TG-FTIR Study of the Influence of Potassium Chloride on Wheat Straw Pyrolysis Anker Jensen* and Kim Dam-Johansen Department of Chemical Engineering, Technical University of Denmark, Building 229, DK-2800, Denmark Marek A. Wo ´jtowicz and Michael A. Serio Advanced Fuel Research, Inc., 87 Church Street, East Hartford, Connecticut 06108 Received January 16, 1998 The interest in utilizing biomass as a CO 2 neutral fuel by combustion, gasification, or pyrolysis processes is increasing due to concern about the emission of greenhouse gases from fossil fuel combustion. In thermal fuel conversion, pyrolysis is an important step which determines the split of products into char, tar, and gas. In this work, a combination of thermogravimetry and evolved gas analysis by Fourier transform infrared analysis (TG-FTIR) has been applied to study the influence of potassium chloride (KCl) on wheat straw pyrolysis. Raw straw, washed straw, and washed straw impregnated with KCl have been investigated. To facilitate interpretation of the results, pyrolysis of biopolymers (cellulose, xylan, lignin) in the presence and absence of KCl was investigated as well. The raw straw decomposed in a single broad featureless peak. By washing, two peaks appeared in the derivative weight loss curve, corresponding to the decomposition of hemicellulose and cellulose components in the straw. Washing reduced the char yield from 23 wt % (daf) to 12 wt % (daf), reduced the yields of gases, and increased the tar yield from 32 wt % (daf) to 66 wt % (daf). Adding 2 wt % (daf) KCl to the washed straw resulted in a char yield which was close to that of the raw straw, and the yields of tar and gases were between those from the raw and washed straw. Furthermore, the peaks corresponding to hemicellulose and cellulose decomposition moved to lower temperatures, from 670 to 633 K for the cellulose peak, but did not collapse to a single peak as in the raw straw. The influence of KCl on the peak temperature of hemicellulose and cellulose decomposition was not observed with the single biopolymers. This indicates that minerals in straw influence the interaction between the biopolymers in whole biomass. Combustion of the char remaining after pyrolysis showed that char combustion is catalyzed by the minerals present in wheat straw. Char from the washed straw with KCl added burned with two peaks in the derivative weight loss curve corresponding to a catalyzed and noncatalyzed part, indicating that the added salt did not behave in the same way as the inherent minerals in the straw. Introduction Pyrolysis of cellulose and lignocellulosic materials has been of great interest in fire research 1,2 and in the production of chemicals and fuels. 3-6 Recently, concern about the emission of greenhouse gases from combustion of fossil fuels 7 has prompted a renewed interest in the combustion of biofuels due to their CO 2 neutrality. In Denmark, the government has decided that by the year 2000 the power plants are obligated to burn 1.4 million tons of biomass per year in order to reduce the emission of CO 2 . In any thermal conversion process, pyrolysis is an important step. Biomass contains mineral matter which may significantly influence its pyrolytic behavior. A large number of studies of the influence of naturally present or artificially added inorganic species on bio- mass pyrolysis have been carried out but a detailed understanding has not been obtained yet. 8 Most of the research has been concerned with wood, 9-14 but differ- ent types of bagasse, 15,16 sunflower stem, 17 and almond * To whom correspondence should be addressed. E-mail: aj@kt.dtu.dk. Fax: +45 45 88 22 58. (1) Broido, A.; Kilzer, F. J. Fire Res. Abstr. Rev. 1963, 5, 157-161. (2) Shafizadeh, F. Adv. Carbohydr. Chem. 1968, 23, 419-474. (3) Serio, M. A.; Wo ´jtowicz, M. A.; Charpenay, S. In Encyclopedia of Energy Technology and the Environment; John Wiley & Sons: New York, 1995; pp 2281-2308. (4) Antal, M. J., Jr. Adv. Solar Energy 1982, 1, 61-112. (5) Antal, M. J., Jr. Adv. Solar Energy 1985, 2, 175-255. (6) Sadakata, M.; Takahashi, K.; Sakai, T. Fuel 1987, 66, 1667- 1671. (7) Garrett, C. W. Prog. Energy Combust. Sci. 1992, 18, 369-407. (8) Antal, M. J., Jr.; Varhegyi, G. Ind. Eng. Chem. Process Des. Dev. 1995, 34, 703-717. (9) Beaumont, O.; Schwob, Y. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 637-641. (10) DeGroot, W.; Shafizadeh, F. J. Anal. Appl. Pyrolysis 1984, 6, 217-232. (11) Gray, M. R.; Corcoran, W. H.; Gavalas, G. R. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 646-651. (12) Pan, W.-P.; Richards, G. N. J. Anal. Appl. Pyrolysis 1989, 16, 117-126. (13) Richards, G. N.; Zheng, G. J. Anal. Appl. Pyrolysis 1991, 16, 133-146. (14) Nik-Azar, M.; Hajaligol, M. R.; Sohrabi, M.; Dabir, B. Fuel Process. Technol. 1997, 51,7-17. 929 Energy & Fuels 1998, 12, 929-938 S0887-0624(98)00008-5 CCC: $15.00 © 1998 American Chemical Society Published on Web 07/03/1998