Solvent design for trace removal of pyridines from aqueous streams using solvent impregnated resins

The removal of pyridine derivatives from wastewater streams is of high environmental importance due to their toxicity and poor biodegradability. Conventional separation technologies such as adsorption and extraction cannot be applied effectively due to the difficulties in regeneration of adsorbents and entrainment of the solvent. The use of solvent impregnated resins (SIRs) in fixed bed operation is proposed as alternative to these technologies, combining the advantages of adsorption and liquid–liquid extraction in a single unit operation. Solvents for SIR technology should have a high capacity for pyridines and negligible solubility in water to prevent rapid loss of solvent. In this study, a solvent is designed for the removal of model compound 4-cyanopyridine from an aqueous stream. COSMO-RS was used and evaluated as solvent design tool. Results show that COSMO-RS is able to qualitatively predict the capacities of the solvents. The optimized solvent was a 1:1 mixture of (E)-3-bromo-4-(3-ethylhept-1-en-1-yl)phenol and (Z)-3-bromo-4-(3-ethylhept-1-en-yl)phenol. The distribution coefficient was 254, corresponding to a SIR capacity of 44 g/kg which was 4.5 times higher than the commercially available solvent 4-nonylphenol with a comparably low aqueous solubility of 9.3 ppm.

► Solvent screening for 4-cyanopyridine from an aqueous waste stream.
► COSMO-RS can qualitatively predict capacities and densities of solvents.
► The criteria of the solvent were based on both stability and capacity.
► The designed solvent had a capacity 4.5 times higher than the commercial solvent.