US3474029A - Catalytic conversion of asphaltene-containing hydrocarbon charge stocks - Google Patents

Description

United States Patent O f US. Cl. 208-251 Claims ABSTRACT OF THE DISCLOSURE The conversion of hydrocarbonaceous charge stocks containing asphaltenes is effected in a fixed-bed catalytic reaction zone. Stable catalyst activity is maintained by adding a thio-ester of an acid of a metal from Groups V-B and VIB to the charge stock as the activity of the catalyst declines. Catalyst regeneration is accomplished by burning the coke deposits which serves also to convert the V-B and VIB metal sulfides (resulting from the added thio-esters), to the oxides. The oxides are converted directly to oil-soluble thio-esters by treatment with tertiary mercaptans, or they are first converted to the acid chloride, which, in turn is reacted with a mercaptan, to form the thio-ester.

RELATED APPLICATIONS The present application is a continuation-in-part of my copending application, Ser. No. 541,122, filed on Apr. 8, 1966 now abandoned.

APPLICABILITY OF INVENTION The invention herein described is adaptable to a process for the conversion of heavy hydrocarbon fractions and/ or distillates containing asphaltenes, and contaminated by high-boiling sulfurous and nitrogenous compounds.

Petroleum crude oils, and topped or reduced crude oils, as well as other heavy hydrocarbon fractions and/or distillates, including black oils, heavy cycle stocks, visbreaker liquid efliuent, atmospheric and vacuum crude tower bottoms product, shale oils, coal tars, tar sand oils, etc., are contaminated by the inclusion of significant quantities of various non-metallic and metallic impurities. Amon gthe non-metallic impurities are nitrogen, sulfur and oxygen which exist as heteroatomic compounds. Both nitrogenous and sulfurous compounds are objectionable since the combustion of fuels containing these impurities results in the release of nitrogen and sulfur oxides which are noxious, corrosive, and present a serious problem with respect to pollution of the atmosphere. With respect to motor fuels, sulfur is particularly objectionable because of odor, gum and varnish formation upon storage, and significantly decreased tetraethyl lead susceptibility.

In addition to the foregoing contaminating influences, heavy hydrocarbonaceous material contains high molecular weight asphaltenic compounds. These are non-distillable coke precursors which contain sulfur, nitrogen, oxygen and various metallic components. Of the metallic contaminants, those containing nickel and vanadium are most common. Although the metallic contaminants may exist within the hydrocarbonaceous material in a variety of forms, they are generally present as complexed organometallic compounds of relatively high molecular weight, for example as metallic porphyrins and various derivatives thereof. With respect to a process for hydrorefining, treating or hydrogenative cracking of hydrocarbon fractions, the presence of large quantities of asphaltenic ma- Patented Oct. 21, 1969 ICC terial and organo metallic compounds interferes considerably with the capability of the catalyst to effect the destructive removal of nitrogenous, sulfurous and oxygenated compounds, which function is normally the easiest for the catalytic composite to perform to an acceptable degree.

A wide variety of heavy hydrocarbon fractions and/ or distillates may be converted and effectively decontaminated through the utilization of the present invention. Suitable charge stocks include full boiling range crude oils, topped or reduced crude oils, visbreaker bottoms product, atmospheric and vacuum tower bottoms, heavy vacuum gas oils, shale oils, coal tars and oils, tar sand oils, etc. Exemplary of these charge stocks is a Wyoming sour crude oil having a gravity of 232 API at 60 F., contaminated by 2.8% by weight of sulfur, 2700 p.p.m. of metallic complexes, computed as elemental metals, and containing a high boiling, pentane-insoluble asphaltenic fraction in an amount of about 8.4% by weight. A more difficult charge stock to convert into useful liquid hydrocarbons, is a crude tower bottoms product, having a gravity, API at 60 F., of 14.3, and contaminated by 3.0% by weight of sulfur, 3830 p.p.m. of total nitrogen, p.p.m. of total metals and about 10.93% by weight of asphaltenic compounds. Similarly, an atmospheric tower bottoms product, having a gravity of 7.0 API at 60 F., is contaminated by about 6,060 p.p.m. of total nitrogen, 4.05% by Weight of sulfur, more than 450 p.p.m. of total metals, and contains an asphaltenic fraction in an amount of 24.0% by weight.

PRIOR ART Heretofore, in the field of catalytic processing of heavy hydrocarbonoceous material, two principal approaches have been advanced: liquid-phase hydrogenation and vapor-phase hydrocracking. In the former type of process, liquid phase oil is passed upfiow or downflow, in admixture with hydrogen, into a fixed-fluidized catalyst bed, or slurry of sub-divided catalyst. Although perhaps effective in converting at least a portion of the oil-soluble organometallic complexes, this type process is relatively ineffective with respect to asphaltics which are dispersed within the charge, with the consequence that the probability of effecting simultaneous contact between the catalyst particle, the hydrogen necessary for prevention of coke formation and the asphaltic molecule is remote. Furthermore, the efficiency of hydrogen to oil contact obtainable by bubbling hydrogen through an extensive liquid body is relatively low. Some processes have been de scribed which rely upon thermal cracking in the presence of hydrogen; in this type of process, any catalyst present rapidly succumbs to deactivation as a result of the deposition of coke thereon, and an attendant high capacity regeneration system is required in order to implement the process on a continuous basis. Furthermore, such processes are unable to effect the conversion of asphaltic material.

OBJECTS A-ND EMBODIMENTS The principal object of the present invention is to provide an economically feasible fixed-bed catalytic process for effecting the conversion of asphaltene-containing hydrocarbon charge stocks. A corollary objective is to maximize the production of lower-boiling liquid products substantially reduced in the concentration of contaminating influences.

Another object is to maintain a stable level of catalyst activity while processing asphaltic, contaminated hydrocarbon charge stocks.

A specific object is to afford a regenerative, fixed-bed catalytic process for the conversion of contaminated, asphaltene-containing hydrocarbonaceous material.

Therefore, in one embodiment, my invention relates to an improvement in a process for converting a contaminated, asphaltene-containing hydrocarbon charge stock in contact with a solid catalytic composite, in which process the catalytic composite experiences a decline in activity as a result of the deposition thereon of coke, which improvement comprises adding a thio-ester of a metal selected from the metals of Groups V-B and VIB to said charge stock, continuing contacting said charge stock with said catalytic composite having increased activity and controlling the addition of said thio-ester to maintain the increased activity.

A more limited embodiment provides a regenerative, fixed-bed catalytic process for the conversion of a contaminated, asphaltene-containing hydrocarbon charge stock, which process comprises the steps of: (a) contacting said charge stock and hydrogen in a reaction zone at conversion conditions including a temperature above about 500 F. and a pressure above about 1000 p.s.i.g., in contact with a solid catalytic composite; (b) as said catalytic composite experiences a decline in activity as a result of the deposition of coke thereon, commencing the addition of a thio-ester, of a metal from Groups V-B and VI-B, to said charge stock; (c) continuing the addition of said thio-ester to maintain said catalytic composite in an activity-stable state through the deposition thereon of the metal component of said thio-ester; (d) as said catalytic composite experiences continuing decline in activity, during the period when said thio-ester is added to said charge stock and when increasing the concentration of said thio-ester in said charge stock has no effect on said activity decline, discontinuing the flow of said charge stock, thio-ester and hydrogen; (e) purging said reaction zone with an inert gas to remove traces of hydrogen and hydrocarbons; (f) introducing an oxygencontaining gas stream into said reaction zone at a temperature sufficient to burn the coke from said catalytic composite and to convert the deposited metals from said thio-ester to the oxides thereof; (g) dissolving said metal oxides in a liquid tertiary mercaptan to form the thioester of said metals and withdrawing said thio-esters from said reaction zone; and (h) reintroducing said charge stock and hydrogen at the aforesaid conversion conditions.

Other embodiments of my invention involve operating conditions, preferably catalytic components for use in the fixed-bed catalyst system, preferred thioesters, tertiary mercaptans, etc. These will hereafter be described in greater detail.

SUMMARY OF THE INVENTION From the foregoing embodiments, it will be noted that the process of the present invention makes use of a particular additive, preferably employed in solution with the charge stock. The additive can be characterized as comprising at least one thio-ester of the V-B and VT-B metals, for example, vanadium thio-methylate, in an amount of from about 0.5% to about 5.0% by Weight, calculated as elemental vanadium, dispersed within the hydrocarbonaceous charge stock. In addition to vanadium thio-methylate, suitable thio-esters include vanadium thio-ethylate, molybdenum thio-tert-amylate, tungsten thio-ethylate, chromium thio-propylate, tantalum thiotert-butylate, niobium thio-tert-decylate, mixtures thereof, etc. Thio-esters for use in the present process, can be represented by the following typical formulae: VO(SR) Mo(SR) MoO-(SR) W(SR) MoO (SR) TaO(SR) In these formulae, R represents an alkyl group containing one to about 18 carbon atoms per molecule, and preferably from four to twelve carbon atoms. The particular thio-ester employed will depend to a large extent upon the precise physical and/or chemical characteristics of the hydrocarbon charge stock. However, it is generally preferable to utilize those thio-esters which are hydrocarbon-soluble.

The thio-ester may be prepared in any convenient, suitable manner, and it is understood that a particular preparation scheme is not limiting upon the broad scope herein defined. One especially convenient method in volves heating the corresponding chloride in the desired mercaptan. For example, when preparing vanadium thioethylate, the acid chloride of vanadium, VOCl is reacted with ethyl mercaptan under pressure, and at a tem perature of about C. The involved reaction proceeds as follows:

Another method involves refluxing a tertiary mercaptan with the oxide of the desired metal. Thus, when the metal is molybdenum,

With a thio-ester of vanadium, the process has additional economic advantages attractive to petroleum refining operations. Since the heavy asphaltenic charge stocks contain considerable quantities of organo-vanadium complexes, catalyst replacement costs are minimal. The vanadium is recovered in the form of vanadium pentoxide which is then reacted with tertiary butyl mercaptan according to the following:

In view of the fact that the tertiary butyl mercaptan is readily available in the refinery, economic considerations are further enhanced.

Fixed-bed catalytic processes for effecting the conversion and decontamination of the charge stocks herein before described, are well-known and thoroughly described in the prior art. Thus, there is no need to detail the process herein; however, for the sake of completeness. a typical process will be briefly described. It is understood that such a process forms no essential part of my invention, the latter being in effect an improvement to be made an integral part of the former. In general, conversion conditions include temperatures above about 650 F., with an upper limit of about 850 F., measured at the inlet to the catalyst bed. Since the bulk of the reactions are exothermic, the reaction zone efiluent will be at a higher temperature. In order that catalyst stability be facilitated, it is preferred to control the inlet temperature such that the effluent temperature does not exceed about 950 F. Hydrogen is admixed with the charge stock, by means of compressive recycle, in an amount of about 3,000 to about 50,000 s.c.f./bbl., at the selected operating pressure, and preferably in an amount of from about 3000 to about 10,000 s.c.f./bbl. The operating pressure will be greater than 1000 p.s.i.g., and generally in the range of about 1500 p.s.i.g., to about 3000 p.s.i.g. The charge stock passes through the catalyst at a liquid hourly space velocity (defined as volumes of liquid hydrocarbon charge per hour, measured at 60 F., per volume of catalyst disposed in the reaction zone), of from about 0.25 to about 2.0. When conducted as a continuous process, it is preferred to introduce the hydrocarbon/hydrogen mixture into the reaction vessel in such a manner that the same passes through in downward flow. The internals of the vessel may be constructed in any suitable manner capable of providing the required intimate contact between the liquid charge stock, the gaseous mixture and the catalyst. In some instances it may be desirable to facilitate distribution of the charge by means of perforated trays or special mechanical means. I

As hereinbefore set forth, hydrogen is employed in admixture with the charge stock, preferably in an amount of from about 3000 to about 10,000 s.c.f./bbl. The hydrogen-containing gas stream, sometimes designated as recycle hydrogen, since it is conveniently recycled externally of the reaction zone, fulfills a number of various functions: it serves as a hydrogenating agent, a heat carrier, and particularly a means for stripping converted material from the catalytic composite, thereby creating more available catalytically active sites for the incoming, unconverted hydrocarbon charge stock. Since some hydrogenation will be effected, there will be a net consumption of hydrogen; to supplement this, hydrogen is added to the system from any suitable external source.

The catalytic composite disposed Within the reaction zone can be characterized as comprising a metallic component having hydrogenation activity, which component is composited with a refractory inorganic oxide carrier material is not considered essential to the present process, composition and method of manufacturing the carrier material is not considered essential to the present process, although a siliceous carrier, such as 88.0% alumina and 12.0% silica, or 63.0% alumina and 37.0% silica, is generally preferred. Suitable metallic components having hydrogenation activity are those selected from the group consisting of the metals of Groups VB, VI-B and VIII of the Periodic Table, as indicated in the Periodic Chart of the Elements, Fisher Scientific Company (1953). Thus,

the catalytic composite may comprise one or more metallic components from the group of molybdenum, tungsten, chromium, iron, cobalt, nickel, vanadium, tantalum, niobium, and mixtures of two or more. The concentration of the catalytically active metallic componet, or components, is primarily dependent upon the particular metal as well as the characteristics of the charge stock. For example, the metallic components of Groups V-B and VI-B are preferably present in an amount within the range of about 1.0% to about 20.0% by weight, the iron-group metals in an amount within the range of about 0.2% to about 10.0% by weight, all of which are calculated as if the components existed within the finished composite as the elemental metal.

The refractory inorganic oxide carrier material may comprise alumina, silica, zirconia, magnesia, titania,

riences a decline in activity. Catalyst deactivation results 0 primarily from the deposition of the high molecular weight metallic complexes and coke. As the coke, or carbonaceous material is formed on the catalyst, the catalytically active sites become shielded from the material being processed, with the result that the catalyst loses activity and cannot function in the desired acceptable fashion. Although at least a portion of the activity can be recovered by way of increasing the severity of operation e.g. decreasing space velocity and/ or increasing temperaturethe increased severity in turn tends to effect an increase in the rate of activity decline. Eventually, the operation must be terminated and the catalyst regenerated.

Through the use of my invention, the on-stream period between required regenerations is considerably increased, and the economic aspects involved with down time more than justify the relatively minor increase in operating expense attributable to the use of the thio-ester additive. At such time as inspections indicate a degree of activity decline such that specifications on the product cannot be economically met, a thio-ester, preferably as a hydrocarbon solution, is added to the charge stock, thereby causing an increase in catalyst activity. Through the use of a thio-ester, fresh metallic components are continuously deposited (probably as metallic sulfides) on the catalytic surfaces, whether these are covered with coke deposits. The quantity of the thio-ester added, usually in the range of from 0.5% to about 5.0% by weight, at any given time is controlled to maintain the catalytic composite in an activity-stable state. That is, the various product analyses-i.e. residual nitrogencan easily be utilized in determining either an increase or decrease in the rate of thio-ester addition.

While the metal oxides resulting from the carbon bumoff may be removed by various other means, the direct use of a tertiary mercaptan is especially preferred. Thus, for example, ammonium salt solutions of the metal oxides can be formed through the use of an ammonium carbonate solution. The salts are evaporated from the catalytic composite, calcined to the metal oxides which, in turn, are easily converted to the acid chlorides. These are then reacted with the mercaptans in accordance with the foregoing Equation 1 to form the thio-esters. It is evident that the direct use of a suitable mercaptan is preferred.

The continuous thio-ester metal deposition and coke formation will eventually fill the pores of the catalytic composite, and further become deposited on the external surfaces. At such time, it will be apparent that the activity decline continues regardless of the addition of the thioester. The flow of charge stock and thio-ester is discontinued, and hydrogen flow continued for the purpose of sweepting the composite free of hydrocarbons. Following a purge with an inert gas such as nitrogen, to remove traces of hydrogen, the coke deposits are removed by burning in a free oxygen-containing atmosphere at temperatures preferably not exceeding 950 F.i.e. from 500 F. to about 950 F. Many such regenerative procedures are known, and are described in detail in the prior art; of themselves, therefore, they form no essential part of my invention other than the accomplishing of the burning coke and, as set forth below, converting the metallic sulfides resulting from the thio-esters to the higher oxides thereof.

During the carbon burn-ofi by any of the procedures known in the art, the surface-deposited metallic sulfides which were formed as a result of the thio-ester addition, are oxidized to form the higher oxides; for example, vanadium pentoxide (V 0 molybdenum trioxide (M00 and tungsten trioxide (W0 At the termination of the burning treatment, these oxides are dissolved in, and reacted with, a liquid tertiary mercaptan to form the thioesters. This particular treatment is effected at elevated temperatures (from 200 F. to 500 F.) and at superatmospheric pressures to about 1,000 p.s.i.g.).

The tertiary mercaptans, butyl and higher, are readily available within the refinery from other product streamsi.e. isobutylene, and its homologues, and hydrogen sulfide react to form the mercaptan as indicated below:

e e 1120 zS HsC-(E-SH where R is CH up to about C H The tertiary mercaptans react with the metal oxides in accordance with the foregoing Equations 2 and 3. Such thio-esters are oilsoluble, and the last traces thereof are easily removed from the catalytic composite by washing, or flushing, with naphthalene or hydrocarbon fraction including a heavy naphtha, kerosene, gas oil, etc.

Following the removal of the oil-soluble thio-esters, hydrogen circulation is begun and, when the desired temperature and pressure are attained, the charge stock is introduced. The above-described cycle is repeated as the catalytic composite once again shows signs of undergoing a decline in activity.

Example In describing my invention by way of an example, it is understood that the charge stock, stream compositions, operating conditions, catalyst composition, reagents, etc.,

are exemplary only, and may be varied widely without departure from the spirit of my invention, the scope of which is defined by the appended claims.

My invention will be described in connection with the conversion of a vacuum residuum charge stock effected in a commercially-sealed unit. Charge stock properties are presented in the following Table I:

TABLE I.-VACUUM RESIDUUM PROPERTIES Gravity, API at 60 F. 8.8

After appropriate heat-exchange, the charge stock, in an amount of 147,000 lbs./hr. at a temperature of 625 F. and a pressure of about 2730 p.s.i.g., is admixed with 31,830 lbs./hr. of a hydrogen-rich gaseous stream. The hydrogen-rich stream results in part from a vapor phase provided by the separation of product eflluent and hydrogen makeup supplied to supplement that consumed in the process. In this particular illustration, the hydrogen-rich phase is 82.4% (on a mol basis) hydrogen, and is in an amount of 27,900 lbs/hr. The mixture is heated from a temperature of about 625 F. to a level of 830 F. The thus-heated mixture is combined with a hot separator liquid phase recycle stream in an amount of 134,000 lbs./ hr. Since this recycled stream is at a temperature of 750 F., the temperature of the total charge to the reaction zone is 800 F., the pressure being about 2685 p.s.i.g.

The fixed-bed catalytic composite consists of 16.0% by weight of molybdenum and 2.0% by weight of nickel, calculated as the elements, and based upon the total composite. The carrier material consists of 68.0% by Weight of alumina, 12.0% by weight of silica and 22.0% by weight of boron phosphate. The fresh charge rate is such that the liquid hourly space velocity (of the fresh feed) is 0.5, the quality of hot liquid recycle being such that the combined feed ratio is 2.0. With respect to the latter, combined feed ratios of from about 1.25 to about 3.0 are well suited to the present process.

The effluent from the reaction zone, at a temperature of 875 F. and a pressure of about 2535 p.s.i.g., passes into a hot separator. A vapor phase is withdrawn from the hot separator, and passes into a cold separator. The latter is maintained at substantially the same pressure, allowing only for the normal pressure drop through the system, but at a significantly lower temperature in the range of 60 F. to about 130 F. In commercial practice, the pressure at the inlet to the reactor would be the critical point, and be controlled by any suitable means such as by adjusting the quantity of make-up hydrogen, or by venting a small quantity of gas from the cold separator. As hereinbefore stated, this pressure is at least about 1000 p.s.i.g., and preferably within the range of from 1500 p.s.i.g. to about 3000 p.s.i.g.

The vapor phase from the hot separator is in an amount of 60,500 lbs./hr., of which 27,900 lbs./hr. are removed as the hydrogen-rich recycle gas from the cold separator. The cold separator liquid phase is in an amount of 32,600 lbs./hr. The net hot separator liquid phase, in an amount of 118,500 lbs./hr., continues into a hot flash zone. The liquid phase from the hot separator is further separated at a pressure from subatmospheric to about 100 p.s.i.g. and a temperature of from 750 F. to about 900 F.,

to provide a residuum fraction containing the unconverted high molecular weight asphatics, and a vapor fraction which may be removed as a vapor, or a liquid after condensation. The residuum fraction in the instant illustration is in an amount of 29,400 lbs./hr., or 19.0% by volume of the fresh charge stock. The material from the vapor phase is in an amount of 89,000 lbs./hr., and is admixed with the 32,600 lbs/hr. of liquid phase from the cold separator, the mixture continuing into a product separation zone.

The product separation zone serves to provide three principal product streams. A vent gas stream, in an amount of about 10,940 lbs./hr. (of which 3,230 lbs. represents hydrogen sulfide), consisting principally of hydrogen, hydrogen sulfide, light paraifinic hydrocarbons and minor quantities of butanes, pentanes, hexanes, and heptane-to400 F. gasoline is removed as overhead. Where desired, this stream can be further treated to recover any one or a number of these components in a substantially pure state. A normally liquid stream, containing that portion of the lower-boiling product boiling up to about 850 F., is removed as an intermediate stream, and consists principally of liquid hydrocarbons, including some butanes and higher boiling material up to about 850 F., in an amount of about 55,160 lbs/hr. As hereinafter indicated, a component analysis of this liquid stream shows the same to be composed in the main of hydrocarbons boiling from about 400 F. to about 850 F., with only a minor quantity boiling at temperatures above 850 F. The bottoms stream, leaving the product separation zone, consists primarily of those distillable hydrocarbons boiling between 800 F. and 1000 F., and is recovered in an amount of 55,500 lbs/hr. In an actual commercial operation, the split between the liquid streams is made such that the lighter intermediate stream contains a minimal quantity of hydrocarbons boiling above 800 F., while the bottoms material, which may be referred to as a heavy vacuum gas oil, will consist of about 10.0% by volume of hydrocarbons boiling between temperatures of from 700 F. to 800 F. Various aspects normally considered in a commercial operation will dictate the exact separations of the liquid product streams, and the indicated separation into the two normally liquid streams, discounting the vent gas stream, is presented solely for the purpose of illustration.

Based upon the indicated charge rate of 147,000 lbs./hr., or 10,000 bbl./d., the yields of the major streams are presented in the following Table II.

' Millions of s.c.f. day.

It should be noted that the weight percent yields given in the foregoing Table II take into account the 2.8% by weight of make-up hydrogen supplied to the process to supplement for the hydrogen consumed. Of interest is the fact that approximately 73.0% by Weight of the original sulfur has been converted into hydrogen sulfide and removed from the process by way of a vent gas stream. Of the remaining 27.0%, the greater share is in the residuum stream; thus, the product streams are recovered substantially reduced in sulfur concentration.

The following Table III indicates the component analyses of the vent gas (1), the heavy vacuum gas oil (3) and the full boiling range gas oil (2).

TABLE III.STREAM ANALYSES, MOLS PER HOUR Stream Component Nitrogen 200300 F Boo-400 F- 400-500" F The composition analyses presented in the foregoing Table [II is intended to be illustrative only, and may vary widely depending upon the precise characteristics of the charge stock, the flow rates and other operating variables, including the particular desired product separation. It should be further pointed out that the three principal product streams are well suited either for further processing, or separation to recover particularly desired components. For example, the heavy vacuum gas oil may be used directly as fuel oil, or subjected to catalytic hydrocracking to produce additional lower boiling hydro carbons. The vent gas stream can be scrubbed to remove the hydrogen sulfide, and subsequently further separated to recover, for example, substantially pure hydrogen and/ or a butane-plus hydrocarbon fraction. With respect to the 850 F. stream, one scheme for further utilization is a separation at about 400 F., accompanied by catalytic hydrocracking of the light fraction for LPG (liquified petroleum gas) production, and hydrocracking for the heavier, 400 F.-plus fraction to produce additional gasoline boiling range hydrocarbons. These, as well as other processing schemes will become evident to those skilled in the art.

As hereinbefore set forth, the catalytic composite will eventually experience a decline in activity to the extent that the specifications placed upon quality of the various product streams are not being met. For example, one of the many available criteria is the concentration of sulfur in the normally liquid portion of the product efiluent boiling from about 400 F. to 800 F. As the catalyst activity declines, the residual sulfurous compound concentration will increase, and to the extent that the as-produced stream requires additional treatment for sulfur removal prior to subsequent use. Another signpost would be a substantial increase in the residuum fraction, indicative of the fact that fewer insoluble asphaltenes are being converted to oil-soluble products.

At the time when the product quality, regardless of which criteria is used, indicates that catalytic activity cannot be economically justified, a thio-esteri.e. vanadium thio-ethylate in admixture with molybdenum thio-amylate-is added to the hydrocarbon charge stock in an initial amount of about 0.5% by weight, based upon the selected quantity of molybdenum and vanadium. The particular criteria chosen as the control point is closely observed to note whether the amount is suflicient to stem the decline in activity, and the quantity of thioester is controlled, generally increased, to raise and maintain increased catalytic activity to the degree called for by the product specification. For example, a gasoline fraction, normally liquid hydrocarbons boiling up to about 400 F., suitable for further processing via catalytic reforming, preferably contains less than 10.0 p.p.m. (by weight) of sulfur. Thus, as the concentration of sulfur in this fraction, produced as above described, commences to increase and approaches 10.0 p.p.m., thio-ester addition is started, and the amount varied to control the sulfur concentration in the gasoline fraction. The addition of the thioester is in an amount within the range of 0.5% to 5.0% 'by weight, on the basis of the metal component thereof.

Following a period of operation during which the thioester is added to the charge stock, and the product specification at the control point is considered acceptable, the continued addition, or increased amount above 5.0% by weight, fails to improve the catalytic activity. At this point, the flow of charge stock and thio-ester is discontinued, and the regeneration procedure hereinbefore described is instituted. To reiterate briefly, this constitutes carbon bum-off with a free oxygen-containing gas, which procedure oxidizes the deposited metals from the decomposed thio-esters. These oxides are later dissolved in and reacted with a liquid tertiary mercaptan such as tertiary butyl mercaptan, and removed from the catalytic composite.

I claim as my invention:

1. In a process for hydrorefining a contaminated, asphaltene-containing hydrocarbon charge stock in contact with hydrogen and a solid catalytic composite comprising at least one-metallic component selected from the group consisting of the metals of Group VB, VI-B and VIII of the Periodic Table, in which process said solid catalytic composite experiences a decline in activity, as a result of the deposition thereon of coke the improvement which comprises adding a thio-ester of a metal selected from the group consisting of the metals of groups VB and VI-B to said charge stock, whereby the activity of said solid catalytic composite is at least partially restored.

2. The process of claim 1 further characterized in that said thio-ester is added in an amount within the range of 0.5 to about 5.0% by weight.

3. The process of claim 1 further characterized in that said charge stock is admixed with a thio-ester of vanadium.

4. The process of claim 1 further characterized in that said charge stock is admixed with a thio-ester of molybdenum.

5. A regenerative, fixed-bed catalytic process for hydrorefining of a contaminated, asphaltene-containing hydrocarbon charge stock which comprises the steps of:

(a) contacting said charge stock and hydrogen in a reaction zone at hydrorefining conditions including a temperature above about 500 F. and a pressure above about 1000 p.s.i.g., in contact with a solid catalytic composite comprising at least one-metallic component selected from the group consisting of the metals of Groups VB, VI-B and VIII of the Periodic Table;

(b) as said solid catalytic composite experiences a decline in activity as a result of the deposition of coke thereon, commencing the addition of a thio-ester of a metal from Groups VB and VI-B, to said charge stock;

(c) continuing the addition of said thio-ester to maintain said solid catalytic composite in an activitystable state through the deposition thereon of the metal component of said thio-ester;

(d) as said solid catalytic composite experiences a second decline in activity, during the period when said thio-ester is added to said charge stock and when increasing the concentration of said thio-ester in said charge stock has no efiFect on said activity decline, discontinuing the flow of said charge stock, thio-ester and hydrogen;

(e) purging said reaction zone with an inert gas to remove traces of hydrogen and hydrocarbons;

(f) introducing an oxygen-containing gas stream into said reaction zone at a temperature sufficient to burn the coke from said solid catalytic composite and to convert the metals, deposited from said thio-ester, to the oxides thereof;

(g) dissolving said metal oxides in a liquid tertiary mercaptan to form the thio-ester of said metals and withdrawing said thio-esters from said reaction zone; and

(h) reintroducing said charge stock and hydrogen at the aforesaid conversion conditions.

6. The process of claim 5 further characterized in that said coke is burned at a temperature of from 500 F. to about 950 F.

7. The process of claim 5 further characterized in that said metal oxides are dissolved in said mercaptan at a temperature of from 200 F. to about 500 F.

8. The process of claim 5 further characterized in that said solid catalytic composite comprises a siliceous carrier material.

'9. The process of claim 5 further characterized in that said charge stock is admixed with a thio-ester of vanadium.

10; The process of claim 5 further characterized in that said charge stock is admixed with a thio-ester of molybdenum.

References Cited UNITED STATES PATENTS 3,252,895 5/1966 Gleim et al. 208264 3,331,769 7/1967 Gatsis 208-210 2,910,432 10/1959 Witten et a1. 208Z16 DELBERT E. GANT Z, Primary Examiner J. M. NELSON, Assistant Examiner US. Cl. X.R. 208-110