Solar adsorption refrigeration : an alternative/auxiliary way for thermal storage for air conditioning

This paper presents an idea of using solar powered adsorption ice making system as an alternative or an auxiliary way for the traditional ice storage air conditioning systems. A simple solar adsorption refrigeration system runs in intermittent cycle. It makes cooling effect at night, and the cooling effect can be stored for the day use. It fits in well with the cycle of the existing off-peak ice storage air conditioning system. On the top of green effect of the solar powered ice making system, the idea is specifically beneficial for places where the price of the off-peak electricity is not significantly lower than peak price. Based on our many years experience on the solar ice making systems, the paper discusses the technical feature of the solar ice making technology and the solutions we are working on to attack the problems which may have potential damage to application of the solar ice making system for air conditioning purposes.

Sodium adsorption using activated alumina for application in the dairy industry

Basic activated alumina with negatively charged surface is considered as a potential adsorbent for a targeted molecule with positive polarity. Adsorption of sodium by basic activated alumina was investigated as a method for desalting dairy waste streams, in which sodium ion concentration averaged 600 mg/L. Sodium equilibrium and kinetic adsorption were investigated using basic activated alumina with synthetic brines. The results of equilibrium adsorption show that uptake of sodium by activated alumina is significantly higher when the pH is greater than 8 and increases as the pH of the brines increases until pH reaches around 10. The results of kinetic adsorption show that 90 hours were needed to reach equilibrium for sodium adsorption. Binding and diffusion processes are suggested to have taken place within the activated alumina.

Using titania photocatalysts to degrade toluene in a combined adsorption and photocatalysis process

Three types of titania supported materials including titanium dioxide and silicon dioxide composite, titania-coated activated carbon and titania-coated glass beads were prepared and used as photocatalysts to remove toluene from an air stream. Their surface areas were analysed. TEM image reveals titania-silica composites were nanostructured aggregates. XRD was used to determine their crystalline phase which was 100% anatase for the titania component. A fixed bed reactor was designed and built in the laboratory, the toluene with initial concentration of 300 ppm (1149 mg/m³) was fed into the reactor, the destruction efficiencies of toluene were determined by the gas analyser. It was also found that TiO₂-SiO₂ aggregates with high surface area (421.1 m²/g) achieved high destruction efficiencies. The combined effects of adsorption and photocatalysis were further studied by comparing the performance of pure activated carbon (surface area of 932.4 m²/g) and TiO₂ coated activated carbon with BET surface area of 848.4 m²/g. It was found that the TiO₂ coated activated carbon demonstrated comparable results to pure activated carbon, and most importantly, the TiO₂-coated activated carbon can be effectively regenerated by UV irradiation, and was reused as adsorbent. The experimental result of titania-coated glass beads demonstrated a steady degradation efficiency of 15% after a period of 17 hours. It helped to understand that photocatalysis degradation ability of the TiO₂ was constant regardless of the adsorption capacity of the catalysts. This photocatalytic property can be used to degrade the adsorbed toluene and regenerate the catalyst. This study revealed that if the experiments were designed to use adsorption to remove toluene and followed by regeneration of adsorbent using photocatalysis, it could achieve a very high removal efficiency of toluene and reduce the regeneration cost of saturated adsorbent.

Effects of clay amendment on adsorption and desorption of copper in water repellent soils

Copper is an important micronutrient and trace amounts are essential for crop growth. However, high concentrations of copper will produce toxic effects. Australia is increasingly developing production of crops in water repellent soils. Clay amendment, a common amelioration techniques used in Australia, has demonstrated agronomic benefits in increased crop or pasture production. The sorption and desorption of copper and the effect of clay treatment on copper behaviour in a water repellent soil collected from an experimental farm in South Australia is studied. We found that the water repellent soils amended with clay have an increased adsorption capacity of copper. Also the clay-amended soils had an increased ratio of specific sorption to total sorption of copper. The implications of this study to the sustainable agro-environmental management of water repellent soils is discussed.

Removal of VOCs by photocatalysis process using adsorption enhanced TiO2–SiO2 catalyst

Volatile organic compounds (VOCs) exist widely in both the indoor and outdoor environment. The main contributing sources of VOCs are motor vehicle exhaust and solvent utilization. Some VOCs are toxic and carcinogenic to human health, such as benzene. In this study, TiO₂–SiO₂ based photocatalysts were synthesized using the sol–gel method, with high surface areas of 274.1–421.1 m²/g obtained. Two types of pellets were used as catalysts in a fixed-bed reactor installed with a UV black light lamp. Experiments were conducted to compare their efficiencies in degrading the VOCs. Toluene was used as the VOC indicator. When the toluene laden gas stream passed through the photocatalytic reactor, the removal efficiencies were determined using a FTIR multi-gas analyser, which was connected to the outlet of the reactor to analyse the toluene concentrations. As the TiO₂–SiO₂ pellets used have a high adsorption capacity, they had dual functions as a photocatalyst and adsorbent in the hybrid photocatalysis and adsorption system. The experiments demonstrated that the porous photocatalyst with very high adsorptive capacity enhanced the subsequent photocatalysis reactions and lead to a positive synergistic effect. The catalyst can be self-regenerated by photocatalytic oxidation of the adsorbed VOCs. When the UV irradiation and feeding gas is continuous, a destruction efficiency of about 25% was achieved over a period of 20 h. Once the system was designed and operated into adsorption/regeneration mode, a higher removal efficiency of about 55% was maintained. It was found that the catalyst pellets with a higher surface area (421 m²/g) achieved higher conversion efficiency (100%) for a longer period than those with a lower surface area. A full spectrum scan was carried out using a Bio-rad Infrared spectrometer, finding that the main components of the treated gas stream leaving the reactor, along with untreated toluene, were CO₂ and water. The suspected intermediates of aliphatic hydrocarbons and CO were found in minimal amounts or were non detectable. The kinetic rate constants were calculated from the experimental results, it appeared that the stronger adsorption capacity, i.e. larger specific surface area, the higher conversion efficiency would be achieved.

Simulation of the solar adsorption refrigeration operating at near atmospheric pressure

To solve the leaking problem faced by current vacuum adsorption refrigeration systems, the authors have carried out a series of studies on the concept of raising the system's pressure to around atmospheric pressure with an inert gas (eg. Helium) as the pressure-adjusting agent. This paper presents the simulation of the performance oj the activated carbon-methanol adsorption refrigeration operating at near atmospheric pressure powered by solar energy. This simulation can be refereed in the prototype design.

Adsorption and voltammetry of butyltin compounds

The adsorption of tributyltin onto materials commonly used for the construction of sampling and analytical equipment from aqueous solutions of varying ionic composition has been examined. The adsorption appears to be controlled by non-polar interactions between tributyltin and the surface involved. Since the speciation and hence polarity of tributyltin is affected by the ionic composition of the medium, the extent of adsorption is affected by the salinity and pH of a sample. The adsorption is rapid and, unless strategies are adopted to eliminate its effects, may render analytical results invalid. The electrochemistry of tributyltin, dibutyltin and monobutyltin, individually and in mixtures, has been investigated in aqueous media at mercury electrodes. The basic electrochemistry of each compound is summarised by the reaction BunSn (4-n)+ + (4-n)e- right left harpoons BunSn where n is the number of butyl groups attached to the tin atom. However, the electrochemistry of each compound is largely confined to the surface of the mercury electrode, and the simplicity of the above reaction is disrupted by polymerisation reactions and by butyl exchange processes occurring with the mercury electrode. When mixtures of butyltin compounds are present, the various processes that occur for each individual compound interfere with each other. A direct voltaminetric method for the determination of butyltin compounds in natural waters is therefore probably not possible.

Granular Activated Carbon (GAC) adsorption in tertiary wastewater treatment : experiments and models

Wastewater treatment has always been a major concern in the developed countries. Over the last few decades, activated carbon adsorption has gained importance as an alternative tertiary wastewater treatment and purification process. In this study, granular activated carbon (GAC) adsorption was evaluated in terms of total organic carbon (TOC) removal from low strength synthetic wastewater. This paper provides details on adsorption experiments conducted on synthetic wastewater to develop suitable adsorption isotherms. Although the inorganics used in the synthetic wastewater solution had an overall unfavourable effect on adsorption of organics, the GAC adsorption system was found to be effective in removing TOC from the wastewater. This study showed that equation of state (EOS) theory was able to fit the adsorption isotherm results more precisely than the most commonly used Freundlich isotherm. Biodegradation of the organics with time was the most crucial and important aspect of the system and it was taken into account in determining the isotherm parameters. Initial organic concentration of the wastewater was the determining factor of the model parameters, and hence the isotherm parameters were determined covering a wide range of initial organic concentrations of the wastewater. As such, the isotherm parameters derived using the EOS theory could predict the batch adsorption and fixed bed adsorption results of the multi-component system successfully. The isotherm parameters showed a significant effect on the determination of the mass transfer coefficients in batch and fixed bed systems.

π-Selective stationary phases: (II) Adsorption behaviour of substituted aromatic compounds on n-alkyl-phenyl stationary phases

The frontal analysis method was used to measure the adsorption isotherms of phenol, 4-chlorophenol, p-cresol, 4-methoxyphenol and caffeine on a series of columns packed with home-made alkyl-phenyl bonded silica particles. These ligands consist of a phenyl ring tethered to the silica support via a carbon chain of length ranging from 0 to 4 atoms. The adsorption isotherm models that fit best to the data account for solute–solute interactions that are likely caused by π–π interactions occurring between aromatic compounds and the phenyl group of the ligand. These interactions are the dominant factor responsible for the separation of low molecular weight aromatic compounds on these phenyl-type stationary phases. The saturation capacities depend on whether the spacer of the ligands have an even or an odd number of carbon atoms, with the even alkyl chain lengths having a greater saturation capacity than the odd alkyl chain lengths. The trends in the adsorption equilibrium constant are also significantly different for the even and the odd chain length ligands.