Arse about face

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The 'AAF' process, jokingly refered to as 'arse-about-face' on the various biodiesel forums is the method whereby the methanol already mixed with the catalyst, NaOH or KOH is pumped into the empty reactor before the oil to be reacted, rather than the more traditional method of having the oil in the reactor then adding the methoxide (methanol and catalyst mixture) on top.

With some designs of machinery this is not easy to achieve, as a separate holding or drying vessel is needed for the oil, as well as the actual processor/reactor vessel.

In particular, the GL type system relies on the pumping of fluid to be able to draw in the methoxide, so to achieve this, the GL type system must have some oil in the system to operate and draw in the methoxide.

The advantage of this process is that conversion from oil into methyl-esters (biodiesel) is slightly faster and can be more complete.