CO₂ capture systems based on saccharides and organic superbases

In this report, novel systems, based on highly abundant saccharides, d-mannose, d-glucose, β-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.