660
I d . Eng. Chem. PrOcessDes. Dev. 1883, 22, 660-662
Coal Liquefaction wlth Encapsulated Catalyst Po-Llang Chicen, Hung Chao,+ and Sol W. Weller' Department of Chemlcal Engheering, State Unlverstty of New York at Buffalo, Buffalo, New York 14260
The liquefaction of a bituminous coal has been studied in the presence of ammonium heptamolywate catalyst added in the form of microcapsules. These were prepared by In situ encapsulatlon of an emulsion of the molybdenum salt in Tetralin. The average diameter of the polymeric microcapsules (resulting from reaction between a diisocyanate and a polyfuncthl amine) was about 6 pm. Autoclave testing of the catalytic effect on liquefaction showed, both for coal conversion and hydrogen consumption, that at 450 O C the microencapsulated catalyst is at least as good as ammonium heptamolywate pre-impregnated on the coal from aqueous solution, and far better than powdered ammonium heptamolybdate. Microencapsulated catalysts of this kind appear to offer some advantages of convenience in use, stability in storage, and flexibility.
Introduction It has been appreciated for more than 30 years that eacellence of dispersion is an important factor in determining the efficiency of many aatalysts useful in coal liquefaction (Weller and Pelipetz, 1951). The relevance of this factor for simple molybdenum compounds, employed in small amount in a once-through mode of operation, has been the subject of a recent review (Weller, 1982). One of the most effective ways of employing small amounts of a liquefaction catalyst is to impregnate the catalyst onto powdered coal in a preliminary step. This is cumbersome and expensive, however. A different approach to achieving high dispersion with a molybdenum catalyst is embodied in the Dow liquefaction process, in which an aqueous solution of ammonium heptamolybdate is introduced into the coal-recycle oil slurry as a waterin-oil microemulsion (Moll and Quarderer, 1979). Under reaction conditions, the molybdenum salt is converted to very small particles of oxide or sulfide which, because of their size, tend to remain in the overflow of the hydroclone used for solids separation. Microemulsions may present problems of stability and lack of generality. This paper presents an alternate approach, derived from the technology of ''carbonless carbon paper", which seems to possess advantages of broad applicability and catalyst stability. The approach uses as catalyst a dilute aqueous solution of a metal salt, contained in microcapsules of a thermolabile polymeric material and prepared in any appropriate organic vehicle (e.g., Tetralin or recycle oil) as the continuous medium. In this paper, ammonium heptamolybdate (AM) was studied as catalyst and Tetralin as the vehicle. Experimental Section Apparatus and Procedures. Reactions were carried out in a 1-L autoclave (Autoclave Engineers Magnedrive) which was fitted with a glass liner to facilitate the introduction of reactants and removal of products. The charge of Tetralin in all experiments was 200 g (1.513 mol). The charge of coal, when used, was 40 g of a high sulfur, high ash, hvab (West Virginia) coal; a detailed description has been given by Scinta and Weller (1977). An initial hydrogen pressure of 1000 psia (cold) was employed in all experiments. The ammonium heptamolybdate (AM) Moore Business Forms, Research Center, Grand Island, NY 14072. 0196-4305/83/1122-0660$01.50/0
Table I. Hydrotreating of Polymer Capsulesa run no. T, "C naphthalene, mol toluene insols., g
1 450 0.008 0.018
2 400 0.005
0.054
0.84 g polymer capsules + 200 g (1.513 mol) Tetralin, 1000 psia H, (cold); 1h at indicated reaction temperature. a
catalyst was tested in various forms: (a) powdered solid (to pass 100 mesh), (b) impregnated on coal from aqueous solution and dried (vacuum oven, 50 "C), or (c) microencapsulated. Microcapsulation of AM was made by the interfacial polycondensation method of Ruus (1969). An aqueous solution of AM was first emulsified in a Tetralin continuous medium; thereafter a polymer wall was formed around the microdrops from reaction of a dissocyanate with a polyfunctional amine. Examination with a scanning electron microscope indicated a range of size of about 1 to 20 pm for the microcapsules, with an average diameter of about 6 pm and about 2 X lo9 capsules/cm3 of a 20% solid suspension. Blank runs were also made with capsules containing water but no AM. A run was initiated by weighing appropriate amounts of Tetralin, coal, and catalyst into the dry glass liner. The faed liner was transferred to the autoclave which was then sealed, evacuated, and filled with hydrogen. The gas pressure was monitored during heating, reaction, and after the autoclave had again cooled to room temperature. In the tables, pf represents the final (cold) autoclave pressure. After the reaction, the autoclave gas was analyzed with an on-line G.C. The glass liner and contents were weighed after the autoclave was opened; solid products were separated by filtration through a Soxhlet thimble and extracted (Soxhlet) overnight with toluene. The weight of the toluene-insoluble residue was used in the calculation of coal conversion. An aliquot of the liquid product from the autoclave was separately extracted with n-pentane for the determination of asphaltene and oil. For the experiments run at 400 "C,a G.C. equipped with a 10-ft column of 3% Dexsil300 was used to analyze the naphthalene to Tetralin ratio of the liquid product. In the case of the 450 "C runs, the liquid product was diluted with n-heptane and analyzed by HPLC (UV detector, 30 cm pBondapack NH column) for determination of naphthalene and Tetralin. Coal 'conversion was calculated (on a moisture- and ash-free basis) from the weight of toluene insolubles. The moles of hydrogen transferred to coal was calculated as 0 1983 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983 661
Table 11. Coal Liquefaction at 400 'Ca run no. catalyst (AM): form amount of Mo, g Pf I Psis H, consumed, mol naphthalene produced, mol H transferred, mol coal conversion, wt % (maf) asphaltene, wt % oil, wt % CH,, wt %
3 none 951 0.104 0.083 0.270 69.0 39.0 28.7 0.6 0.7
c, -c, , wt % a 4 0 g coal + 200 g (1.513 mol) Tetralin, 1000 psia H, t H, consumed.
4 powder 0.40 933 0.146 0.068 0.282 70.4 39.6 29.1 0.6 1.1
5 impreg. 0.40 832 0.325 0.020 0.365 77.8 44.1 32.3 0.5 0.9
6A
6B encapsulated 0.31 868 861 0.295 0.293 0.039 0.033 0.373 0.359 72.6c 73.4c 40.0 42.3 31.4 29.5 0.6 0.6 0.6 1.0
(cold); 1 h at 400 "C. H transferred = 2(naphthalene produced) Coal conversion calculated on basis that polymer becomes completely soluble in toluene after reaction.
Table 111. Coal Liauefaction at 450 "C" run no. catalyst (AM): form amount of Mo, g
7 none
pf, psis
1010 0.104 0.270 0.030 0.614 90.0 34.2 50.7 3.0 2.1
H, consumed, mol naphthalene produced, mol alkyl (C,) benzene mol H transferred, mol coal conversion, wt % (maf) asphaltene, wt % oil, wt % CH,, wt %
c,-c,, wt %
8 powder 0.40 983 0.124 0.237 0.033 0.565 91.4 35.3 51.8 2.7 1.6
9 impreg. 0.40 934 0.196 0.215 0.038 0.578 93.9 36.2 53.9 2.4 1.4
1OA 10B encapsulated 0.31 935 931 0.210 0.211 0.221 0.218 0.032 0.030 0.615 0.622 93.2c 93.1 36.9 36.5 53.0 52.2 2.7 2.6 1.7 1.7
49 g coal t 200 g (1.513 mol) Tetralin, 1000 psia H, (cold); 1 h at 450 "C. H transferred = 2(naphthalene produced) alkylbenzene t H, consumed. Coal conversion calculated on basis that polymer becomes completely soluble in Tetralin after reaction. a
-
twice the moles of naphthalene produced plus the moles of hydrogen gas consumed (less the moles of alkylbenzenes produced, if any).
Results and Discussion Blank runs were first performed to investigate the fate of the polymer capsules alone (no AM present) after reaction at 400 or 450 OC. The results are shown in Table I. At both temperatures, there was no significant change in final pressure from the original 1000 psia, and the amount of naphthalene produced by dissociation of Tetralin was very small (0.5% of Tetralin charged, for run 1, and less for run 2). The behavior of the polymer was different at the two temperatures: the amount of toluene insolubles, attributed to polymer residue, was 2% in run 1and 6% in run 2, based on the weight of polymer capsules charged. The amount of residue is small in both cases, but the difference may be significant with respect to possible adsorption on catalytic sites. The visual appearance of the Soxhlet filtrate was consistent with the amount of residue; the filtrate was clear in run 1but contained dark specks in run 2. Table I1 summarizes the results for runs made with coal at 400 "C. The catalyst (AM) was added either as powdered solid (run 4), impregnated on coal (run 5), or as microencapsulated aqueous solutions (runs 6A and 6B, duplicates). The amount of AM added in runs 4 and 5 corresponded to 1% based on the coal charge; it was slightly less for the microencapsulated AM, where only 0.78% Mo based on coal was present. Since the asphaltene/oil split in the liquid products is difficult to determine accurately, the most reliable indices of catalytic activity are the total coal conversion and the amount of hydrogen consumed. The latter is indicated approximately by the final autoclave pressure after cooling (i.e., by the drop in pressure from the original 1000 psia), and more accurately from measurement of the final volume
of autoclave gas and its analysis. In comparison with the blank (run 3), powdered AM at 400 "C is only marginally catalytic, whereas AM impregnated on coal is a good catalyst; these results are consonant with earlier research. Microencapsulated AM at 400 "C (tested at slightly lower loading) is not quite as active for either coal conversion or hydrogen consumption as the impregnated catalyst, though it is not far behind. I t is possible that the polymer residues noted above at 400 "C (Table I) have some deleterious effect on the catalyst. Table I11 presents results for the experiments conducted at 450 "C, a temperature which is closer to liquefaction practice. Here again AM added as a powdered solid is only marginally catalytic (compare runs 7 and 8), and impregnated AM is markedly catalytic (run 9). The microencapsulated AM is at least as good at 450 "C as the impregnated catalyst, and the index of hydrogen consumption indicates it to be even better than the impregnated one. The use of the encapsulated catalyst would offer the significant advantages of convenience (no necessity to impregnate powdered coal with aqueous solution and to dry), stability (the microencapsulated catalyst has an indefinitely long shelf life), and lower energy consumption (no need to evaporate large amounts of water). The superior activity of AM when added as microcapsules, relative to that when added as a powder (Table 111), can be understood on the basis of comparative surface areas. Without regard to the ultimate fact of the AM during liquefaction, we may consider that the AM contained within one microcapsule forms a small crystallite of MOO, after rupture of the polymer shell and vaporization of the water. Calculation of the amount of AM within one capsule leads to a value of about 1.5 pm for the size of the resultant MOO, crystallite. By contrast, the AM added as "powder" in Table I11 is ground to pass a 100 mesh sieve; its particle size is therefore about 150 pm. Since the specific area is inversely proportional to particle
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Ind. Eng. Chem. Process Des. Dev. 1983, 22, 662-665
size, the encapsulated catalyst ends as particles with surface area roughly 100 times greater than that of the powder. Microencapsulation of coal liquefaction catalysts is not limited to AM. Other catalytic metal salts, such as ferrous sulfate, nickelous chloride, or stannous chloride, could be encapsulated and used in the same way. It is also likely that air-sensitive catalysts (some organometallics) can be similarly prepared and used, since they will be protected by the polymeric shell of the microcapsules against attack by air. Acknowledgment The authors wish to thank Moore Business Forms for
its continued encouragement of this research, and the Department of Energy for its financial support of much of the work. Registry No. Ammonium heptamolybdate, 12027-67-7.
Literature Cited Moll. N. G.; Quarderer, G. J. U.S. Patents 4 136013 and 4172814, 1979. Ruus, H. U.S. Patent 3429 827, 1969, Scinta, J.; Weller, S.W. Fuel Process Tecbnol. 197711978, 1 279. Weller, S.; Pelipetz. M. G. Ind. End. Chem. 1951, 43, 1243. Weller, S. W. 4th International Molybdenum Chemistry Conference, Golden, CO, Aug 1982.
Received for review January 3, 1983 Accepted March 21, 1983
Oxygen Chemisorption and Olefin Disproportionation Activity of W03/Si02 Suk J. Choung and Sol W. Weller" Department of Chemical Enginwring, State University of New York at Buffalo, Buffalo, New York 14260
Tungsten oxide-silica catalysts have been characterized by measurement of oxygen chemisorption and activity for the disproportionation of propylene, over the loading range 5.3 to 15.2 wt % W03. Oxygen chemisorption at -78 "C,on samples reduced in situ in a vacuum microbalance, increases smoothly with W 0 3 loading; the shape of the curve suggests that the higher the loading, the lower the dispersion. Catalytic activities after N, activation vary almost linearly with the O2chemisorption values, when correction is made for the actual extent of reduction during the prereduction (preceding the chemisorption measurement). This correlation suggests, but does not prove, that the relative tungsten oxide area, as measured by O2chemisorption on reduced catalysts, may be causally related to the activity for propylene conversion.
Introduction Molybdenum oxide and tungsten oxide on silica have been the subject of various studies since the report by Banks and Bailey (1964) of their activity in the disproportionation of olefins (Banks, 1980; Heckelsberg et al., 1969; Luckner et al., 1973; Thomas et al., 1979). Until recently, the research has been concerned largely with reaction kinetics and mechanism. In the past several years a series of papers has attempted to elucidate the nature of the active sites in these catalysts by a variety of techniques (Kerkhof et al., 1977; Stork and Pott, 1977; Thomas et al., 1979; Van Roosmalen et al., 1980). There appear to be no published reports on characterization of reduced W03/Si02 by gas chemisorption. Since selective chemisorption of O2 at low temperature has been profitably employed for the study of supported molybdena catalysts (Parekh and Weller, 1977; Liu and Weller, 1980; Garcia Fierro et al., 1980), an attempt has been made in the present work to apply this method to the W03/Si02system. Catalysts with a loading range of 5.3 to 15.2 wt % WO, have been studied, for O2 chemisorption (after prereduction) at -78 "C, and for the disproportionation of propylene to ethylene and butenes at 500 "C. Experimental Section Catalyst Preparation. Catalysts were prepared by impregnation of 60 to 80 mesh SiOzgel (Davison Chemical grade 57; BET surface area 253 m2/g) with aqueous am0196-4305/83/1122-0662$01.50/0
monium metatungstate, (NH4)6H2W12040.5H20, by the no-excess solution technique. After impregnation, the catalysts were dried at 100 "C and calcined at 550 "C for 3 h in flowing dry air. The range of loading was 5.3 to 15.2 wt % W03 in the finished catalyst. The calcined samples have a bright yellow color, characteristic of WO,. Apparatus and Procedures. Oxygen Chemisorption. A static, gravimetric adsorption system, composed of a Cahn 2000 Electrobalance and a high-vacuum system, has been used for prereduction and adsorption measurements. Details of the apparatus and corrections have been give elsewhere (Choung, 1982). The O2 chemisorption values were determined as the difference between two O2 adsorption isotherms a t -78 "C. Prior to the first adsorption isotherm measurement, (typically) 120 mg of catalyst was prereduced in situ with static H2 (400 torr) at 500 "C for 10 h and then outgassed at 500 "C for another 10 h. Between the first and second isotherm measurements, the sample was pumped for 1h at -78 "C in order to desorb the physically adsorbed oxygen. Activity for Propylene Disproportionation. A continuous flow microcatalytic reactor was used for the activity measurements. The reactor was 4.6 mm i.d. stainless steel tube, in which 300 mg of catalyst was placed and held by plugs of glass wool. The propylene used was Matheson C.P. grade (99.2% purity), and its flow rate through the reactor was 40 cm3/min at 14 psig. Product analysis was by G.C. with an analytical column (4.8 m X 0.635 cm) of 20% BMEA on 60-80 mesh Chromosorb P. Column and 0 1983 American Chemical Society
