Desulfurization And Conversion Of Hydrocarbonaceous Black Oils

Abstract

A process for converting asphaltene-containing hydrocarbonaceous black oils into lower boiling, normally liquid hydrocarbon products. The process involves the integration of a thermal cracking coil and fixed-bed catalytic hydrogenation and desulfurization, and is especially applicable to sulfurous charge stocks containing less than 150 p.p.m. of metallic contaminants, and more than about 10.0 percent by volume of nondistillables. The charge stock is initially subjected to fixed-bed catalytic desulfurization and hydrogenation, and a series of separation steps to concentrate that portion of the reaction zone product boiling at temperatures above the normal gasoline boiling range. This high-boiling concentrate is then subjected to a noncatalytic, thermal cracking reaction zone or coil.

Description

APPLICABILITY OF INVENTION

The process described herein is primarily adaptable to the desulfurization of petroleum crude oil residuals having relatively low metals content-- i.e. containing less than 150 p.p.m. of total metals. More specifically, the present invention is directed toward a combination process for hydrogenating and desulfurizing hydrocarbonaceous charge stocks which are commonly referred to as "black oils." Petroleum crude oils, and particularly the heavy residuals extracted from tar sands, topped or reduced crudes, and vacuum residuals, contain high molecular weight sulfurous compounds in exceedingly large quantities, nitrogenous compounds, asphaltic material insoluble in light hydrocarbons such as pentane and/or heptane, and high molecular weight organometallic complexes. With respect to the metallic complexes, containing nickel and vanadium as the metallic components, the various black oil charge stocks can be classified as (1) "high metals" residuals, or (2) "low metals" residuals. The present invention is primarily directed to the processing of those hydrocarbonaceous black oils having low metals content-- i.e. less than about 150 p.p.m. of total metals, computed as if existing in the elemental state. A black oil charge stock is generally characteried as a heavy carbonaceous material of which more than about 10.0 percent by volume boils above a temperature of 1,050.degree. F. (referred to as nondistillables). Such material generally has a gravity less than about 20.0.degree. API and sulfur concentrations greater than about 2.0 percent by weight. With many stocks, the sulfur concentration can range as high as about 5.0 percent by weight. Conradson carbon residue factors generally exceed 1.0 percent by weight, and a great proportion of black oils indicate a Conradson residue factor above 10.0.

Exemplary of those black oils, to the conversion and desulfurization of which the present invention is directed, include a crude tower bottoms product having a gravity of about 14.3.degree. API and contaminated by the presence of about 3.0 percent by weight of sulfur, 3,830 p.p.m. of total nitrogen, 85 p.p.m. of total metals, about 11.0 percent by weight of insoluble asphaltenes, and about 41.0 percent nondistillables. The present invention affords the conversion of such charge stocks into lower boiling, normally liquid hydrocarbon products, and further converts a considerable quantity of nondistillables. Additionally, the normally liquid portion of the product effluent has been substantially desulfurized to a level less than about 1.0 percent by weight.

The principal difficulty, heretofore barring the attainment of an economically feasible process, resides in the lack of sulfur stability of catalytic composites when the charge stock is characterized by the presence of large quantities of asphaltic material and sulfur. This difficulty arises primarily as a consequence of the necessity to effect the process at operating severity levels such that nondistillable conversion simultaneously takes place while sulfurous compounds are being converted into hydrogen sulfide and hydrocarbons. Since the operation must be effected at a high severity level, the asphaltic material, dispersed within of charge stock, has the tendency to flocculate and polymerize whereby the conversion thereof to more valuable oil-soluble products is virtually precluded. Furthermore, the polymerized asphaltic complexes become deposited upon the catalytic composite, steadily increasing the rate at which the same becomes deactivated.

The present invention is founded upon recognition of the fact that acceptable desulfurization of low metals-containing black oils is possible at relatively mild operating severities which favor extended catalyst life without simultaneously effecting asphaltene polymerization Hydrogenation reactions are enhanced at lower severities, particularly with respect to temperature. In order that the process becomes economically attractive from the standpoint of producing the lower boiling, normally liquid hydrocarbon products, an essential feature of the present invention is the subsequent processing of the hydrogenated and desulfurized product effluent from the fixed-bed catalytic reaction zone Therefore, as hereinafter set forth in greater detail, the desulfurized catalytic reaction effluent is separated to produce a hydrocarbon stream boiling substantially completely above the gasoline boiling range, which hydrocarbon stream is subsequently subjected to a noncatalytic thermal reaction zone or coil.

OBJECTS AND EMBODIMENTS

A principal object of our invention is to provide an economical process for effecting the desulfurization and conversion of asphaltene-containing black oils to distillable hydrocarbons of lower molecular weight. A corollary objective is to extend the period of acceptable, economical catalyst life while desulfurizing and hydrogenating hydrocarbonaceous black oils containing less than about 150 p.p.m. of total metals.

Another object is to convert a sulfurous hydrocarbon charge stock, a significant quantity of which exhibits a boiling range above a temperature of 1,050.degree. F., into lower boiling distillable hydrocarbons having a sulfur concentration less than about 1.0 percent by weight.

In one embodiment, therefore, our invention relates to a process for the conversion of a sulfurous, hydrocarbonaceous charge stock, of which at least about 10.0 percent boils above a temperature of about 1,050.degree. F., into lower boiling hydrocarbon products, which process comprises the steps of: (a) heating said charge stock to a temperature of from 500.degree. F. to about 775.degree. F., reacting said charge stock with hydrogen in a first reaction zone, in contact with the catalytic composite and at a pressure above about 1,000 p.s.i.g.; (b) separating the resulting reaction zone effluent, in a first separation zone, at substantially the same pressure imposed upon said first reaction zone, to provide a first vapor phase and a first liquid phase; (c) separating said first vapor phase, in a second separation zone, at substantially the same pressure imposed upon said first separation zone and at a reduced temperature to provide a second vapor phase rich in hydrogen and a second liquid phase; (d) recycling at least a portion of said second vapor phase to said first reaction zone; (e) separating at least a portion of said first liquid phase, in a third separation zone, at substantially the same temperature, to provide a third vapor phase and a third liquid phase; (f) cracking at least a portion of said third liquid phase in a noncatalytic thermal cracking zone, (g) separating the resulting cracked product effluent in a fourth separation zone, at a reduced pressure of from atmospheric to about 100 p.s.i.g. to provide a fourth liquid phase and a fourth vapor phase; and, (h) further separating said fourth liquid phase, in a fifth separation zone, at a reduced pressure of from subatmospheric to about 50 p.s.i.g. to provide a fifth liquid phase containing distillable hydrocarbons, and an asphaltic residuum.

Other embodiments of our invention, as hereinafter set forth in greater detail, reside primarily in preferred ranges for process variables and in various processing techniques. For example, in another embodiment, at least a portion of said fifth liquid phase is recycled to combine with said third liquid phase, to provide a combined feed ratio to said thermal reaction zone of from about 1.1:1 to about 4.5:1. . In a particularly preferred embodiment, the fifth separation zone is a vacuum column which serves to concentrate the unconverted asphaltic residuum and to provide at least a heavy vacuum gas oil, a light vacuum gas oil and a slop-wax cut. Generally, the latter, with or without a portion of the heavy vacuum gas oil, is recycled to the thermal cracking coil. Where the desired product distribution demands, a portion of the slop-wax cut may be recycled to combine with the fresh black oil charge to the fixed-bed reaction zone. The total charge to the first, fixed-bed catalytic hydrogenation zone, including hydrogen recycle and makeup required to maintain pressure and supplant that which is consumed within the overall process, is heated to a temperature within the range of from about 650.degree. to about 775.degree. F. The precise temperature, to which the charge to the catalytic reaction one is heated, is controlled within the aforesaid range by monitoring the temperature of the reaction zone product effluent. Since the principal reactions being effected are exothermic, a temperature rise is experienced as the charge and hydrogen pass through the catalyst bed. Economically acceptable catalyst life is achieved when the maximum catalyst temperature, which is virtually the same as that of the product effluent, is maintained at a maximum level of about 800.degree. F. In another embodiment, the first reaction zone effluent, being introduced into the first separation zone, is at a temperature of from about 700.degree. to about 775.degree. F. in order that the heavier constituents of the reaction zone product effluent are not carried over into the principally vaporous phase. Other objects and embodiments of our invention will be evident from the following, more detailed description of the process encompassed thereby.

SUMMARY OF INVENTION

As hereinbefore set forth, the principal function of the present invention resides in the production of maximum quantities of distillable hydrocarbons which have been substantially reduced with respect to sulfur concentration. Through the utilization of the present combination process, this is accomplished in a highly economical fashion while avoiding the difficulties of currently practiced processing techniques. Paramount is the extension of the period of time during which the fixed-bed of the solid catalytic composite functions in an acceptable manner. With respect to the processing of "high metals" black oils, being those containing more than about 150 p.p.m. of total metals, it has been found that a successful operation involves initially visbreaking the fresh hydrocarbon charge stock in the presence of limited quantities of hydrogen. Although both technical and economical justification exists to support this processing technique, there is incurred a yield loss with respect to that quantity of the original nondistillable asphaltics which are not converted by way of catalytic processing. This yield loss results primarily from the fact that thermal cracking, in the presence of hydrogen, does not achieve the conversion of all the convertible asphaltics within the charge stock, the unconverted portion of which is removed from the system as an asphaltic residuum prior to subjecting the remainder of the thermally cracked product effluent to further conversion in the fixed-bed reaction zone. If the as-received high metals charge stock were processed initially in the fixed-bed catalytic reaction zone, the presence of exceedingly high concentrations of metals in an environment conductive to effecting acceptable desulfurization, results in extreme catalyst deactivation. In accordance with the present process, primarily applicable to those charge stocks of low metals content, the residual charge stock is catalytically desulfurized, and at least partially converted, at relatively mild hydrogenation severities which favor extended catalyst life. The catalytically converted product effluent is subjected to a series of separation steps in order to provide a liquid phase substantially free from gasoline boiling range hydrocarbons. This liquid phase is utilized as the charge to a noncatalytic thermal reaction zone, or coil. As hereinafter indicated, in a specific example integrated into the description of the drawing, this particular process offers maximum production of distillable hydrocarbons accompanied by maximum desulfurization of the charge stock whose original metals content is less than about 150 p.p.m. In a preferred embodiment, the total charge to the fixed-bed catalytic reaction zone includes the fresh hydrocarbon charge stock, a recycled hydrogen-rich gaseous phase, makeup hydrogen, and a recycled diluent, the source of the latter being hereinafter set forth. This mixture is raised to a temperature of from about 500.degree. to about 775.degree. F., as measured at the inlet to the catalyst bed. In order to preserve catalyst stability, the inlet temperature is controlled at a level such that the temperature of the reaction product effluent, or the maximum catalyst bed temperature, does not exceed about 800.degree. F. A certain measure of temperature control, within the fixed-bed of catalyst, is afforded through the conventional utilization of either a quench hydrogen stream, or quench liquid, or both, introduced at one or more intermediate loci of the catalyst bed. The catalytic reaction zone is maintained under an imposed pressure of from about 1,000 to about 4,000 p.s.i.g., and the hydrocarbon charge stock contacts the catalyst at a liquid hourly space velocity of from about 0.5 to 10.0, based upon the fresh hydrocarbon charge stock exclusive of recycled diluent and/or any quench streams employed for temperature control. The hydrogen concentration will be in the range of from about 5,000 to about 50,000 standard cubic feet per barrel, while the combined feed ratio, defined as total volumes of liquid charge per volume of fresh hydrocarbon charge, is in the range from about 1.1:1 to about 3.5:1.

The catalytic composite disposed within the fixed-bed catalytic reaction, or conversion zone, can be characterized as containing a metallic component having hydrogenation activity, which component is combined with a suitable refractory inorganic oxide carrier material of either synthetic, or natural origin. The precise composition and method of manufacturing the carrier material is not considered essential to the present invention, although a siliceous carrier, such as 88.0 percent by weight of alumina and 12.0 percent by weight of silica, or 63.0 percent by weight of alumina and 37.0 percent by weight of silica are generally preferred. Suitable metallic components having hydrogenation activity are those selected from the group consisting of the metals of Groups VI-B and VIII of the Periodic Table, as set forth in The Periodic Table of The Elements, E. H. Sargent & Company, 1964. Thus, the catalytic composite may comprise one or more metallic components selected from the group of molybdenum, tungsten, chromium, iron, cobalt, nickel, platinum, iridium, osmium, rhodium, ruthenium, and mixtures and compounds thereof. The concentration of the catalytic metallic component, or components, is primarily dependent upon the particular metal as well as the characteristics of the charge stock. For example, the metallic components of Group VI-B are generally present in an amount within the range of from about 1.0 percent to about 20.0 percent by weight, the iron-group metals in an amount within the range of about 0.2 percent to about 10.0 percent by weight, whereas the noble metals of Group VIII are preferably present in an amount within the range of about 0.1 percent to about 5.0 percent by weight, all of which are calculated as if these compounds existed within the catalytic composite in the elemental state. The refractory inorganic carrier material, with which the catalytic reactive metallic components are combined, may comprise alumina, silica, zirconia, magnesia, Titania boria, strontia, hafnia, and mixtures of two or more including silica-alumina, alumina-silica-boron phosphate, silica-zirconia silica-magnesia, silica-titania, alumina-zirconia, alumina-magnesia, silica-alumina-titania, alumina-magnesia-zirconia, silica-alumina-boria, etc. Before further summarizing our invention, several definitions are believed necessary in order that a clear understanding of the invention be afforded. In the present specification and the appended claims, the phrase "pressure substantially the same as" is intended to connote the pressure under which a succeeding vessel is maintained, allowing only for the pressure drop experienced as a result of the flow of fluids through the system. For example, where the catalytic first reaction zone is maintained at a pressure of about 2,800 p.s.i.g., the first separation zone, or "hot separator" will function at about 2,680 p.s.i.g. Similarly, unless otherwise specified, the phrase "temperature substantially the same as" is employed to indicate that the only reduction in temperature stems from normally experienced loss due to the flow of material from one piece of equipment to another, or from the conversion of sensible to latent heat by "flashing" where a pressure drop occurs. When utilized, the term "hydrocarbons boiling within the gasoline boiling range" is intended to connote those normally liquid hydrocarbons boiling at temperatures up to about 400.degree. or about 450.degree. F., including pentanes and heavier hydrocarbons, and, as in some localities, butanes. Likewise, a commonly referred to boiling range for gas oil is an initial boiling point of about 650.degree. F. and an end boiling point of about 1,050.degree. F. The higher boiling 70.0 to about 80.0 percent thereof, the heavy gas oil, characteristically is considered having an initial boiling point of about 750.degree. F. It is, of course, recognized that a "light gas oil" can have an initial boiling point as low as about 350.degree. F. and an end boiling point as high as about 800.degree. F. Similarly, the "heavy gas oil" can have an initial boiling point as low as about 650.degree. F.

The total product effluent from the catalytic reaction zone, at a maximum temperature of about 800.degree. F., is passed into a first separation zone hereinafter referred to as the "hot separator." The principal function served by the hot separator is to separate the mixed-phase product effluent into a principally vaporous phase rich in hydrogen and a principally liquid phase containing some dissolved hydrogen. In a preferred embodiment, the total reaction product effluent is utilized as a heat-exchange medium in order to lower the temperature thereof to a level in the range of from about 700.degree. to about 775.degree. F., and preferably below the level of 750.degree. F. The principally vaporous phase from the hot separator is introduced into a second separation zone hereinafter referred to as the "cold separator." The cold separator, operating at substantially the same pressure as the hot separator, but at a significantly lower temperature in the range of about 60.degree. to about 140.degree. F., serves to concentrate the hydrogen in a second principally vaporous phase. The hydrogen-rich vapor phase, comprising about 82.5 mol percent hydrogen, and only about 2.3 mol percent propane and heavier hydrocarbons, is made available for use as a recycle stream to be combined with the fresh black oil charge stock. Butanes and heavier hydrocarbons are condensed in the cold separator, and removed therefrom in a second principally liquid phase.

The first liquid phase from the hot separator may be in part recycled to combine with the fresh hydrocarbon charge stock to serve as a diluent for the heavier constituents thereof. The quantity of the liquid phase diverted in this manner is such that the combined feed ratio to the catalytic reaction zone, being defined as total volumes of liquid charge per volume of fresh liquid charge, is within the range of from about 1.1:1 to about 3.5:1. The remaining portion of the principally liquid phase from the hot separator is introduced into a third separation one hereinafter referred to as the "hot flash zone." The hot flash zone functions at about the same temperature as the liquid phase withdrawn from the hot separator, but at a significantly reduced pressure of from about 150 to about 350 p.s.i.g. The principally vaporous phase from the hot flash zone comprises primarily hydrocarbons boiling below a temperature of about 650.degree. F., and containing a relatively minor quantity of hydrocarbons normally considered to be within the heavy gas oil boiling range. This principally vaporous stream may be combined with the liquid stream from the cold separator, and the mixture introduced into a cold flash zone at a pressure of from atmospheric to about 60 p.s.i.g. and a temperature of from 60.degree. to about 140.degree. F.

The principally liquid phase withdrawn from the hot flash zone is introduced into a thermal cracking reaction zone, or coil, at substantially the same temperature, and a pressure of from about 150 to about 350 p.s.i.g. The thermally cracked product effluent, at a temperature of from about 875.degree. to about 950.degree. F., and a pressure of from about 40 to about 100 p.s.i.g., is cooled to a temperature of about 700.degree. F., and introduced into a fourth separation zone hereinafter referred to as the "flash fractionator." The liquid phase from the flash fractionator is introduced into a vacuum column maintained at about 25 to about 75 mm. of Hg., absolute. The vacuum column serves as the fifth separation zone, the principal function of which is the concentration and separate recovery of an asphaltic residuum, containing high molecular weight sulfurous compounds and being substantially free from distillable hydrocarbons. In general, gas oil streams are recovered from the vacuum column as a separate light vacuum gas oil (LVGO) having a boiling range of from about 320.degree. to about 750.degree. F., a medium vacuum gas oil (MVGO) boiling from about 750.degree. to about 980.degree. F., and a heavy vacuum gas oil containing the remainder of the distillable hydrocarbons. It is understood that the particular boiling ranges of the various gas oil streams, recovered from the vacuum column, are not essential to our invention, but will generally be determined by various refinery and marketing demands. A preferred technique is to separate a slop-wax cut, from the vacuum column, which contains primarily these distillables boiling above 980.degree. F., but may consist of up to about 30.0 percent by volume of the total distillables boiling above 750.degree. F. Although a portion of the slop-wax cut may be recycled to the catalytic hydrogenation/desulfurization reaction zone, it is generally recycled to the thermal coil in order to increase the yield of the more desirable gas oils. The amount of slop-wax so recycled is such that the combined feed ratio to the thermal reaction coil is above about 1.2:1 and generally not higher than about 3.0:1.

The principal advantages, or benefits, attendant the use of our invention, reside in (1) an extension of acceptable catalyst life with respect to the fixed-bed catalytic reaction zone, which stems primarily from the fact that desulfurization, to a level less than about 1.0 percent by weight, is effected at a relatively low severity of operation with the result that the atmosphere within the reaction one is not conductive to the formation of polymer products otherwise resulting from the presence of the hydrocarbon-insoluble asphaltenes; (2) a significant reduction in the required size of the vacuum flash column which, as will be recognized by those having skill in the art of petroleum processing techniques, affords an added advantage with respect to the overall economics of the process; and, (3) increased yields of the more valuable gas oils.

DESCRIPTION OF DRAWING

For the purpose of demonstrating the illustrated embodiment, and the utilization therein of the process of the present invention, the drawing will be described in connection with the conversion of a vacuum column bottoms product having a gravity of 6.0.degree. API and an ASTM 20.0 percent volumetric distillation temperature of about 1,055.degree. F. In addition, the charge stock contains 4,000 p.p.m. of nitrogen, 5.5 percent by weight of sulfur, 100 p.p.m. of nickel and vanadium, 6.0 percent by weight of heptane-insoluble asphaltenes and has a Conradson carbon residue factor of 21.0 percent by weight. The description will be directed toward a commercially scaled unit having a capacity of about 8,000 barrels per stream day. In the drawing, the embodiment is presented by means of a simplified flow diagram in which such details as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, valving, startup lines and similar hardware have been omitted as nonessential to an understanding of the techniques involved. The use of such miscellaneous appurtenances, to modify the illustrated process flow, are well within the purview of those skilled in the art. Similarly, it is further understood that the charge stock, stream compositions, operating conditions, design of fractionators, separators and the like are exemplary only, and may be varied widely without departure from the spirit of our invention, the scope of which is defined by the appended claims.

It is intended that the charge stock be converted into maximum distillable hydrocarbons which are recoverable by ordinary distillation techniques in commonly utilized fractionation systems. The charge stock is processed in a fixed-bed catalytic desulfurization and desulfurization zone in admixture with about 10,000 s.c.f./bl. of hydrogen, based upon fresh feed exclusive of recycle streams, at a catalyst bed inlet temperature of about 700.degree. F., and a pressure of about 3,105 p.s.i.g. The liquid hourly space velocity, based upon fresh feed only, is about 0.5, and the combined liquid feed ratio is about 2.0:1.

With respect now to the drawing, the charge stock, in an amount of about 7,678 bl./day (185.94 mols/hr.), is introduced into the system by way of line 1, and following heat-exchange with various hot effluent streams, is passed into heater 5 in admixture with a recycled hydrogen-rich stream from line 3 and a hot separator bottoms liquid recycle in line 2. Makeup hydrogen, from a suitable external source, to maintain plant pressure, and to replace that hydrogen consumed in the overall process, is introduced by way of line 4. The total charge to the heater is at a temperature of about 500.degree. F.; this is increased to a level of about 700.degree. F., as measured at the inlet to the catalyst bed. The thus-heated total charge passes through line 6 into fixed-bed catalytic reaction one 7. The catalyst disposed in reaction one 7 is a composite of 88.0 percent by weight of alumina and 12.0 percent by weight of silica, with which is combined 2.0 percent by weight of nickel and about 16.0 percent by weight of molybdenum, calculated as the elemental metals.

Component analyses of the total charge to reaction zone are presented in table I. In the table, line 3 includes both recycled and makeup hydrogen, line 2 is the liquid recycle from hot separator 9 and line 1 represents the total charge. --------------------------------------------------------------------------- TABLE I: Reaction one Charge

Line No. 3 2 1 __________________________________________________________________________ Component, mols/hr. __________________________________________________________________________ Nitrogen 11.07 1.85 12.93 Hydrogen 8430.09 175.52 8605.61 Hydrogen Sulfide 739.02 26.36 765.38

Methane 1119.04 31.82 1150.86 Ethane 133.14 7.53 140.67 Propane 67.56 4.17 71.73

Butanes 24.49 2.06 26.55 Pentanes 6.60 0.92 7.52 Hexanes 4.70 1.29 5.99

C.sub.7 -320.degree. F. 2.00 3.19 5.19 320.degree. - 520.degree. F. 0.24 11.23 11.47 520.degree. - 650.degree. F. 16.25 16.25 650.degree. - 750.degree. F. 22.75 22.75

750.degree. - 980.degree. f. 67.16 67.16 980.degree. f.-plus 9.27 9.27 Residuum 78.78 78.78 Charge Stock 185.94 __________________________________________________________________________

The conversion product effluent, in mixed phase in line 8, at a temperature of about 800.degree. F., is utilized as a heat-exchange medium, and is introduced into hot separator 9 at a temperature of 775` F. and a pressure of about 3,040 p.s.i.g. A principally vaporous phase is withdrawn by way of line 10, and a principally liquid phase via line 12. In the present specification, and in the appended claims, the terms "principally vaporous" and "principally liquid," are intended to describe a particular stream, the major proportion of the components of which are either normally gaseous, or normally liquid at standard conditions. At least a portion of the liquid phase, withdrawn from hot separator 9, is diverted via line 2 to combine with the fresh hydrocarbon charge stock, serving as a diluent for the heavier constituents thereof. The quantity of this recycled stream is 7,678 bl./day (460.15 mols/hr.), to provide a combined liquid feed ratio of 2.0:1.

The separation of the reaction zone effluent, being effected in separator 9, is presented in the following table II, wherein line 8 is the feed to the separator (or the reaction zone effluent), line 10 is the vaporous phase and line 12 is the net liquid phase exclusive of the recycled portion in line 2. --------------------------------------------------------------------------- TABLE II: Hot Separator Stream Analyses

Line No. 8 10 12 Component, mols/hr. __________________________________________________________________________ Nitrogen 12.92 9.40 1.67 Hydrogen 7679.21 7345.65 158.04 Hydrogen Sulfide 906.43 856.33 23.74

Methane 1188.95 1128.48 28.65 Ethane 160.61 146.30 6.78 Propane 89.52 81.59 3.76

Butanes 38.85 34.93 1.86 Pentanes 14.55 12.81 0.83 Hexanes 17.60 15.15 1.16

C.sub.7 -320.degree. F. 32.10 26.02 2.88 320.degree. - 520.degree. F. 68.54 47.20 10.11 520.degree. - 650.degree. F. 51.51 20.62 14.63 650.degree. - 750.degree. F. 50.89 7.67 20.48

750.degree. - 980.degree. f. 129.45 1.81 60.47 980.degree. f.- plus 17.61 8.34 Residuum 149.72 70.94 __________________________________________________________________________

It will be noted, from table II, that the material in line 10 is 75.5 mol percent hydrogen, and comprises only about 1.35 mol percent pentanes and heavier normally liquid hydrocarbons. It is therefore, a principally vaporous phase. Likewise, the stream in line 12 comprises about 19.9 mol percent butanes and lighter material, exclusive of hydrogen which is dissolved in the heavier hydrocarbons, and is considered, therefore, a principally liquid phase.

That portion of the hot separator bottoms stream not diverted through line 2, continues through line 12 into hot flash one 13. A reduction in pressure is effected by means of a reducing valve not indicated in the drawing, and the stream enters hot flash one 13 at a pressure of about 250 p.s.i.g. and a temperature of about 768.degree. F. As hereinafter set forth, the principal function of flash zone 13 is to concentrate the heavier components in a liquid phase which serves as the charge to thermal cracking coil 17. As seen in the following table III, the vaporous phase in line 14 comprises about 89.2 mol percent of material boiling below about 520.degree. F. exclusive of hydrogen, while the liquid stream in line 16 comprises about 6.3 mol percent exclusive of hydrogen. --------------------------------------------------------------------------- TABLE III: Hot Flash Zone Stream Analyses

Line No. 14 16 __________________________________________________________________________ Component, mols/hr. __________________________________________________________________________ Nitrogen 1.45 0.22 Hydrogen 151.87 6.17 Hydrogen Sulfide 22.47 1.27

Methane 27.49 1.16 Ethane 6.15 0.63 Propane 3.36 0.40

Butanes 1.61 0.24 Pentanes 0.69 0.14 Hexanes 0.93 0.23

C.sub.7 -320.degree. F. 2.12 0.76 320.degree. -520.degree. F. 5.89 4.22 520.degree.- 650.degree. F. 4.73 9.90 650.degree. - 750.degree. F. 3.10 17.37

750.degree. - 980.degree. f. 1.92 58.55 980.degree. f.- plus 0.01 8.33 Residuum 70.94 __________________________________________________________________________

The liquid phase in line 16 is admixed with about 1.0 wt. percent of 230 p.s.i.g. steam, and the mixture enters thermal coil 17 at a temperature of about 740.degree. F. and a pressure of about 170 p.s.i.g. The thermally cracked produce effluent, at a pressure of about 55 p.s.i.g. and a temperature of about 930.degree. F., and, after being cooled, passes via line 18 into a rectified flash fractionator 19 at a temperature of about 700.degree. F. and a pressure of about 55 p.s.i.g. A vapor phase is withdrawn from flash fractionator 19 through line 20, and a liquid phase through line 24. The latter is introduced into vacuum flash column 25 at a temperature of about 750.degree. F. The vacuum column is functioning at about 25 mm. of Hg., absolute through the utilization of standard vacuum jets which are not illustrated in the drawing. The separation effected in flash fractionator 18 is presented in the following table IV, along with the component analysis of the thermally cracked product effluent in line 18, exclusive of water. --------------------------------------------------------------------------- TABLE IV. Flash Fractionator Stream Analyses

Line No. 18 20 24 __________________________________________________________________________ Component, mols./hr. __________________________________________________________________________ Nitrogen 0.22 0.22 Hydrogen 11.87 11.82 0.05 Hydrogen Sulfide 3.68 3.65 0.03

Methane 22.34 22.23 0.11 Ethane 16.93 16.70 0.23 Propane 22.40 21.92 0.48

Butanes 16.53 15.87 0.66 Pentanes 17.77 16.56 1.21 Hexanes 14.55 13.06 1.49

C.sub.7 -320.degree. F. 33.83 28.31 5.52 320.degree. - 520.degree. F. 50.47 33.80 16.67 520.degree. - 650.degree. F. 30.33 10.29 20.04 650.degree. - 750.degree. F. 24.49 2.75 2.74

750.degree. - 980.degree. f. 56.88 0.26 56.62 980.degree. f.- plus 10.00 10.00 Residuum 39.41 39.41 __________________________________________________________________________

The principally vaporous phase withdrawn from hot separator 9 through line 10, is cooled to a temperature of about 120.degree. F., and is introduced into cold separator 11 at a pressure of about 3,000 p.s.i.g. A hydrogen-rich gaseous phase is withdrawn through line 3, and is recycled therethrough to combine with the fresh hydrocarbon charge stock in line 1. A principally liquid phase is withdrawn from cold separator 11 through line 15. The separation effected in cold separator 11, exclusive of makeup hydrogen, is presented in the following table V. --------------------------------------------------------------------------- TABLE V: Cold Separator Stream Analyses

Line No. 3 15 __________________________________________________________________________ Component, mols/hr. __________________________________________________________________________ Nitrogen 9.29 0.11 Hydrogen 7274.70 70.95 Hydrogen Sulfide 739.02 117.31

Methane 1091.19 37.29 Ethane 133.14 33.16 Propane 67.56 14.03

Butanes 24.49 10.44 Pentanes 6.60 6.21 Hexanes 4.70 10.45

C.sub.7 -320.degree. F. 2.00 24.02 320.degree. - 520.degree. F. 0.24 46.96 520.degree. - 650.degree. F. 20.62 650.degree. - 750.degree. F. 7.67

750.degree. - 980.degree. f. 1.81 980.degree. f.- plus Residuum __________________________________________________________________________

Vacuum flash column 25 serves to concentrate the residuum, 39.41 mols/hr. leaving via line 28, and also to separate a light vacuum gas oil (LVGO), line 26 and a heavy vacuum gas oil (HVGO), line 27. The HVGO, having a boiling range of 750.degree. to 1,050.degree. F., is in an amount of about 66.62 mols/hr., and the LVGO is in a amount of 58.45 mols/hr. Lighter material boiling below 320.degree. F. is removed from vacuum flash column 25 by the jets which are not indicated in the drawing.

Cold flash zone 21 has been illustrated for the sake of completeness, indicating the separation of the mixture of the hot flash vapors (line 14), the flash fractionator vapors (line 20) and the cold separator liquid (line 15). In a commercial installation, the vapors from the flash fractionator would be recovered separately due to the relatively high degree of olefinicity thereof. Component analyses indicating the separation effected in cold flash zone 21 are presented in the following table VI. --------------------------------------------------------------------------- TABLE VI: Cold Flash Zone Stream Analyses

Line No. Feed 22 23 __________________________________________________________________________ Component, mols/hr. __________________________________________________________________________ Nitrogen 1.78 1.78 Hydrogen 234.64 232.53 2.11 Hydrogen Sulfide 143.43 96.75 46.68

Methane 87.01 82.63 4.38 Ethane 56.01 47.12 8.89 Propane 39.31 26.24 13.07

Butanes 27.92 11.87 16.05 Pentanes 23.46 4.84 18.62 Hexanes 24.44 2.54 21.90

C.sub.7 -320.degree. F. 54.45 1.86 52.59 320.degree. -520.degree. F. 86.65 0.05 86.60 520.degree. -650.degree. F. 35.64 35.64 650.degree. -750.degree. F. 13.52 13.52

750.degree. -980.degree. f. 3.99 3.99 980.degree. f.- plus 0.01 0.01 Residuum __________________________________________________________________________

Normally gaseous material is removed via line 22 to a light ends recovery system, while normally liquid hydrocarbons, including butanes, are removed via line 23 for further separation by fractionation

The overall product yields, exclusive of normally gaseous material, but inclusive of butanes and the normally liquid hydrocarbons recoverable from the vacuum jets and light ends recover (line 22), are presented in the following table VII. --------------------------------------------------------------------------- TABLE VII: Overall Product Yields

Component Mols/hr. __________________________________________________________________________ Butanes 28.58 Pentanes 24.67 Hexanes 25.93

C.sub.7 -320 F. 59.97 320.degree. -520.degree. F. 103.32 520.degree. -650.degree. F. 55.68 650.degree. -750.degree. F. 35.26

750.degree. -980.degree. F. 60.61 980.degree. F.-Plus 10.01 Residuum 39.41 __________________________________________________________________________

The sulfur concentration of the distillable hydrocarbon products is about 0.83 percent by weight.

In a process in which the thermal coil is not an integral part, the fixed-bed catalytic reaction one must necessarily be operated at a significantly higher severity level in order to produce the maximum quantity of distillables. The use of the present process affords a reduction in operating severity, as measured by the catalyst bed inlet temperature, of from 50.degree. to as much as 100.degree. F. With respect to extending the period of time during which the catalytic composite functions in an economically acceptable manner, without experiencing deactivation, the present process increases catalyst life (expressed as barrels per pound) from 50 to 80 percent, resulting in longer on-stream cycles. A reduction in the size of the vacuum column, from a nominal diameter of 11.0 to 8.6 feet, is made possible. This, as will be noted by those skilled in the art of petroleum processing techniques, affords a significant reduction in capital outlay for equipment.

The foregoing specification, and especially the example integrated within the description of the drawing, clearly illustrates the process of our invention and indicates the benefits afforded through the utilization thereof.

Claims

We claim as our invention:

1. A process for the conversion of a sulfurous, hydrocarbonaceous charge stock, of which at least about 10.0 percent boils above a temperature of about 1,050.degree. F., into desulfurized lower-boiling hydrocarbon products, which process comprises the steps of:

a. heating said charge stock to a temperature of from 500.degree. to about 775.degree. F., reacting said charge stock with hydrogen in a catalytic reaction one, in contact with a catalytic composite and at a pressure above about 1,000 p.s.i.g.

b. separating the resulting reaction zone effluent, in a first separation one, at substantially the same pressure imposed upon said first reaction one, and at a temperature of 700.degree. to about 775.degree. F., to provide a first vapor phase and a first liquid phase;

c. separating said first vapor phase, in a second separation one, at substantially the same pressure imposed upon said first separation one and at a reduced temperature, to provide a second vapor phase rich in hydrogen, and a second liquid phase;

d. recycling at least a portion of said second vapor phase to said first reaction one;

e. separating at least a portion of said first liquid phase, in a third separation zone at substantially the same temperature, and a reduced pressure of 150 to about 350 p.s.i.g. to provide a third vapor phase and a third liquid phase;

f. cracking at least a portion of said third liquid phase in a noncatalytic, thermal reaction zone

g. separating the resulting cracked product effluent, in a fourth separation zone, at a reduced pressure of form atmospheric to about 100 p.s.i.g. to provide a fourth liquid phase and a fourth vapor phase; and,

h. further separating said fourth liquid phase, in a fifth separation zone, at a reduced pressure of from subatmospheric to about 50 p.s.i.g. to provide an asphaltic residuum and a fifth liquid phase containing distillable hydrocarbons of decreased sulfur content.

2. The process of claim 1 further characterized in that a portion of said fifth liquid phase is recycled to combine with said third liquid phase, to provide a combined feed ratio to said thermal reaction one of from about 1.2:1 to about 3.0:1.

3. The process of claim 1 further characterized in that said first liquid phase is in part recycled to combine with said charge stock to provide a combined feed ratio to said first reaction one of from about 1.1:1 to about 3.5:1.

4. The process of claim 1 further characterized in that said charge stock is heated to a temperature in the range of from about 650.degree. to about 775.degree. F.

5. The process of claim 1 further characterized in that said second liquid phase and said third vapor phase are separated to recover a normally liquid hydrocarbon stream containing gasoline boiling range hydrocarbons.

6. The process of claim 1 further characterized in that a portion of said fifth liquid phase is recycled to combine with the charge stock to said catalytic reaction zone.

7. The process of claim 5 further characterized in that said second liquid phase and said third vapor phase are combined and separated to recover a normally liquid hydrocarbon stream containing gasoline boiling range hydrocarbons.

8. The process of claim 1 further characterized in that the portion of said third liquid phase is introduced, without intermediate heating thereof, into said thermal reaction zone.