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Hi, even though I have been having less than 1% on average of FFA, I am still getting around +5000 ppm of water in my biodiesel. I since now that that much soap is being produced, the FFA's must be retaining water in the BD.

I then decided to try using acid to pretreat the FFA's. Since I work in government I have to minimize waste produced so I didn't like the acid overkill equations that seemed to be used even in literature.

I calculated the number of moles of sulphuric acid needed to exactly neutralize and convert the titrated amount of FFA concentration. It boiled down to 0.72 x titrated amount in ml x volume of WVO in L. I used 18 molar acid and needed about 3 times the amount calculated above to account for protonation. I used about 10% methanol and reacted at 65 C for 3 hours.

What I found was that the acid number roughly stayed the same. This is promising because if the acid wasn't being used the titration would jump.

What I found in the end was that the finished biodiesel was essentially dry. Whether the esterification is actually working or not I don't know but I am getting the desired results.

Note that the equation was calculated using 0.025 M NaOH as the titrant. The equation wouldn't work for KOH and would have to be modified.

If anyone has any input I am always willing to learn or I can clarify anything as well as I love talking about this stuff.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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Red Neck Chemist; I think some of the sulfuric acid participates in a second reaction being electrophilic addition. This might account for some of the sulfuric acid being used up. You said it took three times the amount of acid you calculated to esterify the free fatty acids. Electrophilic addition to the double bonds of the fatty acids might be why. Making the ester from the free fatty acids plus methanol using H2SO4 as catalyst makes water also. You said you had 5 parts per thousand (5000 ppm) of water, and afterwards it was essentially dry. Where did the water go?
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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sulfuric acid is a water mop,(the main reason acid esterfication will not work on wet oil) I know a person who treats his wvo with sulfuric acid (no methanol) prior to base transesterfication to dry the oil, this person is a chemist!


" 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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If FFA's are mostly converted to biodiesel there is less of a water attraction in the biodiesel, so the water easily falls out with the glycerol.

I like the idea of acid soaking up water too, free water would be protonated making it more apt to bind to a more strongly electronegative molecule like glycerol rather than biodiesel.

Whether the first is the case or the acid is just soaking up the water I don't care, the end result passes ASTM.

Maybe I should quadrouple the amount to account for both. It is only like 100 mL over 150 L of WVO.

I have never had better conversion rates after using this amount of acid, I have no need for a second base reaction.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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your going to get better conversion because you remove water and that reduces the soap production which steals caustic from the transesterfication reaction.
why do you think you have ffa's in the biodiesel, ffa,s are turned into soap during the transeserfication process, both reactions happening at the same time. If the biodiesel is poorly made then it could have more mono and dyglicerides than you want, these will hold water.
5000 ppm water (by what method) in the biodiesel, is this after water washing? sounds like you need to spend some time drying the biodiesel.


" 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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My point in describing how sulfuric acids reacts with/attaches to fatty acids is that once you put it into your biodiesel you can't get it all out. There's ultra low sulfur diesel fuel at gas stations. Adding sulfur to biodiesel is bad, unless there's no other way to make it. Even then its bad. When I did acid esterfication followed by base transesterfication on new corn oil, then compared the color to biodiesel made from just base catalysed transesterfication, the acid esterified biodiesel was darker in color. I know from previous experience that sulfates can have a brown color. So using acid esterification puts some amount of sulfur into the biodiesel.
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post



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It would also make sense if there was partially unconverted triglycerides to uptake water into biodiesel as well. I am just assuming that the long chain/carboxyllic of FFA's allow it to be soluble in both biodiesel and hydrophillic compounds as well. The first is more probable but why then would my low concentration acid addition resolve that problem?

I don't do any water washing, I use a different form of washing. I determine my water concentration through distillation.

I am having problems though removing methanol, about 4% in the finished biodiesel. I would be unconcerned with this amount if it didn't lower my flash point and make it fail ASTM. I am looking at providing fuel to our entire region so ASTM is becoming more important.

I use Magnesol which is effective at pulling out unconverted glycerides or water but doesn't seem to pull out methanol without using an uneconomical amount of the powder.

I sent a sample to an analytical lab and it passed everything ASTM but flash point, becuase of dissolved methanol.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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If the only significant impurity left to remove from the biodiesel is 4% methanol, then you might look at and consider a flash evaporator if you're going to make a lot. On a laboratory scale I'd use a vacuum roto-evaporator. They're expensive. A cheap roto-evaporator is about $1500 USA dollars.
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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I will look into that flash evaporator. We make roughly 1000 L a week but are looking to expand so it might be something worth checking out.

I had found that on benchtop that post distilled glycerol is very effective at both drying water and removing methanol when mixed into biodiesel. We are currently building a still to recover methanol so this method may be cheaper.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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