K. Briceño

Carbon-based membranes for membrane reactors

Abstract: Membrane reactor research has been focused on new membrane materials to be integrated in a compact configuration. Carbon membranes have scarcely been explored in the past because of mechanical drawbacks. For this reason, it is recommended that carbon membranes are supported. However, this can cause the formation of defects which are disadvantageous in membrane reactor (MR) applications. This chapter explores the main variables to be considered in the development of carbon membranes, mainly focusing on when the carbon material has to be supported. Some applications are revised for macro and micro reactors.

Characterization of Metal-Doped Methylated Microporous Silica for Molecular Separations

Novel silica xerogels are prepared and developed by sol-gel method in the present study. The preparation involves cobalt-doping within the organic templated silica matrices, where methyltriethoxysilane (MTES), which contains methyl groups as a covalently bonded organic template is used. The synthesis and surface properties of cobalt-doped methylated microporous silica xerogels with different MTES and cobalt content are revealed by surface and microstructural techniques, such as TGA, FTIR, X-ray and N2 adsorption measurements. The doping process enhances the thermal stability of the silica xerogels up to ~ 560 °C in oxidizing atmosphere. Besides, this process has no significant effect on the incorporation of the organic template within the silica matrix. As result of the promoted densification of the xerogels either by increasing MTES content and heat treatment, there is structural change of the silica xerogels such as decreasing the micropore volume and broadening of the pore size distribution. Heat treatment and increasing the cobalt oxide content from 5 to 10% weight ratio resulted in samples with approximately the same structural parameters. This suggests that the cobalt particles are homogeneously dispersed in the silica matrix. The novel silica xerogels exhibit trend toward micropores formation suggesting that these doped silica xerogels can be precursor materials for molecular sieve silica membranes applications. Two silica membranes, hydrophobic and cobalt-doped hydrophobic, are prepared and their performance is examined by the study of transport of He, H2 and N2. Preliminary results show that the microporous structure obtained in the unsupported cobalt-doped hydrophobic material are preserved after coating inside the tubular support.

Characterization of Carbon Molecular Sieve Membranes Supported on Ceramic Tubes

Carbon molecular sieve membranes have been analyzed in supported and unsupported configurations in this experimental study. The membranes were used to adsorb CO2, N2 and CH4, and their adsorption data were analyzed to establish differences in rate and capacity of adsorption between the two types of samples (supported and unsupported). Experimental results show an important effect of the support, which can be considered as an additional parameter to tailor pore size on these carbon membranes. Immersion calorimetry values were measured by immersing the membranes into liquids of different molecular dimensions (dichloromethane, benzene, n-hexane, 2,2-dimethylbutane). Similarities were found between adsorption and calorimetric analysis. The pore volume of the samples analyzed ranged from 0.016 to 0.263 cm3/g. The effect of the pyrolysis temperature, either 550 or 700 °C, under N2 atmosphere was also analyzed. Quantification of the pore-size distribution of the support was done by liquid–liquid displacement porosimetry. The composite membrane was used for CO2/CH4 separation before and after pore plugging was done. The ideal selectivity factors value (4.47) was over the Knudsen theoretical factor (0.60) for membrane pyrolyzed at 600 °C, which indicates the potential application of these membranes for the separation of low-molecular weight gases.