Abstract
Solvent resistant nanofiltration (SRNF) is an energy-efficient separation process suitable for many branches of industry, ranging from petro-chemistry [1] to pharmaceutics [2-6], and it is capable of effective separation of molecules in the range of 200-1000 g mol(-1) in various organic solvents. Most of the SRNF membranes are either asymmetric integrally skinned [7] or composites comprising of a thin separating layer on a suitable support [8-15]. In order to improve chemical resistance to organic solvents, often crosslinking is applied [16]. In the majority of industrial processes, commercial polymeric membranes in a spiral wound form (e.g. SolSep NF 030306; MET Starmem (TM)) are used almost exclusively.
The state-of-the art PI membranes are crosslinked by diamines in an imide-ring opening reaction [17] either during phase separation [16] or in post casting process [18]. The covalent bond created there is not thermally stable and at temperatures above 100 degrees C re-imidization might occur leading to loss of membrane stability [18, 19]. It is beneficial to crosslink the PEI membranes in such a way that the resulting membranes can be applied for separation processes at elevated temperature.
It is well known that a membrane in hollow fibre (HF) or capillary form has some advantages over membranes in a flat sheet configuration. A HF membrane provides a high surface to volume ratio, does not require spacers and thus enables the design of more compact and much simpler modules. Despite this, HF membranes for SRNF are not commercially available and literature reports very little on this [20].
In this work, we describe preparation and characterization of new membranes for organic solvent filtration. The membranes are prepared by either crosslinking of commercial polyamideimide membranes using di-isocyanates or spinning integrally skinned polyimide HF. All membranes are systematically investigated including permeation experiments (permeance/molecular weight cut off (MWCO) with polystyrene (PS) oligomer solutions [21]) and study of morphology using scanning electron microscopy (SEM).