Isolation and structural characterization of sugarcane bagasse lignin after dilute phosphoric acid plus steam explosion pretreatment and its effect on cellulose hydrolysis

Thermal Degradation and Chemical Analysis of Flame-Retardant-Treated Jute Fabrics

Jute is an inherent lignocellulosic fiber, consisting of hemicellulose, α-cellulose, and lignin. Industrial ventilation, automotive composites, upholstery, carpets, military uniforms, hospital furnishings, and curtains necessitate the integration of flame-retardance properties into jute fibers. In this investigation, seven weave-structured jute fabrics were treated using an organophosphorus-based flame-retardant (FR) chemical (ITOFLAM CPN) and a crosslinking agent (KNITTEX CHN) by the pad-dry-cure method. The thermal stability, degradation and pyrolysis behavior of jute was measured using a thermogravimetric analyzer (TGA). Surface morphology and element distribution were scrutinized utilizing a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS). The ATR-FTIR (Attenuated Total Reflection-Fourier Transform Infrared Spectrometer) technique has been employed for analyzing the composition of chemicals in the jute fabrics. According to the protocols specified in ISO 14184-1, free formaldehyde detection was carried out on the jute fabrics. The flame-retardance property was significantly improved on all of the jute fabrics after FR treatment. FTIR and SEM-EDS studies revealed the presence of FR chemical deposition on the surface of the jute fabrics. TGA analysis indicated that the fabrics treated with FR exhibited premature degradation, leading to the generation of more char compared to untreated samples. The jute fabrics specifically demonstrated a notable enhancement in residual mass, exceeding 50% after FR treatment. However, it is noteworthy that the FR-treated fabrics exhibited an elevated level of free formaldehyde content, surpassing the permissible limit of formaldehyde in textiles intended for direct skin contact. The residual mass loss percentage after ten washes of FR-treated fabrics remained in a range from 32% to 36%. Twill weave designed fabrics (FRD4 and FRD5) clearly showed a lower thermal degradation temperature than the other weaves used in this study.

Selective Depolymerization of Lignin Towards Isolated Phenolic Acids Under Mild Conditions

The selective transformation of lignin to value-added biochemicals (e. g., phenolic acids) in high yields is incredibly challenging due to its structural complexity and many possible reaction pathways. Phenolic acids (PA) are key building blocks for various aromatic polymers, but the isolation of PAs from lignin is below 5 wt.% and requires harsh reaction conditions. Herein, we demonstrate an effective route to selectively convert lignin extracted from sweet sorghum and poplar into isolated PA in a high yield (up to 20 wt.% of lignin) using a low-cost graphene oxide-urea hydrogen peroxide (GO-UHP) catalyst under mild conditions (<120 °C). The lignin conversion yield is up to 95 %, and the remaining low molecular weight organic oils are ready for aviation fuel production to complete lignin utilization. Mechanistic studies demonstrate that pre-acetylation allows the selective depolymerization of lignin to aromatic aldehydes with a decent yield by GO through the Cα activation of β-O-4 cleavage. A urea-hydrogen peroxide (UHP) oxidative process is followed to transform aldehydes in the depolymerized product to PAs by avoiding the undesired Dakin side reaction due to the electron-withdrawing effect of the acetyl group. This study opens a new way to selectively cleave lignin side chains to isolated biochemicals under mild conditions.

Enhanced Performance of Lignin Recovery with a Carbon Dioxide Acidification Method

Lignin particles were recovered from the bagasse soda pulping black liquor by acidification with carbon dioxide continuously fed in a semibatch reactor. An experimental model based on the response surface methodology was selected to investigate the effect of parameters and optimize the process for maximizing the lignin yield, and the physicochemical properties of the obtained lignin under the optimum conditions were investigated for further potential applications. A total of 15 experimental runs of three controlled parameters including temperature, pressure, and residence time were carried out based on the Box-Behnken design (BBD). The mathematic model for lignin yield prediction was successfully estimated at 99.7% accuracy. Temperature played a more significant role in lignin yield than pressure and residence time. Higher temperature could faciltate a higher lignin yield. Approximately 85 wt % lignin yield was obtained under the optimum conditions with a purity higher than 90%, high thermal stability, and slightly broad molecular weight distribution. The p-hydroxyphenyl-guaiacyl-syringyl (HGS)-type lignin structure and spherical shape were confirmed by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM). These characteristics confirmed that the obtained lignin could be used in high-value products. Moreover, this work indicated that the CO₂ acidification unit for lignin recovery could be efficiently improved for achieving high yield and purity from black liquor by adjustment of the process.

Systematic review on lignin valorization in the agro-food system: From sources to applications

Lignocellulosic biomass is the most abundant renewable resource on earth and currently most of this biomass is considered a low-value waste. Specifically, lignin is an underrated bioresource that is mostly burned for energy production and few value-added products have been created. Since the agro-food industry produces large amounts of wastes that can be potential sources of high-quality lignin, scientific efforts should be directed to this industry. Thus, this review provides a systematic overview of the trends and evolution of research on agro-food system-derived lignin (from 2010 to 2020), including the extraction of lignin from various agro-food sources and emergent applications of lignin in the agro-food chain. Crops with the highest average production/year (n = 26) were selected as potential lignin sources. The extraction process efficiency (yield) and lignin purity were used as indicators of the raw material potential. Overall, it is notable that research interest on agro-food lignin has increased exponentially over the years, both as source (567%) and application (128%). Wheat, sugarcane, and maize are the most studied sources and are the ones that render the highest lignin yields. As for the extraction methods used, alkaline and organosolv methods are the most employed (∼50%). The main reported applications are related to lignin incorporation in polymers (∼55%) and as antioxidant (∼24%). Studies on agro-food system-derived lignin is of most importance since there are numerous possible sources that are yet to be fully valorized and many promising applications that need to be further developed.

Effects of Inhibitors Generated by Dilute Phosphoric Acid Plus Steam-Exploded Poplar on Saccharomyces cerevisiae Growth

The pretreatment of lignocellulosic biomass is important for efficient bioethanol conversion, but causes undesirable by-products that inhibit microbial growth, conversely affecting the bioconversion efficiency. In this study, the main inhibitors derived from dilute phosphoric acid plus steam-exploded poplar wood were identified as 0.22 g/L furfural, 3.63 g/L acetic acid, 0.08 g/L syringaldehyde, etc., indicating the green nature and low toxicity of the pretreatment process. The effects of the three typical inhibitors (furfural, acetic acid, and syringaldehyde) on Saccharomyces cerevisiae 1517RM growth were analyzed and shown to prolong the lag phase of microbial growth to different degrees. In all the inhibitor groups, the ergosterol secretion was boosted, indicating low cell membrane fluidity and robustness of the strain to an adverse environment. The cell electronegativity and morphology of S. cerevisiae 1517RM also changed under different growth conditions, which was helpful for monitoring the physicochemical properties of cells. Furfural, acetic acid, and syringaldehyde had a synergistic effect on each other, providing an important reference to improving the subsequent ethanol fermentation process.

Extrapolation of design strategies for lignocellulosic biomass conversion to the challenge of plastic waste

The goal of cost-effective production of fuels and chemicals from biomass has been a substantial driver of the development of the field of metabolic engineering. The resulting design principles and procedures provide a guide for the development of cost-effective methods for degradation, and possibly even valorization, of plastic wastes. Here, we highlight these parallels, using the creative work of Lonnie O'Neal (Neal) Ingram in enabling production of fuels and chemicals from lignocellulosic biomass, with a focus on ethanol production as an exemplar process.

Opportunities and challenges for flow-through hydrothermal pretreatment in advanced biorefineries

Hydrothermal pretreatment (HTP) using only water offers great potential to reduce the overall cost of the bioconversion process. However, traditional HTP performed in a batch has limitations in removing lignin and often needs to be performed under severe conditions to achieve reasonable pretreatment effects. Lignin left in the pretreated residue at these conditions is also highly condensed, thus possessing an even more adverse impact on the hydrolysis process, which requires high enzyme loadings. To address these technical challenges, HTP performed in a flow-through configuration was developed to simultaneously achieve near-complete hemicellulose recovery, high lignin removal and high sugar release. Despite facing challenges such as potentially large water usage, flow-through HTP still represents one of the most cost-effective and eco-friendly pretreatment methods. This review mainly covers the latest cutting-edge innovations of flow-through HTP along with structural and compositional changes of cellulose, hemicellulose, and lignin before and after pretreatment.

Enzymatic conversion of pretreated lignocellulosic biomass: A review on influence of structural changes of lignin

The demands of energy sustainability drive efforts to bio-chemical conversion of biomass into biofuels through pretreatment, enzymatic hydrolysis, and microbial fermentation. Pretreatment leads to significant structural changes of the complex lignin polymer that affect yield and productivity of the enzymatic conversion of lignocellulosic biomass. Structural changes of lignin after pretreatment include functional groups, inter unit linkages and compositions. These changes influence non-productive adsorption of enzyme on lignin through hydrophobic interaction and electrostatic interaction as well as hydrogen bonding. This paper reviews the relationships between structural changes of lignin and enzymatic hydrolysis of pretreated lignocellulosic biomass. The formation of pseudo-lignin during dilute acid pretreatment is revealed, and their negative effect on enzymatic hydrolysis is discussed.

Micro- and Nanocellulose in Polymer Composite Materials: A Review

The high demand for plastic and polymeric materials which keeps rising every year makes them important industries, for which sustainability is a crucial aspect to be taken into account. Therefore, it becomes a requirement to makes it a clean and eco-friendly industry. Cellulose creates an excellent opportunity to minimize the effect of non-degradable materials by using it as a filler for either a synthesis matrix or a natural starch matrix. It is the primary substance in the walls of plant cells, helping plants to remain stiff and upright, and can be found in plant sources, agriculture waste, animals, and bacterial pellicle. In this review, we discussed the recent research development and studies in the field of biocomposites that focused on the techniques of extracting micro- and nanocellulose, treatment and modification of cellulose, classification, and applications of cellulose. In addition, this review paper looked inward on how the reinforcement of micro- and nanocellulose can yield a material with improved performance. This article featured the performances, limitations, and possible areas of improvement to fit into the broader range of engineering applications.

Improving probiotic spore yield using rice straw hydrolysate

Spore-forming Bacillus sp. has been extensively studied for their probiotic properties. In this study, an acid-treated rice straw hydrolysate was used as carbon source to produce the spores of Bacillus coagulans. The results showed that this hydrolysate significantly improved the spore yield compared with other carbon sources such as glucose. Three significant medium components including rice straw hydrolysate, MnSO₄ and yeast extract were screened by Plackett-Burman design. These significant variables were further optimized by response surface methodology (RSM). The optimal values of the medium components were rice straw hydolysate of 27% (v/v), MnSO₄ of 0·78 g l^-1 and yeast extract of 1·2 g l^-1 . The optimized medium and RSM model for spore production were validated in a 5 l bioreactor. Overall, this sporulation medium containing acid-treated rice straw hydrolysate has a potential to be used in the production of B. coagulans spores.

Development and validation of mathematical model of hydrotropic-reactive extraction of lignin

Hydrotropes have been largely explored as reactive extraction agent for lignin separation. In this paper, a mathematical model of hydrotropic-reactive extraction of sugarcane bagasse lignin was proposed and validated by experimental data from literature. The mathematical model was developed by assuming the particle is in slab shape, and by considering simultaneous processes of hydrotrope intra particle diffusion, second order reaction of lignin-hydrotrope, and intra-particle soluble delignification product diffusion. The proposed model results in a set of partial differential equations which were then solved by explicit finite difference approximation method. The mathematical model parameters were determined by fitting the model to the hydrotropic reactive extraction experimental data reported by Ansari and Gaikar (2014). Simulations show that the mathematical model of the hydrotropic-reactive extraction were well fitted to the experimental data with the obtained hydrotrope effective diffusivity (DeA) of 5.0 × 10−11 m2/s, effective diffusivity of soluble lignin product (DeC) of 9.0 × 10−12 m2/s and reaction rate constant (kr) of 1.78 × 10−10 m3/(g.s). It was also observed that the reaction was first order to the hydrotrope (n = 1), and one half order to the lignin (m = 0.5). Meanwhile the pseudo-stoichiometric mass ratio of hydrotrope to lignin was 6.4 g hydrotrope/g lignin.

Treatment of Coffee Husk with Ammonium-Based Ionic Liquids: Lignin Extraction, Degradation, and Characterization

Four ammonium-based ionic liquids were synthesized for the selective extraction and degradation of lignin from coffee husk. The extracted lignin samples were characterized by Fourier transform infrared, gel permeation chromatography, gas chromatography-mass spectrometry, UV-vis, ¹H and ¹³C NMR, heteronuclear single-quantum coherence-NMR, thermogravimetric analysis, X-ray diffraction, and field emission scanning electron microscopy analyses. The analyzed results confirmed that these ionic liquids are able to effectively extract and decompose the lignin to smaller molecules from the biomass. Experimental results show that a significantly high yield, 71.2% of the original lignin, has been achieved. This processing method is an efficient, economical, and environmentally friendly green route for producing high-added-value lignin from wasted coffee husk.

Understanding Lignin Aggregation Processes. A Case Study: Budesonide Entrapment and Stimuli Controlled Release from Lignin Nanoparticles

The mechanism of lignin nanoprecipitation and subsequent self-assembly was elucidated by studying generation of lignin nanoparticles (LNPs) from aqueous ethanol. LNP formation was found to follow a kinetically controlled nucleation-growth mechanism in which large lignin molecules formed the initial critical nuclei. Using this information, we demonstrate entrapment of budesonide in LNPs and subsequent pH-triggered and surfactant-responsive release of this synthetic anti-inflammatory corticosteroid. Overall, our results not only provide a promising intestinal delivery system for budesonide but also deliver fundamental mechanistic understanding for the entrapment of actives in LNPs with controlled size and release properties.

Bio-based polyurethane foam preparation employing lignin from corn stalk enzymatic hydrolysis residues

Enzymatic hydrolysis residues (EHR) from corn stalk are industrial waste from the cellulosic ethanol industry. Lignin was separated as a bio-based polyol from EHR replacing partial petroleum-based polyether polyol to prepare bio-based polyurethane (BPU) foams without any other biomass pretreatment. Single factor experiment and response surface methodology (RSM) were employed to optimize separation conditions and reveal the significant influence of the interaction of conditions on the yield of separated lignin (SL). The effect of SL content (2.5, 5.0, 7.5, 10 and 15%) on the foams morphology and mechanical properties was assessed. Scanning electron microscopy (SEM) results implied that the cell shape was considerably affected by the large SL content, which contributed to an irregular, inhomogeneous, and thick cell wall. An astonishing 9.56 times increase in the compressive modulus and exponential 97.93 times boost in the compressive strength of BPU foams were attributed to the content of 15% SL without any further surface chemical modification. This present paper reports a green, potential and promising method for complete utilization of lignin from EHR in consideration of their abundant supply to greatly enhance the mechanical properties of BPU foams.

Enzymatic hydrolysis residues (EHR) from corn stalk are industrial waste from the cellulosic ethanol industry.

Fates of hemicellulose, lignin and cellulose in concentrated phosphoric acid with hydrogen peroxide (PHP) pretreatment

Xylan, de-alkaline lignin and microcrystalline cellulose were employed as representative models of hemicellulose, lignin and cellulose in lignocellulosic biomass. These three model compounds, together with the real-world biomass, wheat straw were pretreated using the newly developed PHP pretreatment (concentrated phosphoric acid plus hydrogen peroxide) to better understand the structural changes of the recovered solid and chemical fractions in the liquid. Results showed that almost all xylan and higher than 70% lignin were removed from wheat straw, and more than 90% cellulose was recovered in the solid fraction. The pretreated model xylan recovered via ethanol-precipitation still maintained its original structural features. The degree of polymerization of soluble xylooligosaccharides in liquid was reduced, resulting in the increase of monomeric xylose release. Further xylose oxidization via the path of 2-furancarboxylic acid → 2(5H)-furanone → acrylic acid → formic acid was mainly responsible for xylan degradation. The chemical structure of de-alkaline lignin was altered significantly by PHP pretreatment. Basic guaiacyl units of lignin were depolymerized, and aromatic rings and side aliphatic chains were partially decomposed. Ring-opening reactions of the aromatics and cleavage of C–O–C linkages were two crucial paths to lignin oxidative degradation. In contrast to lignin, no apparent changes occurred on microcrystalline cellulose. The reason was likely that acid-depolymerization and oxidative degradation of cellulose were greatly prevented by the formed cellulose phosphate.

The transformation of cellulose, hemicellulose, and lignin in lignocellulosic biomass in a novel pretreatment are elucidated based on model fractions.

Evaluation of lignins from side-streams generated in an olive tree pruning-based biorefinery: Bioethanol production and alkaline pulping

In modern lignocellulosic-based biorefineries, carbohydrates can be transformed into biofuels and pulp and paper, whereas lignin is burned to obtain energy. However, a part of lignin could be converted into value-added products including bio-based aromatic chemicals, as well as building blocks for materials. Then, a good knowledge of lignin is necessary to define its valorisation procedure. This study characterized different lignins from side-streams produced from olive tree pruning bioethanol production (lignins collected from steam explosion pretreatment with water or phosphoric acid as catalysts, followed by simultaneous saccharification and fermentation process) and alkaline pulping (lignins recovered from kraft and soda-AQ black liquors). Together with the chemical composition, the structure of lignins was investigated by FTIR, ¹³C NMR, and 2D NMR. Bioethanol lignins had clearly distinct characteristics compared to pulping lignins; a certain number of side-chain linkages (mostly alkyl-aryl ether and resinol) accompanied with lower phenolic hydroxyls content. Bioethanol lignins also showed a significant amount of carbohydrates, mainly glucose and protein impurities. By contrast, pulping lignins revealed xylose together with a dramatical reduction of side-chains (some resinol linkages survive) and thereby higher phenol content, indicating rather severe lignin degradation during alkaline pulping processes. All lignins showed a predominance of syringyl units.

Understanding the structural and chemical changes of plant biomass following steam explosion pretreatment

BACKGROUND

Biorefining of lignocellulosic biomass has become one of the most valuable alternatives for the production of multi-products such as biofuels. Pretreatment is a prerequisite to increase the enzymatic conversion of the recalcitrant lignocellulose. However, there is still considerable debate regarding the key features of biomass impacting the cellulase accessibility. In this study, we evaluate the structural and chemical features of three different representative biomasses (Miscanthus × giganteus, poplar and wheat straw), before and after steam explosion pretreatment at increasing severities, by monitoring chemical analysis, SEM, FTIR and 2D NMR.

RESULTS

Regardless the biomass type, combined steam explosion pretreatment with dilute sulfuric acid impregnation resulted in significant improvement of the cellulose conversion. Chemical analyses revealed that the pretreatment selectively degraded the hemicellulosic fraction and associated cross-linking ferulic acids. As a result, the pretreated residues contained mostly cellulosic glucose and lignin. In addition, the pretreatment directly affected the cellulose crystallinity but these variations were dependent upon the biomass type. Important chemical modifications also occurred in lignin since the β-O-4' aryl-ether linkages were found to be homolytically cleaved, followed by some recoupling/recondensation to β-β' and β-5' linkages, regardless the biomass type. Finally, 2D NMR analysis of the whole biomass showed that the pretreatment preferentially degraded the syringyl-type lignin fractions in miscanthus and wheat straw while it was not affected in the pretreated poplar samples.

CONCLUSIONS

Our findings provide an enhanced understanding of parameters impacting biomass recalcitrance, which can be easily generalized to both woody and non-woody biomass species. Results indeed suggest that the hemicellulose removal accompanied by the significant reduction in the cross-linking phenolic acids and the redistribution of lignin are strongly correlated with the enzymatic saccharification, by loosening the cell wall structure thus allowing easier cellulase accessibility. By contrast, we have shown that the changes in the syringyl/guaiacyl ratio and the cellulose crystallinity do not seem to be relevant factors in assessing the enzymatic digestibility. Some biomass type-dependent and easily measurable FTIR factors are highly correlated to saccharification.

Effect of bisulfite treatment on composition, structure, enzymatic hydrolysis and cellulase adsorption profiles of sugarcane bagasse

The effect of sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) on composition, structure, enzymatic hydrolysis and cellulase adsorption profiles of sugarcane bagasse (SCB) was investigated. SPORL gave a higher SCB hydrolysis yield (85.33%) compared to dilute acid pretreatment (DA) (64.39%). The SEM pictures showed that SPORL SCB structure became more disordered and looser, suggesting SPORL SCB was more accessible to cellulase. The zeta potential of SPORL SCB suspension (-21.89mV) was significantly different from that of DA SCB (-12.87mV), which demonstrated the lignin in SPORL SCB was more hydrophilic. With regard to cellulase adsorption profiles, SPORL SCB had a lower non-productive adsorption (14.87mg/glignin) and a higher productive adsorption (37.67 mg/gcarbohydrate) compared with DA SCB (17.05mg/glignin; 25.79mg/gcarbohydrate). These results indicated that SPORL SCB had better accessibility to cellulase and the higher productive cellulase adsorption of SPORL SCB had improved hydrolysis.

Valorization of lignin and cellulose in acid-steam-exploded corn stover by a moderate alkaline ethanol post-treatment based on an integrated biorefinery concept

BACKGROUND

Due to the unsustainable consumption of fossil resources, great efforts have been made to convert lignocellulose into bioethanol and commodity organic compounds through biological methods. The conversion of cellulose is impeded by the compactness of plant cell wall matrix and crystalline structure of the native cellulose. Therefore, appropriate pretreatment and even post-treatment are indispensable to overcome this problem. Additionally, an adequate utilization of coproduct lignin will be important for improving the economic viability of modern biorefinery industries.

RESULTS

The effectiveness of moderate alkaline ethanol post-treatment on the bioconversion efficiency of cellulose in the acid-steam-exploded corn stover was investigated in this study. Results showed that an increase of the alcoholic sodium hydroxide (NaOH) concentration from 0.05 to 4% led to a decrease in the lignin content in the post-treated samples from 32.8 to 10.7%, while the cellulose digestibility consequently increased. The cellulose conversion of the 4% alcoholic NaOH integrally treated corn stover reached up to 99.3% after 72 h, which was significantly higher than that of the acid steam exploded corn stover without post-treatment (57.3%). In addition to the decrease in lignin content, an expansion of cellulose I lattice induced by the 4% alcoholic NaOH post-treatment played a significant role in promoting the enzymatic hydrolysis of corn stover. More importantly, the lignin fraction (AL) released during the 4% alcoholic NaOH post-treatment and the lignin-rich residue (EHR) remained after the enzymatic hydrolysis of the 4% alcoholic NaOH post-treated acid-steam-exploded corn stover were employed to synthesize lignin-phenol-formaldehyde (LPF) resins. The plywoods prepared with the resins exhibit satisfactory performances.

CONCLUSIONS

An alkaline ethanol system with an appropriate NaOH concentration could improve the removal of lignin and modification of the crystalline structure of cellulose in acid-steam-exploded corn stover, and consequently significantly improve the conversion of cellulose through enzymatic hydrolysis for biofuel production. The lignin fractions obtained as byproducts could be applied in high performance LPF resin preparation. The proposed model for the integral valorization of corn stover in this study is worth of popularization.

Biomass pretreatments capable of enabling lignin valorization in a biorefinery process

Recent techno-economic studies of proposed lignocellulosic biorefineries have concluded that creating value from lignin will assist realization of biomass utilization into valuable fuels, chemicals, and materials due to co-valorization and the new revenues beyond carbohydrates. The pretreatment step within a biorefinery process is essential for recovering carbohydrates, but different techniques and intensities have a variety of effects on lignin. Acidic and alkaline pretreatments have been shown to produce diverse lignins based on delignification chemistry. The valorization potential of pretreated lignin is affected by its chemical structure, which is known to degrade, including inter-lignin condensation under high-severity pretreatment. Co-valorization of lignin and carbohydrates will require dampening of pretreatment intensities to avoid such effects, in spite of tradeoffs in carbohydrate production.

Biomimetic Fenton-catalyzed lignin depolymerization to high-value aromatics and dicarboxylic acids

By mimicking natural lignin degradation systems, the Fenton catalyst (Fe(3+), H2O2) can effectively facilitate lignin depolymerization in supercritical ethanol (7 MPa, 250 °C) to give organic oils that consist of mono- and oligomeric aromatics, phenols, dicarboxylic acids, and their derivatives in yields up to (66.0±8.5) %. The thermal properties, functional groups, and surface chemistry of lignin before and after Fenton treatment were examined by thermogravimetric analysis, pyrolysis-gas chromatography-mass spectrometry, (31)P NMR spectroscopy, and X-ray photoelectron spectroscopy. The results suggest that the Fenton catalyst facilitates lignin depolymerization through cleavage of β-ether bonds between lignin residues. The formation of a lignin-iron chelating complex effectively depresses lignin recondensation; thus minimizing charcoal formation and enhancing the yield of liquid products.

Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure

BACKGROUND

Pretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconversion of lignocelluloses by breaking down the biomass recalcitrance. In this work, a novel pretreatment method using ethylenediamine (EDA) was presented as a simple process to achieve high enzymatic digestibility of corn stover (CS) by heating the biomass-EDA mixture with high solid-to-liquid ratio at ambient pressure. The effect of EDA pretreatment on lignocellulose was further studied.

RESULTS

High enzymatic digestibility of CS was achieved at broad pretreatment temperature range (40-180 °C) during EDA pretreatment. Herein, X-ray diffractogram analysis indicated that cellulose I changed to cellulose III and amorphous cellulose after EDA pretreatment, and cellulose III content increased along with the decrease of drying temperature and the increase of EDA loading. Lignin degradation was also affected by drying temperature and EDA loading. Images from scanning electron microscope and transmission electron microscope indicated that lignin coalesced and deposited on the biomass surface during EDA pretreatment, which led to the delamination of cell wall. HSQC NMR analysis showed that ester bonds of p-coumarate and ferulate units in lignin were partially ammonolyzed and ether bonds linking the phenolic monomers were broken during pretreatment. In addition, EDA-pretreated CS exhibited good fermentability for simultaneous saccharification and co-fermentation process.

CONCLUSIONS

EDA pretreatment improves the enzymatic digestibility of lignocellulosic biomass significantly, and the improvement was caused by the transformation of cellulose allomorph, lignin degradation and relocalization in EDA pretreatment.

Improvement of lignin yield and purity from corncob in the presence of steam explosion and liquid hot pressured alcohol

Non-food biomass such as corncob is a very abundant and promising feedstock for sustainable energy production in China.

Bioethanol from lignocellulosic biomass: current findings determine research priorities

“Second generation” bioethanol, with lignocellulose material as feedstock, is a promising alternative for first generation bioethanol. This paper provides an overview of the current status and reveals the bottlenecks that hamper its implementation. The current literature specifies a conversion of biomass to bioethanol of 30 to ~50% only. Novel processes increase the conversion yield to about 92% of the theoretical yield. New combined processes reduce both the number of operational steps and the production of inhibitors. Recent advances in genetically engineered microorganisms are promising for higher alcohol tolerance and conversion efficiency. By combining advanced systems and by intensive additional research to eliminate current bottlenecks, second generation bioethanol could surpass the traditional first generation processes.

Effects of acid impregnated steam explosion process on xylose recovery and enzymatic conversion of cellulose in corncob

Corncob residue is a cellulose-rich byproduct obtained from industrial xylose production via dilute acid hydrolysis processes. Enzymatic hydrolysis of cellulose in acid hydrolysis residue of corncob (AHRC) is often less efficient without further pretreatment. In this work, the process characteristics of acid impregnated steam explosion were studied in conjunction with a dilute acid process, and their effects on physiochemical changes and enzymatic saccharification of corncob residue were compared. With the acid impregnated steam explosion process, both higher xylose recovery and higher cellulose conversion were obtained. The maximum conversion of cellulose in acid impregnated steam explosion residue of corncob (ASERC) reached 85.3%, which was 1.6 times higher than that of AHRC. Biomass compositional analysis showed similar cellulose and lignin content in ASERC and AHRC. XRD analysis demonstrated comparable crystallinity of ASERC and AHRC. The improved enzymatic hydrolysis efficiency was attributed to higher porosity in ASERC, measured by mercury porosimetry.

Enhancement of total sugar and lignin yields through dissolution of poplar wood by hot water and dilute acid flowthrough pretreatment

BACKGROUND

Pretreatment is a vital but expensive step in biomass biofuel production. Overall, most of this past effort has been directed at maximizing sugar yields from hemicellulose and cellulose through trials with different chemicals, operating conditions, and equipment configurations. Flowthrough pretreatment provides a promising platform to dissolution of lignocellulosic biomass to generate high yields of fermentable sugars and lignin for biofuels productions.

RESULTS

Dissolution of xylan, lignin, and cellulose from poplar wood were significantly enhanced by water-only and dilute acid (0.05% w/w, H2SO4) flowthrough pretreatment when the temperature was raised from 200°C to 280°C over a range of flow rates 10-62.5 mL/min, resulting in more than 98% solid removal. Up to 40% of original xylan was converted to xylose in the hydrolyzate and the rest xylan was solubilized into xylooligomers with negligible furfural formation. Up to 100% cellulose was removed into hydrolyzate with the highest glucose yield of 60% and low 5-hydroxymethylfurfural (5-HMF) formation. The maximal recovered insoluble lignin and soluble lignin were 98% and 15% of original lignin, respectively. In addition, enzymatic hydrolysis of pretreated whole slurries was characterized under various enzyme loadings with or without Bovine serum albumin (BSA) treatment. More than 90% glucose yield and 95% xylose yield were obtained from enzymatic hydrolysis of dilute acid pretreated whole slurries with 10 mg protein Ctec 2 with 2 mg Htec2/g glucan + xylan.

CONCLUSIONS

Nearly complete dissolution of whole biomass was realized through water-only and dilute acid flowthrough pretreatment under tested conditions. Temperature was considered as the most significant factor for cellulose degradation. The cellulose removal significantly increased as temperature reached 240°C for water-only and 220°C for dilute acid. Dilute acid pretreatment resulted in higher yields of recovered xylan and cellulose as monomeric sugars in the hydrolyzate than that for water-only pretreatment. Enzymes readily hydrolyzed the degraded cellulose and xylooligomers in pretreatment hydrolysate. Results suggested that kinetics controlled the flowthrough pretreatment of biomass dissolution, which was also affected by flow rate to certain extent.