Sintering resistant CO2 sorbents prepared by eggshell derived xerogels

Abstract

• Sustainable and stable CO 2 sorbents were prepared from eggshells. • Lime sorbents were prepared by combustion of carboxylic acid derived xerogels. • Release of gas & heat during xerogel combustion modifies sorbents’ morphology. • Sorbents’ unimodal granulometric distribution minimizes particles coalescence. • Eco-friendly lactic acid sorbent showed the slowest carrying capacity decay. A sol–gel like method was used to prepare CaO sorbents from eggshells, and carboxylic acids, with improved sintering resistance. Sorbent materials obtained by calcination (900 °C) of the calcium xerogels presented different morphologies depending on the acid used as the complexing agent (citric, lactic, oxalic, maleic, acetic, and propionic). Sorbents were tested for cyclic carbonation (700 °C, 15% CO 2 in N 2 )/decarbonation (800 °C, in N 2 ) in a thermobalance. Sorbents had distinct specific areas and porosities resulting from the release of gaseous molecules, and heat, from the thermal decomposition of xerogels. The particle size distribution of sorbents was also a function of the acid. The acid carbon chain and the combustion enthalpy have opposite effects on the morphology of sorbents. The lactic acid-derived sorbent was the most performant showing the lowest carrying capacity decay. After 50 cycles the loss of CO 2 capture capacity was 45% for the lactic acid-modified sorbent, while the unmodified sorbent showed a sorption capacity decay of 74%. Scanning electron microscopy showed, after cyclic carbonation/decarbonation, a sintered morphology for the sorbent derived from raw eggshells. This sorbent presented non-porous large aggregates, while the lactic acid-derived sorbent showed a clear network of voids within the crystals agglomerates and a coral-like morphology that is known to confer sorbent stability. This sorbent was the only sorbent with a particle size distribution closer to the unimodal, while the other samples were bimodal. The absence of smaller particles reduces the contact between sorbent grain boundaries at high temperatures, which minimizes the sintering process.