(707d) Biogas Sweetening Via a Carbamate Crystallization Approach

The CO₂ in biogas significantly limited its potential applications. The regeneration process of aqueous alkanolamine based CO₂ capture often requires a large amount of energy, which makes the process costly. In order to enhance the energy efficiency of the capture, a carbamate crystallization approach was proposed in this study where water was replaced with non-aqueous solvents. It was observed that triethylenetetramine (TETA) carbamate crystallize out as supernatant solid from ethanol solution upon the adsorption of CO₂. A TETA/non-aqueous solvent solution shows higher absorption capacity and absorption rate than alkanolamine-water solution. The mole ratio of CO₂/TETA in carbamate was determined to be around 2:1 by elemental analyzer. The regeneration capabilities of solid carbamates was also investigated. Thermal behavior of the carbamate was examined with differential scanning calorimetry and thermogravimetric analysis. It was shown that the decomposition of TETA-carbamate commenced at about 90°C. The separation of carbamate as solid phase can offer great advantage by letting less volume to regenerate and make this approach a promising alternative for biogas sweetening.