Cellulose conversions

Current data indicate that the analysis of cellulase enzyme activities may be the best method for determining the projected cellulose conversion of the overall system, and therefore the hydrolytic power of the system under evaluation. With development, the analysis of enzyme activities may also serve as a "real time" method of monitoring the stability of the system, with radical changes in enzyme activities indicative of potential process upset. 

Because the hydrolysis operation is discontinued before cellulose conversion is complete, small amounts of cellulose also remain in the lignin residue. 

Fig. 6. Cellulose conversion over time for the same experiments as shown in Fig. 5. The data represent cellulose conversions based on glucose production alone. Cellobiose measurements taken at the end of the experiments account for an additional conversion of about 4%. Error bars represent averages 1 SD for three repeated experiments.

McMillan, J. D., Dowe, N., Mohagheghi, A., and Newman, M. (1999), Reducing the Cost of Saccharification and Fermentation by Decreasing the Cellulase Enzyme Loading Requiredfor Cellulose Conversion, National Renewable Energy Laboratory, Golden, CO. 

The composition of poplar wood was usedasamodel for the feedstock composition however, as used in this simulation, the poplar is modeled as consisting of only cellulose, xylan, and lignin, with compositions of 49.47, 27.26, and 23.27%, respectively. Laboratory results for carbonic acid pretreatment are relatively scarce, so for the purpose of this comparative study, stoichiometry of pretreatment reactions was assumed to be equal to those used in the comparison model (3) cellulose conversion to glucose 6.5% xylan conversion to xylose 75 and lignins solubilized 5%. Thus, economic comparisons made with this model assess different equipment and operating costs but not product yields. For the successful convergence of the carbonic acid model, the simulation required initial specification of several variables. These variables included initial estimates for stream variables and inputs for the unit operation blocks. 

Martmez D, Challacombe J, Morgenstem I et al (2009) Genome, transcriptome, and secre-tome analysis of wood decay fungus Postia placenta supports unique mechanisms of ligno-cellulose conversion. Proc Natl Acad Sci USA 106 1954-1959... 

Among the renewable raw materials, cellulose is among the most abundant ones. In contrast to other carbohydrates, such as saccharose or starch cellulose, processing does not compete with food production. In the context of examples of the conversion of carbohydrates, the term cellulose may also include oligosaccharides and monosaccharides, such as sucrose or glucose. This is because cellulose conversion almost always includes a depolymerization to soluble fragments, which are further converted. 

Discover new microbes or thermochemical catalysts for lignin and cellulose conversion... 

Cellulose is converted to ethanol by making glucose and then fermenting the glucose to ethanol using yeast. Cellulose conversion has been studied for many... 

For most cellulosic materials, there is an upper limit to the degree of conversion that can be obtained. At this point, the accessibility of the remaining cellulose to the enzyme is limited, either by its pore structure or the presence of non-cellulosic components. The decrease in rate with increasing cellulose conversion is referred to as substrate recalcitrance . 

Enzyme activity loss because of non-productive adsorption on lignin surface was identified as one of the important factors to decrease enzyme effectiveness, and the effect of surfactants and non-catalytic protein on the enzymatic hydrolysis has been extensively studied to increase the enzymatic hydrolysis of cellulose into fermentable sugars [7, 9 19]. The reported study showed that the non-ionic surfactant poly(oxyethylene)2o-sorbitan-monooleate (Tween 80) enhanced the enzymatic hydrolysis rate and extent of newspaper cellulose by 33 and 14%, respectively [20]. It was also found that 30% more FPU cellulase activity remained in solution, and about three times more recoverable FPU activity could be recycled with the presence of Tween 80. Tween 80 enhanced enzymatic hydrolysis yields for steam-exploded poplar wood by 20% in the simultaneous saccharification and fermentation (SSF) process [21]. Helle et al. [22] reported that hydrolysis yield increased by as much as a factor of 7, whereas enzyme adsorption on cellulose decreased because of the addition of Tween 80. With the presence of poly(oxyethylene)2o-sorbitan-monolaurate (Tween 20) and Tween 80, the conversions of cellulose and xylan in lime-pretreated com stover were increased by 42 and 40%, respectively [23]. Wu and Ju [24] showed that the addition of Tween 20 or Tween 80 to waste newsprint could increase cellulose conversion by about 50% with the saving of cellulase loading of 80%. With the addition of non-ionic, anionic, and cationic surfactants to the hydrolysis of cellulose (Avicel, tissue paper, and reclaimed paper), Ooshima et al. [25] subsequently found that Tween 20 was the most effective for the enhancement of cellulose conversion, and anionic surfactants did not have any effect on cellulose hydrolysis. With the addition of Tween 20 in the SSF process for... 

The specific objectives of this research were to investigate (1) the effect of additives on the cellulose conversion of pretreated CWR, (2) the possible mechanism behind the effect of additives on the enzymatic hydrolysis, (3) the effect of additives on the enzyme adsorption onto several substrates, including Avicel PHIOl, pretreated CWR, and lignaceous residue of pretreated CWR. 

As shown in Fig. 1, the presence of Tween 80, Tween 20, BSA or (BSA + Tween 20) improved the enzymatic hydrolysis of pretreated CWR by 8 to 14% after 72 h of hydrolysis. The initial hydrolysis rate was also increased to some extent The cellulose conversion was increased from approximately 75% (no additives) to 89, 88, and 83% with the presence of Tween 20, Tween 80, and BSA, respectively. Of all three additives. Tween 20 was the most effective additive on the improvement of cellulose conversion, followed by Tween 80 and BSA. The treatment of Tween 20, Tween 80, or BSA gave similar results at an enzyme loading of 15 FPU/g cellulose to those at enzyme loading of 30 FPU/g cellulose but without additive addition (Fig. 1). Therefore, the addition of surfactants and/or non-catalytic protein could help save enzyme loading without decreasing the hydrolysis yield. In addition, it was found that Tween 20 and BSA gave no further increase in cellulose conversion. Thus, the effect of Tween 20 on the hydrolysis of pretreated CWR might be similar to that of BSA [7]. 

Fig. 1 Effect of additives on the cellulose conversion of pretreated CWR (the additive loading was 0.1 g additive/g dry solid and the enzyme loading was 15 FPU +...

Fig. 4 Cellulose conversion of pretreated CWR after 72 h as a function of Tween 20 loading...

Considering the result from Fig. 1 that (0.1 g Tween 20 + 0.1 g BSA)/g dry solid gave no further increase of cellulose conversion compared with the addition of Tween 20 alone, a conclusion could be drawn that the mechanisms of Tween 20 and BSA on the improvement of enzymatic hydrolysis of pretreated CWR might be similar. If Tween 20 and BSA had significantly different mechanisms on the improvement of enzymatic hydrolysis, higher cellulose conversion should be expected after BSA was added to the solution with Tween 20 at saturation loading of 0.1 g/g dry solid. 

When the substrate was Avicel, the cellulose conversion was slightly increased with Tween 20 addition, in contrast to the significant increase of cellulose conversion of pretreated CWR (Fig. 6). After 72 h, the cellulose conversion of Avicel was increased 3% with the presence of 0.1 g Tween 20/g Avicel. 

Adding Tween 20 after 8 h of pretreated CWR hydrolysis had little effect on cellulose conversion (Fig. 10). The final cellulose conversion was improved by about 2%, which was much lower than the 14% more cellulose conversion achieved when Tween 20 was added before enzyme addition (Fig. 1). 

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