Synthesis methods by means of electrodialyies related technologies in concentrated media.

In this PhD, the production of chemicals using various electrodialysis configurations was investigated. The work was focused on two types of reactions namely, metathesis reactions and the acidification of poor water soluble organic acids. It was studied if electrodialysis could compete with existing product processes concerning product purity and additionally provides an alternative environmental friendly production process.

Preferably, a high salt concentration is obtained with the electrodialysis process. Unfortunately, this capability of electrodialysis is hampered by transport of water through ion-exchange membranes. The influence of operating parameters on water transport was quantified. To obtain high purity products, ion-exchange membranes should be solely permeable for counter-ions and impermeable for co-ions. However, in real ion-exchange membranes co-ions can permeate to some extent. The influence of several operating parameters on this co-ion flux was investigated.

For the intended applications, the substitution of cations is of interest. The effect of organic co-solvents on the permselectivity of cation-exchange membranes between counter-ions was tested. For a substitution of sodium by protons, a high permselectivity was obtained in the presence of weak basic anions.

To accomplish the aims, solvent mixtures of water and a primary alcohol wereused. The transport of these organic co-solvents is preferentially avoided. Three co-solvents were tested, namely methanol, ethanol and 1-propanol. Several commercial available ion-exchange membranes and operating parameters were screened.

The production of ionic liquids, in this case choline dihydrogen phosphate, was investigated in a four compartment electrodialysis metathesis configuration and three compartment bipolar membrane configuration. The four compartment configuration was able to achieve a higher product purity than a metathesis process using silver salts. Further, the transport of impurities towards the ionic liquid was quantified in this configuration. An alternative configuration using bipolar membranes had a lower electrical resistance but yielded a lower product purity due to the limited counter-ion permselectivity of bipolar membranes.

The conversion of organic sodium salts in poorly water-soluble organic acids by bipolar membrane electrodialysis was investigated. Due to the limited durability of bipolar membranes in solvent mixtures, a new stack configuration was proposed. In this configuration, cation-exchange membranes separate the solvent mixture from the bipolar membrane. Experimental results showed that a complete conversion was possible with high electrical efficiency. An optimization of process parameters was performed for the production of salicylic acid. The technological feasibility of this process was also investigated and confirmed for the production of sebacic acid from sodium sebacate.