Download Reaction Enthalpy Evaluation for different Amine Solvents for Post

2nd Post Combustion Capture Conference (PCCC2)
Reaction Enthalpy Evaluation for different Amine Solvents for
Post-combustion Capture Applications
Abdurahim Abdulkadir, Mohammad Abu Zahra*
Separation Technology Laboratory, Masdar Institute of Science and T echnology, P.O.Box 542 24, Masd ar City,UAE
A substantial contributor to CO2 emissions is f ossil f uelled power plants and consequen tly, much research is curr ently
under way to reduce emissions f rom this source. The most mature capture technology to date is post combustion capture,
(PCC), using aqueous amine based solvents. Although this technology is well developed, significant improvements are
necessary before it can be economically applied on the scale required for CO 2 capture from power plants. In particula r,
the energy requirements for the currently available systems are very high. This is mostly attributable to the high energy
associated with regeneration of the solvent, to which the enthalpy of CO 2 absorption is the most important contribution.
The enthal py of CO 2 absorption also plays a significant role in the heat released in the absorber column, which influences
the temperature profile in the column. Therefore, major efforts for advance solvent development are directed towards the
evaluation of reaction enthalpies and specific heats of amine solvents. In this work , the reaction enthalpy and specific heat
of CO2 absorption in 30wt% and 40wt% of MEA , DEA , MDEA , AMP and Piperazine are measured using a Micro
Reaction Calorimeter instrument at temperature range between 25 0C and 100 0C.
Keywords: Experimental; Micro -Reaction Calorimeter; Alkanolamines; Carbon dioxide; Enthalpy
1. Introduction
Direct calo rimet ric measurem ents provide accurat e val ues on th e ent halpy of absorption, refl ecting both t he heat
effects due to the physical dissolution of gas in the solvent and the chemical reaction between CO 2 and amine.
Experiments, which are performed at constant temperature, also allow determination of the effect of temperature.
MEA is the most widely used alkanolamine in low-pressure industri al acid gas removal process es. However, there is
only limited in form ation on t he direct m easurements of the enthalpy of absorption of C O2 with MEA in the open
literature. Experimental data on th e heat o f absorption of CO2 with 30 wt % MEA solutions at 40, 80, and 120 °C in
an isotherm al flow calorimeter has been reported [1, 2]. The enthalpy o f absorption of CO2 with 10, 20, and 30 wt %
MEA sol utions at very low loadings have been measured at 25 °C using isothermal displacement calorimeter [3].
The measurements were performed using calorimeters of small volume, with the experimental points representing
the int egral enth alpies of abso rption (i.e., all heat rel eas ed in bringing the solution acid gas content from zero to a
fi nal lo ading). Other authors give val ues derived from solubility dat a whi ch are us ually call ed di fferential enthalpies
of absorption[4, 5]. In this work , the use of micro -reaction calorimeter was chosen to measure the enthalpy of
solution of carbon dioxide with different amine solution under different temperature range. The Micro Reaction
* Corresponding author. Tel.: +971 -2810-9181.
E-mail address: [email protected].
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Calorimeter from THT can perform isothermal enthalpy measurements o n the exothermic reactions that occur when
CO2 gas is absorbed by an amine solution. The versatility of the instrument allows measurement of the heat of
reactio n at di fferent temp eratures, flow rat es, volumes of s olution and gas pressures.
2. Experimental Section
The chemicals used in this study C O 2 (99.99% pure), the MEA, DEA, MDEA, AMP and Piperazine ( Sigma Aldrich, 99% pure), were us ed without any further puri fi cation. The 30wt% and 40wt% of the amine solutions were
prepared from distilled water. The calo rimetric studies involved measurements of the gas phase generation rate, with
respect to time, during the semi -batch isothermal absorption of CO 2 . The system continuously measures heat
production rate, reactor temperature, stirring speed, system pressure, and other parameters. All operating conditions
are reco rded as functions o f tim e. The schem e for the experimental setup is shown in Figure 1
Figure 1: Experimental Set up for the Micro -reaction Gas Flow Option
Author name / Energy Procedia 00 (2013) 000 –000
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Flow rates are kept l ow to minimize bas eline s hi ft due to evaporation of the solution. Reducing gas fl ow rat es also
helps reduce the effect of heat transfer to and from the system via the flowing gas . It was assumed that the gas
injected into the calorimeter was completely dissolved[3 ].
3. Results and Conclusion
A micro reaction calorim eter was u sed to m eas ure the enthal pies of absorption of CO2 in 3 0wt% and 40wt% of
different aqueous solutions of MEA, DEA, MDEA, AMP and Piperazine at temperature range between 25 0 C and
1000 C. Direct calo rimet ric m eas urements provi de an accurate m eans of obtai ning the enthalpy of absorption for acid
gases in solution as function of temperature. The significant difference in enthalpies is mostly due to the
endothermic bicarbonate formation reaction in the case of MDEA, which reduces the magnitude of the enthalpy,
compared to the exothermic carbamate formation reaction in the case of MEA, which further increases the
magnitude of the enthalpy of absorption. This is attributable to a relatively high carbamate stability constant,
resulting i n preferenti al formatio n of carbam ate, rath er th an bi carbonat e in the case of M EA. In contrast, carbamate
form ation is n ot obs erved at all in MDEA solutions, meaning that the absorbed C O2 is present predominantly as bi
carbonate. The results from this work may be used for thermodynamic modeling of CO 2 capture processes using
amines.
4. Reference
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Notz, R., et al., Selection and pilot plant tests of new absorbents for post -combustion carbon dioxide
capture. Chemical Engineering Research and Design, 2007. 85(4): p. 510-515.
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