US2990365A - Process for demetalizing hydrocarbon oils - Google Patents

Description

June 27, 1961 H. BIEBER ETAL PRocEss FOR DEMETALIZING HYnRocARBoN oILs Filed May 1s, 195s :v lv l nl. 95:5 .uDoOma mzON. mbs numanim new By Ar'forney States Patent 2,990,365 PROCESS FOR DEMETALIZING HYDRO- CARBON OILS Herman Bieber, Linden, and Theodore B. Simpson, East Orange, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed May 13, 1958, Ser. No. 734,912

' 20 Claims. (Cl. 208-253) The present invention relates to the upgrading of hydroh carbon oils and more particularly relates to an improved process for the removal of innate organo metallic contaminants from residual hydrocarbon oils boiling in excess of about l000 F.

Organo-metallic contaminants, principally complex iron, nickel, and vanadium compounds, are found as innate constituents in practically all crude oils and may be present therein in concentrations of 200 pounds per 1000 barrels of oil or higher. Upon fractionation of the crudes, these contaminants are concentrated in the residua which normally have initial boiling points of about 1000 F. Such residua are conventionally used as heavy fuels and it has been found that the contaminants therein have a very adverse effect upon the combustion equipment in which the residua are burned. The contaminants not only form ash which leads to slagging and the formation of deposits upon boiler tubes, combustion chamber walls, and gas turbine blades, but also attack the refractories which are used to line boilers and combustion chambersv and severely con-ode boiler tubes and other metallic surfaces with which they come into contact at high temperatures. Although there have been many suggestions in the past as to methods which might be used to remove metallic contaminants from high boiling residua, no wholly satisfactory process for accomplishing this has been available heretofore.

The present invention provides a new and improved method for removing innate organo-metallic contaminants from hydrocarbon oils boiling in excess of about 1000 F. in accordance with which the oils are contacted in liquid phase with a fused alkali metal hydroxide in order to modify the properties of the complex organometallic compounds present therein and permit their physical separation from the product oil. It has been found that treatment with fused alkali metal hydroxides in accordance with the invention results in a decrease in the oil solubility of the metallic compounds and a corresponding increase in their water solubility such that substantial quantities of the contaminants can be removed by water washing, ltering or similar treatment of the oil. Selectivity of the reaction between the fused hydroxides and the metallic contaminants is high and excellent yields of demetalized oil are obtained. The process is' additionally beneficial in that it also removes some undesirable sulfur and acidic materials present in the oil which would otherwise have to be taken out by further processing steps. The invention thus provides a process for upgrading residua containing metallic contaminants' which is highly effective, easily carried out, land economically attractive.

The process of the invention can best be understood by first considering the nature and properties of -the metallic contaminants which` are found in petroleum K residua. These contaminants are innate constituents of crude oil Patented `June 27, 19561 and are nonvolatile at temperatures below about 1050 F., hence they are not present to any appreciable extent in distillates conventionally recovered by fractionating crude oil. Analyses have shown that some of the contaminants are complex organic compounds of the porphyrin type in which a central atom of iron, nickel, vanadium or a similar metal is surrounded by four pyrrole rings interconnected by methene linkages. Various substituents including alkyl chains, alkylene groups, and carboxylic radicals may be attached to each of the pyrrole rings at several positions. In some cases, two or more such molecules apparently polymerize to give an even more complex structure which is nonvolatile at temperatures of 1300 F. or higher.

In treating these complex molecules with fused alkali metal hydroxides in accordance with the process of the invention, it may be that the alkali metal hydroxides react with acid radicals present as side chains on some of the organo-metallic molecules to form alkali metal salts. Such salts areless oil-soluble than the unmodified contaminants and, to some extent, rcan therefore be separated from the oilby filtration, centrifugation or similar procedures. Because the alkali metal salts have greater water solubility than the unreacted organo-metallic compounds, water washing removes substantial quantities of the contaminants, yielding an oil of greatly reduced metals content. On the other hand, it may be that the hydroxides completely degrade some of the contaminants and form water-soluble inorganic compounds rather than alkali metal organo-metallic salts. There is considerable support for this latter view. Other mechanisms may also be postulated.

The alkali metal hydroxides suitable for us'e in carrying out the process of the invention include fused sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like. Because of their particular eifectiveness, sodium hydroxide and potassium hydroxide are the preferred re actants. In order to facilitate handling of the fused hydroxides and to permit treatment at temperatures below those at which degradation of the oil due to thermal cracking occurs', it is usually preferred to employ eutectic mixtures of two or more different hydroxides, particularly mixtures of sodium and potassium hydroxide, which have melting points somewhat lower than those of the pure compounds. By employing such mixtures, hydroxide compositions which are liquid at temperatures as low as 325 F. or somewhat lower may be obtained. Similar low melting eutectic mixtures can be obtained by adding a minor amount of sodium carbonate to sodium hydroxide, a mixture containing about 8% Na2CO3 and 92% NaOH having a melting point of `about 510 F. for example. It is generally preferred to treat the oil with from about .01 to about 2 volumes of alkali metal hydroxide perv volume of oil. Treatment with from about 0.1 to about 1 volume per volume is generally preferred.

In carrying out the process of the invention, the oil from which the metallic contaminants are to be removed is treated with the fused alkali metal hydroxide or eutectic mixture Yat a temperature in the range of from about 325 to about 700 F. Thermal cracking of the oil and product degradation due to undesirable side reactions of the hydroxidev with constituents of ther oil other than the metalliccompounds begin' to takeplace at temperatures between about 60o and 700 F.,whi1e diaicuuies in main- 3 taining the hydroxides in liquid phase are'sometimes encountered -at temperatures between about 325 and about 400'F., even'though eutectic mixtures areemployed," and therefore temperatures of from about 400 to about 650 F. are preferred for carrying out the process.

The contact time employed in carrying out the process may range from a few minutes to about 20 hours, depending upon the particular oil being treated and the treating conditions employed. It has been found that the contaminants can be readily removed from some oils in a very short time and that more extended contacting is required to achieve equivalenfresults with other oils. In general a, contacting time of from about `1 to about 16 hours has beenfound adequate. Any of the conventional liquid-liquid contacting methods may be employed.

Y In a particularly preferred embodimentk of the invention, the oil from which metallic contaminants are to be remoyed is contacted with the alkali metal hydroxide in the presence of oxygen gas. It has been rfound that the addition of oxygen during the treating stepof the process results in a surprising increase in the amount of contaminants removed when the oil is subsequently filtered and/orwater washed. Although the reason for this surprising increase in elfectiyeness when oxygen is added is not fully understood, one explanation for the phenomenon may vbe that the oxygen reacts with Vunsaturated side chains on ,the organo-metallic molecule to form' carboxylic acid groups which areV then free to react with the hydroxide, although this has not been veried. The amount of oxygen employed does'not appear to be highly critical andmay be varied overV a considerable range.y Generally it is preferred `to supply the oxygen by bubbling air ora similar oxygen-contain'mg gas through the oil during treatment with the fused hydroxide but other contacting methods may lalso beemployed.` When air is employed as the oxygen-source, air rates of from about l to 1500 standard cubic feet per barrel of oil may be used. If pure oxygen is used, yery low rates are permissible. "Sparges, distribution plates or other conventional means may be employed to promote contacting of the oxygen and the oil.f

In a further'preferred embodiment of the invention, the oil from which metallic contaminants are to be removed, isY subjected to a thermal pretreatment prior to being contacted with the fused'alkali metal hydroxide, it having been found that such a pretreatment substantially increases the amount ofv themetallic contaminants removed by the process. This pretreatment, referred to as heat soaking, is preferably carried out at temperatures be# tween about 300 F. andabout 900-F. in order to avoid substantial thermal cracking of the oil. Higher temperattires may be also utilized but in that case the yield of treated oil will be appreciably decreased. The thermal pretreatment mayy extend over a period ranging from a few minutes to aboutV 72 hours, depending upon the particular yproperties ofthe oil being treated and the temperature conditions employed. Heat soaking at Vabout 650 F. to 750 F. forabout 3 to about 12 hours has been found to be highly eifective for increasing the removal of metallic contaminants and therefore such treatment is preferred.

V'Physical separation of the modified contaminants from the treated oil may be carried out by filtering, centrifuging or settling; by water washing; or by a combination of these methods. A combination of settling and Water washing has been found to be particularly effective and is therefore preferred.

The exact nature and object of the invention can be more fully understood by referring to the accompanying drawing and the following detailed Vdescription of a specific embodimentV of the process. Y

Referring now to the drawing, a hydrocarbon oil including constituents boiling in-excess ofabout 1000 F. is introduced into the system through line 1 into distillation uum towers or other conventional distillation equipment. The feed is fractionated in tower 2 and low boiling fractions, light gases, naphtha', kerosin and'heating oil may be taken olf through lines 3, 4, 5 and 6. A heavy gas oil may be withdrawn through line 7 and a residual fraction having an initial boiling point of about 1000 F. is taken olf as a bottoms product through line 8. The residual bottoms product is passed through line 9 and if desired, may be combined with the heavy gas oil diverted through line 10. Although the metallic contaminants are not present in significant quantities in oils with final boiling points below about 1000 F., the process does not adversely aifect such lower boiling oils. Because of difficulties in handling the high viscosity residua boiling wholly above 1000 F., it may be desirable to include lower boiling oils in the feedstrearn or to dilute the high boiling residua with suitable hydrocarbon solvents such as hexane, naphtha, or the like. The oil transferred through line Q is fed into contacting tower 11 which is preferably a tower of the spray type wherein the oil is introduced into a downflowing stream of caustic or other alkali metal hydroxide, although contacting vessels of other types may also be employed.

The caustic is introduced into the system through lines 12. and 13 kand passes through heat exchanger 14 where it is heated to the contacting temperature of from about 400 to about 700or F. The heated caustic then passes zone 2. The distillation zone. may comprise an atmosthrough line 15 into contacting tower 11. The mixture of oil and caustic thus formed passes downwardly out of the contacting tower through line 16 and into reactor 17.Y Air or other oxygen-containing gas is introduced Vinto the system through line 18 and may be heated in heat exchanger 19 if desired. The gas stream passes through line 20 and is bubbled upwardly through the mixture of oil and caustic in reactor 17. Following the introduction of the air, the mixture of caustic and oil is transferred through line 21 into holding drum 22. rlhe contacting period in reactor 17 may vary'from' about l to about 5 hours or more and the residence time in holding drum v22 will normally extend from about Vl to about l5 hours. In some cases, however, Vit has been found that the use of a holding drum is unnecessary and the oil andcaustic may be passed directly from the reactor into the separation system. Gas and entrained air reaching the top of reactor 17 is passed through line`23 and cooler 24 and then introduced into knockout drum 25. Gases are vented overhead from the knockout drum 26 and liquids are passed through line 27 into the holding drum.

The mixture of oil and caustic withdrawn from holding drumY 22 is transferred through line 28 into settler 29. An upper predominantly oil phase and a lower predominantly caustic phase are formed in the settler. The oil phase containing some caustic is passed through line 30 into primary washing Azone 31 where -it is contactedV with water introduced through line 32. Water and oil are transferred from the washing zone through line 33 into anelectrostatic precipitator 34. `:Due to the electrostatic field existent in the precipitator, any emulsion which may have formed collapses and separate oil and water phasesA Vperature conditions in line 41 are controlled so that the caustic remains in the fused state. The water condensed in 'condenser 40 is passed through line 42 and, together with freshwater introduced through/line 43, is introduced into the Asecondary washing zone 36. The mixture of, oil andu water formed in the secondary washing zoneV is withdrawn through line 44 andpassedto The oil in the mixture separates out asian upper phase Withdrawn as, Product fbfsuslilis @sa ,tss uwer was.:

phase containing traces of caustic is withdrawn through line 47 and discarded.

The caustic phase formed in-"settler 29 `is withdrav'vnf'"` therefrom through line 48 andpassedl into aprimary sludge extractor 49. In the sludge extractor the caustic phase is Washed with naphtha, hexane, heptane or a similar low boiling, highly paralnic solvent introduced through line 50. The used solventis withdrawn Yfrom The process of the invention may be further illustratedA by reference to results obtained in a series of tests wherein heavy, metals-containing oils are treated with alkali the sludge extractor through line.51 and introduced into stripper 52. ISolvent is taken overhead from the stripper through line 53 and recycled to the feed solvent stream in line 50. Oil washed out of the caustic by the solvent is recovered as a bottoms product fromv stripper 52 through line 54. -This bil is predominantly free of metallic contaminants and may be blended with the product oil recovered through line 46.- Y

The caustic phase from sludge extractor 49 is withdrawnthrough line 55 and passed to a secondary sludgeA extractor 56'where it` is `contacted withra highly aromatic solvent such as benzenetoluene, xylene or the like introduced through line S7. Thespent aromatic solvent is withdrawn from the sludge extractorthrough line 58 and introduced into stripper 59, where 'the aromatic solvent is stripped from the oil-washed out of the caustic and `recycled through line 60 to the aromatic solvent metal hydroxides in the manner described above.

EXAMPLE `1 In order to demonstrate the removal of metallic contaminants from high boiling hydrocarbon oils, -heavy Acrude oils and residua-containing metallic contaminantsY The alkalimetal.hydrox-ide-to-oil ratios used ranged from 0.25/ l to 0.9/1. Following separation of the oil and hydroxide phases by decantati'on or filtration, the oil was 'l water Washed.- v The vanadium contents of the washed oil weredetermined and compared with those of the un-V The leffect of thesetreatments is showninn' treated oils.

stream in line 57.. Oil from the bottom of the stripper rFable I.

I Table I REMOVAL OF METALLIC CONTAMINANTS FROM HIGH BOILING OILS BY TREATMENT 1 vWITH ALKALI METAL HYDROXIDES f Vana- Sulfur Treating Treating Hydroxide- Oil Vana- `Sulfur Feed Stock d lum Content, Temp., Time,` to-Oil Yield, dium, Removal,V

Content, Percent F. l Hrs. Ratio Percent Removal, Percent p.p.m. Percent Heavy Residuun1- 385 2. 7 700 3 1 0. 9/1 73 100 50 Heavy Reduced Crude 390 2. 8 650 3 1 0. 9/1 73 100 40 Do 390 2.8 600 3 1 0. 9/1 95 95 18 Heavy Residuum- 385 2.7 500 16 0. 25/1 96 55 10 1 10% phenol on caustic added in these runs.

contains appreciable quantities o f the metallic contaminants and is therefore recycled through line 61 to the feed stream to contacting tower 11. -The caustic withdrawn from the secondary sludge extractor contains appreciable quantities of the metallic contaminants. In order to maintain these at an acceptable level, a portion of the caustic is purged. The major part of the caustic is recycled through line 62 to the caustic feed line 12 and a minor proportion is withdrawn as purge through line.63.

Although the process of the invention has been described above in terms of using caustic and air as the treating agents, it will be understood that the invention is not so limited and that other alkali metal hydroxides Y and eutectic mixtures and other oxygen-containing gases Y in addition to air may be used. Solutizers such as phenol may be employed to improve contacting of the oil and caustic and are often beneficial. in some cases it may be advantageousto heat-soak the oil to be treated or to employ the process in combination with other processes effective for the removal of metallic contaminants from hydrocarbon oils. Other permissible modifications in the process described include the recycling of the caustic phase withoutv solvent washing; the use ofk alcohol solutions, dilute mineral acids and car-bon dioxide as emulsion breakers in place of an electrostatic precipita-tor; the carrying out of the air oxidation and soaking steps simultaneously; the use of a light quench oil to reduce solubilityof the modied contaminants in the oil and hydroxide and permitA their more rapid .removal by ltration, centrifugation, settlingor the like; the' use of carbon dioxide following 'the' 'hydroxide treatment to convert inorganic compoundsinthe `oil tothe less soluble carbonate The data above demonstrate that the metallic contaminant content of petroleum residua can be signic'antly reduced by treating the residua with alkali metal hydroxides and thereafter filtering and Water washing the treated oil. 'I'he eifect of the treating temperature uponi vanadium removal and upon the yield of treated oil is clearly shown by the data in the table.

temperatures of 600 F. and below, the yield of treated oil recovered at such temperatures was or higher,l as compared to yields of only 73% at the higher temperatures. The amount of metals removed can be considerably improver by the addition of oxygen to the oil-hydroxide mixture and therefore it is preferred to treat in the presence of oxygen at temperatures between about" 400 and 600 F. 'Ihe data also illustrate the effectiveness of the process for the removal of sulfur compounds from Y the oil. Such sulfur compounds are mostly thiophenic in nature and are not removed by well known treatments involving aqueous caustic. l

EXAMPLE 2 Treatment of this oil Without air blowing had been found not to 'remove any Aof the vanadium from the oil. The

vanadium removal is shown in effect of the air blowing on TableH below.

process Will be ap-.

Although the amount ofy vanadium removed was -somewhat lower at Table II EFFECT OF AIR UPON METALS REMOVAL BY TREATMENT -WITH ALKALI METAL Y luflmmrlis i Vana- Sullur Treating Treating l Hydroxlde- Oil Vana- Sulfur Feedstoek dlum Content, Temp.; Tlme, Air to-Oll Yield, dlum Removal,

V Oor.u:ent, Percent F. Hits. Blowing Ratio VPercent Removal, Percent ppm.` L Y I' Percent 43o 4.o y 450W 4 o. 25 Nino o 10 430 4. (l 450 4 0. 25 N100 60 V1li 390 2. 7 v700 '3 1 1. 0 -65 99 G1 430 4; 0 V700 3 l 1. D 50 95 46 430 4.0 750 3 l 1. 0 50 Coke Coke l 10% phenol on caustic added to these runs as a solutizer.

The data in Table II clearly demonstrate the surprising effect of oxygen upon Vthe removal of metallic contaminants from oils vboiling above l000 F. by treatment with fused alkali metal hydroxides. The contaminants in the particular crude treated were exceptionally diicult to remove and were not aiected at all by treatment fused hydroxides in the absence of oxygen. Air blowing during the run permitted the removal of about 60% `of the vanadium present without any appreciable yield loss. The data also illustrate again the effect of treating temperature upon metals removal and oil yield. Thermal cracking at the 700 and 750 F. treating; temperatures was severe and reduced oil yields seriously.

EXAMPLE 3 ,Tests v.on .crude oils. and residua containing metallic contaminants and similar to those Vtreated in the preceding examples were carried out by treating with solid sodium hydroxide at room temperature. It was found that no metals were removed under .these conditions. Similar tests wherein the oil was treated with 10% aqueous caustic at 650 F showed that only minor amounts ofthe metals, below 10% in every case, were removed. These results clearly demonstrate that treating with solid or aqueous alkaliy metal hydroxides does not achieve the results ofr j the present invention.

EXAMPLE 4 In order to demonstrate the necessity for a separation step` following treatement with fused alkali metal hydroxidesin accordance with the invention, a heavy residuum boiling well in excess of 1000 R and containing 385 ppm. of vanadium was treated with a fused eutectic mixtureof sodium and potassium hydroxide at a temperature of 500 The treated oil was then Ifiltered through a Gooch-type asbestos iilter mat and it was found that 22% oi the vanadium originally present had been removed. 'Ihe filtered oil was then water washed and it was found that the vanadium removed had been increased to It is therefore obvious that simply treating residua with fused alkali metal hydroxides does not removethe metals from the oil. Because of the extremely high boiling range of the residua in which the metallic contaminants are concentrated and the factY that refinery distillations, even at high vacuum, are limited to overhead temperatures equivalent -to about 1000 F. to 1050 F. atatmospheric pressure, distillation of a reduced crude or residuum following treatment with fused caustic or a `similar alkali metal hydroxide does, not permit separate recovery of the metals and the oil. lt is essential that the oilbe,s ubjected to filtration, water washingor a similar step following treatment with 4the fused alkali metal hydroxide if metallic contaminants are to be removed from EXAMPLE 5 'Two samples: of heavy residuum,one of v'which had been heat soakedas described earlier; were treated with a fused eutectic 'of sojdium and potassiumhydroxides. at 500" F. inonder toidetermine theelfect of the heat soaking upon the removal of metallic contaminants. The treatment.divasVVV carried out in the absence of air blowingin the manner described in Example l and was followed by liltrationand water washing. The results obtained are shown in the following table:

Table H1 EFFno'i` 0F HEAT soaxrNo UPON METALS REMOVAL BY TREATMENT WITH FUSED ALKALIMETAAL IAIY- DROXIDES Y Itis apparent from the above data that heat soaking of theresiduum had a surprisingly beneficial effect upon the temovalpf metals therefrom and permitted the recovery of product oil having a substantially lower metals content than ,that recovered without the heat soaking step.

What Misclaimed is: 1. An improved process for removing metallic contaminants Ifrom a hydrocarbon oil boiling above about l000 F. which comprises treating said oil with a fused alkali metal hydroxide at a tempratul 0f from about 325 tomabout 700 F. and thereafter water washingtlle treated ,oil to remove therefromrmodjed metallic contaminants. Y

k2. A process asdeiined by claim 1 wherein said o il is contacted, with said fused alkali vmetal hydroxide inthe presence of oxygen.

3. A process as defined by claim 1 wherein said fused alkali metal hydroxide is a fused eutectic mixture of sodium hydroxide and potassium hydroxide. Y

4. A process as deiined by. claim l wherein said oil is contacted with Ifrom about ,0.01 toahout 2 voltunesV of said fusedhydroxide per volume of oil.

7; Ainrocss'as daar@ by daim 6 wherein .Saidoii is treated with said fused alkali metal hydroxide at a temperature between about 400 and about 650 F.

8. A process as deiined by claim' wherein said'. metalv hydroxide is fused caustic.

9. Vprocess asdenedtnr, claim -xwherein `said fused hydroxide, contains` a solutzer.

1.0. .AA process as denedzby, claimv 6 Iwherein.saidoilisf hea;V soaked. atA a temperature off from ahoutto 909.? before; being treated-with.saidlfused-rhydroxide.,

5. A process as defined by claim 1 wherein said oil is 11. An improved process lfor removing innate metallic contaminants from a hydrocarbon oil at least a portion of which boils above about 1000 F. which comprises admixing said oil with from about 0.01 to about 2 volumes of a fused alkali metal hydroxide at a temperature of from about 400 to about 650 F., air-blowing the mixture at a temperature of from about 400 to about 650 F., separating said hydroxide from the oil, removing modied metallic contaminants from the oil by water washing, and recovering an oil of substantially reduced metals content.

12. A process as deined by claim 1l wherein from about 0.1 to about 1 volume of fused hydroxide is admixed with said oil.

13. A process as defined by claim l1 wherein said fused hydroxide is a eutectic mixture of sodium hydroxide and potassium hydroxide containing a minor amount of phenol as a solutizer.

14. A process as defined in claim 6 wherein said oil is contacted with about 0.01 to about 2 volumes of said fused alkali metal hydroxide per volume of oil.

15. A process as defined in claim 6 wherein said oil is contacted Iwith said fused alkali metal hydroxide in the presence of oxygen.

16. An improved process for removing metallic contaminants from a hydrocarbon oil at least a portion of which boils above about 1000 F. which comprises con- 10 tacting said oil with a fused alkali metal hydroxide at a temperature of from about 325 to about 700 F. and thereafter separating modified metallic contaminants from the treated oil at lleast a portion of which boils above about 1000 F.

17. A process as defined by claim 16 wherein modified metallic contaminants are separated from said treated oil by filtering the oil.

18. A process as defined by claim 16 wherein modified metallic contaminants are separated 4from said treated oil by centrifuging the oil.

19. A process as defined by claim 16 wherein modified metallic contaminants are separated from said treated oil by settling the oil.

20. Process as defined in claim 19 wherein the oil after settling is water washed to remove therefrom additional modified metallic contaminants.

References Cited in the iile of this patent UNITED STATES PATENTS 1,704,588 Black Mar. 5, 1929 1,838,031 Stratford Dec. 22, 1931 2,339,875 Pfennig et al. Jan. 25, 1944 2,685,558 Hodges Aug. 3, 1954 2,685,561 Whiteley et al Aug. 3, 1954 2,773,807 Blatz Dec. 11, 1956 2,778,777 Powell Jan. 22, 1957

Claims (1)

1. 6. AN IMPROVED PROCESS FOR REMOVING INNATE METALLIC CONTAMINANTS FROM A HYDROCARBON OIL AT LEAST A PORTION OF WHICH BOILS ABOVE ABOUT 1000* F. WHICH COMPRISES CONTACTING SAID OIL WITH A FUSED ALKALI METAL HYDROXIDE AT A TEMPERATURE OF FROM ABOUT 325 TO ABOUT 700* F., SEPARATING SAID FUSED HYDROXIDE AND SAID OIL, AND THEREAFTER WATER WASHING SAID OIL.

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