Carles Fité

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.

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.

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

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.

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

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–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 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.

Green metrics analysis applied to the simultaneous liquid-phase etherification of isobutene and isoamylenes with ethanol over Amberlyst™ 35

Abstract A case study of the green metrics analysis of several processes is described. The considered system is the simultaneous etherification of isobutene and isoamylenes with ethanol over Amberlyst™ 35. Experimental results are compared under the green metrics methodology with those for the isolated ethyl tert-butyl ether and tert-amyl ethyl ether syntheses previously reported over acid ion-exchange resins using different reaction batch devices and different synthesis pathways, such as the production of both ethers from tertiary alcohols and from ethanol. The best results, from an environmental point of view, were obtained for ether syntheses from olefins and ethanol in terms of the parameters measured in the green metrics analysis. A process allowing the separation of ethers from the product stream and the reactants recirculation has been proposed and simulated. The suggested process depicts a suitable alternative for the simultaneous production of tertiary ethers from pure olefin feed and their downstream implementation as greener fuel additives with environmental benefits.

Synthesis of ethyl hexyl ether over acidic ion-exchange resins for cleaner diesel fuel

The synthesis of ethyl hexyl ether as a suitable diesel additive was investigated using 1-hexanol and diethyl carbonate as reactants and acidic ion-exchange resins as catalysts. Liquid-phase experiments were performed in a batch reactor at the temperature range of 403–463 K and 2.5 MPa. The formation of ethyl hexyl ether proceeded from two routes: thermal decomposition of ethyl hexyl carbonate and intermolecular dehydration of 1-hexanol with ethanol. Both pathways require a previous transesterification reaction between diethyl carbonate and 1-hexanol. It was revealed that this reaction is favoured in polymer zones of 0.4 nm nm−3 polymer density (equivalent to 2.6 nm diameter pores in inorganic materials). Acidic ion-exchange resins containing a significant volume fraction of this polymer density are Dowex 50W×2 and Amberlyst 70. By using this kind of catalyst, reaction rate and selectivity are significantly increased. Finally, it was observed that working at low temperature would favour the selectivity to ethyl hexyl carbonate and hinder the undesired formation of alkenes.

Effect of internal diffusion on liquid-phase synthesis of MTBE

Summary Effectiveness factors for the synthesis of MTBE in the liquid-phase in the presence of the ion exchange resin Bayer K-2631 were theoretically estimated. The behavior of catalyst beads is described in terms of a shell-core model in which diffusion of reactants takes place in the shell region surrounding a central core wherein reaction equilibrium is achieved. Catalyst beads were assumed to be isothermal, and side reactions were neglected. At the usual operation conditions in industrial reactors (molar ratio isobutene/methanol ≈ 1; temperature, 60–90°C; particle size: 0.4–0.8 mm) effectiveness factor ranging from 0.7 to 1 were found. In addition, effectiveness factors greater than 1 were found for catalyst particles in the range of commercial size distribution when isobutene is in excess in the reaction medium. This is explained because diffusion of methanol in macropores controls the reaction rate.

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

The simultaneous liquid-phase etherification of isobutene with ethanol and 1-butanol to give ethyl tert-butyl ether (ETBE) and butyl tert-butyl ether (BTBE) has been studied, at temperatures in the range of 315–353 K and at 2.5 MPa, over six commercial acidic macroreticular ion-exchange resins as catalysts. The initial alcohol to isobutene molar ratio was varied in the range of 0.5–5.5 and the initial ethanol to 1-butanol molar ratio in the range of 0.5– 2.0. Strongly acidic catalysts with a rigid polymer backbone structure enhance reaction rate. This fact, along with the reduced side reactions extent, makes AmberlystTM 35 the most promising catalyst, among the tested ones, for the studied simultaneous etherification process. Irrespectively of the used catalyst, initial ETBE synthesis reaction rate is hardly sensitive to the variation of the ethanol to 1-butanol molar ratio, whereas initial BTBE synthesis reaction rate strongly diminishes at high ethanol concentration. Preferential adsorption of ethanol over 1-butanol on the catalysts active sites has been detected. As expected, both etherification reaction rates increase at increasing isobutene concentration. At 353 K, the highest temperature, both etherification rates are affected by internal mass transfer resistances due to diffusion limitations even when small catalyst beads are used. The simultaneous process has been compared to the individual syntheses of ETBE and BTBE and it has been found that the isobutene selectivity towards ethers is enhanced in the simultaneous system.