CO2 Absorption Reaction of Li4SiO4 studied by the Rate Theory using Thermogravimetry

Abstract

The CO 2 absorption property of Li 4 SiO 4 was investigated by thermogravimetry. Two kinds of sintered Li 4 SiO 4 samples were prepared at 700? C and 1000? C. The CO 2 absorption rate of the powdered Li 4 SiO 4 samples was measured in 100 vol! CO 2 atmosphere at nine selected temperatures in the 620Ĭ700? C region, and the measured data were discussed by the rate theory. The CO 2 absorption reaction of the Li 4 SiO 4 would be a pseudo first order reaction. For these samples, apparent reaction rate constants k were measured at different measurement temperatures, and activation energies were estimated by the Arrhenius plot. For both the samples, the estimated activation energies were about 115 kJmol in the 620-660? C region and about 56 kJmol in the 680-700? C region. The large difference between these activation energies seems to depend on the surface state of the Li 4 SiO 4 particle reacting with CO 2 .

Particle size dependence of CO2 absorption rate of powdered Li4SiO4 with different particle size

“…On the basis of the equation (4), the slope corresponds with kPCO 2 , and PCO 2 was fixed as 0.1 MPa in the measurement. According to our previous report, 14) in this study, we also supposed that the CO2 absorption reaction is a pseudo first order reaction until the time which the break point is found at. Thus, apparent rate constant k for all the samples was estimated from the measured slope (kPCO 2 = k × 0.1) at 620, 630, 640, 650, 660, 670, 680, 690, 700°C.…”

“…5, the reaction lnk = lnA mechanism seems to change around 670°C because the lnk values abruptly increase around 670°C. In our previous report, 14) we discussed that the change in the k (or lnk) values seems to depend ln - …”

“…Since we supposed that the CO2 absorption reaction is a pseudo first order reaction in our previous report, 14) the first order reaction equation was applied for the estimation in this study although some kinds of rate equations have been known. 15)-17) The first order reaction equation used is shown below, (2) (3) (4) where, k is the apparent rate constant, and [Li4SiO4]0 and a are the initial amount of the powdered Li4SiO4 samples used in the measurement, and [Li4SiO4]t and (a -x) are the residual amount of the powdered Li4SiO4 samples at a reaction time t. PCO 2 is the pressure of CO2 gas used as atmosphere for the measurement.…”

“…14) In addition, in the study, particle size dependence of the rate constant k for the powdered Li4SiO4 was † Corresponding author: K. Oh-ishi; E-mail: oh-ishi@oh-ishilab. chem.…”

Regeneration mechanisms of high-lithium content zirconates as CO2capture sorbents: experimental measurements and theoretical investigations

“…8,9 Among these technologies, capture is the area for which effective sorbent materials must be developed. 15,17,18,23,[25][26][27][28][29] As for Li 2 SiO 3 , experimental results showed the kinetics of its CO 2 capture reaction are also too slow, and hence it is not a good candidate for a CO 2 capture technology. Recent experimental investigations found that alkali metal silicates and zirconates are good candidates as solid sorbents for CO 2 capture in terms of large CO 2 sorption capacity, infinite CO 2 /N 2 or CO 2 /H 2 selectivity, good reversibility, and high operating temperatures.…”