Tutorial 1 - Initial Purification and Titration Process

Tutorial 1 - Initial Purification and Titration Process

Motivation  

Purify crude oil feedstock (if needed) of any unwanted material such as cooking residue to be prepared for transesterification.  Titrate sample to determine amount of base catalyst needed for neutralization in transesterification. 

Materials

• crude oil feedstock
• isopropyl alcohol
• toluene
• phenolphthalein indicator
• [0.1M] NaOH
• graduated cylinders (10-150 mL)
• Buchner Flask & Buchner Funnel 
• standard filter paper
• vacuum suction pump w/ tubing
• beakers (50-250 mL)
• burette (approx. 50 mL) w/ stand and clamps
• magnetic stir bar
• stirrer plate
• scientific weighing scale

Procedure

Part A - Initial Purification

1. Connect vacuum pump tubing with buchner flask (Figure 1).  Plug the open part at the top of the flask with the buchner funnel.  Make sure no air can enter through the sides of the rubber plug or plastic tubing.
2. Place one sheet of filter paper in funnel.  Pour a small amount of oil on top to wet the paper.
3. Turn on the pump.  Make sure the paper is covering all of the small holes in the funnel and that suction has been achieved.
4. Slowly, in fixed amounts pour the crude oil feedstock into the funnel.  Sometimes bubbles will form in the flask from the pressure of the vacuum suction.  This will not effect purification.  Repeat until all the crude oil has been processed.  (NOTE: Do NOT let the filtered oil collect in the flask past a half inch below the glass fixture that connects to the vacuum pump tubing.  If this happens stop filtration and pour out the filtered oil into a sterile storage container. When the plug is pulled out of the mouth of the flask, pressure from the suction pushes the oil up and can pass into the plastic tubing.)
5. If filtration is taking a long time or becomes relativity staggering, replace filter paper.  After all of the current oil preset in the funnel has passed through, turn off the pump.  Take a moist paper towel and collect sediment and used filter paper.  Dispose of properly. Repeat steps 2 through 4.

Figure 1 - Filtration Setup: Buchner flask and funnel, vacuum pump and tubing

Part B - Titration 

1. Prepare a burette, containing a minimum of 30 mL of [0.1M] NaOH, on its stand, underneath a magnetic stir plate.
2. Prepare a 1:1 volume co-solvent of isopropyl alcohol and toluene.  This sample should be about 5 mL.  This co-solvent is needed to help react the polar NaOH with the non-polar oil.  This will not effect the results of the titration.  Pour the sample into a reaction vessel.  
3. Weigh 1 to 10 grams of filtered oil feedstock in a beaker using a scale.  Record this measurement   Pour oil into the reaction vessel that contains the co-solvent mixture.  
4. Add a few drops of phenolphthalein to the mixture.  Phenolphthalein is clear in an acidic solution and will change to a pinkish color when in a basic solution.  The indication range is between pH values of 8.3 to 11.  Place the magnetic stir bar in the reaction vessel.
5. Place the reaction vessel onto the stirrer plate.  Turn on the stirrer plate. Record the starting amount of NaOH in the burette. 
6. While the magnetic stir bar is mixing the solution, SLOWLY add fixed amounts of NaOH from the burette.  When the end point of the reaction nears, pink color will appear in the solution where the sodium hydroxide has been added, and then dissolve into solution.  When you first see the pink color the end point has not be reached but is very close; therefore continually add drops of NaOH to the mixture from the burette.  When a pink-ish color persists in solution for more than 30 seconds to a minute, the endpoint of the titration has been reached.  
7. Record the amount of NaOH added to the solution by subtracting the initial volume measurement of NaOH present before the titration with the amount left in the burette after the titration.  
8. Dispose of the solution properly and clean all used glassware.   

NOTE:  Wash all weighing material when switching between material.  This will reduce experimental error.

Calculations

Determine the amount of moles of NaOH added using stoichiometry:

[A]           (Molarity of NaOH used)*(volume of NaOH used in liters)  =  (moles of NaOH used)

This is a direct proportion, assuming the base catalyst in the reaction will be potassium hydroxide (KOH); therefore we can say that:

[B]         (moles of NaOH used)  =   (moles of KOH needed)

Using stoichimetry, determine the amount of KOH needed in grams.

[C]         (moles of KOH needed)*(molecular weight of KOH)/(1 mol KOH)  =  (grams of KOH needed)

Now a total acid number can be determined.  This is a ratio of how many milligrams of soild KOH are needed per gram of oil feedstock.

[D]         Total acid #  =  (mg of KOH needed)/(g of oil used)

Now a simple proportion can help you determine the amount of base catalyst needed to neutralize the free fatty acid content of the oil feedstock.