Vegetable Oil Polymerization: What it is, why should we care, and what PrairieFire is doing about it.

What is vegetable oil fuel polymerization?

When you open the fuel filler cap on your vegetable oil powered vehicle, do you smell something like paint fumes?  Is there a coating of thick, gummy, red-brown substance on the metal filler-cap or in the neck of the fuel tank?  This is polymerized vegetable oil.

This “stuff” is (Quoting Joe Beatty page 4) “…long chain, cross-linked polymer…with a molecular weight in the millions.” 

What’s happening is that the vegetable oil is reacting to oxygen and the metal in the fuel tank, creating a plastic-like film.  This substance largely adheres to the tank wall until it becomes too thick and heavy.  It then falls into the fuel, causing problems in the fuel delivery system.  This chemical reaction is accelerated by certain metals (like copper), heat, and light.  The more of these things to which the fuel is exposed, the faster the polymerization takes place.  It also seems that in the short-term, recycled vegetable oils (WVO) are more likely to polymerize than are virgin oils.

Why do we care about this?

At a minimum, polymerization decreases fuel filter life.  The four-orders-of-magnitude-increase in molecular weight means that the fuel has a more difficult time passing through the filter media.  At a maximum, combined with filter-failure, the polymerized fuel can cause damage to sensitive fuel injection equipment and even engine damage in extreme cases.

The most in-depth discussion of polymerization I have seen was written by Joe Beatty, titled Vegetable Oil as Fuel.  It is available on many vegetable oil-related websites including:

http://www.plantdrive.com/Vegetable_Oil_as_Fuel.pdf

 What is the solution?

Ideally, vegetable oil should be used out of plastic tanks rather than metal tanks.  Copper heat-exchangers should be avoided, and oil should not be allowed to sit around in open containers in the sunlight.  Use fuel systems that heat the fuel only to the extent necessary.  Don’t store vegetable oil for long periods of time.

What is PrairieFire doing about this problem?

PrairieFire is engaging this problem on several fronts.

We are informing those with single-tank conversions on vehicles with steel tanks that polymerization is a problem.  These vehicles include primarily Volkswagens in the 1980’s and Mercedes Benz through the 1990’s.  Interestingly, some of these vehicles seem to develop problems very quickly and dramatically, and others not at all.

We are pursuing coating technologies for the internal sealing of steel tanks.  To this end we applied a hardening plastic-like coating to the inside of a Mercedes fuel tank.  This vehicle will serve as a source of data.  Our fuel-dispensing-equipment expert has recently mentioned a “glassy like coating.”  We are hoping this can be a solution to our storage and dispensing concerns.

We are searching for aftermarket tank solutions.  Perhaps there is a company that already manufactures plastic replacement tanks for these applications.  If there is not a manufacturer of these items, perhaps we can convince someone to begin manufacture.  In the case of VW the tanks are under the vehicle, so the safety of a plastic tank is not a concern.  In the Mercedes sedans, the fuel tank is inside the vehicle behind the rear seat, isolated from the passenger compartment by a steel plate.  This should also not cause a safety concern.

Finally, it is possible that there is a chemical solution to this problem.  Again, this is thanks to Joe Beatty.  He has extensively researched the use of metal inhibitors and antioxidants.  These chemicals used in combination seem very effective in reducing polymerization in vegetable oil fuels.  The last time I spoke to Joe, he was hoping to be able to sell this chemistry as a fuel-additive.  I have yet to see this product on the market.

 

Comments

[Trace]

POLYMERIZATION IN MY TANK - FYI

Ford 1999 F350 7.3 Diesel

I have had a GreaseCar conversion for one year with the regular 40 gallon aluminum tank they provide. The exchanger is a 5/8" copper tube mounted on the left inside of the tank which is a double loop that is about 4 ft long in total length.

I have had polymerization as described above and it has played havoc on my filter and all along the many months of problems I had no clue what in the world was causing the problems.
By the way I use a stainless steel mesh filter unit by "PurePower" located in California. Paper filters just don't cut it. With stainless steel you get a true "pass thru" filtering of the oil unlike all the standard paper filters so commonly used today which just bypass the oil. Washable with any detergent soap or solvent and lasts a lifetime! Fantastic unit. Anyway, I was talking to a chemical engineer from that company and he mentioned that ways to inhibit polymerization is by adding up to 25 percent diesel and even about 1 gallon to a 40 gallon tank. I think more than inhibiting the process it merely emulsified the molecules which then simply got burnt along with the veggie. I was told by this man that in all the years in the race car & stainless steel filter business and as well having a degree in chemical engineering, that he knew that it gets burned and does not effect the diesel in any way. Well it must be true as this is what I found out so far. Time will only tell for sure though.

This adding of addition fuels is against the whole principal of WVO but so far I've only done this once.

Just thought you might like to hear about what I have experienced and maybe help others.

Trace
I love my veggie!

[Jim Anderson]

I have done some rough experiments with various metals - a film of WVO on each of them, and exposed to air with no direct sunlight - not completely dark, but dim. Of course, copper is the worst. However, steel strap hit with a grinder to expose uncoated steel was almost as bad as copper. Surprisingly, stainless steel seemed to be almost as bad as hot rolled steel. Even more surprisingly, brass is not nearly as bad as copper - even though it is a "copper bearing alloy." Is it the presence of zinc? Galvanized steel seemed to retard the process to the level of plastic (where exposure to air is the only bad condition).
If anyone knows the best solvent for the gummy result of polymerization (for cleaning parts), I would be interested in hearing of it.
Jim Anderson 06776
[email protected]

[Ramasubramanian]

i need more..........

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Copper heat-exchangers should be avoided, and oil should not be allowed to sit around in open containers in the sunlight. Use fuel systems that heat the fuel only to the extent necessary

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[[email protected]]

Has anyone tried the product POR15 Fuel Tank Sealer? (along with the appropriate preparation products i.e Marine Clean and Prep&Ready stuff...)
I was reading on another forum that i creates a protective plastic lining inside your tank which is designed to prevent corrosion but also acts to separate WVO from the steel... limiting polymerization... least thats the theory anyway. Anyone tried this?

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The mode of transmission of this signal is either a telephone line or an internet.

[Milan Bosnich]

I have a International Sline Tipper Truck Cummins L10 250hp.
Have 2 tanks steel 1 straight diesel the other 70%WVO / 30% diesel blend. I have polemerization in the blend tank his rusty orange paste. Will be cleaning tank out with hi pressure hot water spitfire. Will run diesel straight 1 tank with an additive called Fuelmaster made in Australia.
This product does not displace water but turns it in to H66 that apparrently gets burnt of in the fuel. This will also stop and clean up polemerization in the fuel frome on vehicle to storage tanks. The company is Austech Industrial Solution. As soon as i clean this tank up inside i will be trying there product before i go to the expense of alluminium tanks. This product looks very impressive. I spoke to a rep told him what i had he is very confident that this product will keep the fuel and tank clean.

[plumbing]

Trans fats are man-made or processed fats, which are made from a liquid oil. When hydrogen is added to liquid vegetable oil and pressure is added, the result is a stiffer fat, like the fat found in a can of Crisco.