Pretreatment of Corn Stover by Low-Liquid Ammonia Recycle Percolation Process

Abstract

A pretreatment method using aqueous ammonia was investigated with the intent of minimizing the liquid throughput. This process uses a flowthrough packed column reactor (or percolation reactor). In comparison to the ammonia recycle percolation (ARP) process developed previously in our laboratory, this process significantly reduces the liquid throughput to one reactor void volume in packed bed (2.0-4.7 mL of liquid/g of corn stover) and, thus, is termed low-liquid ARP (LLARP). In addition to attaining short residence time and reduced energy input, this process achieves 59-70% of lignin removal and 48-57% of xylan retention. With optimum operation of the LLARP to corn stover, enzymatic digestibilities of 95, 90, and 86% were achieved with 60, 15, and 7.5 filter paper units/g of glucan, respectively. In the simultaneous saccharification and fermentation test of the LLARP samples using Saccharomyces cerevisiae (NREL-D5A), an ethanol yield of 84% of the theoretical maximum was achieved with 6% (w/v) glucan loading. In the simultaneous saccharification and cofermentation (SSCF) test using recombinant Escherichia coli (KO11), both the glucan and xylan in the solid were effectively utilized, giving an overall ethanol yield of 109% of the theoretical maximum based on glucan, a clear indication that the xylan content was converted into ethanol. The xylooligomers existing in the LLARP effluent were not effectively hydrolyzed by cellulase enzyme, achieving only 60% of digestibility. SSCF of the treated corn stover was severely hampered when the substrate was supplemented with the LLARP effluent, giving only 56% the overall yield of ethanol. The effluent appears to significantly inhibit cellulase and microbial activities.

Laboratory scale optimization of alkali pretreatment for improving enzymatic hydrolysis of sweet sorghum bagasse

“…Untreated SSB exhibited rigid and ordered fibrils with some deposits on the exterior layer (Figure 5a). This outer most layer was observed with different kind of polysaccharides, waxes, lignin, and different binding materials, which tallied with previously reported in corn stover (Kim, Lee, Sunwoo, Kim, 2006), and sorghum leaves and stems (Corredor et al, 2009). In the pretreated SSB, the surface layer was removed and the cell wall was distorted, resulting in exposure of internal structures ( Figure 5b, and 5c) which was consistent with observations of SSB structure by Goshadrou, et al, (2011).…”

A Review of the Role of Amphiphiles in Biomass to Ethanol Conversion

“…Studies that applied surfactants or protein-based amphiphiles during enzymatic hydrolysis of lignocellulosic biomass with cellulase and/or xylanase, reported that surfactants can increase sugar yield from lignocellulosic substrates [1,19,26,27,37,38,44,45]. In a typical procedure, pretreated biomass is incubated with nonionic surfactants (0.15 to 0.75 g/g glucan) [26,37,38] in a shaking incubator at temperatures of 50-60 °C for 1 h [44], or 15 min-4 h [1,26,36] prior to addition of cellulase.…”

“…A wide range of pretreatment technologies has been developed to enable high saccharification yields at lower enzyme loadings [14,15]. Some of these pretreatments target removal of monomeric sugars [16,17], hemicellulose oligomers [18], lignin and lignin degradation products [19][20][21], while others may also target increased biomass porosity, or a combination of these effects. A more recent approach has been the development of techniques that maintain enzyme secondary structure and solubility, and hence activity for an extended period of time.…”

Pretreatments to Enhance the Digestibility of Wheat Straw

“…Agricultural residue, such as corncobs and stovers, is particularly well suited to dilute acid pretreatment [51,73]. A maximum sugar yield of 541.2 mg g−1 wheat stubble was obtained by pretreatment at 2% H2SO4/90 min/121 •C followed by enzyme saccharification.…”

“…The mechanism is similar to the NaOH pretreatment. When using over lime (0.5g Ca(OH) 2 /g biomass) to pretreated corn stover at 25-55°C, lignin and hemicellulose were selectively uninvolved, so the degree of crystallinity slightly increased from 43% to 60% with delignification, but cellulose was not affected [73]. Both sodium hydroxide and lime have very effective at higher temperatures [79,52].…”