Esterification reaction kinetic modeling

Flory [3, 48] found that the esterification reactions between model compounds on the one hand and polyfunctional reactants on the other are substantially identical. Thus the reaction of two monofunctional compounds (lauric acid, lauryl alcohol), of a bifunctional compound with a monofunctional one (adipic acid, lauryl alcohol) and two bifunctional compounds (adipic acid, decamethylene glycol) followed essentially third-order kinetics. In the absence of added strong-acid catalyst a second molecule of the carboxylic acid functions as catalyst. Thus when the concentrations (C) of the reacting groups are identical, the rate is given by ... 

Three modeling approaches can be applied to the esterification reaction kinetics the molecular species model, the functional group model, and the overall reaction model. These are schematically illustrated in Scheme 4.5. 

With these kinetic data and a knowledge of the reactor configuration, the development of a computer simulation model of the esterification reaction is iavaluable for optimising esterification reaction operation (25—28). However, all esterification reactions do not necessarily permit straightforward mathematical treatment. In a study of the esterification of 2,3-butanediol and acetic acid usiag sulfuric acid catalyst, it was found that the reaction occurs through two pairs of consecutive reversible reactions of approximately equal speeds. These reactions do not conform to any simple first-, second-, or third-order equation, even ia the early stages (29). 

As a model esterification reaction, the formation of ethyl lactate has been studied and its complete kinetic and thermodynamic analysis has been performed. The formation rate of ethyl lactate has been examined as a function of temperature and catalyst loading. In early experiments, it was determined that lactic acid itself catalyzes esterification, so that there is significant conversion even without ion exchange resin present. The Arrhenius plot for both resin-catalyzed and uncatalyzed reactions indicates that the uncatalyzed... 

Most hterature references to pharmaceutical primary process monitoring are for batch processes, where a model of the process is built from calibration experiments [110, 111]. Many of these examples have led to greater understanding of the process monitored and can therefore be a precursor to design of a continuous process. For example, the acid-catalysed esterification of butan-l-ol by acetic acid was monitored through a factorial designed series of experiments in order to establish reaction kinetics, rate constants, end points, yields, equilibrium constants and the influence of initial water. Statistical analysis demonstrated that high temperatures and an excess of acetic acid were the optimal conditions [112]. 

As appears from the examination of the equations (giving the best fit to the rate data) in Table 21, no relation between the form of the kinetic equation and the type of catalyst can be found. It seems likely that the equations are really semi-empirical expressions and it is risky to draw any conclusion about the actual reaction mechanism from the kinetic model. In spite of the formalism of the reported studies, two observations should be mentioned. Maatman et al. [410] calculated from the rate coefficients for the esterification of acetic acid with 1-propanol on silica gel, the site density of the catalyst using a method reported previously [418]. They found a relatively high site density, which justifies the identification of active sites of silica gel with the surface silanol groups made by Fricke and Alpeter [411]. The same authors [411] also estimated the values of the standard enthalpy and entropy changes on adsorption of propanol from kinetic data from the relatively low values they presume that propanol is weakly adsorbed on the surface, retaining much of the character of the liquid alcohol. 

Lehtonen et al. (1998) considered polyesterification of maleic acid with propylene glycol in an experimental batch reactive distillation system. There were two side reactions in addition to the main esterification reaction. The equipment consists of a 4000 ml batch reactor with a one theoretical plate distillation column and a condenser. The reactions took place in the liquid phase of the reactor. By removing the water by distillation, the reaction equilibrium was shifted to the production of more esters. The reaction temperatures were 150-190° C and the catalyst concentrations were varied between 0.01 and 0.1 mol%. The kinetic and mass transfer parameters were estimated via the experiments. These were then used to develop a full-scale dynamic process model for the system. 

Two overall reactions will be considered in the kinetic model esterification of acetic acid with methanol and esterification of hydrogen iodide to methyl iodide. The overall reactions can be written as follows ... 

The successful scale-up of advancement and modification of rubber-modified epoxy resins is discussed. Mechanisms are proposed for both advancement and esterification reactions as catalyzed by triphenylphosphine which are consistent with experimental results. A plausible mechanism for the destruction of the catalyst is also presented. The morphology of these materials is determined to be core-shell structures, dependent upon composition and reaction and processing conditions. Model studies have been performed to determine the effects of thermal history on the kinetics of reaction. These efforts have resulted in the successful scale-up and use of rubber-modified epoxy resins as functional coatings in the electronics industry. 

It has been shown what can be achieved using the tools and methods developed in the last few years and especially in the first EU project. A question that is at least as interesting is what can, and cannot yet be achieved. In this context, attention should be focused on the main and secondary reactions of a simple esterification, see Fig. 2.9. For such a reaction system it is frequently the case, for time and cost reasons, that a complete kinetic model cannot be developed. 

Cross-linked PVA membranes were also used for the PV separation of the liquid mixtures of water-acetic acid and water-acetic acid-n-butanol-BuAc (Liu et al. 2001). The permeation fluxes of water and acetic acid as a function of the composition were studied. The esterification of acetic acid with -butanol catalyzed by Zr(S04) 4H2O was carried out at a temperature range of 60°C-90°C. It was noticed that mostly water, less acetic acid, much less -butanol, and actually no BuAc permeated through the membrane during PV separation of the quaternary mixture of water-acetic acid-n-butanol-BuAc. From the results obtained from this study, Liu et al. (2001) developed a kinetic model equation for the esterification then, it was taken as a model reaction to study the coupling of PV with esterification. 

Simulation Model Results Initially, the assumption was tested that succinic acid can act as its own catalyst in the esterification reaction. In Figure 4.6, the experimental results on the esterification of PPSu are compared to the theoretical model predictions using kinetic rate constant that are either acid catalyzed (dashed and dotted lines) or not (solid line). As can be seen, the simulation of the experimental data by the theoretical model is very good when the kinetic rate constants used are not acid catalyzed. However, when the kinetic rate constants are assumed to be acid catalyzed, using Equations 4.30 and 4.31, the experimental data are not predicted equally well. Using values to accurately predict the initial rate data, the final data are underestimated. In contrast, when such values are used to predict the final experimental data, the initial data are overestimated. Thus, it was concluded that in the synthesis of the poly(alkylene succinates) studied here, the presence of the metal catalyst tetrabutoxy titanium (TBT) leads to a poor activity of self-catalyzed acid. This was also observed for PBSu by Park et al. [42]. Therefore, Equations 4.30 and 4.31 were not used and only parameters and Arg need to be estimated. The values of these parameters were calculated for every different system studied from fitting to the experimental data. The final values are reported in Table 4.2. Notice that these values are correct only for the specific catalyst type. 

The effect of the type of glycol used (i.e., EG, PG, or BG) on the esterification reaction was examined next. It was found that the type of glycol did not affect much the variation of water conversion with time. Using BG, slightly higher reaction rates were observed compared to those for PG, which in turn were shghtly faster compared to those for EG. Again, the theoretical simulation model fitted the experimental data very well. The kinetic parameters evaluated are reported in Table 4.2. As was expected, increases in the order PBSu > PPSu > PESu. 

Furthermore, modeling of the esterification reaction was attempted in the presence of silica nanoparticles during the formation of aliphatic polyester nanocomposites. From the experimental data, it was found that on increasing the Si02 content in esterification, the rate of water production decreases [47]. In addition, it was clear that the total quantity of water released does not depend on the nanoparticle concentration. This suggests that the existence of the particles does not influence the esterification reaction itself. Their main effect is to adsorb the produced water before it evaporates, altering in this way the water evaporation curve. The simplest model for this phenomenon is to assume very fast water adsorption/desorption kinetics on the Si02 particles. In this case, the evaporation kinetics must be explicitly taken into account because it is no more very fast compared to the other phenomena that occur. 

Esterification and polycondensation kinetics of PPSu synthesis can be well described on the basis of rather simple simulation models, taking into account the reaction kinetics and the functional group modeling approach. The latter is a very beneficial technique which includes aspects of the reaction mechanism although with the minimum computational effort. 

Investigation on the kinetics of the esterification reaction in the presence of the ion-exchange resin Amberlyst 15.The Uniquac model is applied to evaluate the activities of the reacting species in the kinetic equation. 

The esterification process of methacrylic acid with n-propanol and isopropanol have been studied in an experimental, isothermal batch reactor. Basing on experimental results, the rigorous kinetic models were derived including the reversible reactions. The equilibrium constants and kinetic parameters have been determined. 

Results from the comparisons between theoretically calculated (solid lines) and experimentally measured (individual symbols) acid numbers are shown for the esterification of methacrylic acid using n-propyl alcohol (Figures 1-3), and for the esterification of metharylic acid using isopropyl alcohol (Figures 4-6). The average error of fit of experimental results to proposed kinetic model is, respectively, 3.5% and 5.7%, for 9 sets of data concerning the reaction with n-propanol, for 9 sets for the esterification with n-isopropanol. 

In the present work, the enzymatic esterification was investigated in order to analyse the influence of the operating conditions on the reaction yield and develop a kinetic model to describe the reaction rate for different operating conditions. 

Esterification of oleic acid with ethanol has been carried out at three different temperatures (T) as it is shown in figure 4. As expected, a temperature rise increases the reaction rate. The simulated results fix>m reversible kinetic model were according to this behaviour and fix>m the adjusted parameters, an endothermic reaction was validated. 

The esterification reaction of castor oil and lauric add was carried out using SnCl2 2H20 as catalyst (0.25,0.5,1.0 and 2.0 % w/w catalyst loadings) at 185°C and the kinetic data were measured. The results showed that there was a good linearity relationship between In [(1—Xb)/(1—Xa)] and t. The plot of k versus Cc was close to a straight line. For the given values of Cbo, Cao and Cc, the kinetic model of esterification of castor oil and lauric acid was obtained at 185°C,... 

The esterification reaction of octanoic acid and n-octyl alcohol was carried out using CoCl2 2H20 as catalyst (0, 0.0385, 0.077 mol/1) at 70°C and the kinetic data were measured. The experimental curves suggest that the kinetics of esterification between octanoic acid and n-octyl alcohol can be described by an irreversible second order power model, considering the catalyst concentration as a constant in the kinetic model proposed. The activation energy is seen to have a value of 53 kcal/mol (Urteaga et al., 1994). 

Although the reaction system of TPA and BDO is heterogeneous, it can be assumed that the esterification occurs only in the liquid phase. The initial rate method is used to predict the reaction rate. The kinetic model of mono-esterification between TPA and BDO catalyzed by Ti(OBu)4 in the temperature of 463-483K was investigated (Bhutada Pangarkar, 1986). The reaction rate r can be described as. 

In 2011, Rattanaphra, et al. also investigated the kinetic model of myristic add esterification with methanol using sulfated zirconia as catalyst. The reaction is shown as follows ... 

The kinetics of esterification reaction can be expressed using a pseudo-homogeneous second-order equilibrium model in the absence of any intraparticle diffusional limitation as... 

Esterification also occurs in high-temperature alcoholysis of aromatic esters, as carboxyl end groups are formed by side reactions, and should also be considered in the kinetic modeling of these processes. 

In spite of being the first reaction ever studied [95], esterification has been under investigation ever since, and much knowledge has accumulated, even if some points are stUl less clear. The basic kinetic model for polyesterification was established by Flory and is summarized in his classic book [5j. Esterification was shown to be acid-catalyzed, it is first-order with respect to hydroxyls and, with respect to carboxyls, its order is either one in the presence of foreign strong protic acids, or two in their absence [Eq. (52)]. 

A Geo bZcq 5O2 catalyst showed desirable catalytic properties for the ketonization of carbohydrate-derived carboxylic acids in the presence of other monofunctional oxygenated species, such as alcohols or ketones. Gaertner et al. developed a kinetic model that describes the ketonization of mixtures containing carboxylic acids and esters over Geo sZro 502 catalysts from 175 to 350°G. " Under these conditions two different reactions take place, esterification and ketonization, both consuming hexanoic acid, used as a model molecule. Ester ketonization is slower than the ketonization of the corresponding acid. 

A detailed literature review on esterification of carboxylic acids with different alcohols has been made. The type of catalysts used, their activity, selectivity, kinetic modeling and reaction engineering aspects have been discussed. A general review of the esterification of carboxylic acid with alcohol in presence of mineral acid or heterogeneous acid catalyst have been presented. Critical analyses of reaction engineering aspects such as external and intraparticle mass transfer effects and reactor performance models have been presented and scope and objective of the present thesis outlined. 

A trickle bed reactor model was developed for the Esterification reactions studied. This model incorporates the contribution of intraparticle mass transfer resistances. The kinetic equations already developed were used for the respective esterification reactions. Experimental data were obtained in a 25 mm diameter glass trickle bed reactor at different concentrations of reactants, flow rates and temperatures. The performance of the reactor was measured in terms of the conversions of the acids obtained at the exit of the reactor. The model predictions were compared with experimental data at different operating conditions. This model would be useful in predicting the performance of a trickle bed reactor for esterification reactions in general. 

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