Environmental Engineering Reference
In-Depth Information
Another important point concerning biorefinery processing is the fact that environmental
impacts and consumption of non renewable resources should be minimized, while complete
and efficient biomass use maximized. This ecological perspective requires: analyses of three
important agricultural and forestry cycles as carbon (respiration, photosynthesis, and organic
matter decomposition), water (precipitation, evaporation, infiltration, and runoff) and nitrogen
(N fixation, mineralization, denitrification) and their interdependencies (Gravitis and Suzuki,
1999); system performance evaluations and environmental impact estimations carried out by
means of Life Cycle Assessment (Cherubini et al., 2007). Especially soil degradation
minimization and biodiversity conservation seems to be two dominating factors to consider in
the assessment of biorefinery systems.
With all this, biorefinery represents a change from the traditional refinery based on large
exploitation of natural resources and large waste production towards integrated systems in
which all resources are used. An example of how the biorefinery of the future will evolve can be
found in the history of the existing corn wet-milling industry (Lasure and Min, 2004). Initially
the corn wet milling industry produced starch as the major product. As technology developed
and the need for higher value products drove the growth of the industry, the product portfolio
expanded from various starch derivatives such as glucose and maltose syrups to high fructose
corn syrup. Later, fermentation products derived from the starch and glucose such as citric acid,
gluconic acid, lactic acid, lysine, threonine and ethanol were added. Many other by-products,
such as corn gluten, corn oil, corn fiber and animal feed are now being produced. The final
vision is then the development of the technical, commercial and political infrastructure for a
biomass refinery (biorefinery), which will be similar to the current oil refinery concept.
3.
O
VERVIEW OF
B
IOREFINERY
F
EEDSTOCKS
,
P
ROCESSES AND
P
LATFORMS
3.1. Biorefinery Feedstocks
The term of feedstock refers to raw materials used in biorefinery, from which biofuels
and biochemicals are produced and recovered by means of a set of jointly applied
technological processes.
The biomass of the world is synthesized via the photosynthetic process that converts
atmospheric carbon dioxide to sugar. Plants use the sugar to synthesize the complex materials
that are biomass. Renewable carbon-based raw materials are produced in agriculture,
silviculture and microbial systems.
Although a tremendous variety of biomass resources is available, only four basic
chemical structures are of significance for production of biofuels and biochemicals:
carbohydrates (sugar, starch, cellulose, hemicellulose), lignin (polyphenols), triglycerides
(lipids, vegetable oils and animal fats) and proteins (vegetable and animal polymers made up
of amino-acids). The average composition of synthesized biomass in the world is 75%
carbohydrates, 20% lignin and 5% other compounds (oils, proteins and so on) (Lichtenthaler,
2006). As a consequence, the main attention of research and development activities should
first be focused on efficient access to carbohydrates, and their subsequent conversion to
chemical intermediates and corresponding final products.
