Impact of hemicellulose–lignin co-pyrolysis interactions on biochar, bio-oil, gas yields, and gas composition: A response surface methodology study

In this work, the co-pyrolysis of hemicellulose and lignin for production of biochar, bio-oil and gaseous products showed interactions between both the components. These interactions were identified by comparing the actual values of product yields with RSM-predicted values derived from individual component pyrolysis. The experiments were designed using response surface methodology (RSM), with co-pyrolysis factors that included temperature (400 – 800 °C), time (5 – 30 min), and hemicellulose percentage (0 – 100%). The results indicated that the co-pyrolysis interactions promoted biochar yield, driven primarily by temperature and residence time. For bio-oil yield, the interaction was temperature-dependent; high temperatures (700–800 °C) combined with optimized residence time enhanced yields. Similarly, the total gas yield was maximized at 600 °C through interaction regulation. In addition, the co-pyrolysis interactions increased the H 2 yield while decreasing the CH 4 yield and the HHV of the gas. RSM optimization identified the optimal conditions for maximizing biochar, bio-oil, CO + H 2 , and gas HHV, with predictions agreeing with experiments (<2% deviation), confirming the model's reliability. DFT calculations revealed the reaction pathways of 2-methoxy-4-methylphenol decomposition to gaseous products. The combination of RSM and DFT enabled the process design and precise mechanistic analysis of gas products from the co-pyrolysis of hemicellulose and lignin in an efficient manner.