Ethanol esterification reactions with acetic acid

A membrane reactor using a H-ZSM5 membrane was used by Bernal et al. [3.42] to carry out the esterification reaction of acetic acid with ethanol. An equimolar etha-nol/acetic acid liquid mixture was fed in the membrane interior, while He gas was used as an inert sweep on the shell-side. In this particular application the membrane, itself, provides the catalysis for the reaction. NaA and T-type zeolite membranes have been utilized for esterification reactions in a PVMR and in a vapor permeation membrane reactor (VPMR) by Tanaka et al [3.43, 3.44]. Both membranes are hydrophilic and show good separation characteristics towards a number of alcohols. The NaA membrane was used to study the oleic/acid esterification in a vapor permeation membrane reactor (VPMR) at 383... 

The first pervaporation membrane reactor model which takes into account solution non-idealities was developed and validated experimentally by Zhu et al [5.90]. Prior studies [5.89, 5.91] also made note of such non-idealities, but offered no unified means for accounting for these phenomena in the description of PVMR. Since the model of Zhu et al. [5.90] appeared, other groups have also utilized similar models [5.92]. A more comprehensive analog of this model was, for example, recently presented and validated experimentally by Park [5.93], and by Lim et al. [5.94]. Zhu et al. [5.90] analyzed a tubular PVMR, in which the homogeneously catalyzed esterification reaction of acetic acid with ethanol to produce ethyl acetate and water took place. The reaction can be expressed generally as ... 

Acid catalysed dehydration of diacetone alcohol to form mesityl oxide followed by selective hydrogenation Acid catalysed esterification of relevant alcohol (methanol, ethanol, propanols, butanols) with acetic acid Tischenko reaction via acetaldehyde is also used for ethyl acetate... 

Ethyl acetate is an oxygenated solvent widely used in the inks, pharmaceuticals and fragrance sectors. The current global capacity for ethyl acetate is 1.2 million tonnes per annum. BP Chemicals is the world s largest producer of ethyl acetate. Conventional methods for the production of ethyl acetate are either via the liquid phase esterification of acetic acid and ethanol or by the coupling of acetaldehyde also known as the Tischenko reaction. Both of these processes require environmentally unfriendly catalysts (e.g. p-toluenesulphonic acid for the esterification and metal chlorides and strong bases for the Tischenko route). In 1997 BP Chemicals disclosed a new route to produce ethyl acetate directly from the reaction of ethylene with acetic acid using supported heteropoly acids... 

An example of esterification is the production of ethyl acetate by the reaction of ethanol with acetic acid. 

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]. 

Kinetics is concerned with the rates of chemical reactions and the factors which influence these rates. The first kinetic measurements were made before 1820, but interpretation in terms of quantitative laws began with the studies on the inversion of sucrose by Wilhelmy/ the esterification of ethanol with acetic acid by Bethelot and St. Gilles, and the reaction between oxalic acid and potassium permanganate by Harcourt and Esson. These investigations established the relations between rate and concentration of reactants. The important contribution of Arrhenius for the effect of temperature was also made in the nineteenth century. 

Pervaporation membrane reactors are not a recent discovery. The use of a PVMR was proposed in a U.S. patent dating back to 1960 [3.6]. Though the technical details on membrane preparation and experimental apparatus were rather sketchy, the basic idea was described there, namely, the use of a water permeable polymeric membrane to drive an esterification reaction to completion. A more detailed description of a PVMR can be found in a later European patent [3.7], which described the use of a flat membrane (commercial PVA or Nafion ) placed in the middle of a reactor consisting of two half-cells. The reaction studied was the acetic acid esterification reaction with ethanol. For an ethanol to acetic acid ratio of 2, liquid hourly space velocities (LHSV) in the range of 2-5, and a temperature of 90 °C complete conversion of the acetic acid was reported. The use of PVMR for this reaction shows promise for process simplification, as indicated schematically in Figure 3.2, which shows a side-by-side comparison of a conventional and a proposed PVMR plant for ethyl acetate production. 

Due to the simplicity of the model, the phenomena causing multiplicity can easily be verified. The multiplicity is caused by the relations between the heat of vaporization and the boiling points of the educts, which are Tfl MeOH < f s.PA and AH MeOH > ffvFA- Such relations have also been identified by Jacobsen and Sko-gestad [48] to cause multiplicity in a separation of non-reacting binary mixtures in a one-stage column. Hence, multiplicity is not caused by the reaction but is just the result of the separation only in methyl formate synthesis. Similar results have also been foimd for the esterification of ethanol with acetic acid [25, 50]. 

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. 

Gao, Yue, and Li (1996) studied the same reaction using a zeolite A-PVA composite membrane (at temperatures ranging from 20 to 50 °C). In this work, together with the pervaporation-aided catalytic esterification of acetic acid with ethanol, the reaction between salicylic acid with methanol was also treated. Among other results, it showed that the continuous removal of water from the system displaced the equilibrium limit (79%), making possible a 95% conversion, when using PVA, PVA -I- KA, and PVA -I- CaA membranes for 20.0, 11.3, and 10.0 h, respectively. 

Mochida, L, Y. Anju, A. Kato T. Seiyama (1971) Elimination reactions on solid acid catalysts II. Esterification of ethanol with acetic acid. Journal of Catalysis, 21, 263-269,ISSN 0021-9517. 

We inspect the esterification of ethanol with acetic acid as an illustrative example for the equilibrium of a liquid phase reaction ... 

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. ... 

A derivative of stearic acid can be obtained by 24 hr standing of a mixture of 4 g of ethyl stearate, 22 ml of 25% sodium ethoxide, 7 ml of pyridine, and 20 g of urea. The product is isolated by pouring the reaction mixture into water acidified with acetic acid and is then crystallized from ethanol. The yield is 90% (24) the excess of urea is necessary to prevent the formation of diacyl urea (25). There are other possibilities for identifying higher acids. For example, esterification (see p. 252), or conversion to hyd-razides which can be converted further to another series of derivatives when reacted with phenylisocyanate or phenylisothiocyanate ... 

The reaction for acetic acid (HAc) esterification with ethanol (EtOH) to produce ethyl acetate (EtAc) and water (H2O) can be expressed as... 

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). 

An example of a reversible reaction in the liquid phase is afforded by the esterification reaction between ethanol and acetic (ethanoic) acid forming ethyl acetate and water. Since, however, ethyl acetate undergoes conversion to acetic acid and ethanol when heated with water, the esterification reaction never proceeds to completion. 

Esterification of acetic acid with ethanol proceeds according to the reaction ... 

Example 6.6 Ethyl acetate can be produced by the esterification of acetic acid with ethanol in the presence of a catalyst such as sulfuric acid or an ion-exchange resin according to the reaction ... 

The esterification of acetic acid with ethanol using sulfonic ion-exchange resins as catalyst/selective sorbent was studied by Mazzotti et al. [164]. The authors developed a detailed mathematical model, which was able to predict correctly the system s behavior. They succeeded in obtaining 100% conversion of acetic acid in addition to a complete separation. Several other studies involving enzymatic reactions were also carried out and will be presented in more detail in the next section. 

During the production of recovery flavours, apple wines or brandies, the interaction with ethanol, acetaldehyde and acetic acid represents the next level of interactions. The reaction products contain compounds which result from esterification and acetal formation reactions, which are summarised in Table 21.4. 

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