https://doi.org/10.1016/j.petlm.2016.11.002
“This energy has not been extensively studied in laboratory scale which is currently a set back because some amine solvents with low regeneration energy might have a high parasitic reclaiming energy (and vice versa).
During CO2 capture process, a slip stream of the CO2 lean amine solution from the regenerator is taken to the reclaiming unit to remove amine degradation products and recover fresh amine solvent, thereby maintaining the CO2 capture performance of the amine solvent. However, reclaiming comes with an additional energy penalty, most especially if thermal reclaiming technology is used [182]. Also, the amine waste generated is occasionally disposed of to avoid accumulation in the reclaiming unit. Results revealed that the reclaiming energy penalty will depend both on the type of reclaiming technology and type of amine used [182].
It is believed that there could be cases where the reclaiming energy will be higher than the regeneration energy. Hence, it is important to quantify or estimate the energy required for reclaiming an amine solution in order to ascertain the main source of energy penalty. This review paper is proposing a new correlation for estimating amine reclaiming energy (especially for thermal reclaiming) which considers the specific heat capacity (Cp, kJ/kg·°C) of the CO2 lean amine solution and atmospheric boiling point (Tbp, °C) of the amine solvent(s) in the amine solution as well as the amine reclamation rate as represented in Eq. (34).
(34)Qrec=(Cpamine)(Tbp)(Fm)rCO2_prod
where; Qrec is also in GJ/tonne CO2 while Fm is the mass flow rate of the CO2 lean amine solution that is reclaimed (kg/min).
The boiling point of the CO2 lean amine solution can be estimated using Eq. (35). Alternatively, any appropriate thermal analytical instrument can be used to determine the boiling point.
(35)Tbp=∑i=1mCiCTTbp_i
where; Tbp is the atmospheric boiling point of the amine solvent(s) in the amine solution (°C), Ci is the concentration of the ith amine in the blended amine solution (wt.%), CT is the total concentration of all components (amine and H2O) in the aqueous amine solution (wt.%), while Tbp_i is the atmospheric boiling point of the ith amine solvent(s) in the amine solution (°C).
When the specific heat capacity is not directly measured or available, Eq. (34) can then be rewritten as shown in Eq. (36).
(36)Qrec=(λα)(1ρ)(Tbp)(Fm)rCO2_prod
where; λ is thermal conductivity (mW/m. oC or mJ/s.m.°C), α is the thermal diffusivity (1E8m2/s) and ρ is the density (kg/m3) of the CO2 lean amine solution.
From Eq. (34) it can be deduced that the rate of amine reclamation, the atmospheric boiling point of the amine solvent(s) in the amine solution and the specific heat capacity of the CO2 lean amine solution are all proportional to the energy penalty for amine reclaiming. Though it has been documented that specific heat capacity of amine solutions do not vary much [158], therefore the energy penalty for reclaiming will depend more on both the atmospheric boiling point of the amine solvent(s) in the amine solution and reclaiming rate of the CO2 lean amine solution.
When CO2 lean amine volumetric flow rate is used, then Eq. (36) can be rewritten as shown in Eq. (37).
(37)Qrec=(λα)(Tbp)(Fv)rCO2_prod
where; Fv is the volumetric flow rate of the CO2 lean amine solution that is reclaimed (m3/min).
For simplicity, all thermophysical parameters of the CO2 lean amine solution as shown in Eqs. (34), (36), (37) can also be estimated using commercial process simulators like Aspen Plus, Aspen HYSYS both licensed by Aspen Technology, Inc., USA; ProMax (licensed by Bryan Research & Engineering, Inc., USA) and ProTreat® (licensed by Optimized Gas Treating Inc. USA) [237], [238], [239], [240] etc.
Additionally, looking at Eqs. (34), (36), (37) the flow rate of the CO2 lean amine solution to be reclaimed was used. However, this parameter might not be available in many pilot plant and bench–scale plant studies as well as in semi–batch experimental set–up. This parameter can be replaced with the disappearance rate of free amine in the amine solution (ramine_dis, kg of amine/hr) as shown in Eqs. (38), (39). This is valid because the faster the free amine disappearance the faster the amine degradation. Since free amine are also lost through emissions, this should be taken into account (subtracted) so that the amine losses used for Eqs. (38), (39) will be amine lost due to degradation.
(38)Qrec=(Cpamine)(Tbp)(ramine_dis)rCO2_prod
(39)Qrec=ramine_disrCO2_prod(Cpamine)(Tbp)
It is important to note that though thermal reclaiming is conducted under vacuum (most amine solvents with very high atmospheric boiling point) the actual atmospheric boiling point of the amine solvent(s) in the amine solution is used in Eqs. (34), (35), (36), (37), (38), (39) for simplicity. This can give the true trend of reclaiming energy because amine solvent(s) with higher atmospheric boiling point will require more vacuum energy than amine solvent(s) with lower boiling point. Vacuum condition is required so that the actual temperature for reclaiming will be reduced (below 100 °C), hence minimize any further thermal degradation of the amine solvents.
Additionally, when a semi–batch experimental set–up is used for analysis where the absorption and desorption experiments were conducted separately, then Eqs. (38), (39) still holds but the rCO2_prod and ramine_dis can be determined using correlations shown in Eqs. (40), (41).
(40)rCO2_prod=[(αCO2rich−αCO2lean)Camine]MCO2timedes
(41)ramine_dis=(Camine_ini−Camine_rem)Maminetimeabs−des
where; ramine_dis, is the rate of free amine disappearance (kg of amine/hr or tonne of amine/hr), rCO2_prod is the CO2 produced (kg of amine/hr or tonne of amine/hr), timedes is the desorption time during the experiment (hr), timeabs-des is the total time of both the absorption and desorption experiment (hr), Mamine is the molecular weight of the amine solvent (g/mol or kg/mol), Camine_ini is the initial amine concentration at the start of the experiment (moles) while Camine_rem is the remaining free amine concentration at the end of the experiment (moles).
From Eqs. (34), (35), (36), (37), (38), (39), (40), (41) and Fig. 21, some assumptions can be made:
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At similar CO2 production rate, an amine solvent with higher reclaiming rate and boiling point with have the higher energy penalty for reclaiming.
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At similar CO2 production rate and reclaiming rate, an amine with lower boiling point will require less reclaiming energy.
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At similar CO2 production rate and boiling point, an amine with higher reclaiming rate will require more reclaiming energy.
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It is most desired to have an amine solution with lower reclaiming rate and low boiling point (at similar CO2 production rate).

Fig. 21. Various scenarios of amine reclaiming rate vs amine solution boiling point (at similar CO2 production rate).
Low boiling point in this case refers to amines with boiling point slightly above that of water (105–140 °C). Most commercial amine solvents have boiling points between (145–248 °C), which means that they are likely to consume high energy for reclaiming (if they degrade fast). Also at constant vacuum pressure (in the reclaimer), amine solvents with low atmospheric boiling point will have much lower boiling point (than those with high atmospheric boiling point) leading to the use of hot water as the heating medium for reclaiming.
Since the boiling points of some nitrosamines, heat stable salts and non–ionic products like N- nitrosodiethylamine (NDEA, 171 °C), N-nitrosodimethylamine (NDMA, 151 °C), N-Nitrosodi-n-propylamine (NDPA, 206 °C), succinic acid (235 °C) and 2-Oxazolidone (220 °C) are high, they are less likely to be produced alongside with the recovered amine solvent during thermal reclaiming process for a low boiling point amine solvent.
It is important to note that low boiling point amine solvents might not necessarily lead to higher emissions because volatility is related more to the vapor pressure than boiling point. However, more research need to be conducted on low boiling point amine solvents to ascertain their overall benefits.
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