ethyl acetate sodium hydroxide - Memo

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					Continuous Stirred Tank Reactor (CSTR)
Safety Procedures and Operating Manual

               Created by
             Cynthia Kuhns
              Paul O’Reilly
              Eric Wright

               Fall, 1999
                                                          T ABL E         OF      C ONTENTS

BACKGROUND AND THEORY:............................................................................................................................. 3

EQUIPMENT DESCRIPTION .................................................................................................................................. 5

START-UP PROCEDURES ....................................................................................................................................... 7

ROUTINE DUTIES ................................................................................................................................................... 10

SHUT-DOWN PROCEDURES................................................................................................................................ 13

EMERGENCY SHUT-DOWN PROCEDURES..................................................................................................... 13

EMERGENCY OPERATIONS................................................................................................................................ 14

TROUBLESHOOTING GUIDE .............................................................................................................................. 15




                                                                                 2
BACKGROUND AND THEORY


        The goals of a typical experiment on the CSTR experiments are: (1) use the CSTR to

determine the Arrhenius and kinetic constants to the hydrolysis of ethyl acetate with sodium

hydroxide and (2) estimate the capital and operating costs for a reactor with a design flow of 2.0

gpm.

        This experiment will employ the hydrolysis of ethyl acetate with sodium hydroxide to form

ethanol and sodium acetate (Equation 1)

                   
NaOH + C 2 H 5 COO   C 2 H 5 OH + NaCHC 3 OO
                               k
                                                                                       (1)

Arrhenius proposed the following for the specific reaction rate k:

                E
k (T )  Ae     RT
                                                                                       (2)

where A = Arrhenius constant

        E = kinetic constant

        R = universal gas constant

        T = absolute temperature

The specific rate of reaction is

R A   k  C A  CB                                                                   (3)

where CA = Concentration of ethyl acetate

        CB = Concentration of sodium hydroxide

The steady-state design equation for a CSTR is

FAO  FA  RAVR  0                                                                    (4)

where FAO = Inlet flow rate of ethyl acetate

        FA = Outlet flow rate of ethyl acetate



                                                   3
        VR = Volume of fluid in the reactor

Substituting RA into the design equation and solving for k gives the following equation:

     C AO  C A
k                                                                               (5)
     C A CB  

where CAO = Inlet concentration of ethyl acetate

        CA = Outlet concentration of ethyl acetate

        CB = Outlet concentration of sodium hydroxide

         = VR/vo = Space time, time necessary to process one reactor volume of fluid



        The inlet concentration of C B is determined when the mixture is prepared. The outlet

concentration is measured through titration experiments. These titration experiments are done after

acid quenching the sample with a known concentration of HCl. Thus, C A is calculated through

stoichiometry. can be computed by dividing the reactor volume by the total volumetric flow rate.

Thus, k can be calculated form Equation 5.

        Next, ln(k) can be plotted as a function of 1/T and a regression line is used to fit the data.

The following equation can be derived by taking the natural log of Equation 2:

            E 1
ln( k )      ln( A)                                                        (6)
            R T

where k = specific rate constant calculated form Equation 5

        -(E/R) = slope of the regression line

        ln (A) = y-intercept of the regression line

Equation 6 is used with the regression line to determine the values of the Arrhenius and kinetic

constant.




                                                      4
EQUIPMENT DESCRIPTION
   Figures 1 and 2 show the equipment used in the CSTR experiment. The table following the

pictures, Nomenclature, lists the individual components of the equipment.




Figure 1: Upper Portion of CSTR Apparatus




                                                 5
Figure 2: Lower Portion of the CSTR Apparatus



Nomenclature
Symbol                                   Definition
V1                                       EtAc rotameter valve
V2                                       NaOH rotameter valve
V3                                       EtAc feed tank drain valve
V4                                       NaOH feed tank drain valve
V5                                       Sump tank drain valve
V6                                       Reactor sample valve
O1                                       Overflow pipe
F1                                       EtAc rotameter
F2                                       NaOH rotameter
EtAc                                     Ethyl acetate
NaOH                                     Sodium hydroxide




                                           6
START-UP PROCEDURES
STEPS                                           NOTES AND ALERTS
Initial Start-Up
1. Verify proper operation of unit

 a. Fill feed tanks 2/3 full with tap water

 b. Close drain, V6, and V5 using yellow        Make sure they operate

     handles (horizontal is closed)

 c. Adjust pumps to zero stroke and turn on     Make sure they operate and that water enters vessel

     (switch is under the table)                from both feed pipes

 d. Stop pumps, adjust to 50%, and restart

2. Check operation of CSTR

 a. Adjust O1 to 2/3 of CSTR height and

     close V6

 b. Operate pumps as in Steps 1d and 1e

 c. Switch on stirrer to lowest setting         Ensure constant level in reactor. If level fluctuates,

                                                there may be insufficient venting to the gas above

                                                the liquid in the reactor. Open the gas inlet line to

                                                the vessel. No bubbles should be present.

3. Remove all tap water from the system and

   repeat Step 1 using distilled or deionized

   water




                                                7
Calibrations
4. Calibrate the rotameters

 a. Use bucket-and-stopwatch method to             Note calibrations will be different for each liquid

     verify flow out from V6

5. Calibrate the thermostat

 a. Set arbitrary temperature, verify that         Low flowrates should show best control

     liquid achieve and maintain this set-point.

 b. Use the heater to change the temperature

     and verify with the thermometer

6. Calibrate vessel volume

 a. Close all valves

 b. Add known volumes of liquid to vessel

 c. Stop when liquid flows into overflow

     pipe, record this volume

Feed Preparation
7. Preparation of feed solution: 0.1 N ethyl

   acetate (EtAc)

 a. Dissolve 8.81 g EtAc per liter of distilled

     water (prepare about 40 L of solution)

8. Preparation of feed solution: 0.1 N sodium

   hydroxide (NaOH)

 a. 4.00 g NaOH per liter of distilled water

     (prepare about 40 L)




                                                   8
   1) Fill burette with 0.1 N HCl (record

       the volume)

   2) Place the feed sample of known

       volume below the burette on a

       stirring mechanism

   3) Add a few drops phenolphthalein to    The feed solution should be clear

       the feed sample

   4) Add HCl drop-wise to the sample;      When the color starts to change to pink more

       when it remains pink, STOP, and      slowly, add smaller volumes of HCl until the mixture

       record the volume of added HCl       remains pink

b. NaOH is hydroscopic, so titrate the

   prepared solution with a standard acid

   solution




                                            9
ROUTINE DUTIES
STEPS                                           NOTES AND ALERTS
1. General operation of unit                    Check periodically for leaks, operational stability,

                                                etc.

2.   Find total inlet volumetric flowrate by

     adding the two feed volumetric flowrates

3. Run the experiment

 a. Start the pumps for EtAc and NaOH           The flowrates should be less than 5% to allow

                                                enough residence time for a large conversion



                                                Make sure drain, V5, is closed if pumps are on!

 b. Turn on the stirrer in the reactor

 c. Turn on the heating mechanism               Note the temperature on the digital meter

4. Steady state is reached when reaction

     temperature and outlet concentrations

     remain constant with time

Sample Collection
5. Collect samples from the CSTR

 a. Open O1

 b. Collect the sample                          It is important to obtain a broad range of

                                                conversion of EtAc to easily distinguish the actual

                                                data trend from the noise inherent to the system.




                                                10
ROUTINE DUTIES
STEPS                                        NOTES AND ALERTS
Sample Analysis
6. Determine outlet concentrations of EtAc

   and NaOH by titration

 a. Fill graduated cylinder with

    predetermined amount of HCl

 b. Add sample from CSTR

 c. Add pH indicator

 d. Titrate with NaOH standard solution      Usually phenolphthalein

    until pH indicated neutral

 e. Calculate moles NaOH in sample           Moles of HCl in quench minus moles NaOH used

                                             in the titration equals moles of NaOH in sample



 f. Calculate NaOH concentration in sample   Moles NaOH divided by sample volume



 g. Calculate inlet concentrations of EtAc   Exiting concentration times species volumetric

    and NaOH                                 flowrate divided by total volumetric flowrate




 h. Calculate exit concentration of EtAc     Initial EtAc concentration plus change in NaOH

                                             concentration




                                             11
Quenching the Reaction
7. Quench the reaction in the samples

 a. Add enough of 0.1 N HCl to the reaction

    mixture samples to quench (stop) the

    reaction. ―Enough‖ NaOH is calculated

    by assuming 100% conversion EtAc and

    adding HCl to ensure excess.

 b. Back titrate the excess HCl

    1) Fill burette with 0.1 N NaOH (record   Use the NaOH feed solution so you do not have to

        the volume)                           remix a solution

    2) Place the reaction mixture sample of

        known volume below the burette on a

        stirring mechanism

    3) Add a few drops phenolphthalein to     The mixture should be pink

        the reaction sample

    4) Add NaOH drop-wise to the sample;      When the color starts to change to clear more

        when it remains clear, STOP, and      slowly, add smaller volumes of NaOH until the

        record the volume of added NaOH       mixture remains clear

 c. Perform the calculation:

  1) [HCl, quench] – [HCl, excess] = [NaOH

      in sample]




                                              12
SHUT-DOWN PROCEDURES
STEPS                                             NOTES AND ALERTS
1. Neutralize leftover feed stock

 a. Neutralize NaOH with muratic acid             Use a pH meter or pH strips to measure the pH

 b. Neutralize EtAc with sodium bicarbonate

     (baking soda)

 c. After the waste is pH = 6-9, dispose of it

     down the drain

2. Turn off the reactor stirrer, feed stirrers,

    pumps, and heater.




EMERGENCY SHUT-DOWN PROCEDURES
STEPS                                             NOTES AND ALERTS
1. In the case of fire:

 a. Since the reactants are non-flammable

     and the sump tank is large enough to

     hold the entire reactant volume, leave the

     unit running and LEAVE

     IMMEDIATELY

2. In the case of tornado:

 a. Leave the unit running and file calmly

     into a suitable tornado shelter




                                                  13
EMERGENCY OPERATIONS

STEPS                                             NOTES AND ALERTS
1. If the heater is left unattended, the reaction Do not leave the experiment unattended!

   mixture will boil and reach temperatures in

   excess of 200°F—which can be dangerous.

2. When muratic acid is mixed with the            Avoid breathing the fumes released!

   sodium hydroxide for neutralization,

   NOXIOUS FUMES ARE RELEASED.

3. If any of the chemicals for this lab come in   Avoid letting these chemicals contact your eyes!

   contact with your eyes, FLUSH YOUR

   EYES IMMEDIATELY in the eye shower

   and let the lab professor know

   immediately.

4. If any of the chemicals for this lab come in

   contact with your skin, wash the affected

   area thoroughly.




                                                  14
TROUBLESHOOTING GUIDE
EQUIPMENT   SAFETY LIMITS       CONSEQUENCE           STEPS TO AVOID DEVIATION
Pumps       5 L of each feed    Cavitation            Never let the feed tanks go dry while
                                                      the pumps are on.
Stirrer     Reactor half full   Bubbles formed in     Watch the level of liquid in the
                                mixture, possible     reactor
                                splash out
Reactor     Ambient pressure                          Keep the vent at the top of the
                                                      reactor clear of debris
Heater      200°F               Boiling, possible     Do not leave the equipment
                                danger to operators   unattended. Watch the temperature
                                                      display.




                                       15

				
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