Tertiary alkyl ethers: Thermodynamics, kinetics and reactor analysis

The objective of this work was to gain a fundamental understanding of thermodynamics, kinetics and reactor behavior associated with the liquid-phase production of tertiary alkyl ethers for use as fuel additives. In particular, thermodynamic non-ideality and its impact on reaction equilibrium, kinetics, intraparticle transport and reactor design are discussed. From a practical standpoint, focus was given to ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-amyl ethyl ether (TAEE) and tert-hexyl ethyl ethers (THEEx). These tertiary ethers could potentially serve as substitutes for methyl. tert-butyl ether (MTBE), which has been linked to contamination of drinking water supplies across the United States.; Equilibrium constants as a function of temperature are provided for various tertiary ethers. It is shown that the Gibbs free energy of formation for TAME appearing in literature leads to erroneous results, and thus a corrected experimentally derived value is provided. A more fundamental justification for the use of species activities in the rate expression for nonideal reaction systems is provided. Generalized kinetic expressions for etherification and isomerization proposed in literature were re-derived by the application of the thermodynarnic-transition-state theory to the elementary steps of the composite catalytic reaction within the Langmuir-Hinshelwood-Hougen-Watson formalism, resulting in rate expressions in terms of species activities, which are more appropriate owing to the nonideality of the reaction mixture, as well as being consistent with reaction thermodynamics.; The thermodynamic and kinetic data were further used to develop generalized transport equations for multicomponent diffusion and flow of n species participating in q reactions based on the dusty-fluid model, in which the diffusional driving force of species i is its chemical potential gradient. It is shown that the n “species” fluxes in the material balance as well as constitutive equations can be replaced by an independent set of “reaction” fluxes, resulting in a more convenient and functional description. The developed transport and reaction model was applied to the case of liquid-phase synthesis of ETBE under isothermal conditions, and provides good agreement between theory and experiments without using any adjustable parameters.; The steady-state and dynamic behavior of a nonisothermal integral packed-bed reactor for the liquid-phase synthesis of ETBE was described with a model that is inherently consistent with thermodynamics. The one-dimensional steady-state model is robust and provides good agreement between experiments and theory with all of the kinetic, thermodynamic and other physicochernical parameters obtained from independent experiments. Under certain conditions, sustained temperature oscillations were observed in the kinetic region of the reactor. These oscillations were attributed to the interplay between axial dispersion of heat and mass transport of reactant to the reaction zone, and were validated by an unsteady-state one-dimensional pseudo-homogeneous dispersion model. This study thus provides for the first time both experimental and theoretical evidence of sustained oscillatory behavior in liquid-phase packed-bed catalytic reactors.