CA1242403A

CA1242403A - Two-stage petroleum residuum hydroconversion using a countercurrent gas-liquid first stage

Info

Publication number: CA1242403A
Application number: CA000466928A
Authority: CA
Inventors: Suenman G. Yu; Christopher W. Kuehler; Arthur J. Dahlberg; Dennis R. Cash
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1983-11-03
Filing date: 1984-11-02
Publication date: 1988-09-27
Also published as: GB2148937B; AU3478884A; JPS60173091A; GB2148937A; GB8427668D0; DE3440133A1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for hydroprocessing a petroleum residuum fraction. In a hydrothermal dissolving-stripping zone a mixture is formed which comprises petroleum residuum and its hydrothermal reaction products. Simul-taneously, substantial amounts of light products are stripped from the mixture by countercurrent contact with a hydrogen gas stream at elevated temperatures. A gaseous stream comprising the light products is withdrawn and the remaining heavier effluent is contacted in a reaction zone with a second hydrogen gas stream and externally supplied hydrocracking catalyst at temperatures generally lower than the temperature of the hydrothermal dissolving-stripping zone.

Description

TWO-STAGE PETROLEUM RESIDUUM HYDROCONVERSION
USING A COUNTERCURRENT GAS-LIQ~ID YIRST STAGE

BACKGROUND OF THE INVENTION
The present invention relates to processes for the hydroconversion of heavy hydrocarbonaceous fractions or residua. In particular, it relates to two-stage pro-cesses for the hydrothermal and hydrocatalytic conversionof petroleum residua.
The production of liquid products by the high temperature and pressure hydrogenation of heavy hydro-carbonaceous fractions or residua derived from petroleum, ; 15 oil shale, tar sands or coal is well known. The resulting liquids, however, are often inefficiently obtained with high consumption of hydrogen and catalyst and excess production of lighter, normally gaseous products.
In a preferred embodiment of a two-stage process ~0 for the hydroconversion of heavy hydrocarbons, the heavy material is first heated and subjected to a high severity hydrothermal treatment, preferably without added catalyst or contact materials, in the presence of hydrogen at about 400C to 480C, i.e., 750F to 900F, then the entire effluent ~rom the first stage ~gases, liquids and solids) may be passed directly to a catalytic,hydrocracking zone, preferably at a temperature below 800F and lower than the temperature in the hydrothermal zone. In a preferred embodiment of that process, the hydrothermal zone and the catalytic reactor are close-coupled. Residuum conversion and distillate yield are maximized. A consequence of higher severity hydrothermal stage operation is that more cracked products and light gases are produced jn the hydrothermal stage. Furthermore, the distillate species formed in the hydrothermal stage are further hydrogenated in the catalytic reactor, and although this improves product quality, hydrogen consumption is higher. The hiyh temperature hydrothermal stage produces saturated light products which can form an unstable mixture with the remaining heavy uncracked materials, which are thought to Ol -2-be aromatic, and other unsaturates. The heavy portion of residuum is mostly asphaltenes which require an aromatic n5 medium for solubilization. There may be insufficient solvency in the bulk of the material to retain the uncracked heavier asphaltenes in solution. The result is phase separation and precipitation of asphaltenes which tends to occur as the temperature is dropped between the hydrothermal stage and the lower temperature hydrocracking stage.
In the case of coal liquefaction with added petroleum residuum, U.S. Patent No. 4,330,393 teaches that the small quantities of water and Cl to C4 gases produced in the hydrothermal stage are preferably removed before the effluent enters the hydrocracking zone for the purpose of increasing the hydrogen partial pressure in the hydro-cracking stage. The physical structuring of the hydrothermal zone in U.S. Patent No. 4,330,393 is such

2~ that the coal/residuum slurry may flow upwardly or downwardly in said zone. In the multistage coal lique-faction process of U.S. Patent No. 4,110,192, it has been found advantageous to vent most of the gases from the dissolver zone while co-currently passing hydrogen and liquids into the dissolver zone and out of the dissolver zone to the catalytic treatment zone.¦
In general, two-stage (hydrothermal-hydrocracking) treatments require more hydrogen, which can be supplied by known processes from natural gas or coal at a price. The cost could be reduced without loss of benefit if (i) light products which consume hydrogen in the catalytic reactors could be separated before the catalytic hydrocracking stage; (ii) some heavy material rejection occurred before the catalytic stage; and (iii) milder operating conditions were selected.
It would be advantageous i f hydrogen utilization efficiency could be improved in two-stage residuum hydro-conversion processes by reducing the hydrogenation of the mid-distillate fraction of the product of the two-stage Ol _3_ process. This could be accomplished if the lighter frac-tions, optionally including mid-distillates, could be 05 continuously removed from the dissolver stage product. It would also be advantageous if the light products, includ-ing light saturated hydrocarbons found in the hydrothermal staye of a two-stage residuum hydroconversion process, could be continuously stripped away from the remaining liquid together with water, carbon monoxide, and other materials which cause instability and are deleterious to the processes of the catalytic hydrocracking stage. By this means the second stage would operate more efficiently and the instability of the product towards asphaltene pre-cipitation would be overcome. This, and other advantages, are achieved by the process of the present invention.
SUMMAR~ OF THE INVENTION
A process for hydroprocessing a petroleum residuum fraction. In a hydrothermal treating-stripping ~0 zone, ~orming a mixture comprising said petroleum residuum fraction and hydrothermal reaction products, and simul-taneously stripping substantial amounts of light products from said mixture by contacting said mixture counter-currently with a first hydrogen gas stream at elevated temperatures. A gaseous stream comprising the light prod-ucts is withdrawn from the hydrothermal treating-stripping zone and a heavier effluent stream is left behind. At least a substantial portion of the heavier effluent stream is contacted in a reaction zone with a second hydrogen gas stream and an externally supplied hydrocracking catalyst under hydrocracking conditions which include a temperature lower than the temperature of the hydrothermal treating-stripping zone. A second effluent stream is withdrawn from the hydrocracking zone.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a block flow diagram of suitable flow paths for use in practicing an embodiment of the invention.

01 _4_ DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS OF THE INVENTION
05 Referring to the drawing, in a preferred embodiment of the present invention, a heated (pumpable) petrolaum residuum fraction enters via line 1 into the hydrothermal treating-stripping zone 10 which it traverses in a generally downflow manner in countercurrent contact with added hydrogen gas entering the hydrother~al treating-stripping zone 10 through line 5. The residuum is heated and hydrotreated in the presence of the added hydrogen gas, thereby forming a mixture of petroleum, residuum and hydrothermal reaction products. The hydrogen gas traverses zone 10 in a generally upflow manner, thereby stripping substantial amounts of the lighter products Erom the mixture and conveying same out of the treating~stripping zone via line 15. The mixture from zone 10 passes via line 20 to zone 25 where it is cooled, if necessary, to a temperature lower than the temperature of the hydrothermal stage and preferably up to about 85C
lower than the temperature of the hydrothermal stage.
The cooled mixture is then conveyed by line 30 to hydro-cracking zone 35 where it is catalytically hydrocracked in the presence of hydrogen supplied via line 40 to produce a relatively low-viscosity liquid produ~t which may be readily separated from any solid residue.
Referring to the drawing in detail, a petroleum residuum fraction may be mixed with a solvent to form a pumpable slurry or the residuum fraction may be heated by conventional means to form a pumpable liquid. The basic feedstock of the invention is a petroleum residuum frac-tion, heavy oil, or hydrocarbonaceous material derived from petroleum, coal, oil shale, tar sands, bitumen, lig-nite, or mixtures thereof. The petroleum residua derivedfrom heavy crudes such as Maya (Mexico), Beta (Offshore California~, Hondo (Offshore California), and Pt. Arguello (Offshore California), are particularly preferred. ~ sol-vent used in preparation of the feedstock may be selected ~1 -5~

from the various solvents known to the art, and it may be process-derived.
o5 The process of the present invention, however, is capable of tolerating a higher metals content in the hydrocracking zone without prior demetalation or pretreat-ment precautions if a small amount, up to about 5 weight percent, of comminuted coal is slurried with the feedstock. A substantial portion of the metals of the crude are bound to or deposited upon the coal residue suspended in the liquid feedstock and thus do not deposit on the cracking catalyst.
The feedstock oil is fed or pumped through line l to a hydrothermal treating-stripping zone lO com-prising one or more treater-strippers wherein the oil is heated, with added hydrogen, to a temperature i'n the range of about 400C to 480C (750E' to 900F), preferably about 425C to 455C (800F to 850F) for a lenyth of time to react a portion of the feedstock, thereby forming a mixture of feedstock and hydrothermal reaction products, including light products. Such lighter products include acid gases, such as carbon monoxide; light saturated hydrocarbons, such as methane, ethane and butane; and the lighter fractions of hydrocarbonaceous oils, optionally including those which are generally kn'ow~ as mid-distillates, i.e., having normal boiling points up to about 370C (700F~.
'It is preferred that the feedstock be heated to at least 490C (750F) to obtain sufficient conversion in the hydrothermal zone. Furthermore, it is usually preferred that the feedstock not be heated to temperatures above about 480C (900F) in order to prevent excessive thermal cracking which could substantially reduce the overall yield of normally liquid product.
The hydrothermal treating-stripping zone lO
basically comprises one or more elongated vessels, preferably free of added external catalysts or contact materials, which are designed so that in at least one vessel of said zone, the feedstock flows downwardly while hydrogen gas flows upwardly in countercurrent contact ~ith the heated feed, and the mixture resulting from the ~5 hydrothermal reaction. More generally, the vessel used for continuous contacting of hydrogen gas and the feed can be a tower filled with solid packing material, or an empty tower into which the feed may be sprayed and through which the gas flows, or a tower which contains a number of bubble-cap sieve or valve-type plates, but the gas and the feed flow in substantially countercurrent contact with each other to obtain the greatest concentration driving force and therefore the greatest rate of desorption, i.e., stripping. Design factors in this unit operation are lS dealt with in "Chemical Engineers Handbook", Perry and Chilton, 5th Edition, McGraw-Hill, Sections 4, 14, and 18.

The hydrothermal treating-stripping zone 10 may comprise one or more treating vessels in which feed and added hydrogen move countercurrently or co-currently, but it is essential that it comprises at least one treating-stripping vessel in which the hydrothermal product mixture of feedstock and reaction product flows countercurrently ; to a hydrogen gas stream. The treating-stripping vessel may be operated as a liquid-full vessel with level control to ensure that the vessel operates with a liquid mixture to a certain level, thereby regulating the residence time of the mixture in the hydrothermal zone. Level control is exemplified by Perry and Chilton, supra, Section 22. ~me latter operating configuration is ~referred under'~conditions where substantial backmixing is not detrimental to the process and its products. Preferably, the treating-stripping vessel is operated as a continuous staged reactor of the vertical type (Perry and Chilton, supra, Section 4, page 21) by the use of the aforementioned reactor inter-nals. The latter operating configuration is preferred under conditions requiring minimum backmixing.
The yield structure of prQducts obtained from the hydrothermal treating-stripping zone 10 is improved J
... .. .

01 _7_ (i.e., less light, normally gaseous products are produced~
i~ the vessels comprising zone 10 are temperature staged oS in series, i.e., going from a higher temperature vessel near the inward of zone 10 at line 1 to a lower tempera-ture vessel near the outlet of zone 10 at line 20, with all the temperatures in zone 10 still within the afore-mentioned range. By dropping the temperature toward the outlet of zone 10, the mixture is not only prepared for the lower temperature next stage in zone 25 and zone 35, but the cracking reactions are turned down. Temperature control along a series of vessels is easily achieved by intermediate cooling between vessels by means of heat exchange or guench gas injection. Similar benefits are obtainable in a single vessel treating-stripping zone 10 by the use of the aforementioned continuous staged reactor. With backmixing eliminated or reduced in a staged reactor, a descending temperature profile is 2~ obtained in the treating-stripping vessel by the use oE, for example, a downflowing preheated feedstock 1 and an upflowing hydrogen quench gas stream 5. In an alternative embodiment, hydrogen gas is injected into the vertically elongated treating-stripping vessel at several positions along the vertical length o the vessel. In yet another embodiment, cooling stage 25 may not ~e necessary to achieve the lower temperature necessary for hydrocracking stage 35 within the ranges of temperatures specified when such a temperature staged dissolving stripping zone is used.
Depending on operating conditions, and the aforementioned design factors which are within the kno~ledge of those skilled in the art, the counterflowing hydrogen gas entering through line 5 and comprising fresh and recycle hydrogen, will strip the mixture more or less deeply as to the amount of the light products stripped and the normal boiling points of the light products stripped from the mixture. It is optionally preferred that substantial amounts of mid-distillates having normal boiling points below about 260C (50~F) be stripped from the hydrothermal treating-stripping zone 10 and removed via line 15. It is preferred that substantial amounts of o5 all light hydrocarbons having normal boiliny points below about 20C (70F) be stripped from the hydrothermal treating-stripping zone 10 and removed via line 15. It is most preferred that substantially all gases having boiling points below about 0C (32F) be stripped from the hydrother~al treating-stripping zone 10 and removed via line 15. Hydrogen should be separated from the effluent stream 15 for recycle to the process. The light hydrocarbon products in the effluent stream should be fractionated and used directly or, if necessary, for particular usages, subjected to further treatment.
Operating conditions in the hydrothermal treating-stripping zone can vary widely, except for tem-perature Other reaction conditions in the hydrothermal treating-stripping zone include a residence time of 0.01 2~ to 3.0 hours, preferably 0.1 to 1.0 hours; a pressure of 0 to 10,000 psig, preferably 1,500 to 5,000 psig, and more preferably 1,500 to 2,500 psig; a hydrogen gas rate of 0 to 20,000 standard cubic feet per barrel of feed, prefera-bly 3,000 to 10,000 standard cubic feet per barrel of feed; and a feed hourly space velocity of about 0.3 to 100 hr~l, preferably about 1 to 10 hr~l.
A remarkable advantage of the process of the present invention is the decoupling of the hydrogen supply to the treating and hydrocracking stages 10 and 35 while the treating and hydrocracking stages may remain closely coupled, if desired. Consequently, optimal hydrogen pres-sure and gas rate may be provided to the hydrothermal treating-stripping zone lC while, simultaneously, a dif-ferent optimal hydrogen pressure and gas rate is provided in the catalytic hydrocracking zone 35. In the co-current hydrogen gas flow and liquid process, this ~lexibility is not practical In general, hydrogen gas flow rate should be higher in the hydrocracking zone because of greater hydrogen consumption. By placing a pump (not shown) in 01 _9_ line 30, one may operate at a lower hydrogen pressure in zone l0 and a higher pressure in zone 35.
The treating zone will, in general, contain no catalyst from any external source, although the mineral matter contained in added coal, if any, may have some catalytic effect. The mixture of heavier products and unconverted feed, as well as any remaining lighter products, is passed via line 20 to a cooling æone 25.
Cooling zone 25 will typically contain a heat exchanger or similar means whereby the effluent from treater l0 is cooled to a temperature below the temperature of the treating stage and at least below 425C (800F). Some cooling in zone 25 may also be effected by the addition of fresh cold hydrogen, if desired. Cooling zone 25 is an optional feature of this embodiment and may not be necessary to effect the temperature gradient between zone l0 and zone 35. Optionally, zone 25 comprises a 2~ flash unit to remove light solvent fractions from the remaining light products in the heavier effluent stream.
The light solvent fractions may be burned to provide process heat.
The mixture of heavier reaction products and feed and remaining light products is fed through line 30 into reaction zone 35 containing a hy'drocracking catalyst.
Hydrogen comprising fresh and/or recycle hydrogen is fed via line 40 into the hydrocracking zone 35. In the hydro-; cracking reaction æone, hydrogenation and cracking occur simultaneously and the higher molecular weight compoundsare converted to lower molecular weight compounds, the sulfur in the sulfur-containing compounds are converted to hydrogen sulfide, the nitrogen in the nitrogen-contcining compounds are converted to ammonia, and the oxygen in the oxygen-containing compounds are converted to water.
Preferably, the catalytic reaction zone is a fixed bed type, but an ebullating or moving bed may also be used.
The mixture of heavier reaction products and unconverted feed preferably passes upwardly through the catalytic 3L24~3 ~1 -10-reaction zone, but may also pass downwardly. Counter-current or co-current movement of the added hydrogen gas oS with respect to the liquid flow is also optional. The primary advantage of passing such a mixture upwardly through the fixed bed of particulate catalysts is that the probability of plugging is reduced.
A particularly desirable method of operating the process is for the fixed catalyst bed to be operated in an upflow mode, with the lower portion of the catalyst in the bed being removed as the catalyst becomes fouled. Fresh catalyst can be added to the top of the fixed bed to replace the catalyst which is removed from the bottom.
This addition and removal of catalyst can take place periodically or in a continuous or semi-continuous manner.
Continuous catalyst replacement according to this inven-tion is carried out at such a low rate that the catalyst bed is properly described as a fixed bed.
~0 The catalyst used in the hydrocracking zone may be any of the well known, commercially available hydro-cracking catalysts. A suitable catalyst for use in the hydrocracking reaction stage comprises a hydrogenation component and a cracking component. Preferably the hydro-genation component is supported on a refractory cracking base. Suitable bases include, for ex'~mple, silica, alumina, or composites of two or more refractory oxides such as silica-alumina, silica-magnesia, silica-zirconia, alumina-boria, silica-titania, silica-zirconia-titania, acid-treated clays, and the like. Acidic metal phosphates such as alumina phosphate may also be used. Preferred cracking bases comprise alumina and composites of silica and alumina. Suitable hydrogenation components are selected from Group VI-B metals, Group VIII metals, and their oxides, or mixtures thereof. Particularly useful are cobalt-molybdenum, nickel-molybdenum, or nickel-tungsten on silica-alumina or alumina supports.
Hydrocracking zone 35 comprises one or more hydrocrac~ing reactor vessels containing one or more of the afore-mentioned catalysts in any combination.

?~

It is preferred to maintain the temperature in the hydrocracking zone below 425C (300F), preferably in 05 the range of 340C to 425C ~645F to 800F), and more preferably 340C to 400C (645F to 750F), to prevent catalyst fouling. The temperature in the hydrocracking zone should be preferably maintained below the temperature in the hydrothermal zone by about 55C to about 85C.
Other hydrocracking conditions include a pressure from 500 ; to 5,000 psig, preferably 1,000 to 3,000 psig, and more preferably 1,500 to 2,500 psig; a hydrogen gas rate of 2,000 to 20,000 standard cubic feet per barrel of slurry, preferably 3,000 to 10,000 standard cubic feet per barrel of slurry; and a slurry hourly space velocity in the range of from 0.1 to 2.0, preferably 0.2 to 0.5.
The product effluent 50 from reaction zone 35 is separated in separation æone 55 into a gaseous fraction 60 comprising light oils boiling below about 150C to 260C
(300F to 500F), preferably below 200C (400F), and normally gaseous components such as hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, and the C1 to C4 hydrocarbons. Preferably, the hydrogen is separated from the other gaseous components and recycled. Liquid fraction 65 is available for fractionation or further processing. , The process of the present invention produces ; extremely clean, normally liquid products. The normally liquid products, that is, all of the product fractions boiling above C4, ha~e an unusually low specific gravity;
a low sulfur content of less than 0.2 weight percent; and a low nitrogen content of less than 0.5 weight percent.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of hydroprocessing a petroleum residuum fraction which comprises:
(a) in a hydrothermal treating-stripping zone, forming a mixture comprising said petroleum residuum fraction and hydrothermal reaction products, and simul-taneously stripping light products from said mixture by contacting said mixture countercurrently with a first hydrogen gas stream at an elevated temperature;
(b) withdrawing from said hydrothermal treating-stripping zone a gaseous stream comprising said light products and leaving a heavier effluent stream;
(c) contacting at least a portion of said heavier effluent stream in a catalytic reaction zone with a second hydrogen gas stream and an externally supplied hydro-cracking catalyst under hydrocracking conditions, including a temperature lower than the temperature of said hydrothermal treating-stripping zone; and (d) withdrawing from said catalytic reaction zone a second effluent stream.

2. A process according to Claim 1 wherein said hydrothermal treating-stripping zone comprises at least one treating-stripping vessel containing internals which substantially reduce backmixing.

3. A process according to Claim 1 wherein said treating-stripping zone is free of externally supplied catalyst or contact particles.

4. A process according to Claim 1 wherein the hydrogen partial pressure in said hydrothermal treating-stripping zone is less than the hydrogen pressure in said reaction zone.

5. A process according to Claim 1 wherein said hydrocracking conditions comprise a pressure of 20-1,000 atmospheres and a petroleum residuum fraction liquid hourly space velocity of 0.1 to 10.

6. A process according to Claim 1 wherein the reaction zone temperature is up to about 85°C lower than the temperature of said hydrothermal treating-stripping zone.

7. A process according to Claim 1 wherein the treating-stripping zone temperature is about 300°F to 1000°F.

8. A process according to Claim 1 wherein the temperature in said dissolving-stripping zone is staged in a descending manner, such that the temperature is lower at the outlet end of the zone than at the inlet end of the zone.