Effect of Microwave-Assisted Aqueous Two-Phase Extraction of α-Solanine from S. retroflexum and Analysis on UHPLC-qTOF-MS

A new, fast and efficient method, hyphenated microwave-assisted aqueous two-phase extraction (MA-ATPE) was applied in the extraction of α-solanine from Solanum retroflexum. This environmentally friendly extraction method applied water and ethanol as extraction solvents. Central composite design (CCD) was performed which included numerical parameters such as time, mass of plant powder and microwave power. The categorical factors included the chaotrope — NaCl or the kosmotrope — Na2CO3. Fitting the central composite design response surface model to the data generated a quadratic model with a good fit (R2 = 0.920). The statistically significant (p < 0.05) parameters such as time and mass of plant powder were influential in the extraction of α-solanine. Quantification of α-solanine was achieved using a robust and sensitive feature of the ultra-high performance quadrupole time of flight mass spectrometer (UHPLC-qTOF-MS), multiple reaction monitoring (MRM). The optimized condition for the extraction of α-solanine in the presence of NaCl and Na2CO3 was a period of 1 min at a mass of 1.2 g using a microwave power of 40%. Maximal extraction of α-solanine was 93.50 mg kg−1 and 72.16 mg kg−1 for Na2CO3 and NaCl, respectively. The synergistic effect of salting-out and microwave extraction was influential in extraction of α-solanine. Furthermore, the higher negative charge density of the kosmotrope (Na2CO3) was responsible for its greater extraction of α-solanine than chaotrope (NaCl). The shorter optimal extraction times of MA-ATPE make it a potential technique that could meet market demand as it is a quick, green and efficient method for removal of toxic metabolites in nutraceuticals.

Experimental Study on Fe3O4 Nanoparticle-Assisted Microwave Enhancing Heavy Oil

Nanoparticle-assisted microwave heating of heavy oil has the advantages of fast temperature rise and high thermal efficiency. Compared with traditional heating methods, it can reduce viscosity in a shorter time. In addition, the heavy components in the heavy oil are cracked into light components at high temperatures (this high temperature cannot be reached by conventional heating methods). This process is irreversible and avoids the problem of viscosity recovery of heavy oil after the temperature is reduced. Through absorbing microwave heating experiments, study the effect of nanoparticles on the improvement of the ability of heavy oil to absorb waves and raise temperature; through the heavy oil upgrading experiment and the four-component analysis experiment, the effect of adding hydrogen donor to assist microwave on the viscosity reduction of heavy oil upgrading by nanoparticles was studied, and the problem of viscosity recovery was determined; Through the gravity drainage experiment, the mechanism of nanoparticle-assisted microwave to improve the recovery of heavy oil is studied, and the influence of water content, nanocatalyst, and microwave power on the production of drainage is analyzed. The results show that nanoparticles can improve the wave absorption and heating capacity of heavy oil, and adding 0.6 wt% of nanomagnetic iron oxide catalyst can increase the heating rate of heavy oil in microwave by 60.6%; nanoparticle-assisted microwave heating method can effectively upgrade heavy oil and reduce viscosity. The experimental conditions are 2 wt% tetralin mass concentration, 0.5 wt% nano-Fe3O4 particle mass concentration, microwave heating time 50-60 min, and microwave power 539 W. Under this experimental condition, the viscosity is reduced by 40%. This method has viscosity recovery problems, but final viscosity reduction effect is still very significant. Obtaining the mechanism of nanoparticle-assisted microwave to enhance oil recovery, one of which is that nanoparticles improve the wave absorption and heating capacity of heavy oil and increase the heating speed of heavy oil; the second is that the nanoparticles form local high temperature under the action of microwave, which catalyzes the hydrocracking reaction between the heavy components in the heavy oil and the hydrogen donor, upgrading and reducing the viscosity of the heavy oil, and accelerating the production of heavy oil.

Plasma-based microwave power limitation in a printed transmission line: a self-consistent model compared with experimental data

Plasma-based microwave power limitation in a suspended microstrip transmission line integrating a micro hollow cathode discharge (MHCD) in its center is experimentally and numerically studied. Transient and steady state microwave power measurements exhibit a limitation threshold of 28 dBm and time responses of 25 microseconds. Intensified charge-coupled device (ICCD) imaging shows that microwave breakdown occurs at the top of the MHCD. The plasma then extends towards the microwave source within the suspended microstrip transmission line. Besides, a self-consistent model is proposed to simulate the non-linear interaction between microwave and plasma. It gives numerical results in great agreement with the measurements, and show that the plasma expansion during the transient response is related to a shift between the ionization source term and the electron density maximum. The propagation speed, under the tested conditions, depends mainly on the stepwise ionization from the excited states.

Design and Analysis of a 35 GHz Rectenna System for Wireless Power Transfer to an Unmanned Air Vehicle

In this article, the concept of a 22-kW microwave-powered unmanned aerial vehicle is presented, where the critical system architecture is analyzed and modeled for wirelessly transferring microwave power to the flying UAVs. The microwave system transmitting power at a 35 GHz frequency was found to be suitable for low-cost and compact architectures. The size of the transmitting and receiving systems are optimized to 108 m2 and 90 m2, respectively. A linearly polarized 4 × 2 rectangular microstrip patch antenna array has been designed and simulated to obtain a high gain, high directivity, and high efficiency in order to satisfy the power transfer requirement. The numerically simulated gain, directivity, and efficiency of the proposed patch antenna array are 13.4 dBi, 14 dBi, and 85%, respectively. Finally, a rectifying system (rectenna) is optimized using the Agilent advanced design system (ADS) software as a microwave power receiving system. The proposed rectenna has an efficiency profile of more than 80% for an RF input power range of 9 to 18 dBm. Moreover, the RF-to-DC conversion efficiency and DC output voltage of the proposed rectenna is 80% and 3.5 V, respectively, for a 10 dBm input power at 35 GHz with a load of 1500 Ω.

DRYING OF ZUCCHINI AND CARROT SLICES: INFLUENCE OF TISSUE STRUCTURE ON MASS TRANSFER PARAMETERS

The present work aimed mainly at investigating the influence of tissue structure on dehydration characteristics of zucchini and carrot. Microwave power levels of 100, 350, 550 and 750 W used to dehydrate the samples with thicknesses of 3, 5, 7 and 9 mm. The results showed that moisture removal from the slices occurred in a short accelerating period at the process beginning followed by a falling rate period. The moisture diffusivity increased with both increasing microwave power and the samples thickness where the average values for zucchini and carrot slices changed from 1.17×10-8 to 9.42×10-8 and from 0.73×10-8 to 5.51×10-8 m2 s-1, respectively. The average activation energy for zucchini and carrot slices varied in the range of 1.22–1.68 and 1.57–1.84 W g-1, respectively and decreased with increasing samples thickness.

Comparison of Microwave-Assisted Extraction to Soxhlet Extraction of Mango Seed Kernel Oil using Ethanol and n-Hexane as Solvents

Mango seed kernel oil was extracted by Soxhlet Extraction (SE) and Microwave-Assisted Extraction (MAE) with ethanol and n-hexane as extraction solvents. To optimize the extraction condition for SE, the temperature was set to 90°C for ethanol and 80°C for n-hexane with varying solvent-to-feed ratios (S/F ratio) of 75/12, 75/10, and 60/6 mL/g. As for MAE, the same S/F ratios were considered. Extraction was done for 5, 10, and 15 minutes with microwave power levels of 120 and 240 W. It was found out that the highest yield per extraction process for SE was: 18.00±0.25 % and 9.38±2.03 % using ethanol and n-hexane, respectively; and 6.69±0.05 % and 4.68±0.06 %using ethanol and n-hexane, respectively for MAE. It was also noted that MAE, with the microwave power level of 120 W has less extraction time for about 15 minutes as compared to SE of 8 hours. Also, the best S/F ratio in this study is 60/6 for all processes. In oil quality determination, the oil extracted was examined through several tests such as FTIR, GC-MS, acid value, % FFA, iodine value, saponification value, and melting point. It was noted that oil extracted in ethanol has a better yield compared to that of n-hexane but the oil extracted using n-hexane would provide superior quality.

Optimization of microwave-assisted extraction of carotenoids from Citrus clementina peels

Background: Citrus fruits, especially clementines, are among the most consumed fruits in the world. Clementine consists of pulp (endocarp) and peel (epicarp) which are rich in carotenoids. After using fruit pulp, peels are usually discarded as waste; the valorization of the latter in the recovery of its beneficial components, mainly carotenoids, may seem to be important. Objective: The main objective of this study is to determine the optimal conditions allowing the extraction of a high carotenoids yield from clementine peels. Methods: The microwave-assisted extraction method (MAE) was applied for extraction of total carotenoids from Citrus clementina peels, and the response surface methodology (RSM) was used to investigate the influence of extraction parameters, including hexane concentration, microwave power, irradiation time, and solvent to solid ratio, on the extraction yield, then the results were modeled using a second order regression. Total carotenoids yield of clementine peel extract obtained under optimal microwave-assisted extraction conditions was compared to extracts performed using two conventional extraction methods (maceration and Soxhlet). Results: The optimal conditions for microwave-assisted extraction were 68% of hexane concentration using 561 W of microwave power during 7.64 min of irradiation time, 43 ml/g of solvent-to-solid ratio using two successive extractions. Under optimized conditions of microwave-assisted extraction, the recovery of carotenoid content was 186.55 µg/g dry matter (DM), which was higher than that obtained by the two conventional methods, maceration extraction (ME; 160.53 µg/g DM) and Soxhlet extraction (SE; 162.68 µg/g DM). Conclusion: From this study, it can be concluded that microwave-assisted extraction is an efficient method for carotenoid recovery and considering its high yield in reduced time, it could be recommended for extraction of these bioactive compounds from clementine peels.

Operation Features of a Coaxial Virtual Cathode Oscillator Emitting Electrons in the Outer Radial Direction

The operation features of the coaxial virtual cathode oscillator emitting electrons in the outer radial direction were investigated through simulations and experiments. A coaxial vircator was compared with an axial vircator when the anode to cathode distance of both vircators was 6 mm. The proposed coaxial vircator was operated when the anode to cathode distance was 5 mm, 6 mm, and 7 mm. The peak power and frequency of the microwave generated from the proposed coaxial vircator when the anode to cathode distance was 6 mm were 20.18 MW and 6.17 GHz, respectively. The simulations and experiments show that the proposed coaxial vircator generates 80% more microwave power than the axial vircator with the same anode to cathode distance. According to the simulations and experiments, the proposed coaxial vircator tends to generate a higher power average when the anode to cathode distance was larger than 5 mm. The frequency of the proposed coaxial vircator when the anode to cathode distance was 5 mm and 7 mm was approximately 8 GHz and 5 GHz, respectively. The geometric factor of the proposed coaxial vircator was considered to be the reason for the greater microwave power generation than the axial vircator. The frequency of the proposed coaxial vircator decreases inversely proportional with the anode to cathode distance as observed in the axial and basic coaxial vircators.