How Molecular Modelling Tools Can Help …
197
physical phenomena of CO 2 capture using absorbents and adsorbents, and (2)
complementing experimental data required for process design and simulation at postcombustion CO 2 capture operating conditions. Accurate and transferable models
capable of characterising the absorption and adsorption processes of CO 2 capture
and separation are built for this purpose as a step towards fostering predictive and
robust models for CO 2 capture, while searching for a fine balance between simplicity,
transferability and accuracy.
4.1 Alternative Solvents for CO 2 Capture
Even though a large number of aqueous amine solutions has been already examined
for CO 2 absorption process [112–114], there is still much work needed to obtain
the best molecule or blend to surmount the shortcomings of the current amine +
water solutions used in industry today, especially in terms of energy requirement.
We present here some representative results obtained with soft-SAFT as a modelling
tool for the development of amine alternative solvents.
The choice of alternative amines was based on the evaluation of parameters
specifically selected to assess their performance with respect to the reference amine,
monoethanolamine (MEA), which is the most used at large scale. Hence, alternative amines were assessed in terms of three key performance indicators (KPIs): CO 2
loading (α— moleCO 2 mole amine
-1 ), heat of absorption (H abs — kJ moleCO 2
-1 )
and absorption rate (k 0 —min
−1 or gCO 2 L
−1 min
−1 ). To allow a direct comparison, these parameters were evaluated for aqueous solutions with 30 wt% amine
at a representative process temperature of 40 °C and a partial pressure of CO 2 of
15 kPa. Out of the 150 + different amines included in our own developed database,
Fig. 12 depicts the results for a number of aqueous amine solutions for which experimental data from screening studies were available. Values were normalized using
those reported for MEA at same conditions (30 wt%, 40 °C and 15 kPaCO 2 ): α MEA
= 0.58 moleCO 2 moleMEA
-1 [115]; H abs MEA = 85.13 kJ moleCO 2
-1 [115] and
k 0 MEA = 0.014 min
−1 [116] or 5.47 gCO 2 L
−1 min
−1 [117].
Towards reducing the costs and energy requirements of amine-based CO 2 capture
processes, amines with high CO 2 loadings, low heats of absorption and high absorption rates are needed. As can be inferred from Fig. 12a, a number of amines
are capable of achieving higher CO 2 loadings and lower heat of absorption than
MEA, as shown by the amines contained in quadrant I. However, a significant
number of these amines present an absorption rate lower than MEA, as depicted
in Fig. 12b—quadrant I. Based on the available data, only piperazine (PZ) shows
a superior performance to MEA in terms of CO 2 loading, heat of absorption
as well as an outstanding rate of absorption at the conditions investigated. Nmethyldiethanolamine (MDEA) shows the lowest heat of absorption, indicating a
lower energy penalty for solvent regeneration, with a CO 2 loading comparable to that
of MEA but slower absorption rates. The highest CO 2 loadings are obtained for multiamines, namely hexamethylenediamine (HMDA), 1,3-diamino-2-propanol (DAP)
197
physical phenomena of CO 2 capture using absorbents and adsorbents, and (2)
complementing experimental data required for process design and simulation at postcombustion CO 2 capture operating conditions. Accurate and transferable models
capable of characterising the absorption and adsorption processes of CO 2 capture
and separation are built for this purpose as a step towards fostering predictive and
robust models for CO 2 capture, while searching for a fine balance between simplicity,
transferability and accuracy.
4.1 Alternative Solvents for CO 2 Capture
Even though a large number of aqueous amine solutions has been already examined
for CO 2 absorption process [112–114], there is still much work needed to obtain
the best molecule or blend to surmount the shortcomings of the current amine +
water solutions used in industry today, especially in terms of energy requirement.
We present here some representative results obtained with soft-SAFT as a modelling
tool for the development of amine alternative solvents.
The choice of alternative amines was based on the evaluation of parameters
specifically selected to assess their performance with respect to the reference amine,
monoethanolamine (MEA), which is the most used at large scale. Hence, alternative amines were assessed in terms of three key performance indicators (KPIs): CO 2
loading (α— moleCO 2 mole amine
-1 ), heat of absorption (H abs — kJ moleCO 2
-1 )
and absorption rate (k 0 —min
−1 or gCO 2 L
−1 min
−1 ). To allow a direct comparison, these parameters were evaluated for aqueous solutions with 30 wt% amine
at a representative process temperature of 40 °C and a partial pressure of CO 2 of
15 kPa. Out of the 150 + different amines included in our own developed database,
Fig. 12 depicts the results for a number of aqueous amine solutions for which experimental data from screening studies were available. Values were normalized using
those reported for MEA at same conditions (30 wt%, 40 °C and 15 kPaCO 2 ): α MEA
= 0.58 moleCO 2 moleMEA
-1 [115]; H abs MEA = 85.13 kJ moleCO 2
-1 [115] and
k 0 MEA = 0.014 min
−1 [116] or 5.47 gCO 2 L
−1 min
−1 [117].
Towards reducing the costs and energy requirements of amine-based CO 2 capture
processes, amines with high CO 2 loadings, low heats of absorption and high absorption rates are needed. As can be inferred from Fig. 12a, a number of amines
are capable of achieving higher CO 2 loadings and lower heat of absorption than
MEA, as shown by the amines contained in quadrant I. However, a significant
number of these amines present an absorption rate lower than MEA, as depicted
in Fig. 12b—quadrant I. Based on the available data, only piperazine (PZ) shows
a superior performance to MEA in terms of CO 2 loading, heat of absorption
as well as an outstanding rate of absorption at the conditions investigated. Nmethyldiethanolamine (MDEA) shows the lowest heat of absorption, indicating a
lower energy penalty for solvent regeneration, with a CO 2 loading comparable to that
of MEA but slower absorption rates. The highest CO 2 loadings are obtained for multiamines, namely hexamethylenediamine (HMDA), 1,3-diamino-2-propanol (DAP)