Novel absorbents with improved characteristics are required to reduce the existing cost and environmental barriers to deployment of large scale CO2 capture. Recently, bespoke absorbent molecules have been specifically designed for CO2 capture applications, and their fundamental properties and suitability for CO2 capture processes evaluated. From the study, two unique diamine molecules, 4-(2-hydroxyethylamino)piperidine (A4) and 1-(2-hydroxyethyl)-4-aminopiperidine (C4), were selected for further evaluation including thermodynamic characterization. The solubilities of CO2 in two diamine solutions with a mass fraction of 15% and 30% were measured at different temperatures (313.15–393.15 K) and CO2 partial pressures (up to 400 kPa) by thermostatic vapor−liquid equilibrium (VLE) stirred cell. The absorption enthalpies of reactions between diamines and CO2 were evaluated at different temperatures (313.15 and 333.15 K) using a CPA201 reaction calorimeter. The amine protonation constants and associated protonation enthalpies were determined by potentiometric titration. The interaction of CO2 with the diamine solutions was summarized and a simple mathematical model established that could make a preliminary but good prediction of the VLE and thermodynamic properties. Based on the analyses in this work, the two designer diamines A4 and C4 showed superior performance compared to amines typically used for CO2 capture and further research will be completed at larger scale.

•A rigorous, rate-based model for the NH3–PZ–CO2–H2O system using Aspen Plus® was developed.•The model was validated against experimental data in a relatively large temperature and CO2 loading range.•The effect of adding PZ as a promoter in a large-scale, NH3-based CO2 capture process was described.•The reaction mechanism in an absorber using PZ-promoted ammonia solution was revealed.•Increasing CO2 absorption capacity of the solvent is the key to reduce sensible heat, which can be done by adding PZ.Due to the fast reaction rate of piperazine (PZ) with CO2, it has the potential to act as a promoter in aqueous ammonia (NH3)-based CO2 capture processes. We have developed a rigorous, rate-based model for the NH3–PZ–CO2–H2O system using Aspen Plus®, and validated the model against experimental results. Absorption and desorption processes were simulated under real flue gas conditions to gain a practical understanding of the behaviour and characteristics of interactions between PZ‐promoted NH3 solution and CO2. Adding PZ significantly increased the CO2 absorption rate in the NH3-based CO2 capture process via a fast reaction between PZ carbamate and CO2. The temperature along the column was higher than in the absence of PZ, and more free ammonia was released into the solution, which led to higher ammonia loss. Adding PZ also reduced the stripping heat, resulting in a smaller energy requirement for solvent regeneration.

An accurate thermodynamic model is the primary element needed for the process simulation and optimization for CO2 absorption in aqueous amine solutions. In this work, the thermodynamic model was built in Aspen Plus, using the electrolyte nonrandom two-liquid (ENRTL) activity coefficient model to represent vapor pressure and heat capacity data, simultaneously, for amine, vapor–liquid equilibrium (VLE), excess enthalpy (HE), and pKa data for amine/H2O, and CO2 solubility data for amine/CO2/H2O. The cyclic diamine 1-methylpiperazine (1MPZ) is a promising amine for CO2 capture. CO2 solubility was measured for 1MPZ aqueous solutions at three concentrations – 10 wt%, 30 wt%, and 40 wt% and four temperatures – 313.15 K, 343.15 K, 373.15 K, and 393.15 K. The excess enthalpy for 1MPZ + H2O was obtained by the Setaram C80 calorimeter at 303.15 K and 323.15 K, within a whole mole-fraction range. The interaction parameters of nonrandom two-liquid model (NRTL) and ENRTL, along with the standard state properties of amine ions – protonated 1MPZ (1MPZH+, 1MPZH2+), 1MPZ carbamate (1MPZCOO−), and protonated 1MPZ carbamate (H1MPZCOO) – were regressed from data obtained from this work as well as literature, which agreed with the model calculation.

•Heat integration of CFPP with CO2 capture and compression process.•Utilizing of waste heat from CO2 capture and compression process.•Taking part of LP cylinders out of service in CFPP.•Adding an auxiliary turbine to decompress the extracted steam.•The efficiency penalty is reduced from 12.3% to 9.75%.Coal-fired power plant (CFPP) is one of the main sources of anthropogenic CO2 emissions. Capturing CO2 from CFPP by post-combustion process plays an important role to mitigate CO2 emissions. However, a significant thermal efficiency drop was observed when integrating CFPP with post-combustion carbon capture (PCC) process due to the steam extraction for capture solvent regeneration. Thus research efforts are required to decrease this energy penalty. In this study, a steady state model for 600 MWe supercritical CFPP was developed as a reference case with a low heating value (LHV) based efficiency of 41.6%. A steady state model for MEA-based PCC process was also developed and scaled up to match the capacity of the CFPP. CO2 compression process was simulated to give an accurate prediction of its electricity consumption and cooling requirement. Different integration cases were set up according to different positions of steam extraction from the CFPP. The results show that the efficiency penalty is 12.29% and 14.9% when steam was extracted at 3.64 bar and at 9.1 bar respectively. Obvious improvements were achieved by utilizing waste heat from CO2 capture and compression process, taking part of low pressure cylinders out of service, and adding an auxiliary turbine to decompress the extracted steam. The efficiency penalty of the best case decreases to 9.75%. This study indicates that comprehensive heat integrations can significantly improve the overall energy efficiency when the CFPP is integrated with PCC and compression process.

The separations of olefin/paraffin, aromatic/aliphatic hydrocarbons or olefin isomers using ionic liquids instead of volatile solvents have interested many researchers. Activity coefficients γ∞ at infinite dilution of a solute in ionic liquid are generally used in the selection of solvents for extraction or extractive distillation. In fact, the measurement of γ−8 by gas-liquid chromatography is a speedy and cost-saving method. Activity coefficients at infinite dilution of hydrocarbon solutes, such as alkanes, hexenes, alkylbenzenes, styrene, in 1-allyl-3-methylimidazolium tetrafluoroborate ([AMIM][BF4]) and 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6]), 1-isobutenyl-3-methylimidazolium tetrafluoroborate ([MPMIM][BF4]) and [MPMIM][BF4]-AgBF4 have been determined by gas-liquid chromatography using ionic liquids as stationary phase. The measurements were carried out at different temperatures from 298 to 318 K. The separating effects of these ionic liquids for alkanes/hexane, aliphatic hydrocarbons/benzene and hexene isomers have been discussed. The hydrophobic parameter, dipole element, frontier molecular orbital energy gap and hydration energy of these hydrocarbons were calculated with the PM3 semi-empirical quantum chemistry method. The quantitative relations among the computed structure parameters and activity coefficients at infinite dilution were also developed. The experimental activity coefficient data are consistent with the correlated and predicted results using QSPR models.

This paper studies the mass transfer performance of structured packings in the absorption of CO2 from air with aqueous NaOH solution. The Eight structured packings tested are sheet metal ones with corrugations of different geometry parameters. Effective mass transfer area and overall gas phase mass transfer coefficient have been measured in an absorption column of 200 mm diameter under the conditions of gas F-factor in 0.38–1.52 Pa0.5 and aqueous NaOH solution concentration of 0.10–0.15 kmol·m− 3. The effects of gas/liquid phase flow rates and packing geometry parameters are also investigated. The results show that the effective mass transfer area changes not only with packing geometry parameters and liquid load, but also with gas F-factor. A new effective mass transfer area correlation on the gas F-factor and the liquid load was proposed, which is found to fit experiment data very well.The effective mass transfer areas of sheet corrugated structured packings were measured in a packing column about 1.2 m tall with an inside diameter of 200 mm, in which the height of packed section is 0.8 m. Air entered at the bottom of the column and flowed upward, while NaOH solution was pumped to the top of the column and flowed downward. The figure shows the effects of addendum angles on effective mass transfer areas of sheet corrugated structured packings. At α of 37.5°, when Fs = 0.76 Pa0.5 or 1.14 Pa0.5, packing with β of 90° has the largest effective mass transfer area. And the effect of α and β on the area was also changed by gas/liquid flow rates. Under most gas/liquid flow rates in this study, α = 30° and β = 75° were the best parameters.Download full-size image