Yields for pretreatments

Several techniques have been used to activate the zinc metal and improve yields. For example, pretreatment of zinc dust with a solution of copper acetate gives a more reactive zinc-copper couple.168 Exposure to trimethylsilyl chloride also activates the zinc.169 Wilkinson s catalyst, RhCl(PPh3)3 catalyzes formation of Reformatsky reagents from diethylzinc, and reaction occurs under very mild conditions.170... 

Even with the pretreated reactor, aging of 16-24 hours was necessary to obtain a high yield of hydrogen peroxide. While for the untreated reactor 10 days for pretreatment were required. 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

A major obstacle to the commercialization of enzymatic hydrolysis of biomass is the high cost of the enzymes. One way to reduce this cost is to use much less enzyme per unit of biomass hydrolyzed. Previous work has shown that the effective enzymatic hydrolysis of AFEX-treated biomass at enzyme loadings as low as 5 filter paper units (FPU)/g of dry biomass was achieved by adjusting the pretreatment parameters (6). The objectives of the present study, were to determine the best AFEX conditions for pretreatment of corn stover, to employ different enzyme loading levels (60,15, and 7.5, FPU/g of glucan), and to compare the enzymatic hydrolysis results and ethanol yield. 

Fig. 6. Monomeric and oligomeric xylose yields for hot water only pretreatment of corn stover at 200°C after (A) 8 min and (B) 16 min.

Steam treatment of an industrial process stream, denoted starch-free wheat fiber, was investigated to improve the formation of monomeric sugars in subsequent enzymatic hydrolysis for further bioconversion into ethanol. The solid fraction in the process stream, derived from a combined starch and ethanol factory, was rich in arabinose (21.1%), xylose (30.1%), and glucose (18.6%), in the form of polysaccharides. Various conditions of steam pretreatment (170-220°C for 5-30 min) were evaluated, and their effect was assessed by enzymatic hydrolysis with 2 g of Celluclast + Ultraflo mixture/ 100 g of starch-free fiber (SFF) slurry at 5% dry matter (DM). The highest overall sugar yield for the combined steam pretreatment and enzymatic hydrolysis, 52 g/100 g of DM of SFF, corresponding to 74% of the theoretical, was achieved with pretreatment at 190°C for 10 min followed by enzymatic hydrolysis. 

Wheat SFF, consisting of about 70 wt% carbohydrates on a DM basis, proved to be a suitable substrate to release sugars for ethanol production. If all the sugars in the SFF could be utilized, this would correspond to more than 25% of the glucose available in the starch fraction, which is used for ethanol production today. Pretreatment of the SFF could thus substantially improve the ethanol yield. Steam pretreatment at the optimal conditions,... 

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. 

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... 

It can be seen fi om Table 4 that the major effect is that of pretreatment time, followed by the three-way interaetion. The interaction between pretieatment time and temperature (1 x 2) and the main effect of temperature are also significant. The main effect of lime loading has no influence on TRS yield, but its two-way interaction with temperature (2 x 3) is significant. It can be observed that all the signifieant effects are positive, which means that maximum TRS yield for the nonscreened bagasse is for high pretreatment time, temperature, and Ume loading (see assay 8 in Table 3). 

Table 5 Scaled regression coefficients of the regression model of glucose yield for nonscreened bagasse pretreated with alkaline hydrogen peroxide.

Table 7 ANOVA for the model describing glucose yield for nonscreened bagasse (NS) pretreated with alkaline peroxide.

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