Lignocellulosic material (LCM) has been considered as a potent feedstock for biofuel production either as gaseous, liquid, and/or solid fuel to meet the energy demands. Conversion of lignocellulosic ...materials to biofuels is possible mainly by two processes, i.e., thermochemical and biochemical. For overall efficiency of processes designed to convert the lignocellulosic materials into the desired biofuel, it is important to understand the characteristics of these lignocellulosic components. The present study aims for physicochemical characterization of common lignocellulosic agricultural residues available in India, i.e., rice straw, rice husk, cotton stalk, wheat straw, bagasse, corn stover, sorghum stalk, mustard stalk, corn cob, and jatropha pruning. Physical and chemical characterization of lignocellulosic samples is carried out by higher heating value, crystallinity index, thermal properties, CHNS/O analysis, FTIR, metal analysis, and compositional analysis. Among all of the biomass samples analyzed, corn cob has the highest content of cellulose and hemicellulose, i.e., 61.2% (w/w), making it the most potent feedstock for production of biofuels using biochemical process, whereas cotton stalk has relatively higher thermochemical potential due to its higher heating value (19.2 MJ/kg). Rice husk and rice straw have the highest ash content, i.e., 17.4 and 13.7% (w/w), respectively, indicating a significant amount of undesirable material.
The production and use of biodiesel has seen a quantum jump in the recent past due to benefits associated with its ability to mitigate greenhouse gas (GHG). There are large number of commercial ...plants producing biodiesel by transesterification of vegetable oils and fats based on base catalyzed (caustic) homogeneous transesterification of oils. However, homogeneous process needs steps of glycerol separation, washings, very stringent and extremely low limits of Na, K, glycerides and moisture limits in biodiesel. Heterogeneous catalyzed production of biodiesel has emerged as a preferred route as it is environmentally benign needs no water washing and product separation is much easier. The present report is review of the progress made in development of heterogeneous catalysts suitable for biodiesel production. This review shall help in selection of suitable catalysts and the optimum conditions for biodiesel production.
•A comparative LCA of Rice straw utilization practices in India.•Four scenarios studied were use as, fertilizer, fodder, electricity and biogas.•Scope of the study starts from collection of straw to ...the end use of the products.•System expansion is used for accounting emissions from the replaced product.•Electricity and biogas give highest benefits in most of the environmental impacts.
The aim of this study is to find potential utilization practice of rice straw in India from an environmental perspective. Life cycle assessment (LCA) is conducted for four most realistic utilization practices of straw including: (1) incorporation into the field as fertilizer (2) animal fodder (3) electricity (4) biogas. The results show that processing of 1 ton straw to electricity and biogas resulted in net reduction of 1471 and 1023kg CO2 eq., 15.0 and 3.4kg SO2 eq. and 6.7 and 7.1kg C2H6 eq. emissions in global warming, acidification and photochemical oxidation creation potential respectively. Electricity production from straw replaces the coal based electricity and resulted in benefits in most of the environmental impacts whereas use as an animal fodder resulted in eutrophication benefits. The burning of straw is a harmful practice of managing straw in India which can be avoided by utilizing straw for bioenergy.
•Total solids of >25% achieved by DA pretreatment of rice straw at pilot scale.•Optimum parameters were 0.35wt% acid concentration, 162°C and 10min.•At a high solids (20 and 25wt%) enzymatic ...hydrolysis was conducted.•Overall glucose recovery was 71 and 89% at 10 and 50FPU/g residue.•Overall sugars (C6+C5) recovery on mass basis was 77% at 50FPU/g residue.
The aim of this work was to study the dilute acid pretreatment of rice straw (RS) and fermentable sugar recovery at high solid loadings at pilot scale. A series of pretreatment experiments were performed on RS resulting in >25wt% solids followed by enzymatic hydrolysis without solid-liquid separation at 20 and 25wt% using 10FPU/g of the pretreated residue. The overall sugar recovery including the sugars released in pretreatment and enzymatic hydrolysis was calculated along with a mass balance. Accordingly, the optimized conditions, i.e. 0.35wt% acid, 162°C and 10min were identified. The final glucose and xylose concentrations obtained were 83.3 and 31.9g/L respectively resulting in total concentration of 115.2g/L, with a potential to produce >50g/L of ethanol. This is the first report on pilot scale study on acid pretreatment of RS in a screw feeder horizontal reactor followed by enzymatic hydrolysis at high solid loadings.
•First LCA study of second generation ethanol based on DA and SE pretreatment technologies in India.•Enzyme production is identified as the major GHG emissions and energy consumption process in ...ethanol production.•SE is better than DA in terms of ethanol yield and GHG emissions reduction.•Surplus electricity produced in the ethanol plant replaces coal based grid electricity and makes the process more greener.•Cellulosic ethanol production in India is sustainable from GHG and energy savings perspective.
The environmental sustainability of cellulosic ethanol production from rice straw in India is conducted using life cycle assessment (LCA). Greenhouse gas (GHG) emissions, net energy ratio (NER) and net energy balance (NEB) are studied for ethanol production system using two diverse pretreatment technologies, i.e. dilute acid (DA) and steam explosion (SE) followed by separate hydrolysis and fermentation. 1ton of rice straw is the reference flow of study and 1MJ transportation fuel is the functional unit while comparing the results with gasoline. The inventory data is collected based on several experiments conducted at our pilot plant and is a novel contribution to country specific LCA. Using DA and SE, the ethanol yields from the processing of 1ton straw are 239 and 253L and life cycle GHG emissions are 292 and 288kgCO2eq./ton straw respectively. The results indicated that production of enzyme used in hydrolysis is the major contributor to GHG emissions in both DA (54%) and SE (57%) methods of ethanol production. The net energy input during the life cycle of ethanol is 1736 and 1377MJ/ton straw in DA and SE respectively. The major GHG emissions and energy benefits are obtained using lignin produced in the plant to generate electricity resulting in displacement of the coal based electricity. With a higher xylose recovery in the SE, it gives larger amount of ethanol and also generates more surplus electricity. Enzyme production and its use are identified as GHG emission and energy consumption hotspot in the ethanol production process. While comparing the results with gasoline, DA and SE resulted in a reduction of 77 and 89% GHG emissions and NER of 2.3 and 2.7 respectively. The E5 blending would reduce GHG emissions by 4.3% (DA) and 4.8% (SE) whereas; E20 blend would lead to a reduction of 17.4% (DA) and 18.8% (SE) respectively. Sensitivity analysis indicates that with every 12.5% increase in the price of rice straw from the base case, there is a 2.3% increase in GHG emissions and vice versa. 1FPU/g WIS increase during hydrolysis gives 2.9% increase in ethanol production, but at the same time there is an increase of 5% emissions from enzyme production. The results of the study conclude that cellulosic ethanol production technology in India is sustainable from GHG reduction and energy efficiency perspective.
•Pretreatment of mustard stalk is conducted using 3 different methodologies.•Surface area, CrI, FT-IR, thermal analysis and cellulase accessibility of biomass studied.•Impact of these characteristics ...on enzymatic hydrolysis is studied.•Glucose yield at 2 and 72h are well correlated with surface area and adsorption.•Dilute acid produces maximum sugar (0.75g/g glucan and xylan) at 10FPU/g.
To overcome the recalcitrant nature of biomass several pretreatment methodologies have been explored to make it amenable to enzymatic hydrolysis. These methodologies alter cell wall structure primarily by removing/altering hemicelluloses and lignin. In this work, alkali, dilute acid, steam explosion pretreatment are systematically studied for mustard stalk. To assess the structural variability after pretreatment, chemical analysis, surface area, crystallinity index, accessibility of cellulose, FT-IR and thermal analysis are conducted. Although the extent of enzymatic hydrolysis varies upon the methodologies used, nevertheless, cellulose conversion increases from <10% to 81% after pretreatment. Glucose yield at 2 and 72h are well correlated with surface area and maximum adsorption capacity. However, no such relationship is observed for xylose yield. Mass balance of the process is also studied. Dilute acid pretreatment is the best methodology in terms of maximum sugar yield at lower enzyme loading.
Investigation of the ionic liquids pretreatment of lignocellulosic biomass for producing fermentable sugar and analyzing the impact of various parameters over the enzymatic digestibility with a ...plausible mechanism.
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•Treatment efficiencies of five ionic liquids studied over mustard stalk and wheat straw.•C2mimOAc with 1.32 β-value resulted 97.7% of glucose using 10 FPU/g of biomass.•Viscosity and surface tension of ILs have a negative correlation with glucose yields.•Explanation of the transformation from cellulose I to II using PXRD and FT-IR.•Postulation of the mechanism for improved enzymatic hydrolysis on cellulose-II.
In this study, five ionic liquids (ILs) have been explored for biomass pretreatment for the production of fermentable sugar. We also investigated the driving factors responsible for improved enzymatic digestibility of various ILs treated biomass along with postulating the plausible mechanism thereof. Post pretreatment, mainly two factors impacted the enzymatic digestibility (i) structural deformation (cellulose I to II) along with xylan/lignin removal and (ii) properties of ILs; wherein, K-T parameters, viscosity and surface tension had a direct influence on pretreatment. A systematic investigation of these parameters and their impact on enzymatic digestibility is drawn. C2mimOAc with β-value 1.32 resulted 97.7% of glucose yield using 10 FPU/g of biomass. A closer insight into the cellulose structural transformation has prompted a plausible mechanism explaining the better digestibility. The impact of these parameters on the digestibility can pave the way to customize the process to make biomass vulnerable to enzymatic attack.
•Dilute acid pretreatment of wheat straw (WS) at pilot scale (250kg/day).•Evaluation of three popular commercial enzymes for pretreated WS hydrolysis efficiency and inhibitor tolerance in rolling ...reactor.•Simultaneous saccharification and fermentation (SSF) employing in-house thermotolerant Saccharomyces cerevisiae.•This study suggests that selecting the right enzyme preparation is an indispensable tool for optimizing the ethanol yield.
Conversion of pretreated lignocellulosic biomass (LCB) into sugars is one of the critical steps for bioethanol production. High LCB hydrolysis could be achieved by employing robust enzymes having high inhibitor tolerance, low irreversible lignin binding, and low end-product inhibition. In this study, acid pretreatment of wheat straw was carried out at pilot scale (250kg/day) and three commercial cellulase preparations from Advanced Enzyme (AD), Novozyme (CL), and Genencor (AC) were evaluated for inhibitor (lignin, furfural, hydroxyl methyl furfural, vanillin) tolerance. Pretreated wheat straw (PWS) hydrolysis was carried out at different enzyme concentrations (1–30mg protein/g of PWS) under optimum pH and temperature in rolling bottle reactor. Simultaneous saccharification and fermentation was performed employing in-house thermotolerant Saccharomyces cerevisiae. Results indicated that, maximum saccharification (more than 85%) was achieved at low protein loadings (10–15mg protein/g PWS) of CL and this enzyme was also found to be more robust in presence of inhibitors. Maximum ethanol yield (78%) was found at 20mg protein/g of PWS using CL. This study suggests that inhibitors have significant detrimental effect on enzymes and better understanding of enzyme-inhibitor correlation with its critical moderation would help in further enhancing the LCB hydrolysis at low enzyme dosage.
Pretreatment of rice straw on pilot scale steam explosion has been attempted to achieve maximum sugar recovery. Three different reaction media viz. water, sulfuric acid and phosphoric acid (0.5%, ...w/w) were explored for pretreatment by varying operating temperature (160, 180 and 200°C) and reaction time (5 and 10min). Using water and 0.5% SA showed almost similar sugar recovery (∼87%) at 200 and 180°C respectively. However, detailed studies showed that the former caused higher production of oligomeric sugars (13.56g/L) than the later (3.34g/L). Monomeric sugar, followed the reverse trend (7.83 and 11.62g/L respectively). Higher oligomers have a pronounced effect in reducing enzymatic sugar yield as observed in case of water. Mass balance studies for water and SA assisted SE gave total saccharification yield as 81.8% and 77.1% respectively. However, techno-economical viability will have a trade-off between these advantages and disadvantages offered by the pretreatment medium.
Economic production of lignocellulose degrading enzymes for biofuel industries is of considerable interest to the biotechnology community. While these enzymes are widely distributed in fungi, their ...industrial production from other sources, particularly by thermophilic anaerobic bacteria (growth Topt ≥ 60 °C), is an emerging field. Thermophilic anaerobic bacteria produce a large number of lignocellulolytic enzymes having unique structural features and employ different schemes for biomass degradation, which can be classified into four systems namely; ‘free enzyme system’, ‘cell anchored enzymes’, ‘complex cellulosome system’, and ‘multifunctional multimodular enzyme system’. Such enzymes exhibit high specific activity and have a natural ability to withstand harsh bioprocessing conditions. However, achieving a higher production of these thermostable enzymes at current bioprocessing targets is challenging. In this review, the research opportunities for these distinct enzyme systems in the biofuel industry and the associated technological challenges are discussed. The current status of research findings is highlighted along with a detailed description of the categorization of the different enzyme production schemes. It is anticipated that high temperature-based bioprocessing will become an integral part of sustainable bioenergy production in the near future.
