US2790751A - Purification of petroleum distillates - Google Patents

Description

F -atented Apr. 30, 1957 PURIFICATION OF PETROLEUM DISTILLATES Curtis F. Gerald, Lake Zurich, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware No Drawing. Application February 21, 1955, Serial No. 489,750

9 Claims. (Cl. 196-==23) This invention relates to the purification of petroleum distillates and more particularly to an improved method to remove nitrogen compounds from petroleum distillates.

Petroleum distillates contain sulfur compounds and nitrogen compounds. The nitrogen compounds generally are present in smaller concentrations than are the sulfur compounds. However, the nitrogen compounds, even though present in smaller concentrations, are objectionable for various reasons and must be removed from the petroleum distillate. For example, certain petroleum distillates may be marketed under specifications which recite a maximum nitrogen content. In other cases, petroleum distillates are subjected to conversion in the presence of catalysts which are detrimentally affected by nitrogen compounds as, for example, noble metal and particularly platinum catalysts, and the nitrogen content of the petroleum distillate must be reduced to below a certain maximum. Another example, nitrogen compounds adversely affect catalytic cracking and the removal of nitrogen compounds from the petroleum distillate charge is desirable.

While the sulfur compounds appear to be readily removed by conventional treatment, the nitrogen compounds are much more diflicult to remove. This, in turn, requires moredrastic treatment of the petroleum distillate to remove the nitrogen compounds and results in more rapid deactivation of the catalyst. The present invention provides a novel method of avoiding the rapid deactivation of the catalyst and thereby provides a more efiicient process for the removal of both nitrogenand sulfur compounds from petroleum distillates. In addition, any olefinic compounds present in the petroleum distillate are hydrogenated to the corresponding parafiinic hydrocarbons. Certain metallic impurities likewise are removed from the petroleum distillate in this process.

As hereinbefore set forth, the sulfur compounds gen erally are present in greater concentrations than are the nitrogen compounds. ,However, in many cases, the ratio of sulfur compounds to nitrogen compounds is not sufficient to provide the improved benefits. When treating such distillates improved nitrogen removal may be obtained by processing in accordance with the teachings of the present invention.

In one embodiment, the present invention relates to .an improvement in the removal of nitrogen from a petroleum distillate, containing nitrogen in a proportion to sulfur greater than hereinafter defined, by treating with hydrogen and a molybdenum containing catalyst at purification conditions. The improvement comprises adding sulfur to said distillate in an amount that the total sulfuris in a concentration at least equal to that expressed by the equation S=25.8N+0.07l, where S is sulfur in weight percent and N is nitrogen in weight percent, provided however that the total sulfur concentration is at least 0.2% by weight of said petroleum distillate.

As described herein, improved nitrogen removal is oblite, etc.

tained when the sulfur to nitrogen ratio is at least equal to the critical concentration defined by the equation. The exact reason for the improved results has not been definitely established, but is believed to be related to the formation and/ or maintenance of one or more particular sulfided forms of the catalyst. Regardless of the exact explanation, it appears necessary that at least a certain concentration of sulfur is present and that such concentration of sulfur appears related to the nitrogen content of the petroleum distillate.

The novel features of the present invention may be utilized for the purification of any petroleum distillate containing nitrogen compounds or nitrogen and sulfur compounds in a proportion greater than herein defined. Thus, the present invention may be utilized for the purification of gasoline, naphtha, aromatic solvent, kerosene, diesel fuel, gas oil, fuel oil, transformer oil, lubricating oil, etc., or mixtures thereof. While the invention is particularly applicable to the treatment of petroleum distillates, it is understood that it may be utilized with other organic compounds containing the impurities as aforesaid and thus may be utilized for the treatment of liquids comprising alcohols, aldehydes, ketones, acids, etc.

The catalyst for use in the present invention contains molybdenum. Generally the molybdenum will be associated with'a carrier or supporting material, which material may be catalytically inert or may be catalytically inert or may be catalytically active, particularly in association with the molybdenum compound. Alumina is particularly preferred for this purpose. Other supporting or carrying materials include silica, zirconia, magnesia, zinc oxide, etc., or composites such as silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-magnesia, silica-alumina-Zirconia, silica-alumina-thoria, etc., which may be synthetically prepared and naturally occurring.

Generally the catalyst also will contain a compound of the iron group metals including cobalt, iron and nickel. Cobalt appears to be particularly preferred.

The composited catalyst may be prepared in any suitable manner including coprecipitation, separate precipita tion or successive precipitation methods. In the coprecipitation method, suitable compounds of aluminum, molybdenum and cobalt are commingled, and the oxides thereof precipitated by the addition of a suitable precipitating agent, or the oxides are developed by heating, depending upon the particular compounds of metals used in preparing the catalyst.

In separate precipitation methods, each component is precipitated separately and then commingled. In this method, the alumina may be synthetically prepared or it may comprise suitable naturally occurring aluminous materials including bauxite, diaspore, gibbsite, hydrargil- Usually the naturally occurring materials are acid or otherwise treated in order to activate the same.

In successive precipitation methods, the oxides of one or more of the components are precipitated, and suitable compounds of the other component or components are cornmingled therewith and the oxide or oxides precipitated in the presence thereof. Here again it is understood that suitable naturally occurring alumina may be employed, again usually with acid or other treatment prior to use in the preparation of the catalyst.

In the successive or separate precipitation methods, it is understood that the oxides may be developed by heating, depending upon the particular metal compounds used in preparing the catalyst, and also that, in these methods, washing and/or drying between steps may be employed.

When synthetically prepared alumina is employed, it generally is prepared by commingling a suitable basic compound, including ammonium hydroxide, ammonium carbonate, etc., with an acidic compound of aluminum, including the chloride, bromide, iodide, fluoride, sulfate,

phosphate, nitrate, acetate, etc., or it may be prepared by the addition of a suitable acidic compound, including hydrogen chloride, sulfuric acid, phosphoric acid, etc., to an alkaline compound of aluminum as, for example, sodium aluminate, etc. ln other than coprecipitation methods, the resultant hydroxide of aluminum may be composited in the wet state with the other components or it may be washed to remove soluble impurities and/or dried at a temperature of from about 200- to about 600 F. for a period of l to 24 hours or more and the composited with the other components.

The aluminum hydroxide or aluminamay be composited with the other components of the catalyst in any suitable manner andeither separately or together. When separate compositing is employed, the intermediate composite may be Washed and/or. dried at intervening stages. In some cases, it may bedcsirable also to calcine at such intervening stages; that is, thealumina or the composition of alumina and one component is calcined prior to compositing with the remaining components. The calcining generally is effected at a temperature of from about 600 to 1600 F. or more for a period of from about 1 to 12 hours or more.

Any suitable compound of molybdenum may be employed and thus may comprise molybdic acid, molybdenum trioxide, molybdenum tetrabromide, molybdenum oxydibromide, molybdenum tetrachloride, molybdenum oxydichloride, molybdenum oxypentachloride, molybdenum oxytctrafluoridc, etc. Similarly any suitablecompound of cobalt may be employed, including cobalt nitrate hexahydrate, cobalt ammonium nitrate, cobalt ammonium chloride, cobalt ammonium sulfate, cobalt bromide, cobalt bromate, cobalt chloride, cobaltchlorate, cobalt fluoride, cobalt fluorate, etc.

In a preferred method, either syntheticallyprepared or naturally occurring alumina, preferably after calcining, is composited with molybdic acid, the resultant composite dried and calcined, after which cobalt nitrate hexahydrate is commingled therewith, and the final composite then is dried and calcined. It is understood that the drying and calcining will be effected at the conditions hereinbefore set forth. In another method, the cobalt may be composited with the alumina and then the molybdenum composited therewith. In still another method, an acidic impregnating solution of molybdic acid and cobalt nitrate is formed and this solution then is utilized to impregnate alumina. It is understood that the impregnation may be effected separately by utilizing different acidic solutions of molybdic acid and of cobalt nitrate. When desired, the acidic solutions may contain nitric acid. hydrochloric acid. sulfuric acid, phosphoric acid, oxalic acid, etc., or mixtures thereof. While acidic impregnation is preferred, it is understood that basic impregnation, that is utilizing basic solutions or introducing suitable basic reagents, either into the solution or onto the support, may be employed, the basic reagent includ ing, for example, ammoniumhydroxide, ammonium carbonate. alkyl amines, basic heterocyclic nitrogen compounds, etc.

While the preferred catalyst comprises a composite of alumina-molybdenum compound-cobalt compound, it is understood that other supporting or carrying materials may be employed as hereinbefore set forth, and also that the iron and nickel compounds may be utilized in place of or in addition to the cobalt compoundbut not necessarily with equivalent results. The iron and nickel compounds may be composited with the catalyst in substantially the same manner as hereinbefore set forth for the cobalt compound.

The components of the catalyst may be utilized in any suitable concentration. In general, the cobalt or other iron group metal compound and molybdenum compound will range from about 1% to 25% by Weight each of final catalyst. Preferred catalysts contain the cobalt in 'a concentration of from about 1% to about 210% :and the inum catalyst.

4 molybdenum in a concentration of from about 2% to about 20% by weight of final catalyst, the remainder comprising alumina.

Regardless of the specific method in which the catalyst is prepared, the final composite generally is calcined at a temperature of from about 600 to about 1600 F. for a period of about 1 to 12 hours or more and usually in the presence of air, oxygen or other oxidizing-medium. In this embodiment, the preferred catalyst comprises almarina-molybdenum oxide-cobalt oxide.

In another embodiment, the catalyst comprises alumina-molybdenum sulfide-cobalt sulfide, and this catalyst is readily obtained by sulfiding the oxide form of the catalyst. The sulfirlation may be effected by passing hydrogen sulfide or other suitable sulfur compound through the catalyst, preferably at a temperature of from about 400 to about l000 F., until sulfidation is complete, which isreadily determined when absorption of hydrogen sulfide or other sulfur compound ceases. In another embodiment, the oxide catalyst may be utilized for the purification of sulfur containing organic compounds and the sulfidation is effected in situ.

While the alumina-molybdenum compound-cobalt compound catalyst is particularly preferred, it is under stood that, in some cases, the catalyst may contain additional components. For example, halogen may be included in the catalyst. The halogen may comprise fluorine, chlorine, iodine and/or bromine, and generally will be present in the catalyst in a combined form. The halogen may be introduced into the catalyst separately or in commingled state with one or more of the other components as, for example, by utilizing a hydrogen fluoride or hydrogen chloride solution of molybdic acid and cobalt nitrate as the impregnating solution. The halogen may be employed in a concentration of from about 0.2% to 15% or more by Weight of the final catalyst.

The purification of petroleum distillates in the presence of a catalyst containing molybdenum-compound, and particularly alumina-molybdenum oxide-cobalt oxide, is effected at a temperature of from about 400 to 800-850 F. and a pressure of from atmospheric to 2000'pounds or more, particularly in the presence of hydrogen, the hydrogen being utilized in a molar ratio to hydrocarbon of from about 0.2:] to about 20:1.

As an essential feature of the present invention, when the petroleum distillate contains nitrogen compounds and substantially no sulfur compounds or both of these types of compounds but in a ratio of sulfur compounds to nitrogen compounds less then that defined by the equation hereinbefore set forth, sulfur is added to the reaction in order that the concentration of sulfur is at least equal to that defined by the equation. duced in any suitable form including free sulfur,hydrogen sulfide, carbon disulfide,thiophene, mercaptan, etc., and conveniently is comrningled with the petroleum distillate prior to heating and introduced along with the distillate into the reaction zone, or it may be supplied directly to the reaction zone in any suitable manner. As hereinbefore set forth, it is believed that the activity of the catalyst is dependent upon a sulfided form and, therefore, requires the presence of a critical amount of sulfur in order to maintain the desired activity. This critical concentration is related to the nitrogen charged to the reaction zone and also must be above a critical minimtun. The concentration of sulfur with relation to nitrogen is expressed by the "equation S=25.8N+0.071, and the critical minimum is maintained by providing at least 0.2% by weight of sulfur based on the petroleum distillate. The sulfur-is calculated as'free sulfur-even though it may be introducedin a combined form.

As hereinbefore set forth, the purification of the petroleum distillate is particularlydesirable when the pe troleum distillate subsequently is subjected to conversion in the presence of a noble metal and particularly a plat- In this embodiment, the present inven- The sulfur may be introtion may comprise a combination process wherein the purification is efiected in the manner hereinbefore set forth and the thus purified gasoline or naphtha is subjected to reforming in the presence of a reforming catalyst, the reforming being defined as a treatment of gasoline or naphtha to improve the antiknock characteristics thereof. In the reforming reaction, hydrogen is produced and the hydrogen thus produced is utilized in part in the purification treatment and in part in the reforming step. A particularly suitable catalyst for the reforming reaction comprises .alumina-platinum-combined halogen. Other catalysts include silica-alumina-platinum, silica-magnesia-platinum, silica-zirconia-platinum, etc., which catalyst may contain halogen when desired. The platinum generally is utilized in a concentration of from about 0.05 to about 1% by weight of the final catalyst and the halogen, when employed, is utilized in a concentration of from about 0.1 to about 5-10% by weight of the catalyst. The reforming is effected at a temperature of from about 800 to about 1100 F. and a pressure of from about 100 to 2000 pounds or more, in the presence of hydrogen in a mol ratio to hydrocarbon of from about 0.2:1 to :1 or more.

Purification of the petroleum distillate or other organic compound with added sulfur may be effected in any suitable manner, including a fixed bed type of operation in which the charge is passed at the desired temperature and pressure through the catalyst, in either upward or downward flow, and the efiiuent therefrom is fractionated or otherwise treated to recover the desired product. When the process is efiected in the presence of hydrogen, it may be preferred to recycle at least a portion of the excess hydrogen for further use in the process. In place of the fixed bed operation, other operations may be used, including the fluidized type in which the charge and catalyst are maintained in turbulent fiow within the reaction zone, the slurry or suspensoid type of operation in which the catalyst and charge are transported as a slurry into the reaction zone, the moving bed type of process in which the catalyst moves as a mass either concurrently or countercurrently to the charge, etc.

Although the catalyst of the present invention will have a long life, it may require regeneration after a long period of service, and the regeneration may be effected in any suitable manner. In one method, regeneration of the catalyst may be effected by burning carbonaceous deposits with air or other oxygen-containing gases. In some cases, regeneration of the catalyst may be effected by treatment at high temperatures with hydrogen or other gases and, in other cases, both of these methods may be employed.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

In this example a selected charge stock was utilized in order to specifically determine the effect of nitrogen and sulfur compounds therein. The charge comprised solvent naphtha to which was added 956 parts per million of nitrogen as quinoline and 0.2% by weight of sulfur as thiophene. The charge had an API gravity at 60 F. of 53.6. The catalyst comprised alumina, about 7% by weight of molybdenum sulfide and about 3% by weight of cobalt sulfide. The charge was subjected to purification at a temperature of about 700 F. and a pressure of about 800 pounds per square inch in the presence of about 3000 cubic feet of hydrogen per barrel of petroleum distillate.

In the run described above, the product contained about 32 parts per million of basic nitrogen. It will be noted that the nitrogen content of the product is too high for many purposes. Also, it will be noted that the amount of sulfur in relation to the nitrogen is below that required by the equation. According to the equation S=25.8N+0.071, the minimum concentration of sul- 6 fur should be about 0.32. When sulfur is added to the charge to give a concentration of at least about 0.32% sulfur and the charge subjected to purification as aforesaid, the product will have a basic nitrogen content of below about 5 parts per million.

i claim as my invention.

1. In the removal of nitrogen from a petroleum distillate containing nitrogen in a proportion to sulfur greater that hereinafter defined, by treatment at purification conditions in the presence of a molybdenum containing catalyst, the improvement which comprises adding sulfur to said distillate in an amount such that the total sulfur is in concentration at least equal to that expressed by the equation S=25.8N+0.071, where S is sulfur in weight percent and N is nitrogen in weight percent, provided, however, that the total sulfur concentration is at least 0.2% by Weight of said petroleum distillate.

2. In the removal of nitrogen from a petroleum dis tillate containing nitrogen in a proportion to sulfur greater that hereinafter defined, by treating with hydrogen and a catalyst comprising alumina and molybdenum compound at purification conditions, the improvement which comprises adding sulfur to said distillate in an amount such that the total sulfur is in a concentration at least equal to that expressed by the equation S=25.8N-|-0.071, where S is sulfur in weight percent and N is nitrogen in weight percent, provided, however, that the total sulfur concentration is at least 0.2% by weight of said petroleum distillate.

3. In the removal of nitrogen from a petroleum distillate containing nitrogen in a proportion to sulfur greater than hereinafter defined, by treatment with hydrogen and a catalyst comprising alumina-molybdenum sulfide-cobalt sulfide at a temperature of from about 400 to about 850 F. and a pressure of from about atmospheric to 2000 pounds, the improvement which comprises adding sulfur to said distillate in an amount such that the total sulfur is in a concentration at least equal to that expressed by the equation S=25.8N+0.07l, where S is sulfur in weight percent and N is nitrogen in weight percent, provided, however, that the total sulfur concentration is at least 0.2% by weight of said petroleum distillate,

4. The process of claim 3 further characterized in that the sulfur is added as free sulfur.

5. The process of claim 3 further characterized in that the sulfur is added as hydrogen sulfide.

6. The process of claim 3 further characterized in that the sulfur is added as carbon disulfide.

7. The process of claim 3 further characterized in that the sulfur is added as thiophene.

8. The process of claim 3 further characterized in that the sulfur is added as mercaptan.

9. In the removal of nitrogen from naphtha containing nitrogen in a proportion to sulfur greater than hereinafter defined, by treatment with hydrogen and a catalyst comprising alumina-molybdenum sulfide-cobalt sulfide at a temperature of from about 400 to about 800 F. and a pressure of from about atmospheric to 2000 pounds, the improvement which comprises adding sulfur to said distillate in an amount such that the total sulfur is in a concentration at least equal to that expressed by the equation S=25.8N+0.071, where S is sulfur in weigh percent and N is nitrogen in weight percent, provided, however, that the total sulfur concentration is at least 0.2% by Weight of said naphtha.

References Cited in the file of this patent UNITED STATES PATENTS 1,852,988 Varga Apr. 5, 1932 2,392,579 Cole Jan. 8, 1946 2,393,288 Byrns Ian. 22, 1946 2,604,438 Bannerot July 22, 1952 2,692,226 Smith Oct. 19, 1954

Claims (1)

1. IN THE REMOVAL OF NITROGEN FROM A PETROLEUM DISTILLATE CONTAINING NITROGEN IN A PROPORTION TO SULFUR GREATER THAT HEREINAFTER DEFINED, BY TREATMENT AT PURIFICATION CONDITIONS IN THE PRESENCE OF A MOLYBDENUM CONTAINING CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING SULFUR TO SAID DISTILLATE IN AN AMOUNT SUCH THAT THE TOTAL SULFUR IS IN CONCENTRATION AT LEAST EQUAL TO THAT EXPRESSED BY THE EQUATION S=25.8N+0.071, WHERE S IS SULFUR IN WEIGHT PERCENT AND N IS NITROGEN IN WEIGHT PERCENT PROVIDED, HOWEVER, THAT THE TOTAL SULFUR CONCENTRATION IS AT LEAST 0.2% BY WEIGHT OF SAID PETROLEUM DISTILLATE.