Insight into a new phenolic-leaching pretreatment on bamboo pyrolysis: Release characteristics of pyrolytic volatiles, upgradation of three phase products, migration of elements, and energy yield

Leaching essentially removes metallic species from biomass and improves the quality of pyrolysis products. However, common acid solutions, such as hydrochloric acid and acetic acid are expensive and difficult to recycle. This paper reports a new leaching pretreatment, using phenol and guaiacol solutions, which are mainly present in liquid by-products from thermal conversion of biomass. The characteristics of releasing of volatiles and upgradation of pyrolytic products of bamboo were investigated. Four key results can be obtained. (i) Phenolic leaching had much higher removal efficiency of metallic species, compared to water leaching. (ii) Pyrolytic behavior of bamboo changed drastically by phenolic leaching. Specifically, it enhanced the release of pyrolytic volatiles, separated the pyrolysis zones of hemicellulose and cellulose, and eliminated pyrolytic peak for extractives. (iii) Phenolic leaching upgraded the three phase pyrolysis products. Specifically, it inhibited the formation of acids, promoted the formation of anhydrosugars in bio-oil, improved the specific surface area of bamboo charcoal, and increased the volume fraction of methane in the gaseous products. (iv) With improved migration of oxygen and carbon from bamboo to bio-oil, the bio-oil replaced bamboo charcoal to become the pyrolysis product with increased energy yield. The above results demonstrated the importance and promise of phenolic-leaching pretreatment in upgradation of products of bamboo pyrolysis. From application perspective, light bamboo vinegar was an alternative for leaching of biomass. The use of bamboo vinegar filtrate containing metallic species had potential benefits for preparation of liquid fertilizer.