US3487008A - Method for the conversion of hydrocarbons - Google Patents

Description

Dec. 30. 1969 we. BORST, JR

METHOD FOR THE CONVERSION OF HYDROCARBONS Filed March 8, 1967 m. ohm

s um ucu v QQQE A //V l/E/V TOR.- William B. Borsf, Jr:

A TTOR/VEYS United States Patent US. Cl. 208-111 4 Claims ABSTRACT OF THE DISCLOSURE Method for hydrodesulfurizing hydrocarbon preferably boiling up to about 1100 F. by subjecting feed hydrocarbons to reaction with hydrogen over hydrogenation catalyst so that the feed hydrocarbons are at least mildly hydrocracked and substantially desulfurized. The reactor efiluent is quenched in a unique manner using water or steam condensate. The amount of quench is responsive to the measurement of the temperature of the vapor stream out of the high pressure separator immediately following the reaction zone such that a predetermined temperature thereof (below 775 F.) is maintained in this vapor stream. Hydrocarbon products of reduced sulfur content are subsequently recovered.

BACKGROUND OF THE INVENTION This invention relates to the conversion of hydrocarbons. It particularly relates to the hydrogenation of relatively high boiling hydrocarbons by catalytic exothermic reaction with a normally gaseous reactant. It specifically relates to a method for hydrocracking black oil hydrocarbons by improved manner of quenching the hydrocracking reaction.

It is well-known in the art that conversion reactions, in general, and hydrocracking reactions, specifically, are exothermic in nature; that is, the reaction releases significant quantities of heat which must be selectively disposed of if the reaction is to be controlled and optimum results are to be obtained. There have been a variety of prior art schemes proposed for such reactions, and in general, these embody indirect heat exchange schemes wherein the heated eflluent is exchanged with a relatively cold material such as incoming feedstock so that the efiluent temperature does not exceed a predetermined value and preheat of the feed is achieved.

It has now been found that there are other aspects for achieving economical thermal balance around an ex- SUMMARY OF THE INVENTION Therefore, it is an object of this invention to provide an improved method for the conversion of hydrocarbons.

It is also an object of this invention to provide a method for quenching an exothermic conversion reaction.

It is a specific object of this invention to provide a method for hydrocracking relatively high boiling hydrocarbons in a facile and economical manner.

Accordingly, the method of the present invention comprises hydrocracking a sulfur-containing hydrocarbon feedstock in a series of interdependent and interrelated sequence of steps, to wit: (a) introducing said feedstock at an inlet temperature from 700 F. to 800 F. into a catalytic reaction zone containing hydrocracking catalyst maintained under hydrocracking conditions including the presence of hydrogen and a relatively high pressure; (b) withdrawing from said zone an efiluent stream containing hydrocracked hydrocarbons; (c) passing said efiluent 3,487,008 Patented Dec. 30, 1969 stream at a temperature exceeding about 700 F. into a first separation zone under substantially the same pressure as maintained in said reaction zone under conditions sufiicient to produce a first vapor stream and a first liquid stream containing hydrocracked hydrocarbons; (d) measuring the temperature of said first vapor stream; (e) introducing water as quench at a temperature from F. to 250 F. directly into the downstream side of said reaction zone in an amount responsive to said temperature measurement sufficient to maintain a predetermined rela tively high temperature of said first vapor stream; (f) cooling said first vapor stream from said measured temperature to a temperature from 50 F. to 150 F. by indirect heat exchange cooling means; (g) separating the cooled vapor stream in a second separation zone at substantially the same pressure as said first separation zone under conditions sufficient to provide a second vapor stream comprising hydrogen, a second liquid stream containing hydrocracked hydrocarbons, and an aqueous stream containing quench water; (h) returning said second vapor stream to said reaction zone; (i) recycling a portion of said first liquid stream to combine with said feedstock in Step (a); and, (j) recovering hydrocracked hydrocarbons in high concentration.

Another embodiment of this invention includes the method hereinabove wherein said aqueous stream of Step (g) is returned to Step (e) as quench.

Another more particular embodiment of this invention includes the hereinabove method wherein said relatively high pressure is more than 1000 p.s.i.g. and said predetermined temperature is more than 700 F. but less than about 775 F.

As previously mentioned, the present invention relates broadly to the conversion of hydrocarbons. Therefore, as used herein the term conversion is intended to include the saturation of olefinic hydrocarbons, desulfurization, denitrogenation, cracking, etc. of hydrocarbons. In short, this term includes any exothermic reaction which operates by reacting a normally gaseous reactant such as hydrogen with at least a portion of a suitable feedstock. Similarly, the terms converted hydrocarbons and hydrogenated hydrocarbons are intended to include any hydrocarbons which have passed through the catalytic reaction zone even though such hydrocarbons, per se, were substantially unchanged in the reaction. Thus, a converted (or hydrogenated) product would be one which has a reduced sulfur content, even though to a considerable extent the hydrocarbons have passed through the reaction zone substantially unchanged. In the illustrative embodiment of the invention, more fully discussed hereinbelow, theterni conversion and the term hydrogenation are used interchangeably to describe the hydrocracking of relatively high boiling hydrocarbon feedstocks with simultaneous desulfurization of such feedstocks.

It was noted from the broad embodiment of the invention that the quench is introduced into the downstream side of the reaction zone. This term is intended to include the introduction of quench into the lower portion of the catalyst bed, into the lower end of the reactor vessel, and/ or into the transfer line between the reactor vessel and the next succeeding vessel which is normally a high pressure separator. The term excludes a locus for quench which is into the catalyst bed wherein significant reaction is taking place, and excludes the introduction of quench directly into the high pressure separator vessel. It is preferable that the quench be introduced into the lower end of the reactor vessel below the catalyst bed to form a physical admixture with the efiluent.

The present invention is uniquely applicable to hydrocarbon conversion methods which may be characterized as hydrogen consuming and in which a large excess of hydrogen gas reactant is maintained in the reaction zone,

thereby necessitating the recovery and recycle of a hydrogen-rich vapor stream in order for economy of operation to be achieved. In many instances, it is also desirable to recycle with the feedstock at least a portion of the normally liquid product efiluent; which recycle acts as a diluent stream and/ or is subject to further conversion in order to increase the yield of converted products from the reaction.

The present invention is distinctly applicable to the hydrocracking reaction which is utilized by the petroleum refining art to convert relatively heavy carbonaceous material into lower boiling (or lower molecular weight) hydrocarbon products such as gasoline and/or fuel oil, and the like. In other instances, the hydrocracking reaction is used for the production of liquified petroleum gas (LPG). Hydrocracking also includes the processing of heavy residual stocks commonly called black oils. These black oils include atmospheric tower bottoms products, vacuum tower bottoms products (vacuum residuum), crude oil residuum, reduced crude oils, synthetic crude oils obtained from tar sand or oil shale, etc. Similarly, the present invention is applicable to the conversion of relatively heavy hydrocarbons such as those having initial boiling points above about 400 F. and end boiling points of about 1100 F. With specific reference to the black oils, this class of relatively heavy hydrocarbons are characterized by having at least by volume boiling above about 1050 F. Normally, in hydrogenating such feedstocks as herein mentioned there is, in addition to the hydrocracking reaction, the desulfurization reaction which converts sulfur compounds into hydrogen sulfide and the denitrogenation reaction which converts nitrogen compounds into ammonia.

Specific feedstocks which may be processed in accordance with this invention include a vacuum tower bottom product having a gravity of 7.1 API at 60 F., and containing 4.1% by weight sulfur and 23.7% by weight asphaltic compounds; a reduced crude oil having a gravity of 11 API at 60 F., and containing 10.1% by weight of asphaltic compounds and about 5.2% by weight sulfur; and a vacuum residuum having a gravity of about 8.8 API at 60 F., and containing 3.0% by weight sulfur and 4300 p.p.m. (parts per million by weight) of nitrogen, and having a 20.0% volumetric distillation point of 1055 F. Generally, the asphaltic compounds are found to be collodially dispersed within the black oil, and, when subjected to elevated temperature and pressure has a tendency to fiocculate and/or polymerize, whereby the conversion thereof to more valuable products becomes extremely diflicult.

In the processing of black oils the conversion conditions are those which are sufficient for the purpose of achieving both desulfurization and conversion of at least a portion of the feed hydrocarbons into lower boiling (or lower molecular weight hydrocarbon products. Generally, these conversion conditions are significantly less severe than those being currently commercially employed in processing similar charge stocks. For example, with respect to black oil processing, the conversion conditions include a temperature from 700 F. to 800 F. and a pressure from 1000 p.s.i.g. to 3000 p.s.i.g. The temperature usually is measured at the inlet to the catalyst bed since the exothermic nature of the reaction wil produce a considerably higher effluent temperature. For example, the efiluent temperature, in the absence of quench, may be as high as 900 F. even though the inlet feed temperature was only about 725 F. Hydrogen is added to the reaction zone in an amount from 1,000 to 30,000 standard cubic feet per barrel, preferably, from about 2,000 to 10,000 s.c.f./b. at the selected operation pressure. The liquid hourly space velocity (volume of hydrocarbon per hour per volume of catalyst) may be selected over a relatively broad range but, preferably, will be within the range from about 025 to about 2.0.

The hydrogenation reaction is carried out in the presence of a catalyst. The catalyst is characterized as comprising a metallic component possessing hydrogenation activity. This metallic component is generally com= posited with a refractory inorganic oxide carrier material which may be of synthetic or natural origin. The precise composition and method of manufacturing the catalyst is not considered an essential element of the present invention; however, a siliceous carrier, such as 88% by weight of alumina and 12% by weight of silica, or 63% by weight alumina and 67% by weight silica are generally preferred in use in the design to convert black oils into more valuable products. Suitable metallic components, having hydrogenation activity, are those selected from the group of metals of Groups 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 consisting of molybdenum, tungsten, chromium, iron, cobalt, nickel, platinum, palladium, iridium, osmium, rhodium, ruthenium, and mixtures thereof. The concentration of the catalytically active metallic component or components is dictated by the particular metal chosen as well as the physical and chemical characteristics of the black oil charge stock. The metallic components of Group VIB are generally present in an amount within the range of about 1.0% to about 20.0% by weight; the iron group metals in an amount from 0.2% to 10% by weight and, the platinum group metals are preferably present in an amount from 0.1% to about 5% by weight; all of which are calculated as if the com ponents existed within the finished catalytic composite as the elemental metal.

The refractory inorganic oxide carrier material may comprise alumina, silica, zirconia, magnesia, titania, boria, strontia, hafnia, and mixtures of two or more including silica-alumina, alumina-silica-boria phosphate, silica-zirconia, silica-magnesia, silica-titania, alumina-zirconia, alumina-magnesia, alumina-titania, magnesia-zirconia, titania-zirconia, magnesia-titania, silica-alumina-zirconia, silica-alumina-magnesia, silica-alumina-titania, silica-magnesia-zirconia, silica-alumina-boria, etc. It is preferred to utilize a carrier material containing at least a portion of silica and preferably a composite of alumina and silica, with alumina being of the greater proportion.

As previously noted, it was discovered in the practice of this invention that the measurement of the temperature in the first vapor stream from the hot separator is a particularly advantageous control point for the amount of quench necessary. It was further found that the predetermined temperature of this vapor stream from the high pressure separator should be maintained below a temperature of about 775 F. but, preferably, above about 700 F. It was found that at temperatures above about 775 F. the heavier normally liquid hydrocarbons are carried over into this vapor phase, thereby considerably contaminating the hydrogen gas stream which subsequently is to be recycled to the reaction zone. If a large amount of the heavier material is carried over into this vapor stream, the size and operating expense of condensing and thereby removing the hydrocarbons from the hydrogen gas would be significantly increased. In addition, it was found that the use of this vapor stream for the control point permitted the complete elimination of all other heat exchange equipment between the reactor vessel and the high pressure separator. Thus, the subsequently separated hydrogen gas is available for recycle at significantly higher pressures than would be the case for prior art schemes using indirect heat exchange means between the reactor vessel and high pressure separator. Obviously, savings in compressing cost can be realized. In other words, the practice of this invention permits the use of solely a direct quench stream, as herein defined, to control this important temperature.

On the other hand, if the temperature of the vapor stream from the high pressure separator is below about 700 F. ammonia salts resulting from the conversion of nitrogenous compounds contained in the feedstock would tend to contaminate the normally liquid hydrocarbon phase from the bottom of the high pressure separator. If such were allowed to happen, the conventional way of removing these ammonia salts would be by Water washing; however, it is presently believed that if an attempt Were made to water wash these relatively heavy converted hydrocarbons an emulsion would be formed by the hydrocarbon and the water wash which would be extremely difficult to break. Therefore, as more fully discussed hereinbelow, the preferred embodiment of this invention teaches that the control or a predetermined temperature level for the vapor stream leaving the high pressure separator should be less than 775 F. and more than 700 F. However, depending upon the characteristics of the hydrocarbon feedstock and the conversion conditions chosen, reasonable exceptions to these temperature limitations may be utilized with satisfactory operating results.

ILLUSTRATIVE DRAWING Other operating conditions and the preferred operating techniques will be given in conjunction with the following description of one embodiment of the invention with specific reference to the drawing which is a diagrammatic representation of apparatus for practicing one embodiment of the invention.

For the purpose of referring to the drawing, it will be assumed that the method will be operated with the conversion of a reduced crude oil having a gravity of 166 API at 60 F., and an ASTM 65.0% volumetric distillation temperature of 1034 F. The reduced crude feedstock contains about 3.8% by weight sulfur, about 2,000 p.p.m. of nitrogen, about 6.5% by weight pentaneinsoluble asphaltic materials, a Conradson carbon residue of about 8.0% by weight, and about 85 p.p.m. of metals, principally nickel and vanadium.

Now, with reference to the drawing, the reduced crude enters the method or process system through line 1. It is admixed with makeup hydrogen of about 97.5 mol percent purity from an external source by line 2. It has been found appropriate in some instances to add water to the reaction zone in admixture with the charge stock. When this is deemed advisable, the water is added via line 3. Normally, however, the use of water is not necessary or desirable. The hydrogen-reduced crude oil mixture is further admixed with a hydrogen-rich recycle vapor stream (about 80.0 mol percent hydrogen) from line 4. The total charge, after suitable heat exchange with various streams not shown, is passed through heater 5 to raise the temperature of the charge mixture to about 705 F. In the practice of this embodiment it is preferred that the heated mixture in line 6 be further admixed with a hot (750 F.) recycle stream from line 7 to produce a total reactor charge mixture of about 720 F. and a pressure of about 2,165 p.s.i.g.

The heated feedstock in admixture with hydrogen is now passed via line 6 into conversion reactor 8 which contains catalyst disposed therein as a fixed bed; such catalyst being a composite of 2.0% by weight nickel, 16.0% by weight molybdenum on a carrier material comprising 68.0% by weight alumina, 22.0% by weight borontrifiuoride, and 10.0% by weight silica. The hydrocarbon phase contacts the catalyst at a liquid hourly space velocity of about 8, based on the original reduced crude oil, or about 2, based on the combined hydrocarbon feed.

The total conversion product effluent leaves reactor 8 via line 9 in admixture with a hereinafter specified quench stream which had been added to the eflluent via line 35 at a temperature of from 50 F. to 250 F., typically at about 120 F. Therefore, in line 9 there is the total conversion product eflluent admixed with the quench stream which had been added via line 35. Prior to the introduction of the quench stream, the conversion product effiuent is at a temperature of about 780 F. and a pressure of about 2,075 p.s.i.g. Sufiicient quench is added via line 35 to lower the temperature of the effluent stream to less than 775 F. but, preferably, no lower than 700 F. prior to entering hot separator 10. Due to pressure drop through the transfer line, primarily, the pressure within hot separator 10 is about 2,060 p.s.i.g. A first liquid stream is withdrawn from separator 10 through line 11 and a portion of this first liquid stream is diverted through line 7 to combine with the heated mixture in line 6 as previously mentioned. The remaining portion of the first liquid stream continues through line 11 into hot flash zone 24.

A first vapor stream is removed from hot separator 10' through line 12. The temperature of this first vapor stream is measured by temperature recording device control (TRC) 36 which opens or closes control valve 37 in accordance with the deviation of the measured temperature from a predetermined temperature (say, 745 F.) for this first vapor stream. Thus, if the measured temperature in line 12 is 760 F., TRC 36 would open control valve 37 thereby increasing the flow of liquid quench in line 35 in an amount sufficient to maintain the ultimate temperature of the vapor stream in line 12 at its predetermined level of say, 745 F. After passing the temperature measurement point, the first vapor stream passes through condenser 13 (or any heat exchange means) whereby the temperature is lowered to about F., with the pressure now being about 2,005 p.s.i.g. again due to the pressure drop through the system.

The various streams flowing into and out of hot separator 10 may have the following illustrative composition (exclusive of quench material):

It should be noted that the 19 mols/ hour of water in the reaction zone eflluent is water of saturation in the recycle hydrogen gas stream and/or is water present in the fresh hydrogen added to the system by means of line 2 and/or water carried in with the feed hydrocarbons.

The cooled first vapor stream passes through line 14 where, preferably, it is admixed with a portion of a fourth liquid stream in line 23 hereinafter described, and the resulting admixture is introduced into cold separator 15. A second vapor stream containing about 80.0 mol percent hydrogen is removed via line 16, is raised to a pressure of about 2,245 p.s.i.g., via compressor 17, and is introduced through line 4 to combine with the feedstock and makeup hydrogen in line 11, as hereinabove described.

As pointed out in discussion presented thus far, the present invention is based upon the concept of using water or steam condensate as the quench medium for the effluent of the hydrocracking reactor 8. The amount of water added via line 35 is in response to the measured temperature of TRC 36 which controls valve 37; therefore, the

water which enters the system via line 35 is immediately turned into vapor in line 9 which passes directly out of hot separator 10 through line 14 into cold separator 15 where it is now removed via line 34. In addition, if any water has been added to the feedstock via line 3 then this water may also be removed from the system via line 34 as indicated. Preferably, however, in the practice of this invention the water in line 34 is returned through line 35 into reactor vessel 8. It is recognized, however, that the water in line 34 may be contaminated with a number of contaminants such as ammonia salts, entrained hydrocarbons, etc.; therefore, it may be still more preferable to introduce the water from line 34 into a conventional water stripper column, not shown, wherein relatively pure water is taken as an overhead product and returned to the system via line 35 and/or 3. Of course, makeup water may be added from an external source, not shown, as needed to accomplish the results desired herein.

In conjunction with the material balance around hot separator 10, the various streams into and out of cold separator 15 may have the following illustrative composition:

*972 mols/hour of water injection for ammonia removal. This, along wlth the 29 mols/hour of ammonia are removed via line 34.

Thus, the liquid stream (line 18) comprises hydrocarbons boiling for the most part below 650 F. (about 78 mol percent 650 F.hydrocarbons).

The first liquid stream in line 11 enters hot flash zone 24 at a temperature of about 745 F. and is at a substantially reduced pressure of from 100 p.s.i.g. to 500 p.s.i.g., typically about 220 p.s.i.g. A third liquid stream is removed via line 27, combined with a fourth liquid stream, hereinafter described, to produce a combined major product stream.

A third vapor stream is removed through line 25, is cooled and condensed to about 105 F. in condenser 26 and then passed into cold flash separator through line 19; however, it is to be noted that the cooled third vapor stream is, preferably, combined with a portion of second liquid stream in line 18 from cold separator 15. The total material entering cold flash separator 20 via line 19 is at a pressure of about 200 p.s.i.g. and a temperature of about 105 F.

A fourth vapor stream comprising, for example, 97.5 mol percent propane and lighter normally gaseous compo nents is removed from separator 20 via line 21. Since this material contains a considerable quantity of hydrogen sulfide it is generally subjected to a suitable treating process prior to being vented and/or burned as flue gas. The particular economic aspects to be considered will dictate when the fourth vapor stream (line 21) is suitably treated to recover the small quantities of C normally liquid hydrocarbons contained therein. A fourth liquid stream is removed from cold flash zone 20 via line 22 and a portion thereof is diverted through line 23 to be combined with the cold first vapor stream in line 14 thereby forming the total feed stream to cold separator 15. The remaining amount of the fourth liquid stream is combined with the third liquid stream in line 27 and passed to heater 28 and, then, via line 29 into distillation tower 30. It is to be understood that the third liquid stream in line 27 is combined with the unrecycled portion of the fourth liquid stream in line 22 for illustrative purposes only. For reasons peculiar to the particular operation involved, these streams may be separately fractionated to recover desired converted hydrocarbons therefrom.

Distillation column 30 will be operated at conditions of temperature and pressure sufiicient to separate the desired fractions of converted hydrocarbons. The particular operating conditions will be known to those skilled in the art from general knowledge and from theteachings presented herein. However, for illustrative purposes, a gasoline boiling range material having an end boiling point of about 380 F. is removed from column 30 via line 31. A middle distillate fraction (380 F' to 650 F.) is also removed via line 32, and, finally, since the primary object of this example was to maximize the production of fuel oil (650 F.+) having a sulfur concentration not greater than 1.0% by weight, a converted hydrocarbon bottoms product is removed from fractionator 30 via line 33.

Therefore, it can be seen from the above specific and illustrative embodiment that the present invention provides a method for hydrogenating (hydrocracking) a relatively heavy hydrocarbon feedstock in a facile and economical manner. The use of a liquid stream as quench (line 35) is particularly advantageous in that it is cooled and at a pressure substantially sufficient for introduction into the reactor effluent Without significant additional high pressure pumping. The use of this stream also permits the complete elimination of heat exchange equipment in the transfer line between reactor 8 and hot separator 10 so that maximum pressure may be maintained through the separation steps in such a manner that the recovered hydrogen-containing stream (line 16) may be advantageously reused in the process.

The invention claimed:

1. Method for hydrocracking a sulfur-containing hydrocarbon feedstock which comprises the steps of:

(a) introducing said feedstock at an inlet temperature from 700 F. to 800 F. into a catalytic reaction zone containing hydrocracking catalyst maintained under hydrocracking conditions including the presence of hydrogen and a relatively high pressure of more than 1000 p.s.i.g.;

(b) withdrawing from said zone an efiiuent stream containing hydrocracked hydrocarbons;

(c) passing said efliuent stream at a temperature exceeding 700 F. into a first separation zone under substantially the same pressure as maintained in said reaction zone under conditions sufficient to produce a first vapor stream and a first liquid stream containing hydrocracked hydrocarbons;

(d) measuring the temperature of said first vapor stream;

(e) introducing water as quench at a temperature from 50 F. to 250 F. directly into the downstream side of said reaction zone in an amount responsive to said temperature measurement sufficient to maintain a predetermined relatively high temperature of more than 700 F. and less than 775 F. of said first vapor stream;

(f) cooling said first vapor stream from said measured temperature to a temperature from 50 F. to F. by indirect heat exchange cooling means;

(g) separating the cooled vapor stream in a second separation zone at substantially the same pressure as said first separation zone under conditions suflicient to provide a second vayor stream comprising hydrogen, a second liquid stream containing hydrocracked hydrocarbons, and an. aqueous stream containing quench water;

(h) returning said second vapor stream to said reae- References Cit tion zone; (i) recycling a portion of said first liquid stream to UNITED STATES PATENTS combine with said feedstock in step (a); and 3,101,380 8/1963 Har1l1 1 0 (j) recovering hydrocracked hydrocarbons in high con- 5 3,119,765 1/ 1964 Cornell a1 centratiom 3,192,281 6/ 1965 Cornell 208-112 2. Method according to claim 1 wherein said aqueous 3'288876 11/1966 Hammond et a1 260672 stream of Step (g) is returned to Step (e) as quench. DELBERT E. GANTZ, P rimary Examiner 3. Method according to claim 1 wherein said feedstock is characterized by having at least 10% boiling above 1050 F.

4. Method according to claim 1 wherein said feedstock boils within the range from 400 F. to 1100 F, 208-108;260-672 10 A. RIMENS, Assistant Examiner

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