Microwave Pretreatment Time Research Articles

Influence of microwave pretreatment on the total phenolics, antioxidant activity, moisture diffusivity, and rehydration rate of dried sweet cherry.

The target of this work was to investigate the influence of microwave pretreatments (at five levels of 0, 30, 60, 90, and 120 s) on the total phenolics content, antioxidant potential, mass transfer rate, effective moisture diffusivity (D eff), and rehydration rate of sweet cherries (SC). The drying duration of microwave-treated SC was shorter than the untreated sample. The average drying time of fresh SC microwaved for 0, 30, 60, 90, and 120 s were 220, 205, 190, 175, and 150 min, respectively. The D eff values, total phenolics, and antioxidant capacity of microwave-treated SC were higher than the untreated sample. In this study, the SC D eff as determined by the second Fick law varied from 8.73 × 10-10 to 1.41 × 10-9 m2/s. The experimental data for the dehydration curves were fitted to different thin-layer equations, and the Midilli equation using the experimental constants best described the drying rate of SC. As the microwave pretreatment time increased from 0 to 120 s, the total phenolics and antioxidant capacity of dried SC increased from 1491.4 μg Gallic acid equivalents (GAE)/g dry to 2272.1 μg GAE/g dry, and 54.47%-62.59% (p < .05). The microwave pretreatment enhanced the rehydration rate of dried SC. The rehydration percent of dried SC microwaved for 0, 30, 60, 90, and 120 s were 127.27%, 136.63%, 136.91%, 137.07%, and 136.72%, respectively.

Effect of microwave pretreatment on oxidization behaviors of bituminous coal: Experimental measurement and quantum chemistry calculation

The poor heat conduction and mass transfer of coal seam causes unsatisfying performance of gas production for in situ combustion, while microwave pretreatment is a promising technology to solve this problem. In this work, microwave heating is adopted as pretreatment method to prepare coal samples at different microwave time. The low temperature oxidization and high temperature combustion behaviors of raw coal and modified coal samples were studied with programmed temperature rising method. The functional group content in coal samples were measured with Fourier transform infrared spectrometer, while the relationship between microstructure and reactivity was studied with quantum chemistry calculation. As microwave heating time extends from 0 s to 180 s, the crossing point temperature decreases, while the combustion reaction rate increases. As microwave time prolongs from 180 s to 240 s, the crossing point temperature becomes larger, while the combustion reaction rate becomes smaller. As microwave time increases from 0 s to 240 s, hydroxyl content and carbonyl content in coal samples reduce while ether content rises. The reduction of hydroxyl and increase of ether result in an enhancement of oxidization reactivity. The decrease of carbonyl is unfavorable for oxidization reactivity. Therefore, the effect of microwave heating on coal reactivity has two sides. This explains why the microwave pretreatment time has a non-monotonic effect on the coal reactivity in both low temperature and high temperature range.

The effects of various enzymatic saccharifications and microwave pretreatment durations on sugar yield and its property alterations of Chinese spirits distillers residues

This study evaluated the effect of different enzymatic hydrolysis and different microwave pretreatment durations on the sugar yield of Chinese spirits distillers residues (CSDR). Addition of both α-amylase and cellulase in the enzymatic hydrolysis of distillers grains resulted in a higher yield of reducing sugar (145.74 ± 4.20 mg·g–1). Fourier transform infrared spectroscopy (FTIR) revealed that different enzyme treatments degraded different functional groups of the cellulose structure. Subsequently, the highest reducing sugar yield (181.33 ± 6.42 mg·g–1) was achieved at microwave pretreatment time of 6 min and was 1.29-fold higher than that of the untreated sample. The differences in the structural features of CSDRs under various microwave pretreatment durations were characterized by scanning electron microscopy, FTIR spectroscopy, and X-ray diffraction. The data revealed that the optimal microwave pretreatment time at 6 min could obviously remove lignin, and then obtain the highest CrI value, achieving the highest reducing sugar yield.

Optimization of process parameters at direct liquefaction of waste PETs

Waste polyethylene terephthalate (wPET) was converted to liquid fuel by direct liquefaction method. Additionally, how the catalyst (sodium borohydride) and microwave pre-treatment affect the total conversion and the char yield were investigated. Direct liquefaction experiments were carried out in a batch reactor under non-catalytic/catalytic conditions, and reaction temperature of 325–425 °C, and solid/solvent ratio of ¼, and reaction time of 15–90 min, and microwave pre-treatment time of 3–10 min, and an initial nitrogen pressure of 20 bar. Both the microwave pre-treatment and sodium borohydride (NaBH4) increased the total conversion in the direct liquefaction of wPETs. According to fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD) analysis of char samples obtained in the direct liquefaction process, the NaBH4 was converted to sodium borate (Na2B8O13). NaBH4 made both hydrogen (H) donating and catalytic effect. The highest total conversion in direct liquefaction of wPETs, which has at the reaction time of 30 min, and the reaction temperature of 400 °C, and in presence of NaBH4, and the microwave pre-treatment of 3 and 8 min, was 62%. The optimum process parameters in direct liquefaction of wPETs are the reaction time of 30 min, and reaction temperature of 400 °C, and the microwave pre-treatment time of 3 min.

Preparation of a high bonding performance soybean protein-based adhesive with low crosslinker addition via microwave chemistry

Human health and environmental protection demand wood-based panel industry for innovative soy-based adhesives with high production efficiency, straightforward synthesis processes, non-toxicity, and high bonding performance. A simple and efficient microwave pretreatment process and low addition of bio-derived crosslinking agent was used in this study to prepare a non-toxic and high-bonding performance soybean protein-based adhesive. After 4 min of microwave pretreatment time, the complex quaternary structure of soybean protein molecule unfolds, the soybean protein disperses evenly and stably, and active groups of soybean protein molecules are exposed. After adding 3.85% crosslinking agent, the moisture absorption rate of the soybean protein-based adhesive decreases by 41.77%, the residual rate increases by 3.68%, and the wet shear strength of the resultant plywood increases to 1.12 MPa, which satisfies requirement of interior use plywood. Compared with previously reported soy-based adhesives, this adhesive is dependent on fewer chemical reagents, but has good bonding performance. The 204.41% of relative cell viability indicates the resultant adhesive was non-toxic. The proposed high-efficiency, high-performance, non-toxic biomass adhesive has great prospects for the industrial application.

Microwave-assisted enzymatic hydrolysis to produce xylooligosaccharides from rice husk alkali-soluble arabinoxylan

The prebiotic properties of xylooligosaccharides (XOS) and arabino-xylooligosaccharides (AXOS) produced from rice husk (RH) using microwave treatment combined with enzymatic hydrolysis were evaluated. The RH was subjected to microwave pretreatment at 140, 160 and 180 °C for 5, 10 and 15 min to obtain crude arabinoxylan (AX). Increasing microwave pretreatment time increased sugar content. Crude AX was extracted with 2% (w/v) sodium hydroxide at 25 °C for 24 h and used as a substrate for XOS production by commercial xylanases. Results showed that oligosaccharides produced by Pentopan Mono BG and Ultraflo Max provided xylobiose and xylotriose as the main products. AXOS was also present in the oligosaccharides that promoted growth of Lactobacillus spp. and resisted degradation by over 70% after exposure to simulated human digestion.

A green extraction method for gelatin and its molecular mechanism

In this work, a green extraction method of gelatin was proposed to replace traditional acid and alkali treatment by microwave-rapid freezing-thawing coupling method. The mechanism of rapid gelatinization of fish skin collagen induced by microwave-rapid freezing-thawing coupling was examined systematically. The results showed that the dense structure of fish skin collagen fibers became loose, the collagen molecular on the surface was gelatinized and degraded gradually, then more internal collagen molecular without gelatinization were exposed with the increase of microwave pre-treatment time (0–60 min), resulting in an increase of gelatin yield (5.32%–19.94%) and a decrease of the gel strength (675.17–419.6 g). With the increase of freezing-thawing cycles (0–3), the gelatinized collagen fibers structure was further loosened and the balance of hydrogen bond was destroyed seriously due to the rapid formation and melting of ice crystals, thus leading to the dissolution and degradation of subunit components. This also resulted in an increases of gelatin yield (13.91%–19.01%) and a decrease of gel strength (580.01–413.33 g). Ultimately, the gelatin yield and gel strength were 17.01% and 591.50 g respectively under optimal conditions (microwave pre-treatment 15 min, one freezing-thawing cycle). This study could provide theoretical basis and guiding significance for the production of gelatin in a green way.

Mechanistic investigation on the microwave-assisted leaching of low-grade coal for low-ash coal production

ABSTRACT The coal-derived energy can potentially be explored by utilizing the low-grade coals after beneficiation for power sector application on a long-term basis. However, beneficiating the low-grade coals of Indian origin to produce low-ash coal by physical or physicochemical techniques is very challenging due to their complex mineralogical nature. In this context, chemical beneficiation or leaching has proved to be an effective method. But, the high cost of chemicals associated with the leaching process limits its commercial practice. An in-depth investigation is, therefore, needed to optimize the chemical consumption so that the requirement of the chemicals can be minimized. Herein, a microwave-assisted leaching study was investigated on Indian low-grade coal to produce low-ash coal suitable for power generation. The raw coal and its flotation product were pretreated under optimized microwave pretreatment time (5 min) and subject to leaching at varying alkali concentrations. Among all the combinations, the leaching of microwave pretreated floated coal showed a higher degree of demineralization (69.57%) together with increased carbon content (55.48%) and gross calorific value (6635 kcal/kg) in its leached product. The leached products were also analyzed using different characterization techniques such as Fourier transform infrared spectrometer, X-ray diffraction, and Thermogravimetric analyzer.

Study on optimization of extraction technique of pericarp essential oil in Litsea Cubeba (Lour) Pers

Litsea cubeba is an important aromatic oil plant. Litsea cubeba pericarp essential oil has various physiological activities such as antibacterial activity, antioxidant capacity, etc., and is widely used. Its main ingredient is citral, which is the raw material for the synthesis of many precious spices. For the purpose of increasing yield, researchers have conducted many studies on the extraction of essential oil from pericarp of Litsea cubeba. But the extraction process still has room for optimization。In this study, Litsea cubeba fruits were subjected to an optimized method of hydrodistillation to increase the yield and biological activity of pericarp essential oils. Three-factor and three-level orthogonal experimental design was performed (fruit preservation time, distillation voltage and fruit microwave pretreatment time) to optimize the process. According to the results of orthogonal experiments, the highest yield of essential oil can be obtained after the fruit has been preserved for 9 days without microwave pretreatment and the distillation voltage is 220 V. The extracted essential oils were analyzed by gas chromatography-mass spectrometry (GC–MS), which indicated that their main components were 2,6-Octadienal, 3,7-dimethyl-, (E)-, 2,6-Octadienal, 3,7-dimethyl-, (Z)-, 1-Heptanol and 1-Octanol. GC–MS results showed that the relative content of citral in the extracted essential oil was the highest after the fruit was preserved for nine days without microwave pretreatment and the distillation voltage was 150 V. Changes in the process will not significantly affect the main component types of essential oils, but will significantly affect the relative content of the same components.

Using microwave pretreatment to improve the high-gradient magnetic-separation desulfurization of pulverized coal before combustion

Coal preparation before combustion is an efficient and low-cost method for the clean utilization of coal. In this study, a dry high-gradient magnetic separator was used to conduct magnetic-separation desulfurization of pulverized coal. The effects of feed size, microwave pretreatment time and background field intensity of the high-gradient magnetic separation on the desulfurization rate, Srej, and specific susceptibility, X0, of the coal were investigated, and the degree of influence of the operating parameters on Srej was explored via an orthogonal test method. The experimental results indicated that microwave pretreatment effectively increased both Srej and X0. Particularly, X0 exhibited a maximum value with increasing pretreatment time and was 1.8 times higher than that for un-pretreated coal. Further, Srej increased monotonically with increasing field intensity and decreasing feed size, which indicated that classification can effectively improve the desulfurization performance of pulverized coal. The optimum desulfurization conditions, which resulted in a maximum Srej value of 52%, were achieved at a microwave pretreatment time of 4 min, a background field strength of 5000 Gs, and a raw coal particle size of −0.074 mm.

Modelling and optimization of wet microalgae Scenedesmus quadricauda lipid extraction using microwave pre-treatment method and response surface methodology

Abstract The process of extracting lipids from high-moisture Scenedesmus quadricauda microalgae biomass disrupted with microwave was examined. The study showed that microwave pre-treatment is effective in algae cell rupture while microwave power was found to be a significant factor to enhance the degree of cell disruption. Though microwave pre-treatment time had some effect, the degree of cell rupture seemed to decrease after a certain pre-treatment time. The total lipid from Scenedesmus quadricauda sp. were extracted using a mixture methanol and sulphuric acid as an organic solvent. In addition, it was discovered that microwave pre-treatment enhances the disruption of microalgae cells to attain a high level of lipid yields. Optimal lipid yield obtained in this study was 49% at power 600 W, heating time of 8 min and extraction time of 3.5 h.

Fine coal desulfurization and modeling based on high-gradient magnetic separation by microwave energy

Fine coal separation is one of the research focuses in the field of clean coal technology. A new type of fine coal dry separation technology was studied. Microwave energy was used to strengthen the magnetic properties of coal pyrite, leading to high- gradient magnetic separation. A high-intensity magnetic separator was used for the separation of fine coal, and an effective way to achieve the clean utilization of pulverized coal before its combustion was investigated. The R2 and corrected R2 values of the two-order model according to the sulfur content of clean coal were small. This shows that the recommended model has a higher fitting degree of response surface. Microwave pretreatment time T has a higher sensitivity to the sulfur content of clean coal than MC in a given range. The response surface has an optimal value, i.e., the highest desulfurization rate. With the increase in magnetic particle size, the desulfurization rate increased continuously. The evaluation index of the clean coal sulfur content of fine coal microwave-enhanced magnetic desulfurization test was optimized by a better two-order fitting model. The constraint conditions of the main influencing factors and the optimization indexes after the response were obtained. The sulfur content of clean coal was in the range of [1.98, 3.35].

Microwave and blanch-assisted drying of white yam (Dioscorea rotundata).

The effect of microwave and blanch pretreatments on the drying kinetics and quality of white yam (Dioscorea rotundata) was investigated. Yam cubes destined for hot air drying at temperatures 70-90°C were predried in a domestic microwave or blanched in hot water for 1-5min. Microwave pretreatment time had a positive significant effect on drying rate but both pretreatments had a negative influence on the ascorbic acid content and the nonenzymatic browning. The optimum drying conditions were a microwave pretreatment time of 5min and a temperature of 70°C and a blanching time of 1min at a temperature of 80°C. Among the models fitted, the Midilli etal. and the Page models gave the best fits for yam cubes predried with microwave and blanch, respectively. The effective moisture diffusivity for microwave-assisted drying increased from 1.05×10(-8)m(2)s(-1) to 2.00×10(-8)m(2)s(-1) while the hot water blanched samples decreased from 1.53×10(-8) to 8.81×10(-9)m(2)s(-1) with time. The study demonstrates that microwave-assisted drying could be used to enhance heat and mass transfer processes to produce better quality dried yam products.

The Improvement of Grindability and Floatability of Oxidized Coal by Microwave Pre-treatment

A laser particle size analyzer was used to analyze the particle size composition of −200 mesh from the coals for different grinding time and/or different microwave pre-treatment time. Fourier-transform infrared was used to show the changes in the main functional chemical groups of oxidized coal upon grinding and/or microwave pre-treatment. All of these were recognized by the flotation behavior using an XFD1.5L flotation cell. Under the same grinding time, −200 mesh coals will be finer when microwave pre-treatment increases. Microwave pre-treatment and grinding improve the floatability of oxidized coal by reducing the content of –OH and/or increasing the content of –CH3. Combustible recovery increases or decreases proportionately with a yield of −74 + 11 μm.

Effect of microwave pretreatment on oxidized coal flotation

The oxidized coal should be well recovered as the demand for energy is increasing. But the hydrophobicity of oxidized coal is much lower than that of fresh coal, the improvement in floatability of oxidized coal is a key issue. Microwave pretreatment is used to improve the floatability of oxidized coal in this investigation. FTIR was used to show the changes in the main functional chemical groups of microwave treated oxidized coal at different times. The moisture content of microwave treated oxidized coal at different times was also measured. The results of FTIR and moisture content measurements show that microwave pretreatment seems to have weak effect on the chemical properties of oxidized coal surface but can reduce the moisture content. The results of flotation tests show that the combustible recovery increases with microwave pretreatment time. The mechanism of microwave pretreatment improving the floatability of oxidized coal is discussed in this investigation. The combustible matter recovery of oxidized coal increases with the increase of microwave pretreatment time and/or the decrease of moisture content. The main purpose of microwave pretreatment, enhancing the oxidized coal flotation may be, to reduce the moisture content of oxidized coal and weaken the peak at 3450 cm − 1 as observed from FTIR spectrums. ► Microwave pretreatment is used to improve the flotation of oxidized coal. ► Microwave pretreatment can reduce the moisture content. ► Combustible matter recovery increases with microwave pretreatment time.

Utilisation of microwave-NaOH pretreatment technology to improve performance and l-lactic acid yield from vinasse

Pretreatment of vinasse is necessary to break down its complex wooden structure, improve the efficiency of enzymolysis, and provide an adequate substrate for fermentation during l -lactic acid production. Independent microwave and NaOH pretreatment processes were carried out in an earlier study. Here a two-way microwave-NaOH coupled method, was investigated to determine the effects of simultaneous saccharification and fermentation (SSF) of vinasse on l -lactic acid production. Compared with the former individual microwave and NaOH pretreatment methods, hemicellulose and lignin in vinasse were more significantly reduced using microwave-NaOH coupled pretreatments, reducing crystallinity to 14.77%. l -lactic acid yield was also higher in the coupled method than the sum of the yields from the independent pretreatment processes. The optimal conditions for the coupled pretreatment method were: 0.06 g g−1 (vinasse dry weight) NaOH; 523 W microwave power; 1:2 solid–liquid ratio; and 8 min microwave pretreatment time. These conditions resulted in an 86.0 mg g−1 l -lactic acid yield. The microwave power and the amount of alkali used were approximately 25% lower than those used prior to the optimisation process. The reduced values indicate that optimisation can significantly decrease energy and reagent consumptions. Thus, microwave-NaOH coupled pretreatment exhibits a synergistic effect for improving l -lactic acid production.

Enhanced extraction of patchouli alcohol from Pogostemon cablin by microwave radiation-accelerated ionic liquid pretreatment

A microwave radiation-accelerated ionic liquid pretreatment (MRAILP) was developed to enhance extraction of patchouli alcohol from Pogostemon cablin. 1- N-butyl-3-methylimidazolium chloride ([C 4mim]Cl) was selected as microwave absorbing and cellulose dissolution medium and microwave was applied to accelerate sample dissolution. The conditions of MRAILP including particle size, solvent, microwave pretreatment time and power and the ratio of ionic liquid (IL) to sample were optimized. Under the optimized conditions, the extraction yield of patchouli alcohol by the MRAILP was 1.94%, which has increased by 166% compared with microwave-assisted extraction. The recovery was in the range of 95.71–103.7% with relative standard deviation lower than 3.0%. It was a novel alternative extraction method for the fast extraction and determination of patchouli alcohol from Pogostemon cablin.

Microwave assisted ionic liquid pretreatment of medicinal plants for fast solvent extraction of active ingredients

For increasing active ingredients accessibility to the solvents, microwave assisted ionic liquid pretreatment (MILP) is introduced to destroy cell walls of medicinal plants before solvent extraction. As a new sample pretreatment method, microwave irradiation on sample pretreatment with ionic liquids (ILs) was investigated. The conditions of MILP including microwave pretreatment time and power, ionic liquid (IL) and sample ratio and particle size were optimized and Cynanchum paniculatum and its active ingredient paeonol were chosen as the representative target analyte. Under the optimized conditions, the paeonol extraction yield by MILP was higher than that of ionic liquid aqueous solution and Soxhlet extraction. In addition, the results of bioassay test showed that the antibacterial effect of crude extract by MILP was almost the same with that of soxhlet extraction. Our results demonstrate that sample pretreatment with ILs and microwave irradiation is a potential alternative method for the pretreatment of medicinal plants before solvent extraction.

MICROWAVE AND ULTRASOUND ASSISTED EXTRACTION OF SOYBEAN OIL

The effect of ultrasound and microwave assistance in enhancing extraction oil yields from soybeans when differentsolvents are used for extraction was investigated in two separate experiments. Each study involved a three-factor factorialfollowing a completely randomized design that was replicated three times. Treatment factors investigated in the microwaveprocessing study were microwave pretreatment time (0, 0.5, 1, and 2 min), solvent (isopropanol, hexane, and 3:2 hexane-isopropanolmixture), and extraction time (0.5, 1, 1.5, 2, and 3 h). Ultrasonic intensity (0, 16.4, 20.9, and 47.6 W/cm2) wassubstituted as a treatment factor in the sonication study. Solvent extraction was accomplished by immersion of groundsoybeans in a given volume of solvent at ambient temperature. While oil yields did not approach the 19.2% analyzed oilcontent of the TN 96-58 used as the test material, they were found to increase with both intensity of the process assistanceand extraction time under the conditions of the studies, particularly with hexane and the mixed solvent. The highest yield resultof 12.21 g from 100 g soybeans was obtained with the mixed solvent under 47.6 W/cm2 sonication. The results obtained withthe mixed solvent with both microwave pretreatment and ultrasound assistance are difficult to explain in terms of physicalchemistry. The results with isopropanol indicate that the efficiency of the extraction process depends greatly on the molecularaffinity between solvent and solute and that process assistance tested in this study cannot overcome inherent deficiencies insolvent-solute interactions.