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Comparison of 2nd order rate constants, k (L/mol*s), and activation energy, Ea [kJ/mol], of the sodium hydroxide and ethyl acetate saponification reaction between studies and techniques.
The primary project goal is to design an industrial plug flow reactor (PFR) system to treat a 10 L/min waste stream composed of 0.2 weight percent aqueous ethyl acetate (EtOAc) down to 0.02 weight percent to comply with current regulations. Aqueous EtOAc is treated via hydrolysis, or saponification, with sodium hydroxide (NaOH) to form sodium acetate (NaOAc) and ethanol (EtOH). The lab team will determine kinetics of hydrolysis in a batch reactor at varying temperatures (20-30°C), such as the second order rate constant, k [L/mol*s], and the activation energy, Ea [kJ/mol]. Measured kinetics will be compared to literature values. Bench scale results will be used to propose a large scale system to treat waste water to specifications.
The hydrolysis of EtOAc with NaOH is a second order reaction according to several pieces of research. Danish et al. [footnoteRef:1] compared the saponification reaction between a PFR and continuously stirred tank reactor (CSTR). The PFR and CSTR were kept at constant temperatures. Three independent variables were chosen: temperature of the reaction, the feed rate of 0.1 M sodium hydroxide and ethyl acetate, and the type of reactor. As seen in Figures 1 & 2, a fractional conversion of 0.9 is not satisfied. [1: Danish M. and Al Mesfer M.K. et al. A Comparative Study of Saponification Reaction in a PFR and CSTR (Research Journal of Chemical Sciences: Vol. 5(11), 13-17) November 2015 http://www.isca.in/rjcs/Archives/v5/i11/3.ISCA-RJCS-2015-137.pdf]
Figure 1: Feed rate, F [mL/min], of 0.1 M sodium hydroxide and ethyl acetate at a constant temperature (30°C) vs conversion rate, XA, and the second order rate constant, k (L/mol*s)
Figure 2: Temperature, T [°C], of 0.1 M sodium hydroxide and ethyl acetate at a constant feed rate (60 mL/min) vs conversion rate, XA, and the second order rate constant, k (L/mol*s)
The optimal feed is 60 mL/min for this 0.4 L PFR and the temperature needs to be above 40°C to reach a conversion of 90%. The current experiment will also test differing feed ratios as well finding the optimal temperature, which will likely be above 40°C.
Kuheli Das et al.[footnoteRef:2] published a research paper studying the kinetics of hydrolysis of EtOAc in a batch reactor. Researchers gathered a collection of rate constants at various temperatures as seen in Table 1 and Figure 3. Conductivity measurements were used to determine compositions, similar to the current experiment. [2: Kuheli Das et al. Kinetic Studies on Saponification of Ethyl Acetate Using an Innovative Conductivity-Monitoring Instrument with a Pulsating Sensor (International Journal of Chemcial Kinetics 19(vol. 43): 648-656, November 2011) https://www.researchgate.net/publication/229360677_Kinetic_Studies_on_Saponification_of_Ethyl_Acetate_Using_an_Innovative_Conductivity-Monitoring_Instrument_with_a_Pulsating_Sensor]
Table 1 provides several rate constants at varying temperatures to compare to the current experiments’ results when completed. Das also compared his results regarding the second order rate constant and activation energy of saponification to others whom used different concentration measuring techniques as seen in Table 2.
Table 2: Comparison of 2nd order rate constants, k (L/mol*s), and activation energy, Ea [kJ/mol], of the sodium hydroxide and ethyl acetate saponification reaction between studies and techniques.
Das attributes the low rate constant (0.11 L/mol*s) and high Ea (61.4 kJ/mol) of the Smith study to the poor precision of the volumetric titration method for measuring concentration. All other studies provide rate constants and activation energies in the same order of magnitude as Das. The research team expects to obtain a similar rate constant of 0.16 L/mol*s at 30°C and predicts that the rate constant will be larger for a PFR at a higher temperature achieving a fractional conversion of 0.9.