ABSTRACT
The basic principles of a steady-state mass transfer model and the resistance-in-series film model are assessed with the aid of a series of experiments in a gas-liquid contact membrane mini-module (3 M Liqui-Cel MM-1.7 × 5.5) using an aqueous solution of diethanolamine (DEA) of 0.25 M (mol/L) for biogas upgrading. Experimental data show that CO2 removal may exceed 67% and reach 100% in combination with the highest possible recovery of CH4 when employing biogas flow rates in the range of 2.8 × 10-5 - 3.6 × 10-5 m3/s and solvent flow rates within 0.47 × 10-5 - 0.58 × 10-5 m3/s. For the experimental data set, a correlation has been developed, effectively interpolating CO2 removal with the gas and liquid flow rates. The wetting values calculated are concentrated close to each other for the same liquid flow rate without considerably depending on the gas flow rate, especially when applying the Hikita-Yun (reaction rate-shell-side correlation) compared with the Hikita-Costello pair. Furthermore, the calculated wetting diminishes with increasing liquid flow rate, a result that is consistent with previous modeling attempts and relevant literature indications. The assumption of enhanced mass transfer in the liquid-filled part of the membrane pores due to the reaction is scrutinized, leading to objectionable computational wetting values. It is shown that for a concentration of DEA equal to 0.25 M the Hatta numbers and the enhancement factors are not equal in the whole reaction path; thus, the choice of the shell-side correlation has an appreciable impact on the overall analysis, especially for the determination of the wetting values.
ABSTRACT
Ceramic membranes have been considered as potential candidates for several gas separation processes of industrial interest, due to their increased thermal and chemical stability compared to polymeric ones. In the present study, commercial Hybrid Silica (HybSi®) membranes have been evaluated and modified accordingly, to enhance their gas separation performance for targeted applications, including CO2 removal from flue gas and H2 recovery from hydrogen-containing natural gas streams. The developed membranes have been characterized before and after modification by relative permeability, single gas permeation, and equimolar separation tests of the respective gas mixtures. The modification procedures, involving in situ chemical vapor deposition and superficial functionalization, aim for precise control of the membranes' pore size and surface chemistry. High performance membranes have been successfully developed, presenting an increase in H2/CH4 permselectivity from 12.8 to 45.6 at 250 °C. Ultimately, the modified HybSi® membrane exhibits a promising separation performance at 250 °C, and 5 bar feed pressure, obtaining above 92% H2 purity in the product stream combined with a notable H2 recovery of 65%, which can be further improved if a vacuum is applied on the permeate side, leading to 94.3% H2 purity and 69% H2 recovery.
ABSTRACT
Recently, metal oxides and magnesium hydroxide nanoparticles (NPs) with high surface-to-volume ratios were shown to possess antibacterial properties with applications in biomedicine and agriculture. To assess recent observations from field trials on tomatoes showing resistance to pathogen attacks, porous micron-scale particles composed of nano-grains of MgO were hydrated and sprayed on the leaves of healthy tomato (Solanum lycopersicum) plants in a 20-day program. The results showed that the spray induced (a) a modest and selective stress gene response that was consistent with the absence of phytotoxicity and the production of salicylic acid as a signalling response to pathogens; (b) a shift of the phylloplane microbiota from near 100% dominance by Gram (-) bacteria, leaving extremophiles and cyanobacteria to cover the void; and (c) a response of the fungal leaf phylloplane that showed that the leaf epiphytome was unchanged but the fungal load was reduced by about 70%. The direct microbiome changes together with the low level priming of the plant's immune system may explain the previously observed resistance to pathogen assaults in field tomato plants sprayed with the same hydrated porous micron-scale particles.
