Selective fast pyrolysis of biomass to produce fuels and chemicals

Abstract

Selective fast pyrolysis, differed from traditional fast pyrolysis which is usually aimed at the maximum bio-oil yield, is to selectively control or alter biomass pyrolytic pathways for obtaining specific products (high-grade liquid fuels or special chemicals). Fast pyrolysis of biomass can be regarded as the pyrolysis of its three major components, mainly including the following three pathways. The decomposition of lignin mainly produces various monomeric phenolic compounds as well as oligomers (pyrolytic lignins). The depolymerization of holocellulose (cellulose and hemicellulose) mainly generates anhydro-oligosaccharides, monomeric anhydrosugars (mainly levoglucosan), furans, and other products. The pyrolytic ring scission of holocellulose obtains various light products, such as hydroxyacetaldehyde and acetol. The pyrolytic pathways and the subsequent products are influenced by a number of factors, including the biomass type, feedstock properties, pyrolysis conditions (pyrolysis temperature, heating rate, vapor residence time, pressure, gaseous environment), catalysts, vapor filtration, and condensation. Therefore, selective fast pyrolysis can be achieved via proper control of these factors, such as biomass pretreatment or catalyst utilization. This chapter reviews the mechanisms and pathways of biomass pyrolysis, as well as the properties and applications of crude bio-oils. It also summarizes the recent advances in the selective fast pyrolysis of biomass, aiming at how to produce quality-improved liquid fuels, and specific chemicals such as levoglucosan, levoglucosenone, acetic acid, hydroxyacetaldehyde, furfural, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one, and phenolic compounds.