US3413307A - Desulfurization process - Google Patents

Description

United States Patent 3,413,307 DESULFURHZATION PROCESS Barry N. Heimlich, Union, and Thomas J. Wallace,

Elizabeth, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 434,643, Feb. 23, 1965. This application May 10, 1965, Ser. No. 454,693

2 Claims. (Cl. 260329.3)

ABSTRACT OF THE DISCLOSURE Organic sulfur is oxidized by means of a mixture of an organic carboxylic acid, an oxy-mineral acid and an oxidizing agent. The oxidation serves to convert the sulfur to a form from which desulfurization may take place more readily. This serves to reduce pollution problems.

This case is a continuation-in-part of our earlier filed application, U.S. Ser. No. 434,643, filed Feb. 23, 1965, and entitled A Desulfurization Process.

This invention relates to an improvement in the desulfurization of a hydrocarbon mixture. More particularly, the invention concerns the desulfurization of heavy hydrocarbon fractions, including residua. More particularly, this invention pertains to a method for converting bivalent sulfur selectively to the sulfone state, to facilitate thermal or caustic desulfurization. This is accomplished by utilizing a unique mixed acid catalyst which with great selectivity successfully converts the bivalent sulfur to sulfones. The mixed acid catalyst comprises hydrogen peroxide, acetic acid and sulfuric acid in critical amounts.

Air pollution is becoming an increasingly important problem to the entire world. Residual fuel oils that contain significant quantities of sulfur form noxious S0 upon combustion and recent studies, substantiating this, indicate that the amount of noxious S0 in the atmosphere is continually growing. These compounds, aside from lending to a generally high level of discomfort for those who are forced to live in areas where they are present, also constitute an extremely dangerous health hazard and have contributed greatly to the growing presence of respiratory diseases.

Recently, a U.S. Patent 3,163,593 was issued concerning a method of desulfurizing heavy oils. This patent teaches a method for changing the state of sulfur which is found in heavy hydrocarbon oils by oxidation with an acid catalyst. The feed stock utilized in that invention is a heavy hydrocarbon oil, that is to say a hydrocarbon oil of which at least 50% by volume boils above 250 C. To oxidize the sulfur in these heavy oils, organic peracids, e.g., performic or peracetic acid or mixtures of hydrogen peroxide with formic or acetic acids are utilized. This is somewhat satisfactory, however, it does present substantial drawbacks. Because of the appreciable solubility of these acids in oils, the use of concentrated organic acids causes significant acid recovery problems. Accordingly, it would be preferable to use dilute aqueous acid mixtures in order to reduce the loss of acid by dissolution in the oil. In the instant invention, it has unexpectedly been found that a unique dilute aqueous acid catalyst media affords excellent rate of oxidation without significant difiiculties in acid recovery. This is accomplished by using dilute aqueous solutions of mixed acetic and sulfuric acids or dilute halogenated acetic acids in mixture with aqueous hydrogen peroxide or other oxidants.

According to one aspect of this invention, a process has been discovered in which residua is treated with a dilute aqueous solution of H 0 acetic acid and H 80 to convert the bivalent sulfur, which is present in organic com- "ice pounds, selectively to the sulfone state whereby the desulfurization of the sulfone may be facilitated by thermal or caustic means. More specifically, the treatment of the present invention concerns a method by which a residua, which is a heavy petroleum fraction whose initial boiling point is usually about 600 F. is treated with a specific oxidizing agent, which comprises an aqueous solution of H 0 acetic acid and H 30 Contacting this mixed acid catalyst with the organic sulfur compounds found in a residua results in the oxidation of these organic compounds to the sulfone state. The sulfone may then be cleaved by means of caustic or heat to produce a product which is substantially sulfur free.

This invention will be most effective when utilized to treat heavy sulfur bearing residua. Residua is what remains after naphtha and gas oil have been removed from a crude oil by atmospheric distillation. It has an initial boiling point of about 600-650" F. This would include residua from the following crudes which are particularly high in sulfur content: Safaniya, Kuwait, Bachequero, Arabian, to name a few. These crudes will profit greatly by the treatment of the instant invention. The previously known treatment of hydrodesulfurization is not nearly so effective as this process since it often results in too much expense or is unsuited for use with the particular sulfur compounds which one desires to convert. The expense is associated with the fact 6 to 10 moles of hydrogen must be consumed per mole of sulfur. This is due to the high aromatics content of the residua.

The instant invention applies to the treatment of all hydrocarbon oils in which a substantial number of molecules contain a sulfur atom as Well as carbon. In particular, this invention is extremely helpful in treating any hydrocarbon fraction which contains thiophenes or thiophene derivatives. This invention may therefore be utilized with organic sulfur-containing whole crude oils or reduced crudes which boil above 300 F., preferably above 600 F. Thus, the invention has an extremely wide range of applicability. However, it is believed it will find its major use in treating residua, either atmospheric, vacuum, or from assorted processes such as catalytic cracking. Other than resins, lubricating oils, transformer oils, gas oils and kerosenes may be treated. In fact, any petroleum fraction boiling between 300 F. and 1050 F., preferably between 600 F. and 1050 P. which contains organic sulfurs may be improved by the process of this invention. Most preferably, the invention will be utilized to treat residua as described above.

With respect to the organic sulfur compounds which may be utilized in the instant invention, these are numerous and varied in scope. Some examples of the organic sulfur compoundn to be treated are dibenzothiophene, benzothiophene, naphthothiophene, naphthobenzothiophene, diphenyl sulfide, alkyl sulfides and derivatives thereof. In general, we are concerned with thiophene derivatives and alkyl, aryl and aralkyl sulfides. Exemplary of the most dilficult to desulfurize of these compounds is dibenzothiophene, which is also the most prevalent class of sulfur compounds in residua. Since it is an excellent example of the general class of organic sulfur compounds found in residua, it will be used as an example to illustrate the entire class. There is no intention, however, to be bound by any particular mechanism or illustration of an entire class.

The organic sulfur compound, as illustrated by dibenzothiophene, is contacted with the mixed acid catalyst of the instant invention. This mixed acid catalyst consists of an aqueous solution of sulfuric acid, acetic acid and hydrogen peroxide. The following ratios of the mixed acid catalysts are applicable; generally about 1 to 50% of volume concentrated sulfuric acid is combined with about 1 to 50% of glacial acetic acid by volume and about 2 to 10 moles of hydrogen peroxide per mole of sulfur compound. Preferably about 10 to 40% by volume of sulfuric acid, 5 to 25 parts by volume of acetic acid and 2 to 10 mole of hydrogen peroxide per mole of sulfur compound are used. In its most preferred form, this invention would involve the use of 25 to 35% of sulfuric acid by volume, 10 to 20% of acetic acid by volume and 2 to 10' moles of hydrogen peroxide per mole of sulfur compound.

A variety of reagents may be substituted for the hydrogen peroxide; they include alkali metal periodates, perchlorates, chromates and permanganates, metal oxides such as manganese dioxide or chromic oxide, perchloric and hypochlorous acids, hydroperoxides such as tertiarybutyl hydroperoxide, peracids such as performic, peracetic, pertrichloroacetic, perbenzoic and perphthalic acids. The acid system must be a mixed acid system; in place of sulfuric acid other oxy-mineral acids such as nitric, boric, phosphoric, chloric and perchloric acids, may be utilized. The acetic acid can be substituted with formic, chloroacetic, dichloroacetic, trichloroacetic, trifiuoroacetic, benzoic, phthalic, or terphthalic acids. The organic acid can be branched, i.e. trimethylacetic and it can contain other funtcional roups such as NH N HO and HS to 4 EXAMPLE I The following example indicates the relative success in converting dibenzothiophene which is attained with vari ous oxidizing mixtures. In all instances, the dibenzothiophene was treated under identical conditions. About 5.14 gm. of dibenzothiophene in a solution made up with 100 cc. of highly refined white oil, to which 5 cc. of n-hexadecane was added to serve as a chromatographic standard, was contacted with various oxidizing mixtures for a period of 120- minutes in a glass vessel. The temperature utilized for all runs was 212 F. and ambient pressures were also utilized. The white oil solutions of the dibenzothiophene and the oxidizing mixtures were separately heated to reaction temperature and then brought into reaction in a well agitated flask. Aliquot samples of the oil were taken initially and periodically as the runs progressed and were analyzed by gas chromatography. The conversion of diben- Zothiophene was determined by measuring its peak area on the chromatograph relative to the peak area of the nhexadecane. The reaction products were isolated and found to be dibenzothiophene sulfone by gas chromatography, infra-red and by melting point. The following table, Table 1, indicates the improvement of the instant name a few. 29 invention.

Run 00. 30% Cc. glacial Cc. water Ce. cone. K min- Percent DBT 0. H203 acetic acid H25 04 conversion 16. 6 10 90 0032 30 (120 min.) 16. 6 10 80 10 0189 68 80 min.) 16. 6 50 50 0255 80 60 min.) 16. 6 50 50 0202 82 (100 min.) 16. 6 50 49 1 296 98 min.) 16. 6 50 40 10 547 94 (5 min.) 16. 6 75 25 6941 90 (24 min.) 16. 6 100 346 90 7 min.) 16. 6 65 25 0866 90 (27 min.) 16. 6 65 10 100 90 (23 min.) 16. 6 75 25 Nil No conversion. 16. 6 50 50 0156 85 (120 min.)

The oxidizing medium of this invention comprises broadly an organic carboxylic acid, an oxy-mineral acid and an oxidizing agent.

The preferred oxdation medium is made up by adding 5 to 25 parts by volume of glacial acetic acid and to 40 parts of concentrated sulfuric acid by volume to 55 to 75 parts water to which 10 to parts .of 30% hydrogen peroxide has been added. From 0.5 to 5 volumes of the organic sulfur containing oil can be treated with 1 volume of the oxidation medium, For purposes of illustration, this invention will be discussed in terms of dibenzothiophene, however, it should be noted that any organic sulfur compound, as defined previously, may be treated in the same fashion.

The thiophene, or thiophene derivative, containing oil should be contacted with the oxidation medium for a period of 10 to 120 minutes, preferably 20 to 90 minutes, most preferably 30 to 60 minutes. Temperatures for the reaction may vary from 100 to 300 F., most preferably from 200 to 250 F. Pressures may vary from atmospheric to superatmospheric. At temperatures below 225 F., ambient pressures may be utilized. At temperatures of about 225 to 300 F. slightly superatmospheric pressures such as 5 to 50 p.s.i.g. may be utilized. The reaction time for the conversion of thiophene to the sulfone is usually about to 60 minutes, during this time the reaction is about 90 to 100% complete.

After the thiophene, or other organic sulfur compounds, have been converted to the sulfone, the ring of the sulfone may be opened by a variety of methods. The sulfone may be contacted with an alkali metal hydroxide as described in our copending application U.S. Ser. No. 434,643, or alternately the sulfone ring may be opened as suggested in U.S. Patent 3,163,593 by means of extreme heat. There is no intention to limit this application to either of those procedures and any method in which the sulfur is removed from the Sulfone is also applicable.

These data clearly show that the addition of sulfuric acid to the aqueous acetic acid-hydrogen peroxide oxidation medium greatly increases the rate of oxidation of dibenzothiophene despite the fact that sulfuric acid alone is a very poor oxidation catalyst, as shown in runs 11 and 12. The addition of 10 cc. of H to the mixture containing 10 cc. of acetic acid in run 2 brought about an increase in the oxidation rate comparable to increasing the amount of acetic acid to 50 cc. in run 4. The addition of 1 cc. of sulfuric acid in run 5 and 10 cc. of sulfuric acid in run 6 brought about very marked improvement. The addition of the 1 cc. of sulfuric acid, with 50 cc. of glacial acetic acid, resulted in a 98% conversion in 15 minutes. This rate is almost as good as that which was effected in run 8 with 100 cc. of glacial acetic acid and no H 50 Furthermore, the presence of only 10 cc. of sulfuric acid in run 6 brought about a result which was markedly superior to the use of 100 cc. of glacial acetic acid alone. Of more practical importance, the presence of 25 cc. of sulfuric acid and 10 cc. of acetic acid in run 9 brought about a rate that is comparable to that with 75 cc. of acetic acid and no H 80 in run 7. Also, 10 cc. of sulfuric acid and 25 cc. of acetic acid in run 10 was superior to the use of 75 cc. of acetic acid alone. Thus, it is possible to use relatively dilute acid media and still accomplish high rates of oxidation.

From the above it is apparent that this invention represents a significant improvement in the oxidation art. The addition of small quantities of sulfuric acid will greatly reduce the amount of acetic acid needed to maintain a high reaction rate and therefore permit the use of large amounts of water. Because acetic acid is more soluble in water than in oils, good recovery of the acetic acid will be possible. Furthermore, the use of dilute aqueous media reduces the possibility of emulsion formation, which would complicate acid recovery in a commercial process.

Since small amounts of sulfuric acid will greatly increase the oxidation rate, large volumes of water may be tolerated in the reaction mixture. The use of more dilute media will result in a considerable financial saving in process equipment and heat requirements. Most important of all, there is considerably less hazard in handling H when it is dilute rather than when it is concentrated. The sulfuric acid which is used in this reaction will also be dilute due to the large amounts of water which are present. It is well-known in the art that dilute sulfuric acid can be more readily recovered from a process than can be concentrated acid. Naturally, a great saving in the amount of glacial acetic acid needed will also ensue since sulfuric acid may be utilized as an effective substitute for large amounts of the acetic acid. Since a dilute acid medium is employed, separation of the hydrocarbon from the aqueous phase is also easier, since emulsions tend to form in the presence of concentrated acid solutions.

It is also within the scope to utilize halogenated acetic acids such as mono-, di-, and tri-chloroacetic acids, as catalysts along the H 0 In this instance, sulfuric acid will not be needed to speed up the reaction since it proceeds satisfactorily. This is further substantiation of the advantage of having strong acids in mixture with acetic acid in the oxidation medium, since the haloacetic acids have very much higher acid strengths than acetic acid itself. Furthermore, because the haloacetic acids are stronger acids and have higher polarities, they are much less oil soluble than acetic acid and would be more readily recovered. The advantages of using haloacetic acids are illustrated in the example below.

EXAMPLE II These experiments were conducted in the same manner as those discussed in the previous example except that the indicated haloacetic acid was used in place of the sulfuric-acetic acid mixtures. Again 5.14 gm. of dibenzothiophene and 5 cc. of n-hexadecane (chromatographic standard) were dissolved in 100 c. of white oil and heated to 212 F. This oil was then brought into reaction with oxidation mixtures made up of 0.435 mole of acid catalyst indicated below in 75 cc. of water to which 16.6 cc. of 30 weight percent H 0 was added. Again aliquot samples of the oil were withdrawn and analyzed by gas chromatography to determine the extent of dibenzothiophene disappearance. The reaction product was found to be dibenzothiophene sulfone.

These runs clearly show the advantage of using haloacetic acids in place of acetic acid. The haloacetic acids are 16 to 57 times as effective as an equimolar quantity of acetic acid. Also, the oxidation rates with these very dilute aqueous solutions are comparable to the use of 75 volume percent acetic acid. The acetic acid used in run 1 was 25 volume percent for comparison.

Although this invention has been described with some degree of particularly, it is intended only to be limited by the attached claims.

What is claimed is:

1. A process for oxidizing bivalent sulfur which is found in a residua, which comprises contacting in an aqueous media the said sulfur-containing residua with 2 to 10 mole of H 0 per mole of sulfur and 1 to 30 mole of haloacetic acid per liter of residua at reaction conditions whereby the said bivalent sulfur is oxidized.

2. Process of claim 1 wherein the said haloacetic acid is trichloroacetic acid.

References Cited UNITED STATES PATENTS 2,624,664 12/1953 Mowry et a1. 71-2.5 3,005,852 10/1961 Freyermuth et al. 260607 3,006,963 10/1961 Buc et a1 260-607 3,102,148 8/1963 Campbell et al. 260-607 3,163,593 12/1964 Webster et al 208-240 OTHER REFERENCES Kambara et al: Chemical Abstracts 46: 1795 (1952).

Fieser et al.: Advanced Organic Chemistry (Reinhold Pub. Co., New York), 1961, pages 360362.

Kalabina et al.: Chemical Abstracts 60: 16301631 1964).

HENRY R. JILES, Primary Examiner. C. M. SHURKO, Assistant Examiner.