Recovery of valuable hydrocarbons from various liquid mixtures is an important objective of chemical and petrochemical industries especially from environmental point of view.
Several energy consuming processes, like azeotropic distillation, extractive distillation and solvent extraction have been used for many years to these purposes. Aromatic/aliphatic hydrocarbon mixtures are categorized as a major branch of organic/organic mixtures. Aromatics are valuable intermediates in chemical industries. There are common aromatic/aliphatic mixtures that can be separated by suitable processes such as benzene/cyclohexane, benzene/iso-octane, toluene/iso-octane and benzene/n-hexane.
In the recent years, separation of organic/organic mixtures using membrane separation technologies has been investigated extensively, and pervaporation (PV) is now considered as a basic unit operation for separation of these mixtures. In this technique, separation is achieved by preferential sorption and diffusion of one component through a dense membrane under reduced pressure due to the chemical potential difference across the membrane.
In the pervaporation process, the separation performance is mostly affected by chemical properties of the membrane material as well as its interaction with the permeating species.
In this work, separation of toluene/n-heptane mixtures via pervaporation using a composite membrane was investigated.
The application of the “pore-filling” concept yielded aromatic hydrocarbon selective composite membranes.
An asymmetric poly(acrylonitrile) ultrafiltration membrane with an average pore size of about 9 nm had been used as support in the “pore-filling” method for the preparation of pervaporation membrane using heterogeneous photo-initiated graft copolymerization in water.
Effects of operating conditions such as feed temperature, feed composition and downstream pressure on the membrane performance were studied. Experimental results were obtained at different feed compositions (10– 30 wt %), operating temperatures (25 – 85 °C) and downstream pressures (2–32 mbar g).
It was found that the membrane was more selective for benzene rather than cyclohexane. According to the results, it was observed that increasing benzene feed concentration and operating temperature enhance the membrane swelling and increase the polymeric chain mobility. Therefore, feed concentration and temperature have the same effects on benzene selectivity and permeation flux of the membrane. An increase in feed concentration and temperature increased permeate flux while decreased selectivity. On the other hand, decreasing downstream pressure enhanced membrane performance.
The maximum selectivity was obtained at experiment with a feed with 10 wt.% of benzene, at temperature of 85 °C and a downstream pressure of 2 mbar g (more than 140). The related permeate flux was 22.92 kg/m2.h.
See more of this Group/Topical: Topical 8: Kister Distillation Symposium