(30e) Biomass decomposition reaction sequence analysis using simultaneous gas sampling and temperature measurements

Understanding the reaction sequence and associated kinetics are imperative for industrial biomass conversion applications. One of the lesser known aspects is the actual energy change happening during the conversion process within the biomass sample. Many literature studies reveal different temperature profiles developing during the process mainly without measuring the gaseous quantification of volatiles released inside the biomass sample. The use of gas component detection methods in concert with thermal analysis can help in better understanding the reaction sequence and mechanisms governing the decomposition behavior. The aim of this paper is to present an innovative intra-particle gas sampling technique that provides insight on the reaction sequence and energy changes inside biomass particle. To our knowledge, this is the first intra-particle gas sampling measurement performed.

The experimental tests have been performed on wooden spheres ranging in diameter from 19.0 mm to 31.8 mm at operating temperatures of 500°C, in a tubular reactor under non-oxidant controlled conditions. Simultaneous measurements were obtained for product gas evolution and temperature during the process.  In addition the behavior of biomass samples during devolatilization was determined by thermal analysis: thermogravimetric (TG) and differential scanning calorimetry (DSC).

The TG analysis revealed a rapid mass loss in the temperature range 290°C to 410°C and a total mass loss of 75% - 76%. The DSC analysis showed exothermic behavior above 305°C and two maximum peaks at 350°C and 413°C. Evolved gases such as H₂, CO_x and hydrocarbons were extracted through a probe using a micro sample system. The measurements showed a simultaneous release of CO₂ and CO with a maximum occurring around 325°C, for larger samples.  The CO release, while lower in absolute concentration, is much more stable during the entire heating of the particle. The measurements showed a pronounced transition between hydrogen release and subsequent hydrocarbons release. The light hydrocarbons such as methane and ethane were observed in high quantities, 19% and 0.9% respectively. It is anticipated this data will help modeling thermochemical processes ultimately leading to predictive capability.