Modelling of pervaporation : Models to analyze and predict the mass transport in pervaporation

The modelling of the ma ss transfer in pervaporation is one of the fundamental aspects to understand and therefore improve the process performance. This paper reviews the different models to analyse and predict the mass transport through the selective layer in pervaporation. It therefore provides an overview combined with some guidance about the different models proposed in the literature and the applicability range of these models. The different models reviewed cover the two key mass transport steps in pervaporation: (1) sorption into the membrane, and (2) diffusion through the membrane. For the two different steps individual models will be proposed as well as models covering the mass transport across the membrane as a whole. The different models will be grouped with respect to the nature of the models: theoretical, semi-empirical or empirical. Further the applicability range of the different models regarding the different polymer classes such as glassy, semi-crystalline, or rubbery will be shown. Finally, it will be commented on the applicability of the models with regard to two main research fields in pervaporation: development of membranes and design of processes and modules. Inorganic and composite-material membranes involve additional models to analyse and predict the mass transport and have been excluded from this review

Simulation and process design of pervaporation plate-and-frame modules to recover organic compounds from waste water

The opportunity of integrating pervaporation within the concept of waste water treatment to recover organic compounds has been widely recognized. Within this paper a process simulation is developed as a design tool to analyse and optimize the process of hydrophobic pervaporation. In the simulation the mass transfer through the membrane and concentration boundary layer are described using a resistance-in-series model. Furthermore, the permeate pressure gradient and the heat balance are integrated in a finite elements-in-succession method to simulate the overall process. The influence of different process and design parameters on the performance, such as permeate pressure, feed temperature, flow pattern on pervaporation are analysed for the recovery process of low concentrations of model substances, pyridine and phenol, from waste water. Based on the results, guidelines for the process design of hydrophobic pervaporation are given

Scale-up of pervaporation for the recovery of natural aroma compounds in the food industry. Part 1: simulation and performance

The possibility of using pervaporation for the recovery of natural aroma compounds in the food industry has been widely recognised. The aim of this study was to build a bridge between experimental studies of multi-component systems and potential applications of pervaporation in the food industry. Therefore, a novel process simulation of pervaporation has been developed for multi-component mixtures. By applying this simulation to 10 aroma compounds of relevance in the food industry, the influence of process parameters such as permeate pressure, feed temperature, degree of aroma folding and membrane area, on the performance of pervaporation has been investigated. Based on the results of the simulations, it has been demonstrated that process simulation can play an important role in integrating and optimising pervaporation in the food industry

Applications of membrane processes in the beet and cane sugar production

Despite their success in different segments of the food industry, membranes are not well-established in the beet and cane sugar industry. A comprehensive overview on the potential applications of membranes in both the beet and cane sugar industry is given. The part on the beet sugar industry focuses on pulp press water recycling, pectin production from beet pulp, beet juice purification, demineralization of beet sugar juice and thin juice concentration. Potiential opportunities of membranes in cane sugar/cane refining industry are raw cane juice purification, clarified cane juice concentration, raw syrup purification, molasses treatment and decolorization of remelted raw sugar. Further, the ion-exchange resin regeneration waste recycling, sweet water concentration and evaporator condensate polishing are discussed. Overall, this article emphasizes the successes and potentials of membrane technology in the sugar industry

Influence of impermeable components on the permeation of aqueous 1-propanol mixtures in hydrophobic pervaporation

Hydrophobic pervaporation is rarely considered in the biotech industry despite several potential advantages and some applications. This is related to fact that the majority of studies have been with binary feed systems, while real feed mixtures are often multi-component and might contain impermeable components, such as salts and sugars. In order to successfully optimise hydrophobic pervaporation, it is essential to understand the influence of impermeable components. Three impermeable components (NaCl, MgCl2, and glucose) were studied for their effect on the permeation of water and 1-propanol through two commercially available pervaporation membranes (Pervap 1060 and 1070). From the experiments, it was found that the addition of salts and sugars increase the selectivity of 1-propanol to water in the order MgCl2>NaCl>glucose. The results were compared with literature data on the addition of other components such as citric acid, acetic acid, glycerine and Na2SO4. Based on these results, two main mechanisms by which permeation is affected were identified: (1) change in activity coefficient due to third component, and (2) fouling and penetration of the membrane by impermeable components. The former factor tends to increase flux of the organic compared with a binary mixture whilst the latter acts to decrease flux. The overall conclusion is that impermeable components can influence the performance of pervaporation significantly

Scale-up of pervaporation for the recovery of natural aroma compounds in the food industry Part 2: optimisation and integration

In this study the integration and optimisation of hydrophobic pervaporation for the recovery of natural aroma compounds in the food industry has been studied. The simulation developed in the first part of this study was applied to the design and scale-up of pervaporation units for the recovery of natural apple juice aroma. Both semi-batch and continuous process configurations were considered and the process conditions were optimised taking the cost of the process into account. For the semi-batch process, the cost per kg concentrated aroma was between 31.30 and 33.60 euro, depending on the membrane type. When returning the recovered aroma to the apple juice after heat treatment, the cost of aroma recovery per kg concentrate was between 0.31 and 0.34 euro. In the case of the continuous process, the cost for the apple juice aroma recovery was between 2.19 and 5.38 euro, while the cost of aroma recovery per kg apple juice was between 0.03 and 0.05 euro. Upon analysing the optimised processes with a sensitivity analysis of the key cost factors associated with pervaporation, membrane life-time and membrane cost, it was revealed that the membrane life-time is more important than the membrane cost and that the continuous process is more sensitive to changes in membrane life-time and membrane cost. Overall, this study revealed that pervaporation has the potential to become an alternative to conventional processes in recovering and concentrating aroma compounds in the food industry