Pretreatment: the key to unlocking low‐cost cellulosic ethanol

Abstract

New transportation fuels are badly needed to reduce our heavy dependence on imported oil and to reduce the release of greenhouse gases that cause global climate change; cellulosic biomass is the only inexpensive resource that can be used for sustainable production of the large volumes of liquid fuels that our transportation sector has historically favored. Furthermore, biological conversion of cellulosic biomass can take advantage of the power of biotechnology to take huge strides toward making biofuels cost competitive. Ethanol production is particularly well suited to marrying this combination of need, resource, and technology. In fact, major advances have already been realized to competitively position cellulosic ethanol with corn ethanol. However, although biotechno logy presents important opportunities to achieve very low costs, pretreatment of naturally resistant cellulosic mate rials is essential if we are to achieve high yields from biological operations; this operation is projected to be the single, most expensive processing step, representing about 20% of the total cost. In addition, pretreatment has pervasive impacts on all other major operations in the overall conversion scheme from choice of feedstock through to size reduction, hydrolysis, and fermentation, and on to product recovery, residue processing, and co-product potential. A number of different pretreatments involving biological, chemical, physical, and thermal approaches have been investigated over the years, but only those that employ chemicals currently offer the high yields and low costs vital to economic success. Among the most promising are pretreatments using dilute acid, sulfur dioxide, near-neutral pH control, ammonia expansion, aqueous ammonia, and lime, with signifi cant differences among the sugar-release patterns. Although projected costs for these options are similar when applied to corn stover, a key need now is to dramatically improve our knowledge of these systems with the goal of advancing pretreatment to substantially reduce costs and to accelerate commercial applications.

Effect of Drying Method of Corn Stover on Sugar Recovery during Dilute Sulfuric Acid Pretreatment

“…The content of lignin for ODCS was lower than control group which indicated a lower lignified degree. The total soluble sugars in this study (17.7% for ODCS and 17.9% for ADCS) were much higher than those found in the literature (2.4-11.6%) due to the distinct climate, humidity, and breed [1,14]. It should be noted that there was little difference of glucan contents between ODCS and ADCS, the pretreatment results were mostly due to the different structures caused by the drying process.…”

Evaluation of the biocompatibile ionic liquid 1-methyl-3-methylimidazolium dimethylphosphite pretreatment of corn cob for improved saccharification

“…The pretreatment process is the key point in biomass conversion to biofuel, for lignocellulose must be pretreated prior to addition of hydrolytic enzymes for saccharification of cellulose, as yields are otherwise too low (Yang and Wyman 2008). Very recently, ILs showed promise as efficient novel solvents for pretreatment of cellulosic materials Liu and Chen 2006).…”

“…Subsequently, after pretreatment and enzymatic hydrolysis, cellulosic materials can be efficiently converted into biofuel by microbial fermentation (Wackett 2008). Therefore, the pretreatment process is one of the key points in biomass conversion to biofuel (Yang and Wyman 2008).…”

Ionic liquid-tolerant microorganisms and microbial communities for lignocellulose conversion to bioproducts

“…Lignocellulosic feedstocks are primarily composed of complex matrices of polysaccharides (cellulose and hemicellulose) and lignin which form plant cell walls (Buchanan et al 2015). These durable cell walls are recalcitrant to biomass pretreatment processes due to the crystallinity of the cellulose (protecting cellulose from chemical and biological degradation), and the presence of covalent cross-linkages between lignin and hemicellulose (Blanch and Wilke 1982;Chandra et al 2007;Li et al 2010), resulting in a high cost for pretreatment (Chandra et al 2007;Merino and Cherry 2007;Simmons et al 2008;Yang and Wyman 2008).…”