Recovering High-purity Furfural From Dilute Aqueous Solutions By Pervaporation Fractional Condensation And Molecular Dynamics Simulation On Sorption-diffusion Behaviors

Separation and purification is one of the most important steps in the process of furfural production. However, separating furfural from the hydrolysate by the conventional methods is energy-intensive and environmentally unfriendly. Recently, pervaporation has attracted attention as a new energy-efficient and environmentally friendly technique. In order to separate and recover furfural more efficiently, the process of pervaporation has been optimized by coupling with the fractional condensation system. Because of that the molecular simulation techniques can provide an in-depth understanding of membrane structure, enabling pervaporation performance analyses at the molecular scale. Therefore, we adopted it to investigate the separation mechanism of our pervaporation experiments.We used the PBEA-2533 membrane which owns excellent sorption selectivity to furfural, revealed by the sorption study, to investigate the effects of membrane thickness, feed concentration and temperature on pervaporation performance respectively. Judging from the permeation activation energy Ep, that sorption step was dominant in the pervaporation process. The pervaporation experiment results showed that the membrane thickness influence the flux of water more than furfural. An increase in temperature increased the permeation flux while decreased the separation factor, and the temperature dependency of the permeation flux followed an Arrhenius type of relationship. The PEBA-2533 membrane owned an excellent pervaporation performance, e.g. both high total flux and high permeate furfural concentration with a satisfactory pervaporation separation factor. PVFC system which can be well simulated by Aspen ONE V7.1 software was perfectly integrated the excellent membrane performance and the fractional condensation operation. We acquired high-purity furfural directly in the first condenser of our PVFC system. The temperature in the first condenser had a significant effect on the distribution of the furfural permeated through the membrane in each condenser. Furfural with a high-purity of 99.98 wt% can be continuously recovered at a production rate of 711(g/m2?h) in the first condenser when its temperature was kept at-12oC, with a feed concentration of 6 wt% and temperature of 70oC(the membrane thickness was 100μm).We successfully used the Materials Studio 6.0 software to construct the PEBA-2533 polymer model. The simulatedglass transition temperature(Tg) and density were very close to the real value, which demonstrated that the PEBA-2533 constructed insimulation was adequate to represent the realistic PEBA-2533 membraneand the used COMPASS force field was suitable. Subsequently, a molecular dynamics technique was adopted to investigate the membrane free volume morphologiesand the sorption-diffusion behaviors of furfural and water molecules in PEBA-2533 membrane during the pervaporationprocess. The sorption simulation showed that the furfural molecules would migrate to the membrane surface prior to the migration of water, which suggested that the furfural molecules had a higher affinity to the membrane than did the water molecules. The fractional accessible volume(FAV), fractional cavity volume(FCV), and mean-squared displacement(MSD) were analyzed to understand the effect of the operational concentrations and temperatures on the membrane structure. A higher feed furfural concentration will enhance the chain mobility of PEBA-2533, causing a higher FAV. Furthermore, the FCV analysis result revealed that the cavity size became larger, which facilitated the molecular diffusion process. A higher feed temperature would enhance the polymeric chain mobility, however, the degree of membrane swelling decreased simultaneously. Hence, it resulted in a lower FAV values and narrower cavities in PEBA-2533 membrane. Despite of that, the increased temperature would enhance the molecular thermal motion, causing a higher diffusion rate. Therefore,the permeate flux still presented a increasing trend. All the simulation results provided more clear explanation and theoretical bases for our experimental phenomena.