Kinetics of CO2 with primary and secondary amines in aqueous solutions - I. Zwitterion deprotonation kinetics for DEA and DIPA in aqueous blends of alkanolamines

The deprotonation kinetics of the DEA—CO2 and the DIPA—CO2 zwitterions have been studied in aqueous blends of amines at 298 K. Amine mixtures investigated were: DEA—TEA, DEA—MDEA, DEA—DMMEA, DEA—DEMEA, DIPA—TEA. DIPA—MDEA, DIPA—DMMEA, DIPA—DEMEA. For each blend the zwitterion deprotonation constant of the additional base present in solution (i.e. the tertiary amine) was determined. The observed deprotonation rate constants for the DEA-zwitterion and for the DIPA-zwitterion could be summarized in two Brønsted-type relationships. These relationships can be used to estimate the overall reaction rate of CO2 with DEA or DIPA in aqueous blends of amines. The present work on the zwitterion deprotonation kinetics of the reaction of CO2 with DEA and DIPA in aqueous amine blends provides additional verification for the validity of the zwitterion mechanism proposed by Caplow(1968) for the description of the reaction between CO2 and primary and secondary alkanolamines

Kinetics of CO2 with primary and secondary amines in aqueous solutions - II. Influence of temperature on zwitterion formation and deprotonation rates

The kinetics of the reaction of CO2 with various alkanolamines (MEA, DGA, DIPA, DEA, MMEA) in aqueous solutions has been studied as a function of temperature. Also kinetic data at 303 K were obtained for the reaction between CO2 and the cyclic amine morpholine in aqueous solutions. All observed phenomena can be explained very satisfactorily with the zwitterion mechanism proposed by Caplow. With respect to the temperature influence on the overall reaction rate for primary and secondary amines, two classes can be distinguished: when the zwitterion formation is rate determining a significant temperature influence is observed whereas only a slight temperature dependence is observed when the zwitterion deprotonation is rate determining. All kinetic experiments were interpreted with the aid of a numerically solved absorption model which describes gas absorption accompanied by reversible chemical reactions. For last reversible reactions like those in the present study, only in this way reliable reaction-rate data can be deduced from absorption experiments. The Brønsted relationship between the zwitterion-formation rate constant and the acid dissociation constant of the alkanolamine, as proposed by Versteeg and van Swaaij (1988a), seems to be valid over a wide range of temperatures and for a great variety of alkanolamines. This relationship is not valid for cyclic amines like MOR

Physical absorption of CO2 and propene into toluene/water emulsions

The physical absorption of CO2 and propene into toluene/water emulsions is studied in a stirred cell and laminar film absorber. Experimentally observed masstransfer rates are compared to an absorption model, based on Higbie's penetration theory describing physical gas absorption into an emulsion. For all absorption experiments in a stirred cell absorber (toluene fractions and stirring rates), experimentally observed mass-transfer rates are considerably higher than the rates predicted by the absorption model. Moreover, the absorption rate decreases with increasing stirring rate, whereas no influence of the stirring rate is predicted by the absorption model. In contradiction to the absorption experiments in a stirred cell absorber, the observed mass-transfer rates in the laminar film absorber agree with the model simulations. Probable existence of a very thin toluene layer is observed on top of the emulsion for the stirred cell experiments, likely due to minor phase separation. Since in the laminar film absorber gas-liquid interface and the gravity force are parallel, this phenomenon does not probably occur significantly for absorption experiments in this absorber. The observed mass-transfer phenomena can be explained, at least qualitatively, from the occurrence of a thin toluene layer

Kinetics of Carbon Dioxide with tertiary Amines in aqueous solution

The reaction of CO2 with TEA, DMMEA, and DEMEA has been studied at 293, 303, 318 and 333 K. All the kinetic experiments were carried out in a stirred cell reactor operated with a flat, smooth and horizontal gas-liquid interface. A numerical method, which describes mass transfer accompanied by reversible chemical reactions, has been applied to infer rate constants from the experimental data. It is argued that the contribution of the CO2 reaction with OH- to the observed reaction rate may have been overstimated in most literature on tertiary amine kinetics as serious depletion of OH- toward the gas-liquid interface usually occurs. \ud For all the amines studied, the reaction order in amine was found to be about one for each temperature investigated. This is in good agreement with the base catalysis mechanism proposed by Donaldson and Nguyen (1980). All kinetic data could be summarized reasonably well in one Brønsted relationship

Diffusivity measurements in some organic solvents by a gas-liquid diaphragm cell

A diaphragm cell has been developed for the measurement of diffusion coefficients of gases In liquids. The diaphragm cell is operated batchwise with respect to both gas and liquid phases, and the diffusion process Is followed by means of the gas pressure decrease which is recorded by means of a pressure transducer. The diaphragm cell has been calibrated with some well-known gas-liquid systems. The present diaphragm cell was shown to be very suitable for the determination of diffusion coefficients at higher temperatures. The diffusion coefficient of C02 and propene In toluene has been measured at temperatures ranging from 298 to 328 K. The dmusivity for various other gas-liquid systems has been determined at 298 K

Solubility and diffusivity data for the absorption of carbonyl sulfide, carbon dioxide, and nitrous oxide in amine solutions

Absorption data for COS and N,O in aqueous solutlons of N-methyldiethanolamine (MDEA), ethylene glycol, and sulfolane (tetrahydrothiophene 1,l-dioxide) at 298 K and solubility data for COS in water at temperatures ranging from 298 to 338 K are presented. Also density, viscosity, N,O solubility, and N,O dlffusivity data are reported for a wide range of aqueous aikanolamine solutions, aqueous mlxtures of alkanoiamines, and solutions of MDEA in water/ethanol. It is shown that an analogy between COS and N,O with respect to gas solubility in aqueous solutions of ethylene glycol and sulfolane holds up to about 25 mass %. This seems to justify, for engineering purposes, the application of this analogy for the estimation of COS solubilitles in diluted aqueous amine solutions. Direct verificatlon of a COS-N,O analogy was provided by absorption of N,O and COS into aqueous MDEA solutions in a laminar film reactor

Kinetic study of COS with tertiary alkanolamine solutions. 2. Modeling and experiments in a stirred cell reactor

Absorption experiments of COS into aqueous solutions of MDEA and DEMEA at 303 K have been carried out in a stirred cell reactor. An absorption model, based on Higbie’s penetration theory, has been developed and applied to interpret the absorption experiments, using the kinetic data obtained in part 1 of the present work. Experimental and calculated absorption rates agreed reasonably well at relatively low amine concentrations but deviated increasingly with increasing amine concentration. These deviations must very probably be attributed to an underestimation, by the COS-N20 analogy, of the COS solubility in rather concentrated amine solutions. The absorption model has been applied to investigate the discrepancies between the present work and kinetic data for MDEA reported in the open literature. It has been shown that these discrepancies were possibly due to small amounts of rapidly reacting contaminants