred r~nga of about 5 part~ to about 7 par~s of solvent per part o~ ~eedstock csn be used successfully ~or the ~olvent of preference ~d other like 801vent8.
~ In ~in~l analysis, h~wev~r, ~hQ ratio i8 ~elected by the i technician based on experience with the particular feed stock and depends i~ part upon whether high recovery or ~` high purity is bein8 emphas~zad, although the ~nst~nt process will lmprov~ puri~y in any case.
The re~lux to the extraction zone i~ generally ~ ~S 5~7 ~ 95~6 made up of ~bout 20 percent to about 5Q percent by weigh~
aliph~tics havlng from 5 to 7carbon atoms and about 50 parcent to about 80 percent by w~ight ar~m~tlc~9 both b~sod on the tot~l weight of the re1ux. The rstio of ~eflux to feedstock in the extraction zone is, generally, maintained in the range of about 0.5 to about 1.5 parts by weight of reflux to one part by welght of feedsto¢k and preferably about 0.5 to about 1.0 p~rt9 by welght o~ reflux to one par~ by weight of feedstock, but, agaln, is selected by the technician ~ust as ~he ra~lo of solvent to ~edstock.
The reflux a}iphfltic~ pa~ into the sxtract rather than belng t~ksn overhead with the raf~inate and are recycled ~o the extr~ctor from the re~lux decanter ~s wilL be aeen hereinafter.
The temperature in the extraction zone i3 maintained in the range o~ about 100C. to about 200-C. and i~ prefer-ably in ~he range of about 130C. to about 180C., e~peci~
~lly for the solvent of preference.
The pressure ln the oxtraction zone i8 maintained ~n th~ range of ~bout 75 p8ig to about 200 psig. As i~ well known in the art, however, one selected pressure i5 not -~ maintained throughout the extractlon zone, b~, ra~her, a high pressure wi~hin the stated range is pre~ent at the bo~tom of the zone and a low pressure again within the stated range i9 present at the top of the zone with an i~t~rmediate pre~3ure in the middle of the zon~ The pressures in the zone depend on the ~esign of the ... . .
, 1~)5~7~ 95û6 equlpment ~nd the temp~ratur~, both o which are ~d~u~ted ts ~intain the preasure wlthin the ~tated range.
The temperature at the top of ~he di~t~llation zone, which, in term~l of ~he spparatu~ used; may ~e referred to ~ a di~t~llation eolumn or stripp~r, i~ at the bolling point of the mixture of aromatic~ pr2s~n~ in the zone wh~le the te~pera~cure at the bottom of th~ ~3tripper i8 g~nerally in the range of: about 135C. to about 200C.
The pre~sure at the top of the ~tripper, an upper fla~h zone in this case,, i8 in the range of about 20 p8ig to about 35 psig. In a lower flash zone ~U8t b~ath the upper flash ~one and connected thereto, the pre~sure i~ in the r~ng~ o~ about 10 p~ig to about 20 p9ig ~nd i8 about 10 or 15 p8ig l~wer than the pressure ln the upper 1ash zone. The pr~s~ure in ~he re~t of the distillation zone i~ m~intained in the range of about 5 p~ig ~o about 30 p8ig with som~ variation throughout the zone.
The 3t~am brought into the bottom of the distillation zone ~nter3 at a tempera~ure o~ abou~ lOO~C. to ~bout 150C.
and i9 under a pres~ure of about 10 p~ig to about 25 p91g.
The total water pre~ent ~n the di3tillation column i8 es~entiAlly in vapor form and i3 generally in the r~nge of about Q.l parts to . bout 0.5 part~ by weight of water-to one par~ by weight of aromatics in the zone ~nd prefer- -ably in the range of about 0.1 parts to about 0~3 p~rt~
by weight of ~a~er to one part by weight of arom~tic~.
The water u~ed for the ~e~m m~y be called 8trip~ping water~
. .
~5~37t;
A small ~mount of water i~ preaent in liquid form in the di3tlllation zone dissolved in the solvent.
Referrirlg to the drawing:
The feedstock i~ introduced through line 1 into heat exchanger 2 where it i8 preheated to a temperattlre in the range of about 50C. to about lOO'~C. It then continues through line 1 to enter extractor 3 at about the middle tray thereo~. An aqueou~ solvent solution : havtng 8 te~perature in the r~nge o~ abou~ 135C. to ~bout 200C. enters ~t the top tray o~ extractor 3 through line
aliphAtic~ are necessarily prese~t in the fin~l product thu3 reduclng purity.
In sum, a~l of the proces~es men,tioned heretoore, while viable ccmmerci~lly, have not succeeded in optimizing process economics together with purity.
Great strides hav~ bsen made in such optimi~ation ~nd in obtaining hlgh purity benzene; a~, or example, :
in Uhited Sta~e~ pat~nt 3,714,033; however, processes which improve process economicsJ obtain high purit~ benz~ne, and, further, achieve hlgher toluene and xylene puritie~
are still being sought ater.
Summa~y of the Invention An ob3ect of this lnvention, therefore, 1~ to provide an improvQment in a process for the ~eparation of aroma~ic hydrocarbon~ from a mixed hydroc~rbon feedstock ln which a ~olvent-w~ter composition 1~ utilized wh~reby aromatic~ are recovered in high purity u~ing a mlnimum o spparatus and heat and making more effective u~e o~
. , .
process componen~s.
O~her objects and atvantagas will beca~e apparent , herein~fter.
According to the pres~nt invention) high p~rity aromatic hydrocarbons are effect~vely recover~d u~ing min~mal 8ppar~tu8 and heat by a oontinuou~ ~01~2n~
.- 4 . , . . ...................... . - .. . - . . . . .
. , .
~ ~ 5 ~8 7 6 9506 extr~ction - ~te~m dl~Z~illation proc~s~ ~or theZ recovery of sromatic hydrocflrbons ha~ing boiling polnts in the range of about 80C. to about 175C. from ~ fe~datock containing ~liphatlc hydrocarbo~ ant said aromatic hydro-carbons ccmpri~ing the following ~tep~:
~a) introducing the ~eed~tock into ~n e~x~raction - zone at about the midpoint Zthereof;
(b) introduc1ng a mixturc o~ water and 301ve,nt into the extraction zone ~t about the top of ~aid extraction zone, ssld ~olvent being a water-misc~,le organic liquid having a bolling point o~ at least about 200C. and having a decomposition teZ~perature of at least about 225C,;
(c) inZ~roducing re1ux hydro¢~rbons into th~
extraction zone at about the bo~ttom thereof;
: (d) contact~ng ~e f~Zedatock in the eZxtraction one with the mixture of w~ter and a solvent, the water phase of stsp (J), and ~he reflux hydro~arbons ~o provide an extract compris~ng aromatic hytrocarbons, reflux ali-phatic hydrocarbons, solvent, and water and a ra~inate co,~prising e~s2ntially aliphatic hydrocarbons;
~) contacting the ex~ract with steam in a di~,Ztillation zone ~o provide an overhead distillate compri~ng a reflux hydrocarbon~ phas~ and a water phase, B a ~ide cut di~tillate co~ rising ~n aromatic~ hydrocarbo~s pha3e and a w~ter ph~e~ and bo~t~oms comprising a mixture o~ solvenZ~ ~nd w~r;
_ 5 .
, .......................... . . .
. . . .
: . . , . . ~ .
~Sj~37~
: ~ .
(f~ contacting the ra~finate with the water phase of step (g~ to provide a raffinate aliphatic :
hydrocarbons phase and a water phase;
~ (g) contacting the raffinate aliphatic hydro-- carbons of step (f) with the water phase of (f) to the side cut distillate to provide a raffinate aliphatic . hydrocarbons phase and a water phase;
(h) contacting ~he water phase of the overhead `~
distillate with an aromatic hydrocarbons stream containing at least 95 percent aromatic hydrocarbons, the amount of said stream being in the range of akout 0.1 percent to -:
about 5 percent by weight of ~he total aromatic hyclrocarbons : ~
, in the eedstock to form an aromatic hydrocarbons phase .
and a water phase;
(i) contactlng the aromatic hydrocarbons phase . ;
`.^f of the side-cut distillate with the water phase of (h) ~ ~
j to form an aromatic hydrocarbons phase and a water phase; `~
(j) recycling the water phase of step (f) to .' the extraction zo~e.at about the midpoint thereof;
~: 20 (k) recycling the water phase of step (i) to the . ~ ,.. .
~. distillation zone where said water phase is essentially ~ :
,::
converted to steam; ~ .
. .. . ..
(1) recycling the reflux hydrocarbons phase of the overhead distillate and the bottoms of step (e) to J the extraction zone to provide, respectively, reflux :~
3 hydrocarbons for step (c) and mixture of water and solvent ~ .. , for step (b); and (m) recovering the aromatic hydrocarbons phase of step 6 - :
...
, 'l ~
. ..
"!
,;''~ :
''' P~ , ' ~
... .
' ;.. ' , . ' ' . '.,. . ' ' . ' '' . '. "' ' . ' '. " . ' I . ' .
~05 ~7 ~ 9506 ~i) and the raffinate ~liphatic hydrocarbon~ phase o s~p (g)~
~I e~ 9~l~5¦9~___ __ __ _.win~
The ~ole flgure is a schemat~c flow diagram of fln illustrative embodiment of the pr~sent inv~ntion~ :
1~5lJ~95L~5 ~____ __ __ d~ E~
A~ noted aboveS there i8 ~n indu~trlal need ~or BTX, whlch i~ available in hi~h propo~ti,on9 e.g.~ greater ~han 30 percent by weight, ln a wide varlety o~ hydro-carbon feed8tocks ~uch as re~onmed ga~oline8; coke oven light oila; cracked ga301ine~; and dripol2ne~ which, ater hydrogenztion, can contain as much a~ 70 to 98 percent BTX. These feedstocks also contain both ~liphatic and cycloaliphatic hydrocarbon~ (herein reerred to collect-ively a8 aliphatic h~droearbon~). Since the individual hydrocsrbon compounts which make up the3e feedstocks are ~: well known, they w~ll not be discuss~d extensively; how-. ever, ~t can be pointed out that the ma~or components o :. the ~eed~tocks u8ed herein are hydrocarbon8 with boiling points ranging from 25C. to 175C~ including straight-chain and branched-chain pa~affln~ and naphthenes, such as n-heptane, i~ooctane, and methyl cyclohexane9 a~d ar3matics such 89 BTX.
The BTX fr~ction c~n include benzene, tolue~e, the~Cg aromatics including ortho-xylens, meta~xylene, pars-xylffne, ~nd ethyl benz~ne, and Cg aromaticfi which9 i~ pre~ent at all~ a~pear ln the gmall~3~ proportion in relation to the other co~ponent~.
The 801ve~t~ used in ~ub~ect proce~ are, a8 . 7 , . :' ;; , .
: .
.. .. . . . :
7 ~
described above, wa~er-miscible organi~ liquids (at process temperatures) having a boillng point of at least about 200C. and having a decomposition temperature of at least about 225C. The term "water-miscible" includes those solvents which are complete miscible over a wide range of temperatures and th~ e solvents which have a high partial miscibility at room temperature since the latter are usually completely miscible at process temperatures.
The solvents are also polar and are generally comprised of car~on, hydrogen and oxygen with some exceptions.
Examples of solvents which may be used in the process ~-of this invention are dipropylene glycol, tripropylene glycol, diethylene glycol, N-methyl-2-pyrrolidonc, triethylene glycol, tetraethylene glycol, acetamide~
diethylenetriamine, triethylenetetramine, diethanolamine~
para-cresol and meta-cresol, and mixtures thereof. The preferred group of solvents is the polyalkylene glycols and the preferred solvent is tetraethylene glycol.
, : , The apparatus used in the process both for the main extraction and the distillation is conventional, e.g., an ,i :
extraction column of the multistage reciprocating type containing a plurality o~ perforated plates centrally mounted on a vertical shaft driven by a motor in an oscillatory manner can be used as well as columns containing ,1 pumps w~ h settling zones, sieve trays with upcomers, or even a hollow tube while the distillation can be conducted in a packed or bubble plate fractionating column. Counter-current flows are utilized in both extraction and ` distillation columns.
` .:
~8--.,.... ~,`, ' " ' . ~' ~ ''.
'. ' , . , . ~. , ' ' ' ' ' ' . .. , " ' ,'~ ' ' ' ' '' ', , " :,', '',.'. . ' .' " , ' ' ` , '' ' ' ' ' ~ , ' ' .. . .. . ..
.
~55~'7~;
Heat exchangers, decanters, reservoir and solvent regenerator are also conventional as well as various extractors other than the main extrac~or~ These oth~r extractors are preferably single stage miixer settlers, but can be any of the well known types.
The solvent is used as an aqueous solution thereof and in the case, e.g. of tetraethylene g;Lycol, it usually contains about 4 percent to about 6 percent by weight of wa~er based on the combined weight of the solvent and water ; 10 and preferably contains water in an amoune of about 4.5 percent to about 5 percent by weight. Generally, however, the aqueous solutions contain about 1 to about 8 percent .; .
' ' ': ,.
.. ` , ,, .
` ' ~
.'.' ,.
"
~, .
,. . _g_ (3S~ 7 ~ 9~06 water and preerably about 2 to ~bout 5 percen~.
Thi~ aqueous ~olution 18 r~f~rred to h~re~ft~r ~n some lng~nce8 ~8 a solvent~water mixture. In thl~ psrticular prQcess, the foregoing amounts of water ~re thoHe used initi-ally and those that will ~ppear in ths ~t:Lll bottoms and the upper portion of the extractor, i.e., ~bove the mid~
point or feed-polnt. It ~g well known that these amount~
of water c~n be ad~usted by ad~usting the ~emperature ~nd pressure at the bottom of the ~till ~shown in the drawing as stripper 23). The amounts of water in the lGwer portion of the extractor, i.e" below the midpoint, will b~
discussed hereina~ter.
GeneraLly, to ~ccomplish th~ extr~ction, the ratio of solvent (exclusive of water) to ~eedstock in the extractor i3 in the range of about 4 to about 8 parts by weight of ~olvent to one part by weight of feedstock. Thi~
broad range can be expanded upon whera nonpreferred ~olvents are u~ed. A broad r~nge of abou~ 3 to about 12 parts by weigh~ of solvqnt t~ one part by welght o ~eedstock ~nd a p~e~erred r~nga of about 5 part~ to about 7 par~s of solvent per part o~ ~eedstock csn be used successfully ~or the ~olvent of preference ~d other like 801vent8.
~ In ~in~l analysis, h~wev~r, ~hQ ratio i8 ~elected by the i technician based on experience with the particular feed stock and depends i~ part upon whether high recovery or ~` high purity is bein8 emphas~zad, although the ~nst~nt process will lmprov~ puri~y in any case.
The re~lux to the extraction zone i~ generally ~ ~S 5~7 ~ 95~6 made up of ~bout 20 percent to about 5Q percent by weigh~
aliph~tics havlng from 5 to 7carbon atoms and about 50 parcent to about 80 percent by w~ight ar~m~tlc~9 both b~sod on the tot~l weight of the re1ux. The rstio of ~eflux to feedstock in the extraction zone is, generally, maintained in the range of about 0.5 to about 1.5 parts by weight of reflux to one part by welght of feedsto¢k and preferably about 0.5 to about 1.0 p~rt9 by welght o~ reflux to one par~ by weight of feedstock, but, agaln, is selected by the technician ~ust as ~he ra~lo of solvent to ~edstock.
The reflux a}iphfltic~ pa~ into the sxtract rather than belng t~ksn overhead with the raf~inate and are recycled ~o the extr~ctor from the re~lux decanter ~s wilL be aeen hereinafter.
The temperature in the extraction zone i3 maintained in the range o~ about 100C. to about 200-C. and i~ prefer-ably in ~he range of about 130C. to about 180C., e~peci~
~lly for the solvent of preference.
The pressure ln the oxtraction zone i8 maintained ~n th~ range of ~bout 75 p8ig to about 200 psig. As i~ well known in the art, however, one selected pressure i5 not -~ maintained throughout the extractlon zone, b~, ra~her, a high pressure wi~hin the stated range is pre~ent at the bo~tom of the zone and a low pressure again within the stated range i9 present at the top of the zone with an i~t~rmediate pre~3ure in the middle of the zon~ The pressures in the zone depend on the ~esign of the ... . .
, 1~)5~7~ 95û6 equlpment ~nd the temp~ratur~, both o which are ~d~u~ted ts ~intain the preasure wlthin the ~tated range.
The temperature at the top of ~he di~t~llation zone, which, in term~l of ~he spparatu~ used; may ~e referred to ~ a di~t~llation eolumn or stripp~r, i~ at the bolling point of the mixture of aromatic~ pr2s~n~ in the zone wh~le the te~pera~cure at the bottom of th~ ~3tripper i8 g~nerally in the range of: about 135C. to about 200C.
The pre~sure at the top of the ~tripper, an upper fla~h zone in this case,, i8 in the range of about 20 p8ig to about 35 psig. In a lower flash zone ~U8t b~ath the upper flash ~one and connected thereto, the pre~sure i~ in the r~ng~ o~ about 10 p~ig to about 20 p9ig ~nd i8 about 10 or 15 p8ig l~wer than the pressure ln the upper 1ash zone. The pr~s~ure in ~he re~t of the distillation zone i~ m~intained in the range of about 5 p~ig ~o about 30 p8ig with som~ variation throughout the zone.
The 3t~am brought into the bottom of the distillation zone ~nter3 at a tempera~ure o~ abou~ lOO~C. to ~bout 150C.
and i9 under a pres~ure of about 10 p~ig to about 25 p91g.
The total water pre~ent ~n the di3tillation column i8 es~entiAlly in vapor form and i3 generally in the r~nge of about Q.l parts to . bout 0.5 part~ by weight of water-to one par~ by weight of aromatics in the zone ~nd prefer- -ably in the range of about 0.1 parts to about 0~3 p~rt~
by weight of ~a~er to one part by weight of arom~tic~.
The water u~ed for the ~e~m m~y be called 8trip~ping water~
. .
~5~37t;
A small ~mount of water i~ preaent in liquid form in the di3tlllation zone dissolved in the solvent.
Referrirlg to the drawing:
The feedstock i~ introduced through line 1 into heat exchanger 2 where it i8 preheated to a temperattlre in the range of about 50C. to about lOO'~C. It then continues through line 1 to enter extractor 3 at about the middle tray thereo~. An aqueou~ solvent solution : havtng 8 te~perature in the r~nge o~ abou~ 135C. to ~bout 200C. enters ~t the top tray o~ extractor 3 through line
4 and percolates down the column removing aromatics rom the ~edstock.
The rafinate, essentially free o aromatics, leaves the top of the column through hea~ exchanger 2 ~ ;
wher~ it i8 used to preheat the ~eed~tock and iB cooled ln -~
turn to a temperature in the range of 75C. to about 125C.
The ra~finate comprises about 95 percent to about 98 percent by weight aliphatic~, abo~t 1 p~rcent to about 3 percQnt by weight dissolved and entrained ~olvent, and abo~t 0 percent to about 3 p~rcent by weigh~ aromatics.
, The rafin~te then pa~ses through cooler 6 where it is ; f~rther cooled to about 25C~ to about 50~C. and proceeds along line 5 to mixer-settler i where it is contacted with a portion of ~he wa~er phase comlng from`mixer~settler 8 via llnes 11, 12, 20~ and 5 combined with a recirculated portio~ of its uwn water phase, w~ich pa88e9 through lines 10, 20, and 5. The first ~tage raffinate wa~h takes . . . . , . . :, ,, . :
. .. . , . ~ .
.
The rafinate, essentially free o aromatics, leaves the top of the column through hea~ exchanger 2 ~ ;
wher~ it i8 used to preheat the ~eed~tock and iB cooled ln -~
turn to a temperature in the range of 75C. to about 125C.
The ra~finate comprises about 95 percent to about 98 percent by weight aliphatic~, abo~t 1 p~rcent to about 3 percQnt by weight dissolved and entrained ~olvent, and abo~t 0 percent to about 3 p~rcent by weigh~ aromatics.
, The rafin~te then pa~ses through cooler 6 where it is ; f~rther cooled to about 25C~ to about 50~C. and proceeds along line 5 to mixer-settler i where it is contacted with a portion of ~he wa~er phase comlng from`mixer~settler 8 via llnes 11, 12, 20~ and 5 combined with a recirculated portio~ of its uwn water phase, w~ich pa88e9 through lines 10, 20, and 5. The first ~tage raffinate wa~h takes . . . . , . . :, ,, . :
. .. . , . ~ .
.
5~
plsce in mixer-settler 8 and the ~econd stage raf~lnate wa~h takes place ln mixer-settler 7~ ïn both mixer-set~lers ; 7 and 8 a raffinate aliphatic hydrocarbon~ phase and a wa~er phase are formed, e~ch water phase belng contaminated with aliphatics. It should be poin~ed out thst ~h~ mixer-~ettler i3 represented by a box to denote a ~one. In fac'c, a mixer-se~tler i~ two pieces o~ apparatus, the ~xer in whi~h the mlxing i~ accomplished and the settler in whlch the settling i~ accomplished, Single stage mixer-settlers are preferred here, but other conv~n~ional types of extractor can be used.
Tt also ~hould be noted that the "phase" i8 named after its main component, which i8 pr~sent in the phase in an amount of at least S0 percent by weight and, in mo~t ca~es, in an amount of at lea~t 90% ~y we~ght.
The aliphatic hydrocarbons phase leaving mixer-~ettler 7 via line 5 can 8till be referred to as the raffinate ~nd : now contains about 96 percent to about 99 percent by weight aliphatics, about 0 percent to about 1 pcrce~t by weight dissolved and entrained solvent~ and about 0 percent to about 3 percent by weight aromaticæ. The water phase, ;. on the other hand, cont~lns about 48 percent to ~bout 84 ., percent by weight water, about 15 percent to about 50 percent by welght sol~ent, and about 1 percent to about ;`! 2 percent by weight aliphatics.
The raf~inate continues overhead through line 5 into mixer-se~tler 8.
~ .
~ ~ 5~7 ~
The balance, generally a major proportion or more than 50% by weight, of ~he combined water phases passing through line 20 is preferably sent through line 20a to join line 1 and enter extractor 3 at about its midpoint.
The raffinate wash which takes pLace in mixer-settler 8 is called the first stage raffinate wash simply because the water used in this wash comes directly from the system whereas the water used in ~he raffinate wash in mixer-settler 7 comes from mixer-settler 8. See above.
The washes are counter-current. It should be noted that a portion of the water phase from mixer-settler 8 is optionally recirculated to mixer-settler 8 via lines 11, 9a, 9b, and 5. Aside from the rec-Lrculated water phase, the water used in mixer-settler 8 is pre~erably obtained from aromatics decanter 36 via lines 37, 38, 32, 9b, and 5, but can be alternatively obtained from reflux decanter 29 via lines 31, 32, 9b, and 5. The aromatics decanter 36 source is used, e.g., where the feed is a high aromatics one and the pentanes present in the feed reduce the water flow from reflux decanter 29. The technician has to make this choice depending on the availability of water from the mentioned sources. In some cases both sources can be used.
Another option open to the technician and also dependent on the composition of the feed is whether a two stage raffinate wash or a single stage raffinate wash is to be used. In most cases the two stage raffinate wash described ;, :
.. , ~ .
.` ~`
. ~
.
lC~5~iY7~;
here i~ to be preferred. Th~ ~ingle ~tag~ raffinate w~sh iB aecompli~h~d, howevar~ by eliminatlng mixer~settLer 7, line 10, flnd l~ne 9b Recirculation to mixer~set~ler 8 would then follow the path along lines 11, 12, 20, and 5. The single stage wa~h i8 generally effected in cases wh~re there i~ ~ small raf~inate, e.g., in dripolenes.
The componen~ in mixer-settler 8 ~ep~ra~e into fln ~liphatlc hydrocarbons pha~e (still called the raff:anate) which i~ e~sentially free of 801vent and water and contains about 97 percent to about 100 percent by weight aliphatics and about 0 percent to about 3 percent by weight aromatics, and a rafinate water phase as bottom~ which contain~ about 95 percent to about 98 percent by weight water, about 0.1 percent to about 3.0 p~rcent by weight solvent, and about 1 percent to about 2 percent by weight aliphatic~. The .
~eparstion in mixer-e~ttler 7 i8 about ~he ~ame, but the ra~in~te ~till ha9 ~ome solvent and water 80 the percent-age of aliphatics ha~ to be revised downward.
As pointed out, p~rt of the raf~inate w~ter pha~e can optionally be recirculated through the m~xer-settler rom which it came. In the cas0 o~ mixer-settler 8, the r2circulation woult take pla¢e along lines 11, 9a, 9b, and 5. In the csse of mixer~aettler 7~ the reclrculation would take pl~ce al~ng lin2s 10, 20, ~nd 5. Thi~ recirculation is convent~bnal with a mixsr-settler arrangement, but may not be ad~antageous with other typ2s of extractors.
The balance of the combined raffinate water phases ~; - 16 -,~; ' ~ 7 ~
whlch was ~aken alon~ llnes 20, 20a, and 1 to enter extractor 3 disso1~e~ ~n the rich ~o1vent passlng down the extractor past the midpoint and pass~!s into the l~wer ha1f of the ~xtractor co1umn. This addi~:isna1 water in the l~wer half o the extractor causes a1iphatic3 to come out of the extract ~olution by disp1acement t:hus purifying ~he aromatics having a particu1ar effect on toluene and xylane puritie~. The lower water content at ~he top of the extractor increa~es so1vency in the top of the extractor for a1iphatics while at th~ bottom so1vency i8 reducecl and se1ectivity for aromatics increased. It wa~ notecl above that ~he water in the upper half o the e~trActor iB used in the amount of about 4 to about 6 percent by weight based on the combined weight of the soLve~t and water and preferably about 4.S to about 5 percent. The water in the lower ha1f o~ ~he extractor is about 0.5 ~o abou~ 1.5 percent above that in the upper ha1 of the e~tractor and i9 preferably about 0.75 to abou~ 1.25 percent above. The percentages here are again based on the total weight of the mlxture of so1vent and water in the e~traction zone.
If there is insufficient water in the raffinate water pha~e, or anywhere in the system, outside water can, of course, be used; however, side stream water via lines 37, 38, 32, 9b and 5 can be and is preferab1y u~ed to make up any 1ack in the rafinate water phase. The use of thi~ side stream water does reduce th~ ~mount of ~LOS~
~ripping water ~vailable, but this can be ~imply taken care of by rai~ing the bottoms temperature of s~ripper 23.
The recycle of the raffinate water pha~e ~o the midpoint of the extractor al~o permits the reduc~lon of the sol~ent ` to feedstock ratio referred to above ~hu~ providing a sa~ing in solvent.
Another option is the addition of water to the bottom of extractor 3 via line~ 20b and 18. This water can be all or part of the balance of the combined ra~inate water phases which, as noted above, was preferably ~en~ along line 20a. While not increasing the water content of the solvent solution below the feed point, this option does : result in the oiling out o~ an addltlonal hydrocarbon layer at the bottom of extractor 3. This hydrocarbon layer passes up the lowcr half of extractor 3 and increase~ the purification in that zone.
It has been noted above that the aqueous solvent percolates down extractor 3 carrying with it the aromatics and Joining the r~ffinate water phase. In the lower half o~ extractor 3, the solvent solution of aromatics comes into countercurrent contact with a reflux liquid, which enter~ extractor 3 below the bottom tray along li~e 18.
Th~ reflux percolates up the lower half of extractor 3 progressively dis~olving lh and purifying the ~olvent solution of aromatics. The ~olution which is ~ormed, i.e., the extract, compri~es about 5 percen~ to about 10 percent by weight feed~tock aromatics, about 3 percent to abou : ., g506 ~ ~ S 5~7 ~
plsce in mixer-settler 8 and the ~econd stage raf~lnate wa~h takes place ln mixer-settler 7~ ïn both mixer-set~lers ; 7 and 8 a raffinate aliphatic hydrocarbon~ phase and a wa~er phase are formed, e~ch water phase belng contaminated with aliphatics. It should be poin~ed out thst ~h~ mixer-~ettler i3 represented by a box to denote a ~one. In fac'c, a mixer-se~tler i~ two pieces o~ apparatus, the ~xer in whi~h the mlxing i~ accomplished and the settler in whlch the settling i~ accomplished, Single stage mixer-settlers are preferred here, but other conv~n~ional types of extractor can be used.
Tt also ~hould be noted that the "phase" i8 named after its main component, which i8 pr~sent in the phase in an amount of at least S0 percent by weight and, in mo~t ca~es, in an amount of at lea~t 90% ~y we~ght.
The aliphatic hydrocarbons phase leaving mixer-~ettler 7 via line 5 can 8till be referred to as the raffinate ~nd : now contains about 96 percent to about 99 percent by weight aliphatics, about 0 percent to about 1 pcrce~t by weight dissolved and entrained solvent~ and about 0 percent to about 3 percent by weight aromaticæ. The water phase, ;. on the other hand, cont~lns about 48 percent to ~bout 84 ., percent by weight water, about 15 percent to about 50 percent by welght sol~ent, and about 1 percent to about ;`! 2 percent by weight aliphatics.
The raf~inate continues overhead through line 5 into mixer-se~tler 8.
~ .
~ ~ 5~7 ~
The balance, generally a major proportion or more than 50% by weight, of ~he combined water phases passing through line 20 is preferably sent through line 20a to join line 1 and enter extractor 3 at about its midpoint.
The raffinate wash which takes pLace in mixer-settler 8 is called the first stage raffinate wash simply because the water used in this wash comes directly from the system whereas the water used in ~he raffinate wash in mixer-settler 7 comes from mixer-settler 8. See above.
The washes are counter-current. It should be noted that a portion of the water phase from mixer-settler 8 is optionally recirculated to mixer-settler 8 via lines 11, 9a, 9b, and 5. Aside from the rec-Lrculated water phase, the water used in mixer-settler 8 is pre~erably obtained from aromatics decanter 36 via lines 37, 38, 32, 9b, and 5, but can be alternatively obtained from reflux decanter 29 via lines 31, 32, 9b, and 5. The aromatics decanter 36 source is used, e.g., where the feed is a high aromatics one and the pentanes present in the feed reduce the water flow from reflux decanter 29. The technician has to make this choice depending on the availability of water from the mentioned sources. In some cases both sources can be used.
Another option open to the technician and also dependent on the composition of the feed is whether a two stage raffinate wash or a single stage raffinate wash is to be used. In most cases the two stage raffinate wash described ;, :
.. , ~ .
.` ~`
. ~
.
lC~5~iY7~;
here i~ to be preferred. Th~ ~ingle ~tag~ raffinate w~sh iB aecompli~h~d, howevar~ by eliminatlng mixer~settLer 7, line 10, flnd l~ne 9b Recirculation to mixer~set~ler 8 would then follow the path along lines 11, 12, 20, and 5. The single stage wa~h i8 generally effected in cases wh~re there i~ ~ small raf~inate, e.g., in dripolenes.
The componen~ in mixer-settler 8 ~ep~ra~e into fln ~liphatlc hydrocarbons pha~e (still called the raff:anate) which i~ e~sentially free of 801vent and water and contains about 97 percent to about 100 percent by weight aliphatics and about 0 percent to about 3 percent by weight aromatics, and a rafinate water phase as bottom~ which contain~ about 95 percent to about 98 percent by weight water, about 0.1 percent to about 3.0 p~rcent by weight solvent, and about 1 percent to about 2 percent by weight aliphatic~. The .
~eparstion in mixer-e~ttler 7 i8 about ~he ~ame, but the ra~in~te ~till ha9 ~ome solvent and water 80 the percent-age of aliphatics ha~ to be revised downward.
As pointed out, p~rt of the raf~inate w~ter pha~e can optionally be recirculated through the m~xer-settler rom which it came. In the cas0 o~ mixer-settler 8, the r2circulation woult take pla¢e along lines 11, 9a, 9b, and 5. In the csse of mixer~aettler 7~ the reclrculation would take pl~ce al~ng lin2s 10, 20, ~nd 5. Thi~ recirculation is convent~bnal with a mixsr-settler arrangement, but may not be ad~antageous with other typ2s of extractors.
The balance of the combined raffinate water phases ~; - 16 -,~; ' ~ 7 ~
whlch was ~aken alon~ llnes 20, 20a, and 1 to enter extractor 3 disso1~e~ ~n the rich ~o1vent passlng down the extractor past the midpoint and pass~!s into the l~wer ha1f of the ~xtractor co1umn. This addi~:isna1 water in the l~wer half o the extractor causes a1iphatic3 to come out of the extract ~olution by disp1acement t:hus purifying ~he aromatics having a particu1ar effect on toluene and xylane puritie~. The lower water content at ~he top of the extractor increa~es so1vency in the top of the extractor for a1iphatics while at th~ bottom so1vency i8 reducecl and se1ectivity for aromatics increased. It wa~ notecl above that ~he water in the upper half o the e~trActor iB used in the amount of about 4 to about 6 percent by weight based on the combined weight of the soLve~t and water and preferably about 4.S to about 5 percent. The water in the lower ha1f o~ ~he extractor is about 0.5 ~o abou~ 1.5 percent above that in the upper ha1 of the e~tractor and i9 preferably about 0.75 to abou~ 1.25 percent above. The percentages here are again based on the total weight of the mlxture of so1vent and water in the e~traction zone.
If there is insufficient water in the raffinate water pha~e, or anywhere in the system, outside water can, of course, be used; however, side stream water via lines 37, 38, 32, 9b and 5 can be and is preferab1y u~ed to make up any 1ack in the rafinate water phase. The use of thi~ side stream water does reduce th~ ~mount of ~LOS~
~ripping water ~vailable, but this can be ~imply taken care of by rai~ing the bottoms temperature of s~ripper 23.
The recycle of the raffinate water pha~e ~o the midpoint of the extractor al~o permits the reduc~lon of the sol~ent ` to feedstock ratio referred to above ~hu~ providing a sa~ing in solvent.
Another option is the addition of water to the bottom of extractor 3 via line~ 20b and 18. This water can be all or part of the balance of the combined ra~inate water phases which, as noted above, was preferably ~en~ along line 20a. While not increasing the water content of the solvent solution below the feed point, this option does : result in the oiling out o~ an addltlonal hydrocarbon layer at the bottom of extractor 3. This hydrocarbon layer passes up the lowcr half of extractor 3 and increase~ the purification in that zone.
It has been noted above that the aqueous solvent percolates down extractor 3 carrying with it the aromatics and Joining the r~ffinate water phase. In the lower half o~ extractor 3, the solvent solution of aromatics comes into countercurrent contact with a reflux liquid, which enter~ extractor 3 below the bottom tray along li~e 18.
Th~ reflux percolates up the lower half of extractor 3 progressively dis~olving lh and purifying the ~olvent solution of aromatics. The ~olution which is ~ormed, i.e., the extract, compri~es about 5 percen~ to about 10 percent by weight feed~tock aromatics, about 3 percent to abou : ., g506 ~ ~ S 5~7 ~
6 percent by weight water, about 75 percent ~o about 85 percent by weight 901vent, about 4 percent ~o about 8 percent by weight re~lux aromatics, and abou~ 3 percen~ ~o about 6 percent by weight reflux allphat:ic~, all based on - the total weight of the extract.
The extract le~ves the bottom o~ ~xtractor 3 through line 19 and p~83e8 through heat exchanger 22 where it i8 cooled to a temperature in the range of about 100C to about 140C. The extract proceeds along line 19 and enters stripper 23, the distillation zone, a~
upper ~lash chamber 24, which, as noted heretofore, i8 at a lower pressure than the ~xtractor. Part of the extract flashes on entering the ~lash chamber and is taken over-head through line 18 in vapor form. Another part o~ the extract pa~ses as a llquid into lower flash chamber 21, :i which is operated a~ an even lower pressure and further flashing occurs. It should be noted that fla~hing is minimized in the present process. The flashed vapors Join the fractionated vapors and pasB through line 30 to 20 ~oin the vapors passing through line 18. The balance o~
the e$trsct ~at least about 80 percent by weight) percolates down the column into the fractionation zone where it c~mes into countercurrent contact with the stripping vapors, i.e., steam, and more vapors are gener~
ated. A part of the vapor rises to the top of the column and mixes ~th ~he flashed vapor~ ~n flash chamber 21 a~
noted. The overhead distillate comprises about 40 to : - 19 -~0 5 ~f~ :
about 75 percent by wslght aromatirs, ~bout 20 to about 40 percent allphatic~, abou~ 2 percen~ t:o about lO percent by weight water, and about 0 percent ~o ~bout 5 percent by we~ght solv~nt, all based on the total weight of the overhead distillate.
After ~he aqueou~ solvent descends ~bout halfway down the column, it becomes essentially ~ree of al~pha~ies.
At thi3 point, a vapor side-~tream distillate is removed through line 26. The side-~tream distillate i~ comprised of about 65 to about 90 percent by w~ight arom~tics, about 10 to ~bout 30 percent by welght water, and about 1 percent to about 10 percent by wei~ht o solvent, based o~ the total weight of the side-stream distillate.
: T~a bulk of the ~olvent and water solution~ an - ~mount equal to over 99 percent by weight of the solvent -, and water entering stripper 23 through line 19, leaves the bo~tom of s~ripper 23 through line 4. A portion of this solution is diYerted into reboiLer 28 and returns as a vapor to a point below the bottom tray of stripper 20 23 to provlde most of the Btripperls heating requirements.
The bal~ce of the w~ter and solvent solutionL i~ recycled . .
to the top tray of extractor 3 through line 4. Recycled strlpping water contalning some di~solved 801vent enters ~tripper 23 through line 2~ from water re~ervolr 51 a~er es~entially all of it ig converted ln hea~ exchanger 22 to steam. Returning to the overhead dlstilla~e mentioned heretofore, such overhead distillate i8 a combination of g506 ~ ~ 5 ~ ~ 7 ~flashed vapors and fr~ctionated vapor~ h~ving the afore-men~ioned composition. This overhe~d di~tillate 1~ ~190 known as a reflux dis~illate. The ~por i8 first condensed and cooled to be~ween about 38C. and 94C. ln refl~c condenser 25. The condensa~e then paese~ into reflux decanter 29 where a reflux hydrocarbons phase i9 deCQnted from a water pha~e. The reflux hydrocarbons ph~e comprises about 20 to 50 percent by weight aliphatics hnving from 5 to 7 c~rbon atoms, and about 50 to abvut 80 percent by weight aromatic~ and is recycl~d ~s reflux through l~ne 18 to extractor 3 ~19 previou~ly de~cribed.
The water phase con~alns about 95 to abou~ 99 p~rcent by weight water, about 0 to ~bout 5 psrcent by weight solvent~ and about 0.1 to a~out 0.5 percent by weight aliphatics. It passes through line 31 and may be ~plit into two streams, lines 32 and 33, a raffinate wa~h stre~m and an aromatics wash stream, respectively, depending, as noted above, on the amount of water available. The preerred mode of operation, how0ver, i9 to use the refl~x distillate water phase or the aromatics wash ~nd the side cut distillate water phase for ths raffinate wash.
As noted heretofore9 the side- tream distillate is withdrawn in vapor fonm from stripper 23 through line 26 and conden~ed in arom~tics condenser 34 and further co~led to R ~emperature in the range of about 25DC. to about 50C.
in cooler 35, which can be a heat exchanger or other type of cooling device. The condensate ~hen pa~se~ into aromatics .
,, ', .. ' ' . ~.. . ' .
~ ~ 5 ~
decanter 36 where ~n aromatic hydroc~rbons ph~s~ con~ain-ing about 99.8 to abou~ 99.9 perc~nt by w~ght aromatics, and about 0.} to about 0.2 percent by weigh~ ~olven~ ant a water ph~e containlng abou~ 90 p~rcent to about 98 percent by welght water, about 2 pQrcent to about 10 psrc~nt by welght solvent, ~nd about 0.1 percen~ to about 0.5 percen~
by weight sromatics are ~ormst. The w~e~r pha0e may pa88 through line 37 to water re~er~oir 51. Preer~bly, however, all or part o~ the water phaæ~ i5 dir~cted throu~h ~lvet line 38 to Join line 32 for u~e as raffinate wash.
The aromatic hydrocarbon~ phase proceeds rom decanter 36 through line 26 a}ong which an aromatics slip-gtream i9 taken through line 14 to wash w~t~r coming from reflux decanter 29 along line 33. The aroma~ic~ slip~tream at it~ source 1~ ~n easentially pure ~tre~m o~ ~romatic~, i.
e., having a purity of at lea3t 95 percent by w~ight, or in other words, at least 95 perc~nt by weight o the 011p-~tream i8 sromatic hydrocarbon~. The purity d ~he slip-stream i9 preferably about 98 percent and or optim~m p~r-ormance, l.e., to obt~in the highest purity product, about 99 percent. I'c i~ called a ~lipstream or ~ldestream becau~e the amount of aromatic~ fet into th~ water pha~ p~ing throttgh line 33 i9 very ~mall. Th~ arnount of sllp~tresm aroma~ic hydroc~rbo~s used ln the proc~ss i~ in the ra~ge of about 0.1 percent to about 5 p~reent by wetght oi~ t:he Broma~CiC hydrscarbons in the ~eed~tol:k and i~ pref~rllbly in ~he r~nge o~ ~botl~ 0.5 p~rc~n'c to about 2.0 perc:~nt by - 22 ~
.
950&
~ ~5 ~ ~7 ~
weigh~ of such aromatic hydrocarbon~. Th¢ ~lipstream wa~hes the water in extractor 39 to remove the small amoun~ of aliphatics, which i9 80 detrimental~to ~h~
efficiency of the proceas. Thi~ aromat~c~ slipstream ~8 then, preerably, 3ent along line 16 to line 1 w~ere it~i~
rein~roduced into the feedstock and pas~es lnto the Rystem once more, or, alternatively, it i9 removed fram the 8ystem.
I~ practice, the weight of the tot~l aroma~lcs is determlned by analysi~ of ~ sampl~ portion of the feed-; stoclc. Aromatlcs added, e.g., as slipstream, during the process oycLe are included in the det~rmination.
The slip~tream can, alternati~ely, be obt~ined from anoth~r source such as the overhe~d product of a benzene : ractionating column, which ~8 not shown in the drawin~, or rom a source completely removed from the system. A~
long as the slipstream has the previously noted high ~rom~tics content, it will be Ratisactory in this process.
The comblnet streams of lines 33 and 14 proceed into wash extractor 39, which can be a slngle stage mixer-~ettLer or other form of extractor. Where a mi~er-settler i~ used, it is adv~ntageous to u8e an aromatics recycle which pa~ses along line 42 and ~oins lines 33 and 14 returni~g to wa~h extractor 39. The slip8tream9 now containing a ~mall amount of aliphatlcs9 pa~e~ from w~sh extractor 39 into line 16 88 discussed prevLously.
Reflux water, now essentially free of ~liphatic~, - 23 ~
. .
. ~
,~ 9506 10 5 ~
is withdrawn from wssh ex~rac~or 3~ and proc~eds along line 43, which ~oln~ line 26, and pa~es ~nto arom~tic~
extractor 44, which c~n be a single stage mixer-settler or other type of extractor. This re1ux water, a}ong with wster recyclet ~rom the settlLng zone in lthe case of a mixer-~ettler via line 45, which ~olns line 43, ~nd proces~
m~keup w~ter from line 46 (80urce not shown) contacts the - aromatic product proceeding ~long line 26 into aromatics extractor 44 and recover3 essentlally all of the ~mall amount of solvent remaining in the arom~tlcs. Th~s water with solvent then proceeds along line 47 to Join line 17, which ~oins line 37 and enters water re~ervoir Sl. This wflter c~n, op~ion~ly, b~ ~ent Prom line 17 to line 38 (connectlng line and ~alve not ~hown) for use in the raf~in--ate wash. High purity arom~tic product i~ withdrawn from the process through line 26.
There i3 a provision for the removal o certain impurities~ which may include some aliphatics, of a type which can build up in the system and affect it in a deleter-ious manner. Thia i9 accomplished by taking a small purge o the water circuit. To ~ccompLish this purge1 water i~
withdrawn from any of the decanters ~nd discarded periodi-cally or continuousl~. One ~uch purga can be accomplished through line 48. It i3 ~ound that only a small proportivn o~ the solvent is lost by such a purge; h~wever, this solvent can be recovered if desired. The water purge stream can be in the range of about 0.25 percent to about :
:
: . . .
~ . . .. , :
, . . .
~ SS~
2.0 perc~nt by weight of the ~otal water ln the system and iR preferably in the r~nge of about 0.5 percent to about 1.0 percen~ by weight of he wster ~n the 3y8tem.
The total water in the ~ystem can be determined easily because th¢ ~mount of water introduc2d can be controlled. All~wance~ mu~t be made for water 108se9 ~;~ through leakage, entrainment and upsets, however.
Solvent can be recovered from thi~ purge by direct-ing the water through line 49 to ~oin llne 53 and enter ~olvent regenerator 52 where the solvent i8 separated from low boiling and high boiling impurities by ste~m distillation under vacuum. The solvent i8 recovered and recycled along line 54 to extractor 3 (connection not shown~ ~nd the water and impurities discarded.
:
,
The extract le~ves the bottom o~ ~xtractor 3 through line 19 and p~83e8 through heat exchanger 22 where it i8 cooled to a temperature in the range of about 100C to about 140C. The extract proceeds along line 19 and enters stripper 23, the distillation zone, a~
upper ~lash chamber 24, which, as noted heretofore, i8 at a lower pressure than the ~xtractor. Part of the extract flashes on entering the ~lash chamber and is taken over-head through line 18 in vapor form. Another part o~ the extract pa~ses as a llquid into lower flash chamber 21, :i which is operated a~ an even lower pressure and further flashing occurs. It should be noted that fla~hing is minimized in the present process. The flashed vapors Join the fractionated vapors and pasB through line 30 to 20 ~oin the vapors passing through line 18. The balance o~
the e$trsct ~at least about 80 percent by weight) percolates down the column into the fractionation zone where it c~mes into countercurrent contact with the stripping vapors, i.e., steam, and more vapors are gener~
ated. A part of the vapor rises to the top of the column and mixes ~th ~he flashed vapor~ ~n flash chamber 21 a~
noted. The overhead distillate comprises about 40 to : - 19 -~0 5 ~f~ :
about 75 percent by wslght aromatirs, ~bout 20 to about 40 percent allphatic~, abou~ 2 percen~ t:o about lO percent by weight water, and about 0 percent ~o ~bout 5 percent by we~ght solv~nt, all based on the total weight of the overhead distillate.
After ~he aqueou~ solvent descends ~bout halfway down the column, it becomes essentially ~ree of al~pha~ies.
At thi3 point, a vapor side-~tream distillate is removed through line 26. The side-~tream distillate i~ comprised of about 65 to about 90 percent by w~ight arom~tics, about 10 to ~bout 30 percent by welght water, and about 1 percent to about 10 percent by wei~ht o solvent, based o~ the total weight of the side-stream distillate.
: T~a bulk of the ~olvent and water solution~ an - ~mount equal to over 99 percent by weight of the solvent -, and water entering stripper 23 through line 19, leaves the bo~tom of s~ripper 23 through line 4. A portion of this solution is diYerted into reboiLer 28 and returns as a vapor to a point below the bottom tray of stripper 20 23 to provlde most of the Btripperls heating requirements.
The bal~ce of the w~ter and solvent solutionL i~ recycled . .
to the top tray of extractor 3 through line 4. Recycled strlpping water contalning some di~solved 801vent enters ~tripper 23 through line 2~ from water re~ervolr 51 a~er es~entially all of it ig converted ln hea~ exchanger 22 to steam. Returning to the overhead dlstilla~e mentioned heretofore, such overhead distillate i8 a combination of g506 ~ ~ 5 ~ ~ 7 ~flashed vapors and fr~ctionated vapor~ h~ving the afore-men~ioned composition. This overhe~d di~tillate 1~ ~190 known as a reflux dis~illate. The ~por i8 first condensed and cooled to be~ween about 38C. and 94C. ln refl~c condenser 25. The condensa~e then paese~ into reflux decanter 29 where a reflux hydrocarbons phase i9 deCQnted from a water pha~e. The reflux hydrocarbons ph~e comprises about 20 to 50 percent by weight aliphatics hnving from 5 to 7 c~rbon atoms, and about 50 to abvut 80 percent by weight aromatic~ and is recycl~d ~s reflux through l~ne 18 to extractor 3 ~19 previou~ly de~cribed.
The water phase con~alns about 95 to abou~ 99 p~rcent by weight water, about 0 to ~bout 5 psrcent by weight solvent~ and about 0.1 to a~out 0.5 percent by weight aliphatics. It passes through line 31 and may be ~plit into two streams, lines 32 and 33, a raffinate wa~h stre~m and an aromatics wash stream, respectively, depending, as noted above, on the amount of water available. The preerred mode of operation, how0ver, i9 to use the refl~x distillate water phase or the aromatics wash ~nd the side cut distillate water phase for ths raffinate wash.
As noted heretofore9 the side- tream distillate is withdrawn in vapor fonm from stripper 23 through line 26 and conden~ed in arom~tics condenser 34 and further co~led to R ~emperature in the range of about 25DC. to about 50C.
in cooler 35, which can be a heat exchanger or other type of cooling device. The condensate ~hen pa~se~ into aromatics .
,, ', .. ' ' . ~.. . ' .
~ ~ 5 ~
decanter 36 where ~n aromatic hydroc~rbons ph~s~ con~ain-ing about 99.8 to abou~ 99.9 perc~nt by w~ght aromatics, and about 0.} to about 0.2 percent by weigh~ ~olven~ ant a water ph~e containlng abou~ 90 p~rcent to about 98 percent by welght water, about 2 pQrcent to about 10 psrc~nt by welght solvent, ~nd about 0.1 percen~ to about 0.5 percen~
by weight sromatics are ~ormst. The w~e~r pha0e may pa88 through line 37 to water re~er~oir 51. Preer~bly, however, all or part o~ the water phaæ~ i5 dir~cted throu~h ~lvet line 38 to Join line 32 for u~e as raffinate wash.
The aromatic hydrocarbon~ phase proceeds rom decanter 36 through line 26 a}ong which an aromatics slip-gtream i9 taken through line 14 to wash w~t~r coming from reflux decanter 29 along line 33. The aroma~ic~ slip~tream at it~ source 1~ ~n easentially pure ~tre~m o~ ~romatic~, i.
e., having a purity of at lea3t 95 percent by w~ight, or in other words, at least 95 perc~nt by weight o the 011p-~tream i8 sromatic hydrocarbon~. The purity d ~he slip-stream i9 preferably about 98 percent and or optim~m p~r-ormance, l.e., to obt~in the highest purity product, about 99 percent. I'c i~ called a ~lipstream or ~ldestream becau~e the amount of aromatic~ fet into th~ water pha~ p~ing throttgh line 33 i9 very ~mall. Th~ arnount of sllp~tresm aroma~ic hydroc~rbo~s used ln the proc~ss i~ in the ra~ge of about 0.1 percent to about 5 p~reent by wetght oi~ t:he Broma~CiC hydrscarbons in the ~eed~tol:k and i~ pref~rllbly in ~he r~nge o~ ~botl~ 0.5 p~rc~n'c to about 2.0 perc:~nt by - 22 ~
.
950&
~ ~5 ~ ~7 ~
weigh~ of such aromatic hydrocarbon~. Th¢ ~lipstream wa~hes the water in extractor 39 to remove the small amoun~ of aliphatics, which i9 80 detrimental~to ~h~
efficiency of the proceas. Thi~ aromat~c~ slipstream ~8 then, preerably, 3ent along line 16 to line 1 w~ere it~i~
rein~roduced into the feedstock and pas~es lnto the Rystem once more, or, alternatively, it i9 removed fram the 8ystem.
I~ practice, the weight of the tot~l aroma~lcs is determlned by analysi~ of ~ sampl~ portion of the feed-; stoclc. Aromatlcs added, e.g., as slipstream, during the process oycLe are included in the det~rmination.
The slip~tream can, alternati~ely, be obt~ined from anoth~r source such as the overhe~d product of a benzene : ractionating column, which ~8 not shown in the drawin~, or rom a source completely removed from the system. A~
long as the slipstream has the previously noted high ~rom~tics content, it will be Ratisactory in this process.
The comblnet streams of lines 33 and 14 proceed into wash extractor 39, which can be a slngle stage mixer-~ettLer or other form of extractor. Where a mi~er-settler i~ used, it is adv~ntageous to u8e an aromatics recycle which pa~ses along line 42 and ~oins lines 33 and 14 returni~g to wa~h extractor 39. The slip8tream9 now containing a ~mall amount of aliphatlcs9 pa~e~ from w~sh extractor 39 into line 16 88 discussed prevLously.
Reflux water, now essentially free of ~liphatic~, - 23 ~
. .
. ~
,~ 9506 10 5 ~
is withdrawn from wssh ex~rac~or 3~ and proc~eds along line 43, which ~oln~ line 26, and pa~es ~nto arom~tic~
extractor 44, which c~n be a single stage mixer-settler or other type of extractor. This re1ux water, a}ong with wster recyclet ~rom the settlLng zone in lthe case of a mixer-~ettler via line 45, which ~olns line 43, ~nd proces~
m~keup w~ter from line 46 (80urce not shown) contacts the - aromatic product proceeding ~long line 26 into aromatics extractor 44 and recover3 essentlally all of the ~mall amount of solvent remaining in the arom~tlcs. Th~s water with solvent then proceeds along line 47 to Join line 17, which ~oins line 37 and enters water re~ervoir Sl. This wflter c~n, op~ion~ly, b~ ~ent Prom line 17 to line 38 (connectlng line and ~alve not ~hown) for use in the raf~in--ate wash. High purity arom~tic product i~ withdrawn from the process through line 26.
There i3 a provision for the removal o certain impurities~ which may include some aliphatics, of a type which can build up in the system and affect it in a deleter-ious manner. Thia i9 accomplished by taking a small purge o the water circuit. To ~ccompLish this purge1 water i~
withdrawn from any of the decanters ~nd discarded periodi-cally or continuousl~. One ~uch purga can be accomplished through line 48. It i3 ~ound that only a small proportivn o~ the solvent is lost by such a purge; h~wever, this solvent can be recovered if desired. The water purge stream can be in the range of about 0.25 percent to about :
:
: . . .
~ . . .. , :
, . . .
~ SS~
2.0 perc~nt by weight of the ~otal water ln the system and iR preferably in the r~nge of about 0.5 percent to about 1.0 percen~ by weight of he wster ~n the 3y8tem.
The total water in the ~ystem can be determined easily because th¢ ~mount of water introduc2d can be controlled. All~wance~ mu~t be made for water 108se9 ~;~ through leakage, entrainment and upsets, however.
Solvent can be recovered from thi~ purge by direct-ing the water through line 49 to ~oin llne 53 and enter ~olvent regenerator 52 where the solvent i8 separated from low boiling and high boiling impurities by ste~m distillation under vacuum. The solvent i8 recovered and recycled along line 54 to extractor 3 (connection not shown~ ~nd the water and impurities discarded.
:
,
Claims (11)
1. In a process for the recovery of aromatic hydrocarbons having boiling points in the range of 80°C
to 175°C from mixtures with aliphatic hydrocarbons comprising the following steps:
(a) contacting the feed-stock in an extraction zone with a mixture of water and a water-miscible organic solvent, said solvent having a boiling point of at least 200°C, and with reflux hydrocarbons at a temperature from 100°C to 200°C and a pressure of 6 to 14.5 atmospheres to provide an extract comprising aromatic hydrocarbons, solvent and water as well as a raffinate comprising aliphatic hydrocarbons;
(b) separating the extract in a distillation zone with flash and fractionation, the fractionation utilizing steam, into an overhead distillate comprising a hydrocarbons phase and a water phase as well as into a side stream of aromatic compounds comprising an aromatics phase and a water phase and furthermore bottoms comprising a mixture of solvent and water;
(c) recycling the hydrocarbons phase of the overhead distillate and the bottoms of step (b) to the extraction zone, the hydrocarbons phase being recycled as reflux to the bottom portion of said zone;
(d) washing all or part of the water phase of the overhead distillate with a slip stream of aromatic compounds, which comprises at least 95 percent by weight of aromatic hydrocarbons, the amount of the slip stream being 0.1 to 5 percent by weight, based on the total weight of the aromatic hydrocarbons in the feedstock, to provide an aromatic hydrocarbons phase and a water phase; and (e) washing the aromatics phase of the side stream of aromatics compounds with the water phase produced in step (d), the improvement comprising washing the raffinate with process water to provide a raffinate aliphatic hydrocarbons phase and one or more solvent containing raffinate water phases, and recycling the raffinate water phases to the extraction zone at the midpoint thereof.
to 175°C from mixtures with aliphatic hydrocarbons comprising the following steps:
(a) contacting the feed-stock in an extraction zone with a mixture of water and a water-miscible organic solvent, said solvent having a boiling point of at least 200°C, and with reflux hydrocarbons at a temperature from 100°C to 200°C and a pressure of 6 to 14.5 atmospheres to provide an extract comprising aromatic hydrocarbons, solvent and water as well as a raffinate comprising aliphatic hydrocarbons;
(b) separating the extract in a distillation zone with flash and fractionation, the fractionation utilizing steam, into an overhead distillate comprising a hydrocarbons phase and a water phase as well as into a side stream of aromatic compounds comprising an aromatics phase and a water phase and furthermore bottoms comprising a mixture of solvent and water;
(c) recycling the hydrocarbons phase of the overhead distillate and the bottoms of step (b) to the extraction zone, the hydrocarbons phase being recycled as reflux to the bottom portion of said zone;
(d) washing all or part of the water phase of the overhead distillate with a slip stream of aromatic compounds, which comprises at least 95 percent by weight of aromatic hydrocarbons, the amount of the slip stream being 0.1 to 5 percent by weight, based on the total weight of the aromatic hydrocarbons in the feedstock, to provide an aromatic hydrocarbons phase and a water phase; and (e) washing the aromatics phase of the side stream of aromatics compounds with the water phase produced in step (d), the improvement comprising washing the raffinate with process water to provide a raffinate aliphatic hydrocarbons phase and one or more solvent containing raffinate water phases, and recycling the raffinate water phases to the extraction zone at the midpoint thereof.
2. A process as claimed in claim 1 wherein the amount of water in the lower half of the extraction zone is 0.5 percent to 1.5 percent above that of the water in the upper half of the extraction zone, said percentages being based on the total weight of the mixture of solvent and water in the upper half of the extraction zone.
3. A process as claimed in claim 2 wherein the amount of water in the lower half of the extraction zone is 0.75 percent to 1.25 percent above that of the water in the upper half of the extraction zone.
4. A process as claimed in claim 2 wherein the reflux aliphatic hydrocarbons contain from 5 to 7 carbon atoms.
5. A process as claimed in claim 4 wherein the ratio of solvent to feedstock inthe extraction zone is in the range of 3 to 12 parts by weight of solvent to one part by weight of feedstock.
6, A process as claimed in claim 5 wherein the amount of water in the upper half of the extraction zone is 4 percent to 6 percent by weight based on the weight of the solvent in said zone.
7. A process as claimed in claim 6 wherein the ratio of reflux to feedstock in the extraction zone is in the range of 0.5 to 1.5 parts by weight of reflux to one part by weight of feedstock.
8. A process as claimed in claim 5 with the following additional step:
(f) recycling the aromatic hydrocarbons phase of step (d) to the extraction zone.
(f) recycling the aromatic hydrocarbons phase of step (d) to the extraction zone.
9. A process as claimed in claim 1 wherein at least part of the process water used to wash the raffinate has its origins in the water phase of the side stream of aromatic compounds.
10. A process as claimed in claim 9 wherein at least part of the process water used to wash the raffinate comes from a prior raffinate water phase.
11. A process as claimed in claim 1 wherein at least part of the process water used to wash the raffinate has its origins in the water phase of the overhead distillate.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US43970974A | 1974-02-05 | 1974-02-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055876A true CA1055876A (en) | 1979-06-05 |
Family
ID=23745825
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA218,599A Expired CA1055876A (en) | 1974-02-05 | 1975-01-24 | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5747717B2 (en) |
| AR (1) | AR214037A1 (en) |
| AU (1) | AU502194B2 (en) |
| BE (1) | BE825173A (en) |
| BR (1) | BR7402696A (en) |
| CA (1) | CA1055876A (en) |
| FR (1) | FR2259891B1 (en) |
| GB (1) | GB1502323A (en) |
| IT (1) | IT1031454B (en) |
| NL (1) | NL182558C (en) |
| SE (1) | SE409119B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62220585A (en) * | 1986-03-14 | 1987-09-28 | ユニオン・カ−バイド・コ−ポレ−シヨン | Separation of hydrocarbon from raw material mixture supplied |
| CA2727906C (en) * | 2008-06-15 | 2016-05-31 | Craig Nazzer | Process for separating solids from valuable or harmful liquids by vaporisation |
| CN102408914B (en) * | 2011-10-10 | 2014-03-05 | 中国石油化工股份有限公司 | Technological process for relieving foaming of stripping tower in aromatic extraction liquid-liquid extraction system |
| KR20240096622A (en) * | 2021-11-12 | 2024-06-26 | 티센크루프 우데 게엠 베하 | Method and apparatus for separation of hydrocarbon-containing feedstock streams by extractive distillation |
| BE1029922B1 (en) * | 2021-11-12 | 2023-06-12 | Thyssenkrupp Uhde Eng Services Gmbh | Process and device for separating a hydrocarbon-containing feed stream by extractive distillation |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE788871A (en) * | 1971-09-16 | 1973-03-15 | Union Carbide Corp | PROCESS OF SEPARATION BY EXTRACTION AND |
| US3788980A (en) * | 1971-12-21 | 1974-01-29 | Union Carbide Corp | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock |
| US3779904A (en) * | 1971-12-21 | 1973-12-18 | Union Carbide Corp | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock |
-
1974
- 1974-04-05 BR BR269674A patent/BR7402696A/en unknown
-
1975
- 1975-01-24 CA CA218,599A patent/CA1055876A/en not_active Expired
- 1975-02-04 IT IT1994075A patent/IT1031454B/en active
- 1975-02-04 AR AR25752075A patent/AR214037A1/en active
- 1975-02-04 NL NL7501311A patent/NL182558C/en not_active IP Right Cessation
- 1975-02-04 SE SE7501226A patent/SE409119B/en not_active IP Right Cessation
- 1975-02-04 FR FR7503413A patent/FR2259891B1/fr not_active Expired
- 1975-02-04 AU AU77879/75A patent/AU502194B2/en not_active Expired
- 1975-02-04 JP JP50014035A patent/JPS5747717B2/ja not_active Expired
- 1975-02-04 GB GB466275A patent/GB1502323A/en not_active Expired
- 1975-02-04 BE BE153051A patent/BE825173A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| JPS50108226A (en) | 1975-08-26 |
| AU502194B2 (en) | 1979-07-19 |
| BR7402696A (en) | 1975-12-09 |
| BE825173A (en) | 1975-08-04 |
| FR2259891A1 (en) | 1975-08-29 |
| DE2504639B2 (en) | 1977-04-21 |
| JPS5747717B2 (en) | 1982-10-12 |
| AR214037A1 (en) | 1979-04-30 |
| SE409119B (en) | 1979-07-30 |
| FR2259891B1 (en) | 1978-12-29 |
| NL7501311A (en) | 1975-08-07 |
| DE2504639A1 (en) | 1975-08-07 |
| GB1502323A (en) | 1978-03-01 |
| IT1031454B (en) | 1979-04-30 |
| NL182558C (en) | 1988-04-05 |
| AU7787975A (en) | 1976-08-05 |
| NL182558B (en) | 1987-11-02 |
| SE7501226L (en) | 1975-08-06 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP3262142B1 (en) | Extractive distillation for aromatics recovery | |
| US3714033A (en) | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock | |
| US3723256A (en) | Aromatic hydrocarbon recovery by extractive distillation, extraction and plural distillations | |
| EP0658615A2 (en) | Process to recover benzene from mixed hydrocarbons | |
| AU601419B2 (en) | Process for the separation of hydrocarbons from a mixed feedstock | |
| US3591490A (en) | Process of separating pure aromatic hydrocarbons from hydrocarbon mixtures | |
| US6500311B1 (en) | Propylene oxide purification | |
| US4311583A (en) | Solvent extraction process | |
| US3492222A (en) | Solvent recovery process | |
| SU1122217A3 (en) | Method of simultaneous separation of heavy and light hydrocarbons flows into aromatic and non-aromatic hydrocarbons | |
| CA1055876A (en) | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock | |
| US3763037A (en) | Aromatic hydrocarbon | |
| US4115247A (en) | Benzene production by solvent extraction and hydrodealkylation | |
| US3544453A (en) | Process for the extraction and recovery of aromatic hydrocarbons | |
| US3466346A (en) | Method for aromatic hydrocarbon recovery | |
| CA1173040A (en) | Production of methylnaphthalenes and tar bases including indole | |
| US4693810A (en) | Process for the separation of hydrocarbons from a mixed feedstock | |
| KR980009212A (en) | Recovery of pure hydrocarbon compounds from hydrocarbon mixtures containing aromatic and non-aromatic compounds | |
| US3788980A (en) | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock | |
| US3864244A (en) | Solvent extraction with internal preparation of stripping steam | |
| US4306945A (en) | Extracting aromatic hydrocarbons from mixtures containing same | |
| US4294689A (en) | Solvent refining process | |
| US3779904A (en) | Process for the separation of aromatic hydrocarbons from a mixed hydrocarbon feedstock | |
| US2803685A (en) | Process for the extraction and recovery of aromatic hydrocarbons from hydrocarbon mixtures | |
| US3470088A (en) | Method for aromatic hydrocarbon recovery |