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

Black Fuel Filters - Asphaltenes - Re-polymerization

Black Fuel Filters – Asphaltene Production and

Re-polymerization in ULSD Fuels

Have you seen filters that look like this.

There is a difficult new problem with ULSD fuels. Today most ULSD is derived using the process of catalytic cracking. This form of refining uses very high temperatures, high pressures, and chemicals known as catalysts to refine crude oils into various fractions including Ultra Low Sulfur Diesel. The fuels derived using these processes suffer from a wide range of problems including a lack of oxidative and thermal stability.

This lack of stability manifests itself in many ways including an increased ability to hold dissolved water, an increased negative reaction with oxygen, and a far greater inability to handle high temperatures over time. Different refining processes and catalysts can make these problems better or worse. It appears that certain refineries produce fuels which are far less stable than that of others.

Diesel engines recirculate fuel to lubricate and cool the fuel system and engine components, In the past fairly large volumes of fuel were recirculated and this tended to keep temperatures lower, generally in the 140°F to 160°F. Today some of the newer engines can heat that fuel to temperatures that can exceed 200°F or even 220°F.

When some catalytically derived fuel is exposed to temperatures above 100°F for extended periods of time such as when fuel is recirculated in a diesel engine, the catalytic process starts up again re-polymerizing parts of the fuel. This results in rapid deterioration and darkening of the fuel. In this process small droplets of asphaltenes (heavy oils) are formed.

When the fuel is again pumped from the tank, the fuel filters will pick up the tiny asphaltene droplets, agglomerating them until the filter or filters are plugged. This can happen in 3000 to 5000 miles with some instances of plugging in less than 1000 miles.

While there are additives that can add thermal and oxidative stability to fuels, they are not commonly used by refiners or fuel distributors. These additives are not found in most aftermarket additives.