INTER Table: Binary Interaction Coefficients Database

This guide documents the INTER table in NeqSim, which contains binary interaction parameters (BIPs) for thermodynamic models including equations of state (EoS), activity coefficient models, and CPA association parameters.

Overview
Table Structure
Column Reference
Relation to Mixing Rules
Usage Examples
Setting Custom Parameters
TBP Fractions and Default Values

Overview

The INTER table is the central repository for all binary interaction parameters in NeqSim. It stores parameters for:

Cubic EoS - Classical $k_{ij}$ values for SRK and PR
CPA EoS - Association and $k_{ij}$ for CPA model
Huron-Vidal - $\alpha$, $g_{ij}$, $g_{ji}$ parameters
Wong-Sandler - Integration with UNIFAC
NRTL - $\alpha$, $g_{ij}$, $g_{ji}$ for activity coefficients
Soreide-Whitson - Oil-water systems
Desmukh-Mather - Amine systems

Location: src/main/resources/data/INTER.csv

Database table name: INTER (or INTERTEMP for temporary tables)

Table Structure

The INTER table contains one row per component pair. Each row has parameters for multiple thermodynamic models, allowing the same fluid definition to be used with different mixing rules.

Example entry:

ID,COMP1,COMP2,HVTYPE,KIJSRK,KIJTSRK,KIJTType,KIJPR,KIJTPR,KIJPCSAFT,...
6950,CO2,methane,Classic,0.0973,0,0,0.0973,0,...

Column Reference

Component Pair Identification

Column	Type	Description
`ID`	Integer	Unique row identifier
`COMP1`	String	First component name (must match COMP table)
`COMP2`	String	Second component name (must match COMP table)

Important: Component pairs are symmetric. NeqSim searches for both (COMP1=A, COMP2=B) and (COMP1=B, COMP2=A).

EoS Interaction Parameters

These parameters are used in the classical van der Waals mixing rules for cubic equations of state.

Column	Type	Description	Used By
`KIJSRK`	Double	Binary interaction parameter for SRK EoS	`SystemSrkEos`
`KIJTSRK`	Double	Temperature correction to $k_{ij}$ for SRK	SRK with T-dependent kij
`KIJTType`	Integer	Type of temperature dependence (0, 1, 2)	All EoS
`KIJPR`	Double	Binary interaction parameter for PR EoS	`SystemPrEos`
`KIJTPR`	Double	Temperature correction to $k_{ij}$ for PR	PR with T-dependent kij
`KIJPCSAFT`	Double	Binary interaction for PC-SAFT EoS	`SystemPCSAFT`

Temperature dependence types (KIJTType):

0 - No temperature dependence: $k_{ij}(T) = k_{ij}$
1 - Inverse temperature: $k_{ij}(T) = k_{ij} + k_{ij}^T / T$
2 - Linear temperature: $k_{ij}(T) = k_{ij} + k_{ij}^T \cdot T$

Mathematical role:

The $k_{ij}$ parameter appears in the classical mixing rule for the EoS attractive parameter:

\[a_{mix} = \sum_i \sum_j x_i x_j \sqrt{a_i a_j} (1 - k_{ij})\]

A positive $k_{ij}$ reduces the attractive interactions between unlike molecules.

Huron-Vidal Parameters

Huron-Vidal mixing rules combine an EoS with an activity coefficient model.

Column	Type	Description
`HVTYPE`	String	Type of mixing rule (`"Classic"` or `"HV"`)
`HVALPHA`	Double	NRTL non-randomness parameter ($\alpha$)
`HVGIJ`	Double	NRTL interaction parameter $g_{ij}$ (J/mol)
`HVGJI`	Double	NRTL interaction parameter $g_{ji}$ (J/mol)
`HVGIJT`	Double	Temperature derivative of $g_{ij}$
`HVGJIT`	Double	Temperature derivative of $g_{ji}$

Note: When HVTYPE = "Classic", the Huron-Vidal parameters are not used.

Mathematical formulation:

\[\tau_{ij} = \frac{g_{ij} - g_{jj}}{RT} = \frac{\Delta g_{ij}}{RT}\] \[G_{ij} = \exp(-\alpha_{ij} \tau_{ij})\]

Wong-Sandler Parameters

Wong-Sandler mixing rules provide thermodynamic consistency between high and low pressure limits.

Column	Type	Description
`WSTYPE`	String	Type (`"Classic"` or `"WS"`)
`KIJWS`	Double	Wong-Sandler interaction parameter
`KIJWSunifac`	Double	WS parameter for UNIFAC integration
`CalcWij`	Integer	Flag for calculated vs fitted W parameters
`W1`, `W2`, `W3`	Double	Second virial coefficient parameters
`WSGIJT`	Double	Temperature derivative for WS $g_{ij}$
`WSGJIT`	Double	Temperature derivative for WS $g_{ji}$

NRTL Parameters

Non-Random Two-Liquid parameters for activity coefficient calculations.

Column	Type	Description
`NRTLALPHA`	Double	Non-randomness parameter $\alpha_{ij}$ (typically 0.2-0.47)
`NRTLGIJ`	Double	Interaction parameter $g_{ij}$ (J/mol)
`NRTLGJI`	Double	Interaction parameter $g_{ji}$ (J/mol)

NRTL Activity Coefficient:

\[\ln \gamma_i = \frac{\sum_j x_j \tau_{ji} G_{ji}}{\sum_k x_k G_{ki}} + \sum_j \frac{x_j G_{ij}}{\sum_k x_k G_{kj}} \left( \tau_{ij} - \frac{\sum_m x_m \tau_{mj} G_{mj}}{\sum_k x_k G_{kj}} \right)\]

CPA Association Parameters

These parameters control cross-association in the CPA (Cubic Plus Association) equation of state.

Column	Type	Description
`cpakij_SRK`	Double	SRK-CPA binary interaction parameter
`cpakijT_SRK`	Double	Temperature correction for CPA $k_{ij}$
`cpakijx_SRK`	Double	Composition-dependent $k_{ij}$ (asymmetric)
`cpakjix_SRK`	Double	Composition-dependent $k_{ji}$ (asymmetric)
`cpakij_PR`	Double	PR-CPA binary interaction parameter
`cpaAssosiationType`	Integer	Association scheme type (0, 1, 2, …)
`cpaBetaCross`	Double	Cross-association volume parameter $\beta^{AB}$
`cpaEpsCross`	Double	Cross-association energy parameter $\epsilon^{AB}$ (K)

Association scheme types:

0 - No induced association
1 - CR1 combining rule (Elliott rule)
2 - CR2 combining rule (geometric mean)
Other values - Custom fitted parameters

Cross-association combining rules:

When cpaAssosiationType = 1 (CR1/Elliott rule): $\epsilon^{AB}_{ij} = \frac{\epsilon^{AA}_{ii} + \epsilon^{BB}_{jj}}{2}$ $\beta^{AB}_{ij} = \sqrt{\beta^{AA}_{ii} \beta^{BB}_{jj}}$

When explicit values are provided in cpaBetaCross and cpaEpsCross, they override the combining rules.

Physical Property Parameters

Column	Type	Description
`GIJVISC`	Double	Viscosity mixing parameter
`KIJWhitsonSoriede`	Double	Soreide-Whitson correlation parameter

Desmukh-Mather Parameters

For amine-gas systems with the Desmukh-Mather model.

Column	Type	Description
`aijDesMath`	Double	Desmukh-Mather $a_{ij}$ parameter
`bijDesMath`	Double	Desmukh-Mather $b_{ij}$ parameter

Relation to Mixing Rules

The INTER table parameters are loaded when you call setMixingRule(). The mixing rule number determines which columns are read:

Mixing Rule	Number	Parameters Used
Classic (kij=0)	1	None (all kij set to 0)
Classic (from database)	2	`KIJSRK`/`KIJPR`
Classic + T-dependent	3	`KIJSRK`, `KIJTSRK`, `KIJTType`
Huron-Vidal	4	`HVALPHA`, `HVGIJ`, `HVGJI`
Wong-Sandler	5	`KIJWS`, `W1-W3`, NRTL params
CPA	7	`cpakij_SRK`, `cpaBetaCross`, `cpaEpsCross`
CPA + T-dependent	9	+ `cpakijT_SRK`
CPA + composition-dependent	10	+ `cpakijx_SRK`, `cpakjix_SRK`

Example:

// Classic with database kij
fluid.setMixingRule(2);  // or fluid.setMixingRule("classic");

// Uses KIJSRK/KIJPR columns from INTER table

Usage Examples

Accessing Binary Interaction Parameters

import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermo.phase.PhaseEos;

SystemInterface fluid = new SystemSrkEos(300.0, 50.0);
fluid.addComponent("methane", 0.8);
fluid.addComponent("CO2", 0.2);
fluid.setMixingRule("classic");  // Loads from INTER table

// Get kij value
PhaseEos phase = (PhaseEos) fluid.getPhase(0);
double kij = phase.getMixingRule().getBinaryInteractionParameter(0, 1);
System.out.println("kij(methane-CO2) = " + kij);  // 0.0973

Setting Custom Binary Parameters

// Method 1: Using component names (recommended)
fluid.setBinaryInteractionParameter("methane", "CO2", 0.10);

// Method 2: Using component indices
((PhaseEos) fluid.getPhase(0)).getMixingRule()
    .setBinaryInteractionParameter(0, 1, 0.10);
((PhaseEos) fluid.getPhase(1)).getMixingRule()
    .setBinaryInteractionParameter(0, 1, 0.10);

Setting Temperature-Dependent Parameters

// Set temperature coefficient
((PhaseEos) fluid.getPhase(0)).getMixingRule()
    .setBinaryInteractionParameterT1(0, 1, -0.001);

// kij(T) = kij + kijT * T  (when KIJTType=2)

Getting All Binary Parameters

double[][] kijMatrix = ((PhaseEos) fluid.getPhase(0))
    .getMixingRule().getBinaryInteractionParameters();

// Print matrix
for (int i = 0; i < fluid.getNumberOfComponents(); i++) {
    for (int j = 0; j < fluid.getNumberOfComponents(); j++) {
        System.out.print(kijMatrix[i][j] + " ");
    }
    System.out.println();
}

CPA Cross-Association Example

SystemInterface fluid = new SystemSrkCPAstatoil(300.0, 50.0);
fluid.addComponent("methane", 0.7);
fluid.addComponent("water", 0.2);
fluid.addComponent("MEG", 0.1);
fluid.setMixingRule(10);  // CPA with composition-dependent kij

// Cross-association parameters are loaded automatically:
// - cpaBetaCross for methane-water
// - cpaEpsCross for water-MEG association

Setting Custom Parameters

Adding New Component Pairs

To add interaction parameters for a new component pair:

Add to INTER.csv:

99999,newcomp1,newcomp2,Classic,0.05,0,0,0.05,0,0,0,0,0,0,0,0,0,Classic,0.5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0.05

Or set programmatically:

fluid.setBinaryInteractionParameter("newcomp1", "newcomp2", 0.05);

Asymmetric Parameters

Some mixing rules support asymmetric $k_{ij} \neq k_{ji}$:

// Set kij (component i with j)
((PhaseEos) fluid.getPhase(0)).getMixingRule()
    .setBinaryInteractionParameterij(i, j, 0.05);

// Set kji (component j with i)
((PhaseEos) fluid.getPhase(0)).getMixingRule()
    .setBinaryInteractionParameterji(i, j, 0.03);

TBP Fractions and Default Values

For undefined pseudo-components (TBP fractions), NeqSim uses correlations or default values:

Default kij Values for TBP Fractions

Component	TBP Fraction	Default $k_{ij}$
CO2	All	0.10
N2	All	0.08
H2O	All	0.20
MEG	All	0.20

Calculated Parameters

When setCalcEOSInteractionParameters(true) is called, NeqSim calculates $k_{ij}$ from critical volumes:

\[k_{ij} = 1 - \left( \frac{2 \sqrt[3]{V_{c,i} V_{c,j}}}{V_{c,i}^{1/3} + V_{c,j}^{1/3}} \right)^n\]

where $n$ is configurable (default = 6).

Column Summary Table

Category	Columns
Identification	ID, COMP1, COMP2
SRK EoS	KIJSRK, KIJTSRK
PR EoS	KIJPR, KIJTPR
PC-SAFT	KIJPCSAFT
Temperature Type	KIJTType
Huron-Vidal	HVTYPE, HVALPHA, HVGIJ, HVGJI, HVGIJT, HVGJIT
Wong-Sandler	WSTYPE, KIJWS, KIJWSunifac, CalcWij, W1, W2, W3, WSGIJT, WSGJIT
NRTL	NRTLALPHA, NRTLGIJ, NRTLGJI
CPA	cpakij_SRK, cpakijT_SRK, cpakijx_SRK, cpakjix_SRK, cpakij_PR, cpaAssosiationType, cpaBetaCross, cpaEpsCross
Physical Properties	GIJVISC
Soreide-Whitson	KIJWhitsonSoriede
Desmukh-Mather	aijDesMath, bijDesMath

Typical Parameter Values

Common $k_{ij}$ Values (SRK/PR)

Pair	$k_{ij}$	Notes
CH4 - C2H6	0.003	Very similar molecules
CH4 - CO2	0.097	Significant non-ideality
CH4 - H2S	0.08	Acid gas
CH4 - N2	0.032	Typical
CH4 - H2O	0.45-0.65	Polar-nonpolar (CPA: ~-0.08)
CO2 - H2S	0.10-0.12	Acid gas pair
CO2 - C3H8	0.12-0.14
H2O - MEG	0.13	CPA model

CPA Association Parameters

Pair	$\beta^{AB}$	$\epsilon^{AB}$ (K)
H2O - MEG	0.055	2000-2500
H2O - methanol	0.039	2000-2500
CO2 - H2O	0.085	0 (solvation)

References

Soave, G. (1972). Equilibrium Constants from a Modified Redlich-Kwong Equation of State. Chem. Eng. Sci.
Peng, D.Y., Robinson, D.B. (1976). A New Two-Constant Equation of State. Ind. Eng. Chem. Fundam.
Huron, M.J., Vidal, J. (1979). New Mixing Rules in Simple Equations of State. Fluid Phase Equilib.
Wong, D.S.H., Sandler, S.I. (1992). A Theoretically Correct Mixing Rule. AIChE J.
Kontogeorgis, G.M., et al. (2006). Multicomponent Phase Equilibrium Calculations for Water-Methanol-Alkane Mixtures. Fluid Phase Equilib.
Soreide, I., Whitson, C.H. (1992). Peng-Robinson Predictions for Hydrocarbons, CO2, N2, and H2S with Pure Water and NaCl Brine. Fluid Phase Equilib.

INTER Table: Binary Interaction Coefficients Database

Comprehensive Java library for thermodynamic, physical property, and process simulation. NeqSim provides tools for PVT analysis, phase equilibria, transport properties, and full process simulation.

INTER Table: Binary Interaction Coefficients Database

Table of Contents

Overview

Table Structure

Column Reference

Component Pair Identification

EoS Interaction Parameters

Huron-Vidal Parameters

Wong-Sandler Parameters

NRTL Parameters

CPA Association Parameters

Physical Property Parameters

Desmukh-Mather Parameters

Relation to Mixing Rules

Usage Examples

Accessing Binary Interaction Parameters

Setting Custom Binary Parameters

Setting Temperature-Dependent Parameters

Getting All Binary Parameters

CPA Cross-Association Example

Setting Custom Parameters

Adding New Component Pairs

Asymmetric Parameters

TBP Fractions and Default Values

Default kij Values for TBP Fractions

Calculated Parameters

Column Summary Table

Typical Parameter Values

Common $k_{ij}$ Values (SRK/PR)

CPA Association Parameters

References