Two stage process with no titration
Introduction
Many experienced brewers will have tried to push a reluctant single stage reaction to 100% completion after a failed 3/27 test by adding more Methanol and catalyst into the mix. However, often the calculated amount of catalyst is insufficient, and the mix just seems to absorb it without much extra conversion taking place. Ultimately too much catalyst may be added, producing the dreaded jelly/soap mix. These problems can be caused by not dewatering your feedstock fully, poor titration technique, a mixture of these 2 or other unknowen things in our oil.
A non titration two stage process avoids non conversion scenarios as any unknown factors are normally taken care of by the 1st stage. by making your 2nd stage methoxide based on the test results after the 1st stage all variables are removed and yields excellent conversion of the source oil because it accounts for both the reversible nature of the reaction, and the water produced by the reaction & any unknowen contaminants. If your oil is very poor you may need to go to a 3rd stage or even a 4th, what you are doing is a softly softly approch instead of hitting the oil with a large load of catalyst and risking a batch of jelly.
Note this process is not a reason to use known wet oil, try to dry as much as possible as you normally would.
The process
- 1 do not Titrate
- 2 make your 1st stage methoxide solution with base amounts 5g/l for Naoh or 7g/l Koh x full batch size + 80% of methanol
- 3 Put this 1st stage Methoxide mix into the processor at normal reaction temperature, and mix for an hour
- 4 Stand for 20 minutes and drain off the Glycerol into a clean container, and seal
- 5 Do your 3/27 or 5/45 test and measure the amount of dropot.
- 6 Determin the amount of unprocessed oil in your batch from the dropout
- 7 Make up the 2nd stage methoxide by mixing "20% batch size methanol" with "unprocessed oil volume x base" catalyst
- 8 Now mix as normal for second stage.
- 9 Now do a second 3/27 test to check conversion - it should give a clear pass. if not go to 5 above and repeat but with minimal methanol.
If your process involves Whole Batch Demeth or Water Prewash, the stage one Glycerol should be returned to the mix first. Although you may be concerned that NaOH Glycerol might solidify, the Methanol present should keep it liquid and it should stay warm for some time.
Otherwise, stand for a further 20 minutes, and drain off any further Glycerol present, leaving just biodiesel ready to settle or filter.
Why 2 stage reactions work
The conversion process is a balanced, reversible reaction that sits somewhere between vegetable oil + Methanol and Biodiesel + Glycerol. We push it to the Biodiesel + Glycerol side by using an excess of Methanol, but as the Methanol is consumed and more Glycerol is present, it becomes harder to get that last little bit of vegetable oil to tip over to Biodiesel. This is because of the Glycerol present in the mix, constantly trying to push the reaction back the other way, despite the excess Methanol. It's a bit like working against a spring.
By stopping mid-reaction and removing the excess Glycerol, the resistance to converting the last bit of vegetable oil is removed, and the reaction completes easily.
Additionally, the biodiesel process itself produces water which consumes some of the catalyst, also impeding the conversion from completing. Removing the Glycerol will take the majority of water away with it to the benefit of the second stage.
