Biopowered - vegetable oil and biodiesel forum
Biodiesel => Chemistry and process => Topic started by: julianf on March 20, 2013, 08:53:47 PM
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I've heard it said that blending feedstocks can keep the product liquid, when components of it would otherwise freeze.
Im thinking about how this works... Im wondering if its simply that the precipitate is kept in solution easier, or if the molecules actually interact to change the melting point of the whole solution.
Anyhow, the reason why im thinking about this is that i have a load of feedstock whose methyl ester melts at around 15c.
When i get a spare moment, i plan to make a 50/50 25/75 and 75/25 mix with some esters made from feedstock that freezes at much lower temp (sub zero - im not sure of the figures yet)
Does anyone have any thoughts, or experience, of what i may find?
Thank you,
Julian
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Ive finally melted out some of my tallow based biodiesel - it melts at about 15c!
I have added this 50/50 to some bio that was made with clear liquid feedstock. Its now in the freezer.
I dont hold out any hope that it will stay liquid, however, ill then melt it and add another 50cc (1:2) of low melting point ester product, and re-freeze.
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A 50/50 blend of tallow based bio, and the liquid feedstock stuff is liquid, but with some hazy precipitation, at 4c.
What im wanting to do is work out a scale of sorts - so as with fixed points (ie one that freezes at -10 and one that freezes at +15) i can calculate the blend for a required temp.
It would be much easier if i had a dedicated freezer that i could adjust the temperature on.
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I haven't tested this, but I wouldn't have thought mixing different melting point methyl esters will make any difference to their melting point,
and it is said that mixing different feedstock oils can help lower the overall melting point of the resulting methyl esters.
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I haven't tested this, but I wouldn't have thought mixing different melting point methyl esters will make any difference to their melting point,
and it is said that mixing different feedstock oils can help lower the overall melting point of the resulting methyl esters.
No/Yes : )
Mixing the esters (or the feedstocks) does not result in the same molecules freezing at the same temperatures - ie my 50/50 sample does not half freeze below 15c.
Its something to do with the molecules getting between each other and disrupting the structures - i tried to read more on the interweb, but have not got that far yet.
Im sure its the same chemistry / physics as the commercial winterisers - im just trying to get some sort of scale for what i have.
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If you think of saturated fats as being straight and unsaturated fats as being bent, straight chains stack together easily(solidify) and bent chains don't stack together so easily, then it would make sense that if the straight chains are mixed in with bent ones they wont stack together so easily.
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I think this is an interesting result.
Feedstocks used were -
100% liquid oil (no whites) of unknown type &
100% beef tallow
Out of the four containers, 3-off are 100% beef tallow esters, and 1-off is a blend:
(http://www.devon-used-cooking-oil-collection.co.uk/forum/blending_1.jpg)
(http://www.devon-used-cooking-oil-collection.co.uk/forum/blending_2.jpg)
You can see in the second photo a more orange'y haze at the top of the left hand container. This is where its close to melting (or not quite all frozen - one or the other)
The containers are 25ltr. What is, to me, interesting is the blend - its 20ltrs of the tallow, and only 5 ltrs of liquid bio. But that 5ltrs is enough to, seemingly, keep the whole fluid.
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So if the tallow is teetering on the edge of it's melting point, you may have only dropped the melting point of your blend by a degree or two to get a liquid result?
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I guess im just pleased that the blend now appears to be usable, whilst i was beginning to worry that it would never be suitable.
What id like would be a dedicated chiller, as working out melting points when you have no real control over the temperature is near impossible. With a small fridge i could set the temp, and graph the results.