Microwave-assisted Acid Pretreatment Research Articles

An efficient chemoenzymatic approach to produce galactose from red macroalgae biomass and its valorization

Marine biomass is receiving much attention as the third-generation feedstock owing to its advantages over terrestrial biomass. Red macroalgae have an impressive high carbohydrate content, with galactose as the most abundant monosaccharide. However, the technology for producing galactose with a high yield and its valorization is not yet available. This study described an efficient chemoenzymatic approach toward upgrading of red macroalgae (Gelidium amansii) into value-added products (taking galactonic acid as an example). With the aid of microwave-assisted maleic acid pretreatment, galactose was obtained with an excellent yield of 92.7%. Various inhibitors were simultaneously generated and their inhibition effects on biocatalysis were overcame by genetic and bioprocess engineering. Finally, the galactose in the hydrolysate was converted into galactonic acid with a yield of 100% by engineered Pseudomonas putida. This approach can be easily expanded to other galactose-derived products and promotes green development of marine biomass biorefinery.

High-performance poplar-polyethylene laminates based on microwave-assisted acetic acid pretreatment process with potential application in construction

High-performance poplar-polyethylene laminates based on microwave-assisted acetic acid pretreatment process with potential application in construction

Conventional and microwave-assisted acid pretreatment of tea waste powder: analysis of functional groups using FTIR.

Tea waste powder (TWP) is one of the potential biomass waste to recover valuable chemicals and materials. The prime objective of this work is to investigate the role of acid pretreatment on TWP. Diluted acids (HCl, H3PO4, CH3COOH, and H2SO4) were used to soak the TWP to understand the role of acids on bond cleavage and chemicals formation. One gram of TWP was soaked in 100 mL of diluted acids for 24 h. The soaked samples were further subjected to a hot air oven (temperature: 80 °C, duration: 6 h), orbital shaking (shaking speed: 80-100 rpm, duration: 6 h), and microwave irradiation (microwave power: 100 W, duration: 10 min) to understand the synergistic effects of acids and mode of exposure. The pretreated solid samples and liquid samples were analyzed using FTIR to understand the presence of functional groups. The mass loss of TWP after treatment significantly varied with the type of acid and exposure mode used. In the orbital shaker, the mass loss was varied in the following order: H2SO4 (36%) > CH3COOH (32%) > H3PO4 (22%) > HCl (15%). In hot air oven, high mass loss was observed compared to orbital shaking [HCl (48%) > CH3COOH (37%) > H2SO4 (35%) > H3PO4 (33%)]. The mass loss in microwave irradiation is lower (19 to 25%) with all acids compared to orbital shaking. In the solid samples, O-H stretching, C-H stretching, C=O stretching, C=C stretching, -C-O-, and -C-OH- functional groups were noticed. Similarly, C=O and C=C peaks and C-O and -C-OH peaks were noticed in liquid samples. Interestingly, microwave irradiation showed promising results in 10 min of pretreatment, whereas orbital shaking and hot air oven pretreatments require 6 h to achieve the same result.

Coffee pulp pretreatment methods: A comparative analysis of hydrolysis efficiency

The Vietnamese food industry produces a lot of coffee pulp, which is a valuable and abundant source of agricultural by-products. It contains a lot of cellulose, which can be converted into bioethanol. However, coffee pulp needs an extensive pretreatment to reduce the amount of lignin and hemicellulose while retaining the initial cellulose composition. This study compared several pre-hydrolysis and pre-fermentation pretreatment methods which involved H2SO4, NaOH, microwaves, and white rot fungus Phanerochaete chrysosporium.
 The hemicellulose dropped by 43.8% after the acidic pretreatment, by 47.1% after the alkaline pretreatment, and by 12.8% after the microbial pretreatment. The lignin contents dropped by 4.2, 76.6, and 50.2% after acidic, alkaline, and microbial pretreatment, respectively. The removal of hemicellulose and lignin in the coffee pulp was much more efficient when two or three of the pretreatment methods were combined. The microwave-assisted acid and alkaline pretreatment was the most efficient method: it removed 71.3% of hemicellulose and 79.2% of lignin. The combined method also had the highest amount of reducing sugars and glucose in hydrolysate. Additionally, concentrations of such yeast inhibitors as 5-hydroxymethyl-2-furaldehyde (HMF) and furfural were 2.11 and 3.37 g/L, respectively.
 The acid pretreatment was effective only in removing hemicellulose while the alkaline pretreatment was effective in lignin removal; the fungal pretreatment had low results for both hemicellulose and lignin removals. Therefore, the combined pretreatment method was found optimal for coffee pulp.

Comprehensive Treatment Strategy for Banana Inflorescence Bract to Synthesize Biodiesel and Bioethanol Through Fungal Biorefinery

Banana inflorescence bract (BIB), an agro-waste is sporadically explored for second-generation biofuel production in spite of having considerable holocellulosic composition (cellulose-35.56%, w/w; hemicellulose-22.41%, w/w). In this study, an attempt has been made to utilize this substrate for fermentable sugars (pentose-C5 and hexose-C6) extraction which were employed for the co-production of microbial lipids and ethanol using Rhodosporidium toruloides NCIM 3547 and Saccharomyces cerevisiae respectively. Since, a considerable amount of lignin (8.78%, w/w) is present in BIB, a hybrid pretreatment and carbohydrate hydrolysis through microwave (160 W) assisted mild H2SO4 acid 2.5% (v/v) was adopted. The resultant liquor contains holocellulosic sugars (C5 and C6 sugars), out of which xylose (10.40 ± 0.49 g/L) and glucose (51.48 ± 1.14 g/L). Hence, it was used as the growth medium for R. toruloides to produce lipids i.e., single cell oil (SCO). The maximum lipid content was found to be 44.89 ± 1.25 (%, w/w) containing total saturated fatty acids of 89.07% which justifies its potential application in biodiesel production. On the other hand, the pretreated solid fraction containing cellulose was saccharified using cellulolytic enzyme produced by Aspergillus sp. with saccharification (%) of 69.99 ± 0.30 (%, v/w) and yield of 27.22 ± 0.33 g/L of reducing sugar. This enzymatic hydrolysate was used for ethanol production by Saccharomyces cerevisiae resulting in an ethanol yield of 12.70 ± 0.09 g/L and productivity of 0.132 g/L/h. Based on this outcome, a sustainable route for agro-waste management of BIB was laid by favouring the integrated production of biodiesel and bioethanol towards a biorefinery approach. Exploration and utilization of an agro-waste, banana inflorescence bract is established as a potent feedstock for the co-production of single cell oil and bioethanol is reported for the first time. Microwave-assisted mild acid pretreatment was performed for effective delignification and hydrolysis of holocellulosic components. The resultant liquid hydrolysate consisting of lignin degradatory compounds, pentose (xylose) and hexose (glucose) sugars was used as a growth medium for producing single cell oil, proving its potential application in biodiesel production. Further, the pretreated solid cellulosic fraction was saccharified using crude cellulolytic enzymes and an enzymatic hydrolysate was used for the production of bioethanol through two different fermentative strategies. This study reveals that banana inflorescence bract could act as suitable biomass towards the biorefinery approach. Its complete utilization paved the way for agro-waste management that is not in existence so far according to the authors’ knowledge

The effect of alkaline-autoclaving delignification on chemical component changes of sugarcane trash

Sugarcane trash (ST) is lignocellulosic biomass that available abundantly during the sugarcane is harvested as a side product of sugarcane plantation. Several research groups have already reported their ST delignification. However, there is still needs to find a suitable delignification technique for improving recovery of cellulose and eliminate lignin and hemicellulose from a complex structure of ST. One of the methods for delignification is used alkaline with a high temperature. Hence, the research aim is to investigate the effect of alkaline-autoclaving delignification method on chemical component changes of ST. The different sample of ST including washing process and microwave-assisted maleic acid pretreatment prior to the delignification process with 2% NaOH combine with autoclaving in 121°C temperature was used in this study compare with the initial sample. The chemical composition changes in pretreated solid fractions and reducing sugar in pretreated liquid were analyzed. The functional properties were also analyzed using Fourier Transform Infrared (FTIR). The results showed that microwave-assisted maleic acid pretreatment before delignification was the effective treatment in this study to eliminate lignin (88.11%) and hemicellulose (44.07%) and cellulose recovery (78.40%) than that other treatment. Besides, the reducing sugar obtained from microwave-assisted maleic acid pretreatment 3.2 times and 3.6 times higher than that initial biomass and washing treatment, respectively. The FTIR spectra showed that washing treatment affects increasing absorbance of hydroxyl group while the maleic acid pretreatment was also increasing absorbance of carbonyl and the aromatic group that is a feature of lignin compound.

Ideal conditions of microwave-assisted acid pretreatment of sugarcane straw allow fermentative butyric acid production without detoxification step

Sugarcane straw (SCS) was pretreated with dilute sulfuric acid assisted by microwave to magnify fermentable sugars and to minimize the concentration of inhibitors in the hydrolysates. The optimum conditions for maximum recovery of sugars were 162 °C and 0.6% (w/v) H2SO4. The low level of inhibitors, such as acetate (2.9 g/L) and total phenolics (1.4 g/L), in the SCS slurry from the pretreatment stage allowed the enzymatic hydrolysis and fermentation steps to occur without detoxification. Besides consuming the total sugar content (31.0 g/L), Clostridium beijerinckii Br21 was able to use acetate from the SCS hydrolysate, to give butyric acid at high conversion factor (0.49 g of butyric acid /g of sugar). The optimized pretreatment conditions spared acid, time, and the detoxification stage, making bio-butyric acid production from SCS extremely attractive.

ZSM-5 catalyzed copyrolysis of sugarcane bagasse with LDPE: Influence of microwave-assisted acid pretreatment of sugarcane bagasse on yield and composition of gasoline range oil

In the present study, microwave-assisted acid pretreatment (MAAP) was employed to reduce the recalcitrance of sugarcane bagasse (SCB). The pretreated SCB was subjected to catalytic copyrolysis with LDPE in a lab-scale pyrolysis reactor using ZSM-5 catalyst. The influence of operating parameters affecting the effectiveness of MAAP (pretreatment time, pretreatment temperature, level of microwave power, and sulfuric acid concentration) on (i) yields of copyrolysis products, (ii) compositions of crude bio-oil, and gasoline range oil (GRO) (a cut obtained by simple distillation of crude bio-oil having boiling point range of 25 to 230 °C) was optimized. Under optimum operating conditions of pretreatment (microwave power, 600 W; sulfuric acid concentration, 1.5 M; pretreatment time, 15 min; pretreatment temperature, 130 °C), the highest crude bio-oil yield of 43.84% and least biochar yield of 17.65% were observed. The crude bio-oil obtained by pretreated SCB (PT SCB) contained 25.63% gasoline range fraction compounds (GRF), which was 1.96 times higher than the corresponding value for untreated SCB (UT SCB). GC HRMS analysis of GRO showed that it contains 33.14% monoaromatic hydrocarbons, 28.87% C5–C12 alkanes, 11.24% C5–C12 olefins, 25.64% oxygenated compounds (including phenols, furans, esters, and other oxygenated compounds), and 1.14% naphthalenes and indanes. The fuel properties of GRO were estimated and found to be reasonably closer to properties of commercial gasoline.

Microwave assisted dilute organic acid pre-treatment of oil palm empty fruit bunch to improve enzyme accessibility

The depletion of fossil fuel is intriguing for researchers to find sustainable energy. Oil palm empty fruit bunch (OPEFB) is abundant biomass in Indonesia which is potential to be converted into bioethanol because of its high cellulose content. Suitable pre-treatment could increase the effectiveness of cellulose conversion into sugars. The aim of this study is to evaluate the effectiveness of Microwave-assisted Oxalic Acid pre-treatment (MOxA) and Enzymatic Hydrolysis (EH) to improve enzyme accessibility through variation of heating temperature, irradiation time, and EH incubation time. The higher the microwave heating temperature, longer irradiation time, and longer EH incubation time, the higher the glucose yield per pulp (GY) and reducing sugar yield (RSY) were observed. After MOxA at 200°C-15 min, as much as 43.22 % GY per initial biomass was obtained by EH for 10 days. SEM images showed more ruptures on the surface area of OPEFB fibre after MOxA that supported in increasing of enzyme digestibility. The XRD spectra demonstrated that the crystallinity index (CI) increased after MOxA because pre-treatment reduced amorphous components in the biomass. In addition, the FTIR spectra showed that peak intensity at 1714 cm−1 corresponded to hemicellulose was gradually reduced after MOxA while peaks corresponded to lignin was more discernible.

Microwave-assisted acid pretreatment for enhancing enzymatic saccharification of sugarcane trash

Sugarcane trash (ST) is an abundant but underused biomass left in the field when the sugarcane is harvested. However, there are only a few studies to evaluate pretreatment of the residual bioresources for enzymatic saccharification. In this study, we aimed to explore the effects of combined severity factor (CSF), resulted from the use of different acids (phosphoric, maleic, and oxalic acids) on the pretreatment efficiency in microwave (MW)-accelerated process. The effects of acids and CSF on pretreated biomass properties and sugars obtained in the pretreatment soluble fraction and in enzymatic hydrolysate were evaluated. The degree of crystallinity of biomass pretreated at the same CSF is different due to different of acids used, and it did not correlate with the sugars obtained in the hydrolysate after enzymatic saccharification. MW-assisted acid pretreatment of ST at CSF of 2.05 affected functional groups and morphology of the biomass significantly. ST exposed to the same severity (CSF 2.05) using different acids resulted in reducing sugars yield 25.3–30.8% (based on initial biomass) from the pretreatment soluble fraction and 26.1–28.8% (based on initial biomass) from enzymatic hydrolysis, with the highest (30.8% and 28.8%) when used maleic acid. We succeeded in the production of total reducing sugars by 59.6% yield (of initial biomass) from recalcitrant sugarcane trash by applying MW-assisted maleic acid pretreatment at CSF of 2.05. The work provided insights into the use of organic acid as the catalyst in MW-accelerated process and can be further developed for application in pretreatment of ST in industry. Graphical abstract

Microwave-assisted Acid Pretreatment of Sago Wastewater for Fermentable Sugar Production

Sago wastewater (SWW) is one of by-products from sago starch industry. In most practice, SWW is discharged to the nearby rivers. As it contains high amount of organic compounds, usual practice of disposing the wastewater will cause a detrimental impact to the environment. The organic compounds found in SWW such as starch can be utilized as substrate for biofuel and biohydrogen fermentations. However, this starch needs to first undergo pretreatment process to breakdown its complex sugars to the simpler ones. This study aimed to investigate the effect of microwave-assisted acid pretreatment of SWW for fermentable sugar (glucose) production using sulphuric acid (H2SO4). Three parameters that influenced microwave-assisted acid pretreatment were chosen for optimization which are residence time (3-9 min), acid concentration (0.2-0.6 M) and solid loading (5-15% w/v). Faced Centered Central Composite Design (FCCCD) tool under Response Surface Methodology (RSM) in Design Expert v9.0.6.2 software was used for designing the experiments and optimization purposes. The response was the amount of glucose converted (g/L). The maximum fermentable sugar produced was 3.920 g/L, obtained at 9 minutes with 15% solid loading using 0.6 M of H2SO4. Then, the kinetic study of acid hydrolysis was performed by following the first order reaction kinetics. The rate constant of reaction obtained was 0.1684 min−1. It can be concluded that microwave-assisted acid pretreatment of SWW is able to produce high amount of fermentable sugar within a short residence time.

Microwave-assisted dilute acid pretreatment in bioethanol production from wheat and rye stillages

The main problem in the production of cellulosic ethanol is to ensure an efficient and cost-effective raw material pretreatment, guaranteeing a high degree of lignocellulose decomposition. Microwave radiation can be an alternative to conventional biomass heating, which in association with the use of dilute acid and a cellulolytic enzyme ensures a high degree of cellulose degradation. We evaluated the effectiveness of microwave dilute acid pretreatment of wheat and rye stillage in terms of the amount of sugars released, formation of fermentation inhibitors and their removal, and fermentation efficiency. Regardless of the type of stillage used, the highest glucose concentration after pretreatment (above 156 mg g−1 of DW) and the highest yield of cellulose hydrolysis after 24 h of the process (over 75%) were obtained using microwave power of 300 W, 15 min, 54 PSI. Fermentation of lignocellulosic hydrolysates obtained under the above-mentioned conditions ensured high ethanol concentrations of up to 20 g L−1 with full attenuation after just 48 h. Too intensive microwave treatment (152 PSI, 10 min) increased the concentration of sugar dehydration products which inhibited yeast fermentation activity and led to a lower ethanol yield. Detoxification with activated carbon reduced the toxic stress caused by the high concentration of HMF in hydrolysates. The application of microwaves is an interesting alternative to conventional barothermal methods. The possibility of an effective use of waste biomass of wheat/rye stillage for the production of cellulosic ethanol creates a prospect of integrating first and second generation ethanol production within one technological process.

Microwave-assisted pyrolysis of formic acid pretreated bamboo sawdust for bio-oil production

The integrated process of formic acid pretreatment and pyrolysis of bamboo sawdust (BS) under microwave irradiation is developed to produce high-quality bio-oil in this study. Experimental results indicated that microwave-assisted formic acid (MFA) pretreatment was able to reduce the contents of hydrogen, ash, and volatile in biomass. In the meanwhile, a distinct increase in the higher heating value of pretreated BS was observed. Although a higher pretreatment temperature led to lower mass yield, the corresponding energy yield of solid product was remarkably higher. X-ray diffraction and Fourier transfer infrared spectrometry analyses of pretreated BS suggested that MFA pretreatment could destruct the pristine structure of BS. Therefore, thermal properties of pretreated BS were significantly altered in terms of thermal stability and decomposition temperature according to thermogravimetric analysis. Microwave-assisted pyrolysis of pretreated samples could produce less acids, phenols, and ketones but more sugars, especially gluopyranose. Furthermore, the relevant mechanism of microwave-assisted pyrolysis of pretreated BS was interpreted. In sum, MFA was a feasible and promising technology to improve the quality of bio-oil from microwave pyrolysis of biomass.

Optimization of Microwave-Assisted Oxalic Acid Pretreatment of Oil Palm Empty Fruit Bunch for Production of Fermentable Sugars

Pretreatment is an important step in the conversion of biomass to bioethanol. In this study microwave-assisted oxalic acid (MOA) pretreatment was chosen to pretreat oil palm empty fruit bunch (OPEFB) to enhance enzymatic saccharification of the biomass. The objective of this study was to determine an optimum pretreatment condition for reducing sugar production, which could be further fermented by yeast to produce ethanol. Preliminary study was conducted to determine the range of duration of heating and temperature that will be used in the optimization by using response surface methodology (RSM). Central composite design (CCD) was used with three independent variables (duration of heating, temperature and acid concentration). Reducing sugar yield per initial biomass was used as a response variable. Preliminary study, that was conducted at 160, 170, 180, 190, and 200 °C for 5, 7.5, 10, 12.5, and 15 min, shows that pretreatment at temperature of 170–190 °C for 5–10 min produced higher reducing sugars than other conditions. Optimization using RSM shows that the optimum condition of MOA pretreatment of OPEFB was at 190 °C for 3 min with 1.1% oxalic acid, which resulted in as much as 34.60% reducing sugars after enzymatic saccharification. The pretreated OPEFB was then characterized and compared with untreated OPEFB. MOA pretreatment successfully removed 50.57% of lignin and 76.56% of hemicellulose from the OPEFB that were confirmed by a decrease or disappearance of the absorption bands of functional groups at 1339–1650 cm−1 and 1735 cm−1, respectively.

The Improvement of Sugar and Bioethanol Production of Oil Palm Empty Fruit Bunches (Elaeis guineensis Jacq) through Microwave-Assisted Maleic Acid Pretreatment

Microwave assisted maleic acid (MA) pretreatment is a potential method for biomass processing. The aim of the present study was to determine the optimum conditions for pretreatment of oil palm empty fruit bunch (OPEFB) for bioethanol production, as well as to understand the changes of functional groups in the pretreated OPEFB. The optimum pretreatment conditions with the highest reducing sugar yield (RSY) (47.21%) were 190 °C for 2.5 min with 1% MA. The temperature had more influence on the chemical components and RSY than the other pretreatment parameters. More severe pretreatment conditions tended to dissolve more sugar into the hydrolysates. Structural changes occurred in the OPEFB pretreated with MA and sulfuric acid, which were observed by the absence of certain functional groups. The simultaneous saccharification and fermentation (SSF) of MA-pretreated OPEFB produced ethanol with a concentration of 18.9 g/L and yield of 0.43 g ethanol/g cellulose after pretreatment, or equivalent to 76.6% of theoretical maximum yield. Microwave assisted MA pretreatment of OPEFB successfully increased the RSY about 300% compared to the untreated one. The MA pretreatment removed hemicellulose and lignin. The highest ethanol concentration and yield were produced after 48 h of SSF of the OPEFB pretreated with MA.

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse.

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid–liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

Disruption of Oil Palm Empty Fruit Bunches by Microwave-assisted Oxalic Acid Pretreatment

Developing an effective pretreatment for the conversion of lignocellulosic biomass to ethanol is an important effort in reducing the cost of this process. Microwave-assisted pretreatment is considered a green technology that can effectively break down lignocellulosic structures. The objective of this study was to investigate the most effective temperature for microwave-assisted oxalic acid pretreatment regarding the structural characteristic changes of oil palm empty fruit bunches (OPEFB) fibers. The fibers were subjected to microwave-assisted oxalic acid pretreatment at 160–200 °C with 2.5 minutes heating time and a liquid to solid ratio of 10. The effectiveness of the pretreatment was determined based on its delignification selectivity, morphological characteristics, and functional group changes. Microwave irradiation of OPEFB fibers at 180 oC was effective in increasing the cellulose content by 24%. This pretreatment resulted in 1.82 delignification selectivity. More than 50% of the hemicellulose of the OPEFB was removed after this treatment, which was confirmed by a decrease of the absorption bands of functional groups at 1732 cm -1 . The increase of pretreatment temperature disrupted the morphological structure of the OPEFB and removed its hemicellulose but did not change its functional groups and lignin content.

Microwave-assisted acid pretreatment of alkali lignin: Effect on characteristics and pyrolysis behavior

This study performed microwave-assisted acid pretreatment on pure lignin. The effects of microwave temperature, microwave time, and hydrochloric acid concentration on characteristics and pyrolysis behavior of lignin were examined. Results of ultimate analysis revealed better properties of all pretreated samples than those of raw lignin. Fourier transform infrared spectroscopy analysis showed breakage of βO4 bond and aliphatic side chain, decrease in OH groups, and formation of CO groups in pretreatment. Microwave temperature exerted more significant influence on lignin structure. Thermal stability of treated lignin was improved and insensitive to short microwave time and acid concentration under mild conditions. Resulting from improved alkyl-phenols and decreased alkoxy-phenols, microwave-assisted acid pretreatment of lignin yielded bio-oil with excellent quality. Total yield of phenols in pyrolysis vapors (200 °C) improved to 14.15%, whereas that of guaiacols decreased to 22.36%. This study shows that microwave-assisted acid pretreatment is a promising technology for lignin conversion.

Properties and pyrolysis behavior of moso bamboo sawdust after microwave-assisted acid pretreatment

The effects of microwave-assisted acid pretreatment on the characteristics and pyrolysis behavior of moso bamboo sawdust (BS) were investigated by ultimate, Fourier transform infrared spectroscopy, thermogravimetric (TG), and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) analyses in this study. Microwave temperature (100°C–200°C), reaction time (30min–90min), and acid concentration (0.5M–1.5M) were the main influencing factors. Results of ultimate analysis indicated that the properties of the pretreated samples are better than those of the raw BS. Moreover, appropriately reducing the oxygen and ash contents and increasing the microwave temperature promoted decarboxylation and dehydration during pretreatment. Microwave-assisted acid pretreatment decreased the acetyl groups and hydrogen bonds. Of the three main influencing factors affecting the structure of moso BS, microwave temperature was the most important. TG analysis results indicated that the thermostability of the pretreated samples is improved after pretreatment. Moreover, the pyrolysis behavior of moso BS is insensitive to the reaction time and acid concentration under mild conditions. The relative contents of acids, furans, aldehydes, and ketones derived from the pretreated samples decreased according to the results of Py-GC/MS. Meanwhile, the relative glucopyranose and phenol contents of the pretreated samples are higher than those of the raw moso BS and achieve the maximum values of 48.31% and 20.18%, respectively, at 200°C.

Study on optimization of reducing sugar yield from corn stalk based on microwave-assisted acid pretreatment process

In this paper, the optimal process condition for microwave-assisted acid pretreatment of the corn stalk was investigated by Central-Composite design using Response Surface Method. Effects of microwave power, reaction time and acid concentration on reducing sugar yield were inspected. Also, analysis of corn stalk before and after the treatment was conducted with ultra depth microscope. The test result shows that, the sequence of factors is: acid concentration>reaction time>microwave power, and the interaction of microwave power and reaction time is significant; The optimal process condition is: microwave power 900W, reaction time 20min, acid concentration 2%, reducing sugar yield 230.9 mg/g. Through the microwave-assisted acid pretreatment, the fiber structures of the corn stalk were destroyed effectively, the treatment increases the degree of surface roughness, improves porosity, thus the rate of enzymolysis was enhanced. The p-value of regression model is 0.0002, and the p-value of Lack of fit is 0.1298, which indicates the regression equation is significant and the model fits well.