Modeling of Solid Acid Catalyzed Alkylation Reactors

Abstract

The current solid acid catalyst based alkylation processes suffer from rapid deactivation of the catalysts which is affected by the shape and size of the catalysts, reactor configuration and the reactants' feeding pattern. In this work, the deactivation of the solid acid catalysts in alkylation of iso-butane with butene and the reactor performance are studied using the multi-scale mathematical models. A pseudo-steady state catalyst pellet level model, incorporating the alkylation and deactivation kinetics, is coupled to the transient model of back mixed reactor configurations like a single CSTR and CSTR-in-series. The effects of catalyst shape, initial acid strength of the catalyst, paraffin-to-olefin feed ratio on the conversion of the olefin, on the yield of alkylates and on the time required for complete deactivation of the catalyst are investigated. The role of the size of the catalyst particles on the types of deactivation mechanism is elucidated. The effect of contacting pattern of iso-butane and butene in the reactor on the catalyst life and on the alkylate yield is also presented.

Group Additivity Determination for Enthalpies of Formation of Carbenium Ions

“…1,3,4 Modeling of alkylation chemistry over solid acid catalysts has the potential to develop a better understanding of potential deactivation mechanisms and the overall process. 2 An approach to developing detailed mechanistic models of alkylation chemistry is to use automated network generation software, 5−7 but this approach produces large reaction networks that make it challenging to determine the rate coefficients necessary for each elementary step.…”

“…Alkylation chemistry is an important process in the petroleum industry that converts light hydrocarbons such as isobutane and butenes into alkylates (high-octane, low-density fuel components with few aromatics), olefins, or sulfur compounds and is a prototypical example of an acid-catalyzed hydrocarbon conversion process. − Alkylate may be blended with other gasoline components to produce fuels with an acceptable octane number according to increasingly stringent environmental regulations . Although solid acid catalysts have the potential to avoid the toxicity and separation difficulties of liquid acids commonly used for alkylation chemistry (i.e., sulfuric or hydrofluoric acids), they are prone to rapid deactivation. ,, Modeling of alkylation chemistry over solid acid catalysts has the potential to develop a better understanding of potential deactivation mechanisms and the overall process . An approach to developing detailed mechanistic models of alkylation chemistry is to use automated network generation software, − but this approach produces large reaction networks that make it challenging to determine the rate coefficients necessary for each elementary step.…”

Deactivation Kinetics of the Catalytic Alkylation Reaction

“…For solid acid zeolite catalysts, it has been proposed that, in liquid-phase catalysis, intraparticle mass transfer is not limiting for catalyst particles less than 0.1 mm and composed of zeolite crystallites not larger than 15 nm. 27,29 We will derive analytical expressions for the respective catalyst deactivation times of CSTR and PFR using kinetics equations derived from microkinetics that are first or second order in reactant propylene concentration.…”

“…On the basis of empirical first- or second-order rate equations deduced from experimental CSTR deactivation measurements, kinetics simulations of the deactivation process are available. ,,− Ramaswamy et al based their comparative study of deactivation in CSTR and PFR on the empirical macroscopic kinetics equations and parameters of de Jong et al They demonstrate a decreased deactivation time in a PFR model compared to that of the CSTR. The deactivation theory rate expressions deduced in this paper will be seen to have close similarity to these empirical kinetics equations.…”

“…In PFR, diffusional limitations are present for larger catalyst particle sizes in liquid-phase alkylation reactions but is not limiting in gas-phase alkylation reactions. For solid acid zeolite catalysts, it has been proposed that, in liquid-phase catalysis, intraparticle mass transfer is not limiting for catalyst particles less than 0.1 mm and composed of zeolite crystallites not larger than 15 nm. , …”