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/m3 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/m3 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.
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