Montserrat Iborra

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.

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.

EQUILIBRIUM CONSTANTS FOR ETHYL tert-BUTYL ETHER LIQUID-PHASE SYNTHESIS

Abstract Thermodynamic equilibrium constants for the liquid-phase synthesis of ethyl terl-butyl ether (ETBE) were determined experimentally in the temperature range 40-80°C (313-353 K) at 1.6 MPa for an initial molar ratio of ethanol to isobutene ranging from 1 to 1.5. To reach etherification equilibrium a macroporous sulphonic acid resin (K-2631, Bayer) was used as a catalyst. The thermodynamic equilibrium constant and the enthalpy, free energy, and entropy changes are given as a temperature function. At 298 K, ΔH° = −34.8 kj mol−1, ΔG° = −11.7kJmol−1, and ΔS° = −77.3J mol−1 K−1. A comparison with the values obtained for MTBE is also included.

Kinetic study of the reaction between sulfur dioxide and calcium hydroxide at low temperature in a fixed-bed reactor.

A quantitative study of the influence of inlet sulfur dioxide concentration (600-3000 ppm), relative humidity (20-60%), reactor temperature (56-86 degrees C) and different amounts (0-30 wt.%) of inorganic additives (NaCl, CaCl(2) and NaOH) on gas desulfurization has been carried out in a continuous downflow fixed-bed reactor containing calcium hydroxide diluted with silica sand. Results show that the reaction rate does not depend on sulfur dioxide partial pressure (zero-order kinetics) and that the temperature and the relative humidity have a positive influence on reaction rate. An apparent activation energy of 32 kJ/mol Ca(OH)(2) has been estimated for the reaction. An empirical reaction rate equation at 71.5 degrees C and 36.7% relative humidity that includes the type and amount of additive is proposed. It has been found that calcium chloride is the best additive studied because it allows for a higher degree of sulfur dioxide removal.

The formation of byproducts in the reaction of synthesis of isopropyl tert-butyl ether from isopropyl alcohol and isobutene on an acidic macroporous copolymer☆

Abstract The effect of temperature and of the initial molar isopropanol-isobutene ratio, R A O , on byproducts formation in isopropyl tert-butyl ether (IPTBE) synthesis in the presence of the resin Bayer K-2631 were determined. The formation of diisopropyl ether, diisobutene (2,4,4-trimethyl-l-pentene, and 2,4,4-trimethyl-2-pentene isomers), and tert-butanol was studied in the temperature range 30–80°C, with R A 0 ranging from 1.0 to 4.3. The formation of tert-butanol is fast, and it reaches quickly the chemical equilibrium. The extent of the reaction is therefore limited by the amount of available water. The reactions forming 2,4,4-trimethyl-l-pentene, and 2,4,4-trimethyl-2-pentene take place gradually in the whole temperature range explored, whereas diisopropyl ether formation only occurs over 60°C once the reaction of IPTBE synthesis is close to equilibrium. These reactions are favoured by high temperatures. Low R A 0 values favour isobutene dimerization and ten-butanol formation. The effect of R A 0 on the reaction forming diisopropyl ether is negligible.

Influence of resin type and water on the kinetics of the decomposition of methyl tert-butyl ether in the gas phase☆

Abstract The rate of decomposition of methyl tert-butyl ether (MTBE) in the gas phase catalysed by macroporous poly(styrene-divinylbenzene) was measured with a packed-bed flow reactor operated at 1 atm and 50.5°C. Rates were obtainedfor several commercial macroporous resins with different degrees of cross-linking [8, 12, and 18% divinylbenzene (DVB)] and water contents in the feed to the reactor (0.1–0.74 wt.%). The results show that the presence of water causes a very strong decrease in the rate of decomposition of MTBE. This effect is greatest for the exchanger containing 18% DVB. The adsorption equilibrium constants of water found in the literature agree fairly well with those obtained in this work (123–170 atm −1 ). The adsorption enthalpy and entropy of water for the exchanger containing 12% DVB were determined and compared with literature data.