US2770579A - Production of special solvent petroleum naphthas by refining with sodium - Google Patents

Description

United States Patent PRODUCTION OF SPECIAL SOLVENT PETRO- NAPHTHAS BY REFINING WITH Weldon G. Annahle, Mundelein, Kenneth Lucas, Woodstock, and Robert M. Haines, Crystal Lake, [1]., asslgnors to The Pure Oil Company, Chicago, 11]., a corporation of Ohio No Drawing. Application September 9, 1954, Serial No. 455,064

Claims. (Cl. 19628) This invention relates to a process for producing sweet hydrocarbon products from hydrocarbons containing corrosive sulfur compounds by chemical treatment with alkali metal at a temperature of about 400 to 500 F. More particularly, the invention relates to a method of producing improved naphthas which are characterized by their ability to pass the distillation-corrosion test by a one-stage treatment with alkali metal for those naphthas having a sulfur content of about 0.025 weight percent or less or a two-stage treatment involving catalytic desulfurization or hydrodesulfurization followed by treating the desulfurized product with alkali metal at a temperature of about 400 to 500 F. for those naphthas having a sulfur content above 0.025 weight percent.

It is known in the prior art to treat various types of sulfur-containing hydrocarbons with catalytic or noncatalytic contact materials including metal oxides or sulfides, fullers earth, clays and bauxite under conditions to remove or convert sulfur compounds to forms which are readily removable from the hydrocarbons. It is taught that such processes successfully desulfurize the hydrocarbons to produce products which are useful for many purposes. However, crude petroleum is the source of a large number of products and in many instances these products must be relatively pure and free of sulfur compounds in order to find acceptance in the industry. Petroleum naphthas comprise a class of petroleum products which must meet rigid requirements for use in dyeing,

rubber, extraction, protective coating, and allied indus-' tries. 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 corrision 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 ice 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. Although the odor of naphthas is important, 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 quantitatively 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 cc. of the naphthas 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. DS6-38 a described in A. S. T. M. Standards on Petroleum Products and Lubricants, published by the American Society for Testing Materials, Philadelphia, Pennsylvania.

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 testis 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 coloration 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 oif-specification naphthas back through such a process, does not produce acceptable naphthas because the sulfur compounds remaining are the most difficult 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 distillationcorrosion 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 these problems and provide a process for producing improved naphthas by chemical reaction or treatment with alkali metals at 400 to 500 F. and preferably at about 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.

A third object of the invention is to provide a process for treating corrosive naphthas containing above about 0.025 weight percent total sulfur by desulfurization followed by treatment with alkali metals at 400 to 500 F.

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

The prior art methods of desulfurization may be roughly divided into two groupsthose involving chemical treatment or absorptive contact at low temperature with the main purpose of removing free sulfur, hydrogen sulfide, and those organic sulfur compounds which may be adsorbed; and a second group of processes, including hydrodesulfuriza'tion react-ions conducted at elevated temperatures, that is, above 500 F. and generally in the order of 800 to 1000 F., which involve the breakdown of the organo sulfur compounds almost entirely into hydrogen sulfide. Products produced by these methods may have their sulfur contents greatly reduced and it is not uncommon to reduce the sulfur content to below 0.01 percent sulfur by these methods. However, these processes cannot be depended upon to produce naphthas which are noncorrosive to the distillation-corrosion test because the types of organic sulfur compounds remaining after these treatments are the very types which are corrosive to copper and, though present in very small amounts, are deleterious and indicate an unsalable naphtha.

Therefore, a sharp distinction must be made between desulfurization gene-rally as indicated in the prior art and the desulfurization necessary to produce non-corrosive naphthas. It has been found that a temperature of 400 to 500 F. and preferably at about 450 F. alkali metals may be used to contact naphtha hydrocarbons to transform the sulfur compounds therein to forms which are non-corrosive to the distillation-corrosion test. At temperatures below 400 F. there may be a large degree of desulfurization but the remaining sulfur compounds are again deleterious and corrosive. 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 pass naphthas. This is especially true in considering crude naphthas which have above about 0.003 percent mercaptans. If the chemical treatment or desulfuriz'ati'on is carried out according to the prior art at temperatures of above 500 B, 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 temperature is maintained or raised to about 450 F. the

5 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 compound-s 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 napthas like Stoddard solvent generally give a more corroded copper strip than lower boiling naphthas, as rubber solvent. Treatment of off-specification 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 suifur compounds are most diflicult to remove and most corrosive.

The present invention is predicated on the finding that the alkali metals may be used to satisfactorily treat naphthas to form non-corrosive products. Since an alkali metal such as sodium is a non-regenerative treating agent, it is preferred that in order to avoid the necessity of using large quantities thereof, the naphthas be previously treated to reduce the total sulfur content to about 0.025 weigh percent. In order to demonstrate one aspect of the invention, an intermediate sweet West Texas naphtha having a boiling range of 250 to 400 F. was treated with sodium, lithium, and potassium metal as shown in the following Table I. The naphtha was vaporized and passed into contact with the alkali metal at a temperature of 450 F. under atmospheric pressure using a space velocity of 1.0. The liquid recovery was 100 percent.

Table I Sulfur Distribution, Lithium Potassium Sodium Weight, Percent Charge Stock Total-S 0.032 0.003 0.003

Doctor Test Positive. Negative Negative- Negative. Mercury Test do 0 0 D0. Lead Acetate Test. do D0. Distillationdo D0.

Corrosion Test.

It is seen from Table I that the alkali metal effectively transforms the sulfur compounds into non-corrosive form.

To further demonstrate theinvention, a 100 to 425 F. naphtha from Worland crude oil was desulfurized by passage over a cobalt molybdate catalyst at about 750 F., under 250 p. s. i. g. with a space velocity of about 1.0. Hydrogen was recirculated to the reaction zone at a rate of 3000 s. c. f./bbl. of charge stock. The resulting product was stabilized to remove hydrogen sulfide formed as a by-product, a sulfur analysis was made and a portion of the product was subjected to the distillation-corrosion test. Following this, the desulfurized product was subjected to treatment with sodium, potassium, and lithium at a temperature of about 450 F. Contact was made by passing the vapors of the desulfurized product through a column containing the alkali metal dispersed in kero- 6 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 sine. The results are shown in Table II. be vaporized and pased over a bauxite catalyst at 700 Table II 1st Stage 2nd Stage Charge Desuliu- Stock rized Sodium Potassium Lithium Product Sulfur Distribution, Weight Percent:

Free-S. H RSHS R2S2-S R S Residual st: I

Total-S 0.018

Doctor Test Mercury Test Lead Acetate Test Distillation-Corrosion Test Negative do do..

Positive...

Negative.

Do. Do. Do.

From Table II it is seen that the desulfurization reaction effected a considerable reduction in the sulfur content of the naphtha but left a corrosive product. Treatment with alkali metal successfully transformed th naphtha into a sweet odor-free product.

In practicing the present invention, any hydrocarbon material from which naphthas or solvents or similar products may be obtained can be subjected to treatment with alkali metal at 400 to 500 F. wherein the objective is to overcome the tendency of the product toward the formation or carry-over 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 example, a crude oil containing from 1.0 to 3.0 'or as high as 7.0 weight percent of sulfur is fractionated to obtain a wide boiling range virgin or straightrun 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. Kerosine fractions may also be used. Preferably a straight-run naphtha fraction having up to 0.025 percent of total sulfur and boiling between 110 and 450 F. is used. I

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 upto high boiling specialty naphthas including, for example, petroleum ether 90140 F., special textile spirits 180-210 F, light mineral spirits 290330 F., Stoddard solvent 310385 F., and high flash dry cleaning solvent 360-400 F., all being noncorrosive, 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 percent sulfur, as, for example, a

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. A particularly eflicient 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 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 alkali metal. 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.

In carrying out the reaction, the naphtha to be treated is heated to a temperature of about 400 to 500 F., preferably 450 F, and the vapors passed through the alkali metal 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 alkali metal 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 100 may be used. 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.

What is claimed is:

l. The method for producing special solvent naphthas from petroleum hydrocarbon mixtures containing small naphtha containing from 0.10 to as high as 7.0 percent amounts of total sulfur of not more than about 0.025

weight percent which comprises contacting said petroleum hydrocarbon mixture with alkali metal at a temperature of above 400 F. and below 500 F. and separating special solvent naphthas therefrom characterized by their ability to pass the distillation-corrosion test.

2. A method in accordance with claim 1 in which the naphtha contains in excess of 0.025 percent by weight of sulfur and it is subjected to catalytic desulfurization to reduce its sulfur content to not more than 0.025 percent by weight prior to treatment with alkali metal.

3. A mehod in accordance with claim 2 in which the naphtha is passed in a vapor form through the alkali metal at a space velocity of about 0.2 to 3.0, at a pressure of about 20 lb./ sq. in., and a temperature of about 450 F.

4. A method in accordance with claim 1 in which the alkali metal is sodium.

5. A method in accordance with claim 1 in which the alkali metal is lithium.

6. A method in accordance with claim 1 in which the alkali metal is potassium.

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

8. A method in accordance with claim 1 in which the naphtha is a straight run naphtha. Y

9. A method in accordance with claim 1 in which the naphtha is passed in the form of vapor through the alkali metal at a space velocity of about 0.2 to 3.0, a pressure of about 20 lb./ sq. in., and a temperature of about 450 F.

10. A method in accordance with claim 1 in which the naphtha is passed in the form of vapor through the alkali metal at a space velocity of about 1.

References Cited in the file of this patent UNITED STATES PATENTS Carlisle .Apr. 21, 1931 Cross May 17, 1932

Claims (1)

1. THE METHOD FOR PRODUCING SPECIAL SOLVENT NAPHTHAS FROM PETROLEUM HYDROCARBON MIXTURES CONTAINING SMALL AMOUNTS OF TOTAL SULFUR OF NOT MORE THAN ABOUT 0.025 WEIGHT PERCENT WHICH COMPRISES CONTACTING SAID PETROLEUM HYDROCARBON MIXTURE WITH ALKALI METAL AT A TEMPERATURE OF ABOVE 400* F. AND BELOW 500* F. AND SEPERATING SPECIAL SOLVENT NAPHTHAS THEREFROM CHARACTERIZED BY THEIR ABILITY TO PASS THE DISTILLATION-CORROSION TEST.