Poulomi Sannigrahi

Pseudo-lignin and pretreatment chemistry

The formation of pseudo-lignin by the combination of carbohydrate and lignin degradation products has been proposed to be responsible for the increased Klason lignin content in biomass pretreated under acidic conditions. Direct evidence for the presence of pseudo-lignin has never been presented. The formation of additional lignin-like material may be detrimental to enzymatic hydrolysis due to the non-productive binding of enzymes with lignin. To investigate the chemistry of pseudo-lignin formation, dilute acid pretreatments were performed on delignified hybrid poplar biomass under conditions of varying severity. The results show a progressive increase in the Klason lignin content of the acid pretreated material with increasing pretreatment severity. NMR and FT-IR spectroscopic characterization shows the development of aliphatic, unsaturated and carbonyl carbon functionalities in the samples pretreated at higher severities. Given the very low Klason lignin content of the starting material, acid catalyzed dehydration of carbohydrates is responsible for the formation of pseudo-lignin.

Effects of Two-Stage Dilute Acid Pretreatment on the Structure and Composition of Lignin and Cellulose in Loblolly Pine

A standard two-step dilute sulfuric acid pretreatment was performed on Loblolly pine to enhance the overall efficiency of enzymatic deconstruction of woody biomass to monomeric sugars. The structure of milled wood lignin and cellulose isolated from the untreated and acid-treated biomass was studied in detail. Solid-state 13C NMR spectroscopy coupled with line shape analyses has been employed to elucidate cellulose crystallinity and ultrastructure. The results indicate an increase in the degree of crystallinity and reduced relative proportion of less ordered cellulose allomorphs following the acid pretreatment. This increase was attributed to a preferential degradation of amorphous cellulose and less ordered crystalline forms during the high temperature pretreatment. Milled wood lignin structural elucidation by quantitative 13C and 31P NMR reveals an increase in the degree of condensation of lignin due to the pretreatment. The increase in degree of condensation is accompanied by a decrease in β-O-4 linkages which were fragmented and recondensed during the high temperature acid-catalyzed reactions.

Carbohydrate derived-pseudo-lignin can retard cellulose biological conversion

Dilute acid as well as water only (hydrothermal) pretreatments often lead to a significant hemicellulose loss to soluble furans and insoluble degradation products, collectively termed as chars and/or pseudo‐lignin. In order to understand the factors contributing to reducing sugar yields from pretreated biomass and the possible influence of hemicellulose derived pseudo‐lignin on cellulose conversion at the moderate to low enzyme loadings necessary for favorable economics, dilute acid pretreatment of Avicel cellulose alone and mixed with beechwood xylan or xylose was performed at various severities. Following pretreatment, the solids were enzymatically hydrolyzed and characterized for chemical composition and physical properties by NMR, FT‐IR, and SEM imaging. It was found that hemicelluloses (xylan) derived‐pseudo‐lignin was formed at even moderate severities and that these insoluble degradation products can significantly retard cellulose hydrolysis. Furthermore, although low severity (CSF ∼ 1.94) dilute acid pretreatment of a xylan–Avicel mixture hydrolyzed most of the xylan (98%) and produced negligible amounts of pseudo‐lignin, enzymatic conversion of cellulose dropped significantly (>25%) compared to cellulose pretreated alone at the same conditions. The drop in cellulose conversion was higher than realized for cellulase inhibition by xylooligomers reported previously. Plausible mechanisms are discussed to explain the observed reductions in cellulose conversions. Biotechnol. Bioeng. 2013; 110: 737–753.

Effects of organosolv pretreatment and enzymatic hydrolysis on cellulose structure and crystallinity in Loblolly pine

Ethanol organosolv pretreatment was performed on Loblolly pine to enhance the efficiency of enzymatic hydrolysis of cellulose to glucose. Solid-state (13)C NMR spectroscopy coupled with line shape analysis was used to determine the structure and crystallinity of cellulose isolated from pretreated and enzyme-hydrolyzed Loblolly pine. The results indicate reduced crystallinity of the cellulose following the organosolv pretreatment, which renders the substrate easily hydrolyzable by cellulase. The degree of crystallinity increases and the relative proportion of para-crystalline and amorphous cellulose decreases after enzymatic hydrolysis, indicating preferential hydrolysis of these regions by cellulase. The structural and compositional changes in this material resulting from the organosolv pretreatment and cellulase enzyme hydrolysis of the pretreated wood were studied with solid-state CP/MAS (13)C NMR spectroscopy. NMR spectra of the solid material before and after the treatments show that hemicelluloses and lignin are degraded during the organosolv pretreatment.

Biomass Characterization of Buddleja davidii: A Potential Feedstock for Biofuel Production

A compositional analysis was performed on Buddleja davidii to determine its general biomass characteristics and provide detailed analysis of the chemical structures of its cellulose and lignin using NMR. B. davidii is a new potential lignocellulosic bioresource for producing bioethanol because it has several attractive agroenergy features. The biomass composition of B. davidii is 30% lignin, 35% cellulose, and 34% hemicellulose. Solid-state CP/MAS (13)C NMR showed that 33% of the cellulose is para-crystalline and 41% is at inaccessible surfaces. Both quantitative (13)C and (31)P NMR were used to examine the structure of lignin. The lignin was determined to be guaiacyl and syringyl with an h:g:s ratio of 0:81:19.

Polyphosphates as a source of enhanced P fluxes in marine sediments overlain by anoxic waters: Evidence from 31P NMR

Sedimentary phosphorus (P) composition was investigated in Effingham Inlet, a fjord located on the west coast of Vancouver Island in Barkley Sound. Solid-state 31P nuclear magnetic resonance (NMR) spectroscopy was applied to demineralized sediment samples from sites overlain by oxic and anoxic bottom waters. The two sites were similar in terms of key diagenetic parameters, including the mass accumulation rate, integrated sulfate reduction rate, and bulk sediment organic carbon content. In contrast, P benthic fluxes were much higher at the anoxic site. 31P NMR results show that P esters and phosphonates are the major organic P species present at the surface and at depth in sediments at both sites. Polyphosphates were only found in the surface sediment of the site overlain by oxic waters. The varying stability of polyphosphates in microorganisms under different redox conditions may, in part, explain their distribution as well as differences in P flux between the two sites.

A Novel Oxidative Pretreatment of Loblolly Pine, Sweetgum, and Miscanthus by Ozone

Abstract Three biomass feedstocks (Loblolly pine, Sweetgum, and Miscanthus) were subjected to a novel, two-step ozone pretreatment to enhance the enzymatic digestibility of cellulose. The results show that ozone pretreatment alone did not significantly reduce recalcitrance of the three feedstocks. However, the ozone pretreatment was capable of generating oxidative biomass fragments that can be utilized in a subsequently conventional pretreatment without the need for exogenous acid to be added. For example, employing a dose of ozone followed by an ethanol organosolv pretreatment led to significant delignification and preserved most of the carbohydrates in the three biomass feedstocks. Likewise, ozone treatment followed by autohydrolysis gave higher solubilization of hemicelluloses and distinctive results in terms of enzymatic glucose release and fermentation yields for both Sweetgum (14.00 g ethanol/100.00 g biomass) and Miscanthus (11.10 g ethanol/100.00 g biomass) feedstocks. Although ozone treatment followed by organosolv pretreatment gave low enzymatic glucose release yield for Loblolly pine, a two-step ozone pretreatment has been shown in this study to be a very promising strategy for Sweetgum and Miscanthus feedstocks.