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Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
Deactivation of Hydrodesulfurization Catalysts under Coal Liquids. 2. Loss of Hydrogenation Activity Due to Adsorption of Metallics Stephen M. Kovach, Linda J. Castle, and James V. Bennett Research and Engineering, Ashiand Oil lnc., Ashland, Kentucky 4 110 1
J. Thomas Schrodt’ Department of Chemical Engineering, University of Kentucky, Lexington, Kentucky 40506
Minerals identified in coal were investigated as to their poisoning effect on the hydrogenation activity of several HDS catalysts under coal liquefaction conditions. Techniques of impregnation and exposure of catalysts to metal compounds were developed that allow the determination of rates of adsorption, poisoning, and loss of activity. The metals Na, K, Mg, Ca, P, Ti, Fe, and Si were shown to permanently poison catalysts at different rates. Deposition of carbonaceous mineral within the catalyst pores suppresses the adsorption of coal-liquid insoluble constituents. However, organometallics, such as those of titanium, are soluble in coal liquids, gain access to the surfaces, and are adsorbed in high concentrations.
Introduction The effects of carbon deposition on the hydrogenation activity of 18commercial HDS catalysts exposed to solvated coal in media of tetralin and hydrogen a t 630 K and 1.4 x lo7 P a were presented and discussed in Part 1of this series (Ocampo et al., 1978). It was observed that the activities of these catalysts declined very rapidly upon initial exposure to the coal liquids and acquired a low level of activity that was related primarily to the deposition of carbonaceous material. No attempt was made in Part 1 to superimpose the effects of adsorption of the inorganic materials emanating from the coals mineral matter on the catalysts’ lives during the early stage of the liquefaction process, because carbon deposition occurred very rapidly and independently of the presence of the mineral matter. It is universally accepted that deactivation resulting from the adsorption of metallics on the surface sites occurs slowly over a much longer span of time and in an irreversible manner.
tributions of the titanium were found throughout the catalyst pellets depending upon their position within the reactor; pellets from the inlet showed uniform distributions, while downstream pellets showed higher concentrations in the pore mouths. Apparently the diameters of the catalyst pores were sufficiently small to screen out the large organometallic compounds. Several catalyst samples showed uniform distributions of sulfur, indicating that the organic sulfur compounds had gained access to the inner catalyst structure. Moritz et al. (1971) suggested that catalysts should possess sieving properties that will screen out the organometallics while permitting sulfur compounds access to the inner structure. Current research results indicate that HDS catalysts deactivate by three mechanisms: (1)rapid deposition of carbonaceous material, (2) adsorption of organometallics such as those of Ti, inorganics such as Fe, Si and the alkali metals, and (3) poisoning by N and S.
Metals Adsorption During investigations on catalyst aging in the “Synthoil” coal liquefaction process, Stanulonis et al. (1976) and Holloway et al. (1976) measured increased concentrations of C, N, S, Si, Fe, Na, K, Mg, Al, Si, and Ca in and on used cobaltmolybdate HDS catalysts with A1203-Si02 supports. Within the catalyst pores and to depths of 200 pm, titanium, silicon, and aluminum were clearly identified. Schuit and Gates (1973) state that organometallics of these elements react particularly in heavy liquids to form inorganics which plug the pores. If true, this would reduce intraparticle transport and result in an intrinsic loss of catalyst activity. Holloway et al. (1976) also found large residue deposits with spatial correlations between Fe and S, Ca and S, and K and Si, indicating the presence of iron and calcium sulfides, and silicates with alkali constituents. In support of this, Stanulonis et al. (1973) also reported seeing coarse, rodlike crystalline material, presumably ferrous sulfide, imbedded beneath the organic layer covering the catalyst pellets. Atoms of N and S were also found within the catalyst pellets themselves. The nitrogen was more concentra+-d a t the outer surfaces, but was also discovered in concentrations of 0.1 to 0.2 wt % within the pores. Various dis-
0bjec tive The objective of this second paper is to describe the poisoning effect of the major components identified in a Western Kentucky coal on a commercial cobalt-molybdate on alumina HDS catalyst. Their effects on catalyst hydrogenation activity were determined through impregnation techniques and by exposure to single organic and inorganic salts in an isolated system followed by a standardized hydrogenation activity test. Inorganic elements studied were Na, Mg, Ca, Fe, Ti, Si, Al, and P. Atomic absorption was used to measure the concentrations of the adsorbed metals and the catalyst activities were evaluated in the same fashion as reported in Part 1.
0019-7890/78/1217-0062$01.00/0
Experimental Section The metallic elements investigated were identified in the mineral matter of Western Kentucky No. 11 coal and their concentrations were determined by the ASTM procedure. In the first test procedure the elements were individually impregnated a t various concentration levels upon the C o o l Mo03IA1203 catalyst through the use of water-soluble salts. These salts were either nitrates or chlorides. Calcination of the impregnated catalysts at 755 K converted the salts to their
0 1978 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
I
O.'
t
I
I
I
1
I
I
I
1
I T i 0, I P,O.
I
I
I
I
I
I
I
1
I
I
4
0. I
0
12.0
I
I
o'21
1
63
1 24.0
36.0
kg C o a l / kg
48.0
60.0
CotolySt
Figure 2. Results from the adsorption of minerals from tetralin on the hydrogenation activity of the CM5 catalyst. oxides; however, in the presence of hydrogen sulfide some of these oxides were converted to sulfides. Samples of these catalysts were then subjected to the same standardized hydrogenation activity test employed earlier in Part 1. Namely, 25 g of impregnated presulfided catalyst was suspended in a 2-L autoclave; this was preheated to 394 K, 1000 cm3 of the reference feedstock was added, the system was pressurized to 1.4 X lo7 P a with hydrogen while stirring, and the temperature then increased to 617 K. The reference feedstock was the same aromatic hydrocarbon used in Part 1. At 15-min intervals very small samples of liquid were withdrawn and their refractive index (RI) measured. When the RI of the feedstock decreased from 1.5877 to 1.5700, this corresponded to a 50% hydrogenation of the bicyclics to the corresponding tetralins. The test procedure was maintained uniformly throughout all evaluations of the catalysts. The effect of the individual ash constituents on the hydrogenation activity of the reference feedstock is shown in Figure 1.As expected, the alkali salts of Na, Ca, and Mg, and iron gave the highest degree of deactivation. The curves in this figure gave a basis for comparison and measurement of deactivation when the catalyst was exposed to a single ash compound in tetralin under coal liquefaction conditions. Upon completion of the impregnation studies, samples of the catalyst were exposed to the individual mineral components under liquefaction conditions but without high rates of carbon deposition. This was accomplished by suspending a single compound in the tetralin donor solvent as a fine powder, in much the same form as present in the coal ash during a coal run. The compounds utilized are given alongside the corresponding activity curves in Figure 2. The purpose of these series of tests was to study the gross effects of individual ash component deposition on the catalyst surface and its effect on catalyst hydrogenation activity. The quantity of each compound utilized represents its concentration in 0.3 kg of Western Kentucky No. 11 coal (amount per test run). After the catalyst had been exposed to five repeat runs (equivalent to 60 kg of coalkg of catalyst), the hydrogenation activity of the catalyst toward the standard feed was measured and recorded as the final activity. The amount of the particular element tested that was adsorbed by the catalyst was then determined and recorded as percent metal oxide by atomic absorption (AA). The last column of
Table I. Final Catalyst Activities Compared to Activities of Impregnated Catalysts Catalyst % Metal oxide activity Ash Concn, Final constituent glrun activity on catalyst (AA) by Figure 1 NaHC03 CaC03 MgCo3 Fez03 TiClZ(CP)z NazSiO3 Si02-Al203 NH4PO4
1.0
0.53
2.20
1.8 1.3
0.69
0.44
0.59
0.30
8.0 2.0 1.0
0.42
50.0 0.5
0.59 0.66
0.70
3.00 10.0 (0.14) 2.2
1.10 0.45 (Na) 7.3 -
0.51
0.89 0.74 (0.38) 0.99 0.90 (Si) 0.80 (Na) 0.90 -
Table I gives the catalyst activities based upon Figure 1;these values were obtained by taking the percent of the poison adsorbed and determining the activity from the corresponding curve in Figure 1. The basic materials Na, Ca, Mg, and Fe follow closely the impregnation values; however, large discrepancies occurred in the occlusion of the acidic components. The results clearly indicate that the various constituents of coal ash when employed singly in a coal liquefaction system can lead to stepwise poisoning of a standard HDS catalysts. Figure 2 shows that the hydrogenation activity declined with repeated exposure of the catalyst to the coal ash constituents at the concentration levels found in the coal. In the next set of experiments, inorganic salts that would represent their exact, one-half, and twice their concentrations in the Kentucky No. 11coal were employed in the system a t liquefaction conditions. Standard concentrations of Na, Ca, Fe, Ti, P, and Si were first used and the results corresponded closely with those obtained earlier. One important aspect noted was the deposition of iron sulfide on the catalyst surface, its effect on activity, and its correlation with concentrations. The effects of sodium, titania, and iron were also investigated a t one-half and twice the normal concentration levels. Figure 3 shows the effect of three concentration levels of Fez03 and (CbH& Tic12 on the hydrogenation activity of the catalyst. The previous tests involved exposure of the heterogeneous catalyst to single coal ash components in tetralin. These ideal
64
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
1.0 x
0.5 X 2.0x LOX 2.0x
‘‘Ashibis Cwl”
Syslam
Tetralin
System
12
24
36
48
3
kg of Coal Proces~ed
0
12.0
24.0 k g Cool
36.0
480
60.0
/ kg COlolyei
Figure 3. Effect of concentration level of two minerals on CM5 cat-
alyst activity. conditions cannot be translated to coal-solvent-catalyst systems with any certainty. Single component poison studies in a real coal system cannot be carried out, because there is no known method for separating the mineral matter of coal from the coal itself. The so-called “ashless coal” that had been used in Part 1 appeared to be the best material for preparation of a single component-coal-solvent-catalyst system free of interference from other coal mineral constituents. The “ashless coal” was prepared from all the materials collected from the coal runs a t 630 K of Part 1.This material was heated to 450 K and filtered hot; the resulting filtrate analyzed less than 0.1 wt % ash. Two components, Na and Ti, representing the alkaline and acidic components, respectively, were individually introduced into the “ashless coal”-tetralin-catalyst system, and their effects relative to the hydrogenation activity of the catalyst were studied. The results are presented in Table I1 and Figure 4. The major portion of the investigation on the effect of coal ash constituents on hydrogenation activity were carried out using the control catalyst. In the previous studies, two other catalysts, a nickel-molybdate-alumina and a proprietary nickel or palladium-silica-alumina, showed initial and sustained activities greater than the control catalyst. These two catalysts were selected for limited poison studies with sodium and titanium to compare their activities, activity declines, and poison adsorption rates to the control catalyst. Tests were carried out in the tetralin system using ash constituent concentrations corresponding to those found in the Kentucky No. 11 coal. Typical results are shown in Figure 5.
Discussions The experiments described above were carried out to measure the rate and extent of adsorption of the individual metallic constituents onto the surfaces of the catalysts and to assess their poisoning effects on the hydrogenation activities of the catalysts. All the clean catalysts showed acceptable levels of hydrogenation activity relative to the standard reference feedstock for prolonged periods. Thus it was concluded that loss of activity following the impregnation of the salts and also following exposure to the coal minerals could pretty much be associated with the adsorbed metals on the surfaces of the catalysts. Only a small amount of carbon was identified on the specimens following the tetralin runs, and it was felt that this
Figure 4. Adsorption of sodium and titanium from tetralin and an “ashless coal” liquid.
was not significant. Study of the individual minerals gave a better insight into their rates of adsorption as a function of time and their concentrations in the tetralin system. In one experiment, using an organometallic form of Ti, a coal liquid soluble component, a decline in hydrogenation activity was observed that was not observed in the impregnation studies. The general findings demonstrate that the catalysts readily adsorb the metals found in the mineral matter of coal, leading to their hydrogenation deactivation. The extent of deactivation was clearly a function of the particular metal adsorbed, its mineral form, and its concentrations in the tetralin and on the catalyst. The results from the impregnation of the metal salts on the CM5 control catalyst presented in Figure 1 show that the alkali metals, Na, Ca, and Mg, and Fe in their oxide forms produced the greatest degree of deactivation. While the salt forms of Ti, P and Si were easily adsorbed upon the catalyst, their oxides showed very little deactivation effect. The quantities of metals adsorbed during the impregnation tests fully covered the ranges encountered during the adsorption studies, with the one exception of iron, which showed a higher level of adsorption than expected.
Transition Metals Results presented in Figure 2 show that iron was adsorbed quickly. After processing 12 and 60 kg of coal/kg of catalyst, 7.2 and 10.0%of the catalyst weights were identified as FepO3, respectively. The latter corresponds to a 70%loss in the relative hydrogenation activity after 72 h of process time. The rate of iron adsorption was very rapid, and a decreasing function of the quality of coal processed, a t least at the standard concentration level employed. There are two values for iron listed in Table I under “% metal on catalyst.” Before AA analyses, all catalyst specimens were carefully regenerated in air to remove carbon deposits. In the case of the tetralin runs the carbon deposits were low, 1-2%. For the catalysts exposed to Fe203 it was observed that after regeneration the porcelain dish contained both pellets and a fine residue. When the residue and pellets were submitted for analysis, a high value of % iron was reported, but when the screened pellets were submitted a low iron value was reported. This might indicate that under liquefaction conditions iron sulfide may complex with certain types of aromatics and deposit as organometallics on the outer catalyst surfaces. For example, cyclopentadiene compounds are known to form
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
65
Table 11. Comparison of Poisons Adsorbed on Catalyst in Tetralin, “Ashless Coal,” and Coal Runs Amount as Wt % Metal on Catalvst Tetralin, amt. Ky. No. 11, adsorbed Hydrog. wt % coal ash on catalvst activitv kg of coal processed/kg of catalyst Component NazO Ti02 Fez03 CaO Concn on catalyst, wt 96 15%C on catalyst 20% C on catalyst Catalyst with carbon Catalyst-regen.
0.5 0.9 12.11
1.4
“Ashless coal,” amt. adsorbed on catalvst
96
48
4.0
0.5 0.37
0.460 0.352 10.7 (0.2) 0.287 0.582 8.0 1.8
... ...
Ill. No. 6 w t % coal ash
0.9 0.9 19.9 3.1
Amt. adsorbed on catalyst Run no. 1 Run no. 2 96
192
0.1 1.4 0.24 0.25 20.1
0.2 2.8 0.28 0.25 22.8
0.1186 0.0817
complexes, i.e., ferrocenes. Results presented by Holloway et al. (1976) and Stanulonis et al. (1976) tend to confirm that the iron deposition is limited to the outer catalyst surfaces. Air regeneration gave a catalyst of low iron content, as compared to total iron content before regeneration. It might be expected that the iron adsorbed on a catalysts used in an ebullating liquefaction bed would probably be kept low by the constant attrition of the surfaces. All the other catalyst samples were checked for residues after regeneration, but with the exception of titanium, none were found. Figure 3 shows that when the Fez03 concentration in the tetralin was doubled, the rate of catalyst deactivation did not change. Thus there appears to be a limit to both the rate and extent of deactivation relative to iron concentration. Titanium displayed an anomalous poisoning behavior. As a deposited oxide it showed little deactivation effect on the hydrogenation activity of the catalysts. However, a high degree of poisoning was uncovered when the catalysts were exposed to titanium as an organometallic salt in tetralin. In this system, after five runs at concentration levels of 2.0 g/run the relative activity had decreased to 0.42. At this point the titanium adsorbed was 2.2% of the catalyst weight, and by the standard of Figure 1 negligible deactivation should have occurred. These results indicate that adsorbed inorganic forms of titanium have no poisoning effects on the catalysts, but that organometallic forms are easily adsorbed from even low concentrations in coal liquids and lower the hydrogenation activity markedly. Unlike iron, the rate of titanium deposited on the catalyst remained relatively constant with time as indicated by the curves in Figure 4. The amount of titanium deposited increased very slowly. The final relative activities are a clear function of the concentration levels of the metal complex in the liquid as Figure 3 indicates, the higher concentrations showing a greater reduction in activity. Regeneration of the titania-organo complex poisoned catalysts in air restores their activity to near 80% of virgin value. The type of poisoning encountered here might be viewed as an intermediate type. The organometallic, being soluble in the coal liquids, can diffuse easily into the inner pore structure, thereby reducing a greater portion of the surface to a state of inactivity. Holloway et al. (1976) found the distribution of Ti in the “Synthoil” reactor catalysts varied with the position of the pellets in the reactor. From the reactor inlet, catalyst pellets showed T i penetration of 200 pm, but from the center and outlet, only 25-pm penetrations. It is likely that a t the inlet, the liquid being essential pure solvent, does not hinder the transport of the Ti-complexes, but further downstream, where the concentration of heavy coal liquids
0.2097 0.940
0.1297 0.900
hg CwI / k g C o t o l p t
Figure 5. The influence of different catalysts on the adsorption of sodium and titanium.
is higher, transport of the T i complex is hindered. The depositions of coke can also be expected to be higher a t this point and this would screen out the T i complexes. Inorganic metallics, being essentially insoluble in the coal liquids, should be less able to diffuse in to the narrow mouth pores. Initially their deactivation effect should be limited to the outer surfaces; however, for long on-stream times, they could diffuse deeper into the pores.
Silicon a n d Phoshorus Silicon was exposed to the control catalyst in two forms: NazSiO3 and SiOrA1~03.The latter form was introduced into the tetralin system a t a concentration of 50 g/run, corresponding to the Si02-Al203 concentration in the coal ash. At this level, a high concentration was deposited on the catalyst, 7.3% by weight, and this lowered the catalyst activity to 0.61. The phosphorus impregnation experiment resulted in a negligible decline in hydrogenation activity; however, when exposed to NH4P04 the catalyst did experience some deactivation. The amount of phosphorus identified in the Western Kentucky coal was almost negligible; therefore, a low concentration value of 0.5 g/run was arbitrarily selected for study. This was the only element studied that was not submitted for analysis by AA.
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
Table 111. Comparison of Amount of Poison Adsorbed on Catalyst Surface as Wt 70 of Total Poison in Feed
System Sodium 12 kg 24 kg 48 kg 96 kg
192 kg Titania 12 kg 24 kg 48 kg 96 kg
192
KY. No. 11 coal 0.12
... ... ... ... ...
0.21
... ... ... ... ...
Ashless coal
Ill. No. 6
Coal
...
...
0.11
...
51.0 39.2 27.6 17.3
39.0 29.9 17.9
... ... ...
... ...
Tetralin
...
... ...
...
...
12.3 13.1 14.1 14.6
17.2 15.6 14.5
...
...
...
... ...
0.11
... ... ... ... ...
...
0.95 0.95
.. ... ... ... ,
13.3 13.3
Alkali Metals When catalysts were exposed to these metals in their mineral forms their final activities were nearly the same as those measured during the impregnation tests. The alkali metals are severe poisons; they were deposited at steady rates on the catalysts from low concentrations in the tetralin and produced high degrees of deactivation. Their depth of penetration into the pores of the HDS catalysts are much greater than would be expected from their insolubility in the organics (Holloway et al., 1976). Sodium was the only alkali selected for study a t three levels of concentration in tetralin. Its rate of deposition on the catalyst and declining activity effect increased with concentration in the liquid system. The control catalyst has a fresh N:! surface area of 280 m2/g. The adsorption of the elements on the catalyst always resulted in a moderate decline in this surface area. For example, under a concentration of 1.0 g of NaHCO&un the surface area declined to 210,205, and 129 m2/g after l, 2, and 4 runs, respectively. Other elements produced comparable surface area reductions. The carbonate forms of Ca and Mg were both readily adsorbed on the catalyst and gave final activities slightly lower than predicted by Figure 1. Calcium was the least adsorbed element of those studied; measurements showed 0.44% of the catalyst weight was CaO after four runs. Adsorption through “Ashless Coal” Liquids The percents of Na and T i deposited on the control catalyst per kilogram of coal processed are shown in Figure 4 to be dependent upon whether deposition occurred in the tetralin or “ashless coal” system. For each constituent the curves are similar and parallel, indicating that the deposition rates are independent of the system. The presence or absence of carbonaceous deposits on the catalyst surfaces has a pronounced effect on the extent of deposition. In the case of Na, the amount deposited was reduced through use of the “ashless coal” system. Evidently the heavy carbonaceous deposits laid down in the early stages of processing interfered with the transport of the sodium component in the organic solvent to the catalyst surfaces. In the tetralin system where there was a minimum of carbon deposition the Na transport was less hindered, and the percent deposited was greater. There is also a general trend depicted toward lower rates per unit of coal processed in the “ashless coal” system. With titanium in the “ashless coal” system, the amount deposited was greater than for the straight tetralin system, although the rates remained constant with processing time. This might indicate that the organometallic titanium complex is soluble in the solvent and heavy coal liquids and experiences no transport problems to the surfaces.
Poison Adsorption: Tetralin vs. “Ashless Coal” vs. Coal The rate of poison deposition on a catalyst surface during coal liquefacticn in the presence of a donor solvent is undoubtedly affected by the amount of heavy carbonaceous material in the solvent and that subsequently deposited on the catalyst surface. These differences were demonstrated by comparison of poison deposition rates and catalyst activity decline rates in the tetralin and “ashless coal” tests. To further study this phenomenon a catalyst was exposed to a coal-donor solvent system under coal liquefaction conditions for 96 and 192 h. The catalyst was discharged, regenerated in air, and submitted for AA elemental analyses. The results of these tests are given in Tables I1 and 111. In these tables a comparison is made between the tetralin, “ashless coal,” and coal systems as to amount (wt % metal oxides on catalyst) deposited on the catalyst surface and the amount of poison on the catalyst surface as wt % of the total poison in the coal ash. Data are presented in Table I1 as to the amount of poison deposited on the catalyst surface, its effect on catalyst hydrogenation activity, the amount of carbon on the catalyst, and its effect on catalyst hydrogenation activity. The first column in Table I1 lists the concentration of several inorganic components in Kentucky No. 11coal ash and the hydrogenation activity of a heterogeneous catalyst that has been exposed to this coal under coal liquefaction conditions to yield a catalyst with 15 wt % and 20 wt 96 carbon on catalyst. The second column lists the amount of poison deposited on the heterogeneous catalyst surface after exposure to the equivalent of 96 kg of coal/kg of catalyst. In this series the catalyst is exposed to a single element in tetralin at a concentration equivalent to that present in Kentucky No. 11coal ash. The catalyst activities for each concentration of poison on the catalyst surface are also listed. The fourth column lists the amount of each poison deposited on the catalyst in the “ashless coal” system. Catalyst hydrogenation activities could not be determined because of interference from carbon laydown. The last three columns list the concentration of several poisons in Illinois No. 6 coal ash and the amount of poison deposited on the catalyst after exposure to the equivalent of 96 and 192 kg of coal/kg of catalyst. In addition, the catalyst hydrogenation activity is listed with carbon and after air regeneration. Table I11 lists the percent of poison adsorbed on the catalyst as a function of the wt % of total feed at different levels of coal processed. Comparison of the values for the amount of poison adsorbed, its rate of disappearance, and their effect on catalyst hydrogenation activity showed that as one progresses from a clean feed as tetralin to a dirty feed as coal there is a tremendous change in these rates. The feed-insoluble inorganic salts were adsorbed on the catalyst surface at an extremely low rate and had only a slight effect on hydrogenation activity. The sodium rate was very low; less than 1%of the total sodium present was adsorbed per unit of poison with time. The iron and calcium values showed an intermediate initial rate but appeared to stabilize with time and showed very little increase. The iron value was interesting in that it approximated that obtained in the tetralin system for a screened catalyst; this catalyst was also screened. The titanium value is identical with values obtained in the tetralin and “ashless coal” system. The rate of adsorption of titanium was constant with time, and the amount adsorbed on the catalyst surface as a function of wt % total poison in feed was almost the same obtained in the tetralin-“ashless coal” tests. The catalyst was tested for hydrogenation activity with 20-25% carbon on itself and compared with the values listed.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 1, 1978
These are similar to that obtained with the Kentucky No. 11. The differences are explained on the basis of reaction temperature. The carbon values for Kentucky No. 11 coal were obtained a t 630 K and the carbon values for Illinois No. 6 coal were obtained at 672 K. Regeneration of these catalysts in air restored catalyst hydrogenation to 90-94% of virgin activity. This demonstrates that the catalyst was not poisoned by the small amount of alkali metals or titania deposited on the catalyst surface but by the large amount of carbonaceous material deposited on the catalyst surface and in the pore structure. The most important corollary that can be drawn from this study is the interaction of heavy carbonaceous laydown on the catalyst surface, coal ash poison deposition rate on the catalyst and hydrogenation activity of the catalyst (used and regenerated). The initial phase of this program demonstrated a t high levels of carbon laydown on the catalyst in the initial phases (4-20 kg of coal/kg of catalyst) was extremely detrimental to catalyst hydrogenation activity (10-30% of virgin activity). The next phase demonstrated that the inorganic salts present in coal ash would deposit on a heterogeneous catalyst in quantities sufficient to deactivate the hydrogenation activity of the catalyst. However, this deactivation was not as severe as coking, but ash component poisoning was permanent (compared to carbon burnout for catalyst regeneration) since no known method is presently available for screening these ash components from the catalyst surface. The last phase showed the differences in rate of adsorption and amount of adsorption of coal ash constituents on a catalyst surface, carbon deposition, and their effects on catalyst hydrogenation activity, when a heterogeneous catalyst is employed in coal liquefaction in the presence of a donor solvent. Thus, the interplay of heavy carbonaceous laydown and inorganic salt deposition is important. A catalyst that has a heavy laydown of carbonaceous material will limit the amount and rate of inorganic salt deposition. Thus, these new findings dictate that future catalyst research be directed to find a catalyst that will have a high carbonaceous laydown rate coupled with high initial hydrogenation rates. O t h e r Catalysts The major portion of the investigation on the effect of coal ash constituents on the hydrogenation activity of a catalyst was performed utilizing CM5 as the baseline catalyst. This catalyst was chosen because of the extensive use of cobaltmolybdate catalysts by other researchers and also its use by
67
Hydrocarbon Research Institute in their ebullating-bed coal liquefaction process. The only deviation from this scheme was the investigation on the hydrogenation activity of other commercial catalysts during coal liquefaction. That investigation showed two catalysts possessing initial (10-100 kg of coalkg of catalyst) hydrogenation activities greater than the CM5 catalyst. These were selected for a short poison study to compare their activities, activity decline, and poison adsorption rates to CM5. Poisons studied were sodium and titanium. Results of this testing are given in Figure 5. Titania presents a different picture than sodium. The CM5 catalyst had a constant rate of deactivation with increasing titania concentration on the catalyst surface. The other two catalysts have higher rates of deactivation than CM5 but the NP1 catalyst does show a promotion in activity in the early stages of titania deposition. With time, further adsorption of sodium and titanium compounds should cause the change in activity to approach the value exhibited by CM5. It was stated that this series of tests gave some insight into future catalyst testing programs. Not only must the areas of support properties such as surface area, pore size and volume, composition, active hydrogenation metals and concentration be investigated, but also the effects of ash constituents on hydrogenation activity, carbon deposition rate, A hydrogenation activity, poison deposition rates, and adsorption rates should be examined. Thus, a catalyst evaluation program becomes not only extensive but complicated due to the determination and evaluation of the interplay of all these variables. Acknowledgment The work was supported by NSF under grant number GI 40533, and the Commonwealth of Kentucky through the Institute for Mining and Minerals Research. The authors wish to thank J. Muccini and R. E. Linder for their AA analyses. L i t e r a t u r e Cited Holloway, P. H., Granoff, E.,Nowak, E. J., Mullendore, A. W., Liberman, M. L.. "Chemical Studies on Synthoil Process." Rept. No. SAND76-0644 to ERDA (1976). Moritz, K. H., Savage, H. R., Traficante, D.. Weissman, W., Young, D. J., Chem. Eng. Prog., 67, 53 (1971). Ocampo, A., Schrodt, J. T. Kovach, S. M., Ind. Eng. Chem. Prod. Res. Dev., preceding article (1978). Schuit, G. C. A., Gates, B. C., AIChEJ., 19, 417 (1973). Stanulonis,J. J., Gates, B. C., Olson, J. H., AlChEJ., 22, 576(1976).
Received for review July 2 2 , 1977 Accepted November 3,1977
