Experimental Manual

Experimental Manual:

Place the oil in the 1L reaction vessel and begin heating to about 5-10 °C above the desired reaction temperature. The reaction vessel has three necks. Insert the stopper with the thermometer into one of the necks, the plain stopper into another, and the condenser into the last neck. Use the alcohol to dissolve the desired catalyst in a separate beaker (if the catalyst is homogeneous). Heat the oil to approximately 5 °C above the desired temperature, as the temperature will drop when the alcohol is added. The exact starting temperature depends on the desired reaction temperature. When the desired temperature has been reached, pour catalyst mixture into the reaction vessel. Note: If using a heterogeneous catalyst, pour the catalyst into the reaction vessel first and then add the alcohol. Take approximately 40-50μL samples at various time points (early times are important for kinetics!). Place each sample in a premeasured toluene vial that has been chilled. Two vials should be measured: one with 20mL and one with 5mL. The 20mL sample is used to monitor the triglyceride, diglyceride, and FAME. The 5mL sample is used to more precisely monitor the monoglyceride concentration. When the reaction is finished, pour the liquid to the separation container. Let the biodiesel settle overnight and separate the glycerin from the biodiesel by purging the lower glycerin level.

The samples are analyzed using high performance liquid chromatography (HPLC) using an evaporative light scattering detector (ELSD) to determine the concentrations of the reaction components. More detailed information can be found in the document specifically covering this machine. The machine is located in Goessmann 106. Students should speak with the Biodiesel TA for information on who to contact to use this machine.

(Note: the following method is no longer used for analysis) In order to run the samples through the GC, they must be derivatized first. After the sample vials have separated overnight, a 1 mL volume of the oil layer must be taken from each time sample. Place these new samples in a glovebox in a pure nitrogen environment. Add 10 μLof MSTFA and cap the sample vials. After 20 minutes, add 8 mL of hexane to quench the reaction.

(Optional) Viscosity is measured with a viscometer and can be used as a rough estimate for conversion. After the sample vials have separated overnight, pipette the oil layer into the viscometer. Use a suction bulb to raise the liquid to the top marking on the viscometer. Remove the bulb and measure the time required for the liquid to flow to the second marker. The sample can be returned to the vial. Between each measurement the viscometer should be cleaned with acetone.

Titration with acid (0.5 M HCL) provides pH measurements. For glycerol, dilute a 3 ml sample with 10 ml of isopropanol along with 1 drop of phenolphthalein. The oil phase can be titrated as-is.

The water content analysis is obtained using the Utah Biodiesel Supply Water Test Kit. See here:

Heterogeneous Catalyst Filtration and Recovery

When using a heterogeneous catalyst, the solid catalyst does not dissolve in the reaction mixture, the samples of the reaction mixture must be filtered before dissolution in the toluene. This is to prevent the solid catalyst particles from reaching the liquid chromatography machine. The samples can be filtered using syringe filters.

It is possible for the catalyst to be removed and reused from the reaction mixture. To do this, a vacuum filtration technique is used. Set-up a vacuum filtration apparatus with a Büchner flask attached to a Büchner funnel. The flask has a glass spout which should be attached to tubing and then a vacuum pump. The filter should be placed in the Büchner funnel. To make filtering easier, the biodiesel and glycerin mixture can be put in a ring-stand to stabilize the mixture. The catalyst will often be located between the FAME and glycerol. For completeness, it is possible to filter the entire reaction mixture, but this will drastically increase the time required for filtration. Ideally, the reaction mixture should be left to separate first, with the FAME layer on top and the glycerol layer. Careful examination of the interface may indicate the presence of the catalyst. Rinse the filter paper with methanol to release any attached particles. Let the filter paper dry in the hood overnight. Any loose catalyst should be scraped off the filter paper to be recovered. If this is difficult, it may be necessary to wash the filter paper in a small amount of methanol or toluene to remove the catalyst from the filter paper. It is desirable to use methanol to wash the catalyst from the filter paper because it is one of the reactants used in the experiment.