GB2135691A - Hydrocracking of heavy oils in presence of dry mixed additive - Google Patents

Abstract

In an process for the hydrocracking of heavy hydrocarbon oil, such as oils extracted from tar sands, the charge oil (10) in the presence of an excess of hydrogen is passed through a tubular hydrocracking zone (13), and the effluent (14) emerging from the top of the zone is separated (15) into a gaseous stream (18) containing a wide boiling range material and a liquid stream (16) containing heavy hydrocarbons. The hydrocracking process is carried out in the presence of an additive consisting of finely divided coal or other carbonaceous material dry mixed with a compound of a metal e.g. catalytically active metals such as iron, cobalt and molybdenum. The additive is slurried with the charge stock and has been found to greatly reduce coke precursors and thereby prevent the formation of carbonaceous deposits in the reaction zone while also being effective in reducing the sulphur concentration of the product. <IMAGE>

Description

SPECIFICATION Hydrocracking of heavy oils in presence of dry mixed additive This invention relates to the treatment of hydrocarbon oils and, more particularly, to the hydrocracking of heavy hydrocarbon oils to produce improved products of lower boiling range.

Hydrocracking processes for the conversion of heavy hydrocarbon oils to light and intermediate naphthas of good quality for reforming feed stocks, fuel oil and gas oil are well known. These heavy hydrocarbon oils can be such materials as petroleum crude oil, atmospheric tar bottoms products, vacuum tar bottoms products, heavy cycle oils, shale oils, coal derived liquids, crude oil residuum, topped crude oils and the heavy bituminous oils extracted from oil sands. Of particular interest are the oils extracted from oil sands and which contain wide boiling range materials from naphthas through kerosene, gas oil, pitch, etc. and which contain a large portion of material boiling above 5240 C, equivalent atmospheric boiling point.

The heavy hydrocarbon oils of the above type tend to contain nitrogenous and sulphurous compounds in exceedingly large concentrations. In addition, such heavy hydrocarbon fractions frequently contain excessive quantities of organo-metallic contaminants which tend to be extremely detrimental to various catalytic processes that may subsequently be carried out, such as hydrofining. Of the metallic contaminants, those containing nickel and vanadium are most common, although other metals are often present. These metallic contaminants, as well as others, are usually present within the bituminous material as organo-metallic compounds of relatively high molecular weight. A considerable quantity of the organometallic complexes are linked with asphaltenic material and contain sulphur.Of course, in catalytic hydrocracking procedures, the presence of large quantities of asphaltenic material and organometallic compounds interferes considerably with the activity of the catalyst with respect to the destructive removal of nitrogenous, sulphurous and oxygenated compounds. A typical Athabasca bitumen may contain 51.5 wt % material boiling above 5240C., 4.48 wt % sulphur, 0.43 wt % nitrogen, 213 ppm vanadium and 67 ppm nickel.

As the reserves of conventional crude oil decline, these heavy oils must be upgraded to meet the demands. In this upgrading, the heavier material is converted to lighter fractions and most of the sulphur, nitrogen and metals must be removed.

This can be done either by a coking process, such as delayed or fluidized coking, or by a hydrogen addition process such as thermal or catalytic hydrocracking. The distillate yield from the coking process is about 70 wt % and this process also yields about 23 wt % coke as by-product which cannot be used as fuel because of low hydrogen:carbon ratio, and high mineral and sulphur content. Depending on operating conditions, hydrogenation processes can give a distillate yield of over 87 wt %.

Recent work has been done on an alternate processing route involving hydrogen addition at high pressures and temperatures and this has been found to be quite promising. In this process, hydrogen and heavy oil are pumped upwardly through an empty tubular reactor in the absence of any catalyst. It has been found that the high molecular weight compounds hydrogenate and/or hydrocrack into lower boiling ranges. Simultaneous desulphurization, demetallization and denitrogenation reactions take place. Reaction pressures up to 24 MPa and temperatures up to 4900C have been employed.

In thermal hydrocracking, the major problem is coke or solid deposition in the reactor, especially when operating at relatively low pressures, and this can result in costly shut-downs. Deposits form at the top of the reactor where the partial pressure of hydrogen and the ash content are at the lowest.

Higher pressures reduce reactor fouling. At 24 MPa and 4700C, the coke deposition can be substantially eliminated. However, plant operations at high pressures involve higher capital and operating costs.

It has been well established that mineral matter present in the feed stock plays an important role in coke deposition. Chervenak et al, U.S. Patent 3,775,296 shows that feed stock containing high mineral content (3.8 wt %) has less tendency to form coke in the reactor than feed containing low mineral matter wt %). Other studies have shown that a high mineral content had no apparent effect on pitch conversion and desulphurization, but suppressed coke deposition in the reactor and general reaction fouling.

It has also previously been shown that coke deposition in the reactor can be suppressed by recirculating a portion of heavy ends to the lower portion of the reaction zone. In Wolk, U.S. Patent 3,844,937 it has been shown that when the mineral concentration of the reactor fluid was maintained between 4 and 10 wt % during thermal hydrocracking, no coke was found in the reactor. It seemed that during the hydrocracking process, carbonaceous material deposited on solid particles instead of the reactor wall, and could thus be carried out with the reactor effluent. This indicated the possibility of continuously adding and withdrawing a coke carrier in the reactor.

The addition of coke carriers was proposed in Schuman et al. U.S. Patent 3,151,057, who suggested the use of "getters" such as sand, quartz, alumina, magnesia, zircon, beryl and bauxite.

These "getters" could be regenerated after use by heating the fouled carrier with oxygen and steam at about 1 0900C to yield regeneration-product-gases containing a substantial amount of hydrogen. It has been shown in Ternan et al, Canadian Patent 1,073,389 issued March 10, 1980 and Ranganathan et al, United States Patent 4,214,977 issued July 29,1 980, that the addition of coal or coal-based catalyst results in a reduction of coke deposition during hydrocracking. The coal additives act as sites for the deposition of coke precursors and thus provide a mechanism for their removal from the system.

The use of these coal based catalysts ailows operation at lower pressures and at higher conversions. The use of coal and Co, Mo and Al on coal catalysts is described in Canadian Patent 1,073,389, the use of iron-coal catalysts in U.S. Patent 4,214,977 and the use of fly ash in Canadian Patent, 1,124,194.

In the U.S. Patent 3,775,286, a process is described for hydrogenating coal in which the coal was either impregnated with hydrated iron oxide or dry hydrated iron oxide powder was physically mixed with powdered coal. However, the conversion rates using the physical mixture were quite poor compared with the impregnated coal.

It is an object of the present invention to provide an improved process for hydrocracking a heavy hydrocarbon feedstock by which some of the problems of deposits forming in the reactor during the hydrocracking process can be overcome, in an economical manner.

According to the invention, there is provided a process for hydrocracking a heavy hydrocarbon oil, a substantial portion of which boils above 5240 C, in which a slurry of heavy hydrocarbon oil and from about 0.01-25 wt % of carbonaceous additive particles in the presence of 500-50,000 s.c.f. of hydrogen per barrel of said hydrocarbon oil is passed through the confined hydrocracking zone, said hydrocracking zone being maintained at a temperature between about 375 and 5000 C, a pressure of at least 3.5 MPa and a space velocity of up to 4 volumes of hydrocarbon oil per hour per volume of hydrocracking zone capacity, a mixed effluent containing a gaseous phase comprising hydrogen and vaporous hydrocarbons and a liquid phase comprising heavy hydrocarbons is removed from the hydrocracking zone, and the effluent is separated into a gaseous stream containing hydrogen and vaporous hydrocarbons and a liquid stream containing heavy hydrocarbons, said carbonaceous additive being in the form of a dry mix of ground coal or other carbonaceous material and a ground metal salt.

This process substantially prevents the formation of carbonaceous deposits in the reaction zone.

These deposits, which may contain quinoline and benzene insoluble organic material, mineral matter, metals, sulphur, and little benzene soluble organic material will hereinafter be referred to as "coke" deposits.

The dry mix is, of course, much cheaper to produce than the usual metal salt impregnated additives. At the same time, it compares favourably with the impregnated additives in reducing coke precursors and preventing formation of coke deposits in the reaction zone.

The process of this invention is particularly well suited for the treatment of heavy oils having a large proportion, preferably at least 50% by volume, which boils above 524"C and which may contain a wide boiling range of materials from naphtha through kerosene, gas oil and pitch. It can be operated at quite moderate pressure, preferably in the range of 3.5 to 24 MPa, without coke formation in the hydrocracking zone.

Although the hydrocracking can be carried out in a variety of known reactors of either up or down flow, it is particularly well suited to a tubular reactor through which feed and gas move upwardly. The effluent from the top is preferably separated in a hot separator and the gaseous stream from the hot separator can be fed to a low temperature-high pressure separator where it is separated into a gaseous stream containing hydrogen and less amounts of gaseous hydrocarbons and a liquid product stream containing light oil product.

The metal compound which is used for the additive is preferably one which converts into metal sulphide from the action of hydrogen and hydrogen sulphide. It may be an oxide of the metal, metal salt, such as sulphate, sulphide, chloride, fluoride, nitrate, oxalate or carbonate or metal hydroxide. The metal is typically a catalytically active metal such as iron, cobalt, nickel, molybdenum, chromium, tungsten, vanadium, zinc, etc. A particularly preferred compound is iron sulphate.

The metal salt and carbonaceous material used in accordance with this invention are preferably of quite small particle size, e.g. less than 60 mesh (Canadian Standard Sieve) and it is particularly preferred to use a material which will pass through a 100 mesh sieve. Nevertheless, it is possible to achieve the benefits of the invention with larger particle sizes of up to 4 inch. A typical additive mix will contain 5 to 95% by weight metal salt and usually the catalyst is mixed with the heavy oil feed in an amount of 0.1-5 wt % based on heavy oil feed, although it may vary as widely as 0.01-25 wt % based on feed.

The additive can conveniently be prepared by grinding, drying and subsequent sieving of a suitable coal to minus 100 mesh, whereupon a calculated amount of 100 mesh metal salt is slowly added into the coal in a mix-muller and the batch mixed for about 10 minutes. Some metal salts must be dried prior to sieving to 100 mesh to decrease the hygroscopy by reducing the moisture or hydrate water content. The drying can conveniently be carried out at about 900 C for 3 hours. The reduced hygroscopy greatly facilitates subsequent sieving.

The particle sizes can be smaller or larger than 100 mesh depending on the reactor geometry and coking tendencies of heavy hydrocarbon oil feed. The dry mixing procedure further allows the metal salt particle size and coal size to be adjusted independently. For example, the coal particle size could be chosen larger to obtain a longer residence time for those particles, which would allow more liquefaction.

It has been found that particularly good results are obtained when the metal salt is mixed with coal, preferably lignite or sub-bituminous coal or mixed with fly ash.

Coal can broadly be defined as a mineral substance consisting of carbonized vegetable matter.

There are many different types of coal, including lignite, bituminous coal and anthracite. Lignite is a material intermediate in character between peat and coal and contains a substantial proportion of volatile hydrocarbons. Bituminous coal is the commonest type of coal and is somewhat harder than lignite, with a higher carbon content and lower volatile hydrocarbon content. Sub-bituminous coal is a material intermediate in character between lignite and bituminous coal. Anthracite is a very hard coal, containing a high proportion of carbon and a very small proportion of volatile compounds. Coke, on the other hand, is the solid product of the action of heat upon coal and consists of a porous, hard mass of carbon containing very little of volatile compounds.

In the present process the additive is being specifically used to suppress coke formation and to remove coke deposits. Thus, it has been found to be particularly advantageous to mix the metal salt with lignite or sub-bituminous coal or fly ash instead of coke or semi-coke. For instance, it has been observed that at hydrocracking conditions, lignite hydrogenates extensively and bituminous coal, coke or semi-coke hydrogenates the least. The extent of the hydrogenation of sub-bituminous coal is between the above extremes. Thus, an ideal slurry catalyst carrier for this hydrocracking process should hydrogenate partially, resulting in a reduction of particle size and these particles should leave with the product stream carrying some of the coke deposited. For the above reasons, it will also be clear that a coke or semi-coke carrier for this purpose is not satisfactory.

According to a preferred embodiment, the heavy hydrocarbon oil feed and metal-coal additive are mixed in a feed tank and pumped along with hydrogen through a vertical reactor. The liquid-gas mixture from the top of the hydrocracking zone can be separated in a number of different ways. One possibility is to separate the liquid-gas mixture in a hot separator kept between 200-4700C and at the pressure of the hydrocracking reaction. The heavy hydrocarbon oil product from the hot separator can either be recycled or sent to secondary treatment.

The gaseous stream from the hot separator containing a mixture of hydrocarbon gases and hydrogen is further cooled and separated in a low temperature-high pressure separator. By using this type of separator, the outlet gaseous stream obtained contains mostly hydrogen with some impurities such as hydrogen sulphide and light hydrocarbon gases. This gaseous stream is passed through a scrubber and the scrubbed hydrogen is recycled as part of the hydrogen feed to the hydrocracking process. The recycled hydrogen gas purity is maintained by adjusting scrubbing conditions and by adding make up hydrogen.

The liquid stream from the low temperature-high pressure separator represents the light hydrocarbon oil product of the present process and can be sent for secondary treatment.

Some of the metal-coal additive will be carried over with the heavy oil product from the hot separator and will be found in the 524"C+ pitch fraction. However, since this is a very cheap additive, it need not be recovered and can be burned or gasified with the pitch. The metal-coal additive concentration in the feed is normally between 0.1-5.0 wt %, preferably about 1.0 wt %. At hydrocracking conditions, the metal salts are converted to metal sulphides.

For a better understanding of the invention, reference is made to the accompanying drawing which illustrates diagrammatically a preferred embodiment of the present invention.

Heavy hydrocarbon oil feed and metal salt-coal additive are mixed together in a feed tank 10 to form a slurry. This slurry is pumped via feed pump 11 through inlet line 1 2 into the bottom of an empty tower 1 3. Recycled hydrogen and make up hydrogen from line 30 is simultaneously fed into the tower through line 12. A gas-liquid mixture is withdrawn from the top of the tower through line 14 and introduced into a hot separator 1 5. In the hot separator the effluent from tower 1 3 is separated into a gaseous stream 1 8 and a liquid stream 1 6. The liquid stream 1 6 is in the form of heavy oil which is collected at 17.

According to an alternative feature, a branch line is connected to line 1 6. This branch line connects through a pump into inlet line 12, and serves as a recycle for recycling the liquid stream containing carried over metal sulphide particles and coal fines from hot separator 1 5 back into the feed slurry to tower 13.

In yet another embodiment, the line 1 6 feeds into a cyclone separator which separates the metal sulphide particles and coal fines from the liquid stream. The separated metal sulphide particles and coal fines are recycled into the feed slurry to tower 13, while the remaining liquid is collected in vessel 17.

The gaseous stream from hot separator 1 5 is carried by way of line 1 8 into a high pressure-low temperature separator 1 9. Within this separator the product is separated into a gaseous stream rich in hydrogen which is drawn off through line 22 and an oil product which is drawn off through line 20 and collected at 21.

The hydrogen rich stream 22 is passed through a packed scrubbing tower 23 where it is scrubbed by means of a scrubbing liquid 24 which is cycled through the tower by means of pump 25 and recycle loop 26. The scrubbed hydrogen rich stream emerges from the scrubber via line 27 and is combined with fresh make up hydrogen added through line 28 and recycled through recycle gas pump 29 and line 30 back to tower 13.

Certain preferred embodiments of this invention will now be further illustrated by the following non-limitative examples.

EXAMPLE 1 An additive was prepared by crushing and screening a sub-bituminous coal to minus 200 mesh.

This material was subsequently mixed with a predetermined amount of iron sulphate and dried, crushed and sieved to minus 200 mesh. The iron sulphate was first dried because it occurs under normal conditions as hepta hydrate, i.e. FeSO4.7H2O. This salt is hygroscopic and forms agglomerates which plug sieve openings. The heptahydrate was dried to the mono hydrate FeSO4.H2O by heating it at 900C for about 3 hours. The dried iron sulphate was then crushed and sieved. It was slowly added to the coal in a mix muller and mixed for approximately 10 minutes. The resulting mixture was placed in a drum and rotated for about 4 hours.

The properties of the dry-mixed additive are set out in Table 1 below together with the properties of a typical impregnated additive.

TABLE 1 Analysis of Dry-mixed and Impregnated Additive Dry-mixed Impregnated Sulphur wt% 4.81 4.72 Ash wt % 21.76 20.8 Pentane insolubles wt % 93.6 Toluene insolubles wt % 93.0 Vanadium ppm 180 79 Nickel ppm 72 119 Iron wt % 8.78 8.96 Carbon wt % 41.31 41.05 Hydrogen wt % 2.97 3.06 Nitrogen wt % 0.51 0.50 The size distribution of the two additives is given in Table 2.

TABLE 2 Dry Sieve Analysis of Dry Mixed Additive and Impregnated Additive Additive Dry Mixed Impregnated Standard Mesh Weight Yield Weight Yield Size ym (grams) (percent) (grams) (percent) -100-+200 147-74 5.17 2.5 4.661 2.91 -200-+325 74-43 48.35 23.0 42.38 26.4 -325 < 43 156.43 74.5 113.51 70.7 +200 mesh The feedstock employed was a Cold Lake3 vacuum residuum having the following properties.

TABLE 3 Properties of Cold Lake Feedstock Gravity API 4.8 Specific gravity 1 5/1 50C 1.038 Sulphur wt % 5.82 Ash wt % 0.05 C.C.R.' wt % 19.8 Pentane insolubles wt % 22.7 Toluene insolubles wt % 0.07 Asphaltenes wt % 22.6 Carbon wt % 82.90 Hydrogen wt % 9.96 Nitrogen wt % 0.68 Vanadium ppm 251 Nickel ppm 93 Iron ppm 13 Sediment (extraction) wt % trace Water (distillation) wt % trace Pitch2 wt % 85.10 'Conradson Carbon Residue 2Material boiling above 5240 C.

3A region in western Canada A blended slurry of the above feedstock and 1% by weight of the dry mixed additive was prepared and this slurry was used as a feedstock to a hydrocracking plant as illustrated in the attached drawing.

The reactor was operated under the following reactor conditions: Reactor temperature C 450 Pressure MPa 13.9 Liquid hourly space velocity 0.75 Recycled gas rate m3/h 5.9 Recycled gas purity (hydrogen) vol % 85 Length of run h 422 The results obtained from this run were as follows: Pitch (5240C+) conversion wt % 87.5 Sulphur conversion wt % 65.5 Liquid product yield (C4+) vol % 106.1 Liquid product yield (C4+) wt % 92.7 C1-C3 gases wt % 5.7 Hydrogen consumption mtonne 221.9 At the end of the run, 143 grams of solid deposits were found in the system.

The results can be compared to a run in which an impregnated iron-coal additive was employed.

A slightly different Cold Lake feedstock was used; its properties are given below: TABLE 4 Properties of Cold Lake Feedstock (Used with Impregnated Additive) Specific gravity 1 5/1 50C 1.026 Sulphur wt % 5.16 Ash wt % 0.064 C.C.R. wt% 18.2 Pentane insolubles wt % 21.0 Asphaltenes wt% 21.0 Toluene insolubles wt % 0.03 Carbon wt % 82.93 Hydrogen wt % 10.29 Nitrogen wt % 0.57 Vanadium ppm 255 Nickel ppm 92 Iron ppm 10 Viscosity cStat820C 5270 Viscosity cStat990C 1489 Pitch wt % 72.95 For this run the operating conditions were:: Reactor temperature "C 448 Pressure MPa 13.9 Liquid hourly space velocity 0.75 Recycled gas rate m3/tonne 5.9 Recycled gas purity (hydrogen) vol % 85 Length of run h 513 The following results were obtained: Pitch conversion wt % 85.5 Sulphur conversion wt % 55.9 Liquid product yield (C4+) vol % 102.7 Liquid product yield (C4+) wt % 92.3 C1-C3 gases wt % 5.1 Hydrogen consumption m3/tonne 196.8 The total amount of solids deposited during this run was 72 grams, which compares favorably with the 143 grams solids deposited in the dry-mix additive run. Runs at the same operating conditions with no metal-coal additive present could only be operated for a short period before excessive deposit formation or plugging occurred.For example, a run with Athabasca bitumen at 4500C and a higher liquid hourly space velocity of 3.0, with no additive, resulted in 6600 grams of deposits after 384 hours.

The properties of the Athabasca bitumen, the operating conditions and the results for this run are given below.

Properties of Athabasca* bitumen: Specific gravity 1 5/1 50C 1.009 Sulphur wt % 4.48 Ash wt % 0.59 Conradson Carbon Residue wt % 13.3 Pentane insolubles wt % 1 5.5 Benzene insolubles wt % 0.72 Vanadium content ppm 213 Nickel content ppm 67 Total acid number mg KOH/g 2.77 Total base number mg KOH/g 1.89 Carbon wt % 83.36 Hydrogen wt % 10.52 Nitrogen (Dohrmann microcoulometer) wt % 0.43 Chlorine wt % 0.00 Viscosity cstat380C 10000 Pitch(5240C) wt% 51.5 *A region in western Canada containing tar sands.

Operating Conditions: Amount of additive wt % 0 Pressure MPA 10.44 Reactor temp C 450 Length of run h 384 Liquid hourly space velocity 3.0 Recycle gas rate m3/h 5.6 Recycle gas purity (hydrogen) vol % 85 Results: Pitch conversion wt % 60.6 Sulphur conversion wt % 29.9 Hydrogen consumed m3/tonne 58.2 Liquid product yield vol % 100 Liquid product yield wt % 94.2 Total solids Deposits in the system g 6600 It can be clearly seen from these results that the iron-coai additives are very effective in preventing solid deposition. The dry mixed and impregnated additives had about equal coke suppressing activities.

Claims (14)

1. A process for hydrocracking a heavy hydrocarbon oil, a substantial proportion of which boils above 5240 C, in which a slurry of said heavy hydrocarbon oil and a carbonaceous additive is passed in the presence of 500-50,000 s.c.f. of hydrogen per barrel of said hydrocarbon oil through a confined hydrocracking zone, said hydrocracking zone being maintained at a temperature between about 375 and 5000C, a pressure above 3.5 MPa and a space velocity of up to 4.0 volumes of heavy hydrocarbon oil per hour per volume of hydrocracking zone capacity; a mixed effluent containing a gaseous phase comprising hydrogen and vaporous hydrocarbons and a liquid phase comprising heavy hydrocarbons is removed from the hydrocracking zone; and the effluent is separated into a gaseous stream containing hydrogen and vaporous hydrocarbons and liquid stream containing heavy hydrocarbons, said carbonaceous additive being a dry mix of coal or fly ash or other carbonaceous material and dry particles of a metal compound.

2. A process according to claim 1, in which the coal is lignite or subbituminous coal.

3. A process according to claim 2, in which the metal compound is one which converts into metal sulphite under reactor conditions.

4. A process according to claim 2, in which the metal compound is a metal salt.

5. A process according to claim 4, in which the metal compound is a catalytically active metal seiected from iron, cobalt, nickel, molybdenum, chromium, tungsten, vanadium and zinc.

6. A process according to claim 5, in which the metal compound is an iron salt.

7. A process according to claim 6, in which the iron salt is iron sulphate.

8. A process according to claim 1, in which the slurry contains about 0.01-25 wt% of said additive.

9. A process according to claim 8, in which the slurry contains 0.1-5 wt% of said additive.

10. A process according to claim 2, in which the additive particles are minus 60 mesh.

11. A process according to claim 1, in which the carbonaceous additive is fly ash.

12. A process according to claim 11, in which the metal compound is one which converts into metal sulphide under reaction conditions.

1 3. A process substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel feature of combination of features described herein.