Frank Lipnizki

Pervaporation-based hybrid process : A review of process design, applications and economics

Abstract Pervaporation is one of the developing membrane technologies that can be used for various industrial applications but for a predefined task, the optimal process design is unlikely to consist solely of pervaporation. Often the optimised solution becomes a hybrid process combining pervaporation with one or more other separation technologies. A distinction will be made between hybrid and integrated processes. Hybrid processes are important and consequently need to be considered in process design. This paper focuses on pervaporation–based hybrid processes that have been realised on an industrial scale. Both present and future prospects of applying these process combinations will be reviewed. The emphasis of this paper is, therefore, on pervaporation combined with distillation and with chemical reactors. The economic potential of these hybrid processes is evaluated, for various applications, by cost comparisons between the pervaporation-based hybrid processes and alternative separation processes. Pervaporation-based processes for waste water treatment and biotechnology applications involve other types of pervaporation based hybrid processes and have been excluded from this review.

Organophilic pervaporation: prospects and performance

Among the different membrane processes, organophilic pervaporation is one of the most promising technologies for environmental applications. The aim of this paper is to give a thorough introduction to organophilic pervaporation in the context of wastewater treatment. The emerging process of organophilic pervaporation is introduced together with other membrane processes relevant for environmental applications. With regard to the performance of pervaporation, an engineering model is presented which will enable ready assessment of process and module design. Sorption and coupled diffusion are covered in the model. Selection criteria for membranes and transport resistances for the mass transport as key process engineering parameters are included. The influences of permeate pressure and temperature upon performance are discussed and a description of commercial pervaporation modules given. Following a brief description of the hierarchy of waste management practice, guidelines for applying and integrating pervaporation into a process are proposed. The importance of considering hybrid processes is highlighted. A case study for phenol recovery with water treatment to 5 ppm is considered. Finally, present restrictions on the use of pervaporation in wastewater treatment such as (a) the unavailability of appropriate membranes and (b) fouling of the membrane are discussed and approaches to overcome the restrictions are presented.

Mass transfer performance for hollow fibre modules with shell-side axial feed flow : using an engineering approach to develop a framework

For several membrane separation processes, hollow fibre modules are either an already established or a promising type of module. Based on the analogy between mass and heat transfer, an engineering approach is proposed to estimate the shell-side mass transfer coefficient for axial flow in hollow fibre modules with due allowance for the void fraction. The approach enables one to take the entrance effects of the hydrodynamic and concentration profile into account. The trends obtained by this generalised approach are similar to those of empirical correlations found in the literature over a wide range of Reynolds numbers and module packing densities. The empirical correlations differ significantly one from the other. The differences between the mass transfer coefficients obtained by the empirical correlations compared to those obtained following the approach proposed in this study are discussed. The different effects influencing mass transfer in hollow fibre modules are identified and discussed as a function of void fraction. Further, an approach to reflect the influence of maldistribution on mass transfer performance is provided.

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.

Use of Pervaporation‐Bioreactor Hybrid Processes in Biotechnology

Pervaporation is a membrane separation process with considerable innovative possibilities in the area of biotechnology. Above all, the combination of bioreactor and pervaporation has potential in the longer term as an alternative to conventional batch processes. This article considers the state of the art pervaporation-bioreactor hybrid processes. The possible applications of such hybrid processes are discussed and compared with conventional processes. It becomes apparent that the use of pervaporation-bioreactor hybrid processes can avoid product inhibition and greatly enhance the productivity of biotechnological processes.

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.

Concepts of industrial-scale diafiltration systems

The use of diafiltration is now the state-of-the-art in the food and beverage, biotech and pharmaceutical industry. In this paper, the advantages and disadvantages of the most common process modes of diafiltration, batch and continuous, are discussed. Further, the new concept of counter-current diafiltration, which leads to a significant reduction of diafiltration liquid consumption, is introduced. The three concepts are compared in a case study of a plant to concentrate a protein solution. In this study, the process layouts are based on a DSS GR 61 membrane (MWCO of 20,000 Dalton and 100% protein rejection) and a DSS plate-and-frame module. Each continuous diafiltration processes consist of 3 pre-filtration steps followed by 2 to 10 diafiltration steps. The different process layouts are optimized and compared considering technical and economical aspects. It is revealed that all three concepts show similar separation performance. However, taking a 4-stage diafiltration process, the continuous diafiltration requires 40% smaller membrane area compared to counter-current diafiltration, but 140% more diafiltration liquid. Further, comparing batch and counter-current diafiltration, the membrane area for counter-current diafiltration is 115% larger, while the diafiltration liquid requirement of batch process is 74% higher. The trends are also reflected in the higher investment cost and membrane area related operating costs of the counter-current diafiltration process but might be balanced by reduced costs for pre-treatment of the diafiltration liquid and concentration/post-treatment of the permeate. Furthermore, the study demonstrates that addition of fresh diafiltration liquid increases the diafiltration liquid consumption but directly reduces investment and membrane area related operating costs. It can be therefore concluded that counter-current diafiltration is a novel approach to develop case-specific optimized diafiltration processes.

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

Abstract 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 , 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 . In the case of the continuous process, the cost for the apple juice aroma recovery was between 2.19 and 5.38 , while the cost of aroma recovery per kg apple juice was between 0.03 and 0.05 . 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.

Hydrophobic pervaporation: Influence of the support layer of composite membranes on the mass transfer

The opportunities of using hydrophobic pervaporation to concentrate organic components in aroma recovery and waste-water treatment have been recognized widely. The focus of this article is on the influence of the support layer on the mass transfer in hydrophobic pervaporation. Even though the influence of the support layer on the overall mass transfer has been observed experimentally, the modeling and analysis of this aspect has been widely neglected. The aim of this study is to build a bridge between modeling of the influence of the support layer and experimental data. Therefore, an improved modeling approach is proposed and used to analyze experimental data for the permeation of the two binary systems water–phenol and water–chloroform through hydrophobic composite polydimetylsiloxane membranes. Comparing the experimental results with the model, it has been observed that the mass transfer of the support layer depends on both physical and chemical properties of the support layer. On the basis of these observations, guidelines for the selection of support layers will be presented.

PERVAPORATION-BASED HYBRID PROCESSES IN TREATING PHENOLIC WASTEWATER: TECHNICAL ASPECTS AND COST ENGINEERING

In this study, the feasibility of combining pervaporation with adsorption in a hybrid process to recover phenol from wastewater is analyzed with the technical aspects and the cost of the processes taken into account. The pervaporation unit in the hybrid process is combined with a decanter on the permeate side and an adsorption unit on the retentate side. Two modes of regeneration, steam and heat, are considered for the adsorption unit. Through comparisons of the stand-alone units with the hybrid processes, we found that hybrid processes were feasible economic alternatives. In addition to meeting the environmental standard, the hybrid processes also recovered over 98% of the phenol at a concentration of 76% (wt). Even though the cost data showed that the use of heat regeneration for the adsorption unit is the cheaper option, the integration of steam regeneration improves the phenol recovery rate to over 99%. A sensitivity analysis of the economic boundaries of the hybrid processes revealed that the membrane life cycle and not the membrane cost is the key cost parameter in the hybrid processes. The advantages of the hybrid process are further increased when the processes are scaled up. Overall, this study demonstrates that pervaporation-based hybrid processes that combine pervaporation, adsorption, and a decanter could be used effectively to recover phenol from industrial waste streams.