Environmental Engineering Reference
In-Depth Information
Enzyme
production
Microbial fermentation
Hexose
sugars
Hydrolytic enzymes
Milling & size
reduction
Lignicellulosic
biomass
(wood, agricultural
and forestry waste)
Pretreated
biomass
Enzymatic hydrolysis
Ethanol
Pretreatment
Pentose
sugars
Removal of
lignin
Microbial fermentation
Figure 7.7
Ethanol production from lignocellulosic biomass.
sugars; and (2) fermentation of the released sugars by yeast or bacteria. Ethanol
can be produced from lignocellulosic material by chemical and microbiological
hydrolysis processes. There are two main types of chemical hydrolysis process,
one that uses high acid concentrations (the concentrated hydrochloride acid pro-
cess, or CHAP) and another that was developed through a collaborative endeavor
between Canada, America, and Sweden (the CASH process) and uses dilute acid.
In the microbiological process, cellulose is broken down to sugar units by cellu-
lase enzymes. One big challenge in this ethanol production process is to avoid
degradation of sugar into other organic compounds such as furfural or 2-methy-
hydroxyfurfural in order to maintain high ethanol yields [59]. These compounds
act as inhibitors in the fermentation step.
A unique pilot plant for ethanol production from lignocellulosic feedstocks was
established at Ö-vik, Sweden in May 2004. The aim of the pilot plant was to develop
efficient continuous technologies for the various process steps in ethanol produc-
tion from forestry raw materials and other lignocellulosic feedstocks. Different raw
materials require different conditions during the production process, which also
needs to be optimized for every raw material. It was also considered important to
demonstrate that large-scale lignocellulosic ethanol production was possible and to
show that the production costs for cellulose-based ethanol could be decreased. The
plant is fitted with several pieces of equipment that make it possible to perform two-
step dilute acid and/or enzymatic hydrolysis on site. In 2005, ethanol from wood
chips (softwood, i.e. spruce) was produced in the plant for the first time. The plant
can process up to 2 tons of biomass per day, producing about 400 L of ethanol.
The lignin by-product is used for other purposes rather than just heat produc-
tion and power generation, and there is ongoing research into its potential applica-
tion as a precursor for the synthesis of other more valuable chemicals. In addition,
the lignin can be pelletized together with other biomass. For example, at the
Biofuel Technology Centre in Umeå, Sweden, lignin has been mixed with other
feedstocks to produce pellets that enable its efficient transportation and use as a
solid biofuel. The cost of ethanol production will decrease dramatically if meth-
ods that enable the conversion of lignin into valuable products can be developed.
