Tsutomu Hirose

The use of psychrometric charts for the optimisation of a thermal swing desiccant wheel

Abstract An effective prediction is proposed to estimate the optimal rotation speed and performance of a rotary adsorber, in which simultaneous enthalpy and humidity changes are dealt with separately by visualising changes of state of product or exhaust air on a psychrometric chart. Assuming that the adsorbent rotor is completely regenerated to equilibrium with the regeneration air during the corresponding period, the optimal rotation speed corresponds to the region of the short time adsorption in which penetration theory holds and enthalpy exchange between both streams through the adsorbent rotor follows the behaviour of a rotary sensible heat exchanger at lower revolution rates. The change of the product/exhaust air condition with increasing rotational speed is presented as a set of simple equations. Also, by considering the relative humidity of product air and that of regeneration air to be almost the same at a sufficiently high flow rates of regeneration air, an optimal rotation speed and the product air condition are easily found by simple calculation. In comparison with experiments, the proposed method gives a rotational speed near the “optimum” and the humidity and temperature of the product air are predicted almost exactly.

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.

Depolymerization of polyethylene terephthalate in supercritical methanol

The degradation of polyethylene terephthalate (PET) in supercritical methanol was investigated with the aim of developing a process for chemical recycling of waste plastics. A batch reactor was used at temperatures of 573–623 K under an estimated pressure of 20 MPa for a reaction time of 2–120 min. PET was decomposed to its monomers, dimethyl terephthalate and ethylene glycol, by methanolysis in supercritical methanol. The reaction products were analysed using size-exclusion chromatography, gas chromatography–mass spectrometry, and reversed-phase liquid chromatography. The molecular weight distribution of the products was obtained as a function of reaction time. The yields of monomer components of the decomposition products including by-products were measured. Continuous kinetics analysis was performed on the experimental data.

Frontal analysis of protein adsorption on a membrane adsorber

The adsorption behaviour of two kinds of proteins, myoglobin and ovalbumin, with a membrane adsorber, DEAE MemSep 1000 (Millipore), was studied in comparison with a bead-based packed-bed adsorber, DEAE Sephacel (Pharmacia-LKB), by means of frontal analysis. Adsorption isotherms were obtained by integrating the breakthrough curves for various feed concentrations. Adsorption isotherms were expressed by the Langmuir equation and the adsorption capacity for the membrane adsorber was smaller than that for the packed-bed adsorber. The breakthrough curves of myoglobin for the membrane adsorber were independent of the flow-rate, but those of ovalbumin were affected by the flow-rate. Abnormal behaviour was observed for the adsorption of ovalbumin on a membrane adsorber. With the packed-bed adsorber, the breakthrough curves for both proteins were significantly affected by the flow-rate. A mathematical model for the membrane adsorber involving axial dispersion and adsorption kinetics was derived. The model simulated the breakthrough curves for myoglobin well. Axial dispersion was dominant for the membrane adsorber whereas intraparticle diffusion was dominant for the packed-bed adsorber.

Supercritical fluid extraction of hazardous metals from CCA wood

Contamination of the environment by waste CCA (Cu, Cr, As) wood, containing the toxic heavy metals, copper, chromium, and arsenic that are hazardous to human health, can be significantly reduced by supercritical fluid extraction (SFE) technology. An environmentally benign solution for the detoxification of these CCA woods is the use of SFE technology for the treatment because no extra pollutant is added. In this work, we studied SFE of Cu, Cr, and As from CCA wood by using supercritical CO2 modified with chelating agents. Effects of pressure and temperature on the extraction efficiency for the heavy metals were studied with organophosphorous chelating agent, Cyanex 302. Some other chelating agents were also compared. Cyanex 302 was the best ligand in our experiments at pressure of 24 MPa and temperature of 333 K. The extraction efficiencies for Cu, Cr, and As were up to 63.5, 28.6, and 31.3%, respectively.

Extraction of Nigella sativa L. using Supercritical CO2: A Study of Antioxidant Activity of the Extract

Abstract Oil from Nigella sativa seed has been extracted by supercritical CO2 as a solvent at various pressures. In this study, two conditions of separation were used; they were low and high pressure separation. The antioxidant activity of the oil extracted was measured using an ultraviolet-visible spectrum (UV‐Vis) spectrophotometer. There was no effect on the change of extraction pressure in apparatus with low pressure. The essential oil content in the extract from apparatus with high pressure was approximately two times higher than it was with low pressure. The antioxidant activity of Nigella sativa oil showed positive result. The antioxidant activity was obtained by the quantity of thymoquinone and carvacrol.

Response surfaces of total oil yield of turmeric (Curcuma longa) in supercritical carbon dioxide

Abstract The process variables pressure, temperature and flow rate were studied for optimisation of total oil yield by response surface methodology following a Box–Behnken design of experiments. The results indicated: (a) a rise in the temperature of extraction leads to decrease in oil yield. (b) The optimum pressure for the extraction of oil was found to be 22.5 MPa. (c) general increase in oil yield with an increase in flow rate. The experimental oil yield is in good agreement with the predicted one. The response surface methodology used in this study was able to predict the optimal extraction conditions for the total yield of turmeric oil.

Numerical analysis of a dual refluxed PSA process during simultaneous removal and concentration of carbon dioxide dilute gas from air

The simultaneous removal and concentration of carbon dioxide present in ambient air were carried out by a dual refluxed Pressure Swing Adsorption (PSA) process with intermediate feed inlet position. The feed inlet position divides each column into rectifying and stripping sections from which enriched and lean gases can be simultaneously produced. A simple isothermal model with negligible axial dispersion and pressure drops through the PSA beds was developed to investigate the effects of various combinations of the operating variables and to analyze semi-quantitatively the effects of the main characteristic parameters such as the dimensionless feed inlet position (Z R /L T ) and the stripping-reflux ratio (R T ). A good agreement between the model prediction and the experimental results was obtained. Moreover, an optimum feed inlet position was found and it corresponded to a position where the carbon dioxide mole ratio in the feed flux and that in the upstream flux leaving the stripping section were equal. The carbon dioxide mole ratio in the enriched product (Y E ) as well as that in the lean product (Y L ) were strongly dependent on the ratio of feed/enriched product flow rates (Q F /Q E ) and the ratio of feed/lean product flow rates (Q F /Q L ). Although the pressure ratio (P a /P d ) was crucially important for the separation performance, a smaller value of R r was sufficient to reach a performance which is unattainable in conventional PSA processes.

Semi-batch operation and countercurrent extraction by supercritical CO2 for the fractionation of lemon oil

Abstract The supercritical fluid extraction of cold-pressed lemon oil was carried out in semi-batch and continuous countercurrent modes. In order to observe the extraction behavior of lemon oil, semi-batch extraction was performed using a rectification column, and the distribution curve for the main constituents of lemon oil was obtained. Separation was improved by applying an internal reflux induced by a temperature gradient along the column. The effects of the reflux on the extraction ratio, the separation selectivity, the concentration factor of each component and the recovery of oxygenated compounds were investigated for continuous operation at pressures of 8.8 and 9.8 MPa. Extraction combined with side-stream withdrawal was useful for lemon oil processing. The continuous operation with a linear temperature gradient from 313 to 333 K at 8.8 MPa showed the highest selectivity. Selectivity increased with the increase in solvent-to-feed (S/F) ratio.

Entropic analysis of adsorption open cycles for air conditioning. Part 2: interpretation of experimental data

The full second-law analysis, developed in Part 1 (M. Pons and A. Kodama, Int. J. Energy Res. 2000; 24: 251–262) is applied to experimental results. That approach takes into account the irreversibilities due to the open character of the cycle. Measurements are performed on a solid desiccant cooling unit operated in the ventilation mode. Experimental data permit us to establish the entropy balance of the unit. The results show that the sum of all the considered entropy productions completely explain the difference between the Carnot COP and the actual COP of the unit. The effects of three experimental parameters are investigated: the rotation speed of the dehumidifier (desiccant wheel), the air velocity and the regeneration temperature. Experimental results show that there exists an optimal rotation speed which results from a combination between the different entropy productions in the cycle. When the air velocity is increased, together with an accordingly optimized rotation speed, the cooling capacity increases while the COP decreases due to increases in the entropy productions in the dehumidifier and sensible heat exchanger. Moreover, it appears that the most significant entropy productions take place in the dehumidifier and heating system. In the investigated experimental unit, these two entropy productions have similar magnitudes. However, when the regeneration temperature is increased, the irreversibilities due to mass exchanges with outside air become comparable to these and surely should not be forgotten in a global optimization of the process. The present analysis is a solid basis for reducing the largest entropy productions thus optimizing the process. Copyright