Van Laar & NRTL Equation in Chemical Engineering Thermodynamicas

Van Laar & NRTL (Non random two liquid) Equation in Chemical Engineering Thermodynamicas

1. Advanced Chemical Engineering Thermodynamics Presented By : Guided By: Satish Movaliya Prof. Zoher Painter ME (Chemical ) Prof. Milap Nayak 150170730008 CHEMICAL ENGINEERING DEPARTMENT VISHWAKARMA GOVERNMENT ENGINEERING COLLEGE CHANDKHEDA

2. Van Laar equation

3. =   =   Where , and are effective volume fraction of separate components in the solution and are the effective molal volumes Above equation is known as Wohl’s three suffix equation . Let = in above equation. The resulting two parameter equation is known as the Van Laar equation . The Van Laar equation can be written as   = A =   = B =   The constant A is the terminal value of at = 0 and B is the terminal value of at = 0. When A and B are equal, the Van Laar equation simplify to Margules equation .  

4. Above the Van Laar equation may be rearranged to the following forms, which are very convenient for the evaluation of constants A and B . A = ; B =   The Van Laar equation are applicable only for solutions of relatively simple, preferably non-polar liquid. The van Laar equations are widely used for vapor-liquid equilibrium calculations because of their flexibility and mathematical simplicity. The van Laar constants vary with temperature unless the temperature range involved is small. The van Laar equations can be used for unsymmetrical solutions.

5. Non-random two-liquid (NRTL ) equation

6. The NRTL model, proposed by Renon and Prausnitz (1968), also is based on the local composition concept. The activity coefficients are = =   In above equation, the adjustable parameters are evaluated as = exp ( - ) ; = exp ( - ) And = ; =  

7. The constants and are similar to the constants representing characteristic energy differences appearing in the Wilson equation. These, as well as the constants are independent of composition and temperature. The parameter is related to the non-randomness in the mixture. If is zero, the mixture is completely random and the NRTL equation reduces to the Margules equation.   NRTL equation is applicable to partially miscible as well as totally miscible systems. For moderately non-ideal systems, it offers no advantage over the Van Laar and Margules equations. But, for strongly non-ideal solutions and especially partially miscible systems, the NRTL equations provide a good representation.

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