Biomedical Engineering Reference
In-Depth Information
the cellulose component. In fact, cellulose is the most abundant organic structure of
biomass. Therefore, how to convert lignocellulose into low-cost raw materials for
chemical industry is a key issue for substituting coal and oil for biomass.
Compared to starch, cellulose can also be used to produce glucose, but it is more
difficult. The main reason is that the lignocellulose is more complex; cellulose,
hemicellulose, and lignin are wrapped to form a more compact three-dimensional
network spatial structure. It is necessary to adopt methods such as pretreatment
and enzymatic hydrolysis to degrade cellulose into glucose. At present, a variety
of pretreatment technologies can be used to fractionate natural lignocellulose
into three components efficiently. Then, the obtained cellulose, hemicellulose, and
lignin are further converted into various chemicals. For example, Professor Mark
Holtzapple from Texas State University invented a simple technique to convert
biomass into animal feed, chemical reagents, and fuel with simple processes such
as lime pretreatment and bacterial fermentation. This work was recognized when
he achieved the Academic Award of the 1996 U.S. Presidential Green Chemistry
Challenge Award [
27
]. The Biofine Company won the Small Business Award of the
1999 U.S. Presidential Green Chemistry Challenge Award. The company developed
a new technology to convert waste cellulose into levulinic acid, a key intermediate
for the production of other chemical products. Using this technology, lignocellulose
such as paper waste, municipal solid waste, nonrecycled waste paper, waste wood,
and even agricultural residues can be degraded by diluted H
2
SO
4
at 200-220
ı
C
within 15 min. Meanwhile, a reactor used to eliminate side effects was also invented
so that the reaction can be conducted in a direction in favor of the desired product.
In this reactor, the levulinic acid yield was up to 70-90 %; at the same time, some
valuable by-products (e.g., formic acid and furfural) can also be obtained. These
pioneering works were successful attempts to open research on major issues in green
chemistry.
However, although the petrochemical industry development has spent more than
a century bringing the biomass-based chemical industry from a vision into reality,
at least some decades of hard work are needed.
1.3.3
Status and Functions of Lignocellulose Biotechnology
in Circulation Economy
As a reinforcing material for terrestrial plants, millions of years of evolution have
made plant fiber materials have a strong self-protection function. Each of the
three main components (cellulose, hemicellulose, and lignin) is a polymer with a
complex structure Combined, they form complex supramolecular complexes and
further various plant cell wall structures [
8
]. The complex three-dimensional spatial
structure makes plants able to avoid attack by microorganisms and various physical
and chemical factors. However, this recalcitrance is also the main reason that
lignocellulose has never been utilized effectively. Thus, the main challenge in taking
