Study of an ammonia-based wet scrubbing process in a continuous flow system

A continuous gas and liquid flow, regenerative scrubbing process for CO{sub 2} capture was demonstrated at the bench-scale level. An aqueous ammonia-based solution captures CO{sub 2} from simulated flue gas in an absorber and releases a nearly pure stream of CO{sub 2} in the regenerator. After the regeneration, the solution of ammonium compounds is recycled to the absorber. The design of a continuous flow unit was based on earlier exploratory results from a semi-batch reactor, where a CO{sub 2} and N{sub 2} simulated flue gas mixture flowed through a well-mixed batch of ammonia-based solution. During the semi-batch tests, the solution was cycled between absorption and regeneration steps to measure the carrying capacity of the solution at various initial ammonia concentrations and temperatures. Consequentially, a series of tests were conducted on the continuous unit to observe the effect of various parameters on CO{sub 2} removal efficiency and regenerator effectiveness within the flow system. The parameters that were studied included absorber temperature, regenerator temperature, initial NH{sub 3} concentration, simulated flue gas flow rate, liquid solvent inventory in the flow system, and height of the packed-bed absorber. From this testing and subsequent testing, ammonia losses from both the absorption and regeneration steps were quantified, and attempts were made to maintain steady state during operations. Implications of experimental results with respect to process design are discussed

Understanding the effect of side groups in ionic liquids on carbon-capture properties: a combined experimental and theoretical effort

Ionic liquids are an emerging class of materials with applications in a variety of fields. Steady progress has been made in the creation of ionic liquids tailored to specific applications. However, the understanding of the underlying structure-property relationships has been slower to develop. As a step in the effort to alleviate this deficiency, the influence of side groups on ionic liquid properties has been studied through an integrated approach utilizing synthesis, experimental determination of properties, and simulation techniques. To achieve this goal, a classical force field in the framework of OPLS/Amber force fields has been developed to predict ionic liquid properties accurately. Cu(i)-catalyzed click chemistry was employed to synthesize triazolium-based ionic liquids with diverse side groups. Values of densities were predicted within 3% of experimental values, whereas self-diffusion coefficients were underestimated by about an order of magnitude though the trends were in excellent agreement, the activation energy calculated in simulation correlates well with experimental values. The predicted Henry coefficient for CO2 solubility reproduced the experimentally observed trends. This study highlights the importance of integrating experimental and computational approaches in property prediction and materials development, which is not only useful in the development of ionic liquids for CO2 capture but has application in many technological fields

Puckering behavior in six new phosphoric triamides containing aliphatic six- and seven-membered ring groups and a database survey of analogous ring-containing structures

The influence of a N heteroatom on the ring conformations of six- and seven- membered aliphatic rings in six new C(O)NHP(O)-based phosphoric triamide structures (analysed by X-ray crystallography) is investigated. Additionally the influence of steric and crystal packing effects is also studied by the analysis of Hirshfeld surfaces. The results are compared to analogous structures with three- to seven- aliphatic membered rings deposited in the Cambridge Structural Database. In the newly determined structures, the six-membered rings only show the near-chair conformation with a maximum deviation of the θ puckering parameter of 4.4° from the ideal chair value of 0°/180°, while the seven-membered rings are found in different conformations such as near-chair, twist chair and twist sofa

Aromaticity in cyanuric acid

This study analyzes the aromatic nature of cyanuric acid (hexahydrotriazine) and some of its derivatives, in terms of aromatic stabilization energy (ASE) and electronic behavior. The simplest molecule (C3N3O3H3) is the most aromatic item out of the entire set, but some of the others also display aromatic character. The structure of all the rings is analyzed considering their molecular orbitals as well as studying the inductive effect

High-resolution slice selection NMR for the measurement of CO_2 diffusion under non-equilibrium conditions

We present a simple and an efficient approach using spatially selective NMR to investigate solvation and diffusion of CO_2 in ionic liquids. The techniques demonstrated here are shown as novel and effective means of studying solvated gas dynamics under nonequilibrium conditions without the need for conventional high power gradients

Sodium Dodecyl Sulfate Monomers Induce XAO Peptide Polyproline II to α‑Helix Transition

XAO peptide (Ac–X₂A₇O₂–NH₂; X: diaminobutyric acid side chain, −CH₂CH₂NH₃⁺; O: ornithine side chain, −CH₂CH₂CH₂NH₃⁺) in aqueous solution shows a predominantly polyproline II (PPII) conformation without any detectable α-helix-like conformations. Here we demonstrate by using circular dichroism (CD), ultraviolet resonance Raman (UVRR) and nuclear magnetic resonance (NMR) spectroscopy that sodium dodecyl sulfate (SDS) monomers bind to XAO and induce formation of α-helix-like conformations. The stoichiometry and the association constants of SDS and XAO were determined from the XAO–SDS diffusion coefficients measured by pulsed field gradient NMR. We developed a model for the formation of XAO–SDS aggregate α-helix-like conformations. Using UVRR spectroscopy, we calculated the Ramachandran ψ angle distributions of aggregated XAO peptides. We resolved α-, π- and 3₁₀- helical conformations and a turn conformation. XAO nucleates SDS aggregation at SDS concentrations below the SDS critical micelle concentration. The XAO₄–SDS₁₆ aggregates have four SDS molecules bound to each XAO to neutralize the four side chain cationic charges. We propose that the SDS alkyl chains partition into a hydrophobic core to minimize the hydrophobic area exposed to water. Neutralization of the flanking XAO charges enables α-helix formation. Four XAO–SDS₄ aggregates form a complex with an SDS alkyl chain-dominated hydrophobic core and a more hydrophilic shell where one face of the α-helix peptide contacts the water environment