Catalytic Pyrolysis of Thermally Pre-treated Biomass for Aromatic Production

Abstract

Torrefaction, a biomass pre-treatment process, is considered to be a promising way to improve biomass properties, aiding in producing highly deoxygenated biofuel. Among several techniques available to convert biomass to bio-fuel, fast pyrolysis has attracted a lot of interest due to its high yield of liquid product, bio-oil. However, the liquid product has certain negative properties such as high oxygen content, high acidity, and low heating value, which make it unfit as an alternate transportation fuel. Among these, the primary property that has to be upgraded is its high oxygen content, as it restricts bio-oil miscibility with hydrocarbon fuels. Catalytic pyrolysis, a promising upgrading technique, focuses on selectively eliminating or reducing oxygen content present in the bio-oil. Hence, the current study is focused on the effect of torrefaction on the aromatic hydrocarbon yield produced from catalytic pyrolysis of biomass and its individual components. A brief introduction and detailed background information are documented in Chapter 1 and Chapter 2, respectively. The combined effect of torrefaction and shape selective catalyst (ZSM-5) on the hydrocarbon yield from pyrolysis of pine wood is discussed in Chapter 3. Pine wood chips were torrefied and the resultant was pyrolyzed at four different temperatures with three different biomass to catalyst ratios. Bio-oil vapors produced from catalytic pyrolysis of torrefied biomass resulted in high aromatic hydrocarbon yield. Guaicols and furans were found to be a possible intermediate in aromatic hydrocarbon production. In addition to this, the presence of certain metals on the catalyst also favored the yield of aromatic hydrocarbons. The effect of torrefaction on individual components of the biomass, namely cellulose and lignin, was studied (Chapter 4 and Chapter 5) along with the influence of catalyst acidity and pyrolysis temperature on pyrolysis products of raw and torrefied cellulose and lignin. Pyrolysis of torrefied cellulose resulted in a significant amount (~10 wt.%) of aromatic hydrocarbons, which were completely absent from raw cellulose pyrolysis. Torrefaction in lignin resulted in more condensed guaiacyl linkages, which are attributed to decreased guaiacols and increased phenol yield from pyrolysis. For both cellulose and lignin, ZSM-5 catalyst acidity played a pivotal role in promoting aromatic hydrocarbon yield.