Hybrid membrane-distillation system

Benali, M. and Aydin, B. (2010) Ethane/ethylene and propane/propylene separation in hybrid membrane distillation systems Optimization and economic analysis. Separation and Purification Technology, 73 (3), 377-390. 

On the other hand, a pervaporation membrane can be coupled with a conventional distillation column, resulting in a hybrid membrane/distillation process (228,229). Some of the investigated applications of such hybrid pervaporation membrane/distillation systems are shown in Table 9. In hybrid pervaporation/ distillation systems, the membrane units can be installed on the overhead vapor of the distillation column, as shown in Figure 13a for the case of propylene/ propane splitting (234), or they can be installed on the feed to the distillation column,... 

Membrane from a 5% NA cellulose sulfate solution and 20% 0% solutions of cationic surfactants e.g., V-dodecylpyridinium chloride or hexadecylpridinium chloride Hybrid PV + distillation systems... 

In a comparative study of an integrated hybrid membrane-based system with an earlier locally designed RO unit, such system comprises NF, RO, and membrane distillation (MD) subsystems [79]. The comparison is essentially based on using the NF technique in pretreatment section, while the MD was contributed to concentrate the two brine streams from both NF and RO. Thus, high recovery rate of product water is aimed for. The proposed system was economically evaluated and compared with the RO unit. It was concluded that 76.2% water recovery was possible with a water production cost of 0.92 m . ... 

Mozia S, Morawski A W,Toyoda M and Tsnmura T (2009), Effect of process parameters on photodegradation of Add Yellow 36 in a hybrid photocatalysis-membrane distillation system , Chem Eng J, 150,152-159. 

For the model validation and the analysis of the heat integration in the hybrid pervaporation distillation process, a laboratory plant has been built at the TU -Berlin and prepared for the connection with the distillation column (see fig. 3). With this plant experiments with a flat PVA-based (Polyvinylalcohol from GKSS) hydrophilic membrane have been done. A heat exchanger has been built within the pervaporation module. The temperature in the heat exchanger has been necessary to avoid the temperature drop between feed and retentate streams in the pervaporation process. In the process a 2-Propanol/ Water mixture has been separated. The concentration of 2-Propanol in the feed is between 80 and 90 % in weight and the temperature range in the experiments was between 70 and 90°C. The feed flow is turbulent and the system fully insulated to avoid heat looses. The pressure in the permeate side has been kept at 30 mbar and the feed pressure at 1.5 bar. 

Caballero, J.A., Grossmann, I.E., Keyvani, M. and Lenz, E.S. (2009) Design of hybrid distillation-vapor membrane separation systems. Industrial Engineering Chemistry Research, 48 (20), 9151-9162. 

Tremendous opportunity exists for hybrid processes consisting solely of membrane processes or a combination of membrane and non-membrane processes. Of the large number of potential combinations, studies of several are reported in the literature including nanofiltration with reverse osmosis [99] nanofiltration with electrodialysis [100] ultrafiltration with nanofiltration and reverse osmosis [101] ultrafiltration with membrane distillation [102] nanofiltration with reverse osmosis and a microfiltration membrane-based sorbent [103] microfiltration with flotation [104] microfiltration and ultrafiltration with ozone and activated carbon adsorption [105] and membrane processes with photocatalysis [106-107]. Despite the activity in this area, a comprehensive approach to designing hybrid systems does not exist future work would benefit from the development of such a design framework. 

Unlike in the case of the PMRs utilizing pressure driven membrane techniques, no membrane fouhng due to the presence of TiOj particles was observed in case of the hybrid photocatalysis-MD system. It was reported (Mozia and Morawski, 2009) that after more than 340 h of operation with a suspension of IIO2 in distilled water, the flux was equal to the maximum permeate flux (i.e., measured for distilled water) and amounted to about 0.16,0.26 and 0.39 m /m. day for the inlet feed temperatures (F, ) of 50,60, and 70°C, respectively. The observed lack of the influence of 1102 on the permeate flux could be explained by the mechanism of mass transport in MD which is due to a difference between the vapor pressure on the two sides of the membrane. Since the process can be conducted without application of pressure difference as a driving force, the main factor responsible for membrane fouling is excluded. In the absence of higher pressure, unlike in the case of pressure driven techniques, cake formation on the membrane surface could be avoided. 

Thus, theoretically, membrane technology may be the best candidate to couple reaction and separation. In the hterature, it is possible to find some hybrid units coupling the reliability of the reactive distillation system with the pervaporative technology when an esterification reaction is mn (Riemenschneider Bolt, 2000 Buchaly et al., 2012 Bida, Gongping, Xueliang, Wang, Wanqin, 2012). This allows for a reduction of energy consumption and an enhancement of process quality compared with stand-alone reactive distillation. 

A membrane separation system may sometimes be coupled with another gas separation unit operation (such as adsorption, absorption or cryogenic distillation) to obtain an economically optimum hybrid process. 

Process Concepts. Hybrid systems involving gas-phase adsorption coupled with catalytic processes and with other separations processes (especially distillation and membrane systems) will be developed to take advantage of the unique features of each. The roles of adsorption systems will be to efficiently achieve very high degrees of purification to lower fouUng contaminant concentrations to very low levels in front of membrane and other separations processes or to provide unique separations of azeotropes, close-boiling isomers, and temperature-sensitive or reactive compounds. 

For the study of the process, a set of partial differential model equations for a flat sheet pervaporation membrane with an integrated heat exchanger (see fig.2) has been developed. The temperature dependence of the permeability coefficient is defined like an Arrhenius function [S. Sommer, 2003] and our new developed model of the pervaporation process is based on the model proposed by [Wijmans and Baker, 1993] (see equation 1). With this model the effect of the heat integration can be studied under different operating conditions and module geometry and material using a turbulent flow in the feed. The model has been developed in gPROMS and coupled with the model of the distillation column described by [J.-U Repke, 2006], for the study of the whole hybrid system pervaporation distillation. 

Many industrially important liquid systems are difficult or impossible to separate by simple continuous distillation because the phase behavior contains an azeotrope, a tangent pinch, or an overall low relative volatility. One solution is to combine distillation with one or more complementary separation technologies to form a hybrid. An example of such a combination is the dehydration of ethanol using a distillation-membrane hybrid, as shown in Figure 6.30. 

EXAMPLE DESIGN OE HYBRID SYSTEMS USING DISTILLATION MEMBRANE PROCESSES 315... 

---