https://doi.org/10.1016/j.ijggc.2018.10.008
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In order to perform a regeneration efficiency comparison between solutions, two regeneration performance parameters (EC and EC2) were calculated. Firstly, as shown by Eq. (1), EC represent the energy consumption after a given time divided by the amount of CO2 stripped after the same time (from integration of curves in Fig. 4). Clearly, a low EC value is desired as it indicates lower energy consumption per mole of stripped CO2. Secondly, in the case where several solutions would give similar EC values, one more parameter was needed to determine the best solutions. EC values were divided by the amount of stripped CO2 to calculate this new parameter, EC2, as shown by Eq. (2). A low EC2 combines two important features: a low EC value and a high quantity of stripped CO2 (needed to have a high cyclic capacity), and can therefore be used as an optimization factor to be minimized in order to find optimal conditions.(1)ECt=Energyt(kJ)CO2strippedt(mol)(2)ECt2=ECt(kJ/mol)CO2strippedt(mol)
The EC results for the three best MEA concentrations at each tested temperature are shown in Fig. 6 while the corresponding EC2 results are displayed in Fig. 7. The three best concentrations only were included to keep these figures as clear as possible. From Fig. 6, it is possible to see that all the data have a minimum EC at the microwave irradiation time around 8 min. The high EC values before 8 min can be explained by the initial sensible heat requirement to heat the solution to the regeneration temperature. Then minimum EC values are obtained following the desorption of a high quantity of CO2. Finally, values start to rise as less CO2 is released from the solutions (see trends in Fig. 4) while a continuous microwave heating is supplied. Lowest EC values were achieved before 10 min of regeneration by solutions at 90 °C while the 50 wt% MEA solution at 70 °C got quite good results for higher regeneration times. The analysis of Fig. 7 confirmed that 90 °C is the best regeneration temperature as EC2 values are the lowest. The 50 wt% MEA solution at 70 °C did not performed as well as its high EC2 values emphasis the fact that the amount of CO2 stripped at 70 °C is significantly lower than the amount stripped at 90 °C after the same irradiation time. The superior regeneration performances, based on EC and EC2, at 90 °C in comparison to the other tested temperatures corroborate the results of McGurk et al. (2017) which were based on solution cyclic loading analysis. This low temperature of 90 °C in comparison to conventional regeneration temperature found in literature (110–140 °C) (Bougie and Iliuta, 2010; Sakwattanapong et al., 2005; Zhang et al., 2008) would be worth considering in a whole process modeling study as solution evaporation rate will be much smaller and amine degradation and corrosion tendency reduced.

Fig. 6. EC as a function of the regeneration time for various MEA concentrations and temperatures.

Fig. 7. EC2 as a function of regeneration time for various MEA concentrations and temperatures.
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