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Green energy
-the water produced in the reaction is a given, we work with that. the problems start when people try to make biodiesel with out drying the wvo enough. Tom " 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. |
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Thanks Biotom!
Do you think if we can get rid of the water from the mixture of KOH/NaOH and methanol before we inject the mixture will improve the biodiesl production? (At lease the soap will reduced)
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I don't think it is possible. At least not for the back yard brewer. You can distill the methanol out of the water. but not water out of methanol.
I am not sure what quick n dry would do. It absorbs water, but the caustic attaches to water as well. Interesting thought, but like Tom said, the amount of water created in the reaction is workable with dry oil. |
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Thats also one of the reasons why we use an excess of methanol rather than the straight 12% used to make the FAME's
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Thanks.
Could you please explain why we need exess of methanol rathan than the 12%? Also, why it is 12%? How this number comes from?
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Green energy
-12% is the amount of methanol consumned in the reaction, the extra methanol is required to push the reaction to the right,(completion) Tom " 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. |
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member 2009 Sponsor |
I wonder you could use a dessicent or molecular sieve of some sort, or perhaps fractional distillation that would input the methanol back into the pot and water to a catch can.
Or you could just use Sodium or Potassium Methylate. |
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Member |
KOH or NaOH will work as a desiccant, of course, there are others too. I'm not sure what would happen if you would run a portion of your Methanol and run it through a tube of excess NaOH salt. I'm doubting that Fractional Distillation will be very effective as typically salts (NaOH, KOH, CH3-O-Na, CH3-O-K) are the last things to boil out when distilling. Sodium and Potassium Methylate were discussed earlier. I believe they can be purchased as a dry salt and more or less replace NaOH/KOH in similar proportions, or you might buy them premixed with Methanol. I think someone also suggested using pure Sodium Metal or Potassium metal... But, those are pretty "hot to handle". You will find that NaOH and KOH are "dirt cheap" and much safer to handle compared to other reagents. It still wouldn't hurt to try the first idea of using a tube of excess NaOH/KOH to use as a desiccant and making the Sodium/Potassium Methoxide. |
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Anarchist Moderator |
A three to one molar ratio of methanol to triglyceride (oil) is required as each FFA on the tri needs a methanol to become a methyl ester. 12% methanol (by volume) is a three to one molar ratio to oil. Extra methanol is required to convert the mono and diglyceride salts that are produced during the reaction into mono's and di's plus a potassium (or sodium) methoxide molecule. Then the mon's and di's (and of course more tri's) can be split again by the methoxide molecule, which creates another fatty acid salt and a methyl ester, and so on, until the last mono is rendered into a methyl ester and a free glycerin molecule. Which of course, never really happens.  Hope this helps, Bob Got Renewable Fuel? |
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Member |
I use 3A molecular sieve to remove residual water from the methanol I distill from my glycerol byproduct. After distilling the methanol is at roughly 80% purity. I add the required amount of molecular sieve pellets and stir for a minute. After 2 hours I pour the methanol through a kitchen sieve to recover the pellets. The methanol now measures over 99% purity. I air dry the pellets for a day or so, then heat them to 250 degrees C for 2 hours to dry them completely. They can be reused many hundreds of times.
The molecular sieve works because the gaps in its crystalline structure are larger than water molecules but smaller than alcohol molecules and so it only absorbs water. What size is the CH3ONa molecule. It has to be larger than three Angstroms. My worry is that the caustic soda would break down the pellets into a silt making them unusable. Molecular sieve is expensive, which doesnt matter if it last for hundreds of uses. In the days before molecular sieve chemists used to use quicklime CaO to remove water from alcohol. The quicklime reacts with the water, forming calcium hydroxide (Lime) which settles to the bottom of the vessel. If this worked you might not need to separate the lime as it would settle into the glycerol layer when the process was finished. |
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Member |
Very clear. Thanks a lot!
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Member |
very good suggestion.
I need to think about that. Thanks all suggestions from you guys.
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Member |
The first part of this answer is roughly right. The amount of methanol used in the reaction is about 11% by weight or 13% by volume. This is called the stoichiometric amount. It is calculated from the molecular weights of the oil and the methanol. More must be used to drive the reaction forward. It turns out that using double the stoichiometric amount gives a very high conversion, a little better than ASTM. Many people of course use less and the motors appear to go properly. Precombustion chamber motors appear to be tolerant of lower conversion and it may be reasonable to leave the excess methanol in the fuel, rather than recovering it.
The second part of the answer is not so good. There is an unwanted side reaction in which the caustic converts a little of the oil and biodiesel to soap. This is increased if the oil is not reasonably dry. Soap is a salt of the free fatty acid. Once this forms it cannot be reversed by additional methanol. It is not an intermediate in the desired reaction. |
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Anarchist Moderator |
I am not talking here about the reaction that creates soap from the FFA existing in the oil reating with the catalyst, I'm pointing out the reactions that create methyl esters out of triglycerides. As you might be aware, the soap reaction your refer to is why we add additional catalyst to account for the FFAs occurring in the feedstock that are saponified by the catalyst, but does not account for the addition of "extra" methanol. Here's the reactions I'm referring to:  Hope this helps, Bob in Moncure Got Renewable Fuel? |
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Member |
Bob, while the net result of your equations produces the right result I do not think they describe what really happens. In your step 3 you have a potassium "salt" which is then attacked by methanol to produce the ester. It seems more likely that the electrons of the methoxide ion attack the carbon atom of the carbonyl group, C=O . This would result in the methoxide group attaching directly to the carbonyl carbon and the bond to the glycerol becoming detached. Thus the ester would be formed without the existence of a "salt". The intermediate would not be this "salt" but a tetrahedral anion. After the glycerol becomes detached it would momentarily be an anion which would scavenge hydrogen to form the neutral species.
At the moment when the glycerol anion forms there would be competition between it and the methoxide ions for the carbonyl carbon, thus the reaction is reversible. We use excess methanol to provide one of the driving forces to ensure that the reaction goes in the desired direction. I believe the main driving force is the low solubility of the glycerol which causes it to fall out of the system while the methanol is fully present and available for reaction. |
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Member |
CaO seems to be the ideal desiccant.
CaO is cheap. If Ca(OH)2 is not react with methanol and is not dissolve in methanol, it is really ideal. If one have available CaO and do an experiment, just disolve CaO into H2O, convert CaO into Ca(OH)2, the Ca(OH)2 should be not dissolve into water, then put some methanol into the solution to see whether the Ca(OH)2 dissolves or not. For the molecular sieve, what's the price? I am also worry about whether the NaOH react with the molecular sieve. Thanks
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Member |
Im not quite sure about the price because it was over a year ago that I bought it but it was roughly 185 GBP for 50 kilos.
CALCIUM OXIDE is relatively cheap and can be bought from anyone making traditional lime mortar. In Ireland there 6 companies that I know of doing this. I contacted one of them and after I explained what I wanted it for said I could have a bag for free. He thought a 25kilo bag would cost about 20 euro. Any body have an estimate how much CaO would be needed to treat 33 litres of methanol and 1200 gms of KOH. This is how much I use in my 150 litre batch. |
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Member |
Hi imakebiodiesel,
CH3OH + KOH -> CH3OK + H2O CaO + H2O → Ca(OH)2 You need exactly the same mass of Cao as that of KOH you used. In your case, you need 1200 grams of CaO. (CaO and KOH have same molecular weight) Hope it helps.
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I heard dissolving aluminum in a KOH/ethanol solution removes the water. I haven't tried it so I don't know if it would work in methanol. Check out the 30 June 2007 post in the discussion here. Ken |
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