Fractionation Of Lignocellulosic Biomass Research Articles

Economic feasibility of gasoline production from lignocellulosic wastes in Hong Kong

In this study, the conceptual process flowsheet was developed and the economic feasibility of woody biomass conversion to biofuel as feedstock was analysed by considering several promising experimental processes for lignin depolymerization, such as hydrodeoxygenation and hydrogenolysis, along with lignocellulosic biomass fractionation processes. The engineering simulation process toward the commercial production of bio-gasoline from lignocellulosic biomass using SuperPro Designer® was modeled. The compatibility of the end products with the current gasoline specifications was evaluated and various blending options were investigated to meet the octane number and Reid vapor pressure requirement of the product. The economic potential of the simulated engineering process was then evaluated from an economic perspective. The operating costs and capital investment of three scenario using three different catalytic systems were estimated and discussed to assess of the potential of commercializing of woody biomass valorization process. The main potential market segments were identified, including the process by-products such as xylose and cellulose pulp. From the economic evaluation study, it was found that selling the biomass fractionation products alone does have a greater profit than valorization of lignin to produce bio-gasoline, with net present value of RMB 22,653,000 and RMB 177,000, respectively at the same return on investment if the plant is set up in Hong Kong. It was also found that catalysts play a pivotal role in determination of the profitability in the valorization process, not only because of the price of the catalyst, but also the product distributions obtained with various types of it. To obtain the same gross profit, the sale price of bio-gasoline has to be set higher with platinum catalysts than with ruthenium catalysts (nearly 10 folds). Thus, catalyst development and process improvement are crucial in the establishment of bio-based circular economy.

Lignocellulosic Biomass Fractionation by Mineral Acids and Resulting Extract Purification Processes: Conditions, Yields, and Purities.

Fractionation of lignocellulose is a fundamental step in the valorization of cellulose, hemicelluloses, and lignin to produce various sustainable fuels and chemicals. Mineral acid fractionation is one of the most applied process and leads to the solubilization and hydrolysis of cellulose and hemicelluloses, whereas most of the lignin remains insoluble and can be separated from the extract. The obtained monomeric sugars in the acid extract are in solution with salts, sugar degradation products, and phenolic molecules. Downstream processing is required to purify the sugars and further valorize them into fuels or chemicals with the use of chemical or biochemical reactions. This purification step also allows the recycling of the mineral acid and the valorization of the sugar degradation products and the co-extracted phenolic molecules, adding value to the whole biorefinery scheme. Many purification techniques have been studied, providing several options in terms of yields, purities, and cost of the process. This review presents the conditions used for the mineral acid fractionation step and a wide variety of purification techniques applied on the obtained hydrolysate, with a focus on the associated yields and purities. Values from the literature are expressed in a standard way in order to simplify comparison between the different processes.

High value‐added monomer chemicals and functional bio‐based materials derived from polymeric components of lignocellulose by organosolv fractionation

AbstractOrganosolv fractionation (OF) is a promising method for lignocellulosic biomass biorefining to produce biofuels, biochemicals, and biomaterials. The fractionated polymeric components may be good feedstocks to produce bio‐based materials such as green polymers via chemical or biological conversion. However, related work to specify the bio‐based materials production via organosolv fractionation of lignocellulosic biomass is relatively scarce. In this work we have provided a comprehensive review of typical organosolv fractionation for isolating cellulose, hemicelluloses, and lignin, as well as the high value‐added monomer chemicals and functional materials derived from the fractionated components and their potential applications developed in recent years, primarily including the modified cellulose fibers for polymer materials, cellulose nanocrystals (CNCs), polysaccharide‐derived platform precursors for synthesis of bio‐based polymers, lignin‐derived dispersants, surfactants, carbon materials, and hemicellulose‐derived functional materials, etc. This work suggests that organosolv fractionation of lignocellulosic biomass could be a good entry to biomass refinery for high value‐added and functional materials production. However, there are still many challenges that should be overcome in terms of the fundamental, technical, and economic aspects for the organosolv fractionation process, formation of precursor compounds, synthesis of the bio‐based materials, design of product properties and functions, and the integration of the entire process. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Facile Fractionation of Bamboo Wood Toward Biomass Valorization by p-TsOH-Based Methanolysis Pretreatment

A mild methanolysis pretreatment strategy was developed with a recyclable acid, p-TsOH, as the catalyst for the fractionation of lignocellulosic biomass toward its main components. Bamboo fiber was fractionated in one step with dissolution of more than 88% lignin and 90% xylan with most of the cellulose (86.8%) retained in pretreated bamboo at mild conditions (110 °C, 30 min, and 10% p-TsOH). Enzymatic hydrolysis of the cellulose-rich fraction was enhanced to 89.2% at an enzyme loading of 15 FPU g–1 substrate, nearly 4-fold higher than the untreated bamboo. Most of the xylan (hemicellulose) and lignin in the biomass were extracted and dissolved into the spent liquor. The extracted lignin had higher purity (>94%) and a moderate and homogeneous molecular weight, which could be adapted to add value to lignin. p-TsOH can be effectively recovered by recrystallization technology after concentrating the spent liquor. Hemicellulose (xylan) was transformed into methyl xyloside and furfural during the pretreatment. Overall, the described process showed practical significance for the effective fractionation and comprehensive utilization of lignocellulosic biomass components.

Sequential Fractionation of Lignocellulosic Biomass Using CO2‐Assisted Hydrolysis Combined with γ‐Valerolactone Treatment

A biomass biorefinery strategy for the selective fractionation of poplar into its three main compositions (hemicellulose sugars, lignin, and high‐purity cellulose) with a two‐step process is developed. The first step consists of the selective hydrolysis of hemicellulose at mild conditions in a CO2/H2O system. This leads to various hemicellulose sugars and other intermediates in the water‐soluble fraction, with more than 87.90% of the hemicellulose being extracted from the original poplar (180 °C, 2.0 MPa CO2, 10 min). The pretreated sample is subsequently used for extracting lignin in a γ‐valerolactone (GVL)/H2O with acid catalysts for the next step. Meanwhile, four acid catalysts, including sulfuric acid and solid heteropoly acids (phosphomolybdic acid, silicotungstic acid, and phosphotungstic acid), are studied for the selective delignification in the GVL/H2O system, resulting in more than 91.35% of the original lignin being removed in the cellulose‐rich substrates (140 °C, 30 mM silicotungstic acid, 3 h). Overall, the biorefinery approach fractions the poplar wood into three primary components: 1) various oligosaccharides, monosaccharides, and other intermediates derived from hemicellulose; 2) cellulose‐rich substrate with a purity of cellulose as high as 90.76%, which has great potential as biochemicals or biomaterials; and 3) high‐purity and proportion lignin recovered from biomass.

Acidic deep eutectic solvents pretreatment for selective lignocellulosic biomass fractionation with enhanced cellulose reactivity

This work tailored a promising two-step pretreatment, i.e., liquid hot water extraction followed by mild acidic deep eutectic solvents pretreatment for clean lignocellulose fractionation while enhancing cellulose reactivity for its subsequent utilization. The abilities of three acidic deep eutectic solvents (formic acid-, acetic acid- and lactic acid-choline chloride) to selectively extract poplar wood lignin and enhance cellulose reactivity were comparatively assessed. Results showed that rather high lignin selectivity of 6.3–7.9 was obtained while the available area and porosity of the resulting cellulose were significantly increased. The resulting cellulose pulps exhibited comparable chemical reactivity to commercial bleached Kraft pulp when cellulose acetate was selected as testing cellulose derivative for demonstrating purpose, showing their great promise for high-value use. It was proposed that the unique ionic properties of these acidic deep eutectic solvents were responsible for their selective lignin removal and cellulose swelling/deconstruction to enhance cellulose chemical reactivity.

DFT investigation on thermochemical analyses of conversion of xylose to linear alkanes in aqueous phase

Xylose is an integral part of hemicellulose fraction of lignocellulosic biomass. Its abundance in the lignocellulose makes it a desirable component for converting into various value-added compounds. In this study, conversion of xylose to four linear alkanes has been discussed by five different schemes including their thermochemistry under the framework of density functional theory. Main products are butane, pentane, octane and tridecane whereas the intermediate products include furfural, tetrahydrofuran, pentane-1,5-diol, etc. The simulations have been performed at B3LYP/6–31 + g(d,p) and M06-2X/6–31 + g(d,p) level of theories in aqueous phase using SMD solvation model. Thermochemical parameters (ΔG, ΔH and Keq) are obtained at a wide range of temperature, i.e. 298–698 K. Single point energy change (ΔE) of all the conversion steps has also been calculated at M05-2X/6–311++g(3df,2p) level of theory in the aqueous phase. It is observed that temperature plays a vital role in the formation of products. At high temperature, only scheme RS 1 (i.e. xylose to butane) can proceed to produce butane. The absolute difference between two functionals, B3LYP and M06-2X, was found to be small (<2 kcal/mol) for ring opening reactions making both the functionals suitable for a qualitative study. For saturation of cyclic compounds, a large difference (>10 kcal/mol) was observed between the two functionals making higher accuracy method more suitable for them. For all other reactions, use of M06-2X can be preferred.

Fractionation of Lignocellulosic Biomass by Selective Precipitation from Ionic Liquid Dissolution

We propose the treatment of barley straw with 1-ethyl-3-methylimidazolium acetate [EMIMAcO] ionic liquids (ILs) and subsequent precipitation with antisolvent mixtures, thus allowing the separation of the sugar-rich fractions (cellulose and hemicellulose) from the lignin fraction. For this purpose, different concentration ranges of acetone:water antisolvent mixtures were studied. In all cases, a high recovery percentage and a high and effective separation of fractions was achieved for 1:1 acetone:water. The fractionated lignocellulosic compounds were studied by using infrared spectroscopy, scanning electron microscopy and 1H nuclear magnetic resonance characterization techniques. This method allows the possibility of reusing IL, confirming the versatility of the established method. The fraction rich in cellulose and hemicellulose was subjected to acid hydrolysis (0.2 mol/L H2SO4) for 5 h at 140 °C, obtaining a yield of total reducing sugars of approximately 80%, much higher than those obtained in non-pretreated samples.

Approaches for More Efficient Biological Conversion of Lignocellulosic Feedstocks to Biofuels and Bioproducts

The future bioeconomy promises drop-in or performance-advantaged biofuels and bioproducts derived from lignocellulosic biomass, substantial greenhouse gas emissions reductions in sectors with few or no alternatives, and increased domestic energy production in countries with sufficient biomass resources. Despite the slower than anticipated pace of commercializing next-generation biofuels, the research community continues to make dramatic improvements at every stage of production, from feedstock cultivation through conversion to final products. However, the interdisciplinary nature of bioenergy research, and the need for cross-coordination among biologists, chemists, agronomists, and engineers, make coordinating and optimizing these strategies challenging. This Perspective surveys recent advancements in bioenergy crop engineering, lignocellulosic biomass deconstruction and fractionation, catabolism of biomass-derived sugars and aromatics, and biological conversion to fuels and products. We organize major research approaches into broad categories and comment on which strategies offer synergies or trade-offs in the context of four approaches to improving the economics and carbon-efficiency of advanced biofuels and bioproducts: (1) maximize sugar conversion to a single product, (2) utilize diverse carbon sources for producing a single product, (3) convert lignin to high-value products, and (4) fractionate the hydrolysate to derive maximum value from each component.

Ultrasound and surfactant assisted ionic liquid pretreatment of sugarcane bagasse for enhancing saccharification using enzymes from an ionic liquid tolerant Aspergillus assiutensis VS34

Ionic liquid (IL) pretreatment represents an effective strategy for effective fractionation of lignocellulosic biomass (LB) to fermentable sugars in a biorefinery. Optimization of combinatorial pretreatment of sugarcane bagasse (SCB) with IL (1-butyl-3-methylimidazolium chloride [Bmim]Cl) and surfactant (PEG-8000) resulted in enhanced sugar yield (16.5%) upon enzymatic saccharification. The saccharification enzymes (cellulase and xylanase) used in the current study were in-house produced from a novel IL-tolerant fungal strain Aspergillus assiutensis VS34, isolated from chemically polluted soil, which produced adequately IL-stable enzymes. This is the first ever report of IL-stable cellulase/xylanase enzyme from Aspergillus assiutensis. To get the mechanistic insights of combinatorial pretreatment physicochemical analysis of variously pretreated biomass was executed using SEM, FT-IR, XRD, and 1H NMR studies. The combined action of IL, surfactant and ultrasound had very severe and distinct effects on the ultrastructure of biomass that subsequently resulted in enhanced accessibility of saccharification enzymes to biomass, and increased sugar yield.

Fractionation of Lignocellulosic Biomass over Core-Shell Ni@Al2 O3 Catalysts with Formic Acid as a Cocatalyst and Hydrogen Source.

Highly dispersed, core-shell Ni@Al2 O3 on activated carbon (AC) catalysts were prepared to develop an effective, external-hydrogen-free fractionation process for various types of lignocellulosic biomass. In a mixture of formic acid, ethanol, and water at 190 °C, the conversion of oak wood produced 23.4 C% lignin-derived phenolic monomers (LDPMs) and highly delignified pulp-rich solid. At an early stage, formic acid acted as a cocatalyst to enhance the delignification by solvolysis, and at a later stage, it acted as a hydrogen source to stabilize the phenolic monomers by hydrodeoxygenation and hydrogenation. Based on the positive correlation between spillover hydrogen on the catalysts and LDPM yields, a new suite of catalyst design criteria was proposed to develop highly active, non-noble-metal based catalysts for realizing economically viable biorefineries. Enzymatic saccharification of the pulp-rich solid indicated that the pulp-rich solid is an excellent source of fermentable sugars.

Fractionation of lignocellulosic biomass to produce uncondensed aldehyde-stabilized lignin.

Lignin is one of the most promising sources of renewable aromatic hydrocarbons. Current methods for its extraction from lignocellulosic biomass-which include the kraft, sulfite, and organosolv processes-result in the rapid formation of carbon-carbon bonds, leading to a condensed lignin that cannot be effectively depolymerized into its constituent monomers. Treatment of lignocellulosic biomass with aldehydes during lignin extraction generates an aldehyde-stabilized lignin that is uncondensed and can be converted into its monomers at near-theoretical yields. Here, we outline an efficient, reproducible, and scalable process for extracting and purifying this aldehyde-stabilized lignin as a solid, which can easily be re-dissolved in an organic solvent. Upon exposure to hydrogenolysis conditions, this material provides near-theoretical yields of aromatic monomers (~40-50% of the Klason lignin for a typical hardwood). Cellulose and hemicellulose are also efficiently fractionated. This protocol requires 6-7 h for the extraction of the stabilized lignin and a basic proficiency in synthetic chemistry.

Liquor re-use strategy in lignocellulosic biomass fractionation with ethanol-water mixtures

Liquor recycle in lignocellulosic biomass fractionation with ethanol-water has been studied. Runs have been carried out in a 6 L tank reactor with liquor recirculation. The liquors obtained in six successive fractioning operations have been analyzed together with the solid phase remnant. Experimental results revealed that the number of re-uses reduces solids recovery (from 52.2 to 42.6%) and cellulose recovery (from 28.1 to 23.3%) with minor or no effect on the hemicelluloses and lignin removal. The more remarkable effect is an increase of the glucose yield (from 76.7 to 95.3% after enzymatic hydrolysis during 72 h). The accumulation of acetic acid in the spent liquors (until 1.3 g/L) seems to be responsible of the higher enzymatic hydrolysis yield, from 76.3 (first use) to 87.7% (fifth re-use). Liquor re-use is effective to improve the sustainability of the pre-treatment obtaining a cellulose-rich solid easy to hydrolysate to sugars reducing energy consumption.

Concept and challenges of modern biorefineries

International R&D community and technology developers for the last decades. However, despite intense efforts, real breakthrough has not been achieved yet. This has been mainly due to a biased view, focusing solely on a certain end product – for example cellulose pulp or ethanol and considering by-products as low value waste streams for energy applications. With the new wave of lignocellulosic biomass fractionation technologies being demonstrated at a pilot scale, success stories are closer than they have ever been. Biomass fractionation to high purity intermediate building blocks of cellulose to C6 sugars and hemicellulose to C5/C6 sugars and lignin, instead of just one main product, provides a way to produce a diversity of products and establish novel bio-based value chains. Especially important is the availability of higher purity lignin for different direct drop-in or after processing (depolymerization etc.) applications, which compared to the conventional lignins derived from pulp mills or ethanol refineries provides totally new applications and perspectives to enable the increased use of biobased raw materials in various industries. A biorefinery is a facility where different low-value renewable biomass materials are the feedstock to the processes where they are transformed, in multiple steps including fractionations, separations and conversions, to several higher-value bio-based products. Examples of these products can include fibres, food, feed, fine chemicals, transportation fuels and heat. A biorefinery can be formed by a single unit or can combine several facilities targeted for a single purpose that further process products as well as by-products or wastes of combined facilities. In biorefining one can find similarities to oil refining, with the exception that in oil refining the raw material comes from fossil resources. According to the International Energy Agency ‘Biorefineries will contribute significantly to the sustainable and efficient use of biomass resources, by providing a variety of products to different markets and sectors. They also have the potential to reduce conflicts and competition over land and feedstock, but it is necessary to measure and compare the benefits of biorefineries with other possible solutions to define the most sustainable option.’1 Although it is possible to produce the same products in a biorefinery as in an oil refinery, this is not the target, which instead is to produce products which can replace the products from oil refining.

Natural deep eutectic solvents (DES) for fractionation of waste lignocellulosic biomass and its cascade conversion to value-added bio-based chemicals

Deep eutectic solvents (DES), prepared from choline chloride (ChCl) compound as hydrogen bond acceptor and lactic acid (LA), oxalic acid (OA), potassium hydroxide or urea (UA) as the electrostatic attracting donors in different amount ratios, were synthetized, applied and studied for lignocellulosic biomass fractionation. The mixtures of ChCl with OA or KOH were found to dissolve beech wood polymers more effectively compared to ChCl with LA or UA. In addition to DES screening test experiments, the influences of the process performance parameters, like measurement reaction time (2–24 h), temperature (60–100 °C) and the chip to solution mass relationship (1:100–1:10), on particle size distribution, solid residue's properties, functional cellulose, hemicellulose and lignin contents, the concentration of sugars, polyphenolics and volatile chemical products in raw liquid extract, as well as kinetics were experimentally determined. The further spectroscopic, microscopic and chromatographic analysis of solubilisation demonstrated that ChCl with OA selectively isolated phenols, could potentially be scalable and could be utilized in lignin-first bio-refinery plant. Purified cellulose-rich material was obtained, according to attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), while polyphenols were above 15 g L−1 (gallic acid equivalent, examined by Folin–Ciocalteu method), revealing predominant dissolution. Conversely, for ChCl with KOH, aromatics were below detection limit value, while polysaccharides dropped for a factor of 10, paralleled to sawdust's fresh sample. The DES recovery by centrifugation, anti-solvent-assisted phase separation and vacuum distillation operation was also performed. While promising, NADES must be additionally developed, especially considering recycling, stability and economics.

Investigations of Alkaline and Enzymatic Membrane Cleaning of Ultrafiltration Membranes Fouled by Thermomechanical Pulping Process Water

The pulp and paper industry is one of the most important industrial sectors worldwide, and has considerable potential for the sustainable fractionation of lignocellulosic biomass to provide valuable compounds. Ultrafiltration (UF) is a suitable separation technique for the profitable production of hemicelluloses from process water from thermomechanical pulping (ThMP), but is limited by membrane fouling. Improvements in cleaning protocols and new alternative cleaning agents are required to ensure a long membrane lifetime, and thus a sustainable process. This study, therefore, focuses on the cleaning of polymeric UF membranes after the filtration of ThMP process water, comparing alkaline with enzymatic cleaning agents. The aim was to develop a cleaning procedure that is efficient under mild conditions, resulting in a lower environmental impact. It was not possible to restore the initial permeability of the membrane when cleaning the membrane with enzymes alone, but the permeability was restored when using a two-step cleaning process with enzymes in the first step and an alkaline cleaning agent in the second step. Scanning electron microscopy gave a deeper inside into the cleaning efficiency. Attenuated total reflectance Fourier-transform infrared spectroscopy analysis confirmed that not only polysaccharides, but also extractives are adsorbed onto the membrane surface.

Physico-chemical characterization and evaluation of neat and aqueous mixtures of choline chloride + lactic acid for lignocellulosic biomass fractionation, enzymatic hydrolysis and fermentation

Comprehensive physico-chemical properties of different molar ratios of neat and aqueous (aq) natural deep eutectic solvent (NADES) mixtures containing choline chloride + lactic acid (CC-LA) were evaluated between the temperature ranges of 283.15 K and 363.15 K, respectively. Vogel-Fulcher-Tamman (VFT) model on dynamic viscosity and density studies clearly showed stronger interactions between water and NADESs. Pretreatment of rice straw (RS) with increasing LA content in the NADESs increased lignin extraction. Maximum lignin removal of 63.6% (w/w) was observed with CC-LA (1:9) mixture and decreased with increasing concentrations of water content in the NADESs. Further, >95% of the solublized lignin was recovered from neat NADESs pretreated liquid fraction, while comparatively lower lignin extraction efficiency was observed with the aqNADESs pretreated mixtures. Alongside, recovery of NADES insoluble fractions (NIF) and hemicelluloses were decreased with increasing LA content in the NADESs. The cellulose content (% w/w) was significantly increased from 40% to 65% after CC-LA-H2O (1:9:2.5) pretreatment. Enzymatic hydrolysis of the cellulose enriched NIF produced maximum reducing sugars of 66.4 g/L with CC-LA-H2O (1:9:2.5). Irrespective of the aqNADESs pretreatment, direct fermentation of the reducing sugars using Clavispora NRRL-Y 50464 produced maximum ethanol yields of 17.11 g/L within 180 min with a theoretical conversion efficiency of 94%, respectively.

Enhanced Furfural Yields from Xylose Dehydration in the γ‐Valerolactone/Water Solvent System at Elevated Temperatures

AbstractInvited for this month's cover is the group of Prof. James Dumesic at the University of Wisconsin–Madison. The image shows a process for the conversion of xylose, obtained from the hemicellulose fraction of lignocellulosic biomass, to furfural at high yields (&gt;90%) using a biomass derived solvent, γ‐valerolactone, at high temperature (e.g., 498 K). The Full Paper itself is available at 10.1002/cssc.201800730.

Lignocellulose Fractionation and Lignin Depolymerization Using Glycerol and Acidic Ionic Liquids: Identification of the Main Products by GC-MS

Difficulties in fractionation and subsequent conversion of lignocellulosic biomass have restricted the development of sustainable biorefineries of lignocellulosic materials. Herein, an aqueous glycerol/acidic ionic liquid (AGAIL) process of coir was carried out under atmospheric and autogenerated pressure to investigate the lignocellulose fractionation and understand the main conversion products generated during the process. Additionally, the depolymerization capacity of the AGAIL system on lignin was also estimated by analyzing the main degradation products. The results indicated that the process under autogenerated pressure presented much higher delignification efficiency and more effective lignocellulose conversion capability than those under atmospheric pressure. Ribitol and monomeric aromatic compounds were identified by gas chromatography-mass spectrometry (GC-MS) as the main conversion products of carbohydrates and lignin, respectively. The glycerol/AIL system was shown to be able to depolymerize coir lignin with a resulting lignin depolymerization extent of 28.1%. The main lignin depolymerization products were monomeric aromatic compounds.

Fractionation of lignocellulosic biopolymers from sugarcane bagasse using formic acid-catalyzed organosolv process.

A one-step formic acid-catalyzed organosolv process using a low-boiling point acid-solvent system was studied for fractionation of sugarcane bagasse. Compared to H2SO4, the use of formic acid as a promoter resulted in higher efficiency and selectivity on removals of hemicellulose and lignin with increased enzymatic digestibility of the cellulose-enriched solid fraction. The optimal condition from central composite design analysis was determined as 40min residence time at 159°C using water/ethanol/ethyl acetate/formic acid in the respective ratios of 43:20:16:21%v/v. Under this condition, a 94.6% recovery of cellulose was obtained in the solid with 80.2% cellulose content while 91.4 and 80.4% of hemicellulose and lignin were removed to the aqueous-alcohol-acid and ethyl acetate phases, respectively. Enzymatic hydrolysis of the solid yielded 84.5% glucose recovery compared to available glucan in the raw material. Physicochemical analysis revealed intact cellulose fibers with decreased crystallinity while the hemicellulose was partially recovered as mono- and oligomeric sugars. High-purity organosolv lignin with < 1% sugar cross-contamination was obtained with no major structural modification according to Fourier-transform infrared spectroscopy. The work represents an alternative process for efficient fractionation of lignocellulosic biomass in biorefineries.