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Possible problem with glycerol prewash
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In order to increase yield and improve quality, I decided to do a glycerol prewash.I added 30litres of glycerine to a 180 litre batch of fairly dry oil and heated to 50deg C for two hrs. Oil titrated at 1.5. After circulating for 2 hrs I let settle for 1 1/2 hrs and started to drain off the glycerol.At first about 2 litres of thick dark glycerol came out then the colour became golden and much thinner in total about 8 litres of glycerol was drained off before oil of almost the same colour appeared.I left it stand for another hour but very little glycerine emerged.
1.I know that the glycerine from a prewash can be less if bio is released from the glycerine.but less than a third d of the added glycerine. I have now left it to settle over night.
Can anyone suggest what to do next
2. Should the temperature be higher.?
3 Should I add some Methanol and KOH and heat and circulate some more?
4.Should I drain more Glycerine and continue to process as usual?
My intention is to do a no titration 2 stage process. I would be grateful for any comments
 
Location: Kokstad.Kwazulu Natal.South Africa | Registered: June 23, 2012Reply With QuoteReport This Post
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Hi Jock, We realised early on that it was not necessary to drain off all the prewash glycerine, just treat it as very good WVO, any remaining glycerine will not affect the end result. Jim.
 
Location: Cape Town | Registered: May 17, 2006Reply With QuoteReport This Post
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Thanks Jim much appreciated Regards Jock
 
Location: Kokstad.Kwazulu Natal.South Africa | Registered: June 23, 2012Reply With QuoteReport This Post
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Hi Jock,
As jim says having some glycerol left in the mix is not a problem, however in your case with a considerable amount left in there your chemical addition would be more as the extra glycerol will absorb some of your added chemicals. To get the pre-wash to work properly it needs to be heated to 60degs and 1 hour is sufficient to mix.

1 1/2 hours is no where near enough time for it to drop. It needs leaving for at least 4 hours and preferably overnight.

A typical amount to drain with 30 litres added would be @ 25 litres (depending on how methanol rich it was)

My batch size is similar to yours, but I add 60 litres of glycerol with 5 litres of methanol added.
Depending on how chemical rich the glycerol was I achieve 10 to 25% conversion using this method. I then deduct the 5 added litres of methanol from the 1st 'normal' reaction chemicals and end up using 10.5 to 12.5% added methanol for full conversion. I use KOH and my average usage is 5 to 6 gms/litre of oil. My oil titrates at only 1.1 KOH.
 
Location: YORK UK | Registered: April 27, 2014Reply With QuoteReport This Post
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Hi Dgs,

quote:
Originally posted by Dgs:
Depending on how chemical rich the glycerol was I achieve 10 to 25% conversion using this method
You have piqued my interest.
I know of no accurate backyard test for conversion percent.
Will you please describe the test you use to determine percent conversion.






 
Location: ลึก ประเทศอินเดีย | Registered: March 03, 2001Reply With QuoteReport This Post
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Thank you for your interest Tilly, however none of my testing can be described as 'backyard'
 
Location: YORK UK | Registered: April 27, 2014Reply With QuoteReport This Post



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Hi Dgs,

quote:
Originally posted by Dgs:
Thank you for your interest Tilly, however none of my testing can be described as 'backyard'
You have piqued my interest even more.
Please describe the test you use to determine percent conversion. Wink






 
Location: ลึก ประเทศอินเดีย | Registered: March 03, 2001Reply With QuoteReport This Post
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Holy hell, this again??

Cheers, John
 
Registered: June 17, 2007Reply With QuoteReport This Post
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Ad nauseam
 
Registered: July 04, 2014Reply With QuoteReport This Post
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Still flogging that dead horse. Oh well, when it's the only pony he knows how to ride, then I guess it's expected. Just ignore him and he will go away.



 
Location: coldest N.America | Registered: May 03, 2005Reply With QuoteReport This Post
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Seems to me that if a marked amount of glycerine is left in the mix then as soon as you add the caustic solution then you will be encouraging heavy soap production as the glyc layer is only about 25% away from being full on soap. Maybe I am missing something ?



** Biodiesel Glycerine Soap - The Guide
- on 5 continents helping people make & sell soap from the Biodiesel Glycerine.


 
Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post
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Hi Legal Eagle,

quote:
Originally posted by Legal Eagle:
Seems to me that if a marked amount of glycerine is left in the mix then as soon as you add the caustic solution then you will be encouraging heavy soap production as the glyc layer is only about 25% away from being full on soap. Maybe I am missing something ?
The caustic solution is composed of methanol, not water and methanol and caustic do not produce soap.

I am not sure what you mean by "glyc layer is only about 25% away from being full on soap"
The amount of soap in the glycerine layer is determined by a number of things including but no doubt not limited to the FFA content of the oil and the amount of water avaiolable






 
Location: ลึก ประเทศอินเดีย | Registered: March 03, 2001Reply With QuoteReport This Post



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Hello Legal Eagle,
a small amount of glycerol left in the oil after pre-treatment actually helps the reaction.
The ability of glycerol absorbing water is considerable and it helps reduce saponification.

A lot of the UK boys use a reaction that they call AAF (arse about face) whereby hot oil at reaction temperature is added to the methoxide. The guys that use this method have reported lower chemical usage and greater yields. I am pretty sure the reason why it works better is that glycerol is produced earlier in the reaction.
 
Location: YORK UK | Registered: April 27, 2014Reply With QuoteReport This Post
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quote:
I am pretty sure the reason why it works better is that glycerol is produced earlier in the reaction.


I read here some years back that the reason was that the reaction starts as a super critical reaction that aids in completing the transesterfication. not sure who posted that but maybe sunwizard? I hope I don't have his name wrong


" I don't know what I don't know until I know"
1994 GMC 6.5 Tubo 2005 Dodge ram 3500, 3 VW's 2000, 2002, 2005.
 
Location: Manitoba Canada | Registered: March 24, 2009Reply With QuoteReport This Post
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Hi Dgs,

quote:
Originally posted by Dgs:
Hello Legal Eagle,
a small amount of glycerol left in the oil after pre-treatment actually helps the reaction.
The ability of glycerol absorbing water is considerable and it helps reduce saponification.

A lot of the UK boys use a reaction that they call AAF (arse about face) whereby hot oil at reaction temperature is added to the methoxide. The guys that use this method have reported lower chemical usage and greater yields. I am pretty sure the reason why it works better is that glycerol is produced earlier in the reaction.
That is interesting.
Please post a link to meaningful comparison testing that supports these claims






 
Location: ลึก ประเทศอินเดีย | Registered: March 03, 2001Reply With QuoteReport This Post
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