Comparison of aqueous and non-aqueous alkanolamines solutions for carbon dioxide desorption in a microreactor

An experimental study of CO2 desorption from aqueous and non-aqueous saturated alkanolamine solutions carried out in a tubular microreactor, consisting of a stainless steel microtube with an internal diameter of 800 mu m and a total length of 35 cm. We tested a total of six solvent mixtures of water or methanol with monoethanolamine, diethanolamine, or activated methyl diethanolamine in a broad range of operational conditions, including temperature (50-100 degrees C), rich solvent flow rate (0.5-4.5 ml/min), and amine concentration in the solvent (10 and 50% w/w). CO2 desorption was thoroughly characterized with respect to the mass transfer rate and energy consumption, and both were expected to improve with the use of a microreactor due to short diffusion distances and a larger surface-to-area ratio. An increase in the operating temperature or concentration of the amine resulted in a higher percentage of desorption and enhanced mass transfer rates, as shown by the local mass transfer coefficient based on the liquid phase values herein disclosed. Increasing the rich solvent flow rate also increased the local mass transfer coefficient values (80%-95%); however, the overall percentage of CO2 desorption reduced (25%-35%) due to shorter residence times in the microreactor. Similarly, the energetic desorption efficiency improved for all the solutions with increasing temperature (65-75% reduction) and concentration of amine in the solvent (20-35% reduction), yet again decreasing with an increasing flow rate of rich solvent (5-15%). Compared to the literature values for the packed columns and microreactors, our data showed the overall energy consumption up to an 88% reduction in specific CO2 desorption, demonstrating great potential for the intensification of solvent-mediated, energetically demanding CO2 desorption. In addition, the results showed that the energy consumption for CO2 desorption was reduced by 73% by choosing a non-aqueous in preference to an aqueous alkanolamine solvent. (C) 2020 Elsevier Ltd. All rights reserved.