Process Intensification: Reactive Distillation for the Production of ETBE With Rigorous Thermodynamic Models

GISELA DURRUTY; MARIA SOLEDAD DIAZ; PATRICIA HOCH

San Francisco

Congreso; AIChE Annual Meeting 2013; 2013

AIChE (American Institute of Chemical Engineers)

Process intensification principles are currently applied at industrial scale. Most successful commercial process intensification applications include reactive distillation, microreactors, rotating packed bed systems, simulating moving bed reactors, etc. (Nikacevic, Huesman, Van Den Hof, & Stankiewicz, 2011). Reactive distillation (RD) is a simultaneous implementation of sequential reaction and distillation in a countercurrent column (Tian, Zhao, Bisowarno, & Tadé, 2003). It consists of a reactive section in the middle of the column, with nonreactive rectifying and stripping sections at the top and bottom, respectively (Taylor & Krishna, 2000). The application of these processes is motivated by significant reductions in capital and operating costs, as compared to the equivalent conventional reactionseparation processes. Reactive distillations have also significant advantages when conversion is thermodynamically limited by chemical equilibrium. The reason is that the continuous removal of products enhances overall conversion. Other benefits include reduced downstream processing and higher energy efficiency due to the utilization of the reaction heat for evaporation of the liquid phase (Sharifzadeh, 2013). ETBE (ethyl tertbutyl ether) synthesis can be efficiently carried out through reactive distillation to achieve high conversion and low implementation/operating costs. The conventional process for ETBE synthesis basically consists of pretreatment of the C4 hydrocarbon feed flow, reaction, purification, and recovery of nonreacted products, which renders high capital and operating costs. The design of 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 RD unit model is formulated with MESH equations (mass, equilibrium, summation and enthalpy) in an equation oriented environment within GAMS (Brooke et al., 2011). The thermodynamic model includes an activity coefficient approach for the liquid phase (UNIFAC, Fredenslund, Gmehling, & Rasmussen, 1977) and a cubic equation of state for the vapor phase (SRK, Soave, 1972). The objective is to minimize total annual cost. The inclusion of rigorous thermodynamic models and kinetic data (AlArfaj & Luyben, 2002); (Sharifzadeh, 2013) allows reliable predictions of reaction kinetics and thermodynamic equilibrium. Numerical results are in good agreement with pilot plant data.