Dorin Boldor

Oil extraction from Scenedesmus obliquus using a continuous microwave system--design, optimization, and quality characterization.

A 1.2 kW, 2450 MHz resonant continuous microwave processing system was designed and optimized for oil extraction from green algae (Scenedesmus obliquus). Algae-water suspension (1:1 w/w) was heated to 80 and 95°C, and subjected to extraction for up to 30 min. Maximum oil yield was achieved at 95°C and 30 min. The microwave system extracted 76-77% of total recoverable oil at 20-30 min and 95°C, compared to only 43-47% for water bath control. Extraction time and temperature had significant influence (p<0.0001) on extraction yield. Oil analysis indicated that microwaves extracted oil containing higher percentages of unsaturated and essential fatty acids (indicating higher quality). This study validates for the first time the efficiency of a continuous microwave system for extraction of lipids from algae. Higher oil yields, faster extraction rates and superior oil quality demonstrate this systems feasibility for oil extraction from a variety of feedstock.

Ethanol production from sorghum by a microwave-assisted dilute ammonia pretreatment.

The efficiency of a batch microwave-assisted ammonia heating system was investigated as pretreatment for sweet sorghum bagasse and its effect on porosity, chemical composition, particle size, enzymatic hydrolysis and fermentation into ethanol evaluated. Sorghum bagasse, fractionated into three particle size groups (9.5-18, 4-6 and 1-2mm), was pretreated with ammonium hydroxide (28% v/v solution) and water at a ratio of 1:0.5:8 at 100, 115, 130, 145 and 160°C for 1h. Simons stain method revealed an increase in the porosity of the biomass compared to untreated biomass. The most lignin removal (46%) was observed at 160°C. About 90% of the cellulose and 73% of the hemicellulose remained within the bagasse. The best glucose yields and ethanol yields (from glucose only) among all different pretreatment conditions averaged 42/100g dry biomass and 21/100g dry biomass, respectively with 1-2mm sorghum bagasse pretreated at 130°C for 1h.

Microwave assisted extraction of biodiesel feedstock from the seeds of invasive Chinese tallow tree.

Chinese tallow tree (TT) seeds are a rich source of lipids and have the potential to be a biodiesel feedstock, but currently, its invasive nature does not favor large scale cultivation. Being a nonfood material, they have many advantages over conventional crops that are used for biodiesel production. The purpose of this study was to determine optimal oil extraction parameters in a batch-type and laboratory scale continuous-flow microwave system to obtain maximum oil recovery from whole TT seeds using ethanol as the extracting solvent. For the batch system, extractions were carried out for different time-temperature combinations ranging from 60 to 120 degrees C for up to 20 min. The batch system was modified for continuous extractions, which were carried out at 50, 60, and 73 degrees C and maintained for various residence times of up to 20 min. Control runs were performed under similar extraction conditions and the results compared well, especially when accounting for extremely short extraction times (minutes vs hours). Maximum yields of 35.32% and 32.51% (by weight of dry mass) were obtained for the continuous and batch process, respectively. The major advantage of microwave assisted solvent extraction is the reduced time of extraction required to obtain total recoverable lipids, with corresponding reduction in energy consumption costs per unit of lipid extracted. This study indicates that microwave extraction using ethanol as a solvent can be used as a viable alternative to conventional lipid extraction techniques for TT seeds.

Continuous microwave-assisted isoflavone extraction system: Design and performance evaluation

The purpose of this research was to design, test, and optimize a continuous microwave extraction method using temperature and residence time during and after microwave exposure as optimizing parameters for extraction of major isoflavones (genistin, genistein, daidzin, and daidzein) from soy flour. The extraction yield of four isoflavones at different heating temperatures (55 and 73 degrees C) and extraction times (0, 4, 8, 12, and 16 min) were investigated and compared with yields provided by a conventional solvent extraction method. The microwave prototype consisted of multiple, commercially available, batch-type, house-hold microwave units placed on top of each other in series to impart a continuous operation. The optimum parameters for microwave-assisted extraction of isoflavones were 73 degrees C for 8 min using a 3:1 ethanol-to soy flour ratio. At these parameters, the total yield of isoflavones extracted doubled, while the amount of oil extracted was 12%. Continuous microwave-assisted solvent extraction is a viable method for extraction of soybean isoflavones at relatively short residence times and high throughput.

A critical comparison of methyl and ethyl esters production from soybean and rice bran oil in the presence of microwaves.

Transesterification of vegetable oils (from soybeans and rice bran) into methyl and ethyl esters using a batch microwave system was investigated in this study. A critical comparison between the two alcohols was performed in terms of yields, quality, and reaction kinetics. Parameters tested were temperature (60, 70 and 80°C) and time (5, 10, 15 and 20 min). At all tested conditions, more than 96% conversion rates were obtained for both ethanol and methanol. Use of microwave technology to assist the transesterification process resulted in faster reaction times and reduced catalyst requirement (about ten-fold decrease). Methanol required lower alcohol:oil ratios than normally used in conventional heating, whereas ethanol required higher molar ratios. All esters produced using this method met ASTM biodiesel quality specifications. Methanol performed better in terms of performance and costs, while ethanol may have some environmental and safety benefits.

Nanophotothermolysis of multiple scattered cancer cells with carbon nanotubes guided by time-resolved infrared thermal imaging

Nanophotothermolysis with long laser pulses for treatment of scattered cancer cells and their clusters is introduced with the main focus on real-time monitoring of temperature dynamics inside and around individual cancer cells labeled with carbon nanotubes. This technique utilizes advanced time- and spatially-resolved thermal radiometry imaging for the visualization of laser-induced temperature distribution in multiple-point absorbing targets. The capability of this approach was demonstrated for monitoring of thermal effects under long laser exposure (from millisecond to seconds, wavelength 1,064 nm, maximum power 1 W) of cervical cancer HeLa cells labeled with carbon nanotubes in vitro. The applications are discussed with a focus on the nanophotothermolysis of small tumors, tumor margins, or micrometastases under the guidance of near-IR and microwave radiometry.

An analysis of the microwave dielectric properties of solvent-oil feedstock mixtures at 300-3000 MHz.

Microwaves can be a more efficient method than traditional thermal treatment to deliver the energy required for heating in solvent-oil extraction due to its volumetric, direct coupling with the material. An understanding of the behavior of dielectric properties of solvent-feedstock mixtures is important for designing and optimizing any microwave-based extraction process. In this study rice bran and soybean flour were mixed separately with four different solvents (methanol, ethanol, hexane and isopropanol) at different ratios (1:2, 1:1, 2:1 w/w). For the samples mixed with ethanol, the dielectric properties were measured at 23, 30, 40 and 50 degrees C, while for all other sample-solvent mixtures experiments were performed at room temperature. Dielectric properties were determined using a vector network analyzer and dielectric probe kit using the open-ended coaxial probe method in the frequency range of 300 MHz to 3 GHz. Results from the study indicate that dielectric constants were dependent on frequency and were strongly influenced by temperature, mix ratio and solvent type. The dielectric loss of all mixtures except those with hexane (which were virtually zero) varied with frequency and temperature, solvent type, and mix ratio. Most of the results presented are emphasized at 433, 915 and 2450 MHz, frequencies allocated by the Federal Communication Commission (F.C.C.) for microwave applications. The results of the study, presented here for the first time to our knowledge, will help in selection of appropriate solvent, mixing ratio and frequency for designing microwave-assisted oil extraction systems.

Numerical Modeling of Continuous Flow Microwave Heating: A Critical Comparison of COMSOL and ANSYS

Abstract Numerical models were developed to simulate temperature profiles in Newtonian fluids during continuous flow microwave heating by one way coupling electromagnetism, fluid flow, and heat transport in ANSYS 8.0 and COMSOL Multiphysics v3.4. Comparison of the results from the COMSOL model with the results from a pre-developed and validated ANSYS model ensured accuracy of the COMSOL model. Prediction of power loss by both models was in close agreement (5–13% variation) and the predicted temperature profiles were similar. COMSOL provided a flexible model setup whereas ANSYS required coupling incompatible elements to transfer load between electromagnetic, fluid flow, and heat transport modules. Overall, both software packages provided the ability to solve multiphysics phenomena accurately.

High Frequency Electromagnetism, Heat Transfer and Fluid Flow Coupling in ANSYS Multiphysics

The goal of this study was to numerically predict the temperature of a liquid product heated in a continuous-flow focused microwave system by coupling high frequency electromagnetism, heat transfer, and fluid flow in ANSYS Multiphysics. The developed model was used to determine the temperature change in water processed in a 915 MHz microwave unit, under steady-state conditions. The influence of the flow rates on the temperature distribution in the liquid was assessed. Results showed that the average temperature of water increased from 25°C to 34°C at 2 l/min, and to 42°C at 1 l/min. The highest temperature regions were found in the liquid near the center of the tube, followed by progressively lower temperature regions as the radial distance from the center increased, and finally followed by a slightly higher temperature region near the tube’s wall corresponding to the energy distribution given by the Mathieu function. The energy distribution resulted in a similar temperature pattern, with the highest temperatures close to the center of the tube and lower at the walls. The presented ANSYS Multiphysics model can be easily improved to account for complex boundary conditions, phase change, temperature dependent properties, and non-Newtonian flows, which makes for an objective of future studies.

In-situ transesterification of seeds of invasive Chinese tallow trees (Triadica sebifera L.) in a microwave batch system (GREEN3) using hexane as co-solvent: biodiesel production and process optimization.

In-situ transesterification (simultaneous extraction and transesterification) of Chinese tallow tree seeds into methyl esters using a batch microwave system was investigated in this study. A high degree of oil extraction and efficient conversion of oil to biodiesel were found in the proposed range. The process was further optimized in terms of product yields and conversion rates using Doehlert optimization methodology. Based on the experimental results and statistical analysis, the optimal production yield conditions for this process were determined as: catalyst concentration of 1.74wt.%, solvent ratio about 3 (v/w), reaction time of 20min and temperature of 58.1°C. H(+)NMR was used to calculate reaction conversion. All methyl esters produced using this method met ASTM biodiesel quality specifications.