Gas separation hollow fiber membranes: Processing conditions for manipulating morphology and performance

Currently, membrane unit operations are widely applied at industrial level, replacing conventional separation systems. Membrane gas separation represents a successful case, with an increasing number of installed plants in chemical processes, petrochemical plants and refineries for the production of nitrogen from air, the hydrogen separation and recovery and the carbon dioxide separation from natural gas. Owing to the low space footprint and low energy consumption, membrane separation is an environmental friendly technique that meets the Process Intensification requirements. The present study concentrates on the hollow fiber (HF) configuration that is the most used in applications of industrial interest. HF modules, having a high membrane packing density, are compact devices with thousands of square meters of membrane area per unit of volume. The required membranes have an asymmetric structure, in which a thin dense layer performs the separation and a porous substructure provides the needed mechanical resistance. The manipulation of the HFs morphology, according to a dry-wet spinning process in a pilot plant apparatus, investigating the effect of the operating conditions adopted for the spinning on the membrane performance and microstructure, is experimentally examined. Commercially available glassy polymers are used to make a comparison of a conventional double orifice spinneret with a triple orifice spinneret. The prepared HF batches are characterized by means of a morphological characterization (SEM analysis) and gas permeation rate measurements.