Modeling of pervaporation processes controlled by concentration polarization

doi:10.1016/j.compchemeng.2006.11.008

Computers & Chemical Engineering

Volume 31, Issue 10, October 2007, Pages 1326-1335

https://doi.org/10.1016/j.compchemeng.2006.11.008 Get rights and content

Abstract

Pervaporation is considered a clean and energetically efficient process used for a wide range of applications, working separately or integrated into a hybrid process. In this work, a mathematical model has been developed accounting for the mass transport phenomena under non-isothermal conditions with strong contribution of polarization concentration that prevail in pervaporation systems.

The mathematical model incorporates characteristics of the module geometry, mass and heat transfer correlations and estimation of the system physicochemical properties. The equation-oriented simulation software g-PROMS^® was used in the solution of the final problem.

Finally, the model was tested against a representative case study, pervaporative dehydration of cyclohexane, the solvent used in the manufacture of synthetic rubber. Model simulated curves described satisfactorily well the kinetic data of cyclohexane dehydration obtained in a pilot plant set-up.

Introduction

Pervaporation (PV) is presented in literature as an economic alternative for saving energy costs when combined in hybrid pervaporation–distillation processes, as reported by Huang (1991), and Jonquières et al. (2002). Azeotropic, close boiling- and high boiling-point mixtures are examples of said hybrid applications.

Solute removal by pervaporation is nowadays a common industrial application (Néel, 1997). One of the most famous plants, owing to its size, is the Betheneville plant for ethanol dehydration (France). In this industrial pervaporation application, plates-and-frames modules provided with hydrophilic polymeric membranes (commonly PVA) are used (Ho & Shirkar, 1992).

Although the number of works dealing with PV opportunities in the last decades is enormous, most part use simplified mathematical models to predict the separation flux (Ahmad, Lau, Abu Bakar, Abd. Shukor, 2005; Cao & Henson, 2002; Urtiaga, Gorri, & Ortiz, 1999). More recently, scarce contributions have considered non-isothermal description of the involved phenomena, under steady state conditions, to determine optimum operation. The works of Han, Li, Chen, and Wickramasinghe (2002), and Eliceche, Daviou, Hoch, and Ortiz (2002) can be mentioned as representative examples.

Simulation of the system behavior is an important tool in the design and optimization of an industrial pervaporation plant (Biegler, Grossmann, & Westerberg, 1997). The aim of this study is to develop a general mathematical model that gives a satisfactory description of PV separations under non-isothermal and non-stationary conditions that are usually encountered in industrial applications and for applications governed by polarization concentration. The equation-oriented simulation software g-PROMS^® has been selected to solve the problem and to obtain results under different operation conditions. The model has been tested against experimental results of the dehydration of industrial cyclohexane obtained in a pilot plant that uses plates-and-frames membrane modules (Ortiz, Urtiaga, Ibáñez, Gómez, & Gorri, 2006).

Section snippets

Mathematical modeling of the PV process

Description of a PV operation working in batch mode under non-isothermal and non-stationary conditions needs the solution of simultaneous first order ordinary equations, which are mass and heat balances, together with algebraic expressions to obtain the transport flux across the pervaporation system. Hydrodynamic influence over the process performance requires a correct geometrical description of the membrane module.

Method of solution

The set of differential and algebraic equations presented in the mathematical model were solved simultaneously using the equation-oriented simulation software g-PROMS^®. The integration of this model required additional information in the form of property correlations, geometrical parameters and mass transport correlations. In addition, the suitable values of the shape parameters ‘a’ and ‘b’ of Eqs. (1) and (3), respectively must be determined for the membrane module used. A set of possible

Case study

To facilitate understanding of model applicability, the performance of the pervaporation process at a pilot plant scale studied satisfactorily in the R&D facilities of the Spanish company Dynasol Elastomeros S.A. was selected as a case of study. A PV pilot plant set-up comprising a plate-and-frame PLC-06 CM-Celfa module (total membrane area of 3 m²), with similar characteristics to an industrial installation, coupled to a 20 l feed tank was installed and conditioned to operate in batch mode. The

Simulation results and discussion

After integrating the mass and heat balances, Eqs. (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16) with the g-PROMS^® software tool, simulated results for different conditions were obtained. Table 4 shows model details in terms of the total number of equations, variables and parameters involved. Table 5 compiles the values of the transport and the temperature dependent variables obtained for a flow rate of 5.00 × 10⁻⁵ m³ s⁻¹ and initial solute content in feed of

Conclusions

In this study, a mathematical model has been developed able to describe the behaviour of pervaporation processes with strong control of concentration polarization under common non-isothermal and non-stationary conditions using plates-and-frames membrane modules. For this purpose, module geometry and mass and heat transport rates in the system were incorporated. Existing correlations that relate the Sherwood and Nusselt numbers to the Reynolds, Schmidt and Prandtl numbers were used and fitting

Acknowledgements

Financial support from projects BQU2002-03357 and PTR1995-0588-OP is gratefully recognised.

The authors are also grateful to Dynasol Elastómeros for the kind support to the experimental work (Gajano-CANTABRIA).

References (35)

A.L. Ahmad et al.
Integrated CFD simulation of concentration polarization in narrow membrane channel
Computer and Chemical Engineering
(2005)
B. Cao et al.
Modeling of spiral wound pervaporation modules with application to the separation of styrene/ethylbenzene mixtures
Journal Membrane Science
(2002)
A.M. Eliceche et al.
Optimisation of azeotropic distillation columns combined with pervaporation membranes
Computer and Chemical Engineering
(2002)
M.C. Georgiadis et al.
Dynamic modelling and simulation of plate heat exchangers under milk fouling
Chemical Engineering Science
(2000)
P. Gómez et al.
Comparative behaviour of hydrophilic membranes in the pervaporative dehydration of cyclohexane
Journal Membrane Science
(2006)
P. Gómez et al.
Optimum design of PV processes for dehydration of organic mixtures
Desalination
(2006)
M. Gryta et al.
Heat transport in the membrane distillation process
Journal Membrane Science
(1998)
B. Han et al.
Computer simulation and optimization of pervaporation process
Desalination
(2002)
W. Ji et al.
Modeling of multicomponent pervaporation for removal of volatile organic compounds from solute
Journal Membrane Science
(1994)
R. Jiraratananon et al.
Pervaporation dehydration of ethanol-water mixtures with chitosan/hydroxyethylcellulose (CS/HEC) composite membranes II. Analysis of mass transport
Journal Membrane Science
(2002)

A. Jonquières et al.

Industrial state-of-the-art of pervaporation and vapour permeation in the western countries

Journal Membrane Science

(2002)

H.O.E. Karlsson et al.

Heat transfer in pervaporation

Journal Membrane Science

(1996)

F. Lipnizki et al.

Simulation and process design of pervaporation plate-and-frame modules to recover organic compounds from waste solute

Transactions of the Institution of Chemical Engineering

(1999)

J.I. Marriott et al.

Detailed mathematical modelling of membrane modules

Computer and Chemical Engineering

(2001)

J. Phattaranawik et al.

Heat transport and membrane distillation coefficients in direct contact membrane distillation

Journal Membrane Science

(2003)

R. Psaume et al.

Pervaporation: Importance of concentration polarization in the extraction of trace organics from solute

Journal Membrane Science

(1988)

A.M. Urtiaga et al.

Modeling of the concentration-polarization effects in a pervaporation cell with radial flow

Separation and Purification Technology

(1999)

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Modeling of pervaporation processes controlled by concentration polarization

Abstract

Introduction

Section snippets

Mathematical modeling of the PV process

Method of solution

Case study

Simulation results and discussion

Conclusions

Acknowledgements

Computer and Chemical Engineering

Journal Membrane Science

Computer and Chemical Engineering

Chemical Engineering Science

Journal Membrane Science

Desalination

Journal Membrane Science

Desalination

Journal Membrane Science

Journal Membrane Science

Journal Membrane Science

Journal Membrane Science

Transactions of the Institution of Chemical Engineering

Computer and Chemical Engineering

Journal Membrane Science

Journal Membrane Science

Separation and Purification Technology