Large heat duty for amine regeneration in absorptionbased CO 2 capture is one of the major drawbacks of this process. Along with a highly endothermic carbamate breakdown reaction in the stripper, the difficulty of proton transfer from protonated amines to water in the amine regeneration process is also considered a basic reason for high heat duty. Transition metal oxide catalysts can play a vital role in decreasing the required thermal energy for amine regeneration in the stripper by providing Bronsted acids and Lewis acids that would help break down the carbamate by direct attack. MEA saturated with CO 2 at 35 °C, with initial loading of 0.56 mole CO 2 /mole amine, was used in this study. The performance of five different transition metal oxide catalysts, V 2 O 5 , MoO 3 , WO 3 , TiO 2 , and Cr 2 O 3 , was studied separately to investigate the effects of these catalysts on amine regeneration in the temperature range of 35−86 °C. It has been observed that MoO 3 performance is much better as it regenerated almost double of the MEA solvent than noncatalytic amine regeneration systems, whereas other catalysts also showed considerable differences in amine regeneration in this temperature range. The amine regeneration performance trend was MoO 3 > V 2 O 5 > Cr 2 O 3 > TiO 2 > WO 3 > blank test. The application of this work would mean that metal oxide catalysts could be used in strippers for a faster CO 2 desorption rate at lower temperature, which would cause a significant reduction of the heat duty.
A capnophilic rumen bacterium Mannheimia succiniciproducens produces succinic acid as a major fermentation end product under CO(2)-rich anaerobic condition. Since succinic acid is produced by carboxylation of C3 compounds during the fermentation, intracellular CO(2) availability is important for efficient succinic acid formation. Here, we investigated the metabolic responses of M. succiniciproducens to the different dissolved CO(2) concentrations (0-260 mM). Cell growth was severely suppressed when the dissolved CO(2) concentration was below 8.74 mM. On the other hand, cell growth and succinic acid production increased proportionally as the dissolved CO(2) concentration increased from 8.74 to 141 mM. The yields of biomass and succinic acid on glucose obtained at the dissolved CO(2) concentration of 141 mM were 1.49 and 1.52 times higher, respectively, than those obtained at the dissolved CO(2) concentration of 8.74 mM. It was also found that the additional CO(2) source provided in the form of NaHCO(3), MgCO(3), or CaCO(3) had positive effects on cell growth and succinic acid production. However, growth inhibition was observed when excessive bicarbonate salts were added. By the comparison of the activities of key enzymes, it was found that PEP carboxylation by PEP carboxykinase (PckA) is the most important for succinic acid production as well as the growth of M. succiniciproducens by providing additional ATP.
The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions.
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