Razi University

The increasing emissions of carbon dioxide and their associated environmental consequences have made the development of effective technologies for the capture and recovery of this gas an important topic in the field of separation processes. Although chemical absorption using amine solvents is one of the conventional methods for carbon dioxide separation, the considerable energy consumption during solvent regeneration is one of the major limitations of this process. In this study, the desorption of carbon dioxide from a biphasic solvent consisting of triethanolamine, n-butanol, and water was experimentally investigated using an ultrasonic falling-film system. To evaluate the process performance, the effects of solvent temperature, flowrate, film thickness, solvent composition, and number of passes on carbon dioxide desorption were investigated, and the performance of the system was compared in the presence and absence of ultrasound. Three solvent compositions containing 30 wt% triethanolamine, 15, 25, and 35 wt% n-butanol, and 55, 45, and 35 wt% water, respectively, were used. Experiments were conducted over a temperature range of 40–70 °C, flow rates of 2–10 mL/min, and different film thicknesses. The results showed that increasing the solvent temperature from 40 to 70 °C increased the carbon dioxide desorption percentage for all three compositions. At 70 °C in the presence of ultrasound, the desorption percentages for the first, second, and third compositions were 49.49%, 76.29%, and 62.77%, respectively, whereas the corresponding values in the absence of ultrasound were 36.87%, 58.51%, and 44.15%. Furthermore, increasing the flow rate from 2 to 10 mL/min decreased the desorption percentage, which was attributed to the reduction in the effective contact time of the solvent with the film surface. At a flow rate of 2 mL/min and in the presence of ultrasound, the highest desorption percentages were 53.46% for the third composition and 52.58% for the second composition.The results also indicated that reducing the film thickness from 3 to 1 mm increased the desorption percentage. At a film thickness of 1 mm, the desorption percentages for the first, second, and third compositions were approximately 49.5%, 76.5%, and 62.8%, respectively. Increasing the number of passes also enhanced the desorption percentage, with the desorption of the second composition reaching approximately 86% as the number of passes increased. Comparison of the results in the presence and absence of ultrasound demonstrated that the application of ultrasound improved process performance and increased the carbon dioxide desorption percentage under all investigated conditions. This enhancement can be attributed to the generation of oscillations and mixing within the liquid layer, resulting in enhanced mass transfer in the film.On the other hand, the energy consumption analysis showed that although increasing the temperature enhanced the desorption percentage, the specific energy consumption also increased. The specific energy consumption for the first composition increased from approximately 2.04 MJ/kg of desorbed carbon dioxide at 40 °C to approximately 4.72 MJ/kg at 70 °C. For the second composition, this value increased from 1.32 to 2.66 MJ/kg, while for the third composition, it increased from 1.29 to 3.20 MJ/kg of desorbed carbon dioxide. In addition, for the second composition, the energy consumption relative to the reference condition decreased from approximately 68.6% at 40 °C to approximately 36.7% at 70 °C. Overall, the results demonstrated that the use of an ultrasonic falling-film system, combined with appropriate solvent composition and operating conditions, can improve the performance of the carbon dioxide desorption process. However, the selection of optimal operating conditions should be based simultaneously on the desorption performance and energy consumption indicators.