Reaction Temperature/Conversion

[dgs]

There is a rough 'Rule of thumb' concerning reaction times versus reaction temperature with our equilibrium transesterification reaction.

Basically it means that for every 10degs C below our ideal reaction temperature (50 to 60 degs?) the reaction takes double the time.

This 'rule of thumb" is not a principle and is a very approximate guideline. In fact it is so 'approximate' it hardly exists at all!

I say this simply because of personal observations over the years, which is why I mostly process S1 at ambient temperatures.

A batch that I have been processing for the heating over the weekend has made me report my findings.

After S1 a 10/90 showed 2.3mls. I added 'roughly' the correct chemicals for S2 and mixed for 1 hour at ambient temperature which was 6degs C. 10/90 was 0.2mls. (more than good enough for the heating)

According to the rough rule of thumb at only 6 degs the process time would have been over 20 hours.

[Manfred]

I bet the reaction temperature wasn't 6'. At 55' when I add chemicals I usually see a 3' increase in temperature, then drops back when I suspect the bulk of the reaction has taken place. I have tried ambient processing as there has been papers written about the benefits of it but the glycerol prewash refuses to drop. So I can't see the point of ambient processing seing as I raise the temperature to demeth. Get it to 60' let the process keep it there then you are almost ready for a demeth. If not using a Glycerol prewash then start cool and let the reaction lift the temperature for you before switching on the heater, but what we save in one hand we loose in the other. Out of interest what did the temperature reach during the main reaction.
 I tried an experiment only last week. 900ml of oil and 100ml of NaOH glycerol. Shook it up and left it in my shed. A week later the glycerol level was still at the 400ml mark. I did this because of having to use heat to allow the Glycerol wash to drop before adding any chemicals when trying an ambient process.
 In one paper I read they said that less soaps were made at low processing temperatures but on another paper you had to have higher temperatures to fully react the free glycerides.

[dgs]

Hi Manfred,

It was at 6degs after the methoxide addition. Fri night was zero here. This processor that I use for heating oil is in the hay barn, so nearly as cold as outside. Before methoxide addition I rekon it was  about 3 degs.

Oil for s1 was slightly heated with the M67 (in the adjacent tank) so I would estimate it was done at about 30 degs.

I take what you say about keeping the processor ,warm throughout all the stages, so making the heating more efficient. I glyc wash my oil in the M67 tank, so don't use any electric for this stage.

As the years have passed I have altered my process to try and make it more efficient.( but not as regards my labour)  It takes me around 1 week to now produce a batch.

S1 is done at ambient and it is left 2 days for the glyc to drop (as you say it takes much longer the cooler it is)
S2 is done at about 40 degs, with an over addition factor for chemicals to minimise the production of the intermediate triglycerides.

[Manfred]

That's where you have a large advantage over me. I only have the one vessel to react in and with NaOH in this temperature I can block a pipe before the evenings out never mind leaving it overnight. I do have a bottom valve but it's the 2" or so before it that sets.
 I do think their is advantages in ambient processing but as you say it's time expensive and really only doable with potassium. As for reaction times as you are finding no great difference.