Chemical Pretreatment Processes for
L.M. Bermúdez López3
Wageningen University & Research centre - Food & Biobased Research (WUR-FBR, NL)
Energy Research Centre of the Netherlands (ECN, NL)
Abengoa Bioenergía Nuevas Tecnologías (ABNT, ES)
This literature review was performed within the BioSynergy project (2007-2010). BioSynergy is a
European Integrated Project supported through the Sixth Framework Programme for Research and
Technological Development (038994-SES6). BioSynergy stands for “BIOmass for the market
competitive and environmentally friendly SYNthesis of bio-products together with the production ofsecondary enERGY carriers through the biorefinery approach”.
Within the BioSynergy project the overall goal of the pretreatment routes being developed is to
convert raw lignocellulosic biomass into its composing sugars and lignin in a market competitive and
environmentally sustainable way. This report reviews lignocellulose pretreatment in general as well as
specific pretreatment technologies that aredeveloped within the BioSynergy project including steam
explosion (ABNT), mechanical/alkaline fractionation (WUR) and organosolv fractionation (ECN). In
addition to these pretreatment technologies, other pretreatment technologies are studied within the
BioSynergy project such as acetic/formic acid pretreatment and mild- and strong acid pretreatment.
SummaryLignocellulose, the most abundant renewable biomass on earth, is composed mainly of cellulose,
hemicellulose and lignin. Both the cellulose and hemicellulose fractions are polymers of sugars and
thereby a potential source of fermentable sugars. Lignin can be used for the production of chemicals,
combined heat and power or other purposes.
After initial biomass processing, the production of fermentablesugars from biomass is usually approached in two steps:
1. A pretreatment process in which the cellulose polymers are made accessible for further conversion. In this step hydrolysis of hemicellulose may occur, as well as separation of the lignin fraction, depending on the process applied.
2. Enzymatic cellulose hydrolysis to fermentable sugars using cellulase enzyme cocktails produced
onlocation or acquired from enzyme manufacturers.
Obstacles in the existing pretreatment processes include insufficient separation of cellulose and lignin,
formation of by-products that inhibit ethanol fermentation, high use of chemicals and/or energy, and
considerable waste production. Research is focussed on converting biomass into its constituents in a
market competitive and environmentallysustainable way.
Different pretreatment technologies published in public literature are described in terms of the mechanisms involved, advantages and disadvantages, and economic assessment. Pretreatment technologies
for lignocellulosic biomass include biological, mechanical, chemical methods and various combinations thereof. The choice of the optimum pretreatment process depends very much on theobjective of
the biomass pretreatment, its economic assessment and environmental impact.
When fermentable sugars are produced, special attention must be paid to the formation of fermentation
inhibitors. Especially the formation of phenolic compounds from lignin degradation should be prevented, as well as the formation of furfural and HMF from sugar degradation by keeping the process
temperature andresidence time as low and as short as possible.
Only a small number of pretreatment methods has been reported as being potentially cost-effective
thus far. These include steam explosion, liquid hot water, concentrated acid hydrolysis and dilute acid
pretreatments. At the moment the production of ethanol from lignocellulose is growing rapidly and by
looking at the industrial activities in this...