Biomass pretreatment

Harvest the cellulase-containing transgenic plants while they are green, macerate them, and separate the solid to produce an enzyme concentrate, which can later be used in the enzymatic hydrolysis of pretreated biomass. Depending on the production level of this enzyme in transgenic plants, the need for externally added cellu-lases in the enzymatic hydrolysis step might be avoided or minimized. 

Irrespective of the type of biomass used for ethanol production, the biomass needs to be pretreated to make the carbohydrates available for fermentation. However, which enzymes can be used depends on the source of the biomass. In addition, the biomass needs pretreatment before the enzymes are used. The first step of the pretreatment can be of a physical nature. Once the biomass is physically pretreated, the cellulose structures are open for enzyme action. In biomass from forests, the substance is mainly in the form of cellulose. Targeted enzymes are selective for the reaction of cellulose to glucose, and therefore there are no degradation byproducts, as occurs in acid conversion technology. There are at least three ways this can be performed. Firstly, in separate hydrolysis and fermentation, the pretreated biomass is treated with cellulase, which hydrolyzes the cellulose to glucose at 50 °C and pH 4.8. Secondly, in simultaneous fermentation and saccharification (SSF) the hydrolysis and fermentation take place in the same bioreactor. Thirdly,... 

Decker, S. R., Selig, M. J. (2006). D Milestone enzyme enhanced conversion of low severity pretreated biomass, DOE, Editor. NREL. p. 1-31. 

As the name implies, the acid hydrolysis pretreatment is intended to partially hydrolyze the lignocellulosic feedstock as well as remove alkali from it. This process converts hemicellulose to pentose sugar as well as removes alkali. Biomass was added to a 5 wt % solution of sulfuric acid in the proportion of about 150 g biomass for every liter of solution and boiled for 2 how s. The mixture was transferred to the glass column and excess liquid drained from the bottom. At this point 2 L of distilled water was pumped through die column at a superficial velocity of 0.08 mm/s to rinse acid from the biomass. The pretreated biomass was then dried at 105°C for subsequent pyrolysis. 

Normally hydroxyacetaldehyde, which is formed in competition with levoglucosan during cellulose pyrolysis (15), is catalyzed by the presence of cations such as alkali metal. Indeed, our results show that hychoxyacetaldehyde declines as levoglucosan increases in pyrolysate. However, hydroxyacetaldehyde remains a significant constituent of the pyrolysate from pretreated biomass, which suggests that some alkali remains in the feedstock even after pretreatment. 

Hydroxyacetaldehyde, which forms in competition with levoglucosan during pyrolysis of cellulose, remains a significant constituent of pyrolysate from pretreated biomass. Further tests are required to determine whether this is the result of residual alkali in the pretreated biomass. 

K.P. Yoon, Method for pretreating biomass to produce bioethanol, US Patent 8 278 080, assigned to Industry Academic Cooperation Foundation Keimyung University (Daegu, KR), October 2, 2012. 

Many well-financed technology development companies are actively pursuing scale-up and commercialization of variations of enzymatic hydrolysis technology for specific pretreated biomass feedstocks. Within the next several years, it is anticipated that enzymatic hydrolysis technologies, as practiced by these companies, will be contributing to commercial production of a range of biofuels and chemical products from lignocellulosic feedstocks. 

Jeoh T, Ishizawa Cl, Davis ME, Himmel ME, Adney WS, Johnson DK. (2007). Cellulase digestibility of pretreated biomass is limited by cellulose accessibility. Biotechnol Bioeng, 98(1), 112-122. 

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... 

One issue with pretreatment is that it is difficult to predict the final chemical composition of the hydrolysate and the behaviour of pretreated biomass (Kumar et al. 2009). Still, a more serious issue of pretreatment, neutralisation and hydrolysis is the creation of a complex blend of microbial inhibitors (Ezeji et al. 2007a). These inhibitors are created regardless of the method used, but are considered that dilute acid pretreatment generates a relatively large amount of inhibitors, in contrast to relatively small concentrations produced by hot water and AFEX pretreatment methods (Ezeji et al. 2007b). 

We tested S. cerevisiae on pretreated pulp fraction from wet separation of Salicornia sinus-persica. The pulp was pretreated using very low process severity of 121 °C for 30 and 60 min. The fibres were subjected to simultaneous saccharification and fermentation using 15 FPU/g DM of ceUulases (Novozymes), with a pre-hydrolysis time of 2 h at 50 °C with intensive shaking (120 rpm) prior to addition of S. cerevisiae at 32 °C for 7 days. Final ethanol yields were analysed by HPLC and calculated as percent of theoretical based on carbohydrate analysis of the pretreated biomass fractions. SSF was carried out both on pretreated fibre fraction resuspended in hydrolysate and on pretreated fibres in water. This was done to examine possible effect of fermentation inhibitors (degradation products) in the hydrolysate. Figure 6 shows the SSF results. 

The general methodology for producing bioethanol is to pretreat biomass in the form of agricultural residue and subject it to a variety of processes such as separate hydrolysis and... 

This is a two-step process in which the hydrolysis of the pretreated biomass is followed by the fermentation process, both taking place separately. The hydrolysis process uses acid or an enzymatic treatment, which converts the cellulose and hemicellulose to fermentable sugars. In the fermentation stage, the sugars are transformed to yield ethanol by the action of microorganisms. 

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