Bhupesh C. Roy

Shrinking-core leaching model for supercritical-fluid extraction

Abstract Extraction or leaching of a solute from a solid material is a process involving mass transfer in the solid matrix. When the solute content in the solid material is sufficiently large as compared to the solubility in fluid phase, the process is similar to that of irreversible desorption. The shrinking-core model was applied to the modeling of the extraction process. The model including axial dispersion in the extraction column was solved numerically. Quasi-steady-state solution without axial dispersion was derived, and the accuracy was discussed in comparison with the numerical solutions. The model calculations gave a good agreement with the experimental extraction curve reported in literature.

Supercritical CO2 extraction of essential oils and cuticular waxes from peppermint leaves

Essential oils and cuticular waxes were extracted from peppermint leaves with supercritical carbon dioxide in a semicontinuous-flow extractor. The effects of CO 2 flow rate and pressure on the extraction rate were studied within the flow rate range of (4.1-9.8)X10 -5 kg/s and the pressure range of 10-30 MPa. Flow rate effect indicated that the intraparticle diffusion resistance was not dominant in this process. The extraction rate of cuticular waxes increased remarkably with the pressure, whereas that of essential oils was almost constant as compared with cuticular waxes. The concentration of cuticular waxes at the exit of the extractor was close to the solubility of triacontane while that of essential oils was much lower than the solubility of 1-menthol.

Negative DC Prebreakdown Phenomena and Breakdown-Voltage Characteristics of Pressurized Carbon Dioxide up to Supercritical Conditions

This paper deals with the experimental results on prebreakdown phenomena and breakdown voltage characteristics of a negative dc point-to-plane gap in-compressed carbon dioxide up to the supercritical pressure as the first step to develop a plasma reactor with supercritical carbon dioxide. The gap length and the curvature radius of the point tip were 200 and around 35 mum, respectively. The experimental results show the following: 1) corona discharge preceding complete breakdown is observed more clearly in liquid and supercritical fluid than in gas; 2) the estimated discharge onset voltage according to the streamer theory is in fairly good agreement with the measured breakdown voltage in the gas density region of 0.1-30 kg ldr m-3; 3) the breakdown mechanism in liquid can be classified into two categories: bubble-triggered breakdown at lower pressure and non bubble-triggered breakdown at higher pressure; 4) the breakdown mechanism in supercritical fluid is similar to that in higher pressured liquid; and 5) the density and temperature dependences of breakdown voltage in liquid and supercritical fluid are related closely with the breakdown mechanism.

Supercritical Carbon Dioxide Extraction of the Volatiles from the Peel of Japanese Citrus Fruits

Abstract Citrus volatiles were extracted from the peel of yuzu and kabosu (Citrus junos Sieb. ex Tanaka and Citrus sphaerocarpa Hort. ex Tanaka) which are typical citrus fruits in Japan, with supercritical carbon dioxide in a semi-continuous flow extractor. The peel of citrus fruits containing oil, water, and solid cellulose materials was used as a feed material in this work. Extraction was carried out at 313–333 K and 10–30 MPa with supercritical CO2 in order to optimize the extraction conditions and to compare the compositions of extracted oils from these fruits. The volatiles were also extracted using hexane (as the solvent) at atmospheric conditions to compare the efficiency of supercritical CO2 extraction. Among the studied conditions, the highest extraction efficiency was observed for both yuzu and kabosu peel at a pressure of 10 MPa and temperature of 333 K that was about 91% and 85%, respectively. The compositions of extracts differed qualitatively and quantitatively from each other in such a way that the monoterpene (C10H16) content obtained was 89.9% in yuzu and 92.5% in kabosu; limonene was the major compound from both fruits. Oxygenated compounds in these oils represented 7.7%, and 4.6% in yuzu and kabosu peel, respectively.

Reaction in Plasma Generated in Supercritical Carbon Dioxide

The generation of non-thermal plasmas was studied under supercritical conditions. This is interesting in view of both the basic phenomena involved and of potential industrial applications. When supercritical fluids are combined with discharge plasma they develop unique characteristics, including an enhanced chemical reactivity. This is the motivation for investigating the generation of discharge plasma in supercritical CO2. In this study, breakdown voltages were measured in CO2 in order to generate electric discharges in supercritical CO2. The experimental data show that the breakdown voltage increased smoothly up to the intersection points, but beyond these points the rates of increase of the breakdown voltage are different. This phenomenon can be explained with the help of pressure-density curves of carbon dioxide at a constant temperature. In addition, the generated plasma in supercritical CO2 was applied to several chemical reactions. The alpha conversion of tocopherols and transesterification of soybean oil with methanol were investigated. In addition, we explored the possibility of replacing catalysts with plasma in supercritical CO2.

Pulsed and DC discharges in supercritical carbon dioxide

This paper reports the experimental results on the breakdown voltage and phenomena in carbon dioxide medium at 298, 304 and 373 K and within the pressure range of 0.1 to 12.0/20.0 MPa under the point-to-plane electrode using negative dc and pulsed discharge. From the experimental results of negative dc discharge, corona discharges with preceding as well as complete breakdown are observed more clearly in liquid and in supercritical phase than in gas phase of carbon dioxide. The calculated electric field intensity on the tip of point electrode at the corona onset voltage is about 450 MV/m; it suggests that corona is triggered by the field emission of electron. The breakdown mechanism of liquid phase can be classified into two categories in comparison with critical pressure of medium. On the other hand, in the experimental result of pulse electric discharge, the time delay of pulse forming and the relevance of the medium density were found.

DC Breakdown Voltage of Carbon Dioxide Medium Under Needle to Plane Electrode

This paper reports the experimental results on the corona onset voltage and breakdown voltage by positive and negative dc discharges in carbon dioxide medium within the pressure range of 0.1 to 15MPa under the needle to plane electrode. From the experimental results of dc discharge, negative corona discharges are observed more clearly in liquid and supercritical phase than in gas phase of carbon dioxide. However, in our experimental condition, positive corona discharge was not found for dc discharges. The breakdown mechanism in liquid can be classified into two categories on account of the bubble-triggered formation.

Pulsed Discharges in Supercritical Carbon Dioxide

Summary form only given. The chemical reaction schemes in supercritical fluids have been accomplished in various ways for its industrial applications. On the other hand, it is well known that electric discharge plasmas have higher chemical reactivity as well as benign properties. In recent years, several studies on discharge plasmas in supercritical carbon dioxide have been carried out. It is very interesting work from both viewpoints of the basic phenomena and the industrial applications because supercritical fluids have unique characteristics that combine with discharge plasmas having higher chemical reactivity. The technology of plasma production in supercritical fluid would play an important role for the enhancement of chemical reactions those are benign to environment, therefore the study on the phenomena of electric discharge in supercritical fluids using pulsed power is paramount work. Generation of pulsed discharge plasma has been carried out at 0.1-15 MPa using spherical electrodes with semi-uniform electric field. The experimental results revealed that the breakdown voltages depend not only on temperature but also on density of carbon dioxide. Further results on chemical reactions in supercritical carbon dioxide (40 C, 15 MPa) using pulse discharges have been reported also.

Pulsed Discharge Plasmas in Supercritical Carbon Dioxide

In recent years, several studies about electrical discharge plasma in supercritical carbon dioxide (CO2) have been carried out. One of the unique characteristics of supercritical fluid is a large density fluctuation near the critical point that can result in marked dramatic changes of thermal conductivity. Therefore, the electrical discharge plasma produced in supercritical fluid has unique features and reactions unlike those of normal plasma produced in gas phase. In our experiments, two types of large volume plasma, namely the pulsed streamer discharge and the pulsed arc discharge have been generated in a supercritical CO2. It was found that the characteristic of the pulsed discharge plasma in supercritical CO2 depends on the change of the CO2 density near the critical region.