Results from a pilot plant using un-promoted potassium carbonate for carbon capture

A pilot plant facility has been designed and built to trial potassium carbonate solvent technology for carbon capture under a range of conditions. The rig is capable of capturing 4 - 10 kg/hr of CO2 from 30 - 55 kg/hr of an air-CO2 mixture, with different packings. A series of trials have been completed with a range of solvent concentrations from 20 wt% to 30 wt% potassium carbonate. The experimental holdup, solvent loading and absorber temperatures have been matched with rate-based simulations in Aspen Plus® software

Dissociation Constants (p<i>K</i>_a) of Tertiary and Cyclic Amines: Structural and Temperature Dependences

The dissociation constants of the conjugate acids of 14 amines (diethylethanolamine, monoethanolamine, <i>n</i>-butyldiethanolamine, <i>t</i>-butyldiethanolamine, <i>n</i>,<i>n</i>-dimethylpropanolamine, methyl-diethanolamine, ethyldiethanolamine, monoethylethanolamine, <i>n</i>,<i>n</i>-dimethylisopropanolamine, triethanolamine, 4-methylpiperazine-1-amine, 3-morpholino propylamine, 4,2-hydroxylethylmorpholine, and triethylamine) were measured over a temperature range between 293.15 and 333.15 K using the potentiometric titration method. The change in standard state thermodynamic properties was derived from the van’t Hoff equation. The influence of the steric hindrance, number of −OH groups, and length of alkyl chain on the dissociation constants was identified. Of the studied amines, few sterically hindered derivatives of piperazine, a secondary amine monoethylethanolamine, and a tertiary amine <i>n</i>,<i>n</i>-dimethylpropanolamine have high p<i>K</i>_a values but lower standard enthalpy than those of the benchmark amine, monoethanolamine (MEA), and thus were deemed promising for CO₂ capture technology. Monoethylethanolamine (MEEA) was found to have the highest basicity (p<i>K</i>_a) with the lowest standard state enthalpy (Δ<i>H</i>°/kJ·mol^–1)

CO₂ Capture Using Fluorinated Hydrophobic Solvents

Finding more efficient gas–liquid scrubbing systems with lower parasitic energy penalties is important for the future deployment of carbon capture plants for large point source CO₂ emitters. Minimization of the energy penalty using advanced solvents is one way to reduce the energy penalty. Nonaqueous, hydrophobic solvents are one type of solvent in which the physical properties of the solvent combined with low heats of absorption and low loading at high temperature even with high CO₂ pressure result in promising solvents with low estimated reboiler heat duty. In this paper, a solvent composed of a hydrophobic amine (2-fluorophenethylamine) combined with an acidic, hydrophobic alcohol (octafluoropentanol) is studied mechanistically, and the experimentally determined reaction products, heats of absorption, and vapor liquid equilibria are reported. Approximating process models are compared and indicate the potential to lower reboiler heat duty in a commercial implementation

Challenges in Predicting Δ_rxn<i>G</i> in Solution: The Mechanism of Ether-Catalyzed Hydroboration of Alkenes

Ab initio (coupled-cluster and density-functional) calculations of Gibbs reaction energies in solution, with new entropy-of-solvation damping terms, were performed for the ether-catalyzed hydroboration of alkenes. The goal was to test the accuracy of continuum-solvation models for reactions of neutral species in nonaqueous solvents, and the hope was to achieve an accuracy sufficient to address the mechanism in the “Pasto case”: B₂H₆ + alkene in THF solvent. Brown’s S_N2/S_N1 “dissociative” mechanism, of S_N2 formation of borane–ether adducts followed by S_N1 alkene attack, was at odds with Pasto’s original S_N2/S_N2 hypothesis, and while Brown could prove his mechanism for a variety of cases, he could not perform the experimental test with THF adducts in THF solvent, where the higher THF concentrations might favor an S_N2 second step. Two diboranes were tested: B₂H₆, used by Pasto, and (9BBN)₂ (9BBN = 9-borabicyclo[3.3.1]­nonane, C₈H₁₅B), used by Brown. The new entropy terms resulted in improved accuracy vs traditional techniques (∼2 kcal mol^–1), but this accuracy was not sufficient to resolve the mechanism in the Pasto case