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Prediction of Vapour Liquid Equilibria for Binary Azeotropic Systems Using Activity Coefficient Models

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Prediction of Vapour Liquid Equilibria for Binary Azeotropic Systems Using Activity Coefficient Models International Journal of Innovative Technology and Exploring Engineering (IJITEE) ISSN: 2278-3075, Volume-8 Issue-12S2, October 2019 Prediction of Vapour Liquid Equilibria for Binary Azeotropic Systems using Activity Coefficient Models Sivaprakash .B, Manojkumar M.S Abstract—Distillation operations are inevitable in chemical and operation of the distillation equipments are important and petrochemical process industries. Design of distillation from economic and also environmental points of view [5]. equipment requires knowledge of precise vapor-liquid The presence of azeotropic mixture however complicates the equilibrium data. Due to the complexity and expenses incurred to design of ordinary distillation principles [6]. It is impossible obtain the VLE data experimentally for those systems for which the data are not available, solution thermodynamics and phase to conduct the distillation process in the case of azeotropic equilibria serve as an important tool in theoretical VLE composition.Azeotropes or close-boiling mixtures. The prediction. In the current investigation five binary azeotropes molecular interactions when two or more components are namely Acetone-water, Acetone-methanol, Ethanol-water, mixed may cause the mixture to form certain “inseparable” Ethanol-benzene, and Methanol-water are taken for study. The compositions where the vapor and liquid compositions at theoretical prediction of VLE for these systems were computed equilibrium are equal within a given pressure and using activity coefficient models namely NRTL, UNIQUAC, UNIFAC and modified form of Florry - Huggins equations (SRS temperature range. These specific mixture compositions are and TCRS). The parameters for the five systems of four models called azeotropes. The defining condition of an azeotropic viz. NRTL, UNIQUAC, SRS and TCRS were computed using mixture and the physical phenomena leads to nonideality. Newton Raphson technique. UNIFAC model was adopted using Nonideal mixtures exhibit positive (γi> 1) or negative (γi< 1) Analytical solution of group contribution (ASOG) method. The deviations from Raoult’s law [. If these deviations become performance of these models are tested using thermodynamic so large that the vapor pressure exhibits an extremal point at consistency test and validation from experimental VLE from literature. It was seen that the Acetone - Water system follows constant temperature, or, equivalently, an extremal point in TCRS model, Acetone - Methanol and Ethanol - Water and the boiling temperature at constant pressure. Azeotropes Methanol - Water systems follow UNIFAC model, whereas SRS play an important role in vapor-liquid equilibrium separation model suits for the Ethanol - Benzene system with highest processes. For efficient design of distillation equipment or accuracies. any other separation processes which are diffusional in nature requires quantitative understanding of vapour liquid Keywords: Vapour liquid Equilibrium, Azeotrope, Non ideal equilibria. In Vapour liquid equilibrium phases are system, Activity Coefficient model, Thermodynamic consistency expressed through vapour phase fugacity coefficients and I. INTRODUCTION the liquid phase activity coefficients. At low or modest pressures fugacity coefficient can be estimated easily for Separation of chemical in to the constituents is an art for very simple mixtures or ideal solutions, but for non-ideal millennia [1]. Chemical Engineers are more concerned with mixtures, estimation of liquid phase activity coefficient is separations process. Separation methods include distillation, quite difficult [7]. In the present work five azeotropic absorption, liquid-liquid extraction, leaching, drying and systems namely acetone-methanol, chloroform-methanol, crystallization etc [2]. Distillation, which is the most widely, acetone-water, ethanol-benzene and methanol-water were used separation technique in the chemical process industries taken for study. Experimental VLE of these systems were [3] accounts for about 3% of the world energy consumption. taken from literature . Applicability of five activity Also it has substantial advantages over the other processes coefficient models to these systems were tested in the study applied in order to separate a mixture, such extraction, viz. NRTL, UNIQUAC, UNIFAC and two forms of crystallization, semi permeable membranes etc. Distillation modified Flory – Huggins equations (SRS and TCRS). Also process is based on the fact that the composition of the thermodynamic consistency test for these models was boiling liquid and that of the vapour over it differ. Thus, if carried out by Redlich-Kister method. the boiling temperature is low (e.g., air separation), it is necessary to use low temperature refrigerants and conduct II.METHODOLOGY &LOW PRESSURE VLE the process at a higher pressure. If it is high (e.g., in DATA REDUCTION separation of heavy oil fractions or metals), high temperature heat carries or fire preheating have to be used There are different methods available for the regression of and the process is run under vacuum [4]. Because of the isothermal and isobaric VLE data. The gamma/phi (γ-ᵩ) high energy demand of these processes the optimal design formulation of VLE or more commonly known as the combined method was used in this work to regress the VLE data [8]. The combined method uses an equation of state to Revised Manuscript Received on September 14, 2019. Sivaprakash .B, Department of Chemical Engineering, Annamalai University, Annamalai Nagar, Tamilnadu, India Manojkumar M.S, Department of Petrochemical Engineering, Mahendra Institute of Engineering and Technology, Nammakkal, Tamilnadu, India Published By: Retrieval Number: L101310812S219/2019©BEIESP Blue Eyes Intelligence Engineering DOI: 10.35940/ijitee.L1013.10812S219 67 & Sciences Publication PREDICTION OF VAPOUR LIQUID EQUILIBRIA FOR BINARY AZEOTROPIC SYSTEMS USING ACTIVITY COEFFICIENT MODELS θ τ calculate the fugacity coefficients that describe the vapour R j ij phase non-idealities, while an activity coefficient model is ln i qi [1 - ln ( jθ jτ ji ) j used to calculate the activity coefficients that describe the kθk τkj liquid phase non-idealities. The gamma/phi method relies (9) upon liquid phase activity coefficient models to represent z VLE data, and give accurate result for non ideal solution li (ri qi ) - (ri 1) 2 (10) which is given by i Sat r Σ v R φi yi P γi xi Pi (1) i k k k (11) i yi is mole fraction in vapour phase; xi is mole fraction in q Σ v Q sat i k k k liquid phase; Pi is vapour pressure and P is operating (12) pressure; ᵠi is fugacity coefficient and γi is activity where segment or volume fraction of the component coefficient. i θi area fraction of the component Fugacity Coefficient: r volume parameter of the component At low to moderate pressure (0 to 10 atm), fugacity i coefficient can be calculated by the following equations. q surface area parameter of the component 0 1 i ln φ (B ω B )P /T i r r (2) UNIquac Functional group Activity Coefficient (UNIFAC) method f φ P i i (3) UNIFAC is based on UNIQUAC model, has a 1.6 combinatorial term that depends on the volume and surface B 0.083 - 0.422/T area of each molecule and a residual term that is the result of 0 r (4) the energies of interaction between the molecules [11]. The 1 4.2 B 0.139 - 0.172/T combinatorial term is evaluated using equation (8) When r (5) using the UNIFAC model one first identifies the functional ϕ is fugacity coefficient; B0& B1 are virial coefficients; ɷ i subgroups present in each molecule. Next the activity is accentric factor; P is reduced pressure; T is reduced r r coefficient for each species is written as temperature. ln ln (combinato rial) ln (residual) Activity Coefficient Models: i i i (13) NRTL (Non-Random Two Liquid) Model i i ln (residual) v [ln ln Γ ] The non random two liquid (NRTL) equation proposed by i k k k k (14) Renon and Prausnitz, [9] is applicable to partially miscible φm ψ as well as completely miscible systems. The equations for km ln ΓK Qk [1 ln (ΣmφmΨmk ) Σm ] the activity coefficients are ΣnφnΨnm 2 (15) G G 2 21 12 12 u u a x exp - mn nn mn 1 2 21 x x G 2 mn exp 1 2 21 (x2 x1G12 ) RT T ln (16) (6) i where k is residual activity coefficient; a is 2 mn interaction parameter; umnis interaction energy between 2 G G x 12 21 21 group m and n. 2 1 12 2 x x G (x x G ) Simplified Ruckenstein and Shulgin model (SRS) 2 1 12 1 2 21 ln The SRS equation for lni s are [12] given as (7) lnγ1 ln(x1 x2L12) x2[A12 A21](lnL12 lnL 21) where G12and G21 energy interaction between the molecules. x 1 x 2 UNIQUAC (UNIversal Quasi-Chemical) model 1 2 2 2 2 1 x1 x1 The UNIQUAC equation was developed by Anderson (19) and Prausnitz [10] who incorporated the two-liquid model ln γ 2 ln(x 2 x1L 21) x1[A12 A 21] (lnL 12 lnL 21) and the theory of local composition. The UNIQUAC 1 2 equation consists of two parts a combinatorial part that takes 12 x12 x11 x x into accounts the differences in sizes and shapes of the 1 1 (20) molecules and the residual part that is due to the Lij intermolecular forces between the molecules. In the form of A ij x x L an equation, this is represented as Where 1 2 ij (21) θ C i z i i ln γi ln qi ln li j x jl j xi 2 i xi (8) Published By: Retrieval Number: L101310812S219/2019©BEIESP Blue Eyes Intelligence Engineering DOI: 10.35940/ijitee.L1013.10812S219 68 & Sciences Publication International Journal of Innovative Technology and Exploring Engineering (IJITEE) ISSN: 2278-3075, Volume-8 Issue-12S2, October 2019 Mathematical Computation Vj λij λii Lij exp The theoretical estimation of VLE using the five activity V RT i (22) coefficient models, NRTL, UNIQUAC, UNIFAC, SRS and x1 TCRS was accomplished using Newton Raphson technique i with computer programming in Java software of 1.6 version.
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