CO2 Sorption-Enhanced Processes by Hydrotalcite-Like Compounds at Different Temperature Levels

Abstract

The aim of this work is to identify solid sorbents for CO 2 capture for coal and biomass syngas conditioning and cleaning by means of a sorption-enhanced reaction process. Hydrotalcite-like compounds (HTlcs) were synthesized with and without K 2 CO 3 impregnation. Samples were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) porosimetry after synthesis and after capture tests, respectively. Sorption and desorption tests were performed in a fluidized bed reactor, under cyclic conditions, at two different temperature levels: 350/450°C and 600/700°C. At low temperature only the Mg-Al HTlcs K promoted samples showed stability and sorption capacity comparable with literature values. On the other hand, results at high temperature indicate that the mixed Mg-Ca-Al HTlcs samples exhibit the best behavior with the highest sorption capacity (1.7 mmol CO2 /g) almost stable over 5 sorption/regeneration cycles; furthermore, addition of steam allowed increasing their reactivity by 70% compared to the dry value. This type of sorbent could be a promising candidate to prepare a bifunctional sorbent-catalyst for sorption-enhanced processes, taking place directly in the fluidized bed gasifier, or downstream the reactor for adjustment of gas composition before further conversion in gaseous energy carriers.

CO2 Sorption by Hydrotalcite-Like Compounds in Dry and Wet Conditions

“…This consideration is corroborated by Gallucci et al where tests in fluidized bed under TSA conditions have been made on the sorbents thermally treated at T ¼ 700°C [20].…”

“…Dry capture tests indicated that sorption capacity of sorbents increases of 30% with respect to atmospheric pressure results obtained by Gallucci et al [20]. The best sorbent considering the first cycle capacity in the dry tests is HT1-700 (1.60 mmol CO2 /g sorbent ).…”

“…Finally, a third compound was synthesized as a Mg/Ca/Al mixed structure with an atomic ratio 1/1/1 (HT3) (M 2 þ /M 3 þ ¼ 2/1). The preparation procedure was reported in previous works [20][21][22]. While vigorously stirring, a basic solution of Na(OH) (2M) and Na 2 CO 3 (0.4M), and an acid one of Al(NO 3 ) 3 · 9H 2 O (0.25M), Mg (NO 3 ) 2 · 6H 2 O and/or Ca(NO 3 ) 2 · 4H 2 O (0.5M), were added separately to deionized water at T ¼ 60°C.…”