Biodiesel Cold Soak Filterability - ASTM D6751 Annex A1

New ASTM Biodiesel Test Specification for Cold Weather Operability

The American Society for Testing of Materials has recently added a new test requirement to the D6751 Biodiesel Specification.

This new requirement is referred to as ASTM 6217 or as Annex A1 of ASTM D6751– Cold Soak Filterability.

Cold Soak Filtration Analysis is defined as: The time in seconds that it takes for cold soaked biodiesel to pass through two 0.8 micron filters and the amount of particulate matter expressed in milligrams per liter (mg/l) collected on the filter.

What does this mean? When biodiesel is stored in temperatures below 40°F for extended periods of time, certain components will precipitate (fall) out of solution and fall to the bottom of the storage tank. This precipitate will build in a thickening layer at or near the tank bottom. In general the colder the temperature and the longer the biodiesel stays at a given temperature, the more material will fall out.

This material can very quickly plug filters and shut down engines, usually at the worst time.

What is this material? It can have to do with the feedstock from which the biodiesel is created. Certain feedstocks, particularly Used Cooking Oils (UCO), Waste Vegetable Oil (WVO), and Animal Fats (Tallow) will produce high levels of precipitate. The material can also be due to incomplete removal of glycerin during the transestrification process.

This new test is a positive step in making biodiesel a more consistent user friendly product.

Diesel Doctor

Copyright 2009© - William Richards

Biodiesel and Cold Weather meet in Minnesota

Biodiesel and Cold Weather meet in Minnesota

The Minnesota Department of Agriculture recently released (February 15, 2009) a report to the legislature regarding the states mandated biodiesel program and the cold weather issues it has caused.

Starting in September 2005 Minnesota required that virtually all diesel fuel sold in the state contain at least 2% biodiesel. This level is supposed to be raised to 5% in 2009, 10% in 2012, and finally 20% in 2015.

This report by the Governors “Biodiesel Task Force” created in 2003 shows that there a number of significant problems with using biodiesel blends, particularly in areas subject to long periods of cold weather.

Some of the issues noted in the report:

· Discussion indicated at least fifteen cases of unusual filter plugging in commercial trucks this winter for which the cause had not been determined. Discussion of possible causes included engine manufacturers’ reduction of truck filter sizes (from 10 to15 microns down to 2 to 5 microns), paraffin from diesel, glycerin from biodiesel, water contamination, biotic contamination as a result of ultra-low sulfur diesel levels plus water contamination, and vehicle designs in which the fuel filter is located away from the engine.

· Discussion that existing cold flow test procedures are not sufficiently predictive of the
cold temperature performance of diesel fuel with or without biodiesel. ASTM International and other organizations at a national level must develop new test methods that are more predictive of the cold weather performance of diesel fuel and biodiesel blends.

· Variations in seasonal availability of fuel were also discussed, specifically routine shortages of diesel fuel at terminals in the fall leading to the practice of bulk plants and fleets buying and storing fuel in the late summer for use in the fall and early winter months when shortages of diesel are anticipated. Such stockpiling of B10 or higher could result in problems in above ground tanks.

· The suggestion was made that the Task Force discussions should freely address the availability and quality of all winter fuel in the state instead of being confined only to biodiesel. Given recent changes in the diesel industry, including biodiesel, low-sulfur diesel fuel and smaller fuel filter pore diameters, a wide range of issues regarding equipment and diesel fuel with and without biodiesel must be addressed.

Laboratory testing has indicated that blending with number one (#1) diesel at 50/50 rate produces results similar to treating with additives but the #1 fuel is at a far higher cost.

There is also a concern over whether the current testing (e.g. Cold Point (CP), Cold Filter Plug Point (CFPP), Pour Point (PP), Low Temperature Flow Test (LTFT)) done to assess cold weather operability characteristics of diesel fuel are adequate for testing biodiesel blends.

Unfortunately this discussion has been complicated by many factors including the change from Low Sulfur (LSD) to Ultra-Low Sulfur diesel (ULSD), that diesel fuel changes seasonally, the fact that biodiesel derived from different base oils have far different characteristics, that transportation and storage affect quality, and that materials will tend to precipitate out of biodiesel when it cold for extended periods of time.

To read the complete Minnesota Report to the Legislature please click here: Report to the Legislature February 2009

Please post your comments, questions, ideas, and thoughts.

Diesel Doctor

Copyright 2009© - William Richards