US2891006A - Method of stabilizing olefinic gasoline by hydrofining with a chromium iron oxide catalyst - Google Patents

Description

United States Patent METHOD OF STABILIZING OLEFINIC GASOLINE BY HYDROFINING WITH A CHROMIUM IRON OXIDE CATALYST Michael C. Chervenak, Trenton, Percival C. Keith, Peapack, and Helmut R. Pichler, Trenton, N.J., assignors to Hydrocarbon Research, Inc., New York, N.Y., a conporation of New Jersey No Drawing. Application August 26, 1954 Serial No. 452,474

11 Claims. (Cl. 208-257) This invention relates to the treatment of hydrocarbon oils and is more particularly concerned with the treatment of raw cracked gasoline fractions. The invention is concerned primarily with the treatment of raw cracked gasoline fractions to produce finished gasoline of commercially acceptable storage stability and octane number.

This application is a continuation-impart of copending application Serial No. 416,446, filed March 15, 1954.

At the present time, motor gasoline is given ASTM D38l-50 test for existent gum; in accordance with ASTM D439-52T gasoline specifications, the gasoline must show not more than 5 mg. of gum per 100 ml. In addition, petroleum refiners generally test gasoline for storage stability in accordance with ASTM D525-49 test. While no ASTM specification has been adopted for the storage stability of gasoline, most refiners strive for an oxygen induction time of at least 300 minutes as measured in ASTM D525-49 test. Finally, the demands of modern high compression engines make necessary the production of motor gasoline possessing a high octane rating, usually determined as clear research octane number in accordance with ASTM D908-48T test.

In modern petroleum refining practice, it is highly advantageous to convert part or all of the higher boiling fractions of the crude oil to materials boiling in the gasoline range. This is effected by processes which involve the cracking of the higher boiling hydrocarbons into hydrocarbons boiling in the gasoline range. However, in many cases, the gasoline fraction which is produced by cracking (hereinafter referred to as raw gasoline) requires further processing to provide a commercially accepta'ble product having low gum content, good storage stability and high octane number. Various processes have been proposed for treating such raw gasoline fractions to bring them within the desired specification limits, and some of these processes have been commercially used with varying effectiveness.

Cracked raw gasolines are generally of moderate to high octane number, containing to 50% by volume of aromatic hydrocarbons and at least 20% by volume. of olefins. Known methods for removing gum-forming compounds bring about the destruction or conversion of some of these unsaturated hydrocarbons. For example, when hydrogenation at relatively high pressures and relatively low temperatures is employed, the olefins present in the cracked gasoline are hydrogenated to parafiins, thus:

It is well known that such paraflins have clear research octane numbers which are as much as 40 octane numbers lower than the corresponding olefins from which they were formed. Thus, such treatment of a cracked raw gasoline fraction produces a finished gasoline which is generally of appreciably lower clear research octane numher than the raw gasoline, and which is in all cases of lower clear research octane number than would have been obtained if said olefins had not been hydrogenated.

2,891,006 Patented June 16, 1959 Where the cracking operation produces a raw gasoline which satisfies octane number requirements without the addition of tetraethyl lead, e.g., above 83 clear research octane number, such utilization of conventional hydrogenation treatment to remove gum-forming compounds results in a finished gasoline which is of considerably reduced clear octane number and which consequently requires significant quantities of anti-knock additives to achieve octane requirements. Thus, the principal problem which these cracked raw gasoline fractions of high octane number and poor storage stability present is the reduction of gum-formers to commercially acceptable limits without adverse. effect upon the clear research octane number.

A principal object of the present invention is to provide a process for treating raw gasoline fractions containing at least 20% by volume of olefins and an appreciable content of gum and/ or gum-forming compounds, which process will substantially eliminate said compounds, while substantially preserving said olefins.

It is a further important object to provide a process for treating said raw gasoline fractions, which will substantially eliminate said gum-forming compounds, while increasing or at least maintaining unimpaired the octane ratings of said raw gasolines,

In accordance with the invention, a cracked raw gasoline fraction containing at least 20% by volume of olefins, and having an objectionable content of gum and gumforming compounds, is introduced, together with hydrogen, into a treating zone maintained at a temperature of 675 to 750 F., preferably at a temperature of about 700 to 725 F., in contact with particulate iron-chromium catalyst of the character hereinbelow described. The total pressure in the treating zone and the introduction of hydrogen and raw gasoline are controlled in known manner to provide a hydrogen partial pressure of 50 to 250 p.s.i. (pounds per square inch), preferably 50 to p.s.i. The total pressure of the system may vary over a relatively wide range, but it is generally preferred to use a total pressure not exceeding about 800 p.s.i.g. (pounds per square inch gage).

The iron-chromium catalyst employed in the treating zone is derived from a mixture of iron. and chromium oxides in which mixture the chromium oxide is the minor component. In most instances, the chromium oxide is in the range of 0.2 to 20% by weight of the catalytic oxide mixture, 0.5 to 5% by weight of chromium oxide being frequently optimum. Such catalytic mixtures have been readily prepared by the co-precipitation of the iron and chromium oxides in the plus three valence states. his noteworthy that the catalyst of this process does not require a support or carrier. In fact, iron-chromium oxide mixtures supported by carriers have been found less efiective than the unsupported oxides.

It is an outstanding advantage of this invention that the hydrogen supplied to the treating zone does not need to be in concentrated or purified form. Rather, the economic attractiveness of the process stems in large part from the fact that commonly available hydrogen-contain ing gases having such components as the carbon oxides, methane and steam may be utilized. In prior processes, such gaseous components have been avoided. For instance, carbon monoxide is a poison to cobalt molybdate catalysts and steam is deleterious to hydrogenation catalysts supported on alumina and silica carriers.

The recently developed hydrocracking process disclosed,

for instance, in US. Patent 2,606,862 and copendingapgasoline is highly olefinic and contains gum-forming bodies. 'The process of this invention is particularly suited for the stabilization'of hydrocracked raw gasoline since the by-product gas of the hydrocracking operation will satisfy the hydrogen requirements of the process without necessitating any refinement of the gas or any supplementation of its hydrogen content from an extraneoussource.

Another recent development which highlights the economic attractiveness of the present invention is the partial combustion of hydrocarbons with high-purity oxygen to produce a gas comprising hydrogen and carbon monoxide as the predominant components. 'U.S. Patent 2,491,-

51 8 of E. W. 'Riblett discloses the production of such gas. Today, thepartial combustion of natural gas with oxygen obtained by the liquefaction and rectification of air o'ffersiin many localities the cheapest source of hydrogen. Consequently, olefinic raw gasolines can now be stabilized against gum formation very economically by this invention utilizing as the hydrogen-containing gas the product of the partial combustion process without any intermediate treatment.

Interestingly enough, when the hydrogen-containing gas fed to the treating zone also contains carbon monoxide and Water vapor in appreciable quantities, the tail gas of this process may be richer in hydrogen than the gas supplied'th'ereto even though hydrogen is consumed or taken up by the gum-forming bodies of the raw gasoline undergoing treatment. This is possible in the present process because the iron-chromium oxide catalyst is capable of promoting simultaneously stabilization and the water-gas shift reaction:

There is reason to believe that treating raw gasoline pursuant to this invention with gas that undergoes the water-gas shift reaction is particularly desirable because nascent hydrogen will more readily attack the gum-forming compounds.

The hydrogen-containing gas will preferably comprise at least about 20% by volume of hydrogen in order to avoid the necessity of passing excessively large amounts ofgas through-the reaction zone to provide the desired hydrogen partial pressure of 50 to 250 'p.s.i. and in order to avoid the necessity of raising the total pressure of the system to a high value. The amount of hydrogen supplied to the treating or reaction zone generally falls in the range of 300 to 3000 standard cubic feet per barrel of raw gasoline, preferably in the range of 1000 to 2000 standard cubic feet per barrel.

Treatment of the cracked raw gasoline in the reaction zone under the specified conditions is carried out to an extent sufficient to improve its stability to the desired degree. Advantageously, the desired reaction is insured by employing a raw gasoline feed "rate in the range of 1 to 5-, preferably 2 to 3, volumes of liquid per hour per volume of catalyst.

The term gasoline fraction as "herein used has its conventional meaning, viz., a hydrocarbon fraction boiling within the temperature range of 90 to 400 F., although it will be apparent that the treating process of this invention is applicable to hydrocarbon fractions in which material boiling within the gasoline range comprises the predominant portion of the fraction.

Cracked raw gasoline fractions from various sources are advantageously treated in accordance with the process of the invention 'but'the-improvedprocess is of particular value, .as already mentioned, in eliminating the gum-formers of hydrocracked ra-w gasoline fractions of relatively high octane'number, e.g., clear research octane numbers ofabout 80 to 90, containing substantial quantities 'of mono-olefins. Frequently, the olefins amount to at least 30% by volume of the raw gasoline. As previously pointed'out, the" present process is effective to remove even large proportions of gum forming bodies,

4 without any appreciable change of the high octane number of the raw gasoline. In some cases the octane number is raised one or two units.

Without tying the invention to any particular theory of operation, the process appears to involve the conversion of gum-forming diolefins to stable mono-olefins. At the same time, aromatic hydrocarbons and monoolefins are substantially not affected so that the excellent anti-knock properties of the raw gasoline are not impaired.

Under the conditions of this process, there is such limited polymerization or other degradation of the gasoline hydrocarbons that the deposition of carbonaceous matter on the catalyst may be held to less than about 0.1% by weight of the raw gasoline and often to less than about 0.01%. Thus, the catalyst may be used for long periods without regeneration to efiect removal of the carbonaceous deposit. For instance, operating the process with a fixed bed of iron-chromium oxide catalyst and a raw gasoline feed rate of 2 liquid volumes per hour per volume of catalyst, the on-stream time will be over 150 hours and may be several times as much. At the same time, no high-boiling hydrocarbons are formed so that the treated gasoline does not require fractionation to separate out any polymers or heavy hydrocarbons. The reated gasoline will generally amount to at least about 99% by volume of the raw gasoline and may even exceed 100%. Not more than about 0.5% by Weight of the raw gasoline is converted to normally gaseous hydrocarbons (C -C The finished gasoline fraction recovered from the reaction efliuent is of high stability and high octane number and meets the specifications for commercial motor gasoline notwithstanding the presence of a substantial quantity of diolefins originally in the cracked raw gasoline.

The particular apparatus used for the process and the particular method of regenerating the catalyst form no part of the present invention and any convenient apparams and method of catalyst regeneration may be employed. In regenerating the catalyst care must be taken, however, in accordance with commercial regeneration techniques, to avoid the use of temperatures which destroy or adversely affect the catalyst. In the regeneration of the catalyst of the present process, temperatures in excess of 1100 F. are generally to be avoided.

In order to facilitate the maintenance of the desired temperature in the reaction zone, the cracked raw gasoline to be treated is advantageously preheated to a temperature of 400 to 750 F., preferably about 500 to 700 F, before being fed into the reaction zone. The hydrogen-containing gas may also be preheated to about the same temperature as the raw gasoline.

For a further understanding of the invention, reference is made to the following specific examples which are intended as illustrative and not limitative of the process.

Example 1 A raw gasoline obtained by high-severity catalytic cracking of a heavy'oil contains 0.19% by weight of sulfur largely in the form of refractory compounds and over 40% by volume of olefins.

This raw gasoline and hydrogen-containing gas are brought into contact with a catalyst composed 'of 92% by weight of iron oxide and 8% by weight of chromium oxide, the mixed oxides having been co-precipitated. The gas has an approximate composition on a volume basis of 37% H 19% CO and 44% H O. This gas is charged to the reaction zone at a rate corresponding to 1500 standard cubic feet of hydrogen per barrel of raw gasoline charged therewith to maintain ahydrogen partial pressure of about 100 psi. in the reaction zone. The space velocity of the raw gasoline is 2.0 liquid volumes per hour per volume of catalyst. The reaction zone is maintained at a temperature of 715 F. The finished gasoline recovered from the reaction eflluent amounts to 99.9% by volume of the raw gasoline.

The improvement of the gasoline achieved by the process is evident from a comparison of its properties, before and after treatment:

Raw Finished Gasoline Gasoline Example 2 The hydrooracking of Mid-Continent 10% residuum yields a raw gasoline containing over 50% by volume of olefins.

This highly olefinic gasoline is treated with the hydrogen-containing gas and iron-chromium oxide catalyst of Example 1 at a temperature of 715 F. The reaction conditions include a hydrogen partial pressure of 100 p.s.i., a hydrogen flow rate of 2600 standard cubic feet per barrel of gasoline and a raw gasoline space velocity of 2.0 liquid volumes per hour per volume of catalyst. The yield of finished gasoline corresponds to 100.5% by volume of the raw gasoline.

The properties of the gasoline, before and after treatment, are as follows:

Raw Finished Gasoline Gasoline While the catalyst used in the process of this invention is customarily supplied to the reactor in the form of mixed iron and chromium oxides, it is well to note that during operation the oxide mixture undergoes some change so that the catalyst comprises iron and chromium as a mixture of the oxides, sulfides and elemental metals. In fact, it is sometimes advisable to pretreat the freshly prepared oxide mixture with hydrogen to eifect partial reduction and thus supply the catalyst to the reaction in a state more nearly like that attained during operation of the process when the catalyst reaches a high level of activity.

It is to be observed that under the process conditions of this invention, refractory sulfur compounds such as thiophenes and like cyclic sulfur compounds remain unaltered. However, these process conditions will generally eliminate a material proportion of mercaptans that may be present in the raw gasoline. Accordingly, the process of this invention is for the degumming and stabilizing treatment of substantially sweet cracked raw gasolines, i.e., gasolines containing not more than about 0.3% by weight of sulfur in the form of refractory compounds. Where the raw gasoline requires elimination of a material quantity of refractory sulfur compounds contained therein, the process conditions of the aforementioned application Serial No. 416,446 should be employed.

The recently developed hydrocracking process for producing gasoline from heavy oils yields raw gasoline fractions having the following approximate composition by volume):

0-20% paraffins and naphthenes 2540% aromatics 30-60% olefins 2-10% diolefins The diolefins, acyclic and cyclic, which are known to be mainly responsible for high gum content and/or poor storage stability of gasoline (Sachanen, Conversion of Petroleum, 2nd edition, 1948, Rheinhold Publishing Corp., page 498), are substantially converted to desirable mono-olefins by the process of this invention. In this Way, the hydrocracked raw gasoline is degummed and stabilized without impairment of the excellent anti-knock properties of the raw gasoline and simultaneously a high yield of finished gasoline that is often on the order of 100.5% by volume of the raw gasoline is obtained.

In view of the various modifications of the invention which will occur to those skilled in the art upon consid eration of the foregoing disclosure without departing from the spirit or scope thereof, only such limitations should be imposed as are indicated by the appended claims.

What is claimed is:

1. A vapor-phase process for eliminating gum-forming constituents from a highly olefinic hydrocarbon fraction, which comprises bringing hydrogen and a vaporized hydrocarbon fraction containing gum-forming constituents and more than 20% by volume of olefins imparting to said hydrocarbon fraction a high octane number into contact with an iron-chromium oxide catalyst containing chromium oxide in the range of 0.2 to 20% by weight of the catalytic oxide mixture in a reaction zone maintained at a temperature in the range of 675 to 750 F., efiecting reaction between said hydrogen and said vaporized hydrocarbon fraction during contact with said catalyst to the extent that there is a net consumption of hydrogen without hydrogenation of at least a major portion of said olefins, passing said hydrocarbon fraction through said reaction zone at a space velocity in the range of about 1 to 5 liquid volumes per hour per volume of said catalyst, maintaining the partial pressure of hydrogen in said reaction zone in the range of 50 to 250 p.s.i., and recovering from the resulting vaporized reaction effluent a highly olefinic hydrocarbon fraction with a substantially decreased content of gum-forming constituents and containing at least a major portion of said olefins and having a high octane number.

2. A vapor-phase process for eliminating gum-forming constituents from a highly olefinic hydrocarbon fraction, which comprises bringing hydrogen and a vaporized hydrocarbon fraction containing gum-forming constituents and more than 30% by volume of olefins imparting to said hydrocarbon fraction a high octane numher into contact with an iron-chromium oxide catalyst containing chromium oxide in the range of 0.2 to 20% by weight of the catalytic oxide mixture in a reaction zone maintained at a temperature in the range of 700 to 725 F., effecting reaction between said hydrogen and said vaporized hydrocarbon fraction during contact with said catalyst to the extent that there is a net consumption of hydrogen Without hydrogenation of at least a major portion of said olefins, passing said hydrocarbon fraction through said reaction zone at a space velocity in the range of about 1 to 5 liquid volumes per hour per volume of said catalyst, maintaining the partial pressure of hydrogen in said reaction zone in the range of 50 to a 250 p.s.i., and recovering from the resulting vaporized reaction effluent a highly olefinic hydrocarbon fraction with a substantially decreased content of gumform constituents and containing at least a major portion of said olefins and having a high octane number.

3. A vapor-phase process for eliminating gum-forming constituents from a highly olefinic gasoline fraction, which comprises bringing hydrogen and a vaporized gasoline fraction containing more than 2% by volume of diolefins and more than 30% by volume of olefins and having a clear research octane number of at least about into contact with an iron-chromium oxide catalyst containing chromium oxide in the range of 0.2 to 20% by weight of the catalytic oxide mixture in a reaction zone maintained at a temperature in the range of 675 to 750 F., effecting reaction between said hydrogen and said vaporized gasoline fraction during contact with said catalyst to the extent that there is a net consumption 'of hydrogen without hydrogenation of at least a major portion of said olefins, passing said gasoline fraction through said reaction zone at a space velocity in the range of about 1 to liquid volumes per hour per volume of said catalyst, maintaining the partial pressure of hydrogen in said reaction zone in the range of 50 to 250 p.s.i., and recovering from the resulting vaporized reac- I tion .eflluent a high olefinic gasoline fraction with a'substantially decreased content of said diolefins and containing at least a major portion of said olefins and having a clear research octane number of at least about 80.

4. A vapor-phase process according to claim 3 wherein the iron-chromium oxide catalyst is derived by the coprecipitation of the iron and chromium oxides, and the hydrogen partial pressure is in the range of 50 to 150 psi.

5. A vapor-phase process according to claim 3 wherein the hydrogen supplied to the reaction zone is admixed with a substantial quantity of a gas selected from the group consisting of carbon monoxide, carbon dioxide, water vaporandmixtures thereof.

6. A vapor-phase process for refining a highly olefinic gasoline, which comprises bringing hydrogen and a vaporized raw gasoline containing a troublesome quantity of gum-forming bodies and containing more than 20% by volume of olefins, said raw gasoline having a clear reasearch octane number of at least about 80, into contact with an iron-chromium oxide catalyst containing chromium oxide in the range of 0.2 to 20% by weight of the catalytic oxide mixture in a reaction zone maint ain ed at a temperature in the range of 700 to 725 F, eflFecting reaction between said hydrogen and said vaporized raw gasoline during contact with said catalyst to the extent that there is a net consumption of hydrogen without hydrogenation of at least a major portion of said olefins, passing said raw gasoline through said reaction zone at a space velocity in the range of about 1 to 5 liquid volumes per hour per volume of said catalyst, maintaining the partial pressure of hydrogen in said reaction zone in the range of 50 to 150 p.s.i., and recovering from the resulting vaporized reaction effluent a highly ole'finic finished gasoline substantially free of said gum-forming bodies and containing at least 20% by volume of said olefins and having a clear research octane number over 80.

7. A vapor-phase process according to claim 6 wherein the iron-chromium oxide catalyst is derived by the coprecipitation of the iron and chromium oxides, the chromium oxide being inthe range of 0.5 to 5% by weight of the co -precipitated oxides. g

8. A vapor-phase process according to claim 6 where in the raw gasoline passes through the reaction zone at a space velocity in the range of about 2 to 3 liquid volumes per hour per volume of catalyst.

9. A vapor-phase process according to claim 8 wherein the raw gasoline contains more than 30% by volume of olefins and the hydrogen supplied to the reaction zoneis admixed With substantial quantities of carbon monoxide and water vapor.

10. A vapor-phase process for refining a highly olefinic gasoline, which comprises bringing hydrogen and a vaporized raw gasoline containing a troublesome quantity of gum-forming bodies and containing more than 20% by volume of olefins imparting to said raw gasoline a high octane number into contact with an iron-chromium oxide catalyst containing chromium oxide in the range of 0.2 to 20% by weight of the catalytic oxide mixture in a reaction zone maintained at a temperature in the range of 675 to 0 F, elfecting reaction between said hydrogen and said vaporized raw gasoline during contact with said catalyst to the extent that there is a net consumption of hydrogen without hydrogenation of at least a major. portion ofsaid olefins, passing said raw gasoline through said reaction zone at a space velocity in the range of about 1 to 5 liquid volumes per hour per volume of said catalyst, maintaining the partial pressure of hydrogen in said reaction zone in the range of 50 to 250 p.s.i., and recovering from the resulting vaporized reaction effluent a highly olefinic finished gasoline substantially free of said gum-forming bodies and containing at least 20% by volume of said olefins and having a high octane number and an oxygen induction time of at least 300 minutes.

11. A vapor-phase process according to claim 10 wherein the raw gasoline passes through the reaction zone at a space velocity in the range of about 2 to 3 liquid volumes per hour per volume of catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 1,889,388 Smith Nov. 29, 1932 1,955,297 Jennings Apr. 17, 1934 2,393,288 Byrns Jan. 22, 1946 2,398,919 Byrns Apr. 23, 1946 2,413,312 Cole Dec. 31, 1946 2,500,146 Fleck Mar. 14, 1950 2,542,970 Jones Feb. 27, 1951 2,640,802 Porter et al. June 2, 1953 2,658,858 Lang et a1 Nov. 10, .1953 2,694,671 Baumgarten et al. Nov. 16, 1954 2,717,857 Bronson et al. Sept. 13, 1955 2,717,858 Bronson et a1 Sept. 13, 1955

Claims (1)

1. A VAPOR-PHASE PROCESS FOR ELIMINATING GUM-FORMING CONSTITUENTS FROM A HIGHLY OLEFINIC HYDROCARBON FRACTION, WHICH COMPRISES BRINGING HYDROGEN AND VAPORIZED HYDROCARBON FRACTION CONTAINING GUM-FORMING CONSTITUENTS AND MORE THAN 20% BY VOLUME OF OLEFINS IMPARTING TO SAID HYDROCARBON FRACTION A HIGH OCTANE NUMBER INTO CONTACT WITH AN IRON-CHROMIUM OXIDE CATALYST CONTAINING CHROMIUM OXIDE IN THE RANGE OF 0.2 TO 20% BY WEIGHT OF THE CATALYTIC OXIDE MIXTURE IN A REACTION ZONE MAINTAINED AT A TEMPERATURE IN THE RANGE OF 675 TO 750* F., EFFECTING REACTION BETWEEN SAID HYDROGEN AND SAID VAPORIZED HYDROCARBON FRACTION DURING CONTACT WITH SAID CATALYST TO THE EXTENT THAT THERE IN A NET COMSUMPTION OF HYDROGEN WITHOUT HYDROGENATION OF AT LEAST A MAJOR PORTION OF SAID OLEFINS, PASSING SAID HYDROCARBON FRACTION THROUGHT SAID REACTION ZONE AT A SPACE VELOCITY IN THE RANGE OF ABOUT 1 TO 5 LIQUID VOLUMES PER HOUR PER VOLUME OF SAID CATALYST, MAINTAINING THE PARTIAL PRESSURE OF HYDROGEN IN SAID REACTION ZONE IN THE RANGE OF 50 TO 250 P.S I., AND RECOVERING FROM THE RESULTING VAPORIZED REACTION EFFLUENT A HIGHLY OLEFINIC HYDROCARBON FRACTION WITH A SUBSTANTIALLY DECREASED CONTENT OF GUM-FORMING CONSTITUENTS AND CONTAINING AT LEAST A MAJOR PORTION OF SAID OLEFINS AND HAVING A HIGH OCTANE NUMBER.