(738a) Visualization Study of Dynamic Shrinkage during Biomass Pyrolysis

Biomass pyrolysis produces both renewable fuels and feedstock for chemical production. Yields and selectivity for pyrolysis is a function of numerous factors including rates of heating and quenching (residence times for heterogeneous and homogeneous events) and condensed phase properties including the dynamic shrinkage of the biomass. The shrinkage of the condensed matter affects many physical properties including the porosity, permeability, overall density, the volume occupied by volatiles (gas and tar), the volume occupied by the solid (wood and char) and consequently the total volume of the particle, all of which change continuously as biomass is thermally decomposed. In this study two different types biomass microspheres (tall fescue and switchgrass) and microcrystalline cellulose were produced and pyrolyzed in a micro-reactor at three different heating rates (10, 20 and 50ËšC/min). The dynamic shrinkage was captured in real time using a CMOS camera and side-by-side weight loss experiments were performed using thermal gravimetric analysis (TGA). The results show that for pyrolysis of single biomass microspheres, the normalized volume-based shrinkage and normalized weight loss are identical for both cellulose and switchgrass. However, for tall fescue at temperatures above 360 ËšC the shrinkage is higher than the weight loss indicating that shrinkage is not directly proportional to the amount of decomposed matter. Although, shrinkage is independent of particle size for these biomass types, yet crystalline cellulose shrinks more than switchgrass and tall fescue. These results will be used to calibrate microstructural pyrolysis models currently being developed by the same team.