REACTOR (CSTR) EXPERIMENT 2024 MCKETTA DEPARTMENT OF CHEMICAL ENGINEERING THE UNIVERSITY OF TEXAS AT AUSTIN ACTUAL SPRING 2024

REACTOR (CSTR) EXPERIMENT 2024 MCKETTA DEPARTMENT OF CHEMICAL ENGINEERING THE UNIVERSITY OF TEXAS AT AUSTIN ACTUAL SPRING 2024 INTRODUCTION This experiment involves a chemical reaction in a 2L continuous-flow stirred tank reactor (CSTR). The conversion in the reactor is related to the kinetic information and reactor operating conditions. The reaction to be studied, the saponification of ethyl acetate by sodium hydroxide, is especially convenient for this study because the conductivity of the solution in the reactor changes with the degree of conversion and can easily be monitored and recorded. Also, the reaction proceeds rapidly at room temperature. These features greatly simplify the chemical analysis and operating procedures. The purpose of this laboratory is to gain experience in the lab operation and analysis of a chemical reactor and study its scale up to industrial operations. You will monitor a continuously stirred tank reactor (CSTR) from start-up (unsteady state) through steady state and you will analyze the reaction kinetics at varied temperatures and flow rates. After collecting the data, the following objectives will be required: • To determine the second order rate constant at each temperature. • To determine the activation energy. • To verify the reaction order assumption for the reaction of ethyl acetate to its sodium salt (sodium acetate) by comparing the performance of the system with that predicted by the theoretical equations that govern the operation and design of the reactor. • To complete simple scale-up calculations. EQUIPMENT The system shown in Figure 1 consists of two feed tanks, a continuous stirred-tank reactor with a heating element, a conductivity meter, two peristaltic pumps, multiple sensors, and several valves to direct flow. Take some time to inspect the system and understand its capabilities, discuss with your group the data logging capabilities and the requirements for the experiment. How will you accomplish your experimental objectives effectively? Figure 1: CSTR equipment THEORY The Chemical Reaction The reaction studied in this experiment is the saponification of ethyl acetate with sodium hydroxide to ethanol and a colorless salt (sodium acetate). The reaction is shown below: NaOH + H3CCOOC2H5  CH3COO- Na+ + C2H5OH [1] Sodium Hydroxide + Ethyl Acetate  Sodium Acetate + Ethyl Alcohol The reaction can be considered elementary and first order with respect to both sodium hydroxide and ethyl acetate, and second order overall with the limits of concentration of 0 to 0.1M and temperature (20-40°C) studied. The rate law is: (- r) = k[NaOH][EtAc] [2] The rate constant k is a function of temperature as defined by the Arrhenius equation:  E k  k 0 e RT [3] It is important to understand that the rate constant that you determine is for a specific temperature and that temperature used for the calculation should be reported. If your calculated activation energy is unreliable, you may use values for the activation energy from literature to estimate the rate constant’s dependence on temperature, if this is the case, be sure to explain why your calculated value is unreliable, and how your rate constant improves by using literature values instead. You will also need to verify the assumption of a second order reaction. Conductivity measurements A conductivity meter will be used to monitor the conductance of the solution in the reactor. The conductivity measurements can be translated into a degree of conversion of the reactants. Both sodium hydroxide and sodium acetate contribute to conductance, but ethyl acetate and ethyl alcohol only contribute to a negligible extent. However, the conductivity of a sodium hydroxide solution at a given concentration and temperature is not the same as that of a sodium acetate solution at the same concentration and temperature, thereby allowing for the determination of a relationship between conductivity and conversion. The following constants will be required from each experiment: FNaOH = volume feed rate of sodium hydroxide (l/s) FEtAc = volume feed rate of ethyl acetate (l/s) [NaOH] = sodium hydroxide concentration in the feed vessel (mol/l) [EtAc] = ethyl acetate concentration in the feed vessel (mol/l) [NaAc] = sodium acetate concentration in the feed vessel (mol/l) T = reactor temperature (K) V = Volume of the reactor (l) You will want to set up a spreadsheet to complete the following calculations for each experiment, using the constants defined above and relations below: [NaOH ]0  F FNaOH  F [NaOH ] (NaOH conc. in mixed feeds) [EtAc]0  F NaOH FEtAc  F EtAc [EtAc] (EtAc conc. in mixed feeds) NaOH EtAc [NaOH]∞ = 0 for [NaOH]0 ≤ [EtAc]0 (NaOH conc. at 100% conversion) [NaOH]∞ = ([NaOH]0-[EtAc]0) for [NaOH]0 > [EtAc]0 [NaAc] ∞ = [NaOH]0 for [NaOH]0 ≤ [EtAc]0 (NaAc conc. at 100% c