Foolproof Room Temperature Biodiesel Manufacture

Videos:

1. Making methoxide solution
2. Transferring methoxide solution to reactor
3. Reaction
4. Stopping pump
5. Postscript
6. Transfer to clarifiers
7. System Overview
8. Cement Processing 1
9. Cement Processing 2
10. Glycerol Processing 1
11. Glycerol Processing 2

Introduction:

This method describes a foolproof method of making biodiesel that doesn’t require any heating or titrations. As well as this it produces glycerol that is very thin and low foaming, and is easily disposed of down the sink. The soap formation and location is also discussed

The advantages of this method over the Dr Pepper method, any method that requires heating are obvious:

1. Since no heating is required you can make as big a batch as your equipment and shed size allows. I make 1000L batches in an IBC

2. It’s utterly foolproof as no titrations are required, and the calculations are simple

3. The disposal of the glycerol waste is very easy

4. The soap that is formed does not interfere with the reaction and is easily disposed of

It is divided into two sections. The first explains the chemistry and the second is a step-by-step guide to the method. You don’t have to understand the chemistry to follow the method.

1 Chemistry:

A triglyceride molecule may be converted into one glycerol molecule and three methyl esters by base-catalysed transesterification. A methoxide ion attacks the ester linkage of the triglyceride (via an SN2 mechanism) and cleaves the molecule into these four segments.

1.1: Methoxide solution:

Eq 1: MeOH + KOH <-> KMeO + H2O

2. Transesterification reaction

Eq 2: C6O6H5R3 + 3KMeO -> C3O3H5K3 (potassium salt of glycerol) + 3(MeOCOR)

3. Regeneration of catalyst

Eq 3: C3O3H5K3 + 3H2O -> C3H8O3 (glycerol) + 3KOH

So the final step in the process results in the regeneration of the catalyst and protonation of the potassium salt of the glycerol to form glycerol.

My method differs in that it removes water from the process.

The methoxide is generated by reaction of NaOH or KOH with MeOH as follows:

Equation 1:     KOH + MeOH  = K⁺MeO^– + H₂O

One thing that may not be obvious from this reaction (due to the formatting limitations of WordPress) is that it is a dynamic equilibrium.

That is, if we consider the reaction of caustic soda with hydrochloric acid we have

Equation 2:     NaOH + HCl = NaCl + H₂O

In this reaction, all the NaOH and HCl have been consumed and have all been converted to salt and water.

For the methoxide reaction above, however, the reaction is proceeding in both directions simultaneously. That is, if we took a snapshot of the solution at any point in time we would find significant concentrations of KOH, MeOH, methoxide and water.

The problem with the conventional method (the so-called Dr Pepper method) is that both the methoxide and water can act as reactive intermediates – the methoxide for transesterification (biodiesel manufacture) and water for saponification (soap manufacture) respectively.

Fortunately, however, the transesterification process is more facile than the saponification reaction, so if the concentration of the base (KOH or NaOH) is carefully controlled, it is possible to facilitate the transesterification reaction without allowing the saponification reaction to proceed.

This means that a titration is required to determine the concentration of free fatty acids, as the base that is added will react with (neutralise) them first. So an exact amount has to be added, to neutralise the FFAs, and then leave enough for generation of sufficient methoxide to enable the transesterification without enabling the saponification.

This does, however, require that the solution be heated (to 55 deg C) to overcome the activation energy for the transesterification process.

When I looked at this process, I saw a modification that was so obvious that I’m frankly astonished that no one thought of it before I did.

Before I describe it, let’s first consider the role of the methoxide. Note that this schematic assumes the presence of water. This method is anhydrous, and the manner in which it modifies the process, and therefore the reactants, is discussed later:

If you look at this figure you will note that the base (NaOH in this case) does not appear as a product or reactant. That is, the reactants are triglyceride and methanol and the products are methyl esters and glycerin.

The base is written on top of the arrow which is, by convention, where catalysts appear in chemical equations. This is telling us that it participates in the reaction as an intermediate, but is not consumed.

This is the definition of a catalyst:

1. It lowers the activation energy of a reaction
2. It is not consumed. That is, it participates as an intermediate but is regenerated afterwards.

In other words, the fact that the NaOH doesn’t appear as a reactant tells us that the reaction will, in theory, proceed without it. In other words, it is telling us that the Free Energy change of the process is negative – in other words, it is a downhill process.

But the fact that it is thermodynamically favourable doesn’t mean much in real terms, as the kinetics of the process must also be taken into account. In other words, before it can proceed, the activation energy must be overcome. That is, enough energy must be supplied to the reactants to allow the energy hump to be overcome, and the reaction to proceed downhill. If this is not supplied, no matter how long you mix the reactants, the reaction will not proceed until all your methanol evaporates.

So, we either supply energy to the system, or add a catalyst to lower the activation energy (or both).

The Dr Pepper method is constrained in the amount of catalyst it can add because of the danger of promoting saponification. So the mixture needs to be heated (to 55 deg C).

When I looked at this method there was an obvious modification to the method that would kill two birds with one stone. This modification was so obvious that I am still scratching my head as to why no one thought of it before me.

Put simply, we dry the methoxide solution. Firstly, it removes water from the equation (literally) thereby eliminating the interfering saponification reaction. Secondly, it pulls the equilibrium to the right (Le Chateleir’s principle), thus generating a far higher concentration of catalyst.

So with a higher concentration of catalyst, we lower the activation energy, allowing the reaction to proceed at room temperature, and we don’t need to worry about the saponification process.

The chemical of choice to dry any alcohol is quicklime (calcium oxide):

Equation 3:    CaO + H₂O = Ca(OH)₂

If we now add Equation 1 and 3 together we get:

Equation 4     KOH + MeOH + CaO = K⁺MeO^– + Ca(OH)₂

When I first developed this method I was living in Melbourne, and had no trouble buying quicklime in bags from the cement factory in Lilydale. When I moved to Perth, however, I found it was not quite so easy to get – and this mirrors feedback I have received from people all over the world.

So I had to find an alternative drying agent, and it’s cement – just the cheap, $6 per bag General Purpose Grey Cement from the hardware store. Note – it’s the cement powder, not the premix concrete containing sand and aggregate.

So then all you do is add the cement to the methoxide solution, allow it to settle, and then it’s right to use. Note – the methoxide solution is unstable as its highly alkaline nature means that it will suck CO2 out of the air at a rapid rate and convert it to CaCO3. So get yourself organised so that you make your biodiesel batch two days after making the methoxide solution (two days is how long it takes for the fines to settle).

1.2: Biodiesel Formation (transesterification):

The potassium methoxide reacts with the triglyceride as follows:

Transesterification reaction:

Eq 5: C6O6H5R3 + 3KMeO -> C3O3H5K3 (potassium salt of glycerol) + 3(MeOCOR)

And this is the final reaction. As the water has been removed, the KOH is not regenerated, and the final state of the glycerol is the potassium salt, which is much thinner than the glycerol and therefore more easily disposed of.

1.3: Formation of soap and Glycerol

The chemistry of the glycerol phase is explained below (2.5.2)

Lets’ now consider the soap. When the highly alkaline methoxide is added to the WVO it will obviously first react with the Free Fatty Acids:

KMeO + RCOOH -> RCOOK (soap) + MeOH

In other words, the methoxide reacts with the FFA to form soap + methanol.

So what happens to the soap?

Soap is the alkaline salt of the Free Fatty Acid. It therefore acts as a surfactant. We want to get rid of it, however, as it will interfere with the water washing process. So we remove it simply by acidifying the water as part of the first wash.

This process protonates the soap: RCOOK + H+ = RCOOH + K+

This makes it insoluble in both phases. The result is that it precipitates out as a light brown, slightly foamy precipitate that sits between the phases. So after your first acid wash, you are draining off the water, and eventually you see this light brown gelatinous material coming out. These are what’s left of the soaps. Keep draining until you’re getting clear bio out, and then you can proceed to the water wash.

2. Manufacturing Process:

This describes how to manufacture a 1080L batch of biodiesel. You do not have to have read or understood the chemistry of the process. The process can be scaled up or down proportionately as required. Calculations included at the end.

2.1: Ingredients:

900L Waste vegetable oil
180L Methanol
18kg KOH (potassium hydroxide or caustic potash)
20kg General Purpose Grey Cement

2.2. Calculations:

Vol MeOH = volume of WVO x 0.2

Mass KOH (kg) = Vol MeOH (l) x 0.1

Mass Cement = 20kg per 180l methoxide solution. Amount of cement is not critical

To work backwards from the total volume of your processor (V):

Volume WVO required = V x 0.833

Volume MeOH = V x 0.166

Alternatively, the volume of methanol may be calculated from above if you know the WVO volume.

 

2.3 Equipment

1 x IBC (1000L)

5 x 200L open-top settling tanks. Each to have a drain valve at the lowest point, and one about 6 inches above it. You don’t necessarily need 5 clarifiers – it depends on the rate at which you use the fuel. I get away with just two

2.4 Manufacture of raw product

1. Set up an open top 200L plastic drum with a valve about 5 inches from the bottom. Position the drum in a well-ventilated area with no naked flames anywhere nearby, preferably near the open door of a garage. Put on long sleeves, gloves, and a repirator (although not strictly necessary if the area is well-ventilated).
2. Add 180L MeOH to the drum. Add 18kg KOH to the methanol – it doesn’t have to be stirred while you do it as it will not clump, although stirring will speed up the process (a shovel will do). The MeOH will get hot and may even boil – if it does step back and wait for the effervescence to die down. The heat helps the KOH dissolve and it will dissolve in a couple of minutes (but there may still be some undissolved impurities in the bottom).
3. Add the cement. Stir with the shovel for about 5 minutes, then leave it to settle for two days. Put a lid on the drum to minimise CO2 exposure and evaporation.
4. Add 900L WVO to IBC. Make sure there is no free-phase water present.
5. Add methoxide solution to the oil. I just do it manually by draining it into plastic water cans and tipping it in. You could use a small pump, but it’s not going to be easy to find a pump that will last long pumping highly alkaline methanol. After this step the methoxide solution will be sitting in a lightly coloured free phase on top of the oil.
6. Open the bottom valve, turn on the pool pump, and pump the mixture back up into the top of the IBC. I used 2 inch hose and fittings. Hold the hose out of the mixture at the top of the IBC so it cascades out of the house and into the free phase methoxide solution at the top of the IBC. This provides the shear required to initiate the reaction.
7. Within a couple of minutes, the free phase will disappear, and the liquid cascading out of the hose will begin to change colour from light murky brown to a dark chocolate brown. About this time you will smell the characteristic smell of the glycerol, and hear the pump change pitch as the viscosity of the solution changes.
8. 8. Once the reaction has commenced, insert the hose into the IBC. The temp of the mixture will increase by about 6 degrees over a period of 15 to 20 min.
9. Allow the reaction to proceed a for an hour and then stop the pump.

2.5 Waste Disposal

2.5.1 Cement Waste

After the methoxide solution has been decanted the cement remaining will still be wet, soaked with both methanol and the water that was generated by the nethoxide reaction. Leave it for at least a few days until it dries a little and then become semi rigid, and then it can be simply tipped out and discarded

2.5.2 Glycerol Waste

The glycerol that is generated by this method is very low viscosity and very low foaming.

Its low foaming is easy to explain – short chain alcohols are well-known as foam suppressants

The low viscosity is a little less obvious to explain, but the answer is simply that the waste glycerol is not glycerol at all, but its potassium salt. In the absence of hydrogen bonding, therefore, it is very thin.

The result is a glycerol phase that is essentially as thin as water and can easily be discarded down the sink (see videos).

Here is the stoichiometry:

C6H5O6R3 + 3KMeO = 3MeO2CR + K3C3H5O3

Note that “R” is shorthand for the carbon chain of unspecified length to the right of the ester linkage.

Note that in the past I have made the mistake of letting the glycerol phase sit for a while until it thickens. I’d always assumed that its thinness was due to unpartitioned biodiesel and methanol, but a quantitative test with a beaker revealed this not to be the case. Upon sitting in an open 1L beaker over several days, there was no significant change in volume (due to MeOH evaporation) or extra biodiesel forming on top.

Here’s why – all that was happening was that the potassium salt of the glycerol was sucking up water from the atmosphere:

K3C3H5O3 + 3H2O = C3H8O3 + 3KOH

But, of course, now I just discard it immediately

3.0 Polishing of Raw Product

3.1: Removal of residual glycerol and methanol:

The raw product will settle into two layers – the lighter brown biodiesel on top and the heavier, thick black syrup that settles out at the bottom.

Wait 24 hours and then transfer the raw product to the clarification tanks. To a close approximation the first drum will be entirely filled with glycerol, and then as you switch to the second drum the raw biodiesel should start coming through (see videos).

 Immediately after manufacture, residual amounts of methanol remain in the biodiesel, and this retains residual amounts of glycerine in solution. As methanol is volatile, it will eventually evaporate, thus precipitating out the last of the glycerol.

This process takes too long, however, and has the added problem that it is difficult to know when the product is ready for use, as it clear at all stages.

Thus we wash it with water.

3.1.1 Acid Wash

The first wash must be acidic, to neutralise the soaps and remove them from interfering with the clarification process. Note – although this method does not produce any soap from the biodiesel manufacture, some soap content is inevitable because of the presence of FFAs in the WVO – soaps are merely the alkaline salts of FFAs.

By acidifying the first wash, the soaps are protonated and thus lose their surfactant properties. This makes them insoluble in both phases and they settle out as a light brown fluffy film on top of the water and below the bio.

When the glycerol is removed you’ll have about 20% of your total volume available. Add water to around 10-15% of the capacity (you don’t need to fill it completely). So in my case, with a 1080L batch I have about 200L capacity once I drain the glycerol. For this step I add about 120L of water.

Add sufficient acid to acidify the water. You can use any acid for this. I add 4-5 L of Hydrochloric Acid to the 120L of water. You’ll know when it’s acidic enough when the water phase turns from a creamy white to a murky orange/white. It’s easy to test the pH with some paper strips off EBay. Acidic is below 7 and alkaline is above 7. I generally get a pH of between 5 and 6. I’ll be posting a video of this process at some stage.

Let it settle for a day, then drain and discard.

3.1.2 Clarification

After this, the biodiesel phase will be cloudy. That is, it’s the brown colour that you expect, but it’s not clear – you can’t see through it. You can let this settle in your settling drums until it’s clear, but the process can be accelerated by pumping air through it. What the evaporation stage does (with or without air bubbling) is to remove the last vestiges of soap from it. This will result in a small amount of fluffy brown soap residue at the interface.

A second water wash is unnecessary. A test on a clarified sample (using a second water wash) shows a pH of about 6.5 in the water. Thus, all the acid has been removed. Once it’s clear it’s right to use.

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