Water washing titrated acid method

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This is a processing method which allows the biodiesel to be water washed and dried within the processor, therefore it is ideal for those with limited space who may not have the room for separate tanks needed for conventional water washing. To work effectively there needs to be a minimal amount of soap in the biodiesel prior to washing. As such, it is best used with the two stage process with no titration

Introduction to the method

In all biodiesel processes, there is a need to remove the soaps, residual processing chemicals, residual glycerol and any other impurities prior to use. This is normally achieved by either washing them out with water in the water washing process or by driving off the methanol which may or not be recovered and allowing the other products to settle out.

Both of these methods take time and extra space.

The idea of this method is to safely water wash the biodiesel whilst still in the processor and immediately after draining the glycerol, with no risk of creating an emulsion.

The dreaded emulsion or 'Chicken Soup' is created when water and biodiesel mix in the presence of soap - this is, after all, why soap is used to wash oils and greases away with water. Clearly, if we intend to mix water with hundreds of litres of biodiesel and mix vigorously with a pump then the soaps need to be removed, or turned into something else, first.

Once the soaps are gone, the biodiesel can safely be washed and the impurities drained out. However, the biodiesel will still be wet and will need to be dried before use.

The process steps

Producing the biodiesel

The first step is to process the biodiesel by your chosen method. Whilst not essential, the two stage process with no titration method is recommended to minimise the amount of soap to be dealt with. Once as fully converted as possible, drain off all the glycerol. The fuel is now ready for the second step.

Determining the amount of acid needed

Bromothymol blue colours - Wikipedia

It is to carry out a titration of the fuel to ascertain the amount of acid needed to neutralise the residual chemicals and convert any soaps to free fatty acids. The titration fluid needs to be a known concentration of the acid you intend to use for this process.

An indicator needs to be used which will clearly show and basic to acidic change around the neutral point. A suitable indicator which works very well is BromoThymol Blue, the colours of which are shown on the right in acidic (yellow), neutral (green) and basic (blue) conditions.

Removing the soaps

Sample during first wash/sulphuric-Julian

The third step is to wash the biodiesel with the diluted acid in the processor by mixing with the pump.

If using a weak acid like vinegar then this can be used neat or slightly diluted. If using a strong acid such as concentrated sulphuric acid then this need to be diluted with a substantial amount of water. If doing this, it is VITAL that the concentrated acid is slowly added to the water. If water is added to concentrated Sulphuric Acid, the strongly exothermic reaction will cause the mixture to boil instantly and spit boiling acid out of the container with potentially devastating results.

After mixing, the processor is left to settle and then the acid/water/impurities mixture is drawn off and discarded.

It is important to take a sample immidiately before switching off the processor. This will give an idea when the mixture has settled and also confirmation that a clean split has occurred.

Water washing

First four washes/sulphuric-Julian

The fourth step is to carry out one or more water washes using clean water for short mix periods. This is done until the water comes out clean after settling. The water washes do not need to be mixed for long and will settle very quickly.

The picture on the right shows the progressively improving clarity of the water after each wash.

Drying the biodiesel

The fifth and final step is to dry the biodiesel, after which it is ready for use.

An example batch with calculations

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Vinegar

Ok this is the method i used today,we tried universal indicator so we could tell when it changed to pH 7 as we wanted it neutral,we also tried methanol instead of IPA because the IPA we had was acidic

280 LITRE BATCH

(1) Titrate bio

(2) Titration fluid: white vinegar

(3) 25 ml of Methanol and some Universal Indicator,added 10 ml of bio shake, Green to Blue

(4) Then add the titration fluid in drips until the colour changes to green/yellow

(5) Multiply the result by the batch size to get the amount of acid needed e.g. if 0.1ml vinegar used to change colour to neutralize 10ml bio, 10ml vinegar neutralizes 1L 10x280 = 2.8L vinegar

(6) Add to 30 litres of water and mix with the bio for 25 minutes

(7) Take sample for reference

Sample taken immediately after the first wash/vinegar-KH

First wash starting to settle/vinegar-KH

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