Brine Wash

The next step of the isolation process is to "wash" the biodiesel with a solution of sodium chloride. This technique is known as a brine wash and is used to draw water and other polar contaminants out of the biodiesel (can you explain why this might happen?). While brine washes are typically performed using a saturated (highly concentrated) sodium chloride solution, a concentration of 1 M is used for this experiment because it was found to work best for this procedure.

Approximately 5 milliliters of 1 molar sodium chloride solution is measured out in a graduated cylinder and added to the biodiesel in the centrifuge tube. After combining the two liquids are combined, they are gently shaken to induce mixing.

Below is a time-lapse sequence of the brine wash mixture after it has been shaken.

Watch the video and record your observations in your lab notebook. What do you notice about the mixture? Does it change over time or remain the same?

The mixture originally starts as an opaque pale yellow liquid. As time passes, a clear layer slowly develops at the bottom of the centrifuge tube.

After letting the brine wash mixture rest for 5 - 10 min, remove the sodium chloride solution and start a second brine wash.

The sodium chloride solution, the bottom layer, is removed with a pipette. Another 5 milliliter portion of 1 molar sodium chloride is measured out and added to the remaining biodiesel in the centrifuge tube and the two liquids are mixed.

The mixture should be left to settle for 5-10 minutes before removing the sodium chloride solution layer from the second brine wash (not shown).

Continue to add drying agent

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