US2949422A - Solvent extraction process for high octane gasoline - Google Patents

Description

Aug. 16, 1960 w. w. GRIMES 2,949,422

SOLVENT EXTRACTION PROCESS FOR HIGH OCTANE GASOLINE Filed June 29, 1956 men OCTANE' RAFFINATE MOTOR FUEL I 3 l7 l2 n 3 m n: o a: o m l- 4 U D O 2 g 2 Q a: E o ln 6 MIX 5' a m ALIPHATIC RM T g REFO A E HYDROCARBON SOLVENT INVENTO R WILLIAM w. GRIMES Ari-onus United States Patent SOLVENT EXTRACTION PROCESS FOR HIGH 'OCTANE GASOLINE William W. Grimes, Cleveland, Ohio, assignor to The Standard Oil Company, Cleveland, Ohio, at corporation of Ohio Filed June 29, 1956, Ser. No. 594,927

1 Claim. (Cl. 208-321) The present invention relates to a process for producing a high octane motor fuel from catalytically reformed petroleum naphthas. More particularly, the invention relates to a process in which catalytically reformed naphthas are extracted with a selective solvent and in which the extracted components of the naphtha are incorporated directly into a motor fuel.

It has been suggested heretofore that the aromatic constituents of a catalytically reformed naphtha could be selectively removed therefrom by means of a selective solvent. The object of the prior art processes was to recover either a relatively pure aromatic hydrocarbon stock or to produce a gasoline blending stock comprising a predominant amount of aromatic compounds. One of the chief difiiculties with the prior art processes has revolved around the problem of separating the aromatics from the extract mixture obtained from the solvent extraction zone. The prior art has suggested that the ammatic compounds be separated from the extract by distillation. It has also been suggested that the aromatic compounds might be recovered from the solvent by reextraction of the extract mixture with a high boiling, predominantly parafiinic hydrocarbon stock such as kerosene. However, even in the latter instance, it is necessary to subsequently distill the aromatic compounds from the high boiling paraffinic hydrocarbon liquid.

All of these processes consume relatively large amounts of heat. In the case where aromatic compounds are distilled directly from the extract, large quantities of heat 'are required to effect the distillation. Even in the instance where the aromatic compounds are first dissolved in a high boiling hydrocarbon, considerable quantities of heat are required to separate the aromatic compounds from the high boiling hydrocarbon. By means of the present invention, it is possible to materially reduce the heat requirements of these processes. Furthermore, most solvents are subject to thermal degradation and, for this reason, it is undesirable to subject the solvent to distillation temperatures.

In brief, my invention is a process comprising the steps of extracting catalytically reformed naphtha with a solvent which will selectively separate aromatic and paraflin compounds so as to obtain a separate raffinate and first extract phase containing the aromatics, re-extracting the first extract phase with a predominantly aliphatic hydrocarbon liquid boiling within the motor gasoline range so as to dissolve the aromatic compounds therein. The raffinate from the first extract step may be recycled to a catalytic reforming zone, if desired, since it is particularly suited to such operations. The solvent which is separated in the second extraction step likewise may be recycled to the first extract zone. The mixture of aro matic and aliphatic hydrocarbons obtained in the second extraction step may be used either alone or in combina- -tion with other stocks as a high octane motor fuel.

As the catalytically reformed naphtha, hereinafter referred to as catalytic reformate, to be used in this invention, I contemplate using any naphtha derived from crude petroleum which has been catalytically reformed. Usually, such reforming operations are limited to stocks boiling in the range of 200 to 400 F. In a catalytic reforming process, naphtha is contacted with a catalyst in the presence of hydrogen at elevated temperature and pressure in a manner which is well understood by those skilled in the art. A variety of catalysts are available for catalytic reforming, including alumina-platinum-halide, alumina: platinum, chromia-alumina, and numerous others. The product of such a catalytic reforming operation will contain benzene, toluene, xylene, ethyl benzene, and higher homologues of such aromatic compounds as well as unreacted parafiinic compounds.

The ideal selective solvent for use in connection with this invention would have the following characteristics: (1) high selectivity as between paraflinic and aromatic hydrocarbons, that is to say, a solvent which has substantially no solubility for paraflinic fractions and very high solubility for aromatic fractions; (2) stability; (3) high selectivity at temperatures approximating normal atmospheric temperatures to avoid the necessity of heating or refrigeration; (4) easy separation of phases; (5) relatively high solubility for aromatic fractions in order to avoid the use of large quantities of solvent; and (6) a boiling point sufficiently high so that it can be readily maintained in a liquid phase under the conditions of extraction.

While the number of solvents possessing all of the aforesaid characteristics is small, a number of solvents which possess at least several of these characteristics are known in the art and such solvents are contemplated for use in this process. One such class of solvents includes the dihydric alcohols which are characterized by having at least one ether group. Dihydric alcohols having at least one other group as, for example, diethylene glycol, triethylene glycol, and tetraethylene glycol, are especially desirable. Certain amine compounds have also been found to be useful in this process; for example, diethylene triamine, triethylene tetramine, and tetraethylene pentamine. These compounds are characterized in that they contain more carbon than nitrogen atoms in their molecules and can be formed by the interaction of ethylene chloride and ammonia followed by liberation of free amine by treatment with caustic. Phenyl ethanol amine and phenyl diethanol amine are particularly suitable solvents. High boiling hydroxy ethers, illustrated by diacetin, dibutyl tartrate, and butyl lactate, are also suitable. Carbitol acetate and butyl Carbitol illustrate operative compounds containing hydroxy, ether, and ester groups.

Experiments also indicate that polar compounds selected from the group consisting of hydroxy benzenes, amines, amides, chlorinated hydrocarbons, esters of polycarboxylic acids, and phosphoric acid esters of hydroxy benzenes are, in general, operative in the process of this invention.

Small amounts of solvents which are selective for paraflinic compounds such as the fluorocarbons may be advantageously combined with some of the aforesaid solvents.

The solvents which I prefer to employ in the process of my invention are solvents comprising mixtures of poly ethylene glycols and phenyl ethanol amine. Such solvents may also contain minor amounts of water. I have found that a solvent comprising 70% phenyl ethanol amine and 30% diethylene glycol may be used with particular advantage in this process.

As the aliphatic hydrocarbon mixture boiling within the gasoline range which I contemplate employing in the second extraction step, any predominantly aliphatic hydrocarbon may be employed and this expression is intended to include olefinic and cycloaliphatic hydrocarbons. This fraction should be suitable for incorporation in a finished gasoline, and a part, preferably a predominant part, has a boiling range overlapping the boiling range of the aromatic hydrocarbon fraction in the first extract. One such suitable hydrocarbon fraction is al kylate, which is produced by the low temperature alkylation of isobutane with butylenes in the presence of a .mineral acid catalyst. A preferred hydrocarbon mixture is a light naphtha fraction boiling between about 75 F. and 300 F., which may be obtained directly from a crude oil by distillation. In some'instances, it may be advantageous to employ a mixture containing butane as the solvent in the second extraction step; however, if butane is employed it may be necessary to stabilize the final product of my process depending upon the vapor pressure desired. As still another example of the hydrocarbon liquid which I contemplate employing in the second extraction step, an isomerized naphtha may be employed, such as is obtained upon the treatment of a virgin naphtha with a Friedel-Crafts catalyst. Motor polymer, which is the product of the catalytic polymerization of propylene and butylenes in the presence of a phosphoric acid catalyst, also has utility in connection with this invention. Combinations of any of the aforesaid hydrocarbons may, of course, be conveniently employed in this process.

So long as the extraction conditions are maintained to give separate rafiinate and extract phases in both the extraction and re-extraction steps, the conditions of temperature and pressure employed during extraction are not critical. Both of the extraction steps may be conducted under atmospheric, sub-atmospheric, or superatmospheric pressure and temperatures in the range of about 50 F. to about 200 F. have been found suitable for both steps. In some instances, the operation of both of the extraction steps under similar conditions of temperature and pressure may ofier advantage.

The attached drawing shows a diagrammatic flow diagram of the process. Valves, pumps, heat exchangers and other conventional auxiliary equipment are not shown on the drawing but the use of such means is contemplated and the manner of using such equipment will be obvious to a person skilled in the art. upon reading this description.

Referring now particularly to the drawing, a general description of the process follows: Catalytic reformate containing an appreciable portion of aromatics is fed to primary extraction zone through a conduit 11. A suitable quantity of solvent is introduced into the extraction zone 10 by means of conduit 12. Separate phases are formed in the extraction zone 10 and the rafiinate phase comprising principally the non-aromatic portions of the catalytic reformate leaves the extraction Zone by means of conduit 13. This non-aromatic fraction may be recycled to a catalytic reformer if desired. The extract phase comprising the solvent and the aromatic portion of the catalytic reformate leaves the extraction zone by means of the conduit 14 whereby it is transferred to a secondary extraction zone 15. -A quantity of low-boiling paraifinic hydrocarbon liquid such as, for example, light naphtha is introduced into the extraction zone 15 by means of conduit 16. Separate phases are again obtained in the extraction zone 15. One phase consists essentially of the solvent and it is withdrawn from the extraction zone 15 via conduit 12, which returns the solvent to the first extraction zone 10. The other phase obtained in the second extraction zone 15 is a mixture of aromatics and parafrinic hydrocarbons and this mixture leaves the extraction zone 15 by means of conduit 17.

Any conventional liquid extraction equipment may be employed to provide extraction zones 10 and 15, but equipment permitting countercurrent extraction is preferred. For example, a tower packed with Raschig rings or other suitable packing comprising one or more theoretical extraction stages may be employed to provide extraction zones 10 and 15. A particularly advantageous type of extraction equipment for use in this process is a centrifugal extractor. Centrifugal extractors are desirable in a process of this type because they require a much lower solvent inventory than other types of conventional extraction equipment. Since most solvents are subject to some degradation with use, a low solvent inventory materially reduces the amount of the solvent which is lost through such degradation. However, if centrifugal extractors are used, provision must be made for a settling zone wherein the necessary phase separation may occur. In most modern centrifugal extractors, a settling zone is an integral feature.

As the best mode of carrying out the process of this invention, I contemplate employing over one volume and up to five volumes of solvent per volume of catalytic reformate in the first extraction step. If reflux is employed this ratio may be somewhat higher. Preferably, the first extraction step should be conducted at a temperature of about 150 F. although other temperatures are operable as has been explained heretofore. As the hydrocarbon liquid to be employed in the second extraction step, I prefer a mixture of light naphtha and alkylate having a boiling range of about F. to 420 F. The amount of light naphtha and alkylate mixture to be employed in the second extraction step should be in the range of about 0.25 to about 3.0 volumes of light naphtha per volume of catalytic reformate. The second extraction step is preferably conducted at a temperature of about 150 F., but other temperatures are also operable.

The non-aromatic fraction of the naphtha feed which is recovered in the primary extraction zone and the highoctane product which is recovered from the secondary extraction zone may contain trace quantities of solvent. I contemplate removing such small quantities of solvent from these hydrocarbon streams by any of the known methods. Water-washing or clay-treating are two methods which may conveniently be employed. It the streams are washed with water, the water containing the solvent may be transferred to a dehydrator where the water can be removed, and the dehydrated solvent may then be recycled to the process. It is also contemplated that it will be necessary from time to time to add makeup quantities of solvent to the process.

As an example of my invention, volumes of a catalytic reformate were treated in accordance with the method outlined above. The reformate was obtained from a commercial Platformer and had the following properties Gravity 493 API Distillation data:

Percent distilled- Temperature, F.

Hydrocarbon type analysis (vol. percent):

saturates, 55.4 Olefins, Nil Aromatics, 44.6

Octane number =(F-l clear), 79.3

This reformate was extracted at a temperature of F. with 250 volumes of a solvent consisting essentially of 70% Phenyl ethanol amine and 30% diethylene glycol in a centrifugal extractor,

42 volumes of a rafiinate were obtained which had the following properties:

Olefins, Nil Aromatics, 8.0 Octane number (F-l clear), 42.3

308 volumes of extract were re-extracted at a temperature of 140 F. with 155 volumes, based on the original reformate feed, of equal parts of light naphtha and alkylate in another centrifugal extractor. The light naphtha had the following properties:

Gravity Distillation data:

Percent distilled- 70.9 API Temperature, F. 86

IBP.

Hydrocarbon type analysis (vol. percent) Saturates, 97.3 Olefins, Nil Aromatics, 2.7 Octane number (F-l clear), 75.4 The alkylate had the following properties: Gravity Distillation data:

Percent distilled Temperature, F.

213 volumes of a mixture of aromatics, light naphtha and alkylate was obtained from the secondary extraction zone in addition to a separate phase which consisted essentially of 250 volumes of solvent. The mixture of aromatics, light naphtha and alkylate recovered had the following properties after water-washing to remove traces of solvent:

Gravity Distillation data:

Percent distilled 61.9 API Temperature, F.

Hydrocarbon type analysis (vol. percent):

Satnrates, 79.7 Olefins, Nil Aromatics, 20.3

Octane number (F-l clear), 89.3

This mixture of aromatics, light naphtha and alkylate is suitable for use as a high-octane motor fuel.

In the above example, it will be noted that the highest temperature to which the solvent is subjected is F., whereas, if the aromatics were separated from the solvent by distillation, the solvent would have been subjected to temperatures well above the boiling range of the reformate (218-328 F.) on the order of 400500 F. for relatively long periods of time with consequent greater decomposition. Since the process of this invention does not require the distillation step which characterized the processes of the prior art and since both extraction zones may be operated at temperatures close to normal atmospheric temperature, it is obvious that the process does not require any large quantifies of heat. The uniquely low heat requirements of this process oifer economic advantages which have not been obtainable heretofore.

It will be obvious to those skilled in the art that modifications of the process described herein may be readily made. I desire this application for Letters Patent to cover such modifications of the invention as would reasonably fall within the scope of the appended claim.

I claim:

A process for producing a high octane motor fuel from a catalytic reformate, comprising the steps of contacting said reformate with a solvent consisting essentially of a mixture of 30% diethylene glycol and 70% phenylethanolamine which will preferentially dissolve aromatic compounds under extraction conditions in a first extraction zone to obtain a first extract mixture comprising an enriched aromatic fraction and solvent, passing said first extract mixture to a second extraction zone and contacting said first extract mixture therein under extraction conditions with a motor polymer fraction a predominant part of which boils within the boiling range of said aromatic fraction to extract said enriched aromatic fraction from said first extract mixture and form a high octane motor fuel comprising said enriched aromatic fraction and said motor polymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,972 Faragher Oct. 19, 1937 2,139,392 Tijmstra Dec. 6, 1938 2,364,517 Burk Dec. 5, 1944 2,572,583 Antle Oct. 23, 1951 2,646,387 Francis July 21, 1953 2,721,164 Fenske Oct. 18, 1955 2,769,752 Evans Nov. 6, 1956 2,874,116 Brown et al Feb. 17, 1959

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