Biomedical Engineering Reference
In-Depth Information
1. The singular utilization of each component. A key reason for the difficulty
in achieving industrial production of biomass feedstock is lack of an efficient
component separation technique. It is impossible to control the characteristics
and quality of the final product if the components of biomass feedstock cannot
be effectively separated. The composition of lignocellulose is complex; thus, it
is difficult to separate it into useful molecular components. Therefore, plants
for the industrialization of biomass raw materials, such as furfural plants, paper
mills, xylitol plants, and so on, just emphasize the use of a single component of
lignocellulose; other components are discarded as waste, causing a serious waste
of resources and environmental pollution. Therefore, insufficient utilization of
lignocellulose did not play an important role in improving economic efficiency,
but became the burden of the efficiency.
2. The singular utilization of technology. The use of a biological or thermochemical
method in the process of biomass conversion was emphasized excessively, and
the concept of multilevel use of the natural solid-phase organic materials was
lacking.
3. Lack of systematic integration of technologies and research of ecological pro-
cesses and engineering. At present, available technologies for treating biomass
still are mostly the traditional technologies of starch fermentation and wood
processing. For example, for raw material pretreatment, applying the traditional
acid hydrolysis techniques in the paper industry caused the high cost of raw
material pretreatment and environment pollution; for cellulase and ethanol
fermentation, applying the fermentation processes and equipment of starch to
ethanol resulted in high production costs because of the large investment of
cellulase and low conversion of alcohol.
4.2
Connotation and Development History of Primary
Refining of Lignocellulose
The three components (cellulose, lignin, and hemicellulose) of lignocellulose,
especially straws, are cross-linked tightly. Because of the completely different
chemical structure and properties, the utilization of each component is limited.
Thus, the primary refining processes, such as appropriate pretreatment, fractionation
and separation of components, and structural disconnection or partial change
of structure, are necessary to achieve high-value utilization of lignocellulosic
materials.
As early as 1890 or even earlier, some researchers in Germany began to use
high-concentration chemical reagents to pretreat lignocellulose. These reagents,
including acids, alkalis, and salt, can destroy the crystal structure of fiber in biomass
and degrade cellulose. This can be considered the earliest form of primary refining
of lignocellulosic materials. In the next 100 years, pretreating technologies were
aimed at obtaining high yields of cellulose without concern for the utilization of
other components. In the last half a century with increasingly in-depth research
