Enzymatic hydrolysis of cellulose

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

Fermentation can be combined with other operations. For example, feedback inhibition of enzymatic hydrolysis of cellulose can be relieved by removal of the product glucose by fermentation as it forms. This is teni ed. simultaneou.s-saccharification-fermentation (SSF). 

Simultaneous saccharification and co-fermentation (SSCF) one-stage enzymatic hydrolysis of cellulose and fermentation of pentoses and hexoses all in one process step. The upstream hydrolysis of the hemicellulose takes place in a separate process step. 

The effective pretreatments for enzymatic hydrolysis of cellulose in hardwoods and agricultural residues have been developed over the past 90 years and new or improved ones are still being developed. The initial impetus for pretreatment research was the expansion of a feed base for ruminants (i.e., cattle and sheep). The concentration of pretreatment research on animal feed preparation placed an additional burden on researchers, because the product must be not only fully convertible to animal live-weight, but also nontoxic and palatable. Early feeding trials of pretreated fine sawdust to cattle produced very dismal results (55). This may be the reason, besides the... 

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 advances made in enzymatic hydrolysis of cellulosic materials (14) are also of interest. This technology involves only moderate temperature processes in simple equipment which promises to be of significantly lower capital cost than the pressure equipment associated with conventional acid wood hydrolysis processes. All of these considerations combined to lead us to study processes for ethanol production from wood, especially in an effort to obtain data for material and energy balances, and possibly for the economics. 

Myers, S.G., Ethanolic Fermentation During Enzymatic Hydrolysis of Cellulose. Second Pacific Chemical Engineering Congress, Denver, Colorado, 1977. 

Indeed, enzymatic hydrolysis of cellulose leads to cellobiose. The molecular weight of cellulose varies with the source but is usually high. Cotton cellulose appears to have about 3000 glucose units per molecule. 

A few animals (especially ruminants and termites) are able to metabolize cellulose, but even these animals depend on appropriate microorganisms in their intestinal tracts to hydrolyze the -1,4 links other animals, including man, cannot utilize cellulose as food because they lack the necessary hydrolytic enzymes. However, such enzymes are distributed widely in nature. In fact, deterioration of cellulose materials —textiles, paper, and wood —by enzymatic degradation (such as by dry rot) is an economic problem that is not yet adequately solved. Efforts to turn this to advantage through enzymatic hydrolysis of cellulose to glucose for practical food production have not been very successful (see Section 25-12). 

Humphrey, A. E. Symp. on Enzymatic Hydrolysis of Cellulose, Aulanko,... 

It is not clear, however, whether electron radiation would have beneficial effects upon the enzymatic hydrolysis of cellulose. It has been shown that the particle size reduction and surface area increase upon ball milling are probably more important than the reduction of crystallinity (19). Electron irradiation may not disrupt the shielding layer provided by the lignin to expose fresh cellulose to the action of large enzyme molecules. 

A common feature of vapor-phase thermohydrolysis, liquid-phase acid hydrolysis, and enzymatic hydrolysis of cellulose is a significant influence of lateral order on the rate of chain cleavage, the DP finally reached, and weight loss. But with regard to this influence of the physical structure of cellulose, there also exist remarkable differences between these three modes of hydrolytic degradation. 

The thermodynamic parameters were calculated and are summarized in Table III. Both enthalpy and entropy decrease considerably with complex formation. Such a large decrease in enthalpy and entropy has not been found in other complex formation systems. For example, the change in enthalpy with the complex formation because of hydrophobic interactions generally is not so large and change in entropy is positive (23,24) and change in enthalpy with the complex formation in enzymatic hydrolysis of cellulose is slightly positive (25). These unusual decreases in enthalpy and entropy are inferred to be characteristics of the present complex formation system. 

Enzymatic Hydrolysis of Cellulose Bailey, M., Enan, T. M., Linko, M., Eds The Finnish National Fund for Research and Development (SITRA) Helsinki, 1975 pp. 231-254. 

The applications of enzymes can be classified into three major categories industrial enzymes, analytical enzymes, and medical enzymes. In this chapter, we review several industrial processes, utilizing industrial enzymes such as starch conversion and enzymatic hydrolysis of celluloses. Before we discuss the enzymatic hydrolysis of starch and cellulose, we review the organic chemistry of carbohydrates. 

The development of a reliable kinetic model for the enzymatic hydrolysis of cellulose is helpful for the understanding of its mechanism and subsequent reactor design. Several kinetic models for the enzymatic hydrolysis of pure cellulose have been proposed by... 

To illustrate the procedure for the development of kinetic models of the cellulose hydrolysis, let s examine the model proposed by Ryu et al. (1982). A kinetic model for the enzymatic hydrolysis of cellulose was derived based on the following assumptions ... 

Table 4.2 Comparison of Various Kinetic Models of Enzymatic Hydrolysis of Cellulose.

By employing the Michelis-Menten approach, derive the rate equation, Eq. (4.19), for the enzymatic hydrolysis of cellulose with the kinetic mechanisms described as Eqs. (4.1) through (4.7). 

Write the mechanism of enzymatic hydrolysis of cellulose based on the following assumptions ... 

Marsden, W. L. and P. P. Gray, "Enzymatic Hydrolysis of Cellulose in Lignocellulosic Materials," CRC Critical Review Biotech. 3 (1986) 235-276. 

Okazaki, M. and M. Moo-Young, "Kinetics of Enzymatic Hydrolysis of Cellulose Analytical Description of a Mechanistic Model," Biotechnol. Bioeng. 20 (1978) 637-663. 

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