Preparation of polyetherimide nanoparticles by electrospray drying, and their use in the preparation of mixed-matrix carbon molecular-sieve (CMS) membranes

The goal of the first part of the Thesis is to prepare carbon molecular-sieve (CMS) particles to be utilized in the preparation of mixed-matrix (MM) membranes. Thus an experimental investigation was carried out using electrospray of polyetherimide (UltemRTM-1000 PEI) solutions in dichloroethane to produce fairly monodisperse, fine PEI particles. The effect of three key experimental parameters was investigated, namely, the applied voltage, the liquid flow rate, and the polymer concentration. The liquid flow rate was found to have the most important effect in determining the particle size. An optimal range of flow rates often exists. Particles obtained within the optimal range of the flow rate have a narrower size distribution, and a dense and spherical morphology, compared with those produced with other liquid flow rates. The CMS particles, prepared ex-situ by the pyrolysis of the electrospray PEI particles, are compared in their properties with the CMS particles that were generated by conventional grinding of pyrolyzed PEI pellets. They were found to, generally, have similar structural properties.; In the second part of the Thesis, the technical feasibility of utilizing the MM-CMS membranes in the separation of H2 and CO2 from gas mixtures of relevance to power generation was studied. The MM membranes were fabricated by incorporating the CMS nanoparticles into a polymer matrix. The CMS nanoparticles were prepared by wet-grinding of pyrolyzed pellets of PEI. Flat-sheet MM polymer-base (MMP) membranes, and supported MM-CMS membranes were both prepared. For the MMP membranes, both the CO2 and CH 4 permeabilities increased with increasing the CMS content, while the CO2/CH4 selectivity remained either unchanged or was slightly reduced. This may be due to the poor adhesion between the polymer and the CMS nanoparticles. In the case of the MM-CMS membranes, the incorporation of the CMS nanoparticles greatly enhanced the permeability and selectivity. An ideal CO2/CH4 separation factor of 120 was obtained with a CO2 permeance around 9.0 x 10-8 mol/m 2.s.Pa for membranes with a CMS particle loadings of 10 wt.%. The corresponding H2 separation factor was 130 and with a H2 permeance of 9.7 x 10-8 mol/m2.s.Pa. Also investigated was the influence of the total solid fraction on the permeation properties of the MM-CMS and CMS membranes.