Predictive Soave-Redlich-Kwong (PSRK)

Generic cubic equation of state

<math> P = { { R \; T } \over { V - b } } - { { a(T) } \over { ( V + \epsilon * b ) * ( V + \sigma * b ) } } </math>

Parameters for Soave-Redlich-Kwong equation are:

<math> \epsilon = 0</math> and <math> \sigma = 1</math>

Thus:

<math> P = { { R \; T } \over { V - b } } - { { a(T) } \over { V * ( V + b ) } } </math>

PSRK mixing rule for calculating a(T) and b

Cohesion pressure (attractive parameter):

<math> a(T) = b*R*T ( \sum x_i { {a_{ii}(T)} \over {b_i*R*T} } + { { { {g_0^E} \over {R*T} } + \sum x_i ln( b / b_i ) } \over { ln( u / (u + 1) )} } )</math>; <math> u = 1.1 </math>

with <math> a_{ii}(T) = \Psi * { { \alpha_i (T_{r,i}) * R^2 T_{C,i}^2 } \over { P_{C,i} } } </math>; <math> \Psi = 0.42748 </math>

Excluded volume or "co-volume" (repulsive parameter):

<math> b = \sum x_i*b_i </math>

with <math> b_i = \Omega * { { R*T_{C,i} } \over { P_{C,i} } } </math>; <math> \Omega = 0.08664 </math>

modified UNIFAC

Procedure for calculating vapour-liquid equilibria (VLE):