Development of integrated separation processes with green solvents

Abstract

This thesis explores the fractionation of mixtures with unconventional solvents, like supercritical carbon dioxide (scCO2) and room temperature ionic liquids (RTILs), and develops new integrated processes which couple these solvents with membranes. It was explored the feasibility of using reverse osmosis membranes for fractionations in scCO2 with a model mixture of oleic acid and squalene, and it was found that all membranes tested were selective towards oleic acid. The effect of coupling the membrane to a supercritical fluid extraction (SFE) process was also tested, achieving a combined enrichment in squalene of 1.6 times. RTILs were used to fractionate the model mixture oleic acid and squalene. By appropriately choosing the anion and cation of the RTIL it was possible to model the fractionation. With [EMIM][MDEGSO4] a selectivity towards oleic acid of 2.96 was achieved, and with [BMIM][NTF2] the selectivity was 0.86. An indirect method of probing the polarities of RTILs is developed using common organic solvents and Reichardt’s dye and a polarity scale is built. It was found that the most polar RTILs have lower selectivities towards oleic acid. Supported ionic liquid membranes were developed and applied in the fractionation of model mixtures. These membranes had negligible selectivities for fractionating the model mixture of oleic acid and squalene, but presented good results when fractionating the products and reactants of a transesterification reaction, retaining completely glycerol and producing a permeate with 0.85 mass fraction of methyl esters. A new type of gel membranes was developed, using gelatine as a support polymer for RTILs. Although these membranes were not able to fractionate the model mixture of oleic acid and squalene, they were able to achieve a separation factor of methyl esters in detriment of glycerol of 166. These membranes were also tested for the separation of gases, but the selectivities obtained were very low.