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Received for review November 4,1983 Accepted January 30,1984
Catalyst for Steam Gasification of Wood to Methanol Synthesis Gas Yoshlnorl Tanaka, Tsuyoshl Yamaguchl, Kenjl Yamasakl, AkHuml Ueno, and Yoshlhlde Kolera Department of Materials Science, Toyohashi University of Technology, Tempaku, Toyohashi, Aichi 440, Japan
A catalyst was developed for steam gasification of wood to generate methanol synthesis gas. Upon screening various metal oxides supported on alumina catalysts, the most favorablecatalyst was NiO/AI,O, since it supplied a gas mainly composed of hydrogen and carbon monoxide with an Hp/CO ratio in volume being close to 2.0. It was proved that a composition and yield of a gas from wood strongly depends upon metal oxides employed and a mean micropore size of alumina support. The effects of gasification temperature and amount of water added upon a composition and yield of a gas generated were also studied.
Introduction Methanol, as well as hydrogen, has been desired to be a clean fuel because of less emissions of NO, and SO, during combustion. Methanol is produced from hydrogen and carbon monoxide, supplied from steam reformation of methane and/or higher hydrocarbons, with a ratio of H,/CO controlled to be 2.0 by a shift reactor. Coal and heavy oil residues are considered to be qualified resources for synthesis gas and their gasification techniques have undergone great progress by Tarrer et al. (1979) and Harney and Mills (1980). In this decade much attention has been paid to wood gasification probably because of the fact that wood is renewable and contains lesser amounts of sulfur compounds than coal and heavy oil residues. Swaaij (1980) and Coffman (1981) studied pyrolysis of wood in the presence of steam and oxygen. Wood can be gasified at 300 "C and produces a gas preferably composed of carbon dioxide, while at 600 "C hydrogen, carbon monoxide, and methane are mainly produced with considerable amounts of higher hydrocarbons, alcohols, and organic acids. The yield of a gas generated by wood pyrolysis at 600 "C is, however, as low as 40% in weight of wood employed, since large amounts of char and tarlike fragments are also produced. Accordingly, an application of a proper catalyst has been desired to improve a yield and composition of a gas generated. In the present communication, a catalyst suitable for the generation of methanol synthesis gas from wood is reported. The effects of metal oxides supported on alumina and a mean pore size of alumina support upon a yield and compositiopl of a gas generated are also discussed. Finally, a life test of the catalyst for wood gasification is briefly mentioned. Experimental Section For the gasification experiments, sawdust of hemlock and spruce (supplied from Ebara Seisakusho Co.) was used. The average size of the sawdust is about 1.0 mm in diameter and the composition was analyzed by conventional chemical techniques; for hydrogen, carbon, and nitrogen a combustion analysis was applied using a CHN corder 0196-4321/84/1223-0225$01.50/0
(Carbon-Hydrogen-Nitrogen Analyser , Y anagimoto Seisakusho Co.), and for sulfur and chlorine gravimetric and a colorimetric analyses were carried out using aqueous solutions of barium chloride and mercury(I1) thiocyanate, respectively. The amount of ash was estimated by weighing the residues after combustion of a certain amount of the sawdust at 600 "C for 2 h. Catalysts employed were prepared by a conventional impregnation method using aqueous solutions of metal nitrates and alumina spheres. For Vz05and Moo3 supported catalysts, aqueous solutions of vanadium oxalate and hexaammonium molybdate were employed, respectively. The loadings of metals were all 20 wt 5%. Several kinds of alumina (7-A1203, supplied from Sumitomo Aluminum Co.) were employed, their micropore sizes being varied from 60 to 2000 8. The catalysts thus prepared were dried at 110 "C and then calcined at 700 "C for 4 h in air. The surface areas of catalysts were measured by the BET method using nitrogen at its liquid temperature. The surface areas of metals in catalysts were measured by hydrogen chemisorption after the reduction of the catalysts at 700 "C in hydrogen stream for 4 h. Two types of reactors were used; one is a batch-feed reactor and the other is a continuous feed reactor equipped with a screw feeder. The batch-type reactor was used for catalysts screening. A catalyst calcined at 700 "C was mixed with the sawdust with a weight ratio of 3:2, and 5 g of this mixture was placed on a bed in the batch reactor. The gasification was carried out at temperatures between 500 and 800 "C in the presence of water vapor. Argon gas was used as an inert gas with a flow rate of 200 mL/min. The argon gas passed through a water reservoir heated at 50 "C before introduction to the reactor. Thus, the argon gas includes ca. 13.7 vol % water vapor. The fraction of water vapor can be varied by changing the temperature of the water reservoir. A gas generated passed through a cold trap to eliminate an excess amount of water vapor and tarlike fragments and then the gas was subjected to gas chromatography using columns packed with molecular sieve 13X and Porapak Q. The gasification reaction was carried out for 1 h and then the catalyst was separated 0 1984 American Chemical Society
226 Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 2, 1984
I
Table I. Composition of the Sawdust in Dry State component
wt 5%
c
48.6 7.2 43.2
