The Three-Parameter NRTL Model

Renon used the concept of local composition to develop a non-random, two-liquid (NRTL) three parameter (al2, tp, ti() equations given below (Prausnitz et al., 1986). 

The parameter g,j is an energy parameter characteristic of the i-j interaction. The parameter an is related to the non-randomness in the mixture. The NRTL model contains three parameters which are independent of temperature and composition. However, experience has shown that for a large number of binary systems the parameter al2 varies from about 0.20 to 0.47. Typically, the value of 0.3 is set. 

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