Speciation studies in aqueous monoethanolamine (MEA) solution at different CO 2 loadings have been conducted via nuclear magnetic resonance (NMR) spectroscopy. The results showed that the diagnostic peaks corresponding to the MEA and the protonated amine (MEAH + ) observed by 1 H NMR spectroscopy were gradually shifted downfield, whereas the corresponding 13 C peaks were shifted upfield as the CO 2 loading increased. Quantitatively, the molar fraction of the carbamate was obtained by integration of the relevant peak areas in the 1 H NMR spectra while the molar fractions of free MEA and MEAH + were determined according to the MEAH + dissociation constant and pH value of the solution. Furthermore, as the CO 2 loading increased, the fraction of free MEA dropped steadily, while the ratio of carbamate and MEAH + increased monotonically. The molar ratio of the carbamate reached its maximum at a CO 2 molar loading of 0.5. The data obtained from this study have led us to propose a modification to the current vapor-liquid equilibrium (VLE) model for this system.

The mass transfer performance of the absorption of CO2 in an aqueous solution of a new amino alcohol, 4-diethylamino-2-butanol (DEAB), which has been developed as an effective postcombustion CO2 capture solvent, was investigated and compared with the performance of CO2 absorption in a conventional amine, MEA. The absorption experiments were conducted in an absorption column containing structured packing, whereas the absorption performance was evaluated in terms of the overall mass transfer coefficient, K G a v. In particular, the effects of parameters such as inert gas flow rate, liquid flow rate, and solution concentration were compared for both DEAB and MEA. The results show that K G a v increases as both the liquid flow rate and concentration of solution increase whereas inert gas flow rate has little or no effect on K G a v. An empirical correlation for the mass transfer coefficient for the CO2-DEAB system has been developed as a function of the process parameters. In terms of comparison, the results show that the mass transfer performance of MEA was greater than that of DEAB. However, with the extremely high solubility and ease of regeneration of DEAB based on our previous study, it may be extremely beneficial to formulate an absorption solvent involving both MEA and DEAB in order to take advantage of the synergy effects of high solubility, ease of regeneration as well as the high mass transfer performance of the mixture.

No abstract

Summary• Sporopollenin is the main constituent of the exine layer of spore and pollen walls. Recently, several Arabidopsis genes, including polyketide synthase A (PKSA), which encodes an anther-specific chalcone synthase-like enzyme (ASCL), have been shown to be involved in sporopollenin biosynthesis. The genome of the moss Physcomitrella patens contains putative orthologs of the Arabidopsis sporopollenin biosynthesis genes.• We analyzed available P. patens expressed sequence tag (EST) data for putative moss orthologs of the Arabidopsis genes of sporopollenin biosynthesis and studied the enzymatic properties and reaction mechanism of recombinant PpASCL, the P. patens ortholog of Arabidopsis PKSA. We also generated structure models of PpASCL and Arabidopsis PKSA to study their substrate specificity.• Physcomitrella patens orthologs of Arabidopsis genes for sporopollenin biosynthesis were found to be expressed in the sporophyte generation. Similarly to Arabidopsis PKSA, PpASCL condenses hydroxy fatty acyl-CoA esters with malonyl-CoA and produces hydroxyalkyl a-pyrones that probably serve as building blocks of sporopollenin. The ASCL-specific set of Gly-Gly-Ala residues predicted by the models to be located at the floor of the putative active site is proposed to serve as the opening of an acyl-binding tunnel in ASCL.• These results suggest that ASCL functions together with other sporophytespecific enzymes to provide polyhydroxylated precursors of sporopollenin in a pathway common to land plants.

No abstract