Vapor-phase esterification of acetic acid

P4-18b Ethyl acettde is an extensively used solvent and can be formed by the vapor-phase esterification of acetic acid and ethanol. The reaction was studied using a microporous resin as a catalyst in packed-bed reactor [Ind. Eng. Chetn. Res., 26(2), 19S(I987)]. The reaction is first-order in ethanol and pseudo-zero-order in acetic acid. Fw tm equal molar feed rate of acetic acid and ethanol the sped fic reaction rate is 1.2 dm /g cat 10111. The total molar feed rate is 10 mol/min, the initial pressure is 10 atm, the temperature is U8°C, and the pressure drop parameter, a, equals O.Ol g K... 

P4C-3 In the ardcie describing vapor phase esterification of acetic acid with ethanol to form ethyl acetate and water [Ind. Eng. Chem. Res., 26 2), 198 (1987)], the pressure drop in the reactor was accounted for in a most unusual manner [i.e., P = Po(l where/is a constant]. 

CDPIO-Bg Analyze the data for the vapor-phase esterification of acetic acid over a resin catalyst at 118°C. 

Rate equation can be expressed in power form or in terms of the Langmuir-Hinshelwood or Eley-Rideal mechanism. For example, the reaction of acetic acid and n-butanol in the liquid phase catalyzed by HZSM-5 proceeds according to a rate equation which is of the first order with respect to acetic acid and of the zeroth order with respect to n-butanol. It has been suggested that vapor-phase esterification of acetic acid with ethanol proceeded on decationized Y zeolites by a reaction between strongly adsorbed acetic acid and ethanol. The reaction rate is expressed by a Rideal-type rate equation, where the influence of the pressures of the acid dimer and products as well as the pressures of the reactants were taken into account. ... 

Other Esters. The esterification of acetic acid with various alcohols in the vapor phase has been studied using several catalysts precipitated on pumice (67). 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

NaA/polyelectrolyte multilayer-pervaporation membrane showing a greater stability under acidic conditions in comparison with a pure zeolite A membrane and maintaining a high selectivity for water over alcohols. For the same purpose, Kita et al. [181-183] proposed a zeolite T membrane, prepared by ex situ crystallization, for the per-vaporation-aided or vapor-permeation-aided esterification of acetic acid with ethanol. This membrane has a higher acid resistance and can be directly immersed in the liquid-phase reaction mixture. The conversions achieved exceed the equilibrium limit and reached to almost 100% after a stabilization period of 8 h. 

Anderianova studied the decomposition of formic acid and esterification of acetic acid with ethyl alcohol in the vapor phase over gel-type resins of divinylbenzene content of 1 % and 20%. At lower temperatures, the resin with lower degree of crosslinking was more active for both reactions. With increasing temperature, the difference in the rates decreased. This was attributed to the change in resin sorption capacity with temperature. On the other hand, it was reported that, for the liquid-phase dehydration of t-butyl alcohol with gel-type resins, the 8%-crosslinked resin had about twice the catalytic activity of the 2% resin. 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

Poly(sulfophenyl)siloxane (2.0 meq g ), poly(sulfobenzyl)siloxane, poly(sul-fophenylethyl)siloxane, and poly(sulfopropyl)siloxane (0.8 meq g ) were prepared by Ono et al [25]. Documented applications of these sulfonated polyorgano-siloxanes include the dehydration of alcohols, the esterification of isobutanol with acetic acid and the vapor-phase nitration of benzene. 

Use the one-phase multireaction algorithm in Figure 11.6 to determine the extent to which formation of tetramers of acetic acid affect the fractional conversion during esterification of ethanol. That is, repeat the vapor-phase calculation at 358 K, 1.0133 bar illustrated in the last part of 11.3.3, but now include not only dimers but also tetramers. (Spectroscopic evidence suggests that formation of trimers is unfavored [32].) Sebastiani and Lacquaniti give the equilibrium constant for formation of tetramers as [32]... 

Industrially important esterifications are the reactions of alcohols with saturated and unsaturated aliphatic c2u-boxylic acids, e.g., acetic acid, fatty acids and acrylic acid, and aromatic dicarboxylic acids such as terephth llic acid. These reactions may be carried out in both liquid and vapor phases. Esterification reactions are usually limited by equilibrium particularly in liquid phase. Continuous removal of water produced and/or operation with an excess of one of the reactants are necessary to obtain higher yields of ester. Vapor-phase esterification is favored from this standpoint, and numerous studies have been directed toward the use of solid acid catalysts. " ... 

Other large-volume esters are vinyl acetate [108-05-4] (VAM, 1.15 x 10 t/yr), methyl methacrylate [80-62-6] (MMA, 0.54 x 10 t/yr), and dioctyl phthalate [117-81-7] (DOP, 0.14 x 10 t/yr). VAM (see Vinyl polymers) is produced for the most part by the vapor-phase oxidative acetoxylation of ethylene. MMA (see Methacrylic polymers) and DOP (see Phthalic acids) are produced by direct esterification techniques involving methacryHc acid and phthaHc anhydride, respectively. 

Unsaturated vinyl esters for use in polymerization reactions are made by the esterification of olefins. The most important ones are vinyl esters vinyl acetate, vinyl chloride, acrylonitrile, and vinyl fluoride. The addition reaction may be carried out in either the liquid, vapor, or mixed phases, depending on the properties of the acid. Care must be taken to reduce the polymerization of the vinyl ester produced. 

We consider esterification of ethanol with acetic acid to form ethyl acetate and water. This reaction has been much used for testing algorithms that perform simultaneous phase and reaction-equilibrium calculations. At ambient pressures, we assume the reaction occurs in a vapor phase but depending on the exact values for T and P, the mixture may exist as one-phase vapor, one-phase liquid, or a two-phase vapor-hquid system. The feed contains equimolar amounts of ethanol and acetic acid. The problem is to determine the equilibrium state the phases present and their compositions at 1.0133 bar and temperatures near 355 K. 

When porous solid catalysts are used, diflusion processes in intra- and intercrystalline and interparticle pores often play important roles in the kinetics. Santacesaria et al. examined the effects of diffusion for both vapor-phase (393 — 427K) and liquid-phase (313 — 343K) esterification of ethanol and acetic acid catalyzed by zeolites. According to them, the vapor-phase reaction proceeded in a condensed phase formed in the pores of catalysts, and intracrystalline diffusion is always a rate-determining step in the case of mordenite and, by contrast, in the case of Y zeolite the influence of intracrystalline diffusion upon reaction rate can be neglected. 

---