US3761392A - Upgrading wide range gasoline stocks - Google Patents

Abstract

A PROCESS FOR UPGRADING WIDE RANGE GASOLINE STOCKS IS DISCLOSED WHEREIN THE FEED IS SEPARATED INTO C5, C6-C8 AND C9+ FRACTIONS, THE C6-C8 AND C9+ FRACTIONS ARE SEPARATELY REFORMED, REFORMATE FROM THE C9+ FRACTION IS DISTILLED TO REMOVE C5-C8 MATERIAL AND YIELD A HEAVY AROMATIC PRODUCT OF HIGH ANTIKNOCK VALUE, SAID C5-C8 MATERIAL IS COMBINED WITH REFORMATE FROM SAID C6-C8 FRACTION AND WITH AROMATIC DEHYDROCYCLIZATE FROM A SUBSEQUENT STEP, THE RESULTING MIXTURE IS EXTRACTED WITH AN AROMATIC-SELECTIVE SOLVENT TO YIELD A RAFFINATE AND C6-C8 AROMATIC PRODUCT OF HIGH PURITY AND ANTIKNOCK VALUE, THE RAFFINATE IS DISTILLED TO OBTAIN A C5-C6 PARAFFINIC FRACTION AND A HEAVY PARAFFINIC FRACTION, THE LATTER IS CATALYTICALLY DEHYDROCYCLIZED TO YIELD SAID AROMATIC DEHYDROCYCLIZATE, THE C5-C6 PARAFFINIC FRACTION IS COMBINED WITH SAID C5 FRACTION AND THE MIXTURE IS CATALYTICALLY ISOMERIZED.

Description

United States Patent 3,761,392 UPGRADING WIDE RANGE GASOLINE STOCKS Andr W. Pollock, West Chester, Pa., assignor to Sun Oil Company of Pennsylvania, Philadelphia, Pa. Filed May 8, 1972, Ser. No. 251,020 Int. Cl. C10g 39/00 US. Cl. 208-93 3 Claims ABSTRACT OF THE DISCLOSURE A process for upgrading wide range gasoline stocks is disclosed wherein the feed is separated into C C -C and C fractions, the C -C and C fractions are separately reformed, reformate from the C fraction is distilled to remove C -C material and yield a heavy aromatic product of high antiknock value, said C -C material is combined with reformate from said C -C fraction and with aromatic dehydrocyclizate from a subsequent step, the resulting mixture is extracted with an aromatic-selective solvent to yield a rafiinate and C -C aromatic product of high purity and antiknock value, the raffinate is distilled to obtain a C -C parafiinic fraction and a heavy parafiinic fraction, the latter is catalytically dehydrocyclized to yield said aromatic dehydrocyclizate, the C -C parafiinic fraction is combined with said C fraction and the mixture is catalytically isomerized.

BACKGROUND OF THE INVENTION This invention relates to a process involving a combination of refining steps for upgrading wide range gasoline stocks to fractions of higher antiknock values.

Numerous processes have been proposed heretofore for upgrading gasoline fractions by employing various combinations of refining steps such as distillation, reforming, dehydrocyclization, extraction and isomerization. The objective generally is to obtain products of good antiknock quality in high yields. Examples of such combination processes appear in the following US. patents: 2,891,902, H. V. Hess et al., issued June 23, 1959; 2,913,- 393, D. H. Sarno, issued Nov. 17, 1959; 2,921,015, R. N. Shiras, issued Jan. 12, 1960; 2,944,959, R. E. Kline et al., issued July 12, 1960; 2,967,143, M. F. Fontaine et al., issued Jan. 3, 1961.

SUMMARY OF THE INVENTION The present invention provides a different processing procedure for upgrading wide range gasoline stocks involving a new combination of known types of refining steps. The process provides a way of securing an optimum yield-octane value relationship in upgrading the feed material to high quality blending stocks for motor fuel manufacture.

The process according to the invention involves the following combination of steps:

(a) Distilling a gasoline stock boiling mainly in the range of 90-400 F. to separate (1) a C fraction, (2) a C -C fraction boiling mainly in the range of ISO-250 F. and (3) a residue boiling mainly in the range of 250'- 400 F.;

(b) Reforming said C -C fraction in the presence of hydrogen and a platinum-containing reforming catalyst at temperatures and pressures in the respective ranges of 875-1000 F. and 150-700 p.s.i.g.;

(c) Separately reforming said residue in the presence of a platinum-containing reforming catalyst at temperatures and pressures in the respective ranges of 875-1000 F. and 150-700 p.s.i.g.;

(d) Distilling the reformate from step (c) to obtain a light reformate fraction boiling mainly in the range of 90-280 F. and to recover a heavy aromatic product of high antiknock value;

(e) Combining said -280 F. light reformate frac tion with the reformate from step (b) and with aromatic dehydrocyclizate from step (g) infra and extracting the resulting mixture with an aromatic-selective solvent to obtain a rafiinate and a light aromatic product of high antiknock value comprising C -C aromatics;

(f) Distilling said raffinate to separate same into a C -C light parafiinic fraction and a heavy paraflinic frac tion boiling, respectively, mainly in the range of 90-165 F. and 165-280 F.;

(g) Reforming said heavy paraffinic fraction from step (f) under catalytic dehydrocyclizing conditions to remove hydrogen therefrom and produce an aromatic dehydrocyclizate for use as specified in step (e);

(h) Combining said C -C light parafiinic fraction from step (f) with said C fraction from step (a) and subjecting the mixture to catalytic isomerization conditions to yield C -C isoparaffins.

BRIEF DESCRIPTION OF DRAWING The invention is described in conjunction with the accompanying drawing which is a schematic flowsheet depicting the sequence of steps of the process.

DESCRIPTION The feedstock for the present process is a wide range, debutanized gasoline fraction including C paraffins and boiling mainly in the range of 90-400 F. The invention is most useful for the processing of straight run gasoline stocks but other stocks, such as naphthas from catalytic or thermal cracking, may be included if desired. The process converts the feedstock into three products: (1) a C -C paraffinic isomerizate; (2) a C -C aromatic product of high purity typically having F-l octane rating in the range of -115; and (3) a heavy aromatic product (C typically having F-l octane rating of 105- 107. These products can be blended in any desired way with each other and/ or with other gasoline components to produce motor fuels of high antiknock value.

With reference to the accompanying drawing, the debutanized feed is introduced through line 10 to a distillation column 11 which fractionates it into three streams. The overhead stream obtained through line 12 is a C fraction which boils below F. A C -C fraction that boils mainly in the range of ISO-250 F. is obtained as a sidestream via line 13. The residue, which is removed through line 14, is a C fraction boiling mainly in the range of 250-400 F.

The C residue fraction is passed through line 14 to a reforming operation, illustrated schematically by reformer 15, wherein it is subjected to catalytic hydroforming. The reforming reaction is carried out by means of a platinum-containing reforming catalyst in the presence of hydrogen at suitable reforming temperatures in the range of 875-1000 F. and pressures of from 150 to 700 p.s.i.g., preferably 300-500 p.s.i.g. A Weight hourly space velocity (WHSV) generally in the range of 05-10 Weights per hour per Weight of catalyst is utilized, with preferred WHSV generally being 1-3. Average inlet temperatures to the reformer reactors usually are in the range of 900- 1000 F. A plurality of reactors in series generally is used in this type of operation, with a heater ahead of each reactor for heating the reformer feed to the desired temperature and reheating the hydrocarbon reactants to compensate for reductions in temperature that occur due to the endothermic reactions which take place. Under these reforming conditions naphthenes dehydrogenate to aromatics and a considerable portion of the C and heavier material is converted to C -C products due to the dealkylation and cracking reactions that occur. These C -C products include both aromatic and saturated hydrocarbon components.

The effiuent from reformer 15 is withdrawn through line 16 and conventionally is passed through a cooler and gas-liquid separator (not shown) so that the hydrogen-containing gas phase can be recycled. A hydrogen recycle rate typically in the range of 3000-9000 s.c.f./bbl. of reformer feed is used and the hydrogen content of the recycle stream is generally in the range of 60-98% by volume.

An of the known or conventional platinum-containing reforming catalysts can be used for effecting the hydroforming reaction in reformer 15. Such catalysts have been described in numerous prior art references and need not be described herein. Reference can be made, for example, to the following: Catalytic Processes and Proven Catalysts by C. L. Thomas, pp. 54-57, Academic Press (1970); U.S. Pat. 2,479,109, V. Haensel, issued Aug. 16, 1949; and U.S. Pat. 2,478,916, V. Haensel et al., issued Aug. 16, 1949. The platinum-containing catalyst can also contain other metals, such as rhenium, ruthenium, rhodium or iridium, which are beneficial. The platinumrhenium reforming catalysts are particularly desirable and such catalysts have been described in U.S. Pat. 3,415,737, H. E. Kluksdohl, issued Dec. 10, 1968 and U.S. Pat. 3,434,960, R. L. Jacobsenson, issued Mar. 25, 1969. Platinum-iridium reforming catalysts are disclosed in U.S. Pat. 3,554,902, W. C. Buss, issued Jan. 12, 1971.

The liquid reformate from the above-described reforming operation is debutanized and the normally liquid portion is separated into two fractions, all as indicated schematically by distillation zone 17. The C and lighter products are removed from the system via line 34. The light reformate fraction composed of the C -C hydrocarbons and boiling mainly in the range of 90280 F. is separately recovered from zone 17 through line 18 for further processing as described below. The heavy reformate stream is obtained as bottoms through line 19 and is removed from the system as one of the desired products. This product is highly aromatic, typically containing 85-90% aromatic components and having F-l clear octane rating of 105107.

The C -C stream obtained from column 11 passes through line 13 and is sent to another reforming zone 32. This reformer also utilizes a platinum-containing catalyst and can be operated at substantially the same conditions as described for reformer 15, with temperatures and pressures in the ranges of 875-l000 F. and 150- 700 p.s.i.g., respectively, and WHSV in the range of 0.5- 10. A preferred pressure range is 250-400 p.s.i.g., WHSV preferably is 1-3 and inlet temperatures to the reactors generally are in the range of 9001000 F.

The liquid reformate obtained from the gas-liquid separator (not shown) after reformer 32 is debutanized in column 21 and the C and ligher components are re moved from the system via line 33. Debutanized reformate, which is obtained through line 22 and which boils mainly in the range of 90280 F., is combined with the C -C fraction from line 18 and with dehydrocyclizate derived as hereinafter described through line 20, both of which latter materials also have about this same boiling range. The mixture is then treated in an extraction unit, schematically illustrated by extractor 23, wherein it is countercurrently extracted with an aromatic-selective solvent in order to separate the aromatic from non-aromatic components. Procedures for carrying out the selective extraction of aromatics from C C naphtha stocks are well known and need not be described in detail here. The Udex process which utilizes a glycol type solvent has had wide commercial use for selectively extracting C -C aromatics and is a preferred way of carrying out the operation represented by extractor 23. This process is described in Hydrocarbon Processing, September 1970, p. 248. Upon recovery of the extract from the solvent phase, a C -C aromatic product of high purity is obtained and is removed through line 24 as another product of the present process. This product has a boiling range of about 175280 F., consists essentially of benzene, toluene and xylenes, and typically has F1 clear octane number in the range of 110- 115. It can be used as a blending stock for high antiknock value gasoline or optionally can be fractionally distilled to recover the individual aromatics as industrial chemical products.

The raffinate from extractor 23 passes through line 25 to distillation zone 26 wherein it is separated into a C -C overhead fraction obtained through line 27 and a C -C bottoms fraction withdrawn through line 28. These fractions are both highly paraffinic and their respective boiling ranges are about 165 F. and 165-280" F.

The C -C parafiinic fraction is sent from line 28 to a dehydrocyclization step illustrated by dehydrocyclizer 29. This is a hydroformer which can be operated under conditions much like those utilized in reformers 15 and 32. Dehydrocyclization of the parafiin feed to this step can be carried out by any suitable reforming catalyst, such as a chromia-alumina catalyst, a molybdena-alumina catalyst, or a platinum-containing reforming catalyst as referred to with reference to the operation of reformers 15 and 32. As a general rule, the pressure level is somewhat lower for the dehydrocyclization step than for either of these reforming steps. Inlet temperatures to dehydrocyclizer 29 usually are in the range of 9001000 F., while the pressure generally is below 500 p.s.i.g. and usually falls within the range of 50-30O p.s.i.g. Suitable reforming conditions for dehydrocyclizing straight chain hydrocarbons are described in the prior art, e.g. in the following U.S. patents: 2,886,508, H. V. Hess et al., issued May 12, 1959 and 2,944,001, C. N. Kimberlin, Jr. et al., issued July 5, 1960. Under the dehydrocyelizing conditions maintained in hydroformer 29 the parafiinic hydrocarbons undergo dehydrogenation and cyclization, as a result of which a reformate or dehydrocyclizate product with a substantial aromatic content is obtained.

The effluent from dehydrocyclizer 29 passes through a cooler and gas-liquid separator (not shown) and the liquid product then goes to debutanizer column 30 from which the C and lighter components are removed via line 31. The debutanized dehydrocyclizate obtained from the bottom of column 30 through line 20 boils mainly in the range of 90-280 F. and is recycled to line 22 to become a component of the feed to extractor 23.

The C fraction obtained from column 11 (line 12) is admixed with the C -C parafiinic fraction from column 26 (line 27) and the mixture is subjected to isomerization as illustrated by isomerizer 35. Numerous procedures have been described in the prior art for isomerizing C -C paraffins and any of them can be used for the present isomerization step. Descriptions of such procedures are given in an article entitled Advances in Isomerization by P. A. Lawrence et al., Proceeding of Seventh World Petroleum Congress, vol. IV, pp. 135-145, Elsevier Publishing Co. (1967). Other examples of processes for isomerizing such parafiins appear in the following U.S. patents: 2,834,823, J. L. Patton et al., issued May 13, 1958; 3,527,835, H. A. Benesi, issued Sept. 8, 1970; 3,577,479 and 3,578,725, D. E. Jost et al., issued May 4 and 9, 1971, respectively.

The isomerizate obtained from isomerizer 35 through line 36 is composed of C -C paraffins with a higher isoparafiin content than the feed to this step. The isomerizate has F-l antiknock value typically in the range of 80-90 and can be withdrawn as the other product of the process. Optionally it can be treated to separate n-parafiins from the isoparafiins, e.g. by means of zeolitic molecular sieves as disclosed in U.S. Pat. 2,888,394, E. R. Christensen et al., issued May 26, 1959, and the separated n-parafiins can be recycled to isomerizer 35 for further conversion.

The following is a specific illustration of the present process based on feeding vols/hr. of straight run gasoline boiling 90-400" F. and containing about 12% aromatics, 31% naphthenes and 57% paraflins:

The feed is fractionated in column 10 to give 10 vols. of C fraction (line 12) which is essentially all paraffins, 40 vols. of C -C fraction (line 13) which is about aromatics, 35% naphthenes and 55% parafiins, and 50 vols. of residue (line 14) which is about 15% aromatics, 35% naphthenes and 50% paraffius. Reforming of the residue in reformer 15, using reactor inlet temperatures of 925-975 F., pressure of about 400 p.s.i.g., WHSV of about 2 and hydrogen recycle rate of about 6000 s.c.f./bbl., followed by fractionation (column 17) gives about vols. of C -C reformate (line 18) and 20 vols. of C aromatic product (line 19). The C -C reformate contains about 3% benzene, 12% toluene and xylenes, the remainder being largely parafiins. The C product contains about 90% aromatics and has F-l clear octane number of about 106.

Reforming of the 40 vols. of C -C fraction in reformer 32, employing about the same conditions as in reformer 15 except a somewhat lower pressure of about 325 p.s.i.g. and a hydrogen recycle rate of about 4000 s.c.f./bbl., followed by debutanization (column 21) yields 32 vols. of C -C reformate (line 22) containing about 6% benzene, 17% toluene and 17% xylenes. This reformate is combined with the other C -C reformate (line 18) and with 23 volumes of dehydrocyclizate (line 20) to give 75 vols. of feed of extractor 23. The C -C extract product (line 24) amounts to 28 vols. composed of about 12% benzene, 42% toluene and 46% xylenes. The raflinate (line 25) amounting to 47 vols. is distilled (column 26), giving 16 volts. of C -C parafiinic fraction (line 27) and 31 vols. of C -C paraflinic fraction (line 28) which latter is fed to dehydrocyclizer 29. This step employs a platinum-containing reforming catalyst, reactor inlet temperatures in the range of 925-975 F., pressure of about 175 p.s.i.g., WHSV of 2, and a hydrogen recycle rate of the order of 6000 s.c.f./bbl. Upon debutanization (column 30) of the reactor product, 23 vols. of C -C dehydrocyclizate are obtained (line 20) having individual aromatic contents of 4% benzene, 23% toluene and 24% xylenes.

The 10 vols. of 0,; fraction (line 12) are combined 9 with the 16 vols. of C -C parafiinic fraction (line 27) and the mixture is hydroisomerized (isomerizer in vapor phase using a highly chlorided platinum-om alumina catalyst, temperature of about 300 F., pressure of about 1000 p.s.i.g., WHSV of 2, and a hydrogen recycle rate of about 3000 s.c.f./bbl. This results in about 25 vols. of C -C isomerizate having F-l clear octane value of about 83.

The invention claimed is:

1. Process for upgrading a wide range gasoline stock which comprises:

(a) distilling a gasoline stock boiling mainly in the range of 400F. to separate(1) a C fraction, (2) a C -C fraction boiling mainly in the range of 15 0-250 F. and (3) a residue boiling mainly in the range of 250-400 F.;

(b) reforming said C -C fraction in the presence of hydrogen and a platinum-containing reforming catalyst at temperatures and pressures in the respective ranges of 875l000 F. and -700 p.s.i.g.;

(c) separately reforming said residue in the presence of a platinum-containing reforming catalyst at temperatures and pressures in the respective ranges of 875-1000 F. and 150-700 p.s.i.g.;

. (d) distilling the reformate from step (c) to obtain a light reformate fraction boiling mainly in the range of 90-280 F. and to recover a heavy aromatic product of high antiknock value;

(e) combining said 90-280 F. light reformate fraction with the reformate from step (b) and with aromatic dehydrocyclizate from step (g) infra and extracting the resulting mixture with an aromatic-selective solvent to obtain a rafi'inate and a light aromatic product of high antiknock value comprising C -C aromatics;

(f) distilling said rafiinate to separate same into a C -C light parafiinic fraction and a heavy paraffinic fraction boiling, respectively, mainly in the ranges of 90-165F. and -280 F.

(g) reforming said heavy paraffinic fraction from step (f) under catalytic dehydrocyclizing conditions to remove hydrogen therefrom and product an aromatic dehydrocyclizate for use as specified in step (e);

(h) combining said C -C light parafiinic fraction from step (f) With said =0 fraction from step (a) and subjecting the mixture to catalytic isomerization conditions to yield C -C isoparaifins.

2. Process according to claim 1 wherein step (g) is carried out at temperatures in the range of 9001000 F. and pressures below 500 p.s.i.g.

3. Process according to claim 2 wherein steps (b), (c) and (g) are carried out a pressures, respectively, in the ranges of 250-400 p.s.i.g., 300-500 p.s.i.g., and 50-300 p.s.i.g.

References Cited UNITED STATES PATENTS 2,891,902 6/1959 Hess et al 20865 2,913,393 11/1959 Sarno 20879 2,921,015 1/1960 Shiras 20879 2,944,959 7/1960 Kline et al. 20879 2,967,143 1/ 1961 Fontaine et al. 20879 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 20879, 80

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