CA2025125C - Process for reducing coke deposition in thermal upgrading processes - Google Patents

Abstract

"IMPROVEMENTS FOR REDUCING COKE DEPOSITION IN THERMAL UPGRADING PROCESSES" In a hydrocracking process, a feed mixture comprising a heavy oil containing asphaltenes and sulfur moieties, an oilsoluble metal compound additive (e.g. Fe(CO)5) which will impede coalescence of coke precursors, and a hydrocarbon diluent which is a solvent for the asphaltenes, is mixed to disperse the additive and then reacted in a reactor wherein a prolific hydrogen flow is passed through the breadth and length of the charge to mix the charge and strip light ends. The combination of features results in impeding the evolution of coke precursors so that a substantial proportion thereof remains in the agglomerate state and in improving the conversion of the 504.degree.C+ part of the feedstock.

Description

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1 FIELD OF THE INV~NTION
2 This invention relates to an improved hydrocracking

3 process wherein inclusion of a combination of light ends

4 stripping, addition of asphaltene - solubilizing diluent, and addition of an additive which inhibits coalescence of coke 6 precursors, results in improved conversion of the 504C+ fraction 7 and reduction of adhesive coke deposition.
., 'J 8 BACKGROUND OF THE INVENTION
9 The present invention was developed in connection with hydrocracking of a heavy hydrocarbon feedstock particularly high 11 in content of asphaltenes and sulfur moieties. More 12 particularly, the feedstock was vacuum tower bottoms produced 13 from distillation of bitumen. The invention is not limited in 14 application to such a feedstock; however, it will be described below with specific respect to it, to highlight the problems that 16 required solution.
17 Bitumen contains a relatively high proportion of 18 asphaltenes. When the bitumen or its vacuum tower bottoms is 19 hydrocracked, the asphaltenes produce coke precursors, from which ; 20 solid coke evolves. The coke deposits on and adheres to the , 21 surfaces of the reactor and downstream equipment. In addition, .. 22 since part of the feedstock i6 consumed in the production of 23 coke, the conversion of the feedstock to useful products is 24 reduced.
The present assignee is an Alberta government research 26 agency which has been given a mandate to foster improvements in 27 the upgrading of bitumen and other heavy oils. Realizing the 28 conversion limitation and operating problems that coke deposition , 2 ~
i 2 ~ 2 ~ ~ 2 3 1 inflicts, it initiated a research project to investigate the 2 mechanisms of coke formation and to look for improvements that 3 might be applied commercially.
, 4 The present processes were generated as a result of this work. The research involved a progression of concepts and 6 experimental discoveries that came together to yield several ;~ 7 distinct process modifications that can be usefully applied~ 8 individually or as sub-combinations. In addition, an overall .,~
:~ 9 process combination has been developed that is capable of providing a high order of conversion coupled with reduced 11 deposition of adhesive coke and reduced production of coke.
12 Searches and prosecution of the parents of this ~i 13 application have identified the following relevant prior art:
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14 U.S. 4,294,686 (Fisher et al) teaches that, when liquid hydrogen donor oil is used along with hydrogenation in connection -~ 16 with hydrocracking of bitumen vacuum tower residua, coke ~; 17 deposition is allegedly eliminated.
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19 above cited patents jointly conducted a large scale hydrocracking test on bitumen residue using a liquid hydrogen donor process.
. 21 This test encountered serious coke production problems. It ' 22 appears that hydrocracking high asphaltene content feed such as : 23 bitumen residue requires more than the preQence of liquid `~ 24 hydrogen donor oil alone.
U.S. 4,455,218 (Dymock et al) teaches use of Fe(CO)s as ` 26 a source of catalyst for hydrocracking heavy oil in the presence 27 of H2. The reaction i8 allegedly characterized by elimination of 28 coking.

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1 U.S. 4,485,004 (Fisher et al) teaches hydrocracking 2 heavy oil in the presence of, hydrogen, hydrogen donor material, -;, 3 and catalyst comprising particulate Ni or Co on alumina.
4 U.S. 4,134,825 (Bearden et al) teaches forming solid, S non-colloidal catalyst in situ in heavy oil using trace amounts 6 of Fe added in the form of an oil-soluble compound such as iron 7 carbonyl. The metal compound may be added to the oil and heated 8 to 325-415C in contact with hydrogen to convert it to a solid, 9 non-colloidal, catalytic form. This catalyst i6 then used in ' 10 hydrocracking the oil and it is stated that coke formation is 11 inhibited.
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:12 SUMMARY OF THE INVENTION
13 In one aspect of the research work underlying the 14 present invention, coke was produced by hydrocracking a mixture . .
lS of diluent and bitumen vacuum tower bottoms ("VTB") and the coke 16 composition was studied microscopically. It was found that at 17 progressive stages of the evolution of the coke precursors into 18 adherent solid coke, there were present different species of 19 isotropic and anisotropic submicron and micron-sized spheroids.
Some of the figures forming part of this specification illustrate 21 these various species, which we have identified with the .:i ~ 22 following labels: , :;
9 23 - isotropic sphere; (Figures 1 and 6) 24 - basic isotropic particle; (Figure 1) 25 - isotropic agglomerates; (Figure 3) 26 - anisotropic spheres; (Figures 2 and 5) 27 - basic anisotropic particles; (Figure 2) ~ 28 - anisotropic fine mosaic particles; (Figure 4) ;~ 4 ,"

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1 - anisotropic coarse mosaic particles; (Figure 4) ~`- 2 and 3 - anisotropic agglomerates (Figure 4).
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4 It was further experimentally discovered:
- That the evolution of the coke precursors into 6 coke involved a coalescence process from the 7 minute isotropic species to the larger species;
8 (Figures 5 and 6) and 9 - that if the coalescence process was inhibited with the major portion of the precursors remaining in 11 the isotropic and anisotropic agglomerate state, 12 then the deposition of adherent and solid coke was 13 significantly reduced and even virtually 14 eliminated.
These recognitions led to seeking out and identifying 16 a compatible additive and a compatible dlluent that would 17 interfere with the coalescence process and assist in reaching an 18 end where, if any coke was present, it would be present 19 predominantly in the form of agglomerate species, preferably in - ~0 the isotropic state. It was postulated that a well dispersed 21 oil-soluble metal compound might be used to react in situ with 22 sulfur moieties of the bitumen VTB to produce a colloldal 23 dispersion having wetting characteristics that would enable the 24 colloidal moieties to collect at the surfaces of the precursor spheroids and prevent the spheroids from coalescing.
26 Furthermore, it was postulated that an appropriate diluent might 27 be used to disperse this additive.
28 It was experimentally determined that if an oil-29 soluble metal compound additive, decomposable at hydrocracking s :, ~, .. 2~2~

1 temperatures and selected from the group consisting of Fe, Ni 2 and Co compounds, most preferably iron pentacarbonyl (Fe(CO)s), 3 was mixed with diluent and bitumen VTB and the mixture underwent 4 hydrocracking, then the postulated mechanism appeared to take place. Stated otherwise, the inclusion of the additive in the ~ 6 reaction mixture undergoing hydrocracking did have the desired -~ 7 effect of greatly reducing the deposition of adherent solid coke.
8 Examination of cooled solid sampleæ after hydrocracking showed - 9 that the major portion of this coke was in the form of isotropic ~ 10 agglomerates. It is believed that at reactor temperature this -~ 11 coke would have taken the form of minute spheroids of coke 12 precursor. Chemical analysis of the sample coke indicated that 13 additive metal sulfide was associated therewith in a significant 14 amount and that most of the metal sulphides were of dimension of the order, 1 nanometer.
16 In summary, it is believed that if an oil-soluble, ;~ 17 decomposable metal compound is firstly well dispersed in the 18 heavy oil and then decomposed by subjecting the mixture to 19 hydrocracking temperature, colloidal metal sulfide moieties are , 20 produced which are thought to accumulate at the surfaces of 21 spheroids rich in coke precursors and interfere with their . 22 coalescence. Upon completion of hydrocracking it i8 believed 23 that the coke precursors were largely transformed into isotropic 24 agglomerates. It is found that the deposition of adhesive solid coke is significantly reduced.
26 Turning now to a second approach that was explored, it 27 was well known that asphaltenes precipitate when pentane is 28 added. Upon considering this known fact, applicants conceived : 29 the notion of emphasizing the removal of light ends during j;,j :'~
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3 1 hydrocracking to determine the effect on coke formation.
2 Experimental work was therefore initiated to determine the effect 3 of stripping light ends (soiling point ("s.p.") <220C) from the 4 hydrocracking zone. The experiment showed that coke formation was reduced when the light ends were consistently removed during 6 hydrocracking. To improve this, it appeared desirable to apply J 7 mixing to the mixture during hydrocracking. Mixing would have 8 the further attribute of dispersing the additive metallic 9 component.
- 10 To further elaborate on the foregoing, it had been ' 11 noted that coke formation is associated with phase separation.
`3, 12 It was postulated that, if the coke precursors became richly 13 concentrated in a distinct phase, then the coke formation process :! 14 would proceed rapidly and quantitatively. To impede this, it appeared desirable to strip the light ends.
'33. 16 Therefore, as a second preferred aspect of the 17 invention, a tube reactor is used, preferably substantially free 3 18 of internals, and the hydrogen flow through the reactor is 19 prolific and is arranged to achieve mixing throughout the length and breadth of the reaction zone. The prolific hydrogen flow 21 functions to strip light ends from the zone. More preferably, 22 mixing and stripping is accomplished by ensuring that the 23 hydrogen flow is sufficient to provide the following Peclet 24 Number ("P.N.") regime in the reactor chamber:
Liquid:
26 axial P.N. = less than 2.0, preferably less than 1.0, most 27 preferably about 0.2 28 Gas:
:~ 29 axial P.N. = more than 3Ø
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In another thrust at reducing phase separation, a 2 diluent for solubilizing the asphaltenes was added to the 3 reaction mixture. The diluent was a hydrocarbon fraction having - 4 a B.P. of about 220-504C, preferably 220-360C. It was hoped

5 that the diluent would in addition function usefully as a liquid , 6 hydrogen donor and, in combination with the metal sulfide (which '5~ 7 is catalytic in nature) and the plentiful hydrogen, would create ' -i 8 a regime that would be favourable to high conversion of the ~7 9 504C+ fraction and low coke deposition. Experimental runs ,10 indicated that when the combination of diluent addition, light 11 ends stripping with hydrogen, and well dispersed additive ~, 12 addition was practised in the context of hydrocracking of heavy 13 oil containing asphaltenes and sulfur moieties, exceptionally - 14 high conversion of the 504C' hydrocarbons could be achieved, ,~ 15 together with virtually no adhesive coke deposition. When the -`, 16 diluent was omitted from the combination, or the diluent was not ~ 17 a good solvent of asphaltenes or when stripping of light ends was ;~ 18 not sufficient, experimental runs showed significant coke ;7 19 deposition.
Dispersion is preferably achieved by preheating the ,' 21 heavy oil plus additive plus diluent mixture to a mild 22 temperature (.e.g 150C), to reduce the viscosity of the oil, and ..
r 23 mixing the three components, prior to heating the mixture to 24 elevated temperature for hydroaracking and introducing it into 25 the hydrocracXing reactor.
26 In a broad form therefore, the invention is an i~ 27 improvement of heavy oil hydrocracking comprising:
28 - mixing an oil-soluble Fe, Ni or Co compound, heavy 29 oil and a solvent for asphaltenes, preferably at ;`,'i~;j '.~

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1 a temperature that i6 sufficiently elevated to 2 reduce the oil viæcosity but less than the , 3 decomposition temperature of the metal compound, 4 to achieve substantially uniform dispersion of the compound in the oil;

6 - heating the mixture sufficiently for hydrocracking

7 to proceed and introducing the heated mixture into

8 the reaction zone of a hydrocracking reactor;
,. 9 - temporarily retaining the charge of mixture in the reactor chamber, passing hydrogen through the 11 breadth and length of the charge and removing .- 12 unreacted hydrogen and entrained light end~ form 13 the reactor;
14 - whereby hydrocracking is achieved in conjunction with inhibition of coke production, inhibition of 16 deposition of adherent solid coke and improvement 17 of conversion of the 504C+ fraction; and 18 - whereby the evolution of coke precursors is 19 arrested sufficiently so that the major portion - 20 of said precursors remains in the agglomerate 21 state.
22 Broadly stated, the invention i8 an improvement ln a 23 hydrocracking process wherein heavy hydrocarbon feedstock 1 24 containing asphaltenes and sulfur moieties is conveyed into the chamber of a reactor and reacted therein with hydrogen and coke 26 is formed as an undesired product. The improvement comprises:
27 mixing the feedstock, an oil-soluble metal compound additive and .~. 28 a hydrocarbon solvent for asphaltenes, said metal in the additive ; 29 being selected from the group consisting of Fe, Ni and Co, to 2~2~2~

1 form a mixture having the metallic component substantially 2 uniformly dispersed therein; heating the mixture to a 3 sufficiently high temperature so that hydrooracking will take 4 place in the reactor; introducing the heated mixture into the - 5 chamber of the reactor; temporarily retaining the charge of 6 heated mixture in the chamber, continuously passing hydrogen i 7 through substantially the breadth and length of the charge, and 3 8 removing unreacted hydrogen and entrained light ends from the .~ 9 upper end of the chamber, to effect hydrocracking, maintain dispersion of the metallic component by mixing the charge by 11 means of the hydrogen flow, and cause stripping of light ends 12 fxom the charge; and removing the reaction products from the !,~', 13 reactor.

.: 14 DESCRIPTION OF THE DRAWINGS
:~' 15 Figure 1 is a photographic representation showing the .~ 16 nature of isotropic spheres(s) and basic isotropic particles (b), 17 magnified 1650X;
18 Figure 2 i8 a photographic representation showing the , 19 nature of anisotropic spheres (6) and basic anisotropic particles , 20 (b), magnified 1650X;
.~ 21 Figure 3 is a photographic representatlon showing the :,~ 22 nature of isotropic agglomerates (g) along with anlsotropic .:~ 23 601ids (a) and iron sulfide particles (s), magnified 1650X;
24 Figure 4 i8 a photographic representation showing the nature of anisotropic agglomerates (a), anisotropic fine mosaic x 26 (f), and anisotropic coarse mosaic (c), magnified 1650X;

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1 Figure 5 is a photographic representation showing 2 anisotropic coke particles growing via the coalescence of smaller : 3 anisotropic spheres (c), magnified 1650X;
: 4 Figure 6 is a photographic representation showing isotropic coke particles growing via the coalescence of smaller . 6 isotropic spheres (s), magnified 1650X;
, 7 - Figure 7 is a photographic representation of the - 8 reactor baffle after run CF-30;
~- 9 Figure 8 is a photographic representation of the reactor baffle after run CF-9;
11 Figure 9 is a photographic representation of the 12 reactor baffle after run CF 31;
13 Figure 10 is a bar chart setting forth coke composition 14 for runs CF-9, CF-31 and CF-30;
Figure 11 is a photographic representation of the 16 reactor baffle after run CF-A3;
: 17 Figure 12 is a bar chart setting forth coke compoæition 18 for runs CF-A3 and FE-1;
19 Figure 13 is a photographic representation of the reactor baffle after run FE-1;
.. , 21 Figure 14 is a photographic representation of the coke , 22 particles from run FE-1, which were mostly isotropic agglomerates ;~ 23 (A) associated with iron sulfides. Isotropic spheres (S) were .. 24 trapped among the agglomerates;
* 25 Figure 15 is a photographic representation of the coke ~3 26 particles from run FE-1 showing isotropic spheres (s) which were ~,f~
.~ 27 effectively prevented from growing into basic isotropic particles 28 by the iron derivative;
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- 2~3 ~ 2~3 ,, 1 Figure 16 is a photographic representation of the 2 reactor baffle after run CF-38;
3 Figure 17 is a plot showing nitrogen flowrate versus 4 coke production for Example V;
Figure 18 is a phase diagram for Example V;
6 Figure 19 is a plot showing pressure profiles for runs 7 involving different additives;
8 Figure 20 i6 a bar plot showing hydrogen consumed for ,,

9 various runs;
~,; 10 Figure 21 is a bar chart setting forth coke composition 11 for a number of the runs;
12 Figure 22 is a photographic representation of coke from 13 run CF-40, showing mostly a continuous sheet of basic isotropic `:~ 14 particles (B), magnified 1650X; and Figure 23 is a photographic representation of the - 16 reactor baffle after run CF-40.

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18 The feedstock to the process is heavy oil. This term 19 is intended to include bitumen, crude oil residues and oils derived from coal-oil co-processing that contain asphaltenes and 21 sulfur moieties. A typical feedstock could be vacuum tower 22 residues derived from Athabasca bitumen.
23 The feedstock is mixed with the oil-soluble compound 24 additive, preferably Fe(CO)s, and a solvent for asphaltenes, preferably a recycled stream having a boiling point in the range 26 220C - 504C. The amount of additive added is in the range 0.01-27 5 wt. % based on the weight of the feedstock. The weight ratio P
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of diluent to feedstock iB in the range 1:10 to 3:1. The 2 preferred weight ratio range is 1:4 to 2:1.
3 Mixing may be accomplished by pumping the mixture from 4 a storage tank, through a pre-heater and back to the tank.
Preferably the mixture is pre-heated to a temperature at which 6 the viscosity is Eufficiently low to permit uniform disper~al of 7 the additive but not so high as to cause decomposition of the 8 additive. This could be 150C.
9 The mixture is then heated to a temperature (e.g.
350C) which is sufficiently high so that hydrocracking 11 temperature (e.g. 455C) will be achieved in the reactor when the 12 mixture is contacted with hydrogen.
13 In the reactor, a Peclet Number regime, within the 14 ranges previously described, is maintained to ensure that stripping of light ends using the hydrogen i8 achieved.
16 The development and background of the claimed invention 17 i8 set forth in the following examples.

19 The following examples are included to demonstrate the operability of the present process.
21 All the tests in examples I-V were performed in a 22 litre, baffled, stirred autoclave. The charge, comprising 23 Athabasca vacuum tower bottoms (504C+) as feedstock, solvent 24 (otherwise referred to as "diluent") and catalyst (if used), was introduced into the autoclave. The autoclave was sealed, purged 26 free of air, pressurized with nitrogen or hydrogen and heated to 27 430C. The reactor was stirred at 800 rpm, with a reaction 28 temperature of 430C and a reaction time of 105 minutes.

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: 1 Properties of the Athabasca vacuum tower bottoms (V~B) 2 are given below.
3 wt %
i, 4 C 81.76 H 9.51 6 S 6.23 7 N 0.78 ~,~, ~ 8 API @ 1 6DC: 2.43 .~ 9 IBP 504C
Table 1 herebelow provides the composition (wt. %) of 11 diluents used during the experimental procedures.
12 It is noteworthy that according to the relative content , 13 of condensed dicycloparaffins and benzocycloparaffins, diluent 14 B has the most hydrogen donor capability and diluent C has the ~, 15 least.

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2 Diluents - 3 Hydrocarbon Type A B C
4 Paraffins 13.0216.38 13.10 Uneondensed 6 Cycloparaffins 7.326.29 5.51 7 Condensed ' 8 Dieyeloparaffins 5.2013.03 3.80 9 Condensed Polycycloparaffins 0.491.27 0.15 11 Alkylbenzenes 18.0715.25 11.50 12 Benzocycloparaffins 32.2937.54 20.36 13 Benzodicycloparaffins 4.77 3.80 5.53 14 Naphthalenes 15.866.11 19.49 Naphthacycloparaffins 1.61 0.26 7.73 16 Fluorenes 0.820.00 6.21 :s 17 Phenathrenes/Anthracene 0.610.00 6.18 ~,~

19This example illustrates the effect of diluent. The 20autoelave was eharged with 109 grams of bitumen and 220 grams of 21diluent A, B or C. A nitrogen overpressure of 0.55 MPa was 22applied and the eontents were thermally eracked at 430C for 105 .. 23 minutes.
3 24The results of the tests are shown in Table 2. The 25reactor was opened and Figures 7, 8 and 9 show the coke deposited 26on the baffles for experiments CF-30, CF-9 and CF-31, 27 respeetively.
28It is noteworthy that experiment CF-31 produeed as mueh 29eoke as experiment CF-9 but that the coke was most easily .. ' 15 ...

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1 dislodged from the baffles and reactor surfaces. Moreover, 2 although experiment CF-31 produced nearly twice as much coke as 3 experiment CF-30, the coke was most easily dislodged. The 4 surface6 of the reactor and baffles of experiment CF-31 were ,~ Sleast fouled.
6The coke from the three experiments was examined ; 7microscopically and the results are shown in Figure 10. It was 8 noted that when the agglomerate content (which was anisotropic) 9 was relatively high (Experiment CF-31), the coke deposition and adhesion was least intense in spite of the fact that diluent C
11 has the least hydrogen donor capability.

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2 Test conditions:430C, 105 min., 800 rpm, 0.55 MPa 3 initial N2 pressure 4 Diluent to Vacuum Tower Bottom ratio is 2:1 - 5 Experiment No. CF-30 CF-9 CF-31 6 Diluent type B A C
7 Yield (wt% vacuum tower bottom) 8 H2 0.21 0.07 0.08 9 Cl - C4 10.3 10.8 14.8 Cs - 200C 42.3 57.1 55.2 11 200 - 360 C -8.6 -37.2 -43.5 . ~.
12 360 - 504C 22.8 26.5 30.6 13 504C' (coke free) 26.3 33.8 34.6 14 Coke 4.3 7.7 7.7 Conversion to 504C & coke73.766.2 65.4 16 Mass Balance 98.2 97.3 96.9 18 This example illustrates the effect of hydrogen 19 overpressure.
The experimental conditions and results are shown in '~
21 Table 3. Experlment CF-A3 is compared with experiment CF-9.
22 Figure 11 shows coke deposited on the baffles for 23 experiment CF-A3. Compared to Experiment CF-9 (Figure 8), the 24 coke yield and deposition of Experiment CF-A3 was least.
~x 25 Figure 12 shows results from a microscopic examination ~' 26 of the coke obtained from experiment CF-A3. It is to be compared ,~

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1 with those results shown in Figure 10 for experiment CF-9. The 2 results are similar.
3 In both experiments, over 80% of the coke components 4 were of the anisotropic type. The agglomerate concentration for experiment CF-A3 was not significantly more than that of 6 experiment CF-9.
7 This example teaches that abundance of hydrogen alone 8 does not neutralize the adhesiveness of the coke precursors nor 9 does it selectively modify the coke composition.

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3 Diluent A A
4 Yield (wt % VTB) H2S 0.07 2.2 6 Cl - C4 10.8 11.6 7 Cs - 200C 57.1 44.0 8 200 - 360C -37.2 -18.0 9 360 - 504C 26.5 30.1 i 10 504C+ tcoke free)33.8 27.7 11 Coke 7.7 3.1 -, 12 Converæion to 504C- & coke 66.2 72.3 13 Mas6 Balance 97.3 98.5 14 Selectivity to Cs - 504C- 77.6 Conditions: CF-9: 430C, 105 min., 800 rpm, 0.55 MPa N2 initial 16 pressure, 17 diluent: VTB ratio 2:1 18 Conditions: CF-A3 430C, 105 min., 800 rpm, 6.8 MPa H2 initial 19 pressure, diluent: VTB ratio 2:1 22 This example illustrates that coke containing mu¢h 23 agglomerate is not adhesive.
24 The results and conditions of experiments CF-A3 and FE-;~ 25 1 are shown in Table 4.
26 Figure 13 shows no coke deposited on the baffles for ;~ 27 experiment FE-1. Compared to Experiment CF-A3 (Figure 11), the 28 coke yield and deposition of Experiment FE-1 was least.

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1The coke from Experiment FE-1 was observed to be minute 2 particles loosely settled in the bottom of the reactor.

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4 Test conditions: 430C, 105 min., diluent/vtb = 2:1, 800 rpm 6 Experiment No. CF-A3 FE-1 - 7 Diluent A A
8 Gas!Pressure (MPa) H2/6-8 H2/6-8 9 Additive (metal, wt% vtb) - Fe/0.5 ,~ 10 Yields on vtb, wt%
~ 11 H2S 1.2 ,?.~ 12 Cl ~ C4 11.6 6.6 13 Cs ~ 200C 44.0 37.7 14 200 - 360C -18.0 -9.1 360 - 504C 30.1 31.2 16 504C+ (coke free) 27.7 31.4 17 Coke 3.1 1.6 18 Figure 12 shows result6 from a microscopic examination 19 of coke obtained from experiments CF-A3 and FE-1. The results are very different. The coke from experiment FE-1 i8 over 80%
21 isotropic agglomerate.
22 Figures 14 and 15 for Experiment FE-1 showed that ~olid :,~
23 particles were all loosely associated with one another. Coke 24 composition showed that over 97% of the components were of the isotropic type - see Figure 12. Isotropic agglomerates accounted ~ 26 for 80% of the coke composition.
..j 27 This data for experiment FE-1 indicated that the ,~ 28 adhesiveness of the coke precursors was effectively neutralized ~.'!' ?.i 20 , . .

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1 by the highly dispersed iron compound. Where isotropic spheres 2 were concentrated (see Figure 15), the isotropic agglomerates 3 effectively prevented the spheres from coalescing into basic 4 isotropic particles.
It is noteworthy also, that additive present as iron 6 sulphide amounts to approximately 1/3 the weight of the coke but 7 is not 80 evident.
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j 8 EXAMPLE IV
;~ 9 This example further illustrates that the choice of

10 diluent i8 important.

11 The experiment CF-38 was done according to the teaching

12 of U.S. 4,455,218 (Dymock et al). The experimental conditions

13 were identical to those shown in Table 4 for experiment FE-1.

14 Whole Athabasca bitumen was used instead of Athabasca VTB and no diluent was added. The whole bitumen contained about 60 wt. %
16 hydrocarbon boiling at temperatures greater than 504C. 0.5%
17 (metal) of iron pentacarbonyl was added on the basis of 18 equivalent 504C+ content in the bitumen.
19 The coke yield was 7.9% (504C+ basis) and this coke adhered very strongly to surfaces of the reactor and baffles.
21 Figure 16 shows the coke deposited on the baffles.

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22 ~-A~M~E-v 23 This example illustrates the effect of the rates of ~ 24 continuously removing highly volatile components from the ::f 25 reacting fluids.

26 The one liter autoclave was fitted with a dip tube for 27 sparging N2 or H2 into the reacting liquid, an outlet permitting ` 21 ....

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~ ~ 2 ~ _~ 2J 3 ' - 1 continuous flow of product gas, and cold trap condensers to 2 remove volatile products from the gas stream before collecting 3 the latter in a sample bag for analysis. Experiments were 4 conducted in the above described reactor at 430C for lOS minutes under 550 KPa pressure both without gas flow and with gas flowing 6 continuously into and out of the reactor. In each experiment, -:' ~5 7 110 g of Athabasca 504C+ vacuum tower bottoms (VTB) and 220 g of , 8 a diluent were used. Table 5 presented herebelow gives the ......
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",;5,1 0 TABLE 5 11 Autoclave Test Results -~ 12 Experiment No. 1 2 3 4 S 6 13 Diluent Type A A B B B B
14 Nitrogen Flow Rate (1/min) 0.0 1.89 0.0 0.2 1.05 2.16 16 Yield (wt% VTB):
17 Cl - C4 15.5 16.5 10.310.0 8.2 13.8 18 Cs - 504C42.3 38.1 56.556.5 56.6 51.4 19 504C+ pitch (coke free) 34.6 38.826.3 27.0 30.0 29.7 21 Coke 7.9 3.8 4.3 3.8 3.4 3.1 22 Condensate .Y 23 recovered from ..,~,'5j` 24 purge gas (wt%
VTB) -- 47.5 -- 3.1 23.9 39.7 . ~

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2 Simulated Distillation Results of Condensate from Ex~eriment No. 5 3 % Off Temp C % Off Temp C

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~ 10 30 111 85 210 ., ~, 11 35 116 90 219 ~ 12 40 123 95 229 ;~ 13 45 131 FBP 262 .~
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Figure 17 shows the amount of coke produced as a 16 function of the rate of flow of nitrogen. As shown for diluents 17 A and B, the amount of coke produced decreased as the rate of 18 flow of nitrogen was increased. At high rates of flow of 19 nitrogen, the amount of coke produced for the experiment using diluent B (the best hydrogen donor solvent) was not very : 21 different from that for the experiment using diluent A (the worst ':
22 hydrogen donor solvent).
23 It i5 noteworthy in Table 5, that for those conditions 24 providing the least amount of coke, the amount of condensate recovered from the purge gas was highest. This was true for both ; 26 diluents A and B.
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1Table 6 shows results of simulated distillation of the - 2condensate from experiment 5. About 90% of this condensate boils 3at temperatures less than 220C.
-, ~ 4This example teaches that coke production is reduced '~ 5if the low boiling products are removed continuously (stripped) 6 from the reacting fluids. Moreover, it teaches that coke 7 production is reduced if the low boiling products are removed 8 from the diluent.
9These observations are consistent with the model that has asphaltenes separate as another liquid phase from the 11 reacting fluids. In analogy with the common experiment that has ,. 12 pentane added to bitumen to yield solid asphaltene as a 13 precipitate at room temperature, such an experiment done at high 14 temperature is expected to yield asphaltene as a separate liquid phase. Moreover, it is expected that this separate liquid phase 16 will be rich in the asphaltenes that thermally crack to form 17 coke.
18This phase separation is shown schematically in Figure 19 18. The three components of this Figure are respectively labelled asphaltPnic, aromatic and paraffinic and alicyclic to . 21represent those fractions having boiling points 504C+, 220 -22504C and 220C , respectively. The arrow indicates the evolution 23of the composition of whole bitumen a~ might occur for Example , 7~
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1 A continuous flow system consisting of a preheater, a 2 2-litre stirred reactor and a product collection system was used.
-~ 3 The baffles and stirrer were similar to those of the previous , 4 examples. A mixture of Athabasca VTB, diluent A and preheated hydrogen were pumped through the preheater into the bottom of the 6 stirred reactor. Products were removed through a dip tube with ~ 7 its entrance set at 60% of the reactor's height.
:, 8 The experimental conditions and results are shown in 9 Table 7 for experiments 7, 8 and 9. In each experiment the hydrogen flow rate was 12 slpm. In experiment 7, the liquid 11 hourly space velocity is twice that of experiment 8 and of ~; 12 experiment 9. The temperature of the reacting fluids is 20C
~, 13 higher than that of experiment 8.
14 Noteworthy is that the amount of coke produced in ~, 15 experiment 8 was less than that of experiment 7 and that almost 16 no coke at all was produced in experiment 9, in spite of the .~ 17 increased severity of hydrocracking from experiment 7 to 8 to 9.
:,.;i -, 18 Such a result is expected if one considers that the highly .~, 19 volatile fractions of the reacting fluids are r~moved with increasing efficiency as conditions are changed from experiment 21 7 to 8 to 9. In experiment 9 the pipe connecting the reactor to 22 the product collection vessel became plugged at the completion 23 of the experiment.
24 In experiment 10, two one-litre reactors were placed in series with the entrances to the dip tubes adjusted at 50% and 26 70% of reactor height. The conditions and results are shown in 27 Table 7.
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2 Continuouæ Bench Unit Test Results :;~ 3 Diluent Type : A
4 Pressure : 10 MPa Experiment No. 7 8 9 10 6 Reactor 1 (l) 1.2 1.2 1.2 O.S
7 Reactor 2 (l) -- -- -- 0-7 .~, 8 Reaction Temperature 9 (C) 440 440 460 440 Liquid Hourly 11 Space Velocity (hrl) 1 0.5 0.5 12 Hydrogen Flow rate 13 (slpm) 12 12 12 16 14 VTB Concentration in feed (Wt%) 63.1065.02 45.5347.3 16 Conversion (Wt% VTB
17 to coke and 504C) 69.0 78.3 98.1 79.8 18 Yield, Wt% VTB
9 Cl - C4 5.2 7.9 17.3 7.2 Cs - 200C 16.3 19.1 31.4 15.1 ;:~.21 200C - 360C 23.4 31.1 43.1 24.2 .
.` 22 360C - 504C 20.3 18.4 9.3 24.8 23 Coke 4.6 3.1 0.1 4.6 ~-~ 24 504C~ Pitch (coke free) 31.0 21.7 1.9 24.8 26 Total distillate .~ 27 Cs - 504C 60.0 68.6 83.8 64.7 28 It is noteworthy that the conversion was similar to :l 29 that of experiment 8. This was expected given the different liquid hourly space velocities and different number of reactor&.

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~, ~ ~ 2 ~ 3 1 However, the amount of coke produced in experiment 10 was higher 2 than that produced in experiment 8 in spite of the higher rate 3 of flow of hydrogen of experiment 10.
4 This example teaches that hydrogen flow and reactor temperature may be used skilfully to remove tstrip) low boiling 6 products from the reacting fluids to reduce the amount of coke 7 that is produced. Moreover it teaches that for one or more 8 hydrocracking reactors in series, a configuration having one -:~ 9 reactor only produces the least amount of coke. Moreover, it teaches that if several hydrocracking reactors are placed in 11 series, then least coke is produced if volatile hydrocarbons are :Ss 12 removed from the fluids as they pass from one reactor to the ;~
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14 X~l5~VII
This example illustrates that by skilful use of reactor 16 configuration, severity of reaction, stripping of volatile 17 components and additive, high conversions of VTB to distillate 18 products can be obtained with acceptable production of coke and 19 minimal fouling of the reactor.
The continuous flow system of experiments 7, 8 and 9 21 of Example VI was used. The additive was iron pentacarbonyl.
22 The conditions and results of experiments 11 and 12 are shown in 23 Table 8.
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than those of experiment 11. Nevertheless, all surfaces in the 26 reactor, pipes and collection vessel remained free of fouling by 27 coke and the coke that was produced was a fine friable matter " 28 that settled in the product collection vessel.

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1 The results of a microscopic examination of the coke 2 produced in experiment 12 are shown in Table 9. 74% of the coke .: ,.
i 3 was in the form of agglomerates. 23% of the coke was in the form ~, 4 of isotropic spheres but these spheres were isolated and trapped : 5 in a matrix of agglomerates.
~, 6 This example teaches that high conversions with minimal .~
7 fouling of the reactor may be obtained when the coke that is 8 produced is mostly agglomerates.
g TABLE 8 10 Experiment No. 11 12 l~ 11 Reactor 1 (1) 1.2 1.2 ;~ 12 Reactor 2 (1) -- --~,i 13 Reaction 14 Temperature (C) 450 450 ? 15 Liquid Hourly Space 16 Velocity (hrl) 1.05 0.73 . 17 Hydrogen Flow rate ,, 18 (slpm) 8 12 :; 19 VTB Concentration in Feed 20 (wt%) 47.5 47.8 ~' 21 Catalyst (Wt% of Fe 22 based on VTB) 0.5 0.5 ~,~ 23 Conversion (Wt% VTB
.j' 24 to coke and 504C) 67.8 82.1 ~ 25 Yield (Wt% VTB) -~ 26 Cl-C~ 5.2 9.4 27 Cs-200C 19.1 22.9 .~
~ 28 200-350C 19.9 27.6 : .~
~ 29 350-504C 21.9 21.1 :,, ~;~ 30 Coke 2.4 2.8 31 504C+ Pitch 32 Coke free 32.2 17.9 33 Total distillate 34 Cs-504C 60.9 71.6 ~.-.~

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1 Note that if H2 flow was not increased in experiment 12, one ~ 2 would expect that a 14% increase in conversion should be .'~, ;~ 3 accompanied by much higher coke yield than the 0.4% recorded.
, Coke Compo~ition of Run No. 12 , 6 Vol %
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7 Ba6ic Isotropy 3 . 8 Isotropic Spheres 23 9 Isotropic Agglomerates 42 ,A3 10 Basic Anisotropy 0 -. 11 Anisotropic Fine-Mosaic 0 12 Anisotropic Coarse-Moæaic 0 13 Anisotropic Spheres 0 ~, 14 Anisotropic Agglomerates 32 ~J
EXAMPLE VIII
16 This example also compares various additive~ and 17 various metal compounds.
18 A series of tests using the following additive~:
19 - fine, Alberta coal char, - oil soluble nickel naphthanate, 21 - oil soluble cobalt naphthanate, and 22 - oil ~oluble molybdenum naphthanate 23 were carried out to compare their relative effectivenes~ in 24 preventing coke formation and deposition. Iron pentacarbonyl was used as the bench mark for comparison.

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~ 3 0.5 wt % tmetal on vacuum tower bottoms) additive, ', 4 Athabasca vacuum tower bottoms t33.3%), diluent (66.7%), 6.8 MPa initial hydrogen presæure, 800 rpm 6 stirrer speed; 430C, and 105 minutes reaction time.
',;~ 7 In the ca~e of Alberta coal char, the amount added wa~
8 eguivalent to 4% of the vacuum tower bottoms.
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~ 9 Pressure profiles presented in ,Figure 19 and the .'~ 10 hydrogen consumption results presented in Figure 20, showed the 11 following observed order for hydrogen consumption:
,., 12 molybdenum additive (CF-40) 68%
, 13 nickel additive (CF-41) 39%
,-,i '' 14 cobalt additive (CF-41) 27 ~: 15 iron additive (FE-1) 26%
16 and coal char (CF-43) 21%
17 Product distributions presented in Table 10 showed the 18 following order of additive for:
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~ 19 - vacuum tower bottoms conversion ,'~ 20 molybdenum > iron > coal > char > nickel > cobalt O
,; 21 - selectivity to Cs - 504 C
~, 22 nickel > iron > cobalt > molybdenum > coal char ', 23 - coke form,ation ', 24 nickel ~ cobalt < coal char < iron < molybdenum.
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Figure 21 shows the effectiveness of the various 26 additive~ in converting the coke precursors to form the non-.:
~ 27 depositing isotropic agglomerate coke particles. Although .~
28 experiments using additlves containing molybdenum con~umed the 29 highest amount of hydrogen, over 90% of the coke was basic . ~s '-; 30 : '~

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1isotropic particles. In Figure 22, coke from CF-40 appeared as , 2a continuous sheet of basic isotropic particles. The coke from 3CF-40 was evidently more densely packed than the coke from FE-i 41 using the iron additive (Figures 14 - 15).
? 5As pointed out earlier, it was discovered that, to ; ~
6 prevent the coke from depositing on the reactor walls, the 7 additive must selectively transform the coke precursor spheres 8 into isotropic agglomerates. The lack of isotropic agglomerates 9 in coke from experiment CF-40 suggested an explanation for the deposition of adherent coke on the reactor baffles (Figure 23).
11 In contrast, the reactor baffles in experiments which iron 12 pentacarbonyl (Figure 13) did not have any adherent coke.
13This example teaches that appropriate selection of additive 14 may inhibit coke production and may inhibit deposition of adherent coke provided that an appropriate diluent is used. Such 16 an additive will maximize the fraction of coke that is in the 17 form, isotropic agglomerate. Oil soluble additives containing 18 iron or carbalt or nickel or combinations of these are preferred.

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2 Test Conditions: 430C, 6.8 MPa H2 initial pressure, 105 ~ 3 min, 800 rpm ~ 4 additive added = metal concentration of 0.5 wt% vtb 6 Diluent/vtb = 2:1 7 Experiment No. CF-A3 CF-43 FE-1 8 Additive -Coal char (4%) Fe 9 Diluent type A C A
3. 10 H2 consumed (wt%
11 initial H2) 21 21 26 12 Yield, wt% vacuum ~ 13 tower bottom H2S 2.2 2.3 1.2 14 Cl - C4 11.6 9.8 6.6 Cs ~ 200C 44.0 36.6 37.7 ~ 16 200 - 360C -18.0 -7.7 -9.1 ~ 17 360 - 504C 30.1 24.4 31.2 18 504C+ (coke free)27.7 33.8 31.4 19 Coke 3.1 1.1 1.6 .,~ 20 Conversion to 504C
:.~ 21 & coke 72.3 66.2 68.6 . 22 Selectivity to . 23 Cs ~ 504C 77.6 80.5 87.0 ~^ 24 Mass Balance98.5 99.0 98.1 . , .~, ,:~
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1 TAsLE 10 (continued) 2 Experiment No. CF-41 CF-42 CF-40 3 Additive Ni Co Mo , 4 Diluent type C C C
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6 initial H2) 39 27 68 .::
7 Yield, wt% vacuum ;~ 8 tower bottom H2S 2.0 1.9 3.3 9 C C 6.1 8.0 8.5 Cs -- 200 C 34.6 36.4 42.4 11 200 - 360C -2.3 -8.9 -11.8 12 360 - 504C 24.9 27.3 29.6 13 504C' (coke free) 34.8 35.3 28.2 14 Coke 0.4 0.9 1.8 : 15 Conversion to 504C
16 & coke 65.6 64.7 71.8 17 Selectivity to 18 Cs - 504C- 87.2 84.7 83.8 19 Mass Balance 99.6 99.5 98.9 ;j ,, ~,~

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Claims (19)

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

1. In a hydrocracking process wherein heavy hydrocarbon feedstock containing asphaltenes and sulfur moieties is conveyed into the chamber of a reactor and reacted therein with hydrogen and coke is formed as an undesired product, the improvement comprising:
mixing the feedstock, an oil-soluble metal compound additive and a hydrocarbon solvent for asphaltenes, said metal in the additive being selected from the group consisting of Fe, Ni and Co, for sufficient time at an elevated temperature that is less than the decomposition temperature of the additive, to form a mixture having the metallic component substantially uniformly dispersed therein;
heating the mixture to a sufficiently high temperature so that hydrocracking will take place in the reactor;
introducing the heated mixture into the chamber of the reactor;
temporarily retaining the charge of heated mixture in the chamber, continuously passing hydrogen through substantially the breadth and length of the charge, and removing unreacted hydrogen and entrained light ends from the upper end of the chamber, to effect hydrocracking, maintain dispersion of the metallic component by mixing the charge by means of the hydrogen flow, and cause stripping of light ends from the charge; and removing the reaction products from the reactor.

2. The improvement as set forth in claim 1 wherein:
the process is controlled by adjusting any of additive addition, solvent addition and hydrogen addition to ensure that at least 30% of the coke produced in the reactor is in the form of agglomerates, whereby the deposition of adhesive solid coke is inhibited.

3. The improvement as set forth in claim 2 wherein:
the additive is iron carbonyl; and the solvent has a boiling point in the range 220°C to 504°C.

4. The improvement as set forth in claim 2 wherein:
the hydrogen flow is sufficient to provide the following Peclet number ("P.N.") regime within the charge:
for liquid:
axial P.N. is less than about 2, and for gas:
axial P.N. is more than about 3.

5. The improvement as set forth in claim 3 wherein:
the hydrogen flow is sufficient to provide the following Peclet number ("P.N.") regime within the charge:
for liquid:
axial P.N. is less than about 2, and for gas:
axial P.N. is more than about 3.

6. The improvement as set forth in claim 4 wherein:
the axial P.N. for liquid is less than about 1Ø

7. The improvement as set forth in claim 3 wherein:
the amount of iron pentacarbonyl added is between about 0.01 and 5.0% by weight based on the feedstock.

8. The improvement as set forth in claim 5 wherein:
the amount of iron pentacarbonyl added is between about 0.01 and 5.0% by weight based on the feedstock.

9. The improvement as set forth in claim 2 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

10. The improvement as set forth in claim 3 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

11. The improvement as set forth in claim 4 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

12. The improvement as set forth in claim 5 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

13. The improvement as set forth in claim 7 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

14. The improvement as set forth in claim 8 wherein:
the solvent/feedstock weight ratio is in the range 1:10 to 3:1.

15. The improvement as set forth in claim 1 wherein:
mixing is conducted at an elevated temperature that is substantially less than hydrocracking temperature, whereby the viscosity of the feedstock is reduced to facilitate dispersion of the additive.

16. The improvement as set forth in claim 3 wherein:
mixing is conducted at an elevated temperature that is substantially less than hydrocracking temperature, whereby the viscosity of the feedstock is reduced to facilitate dispersion of the additive.

17. The improvement as set forth in claim 5 wherein:
mixing is conducted at an elevated temperature that is substantially less than hydrocracking temperature, whereby the viscosity of the feedstock is reduced to facilitate dispersion of the additive.

18. The improvement as set forth in claim 10 wherein:
mixing is conducted at an elevated temperature that is substantially less than hydrocracking temperature, whereby the viscosity of the feedstock is reduced to facilitate dispersion of the additive.

19. The improvement as set forth in claim 12 wherein:
mixing is conducted at an elevated temperature that is substantially less than hydrocracking temperature, whereby the viscosity of the feedstock is reduced to facilitate dispersion of the additive.