Sample Filtration

The drying agent can be removed from the sample by filtration. Filtration techniques separate particles by size. In this case, the biodiesel molecules are small enough in liquid form to pass through the filter paper. The drying agent, however, aggregates together such that the clumps are too large to pass through the filter. This experiment employs vacuum filtration in which a pressure gradient causes the liquid to be drawn through the filter paper.

A vacuum filtration apparatus typically uses a filter flask, which looks like an Erlenmeyer flask with a side-arm, to connect to a vacuum. The filter flask is used to collect the filtrate (the liquid that passes through the filter).

Depending on the experiment, sometimes you will want the solids trapped by the filter paper, but in this experiment you are interested in the filtrate (your biodiesel).

A second filter flask is used as a liquid trap, which prevents any filtrate from inadvertently entering the main vacuum system.

Vacuum filtration also utilizes a special funnel, a Büchner funnel, which allows for better airflow, and a funnel adapter, which helps form a good seal between the funnel and the filter flask.

Use the vacuum to remove the trace acetone from the flask. Open the vacuum line to dry the flask, inverting it so the neck of the flask is resting on the bench top, if needed, to increase the suction.

The flask must be completely dry or your biodiesel may react with water and turn to soap.

Make sure to clamp the side-arm flask to a ring stand for stability before use.

Biodiesel Filtration

To filter, a piece (or two) of filter paper are placed in the Büchner funnel, and the mixture of interest is poured over the filter paper with the vacuum activated. The pressure gradient forces the liquid through the filter and the drying agent is trapped by the filter paper.

Once you have dried and filtered your sample (possibly multiple times), you will have successfully isolated the biodiesel from your synthesis. Store this for another week until you analyze it in Biofuels Part C.