Industrial & Engineering Chemistry Research, Vol.53, No.45, 17770-17781, 2014
Selective Extraction of Lactic Acid from Aqueous Media through a Hydrophobic H-Beta Zeolite/PVDF Mixed Matrix Membrane Contactor
2-Hydroxypropionic acid, commonly known as lactic acid (LA), is a valuable chemical widely used for the manufacture of green solvents such as ethyl lactate and biodegradable polymers such as poly(lactic acid) (PLA). LA is manufactured by fermentation molasses and whey. Isolation of LA from aqueous broths by conventional methods is energy intensive. Reactive extraction through membranes using specific reagents could prove to be a cost-effective alternative for LA recovery. This study focuses on reactive separation of LA using a novel indigenously developed hydrophobic H-beta zeolite/polyvinylidene fluoride (PVDF) mixed matrix membrane. Experiments were conducted using a stirred cell assembly consisting of two bell shaped glass pipe reducers containing aqueous LA separated by the membrane from an organic solution of tri-n-octylamine (TOA) carrier in alcoholic medium. Effects of experimental parameters such as the concentration of TOA in organic phase and zeolite loading on the rate of acid extraction were evaluated by increasing the TOA concentration from 206 to 620 mol/m(3) and the extent of zeolite loading from 1 to 25% (w/w) of (PVDF) polymer. SEM analysis was carried out to oversee zeolite distribution on the PVDF surface, whereas TGA was used to determine the maximum operating temperature. XRD study was done to investigate the influence of zeolite loading on intersegmental spacing in the polymer, while FT-IR helped in the identification of interactions between the inorganic filler and organic polymer. A mass transfer correlation was deduced by taking into account all possible reactions involved in formation of the complexes. An optimum extraction of nearly 34% was obtained using 25% zeolite loading, 206 mol/m(3) TOA in 1-octanol, and 100 mol/m3 acid concentration, at a stirring rate of 400 rpm over a processing time of 1 h. Continuous separation of LA by a membrane contactor could help improve the fermentation yield of the acid by preventing the inhibition of lactate dehydrogenase enzyme, which is affected by the product itself. Such reactive extractions by membrane contactors could be successfully scaled up using a hollow fiber modular configuration.