The use of gas membranes for VOC-air separations

industrial processes commonly emit organic components as dilute or concentr ated streams. Environmental regulations impose stringent emission standards , interest in membrane separation techniques has grown along with their acc eptance for vapour recovery. They compete with absorption, adsorption, cryo genics and incineration. In research carried out In collaboration with GKSS , Geesthacht, Germany, the separation of gases and vapours was experimental ly investigated for various thin film, composite membranes in a flat sheet configuration, with a dense elastomeric silicone film layer over a porous P EI or PVDF support. Available literature data were reviewed and assessed in cluding tbe models to describe mass transfer through the membranes. Experim ental results for pure substances and for binary mixtures were used to dete rmine the permeability as a function of temperature and to calculate the se lectivity toward N-2. The free-volume model [1] approach was used to predic t the permeabilities of hydrocarbons. The necessary surface area of the mem brane separation module was determined for a given flow rate, concentration , operating temperature and pressure and from the characteristic selectivit y of the membrane. The design is illustrated by the separation of butane fr om an air waste stream produced by polyethylene foaming and for the CH4-enr ichment of a landfill biogas. A sensitivity analysis towards operating para meters illustrated the predicted effects. Finally, current industrial appli cations ave briefly reviewed, e.g. enriching landfill gas, recovery of VC-m onomer from PVC-process off gas, etc.