Abstract
Biodegradable polymers have attracted much attention from an environmental point of view. Optically pure lactic acid that can be prepared by fermentation is one of the important raw materials for biodegradable polymer. The separation and purification of lactic acid from the fermentation broth are the major portions of the production costs. We proposed the application of supported ionic liquid membranes to recovering lactic acid. In this paper, the effect of ionic liquids, such as Aliquat 336, CYPHOS IL-101, CYPHOS IL-102, CYPHOS IL-104, CYPHOS IL-109 and CYPHOS IL-111 on the lactic acid permeation have been studied. Aliquat 336, CYPHOS IL-101 and CYPHOS IL-102 were found to be the best membrane solvents as far as membrane stability and permeation of lactic acid are concerned. CYPHOS IL-109 and CYPHOS IL-111 were found to be unsuitable, as they leak out from the pores of the supported liquid membrane (SLM), thereby allowing free transport of lactic acid as well as hydrochloric acid. CYPHOS IL-102 was found to be the most adequate (Permeation rate = 60.41%) among these ionic liquids as far as the separation of lactic acid is concerned. The permeation mechanisms, by which ionic liquid-water complexes act as the carrier of lactate and hydrochloric acid, were proposed. The experimental permeation results have been obtained as opposed to the expected values from the solution-diffusion mechanism.
Highlights
In supported liquid membrane (SLM), usually an organic liquid is embedded in small pores of a polymer support and is kept there by capillary forces
Ionic liquids (ILs)-101 and CYPHOS IL-102 show hardly any loss of ionic liquid from the membrane pores over a period of 24 h. This is in agreement with the established fact that ionic liquids are not displaced from the pores under a cross-membrane pressure difference as they are immobilized by large van der
CYPHOS IL-104-based SLM showed a slight decrease in membrane weight and white streaks appeared on the membrane at the end of 24 h
Summary
In supported liquid membrane (SLM), usually an organic liquid is embedded in small pores of a polymer support and is kept there by capillary forces. SLMs have been widely studied for the separation and concentration of a variety of compounds and present many potential advantages over other separation methods, there have been very few large scale applications of SLM due to insufficient membrane stability. This problem can be due to the loss of the carrier and/or solvent from the membrane, which has an influence on both flux and selectivity [2]. If the organic liquid for the SLM can be chosen such that it remains stable within the capillaries of the porous support, it can be used much more effectively
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