Vapor-phase esterification

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). 

Continuous esterification is used to produce methyl acetate (Fig 2t. Vapor-Phase Esterification... 

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. 

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. " ... 

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. ... 

Table 4.20 Catalytic activities of several solid acids for vapor-phase esterification...

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. 

Catalytic esterification of alcohols and acids in the vapor phase has received attention because the conversions obtained are generally higher than in the corresponding liquid-phase reactions (7). 

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

There are two main processes for the synthesis of ethyl alcohol from ethylene. The eadiest to be developed (in 1930 by Union Carbide Corp.) was the indirect hydration process, variously called the strong sulfuric acid—ethylene process, the ethyl sulfate process, the esterification—hydrolysis process, or the sulfation—hydrolysis process. This process is stiU in use in Russia. The other synthesis process, designed to eliminate the use of sulfuric acid and which, since the early 1970s, has completely supplanted the old sulfuric acid process in the United States, is the direct hydration process. This process, the catalytic vapor-phase hydration of ethylene, is now practiced by only three U.S. companies Union Carbide Corp. (UCC), Quantum Chemical Corp., and Eastman Chemical Co. (a Division of Eastman Kodak Co.). UCC imports cmde industrial ethanol, CIE, from SADAF (the joint venture of SABIC and Pecten [Shell]) in Saudi Arabia, and refines it to industrial grade. 

The newest and most commercially successful process involves vapor phase oxidation of propylene to AA followed by esterification to the acrylate of your choice. Chemical grade propylene (90—95% purity) is premixed with steam and oxygen and then reacted at 650—700°F and 60—70 psi over a molybdate-cobait or nickel metal oxide catalyst on a silica support to give acrolein (CH2=CH-CHO), an intermediate oxidation product on the way to AA. Other catalysts based on cobalt-molybdenum vanadium oxides are sometimes used for the acrolein oxidation step. 

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]. 

When H3PM012O40 was used to catalyze acylation reactions some of the acid dissolved and the reactions were partially promoted by the acid in solution. The H4SiW]204o and H3PW12O40 catalysts, however, did not dissolve under the reaction conditions and were, therefore, effective promoters for liquid phase Freidel-Crafts acylation reactions.Supported and bulk heteropoly acids have also been used to promote vapor phase Freidel-Crafts alkylations and esterifications.. ... 

Mainly PV aided conversions have been studied and more in particular esterifications, a typical example of an equilibrium limited reaction with industrial relevance and well-known reaction mechanisms. " This hybrid process has already made it to several industrial applications. The thermodynamic equilibrium in such a reaction can be easily shifted and obtained in a shorter reaction time by removing one of the products. Pervaporation is especially interesting because it is not limited by relative volatility or azeotropes and energy consumption is generally low, because only the fraction that permeates undergoes the liquid/vapor phase change. It can also be operated at lower temperatures, which can better match the optimal conditions for reaction. 

The major reaction is oxidative dehydrogenation at the secondary hydroxyl site of lactic acid, but the product pyruvic acid in its free-acid form is unstable to decompose. Thus the substrate was supplied as ethyl ester to protect the carboxyl moiety. Esterification is also of benefit to vapor-phase flow operation in making acids more volatile. Hydrolysis of ethyl lactate gives free pyruvic acid with further decarboxylation to actaldehyde. Ethanol, which is another fragment of ester hydrolysis, eould be either oxidized to acetaldehyde or dehydrated to ethylene at higher temperature above 350°G. The reaction network is summerized in Scheme 1. 

It is to be noted that in vapor phase processes such as those described by James the acids produced are aldehydic in nature and may depend upon this aldehydic character for utilization in the form of condensed products such as low grade resins, etc. Attempts to recover these acids in the form of sodium soaps usually leads to the formation of resins due to the resinify-ing action of the caustic. On the other hand, the numerous claims for the liquid phase oxidation process usually mention the formation of simple carboxylic acids or hydroxy-carboxylic acids which may be used to form edible fats by esterification with glycerol. This seems to indicate the somewhat milder oxidation possible in the liquid phase process. 

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. 

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