In recent years, the increasing threat to groundwater quality due to human activities has become a matter of great concern. The groundwater quality problems present today are caused by contamination and by overexploitation, or by combination of both, which are faced by many Indian states. Today, reverse osmosis (RO) membranes are the leading technology for desalination of groundwater because of their strong separation capabilities and exhibiting a great potential for treatment of waters worldwide. However, the RO process had some problems due to the formation of polarization films because high pressure operation and by-products which may generate bacteria and fouling. Also, high energy consumption and brine disposal problem is faced in RO process due to the limited recovery of water. These problems may be overcome by other membrane thermal process such as a membrane distillation (MD). This paper addresses the outline of RO and MD process for desalination. RO has developed over the past 40 years and MD is an emerging technology for brackish water desalination and yet is not fully implemented in industry. The MD is the better alternative to RO for desalination theoretically found in the literature.

Kinetics of the hydrogenation of o-nitrophenol to o-aminophenol over a Pd/carbon (4.82 wt % Pd) catalyst (particle size 30 μm) in an agitated three-phase slurry reactor has been investigated in the chemical control regime at different temperatures (293−328 K), with initial concentration of o-nitrophenol (0.072−0.36 mol dm-3 ) and H2 pressures (442−1476 kPa), using methanol as a reaction medium. To confirm the absence of gas−liquid, liquid−solid, and intraparticle mass-transfer effects on the reaction, the effects of stirring speed (260−1290 rpm), catalyst loading (0.05−1.0 g dm-3), and catalyst particle size (30−165 μm) on the initial reaction rate at the maximum temperature (328 K) and o-nitrophenol concentration (0.36 mol dm-3) have been thoroughly studied. For a catalyst particle size of ≤45 μm and a stirring speed of ≥850 rpm, the reaction rate is not influenced by the mass-transfer processes. Effective intraparticle diffusivity of o-nitrophenol has been determined from the effectiveness factor of the catalyst for its different particle sizes. The observed large tortuosity factor (τ = 22.9 av) and activation energy (28.9 kJ mol-1) for the diffusion indicated a strong influence of adsorption and surface diffusion of o-nitrophenol on the catalyst. From the power law analysis of the initial rate data, the reaction order is found to be 0.53 ± 0.03 for o-nitrophenol in its concentration below 0.18, 0.22, 0.23, and 0.25 mol dm-3 at 293, 308, 318, and 328 K, respectively, and from 0.54 (at 293 K) to 1.0 (at 328 K) for hydrogen. However, the reaction is found to be zero-order for the higher o-nitrophenol concentration (>0.25 mol dm-3). The reaction kinetic data (including the initial rate data) could be fitted well to a Hougen−Watson-type model on the basis of the mechanism involving single-site surface reaction control with all the reaction species molecularly adsorbed. The activation energy for the initial reaction obtained from the power law analysis (70.2 kJ mol-1) is found to agree with that (68.0 kJ mol-1) obtained from the Hougen−Watson model.

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The solubility of hydrogen In methanol In the presence of o -nltrophenol, o-aminophenol, and water at different temperatures (293-328 K) and pressures (439-2145 kPa) has been determined. The presence of the above species caused a significant decrease In the solubility. The dissolution of hydrogen was found to be an endothermic process.

The poisoning of PdÈcarbon (4É1% Pd) catalysts by thiophene, dichloroethane, mercuric chloride and lead, zinc and mercuric acetates at di †erent concentrations (0È5000 g m~3) in the liquid phase hydrogenation of onitrophenol to o-aminophenol (at 308 K and pressure of 1508 kPa) in a H 2 three-phase stirred slurry reactor has been investigated. The hydrogenation activity of the catalyst is drastically reduced due to the presence of these poisons in the reaction mixture, even at a very low concentration of poison (20 g m~3). Among the poisons, mercuric acetate was found to be the most potent. 1998 ( Society of Chemical Industry