US3691246A

US3691246A - Olefin separation process

Info

Publication number: US3691246A
Application number: US101889A
Authority: US
Inventors: Levi Christy Parker; Thomas Allen Cooper; James Lawson Meadows
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1970-12-28
Filing date: 1970-12-28
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12
Also published as: CA966799A; GB1313275A; DE2164451A1

Abstract

A mixture of olefins and n-paraffins is produced by cracking or dehydrogenation of n-paraffins. Separation of an olefin fraction from the mixture of olefins and normal paraffins is effected by forming a solution of said mixture in a selective solvent, cooling said solution to a temperature at which substantially all of said olefins remain in solution in said solvent whereby normal paraffins are precipitated from the remaining solution. The remaining solution of enriched olefin content is separated from precipitated normal paraffins and solvent and to said olefin fractions are separated from the normal paraffin denuded liquid. The separated olefin fraction is suitable for reaction with an aromatic such as benzene in the manufacture of alkyl benzene compounds.

Description

United States Patent Parker et al.

[451 Sept. 12,1972

[54] OLEFIN SEPARATION PROCESS 3,235,471 2/1966 Clay ..260/677 A Inventors: Levi Parker; Th Allen Woodie C ames Lawson M do 5 all ggs 13 ea w Primary Examiner-Curtis R. Davis Attorney-Thomas H. Whaley and Carl G. Ries [73] Assignee: Texaco Inc.,New York,N.Y. 22 Filed: Dec. 28, 1970 [571 ABSTRACT [21] Appl. No.: 101,889 A mi tture of olefins and n-paraffins is produced by cracking or dehydrogenation of n-paraffins. Separation of an olefin fraction from the mixture of olefins [52] US. Cl ..260/671 R, 260/671 B, 260/677 A, and normal paraffins is effected by forming a Solution 260/683'3 of said mixture in a selective solvent, cooling said [51] Int. Cl. ..C07c 3/52, C07c 11/02 Sohnion to a temperauure at which substantiauy a of [58] new of sea'ch-m-260/677 671 676 said olefins remain in solution in said solvent whereby R; 208/33 normal paraffins are precipitated from the remaining solution. The remaining solution of enriched olefin [56] References C'ted content is separated from precipitated normal paraffins and solvent and to said olefin fractions are ATES PAT NT UNITED ST E S separated from the normal paraffin denuded liquid. 2,911,452 1959 Bl'oughton --260/677 A The separated olefin fraction is suitable for reaction Klnchen an aromatic uch as benzene in the manufacture Pokomy et al. of benzene compounds 2,925,452 2/1960 Broughton ..260/677 A Claims, 1 Drawing Figure 280 F/P/ICT/fl/VA T0,? 2/ J0 Df/lVfl/FflfiE/VATOI? ail F/Z 7E1? 7 1: JIfi/flPf/F Jffi/Pfi'l? :7 L azzi/n/ Ja\ P/FMUCT 40 i .19 ALA/V1470? OLEFIN SEPARATION PROCESS BACKGROUND OF THE INVENTION Long chain normal olefins, for example, olefins having chain links of at least carbon atoms are valuable in the manufacture of petrochemically derived products, for example, biodegradable detergents. Such materials are in great demand as a means of reducing the pollution of streams and water sources. An economical and effective method of producing normal olefins is by wax cracking or the dehydrogenation of normal paraffins. Such processes are described in U.S. Pat. No. 2,172,228 which relates to a thermal cracking method and US Pat. No. 3,458,592 which describes a catalytic method of producing n-olefins from n-paraffins. In such processes, the product comprises n-olefins in admixture with unconverted n-paraffins. In processes with the greatest selectivity, that is, processes giving the greatest yield of n-olefin based on n-paraffin conversion, conversion per pass is relatively low, and the olefin product is diluted with unconverted n-paraffin charge. When employing the n-olefin product as feed to an alkylation process for the manufacture of products such as detergent alkylate, it is desirable to concentrate the olefin feed to reduce diluents in the alkylation system and to avoid the production of undesired byproducts. Accordingly, it is an object of this invention to provide a means of separating an olefin fraction of increased olefin content from a mixture of olefins and normal paraffins. It is a further object to concentrate the olefins produced in a n-paraffin cracking process to provide a feedstock suitable for alkylation.

SUMMARY OF THE INVENTION This invention is directed to a process of separating an olefin fraction from a mixture of olefins and n-paraffins which comprises forming a solution of said mixture in a selective solvent, cooling said solution to a temperature at which said n-paraffins are substantially insoluble in said solvent and at which substantially all of said olefins remain in solution in said solvent effecting precipitation of nparaffins from remaining solution of increased olefin concentration, separating precipitated n-paraffins from said remaining liquid, and separating solvent and said olefin fraction from said remaining liquid. The selective solvent employed in this invention may comprise, for example, acetone, methylethyl ketone, methylisobutyl ketone, benzene, toluene, naphtha, gasoline, pentane, dichloromethane, methyl chloride, chloroform, and mixtures thereof. A particularly preferred solvent is a mixture of an aliphatic ketone and an aromatic hydrocarbon, for example, a mixture of methylethyl ketone and toluene. In accordance with this method, the solution of olefins, nparaffins and solvent is cooled to a temperature effecting precipitation of the normal paraffins as a waxy solid from a solution comprising olefins and solvent. The temperature of normal paraffin precipitation depends upon the carbon number of the paraffin or paraffins involved. It is preferred to employ a separation temperature of about the melting point of the corresponding olefin. For example, in the separation of a mixture of olefins from the corresponding paraffins, we prefer to employ separation temperature of about the following: ir le, hi urm ut- 19,

+; G -C C -C +100. Desirably the feedstock to the separation process of this invention is distilled to separate it into cuts of olefins and n-paraffins having carbon numbers differing by not more than two carbon numbers. The separated olefin fraction is suitable for use in alkylation wherein it is contacted with benzene in the presence of an alkylation catalyst under alkylation conditions effecting formation of alkyl benzenes. Advantageously, in a combination process wherein a normal paraffin charge stock is dehydrogenated forming said mixture of olefins and nparaffins and the olefin product is separated by precipitating n-parafiins, the precipitated n-paraffins are recycled to comprise a portion of the normal paraffin charge stock.

In the n-paraffin dehydrogenation process, the olefin content of the n-parafiin-olefin effluent may typically range from 10 to 15 volume percent. It is desirable to separate these olefins from the effluent, in order to use the olefins for further processing, and return the nparaffins to the dehydrogenation process for further conversion to olefins. Alternatively, an enrichment of the olefin-fraction in the n-paraffin-olefin effluent is also desirable as an enriched olefin-n-paraffin mix may be employed as charge stock for further processing. For example, an enriched fraction of olefin and nparaffin may be charged with benzene to an alkylation unit for production of detergent alkylate. Unreacted nparaffins from detergent alkylate manufacture may also be returned as charge stock to the n-paraffin dehydrogenation unit.

We have found that by using a solvent-chilling technique, that n-paraffins can be removed as a waxlike precipitate from an n-paraffin-olefin dehydrogenation effluent providing an olefin stream of enriched olefin content. The solvent-chilling technique is similar to that used for removing wax from lubricating oils.

DESCRIPTION OF THE DRAWING The accompanying drawing diagrammatically illustrates the process ofthis invention. A charge stream comprising n-paraffin hydrocarbons having one, two or three or more carbon numbers spread is introduced through line 10 into dehydrogenator 11. A suitable stream may be for example, a 400 to 500F. boiling range n-paraffin fraction which includes l2, l3, and 14 carbon number paraffin hydrocarbons, i.e., dodecane, tridecane, and tetradecane. In dehydrogenator 11, the charge is contacted with a noble metal-molecular sieve catalyst at a temperature within the range of about 800 to 900F., a pressure of 0 to 200'p.s.i.g. at a liquid hourly space velocity within the range of about 0.5 to 10 and in the presence of hydrogen in an amount within the range of about 0.5:1 to 15:1 moles of hydrogen per mole of paraffin hydrocarbon. The resulting dehydrogenated product is passed through line 12 to fractionator 13. In fractionator 13 the products are separated into fractions lighter boiling than the feedstock discharged through line 15, heavier boiling than the feedstock discharged through line 16 and hydrocarbons boiling within the range of the feedstock discharged through line 17. The lighter and heavier fractions in

lines

15 and 16 may be further processed for separation of the corresponding olefins or may be discharged for other uses not shown.

The n-paraffin olefin mixture in line 17 is combined with solvent, for example, a methylethyl ketonetoluene mixture from line 20 and passed to chiller 21. In chiller 21 the solvent diluted mixture is cooled to a temperature at which the n-paraffin constituents are precipitated. The resulting slurry of waxlike n-paraffin crystals in the remaining liquid is passed through line 22 to filter 23. In filter 23 the crystals of n-paraffins are separated and discharged through line 24 and remaining liquid comprising solvent and enriched olefins is discharged through line 25. The n-paraffin stream is passed to stripping tower 29 wherein dissolved solvent is removed through line 30 and n-paraffins withdrawn through line 31. The n-paraffins in line 31 are recycled to combine with the charge in line 10.

The filtrate of enriched olefins in line 25 is passed to stripper 35 wherein dissolved solvent is removed through line 36. The enriched olefin product is withdrawn through line 37 and a portion or all of this enriched olefin product is passed through line 38 to alkylator 39 as feedstock for alkylation of benzene. Benzene feed is introduced into alkylator 39 through line 40. Benzene and olefin stream are contacted with a Friedel-crafts catalyst such as aluminum chloride-HG] at a temperature within the range of 90 to 140, at a pressure of about atmospheric and an olefin to aromatic feed ratio within the range of about 1:1 to 0.111. Effluent from alkylator 39 is passed through line 45 to separator 46. Separator 46 may comprise decantation, distillation, solvent extraction or other means of separation of the alkylation products from the reactants which are well known in the art and which forms no part of the present invention. Separated alkyl benzene product is withdrawn through line 47. Recovered n-paraffin hydrocarbons are withdrawn through line 48 and may be recycled with the paraffin hydrocarbons in line 31 and the fresh charge in line to dehydrogenator 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an example of the process of this invention, a charge stock consisting essentially of C and C nparaffins and olefins was treated to produce an enriched olefin fraction. The charge stock contained 92.3 weight percent n-paraffins and 7.7 weight percent olefins. The charge stock was diluted with 2 parts of methylethyl ketone and the resulting mixture chilled to 25F. A waxlike solid precipitated which was separated by filtration at -25F. The waxy solid was washed with an additional two volumes of methylethyl ketone to remove occluded liquid and the wash solution added to the first filtrate. The filtrate and wash was stripped to remove solvent producing an olefin concentrate containing 21.0 weight percent olefins.

In another example, the C C, charge stock of the previous example was distilled separating separate C and C cuts. These fractions were also concentrated by the same method. The yields of the C and C fractions upon distillation were 54.3 and 45.7 weight percent respectively. Each fraction was concentrated employing dilution with two volumes of methylethyl ketones and filtration at a temperature of 25F. The resulting solid in each case was washed with an additional two volumes of solvent. Tests on each of the charge stocks and the resulting olefin concentrates and residues are shown in the following tabulation:

It will be observed that the best results are obtained with essentially single carbon number fractions as compared with fractions containing two or more carbon numbers. Olefin enrichment was especially effective for the C fraction where olefin content was increased five-fold, i.e., from 7.8 to 39.7 weight percent. If desired, further enrichment may be effected by repeating the enrichment step.

We claim:

1. A process of separating an olefin fraction from a mixture of olefins and n-paraffins which comprises:

forming a solution of said mixture in a selective solvent,

cooling said solution to a temperature at which said n-paraffin are solid and substantially insoluble in said solvent and at which substantially all of said olefins remain in solution in said solvent effecting precipitation of n-paraffins from remaining solution of increased olefin concentration,

separating precipitated n-paraffins from said remaining liquid, and

separating solvent and said olefin fraction from said remaining liquid.

2. The process of claim 1 wherein said selective solvent is selected from the group consisting of acetone, methylethyl ketone, methylisobutyl ketone, benzene, toluene naphtha, gasoline, pentane, dichloromethane, methylene chloride, chloroform, and mixtures thereof.

3. The process of claim 1 wherein said selective solvent comprises a mixture of an aliphatic ketone selected from the groups consisting of acetone, methylethyl ketone, methylisobutyl ketone, and mixtures thereof and an aromatic hydrocarbon selected from the group consisting of benzene, toluene, and mixtures thereof.

4. The process of claim 1 wherein said olefin fraction comprises 12 and 13 carbon number olefins and solution is cooled to a temperature within the range of about 25F. effecting precipitation of said normal paraffins as a waxy solid.

5. The process of claim 4 wherein said waxy solid is separated from said remaining liquid by filtration at a temperature within the range of about 25F.

6. The process of claim 1 wherein said mixture of olefins and n-paraffins consists essentially of olefins and n-paraffins having carbon numbers differing by not more than two carbon numbers.

7. The process of claim 1 wherein said olefin fraction is contacted with benzene in the presence of an alkylature of olefins and n-parafi'ms and said mixture of olefins and n-paraffins comprises a range of hydrocarbons differing in carbon number by not more than two carbon numbers.

Claims

2. The process of claim 1 wherein said selective solvent is selected from the group consisting of acetone, methylethyl ketone, methylisobutyl ketone, benzene, toluene naphtha, gasoline, pentane, dichloromethane, methylene chloride, chloroform, and mixtures thereof.
3. The process of claim 1 wherein said selective solvent comprises a mixture of an aliphatic ketone selected from the groups consisting of acetone, methylethyl ketone, methylisobutyl ketone, and mixtures thereof and an aromatic hydrocarbon selected from the group consisting of benzene, toluene, and mixtures thereof.
4. The process of claim 1 wherein said olefin fraction comprises 12 and 13 carbon number olefins and solution is cooled to a temperature within the range of about -25*F. effecting precipitation of said normal paraffins as a waxy solid.
5. The process of claim 4 wherein said waxy solid is separated from said remaining liquid by filtration at a temperature within the range of about -25*F.
6. The process of claim 1 wherein said mixture of olefins and n-paraffins consists essentially of olefins and n-paraffins having carbon numbers differing by not more than two carbon numbers.
7. The process of claim 1 wherein said olefin fraction is contacted with benzene in the presence of an alkylation catalyst under alkylation conditions effecting formation of alkyl benzene.
8. The process of claim 1 wherein an n-paraffin charge stock is dehydrogenated forming said mixture of olefins and n-paraffins.
9. The process of claim 8 wherein precipitated n-paraffins are recycled to comprise a portion of said n-paraffin charge stock.
10. The process of claim 8 wherein dehydrogenated n-paraffin charge stock is distilled separating said mixture of olefins and n-paraffins and said mixture of olefins and n-paraffins comprises a range of hydrocarbons differing in carbon number by not more than two carbon numbers.