J.F. Izquierdo

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 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.

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.

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.

Fly Ash Reactivation for the Desulfurization of Coal-Fired Utility Station's Flue Gas

Abstract Fly ash hydration in the liquid phase has been studied by employing temperature, hydration time, and water/fly ash weight ratio as variables. The results show that temperature and hydration time have a large positive effect in surface area development of the hydrated ashes (due to the formation of hydrated tetracalcium aluminate) whereas the water/fly ash weight ratio effect seems to be negative but its influence is very small. Desulfurization tests have been carried out with some of these hydrated fly ashes. Tests consisted of exposing the solid for 1 h to an N2/SO2 gas stream containing 500 ppm SO2. The variables employed were temperature and relative humidity. The results show that SO2 capture rises with temperature and, particularly, with an increase in relative humidity. A correlation between surface area and SO2 capture was found. The greater the surface area, the greater the amount of SO2 captured. This fact shows that hydrated tetracalcium aluminate is a highly reactive substance against SO2.

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.

Equilibrium and thermodynamics for 2-methyl-2-methoxybutane liquid-phase decomposition☆

Abstract The chemical equilibrium for the liquid-phase decomposition of 2-methyl-2-methoxybutane ( tert -amyl methyl ether) was studied experimentally in the temperature range 313–353K and at 700 kPa. To reach decomposition equilibrium, the macroporous acid resin K-2631 (Bayer) was used as the catalyst. Equilibrium constants and standard enthalpies, free energies, and entropies for addition of methanol to 2-methyl-1-butene and 2-methyl-2-butene (forward reactions) were determined as a temperature function and compared with literature data. The unifac estimates of activity coefficients were used to describe the liquid-phase non-ideality.