Surplus availability of rice straw (RS) presents it as a potential feedstock for ethanol production. Steam explosion (SE) is considered as a green approach to extract fermentable sugars at lower ...cost. The present study deals with the reaction condition optimization for water and dilute acid assisted steam explosion of rice straw at different temperatures and explores the effect of structural properties of solid residue on enzymatic hydrolysis along with mass balance. SE conditions were optimized at pilot scale, raising the temperature from 170 to 200 °C in water assisted SE resulting in an increased glucan conversion from 21.4 to 42.5% at 15% solid loading using 1.5 FPU of cellulases g
–1
biomass. Further, it was improved up to 58.7% by increasing the enzyme dosage to 5 FPU, although it might lead to enhanced enzyme cost by threefold. To reduce costs, small amount of dilute acid (DA) was added during SE and lowering of enzyme consumption i.e. 1.5 FPU/g cellulose has been used to achieve 65.5% glucan conversion. Varying temperature and incorporate dilute acid during pretreatment induced structural alterations in biomass evident by compositional analysis, FT-IR and mass balance. Mass balance study revealed that the overall sugar recovery i.e. 58.7 and 38.8% and theoretical yield of ethanol shall be 222 and 186 L ton
–1
RS respectively, with and without DA addition.
Graphical Abstract
Multiple enzymes are required for efficient hydrolysis of lignocellulosic biomass and no wild type organism is capable of producing all enzymes in desired levels. In this study, steam explosion of ...wheat straw was carried out at pilot scale and a synthetic enzyme mixture (EnzMix) was developed by partially replacing the cellulase with critical dosages of commercially available accessory enzymes (β-glucosidase, xylanase and laccase) through central composite design. Highest degree of synergism (DS) was observed with β-glucosidase (1.68) followed by xylanase (1.36). Finally, benchmarking of EnzMix (Celluclast, β-glucosidase and xylanase in a protein ratio of 20.40: 38.43: 41.16, respectively) and other leading commercial enzymes was carried out. Interestingly, hydrolysis improved by 75% at 6 h and 30% at 24 h, respectively in comparison of control. By this approach, 25% reduction in enzyme dosage was observed for obtaining the same hydrolysis yield with opitimized enzyme cocktail. Thus, development of enzyme cocktail is an effective and sustainable approach for high hydrolysis efficiency.
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.
Lignin is produced as a byproduct in cellulosic biorefinery as well in pulp and paper industries and has the potential for the synthesis of a variety of phenolics chemicals, biodegradable polymers, ...and high value-added chemicals surrogate to conventional petro-based fuels. Therefore, in this critical review, we emphasize the possible scenario for lignin isolation, transformation into value addition chemicals/materials for the economic viability of current biorefineries. Additionally, this review covers the chemical structure of lignocellulosic biomass/lignin, worldwide availability of lignin and describe various thermochemical (homogeneous/heterogeneous base/acid-catalyzed depolymerization, oxidative, hydrogenolysis etc.) and biotechnological developments for the production of bio-based low molecular weight phenolics, i.e. polyhydroxyalkanoates, vanillin, adipic acid, lipids etc. Besides, some functional chemicals applications, lignin-formaldehyde ion exchange resin, electrochemical and production of few targeted chemicals are also elaborated. Finally, we examine the challenges, opportunities and prospects way forward related to lignin valorization.
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•2G Lignin as a bio-based biorefineries platform for highly advanced products preparation.•Thermocatalytic and biotechnological approaches were emphasized for lignin value addition.•Thermo catalytic approach is an effective process for lignin valorization in bulk scale.•In biological valorization, adipic acid production is promising towards scale-up.
The present study deals to visualise the impact of various process parameters, i.e. particle size and impregnation media over sugar released during steam explosion pretreatment. For this, 5, 10 and ...20 mm rice straw sizes were impregnated in water and dilute acid media (1%) followed by steam explosion at 180 and 200 °C. Pretreated slurry was further hydrolyzed by 5 and 10 FPU g−1 of residue varying 15 and 20% solid loading. The result showed that 10 mm particle size gave highest glucan conversion (88.7%) in acid impregnated steam explosion at 180 °C using 5 FPU g−1 of residue with 15% solid loading. Comparatively, water impregnated pretreated biomass results significantly lower glucan conversion (61.1%), which was further intensified to 77.7% at 10 FPU g−1 of residue with increased temperature. Furthermore, mass balance, compositional and structural transformation studies support our finding. Overall 30.6–81.1% sugar recovery was achieved with/or without acid pretreatment respectively.
SE pretreatment of rice straw by varying process parameters, i.e. particle size, impregnation media, temperature and solid loading for high glucan conversion. Display omitted
•Effect of varying the biomass particle sizes and solid loading using SE were studied.•Higher particle size significantly performs better on glucan conversion in acid media.•Higher solid loading in enzymatic hydrolysis results in lower glucan conversion.•Impregnation of DA increases the glucan conversion up to 45% at 180 °C using 5 FPU.•Structural transformations were correlated with sugar released with process mass balance.
•Impact of biomass particle size on glucan conversion was studied.•Maximum glucan conversion was obtained for 10 mm particle size.•Increasing the enzyme dosages results in 14% higher glucan ...conversion.•In the current set of parameters 10 mm particle size was found to be optimum.•Lower LOI and higher S/G ratio leading to higher overall sugar recovery.
Rice straw has a great potential for ethanol production due to its richness in polysaccharides and abundant availability, however, for efficient utilization of these polysaccharides, size reduction is a prerequisite step. Therefore, biomass particle size plays a vital role for cellulosic ethanol commercialization. In this study, the effects of rice straw particle size on dilute acid pretreatment efficiency and enzymatic hydrolysis are investigated. Different sizes; 5, 10 and 20 mm were subjected to dilute acid pretreatment in a continuous pilot scale system with a horizontal screw feeder reactor followed by enzymatic hydrolysis at varying solids (10 and 15%) and enzyme dosages (5 and 10 FPU/g of pretreated residue). The glucan hydrolysis for 5, 10 and 20 mm are 65.6, 80.0 and 60.0% using 5 FPU and 79.5, 93.4 and 72.8% using 10 FPU/g pretreated residue respectively at 10% loading, whereas, at 15% it is significantly lower in respective experiment. Overall sugar recovery with 10 mm is 63.8 and 72.9% with 5 and 10 FPU respectively. RS with 10 mm biomass particle size at both solid loadings and enzyme dosages resulted in much higher enzymatic hydrolysis than others and in turn the overall sugar recovery and this was found to be due to the variation in the degradation products and pseudolignin contents in the pretreated biomass. The insight into the structural intricacies of biomass after pretreatment are studied using FT-IR and SEM revealing significant changes in biomass properties responsible for improved sugar recovery.
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•Single-stage steam explosion utilized for high sugar recovery from CS.•Hot water extraction of CS prior to SE improved the glucan conversion by 38%.•Incorporating DA in extraction ...medium further increased glucan conversion by 30%.•Xylo-oligomers inhibited enzymatic hydrolysis evident by post washing experiments.•SA1-RT-200 reduced the CrI, G-lignin & xylan content leading to 79.3% C6 recovery.
Dilute acid (DA) pretreatment at pilot level failed for cotton stalk (CS) due to the technical issues posed by its inherent nature. Reasonable glucan conversion has been reported via two-stage pretreatment but adds on to the process cost. Proposed herewith is a single-stage steam explosion (SE) process preceded by water extraction resulting in high sugar recovery from CS. Raising the extraction temperature to 80°C increased the glucan conversion from 37.9 to 52.4%. Further improvement up to 68.4% was achieved when DA was incorporated during the room temperature extraction. LC-MS revealed the formation of xylo-oligomers limiting the glucan conversion in proportion to the length of xylo-oligomers. Varying extraction conditions induced structural alterations in biomass after SE evident by compositional analysis, Infrared Spectroscopy, X-Ray Diffraction and Scanning Electron Microscopy. Overall glucose recovery, i.e. 75.8–76.7% with and without DA extraction respectively was achieved.
Lignocellulosic material (LCM) is promising alternative resource for sustainable energy production such as ethanol and butanol and biohydrogen. Cellulose is an abundant renewable polymer of LCM found ...in plant cell walls (30–50%). The high crystallinity of cellulose makes it recalcitrant to hydrolysis into its individual sugar subunits for biofuels production. Moreover, ionic liquids are considered as green solvents and have been used for biomass solubilization. The present work describes three properties: Kamlet–Taft (K–T) parameters, viscosity and surface tension of five imidazolium-based ionic liquids (ILs); namely C2mimOAc, C4mimOAc, C2mimCl, C4mimCl and C4mimsBF4, and their efficiency in the cellulose structural transformation for improved enzymatic glucose recovery. Crystalline cellulose was treated with ILs at two different temperatures, i.e. 100 and 130 °C for 5 and 2 h, respectively, with 10% solid loading followed by enzymatic saccharification using 10 and 20 FPU/g substrate of commercial cellulases. ILs treatment of crystalline cellulose significantly reduces the crystallinity, which resulted in a very sharp increase of sugar yields after enzymatic saccharification. Cellulose treated for 130 °C/2 h resulted in better glucose yields as compared to 100 °C/5 h. ILs comprising acetate anion resulted in highest glucose yields and chloride based ILs performed moderately, whereas BF4− based IL was ineffective in transforming the cellulose structure. In order to decipher the possible reasons of varying efficiency of these ILs, the K–T parameters; hydrogen bond acidity (α), hydrogen bond basicity (β), solvent polarizability (π∗), kinematic viscosity (η) and surface tension (σ) were calculated for 100 and 130 °C. These results show that, among all the properties of ILs, hydrogen bond basicity (β) is relatively more important than kinematic viscosity and surface tension for impacting the structural transformation and subsequent enzymatic hydrolysis. C2mimOAc with high β value (1.32) and lower viscosity (4.4 cSt/s) and surface tension (30.3 mN/m) was found to be most efficient in cellulose transformation resulting in higher glucose yields (89.8%) upon saccharification. Effect of size of cation and anion of ILs and properties of regenerated cellulose is also examined by PXRD and FT-IR to further support the findings.
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•Treatment efficiencies of five ionic liquids are studied.•ILs with β > 0.72 resulted >55% glucose yield after 24 h.•Viscosity and surface tension of ILs have a negative correlation with glucose yields.•C2mimOAc with high β, smaller anion and shorter alkyl chain gave highest glucose yields with maximum reduction in CrI.•C4mimBF4 was not at all effective in improving the glucose yields.
Cost of cellulases is a major impediment in commercialization of cellulosic ethanol. To reduce the enzyme doses for the production of fermentable sugars from rice straw (RS), a series of alkali ...conditioning experiments were conducted prior to dilute acid (DA) pretreatment. This approach resulted in removal of a majority of extractives, ash, acetic acid, and part lignin, and thus resulted in lowering pseudolignin formation thereby increasing enzymatic hydrolysis yields. Glucan hydrolysis of 69.8%, 74.0%, and 83.5% was obtained at 10 wt % water insoluble solid (WIS) using 8 FPU enzyme/g WIS of biomass conditioned using 0.2, 0.4, and 0.5 wt % alkali prior to pretreatment, which is 14–37% higher than the control (61.0%). The overall sugar recovery in these experiments were 69.2%, 70.2%, and 68.5% at 15 wt % WIS resulting in a sugar concentration greater than 120 g/L, which in turn can produce approximately 5–6% w/v ethanol concentration in fermentation broth. It was found that this approach resulted in a decrease of the enzyme consumption vis-a-vis the conventional process by 46.4% to recover the same amount of sugars. This lowering of enzyme consumption has resulted in net savings, after taking into account the cost of alkali used in the conditioning steps.
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