Mass transfer accompanied with complete reversible chemical reactions in gas-liquid systems: an overview

In many processes in the chemical industry mass transfer accompanied with reversible, complex chemical reactions in gas-liquid systems are frequently encountered. In point of view of design purposes it is very important that the absorption rates of the transferred reactants can estimated sufficiently accurate. Moreover, mass transfer phenomena can also affect substantially important process variables like selectivity and yield. Therefore large amounts of research effort has been invested in describing these processes and in the development of models that can be used for the calculation of the mass transfer rates and other parameters.\ud \ud The description of the absorption of a gas followed by a single first order irreversible reaction is simple and straightforward. For all mass transfer models, e.g. film, penetration and surface renewal respectively, this process can be analytically solved. For other processes however, only for a limited number of special cases analytical solutions are possible and therefore numerical techniques must be used for the description of these phenomena. Besides numerically solved absorption models the mass transfer rates often can be calculated satisfactory accurate by simplifying the actual process by means of approximations and/or linearizations. In this paper an overview will be given of the absorption models that are available for the calculation of the mass transfer rates in gas-liquid systems with (complex) reversible reactions. Both numerically solved and approximated models respectively will be treated and conclusions on the applicability and restrictions will be presented. Also perspectives and white spots will be indicated

On the kinetics between CO2 and alkanolamines both in aqueous and non-aqueous solutions—I. Primary and secondary amines

The reaction between CO2 and primary and secondary alkanolamines (DEA and DIPA) has been studied both in aqueous and non-aqueous solutions (ethanol and n-butanol) at various temperatures. Reaction kinetics have been established by chemically enhanced mass transfer of CO2 into the various solutions. The experiments were performed in a stirred vessel operated with a horizontal interface which appeared to the eye to be completely smooth. The reaction can be described with the zwitterion-mechanism originally proposed by Caplow (1968) and reintroduced by Danckwerts (1979). Literature data on the reaction rates can be correlated fairly well with this mechanism. As all amines react with CO2 in a reversible way, and the mass transfer models used for the interpretation of the experimental data neglect this reversibility and take only the forward reaction rate into account, the influence of the reversibility is studied. With the aid of numerical mass transfer models (Versteeg et al., 1987b,c) the experimental method with its underlying assumptions have been verified and the applicability and the limits of this method were determined. Special attention has been paid to the influence of small amounts of impurities (amines) on the measured mass transfer rates. A Brønsted relationship exists between the second-order rate constant, k2, for the formation of the zwitterion and the acid dissociation constant of the alkanolamine

On the kinetics between CO2 and alkanolamines both in aqueous and non-aqueous solutions—II. Tertiary amines

The reaction between CO2 and tertiary alkanolamines (MDEA, DMMEA, TREA) has been studied in aqueous solutions at various temperatures. Also the absorption of CO2 in a solution of MDEA in ethanol has been studied. Reaction kinetics have been established by chemically enhanced mass transfer of CO2 into the various solutions. The experiments were performed in a stirred vessel with a horizontal interface which appeared to the eye to be completely smooth. The reaction of CO2 with tertiary amines can be described satisfactorily with the base-catalysis mechanism proposed by Donaldson and Nguyen (1980). Also attention has been paid to the influence of reversibility and small amounts of impurities (primary and secondary amines) on the measured mass transfer rate. For the reaction rate constant, k2, of the reaction between carbon dioxide and tertiary amines exists a Brønsted relation. There is a linear relation between the logarithm of k2 and pKa at 293 K

Project Finance as a Driver of Economic Growth in Low-Income Countries

This study investigates the role of project finance as a driver of economic growth. We hypothesize that project finance is beneficial to the least developed economies as it compensates for any lack of domestic financial development. The contractual structure unique to project finance should lead to better investment management and governance. Investigating 90 countries from 1991 to 2005, we find support for our hypothesis. Project finance indeed fosters economic growth and this effect is strongest in low-income countries, where financial development and governance is weak.financial economics and financial management ;

Human Rights Violations After 9/11 and the Role of Constitutional Constraints

human rights, terrorism, 9/11, checks and balances, constitutions, constitutional courts

A Kinetic Model for Toluene Oxidation Comprising Benzylperoxy Benzoate Ester as Reactive Intermediate in the Formation of Benzaldehyde

During the oxidation of toluene under semibatch conditions, the formation of benzyl alcohol is initially equal to the rate of formation of benzaldehyde. As the overall conversion increases the benzyl alcohol concentration at first decreases much faster than benzaldehyde, but this decrease slows down causing the benzyl alcohol concentration to reduce to zero only very slowly. To account for this phenomenon a new reaction pathway has been proposed where the formation of benzaldehyde out of benzylhydroperoxide is catalysed by benzoic acid. Incorporation of this new reaction in a model improves the description of benzyl alcohol concentration prophiles while maintaining good predictions for benzaldehyde and benzoic acid