PITZER & RK-ASPEN Property Method

Introduction about PITZER & RK-ASPEN Property Method

1. PITZER & RK-ASPEN Property Method Presented by, KANCHAN D. RAMTEKE MT17MCL011

2. Introduction ASPEN plus To optimize throughput , quality and energy use Includes databases Pure component data Phase equilibrium data for various electrolytes , solids and polymers .

3. PITZER Property Method

4. Introduction The Pitzer model was developed as an improvement upon an earlier model proposed by Guggenheim (1935, 1955). The earlier model worked well at low electrolyte concentrations, but contained discrepancies at higher concentrations (>0.1M). The Pitzer model resolved these discrepancies, without resorting to excessive arrays of higher-order terms . It cannot be used for mixed solvent electrolyte systems.

5. The PITZER property method is based on an aqueous electrolyte activity coefficient model. It has no overlap with other activity coefficient models. It can accurately calculate the behavior of aqueous electrolyte solutions with or without molecular solutes up to 6 molal ionic strength. Many interaction parameters from regression of experimental data are included in databanks and data packages Do not use this model if a non-aqueous solvent exists.

6. You can model the solubility of supercritical gases using Henry’s law . Heats of mixing are calculated using the Pitzer model. The Redlich - Kwong -Soave equation of state is used for the vapor phase fugacity coefficient, all other vapor phase properties are assumed ideal. Redlich - Kwong -Soave cannot model association behavior in the vapor phase (for example, carboxylic acids or HF). For carboxylic acids, choose a non-electrolyte activity coefficient model with Hayden-O’Connell or Nothnagel ; for HF choose ENRTL-HF or WILS-HF.

7. Mixture Types You can use the Pitzer model for any aqueous electrolyte solution up to 6M ionic strength, not showing association in the vapor phase . Range Vapor phase fugacities are described accurately up to medium pressures . Interaction parameters should be fitted in the range of operation.

8. Model Development It uses the following expansion as a radial distribution function:

9. Pitzer proposes a general equation for the excess Gibbs energy . The basic equation is:

10. Parameters Required for the Pitzer Property Method Thermodynamic Properties Models Parameter Requirements Fugacity coefficient, Gibbs energy Pitzer Cation -anion: GMPTB0, GMPTB1, GMPTB2, GMPTB3, GMPTC Cation-cation : GMPTTH Anion-anion: GMPTTH Cation1-cation2-common anion: GMPTPS Anion1-anion2-common cation : GMPTPS Molecule-ion, Mol. – Mol.: GMPTB0, GMPTB1, GMPTC

11. Pitzer Activity Coefficient Model The Pitzer model in the Aspen Physical Property System involves user supplied parameters that are used in the calculation of binary and ternary parameters for the electrolyte system . Five elements (P1 through P5) account for the temperature dependencies of parameters β (0 ), β (1 ),β (2 ), β (3 ), cϕ , and θ . These parameters follow the temperature dependency relation:

12. Application of the Pitzer Model to Aqueous Strong Electrolyte Systems Pitzer modified his basic equation to make it more useful for data correlation of aqueous strong electrolytes. He defined a set of more directly observable parameters to represent combinations of the second and third virial coefficients. The cation -anion parameters B and C are characteristic for an aqueous single electrolyte system . These parameters can be determined by the properties of pure (apparent) electrolytes. B is expressed as a function of β(0) and β(1), β(2) and β(3 ) The modified Pitzer equation is: Subscripts c, c′ , and a, a′ denote cations and anions of the solution. B, C, θ, and Ψ are interaction parameters. f(I) is an electrostatic term as a function of ionic strength.

13. RK-ASPEN Property Method

14. Cubic Equations of State in the Aspen Physical Property System Peng -Robinson based Peng -Robinson Peng -Robinson Peng-Robinson-MHV2 Peng -Robinson-WS Redlich-Kwong (-Soave) based Redlich-Kwong Standard Standard Redlich - Kwong -Soave Redlich - Kwong -Soave Redlich - Kwong -ASPEN Schwartzentruber-Renon Redlich-Kwong-Soave-MHV2 Predictive SRK Redlich - Kwong -Soave-WS

15. Introduction

16. Equations E quation-of-state is the basis for the RK-ASPEN property method . The equation is the same as Redlich - Kwong -Soave: A quadratic mixing rule is maintained for : An interaction parameter is introduced in the mixing rule for :

17. For ai an extra polar parameter is used : The interaction parameters are temperature-dependent : For best results, binary parameters kij must be determined from phase-equilibrium data regression, such as VLE data.

18. RK-ASPEN allows temperature-dependent binary parameters. Mixture Types Range You can use the RK-ASPEN property method for mixtures of nonpolar and slightly polar compounds, in combination with light gases . It is especially suited for combinations of small and large molecules , such as nitrogen with n- Decane , or hydrogen-rich systems . RK-ASPEN - E quation-of-state model. You can use the RK-ASPEN property method up to high temperatures and pressures. You can expect reasonable results at any condition, but results are least accurate close to the critical point .

19. Parameters Required for the RK-ASPEN Property Method Thermodynamic Properties Models Parameter Requirements Fugacity coefficient, Density Redlich - Kwong -Aspen TCRKA, PCRKA, OMEGARKA UFGRP, GMUFR, GMUFQ Enthalpy, Entropy, Gibbs energy Ideal heat capacity, Redlich - Kwong -Aspen (CPIG or CPIGDP) and TCRKA, PCRKA, OMEGARKA Vapor and liquid mixture

20. Application It can be used for hydrocarbon processing applications. It is also used for more polar components and mixtures of hydrocarbons, and for light gases at medium to high pressures.