Microwave-assisted Pretreatment Research Articles

A novel microwave-assisted γ-valerolactone and glycolic acid pretreatment for green and sustainable production of hemp fibres

Hemp, a sustainable crop, offers superior material properties suitable for diverse applications. This study aims to produce hemp fibre using a green and sustainable pretreatment method, thus exploring a novel microwave-assisted pretreatment method using a γ-valerolactone (GVL) and glycolic acid (GA) solution system, referred to as the GVL/GA pretreatment method. By optimising solid loading and reaction time, we significantly reduced water usage (50 %) and energy consumption (61.5 %) while maintaining fibre quality. The pretreatment method effectively removed lignin (88.7 %) and hemicellulose (39.3 %) without damaging the cellulose structure. The pretreated samples demonstrated a 45.7 % increase in glucose yield. Additionally, the characterisation of pretreated fibres revealed impressive fineness (4.4 dtex) and tenacity (4.0 cN/dtex), and the crystal structure remained intact with increased crystallinity (86 %). The HSQC NMR analysis unveiled that lignin undergoes structural modifications, enabling efficient lignin removal. GVL/GA pretreatment promotes green chemistry by minimising environmental impact and waste, using renewable resources. It provides a sustainable alternative to traditional methods, contributing to a greener industry.

Delignification and enzymatic hydrolysis kinetics of KOH microwave-assisted pretreated banana stem for bioethanol production

Biomass pretreatment is essential to facilitate lignin removal and enhance cellulose concentration for optimal bioethanol production. Therefore, this research aimed to determine the effects of conventional KOH (KP) and Combined KOH microwave-assisted (CKMP) pretreatment on the banana stem (BS) composition, analyzing the kinetics of lignin removal at various temperatures and KOH concentrations for 25 min. Kinetics variables were calculated by fitting experimental data and cellulose was hydrolyzed to produce reducing sugars. The results showed that the highest lignin removal for KP and CKMP were 37.11%, and 40.39%, respectively, with CKMP having the lowest activation energy of approximately 2.688 kJ mol−1. CMCase and FPase activity were 1988.3474 and 1605.4187 U mL−1, respectively, which were significantly higher than the values reported in previous research. The maximum concentration of reducing sugars achieved was 17.69 g L-1, with an enzyme concentration of 50% (v/w), pH 5, and a hydrolysis duration of 25 h. Michaelis constant varied from 0.0037 to 0.0079, and the maximal rate ranged from 1.28 × 10−6 to 2.76 × 10−6 Mol L−1 s−1 when computing the reaction rate using the Michaelis–Menten kinetics model.

Effect of potassium persulphate-induced microwave pretreatment for cost-effective sludge solubilization and bioenergy recovery

The disintegration of municipal waste activated sludge (MWAS) by energy-intensive physical pretreatments is considered expensive. In the present study, an effort was undertaken to disintegrate the sludge by microwave assisted pretreatment (MAP) in an energy-efficient and economical way by combining the microwave with oxidant potassium persulphate. Besides, the sulphate radicals generated through activated persulfate can efficiently disintegrate and solubilize sludge. In this context, microwave pretreatment was combined with potassium persulfate to activate the generation of sulphate radicals for economically enhanced sludge solubilization. MAP was done by varying the microwave power levels (10 to 50 %) and pretreatment time (0 to 30 min). Microwave assisted potassium persulphate pretreatment (MAPPP) was done by varying the potassium per sulphate dosage (0.005 to 0.04 g/g Total solids (TS) and pretreatment time (0 to 14 min). Combining microwave with potassium persulfate brings about a synergistic effect, generating sulphate and hydroxyl radicals that can effectively disintegrate and solubilize biopolymers of sludge. A higher sludge lysis rate of 37.25 % was achieved by this microwave assisted potassium persulfate pretreatment (MAPPP) when compared to microwave assisted pretreatment (MAP) alone (26.27 % after thickening). A higher methane yield of 219.14 mL/g Volatile solids (VS) was obtained through MAPPP compared to MAP (154.22 mL/g VS). The detailed mass, energy, and economic assessment at a large-scale level for MAP and MAPPP revealed that MAPPP was energetically and economically feasible with an energy ratio of 1.22 and net profit of 42.03 USD/Ton compared to MAP. Thus, it can be confirmed that MAPPP was economically viable to implement on a large scale.

Thermostatic microwave-assisted pretreatment of corn stover at atmospheric pressure to enhance saccharification

A large amount of corn stover waste is produced from processing industries. In this study, the thermostatic microwave-assisted alkali pretreatment (TMAAP) of corn stover at atmospheric pressure was investigated to improve the utilization rate. The optimized conditions include pretreated time, NaOH concentration, temperature, initial power, and solid-liquid ratio. The pretreated corn stover samples for the enzymatic hydrolysis were studied on the crystallinity, surface microstructural changes, functional group changes and compositional analysis. The results showed cellulose recovery and lignin removal in the solid residue reached 87.39 % and 87.59 %, respectively when the corn stover was subjected for 45 min at a microwave reactor with an initial 600 W, 100 °C and 5 % NaOH. After TMAAP, the enzyme hydrolysis efficiency of the corn stove reached 85.40 %, which was higher than that of the untreated (59.96 %). The experiment can be carried out at atmospheric pressure without strict conditions. The techno-economic analysis predicts revenue of 22.82 USD by processing 100 kg of waste corn stover combined with enzyme cost analysis. To conclude, glucose (26.37 kg) and xylose (1.19 kg) were produced from corn stover (100 kg, 39.31 % glucan, 17.34 % xylan, 23.60 % lignin). The results can give insights into establishing an efficient alkali pretreatment of corn stove waste to produce glucose.

Enhanced Cellulose Content in Microwave-Assisted Sulfuric Acid Pretreatment of Java Grass

This study investigated the enhancement of cellulose content in Java grass (Cyperus rotundus) through microwave-assisted sulfuric acid pretreatment. The research involved soaking Java grass in varying concentrations of H2SO4 (1.5%, 3%, and 4.5%) and subjecting it to microwave irradiation at 2450 MHz for different durations (25, 35, and 45 minutes). The results showed that the highest cellulose content of 43.61% was achieved with a 1.5% H2SO4 solution for 45 minutes, representing a 90.3% increase from the pre-treatment level of 22.91%. The microwave-assisted pretreatment effectively disrupted the lignocellulosic structure, reduced cellulose crystallinity, and increased biomass surface area, thereby enhancing enzymatic hydrolysis. However, an anomaly was observed in the lignin content, which increased from 14.3% to 36.65% post-treatment, likely due to errors in lignin determination and the formation of pseudo-lignin.

Unlocking the potential of spent coffee grounds via a comprehensive biorefinery approach: production of microbial oil and carotenoids under fed-batch fermentation.

The valorization of renewable feedstock to produce a plethora of value-added products could promote the transition towards a circular bioeconomy. This study presents the development of cascade processes to bioconvert spent coffee grounds (SCGs) into microbial oil and carotenoids employing sustainable practices. The stepwise recovery of crude phenolic extract and coffee oil was carried out using green or recyclable solvents, i.e., aqueous ethanol and hexane. Palmitic acid (43.3%) and linoleic acid (38.9%) were the major fatty acids in the oil fraction of SCGs. The LC-MS analysis of crude phenolic extracts revealed that chlorogenic acid dominated (45.7%), while neochlorogenic acid was also detected in substantial amounts (24.0%). SCGs free of coffee oil and phenolic compounds were subjected to microwave-assisted pretreatment under different irradiations and solvents to enhance subsequent enzymatic saccharification. Microwave/water pretreatment at 400 W, followed by enzymatic hydrolysis with proteases, hemicellulases, and cellulases, at 50g/L initial SCGs, led to satisfying overall yields of cellulose (75.4%), hemicellulose (50.3%), and holocellulose (55.3%). Mannan was the most extractable polysaccharide followed by galactan and arabinan. SCGs hydrolysate was used in fed-batch bioreactor fermentations with Rhodosporidium toruloides to produce 24.0g/L microbial oil and carotenoids of 432.9μg/g biomass.

Enzymatic hydrolysis of cellulose banana stem (alkaline microwave-assisted pre-treatment)

The banana stem waste holds immense promise as a readily available and abundant source of lignocellulosic biomass, making it a compelling alternative for biofuel and biochemical applications. Therefore, this study focuses on investigating the impact of both time and substrate loading on the enzymatic hydrolysis of banana stem cellulose that has undergone alkaline microwave-assisted pre-treatment. The pre-treatment method involves subjecting the biomass to 5% KOH for 30 min, followed by microwave exposure at 300 W for 5 min, a process aimed at enhancing the accessibility of cellulose. Enzymatic hydrolysis experiments were carried out utilizing cellulase enzymes derived from Aspergillus niger, with variations in hydrolysis times (ranging from 5 to 45 h) and enzyme-to-substrate ratios (ranging from 1:1 to 1:10). The results of this investigation revealed a substantial improvement in hydrolysis efficiency, owing to the synergistic effects of alkaline microwave-assisted pre-treatment, signifying enhanced cellulose accessibility. Notably, the highest concentration of reducing sugars (1.3 mg mL−1) was achieved at a substrate-to-enzyme ratio of 1:1 and a hydrolysis duration of 45 h. These findings provide valuable insights into the conversion of lignocellulosic biomass, emphasizing the potential of integrated pre-treatment strategies for sustainable biorefinery applications. This research contributes to advancing our understanding of lignocellulosic biomass utilization, offering a promising avenue for biofuel and biochemical production from banana stem waste.

Effect of temperature and time on alkaline pretreatment and alkaline microwave-assisted pretreatment on banana stem composition

Effect of temperature and time on alkaline pretreatment and alkaline microwave-assisted pretreatment on banana stem composition

Effect of Acids and Alkaline Pretreatment of Used Tea Waste Powder under Microwave-Assisted Pretreatment

There are numerous methods to enhance the quality of cellulose for efficient and sustainable fuel production, the acid and alkaline pretreatment methods have become increasingly popular due to their accessibility and affordability. These methods are typically used to eliminate lignin, disrupt the cellulose crystalline structure, and reduce its rigidity. This study focuses on the use of pretreatment with four different types of acids (Hydrochloric Acid, Phosphoric Acid, Acetic Acid, and Sulfuric Acid) and four types of alkaline (Calcium Hydroxide, Sodium hydroxide, Potassium Hydroxide, and Ammonium Hydroxide) were used to soak the used tea waste powder as a raw material under microwave-assisted pretreatment. The effectiveness of acid and alkaline pretreatment methods under microwave heating on used tea waste powder was evaluated through infrared analysis. The experiments were conducted at varying microwave temperatures (100–200 °C), reaction times (2–7 min), and with a 2 g doses of used tea waste powder in 100 mL of diluted acid, and 5% of alkaline solution. The weight loss of liquid and solid samples after acid and alkaline pretreatment under the aid of microwave pretreatment were calculated. FTIR analysis results showed a significant improvement in the characteristics of the treated samples compared to the untreated used tea waste powder.

Effect of blanching, freezing and microwave-assisted pretreatment methods on chlorophyll extraction from Sauropus androgynus leaves

Sauropus androgynus is grown commonly in Vietnam, which has a high content of bioactive substances including chlorophyll, polyphenols, and antioxidant activity. Sauropus androgynus is used as food or a colorant for traditional Vietnamese cakes. Green pigments are employed in various industrial sectors, such as food, drinks, soap, and drug. Chlorophyll can be replaced synthetic green pigments that might be unhealthy. In this study, the effect of chlorophyll extraction efficiency and perceptional green color by extraction condition combinined with physical pretreatment methods was investigated using Sauropus androgynus leave as a model. Fresh raw materials were pre-treated by blanching, freezing and microwave treatment at 55w/g for 3 min and then extracted with 40% (v/v) ethanol solvent. The best chlorophyll recovery efficiency (CRE) from Sauropus androgynus by heat pretreatment methods with and without microwave assistance was 32.035% and 25.784% of chlorophyll content in material; or 1.081 mg/g d. w and 0.862 mg/g d. w of fresh leaves, respectively. The chlorophyll extract is then spray-dried to form a water-dispersible powder. Chlorophyll extracted with microwave-assisted pretreatment having high CRE that has potential applications in food production, but green color is not much more favorable than the non-microwave assisted sample.

Enhancing sugar yield for bioconversion of rice straw: Optimization of Microwave-assisted Pretreatment using dilute acid hydrolysis

Producing of biofuels from lignocellulosic biomass, such as rice straw, has increased with the need to reduce dependence on fossil fuels and mitigate climate change. However, the complex structure of lignocellulosic material requires pretreatment to break down the matrix and release the fermentable sugars. In this study, microwave-assisted dilute acid hydrolysis was optimized as a pretreatment method for enhancing the bioconversion of rice straw. Response Surface Methodology was used to investigate the effects of reaction time, temperature, and catalyst concentration on sugar yield. The optimized conditions were determined to be a reaction time of 10 min, reaction temperature of 75 °C, and a catalyst concentration of 1.5 g/L, resulting in a total sugar yield of 27.81 ± 0.73%. The findings demonstrate the potential of this method as an effective pretreatment for enhancing the bioconversion of rice straw, contributing to the development of sustainable energy sources.

Elucidating multi-scale deconstruction of bamboo crystalline cellulose by novel acetylcholine chloride based deep eutectic solvents for enhanced enzymatic hydrolysis

Exploration and application of novel and sustainable deep eutectic solvents (DESs) on lignocellulose pretreatment are promising approaches to efficient bioconversion. However, comprehensive understanding on efficient DESs selection and inner mechanisms of lignocellulose deconstruction are still limited. Herein, bio-based acetylcholine chloride (AChCl) was firstly utilized as hydrogen bond acceptor in cooperation with lactic acid, urea and glycerol respectively for microwave-assisted pretreatment on moso bamboo in short time. High enzymatic conversion yield of bamboo cellulose (∼85%) was achieved by lactic acid-AChCl DES due to its lower pH value and viscosity, followed by glycerol-AChCl and urea-AChCl DES. In addition to the features of proposed DESs, changed chemical and physical properties of highly recalcitrant bamboo biomass after pretreatments were systematically determined. Besides of great amount of lignin (∼90%)/ xylan (100%) removal, micro- to nano-scale variations of cellulose structures including more dissociated microfibrils, lowered crystallinity, and enlarged crystallite sizes all played key roles in promoting bioconversion yields. Moreover, the multi-factors contributing to improved hydrolysis performance were integrated to evaluate the effects of novel DESs pretreatments on lignocellulose deconstruction, which may provide new strategies on bioconversion enhancement and process optimization.

Natural arginine-based deep eutectic solvents for rapid microwave-assisted pretreatment on crystalline bamboo cellulose with boosting enzymatic conversion performance

Development of amino acid-based natural deep eutectic solvents (DESs) pretreatment technology on lignocellulosic biomass is a promising approach to biorefinery. In this study, for arginine-based DESs with different molar ratios, the viscosity and Kamlet-Taft solvation parameters were quantified to evaluate the pretreatment performance on bamboo biomass. Further, microwave assisted DES pretreatment was eminent, evidenced by 84.8% lignin removal and increased saccharification yield (from 6.3% to 81.9%) in moso bamboo at 120 °C and ratio of 1:7 (arginine: lactic acid). Results showed degradation of lignin molecules together with release of phenolic hydroxyl units after DESs pretreatment, which is conducive to subsequent utilization. Meanwhile, DES-pretreated cellulose exhibited unique structural characteristics including destroyed crystalline region of cellulose (Crystallinity Index from 67.2% to 53.0%), decreased crystallite size (from 3.41 nm to 3.14 nm) and roughened fiber surface. Thus, arginine-based DES pretreatment has excellent potential in bamboo lignocellulose pretreatment.

High-pressure microwave-assisted pretreatment of softwood, hardwood and non-wood biomass using different solvents in the production of cellulosic ethanol

BackgroundPretreatment is an indispensable stage of the preparation of lignocellulosic biomass with key significance for the effectiveness of hydrolysis and the efficiency of the production of cellulosic ethanol. A significant increase in the susceptibility of the raw material to further degradation can be attained as a result of effective delignification in high-pressure conditions. With this in mind, a method of high-pressure pretreatment using microwave radiation and various solvents (water, 40% w/v NaCS, 1% v/v H2SO4, 1% w/v NaOH or 60% v/v EtOH with an addition of 1% v/v H2SO4) was developed, enabling the acquisition of biomass with an increased susceptibility to the process of enzymatic hydrolysis. The medium obtained in this way can be used for the production of cellulosic ethanol via high-gravity technology (lignocellulosic media containing from 15 to 20% dry weight of biomass). For every type of biomass (pine chips, beech chips and wheat straw), a solvent was selected to be used during the pretreatment, guaranteeing the acquisition of a medium highly susceptible to the process of enzymatic hydrolysis.ResultsThe highest efficiency of the hydrolysis of biomass, amounting to 71.14 ± 0.97% (glucose concentration 109.26 ± 3.49 g/L) was achieved for wheat straw subjected to microwave-assisted pretreatment using 40% w/v NaCS. Fermentation of this medium produced ethanol concentration at the level of 53.84 ± 1.25 g/L. A slightly lower effectiveness of enzymatic hydrolysis (62.21 ± 0.62%) was achieved after high-pressure microwave-assisted pretreatment of beech chips using 1% w/v NaOH. The hydrolysate contained glucose in the concentration of 91.78 ± 1.91 g/L, and the acquired concentration of ethanol after fermentation amounted to 49.07 ± 2.06 g/L. In the case of pine chips, the most effective delignification was achieved using 60% v/v EtOH with the addition of 1% v/v H2SO4, but after enzymatic hydrolysis, the concentration of glucose in hydrolysate was lower than in the other raw materials and amounted to 39.15 ± 1.62 g/L (the concentration of ethanol after fermentation was ca. 19.67 ± 0.98 g/L). The presence of xylose and galactose was also determined in the obtained fermentation media. The highest initial concentration of these carbohydrates (21.39 ± 1.44 g/L) was observed in beech chips media after microwave-assisted pretreatment using NaOH. The use of wheat straw after pretreatment using EtOH with an addition of 1% v/v H2SO4 for the preparation of fermentation medium, results in the generation of the initial concentration of galactose and xylose at the level of 19.03 ± 0.38 g/L.ConclusionThe achieved results indicate a high effectiveness of the enzymatic hydrolysis of the biomass subjected to high-pressure microwave-assisted pretreatment. The final effect depends on the combined use of correctly selected solvents for the different sources of lignocellulosic biomass. On the basis of the achieved results, we can say that the presented method indicates a very high potential in the area of its use for the production of cellulosic ethanol involving high-gravity technology.

Progress and challenges of Microwave-assisted pretreatment of lignocellulosic biomass from circular bioeconomy perspectives

The recent scenario has witnessed the augmenting demand for energy precursors primarily from renewable ways in respect of the natural environment. The high energy along with the cost-intensive nature of the conventional approaches directed the researchers to find out an effective and promising method that principally uses the microwave for the pretreatment. The formation of heat energy from electromagnetic energy through polar particle rotation would be noted to be the core principle of the aforesaid effective approach. The microwave treatments speed up the destruction of complex structure of the biomass by applying a specific range of heat over the polar parts in a selective manner in the aqueous medium. In this review, the implementation of microwave-assisted green approaches for modeling an integrated circular bioeconomic strategy to potentially use lignocellulosic biomass for bioproducts is discussed.

Cellulosic Ethanol Production Using Waste Wheat Stillage after Microwave-Assisted Hydrotropic Pretreatment.

One of the key elements influencing the efficiency of cellulosic ethanol production is the effective pretreatment of lignocellulosic biomass. The aim of the study was to evaluate the effect of microwave-assisted pretreatment of wheat stillage in the presence of sodium cumene sulphonate (NaCS) hydrotrope used for the production of second-generation bioethanol. As a result of microwave pretreatment, the composition of the wheat stillage biomass changed significantly when compared with the raw material used, before treatment. Microwave-assisted pretreatment with NaCS effectively reduced the lignin content and hemicellulose, making cellulose the dominant component of biomass, which accounted for 42.91 ± 0.10%. In post pretreatment, changes in biomass composition were also visible on FTIR spectra. The peaks of functional groups and bonds characteristic of lignins (C–O vibration in the syringyl ring, asymmetric bending in CH3, and aromatic skeleton C–C stretching) decreased. The pretreatment of the analyzed lignocellulosic raw material with NaCS resulted in the complete conversion of glucose to ethanol after 48 h of the process, with yield (in relation to the theoretical one) of above 91%. The highest observed concentration of ethanol, 23.57 ± 0.10 g/L, indicated the high effectiveness of the method used for the pretreatment of wheat stillage that did not require additional nutrient supplementation.

Unveiling the potential of water as a co-solvent in microwave-assisted delignification of sugarcane bagasse using ternary deep eutectic solvents

Deep eutectic solvents (DESs) have become popular owing to their biodegradability and recyclability. In this study, the influence of water as a co-solvent is demonstrated to enhance the properties of choline based ternary DESs. A fast and energy-efficient microwave-assisted pre-treatment process was developed for delignification of sugarcane bagasse (SB). The effectiveness of SB fractionation was revealed by incorporating Lewis acids (MgCl2.6H20, NiCl2.6H20) with the DESs for pre-treatment and Choline chloride: Ethylene glycol: NiCl2.6H20 (CC:EG:NI) at a molar ratio 1:2:0.016 with 20w% water as a co-solvent provided the most promising result, with 84% delignification and 99% enzyme digestibility. Water was also employed as an anti-solvent to facilitate lignin solubility and exhibited up to 26w% lignin yield from DES liquor with maximum DES recovery of 95% (w/w). Water distinctly affects the density, viscosity, and intermolecular hydrogen bonding of the DES and its impact on the process dynamics is worth further exploration.

Microwave Assisted Pretreatment of Szarvasi (Agropyron elongatum) Biomass to Enhance Enzymatic Saccharification and Direct Glucose Production.

Biomass from perennial plants can be considered a carbon-neutral renewable resource. The tall wheatgrass hybrid Szarvasi-1 (Agropyron elongatum, hereafter referred to as “Szarvasi”) belongs to the perennial Poaceae representing a species, which can grow on marginal soils and produce large amounts of biomass. Several conventional and advanced pretreatment methods have been developed to enhance the saccharification efficiency of plant biomass. Advanced pretreatment methods, such as microwave-assisted pretreatment methods are faster and use less energy compared to conventional pretreatment methods. In this study, we investigated the potential of Szarvasi biomass as a biorefinery feedstock. For this purpose, the lignocellulosic structure of Szarvasi biomass was investigated in detail. In addition, microwave-assisted pretreatments were applied to Szarvasi biomass using different reagents including weak acids and alkali. The produced pulp, hydrolysates, and extracted lignin were quantitatively characterized. In particular, the alkali pretreatment significantly enhanced the saccharification efficiency of the pulp 16-fold compared to untreated biomass of Szarvasi. The acid pretreatment directly converted 25% of the cellulose into glucose without the need of enzymatic digestion. In addition, based on lignin compositional and lignin linkage analysis a lignin chemical model structure present in Szarvasi biomass could be established.

The effect of microwave power on lignocellulose content, physical and chemical characteristics of biomass: A review

Bioethanol is alternative energy derived from biomass that can be obtained from the agricultural industry to replace fossil fuels. The issue with biomass to energy conversion is the presence of lignin in lignocellulose biomass which inhibits the hydrolysis process. Microwave-acid pre-treatment is a method that combines microwaves and H2SO4 to break down lignin. In other studies, various microwave power is studied. The aim of this review is to provide insight and novelty into the effect of microwave power that is used on the lignocellulose content of rape straw and the physical and chemical characteristics of biomass after pre-treatment. Various microwave powers on delignification processes were presented, while the physical and chemical characteristics of pretreated biomass and also the prospect of future applications of microwave-assisted pretreatment were also discussed.

Microwave-assisted pretreatment of wet microalgal biomass for recovery of biofuel precursors

Pretreatment of microalgal biomass is essential for the maximal recovery of biofuel precursors packed inside the complex microalgal cell wall. In the present work, microwaves were exploited for efficient pretreatment of wet microalgal biomass. A response surface methodology – Box Behnken design (RSM-BBD) was utilized to obtain the optimum conditions for biomass pretreatment, and a mathematical model was devised. Using the designed experimental setup, the optimum conditions were obtained as 5 min of microwave irradiation time, 700 W output power, and 2 gL-1 microalgal biomass concentration. The model was further validated experimentally. The pretreatment results were confirmed qualitatively through microscopic observations and quantitatively in terms of sugar release and lipid extraction. The optimum conditions were found promising to enhance the lipid extraction by 55.32% compared to the untreated condition. Additionally, the present design showed the importance of water as a green solvent for biomass pretreatment under microwave irradiation. Overall, the current attempt facilitates a cost-effective, green methodology for wet microalgal biomass pretreatment in a short duration.