A method named as 'volume-expanding and pressure-reducing adsorption' is proposed. It can be used to measure the isotherms under supercritical condition. The adsorption isotherms of phenol on activated carbons and polymeric adsorbents are estimated and compared respectively for the systems of 'phenol-activated carbon-supercritical fluid CO2' and 'phenol-polymeric adsorbent-supercritical fluid CO2'. The results show that the amount of phenol adsorbed on the activated carbons and the polymeric adsorbents under the supercritical condition is much less than that under the general condition, which can be utilized to develop a technology regenerating the activated carbon with supercritical fluid. Moreover, the effects of ethyl alcohol, used as the third component, on the isotherms of phenol on the activated carbons and polymeric adsorbents under the supercritical condition are also investigated.
Phase equilibrium and kinetic experiments of phenol on NKAⅡ resin under ultrasonic field and non-ultrasonic field were separately conducted at normal temperature.The model for estimating diffusion coefficient of phenol on the NKAⅡ resin was established.Results showed that application of ultrasound can change the phase equilibrium state of NKAⅡ/phenol/water system which has reached equilibrium under normal condition.The phase equilibrium state of the system shift towards decrease in the amount adsorbed of phenol on NKAⅡ resin.In addition, acoustic cavitation could make diffusion coefficient of phenol in NKAⅡ resin in ultrasonic field increase by one order of magnitude in comparison with the diffusion coefficient determined in non-ultrasonic field.The diffusion coefficient increased with the increase in acoustic power.However,it was found that if the acoustic intensity was larger than 0.057?W·cm -2 , slight pulverization of the NKAⅡ resin occurred, which should be avoided in application.
A mathematical method was proposed for the determination of absolute adsorption from experimental isotherms. The method is based on the numerical equality of the absolute and the excess adsorption when either the gas phase density or the amount adsorbed is not quite considerable. The initial part of the experimentalisotherms, which represents the absolute adsorption, became linear with some mathematical manipulations. The linear isotherms were reliably formulated. As consequence, either the volume or the density of the supercritical adsorbate could be determined by a non-empirical way. This method was illustrated by the adsorption data of supercritical hydrogen and methane on a superactivated carbon in large ranges of temperature and pressure.
The CO2 adsorption data may show more than one section in the Dubinin-Radushkevich-Kaganer(DRK) plot if samples had been over-activated. Each section in the plot represents a range of pore size. The whole DRK plot provided information on the pore size distribution(PSD) of a sample, which may be used to monitor the effect of activation conditions in activation processes.
Desorption of volatile organic compounds (VOCs) from polymeric adsorbents by microwave was investigated experimentally. Two kinds of organic compounds, benzene and toluene, were separately used as adsorbates in this work. Results showed that the application of microwave to regenerate the polymeric adsorbents not only can get higher regeneration efficiency in comparison with the use of heat regeneration, but also make the temperatures of the fixed beds much lower than that when using the heat regeneration. The weaker the polarity of a polymeric adsorbent, the easier its regeneration was.
Hydrogen storage receives the worldwide attention due to its importance in sustainable energy and the solution of greenhouse effect.Adsorption provides an efficient way to compress gases and,therefore, has been applied to the development of hydrogen storage technology.However,hydrogen is a super- critical gas at the temperature of engineering interest and follows a different adsorption mechanism compared to the sub-critical gases.The present work shows why only monolayer coverage mechanism functions at above-critical temperatures and what consequences will result in the application study. Although there are pros and cons to this point of view,understanding the adsorption mechanism is,in- deed,essential for the research of hydrogen storage method since it claims that any storage material based on adsorption will not satisfy the practical need of on board storage no matter how novel the material is.
A new model, phase equilibrium-kinetics model (PEKM), for estimation of diffusion coefficient was proposed in this paper. Kinetic experiments of phenol desorption on NKAII resin in the presence and the absence of ultrasound were separately conducted, and diffusion coefficients of phenol within an adsorbent particle were estimated by means of proposed PEKM and classic simplified model. Results show that the use of ultrasound not only changes the phase equilibrium state of NKA II resin/phenol/water system which had been equilibrium at normal condition, but also enhances diffusion of phenol within the resin. The diffusion coefficient of phenol in the resin in the field of ultrasound increases in an order of magnitude in comparison with the diffusion coefficient determined under no ultrasound. Experimental results also indicated that the diffusion coefficients estimated by PEKM were more accurate than that estimated by the classic simplified model.
LI XiangbinZHAO YuechunXIA QibinXI HongxiaLI Zhong
