Cellulose biorefineries

The Department of Energy (DOE) is helping six firms build cellulosic biorefineries with grants totaling about 385 million. When fully operational, the six plants will produce more than 130 million gallons of cellulosic ethanol a year. DOE is also investing 375 million into three new Bioenergy Research Centers to speed up the development of cellulosic ethanol and other biofuels. 

Figure 10.11 Example of a biorefinery. A ligno-cellulosic biorefinery.

The DOE recently awarded six cellulosic biorefineries millions of dollars to build on a commercial scale. 

Sannigrahi P, Pu Y, Ragauskas A. Cellulosic biorefineries—unleashing lignin opportunities. Curr Opin Environ Sustain 2010 2 383-93. 

Wood chips can also be utilized as such to produce bioethanol. The cellulose and hemicellulose material is hydrolyzed in the presence of acids (H2SO4, HCl, or HCOOH) or enzymes to yield glucose and other monosaccharides [16]. Lignin is separated by filtration as a solid residue and the monosaccharides are fermented to ethanol, which, in turn, is separated from water and catalyst by distillation. Ethanol can be used not only as energy source but also as a platform component to make various chemicals, such as ethene and polyethene. Today green acetaldehyde and acetic acid from wood-derived bioethanol is manufactured by SEKAB Ab, at the Ornskoldsvik Biorefinery of the Future industrial park. 

An alternative possibility is that of the biorefinery. In this concept a few key chemicals would be isolated from a small number of process steps. Whilst there are many possibilities for this, in one example the raw material, say com, could be cmshed to release oil (the first key product). The resulting mass could then be fermented to give several key platform chemicals such as ethanol, lactic acid and acetic acid. This attractive concept would be more viable if all the cellulose and lignin components could be efficiently used in the fermentation process. 

Fig. 3 Schematic flowsheet of ligno-cellulose transformations in a biorefinery.

Biorefinery includes fractionation for separation of primary refinery products. The fractionation refers to the conversion of wood into its constituent components (cellulose, hemicelluloses and lignin). Processes include steam explosion, aqueous separation and hot water systems. Commercial products of biomass fractionation include levulinic acid, xylitol and alcohols. Figure 3.3 shows the fractionation of wood and chemicals from wood. 

Biorefineries convert the plant fibre into cellulose ethanol, electricity and CO2... 

Microwave heating has also been applied in the solvent-free phosphorylation of microcrystalline cellulose (Gospodinova et al., 2002). In the isolation step of this procedure, only water and ethanol were used as additional solvents. Wax esters have been produced from vegetable oils using a solvent-free enzymatic process (Petersson et al, 2005) this is particularly noteworthy as enzymes are often intolerant to high concentrations of substrates. The examples of solvent-free procedures described here show that solvents are not always required in the transformation of naturally sourced biopolymers and also in the chemistry of small molecules that can be obtained from a biorefinery. 

Carbohydrates would be the predominant raw materials for future biorefineries. The major polysaccharides found in nature are cellulose, hemicellulose and starch (see Chapter 1). These molecules would be mainly utilised after they are broken down to their respective monomers via enzymatic hydrolysis, thermochemical degradation or a combination of these two. Cellulose and hemicellulose, together with lignin, constitute the main structural components of biomass. Starch is the major constituent of cereal crops. This section would focus on the potential utilisation of carbohydrates and lignocellulosic biomass for chemical production. 

In ethanol production from cellulose material, there is a huge amount of lignin left as a by-product. The lignin is a valuable raw material for chemical production in a biorefinery. So in order to reduce the transport cost of the lignin residue, it may be possible to mix it with other raw materials in pellet production in the near future. 

Recent attempts aim at the controlled transformation of cellulose, hemicellulose, and lignin to platform molecules for a potential future biorefinery scenario. In this regard, the U.S. Department of Energy has published studies on potential future platform molecules that could be derived from renewable resources [35, 36]. Tailored transformation of biomass to these platform chemicals could serve as a starting point for biofuel production. This would allow the development of comprehensive biorefinery approaches that incorporate both the production of biofuels and chemicals. The... 

Kraft pulping is the most widely used process in the world for separating cellulose from wood, but is not normally considered as a potential operating unit for biorefineries. Certainly for... 

At high concentrations, corrosion-resistant reactors and an effective acid recovery process are needed, raising the cost of the intermediate glucose. Dilute acid treatments minimize these problems, but a number of kinetic models indicate that the maximum conversion of cellulose to glucose under these conditions is 65 to 70 percent because subsequent degradation reactions of the glucose to HMF and lev-ulinic acid take place. The modem biorefinery is learning to exploit this reaction manifold, because these decomposition products can be manufactured as the primary product of polysaccharide hydrolysis (see below). 

Polymeric carbohydrates available from the biorefinery can serve as starting materials for 5-HMF Recently, LaCl3 has been used to catalyze the conversion of cellulose to 5-HMF (along with glucose, levulinic acid, and cel-lobiose) at elevated temperatures in water.489... 

Iogen, a Canadian biotechnology company, makes just such an enzyme and has been operating a test plant to determine how economical the process may be. The company hopes to construct a 300-million, large-scale biorefinery with a potential output of 50 million gallons per year. Its pilot plant in Ottawa utilizes wheat straw and com stalks. In mid-2009, a Shell gasoline station in Ottawa, Canada became the first retail outlet in that nation to sell a blend of gasoline that features 10% cellulosic ethanol. 

---