Antioxidants For Biodiesel

What Is Biodiesel?

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Petroleum diesel is refined from crude oil and is largely made up of saturated hydrocarbons, whereas biodiesel is a solution of fatty acid methyl esters. Biodiesel began being produced in 1991 as an alternative and more renewable source of fuel. While diesel and biodiesel perform similarly, there are differences due to their chemical composition. Diesel is more chemically inert than biodiesel, has a lower CFPP (Cold Filter Plugging Point) making it less likely to “gel” in cold weather, and demonstrates improved oxidative stability. Comparatively, biodiesel is less toxic than diesel, causes fewer pollution emissions, and is inherently more lubricious (reducing the need for lubricity fuel additives and preventing engine wear). Diesel fuel also tends to have better consistency than biodiesel, as biodiesel is manufactured from various feedstocks. Biodiesel blends are common nowadays, and are named by their percentage of biodiesel (i.e. ‘B20’ has 20% biodiesel and 80% diesel fuel). Blending diesel fuel with biodiesel improves biodiesel’s cold weather performance.

What is the Difference Between Renewable Diesel & Biodiesel?

 

While renewable diesel and biodiesel are both biofuels made from renewable feedstocks, these fuels are NOT chemically the same. Renewable diesel, also known as green diesel, is made via hydrotreatment or another biological, thermal or chemical process to make it chemically identical to petroleum diesel. Renewable diesel meets ASTM D975 specification for petroleum diesel, and is becoming an increasingly popular fuel source in the United States. Biodiesel, on the other hand, meets ASTM D6751 and is made through a transesterification reaction to form fatty acid methyl esters (FAME):

What Is Oxidation & How Is It Measured?

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Oxidation is a type of chemical reaction where there is a loss of electrons that results in unstable molecules that are susceptible to further reaction. Composed primarily of fatty acid methyl esters, biodiesel is more susceptible to oxidation than petroleum diesel fuel. This is bad news for engines, as oxidation in fuel often results in the formation of harmful deposits that clog fuel filters and reduce engine performance.

Fatty acids are oxidized by a free radical oxidation process that has three phases:
 

The biodiesel industry uses the OSI (Oil Stability Index) to measure the oxidation stability of diesel. In the Rancimat method, a stream of air is passed through a biodiesel sample at a high temperature to measure the appearance of oxidation products. The higher the OSI reading, the higher the oxidation stability. 

How Do You Prevent Oxidation?

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Oxidation cannot be entirely prevented, but it CAN be slowed down significantly with antioxidants. Antioxidants disrupt the oxidation process during the propagation phase by reacting with the fat radical to form a stable radical. Oxygen does not react as quickly with the stable radical as it will with the fat radical, so the oxidation process is stalled and the fuel retains its stability.

Not All Antioxidants Are Equal

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There are a variety of antioxidants used to treat biodiesel fuel, but not all antioxidants perform equally. Eastman's BioExtend^™ high performance antioxidants show superior performance over alternative chemistries such as BHT, BKF, TBHQ, BHA, DTBP, and n-propyl gallate. BioExtend^™ is a dual functioning technology that combines a highly effective antioxidant, MTBHQ, with a metal chelating agent. BioExtend^™ shows outstanding antioxidative power in various vegetable oils, in some blends providing 400% longer OSI than other antioxidants.
 

BioExtend^™ antioxidants come in solvent form so they are easy to handle and remove the hassle of needing to dissolve a powder. BioExtend^™ is highly effective at low concentrations, making this antioxidant an ideal choice for meeting European standards and the U.S. suggested OSI. BioExtend^™ antioxidants also remain liquid at low temperatures (<-25°F) making them easy to store and transport during colder weather.
 

How Do Metals Affect Biodiesel?

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The presence of metal contaminants in biodiesel accelerates free radical oxidation. There are various sources of metal contaminants including construction materials, hard water, or contamination during biodiesel production since the production process often uses a metal catalyst. Metal ions act as a catalyst during the initiation phase of the oxidation process, and can have a dramatic negative effect on OSI and biodiesel shelf life.

The metal chelator in BioExtend^™ antioxidants provides additional protection to biodiesel fuels by sequestering metal ions and stalling the initiation reaction.
 

BioExtend^™ Antioxidants

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