Design of Experiments optimisation of Scottish wood biochars and process parameter significance for target applications

Abstract

Biochar production from sustainable materials through pyrolysis remains a key area of research, where additional value can be gained by understanding the influence of initial operating parameters to create optimised carbon products with different characteristics. In this study, native Scottish wood samples were used to produce biochars. Softwood and hardwood samples were investigated to determine feedstock importance, with a focus on the influence of process conditions on the final characteristics of biochars. Screening experiments helped to determine that the softwood feedstock resulted in enhanced product characteristics and identified the optimal pyrolysis temperature. A design of experiments approach was used to scope process variables for softwood feedstock: contact time with activating agent, gas flowrate, and influence of ramp rate during pyrolysis were studied. The response variables were product yield and biochar surface area. As expected, product yield decreased with increasing pyrolysis temperature, and increased ramp rates decreased biochar yield. Pore structure was a combination of micro- and mesopores, and high gas flowrate and pyrolysis temperature produced biochars with the greatest surface areas, while morphological analysis suggests a layered carbon structure. Contact angle analysis suggested hydrophilicity, suggesting compatibility with aqueous media, while a neutral surface charge demonstrates easy application in drinking water treatment systems. The results show the potential of parameter optimisation and insight into the interplay of these variables in biochar development, with characteristics that can be tailored to a range of applications.