Two stage methanol starvation process
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This is a variation on the two stage process with no titration. We recommend that only experienced biodiesel brewers follow this process, as it is quite technical and requires a good understanding of the chemical process taking place.
The process is as follows:
- first stage reaction stalls due to lack of methanol, with the majority of the oil converted
- first stage glycerol is drained, and does not need the methanol recovered from it, as all the methanol has been consumed by the reaction
- second stage reaction uses excess methanol to convert the small amount of remaining oil
- second stage glycerol is low in volume, so only a tiny fraction of the remaining excess methanol is lost when it is drained
- demething/methanol recovery on the remaining biodiesel is quicker and less energy intense than whole batch demeth
The biodiesel reaction will need an average of 12.5% methanol (this varies with different types of wvo feedstock from about 11% -16%) But we take 12.5% as our average. This is referred to as the stoichiometric ratio.
By limiting the first stage reaction to 11-12% methanol by oil volume, the reaction is guaranteed to stall due to lack of methanol. This is on the condition that there is at least enough catalyst present to complete the reaction (find this by titration, or if your oil is nice and dry, by using excess catalyst).
The second stage reaction can use an additional 4% methanol, for a total of 16%. When the final biodiesel has the methanol recovered from it, total methanol use can easily be brought down to 14%.
When first stage glycerol is drained, ALL the catalyst goes with it. Do a 10/90 to determine how much unconverted oil there is and use the base amount per unconverted litre for the second stage.