Phase Equilibrium in Amino Acid Salt Systems for CO2 Capture

Transcription

1 Downloaded from orbit.dtu.dk on: Dec 22, 217 Phase Equilibrium in Amino Acid Salt Systems for CO2 Capture Sengeløv, Louise With; Thomsen, Kaj Publication date: 211 Document Version Early version, also known as pre-print Link back to DTU Orbit Citation (APA): Sengeløv, L. W., & Thomsen, K. (211). Phase Equilibrium in Amino Acid Salt Systems for CO2 Capture [Sound/Visual production (digital)]. WORKSHOP - Amino Acid Salts for CO2 Capture, Adminiet, Porsgrunn, Norway, 1/1/211 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

2 Phase Equilibrium in Amino Acid Salt Systems for CO 2 Capture Louise With Sengeløv and Kaj Thomsen (kth@kt.dtu.dk) Porsgrunn, February 3rd 211

3 Outline Introduction General introduction Experimental data for amino acid salt systems Methionineas a case study Carbonate Methionine system Equilibrium constants Vapor Liquid equilibrium data Freezing point depression data Thermodynamic modelling Comparison of absorbents Absorber conditions Desorber conditions Heat of desorption Conclusion 2

4 Introduction Advantages in using amino acid salts instead of alkanolamines: Might be less prone to degradation in oxygen rich environments Less volatile than alkanolamines due to their ionic nature Same affinity towards CO 2 as alkanolamines Form carbamates Amino acids participate in the transportation of CO 2 in the blood by the formation of carbamate Problems and drawbacks: More expensive Limited solubility of amino acids in water Limited amount of experimental data available in literature 3

5 Experimental data for amino acid salt solutions CO 2 Equilibrium data Potassium taurate Kumar et al. (23) 38 data points, T=25 and 4 C Potassium glycinate (Portugal et al. 29) 13 data points, T= 2 5 C Potassium methionate (Kumelan et al. 21) 65 data points,, T= 8 12 C Potassium sarcosinate (Aronu et al. 21) graph with 55 points, T=4 12 C Potassium prolinate (unpublished, DTU, UTwente) Absorption kinetics Kumar et al. (23) (potassium salt of taurine and glycine) Van Holst et al. 29 (potassium salts of 7 different amino acids) Prakash et al. 21 (potassium salts of taurine and glycine) Equilibrium constants Sharma et al. 23 Hamborg et al. 27 Heat capacity and other thermal properties p none Freezing point depression data Sengeløv (21) (loaded and unloaded potassium salt of ) 2 data points 14 to C 4

6 Methionine, C 5 H 11 NO 2 S Molar mass g/mol Decomposition temperature 281 C Solubility in water at 25 C:.38 molal pka 2.28 and 9.21 Found in cereal grains and in nuts 5

7 Iso electric point of 1.9 Isoelectric point: 5, pka=2,28 28 pka=9, ph 6

8 Solubility of in water O and in NaCl solution X Hill and Robson, Biochemical Journal, 28(1934)

9 Equilibrium constants Sharma VK; Zinger A; Millero FJ; De Stefano C; Dissociation constants of protonated species in NaCl media, Biophysical Chemistry, 15(23)79 87 Determined in temperature range 5 45 C Hamborg ES; Niederer JPM; Versteeg GF; Dissociation constants and thermodynamic properties of amino acids used in CO 2 absorption from (293 to 353) K, J. Chem. Eng. Data, 52(27) Determined in temperature range 2 8 C Equilibrium constant for the carbamate formation of not available Equilibrium constant for the protonated form of not relevant at ph above 6 8

10 experimental data Kumelan J, Pérez Salado Sld Kamps A, Maurer G, Solubility of CO 2 in Aqueous Solutions of Methionine and in Aqueous Solutions of (K 2 CO 3 + Methionine), Ind. & Eng. Chem. Res. 49(21) VLE data for the system CO 2 H 2 O K 2 CO 3 Methionine at 8 12 C It corresponds to loaded solutions of potassium salt of Some precipitation in experiments at 8 C with 2.5 molal K 2 CO 3 and.83 83molal Sengeløv L., Bachelor Thesis, Technical University of Denmark, 21 Freezing point depression data for potassium salt of and for loaded solutions of this salt 9

11 essure in MPa Total pr Results for 1 the CO 2 H 2O K 2 CO 3 1 Methionine 9 system (Eq. constant from Sharma et al.) To otal pressure in MPa Kumelan et al. (21), 353K Extended UNIQUAC Extended UNIQUAC, CO2 in water Without K 2 CO K.83 molal Methionine 25molal 2.5 K 2 CO 3 m(met)=.4826 mol/(kg H 2 O) m(co 2 ) in mol/(kg H 2 O) m(co 2 ) in mol/(kg H 2 O) Kumelan et al. (21), 353K Extended UNIQUAC K Extended UNIQUAC K without Kumelan et al. (21), 373K Extended UNIQUAC K Extended UNIQUAC K without Kumelan et al. (21), 393K Extended UNIQUAC K Extended UNIQUAC K without 1

12 Results for the CO 2 H 2 O K 2 CO 3 Methionine system (Equilibrium quilibriumconstant fromsharma et al.) Total pr ressure in MPa 1 Kumelan et al..42 molal Methionine (21), 353K Extended UNIQUAC model 1.27 molal K 2 CO 3 Extended UNIQUAC 353 K Extended UNIQUAC 353 K without i Kumelan et al. (21), 373K Extended UNIQUAC 373 K Extended UNIQUAC 373 K without Kumelan et al. (21), 393K Extended UNIQUAC K Pitzer model, Kumelan et al Extended UNIQUAC K without m(co 2 ) in mol/(kg H 2 O) m(k 2 CO 3 ) 1.27 mol/(kg H 2 O) & m(met).42 mol/(kg H 2 O) 11

13 Measurements of freezing point depressions for mixtures of 1:1 (mole ratio) aqueous Met KOH and 1:3 (mole ratio) aqueous Met K 2 CO 3 12

14 Freezing point depressions: Results and model correlation (Equilibrium quilibriumconstant fromsharma et al.) 1 1 mol ratio :K 2 CO 3 1:3 Freezin ng point in C Freezing po oint in C Experimental Extended UNIQUAC m ( ) in mol/(kg H 2 O) Experimental Extended UNIQUAC mol ratio :KOH 1: m(potassium salt of ) in mol/(kg H 2 O) 13

15 Absorber conditions The potassium salt of as an absorbent in postcombustion contra, and K 2 CO 3 Equilibrium constant from Sharma et al. f CO 2 in kpa Pa artial pressure of molal llabsorbent, b 3 C 6 2 molal llabsorbent, b 3 C f CO 2 in kpa Pa artial pressure of Equilibrium constant from Hamborg et al. 2 in kpa l pressure of CO 2 Partia molal absorbent, 3 C n kpa Partial pressure of CO 2 i 4 Methionine molal absorbent, 3 C Methionine

16 Desorber conditions The potassium salt of as an absorbent in post combustion contra, MA, Aand K 2 CO 3 Partial pres ssure of CO 2 in kp Pa Equilibrium 1 constant from 8 Sharma et al molal absorbent, 115 C ssure of CO 2 in kpa Partial pre molalabsorbent, 115 C ) f reaction in kj/(k kg CO 2 captured) Heat of molal absorbent, 115 C ) f reaction in kj/(k kg CO 2 captured) Heat of molal absorbent, 115 C

17 Desorber conditions Equilibrium constant from Hamborg et al. The potassium salt of as an absorbent in postcombustion contra, and K 2 CO 3 in kpa pressure of CO 2 Partial ) Hea at of reaction in kj/ /(kg CO 2 captured) molal absorbent, 115 C molal absorbent, 115 C in kpa pressure of CO 2 i Partial kj/(kg CO 2 caputre ed) Heat of reaction in molal absorbent, 115 C molal absorbent, 115 C

18 Conclusion I The extreme difference between the properties of the potassium salt of at absorber conditions and at desorber conditions indicates: A strong temperature dependence of the equilibrium constant of Acidic properties of strongest at desorber temperature Portugal et al. found that the carbon dioxide solubility in potassium glycinate did not change much in the temperature range investigated (2 5 C) 17

19 Conclusion II Due to the limited amount of experimental data available, it is possible to model CO 2 solubility in amino acid salt solutions without taking carbamate formation into account The potassium salt of seems to have very interesting properties for post combustion usage. However VLE data at absorber column conditions are needed to validate the results The limited solubility and risk of precipitation provide challenges in the use of the potassium salt of and must be investigated further The 2 molal solutions for which calculations were shown here might be precipitating! More research is required to clarify the role of in the absorption process: Especially regarding carbamate formation and kinetics Much more research is required on amino acid salt solutions. They have very interesting properties and could be real alternatives to alkanolamines. 18