US2309337A - Production of organic sulphur compounds - Google Patents

Description

Patented Jan. 26, 1943 raonuc'nos or oacmc sorrmm comounns J Alva C. Byrns', Palos Verdes Estates, Calif., as-

shoot to Union Oil Company or California, Los Anxeles, Calif., a corporation of California No Drawing. Application February 12, 1940, i 1 Serial No. 1

I 8 Claims. -(Cl. 260-609 This invention relates to a process for separatins and recovering organic sulphur compounds from hydrocarbon fractions containing the same.

In a more specific sense the invention is concerned with'a process for selectively extracting sulphur compounds from petroleum fractions in which they are present and the isolation and recovery of these sulphur compounds in usable from from the extracts.

It is well known that petroleumcrude oil distillatss contain various types of organic sulphur compounds. The amounts and types of these sulphur compounds present in any particular distillate fraction will depend primarily on the source of the crude oil and previous treatment such as distillation, cracking, contact with sulphuric acid, contact with caustic soda solution, etc. For example, it has been shown that fractions derived from any petroleum crude oil by distillation and boilingoveraranseof 100'F.to400' F.wil1 contain varying proportions of mercaptans, alkyi ent invention to produce petroleum distillates of relatively low sulphur content. 1

I have now discovered that at ordinary atmospheric temperatures, anhydrous aluminum chloride readily forms complexes with various types of organic sulphur compounds such as those commonly found in petroleum fractions namely,

thiophanes, allgvl sulphides, alkyl disulphides, etc.

sulphides, alkyl disulphides, thiophenes and thlophanes.

It has been recognized that sulphur compounds of acidic character, such as the mercaptans, can 'be more or less readily removed and recovered from petroleum distillates. by treatment of the latter with aqueous caustic soda solution and subsequent acidification of the separated aqueous phase. However, such a treatment fails to remove any of the alkyl sulphides, alkyl'disulphides, thiophaues and thiophenes which are present in many petroleum dis'tillates in appreciable proportions, particularly in those boiling aboveabout 200 1''. Treatment with strong sulphuric acid serves to remove sulphur compounds from petroleum distiliates but the sulphur compoimds cannot be recovered from the acid sludse. Some attempts have been made to extract selectively the non- These complexes are-apparentlynot of definite chemical composition but may comprise one or more molecules of aluminum chloride in combination with. one or more molecules of-the sulphur compounds. The complexes formed when one moi of aluminum chloride is present for each mol of sulphur compound are fairly fluid at the usual atmospheric temperatures, are-relatively insoluble in hydrocarbons boiling below about 500 F., particularly the lower molecular weight paramn hydrocarbons. and are readfly decomposed by water to yield ,an aqueous phase containing hydrated aluminum chloride and an oily phase containing the sulphur compounds- As the molal proportion of aluminum chloride to sulphur compound isincreasedfrom 1 to 1 uptofitol oreven loto l. the solubility of the resulting complex in petroleum hydrocarbons decreases. On the other hand as the molal proportion of aluminum chloride to sulphur compound decreases below 1 to 1, the solb ubility of the resulting complex in petroleum hydrocarbons increases.

-' proportion of aluminum chloride to sulphur compound'lncreases as the temperature is increased. However, where it is desired to avoid any excessive decomposition of the sulphur compounds in the complex, the latter should not be heated to temperatures much in excess of 125' I. and deflacidic orsanic sulphur compounds present in pe- '.thesulphuroompo\mdsinusable formfromthc extracts. It is an additional object of the presnitely not in excess of 1 temperatures dec'omposi pounds is observed and hydrosen sulphide is iib-' erated. At temperatures much below about 30 1". 'Atmoreelevated F. the aluminum chloride-sulphur compound complexes become viscous.

The aluminum chloride-sulphur compound complexes are readilydecomposed eitherbywater orbydiluteaqueousacidsolutioni Theuse ofth'e dilute aqueous acid solutions, such as dilute bydrochloric or acetic acid solution. for hydrolysis of the complexes to recover orsanic sulphur compounds is preferred as hydrolysis of the aluminum chloride to aluminum oxychloride is repressed and a more rapid-separation of the oily sulphur compound phase from the aqueous phase is obtained. In the hydrolysis of the complex considerable heat is liberated and care must be of the sulphur com- 7 exercised that the temperature or the mixture does not exceed about 125 F. and definitely must not exceed 150 F.

1 In view of the aforementioned properties of aluminum chloride-organic sulphur compound complexes, I have discovered that organic sulphur compounds can be selectively removed from petroleum fractions by treatment of the latter with anhydrous aluminum chloride at temperatures above about 30' F. but not much in excess 7 of about 125 F. and below 150 F. and preferably in the range of 60 to 90 F. The amount of anhydrous aluminum chloride used toextract sulphur compounds from petroleum fractions mayvary depending upon whether it is desired to effect a relatively complete removal of the sulphur compounds from the petroleum fraction or a more-efllcient utilization of the aluminum chloride. Preferably it is desired to treat petroleum fractions with about 4.0 pounds of aluminum chloride for each 1.0 pound of'sulphur present in the form of organic sulphur compounds in order to obtain a relatively eflicient utilization of the aluminum chloride and at the same time a maximum desulphurization of the petroleum fraction. Amounts of anhydrous aluminum chloride as low as about 2.0 pounds and as high as to 30 pounds per poundrof sulphur present in the form of organic sulphur compounds can be employed where a more complete desulphurization of the'pa rticular petroleum fraction is desired. I

The sulphur compounds can be selectively extracted from petroleum fractions by simply adding the required amount of. aluminum chloride, intimately commingling the aluminum vchloride and petroleum fraction at a temperature below 150 F. and subsequently allowing the complex formed to collect at the bottom of they container. The treated petroleum fraction can then be decanted and the sulphur compounds recovered by hydrolysis of the extract phase in the manner previcusly described However, in view of the fluid character of the aluminum chloride-organic sulphur compound complex, a more eflicient utilization of the aluminum chloride can be obtained simultaneously with a more effective desulphurization of the petroleum fraction by contacting the aluminum chloride with the petroleum-fraction in a counter-current manner. That is, aluminum chloride is introduced into the top of a treatingcolumn and is allowed 'to descend against an upwardly moving stream of the petroleum fraction being In some a certain amount of the petroleum fraction may be mechanically occluded in the extract phase comprising the aluminum chloride-sulphur compound complex. This oc .cluded material may be eifectively removed by extraction of the with a low boilinghydrocarbon fraction such as, pentane or butane.

Any boiling solvent remaining m -fractionandsubsequentlyjtoseparate the extract phase from fraction. said treatment being conducted at a temperature -above about 30 F. and below about 150 F. and preferably at a temperature in the range of 60 F.'to F. It is an additional object of the present invention to recover organic sulphur compounds in usable form from the separated aluminum chloride extract by hydrolysis ofthe latter with water or dilute aqueous acid solutions, and subsequent separation of the oily organic sulphur compound phase from the aqueous phase, the temperature of hydrolysis being maintained below 150 F. and preferably below about F. It is a further object to obtain fractions comprising relatively pure sulphur compounds by fractional distillation of the recovered hydroly zate.

In the foregoing specification it was observed that aluminum chloride-organic sulphur compound complexes are somewhat soluble in higher boiling petroleum fractions, particularly in those boiling above about 500 F. but are practically insoluble in the low boiling paraflinhydrocarbons. As a result, I have found that sulphur compounds can be effectively extracted from the higher boiling petroleum fractions by either diluting the said fractions with one or more vol-. umes of a low boiling paraflin hydrocarbon such as, for example, propane, butane, or pentane and subsequent addition of the required amount of anhydrous aluminum chloride or treatment of the higher boiling petroleum fractions with the desired amount of anhydrous aluminum chloride and subsequent addition'of one or more volumes of a low boiling paraflinhydfocarbon; Obviously, the above method need not be limited to the higher boiling petroleum fractions but can be applied if desirable to any petroleum fraction.

It is an object of the present invention to effect a more complete separation of organic sulphur compounds from petroleum fractions, particularly those boiling above about 500 F., by dilution of the said fractions with one or more volumes of a low boiling paraiiin hydrocarbon eith'er before or after treatment of the said fractions with anhydrous aluminum chloride- Many petroleum fractions contain smal amounts of acidic and basic compounds, such as, for example,.naphthenic acids, phenols, nitrogen bases, etc. Many of these compounds will form complexes with aluminum chloride and if present in the petroleum fraction will be removed into the extract along with the sulphur compounds upontreatment with aluminum chloride; In order to conserve aluminum chloride and obtain organic sulphur compounds free of such acidic and basic materials, it is desirable to treat petroleum fractions successively with dilute sulphuric acid); or v other acidic material and caustic soda or other alkaline solution prior to treatment withanhydrous aluminum chloride in order to remove any basic and acidic materials, respectively, which may be present. On the other hand, if it is desired, the petroleum fraction may be first extracted with aluminum chloride and the 'hydrolyzate obtained washed successively' with dilute acid and caustic soda solution in order to remove basic and acidic compounds, respectively, extracted from the petroleum fraction by the aluminum chloride,

In the foregoing specification and in the claims, the terms "petroleum fraction and pe troleum distilla are meant to include any material produced from a petroleum crude oil by distillation or extraction. Furthermore, it is meant to include materials produced from petroamples:

leum crude 011 distillat'es by solvent extraction, such as, for example, a sulphur dioxide extract of kerosene or gasoline distillate. However, the terms are not meant to include materials producedby the cracking of petroleum fractions.

Other features, advantages and obiects of'th'e present invention will become apparent to those skilled in the art from the following specific ex- Emmple 1 Twenty liters of a 400 F. end-point straightrun gasoline derived from Santa Maria Valley (California) crude oil by distillation, and having a gravity of 55.5 A. .P. I. at 80 1''. and a sulphur content of 0.61% was intimately mixed at atmospheric temperature with 800 grams of anhydrous aluminum chloride for a period of approximately two hours. i The length of the period of agitation of the aluminum chloride with any given petroleum fraction is dependent upon the efliciency of the mixing and may vary from fifteen minutes to several hours depending upon the nature of the equipment. The mixture was allowed to standv for twelve hours in order to obtain complete separation of the extract phase. The treated gasoline was decanted from the separated extract which collected as a heavy tar in the bottom of the treating vessel. refined gasoline, after being washed with dilute alkali had substantially the same boiling range as the untreated material and contained only 0.072% sulphur. ,1 p

The separated. extract was washed with pentane and subsequently hydrolyzed with ice to obtain 323 grams of an oil having a" gravity of 25.1

A. P. r. and a sulphur content r 13.7%. An ad ditional 52 grams of sulphur compounds were obtained by extracting the aqeuous hydrolysis phase with pentane. In ali; 375 grams of extract oil were obtained from'the 20 liters of gasoline treated. 1

The extract oil was dried and a 250 ml. portion was fractionated into a number of cuts as'foi The mospheric temperature with 37.5 grams of anhydrous aluminum chloride. on subsequent standing a small amount of extract separated but the oil phase remained dark colored. The decanted 5 oil phase was diluted with cleaners naphtha.

filtered, washed with water and the naphtha removed by distillation. The recovered oil had a sulphur content of 3.06% indicating that only a small proportion oi the sulphur compounds had been removed.

The above experiment was repeated under somewhat different conditions. Seven hundred and fifty milliliters of the same gas oil was diluted with 500 milliliters of a hexane-heptane mixture and subsequently intimately mixed at atmospheric temperatures with 200 grams of anhydrous aluminum chloride for onehour. An additional 250 milliliters of the hexane-heptane mixture was then added and the material allowed to stand undisturbed for sixteen hours. The upper layer was then decanted, filtered. washed with water and the hexane-heptane mixture r moved by distillation. The resultant treated oil had a sulphur content of only 1.83% and a gravity of 23.8

A. P. I. The separated aluminum chloride excontent at 6.91%. I Approximately 120 grams of the recovered extract was hydrolyzed with dilute hydrochloric acid. The oil recovered from the hydrolyzate by' toppin to remove the hexane and heptane. had F.'and a sulphur a gravity of 10.8 A. P.- I. at

tract oil was fractionated under a pressure corresponding to 2 mm. of mercury, six overhead cuts and a solid black residuebeing obtained.

. B. P.C

Cut No. at 2min. 8. Hg

Gram Pereentbgwl n0 8. 14.3 7.1 22.2 0. n1 6. 17.0 6. 14.1 Notdetermined Example 3 One liter of an aromatic hydrocarbon fraction having a gravity of 35.8 A. P. I. at 60 1''. and a sulphur content of 0.043% and derived from the so acid treatment of a sulphur dioxide extract of It will be noted that cut 1 is low in sulphur content and isprobably largely of hydrocarbon character. Cuts 4, 5, 6, 7 and the bottoms are h her in sulphur content than the crude extract. If the average molecular weight of cut 5 is assumed to be approximately .100, a reasonable assumption considering the boiling range' of the material, it is readily seen that this fraction consists only of sulphur compounds. The

compounds in this particular fraction have been found to be largel'ythiophanes. I 1

g 7 Example 2 V i Two fifty millilitersof a heavy gas oil derived from-Santa Maria Valley (California) crude oil -by'distillatiom and having a gravity of 18.8 A." P. I. at-BO l". and a sulphur content of 3.82% was mixed at atkerosene distillate. was intimately mixed at at mospheric temperature with 15 grams of anhydrous aluminum chloride. The mixture was allowed to stand undisturbed for several hours and with water and dilute caustic soda. The treated oil had a sulphur content oi only-0.005%. The

extract oil recovered from the hydrolysis of the extract phase had a sulphur content of 2.73%.

The sulphur compounds removed from petroum distiilates iind application as special solvents, as odorants, and for use in chemical synthesis. As anexample of the latter the sulphur compounds present in cut 5 of Example 1 mentioned hereinabove have been converted into ket'ones which exhibit excellent solvent properties and may be useful as flotation agents. The foregoing exemplary description of my invention is not to be considered as limiting since many variations may be made within the scope of the following claims by those skilled'in the art without departing from the spirit thereof. I-claim:

1. A method of isolating sulphur compoimds '75 from petroleum which comprises treating petrothe hydrocarbon phase then. decanted; washed,

leum with anhydrous aluminum choride at'a tem-' perature not lower than 30 F. or in excess 01 125 F. thereby forming an aluminum chloride-sulphur compound complex, recovering said complex from said petroleum, hydrolyzing said complex: and separating the sulphur compounds from the aluminum residue in the same form as said sulphur compounds exist in the original petroleum.

2. A method of isolating sulphur compounds from petroleum which comprises reacting said petroleum with anhydrous aluminum chloride at a temperature of the order of 60 to 90 F. thereby forming a complex between the sulphur compounds contained in said oil and the aluminum chloride, separating said complex from the oil, hydrolyzing the complex with water to liberate the sulphur. compounds and fractionating the.

sulphur compounds from the hydrolyzed mixture in the same form as said sulphur compounds exist in the original petroleum.

proportion of one half to ten mols of aluminum 7 chloride per mol of. sulphur compound present in said oil and at a temperature between F. and 125 F. thereby forming an aluminum chlo-- ride-sulphur compound complex, separating said complex from the petroleum, hydrolyzing said complex and fractlonating the organic sulphur compound from the. hydrolyzed mixture without any substantial change in structure of the sulphur compounds from the form in which they exist in the original petroleum.

4. A process as claimed in claim 1 in which 4 a low boiling parafllnic hydrocarbon is added to the petroleum to aidin the separation of the aluminum chloride-sulphur compound complex from the oil.

5. A method of isolating sulphur compounds froma hydrocarbon fraction which comprises contacting said hydrocarbon fraction with can'- hydrous aluminum chloride at a temperature not arating the liberated sulphur compound from the aluminum residue. 1

6. A method of isolating sulphur compounds from a hydrocarbon fraction which comprises diluting said fraction with a liquid hydrocarbon fraction having a boilingpoint not substantially higher than that of heptane, treating said diluted fraction with anhydrous aluminum chloride at a temperature not substantialy lower than 30 F.

vor substantially higher than F. and thereby aflinic hydrocarbon fraction having a boiling point not substantially higher than that of heptane, treating the diluted fraction with anhydrous aluminum'chlorlde at a temperature not substantially lower than 30 F. or substantially higher than 125 F. and thereby forming an aluminum chloride-sulphur compound complex, separating the complex from the hydrocarbon fraction, hydrolyzing the complex thereby liberating the sulphur compound and recovering the liberated sulphur compound from the aluminum residue.

8. A process for the recovery-of sulphur compounds from a hydrocarbon fraction which comprises diluting said fraction with a low boiling liquid hydrocarbon selected from the group consisting of propane, butane, pentaue, hexane and heptane, contacting said diluted hydrocarbon fraction with anhydrous aluminum chloride at a temperature not substantially below 30 F. or substantially above 125 F. thereby forming an aluminum chloride-sulphur compound complex, separating the complex from the hydrocarbon fraction, hydrolyzing said complex thereby liberating the sulphur compound contained therein and recovering the liberated sulphur compound from the aluminum residue.

ALVA C. BYRN S.