Determining the Enthalpy of Pyrolysis of a Small-Scale Semi-Batch Reactor

Carbon dioxide removal technologies have been recognized as a critical component for the global greenhouse gas reductions needed by 2050; however, their potential is still unclear. For biochar production in particular, life cycle assessments rely on experimental data. Yet, data like the enthalpy of the pyrolysis reaction is highly variable with conditions and feedstocks and can be difficult to measure. This study determined the heat loss, heat capacity, and heat of reaction of the pyrolysis reaction using a small-scale semi-batch reactor. An energy balance on the empty reactor during cool down quantified heat loss, which decreased from 63.90 W to 49.88 W after insulation improvements. Additionally, by adjusting the power supplied, the reactor was held at a constant temperature, yielding a specific heat of reactor of 0.70 J/g°C, slightly higher than the reported literature value of 0.50 J/g°C for the stainless-steel apparatus. Using the measurements of heat loss and reactor heat capacity, two balances were performed with a pine feedstock: one prior to the reaction (<200°C) and one during reaction (200–250°C). Comparison of the two yielded the heat capacity of pine (3.74 J/g°C) and an estimated enthalpy of reaction of 125.71 J/g at 250°C, which falls within literature range of 100 to 200 J/g. These results establish a framework to include syngas and bio-oil products in the energy balance as needed for higher pyrolysis temperatures. Collectively, this study presents one method for measuring these values and the foundation for the determination of additional variables, allowing for accurate energy consumption measurements in life cycle assessments.