The chemistry of resorcinol carboxylation and its possible application to the CO2 removal from exhaust gases

The carbon dioxide uptake by resorcinol solutions has been investigated under different operational procedures and experimental conditions. Batch experiments have been carried out in aqueous and glycerol–water solutions of KOH, KHCO3 or K2CO3, and the yield of resorcinol carbonatation has been investigated as a function of the CO2 partial pressure as well as reaction temperature and time. The beta-resorcylic acid (2,4-dihydroxy benzoic acid) has been isolated in the solid state and identified on the basis of its IR spectrum. The 13C NMR analysis has been applied to identify and quantify the carbonated species in solution upon CO2 uptake and after thermal resorcinol regeneration. The maximum yield of resorcinol conversion into b-resorcylic acid was 60% with 1.0 bar of CO2 and 120 min reaction time at 110 °C. A 34% yield of resorcinol conversion was also obtained with the resorcinol/K2CO3 solution in the absence of CO2. A relationship between the CO2 absorption capacity and the possible mechanism of CO2 capture has been proposed. The CO2 absorption efficiency from a simulated flue gases (15% CO2 in air) has been measured in continuous cycles of CO2 absorption–desorption carried out in packed columns and with a glycerol–water solution of resorcinol/KOH/KHCO3. The maximum absorption efficiency was 82% at absorption-desorption temperatures of 70 °C and, respectively, 170 °C. Oxidative conditions and the presence of H2S did not affect the yield of b-resorcylic acid and the resorcinol capacity of CO2 capture. Finally, a simple method for the selective separation of H2S from CO2 has been reported.