Simultaneous Etherification Research Articles

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 315–353K and at 2.5MPa, 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 Amberlyst™ 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 353K, 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.

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

A kinetic study on the simultaneous liquid-phase etherification of ethanol with isobutene (IB), 2-methyl-1-butene (2M1B) and 2-methyl-2-butene (2M2B) catalyzed by Amberlyst™ 35 to form ethyl tert-butyl ether (ETBE) and tert-amyl ethyl ether (TAEE) is presented. Isothermal experimental runs were carried out in a stirred tank batch reactor in the temperature range 323–353K at 2.0MPa, starting from different initial concentrations. Obtained reaction rates were free of catalyst load, internal, and external mass transfer effects. Mathematical fitting of a series of systematically originated models, model selection, and model averaging procedures were applied to find the best model and to draw conclusions about the reaction mechanism. The selected model involves a saturated catalytic surface with the participation of two active sites in etherification reactions and one active site in isoamylenes isomerization. Apparent activation energies for ETBE formation from IB and EtOH, TAEE formation from 2M1B and EtOH, TAEE formation from 2M2B and EtOH, and double bond isomerization between 2M1B and 2M2B were 72.8±1.4, 74.9±2.8, 81.2±2.2 and, 76.5±7.2kJ/mol, respectively. The alkenes with the double bond in terminal position were more reactive towards EtOH than 2M2B, with the double bond in internal position.

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

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.

Equilibrium of the simultaneous etherification of isobutene and isoamylenes with ethanol in liquid-phase

The simultaneous etherification of isobutene and isoamylenes with ethanol has been studied using macroreticular acid ion-exchange resins as catalyst. Most of the experiments were carried out over Amberlyst-35. In addition, Amberlyst-15 and Purolite CT-275 were also tested. Chemical equilibrium of four chemical reactions was studied: ethyl tert-butyl ether formation, tert-amyl ethyl ether formation from isoamylenes (2-methyl-1-butene and 2-methyl-2-butene) and isomerization reaction between both isoamylenes. Equilibrium data were obtained in a batchwise stirred tank reactor operated at 2.0MPa and within the temperature range from 323 to 353K. Experimental molar standard enthalpy and entropy changes of reaction were determined for each reaction. From these data, the molar enthalpy change of formation of ethyl tert-butyl ether and tert-amyl ethyl ether were estimated. Besides, the chemical equilibrium between both diisobutene dimers, 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, was evaluated. A good agreement between thermodynamic results for the simultaneous etherification carried out in this work and those obtained for the isolated ethyl tert-butyl ether and tert-amyl ethyl ether systems was obtained.

Simultaneous Production of tert-Amyl Ethyl Ether and tert-Amyl Alcohol from Isoamylene−Ethanol−Water Mixtures in a Batch−Reactive Distillation Column

tert-Amyl ethyl ether (TAEE) and tert-amyl alcohol (TAA), which are the attractive alternatives to methyl tert-butyl ether as octane-enhancing gasoline-blending components, are produced by the simultaneous etherification and hydration of 2-methyl-2-butene (2M2B) in a batch−reactive distillation column. It was shown that, by changing the reboiler temperature in the range of 90−124 °C, significant increases of the overall fractional conversion of 2M2B, reaching values of 0.99, were achieved in this system. In the presence of water, the formation of TAA was also found to take place by the reactions of 2M2B and TAEE with water. Higher selectivities were observed for TAA than for TAEE, in the presence of water. This is due to the higher adsorption equilibrium constant of water than of ethanol on an Amberlyst-15 resin catalyst. A significant increase in the fractional conversion of 2M2B to TAEE was observed in the absence of water.

Etherification of dimethylbutenes in excess methanol

Oxygenated compounds such as ethers produced by the reaction of alcohols and alkenes have good potential for use as performance and environmental enhancing additives for transportation fuels. In this study, the production of the C 7 ether, 2,3-dimethyl-2-methoxybutane (DM2MB), was investigated in a batch reactor from 323–343 K at high methanol concentrations. A macroporous cation exchange resin, Amberlyst 15, was employed as catalyst for the etherification of 2,3-dimethyl-1-butene (DM1B) and 2,3-dimethyl-2-butene (DM2B) with methanol. Kinetic rate constants were correlated by fitting the experimental data to kinetic equations based on a pseudo-homogeneous model. Experimental results were obtained for the effects of temperature on simultaneous etherification and isomerization of DM1B and DM2B and differences in the reactivities of the two alkenes were noted. Kinetic and equilibrium parameters obtained from the Arrhenius and Van't Hoff equations agreed well with values obtained from similar studies in the literature.

Simultaneous Isomerization and Etherification of Isoamylenes

The etherification of isoamylenes (2-methyl-1-butene, 2M1B, and 2-methyl-2-butene, 2M2B) with methanol, ethanol, and n-propanol was studied using a commercial ion-exchange resin as a catalyst. The steady-state reaction rates for the formation of tert-amyl ethyl ether from isoamylenes and ethanol were measured in a continuous stirred tank reactor. At 333 K the reaction rate of the ether formation was measured to be zero order with respect to the ethanol (ETOH) and positive with respect to the olefin. Initial reaction rates for the simultaneous etherification and isomerization of 2M1B were measured in a batch reactor. Initial reaction rates measured at temperatures of 333 and 353 K showed that the different alcohols (methanol, ethanol, and 1-propanol) affected the isomerization rate but not the etherification rate. Measurements were also made with different initial ETOH/2M1B mole ratios. According to the results, etherification and isomerization rates are equal until the lowest mole ratio (0.2) is reached. It was also found that the reaction rates have a constant value at stoichiometric or higher ETOH/2M1B mole ratios. A new model was developed to explain the obtained results.

Etherification and hydration of isoamylenes with ion exchange resin

The simultaneous etherification and hydration of 2-methyl-2-butene and 2-methyl-1-butene were studied in a continuous stirred tank reactor (CSTR). The heterogeneous liquid-phase formation of tert-amyl ethyl ether (TAEE) and tert-amyl alcohol (TAOH) was catalyzed by a commercial sulfonic acid ion exchange resin. Addition of a small amount of water to the feed, caused a marked drop in the overall olefin (isoamylenes) conversion and in the etherification rate. The measured reaction rates of the etherification and alcohol formation were fitted to kinetic models of Langmuir–Hinshelwood type. These models are based on single site adsorption of every component and the surface reaction being the rate limiting step. The activation energies for the simultaneous etherification and hydration of isoamylenes were 117.7 and 79.9 kJ mol −1, respectively. The activation energy obtained for the etherification corresponds well with the value of 108 kJ mol −1 obtained in the experiments without water for the etherification of β-olefin (2-methyl-2-butene) with ethanol.

Ethers from ethanol—5. Equilibria and kinetics of the coupled reaction network of liquid-phase 3-methyl-3-ethoxy-pentane synthesis

The thermodynamic equilibria and kinetics of the reaction network involved in the liquid-phase synthesis of 3-methyl-3-ethoxy--pentane (THEE3), one of the three isomers of t-hexyl ethyl ether (THEE) formed from the etherification reactions of C 6 tertiary olefins with ethanol, are described here. This ether is potentially of interest as an oxygenate for blending with gasoline for octane enhancement and air quality improvement. The coupled reaction network of THEE3 synthesis involves three simultaneous etherification and three isomerization reactions, all of which are reversible. Equilibrium and kinetics experiments were conducted over the temperature range of practical interest, i.e. 298 to 353 K, over Amberlyst 15 resin catalyst. Expressions for the thermodynamic equilibrium constants, K i = K xi K yi , were developed based on the experimental equilibrium composition used to calculate K xi and the corresponding activity coefficients estimated by the UNIFAC method to compute K yi . Reaction rate expressions in terms of species activities were developed based on the data obtained in a differential packed-bed reactor, and were subsequently tested for reliability in the prediction of integral packed-bed reactor performance. The rate expressions are based on the LHHW formalism involving a dual-site surface etherification reaction and a single-site surface isomerization reaction as the rate-limiting steps, along with the assumption of adsorbed ethanol as the most abundant surface species.

Modeling strategy for systems with both stepwise and chainwise chemistry revisited. The directionality effect on the build‐up of the network structure

AbstractA comparison of rigorous and approximate models for the build‐up of epoxy‐amine networks with simultaneous etherification is presented. Contrary to a recent publication, it is shown that naïve statistical models perform very well in predicting statistical parameters when the different directions of network growth are distinguished in the statement of the recursive procedure. Slightly lower values of gel conversions are predicted by the approximate model, a fact that is consistent with the wider distribution of chain lengths resulting from the random recombination procedure. © 1993 John Wiley & Sons, Inc.

A kinetic scheme for an amine‐epoxy reaction with simultaneous etherification

AbstractThe curing reaction of an epoxy resin with a diamine is analyzed, taking into account the possibility of simultaneous etherification. A kinetic scheme is derived and fitted to experimental results for the reaction of commercial bisphenol A diglycidyl ether (BADGE) with diaminodiphenyl sulfone (DDS). Total reaction heat, vitrification curve, and reactivity ratio of secondary to primary amine hydrogens are experimentally characterized. It is shown that the etherification reaction is significant at T > 150°C, at intermediate and high reaction extents when the primary amine has been sufficiently depleted.

Statistical structural model for the build-up of epoxy-amine networks with simultaneous etherification

A statistical structural model is developed to describe a diepoxy-diamine cure, taking into account the possibility of simultaneous epoxy-hydroxy reaction (etherification). Expressions for the number- and weight-average molecular weights, gel conversion, sol fraction, mass fraction of pendant and elastically active network chains (EANC) and concentration of EANC are derived. The different reactivity of primary and secondary amine hydrogens is taken into account, but intramolecular reactions in the pregel stage are neglected. The model is applied to the cure of bisphenol A diglycidyl ether with diaminodiphenyl sulphone, where a previous kinetic analysis showed the presence of etherification. It is shown that, for stoichiometric formulations, etherification acts to decrease both the gel conversion and the concentration of EANC at full epoxy conversion. However, the elastic modulus of the material is not expected to change significantly. Instead, for formulations containing a 100% epoxy excess, the predicted elastic modulus at full epoxy conversion is 50% higher than that predicted for a stoichiometric mixture.