Parameter Estimation with Equation Oriented Approaches in ETBE Reactive Distillation

ETBE (ethyl tert-butyl ether) synthesis can be efficiently carried out through reactive distillation to achieve high conversion and low implementation/operating costs (Sharifzadeh, 2013; Recker et al., 2015; Dominguez 2014) . The conventional process for ETBE synthesis basically consists of pretreatment of the C4 hydrocarbon feed flow, reaction, purification, and recovery of non-reacted products, which renders high capital and operating costs (Sneesby et al., 1997; Werber de Menezes and Cataluña,2008). The design of reactive distillation (RD) for ETBE synthesis, requiring good kinetic models integrated to reliable thermodynamic predictions still requires further analysis.

In this work, we propose a model for the design of a reactive distillation unit for ETBE synthesis from ethanol and isobutene, with both rigorous thermodynamic models and hydraulic constraints. The thermodynamic model includes an activity coefficient approach for the liquid phase (UNIFAC, Fredenslund et al., 1977) and a cubic equation of state for the vapor phase (SRK, Soave, 1972). The estimation of interaction parameters for both models has to be done to accurately predict the equilibrium. The model has been implemented within an equation oriented framework (Brooke, 2011), including additional constraints for root selection (Kamath et al., 2010). Binary interaction parameters have been estimated for the systems ethanol-ETBE; ibutene-ETBE; nbutene-ethanol and ibutene-ethanol. A comparison of model predictions for the studied systems is provided, showing good agreement with experimental data.

References

Brooke, A., Kendrick, D., Meeraus, A., Raman, R. (2011), GAMS, A User Guide. Washington, DC, USA.

Dominguez L., Pinheiro C.I.C., Oliveira N.M.C. (2014). Optimal design of reactive distillation systems: Application to the production of ethyl tert-butyl ether (ETBE). Computers and Chemical Engineering64, 81-94.

Fredenslund, Gmehling, & Rasmussen. (1977). Vapor-liquid equilibria using UNIFAC - a group-contribution method. Elsevier scientific publishing company, 2800. doi:10.1016/B978-0-444-41621-6.50001-6

Kamath R.S., Biegler L.T., Grossmann I.E. (2010). An equation-oriented approach for handling thermodynamics based on cubic equation of state in process optimization. Computers ans Chemical Engineering 34 2085-2096.

Recker S., Skiborowski M., Redepenning C., Marquardt W. (2015). A unifying framework for optimization-based design of integrates reaction-separation processes. Computers and Chemical Engineering81, 260-271.

Sharifzadeh, M. (2013). Implementation of a steady-state inversely controlled process model for integrated design and control of an ETBE reactive distillation. Chemical Engineering Science, 92, 21–39. doi:10.1016/j.ces.2013.01.026

Sneesby M.G., Tadé M.O., Datta R. and Smith T.N. (1997). ETBE Synthesis via Reactive Distillation. 1. Steady-State Simulation and Design Aspects. Ind. Eng. Chem. Res. , 36, 1855-1869.

Soave G. (1972). Equilibrium constants from a modified Redlich-Kwong equation of state. Chemical Engineering Science, Vol.27, 1197-1203.

Werber de Menezes E. and Cataluña R. (2008). Optimization of ETBE (ethyl tert-butyl ether) production process. Fuel Processing Technologies 89, 1148-1152.