Biomass deconstruction

While the main goal of this chapter has been to highlight the role that ethanol has played in the development of the metabolic engineering field, the latter has also played a similar role in the development of biomass deconstruction methods. Here we discuss examples of biomass deconstruction techniques that were first demonstrated with ethanol production but have since been extrapolated to other biorenewable fuels and chemicals. 

A variety of methods have been demonstrated for biomass deconstruction. These can be broadly classified as chemical, biological, physical, and physicochemical [155]. Chemical methods include steam, lime, liquid hot water, ionic liquids, organosolve, ammonia, oxidative delignification, and ozonolysis [150, 155]. Physical and physiochemical methods include milling, steam explosion (autohydrolysis), ammonia fiber explosion (AFEX), microwave, extrusion, pulsed electric field, pyrolysis, and ultrasound. Consistent with the theme of this chapter, the first description of a novel non-enzymatic biomass deconstruction technique demonstrated the effectiveness of this method by producing ethanol [156]. 

Many of the available biomass deconstruction techniques lead to the production of dirty streams that contain not only sugars but also microbial inhibitors such as acetate and furfural. Extensive efforts have been described by the metabolic engineering community to understand and address the toxicity imposed by these streams, as reviewed elsewhere [157-163] and not discussed here. 

Although the metabolic engineering strategies described in Section 18.2 have made enormous strides in enabling the production of ethanol at high yields and titers from biomass-derived sugars, improvements in biomass deconstruction have also advanced the economic viability of ethanol production. 

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Fig. 33.24. Biomass deconstruction is a Key step in its conversion to chemical products and fuels.

In this section, we seek to identify materials that are the reasonable first structures to arise from biomass deconstruction, and to describe how chemically catalyzed processes are being developed for their production. For that reason, commercially practiced processes that use catalysis, such as the reduction of glucose to sorbitol, are mentioned only briefly or not at all. Chemical catalysis will certainly play an additional role in the further conversion of these initial building blocks into secondary intermediates or final marketplace products (e.g., oxidative conversion of levulinic acid into succinic acid), but such multistep possibilities are outside the scope of this discussion. 

A considerable amount of recent work has focused on the oxidation of polymeric and monomeric carbohydrates in aqueous media. In the context of the biorefinery, these processes could be used for the preparation of oxidized carbohydrates as primary outputs of biomass deconstruction. Of particular interest are processes catalyzed with stable oxygen-centered radicals such as the nitroxyl radical TEMPO (2) (2,2,6,6-tetramethylpiperidi-noxyl) and using bleach as the stoichiometric oxidant. 

Under proper conditions, biomass deconstruction will generate streams of monomeric or oligomeric carbohydrates, with glucose and xylose (from cellulose/starch or hemicel-... 

Groom, J., Chung, D., Young, J., and Westpheling, J. (2014) Fleterologous complementation of a pyrE deletion in Caldicellulosiruptor hydrothermalis generates a new host for the analysis of biomass deconstruction. Biotechnol Biofuels, 7, 132. 

Figure 18.1 Mankind s desire to improve ethanol production has shaped our development of techniques for biomass deconstruction, metabolic engineering, and separations, and has thereby heavily influenced the fields...

Just as interest in ethanol has driven the development of chemical models, distillation technology, and the field of metabolic engineering, it has also driven the development of the field of biomass deconstruction. Given that the focus of this book series is on biotechnology, this chapter will place more emphasis on the metabolic engineering aspect. However, key examples are briefly discussed in Section 18.3. 

Bhataya A, Schmidt-Dannert C, Lee PC (2009) Metabolic engineering of Pichia pastoris X-33 for lycopene production. Process Biochem 44(10) 1095-1102. doi 10.1016/j.procbio.2009.05.012 Bisson LF, Karpel JE (2010) Genetics of yeast impacting wine quality. Annu Rev Food Sci Technol 1(1) 139-162. doi 10.1146/annuiev.food.080708.100734 Blanch HW, Simmons BA, Klein-Marcuschamer D (2011) Biomass deconstruction to sugars. 

The team from Icongenetics used the deconstructed virus system to attain protein yields of up to 80% of total soluble protein or 5 g/kg of freshwater biomass, a process that only takes 3-14 days. Development of a scaled-up version of this expression system in transgenic plants by controlling the activation of an encrypted version of a replicon present in the plant chromosome of a production host is currently under investigation. One enormous advantage to the system would be the lack of requirement of systemic movement of the virus. 

Harris, P. J., Stone, B. A. (2008). Chemistry and moleeular organization of plant eell walls. In M. E. Himmel (Ed.), Biomass recalcitrance deconstructing the plant cell wall for bioenergy (pp. 61-93). Blaekwell Publishing, Oxford. 

Lignocellulosic biomass is a valuable and plentiful feedstock commodity and its high cellulose and hemicellulose content (about 80% of total) provides considerable potential for inexpensive sugars production. However, enzymatic deconstruction of these polysaccharides remains a costly prospect. Strides in cellulase cost reduction have been made, yet further improvements are needed to reach the goal of 0.10/gal of EtOH expected to enable this new industry. Strategies to reach this goal will combine reduction in the cost to produce the needed enzymes as well as efforts to increase enzyme efficiency (specific activity). As this work proceeds, the more easily attained achievements will be made first, and thus the overall difficulty increases with time. 

The options for practical operation of a biorefinery are also complex. Very broadly, the biorefinery will have the capability of deconstructing biomass into several categories of outputs including ... 

Initial separation of biomass raw materials can yield separate streams of biopolymers, each of which has potential utility as a product within the biorefinery. Further selective deconstruction processes can convert these biopolymers into their individual monomeric units, or to structurally rearranged materials. The following are examples of processes that have been improved through the use of chemical catalysis. 

Advanced catalysts for conversion of biologically derived feedstocks and specifically the deconstruction and catalytic conversion to fuels of lignocellulosic biomass. 

L. B. Davin A. M. Patten M. Jourdes N. G. Lewis, Lignins A Twenty-First Century Chaiienge. in Biomass Recalcitrance. Deconstructing the Plant Cell Wall for Bioenergy, M. E. Himmei, Ed. Biackweii Pubiishing Oxford, UK, 2008 pp 213-305. 

R. L., and Kelly, R.M. (2012) Caldicellulosiruptor core and pangenomes reveal determinants for noncellulosomal thermophilic deconstruction of plant biomass./. Bacteriol, 194, 4015-4028. 

Davis R, Tao L, Tan ECD, Biddy MJ, Beckham GT, Scarlata C, et al. Schoen, process design and economics for the conversion of hgnoceUulosic biomass to hydrocarbons dilute-acid and enzymatic deconstruction of biomass to sugars and biological conversion of sugars to hydrocarbons. NREL 2013. Report No. NREL-TP-5100-60223. 

Biotechnology for Biofuels. 2007- London BioMed Central Ltd. (1754-6834). Online http // www.biotechnologyforbiofuels.com/. An open access online journal publishing research on advances in the production of biofuels from biomass, including development of plants for biofuels production, plant deconstruction, pretreatment and fractionation, enzyme production and enzymatic conversion, and fermentation and bioconversion. 

BTO [Biomass-To-Olefins] A process for converting lignocellulose to olefins developed by Exelus, NJ. Tested with pine sawdust, paulownia, and switchgrass. The biomass is first deconstructed to oligosaccharides that are then hydrolyzed to glucose. This is selectively deoxygenated to short-chain alcohols that are then dehydrated to their respective olefins. 

NMR spectroscopy is a well-established analytical technique in biofuel research. Over the past few decades, lignocellulosic biomass and its conversion to supplement or displace non-renewable feedstocks has attracted increasing interest. The application of solid-state NMR spectroscopy has long been seen as an important tool in the study of cellulose and lignocellulose structure, biosynthesis, and deconstruction, especially considering the limited number of effective solvent systems and the significance of plant cell wall three-dimensional microstructure and component interaction to conversion yield and rate profiles. The article by Foston reviews common and recent applications of solid-state NMR spectroscopy methods that provide insight into the structural and dynamic processes of cellulose that control bulk properties and biofuel conversion. 

Banerjee G, Car S, Scott-Craig JS, Borrusch MS, Walton ID (2010a) Rapid optimizatirai of enzyme mixtures for deconstruction of diverse pretreatment/biomass feedstock combinations. Biotechnol Biofuels 3 22... 

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