US2755226A - Method for producing naphthas of improved characteristics by treating them with copper chromite or copper molybdate - Google Patents

Description

ie States METHOD FOR PRODUQENG NAPHTHAS OF IM- PRQVED CHARACTERiEaTICS BY TREATING THEM WITH CUPPER Ci-ERQMITE OR CGPI'ER MGLYBDATE No Drawing. Application April 1, 1954, Serial No. 420,461

15 Claims. 01. 19628) This invention is directed to a method for the production of petroleum naphthas characterized by their ability to pass the Distillation-Corrosion test and, more particularly, the invention relates to the production of noncorrosive naphtha hydrocarbons by chemical reaction or treatment with a copper compound selected from the group consisting of copper chromite and copper molybdate at a temperature of about 400 to 500 F.

Crude petroleum has long been the source of widely known products including 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 chemicais and a large number of products 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 directed to a method of transforming deleterious sulfur compounds present in hydrocarbon mixtures into forms which are less obnoxious and non-corrosive and will be illustrated by the treatment of straight-run naphthas. The examples given are not to be construed as limiting the invention. The term naphthas as used herein shall mean straight-run petroleum naphthas and other hydrocarbon mixtures or their equivalents containing deleterious sulfur compounds which must be transformed to meet rigid corrosion tests.

Naphthas prepared from petroleum by physical means inevitably contain other types of organic and inorganic compounds due to the complex nature of petroleum which are 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 persistent and cling tenaciously to any environment in which 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 odor of a well refined naphtha is generally described as sweet.

Tests have been devised to determine both quantatively and qualitatively the presence of these odious compounds in an attempt to control the properties and quality of naphthas from petroleum sources. For this purpose, various copper strip corrosion tests, the mercury test, the lead acetate test, and the Doctor test are used. Procedures established by A. S. T. M. are 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 testby any name, a particularly rigorous 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 100 cc. of the naphtha to be tested. The copper strip is so positioned in the flask 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. D86-38 as described in A. S. T. M. Standards on Petroleum Products and Lubricants, published by the American Society for Testing Materials, Philadelphia, Pennslyvania.

At the completion of the test, wherein the flask has been heated to dryness, the color of the copper strip is an indication of the relative amount of corrosive sulfur compounds present in the naphtha sample. A negative test is shown by the presence of a very slight or moderate tarnish on the strip and stamps the naphtha as satisfactory. 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.

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 the sulfur compounds remaining are the most difiicult to remove and the most corrosive. 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 may pass the other tests for sulfur compounds but do not pass the Distillation-Corrosion test. Often naphthas are produced which are negative or borderline to the Distillation-Corrosion test and which exhibit a positive reaction to one or more of the other tests for sulfur compounds. Since naphthas must pass all such tests to be acceptable, further treatment is necessary. Prior art methods of desulfurization when applied to such naphthas may produce a Doctor negative or mercury negative product, but in so doing the end result is a positive Distillation-Corrosion. test.

Accordingly, the primary object of this invention is to overcome this problem and provide a process for producing improved naphthas by chemical reaction or treatment with certain copper compounds at 400 to 500 F. and preferably at 450 F.

A second object of the invention is to provide a method of producing naphthas which pass the Distillation-Corrosion test from naphthas containing unacceptable amounts of sulfur compounds.

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

In the prior art there are described many methods for desulfurizing and sweetening hydrocarbon mixtures. These processes may be roughly divided into two groups those involving chemical treatment or adsorptive contact at low temperatures with the main purpose being the removal of free sulfur, hydrogen sulfide, and those organic sulfur compounds which may be adsorbed; the second group of processes, which include hydrodesulfurization reactions, are conducted at elevated temperatures and involve the breakdown of the organo sulfur compounds into products including hydrogen sulfide. During these hydrodesulfurization processes, the sulfur compounds present are substantially completely destroyed and there take place reactions involving hydrogenation, dehydrogenation, reforming, and the like, depending on the particular catalyst used and the operating conditions. In general, especially in the presence of hydrogen under optimum conditions, gasoline products are obtained which have increased octane numbers and good lead susceptibility. Products produced by these methods may have their sulfur contents greatly reduced, and it is not uncommon to reduce the sulfur content to points below 0.01 per cent sulfur. These prior art processes cannot be depended upon to produce naphthas which are non-corrosive to the DistillationCorrosion test because the types of organic sulfur compounds remaining after these treatments are the very types that are corrosive to copper and, though present in a very small amount, are deleterious and indicate an unsalable product. Therefore, a sharp distinction must be made between desulfurization generally as meant in the prior art and the desulfurization necessary to produce non-corrosive naphthas. The present invention is directed to the finding that at a temperature of about 400 to 500 F. copper chromite or copper molybdate or their mixtures may be used to contact naphtha hydrocarbons to transform the sulfur compounds therein to forms which are non-corrosive to the Distillation-Corrosion test. It has been found that at temperatures below 400 F., although there may be a large degree of desulfurization, the remaining sulfur compounds are corrosive to the Distillation-Corrosion test. In ordinary gasoline sweetening processes using oxidizing agents, the general object is to convert the mercaptans to disulfides. At temperatures above about 350 F., the disulfides break down and form lesser amounts of corrosive sulfur compounds. Thus, because of the instability of the disulfides, these methods of desulfurization or sweetening cannot be used to produce sweet naphthas. This is especially true in considering crude naphthas which have above about 0.003 per cent mercaptans. If the chemical treatment or desulfurization is carried out according to the prior art at temperatures of above 500 F., there may be adequate desulfurization, but by-products are formed at these elevated temperatures which deleteriously affect the color of the resultant naphthas. This color cannot be removed by ordinary adsorbents, and again the product is unsalable.

It has been found that at a temperature of about or above 400 F. some of the mercaptans are converted to metal mercaptides instead of disulfides and as the tempera ture is maintained or raised to about 450 F. the metal mercaptides break down into metal sulfides and organic mono-sulfides which are non-corrosive and stable. This is the type of sweetening reaction which is contemplated by the present invention. There is no minimum sulfur content requirement for naphthas but, since they must meet the Doctor test, contain no hydrogen sulfide or free sulfur, and pass the Distillation-Corrosion test, the amount of total sulfur present in the finished product is necessarily small. The principal factors pertaining to the influences exerted by this small content of sulfur compounds on the various corrosion tests are the boiling points of the sulfur compounds in relation to the boiling range and end point of the naphtha, and the stability of the sulfur compounds at moderately high temperatures. Mercaptans are rather unstable at moderately high temperature and break down into products corrosive to the Distillation-Corrosion test. Disulfides are more unstable and produce very corrosive decomposition products, especially under the conditions present in the distillation residue. High boiling naphthas like Stoddard solvent generally give a more corroded copper strip than lower boiling naphthas, as rubber solvent. Treatment of offspecification naphthas by prior art methods may break down the sulfur compounds into those types which are more corrosive to the Distillation-Corrosion test, especially Where low sulfur naphthas are concerned since these sulfur compounds are most difficult to remove and most corrosive.

Accordingly, the present invention is primarily directed to the treatment of naphthas or hydrocarbon mixtures containing low sulfur contents in the order of 0.025 per cent by weight or less of total sulfur. The total sulfur may comprise elemental sulfur or sulfur compounds or mixtures of sulfur and one or more types of sulfur compounds. Crude naphthas having more than this amount of total sulfur may be treated in accordance with the invention but it is preferred that such naphthas be previously desulfurized to bring the sulfur content down to 0.025 per cent or less total sulfur. The 0.025 per cent total sulfur may be mercaptan sulfur only and one embodiment of the invention comprises the treatment of naphthas containing substantially only mercaptan sulfur compounds. The chemical treatment with copper chromite and/or copper molybdate at 400 to 500 F., in combination with prior desulfurization as described in accordance with this invention, may effect a considerable reduction in the total sulfur content of the naphthas, as by as much as per cent, but generally the reaction is one of sweetening or transformation of the sulfur compounds into non-corrosive form.

In order to demonstrate the invention, a series of experiments were conducted in which an intermediate sweet West Texas naphtha having a boiling range of 250 to 400 F. was subjected to vaporization and passage separately over copper chromite and copper molybdate at a temperature of about 450 F. under atmospheric pressure and with a space velocity of 1.0 with a per cent liquid recovery. The following table makes a comparison of the sulfur distribution in the charge stock, which gave a negative to borderline Distillation-Corrosion test, with that of the products after treatment with these copper compounds. In each instance, the naphtha produced was negative to the Distillation-Corrosion test and was Doctor negative.

TABLE I The production of non-corrosive naphthas using copper In order to further demonstrate the invention, the following table is shown wherein various treating agents were investigated as to their ability to transform the corrosive sulfur compounds in a naphtha to non-corrosive forms as evidenced by a good or bad Distillation-Corrosion test. In these tests, the same West Texas naphtha was used as in the previous experiments and the same reaction conditions were used. In each instance, with the exception of copper nitrate, the materials used gave a product of good color. The table shows whether or not there has been a reduction in sulfur content and whether or not the product passed the Distillation- Corrosion test.

g TABLE II Treatment of a naphtha with various agents at 450 F.

Good Dis- Desulfuritillationzation Corrosion Test 1. Aluminum chloride Yes N0. 2. Cobalt oxide Yes No. 3. Cobalt molybdate. No. 4. Copper chromite Yes 6. Copper molybdate Yes. 6. Copper oxalate No. 7. Copper nitrate" No. 8. Copper chloride. No. 9. Active carbon No. 10. Porocel (regenerated) N0. 11. Fullers earth No. 12. Filtrol X-417 No. 13. F11trolX-466 No. 14. Nickel vanadete... No. 15. Sea Sorb (MgO) No. 16. Ammonium molybda N0. 17. Borax glass No. 18. Sodium bicarbonate" N0. 19. Lithium carbonate No. 20. Molybdenum oxide No. 21. Vanadium pentoxide No. 22. Chromic oxide Yes No.

In practlcmg the present invention, any hydrocarbon material from which naphthas or solvents or similar products may be obtained can be used and subjected to treatment with copper chromite and/or copper molybdate at 400 to 500 F. wherein the objective is to overcome the tendency of the product toward the formation or carryover of those types of sulfur compounds which cause a positive Distillation-Corrosion test. Fractionation into various specialty naphthas may precede or follow treatment in accordance with the invention. To prolong the life of the treating agents, it is preferred that the more volatile components and the high boiling residues present be removed by fractionation or other methods prior to treatment in accordance with the invention. For ex ample, a crude oil containing from 1.0 to 3.0 or as high as 7.0 weight per cent of sulfur is fractionated to obtain a wide boiling range virgin or straight-run naphtha having an end boiling point of about 500 F. A gas oil fraction may be used which may boil between about 500 and 700 F. Kerosene fractions may also be used. Preferably a straight-run naphtha fraction having up to 0.025 per cent of total sulfur and boiling between 110 and 450 F. is used.

The boiling range of the particular fraction removed for treatment or after 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 180-210 F., light mineral spirits 290330 F., Stoddard solvent 310385 F., and high flash dry cleaning solvent 360400 F., all being non-corrosive, odorless, and meeting the rigorous requirements of the industry, is contemplated.

In treating naphtha fractions or hydrocarbon mixtures from which naphtha fractions may be separated, which contain above 0.025 per cent sulfur, as, for example, a naphtha containing from 0.10 to as high as 7.0 per cent total sulfur, it is desirable to subject the naphtha to a desulfurization reaction before treatment in accordance with the invention. For this purpose, the naphtha may be vaporized and passed over a bauxite catalyst at 700 to 800 F. A hydrodesulfurization reaction may be employed if the naphtha contains a considerable portion of sulfur compounds. Treatment with such desulfurization catalysts 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, with or Without the presence of hydrogen at temperatures from 500 F. to 800 F. and under pressures from 20 to 500 pounds per square inch will effectively desulfurize the naphthas as a pretreatment. Although treatment at about 450 F. with copper compounds in accordance with the invention may be used for naphthas containing in excess of 0.1 per cent mercaptan sulfur, from the standpoint of product quality and economics of the process, desulfurization prior to sweetening is recommended for stocks containing more than about 0.025 per cent mercaptan sulfur. A particularly etficient catalyst for this purpose is cobalt oxide-molybdena-alumina or a chromia-molybdena-alumina catalyst employed at about 750 F. under 250 pounds pressure of hydrogen. After such treatment it is customary to subject the naphtha to stripping at about 400 F. and 240 p. s. i. g. to remove the hydrogen and hydrogen sulfide. In order to demonstrate desulfurization prior to sweetening in accordance with the invention, the following table is presented:

TABLE III Desalfurization prior to sweetening N aphtha Desulfursweetening Charge ization Catalyst or Treating Material. Bauxite..- Copper Average Reactor Temp, F Reactor Pressure, p. s. i. g. Space Velocity Liquid Recovery, Vol. percent.

1 Caustic Washed to remove H25. 2 Distilled after sweetening to 400 F. end point.

In certain instances, it may be desirable to increase the solvency of the naphthas produced. For this purpose, the naphthas may be first subjected to a mild reforming or hydroreforming operation preceding the chemical treatment with cooper chromite or copper molybdate. The hydroreforming may be conducted using a cobalt molybdate or copper molybdate catalyst and the sour naphtha passed thereover at temperatures between 825 and 850 F. The aromatization may be promoted by a platinum-containing catalyst at 800 to 825 F. Since these processes of desulfurization and aromatization are well known and merely used as preliminary treatments for the present process, further description is unnecessary.

In carrying out the reaction, the naphtha to be treated is heated to a temperature of about 400 to 500 F. and preferably 450 F. and the vapors passed through the copper treating agent. Adequate conversion of the sulfur compounds to non-corrosive form may be obtained by passing the hot liquid naphtha under pressure through the copper treating agent. The vapor treatment is preferred because of the ease with which the reaction may be carried out. Space velocities of from 0.2 to 10 may be used. Any of the well known percolation, fixed bed, fluidized reaction zone, or plural bed vapor-solid contact methods of the prior art may be used as long as intimate contact is obtained at a temperature within 400 to 500 F. Since the degree of treatment depends somewhat on the correlation between temperature and time of contact as in all such chemical transformations, it is usually desirable to conduct the treatment at relatively high space velocities when temperatures above 450 F. are used and at lower space velocities when temperatures below 450 F. are used. In general, the space velocity is selected to give results corresponding to those obtained at a vapor space velocity in the range of about 0.2 to 3.0 at 20 pounds per square inch pressure at about 450 F. These conditions consistently give satisfactory results.

The chemical agents used hrein are available commercially or may be prepared from raw materials. Copper chromite, Cu(CrO2)2, may be formed from chromic oxide or chromic hydroxide by fusion with copper salts. Chromic oxide for the reaction may be obtained by heat decomposition of ammonium dichromate or mixture of potassium dichromate and ammonium chloride. Copper permolybdate or, as it is sometimes called, copper molybdate, Cu(MoO4)2-H2O, is a greenish-yellow powder soluble in ammonia. It is a chemical compound or complex and is not the equivalent of a simple mixture of copper oxide and molybdenum oxide. Copper permolybdate is formed from ammonium molybdate. These copper salts may be used alone, or in admixture as contact materials.

It is preferred that the copper treating agents be used with an inert carrier to insure intimate contact and simplify handling. Such carriers as silica, bauxite, titania, zirconia, chromia, kieselguhr, bentonite, activated carbon, clays, pumice, and alumina may be used. The various well known ctr-precipitation, separate precipitation, imprcgnation, and simple mixing processes may be used to prepare the copper compound and inert carrier for use in the process. To avoid the danger of fusing during use or regeneration, it has been found that a maximum of about 8 to 10 per cent by weight of copper, as copper compounds, should be used in the carrier material. The copper chromite used in the experiments was a commercial catalyst normally offered for use in hydrogenation reactions. This product contains about 60 per cent of copper.

The contacting may be carried out with the copper compounds in the pelleted or tablet form. The copper molybdate used in the experiments was pelleted with alumina as the carrier. It was found that when the copper content of the treating agent exceeded about 10 per cent, it tended to fuse during use and the fused mass was difficult to handle. Regeneration was more difiicult also, since the material lost its free flowing properties. Consequently, it is recommended that the copper content of the completed mass or pellets be below about 10 per cent. In preparing the pellets the copper salts, in powder form, are admixed in proportions such that less than 10 per cent by weight based on copper is present and the mixture is subjected to compression into pellets or tablets. Following this, the pellets are calcined at 900 to 1200 F. The methods of pelleting described in United States Patents 2,499,675, 2,592,016, and 2,606,159 may be used. It is probable that during the treatment the copper compounds act to convert the mercaptans present to copper mercaptides, which in turn are converted to organic sulfides and copper sulfide. If any disulfides are present in the untreated naphtha or are formed during the reaction they are decomposed at the temperature of treatment so that the treated product is substantially free of disulfides.

Upon completion of the treatment with copper chromite and/or copper molybdate, the products may sometimes have a slight acrid odor. This odor may be removed by caustic wash since it is due to a trace of sulfur dioxide. The used treating material may be regenerated by passing an oxygen-containing gas through the bed of material at 1100 to 1300 F. The methods of regeneration described in United States Patents 2,506,552, 2,506,- 545, and 2,506,542 as applicable to spent contact masses of this type may be used.

What is claimed is:

1. The method of transforming hydrocarbon mixtures containing sulfur compounds which give a positive Distillation-Corrosion test into products which pass that test, comprising subjecting said hydrocarbon mixtures to contact with a material selected from the group consisting of copper chromite and copper molybdate and their mixtures at a temperature between about 400 and 500 F. and separating non-corrosive hydrocarbon products therefrom.

2. The method in accordance with claim 1 in which the contact material is copper chromite.

3. The method in accordance with claim 1 in which the contact material is copper molybdate.

4. The method in accordance with claim 1 in which the temperature of contact is about 450 F.

5. The method in accordance with claim 1 in which the hydrocarbon mixture comprises a straight-run naphtha containing up to about 0.025 weight per cent of total sulfur.

6. The method in accordance with claim 1 in which the hydrocarbon mixture comprises a straight-run naphtha containing up to about 0.025 weight per cent of mercaptan sulfur.

7. A process for producing non-corrosive naphthas from hydrocarbon mixtures containing corrosive sulfur compounds, which comprises subjecting said hydrocarbons to contact with a material selected from the group consisting of copper chromite and copper molybdate at a temperature between about 400 and 500 F. and separating non-corrosive naphthas therefrom.

8. The process is accordance with claim 7 in which the contacting is carried out at a temperature of about 450 F., at substantially atmospheric pressure, and with a space velocity of about 1.0.

9. The method is accordance with claim 7 in which the hydrocarbon mixture to be treated contains up to about 0.025 weight per cent of total sulfur compounds.

10. The method in accordance with claim 7 in which said naphtha products pass the Distillation-Corrosion test.

11. The method in accordance with claim 7 in which the contact material is copper chromite.

12. The method in accordance with claim 7 in which the contact material is copper molybdate.

13. The method in accordance with claim 7 in which the contact material is copper chromite supported on an inert carrier in an amount such that the copper content of the total mass is less than about 10 per cent.

14. The method in accordance with claim 7 in which the contact material is copper molybdate supported on an inert carrier in an amount such that the copper content of the total mass is less than about 10 per cent.

15. In the process for producing naphthas from hydrocarbons having a high content of corrosive sulfur compounds wherein said hydrocarbons are subjected to vapor phase desulfurization in the presence of a desulfurizing catalyst at a temperature of about 700 to 800 F., the improvement comprising conducting said desulfurization reaction for a time suflicient to reduce the total sulfur content of said hydrocarbons to not more than about 0.025 weight per cent and thereafter subjecting said desulfurized hydrocarbons to treatment with a material selected from the group consisting of copper chromite, copper molybdate and their mixtures at a temperature of between about 400 to 500 F. and recovering a naphtha which is characterized by its ability to pass the Distillation-Corrosion test.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,141 Heard Jun. 18, 1940 2,547,380 Fleck Apr. 3, 1951 2,608,534 Fleck Aug. 26, 1952 2,620,362 Stiles Dec. 2, 1952

Claims (1)

1. THE METHOD OF TRANSFORMING HYDROCARBON MIXTURES CONTAINING SULFUR COMPOUNDS WHICH GIVE A POSITIVE DISTILLATION-CORROSION TEST INTO PRODUCTS WHICH PASS THAT TEST, COMPRISING SUBJECTING SAID HYDROCARBON MIXTURES TO CONTACT WITH A MATERIAL SELECTED FROM THE GROUP CONSISTING OF COPPER CHROMITE AND COPPER MOLYBDATE AND THEIR MIXTURES AT A TEMPERATURE BETWEEN ABOUT 400* AND 500* F. AND SEPARATING NON-CORROSIVE HYDROCARBON PRODUCTS THEREFROM.