A. G. Okunev

Sorption of Carbon Dioxide from Wet Gases by K2CO3-in-Porous Matrix: Influence of the Matrix Nature

In a fixed-bed absorber at 40°C, the dynamics of carbon dioxide sorption over composite sorbents prepared by impregnation of potassium carbonate in various porous matrixes is studied. The dynamic capacity of the synthesized sorbents is shown to reach 0.12 g CO2 per 1 g of the sorbent. The composite dynamic capacity depends on the nature of the host matrix and decreases in the sequence alumina > activated carbon > vermiculite > silica gel. For K2CO3-on-alumina, the sorption capacity decreases considerably after the first cycle of «absorption and regeneration under 200–350°C», whereas the sorbents based on active carbons could be reversibly restored. The findings are discussed within the idea on a chemical interaction between the host matrix and the impregnated salt.

Thermal conductivity of selective water sorbents under the working conditions of a sorption chiller

Abstract This paper presents the experimental data on the thermal conductivity of the composite sorbents, CaCl2/SiO2 and LiBr/SiO2, measured by the “hot wire method” under various conditions of vapour pressure PH2O, temperature T and water uptake w. The measurement ranges were chosen according to the operating conditions of a typical sorption cooling cycle ( 10 H 2 O mbar , 40 ° C ). The obtained results show that the sorbent thermal conductivity λ(T,PH2O,w) increases considerably as the uptake of sorbate rises, while its dependence on pressure and temperature is, in the studied range, almost negligible. Finally, the influence of thermal conductivity on the specific power of the sorption chiller is discussed.

Sorption of carbon dioxide by the composite sorbent "potassium carbonate in porous matrix"

Sorption of CO2 in the presence of water vapor by the K2CO3—γ-Al2O3 composite sorbent was studied by IR spectroscopy in situ, X-ray diffraction analysis, and the differentiating dissolution method and reasons for a decrease in its dynamic capacity are given. The samples containing K2CO3·1.5H2O in pores are characterized by the maximal dynamic capacity. A mechanism for CO2 sorption was proposed, which qualitatively explains the obtained dependence of the capacity on the water content in the composite sorbent. A high dynamic capacity can be maintained by regeneration of the sorbents by water vapor at 170 °N. The capacity of the sorbents decreases during the first 10 sorption—regeneration cycles due to the formation of an inactive phase of potassium aluminum carbonate.

Sorption of CO2 from Humid Gases on Potassium Carbonate Supported by Porous Matrix

Kinetics of sorption of carbon dioxide on potassium carbonate supported by different porous matrices was studied in a flow reactor at 40°C. The structural and chemical changes of potassium carbonate-aluminum oxide composite sorbents were studied by powder X-ray diffraction, thermogravimetry, and low-temperature nitrogen sorption.

ACETONE ADSORPTION ON HYDROXYLATED SILICA GEL : CORRELATION OF SORPTION ISOTHERMS AND IR SPECTRA

Results of adsorption and IR studies on the interaction of acetone with fully and partially hydroxylated surfaces of a KSS-3 silica gel are presented. Two plateaus on adsorption isotherms and two CO bands in IR absorption spectra are in close connection, which clearly indicates two adsorption complexes of acetone with different surface OH groups of silica. The weaker adsorption form (CO stretching vibration at 1705 cm−1) corresponds to the formation of an adsorption complex between an acetone molecule and a terminal OH-group (OH stretching vibration at 3740 cm−1). An abnormally high fractal dimension of the silica gel surface has been obtained and discussed.

Monolayer physical adsorption in narrow pores. Apparent surface dimension

Monolayer physical adsorption has been considered, taking into consideration the intrinsic volume of the adsorbate molecules. Since an adsorbed molecule occupies not only the site on the surface but also some of the neighboring volume, it creates steric difficulties for the adsorption of other molecules and leads to underestimation of the measured surface area. As a result, this value depends on the size of the adsorbate molecules and the apparent surface dimension can be introduced, even if the surface of narrow pores has no irregularities of atomic scale size. This effect was shown by simulation of adsorption on the surface of Menger sponge. Experimental data for measuring D-values on silica gels with different pore size distributions are in line with this effect.

RADIATION CATALYSIS : DEFECT TRANSPORT TOWARDS A FRACTALLY ROUGH SURFACE

Using a self-similar model of rough surface, equations were obtained which describe the probabilityP of radiation defects generated in the near-surface volume to reach the surface. The influence of surface irregularity was analyzed in the case when the ionization depthl0 and the escape depthR0 are within the lowera and upperb cut-offs of surface fractality. It was shown that a surface roughening and an increase of the ratiol0/R0 result in a marked raise of probabilityP. Taking the effect into consideration may be of importance for quantitative analysis of radiation catalytic processes on real surfaces.

A Monte Carlo simulation of the development of surface roughness and its effect on the dissolution kinetics of SiO2 aerogels

The development of surface roughness during dissolution of spherical particles is studied by the Monte Carlo method. The simulation results are used to analyze the dissolution kinetics of silicon dioxide aerogels in an aqueous solution of alkali (NaOH). The suggested model is shown to be suitable for describing the experimental dissolution curves obtained for aerogels with a small diameter of primary particles (3.5 and 2.9 nm). For aerogels with larger particles, a good agreement with the experiment can be achieved under the additional assumption that only part (p < 1) of the particle surface is originally active in dissolution; the best agreement is reached at p ≈ 0.5. In the kinetic regime of dissolution, the dissolution rate may be more than three times higher (owing to the formation of rough surfaces of primary particles with relatively large diameters, 40 atoms or more) than the rate calculated for the same parameters within the framework of the modified Delmon model, which does not make allowance for the development of roughness. Relatively small particles (with the diameter of less than 15 atoms) are dissolved before a significant roughness can be developed; therefore, the kinetic curves obtained for both models have virtually identical shapes in this case. The formation of roughness has an especially large effect on the dissolution of intermediate-size particles, whose dissolution time has the same order of magnitude as the time required for establishment of the steady-state roughness.