Urea Clathration | Biodiesel Chemistry

Gel 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. Most biodiesel has a rather high cloud point. It will gel up quicker than diesel so we will either stop using it or mix it with diesel.

In the past we have used 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, it's best to leave your oil where it can get really cold, then first thing in the morning, decant off the liquid oil for making winter biodiesel. It's about the only way up until now that we have been able to make low gel point biodiesel. Unfortunately it also makes low energy biodiesel as well.

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.

That is until 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 -67F. 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 20C 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.

Comments

0 #2 Rickdatech 2011-05-07 05:12

Originally posted by Rickdatech 4 Jun 2010

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It looks like biodiesel processed with urea clathration can be used as a cloud point lowering additive. According to published research cloud point temperature is primarily a function of the percentage of saturated fatty acids in biodiesel. The researchers found they could predict the new cloud point of any blend of high and low gel point biodiesel based entirely on the percentage of saturated fats.They found that above about 10% saturated fat, the relationship was linear. A simple formula can translate cloud point to the percent saturated fats:

Ratio = ( CP / 41 ) + 0.14

CP - is the cloud point temp in deg C.
To get the percentage multiply the ratio times 100.

Assume that biodiesel processed via urea clathration has no saturated fats. a 50/50 blend will cut the percentage saturated fats in half. A blend 1/3 regular bio and 2/3's urea clathration bio will reduce saturated fats to 1/3 of the original number.

Lets say your biodiesel has a cloud point of 10 deg C (50F) then your biodiesel would be about 38% saturated fats. If we blend 50/50 we can cut that in half down to 19%. We can rearrange the formula above solving for CP and we get a new cloud point of 2C (36F) or an 8C (14F) drop in cloud point.

Increasing the blend to one part untreated and two parts treated we lower out cloud point to -0.5C (31F) for a 9.5C (19F) reduction in cloud point.

The higher the cloud point of the original biodiesel, the bigger the effect blending has on it.

What this means is that we can target our gel point with blending so that we process via urea clathration only as much as we need to meet our needs. It also means that in the commercial plant, biodiesel with specific cloud points can be easily manufactured based on customer demand and the climate of the target market.

Please note the research did not investigate the relationship of cloud point to percent saturated fat below about 10%. It is assumed that below 10% the relationship between cloud point and percent saturated fat changes from near linear to near logarithmic.

0 #1 Rickdatech 2011-05-07 05:05

Originally posted by Rickdatech 22 Apr 2010

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I received the following in email:

For your reference,pleas e 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 -21Deg.C (Min.lowest tem.of refrigerator) without difficulty if small amounts.

Sample Biodiesel:500g

Original Urea:200g

Methanol:3 times of urea

I tried three step wise processes(1st:urea:200g,2n d: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 -20Deg.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(approximate ly at 130 Deg.C),if use heating methods

I hope above information us some help for you.

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WARNING

Making Biodiesel requires the use of flammable, toxic liquids and strong caustics to make a fuel. No matter what safety precautions are put in place or what equipment you use, making biodiesel will never be a safe hobby and can place you, your property, and your family at risk of injury or even death. Make Biodiesel at your own risk.