Akio Kodama

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 WATER OXIDATION FOR THE DESTRUCTION OF MUNICIPAL EXCESS SLUDGE AND ALCOHOL DISTILLERY WASTEWATER OF MOLASSES

Abstract Supercritical water oxidation has been focused as an environmentally attractive technology where organic materials are oxidized to carbon dioxide, water, and N2. We have applied the supercritical water oxidation to municipal excess sludge and alcohol distillery wastewater of molasses. The reaction was carried out in a batch reactor or a flow reactor with hydrogen peroxide as an oxidant in the temperature range 473–873xa0K. The liquid phase products were colorless and odorless. The reaction products were analyzed in terms of total organic carbon (TOC), organic acids, and ammonium ion. TOC decreased with temperature and the oxidant amount. Acetic acid and ammonia were detected as major refractory intermediates in the product. When more than stoichiometric demand of oxidant was used, organic carbon in liquid phase was almost completely destroyed. Complete destruction of ammonia produced in the reaction required higher temperature than that of acetic acid. A tube-type flow reactor (1/8xa0in×1.7xa0m) was constructed for the continuous treatment of wastes. The sludge was destroyed efficiently in the flow reactor.

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.

Entropic analysis of adsorption open cycles for air conditioning. Part 1: first and second law analyses

Rotary desiccant units for air-conditioning and ventilation use the principle of adsorption open cycles. In this study, a thermodynamic analysis is first developed that emphasises the open character of the cycle, and especially the consumption of liquid water. Then, the system is ‘closed’ with the help of virtual open systems that exchange mass flows with the cooling unit and only heat fluxes with heat sources. The entropic analysis is developed, first for these virtual systems showing that they are irreversible, second for each component of the unit where heat losses are taken into account. The equations are derived in such a manner that the different irreversibilities can directly be compared. In addition, the concept of entropic mean temperature is introduced and applied to the two virtual systems because it is very helpful for representing the variations of the entropy productions in these systems. In Part 2, these analyses will be applied to experimental data showing that they bring lots of information. Copyright

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.

Fractionation of citrus oil by supercritical countercurrent extractor with side-stream withdrawal

Abstract Supercritical fluid extraction of cold-pressed orange oil was carried out in the total reflux operation and continuous countercurrent operation. Internal reflux induced by temperature gradient along the column was applied to achieve the effective separation. For a total reflux operation, raffinate could not be withdrawn at the bottom of the column having a temperature gradient from 313xa0K at the bottom to 333xa0K at the top of the column at 8.8xa0MPa, because the homogeneous phase is formed at the bottom of the column. For the total reflux operation using the column with a uniform temperature at 333xa0K and 8.8xa0MPa, terpenes concentration in raffinate was dramatically reduced with an increase in CO2 flow rate and the selectivity between terpenes and oxygenated compounds was increased. For a continuous operation, the effect of the reflux on the selectivity was investigated. A new extraction process which can selectively and simultaneously fractionate the terpenes, oxygenated compounds, and waxes in citrus oil into extract, side stream, and raffinate, respectively, were proposed.

The Petlyuk PSA process for the separation of ternary gas mixtures: exemplification by separating a mixture of CO2–CH4–N2

The Petlyuk PSA process, proposed for the separation of ternary gas mixtures, consists of two pairs of adsorption columns, intermediate feed inlet and side stream outlet. An experimental study, involving the separation of a ternary gas mixture containing carbon dioxide, methane and nitrogen, was conducted to testify to its feasibility and investigate its performance by utilizing three kinds of adsorbent of activated carbon, zeolite 13X, and carbon molecular sieve. The results demonstrated that CO2, CH4 and N2 could apparently be enriched in the top, side and bottom product streams, respectively. Under the operating conditions, with the feed containing CO2 and CH4 both over 12%, CO2 could be enriched up to 60% in the top product, CH4 could be enriched above 60% in the side product, and N2 could be concentrated to higher than 95% in the bottom product. It could be concluded that the Petlyuk PSA process is feasible to separate ternary gas mixtures, and the operating parameters such as reflux ratios, half cycle time, etc. have apparent effects on its performance.

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.

New fractionation process for citrus oil by pressure swing adsorption in supercritical carbon dioxide

Abstract A new technique for fractionation of citrus oil was proposed. A pressure swing adsorption process in supercritical carbon dioxide (SC-CO2) was developed with silica gel as adsorbent. Adsorption equilibrium properties and adsorption–desorption dynamics were measured. Adsorption isotherms were represented by a multicomponent Langmuir equation. Desorption curve after the equilibrium saturation indicated that the rinse step to elute the solutes in the void space of the adsorber is required in order to achieve a higher concentration factor. Based on these results, continuous pressure swing operation between the adsorption step at 8.8xa0MPa and 313xa0K and the desorption step at 19.4xa0MPa and 313xa0K, including the rinse step, was demonstrated. Effects of feed concentration, half cycle time, and CO2 flow ratio were studied. Highly concentrated fraction of oxygenated compounds was continuously obtained for the desorption step and the blowdown step (depressurization). A mathematical model simulated well the behavior of the pressure swing adsorption.