Microwave Irradiation Time Research Articles

Separation of essential oil from fresh leaves of Phellodendron amurense rupr. By solvent-free microwave-assisted distillation with the addition of lithium salts

The essential oil was separated from the fresh leaves of Phellodendron amurense Rupr. by solvent-free microwave-assisted distillation in a rotating state with n-hexane extraction and LiCl addition, which ingeniously designed lithium salt addition, rotation unit, and n-hexane extraction effectively improved the yield and separation rate of essential oils. The factors that may affect essential oils yield were screened and optimized by single factor optimization, response surface methodology, and kinetic model to obtain the optimal conditions for the separation of essential oils by this method, which were LiCl content of 8%FW, microwave irradiation power 600 W and microwave irradiation time 40 min. And the yield of essential oils is 2.39 ± 0.12 mg/g in the optimum conditions by this method, which is highly consistent with the predictions from the response surface method (2.39 mg/g) and the first-order kinetic model (2.42 ± 0.04 mg/g). This method effectively ensures the uniform heating of the plant material and the rapid overflow of the essential oil by employing the rotating unit and the addition of LiCl, which effectively avoids the loss of the heat-sensitive components in the essential oil. Moreover, the solvent-free distillation of this method highly improves the heating rate, and the added LiCl can also be effectively recovered and reused, which effectively reduces the economic cost, and environmental stress and will result in a cleaner product. And an accurate quantitative analysis method of essential oils was established by n-hexane extraction-ultraviolet spectroscopy, which not only effectively avoided the loss of water-soluble components but also provided a new strategy for quantitative analysis of essential oils. In addition, the results of the kinetic model indicated that the separation rate constant of essential oils in this method was 1.34 times that of microwave-assisted hydrodistillation and 5.05 times that of conventional hydrodistillation. Therefore, this method is an efficient, green, and clean essential oil preparation method, which is very promising to replace existing methods in the future.

Effect of microwave heating on the mechanical properties and energy dissipation characteristics of hard rock

To study the effect of microwave on the weakening mechanism of hard rock, uniaxial compression tests were conducted on granite samples after microwave treatment, and an acoustic emission system was established to monitor the fracture evolution in such rock samples. The effects of microwave irradiation on the stress–strain curve, acoustic emission characteristics, and energy dissipation characteristics of granite were investigated in the experiment. The results show that: (1) With the continuous increase of microwave irradiation power and time, the compaction stage and crack development stage of the sample gradually increase, and the elastic stage gradually becomes shorter; the trend of post-peak stress drop becomes slower, changing from “cliff type” to multi-step type “. The failure of the sample indicates that they become less brittle and more ductile; (2) Microwave irradiation reduces the strength. The overall acoustic emission count rate is weak before the peak and increases rapidly near the peak. The count rate has also changed from sparse to dense, and with the increase in the irradiation power and time, the total acoustic emission count rate increases; (3) From the energy point of view, the weakening of granite by microwave irradiation will not only decrease the energy-storage limit of granite and increase the proportion of dissipated energy in the failure process, but also decrease the rate of release of elastic energy after the peak. Therefore, microwave irradiation will not only reduce the mechanical energy dissipated during damage, but also reduce the intensity of potential dynamic disasters.

Iron-enriched coal and volcanic rock waste powder composite with enhanced microwave absorption capacity for the degradation of 2,4-D and atrazine pesticides in single and binary systems

A novel catalyst was synthesized employing coal and volcanic rock waste (VRW) residues enriched with iron nanoparticles, and its efficiency was investigated upon the degradation of (2,4-dichlorophenoxy)acetic acid (2,4-D) and atrazine (ATZ) pesticides. The composite was synthesized by a facile and effective chemical precipitation technique and extensively characterized by XRD, FTIR, XRF, ICP-OES, ICP-MS, and SEM-EDS. The effects of pH, catalyst dosage, and initial pollutant concentration were investigated in single and binary systems irradiated with microwave (MW) under atmospheric pressure. The optimal reaction conditions were obtained at pH 3 and 5 for 2,4-D and ATZ in single systems and pH 3 in binary systems, respectively, with 20 mg L−1 of initial pollutant concentration and 0.1 g L−1 of CVRWMag (coal, VRW, and nano-Fe3O4) catalyst. The kinetic data fitted better to the pseudo-first-order model (R2 > 0.965). In addition, the phytotoxicity was investigated with Lactuca sativa seeds, and the root elongation and the seed germination rate were enhanced as the MW irradiation time increased. The complete degradation of both compounds was reached within 30 min, with outstanding mineralization efficiency. The degradation efficiency was attributed to hydroxyl radical (OH) formation and electrostatic surface interaction, enhanced by hot spot formation. Therefore, the CVRWMag is a promising MW absorbing catalyst for the removal and degradation of pesticides without the need for H2O2 or any radical enhancing agent addition.

Coal and Gangue Active Identification Method Using Microwave Irradiation-Infrared Detection

In the process of the longwall top coal caving method, automatic distinction between coal and gangue at the working face is one of the most critical factors for the success of the operation. An active coal and gangue identification method using microwave irradiation combined with infrared detection is proposed in this paper. Coal and gangue are irradiated with microwave to actively enhance the external differences between them, and then the quantitative data of the difference are quickly collected by a noncontact infrared thermal imager, to perform identification of coal and gangue. Using theoretical analysis and laboratory experiments, the physical and chemical properties of coal and gangue are analyzed in order to reveal the thermal sensitivity of coal and gangue to microwave irradiation. The influences of the coal and gangue particle size, microwave irradiation time and microwave frequency on the thermal sensitivity to microwave irradiation are investigated. The experimental results show that the average temperature rise in coal is approximately 1.5 times that in gangue material under the same microwave irradiation conditions. This supports the feasibility of this identification method, and provides theoretical and experimental bases for achieving rapid and accurate identification of coal and gangue in top coal caving operations.

Study on Microwave Curing of Unsaturated Polyester Resin and Its Composites Containing Calcium Carbonate.

Microwave curing technology has been widely used in resin and its composite materials. In order to study its effect for curing unsaturated polyester resin (UPR) composites containing calcium carbonate (CaCO3) filler, this paper first investigated the influence of microwave power and microwave irradiation time on the curing characteristics of UPR. Then, CaCO3 particles were added to the UPR to investigate the microwave curing effect of the UPR composites containing the CaCO3. The results showed that microwave irradiation could heat the UPR sample evenly, and rapidly cause the chain growth reaction, thus greatly shortening the curing time. The curing degree and products of the samples after microwave curing were consistent with that of the thermal curing. The addition of CaCO3 particles could increase the heating rate of the UPR composites, which would accelerate the curing rate of the UPR. However, higher microwave power could lead to pore defects inside the UPR composites with higher CaCO3 content, resulting in a lower strength. Thus, the compactness of the samples should be improved by reducing the microwave power and prolonging the microwave treatment time.

Effect of microwave irradiation time on structural and optical properties of ZnS nanoparticles

In this communication, we report the synthesis of ZnS nanoparticles by chemical precipitation of Zn2+ ions with S2- ions in aqueous solution. Freshly formed ZnS nanoparticles (NPs) in colloidal suspension were microwave irradiated for different time intervals in a domestic microwave oven. Effect of microwave irradiation (MWI) time on microstructure, surface morphology and optical properties of NPs are studied using various characterization tools. The structural analysis confirms the influence of MWI time on cubic and crystalline nature of the samples which are in good agreement with selected area electron diffraction (SAED) pattern. The size of the NPs increased with increase in time of MWI. The size increase is consistent with literature reports that microwave irradiation accelerates not only the nucleation but also crystal growth. The band gap of the material tends to decrease as a function of irradiation time. The role of MWI time on surface defect removing process is also explained in detail.

Effect of chemical desulfurization on coal properties and sulfur structure based on microwave technology

AbstractUnder the two frequency microwave conditions of 915 and 2450 MHz, orthogonal tests were designed to investigate the effects of organic acid reagent, microwave irradiation time, and mixing time of additives and coal samples on the desulfurization effect of coal. Results show that the effect of irradiation time on the experimental desulfurization efficiency under frequency microwave conditions is large and is the main factor. The desulfurization effect under 915 MHz microwave condition is better than 2450 MHz microwave condition. Two sets of experimental optimal coal samples were used for characterization and analysis. Thermogravimetric analysis revealed that the combustion temperature range of the coal samples is shortened and the integrated combustion index is considerably higher after the microwave irradiation experiment. Fourier‐transform infrared spectroscopy analysis showed that the overall chemical structure of the coal samples does not change significantly after the experimental treatment. X‐ray photoelectron spectroscopy analysis showed that the intensity of organic sulfur in coal samples is weakened after microwave irradiation, the characteristic peaks of thiols and thioethers are reduced to a great extent, and an increase in the intensity of sulfoxide organic sulfur is observed. On the basis of the results of experimental analysis and quantum chemical simulation calculations, the mechanism of organosulfur structure removal under the action of microwave is revealed.

Assessment of microwave susceptors for optimum temperature rise using parametric numerical simulation

Microwave hybrid heating or indirect microwave heating has been an important development in the processing of metals using microwave energy. In this method of heating, a “susceptor” is used to absorb and convert microwave energy into thermal energy which is utilized for materials processing. Few of these processing applications are sintering, joining, cladding, casting, and composite development. However, the precise selection of a susceptor for a given process is challenging and requires a thorough understanding of the microwave heating phenomenon. In addition, predicting temperature rise in a microwave cavity is a complex task. Numerical simulation can serve to solve these two significant problems. In this work, parametric simulation of microwave heating of three major susceptor materials; silicon carbide, alumina, and coal has been carried out using a multiphysics approach. Initially, a model was developed to validate the simulation procedure. The results were in good agreement with the available data in published literature. Thereafter, the effect of microwave power, position of susceptor block, and time of irradiation on temperature rise in these materials were investigated. On comparing these susceptor blocks after altering the parametric combinations, coal exhibited the formation of hot spots and uneven temperature field with a maximum temperature of 901°C. On the contrary, the temperature attained in silicon carbide (529°C) and alumina (616°C) were lower but distributed in a relatively uniform field across the block. Regression models have also been built to correlate maximum temperature achieved with the parametric variation of parameters. It has been found that microwave power and the time of microwave irradiation have a significant coactive effect on the maximum temperature reached by the material. While the rise in the position of the susceptor block from the base leads to an adverse effect on the temperature rise. The study demonstrates that indirect microwave heating can be harnessed using the proper selection of susceptors as per the temperature requirement of the process. The regression models can be used for the accurate prediction of temperature attainment for given power input, position, and time.

Simple and Fast Microwave-Assisted Synthesis Methods of Nanocrystalline TiO2 and rGO Materials for Low-Cost Metal-Free DSSC Applications.

Nanocrystalline TiO2 and reduced graphene oxide (rGO) materials have been synthesized by a simple and low-cost microwave-assisted hydrothermal method and applied in dye-sensitized solar cells (DSSCs) as photoactive and metal-free counter electrodes, respectively. Different TiO2 nanocrystalline materials have been synthesized via the acid hydrolysis sol–gel method, followed by microwave hydrothermal treatment at 210 °C and 300 psi and at different microwave irradiation times (20, 30, 45, and 60 min) instead of the usual hydrothermal time of 12 h. The properties of the produced mesoporous nanocrystalline TiO2 are investigated in terms of their morphology, crystal structure, optical properties, and surface area behavior using relevant characterization techniques. Maximum specific surface area values (SBET) of 97.77 and 100.7 m2 g–1 are measured for TiO2, with the average crystallite sizes of 18.6 and 17.5 nm, at microwave irradiation times of 30 and 45 min, respectively. Different rGO samples have been prepared by the modified Hummers method, followed by microwave-assisted reduction at a temperature of 200 °C and pressure of 300 psi at different microwave irradiation times (3, 17, and 25 min). The physicochemical properties of the different rGO samples in terms of morphology, crystallization, and optical properties are characterized by TEM, XRD, and Raman spectroscopic analysis. The current density Jsc of the fabricated DSSCs based on TiO2 as the photoelectrode and rGO as the counter electrode compared with DSSCs based on Pt as the counter electrode is found to be 11.25 and 9.28 mA cm–2, respectively. Although the overall power efficiency of the fabricated DSSCs based on rGO as the counter electrode is lower than that based on the Pt electrode, the former still exhibits promising prospects for replacing Pt with low-cost metal-free carbon-based DSSCs.

Polydimethylsiloxane/graphene oxide/β‐cyclodextrin sponge as a solid‐phase extraction sorbent coupled with gas chromatography‐mass spectrometry for rapid adsorption and sensitive determination of lavender essential oil

An adsorbent polydimethylsiloxane/graphene oxide/β-cyclodextrin sponge, which possessed the merits of high surface area, chemical stability, environment friendly, and excellent extraction capacity, was successfully fabricated. Based on the advantages, a novel microwave-assisted headspace solid-phase extraction method for lavender essential oil using polydimethylsiloxane/graphene oxide/β-cyclodextrin sponge as adsorbents was developed in this study. Various experimental parameters were studied. The optimal extraction conditions were as follows: 1mg/mL as dopamine solution concentration, graphene oxide dosages of 30mg, microwave power of 700 W, microwave irradiation time of 10min, and desorption solvent of n-hexane. Under the optimal extraction condition, linearities ranging from 10 to 800ng were achieved for six representative compounds with a correlation coefficients value of>0.99. The intra-day and inter-day precisions were in the ranges of 0.40-1.56 and 0.67-2.56%, respectively. Finally, the proposed technique was applied to analyze essential oil constituents in 14 samples of three lavender varieties, and 48 compounds were identified. Lavender varieties were distinguished using principal component analysis and partial least squares discriminant analysis. The results showed that the method developed in this study is a novel, simple, and sensitive method for the determination of essential oil in complex plant samples.

Microwave-Assisted Synthesis and Characterization of Zeolite Prepared From South Africa Coal Fly Ash

In industry, synthetic zeolites are commonly used as ion-exchange materials, catalyst supports, and adsorbents. As a result, a more energy-efficient alternative for its synthesis from low-cost and accessible raw materials is needed. This study, presents the possibility of using class F South African coal fly ash (SACFA) from Lethaba thermal-power station as a precursor to produce zeolites via a microwave (MW) assisted synthesis route. The mineral content of synthetic materials was determined using X-ray florescence (XRF). Morphology was determined using a Scanning electron microscopy (SEM), elemental composition by energy dispersive spectrometer (EDS). X-ray diffractometry (XRD) was used to get structural characterization. Microwave (MW) irradiation time and intensity enhance the crystallization of the zeolite phase as a result of sufficient energy required to enable the solubility of alumina and silica from coal fly ash. The use of MW irradiation provides a green alternative to zeolite synthesis from fly ash (FA) than traditional thermal and fusion techniques, which uses a great deal of energy consumption and a longer reaction time.

Activation of Carbon Using Microwave-Assisted Hydrochloric Acid for Urea Adsorbtion

The activation of activated carbon using microwave-assisted hydrochloric acid (HCl) has been carried out. This objective of this study was to investigate the effects of the concentration of HCl (1M to 6 M) and time of microwave irradiation (5 to 25 mins) on the iodine number and urea adsorption. The results showed that the concentration of HCl had a significant effect on the quality of the activated carbon. Activation of carbon using 6 mol/L of HCl resulted the iodine adsorption capacity of 1002 mg/g and urea adsorption of 99 mg/g. Microwave irradition time also has a significant effect on the quality of activated carbon. The best microwave irradiation time showed at 25 minutes that resulted in iodine adsorption capacity of 1112 mg/g and urea adsorption capacity of 97 mg/g.

One-step preparation of N-doped grapheme quantum dots with high quantum yield for bioimaging and highly sensitive electrochemical detection of isoniazid.

Conventional techniques for synthesizing GQDs have a poor quantum yield (QY) that restricts their biological applications. Herein, we present a rapid, cost-effective and high quantum yield synthesis of nitrogen-doped graphene quantum dots (N-GQDs) through a scientific microwave reactor. The reaction parameters like microwave irradiation time, temperature, precursor concentration and pressure were optimized for achieving high quantum yield. The prepared N-GQDs exhibit bright blue fluorescence and excitation independent emission property with a quantum yield of 42.81%. In-vivo investigations on C. elegans revealed that the as-prepared N-GQDs are exceptionally biocompatible and maintain the normal physiological functioning of the primary and secondary targeted organs in nematodes. The synergetic effect of intestinal barrier and defecation behavior mitigates N-GQDs translocation into reproductive organs of nematode. In addition, the N-GQDs modified GCE was tested for electrochemical sensing characteristics towards the anti-tuberculosis drug isoniazid (INZ). The N-GQDs showed appreciable electrocatalytic performance towards INZ with high sensitivity (3.76μAμM-1cm-1). The differential pulse voltammetry (DPV) analysis of N-GQDs exhibit a lower detection limit of 10.91nM for INZ. The N-GQDs modified sensor exhibits good reproducibility, excellent anti-interference ability and excellent analytical performance for INZ in real samples like human blood serum and urine samples.

Synthesis of silver/K-Caragenan nanocomposites assisted with microwave iradiation as a potential antibacterial material

In this research, a silver/K-carrageenan nanocomposite was synthesized using a chemical reduction method assisted by microwave irradiation using NaOH as an accelerator. The aims of this research is to determine the optimum conditions for the preparation of silver nanoparticles with NaOH variations, microwave irradiation time and, AgNO3 concentration. AgNO3 compounds function as precursors and K-carrageenan as a reducing agent, stabilizer and also a matrix in silver-K-Carrageenan nanocomposites. The formation of silver nanoparticles was identified using a UV-Vis spectrophotometer which is associated with the LSPR phenomenon. Testing of antibacterial activity using the diffusion method against S.Aureus bacteria. The results showed that the silver nanoparticles formed on the silver/K-Carrageenan nanocomposite were characterized by the appearance of an absorption band in the 400 nm region. NaOH concentration, irradiation time and AgNO3 concentration affect the absorbance value at the maximum absorption, which indicates the effect on the amount of silver nanoparticles. The optimal condition for the synthesis of silver nanoparticles is the use of NaOH 0,014 M with an irradiation time of 6 minutes. The concentration of AgNO3 precursor is directly proportional to the amount of silver nanoparticles formed in the nanocomposite. Silver/K-Carrageenan nanocomposite has high antibacterial activity and potential as antibacterial material.

Preparation of Sludge Ash–Desulfurization Gypsum-Based Backfill Materials Using Microwave Calcination

Paper mill sludge ash (PMSA), sewage sludge ash (SSA), and desulfurization gypsum (DG) were mixed and calcined by microwave radiation to acquire a product with higher hydration activity. The resulting mixture was used as a supplementary cementitious material to prepare backfill materials for mining. The influence of the mixing ratio of raw materials, microwave parameters, and sample size on the properties and microstructure of the microwave-sintered sludge ash (MSSA) and MSSA-cement pastes was determined. Both the MSSA and the prepared pastes were characterized using X-ray diffraction (XRD), Fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). Results indicated that the minerals in the MSSA were rankinite, mayenite, and belite, which all exhibited relatively high hydration activity and significantly improved the degree of hydration of the MSSA–cement system. As the microwave power and irradiation time increased, the water demand of the MSSA–cement pastes decreased, the setting time decreased, and the compressive strength increased. The MSSA prepared with a small length-to-diameter ratio produced more crystals and gels compared with that prepared with a larger length-to-diameter ratio. The gels mutually fused to form a dense structure, and this further enhanced the strength of the MSSA–cement pastes.

Kinetics of microwave-assisted extraction of virgin coconut oil from solid coconut waste

Solid coconut waste (SCW) is a by-product of coconut milk production which still contains virgin coconut oil (VCO). This waste usually is thrown away or left in fields. This study aims to optimize the effects of Microwave power (80–400 W), irradiation time (1–4 minutes), and solvent to feed ratio (SF) (10–30 ml/g) on the extraction of VCO from SCW using microwave-assisted extraction. The optimized conditions were microwave power: 160 W, Irradiation time: 2.5 minutes, and SF: 30 ml/g (15.93% yield). After the extraction, the characteristics of the oil such as matters volatile at 105 °C (0.193%), Free Fatty Acid (FFA) (1.38%), peroxide value (undetectable), insoluble impurities (0.0015%), saponification value (258 mg/g), iodine value (7.60), specific gravity at 30 °C (0.918), and total plate count (0 CFU/ml) were determined. The second-order kinetic model described the extraction the best (R2 adj = 0.9994). This method proves to be more efficient than the conventional virgin coconut oil extraction method.

Microwave biochars produced with activated carbon catalyst: Characterization and sorption of volatile organic compounds (VOCs)

A series of microwave biochars derived from wheat straw in the presence of a granulated activated carbon (GAC) catalyst, using a range of microwave conditions, were produced, characterized and tested as sorbents of three benzene series volatile organic compounds (VOCs). The microwave biochar with the greatest specific surface area (SSA), total pore volume (TPV), and micropore volume (312.62 m2 g−1, 0.2218 cm3 g−1, and 0.1380 cm3 g−1, respectively), were produced with 1:3 biomass:GAC catalyst mass ratio, 10 min microwave irradiation time, and at 500 W power level (WB500). Maximum adsorption capacities of WB500 to benzene, toluene and o-xylene were 53.9 mg g−1, 75.8 mg g−1 and 63.0 mg g−1, respectively, and were directly correlated to microwave biochar properties such as SSA, TPV or micropore volume, but were also influenced by VOC properties such as molecular polarity and boiling point. Kinetic modeling suggested that adsorption was governed by both physical partitioning and chemisorption mechanisms. In addition, microwave biochars maintained 79% to 92% of their initial adsorption capacity after ten adsorption/desorption cycles. These results suggest that microwave biochars produced with an GAC catalyst have excellent potential for efficient use in the removal of VOCs from waste gas.

Strain-size features of bare ZnSe:Cu and ZnSe:Cu@ZnS core/shell quantum dots from extensive X-ray diffraction analysis, and their photoluminescence properties

ZnSe:Cu d-dots and ZnSe:Cu@ZnS core/shell quantum dots (QDs) were synthesized under different synthesis regimes of Cu-dopant content, microwave irradiation time (MWIRT) and over-coating of ZnSe:Cu by ZnS shell in order to optimize their structural and photoluminescence (PL) properties. The morphological and microstructural characterizations broadly done by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), revealed the spherical shape, synthesis-condition tunable and almost uniform size distribution of bare and core/shell QDs. Extended X-ray diffraction analysis (XDA) was performed by employing both Williamson-Hall (W–H) and Williamson-Smallman (W–S) approaches in order to validate these methods and obtain lattice strain (ε), dislocation density (δ) and particle size. The results indicated that all the QDs had cubic zinc-blend structure with an average crystallite size of ∼1.5 nm, and shift of peak positions shift toward higher angles for core/shells compared with bare QDs. W–S and W–H's outputs for bare and core/shell QDs showed similar trends, i.e. the optimal Cu-content of 0.1 mol% with higher crystalline quality. In addition, bare and core/shell QDs were investigated by Ultraviolet–Visible and PL spectroscopy. The blue-shift of band gap for the synthesized ZnSe QDs (∼3.5 eV) in comparison with bulk counterpart (∼2.7 eV) confirmed the formation of nano-sized particles. It was found that these QDs exhibited PL emission in the range of 423–559 nm. After changing the experimental variables during the experiment, the samples with optimal PL were identified. In reasonable relation to the microstructural aspects, ZnSe:Cu(1.5%) under MWIRT = 6 min has the highest band-edge PL intensity, which was associated with increased particle size, reduced lattice strain and higher atomic order raised from MWIR. Among the core/shell QDs, ZnSe:Cu(1.5%)@ZnS under MWIR indicated the highest band-edge emission intensity, which besides the microstructural parameters, may be a result of the morphological change from spherical to nanorod as certified by TEM. In addition, ZnSe@ZnS under MWIR showed the highest trap-defect emission intensity. In brief, due to the strong experimental condition-dependence of studied features, which is very important in tuning the properties, the studied bare and core/shells can be promising agents in green-blue luminescent photometric-biological applications.

Effect of Microwave Pretreatment on Some Properties of Bamboo (Gigantochloa apus) for Bioethanol Production

Pretreatment of lignocellulosic biomass plays an essential role in bioethanol production as an alternative biofuel. This process reduces biomass recalcitrance in order to improve cellulose digestibility for saccharification and further fermentation reactions. In this study, microwave (MW) pretreatment was done on bamboo (Gigantochloa apus) to investigate the resulting physicochemical properties and bioethanol produced. Bamboo was irradiated in the microwave at different power (100-600 Watt) and irradiation time (5-20 minutes) followed by Water Soluble content (WSC) and lignin analysis. Simultaneous saccharification and fermentation (SSF) using cellulase enzyme was also done in five different treatment combinations (C1-C5) to investigate the effect of produced reducing sugar and bioethanol. The result shows that increasing MW power and irradiation time could decrease WSC gradually. The lowest WSC of 0.3% was obtained at 600-Watt MW power and 20 minutes irradiation time. Lignin content decreased from 18.9% to 16.0% concerning increasing irradiation time from 5 to 20 minutes under 300-Watt MW power. SEM images show that partial disruption and micro-scale pores existed in pretreated samples. The highest amount of ethanol was obtained at 24 hours fermentation for pretreated bamboo at 300-Watt MW power for 15 minutes followed by cellulase enzyme addition. The overall results showed that microwave pretreatment is a prospective method for future bioethanol production from bamboo due to effective WSC reduction and lignin degradation in a relatively short period of time.

OPTIMIZATION OF CONTINUOUS MICROWAVE INACTIVATOR FOR POLYPHENOL OXIDASE INACTIVATION ON GREEN TEA PROCESSING USING RESPONSE SURFACE METHODOLOGY

Microwave treatment is a promising technology for food processing such as drying, extraction, and enzyme inactivation because of its ionic heat transfer. This study develops and optimizes the fixation process in green tea using a microwave-based enzyme inactivator. A continuous microwave enzyme inactivator with a dimension of 3300 (L) × 550 (W) × 600 mm3 (H) was built to study the effect of temperature, microwave radiation time, and the number of microwaves on the catechin content of green tea. The optimum condition for the inactivation process was determined using response surface methodology and central composite design. The result shows that the model can predict the effect of temperature, microwave radiation time, and the number of microwaves on catechin content. Temperature, fixation time (conveyor velocity), and the number of microwaves, have a significant impact on enzyme inactivation when using a continuous microwave. The optimum microwave inactivation condition for polyphenol oxidase enzyme was four at 70C temperature and 30 rpm conveyor speed.