Kinetics of the reaction of carbon dioxide with aqueous 2‐piperidineethanol solutions

Abstract

Sterically hindered amines have been proposed recently as attractive solvents for acid gas purification, since they have not only greater capacity for C 0 2 but also a low tendency to form carbamate and an appreciable absorption rate for C 0 2 (Sharma, 1965;Sartori and Savage, 1983;Savage et al., 1984;Say et al., 1984). The advantages of sterically hindered amines result from the bulkiness of the substituent attached to the amino group which causes an increased cyclic capacity and a decreased energy consumption in industrial operations. 2-piperidineethanol(2-PE) is a secondary amine in which the amino group is not only attached to a naphthenic ring group but also sterically hindered by a hydroxyethyl group that is connected to the Q carbon atom of the cyclic system. It has been used for the bulk removal of C 0 2 or the selective removal of H2S (Goldstein et al., 1986).Little information on 2-PE is available. Shen et al. (1991) investigated the kinetic rate of C 0 2 in aqueous 2-PE solutions at 40°C within the amine concentration range 0.2-1.0 kmol/ m3. Their results showed that the reaction of C 0 2 in aqueous 2-PE solutions is first-order with respect to both C 0 2 and the amine. The second-order forward rate constant at 40°C was found to be 195 m'/(kmol-s), which is much lower than that of 2-amino-2-methyl-1-propanol (AMP). Xu et al. (1992) presented the physicochemical properties of 2-PE and its aqueous solutions over a wide range of temperature and concentration. They found that the value of pKa for 2-PE at 25°C is 10.14, which is higher than that of AMP (the pKa of AMP is 9.694).The aim of this work is to investigate the kinetic rate of absorption of C02 in aqueous 2-PE solutions using a stirredcell absorber. The reaction mechanism and the kinetic order with respect to both the reactants C 0 2 and 2-PE are studied within the amine concentration range of 0.25-2.5 kmol/m3, over the temperature range from 10-40°C. Reaction MechanismThe main reaction is to form the carbamate even though there are several parallel and series reversible reactions simultaneously occurring in the solution. This reaction can be described by the zwitterion mechanism:Correspondence concerning this work should be addressed to A.

Absorption of carbon dioxide into sterically hindered amines: Kinetics analysis and the influence of promoters

“…Plots of log R CO2 = ½CO 2 Ã ffiffiffiffiffiffiffiffiffiffi D CO2 p À Á È É versus log [PE] at 298, 303, and 308 K are shown in Figure 7. Our k 2 value at T ¼ 303 K is close to that reported by Xu et al [23] From the dependence of our values of k 2 on temperature, the activation energy was found to be 54.2 kJ/mol (see Figure 8). The slope equals 0.51, 0.51, and 0.55 thereby suggesting that the reaction order with respect to PE is close to unity (viz., 1.02-1.1).…”

“…[21] The CO 2 reaction with PE is faster than that with MDEA, according to Shen et al [22] Their value of the second-order rate constant is equal to 195 m 3 / (kmol s) at 313 K. The value published in Xu et al [23] is much higher (1468 m 3 /(kmol s)). It is a promising candidate absorbent for CO 2 capture in terms of both absorption capacity and kinetics.…”

Aqueous piperazine derivatives for CO2 capture: Accurate screening by a wetted wall column

“…Accurate measurement of vapor-liquid-equilibrium (VLE) and absorption/desorption rates was made possible by using a wetted wall column, which better represents mass transfer between gas and liquid in real packing. Although some thermodynamic or kinetic studies had been reported for some of the amines (Xu et al, 1993;Paul et al, 2009a,b), the amine concentration in this study is much higher (>3 kmol/m 3 ), close to the practical range that is most interesting for industrial application. The concentration for aqueous amine solution is expressed in molality (m, mol amine/kg water) throughout this paper.…”

“…2-PE is a hindered amine because of the hydroxyethyl group attached to amino group, so there forms no or very little carbamate as 2-PE reacts with CO 2 (Sartori and Savage, 1983). The second order reaction rate constant (k 2 ) of 2-PE with CO 2 was reported by Xu et al (1993) to be 0.6 m 3 /mol s, which is two orders of magnitude smaller than the value for PZ of 54 m 3 /mol s (Bishnoi and Rochelle, 2000). However, 2-PE is not considerably slower than PZ as what would be expected from the k 2 values.…”

Kinetics of absorption of carbon dioxide into aqueous solutions of 2-amino-2-hydroxymethyl-1,3-propanediol

“…In the extensive field of gas treating, alkanolamines have become one of the most important classes of chemicals for the removal of CO 2 . Sterically hindered amines such as 2-amino-2-methyl-1-propanol (AMP), 2-piperidineethanol (2-PE) have been proposed as commercially attractive new solvents for acid gas treating over conventional amines such as monoethanolamine (MEA), diethanolamine (DEA), di-2-propanolamine (DIPA) and Nmethyldiethanolamine (MDEA) [3][4][5][6][7][8][9][10][11][12]. The advantages of these sterically hindered amines are mainly due to their particular structure which results in increased cyclic capacity and thermodynamic capacity for CO 2 absorption.…”