Microwave Assisted Alkaline Pretreatment Research Articles

Development of microwave-assisted alkaline pretreatment methods for enhanced sugar recovery from bamboo and corn cobs: Process optimization, chemical recyclability and kinetics of bioethanol production

The present study optimized two microwave-assisted alkaline (Na3PO4.12H2O and NaOH) pretreatment methods for the enhancement of sugar recovery from different lignocellulosic substrates (bamboo and corn cobs) with varying structural compositions. Subsequently, the chemical recyclability of the optimized alkaline pretreatments were evaluated on corn cobs. Furthermore, kinetics of microbial cell growth and bioethanol production in simultaneous saccharification and fermentation (SSF) processes were assessed. The optimized Na3PO4.12H2O pretreatment conditions resulted in the maximum reducing sugar yield (0.512 g/g) from corn cobs. Interestingly, the recyclability studies demonstrated that the NaOH-based black liquor resulted in a slightly higher average sugar yield (0.37 g/g) compared to the Na3PO4.12H2O (0.31 g/g) over three pretreatment cycles. Kinetics showed a maximum specific growth rate and maximum potential bioethanol concentration of 0.175 h−1 and 16.928 g/L respectively for the optimized NaOH pretreated corn cobs. The findings from this study provide significant knowledge enhancements pertaining to the use of gold standard, well-known NaOH methods, in addition to the emerging Na3PO4.12H2O alkaline catalyst for the pretreatment of lignocellulosic substrates with varying structural compositions. Moreover, recyclability of Na3PO4.12H2O and NaOH black liquor demonstrated the potential to reduce costs associated with the application of chemicals and fresh water in pretreatment systems. Kinetics of cell growth and bioethanol production elucidates noteworthy indices such as the maximum specific growth rate of the cells, lag time and maximum bioethanol production for lignocellulosic process development and scale-up procedures.

Microwave Assisted Alkaline Pretreatment of Algae Waste in the Production of Cellulosic Bioethanol

Biomass pretreatment has an important role in the production of cellulosic bioethanol. In this study, the effectiveness of microwave assisted alkaline pretreatment of algae waste was analysed. After pretreatment, the product was hydrolysed using sulphuric acid. The effects of microwave power, irradiating time, solid–liquid ratio and NaOH concentration were examined. Under the best conditions, the fermentable sugars were converted to cellulosic bioethanol using Saccharomyces Cerevisiae with a bioethanol yield of 1.93 ± 0.01 g/g and a fermentation efficiency of 40.4%. The reducing sugars concentration was 30% higher than that obtained from conventional hydrolysis without pretreatment. The obtained results suggest that microwave assisted alkaline pretreatment is effective in improving the production of cellulosic bioethanol of algae waste compared to that without microwave effect. Considering energy consumption, low microwave power and short microwave irradiation time are favourable for this pretreatment.

A biorefinery based on brewer`s spent grains: Arabinoxylans recovery by microwave assisted pretreatment integrated with butanol production

This study proposes an integrated biorefinery of brewer’s spent grain (BSG) based on the application of a microwave pretreatment to obtain bioproducts, such as arabinoxylans (AX) and an advanced biofuel, such as biobutanol. A prehydrolysate with 17 g/L AX was obtained at 172 °C and 0.38 M NaOH, which were subsequently precipitated using an organosolvent process, recovering 133 kg AX/t BSG. The subsequent enzymatic hydrolysis with endo-xylanases significantly increased the concentration of oligomers with 2–6 units of xylose. The presence of oligosaccharides with a degree of polymerization (DP) from 3 to 27 was confirmed by MALDI-TOF MS. On the other hand, the pretreated solid residue obtained in the microwave assisted alkaline pretreatment was enzymatically hydrolyzed with cellulases and fermented by Clostridium beijerinckii, producing 9.9 g/L butanol (28 kg butanol/t BSG and 37 kg ABE/t BSG). Thus, the potential for the efficient use of BSG in an integrated biorefinery was demonstrated.

Investigation of Rheological Behavior of Untreated and Microwave-Assisted Alkaline Pretreated Sugarcane Straw for Biofuel Production

Biomass slurries, such as those subjected to microwave-assisted alkaline (MAA) pretreatment, will become common substrates for the production of biofuels in the future. While the rheology of acid and ionic liquid pretreated biomass is known, the rheology of alkaline pretreated biomass is not yet reported; hence, the goal of this study was to establish the rheological characteristics of untreated and MAA pretreated sugarcane straw (SC). Using rotational rheometry and rheological models, the rheology of SC slurries was assessed as a function of particle size and insoluble solids concentration. In the range of 5–17% insoluble solids concentration, the slurries were consistently pseudo-plastic (n = 0.33 ± 0.02), possessed yield stress with their flow accurately described by the Casson rheological model (R2 = 0.98–0.99). The apparent viscosity and yield stress increased by two orders of magnitude with an increase in insoluble solids concentration. Essentially, MAA pretreated slurries exhibited significantly higher values of apparent viscosity and yield stress than the untreated ones, in the range of 55–80% and 21–63% for particle sizes of < 63 µm (P63) and 90–180 µm (P90), respectively. Pretreated P63 samples exhibited higher apparent viscosity and yield stress than the P90. On the other hand, for untreated samples, P63 samples had a reduced apparent viscosity than P90 samples. The results of this study definitively reveal that MAA significantly increases the shear rate dependent shear viscosity values along with the yield stress of biomass slurries. This will, therefore, serve as a benchmark for characterizing other MAA pretreated biomass slurries to guide the design of industrial-scale production equipment.

Enhanced production of reducing sugars from paragrass using microwave-assisted alkaline pretreatment

The main aims of this study were to examine the effectiveness of pretreatment methods for enhancing the conversion of Brachiara mutica (paragrass) lignocellulose into valuable reducing sugars by enzymatic hydrolysis. The pretreatments studied included alkali alone, microwave-assisted alkali, acid alone, and microwave-assisted acid. It was found that the application of microwave irradiation during alkaline pretreatment with an alkali-to-biomass ratio of 5% (w w−1) for 30 min at 120 °C markedly increased the total reducing sugar (TRS) yield after enzymatic hydrolysis from 316 mg g−1 dry pretreated paragrass without microwave irradiation to 750 mg g−1 dry pretreated paragrass with microwave irradiation. In particular, the microwave-assisted alkaline pretreatment markedly increased xylose production and enhanced the enzymatic digestibility of cellulose. The concentrations of 5-hydroxymethylfurfural (HMF) and furfural after the microwave-assisted pretreatment were well below 1.0 kg m−3, the suggested threshold concentration of furfurals where yeast inhibition may begin.

Production of formic acid from oil palm empty fruit bunch via dilute acid hydrolysis by response surface methodology

Formic acid is the simplest carboxylic acid which has myriad applications in food, textiles, agriculture, pharmaceutics, and chemicals. Formic acid can be synthesized from hydrolysis of lignocellulosic biomass. Oil palm empty fruit bunch (OPEFB) is lignocellulosic biomass produced by oil palm industries to which cellulose content has potential for conversion into formic acid by hydrolysis. We investigated effects of three parameters in acid-catalysed hydrolysis reaction of OPEFB such as reaction time (20, 40, 60 minutes), temperature (140, 160, 180 °C), and H2SO4 concentration (0.3; 0.5; 0.7 M) and optimized them to obtain maximum formic acid concentration by using response surface methodology. Microwave assisted alkaline pretreatment of OPEFB sample under microwave radiation at 840 Watt for 9 minutes with 2% NaOH concentration was done prior to hydrolysis. The pretreatment was effective to reduce lignin content of OPEFB from 28.9% to 7.6%. The highest actual formic acid concentration we obtained from the experiment was 2725 ppm at 180 °C, 60 minutes reaction time, and 0.5 M H2SO4. While according to the polynomial model, the optimal condition for obtaining maximum formic acid concentration of 2890.673 ppm was at 180 °C, reaction time of 60 minutes, and 0.3 M H2SO4.

Optimization of microwave-assisted alkaline pre-treatment method for the cellulolytic fermentation of abaca stripping waste into glucose

Abaca fiber remains a vital export product that contributes primarily to the continuous economic growth of the Philippines. However, the voluminous amount of byproducts generated has consistently caused setbacks which often result to major losses to the growing abaca industry in the country. In an attempt to provide a practical solution to the emerging problem, we investigate the utilization of abaca stripping waste (ASW) as a precursor material to produce bioethanol. We test the extent of conversion of the hemicellulose-rich by product to glucose. A box-behnken experimental design was used to obtain the optimal conditions in the conversion process. Alkaline concentration (%), microwave power (W), and microwave time (min) were found to have significant influence on the glucose yield. Actual values of these independent variables were chosen on the basis of preliminary experimental results. Optimum conditions using ridge analysis were found to be: alkaline concentration 2.55%, microwave power 124.0 W, and microwave time at 1.0 min. Conversion to glucose was also performed at optimum conditions. In conclusion, a high glucose yield obtained which is suitable for bioethanol fermentation presents evidence encouraging the utilization of abaca stripping waste to produce high value products.

Valorization of Brewers' Spent Grain for the Production of Lipids by Oleaginous Yeast.

Brewers’ spent grain (BSG) accounts for 85% of the total amount of by-products generated by the brewing industries. BSG is a lignocellulosic biomass that is rich in proteins, lipids, minerals, and vitamins. In the present study, BSG was subjected to pretreatment by two different methods (microwave assisted alkaline pretreatment and organosolv) and was evaluated for the liberation of glucose and xylose during enzymatic saccharification trials. The highest amount of glucose (46.45 ± 1.43 g/L) and xylose (25.15 ± 1.36 g/L) were observed after enzymatic saccharification of the organosolv pretreated BSG. The glucose and xylose yield for the microwave assisted alkaline pretreated BSG were 34.86 ± 1.27 g/L and 16.54 ± 2.1 g/L, respectively. The hydrolysates from the organosolv pretreated BSG were used as substrate for the cultivation of the oleaginous yeast Rhodosporidium toruloides, aiming to produce microbial lipids. The yeast synthesized as high as 18.44 ± 0.96 g/L of cell dry weight and 10.41 ± 0.34 g/L lipids (lipid content of 56.45 ± 0.76%) when cultivated on BSG hydrolysate with a C/N ratio of 500. The cell dry weight, total lipid concentration and lipid content were higher compared to the results obtained when grown on synthetic media containing glucose, xylose or mixture of glucose and xylose. To the best of our knowledge, this is the first report using hydrolysates of organosolv pretreated BSG for the growth and lipid production of oleaginous yeast in literature. The lipid profile of this oleaginous yeast showed similar fatty acid contents to vegetable oils, which can result in good biodiesel properties of the produced biodiesel.

Optimization of sugar recovery efficiency using microwave assisted alkaline pretreatment of cassava stem using response surface methodology and its structural characterization

Cassava stem is one of the prominent lignocellulosic wastes and has potential as a feedstock for fermentable sugar production. In this study, response surface methodology (RSM) with Box-Behnken design (BBD) was employed to investigate optimum conditions for microwave assisted alkaline pretreatment of cassava stem. Effect of four variables such as reaction time (60–120 s), NaOH concentration (2–4% w/v), solid to liquid ratio (1:25–1:75 g/ml), and microwave frequency (360–720 Hz) were evaluated to improve the sugar recovery. The quadratic model indicated that, reaction time of 116.4 s, NaOH concentration of 3.21% (w/v), substrate to liquid ratio of 1:62.07 g/ml and microwave frequency of 719.86 Hz was found to be optimum and obtained a maximum yield of 43.60 μg/ml of reducing sugar and 91.71 μg/ml of xylose. Under this condition, the cellulose content of cassava stem was increased from 33.27% to 52.34%, while the hemicellulose and lignin content was decreased from 32.30% to 27.15% and 27.15% 14.59%, respectively. Moreover, to evaluate the effectiveness of the pretreatment, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis were employed on the untreated and pretreated cassava stem. These results suggest that the microwave assisted alkaline NaOH pretreatment (MAASHP) influences the fermentable sugar production significantly and further it can be utilized effectively for bioethanol production.

Wheat Straw Bio-refining Part II: Optimization of Alkali Pre-treatment Method with Microwave Radiation for Fermentable Sugars Separation

Background: The potential of microwave-assisted heating for enhancing the alkaline pretreatment of lignocellulosic waste is highlighted in this work. Objective: To maximize separation of fermentable sugars from wheat straw. Methods: Wheat straw hydrolysis assisted by microwave was carried out by setting up a statistical experimental design method and further investigating the main process parameters, namely: temperature (°C), microwave power (W), NaOH concentration (M) and wheat straw pre-treatment time (min) towards maximization of fermentable sugars extraction from wheat straw. The reducing sugars yield (response) of the alkaline pre-treated and microwaved wheat straw in lab scale provided data for building a predictive model which reflected interactions, significance and impact of the process parameters (factors) on the wheat straw hydrolysis yield. Results: SEM and FTIR images of untreated and alkaline pre-treated wheat straw were studied for investigating the morphological changes of wheat straw surface quality and structure resulting from the microwave and/or alkaline pre-treatment. In addition reducing sugars yield of 87%wt. from wheat straw pre-treated at 180°C, 550W microwave power, 0.65M of NaOH for 25min was achieved. This result was significantly higher compared to the one from the straw which was only hydrolysed enzymatically (30 %wt). Conclusion: It was found that shorter pre-treatment times were obtained at higher temperatures, alkali concentration and moderate microwave power levels. The results obtained were further optimized and indicated that the microwave-assisted alkaline pre-treatment of wheat straw technique is an attractive pre-treatment method which reduces the wheat straw pre-treatment time and enhances the hydrolysis yield.

Microwave assisted alkaline pretreatment to enhance enzymatic saccharification of catalpa sawdust

Catalpa sawdust, a promising biofuel production biomass, was pretreated by microwave-water, -NaOH, and -Ca(OH)2 to enhance enzymatic digestibility. After 48h enzymatic hydrolysis, microwave-Ca(OH)2 pretreated sample showed the highest reducing sugar yield. The content of hemicellulose and lignin in catalpa sawdust decreased after microwave-alkali pretreatment. SEM observation showed that the catalpa sawdust surface with microwave-Ca(OH)2 pretreatment suffered the most serious erosion. Crystallinity index of catalpa sawdust increased after all three kinds of pretreatment. The optimum conditions of microwave-Ca(OH)2 pretreatment were particle size of 40mesh, Ca(OH)2 dosage of 2.25% (w/v), microwave power of 400W, pretreatment time of 6min, enzyme loading of 175FPU/g, and hydrolysis time of 96h, and the reducing sugar yield of microwave-Ca(OH)2 pretreated catalpa sawdust reached 402.73mg/g, which increased by 682.15% compared with that of raw catalpa sawdust. The catalpa sawdust with microwave-Ca(OH)2 pretreatment is promising for biofuel production with great potential.

Isolation and Characterization of Corncob Cellulose Fibers using Microwave-Assisted Chemical Treatments

Abstract Cellulose fibers were obtained from corncob by using microwave-assisted chemical treatments (microwave-assisted alkaline pretreatment and microwave-assisted bleaching). These treatments efficiently removed the hemicellulose and lignin from the original corncob and increased the cellulose fiber content. The morphology, chemical structure, degree of crystallinity and thermal degradation characteristics of the resultant cellulose fibers were studied by using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. These microwave-assisted chemical treatments decreased the diameter of the cellulose fibers from 25–125 µm to 10–20 µm. The crystallinity of the corncob cellulose fibers increased from 32.7% to 73% due to the chemical treatments. The degradation temperature of the cellulose fibers was &gt;260°C. The cellulose fibers obtained from these treatments can be used as biocomposites in reinforced polymer manufacturing.

Microwave Assisted Alkaline Pretreatment and Microwave Assisted Enzymatic Hydrolysis of Palm Oil Mill Effluent (POME) for Optimum Fermentable Sugar Yield

Microwave Assisted Alkaline Pretreatment and Microwave Assisted Enzymatic Hydrolysis of Palm Oil Mill Effluent (POME) for Optimum Fermentable Sugar Yield

Total fractionation of green tea residue by microwave-assisted alkaline pretreatment and enzymatic hydrolysis

Total refinery of constituents of green tea residue was achieved by combination of microwave-assisted alkaline pretreatment and enzymatic hydrolysis. Alkaline pretreatment was effective at separating pectic polysaccharides, protein, phenolic compounds and aliphatic compounds (probably originating from cuticular components), and the solubilization rate was attained 64–74% by heating at 120–200°C. The higher heating value (HHV) of alkali-soluble fraction attained 20.1MJ/kg, indicating its usability as black-liquor-like biofuel. Successive cellulolytic enzymatic hydrolysis mainly converted cellulose into glucose and attained the maximum solubilization rate of 89%. Final residue was predominantly composed of aliphatic cuticular components with high proportion in 9,10,18-trihydroxyoctadecanoic acid (30.1–48.6%). These cuticular components are potential alternative feedstock for aliphatic compounds commonly found in oil plants.

Microwave-Assisted Alkaline Pretreatment and Microwave Assisted Enzymatic Saccharification of Oil Palm Empty Fruit Bunch Fiber for Enhanced Fermentable Sugar Yield

Lignocellulosic materials are promising alternative feedstocks for bioethanol production. However, the recalcitrant nature of lignocellulosic biomass necessitates an efficient pretreatment pretreatment step to improve the yield of fermentable sugars and maximizing the enzymatic hydrolysis efficiency. Microwave pretreatment may be a good alternative as it can reduce the pretreatment time and improve the enzymatic activity during hydrolysis. The overall goal of this paper is to expand the current state of knowledge on microwave-based pretreatment of lignocellulosic biomass and microwave assisted enzymatic reaction or Microwave Irradiation-Enzyme Coupling Catalysis (MIECC). In the present study, a comparison of microwave assisted alkali pretreatment was tried using Oil Palm empty fruit bunch. The microwave assisted alkali pretreatment of EFB using NaOH, significantly improved the enzymatic saccharification of EFB by removing more lignin and hemicellulose and increasing its accessibility to hydrolytic enzymes. The results showed that the optimum pretreatment condition was 3% (w/v) NaOH at 180 W for 12 minutes with the optimum component loss of lignin and holocellulose of about 74% and 24.5% respectively. The subsequent enzymatic saccharification of EFB pretreated by microwave assisted NaOH (3% w/v); resulted in 411 mg of reducing sugar per gram EFB at cellulose enzyme dosage of 20 FPU. The overall enhancement by the microwave treatment during the microwave assisted alkali pretreatment and microwave assisted enzymatic hydrolysis was 5.8 fold. The present study has highlighted the importance of well controlled microwave assisted enzymatic reaction to enhance the overall reaction rate of the process.

Overcoming the Recalcitrance for the Conversion of Kenaf Pulp to Glucose via Microwave-Assisted Pre-Treatment Processes

This study evaluates the pre-treatment of cellulose from kenaf plant to yield sugar precursors for the production of ethanol or butanol for use as biofuel additives. In order to convert the crystalline cellulosic form to the amorphous form that can undergo enzymatic hydrolysis of the glycosidic bond to yield sugars, kenaf pulp samples were subjected to two different pre-treatment processes. In the acid pre-treatment, the pulp samples were treated with 37.5% hydrochloric acid in the presence of FeCl3 at 50 °C or 90 °C whereas in the alkaline method, the pulp samples were treated with 25% sodium hydroxide at room temperature and with 2% or 5% sodium hydroxide at 50 °C. Microwave-assisted NaOH-treatment of the cellulose was also investigated and demonstrated to be capable of producing high glucose yield without adverse environmental impact by circumventing the use of large amounts of concentrated acids i.e., 83–85% phosphoric acid employed in most digestion processes. The treated samples were digested with the cellulase enzyme from Trichoderma reesei. The amount of glucose produced was quantified using the Quantichrom™ glucose bioassay for assessing the efficiency of glucose production for each of the treatment processes. The microwave-assisted alkaline pre-treatment processes conducted at 50 °C were found to be the most effective in the conversion of the crystalline cellulose to the amorphous form based on the significantly higher yields of sugar produced by enzymatic hydrolysis compared to the untreated sample.

Enhanced biogas production from herbal‐extraction process residues by microwave‐assisted alkaline pretreatment

AbstractBACKGROUND: Lignocellulosic wastes such as herbal‐extraction process residues (HPR) are not easily utilized by microorganisms owing to their physical shielding of cellulose imparted by the non‐digestible lignin. Therefore, there is a great interest to develop an efficient pretreatment technique to disrupt recalcitrant structures of lignocellulosic wastes and improve renewable energy production.RESULTS: A microwave‐assisted alkaline pretreatment (MAP) method has been developed for the enhancement of biogas production from HPR. The maximum cumulative biogas production reached 1477 mL when the HPR was hydrolyzed by MAP for 30 min with an alkali loading of 0.12 g‐NaOH/g‐HPR, where the maximum weight loss of HPR after biogas fermentation reached 72.1%.CONCLUSION: The present work demonstrated that MAP is a promising method for improving bioconversion of lignocellulosic wastes to biogas. HPR pretreated by combining microwave irradiation and alkali resulted in releasing more soluble substances from HPR and increasing the accessibility of HPR for anaerobic biodigestion compared with traditional alkaline pretreatment (AP) and microwave‐assisted water pretreatment (MWP). Copyright © 2009 Society of Chemical Industry