Environmental Engineering Reference
In-Depth Information
photosynthesis. Plant materials are then transported to biorefineries where they are transformed
into fuels and chemicals using different processes.
The creation of an economic system based on plant materials as feedstocks to produce
fuels, energy, and chemicals is often referred to as a biobased economy.
THE BIOREFINERY
The biorefinery is a concept equivalent to the traditional oil refinery, which besides fuels,
produces an array of other products from petroleum. A biorefinery uses biomass as feedstocks
to produce fuels, and the by-products are used to produce heat, power, and chemicals in the
same facility. Biomass is plant materials that contain carbohydrates—in the form of free
sugars, starch, oligosaccharides, and cellulose—lignin, proteins, fats, and in less quantities
pigments, flavors, and secondary metabolites.
Usual feedstocks for biorefineries are agricultural crops, agricultural residues, trees, and
grasses. In addition, animal wastes and municipal solid waste can be added to the mix.
Conversion processes include acid/enzymatic hydrolysis, fermentation, bioconversion, chem-
ical conversion, gasification/pyrolysis, and co-firing (Fernando et al., 2006).
Types of biorefineries
According to the feedstock used, biorefineries are classified in two types: biomass using and
waste-material using. Countries producing sugary or starchy materials (e.g., sugarcane, sugar
beets, corn, cassava, and potatoes) can use these substrates to feed the biorefinery. In places
where waste disposal is an issue (e.g., Japan and some European countries) and where there is
not an abundance of agricultural products, waste materials, including paper, lumber, animal
waste, and food scraps, could be preferred feedstocks for the biorefinery (Ohara, 2003).
From the platform point of view, biorefineries are classified in two types:
1. The sugar platform based on the fermentation of hexose and pentose sugars, which are
extracted directly from sugary substrates by hydrolysis of starch obtained from dry or wet
milling or by hydrolysis of cellulosic materials (Fig. 14.1).
2. The thermochemical platform based on the transformation of lignocellulosic materials
into syngas, which is then transformed into fuels and chemicals (National Renewable
Energy Laboratory [NREL], n.d.).
Often, a third platform is added:
3.
The carbon-rich chain platform that at the moment is used to produce biodiesel from long
chain fatty acids from fats and oils (Chang et al., 2010).
From the evolutionary point of view, biorefineries are classified in three groups known as:
Phase I, Phase II, and Phase III (Fernando et al., 2006). This designation indicates the progres-
sion of technologies with time.
A Phase I biorefinery, the oldest type, has little flexibility, fixed capacity, fixed raw materi-
als, and produces one, sometimes two, major products and few co-products. An example of a
Phase I biorefinery is the production of ethanol from corn starch or from sugar cane (Fernando
et al., 2006).
A Phase II biorefinery produces multiple products with more flexibility on the production.
Still these refineries use specific raw materials. An example is the integrated corn wet milling
operation that produces starch, ethanol, lactic acid, or 1,3-propanediol along with high fructose
corn syrup, corn oil, and corn meal.
