US3446729A - Process for removing sulfur,oxygen and nitrogen compounds from petroleum distillates - Google Patents

Description

May 27, 1969 D PROCESS FOR M* JEWELL ETAL 3,446,729 REMOVING SULFUR, OXYGEN ANU NITROGEN COMPOUNDS FROM PETROLEUM Sheet DISTILLATES Filed Nov. L, 1966 TXI May 27, 1969 PROCESS OXYGEN AND NITROGEN COMPOUNDS FROM PETROLEUM Sheet DISTILLATES Filed Nov. 2, 1966 I @im I: T e

ww @N NN away/army United States Patent O U.S. Cl. 208-236 Claims ABSTRACT OF THE DISCLOSURE A process for removing heterocyclic nitrogen, oxygen and sulfur compounds from hydrocarbon distillates by contacting the distillate with solid calcium hexammine.

This invention relates to the removal of impurities from petroleum distillates. More specifically, this invention relates to the removal of sulfur, oxygen and nitrogen compounds from petroleum distillates.

Hydrocarbon fiuids, such as those obtained from crude petroleum oils and other sources, usually contain varying amounts of deleterious sulfur, oxygen and nitrogen cornpounds as impurities. The kinds and amounts of sulfur, oxygen and nitrogen compounds occurring in any hydrocarbon uid vary with the source material and with the method of manufacturing and processing said uid. The presence of such impurities in hydrocarbons is undesirable from the standpoint of the further use of the hydrocarbon as a fuel, lubricant or other use wherein a highly refined hydrocarbon is desired. Several prior art methods such as acid treating and catalytic hydrogenation have been devised to remove most of the impurities contained in hydrocarbon distillates. However, these prior art methods are not capable of removing certain sulfur, oxygen and nitrogen compounds without using extreme and expensive operating conditions and techniques. Among those compounds which are not normally removed from hydrocarbon fluids during standard treating procedures are heterocyclic sulfur, oxygen and nitrogen compounds containing from 3 to 6 members.

We have discovered an improved method of removing sulfur, oxygen and nitrogen compounds by treating petroleum distillates containing such compounds with calcium hexammine. We have found that by employing calcium hexammine it is possible to remove heretofore very unreactive heterocyclic sulfur, oxygen and nitrogen compounds as well as other sulfur, oxygen and nitrogen compounds present in petroleum distillates. Briefly, our invention comprises preparing a suspension of calcium hexammine in an inert, non-polar solvent and contacting the hydrocarbon to be treated with calcium hexammine reagent while the calcium hexammine is in the solid state. Thereafter, solid materials can be filtered off and the solvent material can be stripped from the purified hydrocarbon fraction. The calcium hexammine can be maintained in the solid state by proper selection of temperature and pressure, for instance a temperature at or below room temperature and at atmospheric pressure. In a preferred embodiment of our invention we employ added hydrogen with the calcium hexammine reagent thereby greatly increasing the amount of impurities removed by the calcium hexammine. The limitations in the amount of impurity removed are governed only by the stoichiometric amounts of calcium hexammine employed and the individual chemical characteristics of the impurity being attacked.

ln general, the feed stocks which can be employed with this invention are petroleum distillates including materials 3,446,729 Patented May 27, 1969 boiling in the gasoline range and above, i.e., C5 up to about 900 F. These stocks include furnace oils (400 F.- 650 F.) as well as gas oils (650 F.-900 F.). Preferred stocks are those which have been pretreated substantially to reduce the sulfur, oxygen and nitrogen content thereof, such as f or example, hydrogenated or hydrotined feed stock.

The calcium hexammine may be prepared by any standard procedure. We prefer to suspend discrete particles of calcium, such as calcium turnings or calcium powder, in an organic solvent medium, including, for example, an ethereal (diethylether) or pentane solvent, at a low temperature, advantageously about 0 to about 10 C., and then contact the calcium suspension with gaseous ammonia. The ammonia gas is contacted with the suspended calcium at such a rate that only a small amount of unreacted gas escapes from the reaction vessel. A occulent gray solid complex slowly forms. At a temperature of 0 C. a conversion of 20 grams of calcium per hour is easily obtained. The complex is stable at lower temperatures and can be stored at or below 0 C. for several days if necessary. However, the resulting solid calcium hexammine is relatively unstable at moderate to higher temperatures, i.e., those generally above room temperature. Experimentation has substantiated that the solid ammine will decompose by warming to room temperature according to the following empirical equation:

Therefore, we prefer to carry out all reactions between hydrocarbon distillates and calcium hexammine at or below room temperature, preferably about 0 C. When -contacting the calcium hexammine with the hydrocarbon distillates to be treated, a suspending agent is employed. Any non-polar compound can -be utilized, preferably a saturated hydrocarbon in the C5 to C7 range such as pentane. The calcium hexammine remains relatively stable in this media.

As stated previously, we have found that the addition of hydrogen to the reaction media increases the amount of impurities removed without the necessity of increasing the amount of calcium hexammine employed. While our invention can be used without added hydrogen, we have found it very desirable to add the hydrogen. Normally we employ from about 3 to 4 atmospheres of hydrogen during the course of treatment. Excess hydrogen has no deleterious effect on the process and there are no theoretic-al upper limits as to how much hydrogen may be used, the only upper limitations being those of practical consideration such as the type and cost of the equipment to be employed. The reaction vessel -may be pressured with hydrogen initially or after the reaction has commenced. Specific examples of the use of added hydrogen will be further described as our description lproceeds.

Our invention can be employed to remove a variety of sulfur, oxygen and nitrogen impurities. However, we have found calcium hexammine to be especially useful in the removal of heterocyclic compounds containing sulfur, oxygen and nitrogen. Furthermore, we have found that calicum hexammine reacts quantitatively with these cornpounds, thereby enabling one to conduct qualitative and quantitative studies on the impurities contained in the hydrocarbon being treated. While stoichiometric amounts `of calcium hexammine can be employed in laboratory procedures with our invention, it is preferable to employ excess calcium hexammine fwhen conducting large scale refinery runs. When employing a continuous treating process it is preferable to adjust the flow rates of the hydrocarbon and calcium hexammine stream so as to insure that there is a stroichiometric excess of calcium hexammine in contact with the quantity of hydrocarbon present in the reactor at any one time.

Among the most common heterocyclic compounds contained in petroleum distillates are thiophenes and furans and their hydrocarbon radical substituted derivatives. We have found that calcium hexammine reacts with these compounds to form thiophenols and phenols respectively. These compounds are adsorbed on the solids in the reaction mixture which is essentially calcium amide. As a result of this adsorption, separation of sulfur and oxygen containing reaction products from the petroleum fraction can be accomplished simply by filtration. These thioa phenols and phenols can be recovered for use or analysis by washing with hydrochloric acid. It is believed that the calcium hexammine cleaves the carbon-sulfur bonds and carbon-oxygen bonds to form thiophenol and phenol compounds respectively.

As stated previously, calcium hexammine is also particularly effective in removing sulfur, oxygen and nitrogen impurities which are resistive to standard refinery procedures. We have found our process particularly useful in removing impurities from stocks that have been subjected to catalytic hydrogenation to reduce sulfur, oxygen and nitrogen compounds so that they contain less than yabout 350 p.p.m. oxygen, less than about 2% by weight sulfur, and less than about 130 ppm. nitrogen. Among the nitrogen compounds generally resistive to standard renery procedures are carbazoles. We have found that calcium hexammine is effective in removing these compounds from petroleum distillates along with sulfur and oxygen compounds. However, we have found that carbon-nitrogen bonds are not cleaved as in carbon-sulfur and carbo-noxygen reductions. It is believed that this is due to the difference in the electronegativities of sulfur, oxygen and nitrogen, nitrogen being less electronegative than sulfur and oxygen. Instead of cleaving the carbon-nitrogen bond in carbazole, the calcium hexammine reduces carbaziole to the tetrahydro-stage. In addition, we have found that when the hetero-nitrogen atom in carbazole is substituted, more extensive reduction of the ring system is possible.

To determine more precisely the manner in which calciurn hexammine attacks various sulfur, oxygen and nitrogen impurities in petroleum stocks we conducted studies on some of the more resistant impurities found in hydrocarbon distillates. The following examples are illustrative of some of our investigations.

EXAMPLE I Dibenzothiophene is typical of an impurity which is resistant to many hydrogenolysis refinery techniques. Dibenzothiophene lwas contacted with a stoichiometric excess of calcium hexammine inthe presence of hydrogen under 3 to 4 atmospheres of pressure. Investigation of the products revealed that three different thiols were formed. A near quantitative conversion of more than 90% dibenzothiophene to the thiol stage was achieved. When the products were separated by gas chromatography three thiol peaks were observed. The ultraviolet spectra of these components in methanol is shown in FIGURE aromatic moiety is identical in all three thiols. When these spectra were compared with the specturn of o-'ethylthiophenol, the shift of the absorption maxima clearly indicated the absence of a saturated ortho-substituent. A low voltage mass spectrum lof the concentrate indicated m/e 188 and 190 as the major components of the reaction product, and these corresponded to a cyclohexenyland cyclohexadienyl-thiophenol structure. Since double bonds are not conjugated with the benzene ring, it was concluded that all three possible structures were present; these structures are also shown in FIGURE I. The presence 'of a cyclooleiin lwas also indicated by the presence of an infrared band at 1675 cml. The presence of the three thiols is indicative of the precursor.

EXAMPLE II This example is illustrative of the employment of our invention when dealing with unsym'metrical thiophenes I. The.

and the effect of substituents on the choice of bond cleavage. This type of study is important because of the nature of some of the more complex thiophenes contained in petroleum distillates such as thionaphtheno(3,2b)thianaphthene, alkyldib'enzothiophenes, and 2,2naphthyl benzo[b]thiophene.

2,2naphthylbenzo[b]thiophene was treated with calcium hexammine. The following equation illustrates the two possible cleavage paths for this compound:

It was observed that compound (I) was formed in approximately yield; 5% of the starting material did not react. Compound (I) was extracted from the reaction mixture with NaOH by virtue of its acidic thiol group; compound (II) is not sutiiciently acidic to react with NaOH. Identiiication of compound (I) was based on ultraviolet and infrared spectroscopy. Compound (II), if present would exhibit spectral patterns (ultraviolet and infrared) similar to that of the corresponding hydrocarbon i.e., phenethylnaphthalene; compound (I) is characteristically diferent from this hydrocarbon. FIGURE 1I compares the ultraviolet spectra of 2,2 naphthylbenzo[b] thiophene, 2-[2(2-naphthyl)ethyl]thiophenol (compound I) and Z-phenethylnapthalene. The predominance of compound (l) demonstrates that the stability of the intermediate is a determining factor. The carbon atom, designated by the letter X in the above equation, is saturated, followed by a rapid cleavage of this Cx-S bond yielding the resonance-stabilized thiophenolate anions. These anions are very stable in the presence of anhydrous calcium amide. This pattern of cleavage was illustrated further by the observation that phenyl methylsulde and benzo- [blthiophene were quantitatively converted to the corresponding thiophenols. From these studies and resulting data, it will be seen that calcium hexammine reduction favors the cleavage of an alkyl-sulfur bond rather than an aryl-sulfur bond when the two possibilities exist in the same molecule. Again, as in Example I, the presence of the thiol is indicative of the precursor.

In addition to studying individual sulfur impurities as set out above we conducted studies on the effect calcium hexammine had in reducing sulfur concentrates in gas oils which had previously been severely hydrogenated. The true complexity and variety of sulfur compounds present in such gas oils is at best a matter of speculation, although several individual families may be identified. This is illustrated by the following example.

EXAMPLE III An aromatic sulfur concentrate containing all sulfur compounds found in a hydrodesulfurized gas oil was subjected to treatment with calcium hexammine aud hydrogen. Since, as it was shown earlier, the symmetrical thiophene, dibenzothiophene, yields a mixture of three thiols, it is apparent, that unknown thiophenes could not be studied at the thiol stage. Therefore, a series of reactions had to be conducted which resulted in a concentrate of hydrocarbons attributable solely to a sulfur precursor.

Phenols Batm. H2 Thiophenols Raney Ni Et OH Sulfur Concentrate -I- Ca(NH3) 1. Partially satd hydrocarbons 2. Phenols NaOH Extractionl Vapor-phase Aromatic Hydrocarbons Partially satd dehydrogenation Hydrocarbons Since furan-type compounds are also cleaved during this reaction, substituted phenols are found with the thiols. However, the phenols are removed and concentrated with a NaOH extraction after desulfurizing the thiols with Raney nickel. The ammine and nickel reactions convert the sulfur compounds to a partially saturated stage; the corresponding aromatic hydrocarbon is formed by a vapor phase dehydrogenation over a platinum-nugel catalyst. The concentrate of aromatic hydrocarbons resulting from the inherent thiophene compounds were separated by gas-liquid chromatography. A total of 42 compounds were detected, nine of which were alkylbenzenes. Analysis of these hydrocarbons by low voltage mass spectrometry and ultraviolet spectroscopy revealed a predominance of alkylbiphenyls. The various biphenyl homologs were distributed as shown in Table I. Table II illustrates the major hydrocarbon types identified together with the most common thiophene precursor of each.

Table L-Distribution of biphenyls from desulfurized Table II.-Hydrocarbontypes from desulfurized Aromatic Hydrocarbon Thiophene ce ce While this technique cannot always provide an absolute identification of all these sulfur compounds, it provides an extremely accurate qualitative description of the type of compound present. It also provides a means of indirectly studying furans if desired. The presence of four ring thiophenes was confirmed during the study of the sulfur concentrates; these compounds are usually masked when a direct search is made for them. The reaction sequence outlined previously also provides excellent method for determining the structures of those sulfur compounds which can be isolated in a rather pure form.

EXAMPLE IV In addition to conducting specific experiments on individual thiophene compounds a study was conducted with respect to a reduction by calcium hexammine of a furan commonly found in petroleum distillates, i.e., dibenzofuran. The following is a description of the procedures employed and results obtained with this compound. A 0.4989 gram sample of recrystallized dibenzofuran was dissolved in 30 ml. of diethyl ether and the cooled solution was added to an ethereal suspension of calcium hexammine (prepared from seven grams of calcium turnings). The mixture Was maintained at 0 C. for one-half hour and was then agitated at room temperature for two and one-half hours under 45 p.s.i.g. hydrogen. The reaction mixture was ltered on a glass frit. The iiltrate was stripped of ether leaving .17 gram of a semicrystalline solid. The ultraviolet adsorption spectrum of this material was identical to that of dibenzoi'uran.

The calcium amide was decomposed with water and 1 to 1 hydrochloric acid. The resulting aqueous suspension was extracted with ether. The extract was water washed, dried, and stripped `of solvent leaving a viscous dark brown oil. This concentrate of reaction products was resolved into four components via gas chromatography on a fourfoot ethylene glycol succinate column. The fraction of the total peak area for each of the four peaks was as follows: peak (l), 56.4%, peak (2), 12.7%, peak (3), 14.6%, peak (4), 16.3%. Ultraviolet spectra of the lfour gas chromatographic cuts were obtained in neutral and caustic methanol. The spectrum of the initial cut (peak 1) corresponded closely to that of o-phenyl phenol while the spectrum of the cut corresponding to peak (4) was indicative of o-cyclohexyl phenol. Peaks (2) and (3) corresponded to a cyclohexadienyl and o-cyclohexenyl phenol, respectively.

On the basis of recovered starting material, it was concluded that 65.3% of the dibenzofuran was converted to reaction products. These products, as expected, arose from cleavage of a carbon-oxygen bond. This cleavage yielded a mixture of ortho-substituted phenols. The predominant product was phenyl phenol. The other reaction products are those in which the aromatic ring ortho to the hydroxy group is partially or totally saturated.

Since heterocyclic nitrogen compounds are found as impurities in petroleum distillates along with sulfur and oxygen compounds, studies were conducted on the behavior of nitrogen heterocyclics when treated with calcium hexammine. Generally, carbon-nitrogen bonds conjugated with aromatic nuclei are not cleaved because nitrogen is less electronegative than oxygen or sulfur. Our studies showed that quinoline and indole were inert to calcium hexammine. However, carbazole was reduced to the tetrahydro-stage. When carbazole was alkylated at the nine position (N-alkyl) a substantial amount of hexaand octahydro-derivatives were isolated. Due to the didiculty in preparing hexaand octahydro-derivatives, it may be seen that calcium hexammine has substantial value in organic synthesis of these compounds. It was further observed that when treating nitrogen compounds with calcium hexammine, the ammine and amide were completely saturated with polar nitrogen organic compound, whether reduction occurred or not. This illustrates the non-specicity of the reagent for any particular type of non-hydrocarbon when reducing complex mixtures.

The following specific examples will illustrate more fully the ability of calcium hexammine .to remove sulfur, oxygen and nitrogen impurities from pretreated hydrocarbon distillates.

EXAMPLE V Sixty grams of FCC furnace oil, pretreated by hydrogenation to remove substantial quantities of sulfur, oxygen and nitrogen compounds, which after pretreatment contained 330 p.p.m. oxygen and 44 p.p.m. sulfur were treated with calcium hexammine prepared from 8 grams of calcium turnings. The oil was dissolved in pentane and added to a pentane suspension of the hexammine. The mixture was maintained at C. for 30 minutes; it was then placed in a rocker type hydrogenation apparatus under 45 p.s.i.g. hydrogen and agitated at room temperature for 31/2 hours. The liquid phase of the reaction mixture was iiltered from the calcium amide which was decomposed and discarded. The pentane was stripped from the liquid phase leaving a pale yellow oil. Analysis of this liquid showed that it contained 150 p.p.m. oxygen and 2 p.p.m. sulfur. Thus 54.5% of the oxygen containing impurities and 95.4% of the sulfur impurities were removed by calcium hexammine treatment.

EXAMPLE VI Sixty grams of FCC furnace oil pretreated by hydrogenation to remove substantial quantities of sulfur, oxygen `and nitrogen compounds which after pretreatment contained 127 p.p.m. nitrogen and 0.145 weight percent sulfur, were treated with calcium hexammine prepared tfrom 8 grams of calcium turnings. The reaction conditions and reaction times were the same as those in Example V. The oil obtained after filtering off the calcium amide and stripping ott the pentane contained less than p.p.m. and 0.090 weight percent sulfur-a 96% reduction of nitrogen impurities and a 38% (by weight) of sulfur impurities. The failure to remove more sulfur impurities was due to a stoichiometric deliciency in the amount of calcium hexammine present.

EXAMPLE VII A synthetic blend containing nitrogen, sulfur and oxygen compounds which was typical of a pretreated gas oil was treated with calcium hexammine. The compounds used in making up the blend were representative of those commonly found in petroleum distillates in the gas oil range, i.e., the nitrogen compound being N-ethyl carbazole, the sulfur compound being dibenzothiophene and the oxygen compound being dibenzofuran. Quantities of these compounds were dissolved in n-decane to give a blend containing 85 p.p.m. nitrogen, 48 p.p.m. sulfur and 280 p.p.m.

oxygen. One hundred grams of 'the blend were added to a pentane suspension of calcium hexammine prepared from seven grams of calcium. The mixture was maintained at 0 C. for 30 minutes. It was then agitated at room temperature -for 31/2 hours at 45 p.s.i.g. hydrogen. The ltrate from the reaction mixture was stripped of pentane. Analysis of the filtrate showed a content of 28 p.p.m. nitrogen, 1 p.p.m. sulfur, and 150 p.p.m. oxygen. Thus 67.1% of nitrogen, 98.1% of sulfur and 46.4% of oxygen impurities were removed via calcium hexammine treatment.

We claim:

1. A process for removing heterocyclic nitrogen, oxygen and sulfur compounds from hydrocarbon distillates, comprising reacting said hydrocarbon distillates with calcium hexammine suspended in a non-polar solvent at a temperature up to about room temperature.

2. The process of claim 1 wherein the hydrocarbon distillate is one which has a boiling point range from about the boiling point of C5 hydrocarbons to about 900 F.

3. The process of claim 1 wherein the reaction is carried out at from about room temperature to about 10 C.

4. The process of claim 1 wherein the calcium hexammine is suspended in a saturated hydrocarbon containing 'from 5 to 7 carbon atoms.

5. The process of claim 1 wherein the reaction is carried out in the presence of hydrogen.

6. The process of claim 5 wherein hydrogen is maintained at from about 3 atmospheres to about 4 atmospheres of pressure.

7. The process of claim 1 wherein the hydrocarbon distillate has been pretreated to remove substantial amounts of impurities, which consist of the group of sulfur, oxygen and nitrogen compounds.

8. The process ot claim 1 wherein the nitrogen irnpurity consists of the group of carbazole and the hydrocarbon radical substituted derivatives thereof.

9. The process of claim l wherein the oxygen impurity consists of the group of furan and the hydrocarbon radical substituted derivatives thereof.

10. The process of claim 1 wherein the sulfur impurity consists of the group of thiophene and the hydrocarbon radical substituted derivatives thereof.

No references cited.

DELBERT E. GANTZ, Primary Examiner.

J. D. MYERS, Assistant Examiner.

U.S. Cl. X.R. 208-254 gjgggo UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIGN Patent No. 3,446,729 Dated M a 27, 1969 Inventor(s) Douglas M. Jewell and Joseph P. Yevich It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, Table II in the title, after "desulfurized" insertthiophenes-.

SIGNED AND SEALED SEP 3 0 195.9

(SEAL) Attest:

WILLIAM E. SGIUYLR, JR- Edwlrd M member J" Gomissioner of Patents Attesting Officer

Images