Effect of dolomite on the thermokinetics of Biomass Pyrolysis

Abstract

Currently, the pyrolysis of biomass is paid much attention for the production of sustainable energy. However, suitable catalysts are needed for complete conversion of biomass to useful fuels at low temperature. This may also in-necessitate the use of high pressure in order to maximize the liquid yield. In this study, the catalytic effect of calcined dolomite on kinetic behavior of biomass pyrolysis has been examined thermogravimetrically. The thermogravimetric analyses were conducted during heating the biomass from room temperature to 800°C. The kinetic parameters for the pyrolysis were determined by analyzing the weight loss curves using the integral Coats-Redfern method on global kinetics with reaction order conversion function. The effect of dolomite as a catalyst and/or additive for the biomass pyrolysis was studied by comparing the kinetics with and without using the dolomite. Results showed that the presence of dolomite does not affect much on the rate of pyrolysis at low temperatures, but has significantly higher rate of pyrolysis at high temperatures. The global apparent activation energy increases slightly while the pre-exponential factor increases about two-fold in the presence of dolomite. The two-fold increase in the pre-exponential factor more than offsets the slight increase in the global apparent activation energy, thereby causing the net increase in the rate constant, especially at high temperatures. Thus, in light of the fact that catalysts should decrease the apparent activation energy to increase the reaction rate, it can be concluded that the dolomite acted as an additive rather than catalyst in the pyrolysis of biomass. The additive effect of dolomite may be only due to the decomposition of lignin and probably tar and char at high temperatures.