Although the content of MAG, DAG and TAG was virtually unchanged by the filtration treatment at 25 degrees, the FBT value was greatly affected. The untreated biodiesel failed the FBT test by reaching the maximum pressure increase possible in the FBT test after only 20 milliliters had passed through the FBT filter, but the treated biodiesel had an excellent FBT value. Thus, the improvement of FBT wasn’t dependent on the removal of the MAG, DAG and TAG.

Confirming Filter-Blocking Role
Biodiesel containing 22 ppm SG was obtained by treating commercial-grade biodiesel. Purified SGs (10, 30 and 50 ppm) were added to the treated biodiesel to produce biodiesel of various SG contents, which were subjected to the FBT test at 25 degrees Celsius (see Table 2). The purified SGs were added in such a manner to ensure homogeneity.



As the level of SG was increased, the FBT values increased, with the 72 ppm SG sample reaching the highest value that the test permits. This confirms that an SG presence at high enough levels could potentially cause filter problems on a dispensing pump or vehicle.

Conclusions
The presence of SG in biodiesel may cause filter blockage at temperatures above the cloud point. Cold temperatures are likely to exacerbate the negative impact of the presence of SG in both pure biodiesel and biodiesel blends. Biodiesel having reduced levels of SG can be obtained by filtering biodiesel through diatomaceous earth. The contribution of SG to filter blocking should be considered in addressing filter problems with biodiesel and biodiesel blends, and it may be necessary to put an appropriate filter blocking test or particulate measurement into practice. The FBT test is an especially sensitive test. Current efforts to include a particulate matter specification within ASTM should take the potential presence of SG into consideration.

The foregoing experimental results were supplied by ADM as part of its patent-pending biodiesel purification technology. In order to promote the welfare of the biodiesel industry in North America, ADM intends to provide licenses for this technology on a royalty-free basis. Additional background information was provided by arc-IV Consulting Inc.

1.Dunn, R. "Cold Weather Properties and Performance of Biodiesel" in The Biodiesel Handbook, Knothe, Van Gerpen and Krahl, eds; 2005, AOCS Press, Champaign, Ill.

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