Heat of absorption of CO 2 in aqueous ammonia, piperazine solutions and their mixtures

Transcription

1 Heat of absorption of CO 2 in aqueous ammonia, piperazine solutions and their mixtures Jinzhao Liu, Shujuan Wang, Hallvard F Svendsen*, Muhammad Usman Idrees, Inna Kim and Changhe Chen The 6th Trondheim Conference on CO 2 Capture, Transport and Storage Trondheim, June 14-16, 11 1

2 Outline Introduction Experimental apparatus and methods Results and discussion Conclusions

3 Back ground Introduction CO 2 Capture Chemical absorption Research area Heat of absorption ΔH abs Absorbent Aqueous ammonia (Qin F., 1) Piperazine solution (Hilliard M., 8; Kim I., 9) NH 3 /PZ blended solution

4 Chemical reactions of CO 2 with NH 3 (aq) The reaction of CO 2 with NH 3 (aq) is deeply discussed by Kohl et al (1997) and Yeh et al (5). The total reaction can be described as the equation (1): CO NH H O NH HCO ΔH rx =64.26 kj/mol (1) The actual process of the reaction can be described as step-by-step reactions. First of all, reaction (2) occurs as: CO 2 NH NH COONH ΔH rx =72.32 kj/mol (2) Then, NH COONH has an irreversible reaction (3) in solution: 2 4 NH COONH H O NH HCO NH ΔH rx =8.6 kj/mol (3) At the same time, the following two reactions are possible to occur: CO 2 NH H O ( NH ) CO CO H O ( NH ) CO 2NH HCO ΔH rx =11.22 kj/mol (4) ΔH rx =26.88 kj/mol (5)

5 Chemical reactions of CO 2 with PZ solution Heat of reaction of CO 2 with PZ solution was determined mainly by the following two reversible reactions (Bishnoi and Rochelle, ; Ermatchkov et al., 2; Derks and Versteeg, 6). First of all, at the beginning of the absorption process, reaction (6) mainly determined the ΔH abs : PZ H OCO PZCOO H O (6) As the absorption process going on, the CO 2 loading of solution increased, free PZ decreased, and the generation of PZCOO made reaction (7) gradually began to occur. PZCOO H O CO PZ( COO ) H O (7)

6 ΔH abs estimated by VLE data (Xu et al, 9) ln f i H (1 / T) R Px, (Gibbs-Helmholtz Equation)

7 Experimental apparatus in this work The experimental setup of the 2L reaction calorimeter CPA-122 (ChemiSens AB, Lund, Sweden)

8 c c Experimental methods n CO2 (mol) added from the cylinder in to the reactor could be calculated using Peng- Robinson equation: RT a p v 2 2 b v 2 bv b RTc a [1 ( )(1 T )] p RTc b.778 p r The total uncertainty can be expressed as following: The uncertainty in the calculation of n CO2 (mol) has 5 been estimated to be 1.2% and 1.4% (only at 8 for contain NH 3 system, caused by the partial pressure of NH 3 changed in gas-phase 3 when adding CO 2 ). abs total CO2 Habs Qtotal n CO2 2 3%MEA_Kim,7 3%MEA_this work Baseline Heat flow; CO 2 flow The uncertainty in the calculation of total heat Q total (kj) has been estimated to be.5% at, 1% at and 2.7% at 8.,,1,2,3,4,5,6,7,8 2 The total uncertainty was estimated H Q n Fig.3. Heat of absorption to be of 1.5% CO 2 with at 3wt% MEA and compared, and with Kim s experimental data at be 3% at 8

9 NH 3 (aq) Experimental section Concentration: 3.1 m (5 wt% ) Temperature:,, 8 PZ solution Concentration:.86 m (6.9 wt%) Temperature:,, 8 NH 3 /PZ blended solution Concentration: 3.1m NH m PZ; 3.1m NH m PZ; 1.5m NH m PZ Temperature:,, 8

10 Chemicals CO 2 (AGA, 99.99% pure) Distilled water (NTNU Lab) Piperazine (SIGMA-ALDRICH, > 99 % pure) Ammonia (SIGMA-ALDRICH, 25wt% ) All the concentrations of tested solutions were determined by Metrohm 89 Titrando auto titrator.

11 Heat of absorption of CO 2 in NH 3 (aq) 5%NH3_this work_1 5%NH3_this work_2 2.5%NH3_Qin,1_1 2.5%NH3_Qin,1_2 VLE data_gibbs-helmholtz equation_kurz, Mani (6) using NMR data estimated,2,4,6,8 1,2,4,6,8 1 ΔH abs 8 kj/mol CO 2 8 ΔH abs 74.8 kj/mol CO 2 Fig.4. Heat of absorption of CO 2 with NH 3 (aq) at Fig.5. Heat of absorption of CO 2 with NH 3 (aq) at CO2 NH3 H 2O NH 4HCO3 ΔHrx=64.26 kj/mol CO 2 ΔH abs 65.9 kj/mol CO 2 5%NH3_this work_1 5%NH3_this work_2 2.5%NH3_Qin,1_1 2.5%NH3_Qin,1_2 VLE data_gibbs-helmholtz equation_kurz,1995,2,4,6,8 1 1 CO 2NH NH COONH ΔHrx=72.32 kj/mol CO %NH3_this work_1 5%NH3_this work_2 2.5%NH3_Qin,1_1 Kurz (1995) using VLE data estimated ΔH abs 65 kj/mol CO %NH3_Qin,1_2 VLE data_gibbs-helmholtz equation_kurz,1995 _1 _2 _1 _2 8 _1 8 _2 ΔH abs 8 kj/mol CO 2 NH COONH H O NH HCO NH ΔHrx=8.6 kj/mol CO 2 VLE data_gibbs-helmholtz equation_kurz,1995 all,2,4,6,8 1 Fig.6. Heat of absorption of CO 2 with NH 3 (aq) at 8 Fig.7. Heat of absorption of CO 2 with 5wt% NH 3 (aq) at, and 8

12 Heat of absorption of CO 2 in PZ solutions m_this work_test1.86m_this work_test2 2.4m_Kim, m_this work_test1 1.86m_this work_test ,2,4,6,8 1 1,2 1,4,2,4,6,8 1 Fig.8. Heat of absorption of CO 2 with PZ solution at Fig.9. Heat of absorption of CO 2 with PZ solution at.86m_this work_test1.86m_this work_test2 2.4m_Kim,9,2,4,6,8 1 1, all 8 ΔH abs kj/mol CO 2 _1 _1 8 _1 _ _2 PZ H O CO PZCOO H O Xu (11) using VLE data estimated ΔH abs kj/mol CO 2 8 _2,2,4,6,8 1 1,2 Fig.1. Heat of absorption of CO 2 with PZ solution at 8 Fig.11. Heat of absorption of CO 2 with.86m PZ solution at, and 8

13 Heat of absorption of CO 2 in 3.1m NH 3 /.86m PZ blended solutons m NH3_1 3.1m NH3_2.86m PZ_1.86m PZ_ m NH3_1 3.1m NH3_2.86m PZ_1.86m PZ_ m NH3+.86m PZ_1 3.1m NH3+.86m PZ_ m NH3+.86m PZ_1 3.1m NH3+.86m PZ_2,2,4,6,8 1 1,2,2,4,6,8 1 Fig.14. Heat of absorption of CO 2 with NH 3 /PZ blended solutions at Fig.15. Heat of absorption of CO 2 with NH 3 /PZ blended solutions at m NH3_1 3.1m NH3_2.86m PZ_1.86m PZ_2 3.1m NH3+.86m PZ_1 3.1m NH3+.86m PZ_2 8,2,4,6,8 1 Fig.16. Heat of absorption of CO 2 with NH 3 /PZ blended solutions at 8 Fig.19. Heat of absorption of CO 2 with NH 3 /PZ blended solutions at _1 _1 8 _1 _2 _2 8 _2 all,1,2,3,4,5,6,7,8

14 Effect of PZ concentration to the heat of absorption m NH3 3.1m NH3+.43m PZ m NH3 3.1m NH3+.43m PZ 1 3.1m NH3+.8m PZ 1 3.1m NH3+.86m PZ,2,4,6,8 1 Fig.17. Heat of absorption of CO 2 with NH 3 (aq) and NH 3 blended PZ in different concentrations at,1,2,3,4,5,6,7,8 Fig.18. Heat of absorption of CO 2 with NH 3 (aq) and NH 3 blended PZ in different concentrations at

15 Comparison of NH 3 /PZ blends with MEA/PZ blends at o C mMEA_Kim,9 2.4m PZ_Kim,9 7mMEA+2.4m PZ_Kim, m PZ 1.5m NH3+.86m PZ 3.1m NH3+.86m PZ,1,2,3,4,5,6,7,8,2,4,6,8 1 Fig.. Heat of absorption of CO 2 with MEA/PZ blended solutions compared with individual MEA and PZ solutions at Fig.21. Heat Heat of of absorption of CO of CO 2 with 2 with PZ PZ and and PZ PZ blended NH NH 3 (aq) 3 (aq) in in different concentrations at

16 NH 3 /PZ blended solutions compared with other mixtures m NH3+.86m PZ_this work 3 wt% MEA+ wt% AMP_Kim,9 7m MEA+2m PZ_Kim,9 6m K(+)+1.2m PZ_Kim,9 7m MEA+3.5m PZ_Kim,9 5m K(+)+2.5m PZ_Kim,9,1,2,3,4,5,6,7,8 3.1m NH3+.86m PZ_this work 3 wt% MEA+ wt% AMP_Kim,9 7m MEA+2m PZ_Kim,9 6m K(+)+1.2m PZ_Kim,9 7m MEA+3.5m PZ_Kim,9 5m K(+)+2.5m PZ_Kim,9,1,2,3,4,5,6,7,8 Fig.22. Heat of absorption of CO 2 with NH 3 /PZ blended solutions measured by this work compared with other mixtures at Fig.23. Heat of absorption of CO 2 with NH 3 /PZ blended solutions measured by this work compared with other mixtures at 8

17 Conclusions A reaction calorimeter CPA-122 was used to determine the heats of absorption (ΔH abs ) of CO 2 in NH 3 (aq), PZ solutions and their mixtures at, and 8. The trends of ΔH abs changing with CO 2 loading α were obtained at each temperature. ΔH abs of CO 2 in 5 wt% NH 3 (aq) at low CO 2 loading interval (-.5) was estimated to be 74.8 kj/mol CO 2 at and 65.9 kj/mol CO 2 at 8. ΔH abs of CO 2 in.86m PZ solution were estimated to be kj/mol CO 2 at low CO 2 loading interval (-.5) at -8. ΔH abs of CO 2 in NH 3 /PZ blended solutions were measured and found to demonstrate a high degree of consistency with only NH 3 (aq) s results during entire CO 2 loading interval at each temperature. The mechanism of the heat of absorption controlled by the reactions of CO 2 with NH 3 and PZ in the mixtures was also discussed.

18