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

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

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:

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.