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Acid / base processing, but not for biodiesel

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February 09, 2017, 04:44 PM
imakebiodiesel
Acid / base processing, but not for biodiesel
I have been commissioned by a client to design and build a 1000litre processor for a specialist purpose. The desired product is glycerol that is very low in FFAs and soaps. The methyl esters will be a saleable byproduct.
The wvo supply is fairly clean , fairly dry oil with minimal fats titrating between 8 amd 12ml KOH
I propose to use a 2 stage process with acid esterification using sulphuric acid followed by base esterification with KOH. In the past when I made my own small scale biodiesel I used the Dkenny method and found it reliable. I see from reading the sticky post above no new recipes have been posted since 2009, is the Dkenny method still the gold standard for this type of processing?
are there any refinements that might be usefull bearing in mind that it is the glycerol we are concentrating on.
The acid esterification stage should dispense with most of the FFas and I thought that perhaps drying between the two stages would avoid any saponification during the second stage.
Perhaps some of you guys who have experience with AE might have some ideas.
February 09, 2017, 06:19 PM
fabricator
I used it for several years with pretty much complete success, the last couple years because of the consistency of my oil supply I just use 1ml/L on the acid stage. If your oil is more or less consistent you should probably be able to settle on a solid recipe also.
My question would be how do you intend to have an end product of glycerol with low soap? Glycerine is soap.
February 09, 2017, 07:34 PM
imakebiodiesel
The idea that glycerol and soap are the same thing is commonly held in the biodiesel world but in fact its not true. Glycerol is a polyol made up only of carbon,hydrogen and oxygen. Soaps are metal salts of fatty acids. The metals involved are usually sodium and potassium. Im lucky in this project as we have a pharmaceutical lab and its staff at our disposal. They have analysed numerous samples of glycerol and are able to measure the soap content very accurately. We have found that the samples that performed best in our practical field tests all exhibited low soap content.
Previously in our development of the chainsaw bar oil, soaps and free fatty acids were good for lubrication but in this new product they are undesirable.
So the reason Im looking at AE is that the free fatty acids will be converted into biodiesel and separated from the glycerol. If we were to remove most of the water produced by the acid stage before progressing to the base stage we should be able to reduce saponification, which is a reaction of water oil and sodium or potassium hydroxide.
February 09, 2017, 08:32 PM
Tilly
Hi imakebiodiesel,
It sounds interesting.

How much are you offering per hour for someone to be your consultant? Wink

Glycerine/ Glycerol is an alcohol- propane-1,2,3-triol






February 10, 2017, 11:35 AM
Dgs
Hi John,
I think the soaps formed within a normal 2 stage base process are from saponification as a result of water formed when the methoxide is mixed.

To reduce these to a minimum I would suggest using a methoxide mix as dry as possible, to this end using ASM or drying the methoxide with CaO would probably be advantageous.

I would also suggest that using Sulphuric is complicating things for you.
Why not 'enhance' some glycerol for a pre treatment so that your oil doesn't titrate ie any water from FFA neutralisation has been absorbed by the glycerol and removed.

From testing I have found this leaves the oil at around 3 to 400ppm. Then using a 'dry' methoxide you will produce minimal soap.
February 10, 2017, 11:51 AM
Dgs
fabricator, from some recent (combinations of tests and assumptions) I came up with this.

Glycerol from a 100 litre batch was 16 litres and was composed of;

glycerine 6.2 litres 38.8%

methanol 2.63 litres 16.4%

water 484mls 3%

bio 500mls 3.1%

soap 6.2 litres 38.8%
February 10, 2017, 02:06 PM
imakebiodiesel
Those figures are not exceptional, I have found that its rare to have any more than 50% glycerine/ glycerol in raw glycerol from homebrew processors. You are right that the water in methoxide is a major cause of saponification and either drying the methoxide or using asm will solve that problem. Have you any experience using CaO, I can obtain it cheaply but Ive never used it for this.
We will have to use Ae because this process will not yeild any glycerol that we can spare to strip or enhance the feedstock. The glycerol is the primary product. If this project pans out the semi refined glycerol plus additives will be worth about 10 times the value of biodiesel.
February 10, 2017, 03:53 PM
Dgs
Drying the methoxide worked really well with CaO as regards the very low production of potassium soap. During the first aggressive (compressor) water wash the resultant water was barely cloudy, a sign that K soap was minimal.

Big disadvantage was the formation of some Calcium soap which couldn't be washed out of the bio and left it cloudy. The only thing that was any use was oak chips. For this reason I've never tried it since.

The yield was amazing at around 104% You need to use about 1.2 x the weight of K to remove enough water. I mixed it in cubies with the methoxide. Because you can't use the bottom layer (too much excess CaO floating around) you need to mix up more than you need.

The cubies need to settle a couple of days, then they will clear. What you want to see is some unreacted CaO on top of the lower layer of really hard and solid Calcium Hydroxide. This is a sign that all the water has reacted and that there is an excess of CaO.

Keep an accurate record of the ratio as you will need to measure it by volume and from this the weight of K added.

Remember also you can add more virgin methanol to the methoxide, but not K as you will then produce more water.
February 10, 2017, 03:58 PM
WesleyB
I know some answers to that question. The Fischer Esterification formula is carboxylic acid (free fatty acids) plus dry alcohol plus catalytic quantity of strong mineral acid plus heat with stirring yeilds normal biodiesel plus water . But reacting triglyceride fatty acids and free fatty acids in the mix by acid esterification produces something else, a brownish organic product that will damage the purity and cash value of the end product glycerine. Making methoxide is not the only water source in this series of reactions, formation of the methyl ester of fatty acids produces about 18 grams per mole of water biproduct per mole of methyl ester formed. The average molecular weight of methyl biodiesel made from corn oil is about 292 grams per mole, with a density of about 0.87 grams per milliliter. The measured volume of methyl ester product can help a lot to determine how much water was produced by the esterification reaction. So after the Fischer esterification water is present, formed that was not present in the starting materials. For best result a minimum of water should be present in the transesterification reaction of methoxide plus triglyceride fatty acid esters to produce methyl biodiesel plus glycerine plus some soap. It hinders soap formation to have very dry starting materials.Its an expensive hassle to vacuum distill out water afer acid esterification, the methanol will also distill out, but leaves a relatively dry liquid for the caustic plus methanol step (transesterification rection). The transesterification reaction does not produce water as a byproduct. So the big thing you said you wanted was pure glycerol as the desired product, so do your acid reaction , dry your product with vacuum distillation, then do your base reaction , separate the glycerine fall out, lower layer from the upper layer methyl biodiesel. Then you have impure glycerine starting liquid material to purify. De-Meth the glycerol. The impurities are the brown crud from acid esterification which is what forms when sulfuric acid adds to one end of a double bond in a fatty acid chain, plus soap. The fatty acid chain is a chain of carbons bonded to each other but each carbon is bonded to one or two hydrogen atoms. There is a concept called electronegativity which is a measur of how strongly the outer electron is pulled towards the nucleus of the atom, which can cause increased volumes of electron density around the atom with the highest electronegativity. But if the difference in electronegativity is small and the same element (hydrogen) surround carbon then there is not an appreciable difference in electron density, so the long tail of fatty acids are non-polar. In solubility considerations like dissolves like. A non polar molecule dissolves a non polar molecule, like gasoline (light fraction) dissolves kerosene (a heavier fraction from petroleum distillation) The two liquids are not the same but both are non-polar so they dissolve in each other. Removing the brown crud (organic sulfite?) and soap in a good enough cost effective manner might be done in two steps, activated charcoal treating warm+time+agitation then removal of all activated charcoal by whatever cost effective means (filtering?). The activated charcoal lets non-polar chemicals absorb or adsorb to its surface, then removal of all activated charcoal. If this is pure enough fine. If you need it purer you can vacuum distil this faily pure glycerine at low pressure. But distilling glycerol is high heat, energy expensive.
February 10, 2017, 05:43 PM
WesleyB
Sorry, I forgot to mention some points in my last post. You asked about drying methanol containing liquid with CaO . It's true that CaO + H20 yields Ca2(OH) seeming to react with water removing it from solution to cause dryer starting materials and therefore a more complete faster reaction. But in what I read about "The Imisides Reaction Method" using CaO as one of the present materials during transesterification reaction (base step reaction) is Calcium Soap is one of the products. Calcium soap is know here as ring around the tub here. One calcium atom reacts with two free fatty acid molecules which makes a molecule with two long non-polar fatty acid tails pointing opposite directions from a calcium atom bonded to two organic acids, carboxylic acid groups bonded to the calcium through an oyxgen atom to the carbon chains through two single bonds, plus one oxygen atom bonded to each of the two first carbons in the long carbon chains. That makes a molecule with two long non-polar tails and a center of the molecule with two oyxgen atoms (increased electron densities around the two oxygen atoms). I don't know of anything calcium soap will dissolve in, maybe activated charcoal would stick to it. If you put in a chemical into the reaction and the product calcium soap is not to be in the end product, how are you going to remove it 100% from your biodiesel, the inside of your reaction vessel and maybe from the inside of the boiling pot of your distillation apparatus? Rather than put a chemical in that makes a material that's hard to get out, figure another way to do it. I did an experiment 12/26/16 after Tilly mentioned that common, inexpensive, sodium hydroxide was about 15% water. I put 157.3 grams technical grade sodium hydroxide pellets into a vacuum still. I did not put my expensive $150 ground glass joint mercury thermometer into the still because it might have broken. Here they are difficult to replace. I guessed the setting on heating the heating mantle to be between 200-250 degrees centigrade. I ran the vacuum pump at about 100 millimeters of pressure inside the still. After the still pot heated up the previously solid lye pellets turned into a boiling clear liquid. I distilled off 3.9 grams of water from the technical grade sodium hydroxide via heat and vacuuum distillation. Caustic absorbs, reacts with carbon dioxide from the air which produces a chemical that will not act as catalyst for the base phase of the biodiesel making reaction. A slight reduction in water by mass of something like 2.8% might make a big difference in increase of methoxide concentration and in reduction of soap production via the saponification reaction by removing water from the starting catalyst. Tests would be needed to determine advantage gained by doing that. Maybe better conditions, higher vacuum, higher heat, longer time would improve water removal from inexpensive technical grade catalyst via vaccuum distillation. Removing water under vacuum minimizes carbon dioxide absorption from the air. The viscosity of your distilled pure glycerine product is a function of temperature. A condenser in a glycerine still might need to be 90 degrees celcius so the glycerine would quickly flow out of the condenser into a receiving flask. Increasing vacuum decreases boiling temperature. You might need a good vacuum pump that would pull down to 10 millimeters of pressure to get a satisfactory boiling temperature for the glycerine in the still pot. A 10 millimeter vacuum still would need thick walls to keep from collapsing in, imploding. Glycerine boils very hot under higher pressures. In vacuum stills bumping is an important problem to overcome. If you add boiling stones/chips to a vacuum still before pulling the vacuum then maintain identical pressure while heating to a boil till enough is distiiled, bumping may not occur. Boiling occurs around gas seeds in stones or types of boiling chips. But if the vacuum pressure increases, then drops, then increases, the liquid has forced tiself into the gas seeds inside the stones and boiling would cease, superheating will occur then with some subtle trigger a lot of liquid will vaporize quickly and a lot of the still pot contents will energetically go across the still head in a short period of time. I've run small vacuum stills but a big one, a good one would take a while to learn how to operate. If it's distilled it might be acceptable purity for medical grade.
February 10, 2017, 07:18 PM
WesleyB
Another point in preparing optimum purity products is if using distillation as part of the process, then generally if composition of liquid still pot's components is a greater boiling point difference, then better separation might be achieved. One of the impurities in whatever percentage in your glycerine still pot liquid to be distilled would be sodium or potassium soap. The electronegativity of sodium atoms is 0.93 the electronegativity of potassium is 0.82. The electronegativity of oxygen is 3.44. Electronegativity is a relative measure of how strongly the atom pulls the outermost electron towards it. You subtract the higher number from the lower number to see polarity a plus versus minus charge difference that caused polarity of a molecule. A higher electron density difference probably indicates a greater charge separation in the volume around two adjacent atoms. Sodium chloride has an electronegativity of 0.93 for sodium and 3.16 for a chlorine atom, an electronegativity difference of 2.23. A difference of over 1.5 is considered polar, in which the atoms actually separate when dissolved in water, in NaCl actual charged ions individual charged atoms dispersed in water solution. I believe, under 1.5 electronegativity difference the atoms do not separate, ionize when dissolved in a polar liquid like water. THe dry molecule of sodium chloride are attracted (relatively) positive end to relatively negative end, in a three dimensional structure where the molecules are strongly attracted to each other. The melting point of sodium chloride, plain table salt is 801 degrees centigrade and its boiling point is 1431 degrees centigrade because of the electronegativity difference and the strong attraction of negative molecule ends to positive molecule ends. To boil a material the intermolecular force has to be broken and the molecules separate into a gas rather than a liquid or solid. Also generally, the higher the molecular weight, the higher the boiling point. To revove soap more effectively from glycerine during distillation, a higher molecular weight soap is potassium with an atomic mass of 39.09 grams per mole compared to sodium with an atomic weight of 22.98 grams per mole. A mole is a specific number of atoms or molecules that enables measuring masses relative to an equivalent number of different types of atoms or molecules. A mole is 6.02 times ten raised to the twenty third power atoms or molecules. A mole is 6.02 multiplied by 1 followed by twenty three zeros. It's a big number. The 23 is an exponent number on ten. A mole is that many molecules or atoms, comparing mass of equivalent number of atoms or molecules or particles. So a mole of potassium soap weighs more per mole, made with octadecanoate (a specific fatty acid) compared to one mole of sodium octadecanoate (chemical name of a type of soap. In sodium soap a sodium atom is single bonded to an oxygen atom with an electronegativity difference of 2.51 between sodium and oxygen bonded to each other. Potassium soap has an electronegativity difference of 2.63 in the electron bond between a potassium atom and an oxygen atom in the organic acid group on the end of the long chain of carbons. There are other factors, but the greater electron density difference in the bond with the oxygen atom on the end of the chain would make the potassium soap have a higher boiling point that sodium soap, if they would boil without decomposing. So for better purity of product glycerine you might use potassium hydroxide rather than sodium hydroxide in the base part of making biodiesel from triglyceride fatty acid esters (vegetable oil). It might not make a difference though. Lowering the boiling point in distilling glycerine by low vacuum (10 milliliters vacuum?) is also important for purity is glycerine decomposes at 290 degrees centigrade at atmospheric pressure, without boiling, but it boils at 182 degrees centigrade at a vacuum still pressure of 20 milliliters , which can be done. Also soap won't boil into a gas but it will decompose into unwanted impurities that will pass across the still head into the receiving flask of your very pure, distilled glycerine, polluting it with unacceptable chemicals that are pyrolyic breakdown products of soaps.
February 11, 2017, 08:32 AM
imakebiodiesel
Thanks to Wesley and Dgs, for all that information, It will take me a while to absorb it all.

Just to give you a bit more background to the project. For confidentiality reasons I cant tell you what the the product is we are trying to produce but we have done a number of preliminary field tests and found that refined pharma grade glycerol with an additive is the perfect product but far too expensive. We have also tested several samples of raw glycerol with the same additive. The worst performing samples all had high levels of FFAs and soap while the best had low levels of FFAs and soaps.

We are looking at two ways to produce Glycerol with low levels of FFAs and soaps.

First, convert WVO using a 2 stage acid base process taking the measures discussed above to eliminate FFAs and soap. This will hopefully produce both suitable glycerol and of course methylyl esters which are very saleable.

Another possible path is to purchase raw glycerol from large biodiesel plants and neutralize it using sulphuric acid ( sometimes called cracking) this separates the raw glycerol into 3 layers of FFAs on top , semi refined glycerol middle and water/ potassium sulphate bottom. I have done several batches of this and it looks promising. Dgs, you told me a while ago you had a contact who had done this on a commercial scale, I would be very interested to contact him with a view to offering him some paid consultancy work.
February 11, 2017, 09:49 AM
Dgs
Hi John,

I pm'd you some time ago with Russells' telephone number. Just tell me if you need me to send the details again.

Dave.
February 14, 2017, 01:52 PM
imakebiodiesel
My client Tony has made contact with Russell and is making an arrangement for us to fly over to Leeds and spend a couple of days possible=y next week, perhaps we could meet up if its not too far from you.
February 14, 2017, 04:46 PM
Dgs
Indeed, that would be nice, Please let me know.
February 18, 2017, 09:41 AM
imakebiodiesel
Dgs Im going to be yurs in neck of the woods on Wednesday. Russell is picking us up at the airport and taking us to Halifax to see his equipment. We arrive at 9am and will fly out at 7pm. If you can meet up with us that would be great my mobile number is 00353 86 3169230.
February 23, 2017, 05:55 AM
imakebiodiesel
Sorry we didnt manage to meet up yesterday, Russell picked us up from the airport and took us to the fabrication workshop in Halifax, very impressive. We had a great discussion about his system of neutralizing glycerol, we was very generous in imparting valuable information and in the next few weeks Im going to set up a pilot processor to duplicate his method. His method is different from most others because you can monitor the progress of the reaction as it happens and stop at the exact point the neutralization is complete.
We had a look at some of his surplus equipment including a very impressive Alpha Laval centrifuge that Tony may buy for his process.
Many thanks for putting us in touch with him, his advice was invaluable.
February 23, 2017, 11:27 AM
Dgs
No worries John, I'm pleased your meeting went well and hope to meet up with you next time you are over.