Separation and Fixation of Carbon Dioxide Using Polymeric Membrane Contactor

Polypropylene hollow fiber membrane (PPHFM) contactor, with aqueous solution absorbent such as sodium hydroxide (NaOH), monoethanolamine (MEA) and diethanolamine (DEA), was designed and used to separate and fix CO2 from CO2/N2 gas mixtures. The factors that influence the separation properties of CO2/N2 were investigated. It was found that the CO2 removal efficiency is the best by using MEA solution as absorbent. The overall mass transfer coefficient (K) increases with the increase of liquid flow, gas flow and the concentration of the absorbent; however, it decreases with the carbon dioxide concentration in the gas mixture and the temperature of the absorbent solution. Preliminary results showed that carbon dioxide can be fixed efficiently into sodium carbonate and/or sodium bicarbonate with NaOH as the absorbent in the membrane contactor. Pure carbon dioxide, on the other hand, can be produced when MEA or DEA was used as the absorbent. INTRODUCTION Membrane separation of gases has emerged into an important unit operations technique offering specific advantages over more conventional separation procedures (e.g. cryogenic distillation and adsorption). One can envisage that these technologies will also make great contribution to the growth of new research area, such as carbon dioxide capture from flue gas. However, even through there are a large number of potential applications for gas separation with polymer membranes, only relatively few of them have become applied in practice. The potential application of a polymer as a separation membrane depends upon the possible throughput and the purity of product. This means that both the permeability coefficient for the gas that is transported more rapidly and the selectivity should be as large as possible. However, it was found that simple structural modifications, which lead to increases in polymer permeability usually, cause losses in permselectivity and vice versa. This so-called ′′trade-off′′ relationship is well described in the literature. It is thus possible to find polymers that exhibit high selectivity and low permeability and vice versa, in addition to that combine low selectivity with low permeability. There do not appear to be any polymers that show the desired trend to large values for both permeability and selectivity. Therefore, new membrane materials and technologies should be exploited to accommodate new applications, such as the simultaneous separation and capture of carbon dioxide from flue gas. TECHNOLOGY Membrane contactors are devices that achieve gas/liquid or liquid/liquid mass transfer without dispersed one phase within another. As schematically represented in Figure 1, they are accomplished by passing the fluid on opposite side of a microporous membrane or a composite membrane (e.g. microporous membrane coated with PDMS rubber). The porous membrane acts as a non-selective barrier between both phases. Separation is determined by the reaction of one component in the gas mixture with the absorbent in the liquid. Figure 1. Schematic rep This approach offers a numb contactor for gas sorption, such m), no flooding and foaming p low energy consumption and eas composite membranes, the main turn, low energy consumption), with absorbent variation. A sim listed in Table 1. P