US3551328A

US3551328A - Desulfurization of a heavy hydrocarbon fraction

Info

Publication number: US3551328A
Application number: US779202A
Authority: US
Inventors: Edward L Cole; Raymond F Wilson; Sheldon Herbstman
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1968-11-26
Filing date: 1968-11-26
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

3,551,328 DESULFURIZATION OF A HEAVY HYDROCARBON FRACTION Edward L. Cole and Raymond F. Wilson, Fishkill, and

Sheldon Herbstman, Spring Valley, N.Y., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 26, 1968, Ser. No. 779,202 Int. Cl. (110g 29/22, 27/04 US. Cl. 208-240 15 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for reducing the sulfur content of heavy hydrocarbon petroleum fractions and more particularly to the reduction in sulfur content of such hydrocarbon fraction by the oxidation of sulfur impurities and the subsequent removal of such oxidized sulfur impurities by treatment with a lower paraflinic hydrocarbon solvent.

Petroleum crude oils, and topped or reduced crude oils, as well as other heavy hydrocarbon fractions and/or distillates including vacuum tower bottoms, atmospheric tower bottoms, black oils, heavy cycle stocks, visbreaker product effluent, etc., are contaminated by the presence of excessive concentrations of various non-metallic and metallic impurites which detrimentally affect various processes to which such heavy hydrocarbon mixtures may be subjected. Among the non-metallic impurities is sulfur which exists in heteroatomic compounds and which effectively poisons various catalytic systems employed in a process for the conversion of such heavy hydrocarbon fractions to other hydrocarbon materials such as gasoline. Sulfur compounds are further objectionable because combustion of fuels containing these impurities results in the release of sulfur oxides which are noxious, corrosive and in addition presents a serious problem with respect to pollution of the atmosphere.

It is therefore an object of this invention to reduce the sulfur content of heavy hydrocarbon fractions.

It has now been found that the sulfur content of heavy hydrocarbon fractions can be reduced by contacting a heavy hydrocarbon fraction which contains sulfur compounds with an oxidizing amount of an oxidant optionally in the presence of an oxidation promoting catalyst, treating such heavy hydrocarbon fraction which contains oxidized sulfur compounds with a lower paraffinic hydrocarbon solvent in a concentration sufiicient to separate at least a part of the oxidized sulfur compounds from the heavy hydrocarbon fraction, separating the solvent-heavy hydrocarbon fraction from such oxidized sulfur compounds and recovering a heavy hydrocarbon fraction of reduced sulfur content. Thus it has been discovered that the oxidation of sulfur impurities in a heavy hydrocarbon fraction in combination with a solvent treatment step using a lower parafiinic hydrocarbon solvent produces a significant reduction in the sulfur content of the heavy hydrocarbon fraction, especially when compared to the treatment of such sulfur-containing heavy hydrocarbon United States Patent Patented Dec. 29, 1970 fraction utilizing a single treating step with a lower parafiinic hydrocarbon solvent.

In general the process of this invention is carried out by first contacting the heavy hydrocarbon fraction which contains sulfur impurities (hereinafter referred to as sulfur containing hydrocarbon fraction) with an oxidizing amount of an oxidant for a time sufficient to effect oxidation of at least a part of the sulfur impurities present in the sulfur containing heavy hydrocarbon fraction. The sulfur containing heavy hydrocarbon fraction which contains oxidized sulfur compounds is then treated with a lower paraffinic hydrocarbon solvent at a concentration sufiicient to precipitate or obtain phase separation of at least a part of the oxidized sulfur compounds from the heavy hydrocarbon fraction. The heavy hydrocarbon fraction of reduced sulfur content is then recovered from the oxidized sulfur compounds by conventional means, such as the separating of the solvent-heavy hydrocarbon fraction from the oxidized sulfur compounds and the removal of the parafiinic hydrocarbon solvent by distillation or vacuum stripping optionally using an inert stripping gas. As stated above, the oxidation step requires the oxidation of at least a part of the sulfur impurities and the solvent treating step requires the precipitation or phase separation of at least a part of the oxidized sulfur compounds from the heavy hydrocarbon fractions. By the use of the term at least a part is meant that the combined use of oxidation and solvent treating steps produces sulfur reduction in the heavy hydrocarbon fraction greater than that obtained by the use of the solvent treating step singly in the absence of the oxidation step. Thus, the reduction in sulfur content utilizing the process of this invention in general bring about reductions in sulfur content 20% greater than the sulfur reduction obtained utilizing a single solvent treating step in the absence of the oxidation step.

The type of oxidant, the concentration of oxidant, the presence or absence of an oxidation promoting catalyst (hereinafter referred to as catalyst), the temperature and pressure during the oxidation step can be varied over a wide range depending upon the nature of and the percent sulfur in such hydrocarbon fraction, the particular conditions being those conditions which effect oxidation of at least a part of the sulfur impurities. In addition the conditions for solvent treating can be varied over a wide range, both as to the ratio of volume of solvent to volume of sulfur containing heavy hydrocarbon fractions, as well as to time, temperature, pressure, and the nature of and the percent sulfur present in the heavy hydrocarbon fraction. These conditions are adjusted in order to produce a solvent treating step wherein the solvent is present in a concentration sufficient to effect precipitation or separation of at least a part of the oxidized sulfur compounds from the heavy hydrocarbon fraction and are adjusted in order to maximize the percentage of oxidized sulfur compounds which are removed from the heavy hydrocarbon fraction.

In carrying out the oxidation step in the process of this invention an oxidant is utilized such as oxygen ineluding activated oxygen and air, ozone, organic peroxides, organic hydroperoxides, organic peracids, optionally in the presence of a metal containing catalyst.

Thus the oxidation step is carried out by contacting the sulfur containing heavy hydrocarbon fraction with an oxidant optionally in the presence of a metal containing catalyst for a time sufficient to effect oxidation of at least a part of the sulfur present in the hydrocarbon fraction. The concentration of oxidant is usually dependent upon the percent sulfur present in the heavy hydrocarbon fraction and in general the mole ratio of oxidant to sulfur is from about 0.5 to about 10 mole of oxidant per mole of sulfur, more preferably from about 1 to about 8 moles of oxidant per mole of sulfur and still more preferably J from about 2 to about 5 moles of oxidant per mole of sulfur. When a catalyst is employed, it is preferred that the catalyst concentration vary from about 0.0001 to about Wt. percent based upon the weight of the heavy hydrocarbon fraction, more preferably from about 0.10 to about 10 wt. percent, the catalyst concentration being sufficient to promote the effectiveness of the oxidant. The temperature utilized in carrying out the oxidation step can vary over a wide range and in general a temperature of from about 20 F. to about 450 F. is utilized, depending upon the oxidant, although higher and lower temperatures can be utilized. In general the oxidant contacts the sulfur containing heavy hydrocarbon fractions for a time generally Within the range of from about minutes to 24 hours preferably from about one half hour to hours. The time that is utilized of necessity depends upon the percent sulfur present in the heavy hydrocarbon fraction and the type of oxidant. Thus, in the case of a gas, the time can vary over a wide range depending upon the particular amount of gas such as ozone which is passed into the reaction mixture, that is, the rate of introduction of ozone into the heavy hydrocarbon fraction. In general for the oxidation step utilizing ozone, a low temperature is utilized (such as from 20 F. to about 120 F.) and the mole ratio of oxidant to sulfur within the above range can be obtained during the time utilized during the oxidation step. The process of this invention in general is carried out at atmospheric pressure although pressures above atmospheric for example up to about 100 atmospheres can be utilized.

The preferred oxidants which are utilized in carrying out the oxidation step of the process of this invention are ozone, organic peroxides, organic hydroperoxides and organic peracids. These oxidants are particularly preferred since such oxidants have been found to give excellent reduction in percent sulfur when combined with the solvent treating step. In addition the use of the preferred oxidants have been found to be selective for oxidation of the sulfur compounds, that is, substantial amount of oxidation products such as acids and ketones are not formed. In addition, high product yields in the oxidation step, both as to the high product yield of oxidized sulfur impurities and the high product yield of heavy hydrocarbon fractions which remains after the oxidation step and in particular after the solvent treating step are obtained utilizing the preferred oxidants. The organic oxidants include by way of example hydrocarbon peroxides, hydroperoxides and hydrocarbon peracids wherein the hydrocarbon radicals in general contains from about 1 to about carbon atoms per linkage. With respect to the hydrocarbon peroxides and hydrocarbon hydroperoxides, it is particularly preferred that such hydrocarbon radical contain from 4 to 18 carbon atoms per peroxide linkage and more particularly from 4 to 16 carbon atoms per peroxide linkage. With respect to the hydrocarbon peracids the hydrocarbon radical is defined as that radical which is attached to the carbonyl carbon and in general such hydrocarbon radical can be from 1 to about 12 carbon atoms more preferably from about 1 to about 8 carbon atoms. It is intended that the term organic peracid includes by way of definition performic acid.

In addition it is contemplated within the scope of this invention that the organic oxidants can be prepared in situ, that is the peroxide, hydroperoxide or peracid can be generated in the sulfur containing heavy hydrocarbon fraction and such organic oxidant is contemplated for use within the scope of this invention.

Typical examples of hydrocarbon radicals are alkyl such as methyl, ethyl, butyl, t-butyl, pentyl, n-octyl and those aliphatic radicals which represent the hydrocarbon portion of a middle distillate or kerosene, cyclealkyl radicals such as cyclopentyl, alkylated cycloalkyl radicals such as monoand polymethylcyclo-pentyl radicals, aryl and cycloalkyl substituted alkyl radicals such as phenyl and alkyl phenyl substituted alkyl radicals examples of which are benzyl, methylbenzyl, caprylbenzyl, phenylethyl, phenylpropyl, naphthylmethyl, naphthylethyl, aryl radicals such as phenyl, and naphthyl, alkaryl radicals such as xylyl, alkylphenyl, and ethylphenyl.

Typical examples of oxidants are hydroxyheptyl peroxide, cyclohexanone peroxide, t-butyl peracetate, di-tbutyl diperphthalate, t-butyl-perbenzoate, methyl ethyl ketone peroxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, p-methane hydroperoxide, pinane hydroperoxide, 2,S-dimethylhexane-2,5-dihydroperoxide and cumene hydroperoxide, organic peracids, such as performic acid, peracetic acid, trichloroperacetic acid, perbenzoic acid and perphthalic acid.

The catalyst which is utilized to promote the oxidation of sulfur using the preferred oxidants are catalysts selected from Group IV-B, Group VB and Group VI-B metals. These catalysts can be incorporated into the oxidation system by any means known to those skilled in the art, and can be either a homogeneous or heterogeneous catalyst system. The catalyst can be incorporated by a variety of means and by the use of a variety of carriers. The particular catalyst carrier which is utilized is not critical with respect to the practice of this invention and can be for example, a support medium or an anion (including complex formation) which is attached to the metal (e.g. a ligand). The particularly preferred catalyst metals are titanium, zirconium, vanadium, tantalum, chromium, molybdenum and tungsten. Illustrative ligands include halides, organic acids, alcoholates, mercaptides sulfonates and phenolates. These metals may be also bound by a variety of complexing agents including acetonylacetonates, amines, ammonia, carbon monoxide and olefins, amongst others. The metals may also be introduced in the form of organometallics including ferrocene type structures. The various ligands illustrated above which are utilized solely as carriers to incorporate the metal into the process system, in general have an organic radical attached to a functional group such as the oxygen atom of carbonyloxy group of the acid, the oxygen of the alcohol, the sulfur of the mercaptan, the

of the sulfonate, the oxygen of the phenolic compound and the nitrogen of the amines. The organic radical attached to the afore described functional groups can be defined as a hydrocarbon radical and in general can contain from 1 to about 30 carbon atoms. Typical examples of hydrocarbon radicals are set forth above.

The metals contained on the heterogeneous catalyst can include individual or combinations of metals. These metals can be suspended on a suitable material, for example, alumina, silica (or combinations of both) as Well as activated clays or carbon, amongst others. The modes of contacting whereby the catalytic effect may be achieved may include slurry-bed reactions or continuous contacting over a stationary phase in a trickle-tube reactor. The particularly preferred catalyst for carrying out the oxidation step of the process of this invention is molybdenum such as in the form of molybdenum hexacarbonyl.

The solvent treating step is carried out at any suitable temperature and pressure, the temperature and pressure being adjusted so as to maintain the parafiinic hydrocarbon solvent (hereinafter referred to as solvent) in the liquid phase during the solvent treating step. A solvent treating temperature in the range of from about 50 F. to about 325 F., and a pressure in the range of from about atmospheric to about atmospheres are employed depending upon the composition of the solvent employed and to some extent the composition of the heavy hydrocarbon fraction undergoing solvent treating. Generally, a ratio of solvent to heavy hydrocarbon fraction in the range of from about 1 to 1 to about 20 to 1 is employed in the solvent treating step. The solvent treating step may be operated under substantially isothermal conditions or under a temperature gradient, such as in the use of a solvent extraction tower where the top extraction temperature is greater than bottom extraction tower temperature by not usually more than about 40 degrees Fahrenheit. Also in the case of the use of a solvent extraction tower the solvent treating step may be operated so that the sulfur containing heavy hydrocarbon fraction is introduced thereinto at a number of points along the height of such extraction tower and/or so that the aliphatic solvent is introduced thereinto at a number of points.

The paraffinic hydrocarbon solvent generally comprises one or more paraifinic hydrocarbons having from 3 to carbon atoms in the molecule, examples of which are propane, butane, isobutane, pentane, isopentane, hexane, isohexane, heohexane, heptane octane and mixtures thereof. Instead of pure hydrocarbons or mixtures thereof, technical mixtures, such as paraffinic hydrocarbon oil fractions, e.g., light low-aromatic naphtha fractions with boiling ranges between 50 F. and 350 F., may be used. These mixtures may also contain minor quantities of other hydrocarbons as long as the paraffinic mixture as such retains the character of at least a C to C hydrocarbon. In addition it is contemplated within the scope of this invention that the paraffinic hydrocarbon can contain a minor amount of additive materials to improve the separation of the oxidized sulfur compounds from the heavy hydrocarbon fraction and/or otherwise increase the quality of the reduced sulfur containing heavy hydrocarbon fractions. Additives which can be used are for example, carbonates of aliphatic, cycloaliphatic, aromatic and heterocyclic compounds examples of which are methyl and ethyl carbonates.

A wide variety of heavy hydrocarbon fractions and/or distillates may be treated, or made suitable for further processing, through the utilization of the method encom- 3 passed by the present invention. Such heavy hydrocarbon fractions include full boiling range crude oils, topped or reduced crude oils, atmospheric distillates, vacuum tower bottoms, visbreaker bottoms product, heavy cycle stocks from thermally or catalytically-cracked charge stocks, etc. The present method is particularly well adaptable to the treating of crude oils and topped or reduced crude oils containing large quantities of asphaltenic material, and is especially advantageous when applied to the treating of atmospheric or vacuum tower bottoms e.g. especially 550 F. or higher reduced crude oils at atmospheric pressure.

A particularly preferred heavy hydrocarbon fraction which can be utilized in the process of this invention are the deasphalted atmospheric and 'vacuum residues which have been topped at temperatures of a least 550 F. at atmospheric pressure. These deasphalted materials in general are deasphalted according to conventional means such as the processes disclosed in US. Pat. No. 2,943,050 and U8. Pat. No. 3,364,138.

The present invention can be carried out in batch, continuous or semi-continuous operating cycles, and in one or more actual or theoretical stages, employing contacting and separation equipment such as has heretofore been employed in the selective solvent refining of petroleum stocks. In addition a multi-stage mode of operation that is a repeating of the process several times can be utilized in carrying out the process of this invention. It should be understood that the specific equipment employed forms no part of the present invention.

The process of this invention can be better appreciated by the following non-limiting examples.

EXAMPLE 1 To a reactor equipped with stirrer and heating means is charged 42160 grams of reduced Arabian Crude (550+F. 2.6 wt. percent sulfur, 6.03 wt. percent carbon residue) and 8854 grams of tertiary butyl hydroperoxide (90% To this reaction mixture is added 126 grams of a molybdenum catalyst 8% by weight molybdenum and 6 the mixture is heated to F. for a period of 60 hours. The reaction mixture is cooled and stabilized to remove tertiary butyl hydroperoxide decomposition products. This reaction mixture (250 grams) is then mixed with 2500 milliliters of n-pentane in a glass separator at ambient temperature for a period of about 12 hours. Two layers are formed and the top layer containing the heavy hydrocarbon fractions of reduced sulfur content is removed and stripped of n-pentane solvent. The percent sulfur of the heavy hydrocarbon fraction is found to be 1.6 percent by weight with a carbon residue of 3.06 percent by weight.

EXAMPLE 2 The solvent treating step only of Example 1 is repeated using 250 grams of the same reduced Arabian Crude (550+F.) and 2500 milliliters of n-pentane. After the formation of two phases, the separation of the solvent heavy hydrocarbon fraction layer and the stripping of solvent, the heavy hydrocarbon fraction has a percent sulfur of 2.6 weight percent and a carbon residue of 3.9 weight percent.

EXAMPLE 3 To a reactor equipped with stirrer and heating means is added 1,000 grams of reduced Arabian Crude (550+F. 2.6 percent by weight sulfur, 6.03 percent by weight carbon residue) and 148 grams of tertiary butyl hydroperoxide. To this mixture is added 5 grams of a molybdenum catalyst containing 8% by weight molybdenum. The mixture is heated at 188 F. for a period of 8 hours. The temperature is allowed to reach ambient temperature and 250 grams of this material is mixed with 2500 milliliters of n-pentane in a glass separator. Two layers are formed and the top layer containing solvent and heavy hydrocarbon fraction is removed and stripped of solvent. The heavy hydrocarbon fraction (reduced Arabian Crude) has a percent sulfur of 1.79 percent by weight and a carbon residue of 3.07 percent by weight.

EXAMPLE 4 A Lago medium vacuum residuum (2.6% by weight sulfur, 6% by weight carbon residue) is charged to a deasphalting tower together with isobutane at a top deasphalting tower temperature of 264 F. a middle tower temperature of 260 F. and a bottom tower temperature of 258 F. The pressure is maintained at about 700 p.s.i.g. and a volume percent of isobutane to vacuum residuum is maintained at about 490%. A deasphalted residuum is recovered from the deasphalting tower and charged to a reactor. To the deasphalted residuum plus isobutane is charged tertiary butyl hydroperoxide at a concentration of about 8% by weight based upon the deasphalted vacuum residuum. To this mixture is charged a molybdenum catalyst at a concentration of 0.10 wt. percent based upon the charge of deasphalted vacuum residuum. The temperature is maintained at about 200 F. for an average residence time of about 1 /2 to 2 hours. The reaction mixture is transferred to a settler where it is contacted with about 10 volumes of isobutane in countercurrent flow until phase separation occurs. The heavy hydrocarbon fraction and solvent is removed from the settler and the solvent removed. The heavy hydrocarbon fraction has a reduced sulfur content of about 1.7% and a carbon residue of about 3.8 weight percent.

Examples 1 through 4 clearly demonstrate the significant reduction in sulfur content that is obtained utilizing the combination of oxidation step plus solvent treating step with a paraffinic hydrocarbon solvent. More particularly, examples 1 and 2 demonstrate that the percent sulfur reduction obtained utilizing the process of this invention is considerably in excess of that which is obtained when utilizing a solvent treating step singly. Thus, in Example 1 the percent sulfur was 1.76 wt. percent compared to a sulfur content of the starting material of 2.6 percent, whereas in Example 2 a percent sulfur was obtained after treatment with pentane of 2.6 wt. percent.

7 Example 4 demonstrates that the process of this invention can be combined with additional processes such as a deasphalting process to produce a combined process whereby deasphalting and desulfurization occurs to produce a material which has particular utility as a charging stock.

While this invention has been described with respect to various specific examples and embodiments it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

We claim:

1. A process which comprises contacting a heavy hydrocarbon fraction which contains sulfur compounds with 0.5 to about 10 mole of an oxidant per mole of sulfur present wherein said oxidant is selected from the group consisting of ozone, organic peracids, organic hydroperoxides, organic peroxides and their mixtures, thereafter treating said heavy hydrocarbon fraction containing oxidized sulfur compounds with a lower paraffinic hydrocarbon solvent containing from 3 to 10 carbon atoms at a concentration suflicient to separate at least a part of the oxidized sulfur compounds from the heavy hydrocarbon fraction, separating the heavy hydrocarbon fraction from the oxidized sulfur compounds and recovering the heavy hydrocarbon fraction of reduced sulfur content.

2. A process of claim 1 wherein the process is carried out in the presence of an oxidation promoting catalyst selected from the group consisting of a group 4-B metal, a group 5-B metal, a group 6-B metal and mixtures thereof.

3. A process of claim 2 wherein the oxidant is selected from the group consisting of a hydrocarbon peroxide, a hydrocarbon hydroperoxide, a hydrocarbon peracid, performic acid and mixtures thereof wherein each hydrocarbon radical contains from 1 to about 30 carbon atoms.

4. A process of claim 3 wherein each hydrocarbon radical contains from about 1 to about 12 carbon atoms.

5. A process of claim 4 wherein the oxidant is selected from the group consisting of tertiary butyl hydroperoxide, 40

cumene hydroperoxide and mixtures thereof.

6. A process of claim 1 wherein the lower parafiinic hydrocarbon solvent contains from 3 to 6 carbon atoms.

7. A process of claim 1 wherein the lower paraffinic hydrocarbon solvent contains from 3 to 6 carbon atoms.

8. A process of claim 2 wherein the lower paraflinic hydrocarbon solvent contains from 3 to 6 carbon atoms.

9. A process of claim 4 wherein the lower paraffinic hydrocarbon solvent contains from 3 to 6 carbon atoms.

10. A process of claim 5 wherein the lower paraffinic hydrocarbon solvent contains from 3 to 5 carbon atoms.

11. A process of claim 1 wherein the heavy hydrocarbon fraction which contains sulfur compounds is a reduced crude oil.

12. A process of claim 1 wherein the heavy hydrocarbon fraction which contains sulfur compounds is a deasphalted reduced crude oil.

13. A process of claim 6 wherein the heavy hydrocarbon fraction which contains sulfur compounds is a deasphalted reduced crude oil.

14. A process of claim 7 wherein the heavy hydrocarbon fraction which contains sulfur compounds is a deasphalted reduced crude oil.

15. A process of claim 10 wherein the heavy hydrocarbon fraction which contains sulfur compounds is a deasphalted reduced crude oil.

References Cited UNITED STATES PATENTS 2,143,882 1/1939 Keith et a]. 20829O 2,110,845 3/1938 Whiteleg et a]. 19613 2,593,761 4/1952 Johnstone 196-29 2,670,319 2/1954 Ayers et al 196-29 1,840,269 1/1932 Borstrom 208-196 2,749,284 6/ 1956 Noble 208240 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner U.S. Cl. X.R. 208196