Pervaporation Disadvantages

Compared with the process of distillation, pervaporation has advantages, such as can be separated into each other with a similar molecular weight, can separate azeotropic solution, effective for small-scale separation, not require additives, pollution-free, takes little space (compact module), low investment costs, and requires less cooling water.

The pervaporation process is complicated and involves the transfer of mass and energy. In the process, the feed is in the liquid phase and the permeate obtained in the gas phase.

The mechanism of separation takes place based on the solubility and diffusion that occurs in three phases :

1. Selective absorption by the membrane on the feed side

2. Selective diffusion through the membrane

3. Desorption

Pervaporation already is one of the membrane separation process with interest by industry-related chemical industry (Wee, et al., 2008)

2.4.2. Separation by Pervaporation

Separation of ethanol-water mixture is done by using the membrane separation technique with pervaporation. Pervaporation is a membrane process which liquid mixture is contacted directly on the side (upstream) of the membrane and the product obtained in the vapor phase on the permeate side (downstream) very low pressure (vacuum). The low vapor pressure at the permeate side can be achieved with a vacuum pump or by utilizing gas (carrier gas). Pervaporation process scheme is shown in Figure 2.5. Figure 2.5. Schematic pervaporation (a) the vacuum pressure on the side Downstream and (b) with an inert carrier gas

In pervaporation, penetrant interact with membrane in the entry phase to membrane surface penetrant (sorption). Swelling of the membrane volume will affect the amount of permeate flux. Swelling relatively low and the result is decreased in permeates flux; a relatively large swelling on the contrary will result in separation selectivity

Influential Factors on Pervaporation There are several factors that influence the pervaporation. Factors that influence the pervaporation include pressure, time, operating temperature and feed concentration.

2.6.1. Operating Pressure

Driving force in pervaporation is different of pressure. Permeate pressure has always attempted as small as possible (near vacuum) in order to generate a maximum permeation rate. Vacuum pressure is obtained by adjusting the vacuum pump such that the obtained pressure is much smaller than the vapor pressure of each component. Increased pressure on the bottom side of the membrane in pervaporation can reduce the separation factor.

2.6.2. Operating Temperature

The higher temperature, the flux will also increase. In addition, the higher temperature, vapor pressure penetrant will also increase, so that activity in upstream side is greater and it will cause a flux increases.

2.6.3 Concentration Feed

Various in feed composition directly affect the sorption phenomena in liquid-membrane interface. Penetrant mass transfer characteristics of the membrane are very dependent on the concentration of the feed for the diffusion in the membrane. The higher concentration of penetrant which interacts with the