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Tailor‐Made Anion‐Exchange Membranes for Salinity Gradient Power Generation Using Reverse Electrodialysis

Reverse electrodialysis (RED) or blue energy is a non-polluting, sustainable technology for generating power from the mixing of solutions with different salinity, that is, seawater and river water. A concentrated salt solution (e.g., seawater) and a diluted salt solution (e.g., river water) are brought into contact through an alternating series of polymeric anion-exchange membranes (AEMs) and cation-exchange membranes (CEMs), which are either selective for anions or cations. Currently available ion-exchange membranes are not optimized for RED, whereas successful RED operation notably depends on the used ion-exchange membranes. We designed such ion-exchange membranes and for the first time we show the performance of tailor-made membranes in RED. More specifically, we focus on the development of AEMs because these are much more complex to prepare. Herein we propose a safe and more environmentally friendly method and use halogenated polyethers, such as polyepichlorohydrin (PECH) as the starting material. A tertiary diamine (1,4-diazabicyclo[2.2.2]octane, DABCO) was used to introduce the ion-exchange groups by amination and for simultaneous cross-linking of the polymer membrane. Area resistances of the series of membranes ranged from 0.82 to 2.05 Ω cm² and permselectivities from 87 to 90 %. For the first time we showed that tailor-made ion-exchange membranes can be applied in RED. Depending on the properties and especially membrane thickness, application of these membranes in RED resulted in a high power density of 1.27 W m⁻², which exceeds the power output obtained with the commercially available AMX membranes. This shows the potential of the design of ion-exchange membranes for a viable blue energy process.

Effect of temperature on seawater desalination-water quality analyses for desalinated seawater for its use as drinking and irrigation water

The effect of feed seawater temperature on the quality of product water in a reverse osmosis process was investigated using typical seawater at Urla Bay, Izmir region, Turkey. The tests were carried out at different feed seawater temperatures (11–23°C) using two RO modules with one membrane element each. A number of variables, including pH, conductivity, total dissolved solids, salinity, rejection percentage of a number of ions (Na+, K+, Ca2+, Mg2+, Cl−, HCO3−, and SO42−), and the levels of boron and turbidities in collected permeates, were measured. The suitability of these permeates as irrigation and drinking water was checked by comparison with water quality standards.

Removal of Boron from Water by Ion Exchange and Hybrid Processes

The growing concern for the environment, increasingly stringent standards for the release of chemicals into the environment and economic competitiveness have prompted extensive efforts to improve chemical synthesis and manufacturing methods as well as development of new synthetic methodologies that minimise or completely eliminate pollutants. As a consequence, more and more attention has been focused on the use of safer chemicals through proper design of clean processes and products. Epoxides are key raw materials or intermediates in organic synthesis, particularly for the functionalisation of substrates and production of a wide variety of chemicals such as pharmaceuticals, plastics, paints, perfumes, food additives and adhesives. The conventional methods for the industrial production of epoxides employ either stoichiometric peracids or chlorohydrin as an oxygen source. However, both methods have serious environmental impact as the former produces an equivalent amount of acid waste, whilst the later yields chlorinated by-products and calcium chloride waste. Hence, a greener and efficient route for catalytic epoxidation that could improve manufacturing efficiency by reducing operational cost and minimising waste products is highly desired. In this chapter, a greener alkene epoxidation process using molybdenum (Mo) based heterogeneous catalyst and tert-butyl hydroperoxide (TBHP) as an oxidant has been presented. A polystyrene 2-(aminomethyl)pyridine supported molybdenum(VI) complex, i.e. Ps.AMP.Mo and a polybenzimidazole supported Mo(VI) complex, i.e. PBI.Mo have been successfully prepared and characterised. The catalytic activities of the polymer supported Mo(VI) complexes have been evaluated for epoxidation of 1-hexene and 4-vinyl-1-cyclohexene (4-VCH) in a batch reactor. Experiments have been carried out to study the effect of reaction temperature, feed molar ratio of alkene to TBHP and catalyst loading on the yield of epoxide for optimisation of reaction conditions in a batch reactor. The long term stability of the polymer supported Mo(VI) catalysts have been evaluated by recycling the catalysts several times in batch experiments using conditions that form the basis for continuous epoxidation studies. The extent of Mo leaching from each polymer supported catalyst has been investigated by isolating any residue from reaction supernatant studies after removal of heterogeneous catalyst and using the residue as potential catalyst for epoxidation. The efficiency of Ps.AMP.Mo catalyst has been assessed for continuous epoxidation of 1-hexene and 4-vinyl-1-cyclohexne with TBHP as an oxidant using a FlowSyn reactor by studying the effect of reaction temperature, feed molar ratio of alkene to TBHP and feed flow rate on the conversion of TBHP and the yield of epoxide. The catalysts were found to be active and selective for batch and continuous epoxidation of alkenes using TBHP as an oxidant. The continuous epoxidation in a FlowSyn reactor has shown considerable time savings, high reproducibility and selectivity along with remarkable improvement in catalyst stability compared to the reactions carried out in a batch reactor.