Vapor permeation is a membrane process for separating vapor/gas mixture. The application is classified into three categories as follows;

• Recovery of monomer from polymerization
• Recovery of petroleum vapor from storage tank
• Recovery of organic vapor from vent stream

In petroleum and chemical industries, vent stream discharged into environment contains a considerable amount of valuable VOCs losing valuable materials. Also the discharged VOCs can cause to climate change as well as a threat to public health. Therefore the VOCs must be recovered from the view points of the economical and environmental aspects. Vapor permeation is very efficient to do the duty, in compared with existing processes for treatment of VOCs/gas mixture.

Vapor Permeation Membranes

In vapor permeation, composite membranes which have a fabric structure of reinforcement, a porous layer and an active layer on the top of membrane are used. As a rule of thumb discussed in previous chapter, an active organophilic separating layer is employed for preferentially permeating the organic component. Usually, rubbery materials show a good selectivity as well as high permeability, especially, PDMS (polydimethylsiloxane) and PEBA (poly ether-block-amide). A number of organic solvents are prone to attack polymeric materials. Therefore, the support layer as well as the active layer must be chosen to have stability against VOCs to be separated.

Vapor Permeation Process Features

tailored non-porous membranes which selectively absorb and permeate a specific component, i.e. VOCs.

employing porous support stable against VOCs selectively permeating

driving force from vacuum applied to back side of the membranes, allowing almost complete removal of the permeating component

simple process and equipment: compact and easily scalable

feed can be vapor/gas mixture or saturated vapor/vapor(VOC/water) mixture

no phase change taking place in permeation - low energy consumption compared with pervaporation process in which the permeate undergoes phase change from liquid to vapor

consuming low energy for condensing the permeate discharged from vacuum pump.