Hydrolysis of cellulosic biomass

While this reaction is substantially exothermic (6), it provides an intriguing approach to the production of fuels from renewable resources, as the required acids (including acetic acid, butyric acid, and a variety of other simple aliphatic carboxylic acids) can be produced in abundant yields by the enzymatic fermentation of simple sugars which are, in turn, available from the microbiological hydrolysis of cellulosic biomass materials ( ] ) These considerations have led us to suggest the concept of a "tandem" photoelectrolysis system, in which a solar photoelectrolysis device for the production of fuels via the photo-Kolbe reaction might derive its acid-rich aqueous feedstock from a biomass conversion plant for the hydrolysis and fermentation of crop wastes or other cellulosic materials (4). 

Economically feasible processes for biomass conversion to ethanol requires the fermentation of the sugars generated in the pretreatment and hydrolysis steps. In agricultural residues and hardwoods, xylose constitutes about 45% of the total sugars, and therefore xylose conversion to ethanol is important for high yields. Dilute acid hydrolysis of cellulosic biomass generates inhibitory compounds such as furfural, hydroxymethyl furfural, and acetic acid [1], These inhibitors affect the ability of yeasts to ferment the hydrolyzates, and therefore a detoxification step is usually included in fermenting acid... 

Acid or alkaline treatments of particulate feeds have been shown to improve digester gas yields (17.22-25). Acid hydrolysis was not used in our work because severe reaction conditions are required, and there is considerable decomposition of the hydrolytic products under these conditions ( ). Dilute alkaline pretreatment was evaluated because alkali was shown to be more effective in promoting hydrolysis of cellulosic biomass than acid (17,26). It is postulated, for example, that sodium hydroxide breaks down the cross-linked lignin macro-molecules surrounding the cellulose fibers into alkali-soluble lower-molecular-weight units. In this way, the cellulose fibers are exposed for... 

To reconcile these differences, we have proposed that pretreatment models should combine reaction with mass transfer and solubility limitations so that the concentration gradient between the solid and the liquid phases is taken into account. Furthermore, we have applied depolymerization kinetics to account for the production of sugar monomers and oligomers observed during the hydrolysis of cellulosic biomass, particularly at low acid levels. Some aspects of these studies will be summarized in this chapter. 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

Levulinic acid is obtained by hydrolysis of cellulose-containing biomass. R D is actively conducted at DuPont Co. to employ levulinic acid for the synthesis of pyr-rolidones (solvents and surfactants), a-methylene-y-valerolactone [monomer for the preparation of polymers similar to poly(methyl methacrylate)], and levulinic acid esters (fuel additives) [26]. 

A new generation of cheap enzymes for hydrolysis of cellulose and lignocellu-lose to fermentable sugars (able to complete the biomass hydrolysis during fermentation). 

Further research is also needed in this area. Particularly, (a) to create a new generation of cheap enzymes for hydrolysis of cellulose and lignocellulose to fermentable sugars (able to complete the biomass hydrolysis during fermentation) (b) to develop improved biocatalysts that allow us to simplify the process and reduce energy input and (c) to improve separation and recovery. 

Spano, L.A., "Enzymatic Hydrolysis of Cellulosic Wastes to Fermentable Sugars for Alcohol Production", in "Symposium on Clean Fuels from Biomass, Sewage, Urban Refuse, Agricultural Wastes", 325-348, Inst, of Gas Technology, Chicago (1976). Wilke, C.R., Stockar, V. and Yang, R.D., AIChE Symposium Series No. 158, (1976) 104. 

The approach "select favorable raw material has a major impact on the selection of pretreatment processes. For example, the poplar responds splendidly to many pretreatments that fail with Douglas fir or pine-based materials (I). Specific tissues and cells of a given biomass raw material will respond quite differently. For example, the rind fiber of sugarcane bagasse behaves quite differently from the pith fiber (11)- In woody species, the selection of tissues low in bark and extractives is an important factor in the ease or resistance to cellulose hydrolysis. Before embarking on development of processes for hydrolysis of a biomass resource, it is highly desirable to exercise discretion with respect to the choice of raw materials at both the species and tissue levels. This idea is all the more important in an initial choice of species and pretreatment process. 

Direct conversion of cellulose in an unpurifled state has been shown in the case of levulinic acid production. Production of levulinic acid as a high-yield direct product of controlled acid hydrolysis of cellulose is an exception to the complex product slate typically produced from biomass feedstocks. While the levulinic acid is only derived from the cellulose portion of the biomass and other components end up as byproducts, technology has now been demonstrated for recovery of the levulinic acid product at yields and purity sufiident to generate market interest". Based on related research developments, levulinic acid may prove to be an important building block for... 

Derivation (1) From ethylene by direct catalytic hydration or with ethyl sulfate as intermediate (2) fermentation of biomass, especially agricultural wastes (3) enzymatic hydrolysis of cellulose... 

See alcohol, denatured alcohol, industrial biomass. Note Ethanol from fermentation of biomass and hydrolysis of cellulose is a significant alternate energy source, especially as an automotive fuel. Its use in gasoline will continue to increase. 

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