CA2030975C - Hydrocracking of asphaltene-rich heavy oil - Google Patents

Abstract

An oil-soluble molybdenum compound (preferably molybdenum naphthenate) is mixed with a heavy oil fraction containing asphaltenes and sulfur. Mixing is conducted at an elevated temperature (150-300°C), whereby the Mo is dispersed and preferentially becomes associated with the asphaltenes in a colloidal form. The product is then further heated to hydrocracking temperature. Hydrocracking is conducted with sufficient hydrogen flow to ensure a hydrogen flow/liquid flow ratio greater than 10, a liquid Peclet No. less than 0.5 and a gas Peclet No. greater than 3Ø At these conditions the liquid is mixed in the reactor and light ends are stripped as they are produced. It is found that asphaltene conversion is high and solid coke formation is low when the process is practiced.

Description

2 This invention relates to an improved catalytic

3 hydrocracking process which finds application for treating heavy

4 oil containing high asphaltene and sulfur contents. The process incorporates use of an oil-soluble molybdenum compound which 6 reacts in situ with sulfur moieties of the asphaltenes to form 7 a colloidal catalyst for the hydrocracking reaction.

9 The invention was developed in connection with a research project undertaken to find a way to reduce coke 11 formation in the refining of heavy oil fractions and improve the 12 conversion of asphaltenes in the feedstock to useful products.
13 The feedstock which was used in the research was vacuum 14 distillation bottoms derived from bitumen. The composition of this material included high contents of pentane-insoluble 16 asphaltenes (typically 25% by weight) and sulfur (typically 5%
17 by weight).
18 It was proposed to apply catalytic hydrocracking to the 19 feedstock, to upgrade it to refinery-treatable fractions.
However the production of solid coke and the low asphaltenes 21 conversion have heretofore made it impractical to practise 22 hydrocracking on such a feed. In practice, it is discarded as 23 waste material. So the objective of the work was to modify ~030975 1 conventional hydrocracking to develop a process characterized by 2 improved asphaltene conversion and reduced solid coke formation.
3 The present work has much in common with a process 4 described in the published literature of R. Bearden and C. L.
Aldrich of Exxon Research and Development Laboratories.
6 More particularly, in their paper entitled "Novel 7 catalyst and process to upgrade heavy oils", published December, 8 1981, in Energy Progress, Vol. 1, No. 1-4, they taught:
9 - adding a small àmount (as little as 100 ppm by weight) of an oil-soluble compound that is a 11 catalyst precursor, specifically molybdenum 12 naphthenate, to a heavy oil fraction, and 13 - subjecting the mixture to hydrocracking 14 conditions, that is, temperature in the range 400-454~C and hydrogen overpressure of 6.9 MPa to 17.2 16 MPa;
17 - with the result that coking is suppressed and high 18 conversion to distillable products is achieved.
19 They further disclosed:
- that by using an oil-soluble compound, good 21 distribution of the precursor is achieved;
22 - that, at hydrocracking conditions, closely spaced, 23 solid, micron-sized, catalytic particles, 24 comprising metal and coke, materialize in the oil;
and 26 - that these well dispersed, catalytically active 27 "M-coke" particles are operative to enable 28 effective hydrocracking to take place.

203Q~75 1 In their U.S. patent No. 4,226,742, Bearden and Aldridge 2 further teach adding molybdenum naphthenate to heavy oil and 3 reacting the mixture at a temperature in the range 325 - 415~C and 4 at a hydrogen overpressure of 500 - 5000 psig, to form in situ what are asserted to be non-colloidal solid particles that are 6 catalytically active, for hydrocracking and suppression of coke 7 formation.
8 It will be noted that, in order to conduct this prior art 9 process, one must produce some solid coke, which requires hydrocracking conditions (that is a temperature greater than about 11 300~C and a hydrogen overpressure).

13 In the first step of the present invention, an oil-14 soluble, hydrocracking catalyst precursor, specifically a molybdenum compound, preferably molybdenum naphthenate, is mixed 16 with heavy oil at an elevated temperature, typically in the order 17 of 150~C. The heavy oil contains a high asphaltene content 18 (greater than 10% by weight) and a high sulfur content (greater 19 than 2.5% by weight). Preferably, the precursor is provided in an amount in the range 5-100 ppm weight molybdenum of the precursor in 21 heavy oil, most preferably in an amount in the range 10-30 ppm.
22 The purpose of this first step is to achieve a needed 23 extent of dispersion of the precursor through the oil and to 24 preferentially associate the molybdenum with the asphaltenes, apparently with their sulfur moieties. At the temperature 26 involved, the viscosity of the oil is sufficiently high to enable 27 dispersion, yet it is below the temperature at which significant 28 decomposition of the precursor takes place. Such dispersion of the precursor and its association with the sulphur moieties of 2 the asphaltenes is essential for the subsequent formation of a 3 colloidal catalyst, thought to be molybdenum sulphide, that shows 4 high selectivity for conversion of asphaltenes in a hydrocracking process.
6 The product from the mixing step is then further heated 7 to hydrocracking temperature (preferably to 440-485~C, most 8 preferably about 455~C) and is introduced into a hydrocracking 9 reactor. Here the mixture is reacted with hydrogen supplied and vented at a sufficient rate so as to maintain mixing of the 11 liquid and to strip light ends from the liquid, as they are 12 produced. Preferably, in the reactor the volumetric flow of 13 hydrogen should be greater than about 8 times (most preferably 14 greater than 10 times) the liquid flow, the Peclet number for the liquid phase should be less than about 0.5, more preferably less 16 than 0.2, and the Peclet number for the gas phase should be 17 greater than about 3Ø These limitations in effect define a 18 single reactor system in which the liquid phase in the reactor 19 is well mixed and the light ends produced are continually being stripped from the liquid.
21 The invention is based on the following discoveries:
22 - that formation of coke is associated with the 23 formation of a separate liquid phase rich in 24 asphaltenes and other coke precursors. This separation is exacerbated by the presence of light 26 ends - therefore the light ends are stripped from 27 the liquid in the reactor using a prolific 28 hydrogen flow; and ~ that it is necessary to ensure that the catalytic 2 species (which appears to be a form of molybdenum 3 sulfide) is colloidal in form, associated with 4 the asphaltenes, and is well dispersed. This is achieved by mixing the oil-soluble compound with 6 the partly heated oil, as a result of which the 7 molybdenum selectively becomes concentrated in 8 the asphaltenes and appears to loosely bond with 9 their sulfur moieties. When the temperature is later increased in the hydrocracking pre-heating 11 step, the molybdenum apparently combines with the 12 sulfur moieties to provide a colloidal catalyst 13 concentrated in the asphaltenes which in turn may 14 be concentrated in separate liquid phases rich in coke precursors such as asphaltenes.
16 The practice of the invention on an experimental basis 17 has led to conversion in the order of 99% with little or no solid 18 coke formation.
19 Broadly stated, the invention is a process for hydrocracking heavy oil containing asphaltenes and sulfur 21 moieties, comprising: mixing the heavy oil with an oil-soluble 22 molybdenum compound hydrocracking catalyst precursor at an 23 elevated temperature that is sufficiently high to enable 24 dispersion of the precursor in the oil but sufficiently low so that significant decomposition of the precursor is avoided, for 26 sufficient time to disperse the precursor and associate it with 27 the asphaltenes; then further heating the mixture to 28 hydrocracking temperature and reacting it with hydrogen in a 29 hydrocracking reactor at hydrocracking pressure, said hydrogen -~ eing supplied and vented at a rate sufficient to ensure mixing 2 of the liquid in the reactor and stripping of light ends, so that 3 catalyst particles are formed which are colloidal in size; and 4 recovering and separating the gaseous and liquid products from the hydrocracking step.

6 DF-~GPTPTION OF TE~E DRAWINGS
7 Figure l is a block diagram showing the steps, 8 reactants and conditions of the process;
9 Figure 2 is a schematic showing in broad outline the laboratory circuit used to conduct the research;
11 Figure 3 is a series of IR spectra demonstrating the 12 effect of change in temperature in the mixing step; and 13 Figure 4 shows asphaltene conversion versus pitch 14 conversion for experiments providing pitch conversions between 42 and 99%.

16 ~-~G~TPTION OF TE~E ~S~"~ EMBODIMENT
17 The preferred feedstock for the present process is a 18 heavy oil fraction having an asphaltene content of at least 25%
19 by wt. and a sulfur content of at least 3% by wt. Typically the feedstock is a high boiling fraction derived from bitumen. In a 21 particular example of such a feed, vacuum tower bottoms derived 22 from bitumen were used in developing the process. The 23 characteristics and composition of this feed were as follows:

C~

- 2030q75 -- TABLE I
2 Distillation Wt. % IBP - 430~C
3 IBP - 525~C 24.0 4 +525~C 76.0 Elemental ComPosition Wt. %
6 Carbon 83.6 7 Hydrogen 9.7 8 Nitrogen 0.8 9 Sulfur 5.9 Oxygen 0.0 11 H/C 1.4 12 TLC/FID Class Composition, Hydrocarbons 75.0 13 Asphaltene (includes Pre-asphaltene)25.0 14 The catalyst precursor used is an oil-soluble 15 molybdenum compound that decomposes in the oil when heated above 16 about 300~C. Preferably, the catalyst precursor is molybdenum 17 naphthenate. The precursor is supplied in an amount sufficient 18 to provide about 5 to l00 ppm weight of Mo in the catalyst 19 precursor per weight of bitumen. Preferably, the amount is l0 to 20 30 ppm.
21 The catalyst precursor is first mixed with the heavy 22 oil feedstock at atmospheric pressure at a temperature, typically 23 150~C. At this temperature the viscosity of the oil is reduced, 24 to assist in dispersion of the catalyst precursor, but the 25 temperature is still low enough to preclude significant 26 decomposition of the catalyst precursor or the formation of solid 27 coke in any significant amount. In this step, it is observed that 28 the catalyst precursor becomes preferentially associated with the 203097~

1asphaltenes and subsequent heating provides the catalyst, 2believed to be MoS2 in a colloidal, well distributed form that 3remains associated with the asphaltene.
4In the standard experimental embodiments the runs were 5conducted at various conditions that are now described by way of 6ranges and specific preferred values. The standard experimental 7procedure will also be described with reference to the 8experimental circuit shown in Figure 2.
9The oil feedstock previously described in Table I and 10the molybdenum naphthenate catalyst precursor were placed in a 11heated tank 1. The precursor was added in an amount in the range 1215-300 ppm. These components were mixed for 10 hours at 150~C by 13means of the mixing pump la.
14The mixing step product was pumped out of the heated 15tank 1 and passed through a line 2 and process pump 3 to the 16process heater 5. Hydrogen was added to the product in the line 174. The hydrogen was at conventional hydrocracking pressure, more 18particularly 1000 to 3500 psig. The resultant reaction mixture 19was heated to a temperature in the range 440-485~C as it passed 20through the heater 5.
21The hot reaction mixture was then introduced through 22line 6a to a conventional tubular reactor 6 where the temperature 23was maintained in the hydrocracking range 440-485~C.
24The hydrogen was added in an amount sufficient to 25ensure vigorous mixing of the liquid during hydrocracking and to 26strip off light ends. The hydrogen was supplied at an amount in 27the range 5000 - 20,000 SCF/BBL. The oil was pumped into the 28reactor at a rate in the range 0.4 - 4.0 LHSV. More particulary, the hydrogen was preferably supplied in an amount sufficient to 2 provide the following conditions in the reactor 6:
3 Volumetric flow of H2/liquid = about 19,000 SCF/Barrel 4 Liquid Peclet No. = about 0.3 Gas Peclet No. = about 12.0 6 These Peclet numbers were determined from tracer 7 studies using Xe133 and I131.
8 The reaction products from the reactor 6 were passed 9 through line 7 to a gas-liquid separator 8. The light ends and 10 unreacted hydrogen exited the separator 8 through the line 9 and 11 were condensed to yield distillable hydrocarbon fractions and 12 hydrogen gas. The liquid products exited the separator 8 through 13 line 10. For the feedstock described in Table 1, these 14 conditions provided a pitch conversion in the range 42 - 99%.
The process is illustrated by the following examples.

17 This example describes in greater detail the process 18 as practised in specific runs in the laboratory and shows that 19 high conversion of asphaltenes with minimal production of solid 20 coke was achieved.
21 An asphaltene-rich feedstock of Cold Lake vacuum 22 residuum IBP greater than 430~C was charged to a O.Olm3 surge 23 tank. 300 ppm of molybdenum, as molybdenum naphthenate, was 24 added to the tank which was equipped with a stirrer and recycle 25 pump and mixed homogeneously therewith. The mixture was heated 26 under a nitrogen blanket to 200~C. The mixture was then pumped 27 through the process heater into the reactor. Hydrogen was 28 admixed with the mixture at the entrance to the process heater.

1 The process heater consisted of a 2.9 mm I.D. 6100 mm long coil 2 immersed in tin at about the hydrocracking temperature.
3 The volume of the hydrocracking reactor was 669 cc.
4 It was a stainless steel cylinder 25 mm I.D. and 1370 mm high, manufactured by Autoclave Engineers, Erie, Pa.
6 The LHSV was 0.4 to 1.0 hl. It usually required 10-7 12 hours for the reactor to reach steady state operating 8 conditions. The hydrocracking took place at a temperature of 9 455~C and pressure of 2000 psig. The reactor effluent comprising a mixture of gases and liquids was fed to the hot separator where 11 gases and liquid were separated.
12 Table II provides typical results for the process.

203097~

2 Reaction Temperature, ~C 455 455 3 LHSV, h~1 0.41 1.03 4 Pressure, psig 2000 2000 H2 flow rate, scf/bbl 18,800 13,400 6 Product Yields. wt.% on feed 7 H2S 4.41 3.88 8 Cl-C3 8.00 9.01 9 C4-195~C 20.30 6.88 195-350~C 46.00 39.73 11 350-525~C 21.42 35.21 12 +525~C 0.11 5.76 13 Coke 0.00 0.86 14 C4-525~C 88.40 81.82 C4-525~C, vol. % 108.42 96.44 16 Pitch Conversion, wt.% 99.2 91.2 17 Asphaltene Conversion, wt.% 100.0 84.4 18 HDS, % 82.8 72.7 19 H2 Cons., wt.% of feed 2.5 1.9 The above hydrocracking tests were conducted on Cold 21 Lake vacuum bottoms described in Table I and the precursor 22 concentration was 300 ppm Mo on feed. After each test, all units 23 of the experimental circuit were opened, examined and found to 24 be free of coke or other fouling.

EXAMPLE II
26 This example shows the catalyst to be colloidal in 27 form.

~.~,, 1 Hydrocracking residuum was dispersed in methylene 2 chloride and the mixture was injected into a gel permeation 3 column. The molybdenum containing component was found to have 4 an apparent molecular weight range 400 to 3000 with respect to this particular gel permeation column calibrated with respect to 6 polystyrene. This range corresponds to colloidal particles of 7 diameter greater than 0.002 micron but less than 0.01 microns.

9 This example shows the effect of preferential association of catalyst precursor with the asphaltenic fraction 11 of bitumen residue feedstock.
12 Table III shows data from two tests, one with catalyst 13 and one without catalyst. These tests demonstrated the 14 differences on asphaltene conversion and coke yield, in particular. Although the pitch conversions for the two 16 experiments were similar, the asphaltene conversions differed by 17 a factor of 2; the catalyst selectively converted the asphaltene.

203097~

.., ~

2 No Catalyst 300 ppm Mo 3 Reaction Temperature; ~C 455 455 4 LHSV; h1 3.63 3.65 Pressure; psig 2500 2500 6 H2 flow rate; scf/bbl 7900 7800 7 Product Yields. wt.% on feed 8 HzS 1.94 2.40 g Cl-C3 2.59 2.22 C4-195~C 5.16 3.55 11 195~C-350~C 22.40 20.20 12 350~-525~C 31.78 35.82 13 +525~C 36.25 36.09 14 C4-525~C 59.9 60.10 Coke 6.5 0.79 16 Pitch Conversion, % 52.9 52.6 17 Asphaltene Conversion, % 23.1 58.5 18 HDS, % 31.8 39.3 19 H2 cons., wt.% of feed 0.42 0.91 Additional evidence of the effect of catalyst precursor 21 on selective asphaltene conversion and coke suppression is shown 22 in Table IV where the compositions of two +525~C hydrocracking 23 residua (pitch) are compared.

2030g75 TABLE IV
2 Fraction Pitch I Pitch II
3 Yield % Sulfur % Yield % Sulfur %
4 Maltenes 63.2 3.9 41.5 4.7 Asphaltenes 36.6 5.8 33.4 6.3 6 Preasphaltenes 16.3 6.2 7 Coke 0.2 -- 8.3 6.7 8 Pitch I was derived from a test containing molybdenum 9 naphthenate catalyst precursor. Pitch II was derived from a test not containing molybdenum napthenate catalyst precursor.
11 Figure 4 shows that asphaltene conversion was favoured 12 by the presence of the catalyst for a broad range of pitch 13 conversion, 42 to 99%. In the presence of catalyst the process 14 units remained clean and free of coke. In the absence of catalyst, the process units became fouled by coke.

17 This example shows that the process operates very 18 successfully over a broad range of concentration of precursor in 19 the bitumen residuum.

2 30 ppm Mo 300 ppm Mo 3 Reaction Temperature 455 455 4 LHSV; hl 1.03 1.03 Pressure; psig 2000 2000 6 H2 flow rate; scf/bbl 16,400 13,400 7 Product Yields wt.% on feed 8 H2S 2.86 3.88 g C1-C3 8.43 9.01 C4 - 195~C 12.13 6.88 11 195~-350~C 36.92 39.73 12 350~-525~C 34.37 35.21 13 t525~C 5.88 5.76 14 Coke 0.43 0.86 C4-525~C 83.42 81.82 16 C4-525~C; vol.% 100.52 96.44 17 Pitch Conversion, % 91.6 91.2 18 Asphaltene Conversion,% 87.4 84.4 19 HDS, % 53.6 72.7 H2 Cons., wt.% of feed 1.66 1.90 22 This example shows that the catalyst precursor, 23 molybdenum naphthenate, decomposes at temperatures greater than 24 about 300~C in the absence or presence of bitumen residuum.
Figures 3a and 3b show that the catalyst precursor is 26 stable at temperatures less than 250~C. Figure 3c shows that the 27 catalyst precursor begins to decompose and polymerize slowly at -1 a temperature of 300~C. At higher temperatures the decomposition 2 was more rapid and coke was produced.
3 Figures 3d and 3e show that the catalyst precursor 4 dissolved in bitumen residuum was stable at temperatures less than 250~C. Figure 3f shows that the catalyst precursor 6 dissolved in bitumen began to decompose slowly at a temperature 7 of 300~C. No coking was evident for the low heating rates 8 obtained.
9 Injection of the catalyst precursor into bitumen residuum at 350~C produced coke containing molybdenum.

Claims (12)

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

1. A process for hydrocracking heavy oil containing asphaltenes and sulfur moieties, comprising:
mixing the heavy oil with an oil-soluble molybdenum compound hydrocracking catalyst precursor at an elevated temperature that is sufficiently high to enable dispersion of the precursor in the oil but sufficiently low so that significant decomposition of the precursor is avoided, for sufficient time to disperse the precursor and associate it with the asphaltenes;
then further heating the mixture to hydrocracking temperature and reacting it with hydrogen in a hydrocracking reactor at hydrocracking pressure, said hydrogen being supplied and vented at a rate sufficient to ensure mixing of the liquid in the reactor and stripping of light ends, so that catalyst particles are formed which are colloidal in size; and recovering and separating the gaseous and liquid products from the hydrocracking step.

2. The process as set forth in claim 1 wherein:
the hydrogen is supplied to the reactor in an amount sufficient to ensure that the volumetric flow of hydrogen is greater than about 8 times the liquid flow, the liquid Peclet number in the reactor is less than about 0.5 and the gas Peclet number in the reactor is greater than about 3Ø

3. The process as set forth in claim 1 wherein the precursor is molybdenum naphthenate.

4. The process as set forth in claim 2 wherein the precursor is molybdenum naphthenate and the volumetric flow of hydrogen is greater than about 10 times the liquid flow.

5. The process as set forth in claim 2 wherein the molybdenum compound is provided in an amount sufficient to provide 5 to 100 ppm weight of molybdenum of the precursor in the oil.

6. The process as set forth in claim 4 wherein the molybdenum naphthenate is provided in an amount sufficient to provide 5 to 100 ppm weight of molybdenum of the precursor in the oil.

7. The process as set forth in claim 1 wherein the hydrocracking temperature is in the range 440°C to 485°C.

8. The process as set forth in claim 2 wherein the hydrocracking temperature is in the range 440°C to 485°C.

9. The process as set forth in claim 5 or 6 wherein the hydrocracking temperature is in the range 440°C to 485°C.

10. The process as set forth in claim 6 wherein the molybdenum naphthenate amount is provided in an amount sufficient to provide 10 - 30 ppm of molybdenum of the precursor in the oil.

11. The process as set forth in claim 2 wherein the mixing step is carried out at a temperature of about 150°C.

12. The process as set forth in claim 11 wherein the precursor is molybdenum naphthenate and it is provided in an amount sufficient to provide 5 to 100 ppm weight of molybdenum of the precursor in the oil.