Modern Biorefineries Research Articles

Impact of hot water pretreatment temperature on the pyrolysis of birch wood

Hydrothermal treatment of wood is an integral part of a modern biorefinery concept. Our research is devoted to the study of properties of birch wood and lignocelluloses at its base after hydrothermal treatment at various temperatures using TG and Py-GC/FID/MS. It was found that treatment in temperature range 150–200°C led to increase of the content of pyrolysis volatiles due to the increase of the content of the main cellulose product—levoglucosan, while the content of the phenolic products was practically constant. Due to hydrolytic processes and condensation reactions in the temperature range 200–250°C the content of all carbohydrate derived volatiles decreased and the content of lignin destruction products increased mainly at the expense of dimethoxylated derivatives.

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

BackgroundDue 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.ResultsThe 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.ConclusionsAn 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.

A review of the potential of pretreated solids to improve gas biofuels production in the context of an OFMSW biorefinery

The organic fraction of municipal solid waste (OFMSW), mainly composed of lignocellulosic polymers, is extremely complex. Therefore, it is necessary to apply pretreatments to remove the lignin content and decrease the cellulose crystallinity in order to use the OFMSW for gas biofuels production in the context of biorefineries from waste. This work focused on critically reviewing the conventional pretreatments applied to OFMSW, with the goal of improving the H2 production, as well as other biofuels in modern biorefineries. There are a wide variety of pretreatments that have successfully been used, mainly alkaline, milling and dilute acid. In addition, some research has focused on the recovery and reutilization of the alkali, acid or solvents after the pretreatment, to be incorporated into new cycles of production, minimizing the environmental impacts. Moreover, it would be necessary to incorporate analytical tools, in order to determine the sustainability of the biorefinery project. It is concluded that waste pretreatments could significantly contribute to increased yields of biogas fuels in organic waste-based biorefineries. Therefore, establishing preliminary stages for conditioning biomass or wastes is essential to improve the degradation of wastes and bio-product generation. © 2016 Society of Chemical Industry

Advances in Upgrading Lignin Pyrolysis Vapors by Ex Situ Catalytic Fast Pyrolysis

AbstractLignin, a highly branched, substituted, mononuclear aromatic polymer, is one of the principal components of lignocellulosic biomass. Its valorization is considered an important part of the modern biorefinery scheme. However, as a result of the natural complexity and high stability of lignin, its depolymerization and the following conversion are challenging. The unique structure and composition of lignin offer many possible routes to produce liquid fuels and chemicals. Recognized as an efficient and feasible process, ex situ catalytic fast pyrolysis (CFP) has attracted much attention for upgrading lignin and lignin pyrolysis vapors. The main challenge of this process is the development of active and stable catalysts that can effectively break the C−O bond of lignin and decompose the intermediates. In this Review, we aim to provide an overview of recent advances on a related topic. The Review introduces ex situ CFP, the reactions and pathways of lignin vapors in the ex situ CFP process, and summarizes in detail recent progress in experimental studies on upgrading lignin‐derived model phenols, lignin, and lignin pyrolysis vapors to hydrocarbons by the ex situ CFP process over different catalysts.

Carbon Sources for Polyhydroxyalkanoates and an Integrated Biorefinery

Polyhydroxyalkanoates (PHAs) are a group of bioplastics that have a wide range of applications. Extensive progress has been made in our understanding of PHAs’ biosynthesis, and currently, it is possible to engineer bacterial strains to produce PHAs with desired properties. The substrates for the fermentative production of PHAs are primarily derived from food-based carbon sources, raising concerns over the sustainability of their production in terms of their impact on food prices. This paper gives an overview of the current carbon sources used for PHA production and the methods used to transform these sources into fermentable forms. This allows us to identify the opportunities and restraints linked to future sustainable PHA production. Hemicellulose hydrolysates and crude glycerol are identified as two promising carbon sources for a sustainable production of PHAs. Hemicellulose hydrolysates and crude glycerol can be produced on a large scale during various second generation biofuels’ production. An integration of PHA production within a modern biorefinery is therefore proposed to produce biofuels and bioplastics simultaneously. This will create the potential to offset the production cost of biofuels and reduce the overall production cost of PHAs.

Lignin Conversion: Opportunities and Challenges for the Integrated Biorefinery

Abstract The utilization of lignin for fungible fuels and products represents one of the most imminent challenges in the modern biorefinery because most of the bioprocesses for lignocellulosic biofuels results in a lignin-containing waste stream. Considering lignin's abundance and relatively high energy content, this waste stream can be used as a feedstock for value-added products to improve the sustainability and economic feasibility of the biorefinery. Bioconversion of lignin with microbes recently emerged as an alternative lignin-valorization approach with significant potential. Typically, the microbial bioconversion of lignin requires three major steps: lignin depolymerization, aromatic compounds catabolism, and target product biosynthesis. In this review, we summarize the most recent advances in lignin bioconversion to address the challenges in each of the three steps. We further discuss strategies and perspectives for future research to address the challenges in bioconversion of lignin.

Performance of New and Traditional Fiber Hemp (Cannabis sativa L.) Cultivars for Novel Applications: Stem, Bark, and Core Yield and Chemical Composition

Finding a use for all components of hemp is key to improving the overall economics of fiber production from this crop. In this context, the core, a by-product of fiber production, has become increasingly important for new innovative applications. The aim of the present study was to compare traditional and new dioecious and monoecious fiber hemp cultivars in a 2-year field experiment in Central Italy, evaluating the variations on their fiber yield, bark and core production, and their chemical composition. The obtained results underlined the interesting potentiality of the new dioecious genotypes characterized by interesting fiber and nonfiber components which make their utilization appealing in several woven and nonwoven applications. Thanks to the interesting chemical properties recorded for the core fraction, the full use of hemp biomass in a cascade approach can contribute to the total valorization of this versatile fiber crop for a modern biorefinery facility.

Base-Catalyzed Depolymerization of Biorefinery Lignins

Lignocellulosic biorefineries will produce a substantial pool of lignin-enriched residues, which are currently slated to be burned for heat and power. Going forward, however, valorization strategies for residual solid lignin will be essential to the economic viability of modern biorefineries. To achieve these strategies, effective lignin depolymerization processes will be required that can convert specific lignin-enriched biorefinery substrates into products of sufficient value and market size. Base-catalyzed depolymerization (BCD) of lignin using sodium hydroxide and other basic media has been shown to be an effective depolymerization approach when using technical and isolated lignins relevant to the pulp and paper industry. To gain insights in the application of BCD to lignin-rich, biofuels-relevant residues, here we apply BCD with sodium hydroxide at two catalyst loadings and temperatures of 270, 300, and 330 °C for 40 min to residual biomass from typical and emerging biochemical conversion processes. We obtained mass balances for each fraction from BCD, and characterized the resulting aqueous and solid residues using gel permeation chromatography, NMR, and GC–MS. When taken together, these results indicate that a significant fraction (45–78%) of the starting lignin-rich material can be depolymerized to low molecular weight, water-soluble species. The yield of the aqueous soluble fraction depends significantly on biomass processing method used prior to BCD. Namely, dilute acid pretreatment results in lower water-soluble yields compared to biomass processing that involves no acid pretreatment. Also, we find that the BCD product selectivity can be tuned with temperature to give higher yields of methoxyphenols at lower temperature, and a higher relative content of benzenediols with a greater extent of alkylation on the aromatic rings at higher temperature. Overall, this study shows that residual, lignin-rich biomass produced from conventional and emerging biochemical conversion processes can be depolymerized with sodium hydroxide to produce significant yields of low molecular weight aromatics that potentially can be upgraded to fuels or chemicals.

Catalytic Conversion of Empty Fruit Bunch (EFB) Fibres into Lactic Acid by Lead (II) ions

Lactic acid (LA) is a potential platform chemical that can be produced from lignocellulosic biomass. The development of a cost-competitive, catalytic-based LA production system is gaining significant attention in modern biorefineries. A series of experimental study was carried out to investigate the chemocatalytic effect of the conversion of oil palm empty fruit bunch (EFB) fibers into lactic acid under hydrothermal conditions. Synthesis of chemicals from lignocellulosic biomass involves complex mechanisms because of the complex composition of the biomass. Therefore, experimental parameters, i.e., temperature, Pb(II) concentration, and reaction time were studied. It was found that production of LA is highly dependent on the experimental conditions. In this study, the highest LA yield obtained from EFB fibers was > 46% (230 °C, 2 mM Pb(II) after 4 h of reaction). However, a similar yield can be achieved either using higher Pb(II) and shorter reactions time or vice versa. The selective production of chemical compounds (glucose, 5-hydroxymethyl furfural (5-HMF), furfural, levulinic acid, and lactic acid) from EFB fibers is highly dependent on the availability of Pb(II) ions.

Synergistic enzymatic and microbial lignin conversion

The utilization of lignin for fungible fuels and chemicals represents one of the most imminent challenges in modern biorefineries.

Development of Lignocellulosic Biorefinery Technologies: Recent Advances and Current Challenges

Recent developments of the biorefinery concept are described within this review, which focuses on the efforts required to make the lignocellulosic biorefinery a sustainable and economically viable reality. Despite the major research and development endeavours directed towards this goal over the past several decades, the integrated production of biofuel and other bio-based products still needs to be optimized from both technical and economical perspectives. This review will highlight recent progress towards the optimization of the major biorefinery processes, including biomass pretreatment and fractionation, saccharification of sugars, and conversion of sugars and lignin into fuels and chemical precursors. In addition, advances in genetic modification of biomass structure and composition for the purpose of enhancing the efficacy of conversion processes, which is emerging as a powerful tool for tailoring biomass fated for the biorefinery, will be overviewed. The continual improvement of these processes and their integration in the format of a modern biorefinery is paving the way for a sustainable bio-economy which will displace large portions of petroleum-derived fuels and chemicals with renewable substitutes.

ChemInform Abstract: Thermochemical Conversion of Lignin to Functional Materials: A Review and Future Directions

AbstractReview: 208 refs.

Laccases for biorefinery applications: a critical review on challenges and perspectives.

Modern biorefinery concepts focus on lignocellulosic biomass as a feedstock for the production of next generation biofuels and platform chemicals. Lignocellulose is a recalcitrant composite consisting of several tightly packed components which are stuck together by the phenolic polymer lignin hampering the access to the carbohydrate compounds of biomass. Certain saprophytic organisms are able to degrade lignin by the use of an enzymatic cocktail. Laccases have been found to play a major role during lignin degradation and have therefore been intensively researched with regard to potential applications for biomass processing. Within this review, we go along the process chain of a third generation biorefinery and highlight the process steps which could benefit from laccase applications. Laccases can assist the pretreatment of biomass and promote the subsequent enzymatic hydrolysis of cellulose by the oxidative modification of residual lignin on the biomass surface. In combination with mediator molecules laccases are often reported being able to catalyze the depolymerization of lignin. Studies with lignin model compounds confirm the chemical possibility of a laccase-catalyzed cleavage of lignin bonds, but the strong polymerization activity of laccase counters the decomposition of lignin by repolymerizing the degradation products. Therefore, it is a key challenge to shift the catalytic performance of laccase towards lignin cleavage by optimizing the process conditions. Another field of application for laccases is the detoxification of biomass hydrolyzates by the oxidative elimination of lignin-derived phenolics which inhibit hydrolytic enzymes and are toxic for fermentation organisms. This review critically discusses the potential applications for laccases in biorefinery processes and emphasizes the challenges and perspectives which go along with the use of this enzyme for the technical utilization of lignocellulose.

From lignocellulosic biomass to lactic- and glycolic-acid oligomers: a gram-scale microwave-assisted protocol.

The conversion of lignocellulosic biomass into platform chemicals is the key step in the valorization of agricultural waste. Of the biomass-derived platform chemicals currently produced, lactic acid plays a particularly pivotal role in modern biorefineries as it is a versatile commodity chemical and building block for the synthesis of biodegradable polymers. Microwave-assisted processes that furnish lactic acid avoid harsh depolymerization conditions while cutting down reaction time and energy consumption. We herein report a flash catalytic conversion (2 min) of lignocellulosic biomass into lactic and glycolic acids under microwave irradiation. The batch procedure was successfully adapted to a microwave-assisted flow process (35 mL min(-1) ), with the aim of designing a scalable process with higher productivity. The C2 and C4 units recovered from the depolymerization were directly used as the starting material for a solvent and catalyst-free microwave-assisted polycondensation that afforded oligomers in good yields.

Aromatic catabolic pathway selection for optimal production of pyruvate and lactate from lignin

Lignin represents an untapped feedstock for the production of fuels and chemicals, but its intrinsic heterogeneity makes lignin valorization a significant challenge. In nature, many aerobic organisms degrade lignin-derived aromatic molecules through conserved central intermediates including catechol and protocatechuate. Harnessing this microbial approach offers potential for lignin upgrading in modern biorefineries, but significant technical development is needed to achieve this end. Catechol and protocatechuate are subjected to aromatic ring cleavage by dioxygenase enzymes that, depending on the position, ortho or meta relative to adjacent hydroxyl groups, result in different products that are metabolized through parallel pathways for entry into the TCA cycle. These degradation pathways differ in the combination of succinate, acetyl-CoA, and pyruvate produced, the reducing equivalents regenerated, and the amount of carbon emitted as CO2—factors that will ultimately impact the yield of the targeted product. As shown here, the ring-cleavage pathways can be interchanged with one another, and such substitutions have a predictable and substantial impact on product yield. We demonstrate that replacement of the catechol ortho degradation pathway endogenous to Pseudomonas putida KT2440 with an exogenous meta-cleavage pathway from P. putida mt-2 increases yields of pyruvate produced from aromatic molecules in engineered strains. Even more dramatically, replacing the endogenous protocatechuate ortho pathway with a meta-cleavage pathway from Sphingobium sp. SYK-6 results in a nearly five-fold increase in pyruvate production. We further demonstrate the aerobic conversion of pyruvate to l-lactate with a yield of 41.1±2.6% (wt/wt). Overall, this study illustrates how aromatic degradation pathways can be tuned to optimize the yield of a desired product in biological lignin upgrading.

Preparation of Different Carbon Materials by Thermochemical Conversion of Lignin

Lignin valorization plays a crucial role within the modern biorefinery scheme from both the economic and environmental points of view; and the structure and composition of lignin becomes it an ideal precursor for the preparation of advanced carbon materials with high added-value. This review provides an overview of the different carbonaceous materials obtained by thermochemical conversion of lignin, such as activated carbons, carbon fibers, template carbons; high ordered carbons; giving information about the new strategies in terms of the preparation method and their possible applications.

Developing an integrated supercritical fluid biorefinery for the processing of grains

With the rapid growth of the bioeconomy, there are major developments in the biorefinery concept to maximize utilization of renewable resources, including grains of cereals and oilseeds, targeting applications not only in food, nutraceutical, pharmaceutical and cosmetic products but also in biofuel, biochemical and biomaterial sectors. Supercritical carbon dioxide (SC-CO2) technology could have a major role to play in modern biorefineries. Know-how has been building on individual unit operations based on SC-CO2, especially extraction, fractionation and reactions involving lipids and particle formation for delivery of bioactives as summarized in this study mostly based on the previous work of the authors. Based on a solid understanding of fundamentals, the focus is now on optimal integration of these unit operations to build supercritical biorefineries. Such approaches should also consider integration of supercritical operations with conventional technologies for efficient and optimal process design. Even though the future of supercritical biorefineries seems to be bright, offering numerous advantages, there are also some substantial technical and economic challenges requiring further research.

The prominent role of fungi and fungal enzymes in the ant-fungus biomass conversion symbiosis.

Molecular studies have added significantly to understanding of the role of fungi and fungal enzymes in the efficient biomass conversion, which takes place in the fungus garden of leaf-cutting ants. It is now clear that the fungal symbiont expresses the full spectrum of genes for degrading cellulose and other plant cell wall polysaccharides. Since the start of the genomics era, numerous interesting studies have especially focused on evolutionary, molecular, and organismal aspects of the biological and biochemical functions of the symbiosis between leaf-cutting ants (Atta spp. and Acromyrmex spp.) and their fungal symbiont Leucoagaricus gongylophorus. Macroscopic observations of the fungus-farming ant colony inherently depict the ants as the leading part of the symbiosis (the myrmicocentric approach, overshadowing the mycocentric aspects). However, at the molecular level, it is fungal enzymes that enable the ants to access the nutrition embedded in recalcitrant plant biomass. Our hypothesis is that the evolutionary events that established fungus-farming practice were predisposed by a fascinating fungal evolution toward increasing attractiveness to ants. This resulted in the ants allowing the fungus to grow in the nests and began to supply plant materials for more fungal growth. Molecular studies also confirm that specialized fungal structures, the gongylidia, with high levels of proteins and rich blend of enzymes, are essential for symbiosis. Harvested and used as ant feed, the gongylidia are the key factor for sustaining the highly complex leaf-cutting ant colony. This microbial upgrade of fresh leaves to protein-enriched animal feed can serve as inspiration for modern biorefinery technology.

Understanding lignin biodegradation for the improved utilization of plant biomass in modern biorefineries

AbstractWood‐rotting fungi are the sole organisms in nature able to degrade the lignin polymer making the polysaccharide components of lignocellulose fully accessible. This process has been investigated for decades as a model for biotechnological application in the pulp and paper industry, animal feeding, and ethanol production. In the current lignocellulose biorefinery concept, ligninolytic fungi and the oxidoreductases (laccases and peroxidases) secreted by these fungi constitute powerful biotechnological tools for the complete utilization of plant biomass. The evolution of molecular biology, which brings into play specifically designed biological systems and on‐demand enzymes, together with the technological advances in processing of plant biomass, smoothes the way for a sustainable conversion of renewable feedstocks to new added‐value products, with lower energy costs and less environmental impact. The present study reviews some of the main achievements attained by our group in the field of lignin biodegradation that have contributed to: (i) better understanding of the mechanisms by which fungi delignify the lignocellulosic materials; and (ii) assessing the applicability of these ligninolytic systems to increase the efficiency of some industrial processes and to develop new means for sustainable and environmentally sound production of chemicals, materials, and fuels. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd

Biorefinery process water effluent treatments by salt coagulation

Acid pretreatment is one of the critical pretreatments for the biorefinery. However, little information is available on water effluent that results from this acidic pretreatment compared to alkaline pretreatment. In this study, the wastewaters from an integrated modern magnesium bisulphite pulp mill (acidic) were utilized as models for the acid pretreatment effluents of a modern biorefinery. The coagulation technique, using high valency electrolytes, was applied for the treatment of treated and untreated process water from the pulp mill. The effectiveness of some electrolytes and the selectivity of the coagulation process were compared by measuring the removal extent of critical contaminants such as organics, phosphorus and colour. The salt coagulation process was found to be selective for colour and total phosphorus removal from the wastewater, achieving more than 90% removal of contaminants.