CO2 capture systems based on saccharides and organic superbases

In this report, novel systems, based on highly abundant saccharides, D-mannose, D-glucose, beta-cyclodextrin, alginic acid and mannitol, in combination with an organic superbase, tetramethylguanidine (TMG) or 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU), are studied for carbon dioxide capture. With D-mannose and D-glucose, several ratios of equivalents of alcohol groups of saccharide : superbase were tested: 1, 0.625, 0.5 and 0.25. High wt% values of CO2 uptake were obtained with TMG-based systems. However, TMG itself can react directly with CO2, and, in the presence of D-mannose, competition between carbonate and carbamate based products was established. In order to circumvent this competition and obtain exclusively the carbonate-based product, DBU was used instead as an organic superbase. In the D-mannose series the highest result was obtained with a D-mannose : DBU ratio eq. = 0.625 (13.9% CO2 uptake, 3.3/5 alcohol groups converted into carbonates). A more effective stirring system, designed to overcome the high viscosity of the products, allowed the use of a D-glucose : DBU = 1 : 1 ratio with 11.5 wt% of CO2 uptake and 2.47/5 alcohol groups converted into carbonates. Additionally a DSC thermal study was performed in order to study the stability/reversibility of the CO2 loaded systems.