Lignocellulosic biomass such as agricultural and forest residues consists of cellulose, hemicellulose, lignin and a small fraction of metabolites. Fast pyrolysis is one of the potential thermochemical routes to generate fuels and platform chemicals. During fast pyrolysis, biomass undergoes rapid heating in an inert atmosphere yielding a large fraction of bio-oil (70 wt.%), gases (10-15 wt.%) and char (10-15 wt.%). Bio-oil is a condensed mixture of alcohols, aldehydes, ketones, carboxylic acids, ethers, esters, furans, water and aromatic oxygenates like guaiacols and syringols.
As a pre-requisite to design an efficient fast pyrolysis process, a detailed understanding the underlying chemistry and product distribution is needed. Owing to the complex structure of biomass efforts have been made to unravel its thermal degradation reactions using model compounds, reactors that are free from transport effects and advanced analytical techniques, over the years.
In WIREs Energy and Environment, a group of engineers from the Laboratory for Chemical Technology at Ghent University presented a critical overview of the experimental techniques employed to derive biomass pyrolysis kinetics and identify the parameters that can alter the product composition.
These studies have provided numerous insights on dominant reaction pathways, necessary pre-treatments, unwanted by-products, and consequently, process optimization and upgrading.
Despite of tremendous progress made in the past decade, there are quite a few issues that remain unaddressed as mentioned in the review. A holistic perception of the chemistry behind biomass transformation to gas/liquid is very much needed, with the application of advanced pyrolysis practices.
Above all, large-scale commercialization of the process and complete substitution of fossil fuels is far from achieved owing to the technical and economic limitations. Integration of the knowledge obtained on pyrolysis kinetics, reactors and catalyst technology needs much more attention to realize bio-fuels dream. With the low oil prices in today’s market, research is underway to make bio-fuels economically competitive.
Kindly contributed by Kevin Van Geem.