Catalytic Activity and Accessibility of Acidic Ion-Exchange Resins in Liquid Phase Etherification Reactions

Abstract

Although macroreticular acidic ion-exchange resins have been widely used as catalysts in the industrial world for decades, their catalytic behavior is still far from being completely understood at a molecular level. Several characterization techniques coexist, which provide information about their properties. Only few of these techniques give an actual picture of their working-state features when swollen in anhydrous polar reactive media such as in etherification processes, where they are extensively used. The inverse steric exclusion chromatography technique, based on modeling the micropores structure, or gel-phase, as a set of discrete volume fractions with a characteristic polymer chain density, constitutes an appropriate procedure to assess the morphology of ion-exchangers in the swollen state. Present work proposes an empirical model to correlate the properties of the volume fractions with their catalytic activity in the etherification reaction rates of isobutene by addition of C1 to C4 linear primary alcohols. Sixteen different macroreticular acidic ion-exchange catalysts, both commercial and lab-made, have been used, which differ in acid capacity, sulfonation type, cross-linking degree and swollen-phase volume fractions distribution. Experimental reaction rates have been expressed as a sum of contributions of each individual volume fraction. The contribution of each polymer volume fraction corresponds to the product of the catalyst acidity, the characteristic volume fraction within the gel-phase of the catalyst, and a specific turnover frequency (TOF) of that fraction. Accessibility of the reacting alcohol, expressed in terms of the Ogston coefficient, has been also included in the empirical dependency equation presented in this work.

Efficient epoxidation of vegetable oils through the employment of acidic ion exchange resins

“…On the other hand, resins with a low external surface area limit the presence of undesirable glycols formed by the reaction between epoxides and water in the catalyst surface, where few active centres are located . The relation between the catalytic activity and the degree of the matrix cross‐linking in macroporous resins was defined in previous articles . High levels of divinylbenzene content are not adequate because the accessibility of the reactants to the catalytic sites is hindered by the resin structure.…”

“…[17] The relation between the catalytic activity and the degree of the matrix crosslinking in macroporous resins was defined in previous articles. [17,18] High levels of divinylbenzene content are not adequate because the accessibility of the reactants to the catalytic sites is hindered by the resin structure. Nevertheless, too low crosslinking degrees lead higher conversion but decrease the selectivity to epoxides.…”

Kinetic modeling of the simultaneous etherification of ethanol with C4 and C5 olefins over Amberlyst™ 35 using model averaging

“…Amberlyst™ 35 (A-35; Rohm & Haas, Chauny, France) was used as the acidic macroreticular resin catalyst, since it is a very active catalyst in etherification reactions [25] with high acid capacity (5.32 eq H + ·kg -1 ). The main physical and structural properties of the commercial catalyst are described elsewhere [4].…”

Simultaneous etherification of isobutene with ethanol and 1-butanol over ion-exchange resins

“…Since resins swell significantly in the reaction medium, dry state properties would not be an accurate picture of the actual resin morphology under reacting conditions [16]. Swollen-state morphological properties have been found to better describe the real resin morphology, and therefore they should be better related to its catalytic behavior [15,17]. As shown in Fig.…”