Innovative Ceramic Membranes for Sweeping Gas Membrane Distillation: Membrane Characterization and Process Development

The employment of tubular hydrophobic carbon-based titania membranes in sweeping gas membrane distillation (SGMD) was studied in this PhD thesis. The characterization of some of the membrane morphological properties was implemented by experimental and modeled results of gas permeation tests. The dusty gas model was adopted in gas permeation modeling. Two different approaches were followed during modeling. The first approach considered the morphological properties of each single membrane layer. As for the second approach, average membrane morphological properties were characterized without considering the unique contribution of each layer. The investigation of the module performance during SGMD operations was achieved by experimental and modeling studies for NaCl (aq.). The model considered the Knudsen and molecular diffusion mechanisms. The module was capable of undergoing experiments at temperatures up to 110°C. Experimental flux results went in agreement with the modeled values obtained on using the morphological properties of each membrane layer. On the contrary, the modeled values obtained on considering average membrane morphological properties deviated significantly from the experimental results. The model was also used to estimate the effect of the operating conditions and flow configuration on water flux. Other modeling studies of the modules were performed for ethanol (aq.) to predict the effect of the operating conditions on the membrane selectivity. The Maxwell-Stefan approach was followed in this case. Eventually, a hypothetical sweater desalination process was proposed incorporating SGMD (using the modules studied in this thesis) as the desalination unit. Process development and optimization were carried out. The optimized case corresponded to SGMD liquid inlet temperature of 107°C for an SGMD vessel having a length of 5.4 m. This corresponded to a water production cost of 20.9 $/m3 such that the feed heating was the determinant cost item. This cost could be mitigated in case of using a waste heat source.