Urea Clathration: Ultra Low Gel Point Biodiesel

By Rick Da Tech


Ultra Low Gel Point Biodiesel via Urea ClathrationGel Point, Cloud Point, Pour Point. These are the bane of biodiesel. It is the the cause of winter nightmares for homebrewers. It's the reason we leave jars of fuel on the stoop all winter, and the reason why our trucks stop dead in the coldest winter. Urea Clathration is a commercial process that gives extremely low gel point biodiesel. Unfortunately, it may be a little too much for the homebrewer.

In winter we normally blend with winter diesel and use additives like DFS artic express antigel for biodiesel which work primarily on the diesel part of a blend. Other additives have been tried and used with varying degrees of success. If you do make biodiesel in the winter, you can leave your oil outside where it can get really cold, then first thing in the morning, decant off the liquid oil for making winter biodiesel. It's one of the few ways that hobbyist biodieselers have to make low gel point biodiesel. 

We perform the homebrew cloudpoint test by placing biodiesel in a jar with a thermometer and putting it in the wife's refrigerator. We record the temperature at which the biodiesel starts to form crystals. It is important that our biodiesel be dry for this test or we can get a false reading when the water in the biodiesel becomes undissolved and forces the biodiesel to go turbid.

The most important test we can perform in the winter is to keep a sample of the exact fuel we have in our fuel tanks in a jar or jug outside near the vehicle. Check on it before driving off. If the fuel is not fully liquid, then it's time to take another vehicle. If it's not liquid, we may be able to get it started, but it won't be long before we're calling a tow truck to drag it back to a warm garage.

We may soon have another option, in 2008 Purdue University developed a revolutionary way to reduce cloud point in biodiesel using Urea Clathration. It is a process dating back to the 1940's that separates the saturated methyl esters from the unsaturated methyl esters. Clathration is the process of forming a crystline latice structure around a molecule. We can dissolve the urea into biodiesel containing methanol using heat and stirring, then on cooling the urea forms a lattice structure that traps saturated fatty acids. Saturated fatty acids are straight and fit perfectly inside the lattice. however unsaturated fatty acids are bent at the point of their double bond. They will not fit inside the lattice and are rejected. Once the biodiesel cools and the urea goes solid, the urea and saturated fatty acids can be mechanically filtered out of the low cloud point (and still liquid) biodiesel. The urea can be recovered later by water washing the thawed material from the filter, then evaporating the excess water from the urea. The residual methanol can be recovered in a vacuum or low temperature still to avoid overheating urea, which would turn it into ammonia.

Permaflow Test in Fairbanks

The Indiana Soybean Alliance, The University of Alaska Fairbanks, the Alaska Agricultural and Forestry Experiment Station, and Purdue University partnered to test 250 gallons of Urea Clathrated biodiesel they called Permaflow. It is capable of working at temperatures below -67°F. The test took place in the Artic Circle and was documented by the Indiana Soybean Alliance on their web site.


The Process

It just so happens that the saturated methyl esters have a high cloud point and the unsaturated methyl esters have a low cloud point.

The process is described somewhat in the patent application. In this process Urea, commonly used as a fertilizer, is added to unwashed biodiesel, heated and stirred until it is fully dissolved in the biodiesel. Then it's cooled to 20°C where the saturated methyl esters become trapped inside the solid urea. The biodiesel is then filtered and the resulting biodiesel is extrememly low cloud point biodiesel. The stuff caught in the filter is washed to release the biodiesel and the urea is reused on the next batch.


Reader Comments

urea clathration

For your reference,please see attached my pictures tested and made from using Soy based WVO biodiesel at Jan. of this year.

Using Urea, I could make winter grade Biodiesel not Cloud or pour point down to -19° to -21°C (Min.lowest tem.of refrigerator) without difficulty if small amounts.


  • Biodiesel:500g
  • Original Urea:200g
  • Methanol:3 times of urea

I tried three step wise processes(1st:urea:200g,2nd:recovered175g,3rd;recovered150g) to minimize consuming methanol and ureas.

It is also to do one step process,but require more ureas(500g) and methanols(1500CC or more).

By changing ureas and corresponding methanols,I could make several types of Biodiesel were obtained from -5° ,-8°,10°,-15°, and -20°C of Cloud point. I used fertilizer grades of Ureas,not chemicals grade.

This urea based methods are not new ones and several researchers were tried since 1950-2010 time frame.

I would not use this method for lowering C.P. of Biodiesel. Main reasons are :

  1. Too much volumes of methanols compare to Biodiesel (3-5 Times) and not easy to methanol recovery within closed circuit system..
  2. Not so easy to remove urea and purify biodiesel completely.
  3. Saturated Biodiesel were recovered by using water or heating methods.

If use water method,urea condensation from water was not easy and urea molecules becomes ammonia gas(approximately at 130°C),if use heating methods

I hope above information us some help for you.



Related Links


Patent application for Urea Clathration Process (html)

Biodiesel Cloud Point and Cold Weather Issues - eXtension training (html)

Preparation and characterization of bio-diesels from various bio-oils
Purchase required
X. Langa, A. K. Dalai, , a, N. N. Bakhshia, M. J. Reaneyb and P. B. Hertzc
Mar 2001

Cold Flow Behavior of Biodiesels Derived from Biomass Sources
Purchase required
C. R. Krishna, Kaitlin Thomassen, Christopher Brown, Thomas A. Butcher,Mouzhgun Anjom, and Devinder Mahajan, Oct 2007

Cloud and pour points in fuel blends
Purchase required
J. A. P. Coutinho, , a, F. Mirantea, J. C. Ribeirob, J. M. Sansotc and J. L. Daridon; Jan 2002

Thermodynamic study on cloud point of biodiesel with its fatty acid composition
Purchase required
Hiroaki Imahara, Eiji Minami and Shiro Saka; Mar 2006


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