Microwave-assisted pyrolysis of pine sawdust: Process modelling, performance optimization and economic evaluation for bioenergy recovery

This study aims at optimizing the process conditions to extract maximum yields of bio-oil from pine sawdust using microwave-assisted pyrolysis (MAP). Aspen Plus® V11 was used to model the thermochemical conversion of pine sawdust to pyrolysis products, and response surface methodology (RSM) based on a central composite design (CCD) was employed in the optimization of the process parameters. The mutual effects of pyrolysis temperature and reactor pressure on the product distribution were investigated. The findings have shown that the optimal operating conditions for producing the highest amount of bio-oil (65.8 wt%) were achieved at 550 °C and 1 atm. The product distribution of the simulated model was more significantly influenced by linear and quadratic terms of the reaction temperature. In addition, a high determination coefficient (R(2) = 0.9883) was obtained for the developed quadratic model. A set of three published experimental results acquired under circumstances comparable to the simulations' operating limitations were used to further validate the simulation results. The process’s economic viability was assessed in order to establish the bio-oil minimum selling price (MSP). A MSP of $1.14/L of liquid bio-oil was evaluated. An economic sensitivity analysis has shown that the annual fuel yield, required rate of return, annual income tax, annual operating costs and initial capital investment have a substantial impact on the MSP of bio-oil. It was inferred that using the optimized process parameters may improve the process' competitiveness on an industrial scale due to its better product yields and improved sustainability in biorefineries, as well as assure waste reduction.