Direct Conversion Of Lignocellulosic Biomass Research Articles

Integrated Catalytic Upgrading of Biomass-Derived Alcohols for Advanced Biofuel Production

Sustainable biofuel production is necessary to meet the daunting challenge of “fueling” growing economies with a significantly reduced carbon footprint. Although its higher oxygen content often hinders the direct conversion of lignocellulosic biomass (LCB) into energy-dense biofuels, microbial biofuel production from LCB still has potential. The production of primary alcohols by acetone–butanol–ethanol (ABE) fermentation has been practiced for more than a century to attain near-theoretical maximum. However, ABE produced conventionally by native microorganisms is not equivalent to fossil fuel-based aviation fuels in terms of energy density, volatility, and cost-efficiency. Various strategies have been adapted for the microbial synthesis of advanced fuels from renewable feedstock with the advancements in genetic engineering. Yet, the presence of inhibitors and the inefficiency of microbes to utilize or transport the sugar mixtures from LCB often impede titer and yield. However, ABE mixtures can act as platform chemicals to synthesize high-value biofuels by biocatalytic or chemo-catalytic applications. Chemical catalysts, in particular, are used to produce higher alcohols ranging from 3-carbon to 20-carbon fuels from the ABE fermentation mixture. This article reviews the recent trends in the production of higher biofuels from ABE mixtures using biological and chemical catalysts. Focus is placed on genomic and metabolic engineering strategies implemented to upgrade microbes for higher biofuel production via the fermentation of renewable feedstocks. This paper also summarizes the advancements in the chemical conversion route of an ABE fermentation mixture into higher biofuels. Finally, the review provides insights into future research toward commercializing renewable and sustainable higher biofuels and chemicals.

Highly Efficient Synthesis of C5/C6 Sugar Alcohols from Bamboo Enabled by Mechanocatalytic Depolymerization

The exploitation of an efficient method for direct conversion of lignocellulosic biomass into various high valuable chemicals remains a huge challenge in the chemical industry. Here, mechanocatalytic depolymerization in the presence of H2SO4 combined with hydrogenation with Ru/C was used to produce C5/C6 sugar alcohols starting from bamboo, which are important platform chemicals. A high yield of C5/C6 sugar alcohols was obtained, up to 91.9%, under optimal reaction conditions. The pretreatment improved the conversion and yield of the desired products by effective depolymerization of bamboo into oligosaccharides through “dry” acid-catalyzed hydrolysis of 1,4-β-glycosidic bonds. It was found that the state of Ru species significantly influenced the activity of the Ru/C catalyst. The Ru/C catalyst containing Ru and RuO2 species with the RuO2/Ru ratio of 0.56–1.44 exhibited high catalytic activity in the transformation of bamboo into C5/C6 sugar alcohols. This work provided an effective and potential route to utilize bamboo processing residues to produce high-valued chemicals.

Efficient direct conversion of lignocellulosic biomass into biobased platform chemicals in ionic liquid-water medium

In this study, the conversion of corn straw, sorghum and cellulose into valuable chemicals (furfural, 5-hydroxymethylfurfural, levulinic acid) in different ionic liquid-water medium were investigated. Different reaction parameters such as reaction temperature, time and solvent ratio were optimized to achieve the highest conversion of biomass and selectivity of the products. Under the optimal reaction conditions (180 °C, 30 min, 1:5 ratio), 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) was found to display the highest efficiency which can be attributed to the acidic character of the ionic liquid. 117.4 mg levulinic acid, 11.8 mg 5-hydroxymethylfurfural and 9.4 mg furfural were obtained per g of sorghum. The results showed that 5-fold higher quantity of LA was obtained from sorghum biomass in comparison with pure cellulose. In addition, Amberlyst-15 was examined as a solid acid catalyst for conversion of cellulose in [BMIM]HSO4-water solvent system resulting in 4.6-fold increase in the quantity of levulinic acid. This study provides an alternative single step approach for production of valuable chemicals from renewable biomass.

Endogenous carbohydrate esterases of Clostridium thermocellum are identified and disrupted for enhanced isobutyl acetate production from cellulose.

Medium-chain esters are versatile chemicals with broad applications as flavors, fragrances, solvents, and potential drop-in biofuels. Currently, these esters are largely produced by the conventional chemical process that uses harsh operating conditions and requires high energy input. Alternatively, the microbial conversion route has recently emerged as a promising platform for sustainable and renewable ester production. The ester biosynthesis pathways can utilize either lipases or alcohol acyltransferase (AAT), but the AAT-dependent pathway is more thermodynamically favorable in an aqueous fermentation environment. Even though a cellulolytic thermophile Clostridium thermocellum harboring an AAT-dependent pathway has recently been engineered for direct conversion of lignocellulosic biomass into esters, the production is not efficient. One potential bottleneck is the ester degradation caused by the endogenous carbohydrate esterases (CEs) whose functional roles are poorly understood. The challenge is to identify and disrupt CEs that can alleviate ester degradation while not negatively affecting the efficient and robust capability of C. thermocellum for lignocellulosic biomass deconstruction. In this study, by using bioinformatics, comparative genomics, and enzymatic analysis to screen a library of CEs, we identified and disrupted the two most critical CEs, Clo1313_0613 and Clo1313_0693, that significantly contribute to isobutyl acetate degradation in C. thermocellum. We demonstrated that an engineered esterase-deficient C. thermocellum strain not only reduced ester hydrolysis but also improved isobutyl acetate production while maintaining effective cellulose assimilation.

Construction of electron transfer chains with methylene blue and ferric ions for direct conversion of lignocellulosic biomass to electricity in a wide pH range

To achieve direct conversion of lignocellulosic biomass to electricity, electron transfer chains (ETCs) were constructed with organic redox compounds and ferric ions as the anode and cathode electron carriers, respectively. Methylene blue (MB) was screened as a promising anode electron carrier with good redox properties and being capable of efficiently working under both acidic and alkaline conditions. Acid or alkali electrolyte played important roles in depolymerization of cellulose and lignin, as well as the deconstruction of biomass (wheat straw) cell wall; however, the presence of MB well facilitated the degradation of cellulose and solublization of wheat straw polymeric components. The reduced MB (MBH) could be well re-oxidized and discharged in a liquid-flow fuel cell (LFFC). The highest out-put power densities (Pmax) of the LFFC under acidic and alkali conditions reached 12.3 and 41.8 mW/cm2 with open circuit voltages of 560 and 1560 mV, respectively.

Direct conversion of lignocellulosic biomass into aromatic monomers over supported metal catalysts in supercritical water

With the goal of contributing to the valorization of lignocellulosic biomass, we investigated the conversion of Japanese cedar and bagasse into aromatic monomers over charcoal-supported metal catalysts in supercritical water. Over Ru/C, Japanese cedar was converted into gaseous products such as methane and carbon dioxide. Pd/C, Pt/C, and Rh/C were active for the conversion of Japanese cedar into aromatic monomers, and the monomer yields over these catalysts decreased in the order Pt/C > Rh/C > Pd/C when the conversion reaction was carried out at 673 K for 1 h. Bagasse, an herbaceous biomass, could also be converted into aromatic monomers by reaction over Pt/C, Rh/C, or Pd/C at 673 K for 1 h. Catalyst reusability experiments revealed that the activities of Pt/C and Rh/C for Japanese cedar conversion increased with reuse, up until the third reuse.

Bioaugmentation with Clostridium tyrobutyricum to improve butyric acid production through direct rice straw bioconversion

One-pot bioconversion is an economically attractive biorefinery strategy to reduce enzyme consumption. Direct conversion of lignocellulosic biomass for butyric acid production is still challenging because of competition among microorganisms. In a consolidated hydrolysis/fermentation bioprocessing (CBP) the microbial structure may eventually prefer the production of caproic acid rather than butyric acid production. This paper presents a new bioaugmentation approach for high butyric acid production from rice straw. By dosing 0.03 g/L of Clostridium tyrobutyricum ATCC 25755 in the CBP, an increase of 226% higher butyric acid was yielded. The selectivity and concentration also increased to 60.7% and 18.05 g/L, respectively. DNA-sequencing confirmed the shift of bacterial community in the augmented CBP. Butyric acid producer was enriched in the bioaugmented bacterial community and the bacteria related to long chain acids production was degenerated. The findings may be useful in future research and process design to enhance productivity of desired bio-products.

Direct conversion of lignocellulosic biomass to biomimetic tendril-like functional carbon helices: a protein friendly host for cytochrome C

Tendril-like functional carbon helices (TLFCHs) was successfully prepared directly from Parthenium hysterophorus using a solvothermal method employing a deep eutectic solvent as both soft template and catalyst. TLFCHs showed significant potential as a host for an enzyme without compromising the catalytic activity.

Solid state fermentation by cellulolytic oleaginous fungi for direct conversion of lignocellulosic biomass into lipids: Fed-batch and repeated-batch fermentations

Lignocellulosic wastes from palm oil mill are one of attractive feedstocks for microbial lipid production by oleaginous microorganisms because of their low cost, renewable nature and abundance. In this study, four filamentous fungi with cellulolytic activity were screened as potential oleaginous microorganisms for direct conversion of these lignocellulosic wastes into lipid. Among them, Aspergillus tubingensis TSIP9 accumulated lipid at the highest amount of 39.5±2.2mg per gram dry substrate (gds), and simultaneously produced high activities of cellulase (2.35±0.22U/gds) and xylanase (11.83±0.18U/gds) through solid state fermentation (SSF) of palm empty fruit bunches (EFB). The use of EFB mixed with palm kernel cake (PK) promoted lipid production by the fungi up to 79.9±3.5mg/gds. When the enzymes were extracted from the first batch and reused in the next batch, A. tubingensis TSIP9 produced much higher amount of enzymes and accumulated lipid faster. Fed-batch SSF with intermittent adding of EFB could be applied for lipid production but with a decrease in the enzyme activity. When repeated-batch SSF with 90% replacement with new substrate was applied, both lipid and enzymes were efficiently produced for long period of fermentation. This new strategy for solid state fermentation may contribute greatly to the commercialized enzyme and lipid productions from abundant lignocellulosic biomass.

Bioconversion of lignocellulosic palm byproducts into enzymes and lipid by newly isolated oleaginous fungi

Direct conversion of palm pressed fiber (PPF) and palm empty fruit bunches (EFB) into enzymes and lipid by oleaginous fungi were performed through solid-state fermentation (SSF). Among the strains tested, TSIP9 converted PPF and EFB into lipid with the highest yield of 31.1±1.7mg/gram dry substrate (gds) and 37.5±2.2mg/gds, respectively. It also produced high activity of cellulolytic enzymes. It was identified as Aspergillus tubingensis. The similar fatty acids of its lipid to those of plant oil indicate its suitable use as biodiesel feedstock. The cellulase and xylanase production by this strain was improved when EFB was pretreated with alkaline. When alkaline-pretreated EFB was added with palm kernel cake (PK) as an alternative nitrogen source and the culture conditions were optimized through response surface methodology (RSM), the production of lipid, cellulase and xylanase were increased up to 88.5±4.9mg/gds, 26.1±0.1U/gds and 59.3±0.3U/gds, respectively. This study reveals the potential use of in situ cellulolytic enzymes producing fungi and the optimal conditions for direct conversion of lignocellulosic biomass into lipid.