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Esterlesme reaksiyonlarının dönüsümlerinin yavas bir reaksiyon hızıyla vetersinir reaksiyonların varlıgıyla sınırlı oldukları bilinmektedir. Reaksiyon hızınıarttırmak için katı asit katalizatörlerinin kullanımı homojen asit katalizatörlere göresahip oldukları avantajlar nedeniyle oldukça dikkat çekmektedir. Tasıyıcı iyon olarakkatalizatör iyonunu içeren iyon degistirici reçineler kullanılarak homojen katalizkabullenmesi yapılabilir. Çünkü reaksiyon mekanizması ve kinetik mertebe homojenkatalizinkiler seklinde belirlenmistir.Bu çalısmada, metil alkol ile asetik asit ve n-amil alkol ile propiyonik asitarasındaki esterlesmeler model reaksiyon olarak seçilmistir. Çalısmanın amacı, ikincimertebe homojen reaksiyona göre korele edilmis hız sabitlerine baglı olarak her birmodel reaksiyonu analiz etmede kullanılan volumetrik, kromatografik ve refraktometrikmetodların tekrarlanabilirlik sıralamasını belirlemektir. Ayrıca karıstırma hızı,katalizatör konsantrasyonu, tanecik büyüklügü, divinilbenzen içerigi, sıcaklık, mol oranıve farklı katalizatör gibi reaksiyon hızını etkileyen önemli degiskenler çalısılmıstır.Makro gözenekli (Ambelyst-15) ve mikro gözenekli (Dowex 50W, Amberlite IR-120)reçine katalizatörleri için aktivasyon enerjileri, reaksiyon entalpi ve entropi degerlerihesaplanmıstır.Bu yöntemlerin duyarlılık sıralaması söyle belirlenmistir: volumetrik >kromatografik > refraktometrik. Ayrıca kurutulduktan sonra katalizatör olarakkullanılan reçineler arasında Dowex 50Wx2' nin mikro gözenekli olmasına ragmen enetkili reçine oldugu bulunmustur.Anahtar Kelimeler: Esterlesme, kinetik, iyon degistirici reçineler, propiyonik asit, namilalkol, asetik asit, metil alkol. Conversions for the esterification reactions have long been known to be limitedby a slow reaction rate and the existence of reversible reactions. To accelerate thereaction rate, the use of solid acid catalysts has received great attention because ofhaving advantages compared to homogeneous acid catalysts. Homogeneous catalysiscan be accepted by using ion-exchange resins containing the catalyst ion as their counterions. Because the reaction mechanisms and kinetic orders have been determined asthose of homogeneous catalysis.In the present study the esterifications of acetic acid with methyl alcohol andpropionic acid with n-amyl alcohol were chosen as model reactions. The aim of thisstudy is to find that the reproducibility order of volumetric, chromatographic andrefractometric methods used in analysis of the each model reaction according to rateconstants correlated with a second-order homogeneous reaction. Furthermore, theimportant variables such as stirring speed, catalyst concentration, particle size,divinylbenzene content, temperature, mole ratio, different catalysts affecting the rate ofthe reaction were studied. The apparent activation energies, reaction enthalpies andentropy values were calculated for macroporous (Amberlyst-15) and microporous resin(Dowex 50W, Amberlite IR-120) catalysts.The sensitivity order of these methods was determined as follows: volumetric>chromatographic > refractometric. In addition that Dowex 50Wx2 was found the mosteffective one among the resins used as catalysts after being dried, although it is amicroporous resin.Key Words: Esterification, kinetic, ion exchange resins, propionic acid, n-amylalcohol, acetic acid, methyl alcohol. 167

Kinetics of heterogeneous catalysed esterification of propionic acid with n-amyl alcohol was studied with a microporous cation-exchange resin catalyst, Dowex 50Wx4, in a stirred batch reactor to synthesise amyl propionate. Effects of various parameters such as speed of agitation, catalyst loading, and reaction temperature on reaction rate were investigated. The equilibrium conversion of propionic acid increased with in catalyst loading and reaction temperature. Stirrer speed had virtually no effect on the reaction rate under the experimental conditions. The apparent activation energy was found to be 43.167 kJmol−1 for the formation of amyl propionate and the equilibrium constant, which is independent of temperature ranging from 318 to 348 K, was found to be 4.05. It was also observed that the initial reaction rate decreased with water concentrations and increased with that of acid and increased with that of alcohol linearly. The reaction was found to occur between an adsorbed acid molecule and a molecule of alcohol in the bulk and it was concluded that the reaction mechanism can be represented by Eley-Rideal model.

Sulfonic acid functionalized poly(ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole), poly(EGDMA-VTAZ-SO 3 H), is evaluated in the esterification of lactic acid with methanol. From nitrogen physisorption data, high surface area (220 m 2 /g) and type IV isotherm are obtained. Conversion measurements indicate a stronger interaction of poly(EGDMA-VTAZ-20%SO 3 H) with water molecules than that occurring in poly(EGDMA-VTAZ-10%SO 3 H). Hence, the higher catalytic activity of poly(EGDMA-VTAZ-10%SO 3 H) is related to the more hydrophobic microenvironment of –SO 3 H sites, which reduces the acid site deactivation associated with adsorption of water generated during the reaction. Moreover, apparent activation energy is found to be 48.02 kJ mol −1 , which can be comparable with the literature values.

Sulfonic acid functionalized poly (ethylene glycol dimethacrylate-1-vinyl-1,2,4-triazole), poly (EGDMA–VTAZ–SO3H) (average diameter 1.0–1.5 mm), was found to be efficient solid acid catalyst for the esterification of methanol and propionic acid under heterogeneous reaction conditions. The pristine polymer, poly (EGDMA–VTAZ), was produced by suspension polymerization and then proton-conducting polymer was obtained by blending of poly (EGDMA–VTAZ) with different percentage of H2SO4 solutions. The protonation of aromatic heterocyclic rings was proved with Fourier-transform infrared spectroscopy (FT-IR). Thermo gravimetric (TG) analysis showed that the catalyst is thermally stable up to 573 K. The surface morphology of the catalyst was characterized by scanning electron microscopy (SEM). Poly (EGDMA–VTAZ–SO3H) beads can be regenerated and reused, so this provides a potential application. It has a rate constant which exceeds that of Amberlyst-15 by a factor of about four at 333 K. As for the reaction equilibrium constant (Ke), which is independent of temperature ranging from 318 to 343 K, was determined to be 3.16. The apparent activation energy was found to be 41.6 kJ mol−1 for poly (EGDMA–VTAZ–SO3H).

This paper describes the application of LFER in the form of Taft correlation to understand the mechanism of the esterification of propanoic acid with different alcohols over heterogeneous catalyst, Dowex 50Wx4. The rate constant (k1) in the rate equation decreases with change of alcohols in the order methanol, ethanol, n-propyl, n-butyl, n-pentyl, iso-butyl, iso-propyl and sec-butyl (2-buthanol). The reaction of propanoic acid with alcohols fits the Taft equation, log k1/kCH3= 1.0061 Es- 0.0012, which implies that the steric effect of the substituent governs that reaction and the mechanism is similar between the different alcohols. The experimental results were modelled according to a simple second-order model. It was found that the equilibrium constant of this reaction does not depend on the structure of the organic alcohols, and has for 333 K the value 4.04.

Summary Esterification of methyl alcohol with acetic acid catalysed by commercially available polymeric ion-exchange resins Amberlyst-15, Dowex 50W and Amberlite IR-120 was carried out in the temperature ranging between 323–338K. Mesh sizes and divinylbenzene contents had virtually no effect on the rate the data of which were correlated with a second-order homogeneous reaction. The samples were analysed with gas chromatography, refractometry and volumetry. The reproducibilities were the order of ±2.89%, ±5.07% and the order of ±6.58% respectively for the volumetric, chromatographic and refractometric methods.