Biomedical Engineering Reference
In-Depth Information
Many polymers conventionally derived from petrochemicals can be produced from
renewable resources such as lignocellulosic biomass. Tremendous efforts have been made
to produce biological substitutes for petrochemical feedstocks. Many technically feasible
approaches are available to convert biomass to biopolymers. However, no large-scale
commercial facility is operating to date. This situation can be attributed to a combination of
the following three factors: technical inadequacy, lack of economic competitiveness, and
lack of understanding of the industrial need.
The market potential for bio-based products is very promising. The Roadmap for Biomass
Technologies in the United States (USDOE, 2007) forecasts a large increase in bio-based
products. Production of chemicals and materials from biomass increases substantially from
approximately 5.67 billion kg or 5% of the current production of target United States
chemical commodities in 2001, to 12% in 2010, 18% in 2020 and 25% in 2030.
There are several biological processes for converting lignocellulosic biomass, such as
anaerobic digestion and fermentation. However, many technical and economic barriers
remain. There also exist various thermochemical conversion mechanisms to breakdown
biomass feedstocks, including combustion, liquefaction, fast pyrolysis and gasification.
Future bio-based production technologies have the opportunity to increase the attractiveness
of scale-up and commercialization by improving the conversion of biomass to viable
chemicals and biofuels.
12.3.1 Biological conversion
Ethanol produced from corn is a major renewable transportation fuel in the United States.
The amount of ethanol produced in 2009 was in excess of 38 billion liters and the
produced amount anticipated by the end of 2015 is expected to be around 60 billion liters.
However, the main drawback of modern ethanol technologies is that the corn-based
ethanol is mostly starch based. There are also non-starch materials that can be utilized to
produce ethanol. Agricultural and forest residue and dedicated energy crops are the major
sources of lignocellulosic feedstock available for ethanol production. Rooney (1998)
estimate that the United States annually produces 306 million metric dry weight tons
(tonnes) of agricultural residues like sugarcane bagasse, corn stover, wheat straw, and rice
hulls that could be used as biofuel feedstock. Arkenol, BC International, Iogen/Petro
Canada, and the Masada Resources Group are working on these low- to no-cost feed-
stocks in current commercial bioenergy development projects in North America (Glassner,
1999). However, large scale production of ethanol and/or the dynamics of providing
ethanol production plants with sustainable supplies of feedstock will require dedicated
energy crops as part of a supply system.
12.3.2 Thermochemical conversion
Liquefaction is an effective way to convert lignocellulosic materials into bio-based
chemicals. Liquefaction is a process in which solid biomass is liquefied in organic solvents
with or without catalysts, resulting in a liquid containing smaller solvent-soluble chemicals
that can be used directly or from which other products can be derived. Liquefied materials
have been made into reactive adhesives, foams, moldings, fibers, carbon fibers, and so on.
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