Microwave Irradiation Pretreatment Research Articles

Numerical modelling of microwave irradiated rock fracture

Rock fracturing through microwave irradiation has received significant attention recently as a viable pretreatment for improving the energy efficiency of comminution processes. This study presents a numerical analysis on the effects of microwave heating on the mechanical properties of hard rock. In particular, the reduction of the uniaxial compressive and tensile strength of granite-like rock due to microwave irradiation induced damage is numerically assessed.Rock fracture is modelled by a damage-viscoplasticity model, with separate damage variables for tension and compression types of failure. A global solution strategy is developed where first the electromagnetic problem is solved in COMSOL multiphysics software, then its solution is used as an input for the thermo-mechanical problem, which is finally solved by means of a staggered explicit solution method. Due to the preeminence of the thermal radiation, the thermal and the mechanical parts of the problem are considered as uncoupled.The model behaviour is tested in 3D finite element simulations of three-mineral numerical rock specimens, with mesostructures explicitly defined, pretreated first in a microwave oven and then subjected to uniaxial compression and tension tests. The results show that the compressive and tensile strength of rock can be considerably reduced by the microwave irradiation pretreatment.

Permeability of wood impregnated with polyethylene wax emulsion in vacuum

Polyethylene wax (PEW) has emerged as a commonly used material for maintaining the quality of wood. The emulsification of solid PEW before being injected into wood can effectively overcome the shortcomings of the high-temperature melting and injection process of solid PEW. The permeability of Eucalyptus (Eucalyptus saligna) and Mongolian Scotch pine (Pinus sylvestris var. Mongolica) to PEW emulsion in vacuum environment was investigated using impregnation tests, and steaming pretreatment and microwave irradiation pretreatment were applied. The small particle size and low viscosity of the PEW emulsion, whose median particle size was 0.256 μm and viscosity was 52.2 mPa s (at 60 r/s), facilitated its penetration into the wood capillary system. The weight percent gain (WPG) of Eucalyptus and Mongolian Scotch pine post impregnation in vacuum was positively correlated with both the vacuum-holding time and the impregnation temperature, but after 60 min of impregnation the WPG of both wood species decreased significantly. Both pretreatment methods could substantially improve the wood permeability and effectively promote the penetration of the PEW emulsion into the wood. The maximum WPG was achieved when Eucalyptus and Mongolian Scotch pine were respectively steamed for 80 min and 120 min. There was an increase of 0.24 times for the former and an increase of 0.53 times for the latter compared to unpretreated wood. Both species exhibited the highest WPG after water immersion for 60 min (with average moisture content close to their fibre saturation point) and microwave irradiation for 30 s, which was respectively 0.28 and 0.75 times higher than that of unpretreated wood. There was a significant variation in WPG between the two species with the same pretreatment method. The relatively lower density and better-developed capillary system of Mongolian Scotch pine allowed more efficient penetration of PEW emulsion. It is recommended that, considering the time cost and practical enhancement, microwave irradiation should be given priority to when pretreating wood.

Effect of calcium peroxide assisted microwave irradiation pretreatment on humus formation and microbial community in straw and dairy manure composting

In this study, the effects of four pretreatment methods on the crystallinity of maize straw were compared, and the CaO2 assisted microwave pretreatment was selected for straw and dairy manure composting. The humification and microbial community were investigated. Results showed that the pretreatment increased the initial water-soluble carbon, which favored the microbial activity, and the CO2 release increased by 15.71%. Pretreatment promoted the lignocellulose degradation, with total degradation ratio of 37.06%. The final humic acid content was 11.39 g/kg higher than the control. Spearman correlation analysis indicated that polyphenols and amino acids were significantly related to humus formation. In addition, pretreatment rendered the Firmicutes the most dominant phylum, and increased the metabolic intensity of reducing sugar metabolism, aromatic amino acid biosynthesis and carbon fixation pathways. Redundancy analysis revealed that the dominant genus of Firmicutes was significantly positively correlated with humus, while that of Actinobacteriota was correlated with CO2 release.

Surfactant assisted microwave irradiation pretreatment of corncob: Effect on hydrogen production capacity, energy consumption and physiochemical structure

The combination pretreatment strategy is an effective way to intensify photo-fermentative biohydrogen production (PFHP) process. In this study, the synergistic effects of microwave irradiation and surfactants on the hydrogen production performance, energy analysis and structural characteristics was evaluated. Results revealed that hydrogen production performance was improved after microwave irradiation pretreatment (MIP) and surfactants assisted microwave irradiation pretreatment (SMIP). SMIP group had a higher cumulative hydrogen yield (CHY) of 367.87 ± 6.481 mL compared with control group (223.26 ± 4.329 mL) and MIP group (303.66 ± 3.366 mL), which was an increase of 36.01% and 64.77%, respectively. Energy evaluation analysis showed that the energy ratio of SMIP (0.49) was higher than that of MIP (0.37) in the PFHP system, therefore, SMIP can save more energy. After SMIP, the corncob lignocellulose structure was greatly damaged, which was verified by SEM, FTIR, XRD and XPS analyses.

The isolation of lignan containing fractions from flaxseed Linum usitatissimum L.

This article is dedicated to the isolation of lignin-containing fractions from the flaxseeds Linum usitatissimum L. The main component of these fractions is lignan-secoisolariciresinol diglucoside (SDG). The authors have developed an effective extraction method for obtaining lignan-containing fractions from flaxseed with a satisfactory yield of SDG-containing fraction and its isomers. This method was implemented by microwave irradiation pretreatment of the seeds and by using environmentally friendly extraction solvents. A 50/50 mixture of water and ethanol was chosen as extraction agents. Microwave irradiation pretreatment of ground flaxseeds was carried out at 450W and 800W for 5 seconds, 4 times with an interval of 5 seconds. SDG-identification was performed on an Agilent 1200 series high performance liquid chromatograph and a Shimadzu UV-1900 automatic dual-beam UV spectrophotometer. The results of the conducted studies showed that the microwave irradiation pretreatment of flaxseeds at 800W increases the yield of SDG relative to the dry residue by 34.76% in comparison with the classical alkaline method, and the content of the amount of lignans in recalculation on chicory acid was 43.53%.  Thus, the extraction method of lignans-containing extract including the stage of pretreatment by microwave irradiation with power of 800W is the most effective method.

Practical Application of Novel Semi-dried Fruit Prepared by Microwave Irradiation Pretreatment and Hot Air Drying

Practical Application of Novel Semi-dried Fruit Prepared by Microwave Irradiation Pretreatment and Hot Air Drying

Effects of microwave pre-treatment on the flotation of ilmenite and titanaugite

The selective separation of titanium-containing minerals is industrially important. Microwave irradiation pre-treatment can be used to modify the surface properties of minerals to promote selective flotation. However, the effects of MW treatment on titanium-containing minerals is not well understood. Therefore, in this study, we investigated the effects of microwave treatment on the flotation behaviour of ilmenite and titanaugite in a mixture of these minerals. The effects of this pre-treatment method were investigated by various techniques, including flotation tests, scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) spectroscopy. The flotation tests results reveal that, under the optimum microwave conditions (800 W, 450 s), microwave irradiation has a remarkable effect on the flotation of ilmenite but no significant effect on the floatability of titanaugite at pH 6.0. The results of the SEM and ICP-OES analyses indicate that microwave irradiation promotes the dissolution of Ca2+ and Mg2+ ions from the titanaugite surface, whereas the dissolution of these ions from ilmenite is limited. Further, the zeta potential of the microwave-irradiated ilmenite shifted toward negative values, and the isoelectric point shifted from pH 4.9 to pH ~1.9. In addition, the XPS results reveal that microwave irradiation facilitates the conversion of Fe2+ to Fe3+ on the mineral surfaces. The FTIR spectra and zeta potential values indicate that microwave irradiation can enhance the chemical adsorption of oleate ions on the surface of the ilmenite. After microwave irradiation, the effects of both the dissolution of Ca2+ and Mg2+ ions and the oxidation of Fe2+ to Fe3+, the floatability of ilmenite was significantly improved, whereas that of titanaugite was not changed significantly.

Torrefaction of palm kernel shell using conventional and microwave irradiation pretreatment

This study describes the properties of torrefied palm kernel shell (PKS) by conventional and microwave irradiation (MI) pretreatment. In conventional pretreatment, the untreated PKS was torrefied using fixed bed reactor at temperature of 210, 230, 250, 270 and 290 °C for 60 min of holding time. In MI pretreatment, the untreated PKS was irradiated with microwave power of 200, 300, 450 and 600 W for 8 min of holding time. The torrefied samples were analysed for mass and energy yield, energy density, calorific value and proximate and ultimate analysis. The results showed that, the properties of torrefied samples were improved with increasing torrefaction temperature and microwave power. The mass and energy yield, moisture, volatile matter and oxygen content of torrefied PKS decreased, whereas, the calorific value, energy density and carbon content increased with increasing torrefaction temperature and microwave power. The torrefaction temperature of 270 °C and microwave power of 450 W were appropriate to upgrade the PKS properties. Therefore, the change in properties of torrefied PKS revealed the potential of applying pretreatment prior to further thermal conversion such as pyrolysis and gasification.

Influence of microwave pre-treated Palm Kernel Shell and Mukah Balingian coal on co-gasification

In this study, microwave irradiation pretreatment of palm kernel shell (PKS) and Mukah Balingian (MB) coal was carried out in a fixed bed reactor. The effect of microwave power and processing time was investigated on pretreated PKS and MB coal characteristic. Then, the co-gasification of microwave pretreated PKS and MB coal was conducted to examine the effect of product yield and gases composition. The results showed that, the characteristics of pretreated sample was improved with increasing microwave power and processing time. The volatile matter, oxygen content and O/C ratio of pretreated sample decreased, while the calorific value, fixed carbon and carbon content of pretreated sample increased with increasing microwave power. The carbon content of pretreated PKS was closed to the untreated MB coal with comparable calorific value was obtained. The microwave power level of 450 W and processing time of 8 min were appropriate to upgrade the PKS and MB coal for co-gasification. The pretreated sample produced higher gas yield and lower tar and char yield than the untreated sample during co-gasification. This result was due to low moisture and oxygenated compound of pretreated feedstock made it appropriate to be converted in co-gasification. Moreover, co-gasification of pretreated sample produced the higher H2+CO and CH4 and lower CO2 composition than untreated sample. Thus, it can be concluded that the microwave irradiation pretreatment on PKS and MB coal performed the significant impact on the product distribution and composition during the co-gasification.

Microwave Irradiation Assisted Supercritical Carbon Dioxide Extraction of Bio-Oils from Chlorella Vulgaris Microalgae

Chlorella vulgaris is one of the promising microalgae strains that can produce high yield of bio-oils. The C. vulgaris was pretreated with microwave irradiation prior to extraction using supercritical carbon dioxide (SCCO2). Fourier transform infrared spectroscopy (FTIR) analysis showed microwave irradiation pretreatment does not affect the material composition of C. vulgaris. Scanning electron microscopy (SEM) of the microwave irradiation pretreated microalgae showed an agglomeration of the cells with the cells shape became distorted due to rupturing of the cell walls. Optimization of the SCCO2 process parameters (pressure, temperature and CO2 flow rate) was performed by using response surface methodology (RSM) with central composite design (CCD). Two factors significantly affecting the extraction yield were temperature and pressure. The model equation also predicted the optimum condition for the SCCO2 (without microwave pretreatment) at 70 , 5676 psi and 7 sL/ min while optimum condition for SCCO2 (microwave irradiation pretreatment) at 63 , 5948 psi and 10 sL/ min. High amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), -linolenic acid and palmitoleic acid were found in the extracted oil with microwave irradiation pre-treatment sample. In addition, the polyunsaturated fatty acids (PUFA) content in the microwave irradiation pretreated oil was considerably low and is desirable for biodiesel production.

Microwave irradiation pre-treatment in third generation bioethanol production from tropical green algae

Through centuries the side effect of the massively growing of population is the energy demand and consumption. As a result of this, the world energy used from the non-renewable fossil fuel has reached 80%. To counter this, researchers have found alternatives for this fossil fuel; and bioethanol is one of the alternative and sustainable options. One source of bioethanol that is believed carrying high production potential is photosynthetic algae or green algae. In this study, Chlorophyta (Green Algae) was hydrolyzed using microwave irradiation. Operation Mode (OM) was varied to observe its effect during the hydrolysis stage. Further, hydrolysis time (t) was also selected as the variable in this study to examine the result of reducing sugar. From the result of this experiment, it is projected that the sugar produced from hydrolysis assisted by microwave irradiation would bring a high-quality bioethanol production. Also, from this study, it would exhibit the great potential of bioethanol from green algae as the fossil fuel substitute in order to create a more sustainable and environmentally friendly energy source.

Sugarcane Bagasse Hydrolysis Enhancement by Microwave-Assisted Sulfolane Pretreatment

Sugarcane bagasse is the major by-product of the sugarcane industry and, due to its abundant availability, it has been extensively studied for lignocellulosic bioconversion in the production of bioethanol and other value-added commercial products. In the study presented herein, a combined pretreatment using sulfolane, TiO2 and alkali microwave irradiation (MW-A) was assessed for the dissolution of lignin prior to enzymatic saccharification of holocellulose. Total reducing sugars (TRS) and saccharinic acid yields were investigated. The increase in NaOH concentration up to 5% and in temperature from 120 °C to 140 °C were found to have a positive influence on both yields. While increasing the reaction time from 5 to 60 min only led to an increase in TRS yield <2%, a reaction time of 30 min almost doubled the saccharinic acids production. TRS yields and saccharinic acid production were approximately 5% and 33% higher when the sulfolane-TiO2 reaction medium was used, as compared to MW-A in water, reaching up to 64.8% and 15.24 g/L of saccharinic acids, respectively. The proposed MW-A pretreatment may hold promise for industrial applications, given the good TRS yields obtained, and the associated enzyme and time/energy savings. The use of sulfolane-TiO2 reaction medium is encouraged if saccharinic acids are to be recovered too.

マイクロ波前処理および熱風乾燥による新規セミドライフルーツの開発と普及

Hot air drying is conventionally applied for the production of dried fruit; however, hardening and browning of the fruit pulp surface often occurs during processing. We demonstrated that microwave irradiation of Japanese pear pulp or grape, followed by hot air drying, produced high quality semi-dried fruit. Dried Japanese pear produced using this method showed uniform softness and a vivid yellow-orange color. In the case of dried grape products, microwave irradiation pretreatment improved the retention of both skin color (yellow-green and red) and original flavor (such as muscat and foxy). In addition, microwave pretreatment shortened the subsequent hot air drying period by approximately 30% for Japanese pear and 60% for grape. This method could be applied to other fruits such as apple, pear and peach. Dissemination of the method has resulted in commercialization of some dried fruit and confectionary products. However, a system capable of mass production, resulting in reduced production costs, is needed to promote the practical use of this method.

Transformation of Starchy Lignocellulosic Biomass to Ethanol using Ragi Tapai Synergized with Microwave Irradiation Pretreatment

Ethanol production strategy was studied using multiple strain microbes from microwave irradiation (MI) pretreated sago waste. Sago waste (SW) was MI-pretreated for reducing sugars production using 2 heating media (water and sulfuric acid) under pretreatment conditions including MI power, pretreatment duration, and solid loading. When water was used, the pretreatment parameters were optimized using Box-Behnken Design (BBD). However, gelatinized starch and charring of SW led to an insignificant quadratic model. To mitigate the gelatinization problem while determining the best MI pretreatment conditions, water was substituted by sulfuric acid using single factor method. The highest reducing sugar yield of 261.5 mg/g SW was achieved at 7.5% solid loading, 6 min pretreatment duration, and 300 W MI power. The effectiveness of the pretreatment was ascertained by field-emission scanning electron microscopy (FESEM) and chemical-composition analysis. When fermenting MI-pretreated SW using ragi tapai, simultaneous saccharification of starch and ethanol production was evidenced from the sugar/ethanol profile. A resulted yield of 7.24 g ethanol/100 g SW confirmed the fermentability of MI-pretreated SW. The ethanol production was well fitted into the modified Gompertz model.

An approach of ionic liquids/lithium salts based microwave irradiation pretreatment followed by ultrasound-microwave synergistic extraction for two coumarins preparation from Cortex fraxini

Ionic liquids/lithium salts solvent system was successfully introduced into the separation technique for the preparation of two coumarins (aesculin and aesculetin) from Cortex fraxini. Ionic liquids/lithium salts based microwave irradiation pretreatment followed by ultrasound-microwave synergy extraction (ILSMP-UMSE) procedure was developed and optimized for the sufficient extraction of these two analytes. Several variables which can potentially influence the extraction yields, including pretreatment time and temperature, [C4mim]Br concentration, LiAc content, ultrasound-microwave synergy extraction (UMSE) time, liquid–solid ratio, and UMSE power were optimized by Plackett–Burman design. Among seven variables, UMSE time, liquid–solid ratio, and UMSE power were the statistically significant variables and these three factors were further optimized by Box–Behnken design to predict optimal extraction conditions and find out operability ranges with maximum extraction yields. Under optimum operating conditions, ILSMP-UMSE showed higher extraction yields of two target compounds than those obtained by reference extraction solvents. Method validation studies also evidenced that ILSMP-UMSE is credible for the preparation of two coumarins from Cortex fraxini. This study is indicative of the proposed procedure that has huge application prospects for the preparation of natural products from plant materials.

マイクロ波照射および熱風乾燥により製造したブドウの新規ドライフルーツ

マイクロ波照射による前処理と熱風乾燥によりドライフルーツを製造する特許手法を用いて，ブドウのセミドライフルーツを作製する場合の加工適性を検討した．ブドウの果粒にマイクロ波を一定時間照射した後で熱風乾燥を行えば，前処理を行わない場合より乾燥初期の含水率の低下が大きく，セミドライフルーツを製造する乾燥時間が約6割短縮された．また，果皮が黄緑色および赤色のブドウについては，この製造法により作製したセミドライフルーツは褐変が少なく，それぞれ黄緑色および赤色の色彩をやや残していた．さらに，本製法によれば，マスカット香，フォクシー香など，ブドウ固有の風味をやや残すことができた．本製法によりブドウ6品種のドライフルーツを製造したところ，果皮が比較的薄く，皮ごと食べやすい品種の食感が良好であった．

Total utilization of Japanese pear tree prunings: extraction of arbutin and production of bioethanol

Discarded branch prunings from Japanese pear trees (Pyrus pyrifolia cv. Kousui) are promising resources containing polysaccharides and polyphenols. This study aimed at the total utilization of discarded branches. Arbutin is an inhibitor of biosynthesis of the human pigment melanin and extensively used as a human skin-whitening agent. It was found that most of the arbutin in the branches was contained in the bark (27.1 mg/g dry matter) compared with that in wood (5.2 mg/g dry matter). We evaluated the effect of the extracted solution containing arbutin (ESCA) from the bark on melanin formation in B16 melanoma cells. At a concentration of 4.0 × 10−3 % of ESCA, treated B16 melanoma cells showed 77.9 ± 3.9 % of the melanin production of untreated cells, with no cytotoxicity. The residue (wood) after arbutin extraction contained abundant holocellulose (69.8 %), and was accordingly hydrolyzed with cellulase and then converted into ethanol by Saccharomyces cerevisiae BA11, after microwave irradiation pretreatment. In total, 0.79 g of arbutin and 8.84 g of ethanol were produced from the 100 g of dry branches.

Influence of microwave irradiation on ilmenite surface properties

Abstract In this study, the effect of microwave irradiation on ilmenite surface properties and its flotation behavior was investigated. After microwave irradiation, Fe 2+ ions on the ilmenite surface are oxidized to Fe 3+ ions. XPS analysis indicated that the relative content of Fe 3+ increased from 48.5% to 66% after microwave irradiation for 2.5 min. This conversion decreased the ilmenite surface zeta potential in a wide pH range and resulted in the shift of PZC from a pH of 5.4 to a pH of 2.7. FTIR spectra and zeta potential measurements showed that the microwave irradiation enhances the adsorption of oleate ions on the ilmenite Helmholtz layer. The greater stability of chemisorbed ferric iron oleate than ferrous iron oleate resulted in the increase of contact angle and the decrease of surface zeta potential. Therefore, the microwave irradiation pretreatment improves the ilmenite hydrophobicity and floatability in a wide pH range. The maximum floatability of ilmenite occurring at a pH of 6.3 was 73.5% and 94% for non-irradiated and irradiated ilmenite, respectively.

The Effect of Pretreatment with Dilute Acid on the Microwave-assisted Pyrolysis of Wheat Stalk

Wheat stalk was pyrolyzed under microwave irradiation and different dilute acids pretreatment, and the pyrolytic mixture were extracted with tetrahydrofuran. The effects of dilute acids pretreatment on the yield of tetrahydrofuran-extractable fraction and the selective conversion of wheat stalk under microwave irradiation were investigated. Compositions of extractable fraction were analyzed with gas chromatography/mass spectrometry. The results indicated that acids can remarkably improve the formation of furfural, pyran-2-one, and 2-butenal, etc.

マイクロ波照射および熱風乾燥により製造したニホンナシの新規ドライフルーツ

ドライフルーツの製造にける一般的な方法である熱風乾燥は，果実表層部が早く乾燥・硬化し，内部は乾燥しにくいため，乾燥時間の長さ，製品水分の不均一性および食感の悪化が問題となる場合が多い．さらに，ポリフェノールの酸化等による褐変も製品の品質を落とす要因である．ニホンナシの果実片にマイクロ波を照射した後で熱風乾燥を行えば，前処理を行わない場合と比較し約2/3の時間で乾燥が終了し，色彩が鮮やかで褐変がなく，水分や硬さが均一なセミドライフルーツが得られることがわかった．以上の効果が得られるために必要なマイクロ波処理時間は，果実片の処理重量に比例するとともに，電子レンジ出力に反比例した．40°Cから70°Cの熱風乾燥温度でセミドライフルーツの作製が可能であり，温度が高いほど濃い色調を呈した．消費者による官能検査を実施したところ，マイクロ波処理を行ったニホンナシのセミドライフルーツは，無処理のものより外観，味，食感および総合評価において好ましいと判断された．以上より，マイクロ波による前処理と熱風乾燥により製造されたニホンナシのセミドライフルーツは，高品質な果実加工品として，今後の普及が期待される．