Fidel Cunill

Dehydration of 1-pentanol to di-n-pentyl ether over ion-exchange resin catalysts

The dehydration reaction of 1-pentanol to di-n-pentyl ether (DNPE) and water in the liquid phase was studied at 110–180 ◦ C and 1 MPa on sulfonic styrene–divinylbenzene (S/DVB) copolymers and the perfluoroalkanesulfonic resin NR50. S/DVB-based catalysts were macroreticular and gel-type resins both sulfonated conventionally and oversulfonated. Macroreticular resins tested include resins whose working phase in catalysis is gel phase (i.e. Amberlyst-15 and Amberlyst-35) and XN1010 whose working phase in catalysis is macropores surface. By comparing 1-pentanol conversion, selectivity to DNPE and initial reaction rates at 150 ◦ C it is concluded that gel-type S/DVB resins that swell moderately in the reaction medium, as CT-224, are the more suitable catalysts for the reaction. NR50, which is thermally stable up to 200 ◦ C, is the most selective catalyst tested but it is too much expensive for industrial use. Selectivity to DNPE decreases as temperature increases showing that side reaction of dehydration to 1-pentene is more sensitive to temperature. Apparent activation energies for the dehydration reaction of 1-pentanol to DNPE were found to be about 100 kJ/mol.

Scope and limitations of mechanistic inferences from kinetic studies on acidic macroporous resins The MTBE liquid-phase synthesis case

Abstract It has been hypothesized hitherto that the liquid-phase synthesis of MTBE on ion-exchange resins proceeds quasi-homogeneously in excess methanol by an ionic mechanism whose rate-limiting step is the protonation of the alkene, and quasi-heterogeneously at very low methanol content likely by a concerted proton transfer involving adsorbed reactants. However, recent knowledge of the reaction involving the effect of the non-ideality of the liquid phase on the kinetics of the reaction, and the inhibitor effect of MTBE on the reaction rate, in addition to new data on byproducts formation, suggest that MTBE synthesis can be looked at as a quasi-heterogeneous catalysis independently of the methanol content of the liquid phase. Moreover, a transition between a Eley-Rideal mechanism and an Langmuir-Hinshelwood one can be assumed as the methanol concentration of the liquid phase decreases.

Kinetic study of mtbe liquid-phase synthesis using C4 olefinic cut

Abstract The liquid-phase addition of methanol to isobutene to give methyl tert.-butyl ether (MTBE) on the ion exchange resin Bayer Catalyst K2631 has been studied using a C4 olefinic cut as the source of isobutene. Rate data were obtained free of mass transfer influence in a continuous differential reactor operated at 1.5 MPa and 45–90°C. Data show that isobutene has an enhancing effect on the rate whereas methanol has an inhibitory one. As alcohol-olefin-ether mixtures behave non-ideally, kinetic analysis has been performed by using the UNIFAC liquid-phase activities of isobutene, methanol and MTBE. The experimental data can be described by a three-parameter expression based on an Eley-Rideal mechanism in which methanol, adsorbed on one catalytic center, reacts with isobutene from solution to give the ether adsorbed on one center. Surface reaction is the rate-limiting step, and an additional center takes part in this step. The kinetic model emphasizes the relevant role of MTBE in the reaction, which competes for the active centers with the methanol. An activation energy of 81.1 ± 4.2 kJ/mol, in good agreement with literature values, was found.

Kinetic study of isobutene dimerization catalyzed by a macroporous sulphonic acid resin

Abstract The kinetics of the liquid-phase dimerization of isobutene in the presence of a macroporous acidic resin (Lewatit K-2631, Bayer) has been studied. Rate data were obtained in a batchwise stirred tank reactor operated at 1.6 MPa and 40–60°C. The best rate model is a two-phase semiempirical one which implies the coexistence of a Langmuir-Hinshelwood-Hougen-Watson mechanism and a modified Eley-Rideal one.

Drying of acidic macroporous styrene-divinylbenzene resins

Abstract Drying of the acidic macroporous resin Lewatit K 2631 has been studied. Oven drying at 84–112°C and 0.015 atm water partial pressure shows that the resin behaves as a fibrous solid. Drying by methanol percolation at 20°C leads to moisture contents in the resin slighty lower than in the previous method. Finally, oven drying of the resin previously washed with methanol shows that the residual water content increases with increasing amounts of the methanol. Estimates of the water-effective diffusivity suggest that the last method gives rise to a lower polymer shrinkage. The changes in the polymer morphology probably result from the formation of a large number of small pores.

Kinetics of decomposition of methyl tert-butyl ether in the gas phase on amberlyst 15 as a catalyst

Abstract The kinetics of methyl tert-butyl ether (MTBE) decomposition catalyzed by a sulfonated macroporous poly(styrene-divinyl benzene) with 20% DVB was measured with a packed-bed flow reactor operated at 1 atm and 40–60°C. Data show a reaction rate maximum at roughly 0.15 atm partial pressure of the ether. This maximum rate illustrates reaction inhibition by the ether itself at higher partial pressures. The presence of methanol or isobutene inhibits reaction as well. A form of Langmuir-Hinshelwood-Hougen-Watson (L-H-H-W) rate equation represents the data. The best-fitting rate equation is derived from a mechanism that assumes that the rate-determining step is the reaction of MTBE bridged into two -SO3H groups of the polymeric network with a third active site. This mechanism is thermodynamically consistent since it fulfills Boudarts rules. The adsorption equilibrium constant of methanol is compared to the data in the literature.

The role of by-products formation in methyltert-butyl ether synthesis catalyzed by a macroporous acidic resin

Abstract The effect of temperature and of the initial molar methanol-isobutene ratio on by-products formation in methyl tert -butyl ether synthesis catalyzed by a macroporous acidic resin were determined. The presence of dimethyl ether, methyl sec -butyl ether and diisobutene was studied in the temperature range 50–82°C, using an initial molar methanol-isobutene ratio ranging from 1.0 to 3.5. The byproducts formation was favoured by high temperatures. A low initial molar methanol-isobutene ratio favoured methyl sec -butyl ether and diisobutene formation, whereas high molar ratios favoured dimethyl ether formation. Results were explained by reaction mechanisms and compared with literature data.

Influence of water on the gas-phase decomposition of methyl tert.-Butyl ether catalysed by a macroporous ion-exchange resin

Abstract Sulphonic ion-exchange resins are very hygroscopic and readily adsorb water. As a result, the catalytic activity of this type of ion-exchange resin decreases substantially when water contaminates the reaction medium. The influence of water on the gas-phase decomposition of methyl tert.-butyl ether (MTBE) at 50.5°C catalysed by the macroporous ion-exchange resin Amberlyst 15 was studied. The results show that the addition of small amounts of water causes a very strong decrease in decomposition rate of MTBE. A set of Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models are proposed. The statistical discrimination between them permits the selection of two models whose only difference lies in the adsorption model of MTBE: on two active centres with or without dissociation. The values of the parameters of these models (overall kinetic constant, kK I K M ; MTBE adsorption constant, K E ; and water adsorption constant, K W ) obtained from the fit of data coincide, within the limits of experimental error, with those obtained from the fit of each of the curves r E vs. P E corresponding to different amounts of water in the feed. It is concluded that water reduces the rate of the MTBE decomposition reaction by occupying active centres in a competitive way with the ether. Finally, the values for K W in the literature agree fairly well with those determined in this work.

Molecular mechanisms of MTBE synthesis on a sulphonic acid ion exchange resin

Abstract In the present work, molecular mechanisms of methyl t-butyl ether (MTBE) synthesis by methanol addition to isobutene in the gaseous and liquid phases are presented as an example of general and specific acid catalysis by sulphonated ion exchange resins, respectively. In the liquid phase and in a reaction medium with excess methanol (specific acid catalysis), the literature provides enough experimental evidence to support an ionic mechanism whose rate-determining step is olefin protonation. As an example of general acid catalysis, a concerted mechanism with a cyclical intermediate of six centers is proposed for this reaction in gaseous phase. It is based on the LHHW kinetic model determined for the reaction that explains rate data in a statistically significant fashion. Analysis of the significance of the LHHW model shows that it is thermodynamically consistent. Therefore, we can assume that the kinetic model is a simplified picture of the molecular process. The bibliography gives supplementary experimental evidence supporting the proposed concerted mechanism.

Esterification of levulinic acid with butanol over ion exchange resins

Amberlyst 15 111 ± 2 110 ± 3 4.70 ± 0.1 4.73 ± 0.1 4.81 48 80 Amberlyst 35 117 ± 2 5.20 ± 0.1 5.32 48 Amberlyst 16 108 ± 3 4.72 4.80 80 Amberlyst 36 117 ± 2 5.30 ± 0.1 5.40 48 Amberlyst 39 111 ± 3 4.66 4.82 80 Amberlyst 70 117 ± 3 1.65 ± 0.05 2.55 48 Dowex 50Wx4 113 ± 3 4.65 4,95 80 Dowex 50Wx2 106 ± 3 3.80 4.83 80 Purolite CT224 112 ± 3 4.51 5.34 80 Amberlyst 46 108 ± 3 0.91 0.87 80 The experimental technique can be found in Siril et al. [48] a From microcalorimetry of NH3 adsorption. It considers those centers with -HNH3 ≥ 80 kJ/mol b From titration with NaOH