V. N. Parmon

A family of new working materials for solid sorption air conditioning systems

Abstract In this communication a family of new working materials, so called selective water sorbents, is presented for sorption air conditioning. These materials are composites “hygroscopic salt inside porous matrix with open pores” and possess intermediate behaviour between solid adsorbents, salt hydrates and liquid absorbents, so that their water sorption properties can be controllably modified by varying (a) porous structure of the host matrix, (b) chemical nature of the impregnated salt and (c) the amount of the salt inside the pores. For these materials the water sorption equilibrium and specific heat have been measured in a wide temperature and uptake range. This study shows that composites based on CaCl2 and LiBr as impregnated salts and different micro- and mesoporous silica gels as host matrices are able to absorb up to 0.75 g H2O per 1 g of the dry sorbent. After presentation of sorption equilibrium curves, the thermodynamic performance for their utilisation in heat pump and refrigeration systems, is calculated. The results show that these new materials can be operated with cycles whose maximum temperature is about 95 °C (for cooling) and 140 °C (for heating) that are lower than those for other pairs known so far. The values of coefficient of performance are considerably higher than those reported for silica gel/water system at the same temperature of the heat source.

“Chemical Heat Accumulators”: A new approach to accumulating low potential heat

The first presentation of new composite Chemical Heat Accumulation materials based on granulated open-porous matrix filled with a hygroscopic substance is given. At storing heat, the materials operate in a reversible hydration/dehydration mode. When crystalline hydrates of simple salts are used as the hygroscopic substance, the new materials allow to reach the heat storing capacity up to 2000 kJ kg−1 even for accumulation of low temperature heat (of circa 20–40°C). The materials also possess improved properties for mass and heat transfer. All these make a serious advantage of these materials in comparison with those using a latent melting-solidification heat as well as with zeolites capable of reversible hydration/dehydration. The new materials can be widely used in energy efficient and freons-less air conditioning devices, for cooling the electronic units, fire-extinguishing and some other applications.

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.

NEW COMPOSITE SORBENTS FOR SOLAR-DRIVEN TECHNOLOGY OF FRESH WATER PRODUCTION FROM THE ATMOSPHERE

Abstract In this communication we present new selective water sorbents developed at the Boreskov Institute of Catalysis (Novosibirsk, Russia) and discuss their application for fresh water production from the atmosphere. We present a general scheme of the water production and suggest the particular solar-driven unit which may be recommended for desert areas with a hot and dry climate. The results of our lab- scale tests have demonstrated a feasibility of the fresh water production with the output of 3–5 tonnes of water per 10 tonnes of the dry sorbent per day.

Thermodynamic Analysis of the Effect of the Nanoparticle Size of the Active Component on the Adsorption Equilibrium and the Rate of Heterogeneous Catalytic Processes

An enormous body of experimental data on the effect of the particle size of the active component of a catalyst on the specific catalytic activity (SCA) and on a similar parameter, the catalyst turnover frequency (TOF), has been accumulated to date (see, for example, [1, 2]). These parameters are not related to the total surface of the catalyst active phase or to the number of active sites; therefore, they characterize the properties of the active site itself. Experimental data on the influence of small metal particles on the adsorption properties [2] and on the selectivity of the catalyzed reaction [3] have also been reported. It is significant that these data often refer to situations where the small particles of the active component are treated as a continuous phase described using standard thermodynamic approaches rather than as atomic clusters requiring strict account of quantum-size effects. Analysis of experimental data indicates that the SCA and TOF values usually markedly decrease with a decrease in the particle size of the active component, these changes being visible for particle sizes of about or less than 10 nm. This study represents an attempt at a consistent consideration of the reasons for and the expected scale of these phenomena based on analysis of the variation of thermodynamic properties of the catalyst active component on dispersion.

A quantitative NMR imaging study of mass transport in porous solids during drying

Abstract The temporal transformations of the radial distribution of a liquid in a presoaked porous cylindrical catalyst support pellet detected by 1 H NMR microimaging technique in the course of the pellet drying are analyzed quantitatively in terms of the diffusion equation. The approach is shown to be adequate for evaluating the diffusivity and its dependence on the degree of pellet saturation with a liquid, provided that the NMR microimaging data are properly corrected for the relaxation weighting effects. It is demonstrated that for liquids characterized by a low surface tension, such as acetone, benzene and cyclohexane, transformations of the concentration profiles can be adequately modeled assuming a liquid content-independent diffusivity. In contrast, the diffusivity of water in titania and alumina pellets substantially decreases with the decrease of water content. For alumina pellets with a pronounced “bimodality” in the pore size distribution the water concentration dependence of diffusivity is shown to be non-monotonic. It is argued that for liquids with high surface tension, the shape of the concentration profiles and the behavior of diffusivity as a function of liquid content are both related to the shape of the cummulative pore size distribution of the porous solid under study due to the existence of efficient capillary flows induced by capillary suction.

Selective water sorbents for multiple applications, 3. CaCl2 solution confined in micro- and mesoporous silica gels: Pore size effect on the “solidification-melting” diagram

In this communication we present a low-temperature “solidification-melting” phase diagram for CaCl2/H2O solutions confined in KSK and KSM silica gels. At salt concentrations of 0–48 wt. %, the diagram has been found to lie below the diagram reported for the bulk system by 15–30°C. It shows a depression of the solution melting point due to its confinment to the pores. Several other peculiarities of melting and solidification in this system are also reported and discussed. Beside fundamental interest, the data obtained could be of importance in many commercial areas such as refrigeration, accumulation of low temperature heat, frost prevention in building materials,etc.

Guaiacol hydrodeoxygenation in the presence of Ni-containing catalysts

A series of Ni-containing catalysts supported on different materials has been tested in the hydrodeoxygenation of guaiacol, a compound modeling the products of biomass fast pyrolysis. The reaction has been carried out in an autoclave at 320°C and a hydrogen pressure of 17 MPa. The main guaiacol hydrodeoxygenation products are cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone (which result from aromatic ring reduction). A guaiacol conversion scheme explaining the formation of the main products is suggested. The highest activity is shown by the Ni-containing catalysts on SiO2 and SiO2-ZrO2 supports prepared by the sol-gel method. According to X-ray diffraction and electron microscopic data, the high activity of these catalysts is due to the high concentration of dispersed nickel as reduced films on the surface of the silicate structures. The catalysts offer promise for refining the biomass fast pyrolysis products (bio-oil) into hydrocarbon fuel.

Properties and deactivation of the active sites of an MoZSM-5 catalyst for methane dehydroaromatization : Electron microscopic and EPR studies

The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo5+. The surface Mo2C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores.

In situ NMR spectroscopy in heterogeneous catalysis: Kinetic study of hydrocarbon conversion mechanisms

The potential of high-resolution solid-state NMR spectroscopy for kinetic and mechanistic studies of hydrocarbon conversion on solid acid catalysis between 20 and 300°C is considered. The use of this technique is illustrated by the elucidation of the mechanisms of hydrogen exchange and 13C label transfer in alkanes and olefins, n-butane isomerization on sulfated zirconia, and ethane aromatization on zinc-containing zeolite beta. The kinetic parameters determined in these studies provide a basis for quantum chemical calculations of possible hydrocarbon activation and conversion pathways and for evaluating the reliability and accuracy of these theoretical calculations.