US2769761A - Combination process for catalytic hydrodesulfurization and mild dehydrogenation of high sulfur hydrocarbon mixtures - Google Patents

Description

1956 w. G. ANNABLE ET AL 2,769,761

COMBINATION PROCESS FOR CATALYTIC HYDRODESULFURIZATION AND I MILD DEHYDROGENATION OF HIGH SULFUR HYDROCARBON MIXTURES Filed Sept. 10. 1953 mun: PETROLEUM FRAO 7' IONAT ION vmaw NAH-ITHA FRACTION H 2 5 H YDRODE 5 ULF UR/ZA T ION REMOVAL REGYGLE H2 STABILIZATION MILD 05 h YDROQE NA T/ON REGYOLE H2 INVENTOR.

"(GRANT AlV/VABLE By LEROI E. HUTCH/NGS KENNETH LUCAS A 7' TORNE United States Patent COMBINATION PROCESS FOR CATALYTIC HY- DRODESULFURIZATION AND MELD DEHY- -DROGENATION OF HIGH SULFUR HYDRO- CARBON MIXTURES Weldon Grant Annable, Mundelein, Le Roi E. Hutchings,

Crystal Lake, and Kenneth Lucas, Woodstock, 11]., assignors to The Pure Oil Company, Chicago, EL, a corporation of Ohio Application September 10, 1953, Serial No. 379,392

4 Claims. (Cl. 196-28) The present invention relates to a combination process of catalytic hydrodesulfurization and mild or relatively low temperature dehydrogenation of high sulfur hydrocarbon mixtures and, more particularly, to a method of treating high or low sulfur stocks or of relatively low aromatic content stocks to produce improved naphthas having increased solvency power, decreased aniline point, and low corrosive sulfur content. The naphtha products produced by the integrated process of hydrodesulfurization and mild dehydrogenation in combination are further characterized by their ability to pass the distillation-corrosion test. 7

Crude petroleum is the source of a large number of products ranging from simple distillation products including pure hydrocarbons to high molecular weight natural and synthetic resins, elastomers, and polymers produced through physical and chemical transformations. Widely known petroleum derived products include gasoline, kerosene, diesel fuels, lubricating oils, and heavy tars; In many instances, the products obtained from petroleum are employed as reactants in the synthesis of additional petroleum derivatives and chemicals and a large number of pro-ducts of petroleum are used directly without extended treatment or modification. Petroleum naphthas comprise a wide variety of such latter products used extensively in the dyeing, rubber, extraction, protective coating, and allied industries. A large portion of the petroleum naphthas used is the straight run naphthas which are selected fractions of the lower boiling, more volatile constituents of crude petroleum. The present invention is particularly directed to a method of preparing such straight run naphthas and to naphtha compositions of this variety and, accordingly, the term naphthas as used herein shall mean straight run petroleum naphthas or their equivalents.

If the preparation of naphthas from petroleum is confined to physical means, the products inevitably contain other types of organic and inorganic compounds due to the complex nature of petroleum which have been found to be deleterious as far as certain end uses of the naphthas are concerned and necessitate the application of additional refining steps. Even with such additional refining, it is exceedingly difficult to prepare naphthas which meet the exacting specifications that have been established by the industry. Of these deleterious non-hydrocarbon compounds, the sulfur and sulfur-containing constituents are generally the most bellicose and cling tenaciously to any environment inwhich they exist, imparting objectionable odor, corrosiveness, color, and other physical and chemical properties thereto. The odor of naphthas is important; however, no standard test exists to cover this property and the odorof a well refined naphtha is generally described as sweet.

:Tests have been devised todetermine both quantitatively andqualitatively the presence of these odious com- 2,769,7si Patented Nov. 6, 1956 pounds in an attempt to control the properties and quality of naphthas from petroleum sources. For this purpose, various copper strip corrosion tests and the doctor test have been used. Procedures established by A. S. T. M. may be used to determine the content and distribution of these sulfur compounds. Perhaps the most critical and rigorous qualitative test for determining the presence of corrosive sulfur compounds in naphthas is the distillation-corrosion test, known also as the Philadelphia test, the Amsco corrosion test, or the full boiling range corrosion test--by any name, a species of copper strip corrosion test. The test, widely applied by the manufacturers, distributors, and users of specialty naphthas, is carried out by the addition of a small pure copper coupon to an ordinary A. S. T. M. distillation flask containing cc. of the naphtha to be tested. The copper strip is so positioned in the fiask that one end of the strip contacts the residue at the end of the distillation, and the distillation is conducted according to A. S, T. M. D8638 as described in A. S. T. M. Standards on Petroleum Products and Lubricants, published by the American Society 'for Testing Materials, Philadelphia, Pennsylvania.

test is shown by the presence of a very slight or moderate tarnish on the strip and stamps the naphtha assatisfactory. If the copper strip becomes moderately blackened, the results are interpreted as positive or unsatisfactory. The production of a slightly tarnished or slightly colored or corroded strip, indicated by a dark orange with peacock colorations thereon, is termed borderline and as .such denotes a naphtha which is not acceptable and must be further refined. The market is limited for off-specification naphthas and further refining is expensive since even then there is no assurance that the product will pass the severe distillation-corrosion test. I

The subjection of high sulfur content naphthas to various refining and sweetening operations which may include oxidation and extraction methods, or the recycling of rejected off-specification naphthas back through such a process, does not produce acceptable naphthas because thesulfur compounds remaining are corrosive in nature. High sulfur content naphthas usually have a poor odor as well as other undesirable properties. If straight run naphthas from high sulfur crudes are subjected to other more severe refining methods, the resulting products do not pass the distillation-corrosion test. Even subjecting these naphthas to the usual desulfurization treatments involving vapor or liquid phase contact with clay or catalytic materials having strong affinity for effecting desulfurization does not produce a satisfactory product.

Accordingly, the primary object of this invention is to provide a process of producing improved naphthas of increased solvency, decreased aniline point, and low corrosive sulfur content.

Another object is to provide a combination process of hydrodesulfurization and mild dehydrogenation which produces improved naphthas.

A third object of this invention is to provide a method of producing naphthas which pass the distillation-corrosion test.

A fourth object of this invention is to provide a method of producing naphtha solvent products having increased Kauri-butanol value, decreased aniline point, and low tion-corrosion test.

A fifth object is to provide a combination hydrodesulfurization and dehydrogenation process to produce acceptable, sweet, odor-free, and corrosive sulfur-free special solvent naphthas.

These and other objects will become apparent as the description of the invention proceeds.

The attached drawing is a diagrammatic representation illustrating the application of the combination process to a naphtha feed.

It is known to be advantageous to successively treat hydrocarbons containing sulfur compounds to hydrodesulfurization processes followed by reactions which predominate in hydrogenation-dehydrogenation. For example, in the first stage hydrosulfurization, it is known that the sulfur compounds present in the stock are substantially completely destroyed, with the formation of hydrogen sulfide, and a proportion of the unstable, olefinic hydrocarbons present in the stock or formed during the desulfurization is hydrogenated and converted to more stable compounds. During the second stage, generally conducted in the presence of a catalyst, the predominant reactions are cracking and reforming in the presence of hydrogen under optimum conditions to obtain gasoline products which have high octane numbers and good lead susceptibility. One particular advantage of these prior art processes is that the bulk of the sulfur compounds and the majority of the coke-forming olefins are eliminated in the first stage so that the catalyst in the second stage is not substantially converted to sulfides nor is it subjected to conditions of rapid coke deposition. The products formed are entirely free of hydrogen sulfide and corrosive elemental sulfur. Products may be produced containing only 0.016 to 0.09 percent sulfur in the form of organic sulfur compounds other than mercaptans in accordance with prior art teachings. Further, it is sometimes the practice, after the desulfurization reaction, to subject the feed to dehydrogenation and reforming at temperatures in the range of 950 F. to 1100 F. for the purpose of increasing the value of the products as motor fuel by reason of increased antiknock rating.

These prior art processes cannot be depended upon to produce products which are consistently free of corrosive sulfur compounds as indicated by their ability to pass the distillation-corrosion test because there is a sharp distinction between desulfurization as meant in the prior art and the desulfurization necessary to produce a non-corrosive naphtha. In addition it is desirable that the specialty naphthas to be produced have a high solvency power, that is, a high aromatic content, while at the same time maintaining an odor-free consistency. It is desirable to have aromatics present because they improve the solvency of the naphtha. However, all aromatics have a somewhat characteristic odor which, in high concentration, may be objectionable. A certain percentage of aromatics can be tolerated because their odor is masked by other constituents present, but they may be accompanied by odorous sulfur compounds or corrosive sulfur compounds which must be removed. Thus, the desulfurization by whatever method may take place to the extent of 90 to 98 percent sulfur removal, yet the products produced will not be non-corrosive and will give a positive distillation-corrosion test. On the other hand, desulfurization may be of such a nature that noncorrosive naphthas are produced through the conversion of corrosive sulfur compounds to a non-corrosive variety without appreciable total sulfur reduction taking place. It follows, therefore, that certain naphthas may be more corrosive after desulfurization than before and, further, a naphtha which gives a sour doctor test may be noncorrosive while a sweet naphtha may be corrosive.

In view of these observations, it was found that the aromatic content of the desired naphthas could be increased without imparting an objectionable odor and while at the same time removing corrosive sulfur com:

pounds by the integrated hydrodesulfurization-dehydrogenation process of the present invention. The first step of the present process is a conventional one. However, the second step is a mild or low temperature dehydrogenation or hydroforming reaction having many advantages. In the first instance, since desulfurization has preceded the dehydrogenation, the dehydrogenation catalyst may be used for long periods without regeneration. The second step of the process is conducted under mild conditions because it has been found that if the second step is conducted under normal conditions with or Without the prior desulfurization, a sweet product which is non-corrosive may be produced but the aromatic content is high enough to impart an objectionable odor. The excess aromatics in such a product could be removed by solvent extraction leaving a rafiinate for fractionation into various naphthas. This would be a costly solution to the problem.

Accordingly, the present invention is directed to a method of producing low sulfur sweet non-corrosive naphthas from hydrocarbon mixtures regardless of their sulfur contents by applying a certain combination of re fining treatments to such products. It has been found that in order to prepare satisfactory specialty naphthas which meet certain rigorous corrosion test, refining methods must be used which not only attack hydrogen sulfide, mercaptans, free sulfur, and disulfides, but which also attack or transform certain of the thermally stable sulfur compounds, whether cyclic, heterocyclic, aromatic, or polymeric, to a non-corrosive form while effecting a slight increase in the aromatic content of the naphthas.

In carrying out the present invention, the crude oil, particularly a high sulfur crude oil containing from 1.0 to 3.0 weight percent of sulfur, is fractionated to remove the more volatile components and the high boiling residues leaving a wide boiling range virgin or straight run naphtha or gas oil fraction which may boil from about to 500 F. and preferably boils from about to 450 F. The boiling range of the particular fraction removed for treatment in accordance with this invention may be varied somewhat from the boiling ranges given depending upon the relative amounts of specialty naphtha, rubber solvent, V. M. & P. naphthas desired. By narrowing the boiling range of the virgin naphtha to within 100 to 250 F., the process may be directed to obtaining rubber solvents almost exclusively. On the other hand, by starting with a fraction boiling between 200 and 400 F., the process may be directed to production of V. M. & P. solvents and specialty naphthas. In one specific embodiment of the invention, the treatment of the entire first fraction boiling up to 500 F. or more to produce a wide variety of products ranging from rubber solvents up to high boiling specialty naphthas including, for example, petroleum ether 90-140 F., Special Textile Spirits 1802l0 F., Light Mineral Spirits 290-330 F., Stoddard Solvent 310385 F., and High Flash Dry Cleaning Solvent 360-400 F., all being non-corrosive, odorless, and meeting the rigorous requirements of the industry, is contemplated.

The virgin naphtha fraction selected from the crude is subjected to a catalytic hydrodesulfurization treatment carried out in accordance with well known techniques at elevated temperatures. In the treatment, the sulfur content of the charge stock is removed in the form of a gas such as hydrogen sulfide by the action of hydrogen and desulfurization catalysts, such as molybdates, sulfides, and oxides of iron group metals and mixtures including cobalt molybdate, chromic oxide, vanadium oxide with molybdena and alumina, and sulfides of tungsten, chromium, or uranium. Preferred catalysts for the reaction include cobalt molybdate, cobalt oxide-molybdena-alumi- 11a, and chromia-molybdena-alumina. The process may be carried out in either the liquid or gaseous phase at temperatures ranging from 500 to 800 F. and under pressures from 20 to 1000 pounds per square inch. The virgin naphtha fraction subjected to hydrodesulfurization may contain from about 0.1 to 3.0 percent by weight of sulfur. The charge may be introduced to the catalyst zone at from 0.5 to liquid volumes per bulk volume of catalyst per hour. a

The preferred conditions of hydrodesulfurization are at approximately 750 F. under 250 pounds per square inch pressure and with a space velocity of 0.3 to 2.0 with hydrogen recirculated at a rate of about 3000 s. c. f. of hydrogen per barrel of charge.

The products from the hydrodesulfurization are subjected to stabilization wherein the hydrogen sulfide and any fixed gases are removed and the resulting stabilized liquid products are next subjected to a mild low temperature dehydrogenation or hydroforming reaction. During the stabilization, hydrogen sulfide is removed from the liquid products. The removal of the hydrogen sulfide may also be accomplished by extraction with an amial solution. The hydrogen may be purified and recycled to the first stage of the process. The hydrogen sulfide removed may be used to prepare free sulfur. The sour product from the hydrodesulfurization is conducted to a mild dehydrogenation reaction wherein the conditions are somewhat cirtical, being preferably at about 820 to 880 F. with superatmospheric pressures of about 250 pounds per square inch. The preferred conditions for the dehydrogenation are approximately 875 F., 250 pounds per square inch pressure, under a space velocity of about 1.0 with a hydrogen recirculation rate of about 3000 s. c. f. of hydrogen per barrel of charge. During this second treatment, the product is sweetened and about 3 to 10 percent of aromatics are formed through the dehydrogenation of naphthenes. Sufiicient hydrogen substantially free of hydrogen sulfide is produced from the dehydrogenation reaction to supply practically all of the hydrogen requirements for the catalytic hydrodesulfurization reaction.

In order to illustrate the invention, the following example is given. A 425 F. end point straight run fraction was taken from a Yates crude and subjected to hydrodesulfurization at 750 F., 250 p. s. i. g., with a space velocity of about 1 and with a hydrogen recirculation rate of about 3000 s. c. f. per barrel of charge in the presence of a cobalt molybdate catalyst. The hydrogen used was produced by the second step of the process. The hydrodesulfurized but corrosive product was subjected to fractionation in order to remove the hydrogen sulfide. After removal of the hydrogen sulfide, the product was still corrosive and in this condition was charged to the mild dehydrogenation step of the process operating under a temperature of about 825 F. The following table gives an analysis of the charge stock and the products from each step of the process:

Charge Hydrode- Dehydra- Sulfur Distribution Stock sulfurized genated Product Product Wt. percent:

Free Sulfur Nil Nil Nil H Nil Nil Nil 0.100 Nil Nil 0.021 Nil Nil 0. 071 0. 006 0. 003 0. 016 Nil 0. 003

Total-S 0. 208 0. 006 0. 006

Aromatics-Vol. percent 15 24 Doctor Test (for mcrcaptans) Pos. 1 Neg. Neg. Lead acetate Test (for HzS) Pos. 1 Pos Neg. Mercury Test (for free S)-.. Pos 1 Pos. Neg. Distillation Corrosion Pos. Pos. Neg.

1 After H28 removal. 3 Before H S removal.

It is well known that increase in the aromatic content of a naphtha accomplishes the desired result of improving the solvency as indicated by increased Kauributanol value and decreased aniline points. Referring to the table, it is not apparent why the hydrodesulfurized product is corrosive and the final product is non-corrosive when considering the'sulfur distributions of each of these products. One reason for this is the fact that the full boiling range copper strip test (distillation-corrosion test) is sensitive to smaller quantities of sulfur compounds than shown by the sulfur distribution. When the sulfur distribution is considered in conjunction with the doctor, lead acetate, and mercury test results, the reason becomes apparent, lying in the very small amount of free sulfur present. Accordingly, it is seen that the mild dehydrogenation has served the purpose of making the product non-corrosive and one having increased solvency while at the same time supplying hydrogen for the hydrodesulfurization step.

The general steps of the process are shown in the diagram, which particularly illustrates the preparation of a series of four naphthas from a virgin naphtha fraction separated from a crude oil. Such crude oil may contain from 1.0 to as high as 7.0 percent by weight of sulfur. The virgin naphthas therefrom may contain from 0.10 to 3.0 percent of sulfur. Where the charge stock contains higher than 3.0 percent of sulfur, it may be necessary to adjust the conditions of hydrodesulfurization to accomplish a more substantial reduction of the sulfur content in the first step. In general, the hydrodesulfurized product entering the mild dehydrogenation step of the process may contain from about 0.006 or below to about 0.10 percent of sulfur. It is preferred that the hydrodesulfurized product contain about 0.01 to 0.003 percent of sulfur in order to eliminate the necessity of a prolonged dehydrogenation step and insure consistent and reproducible results.

Various catalytic materials may be used in the mild dehydrogenation step of the present process including oxides and sulfides of metals of groups VI and VIII of the periodic table. A good catalyst for this purpose consists of pellets formed from a mixture of about 2 mols of nickel sulfide and about 1 mol of tungsten sulfide. Also, various alumina-molybdena catalysts containing from 5 to 9 percent by weight of the oxides of molybdenum are advantageous for the dehydrogenation. Pellets or granules of magnesium oxide composited with a chromate of a metal selected from the group consisting of zinc, lead, magnesium, cadmium, nickel, iron, cobalt, copper, aluminum, and the alkali metals may be used. Certain metallic oxygen-containing salts as the sulfates, nitrates, and acetates of zinc, copper, and aluminum are also useful.

What is claimed is:

l. The process for producing improved special solvent naphthas from petroleum hydrocarbon mixtures containing corrosive sulfur compounds which comprises, subjecting said hydrocarbon mixtures to catalytic hydrodesulfurization in the presence of cobalt molybdate at a temperature of about 500 to 800 F. under conditions such that said sulfur compounds are converted to hydrogen sulfide, stabilizing the products therefrom to separate said hydrogen sulfide to produce a highly refined product, subjecting said highly refined product to mild dehydrogenation in the presence of a catalyst selected from the groups consisting of oxides and sulfides of metals of groups VI and VIII of the periodic table and mixtures thereof, at temperatures between about 820 to 880 F. and separating special solvent naphthas therefrom characterized by their increased solvency power and their ability to pass the distillation-corrosion test.

2. The process in accordance with claim 1 in which the hydrocarbon mixture being treated comprises a to 550 F. boiling range fraction containing about 0.30 weight percent of total sulfur, said fraction being obtained from the distillation of crude oil having a total sulfur content of about 1.0 to 3.0 weight percent.

3. The process in accordance with claim 2 in which the boiling range of the fraction being treated is about to 450 F.

4. The method in accordance with claim 1 in which the hydrodesulfurization reaction is conducted at a tem- References Cited in the file of this patent

Claims (1)

1. THE PROCESS FOR PRODUCING IMPROVED SPECIAL SOLVENT NATHTHAS FROM PETROLEUM HYDROCARBON MIXTURES CONTAINING CORROSIVE SULFUR COMPOUNS WHICH COMPRISES, SUBJECTING SAID HYDROCARBON MIXTURES TO CATALYLIC HYDRODESULFURIZATION IN THE PRESENCE OF COBALT MOLYBDATE AT A TEMPERATURE OF ABOUT 500* TO 800* F. UNDER CONDITIONS SUCH THAT SAID SULFUR COMPOUNDS ARE CONVERTED TO HYDROGEN SULFIDE, STABILIZING THE PRODUCTS THEREFROM TO SEPARATE SAID HYDROGEN SULFIDE TO PRODUCE A HIGHLY REFINED PRODUCT, SUBJECTING SAID HIGHLY REFINED PRODUCT TO MILD DEHYDROGENATION IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUPS CONSISTING OF OXIDES AND SULFIDES OF METALS OF GROUPS VI AND VIII OF THE PERIODIC TABLE AND MIXTURES THEREOF, AT TEMPERATURES BETWEEN ABOUT 820* TO 880* F, AND SEPARATNG SPECIAL SOLVENT NAPHTHAS THEREFROM CHARACTERIZED BY THE INCREASED SOLVENCY POWER AND THEIR ABILITY TO PASS THE DISTILLATION-CORROSION TEST.

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