Larisa G. Gordeeva

SELECTIVE WATER SORBENTS FOR MULTIPLE APPLICATIONS, 2. CACL2 CONFINED IN MICROPORES OF SILICA GEL : SORPTION PROPERTIES

This paper presents sorption properties of a selective water sorbent based on mesoporous KSKG silica gel as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isochores and isotherms at T=20–150°C and vapor partial pressures of 8–133 mbar clearly showed two types of water sorption: 1) the formation of solid crystal hydrates at low amounts N of sorbed water, and 2) vapor absorption mainly by the salt solution at higher N. Sorption properties of CaCl2 crystal hydrates were found to change strongly due to their impregnation into mesoporous silica gel, whereas the solution confinement to the mesopores did not change its water sorption properties with respect to the bulk solution. Isosteric sorption heat was measured to depend on water sorption and to change from 62.5 kJ/mol for solid hydrates to 42.2–45.6 kJ/mol for solution.

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.

Water sorption on composites LiBr in a porous carbon

Water sorption equilibrium of LiBr confined to pores of a mesoporous synthetic carbon Sibunit and a macroporous expanded graphite (samples SWS-2C and SWS-2EG, respectively) was studied. Isobars of water sorption on these composites are measured at vapor pressure 6–81 mbar and temperature 30–145 jC. The type of sorption equilibrium for the two composites appears to be quite different. The isobars for SWS-2EG have a plateau corresponding to one molecule of H2O adsorbed by one molecule of LiBr, which indicates the formation of crystalline hydrate LiBrH2O inside pores with a monovariant type of equilibrium. At lower temperatures, the equilibrium becomes divariant that is typical for LiBr–water solutions. On the contrary, the water sorption equilibrium for SWS-2C is divariant over the whole temperature and pressure range which means that no crystalline hydrates are formed inside Sibunit pores. In our opinion, this distinction results from differences in a pore structure of the host carbons. The composite sorption capacity can reach 0.6–1.1 g H2O per 1 g of the dry sorbent at relative humidity 70%. The advanced sorption capacity makes the sorbents promising for gas drying, thermal storage of energy and other applications. D 2002 Elsevier Science B.V. All rights reserved.

Selective water sorbents for multiple application, 6. Freshwater production from the atmosphere

In this communication we consider an application of new selective water sorbents for freshwater production from the atmosphere. We present a general scheme of water production and discuss its efficiency in different climatic areas. The results of our lab-scale tests have demonstrated the feasibility of this method with the output of 3–5 kg of water per 10 kg of the dry sorbent per day.

Preparation and study of porous uranium oxides as supports for new catalysts of stream reforming of methane

Abstract We describe the method of synthesis of the porous uranium oxides (U 3 O 8 and UO 2 ) with specific surface area as high as 10–15 m 2 /g. Physico-chemical structure and properties of these materials were studied by X-ray diffraction, scanning electron microscopy and adsorption techniques. Porous U 3 O 8 was used as a support for Ni- and Ru-catalysts for steam reforming of methane for new ICAR-process of direct nuclear-to-chemical energy conversion (Int. J. Hydrogen Energy 18 (1) (1993)) Catalytic activity as a function of the metal (Ni or Ru) content, temperature and contact time was studied in non-gradient catalytic reactor at P =1 atm and T =600–780°C. The catalysts studied were shown to be very active in methane reforming by steam and allow to reach at these conditions the hydrogen production rate as high as 17–18 n cm 3 /s per 1 gram of the catalyst. The reaction rate obeys the law r = k 0 exp(− E a / RT)(p m - p m ∗ ), where p m is a partial pressure of methane, p m ∗ is close to the equilibrium pressure of methane at temperature T . The activation energy E a was found to be 54 kJ/mol for Ru/U 3 O 8 catalysts. To reduce the expected contamination of the produced syn-gas by radioactive products of nuclear splitting under application in the ICAR process we build up a thin oxide (MgO, Al 2 O 3 ) layer, coating the porous uranium particle. The results of the coating study are also presented.

Selective water sorbents for multiple applications, 8. sorption properties of CaCl2−SiO2 sol-gel composites

This paper presents sorption properties of CaCl2/SiO2 composites synthesized by a sol-gel approach. Desorption isobars measured at T=30–140°C and vapor pressure 12.8–81.0 mbar clearly show a correlation between the sorbents pore structure and their sorption properties. The sample adsorptivities are found to exceed 1.2 kg H2O/kg adsorbent (or 20–25 mol H2O/mol of the salt). That is markedly higher than any reported before for silica-based materials. This results in a high energy storage capacity reaching 3,400 kJ/kg of dry sorbent, as confirmed by direct calorimetric measurements. The isosteric desorption heat is found to decrease from 67±5 kJ/mol to 46±5 kJ/mol with increase in the surface coverage.

ICAR process (immediate catalytic accumulation of ionizing radiation energy) as a new promising approach to the development of cheminuclear power plants

Abstract A new thermocatalytic method, ICAR, for nuclear-to-chemical energy conversion is suggested. The method is based on a combination of both nuclear and catalytic reactors in the same technological volume, by loading the catalyst directly into the active (energy releasing) zone of a nuclear reactor. Two variations of the suggested method are studied, based on the endothermic catalytic reactions of methane- and methanol - steam reforming as well as on ammonia decomposition. The conditions of intensive heat release immediately inside the catalyst bed were simulated by means of an electron accelerator. A new type of uranium-containing catalyst for steam reforming of methane was synthesized and studied. These special catalysts, as well as conventional commercial catalysts being used in the ICAR method were shown to be capable of ensuring a considerable intensification of the energy-accumulating chemical reaction and of increasing the specific power loading of the energy conversion up to 100–150 kW dm−3. The results of mathematical simulation of direct thermochemical conversion of radiation (nuclear) energy are also presented. Some advantages of the ICAR method and expected difficulties of its practical application are discussed here in order to point out some problems that should be solved in the near future.

ARTIC-1: A New Humidity Buffer for Showcases

Abstract This paper considers an efficient approach to passive humidity control for art objects in exhibition cases, picture frames and transporting containers. This approach is based on a gas–solid chemical reaction between an inorganic salt and water vapor. Requirements for hydration/dehydration reactions and salt hydrates, which are optimal for hydrostats for safe display, conservation and transportation of various works of art, ancient manuscripts, books, archival documents, etc., have been formulated. New materials for maintaining the relative humidity between 40 and 70% have been synthesized and studied. Tests on a novel material (the so-called ARTIC-1) for maintaining the relative humidity between 50 and 60% at the Museum of the History and Culture of Siberian Nations (Novosibirsk, Russia) and the State Scientific Library of the Siberian branch of the Russian Academy of Sciences showed its feasibility for the efficient smoothing of daily and seasonal variations of the relative humidity. These trials confirmed that ARTIC-1 is an effective adsorbent for use in sufficiently airtight showcases and containers.

New Adsorption Cycle for Upgrading the Ambient Heat

Adsorption (chemical) heat transformation (AHT) is a new energy conservation and environmentally friendly technology that allows efficient use of heat sources with low temperature potential. Recently, a new cycle, called “Heat from Cold” (or HeCol) has been proposed to upgrade the temperature potential of the ambient heat. In the HeCol cycle, a natural reservoir of water with a temperature above 0°C is used as a heat source, and ambient air at T = (–20)–(–50)°C as a heat sink. The cycle is designed to produce heat at a temperature of 30–50°C, which can be used for heating of dwellings. The aim of this work is to select the adsorbent for the HeCol cycle and to test the laboratory prototype with the selected adsorbent. The work consists of three parts: (a) formulation of requirements to adsorbent, specialized for the HeCol cycles under various conditions; (b) analysis of data on adsorption equilibrium of commercial activated carbons and selection among them the materials suitable for the new cycle; and c) study of the laboratory prototype HeCol with the chosen adsorbent to analyze the feasibility of the new cycle. The main findings of this study are (i) the experimental demonstration of the HeCol cycle feasibility and (ii) the achievement of the specific heat generation power 8 kW/kg, which is of practical interest.

Extraction of Water from the Atmosphere in Arid Areas by Employing Composites “A Salt Inside a Porous Matrix”

This communication is addressed to sorptive extraction of water from the atmosphere in arid areas. The method includes (a) sorption of water vapour in an adsorber in the night-time when the air relative humidity is comparatively high, and (b) desorption of the stored water and its subsequent collection in a condenser in the day-time. New materials adapted to this process are highly welcome. Composites “a salt inside a porous matrix” (CSPMs) have enhanced water sorption capacity and their properties may be intently varied in a wide range. In this communication, we make a preliminary analysis of CSPMs application for extraction of water from the atmosphere. Firstly, a general scheme of the water extraction is described. Then, we form a mental representation of an ideal solid sorbent that is optimal for the extraction of water from the atmosphere. Finally, we discuss how to design a real CSPM with properties meeting the formulated requirements, what are roles of the salt and the matrix, etc.