Energy & Fuels 1991,5,613-614
scrubbing agents, in particular lime or limestone, the alkaline earth metal cations in the lignite are readily reactive in solution and cost nothing. The product solution from the scrubber would contain a mixture of calcium, magnesium, and sodium sulfites and sulfates, similar to the product from conventional alkaline scrubbing. Removal of sodium, in particular, from the coal might considerably alleviate the formation of serious deposita on fire tubes of boilers which have been related to sodium content. Registry No. Na, 7440-23-5; SOz, 7446-09-5. Donald 5.Scott,* Alan J. Royce Department of Chemical Engineering University of Waterloo Waterloo, Ontario, Canada Received December 21, 1990 Revised Manuscript Received March 22, 1991
Catalyzed Conversion of Acetylene to Higher Hydrocarbons Sir: The continuous catalyzed conversion of acetylene to higher hydrocarbons has been the subject of numerous Interest in this process reflects the fact that a succesful conversion of this type could serve as a possible alternative source of synthetic fuel.'" The synthetic fuel possibility is centered on the fact that acetylene is obtainable in industrial quantities from coal and methane.5 However, as noted explicitly by previous workers, the unavailability of an effective catalyst for continuous C2H2 conversion has prevented development of this alternative fuel route.'-3 The difficulty encountered with C2H2conversions is the rapid deactivation of the catalysts employed. This loss in catalytic activity is believed to arise primarily from the rapid polymerization of CzH2 to polycyclic aromatics. These polycyclic aromatics serve as precursors to coke formation and eventual catalytic deactivation. For example, Tsai and Anderson,' using a ZSM-5 zeolite catalyst, report an approximate 70% decrease in C2H2conversion after only 190 min of on-stream conversion at a C2H2space velocity of only 460 h-' and reaction temperature of 573 K. Similarly,Allenger et al.? in a study of C2H2conversion over amorphous fluorinated alumina catalysts, report significant decreases in C2H2 conversion with time on stream, with this rate of catalytic deactivation increasing rapidly with increasing C2H2concentration in the reactant stream. Details of the catalyst deactivation in this system have been r e p ~ r t e d . ~ In sharp contrast with previous studies, the present report communicates a dramatically improved continuous flow catalyzed conversion of C2H2to higher hydrocarbons. This conversion is achieved by using a modified H-ZSM5 zeolite catalyst and a reactant gas feed consisting solely of C2H2 plus water. Using this combination, we have demonstrated efficient continuous 100% conversion of C2H2to higher hydrocarbons for over 24 h at a C2H2space velocity of 2.1 X 103 h-' and a reaction temperature of only 623 K. (1)Teai, P.;Anderson, J. R. J. Catal. 1989,80,207-214. (2) Ailenaer, V. M.: Fairbridae, - C.: Mchan, D. D.; Ternan, M. J. Catal. 1987;105,71-80. (3)AUenger, V. M.; McLean, D. D.;Teman, M. Fuel 1987,66,43+43f3. (4) Allenner. V. M.: Brown. J. R.: Clunston.. D.:. Teman, M. McLean, D.D:Appi.-c&ai. isie,39,igi-2ii. (5) Cf. Tedeschi, R. J. Acetylene-Based Chemicals from Coal and Other Natural Resources; Marcel Dekker: New York, 1982.
-
0887-0624/91/2505-0613$02.50/0
613
100.0
3 v
2
8 a >r0
60.0
W
40.0
0
20.0
0.0
TIME ON STREAM (Min)
Figure 1. Comparison of catalytic lifetimes for H-ZSM5 unmodified (curve A) and modified (curve B) in C2Hzconversion. Curve A reactant gas, CzHz;space velocity, 315 h-l; temperature, 673 K; catalyst, H-ZSM5. Curve B: reactant gas, CzHz/H20= 2.3; total gaseous flow space velocity, 2100 h-l; temperature, 623 K; catalyst, Ni/H-ZSM5/A1209.
70.0
--5
k-
60.0
'
50.0
'
40.0
'
s
"
e h a
g 3
a
30.0 20.0 10.0
0.0 0
300
600
900
1200
1500
Time On Stream (Mln)
Figure 2. Hydrocarbon product distribution obtained in C2Hz/H20conversion as a function of time on-stream under experimental conditions shown for curve B, Figure 1. The shape-selective ZSM-5 zeolite catalyst employed has a Si/Al ratio of 30. This catalyst was converted to a more active form by using the ZSM-5 activation procedure described by Rajadhyaksha and Anderson! The resultant H-ZSM5 was then mixed with Al(OH)3 (weight ratio HZSM5/A1203= 2/3) which was followed by addition of a solution of Ni(N03)2. This mixture was dried at 110 "C and then calcined a t 550 "C for 2 h. The resulting solid was ground and then screened to grains of 20-40 mesh. Finally, this solid was subjected to temperature-programmed reduction by H2by using the recommended procedure for NiO reduction.' The resulting Ni/H-ZSM5/A1203 catalyst was employed in this study. Reactions were carried out in a fixed-bed continuous flow microreactor at 1 atm pressure. A reactant feed gas of C2H2+ H20 was obtained by bubbling C2H2through a thermostated vessel containing water. The effluent gas mixture of C2H2and H 2 0 was fed directly to the catalyst, using a heated transfer line to prevent condensation. Preliminary control experiments using only the H-ZSM5 without added Ni and pure C2H2reactant feed resulted (6) Rajadhyakaha, R. A.; Anderson, J. R. J . Catal. 1980,63,510. (7)Bartholomew, C. H.;Farruato, R. J. J. Catal. 1976,45,41-53. 0 - 1991 _. . American Chemical Societv ~
Energy & Fuels 1991,5,614-615
614
in very rapid catalyst deactivation in agreement with previous studies.' Figure 1,curve A, illustrates the magnitude of this catalyst deactivation. In contrast, the 100% conversion of C2H2is maintained when the experiment is carried out using the Ni-modified catalyst and a reactant feed of C2H2/H20of 2.3. This result is shown in curve B, Figure 1, for a Ni/H-ZSM5/A1203 catalyst containing 13.3% Ni relative to the ZSM-5 for conversion a t 623 K and a total gaseous space velocity of 2.1 X lo3h-l. The product distribution obtained in the conversion described by curve B, Figure 1,is shown in Figure 2 in terms of total olefins, paraffins and aromatics. As shown in this figure, the aromatic yield remains relatively constant with time while a slow decrease in olefm/parafEi ratio is noted. The aromatic fraction consists almost exclusively of monocyclic compounds (i.e., benzene, toluene, xylenes, etc.) with less than 3% of the total products being polycyclic compounds. We feel this relatively small yield of polycyclic aromatics (as contrasted with previous studies of C2H2conversion) accounts for the continued catalytic activity in this system. The roles of the Ni on the catalytic activity and H 2 0 added to the reactant stream are under investigation and will be analyzed in subsequent reports. However, it is significant at this point to note that both the added Ni and H 2 0 are required in order to maintain catalytic activity in the C2H2conversion. Separate experiments with the Ni-modified catalyst and no H20resulted in rapid catalyst deactivation. Similarly, studies of a non-nickel-containing H-ZSM5/iil2O3catalyst with a C2H2/H20reactant stream resulted in catalytic deactivation. Based on our results obtained to date, it is believed that the C2H2/H20conversion process proceeds (at least in part) via formation of an acetaldehyde intermediate. The continuous catalytic conversion of CzHzto higher hydrocarbons observed in our laboratory is clearly of interest with respect to synthetic fuel production. This is particularly true in view of the fact that the proposed process avoids the need for the addition of a relatively expensive hydrogen source as encountered in other fossil fuel synthetic fuel upgrades. Instead, the conversion process discovered requires simply the addition of H20 to the fossil-fuel-derived C2H2and the conversion is achieved in a simple one-step catalyzed reaction. Acknowledgment. We thank Mobile Corporation for the gift of the ZSM-5 catalyst. This material is based, in part, upon work supported by the Texas Advanced Research Program (Advanced Technology Program) under Grant No. 003656-116. Registry No. C2H2, 74-86-2.
-
Y. He, W. L. Jang, R. B. Timmons* Department of Chemistry Box 19065 The University of Texas at Arlington Arlington, Texas 76019-0065 Received February 4,1991 Revised Manuscript Received April 5,1991
Synthesis of Carbons with Controlled Macrovoidage Sir: When pulverized bituminous coal particles are rapidly heated to combustor or gasifier temperatures, they are transformed into cenospheres and mesospheres' which have voids throughout significant fractions of the particle (1) Bailey, J. G.; Tab, A.; Dieeeel, C. F.K.; Wall,T. F.Fuel 1990,69, 225.
0887-0624/91/2505-0614$02.50/0
1()p111
Figure 1. Scanning electron micrograph at 3000X of a 28-pm lycopodium spore.
volumes. Such chars present distinctive issues for research, including unhindered oxygen penetration onto the relatively large surface area of the voids and extensive disintegration of the char particle into ash-laden fragments during the latest stages of burnout. Recently, research issues such as these have been clarified in studies with synthetic carbons having tailored pore systems or idealized mineral systems. However, cenospheres and mesospheres have much larger void sizes and porosities than any of the available synthetic carbons.2-12 Our carbon synthesis scheme controls the size and loading of monodisperse macrovoids in a glassy carbon matrix. It is compatible with all of the available methods to tailor size, shape, and microporosity in poly(furfury1 alcohol) (PFA) carbons,66 or to load them with minerals and catalysts.' We use Senior and Flagan's3 polymerization of furfuryl alcohol catalyzed by p-toluenesulfonic acid, as elaborated else~here.'~Briefly, this scheme involves polymerization at 345 K; recovery of the polymer from an aqueous phase; thinning with acetone; vigorous addition of inclusions; curing a t 400 K for 6 h; curing at 475 K for 10 h; curing at 825 K for 1 h; and pulverization and classification of the carbon into a desired size grade. Our modifications are twofold: first, lycopodium spores are added as the macrovoid formers and, second, samples of uniform bulk density are recovered after classification in a centrifuge. Lycopodium, a hollow, waxy, hydrocarbon plant spore, is an ideal void former because (1)its size is uniform; (2) its mass loading in the polymer determines the ultimate (2) Walker, P. L. Jr.; Oya, A.; Mahajan, 0. P. Carbon 1980,18,377.
(3) Senior, C. L.; Flagan,R C. n e n t i e t h Symposium (International) on Combustion [Proceedings];The Combustion Institute: Pittsburgh, 1984; p 921. (4) Levendis, Y. k,Flagan, R C. Combust. Sci. Technol. 1987,53,117.
( 5 ) Levendis, Y. A.; Flagan, R C.; Gavalas, G. R. Combust. Flame
1989, 76(3+4), 221. (6) Levendis, Y. A.; Flagan, R. C. Carbon 1989,27(2), 265. (7) Levendis, Y. A.; Nam,S. W.; Lowenberg, M.; Flagan, R. C.; Gavalas, G. R. Energy Fuels 1989,3,28. (8) Waters, B. J.; Mitchell, R E.; Squires, R G.; Laurendeau, N. M.
n e n t i e t h Symposium (International) on Combustion [Proceedings]; The Combustion Institute: Pittsburgh, 1984; p 17. (9) Waters, B. J.; Squires, R. G.; Laurendeau, N. M. Combust. Sci. Technol. 1988,62, 187. (10) Waters, B. J.; Squires,R. G.; Laurendeau, N. M.; Mitchell, R E. Combust. Flame 1988, 74(1), 91. (11) Helble, J. J.; Sarofim,A. F. Combust. Flame 1989, 76(2), 183. (12) Helble, J. J.; Sarofim, A. F. J. Colloid Interface Sci. 1989,128(2), 348. (13) Akan-Etuk, A. 'Pyrite Transformations During I'yrolysh'. Engineer's Thesis, Mechanical Engineering Department, Stanford University, 1991.
0 1991 American Chemical Society
