US2585525A - Separation of xylene - Google Patents

Description

:xylene content of the crude xylene.

Patented Feb. 12, 1952 UNITED STATES PATEL 1 KOFFI CE Monsanto Chemical Company, .St.;L'ouis, Mm,

a corporation of Delaware No Drawing. Application May 26, 1950, Serial No. 164,620

7 Claims. 1

The-present invention relates to hydrocarbon recovery, and deals more particularly with the separation of para-xylene from technical Xylene fractions.

A'gre'at-deal'of effort has been directed to the provision -of processes for the isolation of the isomeric xylenes from hydrocarbon fractions 'containing the same. Based on the fact that'meta- "xylene is more readily sulfonate'd than the other xylenes, a number of prior processes have employed sulfonation procedures, particularly for therecover-yoi meta-xylene.

The difierence known to exist in the ease of hydrolysis of the various xylenesulfonic acids'has also contributed to theirequent use of the-sulfonationtprocedure.

FI'hus,iin'.pri0r art, it was known that the partialfsulfonationof a crude xylene fraotion e. g., byramoderately strong sulfuric'acid under-conditions preventing complete-sulfonation would dissolve, or 'sulfonate, apredominance of the m- The other :xylenes were believed to be either undissolvedor only-partially. affected under the same conditions.

It -was also known that Xylenesulfonic acids canbe fracticnally hydrolyzed to the corresponding Xylenes. For example, in a steam-distillationhydrolysis, m-xylenesulfonic acid was found .tohydrolyze at temperatures of from 125 to I50 .C., paraxylenesulfonic acid at temperatures of from 150 to 170 0., and o-xylenesulfonic acid and thylbenzenesul'fonic acid at above 170 C.

Based on the above, there'have'been devised various methods 'for the separation of 'theindividual 'xylenes as Well as of the ethylbenzene :present in "technical xylene fractions. The xylene was first "partially -sulfonated, "e. e., by treatmenttvith a"sulfuric"aci'd, o'f sayless'thaniQ'S per cent H2804 concentration, and the unsulfonate'd oil was separated, "and submitted to complete 40 'sul'fonation, i. e., treatment with a stronger "sulfuric acid. Separation of the Xylenes present "inihe 'two dii ferent sulfonic acid fractions "thus obtained was then efiected either by selective :hydrolysis, fractional crystallization or --a combinati'on' of the two procedures.

Depending upon the individual xylene isomer :desired, the procedure generally outlined above has :been somewhat varied. However, the prior artshas :not provided an industrially Ieasible (CLaZGO-s-GZ l) ,12 method for ltheasiibstantiallyatotal "recovery of a high gr'ade para-xylene :and wot .-a -=high+grade e'thylbenzen'e isfromztechnical :xyl'ene mixtures.

An object of "the present :invention is to "re- "cover in good yields tpure or. substantially .Pure para-xy lene from imix'tures thereof with other stylen'es. knother obie'ctirof @the invention .:is to recover -pure .:or substantially aaure ethylhenzene from technical :xylene &fractions containing 'ethylbenzene. Other objects will :be hereinafter disclosed.

According to the .inventiona'azrecovery of para- "xyl'ene and, 'if:desired, of ethylb'enzene fromtcrude xylene, i. e., xylene ifrom .commercial sources 15 -such as coal-tar, cokeoven zdistillates,:petroleum tarbils, etcxis efi ectedzin ib'etterpyields thanshave "been -previous'ly attained on :a technical sscale by operating substantially as follows:

Crude xylene is--dis'til1'e'dto remove a majo'r portion of its-ortho xylene"content to give a hy- 'drocarboniraction" havinga boiling point of' approx'im'ately 130 C. to '145" "'Cxandmon'ta'ining a predominance ofmeta xylene,fa*lesseriproportion of para-xylene and small "amounts of ethyllbenzenean'd ortho-xyllene. This distilled pro'dnot will be deferred .tofhereinafteras technical .xylene. LThis hydrocarbon :fraction is.submitted :to partial sulfonation, the .unsul fonated voil .(a) .is separated .from .theqproduct and-the sulfonated -material ..(b) .is subjected-to iractional distillastion hydrolysis. -'.Foreruns 'tc) :obtainedbytfractional distillation hydrolysis rat etemperatures-of up to 120 C.' are 1addeii toithe unsulfonatedtmaterial (a), intermediate material hydrolyzing at from 120 C. to 145 C. and comprising substantially m-xylene is separatedand hydrolysis prod- .uct .(d) .ohtained by :hydrolyzing at above 145 C. is alsoadiiedto the wunsulfonatedoil (a). The mixture-- .of nnsu lfonated oil la), .hydrolys'is (foreruns (0) and hydrolysis roduct (d) is thencom- .pletely sulfonated, e. g. by treatment with strong isulfuric acid, i. e., of above 95 per cent .H2SO4 45 concentration. Distillation "hydrolysis 'of :the

-.comple"tely sulfona'ted material yields, at a tem- .perature (if "from T50" C. "to TTO C. air'ation containing a predominance of para-xylene and :above 1:7.0" E. :a ifractinn -icontainmg 51a :preiiomi- 50 mancemnethylbenzener 3 Briefly, the present process may be outlined as follows:

Technical xylene partial sulionetlon Suionlc acid (b) iracltional hydrolysis l 120 C. 125-145 0. 145 C. l oreruns (c) m-Xyilene Hydrolysis I on Product (d) Unsulionated 011 (a) [Hydrolysis product (d) Foreruns Complete sulionation Sulionic acid (e) Fractional h l'drolys is 1 150 C. 150-170" C. 170C. I mylene cut p-Xylelne cut Etltiylbenzene cooling Crystalline p-xylene the hydrolysis step material coming over at below 120 C. consisted essentially of water and paraffinic compounds. Also unappreciated were the advantages obtainable by a re-sulfonating the hydrolysis product ((7.) along with the unsulfonated oil (a). Contrary to previous practice, we have found that incorporation of the hitherto discarded foreruns (0) into the material which is to be re-sulfonated results in a substantially increased recovery of xylenes, particularly p-xylene, as well as of ethylbenzene. With respect to p-xylene, our investigations have shown that while re-sulfonation of only the unsulfonated oil (a) results in the recovery of but about 50 per cent of the p-xylene present in the xylene mixture, addition of the foreruns (c) to the unsulfonated oil (a), and complete sulfonation of the resulting mixture results in the recovery of about 70 per cent of the p-xylene. Addition to the unsulfonated oil (a) of not only the foreruns (0) but also the hydrolyzed product ((1) results in the recovery of about 85 per cent of the p-xylene. The present process also permits substantially complete recovery of ethylbenzene from technical xylene mixtures.

The invention is further illustrated, but not limited, by the following example:

Example A technical xylene fraction having a boiling point of 125 C. to 141.7 C. after removal of 191.8 pounds of the above fraction was reacted with 85 per cent sulfuricacid fora time of 30 minutes at a temperature of from C. to C. The quantity of acid employed was 2.74 lbs. of 85 per cent H2804 per lb. of the fraction.

The unsulfonated oil (a) weighing 67.8 lbs. was separated from the reaction mixture, and the remaining sulfonic-sulfuric acid mixture was diluted with water and steam distilled to a temperature of C. There was thus obtained 18 lbs. of the forerun (c), which was added to the unsulfonated oil (a). Further distillation of the remainder of the sulfonic-sulfuric acid mixture at a temperature of from 120 C. to C. gave 90 lbs. of a fraction consistin predominantly of meta-xylene. Distillation of the residue at a temperature of over 145 C. gave 16 lbs. of a hydrolysis product (d), which was also added to the unsulfonated oil (a) The 101.8 lbs. of the mixture of unsulfonated oil (a), forerun (c) and hydrolyzed product (d) were then sulfonated completely by reaction with 96 per cent sulfuric acid. The resulting sulfonic-sulfuric acid mixture was then diluted with water and the temperature of the diluted mixture was raised to 145 C. to C. At this temperature there was obtained a fraction consisting essentially of 40.1 lbs. of meta-xylene. Distillation hydrolysis of the remainder at a temperature of from 150 C. to C. yielded 49.7 lbs. of a fraction containing 44.9 lbs. (90.4 per cent) of para-xylene. At over 170 C. there was obtained 12 lbs. of a fraction consisting essentially of ethylbenzene.

The fraction distilling at 150 C. to 170 C. and consisting of 90.4 per cent para-xylene, 4.0 per cent of meta-xylene and 5.6 per cent of orthoxylene may be used as such for many industrial purposes, or the para-xylene may be further concentrated by cooling the fraction to minus 12 C. whereby the para-xylene solidifies. Filtration of the solid para-xylene yields 40.1 lbs. of an approximately 98 per cent pure para-xylene.

The above procedure may be somewhat varied, particular with respect to the composition of the xylene fraction employed in the first sulfonation.

It has been found that in order to obtain paraxylene of at least 90 per cent purity, the ratio of ortho-xylene to para-xylene in the xylene fraction should not be greater than 1:20, and that the purity of the para-xylene increases with decreasing content of ortho-xylene in the material which is to be sulfonated. Thus, careful fractional distillation to give a fraction containing only from 0.2 to 0.3 per cent of ortho-xylene, instead of the fraction employed for the first sulfonation in the above example, may yield a para-xylene in the second distillation hydrolysis step of approximately 95 per cent purity. In this case further concentration by fractional crystallization will be unnecessary for most purposes.

The first sulfonating procedure may also be somewhat varied. The acid need not be of 85 per cent strength; however, the acid strength and the conditions of time and temperature employed for the sulfonation should be such as to permit only partial sulfonation, for example sulfonation of from, say, 30 per cent to 80 per cent of the xylene fraction, depending upon the metaxylene content of the fraction.

The present process is suitably employed for the recovery of para-Xylene and of the ethylbenzone from technical xylenes of varying compositions containing preponderant quantities of meta-xylene and para-xylene together with lesser quantities of ortho-xylene and ethylbenzene.

What I claim is:

1. In a process for the recovery of para-xylene from technical xylene, the steps which include partially sulfonating said xylene, removing unsulfonated oil from the partially sulfonated product, fractionally hydrolyzing the residue at a temperature of up to 120 C., bringing together the hydrolyzed fraction with the unsulfonated oil, completely sulfonating the resulting mixture and fractionally hydrolyzing the completely sulfonated material to obtain a predominantly pxylene-containing fraction.

2. In a process for the recovery of para-xylene from technical xylene, the steps which include partially sulfonating said xylene, removing unsulionated oil from the partially sulfonated product, fractionally hydrolyzing the residue to obtain a first hydrolyzed product boiling at a temperature of up to 120 C. and a second hydrolyzed product boiling above a temperature of 145 C., 1.:

adding the first and the second hydrolyzed products to said unsulfonated oil, completely sulfonating the resulting mixture and fractionally hydrolyzing the completely sulfonated material to obtain a predominantly p-xylene-containing fracn tion.

3. In a process for the recovery of para-xylene and of ethylbenzene from technical xylene, the steps which include partially sulfonating said xylene, removing unsulfonated oil from the partially sulfonated product, fractionally hydrolyzing the residue to obtain a hydrolyzed product boiling up to a temperature of 120 C., bringing together the hydrolyzed product with the unsulfonated oil, completely sulfonating the resulting mixture, and iractionally hydrolyzing the completely sulfonated material to obtain a predominantly para-xylene-containing fraction and a predominantly ethylbenzene-containing fraction.

4. In a process for the recovery of para-xylene and of ethylbenzene from technical xylene, the steps which include partially sulfonating said xylene, removing unsulfonated oil from the partially sulfonated product, fractionally hydrolyzing the residue to obtain a first hydrolyzed product boiling at a temperature of up to 120 C. and a second hydrolyzed product boiling at a temperature of over 145 0., adding the first and second hydrolyzed products to said unsulfonated oil,

completely sulfonating the resulting mixture, and fractionally hydrolyzing the resulting material to obtain a predominantly para-xylene-containing fraction and a predominantly ethylbenzene-containing fraction.

5. A process for the recovery of para-xylene and ethylbenzene from technical xylene containing major proportions of meta-xylene and of para-xylene and minor proportions of orthoxylene and of ethylbenzene which comprises reacting said technical xylene with sulfuric acid under conditions permitting only partial sulfonation of the technical xylene, removing unsulfonated oil from the resulting reaction mixture, diluting the residue with water, distilling the diluted material to obtain a forerun boiling up to a temperature of approximately 120 C., an intermediate hydrolysis fraction boiling at a temperature of from 120 C. to 145 C, and another hydrolysis product boiling above 145 0., adding said forerun and the last hydrolysis product to the unsulfonated oil, treatingthe resulting mixture with sulfuric acid for a complete sulfonation Ill of said mixture, diluting the completely sulfonated material with water, distilling the diluted material to obtain a predominantly para-xylenecontaining fraction boiling between a temperature of from 150 C. to 170 C. and a predominantly ethylbenzene-containing fraction boiling above 170 C.

6. A process for the recovery of para-xylene and ethylbenzene from technical zylene containing major proportions of meta-xylene and of para-xylene and minor proportions of orthoxylene and of ethylbenzene which comprises reacting saidtechnical xylene with sulfuric acid under conditions permitting only partial sulfonation of the technical xylene, removing unsulfonated oil from the resulting reaction mixture, diluting the residue with water, distilling the diluted material to obtain a forerun boiling up to a temperature of approximately 120 C., an intermediate hydrolysis fraction boiling at a temperature of from 120 C. to 145 C. and another hydrolysis product boiling above 145 0., adding said forerun and the last hydrolysis product to the unsulfonated oil, treating the resulting mixture with sulfuric acid for complete sulfonation of said mixture, diluting the completely sulfonated material with water, distilling the diluted material to obtain a predominantly para-xylenecontaining fraction boiling between a temperature of from 150 C. to 170 C. and a predominantly ethylbenzene-containing fraction boiling above 170 C., cooling the fraction which boils at a temperature of from 150 C. to170 C. to solidify paraxylene and filtering the solidified para-xylene from the cooled fraction.

'7. A process for the recovery of para-xylene and ethylbenzene from technical xylene containing major proportions of meta-xylene and of para-xylene and minor proportions of orthoxylene and of ethylbenzene which comprises reacting said technical xylene with sulfuric acid of less than per cent H2804 concentration under conditions permitting only partial sulfonation of the technical xylene, removing unsulfonated oil from the resulting reaction mixture, diluting the residue with water, distilling the diluted material to obtain a forerun boiling up to a temperature of approximately C., an intermediate hydrolysis fraction boiling at a temperature of from 120 C. to C. and another hydrolysis product boiling above 145 0., adding said forerun and the last hydrolysis product to the unsulfonated oil, treating the resulting mixture with sulfuric acid of greater than 95 per cent concentration for complete sulfonation of said mixture, diluting the completely sulfonated material with water, distilling the diluted material to obtain a predominantly para-xylene-containing fraction boiling between a temperature of from C. to C. and a predominantly ethylbenzene-containing fraction boiling above 170 C.

WILLIAM F. YATES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,311,848 Lepers July 29, 1919 2,282,231 Mattox May 5, 1942 2,511,711 I-Ietzner et al. June 13, 1950 2,519,336 Beach Aug. 22, 1950

Claims (1)

1. IN A PROCESS OF THE RECOVERY OF PARA-XYLENE FROM TECHNICAL XYLENE, THE STEPS WHICH INCLUDE PARTIALLY SULFONATING SAID XYLENE, REMOVING UNSULFONATED OIL FROM THE PARTIALLY SULFONATED PRODUCT, FRACTIONALLY HYDROLYZING THE RESIDUE AT A TEMPERATURE OF UP TO 120* C., BRINGING TOGETHER THE HYDROLYZED FRACTION WITH THE UNSULFONATED OIL, COMPLETELY SULFONATING THE RESULTING MIXTURE AND FRACTIONALLY HYDROLYZING THE COMPLETELY SULFONATED MATERIAL TO OBTAIN A PREDOMINATNTLY PXYLENE-CONTAINING FRACTION.