Kinetics of 1-hexanol etherification on Amberlyst 70

Abstract

The kinetics of the liquid-phase etherification of 1-hexanol to di-n-ethyl ether and water on the ion-exchange resin Amberlyst 70 in the temperature range 423-463K is studied.The strong inhibition effect of water is considered following two approaches. First, a model stemming from a Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism was used, wherein the inhibitor effect of water was explained by the competitive adsorption of water and hexanol. Secondly, a modified Eley-Rideal (ER) model that includes an inhibition factor, in which a Freundlich-like function is used to explain the inhibitor effect of water by blocking the access of hexanol to the active centers. Both models fitted data quite well, although the best fitting results were obtained with the modified ER model. The activation energy was 125 ± 3 kJ/mol for the LHHW model and 121 ± 3 kJ/mol for the modified ER one.

Synthesis of Biomass‐Derived Ethers for Use as Fuels and Lubricants

“…Amberlyst 70 is a macroporous sulfonic styrene–divinyl benzene (DVB) resin catalyst with a surface area of 36 m 2 g −1 and an acid site concentration of 3 equiv H + kg −1 . Nafion NR‐50 is a sulfonated Brønsted‐acid catalyst that has a fluorinated backbone, as shown in Figure b. Amberlyst 70 and Nafion NR‐50 stand out as active and selective Brønsted‐acid catalysts for the direct etherification of the linear primary alcohols 1‐octanol, 1‐hexanol, and 1‐pentanol . Table , entries 1, 2, 5, 6, 8, 9, and 11, show that Amberlyst 70, Nafion NR‐50, as well as the resins Purolite CT‐224, Amberlyst DL‐H/03, and Dowex 50WX4 are highly selective for the synthesis of symmetrical ethers from linear alcohols at 423 K, which is above the critical temperature at which unimolecular dehydration is thermodynamically favored.…”

Kinetics of the liquid phase dehydration of 1‐octanol to di‐n‐octyl ether on Amberlyst 70

“…Correction factors based on the Freundlich isotherm has been successfully used to explain inhibition by water in the acetone dehydration to mesityl oxide on Amberlyst 16, ,41 and in the dehydration reaction of 1‐alkanol to linear symmetrical ether on Amberlyst 70 . Figure compares the correction factors, , for the dehydration reactions of 1‐pentanol to DNPE, 1‐hexanol to DNPE 27 and 1‐butanol to di‐n‐butyl ether (DNBE) at 443 K found in our previous works.…”

“…From the slope of the plot an apparent activation energy of 110 6 6 kJÁmol 21 is estimated, in line with literature data on alcohol dehydration to linear ether over acidic resins. 26,27 This fact also backs up that r DNOE measures are free from mass transfer effects at the working conditions selected…”

“…Fit e et al reported that three active sites could take part in the rate-limiting step of ethanol addition to isobutene to yield ETBE, 35 and Sol a et al described ETBE synthesis through an ER mechanism with two active sites involved. 36 However, dehydration reactions of 1-pentanol to DNPE and 1-hexanol to DNHE proceed by means of ER mechanisms but only 1 active site is involved, 26,27 just as the reaction of 1-octanol with ethanol to yield ethyl-octyl ether reported by Guilera et al 37 To achieve a good fit to rate data, n was varied from 1 to 3; n values higher than 1 for the ER mechanism, and 2 for the LHHW one, represent a scenario where additional active sites were required, for instance, to settle the long linear ether formed, or stabilize the reaction intermediate. Table 3, the surface rate coefficient,k 0 , and the adsorption equilibrium constants, K a,OcOH , K a,DNOE , and K a,H2O , have been grouped into factors for mathematical fitting purposes, called A, B, C, and D. The particular way in which those constants are grouped depends on the mechanism (LHHW or ER) and the neglected adsorption term, if any.…”

“…With this view, an usual procedure is to modify empirically LHHW-ER kinetic models, by splitting the rate coefficient,k 0 ; into a "true" one,k 0 0 , and a correction factor able to represent the rate decrease by the effect of water. 26,27,45 A first approach was developed by Fit e et al in an attempt to account for the effect of the reaction medium-resin interaction on the reaction rate. 46 They proposed a correction factor, the parameter w, related to resin swelling and to the accessibility to resin sulfonic groups, which was useful in nonaqueous reaction media, where resins are partly swollen.…”