Power plant emissions of flue gas releases considerable CO2 to the atmosphere; CO2 is considered to be the main contributor to global warming. Several gas absorption techniques are being investigated to reduce the capital and operating costs for CO2 capture from post-combustion flue gas. Conventional method of CO2 capture by an aqueous solution of monoethanolamine (MEA) and its subsequent stripping in a separate tower with steam at 120°C, is a highly energy intensive process. The low partial pressure of CO2 in the flue gas inhibits the application of CO2-selective membranes unless methods are employed to increase the CO2 partial pressure in the flue gas to be treated. A novel technique to potentially bypass the shortcomings of many existing approaches is described.
A bench-scale CO2 capture and recovery from simulated flue gas is demonstrated using an advanced polypropylene hollow fiber membrane contactor. This is achieved by the use of a novel non-volatile absorbent, consisting of the ionic liquid [bmim] [DCA] containing 20 wt % polyamidoamine PAMAM dendrimer Gen 0. A simulated humidified flue gas containing around 14% CO2 is used and successful removal of bulk of the CO2 and its recovery in a CO2-concentrated stream up to 92% is demonstrated. An estimate of the overall volumetric mass transfer coefficient, Kla for the current CO2-IL-PAMAM Gen 0 system was obtained.
Apart from the capture of CO2 by an absorption-stripping process in a liquid flowing absorbent, a lot of research involves capture of the anthropogenic CO2 by the use of solid adsorbents. Solid amine adsorption renders higher adsorption capacities via fast CO2 reaction with amines. Impregnations of solids, direct condensation of the organic amines onto large surface area porous solids are few of the approaches being practiced to capture the CO2 via adsorption. Regeneration of Ca(OH)2 , Na(OH) based adsorbents are highly energy intensive. Some of the other physical adsorbents in practice, zeol ites, mesoporous silica, activated carbons are known to require high temperatures for effective desorption of CO2. It is reported that these physical adsorbents have relatively low selectivity towards CO2.
The novel absorbent of a mixture of 80 wt % polyamidoamine dendrimer Gen 0 (PAMAM) and 20 wt % ionic liquid [bmim][DCA] is chosen for the absorption study. Equilibrium CO2 sorption uptake and temperature swing absorption (TSAB) of this nonvolatile organic CO2-reactive liquid amine absorbent is reported in the present study. A mixture of 80% PAMAM in [bmim] [DCA] is highly viscous at room temperature and acts like a superefficient adsorbent by capturing CO2 via fast reaction CO2 reaction with amines. The equilibrium sorption uptake of this absorbent is studied in a pressure decay dual transducer apparatus for different weights and different temperatures of the absorbent. For the study of the TSA B process, a two- hollow fiber system is designed with porous PVDF and solid nonporous PEEK hollow fibers. A highly porous hydrophobic polymeric hollow fiber membrane absorbent-based device will have on the shell side the nonvolatile organic CO2-reactive liquid amine, 80 wt. % PAMAM - IL, which will absorb CO2 for a brief period from flue gas flowing through the bore of many hydrophobic hollow fibers whose thin walls have a high porosity. Temperature-swing desorption of the absorbed CO2 gas is done to regenerate the 80 wt. % PA MA M - IL absorbent. Hot water is passed through the bore of the solid PEEK hollow fibers of the two fiber system in order to desorb the sorbent of the absorbed CO2 gas. Regeneration of the absorbent is studied at different temperatures and reported as a part of the present study.
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