Development of carboxyl-layered double hydrotalcites of enhanced CO2 capture capacity by K2CO3 promotion

Abstract

Layered double hydroxides have been comprehensively studied as adsorbent precursors for CO2 capture at 250–500 °C. Layered double hydroxides take advantages of partial reversibility by pressure change of adsorbate and good selectivity to CO2 contributed by active basic sites. However, they suffer from comparatively lower CO2 capture capacity, commonly 0.28–0.70 mmol/g in previous studies, compared with typical physical adsorbents like zeolites or chemical sorbents such as calcium oxide. In this paper, K2CO3 promoted n-caprylate (CH3(CH2)6COO−) LDH and K2CO3 promoted stearate (CH3(CH2)16COO−) LDH were synthesized by combining long carbon-chain carboxylic anion intercalation and K2CO3 promotion. K2CO3 surface promotion raised CO2 capacity to 1.36 mmol/g for K-promoted magnesium–aluminum n-caprylate LDH and 1.97 mmol/g for K-promoted magnesium–aluminum stearate LDH respectively. Thermal gravimetric analysis was used to test CO2 uptake up to 1000 kPa. It was found that adsorption kinetics fitted Elovich equation. X-ray diffraction was deployed to detect the crystal patterns of both precursors and adsorbents. In situ fourier transformation infrared spectroscopy and temperature programmed desorption were used to monitor the bonding between surface basic sites and adsorbate during adsorption and desorption process, in order to illustrate the adsorption mechanism of CO2 on LDHs only by changing the partial pressure of CO2 at the same operation temperature. Both novel LDHs show good potential for PSA application.