Study on Redressing the Thermodynamic Property Package forProcess Simulator

DOI : 10.17577/IJERTV2IS101136

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Study on Redressing the Thermodynamic Property Package forProcess Simulator

Vikas Dinkar Gosavi 1*, Mohini Premmurari Dubey 1

1Department of Chemical Engineering, Institute of Technology, Nirma University, Ahmedabad 382481, Gujarat, India

Abstract

This paper describes the importance of redression of binary interaction parameter for selected thermodynamic property package in process simulator. The work has been made in this paper to redress the binary interaction parameter for non-ideal or complex binary systems of 2-ethoxyethanol + di-n-propyl ether, 1-propanol + 2-ethoxyethanol, 1-propanol + di-n- propyl ether. In this study, redressed value of the binary interaction parameters for UNIQUAC model fitted in CHEMCAD simulation software for comparing the bubble point pressure from experimental data and simulator data to increase the accuracy of simulation result.

Keywords: Activity coefficient, Binary interaction parameter, Redression, Regression, 2-ethoxyethanol, 1- propanol.

  1. Introduction

    Di-n-propyl ether (DPE) can be manufactured from reaction of 1-propanol (PA) with H2SO4, and complete separation of di-n-propyl ether can be archived with the help of 2-ethoxyethanol (trade name is Cellosolve) as solvent. Cellosolve mainly used as a solvent in industries or laboratory practices to dissolve resin, waxes, lacquers, grease, oils and nitrocellulose. Extractive distillation operation is used for separation of a DPE + PA. Cellosolve form a complex or non- ideal mixture with 1-propanol and di-n-propyl ether [1]. For designing of a distillation system vapor liquid equilibrium (VLE) data play vital role in it [2]. Process simulator like CHEMCAD simulation software can be used for design of such distillation system.

    Process simulator is an outstanding tool for analyzing, designing, rating and optimizing the process plants, refineries, chemical plants. In process simulator, various kind of thermodynamic property packages are used such as equation of state (EOS), activity models, vapor pressure models, chao seader and grayson streed

    models, other special models etc. Mainly thermodynamic activity models are used for non- standard or complex system. Binary interaction parameter (BIP) is the heart of the activity model and its value calculated with the help of the data regression analysis from experimental vapor liquid equilibrium (VLE) data. However, no one of activity model is accurate and often some adjustment must be done before their applications. Researchers have already provided BIP data for various mixtures in databank of process simulator. Before actual simulation, must check the accuracy and validity of thermodynamic property package. Convergence of flowsheet in process simulator does not give the guaranty of correct results [3]. Use of improper redressed binary interaction parameter (BIP) in process simulator which generates the result which deviates from reality. Prior to their application of process simulator with thermodynamic property package redressing of the binary interaction parameter with checking the converged result and its accuracy within allowable range, if not then thermodynamic property package should be redressed to enhance its accuracy [4]. This redressing can be done by VLE calculation such as dew point, bubble point or flash calculation and comparing the result with experimental data. Experimental VLE data for 2- ethoxyethanol + DPE (Table 1) [5], PA + 2-

    ethoxyethanol (Table 2) [6], PA + DPE (Table 3) [7] system has taken from literature and simulated VLE data is generated from CHEMCAD V6.0, using UNIQUAC thermodynamic activity model.

  2. Theory

    1. UNIQAC Activity Model

      UNIQUAC equation is equipped with two parts; a combinatorial part of UNIQUAC equation is describing the entropic contribution and residual part stand for the intermolecular forces. The combinatorial part requires only pure component data like sizes and shapes of molecules. The two binary interaction parameters arise only in the residual part of UNIQUAC equation [8].

      GE

      The UNIQUAC equation, substituting = G , is

      RT

      Table 1: Experimental vapor-liquid equilibrium data for the binary system of 2-ethoxyethanol (1) + di-n-

      given by 2 2 2 propyl ether (2) at 333.15K [5]

      G = GC(combinatori2al) + GR(residual) (1)

      C

      2 2 2

      2 21 2 12

      P (N/m2) X

      G =[x1ln

      X

      R

      + x ln

      X2

      + (q1x1ln

      + q x ln )J

      2

      1

      37092 0.0000

      G = q1x1ln(01 + 0 r21) q x ln(0 + 01r12)]

      Where,

      i

      i

      8 = Area fraction of component i = Xiqi

      Xjqj

      i

      i

      = Volume fraction of component i = Xiri

      j j

      j j

      X r

      qi = Surface area parameter of component i ri = Volume parameter of component i

      rij= Area Parameter

      (uij-ujj)

      36634 0.0395

      35738 0.0895

      34283 0.1778

      32637 0.2878

      30856 0.4081

      28594 0.5361

      26455 0.6310

      23462 0.7311

      21037 0.7923

      17717 0.8573

      ij

      ij

      = exp [A

      RT

      + Cijln(T) + Dij T]

      14328 0.9072

      11746 0.9414

      T = Temperature in degrees Kelvin

      Z = 10 (coordination number)

      The UNIQUAC BIPs of Aij, (UijUjj), and (UjiUii) are in cal/gmol. The binary interaction parameters Cij and Dij are optional. When regressing BIPs for UNIQUAC model, calculates only (U U ), and (U U ) with

      9057 0.9655

      7471 0.9817

      6787 0.9864

      5874 0.9947

      5486 0.9981

      5278 1.0000

      ij jj ji ii

      considering Aij and Aji are set to zero.

      2.2 Effect of BIP on prediction of bubble point pressure

      Bubble point pressure is defined as the pressure point at which the first bubble of gas comes out of the solution. At constant temperature bubble point pressure data with their corresponding liquid composition data arise

      Table 2: Experimental vapor-liquid equilibrium data for the binary system of n-propyl alcohol (1) + 2- ethoxyethanol (2) at 313.15K [6]

      P (N/m2) X1

      1865 0.0000

      from VLE experiment. According to the research

      2224

      0.0606

      studies, BIP value shows inherent temperature

      2452

      0.1001

      dependency [9,10]. The degree of temperature

      2732

      0.1500

      dependency of BIP is closely related to complexity in

      3005

      0.1997

      thermodynamic model. Those complexities increase the

      3282

      0.2503

      temperature dependency of BIP which lead to decrease

      3550

      0.2997

      the property prediction ability [11]. BIP is an empirical

      3813

      0.3497

      from VLE experiment. According to the research

      2224

      0.0606

      studies, BIP value shows inherent temperature

      2452

      0.1001

      dependency [9,10]. The degree of temperature

      2732

      0.1500

      dependency of BIP is closely related to complexity in

      3005

      0.1997

      thermodynamic model. Those complexities increase the

      3282

      0.2503

      temperature dependency of BIP which lead to decrease

      3550

      0.2997

      the property prediction ability [11]. BIP is an empirical

      3813

      0.3497

      2046 0.0298

      value and it has no theoretical explanation. Binary interaction parameters are calculated from data regression analysis. In data regression analysis,

      4070 0.3997

      4326 0.4498

      4578 0.4998

      minimise the objective function to find out the accurate

      4829

      0.5499

      binary interaction parameter for thermodynamic model

      5072

      0.5999

      [12,13]. UNIQAUC model were capable of precisely

      5309

      0.6499

      correlating the highly non-ideal or complex binary and

      5554

      0.7000

      ternary systems [14]. For redressing the BIP, try to

      5785

      0.7498

      simulate the same condition with UNIQAUC model in

      6022

      0.7998

      CHEMCAD simulator as the condition at which

      6249

      0.8496

      experimental data were obtained, and observed how 6477

      0.8998

      accurately the model can match them. Then find out the 6662

      0.9401

      6785

      0.9701

      minimise the objective function to find out the accurate

      4829

      0.5499

      binary interaction parameter for thermodynamic model

      5072

      0.5999

      [12,13]. UNIQAUC model were capable of precisely

      5309

      0.6499

      correlating the highly non-ideal or complex binary and

      5554

      0.7000

      ternary systems [14]. For redressing the BIP, try to

      5785

      0.7498

      simulate the same condition with UNIQAUC model in

      6022

      0.7998

      CHEMCAD simulator as the condition at which

      6249

      0.8496

      experimental data were obtained, and observed how 6477

      0.8998

      accurately the model can match them. Then find out the 6662

      0.9401

      6785

      0.9701

      4825 0.5498

      absolute relative deviation (ARD) from simulated result and experimental value.

      1

      1

      % ARD = N Pexp – Psim × 100

      N i Pexp

      6939 1.0000

      Step to analyze the effect of BIP on prediction of bubble point pressure:-

      1. Find out the BIPs (UijUii and UjiUjj) for UNIQUAC model from data regression with help of experimental VLE data.

      2. Compared the experimental values with result generated from process simulator with default value of BIPs as well as redressed value of BIPs.

      3. Calculate the average relative deviation (ARD) between experimental values and CHEMCAD simulator generated result.

      4. Redresses the BIP to minimize the %ARD till simulated result match with experimental

        table 4. Compare the simulator generated results of bubble point pressure for binary mixtures of PA (i) + 2- ethoxyethanol (j) and PA (i) + DPE (j) with their corresponding experimental data and that comparison graphically demonstrates in figure 2 and 3 respectively. Reductions in average relative deviation (ARD) for binary mixtures of PA (i) + 2-ethoxyethanol (j) and PA

        (i) + DPE (j) are tabulated in table 5.

        value.

        Table 3: Experimental vapor-liquid equilibrium data for the binary system of n-propyl alcohol (1) + di-n- propyl ether (2) at 333.15K [7]

        P (N/m2) X1

        26566

        0.0842

        26772

        26923

        0.1105

        0.1462

        10000

        27019

        0.1759

        27116

        0.2037

        27026

        0.2854

        0

        26379

        0.4165

        0

        0.2

        0.4

        0.6

        0.8 1

        25521

        0.5314

        Mole % of 2-ethoxyethanol

        25093

        0.5821

        23070

        0.7128

        22891

        0.7226

        Figure 1: Effect of BIP on B.P.P. of 2-ethoxyethanol +

        20953

        0.8075

        DPE at 333.15K

        16117

        0.9337

        26566

        0.0842

        26772

        26923

        0.1105

        0.1462

        10000

        27019

        0.1759

        27116

        0.2037

        27026

        0.2854

        0

        26379

        0.4165

        0

        0.2

        0.4

        0.6

        0.8 1

        25521

        0.5314

        Mole % of 2-ethoxyethanol

        25093

        0.5821

        23070

        0.7128

        22891

        0.7226

        Figure 1: Effect of BIP on B.P.P. of 2-ethoxyethanol +

        20953

        0.8075

        DPE at 333.15K

        16117

        0.9337

        25145 0.0000

        40000

        Bubble point pressure (N/m2)

        Bubble point pressure (N/m2)

        30000

        20000

        Redressed value of BIP

        Experimental Data

        Default value of BIP in CHEMCAD

        12238 1.0000

  3. Result and Discussion

    The effects of BIP (UijUii / UjiUjj) on bubble point pressure for mixture 2-ethoxyethanol (i) + DPE (j) at 333.15K for a 2-ethoxyethanol in liquid phase were forecasted using UNIQUAC in CHEMCAD V 6.0. Initially, the default value of the BIP in the databank of CHEMCAD UijUii = 0 and UjiUjj = 0 was used. The simulator generator result compared with experimental data and average relative deviation (ARD) for nineteen data point to be 20.347%. Redressed value of BIPs Uij Uii = -249.89 and UjiUjj = 629.102 was predicted with the help of data regression analysis of experimental value with UNIQUAC model. That redressed value of BIPs was reducing the 20.347% ARD to 3.483% ARD. The effects of BIP on bubble point pressure graphically represented in fig 1. That figure 1 clearly shows that the importance of redression of BIP for improving the accuracy of simulation result. Redression is substantial and accuracy of simulation much more improved. Similar improvements are observed for binary mixtures of PA (i) + 2-ethoxyethanol (j) and PA (i) + DPE (j) at 313.15K and 323.15K respectively, the default value of BIP in databank of CHEMCAD for both binary mixtures are UijUii = 0 and UjiUjj = 0 and redressed value of BIP for binary mixtures of PA (i) + 2- ethoxyethanol (j) and PA (i) + DPE (j) are tabulated in

    Table 4: BIP for binary mixture

    Binar mixture

    Default value of BIP in CHEMCAD

    Redressed value of BIP

    2-ethoxyethanol

    (i) + DPE (j)

    UijUii = 0

    UjiUjj = 0

    UijUii = -249.89

    UjiUjj = 629.102

    PA (i) + 2-

    ethoxyethanol (j)

    UijUii = 0

    UjiUjj = 0

    UijUii = -69.3672

    UjiUjj = 116.633

    PA (i) + DPE (j)

    UijUii = 0

    UjiUjj = 0

    UijUii = -240.7538

    UjiUjj = 703.182

    Redressed values of BIP in UNIQUAC model has been shown remarkable improvement in the simulation result. Table 5 clearly shows that the importance of binary interaction parameters in UNIQUAC for enhancing the predictability of process simulator. Remarkable improvement is observed in % ARD for binary systems of 2-ethoxyethanol + DPE, PA + 2- ethoxyethanol, PA + DPE. Property prediction of the binary and ternary systems or behaviour of the system with other process variable is greatly predicted with the help of redressed value of BIP in model.

    Bubble point pressure (N/m2)

    Bubble point pressure (N/m2)

    8000

    6000

    4000

    2000

    0

    Experimental Data Default value of BIP

    in CHEMCAD

    Redressed value of BIP

    0 0.2 0.4 0.6 0.8 1

    Mole % of 1-propanol

  4. Conclusion

    This paper demonstrate that the binary interaction parameters of an UNIQUAC model can be redressed to enhance the accuracy of process simulator considerably and also provide a step wise procedure for redression of the binary interaction parameter for thermodynamic model in process simulator. In this work, current discrepancies between default value of BIP in CHEMCAD simulation software and redressed value of BIP were analysed and study the impact of redression of binary interaction parameter for prediction of bubble point pressure for given system. These studies are clearly shows that the necessities of validation of the accuracy of thermodynamic models prior to performing simulation work. While accurately redressed value of BIPs for thermodynamic model in process simulator which has ensures that the simulator generated result as

    Figure 2: Effect of BIP on B.P.P. of PA + 2-

    ethoxyethanol at 313.15K

    good as experimental value.

  5. Acknowledgements

    Bubble point pressure (N/m2)

    Bubble point pressure (N/m2)

    40000

    30000

    20000

    10000

    0

    Default value of BIP in CHEMCAD

    Experimental Data

    Redressed value of BIP

    0 0.2 0.4 0.6 0.8 1

    Mole % of 1-propanol

    The authors would like to acknowledge from beneath of the heart to the Department of Chemical Engineering, Nirma University for providing congenial environment for completing this study.

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    Table 5: Average relative deviations for binary mixture

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    % ARD with default value of BIP

    % ARD with redressed value of BIP

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    + DPE (j)

    20.347 %

    3.483 %

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    0.36398 %

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    1.154 %

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