Abstract
Novel hybrid process based on thermopervaporation (TPV) assisted by liquid-liquid phase separation in liquid permeate is proposed. The key component of the proposed process is a new concept of the TPV process with a porous condenser (TPV-PC). The TPV-PC approach makes it possible: i) to use the permeate as a coolant, ii) to solve the problem of the air-gap flooding and iii) to reduce the air-gap width below 1 mm. Limited miscibility of the water-butanol system leads to the phase separation of the permeate solution. Water-enriched phase from the decanter is used as the coolant in TPV-PC. The equilibrium vapor pressure remains constant value in the whole range of phase separation of butanol-water mixture providing the constant value of driving force of the TPV-PC.
The novel hybrid process was studied for separation of multicomponent model mixtures and the centrifuged real ABE fermentation broth. Four commercial pervaporation membranes were benchmarked and the MDK-3 membrane (Vladipor, Russia) was selected for further process investigation because of the highest pervaporation separation index. The effect of feed composition and temperature on the recovery and concentration of ABE components as well as membrane fouling was investigated. To mitigate the inhibiting effect of butanol and its concentration in the permeate above the phase separation point the proposed hybrid process should be performed at temperatures above 50 degrees C if the coolant/permeate temperature is 10 degrees C. For instance, at feed temperature of 60 degrees C, the degree of recovery of ABE components was nearly 80%, and concentration of butanol in the fermentation broth was decreases below 0.5 wt% from the initial value of 1.6 wt%. This hybrid process is expected to be also applied for other liquid mixtures treatment if and when liquid-liquid phase separation occurs in the permeate.