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Solubility of K 2 SO 4 in CO 2 Loaded MEA/PZ Solution Jan 10th, 2008 Qing Xu Rochelle group Department of Chemical Engineering University of Texas at Austin

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Outline Reclaiming process Why reclaiming Reclaiming processes Experiment Conductivity for K 2 SO 4 solution Ranges of the experiments Apparent K sp dependence on T, amine and I Regression Analysis – Electrolyte-NRTL (in Aspen Plus ) Interaction parameters regression Flash simulation test for regression results Conclusion Future work

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Why reclaiming ? What to reclaim: SO 2, HCl, NO x SO 4 -2, Cl -, NO 3 - … Organic acids, amine polymers Why reclaiming? To remove heat stable salts and degradation products, which may cause corrosion, foaming, and will affect the capacity of amine solution. Chemical reactions:

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Reclaiming Processes: Thermal reclaiming with addition of NaOH Na 2 SO 4 (s) MEA degradation products Sodium formate Electrodialysis Ion exchange Sulfate precipitation Fertilizer

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CO 2 Capture Process High T Low T CaSO 4 CaCO 3

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Precipitation Reclaiming for Hot Lean Solvent 3×3× Hot Lean Cool Lean CO 2 H2OH2O K 2 SO 4 (s) KOH

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Solubility of K 2 SO 4 in CO 2 Loaded Amine can Determine: Solvent flow rate for reclaiming. Operating condition to avoid scaling. Energy and equipment cost.

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Apparatus and Method - 1 Stirrer K 2 SO 4 Conductivity meter Water Bath

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Apparatus and Method - 2 BottleTop Water Bath Conductivity Meter Water Bath

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11m MEA, [CO 2 ] t =0.4 mol/mol MEA, 80 o C Conductivity~[K 2 SO 4 ] Start with K 2 SO 4 slurry End, clear solution

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Ranges of the Experiments T: 25 ℃, 40 ℃, 80 ℃ Amine: 7m MEA, 11m MEA, 4m PZ, 7m MEA/2m PZ, 8m PZ, 10m PZ, etc. CO 2 loading: Loading Extra K + : 0, 0.35m Extra SO 4 = : 0, 0.15m

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K sp dependence on T, amine concentration, and ionic strength 7m 11m 80C 40C

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Regression Analysis - K sp K sp of K 2 SO 4 : Property method: elecNRTL in Aspen Plus Based on solubility data of K 2 SO 4 in water by Söhnel, 1985, regress A, B, and C in K sp (T): ParameterValue (SI units)σ A B C

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Originally by Chen et al., for aqueous electrolyte systems. Later extended to mixed solvent electrolyte systems (Mock et al., 1984, 1986). A versatile model for the calculation of activity coefficients. Adjustable ENRTL interaction parameters: Molecule-molecule Molecule-electrolyte Electrolyte-electrolyte Each interaction consists of both the nonrandomness factor and energy parameters . Regression Analysis – Electrolyte NRTL Model

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Regression Analysis – Interaction parameters Framework Data Regression System in Aspen Plus Electrolyte-NRTL model Chemistry: K sp (T) from previous regression. ｝

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Existing parameters Electrolyte-NRTL default values in Aspen Plus Hilliard, 2005 (10 C, D & E for MEA-H 2 O-CO 2 system and parameters for pure/binary components) Objective Parameters (C) and (D) related to K + and SO 4 = Solubility data used Water data by Söhnel, 1985; MEA data by Xu, 2006~2007. Method Select parameters with small correlation coefficients. Small residual root mean square error. Small AARD (average absolute relative deviations) in flash simulation test Regression Analysis – Interaction parameters

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Regression Analysis - Results Component iComponent j CD H2OH2O(K +,MEACOO - ) xx MEA xx (MEA +,SO 4 -2 )H2OH2O xx MEA x (MEA +,SO 4 -2 ) x (K +, SO 4 -2 )MEA xx (K +, HCO 3 - )MEA xx

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A series of flash simulation Using the regressed interaction parameter set Simulate under each experimental condition Get activity coefficient and mole fraction for each case, calculate K sp and the error from K sp (T). AARD: 45.6% Regression Analysis – Test

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Dependence of K sp (meas)/K sp (T) on [CO 2 ]

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Dependence of K sp (meas)/K sp (T) on [MEA]

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Dependence of K sp (meas)/K sp (T) on T

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Conclusions K sp dependence on T, equivalent amine concentration, and ionic strength: A parameter set in Electrolyte-NRTL model for the CO 2 -MEA-H 2 O-K + -SO 4 = system was developed. Still need modification. K sp (meas)/K sp (T) is dependent on MEA concentration and CO 2 loading, independent on temperature.

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Future work Modify the regression; get more accurate C/D/E parameter set for the . Conduct experiments of K 2 SO 4 crystallization Slurry characteristics: settling rates, filterability, drying rates and final moisture contents. Crystal characteristics: composition, form, habit, shape factors, and solid density. Crystallization kinetics: crystal nucleation, growth. Modify Aspen reclaiming process model with regressed parameters, optimize conditions, add crystallization data into the model.

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