Pretreatment combining ultrasound and sodium percarbonate under mild conditions for efficient degradation of corn stover

Ultrasound (US) can be used to disrupt microcrystalline cellulose to give nanofibers via ultrasonic cavitation. Sodium percarbonate (SP), consisting of sodium carbonate and hydrogen peroxide, generates highly reactive radicals, which cause oxidative delignification. Here, we describe a novel pretreatment technique using a combination of US and SP (US–SP) for the efficient saccharification of cellulose and hemicellulose in lignocellulosic corn stover. Although US–SP pretreatment was conducted under mild condition (i.e., at room temperature and atmospheric pressure), the pretreatment greatly increased lignin removal and cellulose digestibility. We also determined the optimum US–SP treatment conditions, such as ultrasonic power output, pretreatment time, pretreatment temperature, and SP concentration for an efficient cellulose saccharification. Moreover, xylose could be effectively recovered from US–SP pretreated biomass without the formation of microbial inhibitor furfural.     

Effects of ultrasound synergized with microwave on structure and functional properties of transglutaminase-crosslinked whey protein isolate

In the present study, ultrasound (400 W, U), microwave heating (75 ℃ for 15 min, M) and ultrasound synergized with microwave heating (UM) pretreatments of whey protein isolate (WPI) were applied to investigate and compare their influence on structure, physicochemical and functional characteristic of transglutaminase (TGase)-induced WPI. From the results of size exclusion chromatography, it could be seen that all three physical pretreatments could promote the formation of polymers in TGase cross-linked WPI, whose polymer amounts were increased by the order of U, UM and M pretreatment. Among three physical methods, M pretreatment had the strongest effect on structure and functional characteristics of TGase-induced WPI. Furthermore, compared with TGase-induced WPI, α-helix and β-turn of M−treated TGase-induced WPI (M−WPI−TGase) were reduced by 7.86% and 2.93%, whereas its β-sheet and irregular curl were increased by 15.37% and 7.23%. Zeta potential, emulsion stability and foaming stability of M−WPI−TGase were increased by 7.8%, 59.27% and 28.95%, respectively. This experiment exhibited that M was a more effective pretreatment method than U, UM for WPI, which could promote its reaction with TGase and improve its functional properties.     

Cavitation assisted delignification of wheat straw: a review

Wheat is grown in most of the Indian and Chinese regions and after harvesting, the remaining straw offers considerable promise as a renewable source most suitable for papermaking and as a pulping resource. Delignification of wheat straw offers ample scope for energy conservation by way of the application of the process intensification principles. The present work reviews the pretreatment techniques available for improving the effectiveness of the conventional approach for polysaccharide component separation, softening and delignification. A detailed overview of the cavitation assisted delignification process has been presented based on the earlier literature illustrations and important operational guidelines have been presented for overall low-cost and amenable energy utilization in the processes. The effectiveness of the methods has been evaluated according to yield and properties of the isolated fibers in comparison to the conventional treatment. Also the experimental results of one such non-conventional treatment scheme based on the use of hydrodynamic cavitation have been presented for the pulping of wheat straw. The effect of hydrodynamically induced cavitation on cell wall matrix and its components have been characterized using FT-IR analysis with an objective of understanding the cavitation assisted digestion mechanism on straws. It has been observed that the use of hydrodynamic cavitation does not degrade the fibrillar structure of cellulose but causes relocalisation and partial removal of lignin. Overall it appears that considerable improvement can be obtained due to the use of pretreatment or alternate techniques for delignification, which is an energy intensive step in the paper making industries.     

Ultrasound-ionic liquid enhanced enzymatic and acid hydrolysis of biomass cellulose

The purpose of this paper was to investigate the effect of ultrasound-ionic liquid (IL) pretreatment on the enzymatic and acid hydrolysis of the sugarcane bagasse and wheat straw. The lignocellulosic biomass was dissociated in ILs ([Bmim]Cl and [Bmim]AOC) aided by ultrasound waves. Sonication was performed at different frequencies (20, 28, 35, 40, and 50 kHz), a power of 100 W, a time of 30 min and a temperature of 80 °C. The changes in the structure and crystallinity of the cellulose were studied by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The amounts of the total reducing sugars, glucose, cellobiose, xylose and arabinose in the hydrolysates were determined. The results of FT-IR, XRD and TGA revealed that the structure of cellulose of both biomass samples remained intact after the pretreatment, but the crystallinity decreased. The enzymatic and acid hydrolysis of the biomass samples pretreated with the ultrasound-IL result in higher yields of the reducing sugars compared with the IL-pretreated sample. Enzymatic hydrolysis of bagasse and wheat straw pretreated with [Bmim]Cl-ultrasound resulted in maximal yields of glucose at 20 kHz (40.32% and 53.17%) and acid hydrolysis resulted in maximal yields of glucose at 40 kHz (33.32% and 48.07%). Enzymatic hydrolysis of bagasse and wheat straw pretreated with [Bmim]OAc-ultrasound show maximal yields of glucose at 28 kHz and acid hydrolysis at 50 kHz. Combination of ultrasound with [Bmim]OAc is more effective than [Bmim]Cl in terms of the yields of reducing sugar.     

Alkaline and ultrasound assisted alkaline pretreatment for intensification of delignification process from sustainable raw-material

Alkaline and ultrasound-assisted alkaline pretreatment under mild operating conditions have been investigated for intensification of delignification. The effect of NaOH concentration, biomass loading, temperature, ultrasonic power and duty cycle on the delignification has been studied. Most favorable conditions for only alkaline pretreatment were alkali concentration of 1.75 N, solid loading of 0.8% (w/v), temperature of 353 K and pretreatment time of 6 h and under these conditions, 40.2% delignification was obtained. In case of ultrasound-assisted alkaline approach, most favorable conditions obtained were alkali concentration of 1 N, paper loading of 0.5% (w/v), sonication power of 100 W, duty cycle of 80% and pretreatment time of 70 min and the delignification obtained in ultrasound-assisted alkaline approach under these conditions was 80%. The material samples were characterized by FTIR, SEM, XRD and TGA technique. The lignin was recovered from solution by precipitation method and was characterized by FTIR, GPC and TGA technique.     

Effects of ultrasound treatment on the starch properties and oil absorption of potato chips

As a non-thermal processing method, the ultrasound treatment prior to the frying process has been demonstrated with great potential in reducing the oil absorption of fried food. This research aimed to evaluate the effect of ultrasound pretreatment on starch properties, water status, pore characteristics, and the oil absorption of potato slices. Ultrasound probe set with two power (360 W and 600 W) at the frequency of 20 kHz for 60 min was applied to perform the pretreatments. The results showed that ultrasound pretreatment led to the surface erosion of starch granules and higher power made the structure of starch disorganized. Moreover, the fraction of bound water and immobilized water were changed after ultrasonic pretreatment. Pores with the minor diameters (0.4–3 μm and 7–12 μm) were formed after ultrasound pretreatment. The penetrated surface oil (PSO) content, and structure oil (STO) content were reduced by 27.31% and 22.25% respectively with lower power ultrasound pretreatment. As the ultrasound power increased, the surface oil (SO) content and PSO content increased by 25.34% and 12.89% respectively, while STO content decreased by 38.05%. By using ultrasonic prior to frying, the quality of potato chips has been greatly improved.     

Effects of multi-frequency power ultrasound on the enzymolysis and structural characteristics of corn gluten meal

The aim of this study was to investigate the effect of multi-frequency power ultrasound (sweeping frequency and pulsed ultrasound (SFPU) and sequential dual frequency ultrasound (SDFU)) on the enzymolysis of corn gluten meal (CGM) and on the structures of the major protein fractions (zein, glutelin) of CGM. The results showed that multi-frequency power ultrasound pretreatments improved significantly (P < 0.05) the degree of hydrolysis and conversion rate of CGM. The changes in UV–Vis spectra, fluorescence emission spectra, surface hydrophobicity (H₀), and the content of SH and SS groups indicated unfolding of zein and glutelin by ultrasound. The circular dichroism analysis showed that both pretreatments decreased α-helix and increased β-sheet of glutelin. The SFPU pretreatment had little impact on the secondary structure of zein, while the SDFU increased the α-helix and decreased the β-sheet remarkably. Scanning electron microscope indicated that both pretreatments destroyed the microstructures of glutelin and CGM, reduced the particle size of zein despite that the SDFU induced aggregation was observed. In conclusion, multi-frequency power ultrasound pretreatment is an efficient method in protein proteolysis due to its sonochemistry effect on the molecular conformation as well as on the microstructure of protein.     

Intensification of alkaline delignification of sugarcane bagasse using ultrasound assisted approach

Ultrasound-assisted approach has been investigated for delignification so as to develop green and sustainable technology. Combination of NaOH with ultrasound has been applied with detailed study into effect of various parameters such as time (operating range of 15–90 min), alkali concentration (0.25 M−2.5 M), solvent loading (1:15–1:30 w/v), temperature (50–90 ˚C), power (40–140 W) and duty cycle (40–70 %) at fixed frequency of 20 kHz. The optimized operating conditions established for the ultrasonic horn were 1 M as the NaOH concentration, 1 h as treatment time, 70˚C as the operating temperature, 1:20 as the biomass loading ratio, 100 W as the ultrasonic power and 70% duty cycle yielding 67.30% as the delignification extent. Comparative study performed using conventional and ultrasonic bath assisted alkaline treatment revealed lower delignification as 48.09% and 61.55% respectively. The biomass samples were characterized by SEM, XRD, FTIR and BET techniques to establish the role of ultrasound during the treatment. The morphological changes based on the ultrasound treatment demonstrated by SEM were favorable for enhanced delignification and also the crystallinity index was more in the case of ultrasound treated material than that obtained by conventional method. Specific surface area and pore size determinations based on BET analysis also confirmed beneficial role of ultrasound. The overall results clearly demonstrated the intensification obtained due to the use of ultrasonic reactors.     

Intensified recovery of lipids,proteins, and carbohydrates from wastewater-grown microalgae Desmodesmus sp. by using ultrasound or ozone

This study evaluates the effect of ultrasound and ozone pretreatments for the subsequent recovery of Desmodesmus sp. biocomponents—lipids, proteins, and carbohydrates—using a response surface methodology. Both pretreatments impact on the recovered lipids quality, solvent waste production and extraction time is analysed for process intensification purposes. For ultrasound pretreatment, independent parameters were energy applied (50–200 kWh/kg dry biomass), biomass concentration (25–75 g/L), and ultrasonic intensity (0.32 and 0.53 W/mL). While for ozone pretreatment, independent parameters were ozone concentration (3–9 mg O₃/L), biomass concentration (25–75 g/L), and contact time (5–15 min). In the case of ultrasound pretreatment, recovery yield reached 97 ± 0.4%, 89 ± 3%, and 73 ± 0.6% for proteins, carbohydrates and lipids respectively. Given process required: energy applied of 50 kWh/kg dry biomass, 75 g/L of biomass concentration, 0.32 W/mL of ultrasonic intensity, and 56 min of time process. Ultrasound caused high cell disruption releasing all proteins, thereby obviating downstream processing for its recovery. Ozone pretreatment recovery yield was 85 ± 2%, 48 ± 1.4%, and 25 ± 1.3%, for carbohydrates, lipids and proteins respectively, under the following conditions: 9 mg O₃/L of ozone concentration, 25 g/L of biomass concentration, and 5 min of contact time that depicts an energy consumption of 30.64 kWh/kg dry biomass. It was found that ultrasound and ozone pretreatments intensified the lysis and biocomponents recovery process by reducing solvent consumption by at least 92% and extraction time between 80% and 90% compared with extraction of untreated biomass biocomponents. Both pretreatments improve the composition of the recovered lipids. It was noted that the yield of neutral lipids increased from 28% to 67% for ultrasound pretreatment while for ozone pretreatment from 49% to 63%. The method used for lipid extraction may also have an effect but here it was kept constant.     

Sonocatalytic–Fenton reaction for enhanced OH radical generation and its application to lignin degradation

The present study demonstrated that the combined use of the sonocatalytic reaction (using ultrasound and titanium dioxide) and the Fenton reaction exhibited synergistically enhanced hydroxyl (OH) radical generation. Dihydroxybenzoic acid (DHBA) concentration as index of OH radical generation was 13 and 115 μM at 10 min in the sonocatalytic reaction and Fenton reaction, respectively. On the other hand, the DHBA concentration was 378 μM at 10 min in the sonocatalytic–Fenton reaction. The sonocatalytic–Fenton reaction was used for degradation of lignin. The lignin degradation ratio was 1.8%, 49.9%, and 60.0% at 180 min in the sonocatalytic reaction, Fenton reaction, and sonocatalytic–Fenton reaction, respectively. Moreover, the sonocatalytic–Fenton reaction was applied to pretreatment of lignocellulosic biomass to enhance subsequent enzymatic saccharification. The cellulose saccharification ratio was 11%, 14%, 16% and 25% at 360 min of pretreatment by control reaction, the sonocatalytic reaction, Fenton reaction, and sonocatalytic–Fenton reaction, respectively.     

Effects of ultrasound and ultrasound assisted alkaline pretreatments on the enzymolysis and structural characteristics of rice protein

The objectives of this study were to investigate the effects of multi-frequency energy-gathered ultrasound (MFEGU) and MFEGU assisted alkaline pretreatments on the enzymolysis and the mechanism of two pretreatments accelerating the rice protein (RP) proteolysis process. The results showed that MFEGU and MFEGU assisted alkaline pretreatments improved significantly (P < 0.05) the degree of hydrolysis (DH) and the protein elution amount of RP. Furthermore under the same DH conditions, ultrasound and ultrasound assisted alkaline pretreatments were more save the enzymolysis time than the unpretreatment. The changes in UV–vis spectra, fluorescence emission spectra indicated unfolding and destruction of RP by MFEGU and MFEGU assisted alkaline pretreatments. The circular dichroism analysis showed that both pretreatments decreased α-helix but increased β-sheet and random coil of RP. Amino acid composition revealed that MFEGU and MFEGU assisted alkaline pretreatments could increase the protein elution amount and the ratio of hydrophobic amino acids. Atomic force microscopy (AFM) indicated that both pretreatments destroyed the microstructures and reduced the particle size of RP. Therefore, MFEGU and MFEGU assisted alkaline pretreatments are beneficial to improving the degree of hydrolysis due to its sonochemistry effect on the molecular conformation as well as on the microstructure of protein.     

Influence of ultrasound pretreatment on wood physiochemical structure

As an initial step to increase the use of renewable biomass resources, this study was aimed at investigating the effects of ultrasound pretreatment on structural changes of wood. Samples were pretreated by ultrasound with the power of 300 W and frequency of 28 kHz in aqueous soda solution, aqueous acetic acid, or distilled water, then pretreated and control samples were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results shown that ultrasound pretreatment is indeed effective in modifying the physiochemical structure of eucalyptus wood; the pretreatment decreased the quantity of alkali metals (e.g., potassium, calcium and magnesium) in the resulting material. Compared to the control group, the residual char content of samples pretreated in aqueous soda solution increased by 10.08%–20.12% and the reaction temperature decreased from 361 °C to 341 °C, however, in samples pretreated by ultrasound in acetic solution or distilled water, the residual char content decreased by 12.40%–21.45% and there were no significant differences in reactivity apart from a slightly higher maximum reaction rate. Ultrasound pretreatment increased the samples’ crystallinity up to 35.5% and successfully removed cellulose, hemicellulose, and lignin from the samples; the pretreatment also increased the exposure of the sample to the treatment solutions, broke down sample pits, and generated collapses and microchannels on sample pits, and removed attachments in the samples.     

水-四氢呋喃混合溶剂中硫酸氢钠催化生物质转化制备5-羟甲基糠醛及糠醛

报道了在水-四氢呋喃组成的混合溶剂中,采用硫酸氢钠催化各种生物质原料(玉米芯、玉米秸秆、麦秆、稻秆和甘蔗渣)制备重要的生物质基平台化学品5-羟甲基糠醛和糠醛的研究. 考察了反应温度(160～200 oC)、反应时间(30～120 min)、水与四氢呋喃的溶剂比例(1:1～1:10)和原料质量分数(2.4wt%～11.1wt%)等反应工艺的影响.在优化的工艺条件下(190 oC, 90 min, 10:1 THF:H₂O),转化玉米芯得到了47mol%的HMF和56mol%的糠醛. 此外,原料中的木质素也被有效地转化为有机溶木质素.     

共聚焦显微拉曼光谱在木质纤维细胞壁预处理中的应用进展

在能源紧缺和环境恶化的双重压力下,利用农林生物质替代化石资源生产生物燃料、生物基化学品和材料逐步发展成为世界范围内的研究热点,而细胞壁中纤维素、半纤维素、木质素以及其他少量组分的空间分布不均一性和化学结构复杂性构成了天然抗降解屏障,严重阻碍生物质的转化效率,因此需要对木质纤维原料进行预处理,以期破坏细胞壁的宏观壁垒,实现生物质的低成本高效转化。在此过程中,全面了解木质纤维细胞壁的化学组成、结构特性及其在生物质转化过程中的解构机理是高效利用农林生物质的重要前提。由于拉曼光谱具有样品制备要求低、灵敏度高、且能在原位状态下对样品进行定性、定量分析等特点,使得拉曼光谱成为研究木质细胞壁结构的有力工具。尤其与显微技术相结合时,可以同时获得木质纤维细胞壁主要组分的微区分布与超分子结构信息,实现生物质转化过程中化学组分动态变化的可视化研究。首先介绍了拉曼光谱成像的工作原理,并对纤维素、半纤维素和木质素的拉曼特征信号进行了归属。其次,总结了近几年拉曼光谱在生物质转化领域内的应用与研究进展,综述了拉曼光谱在未处理状态下以及稀酸、水热、稀碱等不同预处理过程中的分析方法,对细胞壁主要组分的分布进行表征,以揭示预处理过程中各组分的溶出过程及迁移规律,为在细胞及亚细胞水平探究预处理诱导细胞壁主要组分动态溶解机制提供了有效路径。此外,针对检测中收集的光谱数量过多、分析难等问题,文章重点介绍了主成分聚类分析法和顶点成分分析法两种拉曼数据分析方法,用于提取特征信息并对光谱进行分类研究,以深入探究特定组分的空间分布和分子结构。最后,根据上述分析展望了拉曼光谱在生物质转化领域的研究趋势,为相关研究提供技术参考。     

生物质在闪速加热条件下的挥发特性研究

生物质快速热裂解技术是实现生物质液化的重要手段。研究在闪速加热条件下(达到104K／s)生物质的热挥发特性对于热裂解装置的设计非常重要。在等离子体加热的层流炉上对于几种典型的生物质材料,包括玉米秸秆、麦秸、稻壳、椰子壳等,进行了实验研究,获得了它们热挥发的活化能、反应频率因子等。研究发现,在闪速加热条件下,生物质热挥发的动力学参数与升温速率无关。     

热处理竹材的化学成分傅里叶变换红外光谱分析

化学热处理是实现可再生木质生物能源中纤维素高效利用及半纤维素糖化转换的关键步骤。通过预处理过程可以快速去除难溶木质素,实现细胞壁中半纤维素的物理化分离,使得植物细胞壁中化学成分发生变化,从而增加木质纤维素的产出量。以硫酸(H₂SO₄)、稀碱(NaOH)及甘油(glycerol)为预处理介质,采用不同的热处理温度(硫酸(H₂SO₄)、稀碱(NaOH)热处理温度为117和135 ℃;甘油(glycerol)热处理温度为117 ℃)),对竹材处理前后的主要化学组分进行对比分析,并通过傅里叶变换红外光谱进一步证实化学热处理前后竹材化学组分的变化,以获得不同的化学热处理介入下竹材化学成分转换的主要变化规律和机理。结果表明：热化学处理后竹材的纤维素产出量明显增加。纤维素得率及木质素的去除率在不同的处理介质条件下的变化规律为,稀碱(NaOH)处理效果优于稀酸(H₂SO₄)和甘油(glycerol);此外,在相同介质条件下135 ℃热处理效果比117 ℃热处理效果显著。对于不同处理条件的半纤维素的降解程度大小变化结果与此相同。通过红外光谱分析可知,热处理后纤维素环状C-O-C不对称伸缩振动峰出现峰值分解,半纤维素的红外吸收特征峰出现明显陡降变化,木质素苯环特征吸收峰明显减弱,证明纤维素产出量明显增加,半纤维素降解趋势明显,木质素去除效果良好。傅里叶红外变换光谱分析结果与标准测定结果一致。     

Hydrodynamic cavitation as a novel approach for delignification of wheat straw for paper manufacturing

The present work deals with application of hydrodynamic cavitation for intensification of delignification of wheat straw as an essential step in the paper manufacturing process. Wheat straw was first treated with potassium hydroxide (KOH) for 48 h and subsequently alkali treated wheat straw was subjected to hydrodynamic cavitation. Hydrodynamic cavitation reactor used in the work is basically a stator and rotor assembly, where the rotor is provided with indentations and cavitational events are expected to occur on the surface of rotor as well as within the indentations. It has been observed that treatment of alkali treated wheat straw in hydrodynamic cavitation reactor for 10–15 min increases the tensile index of the synthesized paper sheets to about 50–55%, which is sufficient for paper board manufacture. The final mechanical properties of the paper can be effectively managed by controlling the processing parameters as well as the cavitational parameters. It has also been established that hydrodynamic cavitation proves to be an effective method over other standard digestion techniques of delignification in terms of electrical energy requirements as well as the required time for processing. Overall, the work is first of its kind application of hydrodynamic cavitation for enhancing the effectiveness of delignification and presents novel results of significant interest to the paper and pulp industry opening an entirely new area of application of cavitational reactors.     

Enzymolysis kinetics and structural characteristics of rice protein with energy-gathered ultrasound and ultrasound assisted alkali pretreatments

This research investigated the structural characteristics and enzymolysis kinetics of rice protein which was pretreated by energy-gathered ultrasound and ultrasound assisted alkali. The structural characteristics of rice protein before and after the pretreatment were performed with surface hydrophobicity and Fourier transform infrared (FTIR). There was an increase in the intensity of fluorescence spectrum and changes in functional groups after the pretreatment on rice protein compared with the control (without ultrasound and ultrasound assisted alkali processed), thus significantly enhancing efficiency of the enzymatic hydrolysis. A simplified kinetic equation for the enzymolysis model with the impeded reaction of enzyme was deduced to successfully describe the enzymatic hydrolysis of rice protein by different pretreatments. The initial observed rate constants (K_in,0) as well as ineffective coefficients (k_imp) were proposed and obtained based on the experimental observation. The results showed that the parameter of k_in,0 increased after ultrasound and ultrasound assisted alkali pretreatments, which proved the effects of the pretreatments on the substrate enhancing the enzymolysis process and had relation to the structure changes of the pretreatments on the substrate. Furthermore, the applicability of the simplified model was demonstrated by the enzymatic hydrolysis process for other materials.     

红外拟合光谱分析微波对重晶石浮选的影响机理

目前浮选提高重晶石品位的方法通常采用新型浮选药剂从低品位重晶石矿中进行分选,采用微波加热预处理矿物可提高浮选回收率,但微波对浮选药剂与矿物的作用机理还不清楚。微波加热技术近年来用于矿物加工、冶金与材料制备等领域,具有反应速度快、产品指标高等优点。以油酸钠为捕收剂,对微波预处理后的重晶石纯矿物进行浮选,并对不同微波作用时间下的重晶石浮选样品进行红外光谱检测,通过红外拟合平滑光谱和二阶导数光谱计算分析,研究微波对重晶石浮选的影响机理。浮选试验结果表明,未经微波预处理的重晶石,在油酸钠用量为55 mg·L-1、pH值为8.0的条件下,浮选指标最佳,回收率为91.41%;而对比之下,经微波作用后的重晶石进行浮选,随着微波处理时间的增加浮选指标逐渐提高,且在微波作用60s时的回收率最高,达95.27%。基于浮选试验的红外光谱分析表明,重晶石未经微波预处理进行浮选,与油酸钠作用,在波数为3 004 cm-1处-CH₂-的对称伸缩振动峰、2 953 cm-1处-CH₃的反对称伸缩振动峰、1 119和1 077 cm-1处SO2-₄的非对称伸缩振动峰均发生了红移,说明油酸钠在重晶石表面发生化学吸附;而经微波预处理后的重晶石浮选时,在波数为2 853 cm-1处-CH₂-对称伸缩振动峰、2 923 cm-1处-CH₂-反对称伸缩振动峰、2 958 cm-1处-CH₃反对称伸缩振动峰、1 181,1 122和1 086 cm-1处SO2-₄非对称伸缩振动峰、982 cm-1处SO2-₄对称伸缩振动峰、635和610 cm-1处SO2-₄弯曲振动峰,其峰位并未发生红移,但峰强随着微波作用时间的增加明显加强,且微波作用60 s时其峰强增加最明显;对微波处理后的红外光谱进行拟合平滑光谱和二阶导数光谱计算发现,在波数为2 958,2 923,2 853,1 181,1 122,1 086,982,635和610 cm-1处峰面积均有不同程度的增加,且在微波作用60s时峰面积分别增加了1.84%,259.12%,761.15%,235.72%,145.61%,198.50%,641.16%,549.67%和744.97%,表明微波预处理并未诱发重晶石表面发生化学反应,但强化了捕收剂油酸钠与重晶石矿之间的化学吸附,使其与重晶石表面的化学吸附更加致密,吸附量增加,因此重晶石回收率增加,浮选指标提高。     

Synergism of sweeping frequency ultrasound and deep eutectic solvents pretreatment for fractionation of sugarcane bagasse and enhancing enzymatic hydrolysis

Sugarcane bagasse (SCB) is an abundant agricultural waste in China and the conversion of the waste into plethora of useful resources is very vital. To achieve this, fractionation of the waste is highly important in the biomass biorefinery. The present study aims at investigating the synergistic role of deep eutectic solvents (DES) with sweeping frequency ultrasound (SFUS) and fixed frequency ultrasound (FFUS) in the fractionation of SCB to enhance the enzymatic saccharification process. Therefore, the effects of ultrasound (US) and DES conditions on the pretreatment efficiency were investigated. Under optimum SCB pretreatment conditions, FFUS (40 kHz, 60 min) + DES (choline chloride (ChCl)-lactic acid (LA), 120 °C, 3 h) and SFUS (40 kHz, 60 min) + DES (ChCl-LA, 120 °C, 3 h), the lignin removal rates were 80.13 and 85.62%, respectively. The hemicellulose removal rates were 78.08 and 90.46%, respectively; and the contents of glucose, xylose and arabinose in the liquid fractions after FFUS + DES pretreatment were 7.07, 17.95 and 3.01%, respectively. However, the yield of glucose, xylose, and cellobiose after enzymatic hydrolysis of the SFUS + DES pretreated SCB were 86.76, 38.68, and 20.76%. Analytical studies revealed that the SFUS + DES pretreatment can effectively destroy the ultrastructure of SCB and reduce the crystallinity of cellulose. Furthermore, the mechanism of pretreatment with SFUS + DES was proposed, which confirmed the excellent performance of SFUS + DES. Thus, the application of SFUS + DES pretreatment was able to improve the removal of lignin and hemicellulose from SCBs.