Prewash questions

[thewormman]

Got some questions on prewash

I understand it's done in the processor once fully converted and at least half the drained glyc is reintroduced before the 5-7% water so is there no demething done at all?

Is it possible to drain first and second stage glyc demeth THEN add the glyc and water back in or does all the meth need to be there?

What does the prewash take out? Soap, catalyst?
What is it about the glyc that does this?
Is it that they are more miscible with glyc compared to bio?

Why does it help stop HMPEs?

What are your thoughts?

[julianf]

HCII did some tests some time back (or so i recall) and the general result was that the pre-wash reduced the soap (settling time?)

Im not sure that many people do it now?  So long as the fuel is fully demethed, then the soaps precipitate out anyhow.

I think another factor in the reduced popularity is the introduction of glycerol prewashing (at the start of the process) and people liking dry glycerol for that.

[Julian]

I still do a 7% pre-water wash during the summer when I don't use the glycerin for glogs.  I don't glycerin wash ... too much hassle with my set up, but I do put a lot of effort in to filtering and drying my feedstock.

My process with a 7% pre-wash is to return the first stage glycerin after a 3/27 pass and then demeth as completely as possible.  After demeth I do the 7% pre-wash, followed by a titrated acid wash and a couple of water washes still in the processor.  I then heat to about 80°C without the pumps and drain a large percentage of the water.  That's followed by a short period running the condenser with additional heat.

Most times the bio comes out clear, but I usually bubble over night while it's still hot.

[willbuild]

does that mean that you do the 7% pre wash after removing the glycol that has been demethed?therefore being able to use the glycol for glogs?

[Julian]

Pre-wash, sort of by definition, is always done in conjunction with the glycerin.  Otherwise it's just a pump wash!

Not quite sure what I'll do when I need the glycerin for glogs, I was previously mist washing in a separate tank.  Thanks for raising the question.  I'll have to have a think which way to go, as I'll need more glogs very soon.

I'll probably drop the 7% pre-wash and rely on the titrated acid wash to prevent emulsions. I'm certainly not going back to mist washing ... right pain in the backside (ducks and waits for incoming).

[Head Womble]

You can have the best of both worlds, keep the gly from the first stage for a prewash on the next batch,
then do a 5% post reaction prewash with just the second stage gly pressent, this can be done after WBD if you wish (although this may produce HMPE's).

But I personally I'd keep all the gly for the next prewash and not worry about the post reaction prewash,
this way you'll produce less soap so settling will be easy anyway.

[Head Womble]

I'll probably drop the 7% pre-wash and rely on the titrated acid wash to prevent emulsions. I'm certainly not going back to mist washing ... right pain in the backside (ducks and waits for incoming).

I've just gone back to mist washing, but do an acid wash before hand, this way I have no worries about emulsions.
To speed things up I also bubble while washing.

Ok so I've only done one batch like this so far, but it worked quite well and was soap free in 5hrs.

[thewormman]

Thanks for your thoughts 

I've just gone back to mist washing, but do an acid wash before hand, this way I have no worries about emulsions.
To speed things up I also bubble while washing.

Ok so I've only done one batch like this so far, but it worked quite well and was soap free in 5hrs.

What I have been doing is full conversion, drain glyc, demeth, acid wash with vinegar and 20l of water 1 hour then a 20L pumped water wash for a couple of hours. This seems to take soap down to about 25 PPM. I then pump another 20l overnight which seems to take out all that brown sediment stuff as well. It is all pumped through a static mixer which doesn't introduce air and helps to avoid oxidation (possibly)

I was asking about prewash as I usually have about 30 litres of glyc from my 180 batch and only use 20l for treating my WVO so wondered if I could use the other 10 in a productive way

[thewormman]

Just in case you wonder what a static mixer is

http://en.m.wikipedia.org/wiki/Static_mixer

I made mine in a 22mm copper pipe quite easy really I took pics when I made it if anyone is interested

[nigelb]

The prewash is as important and popular now with water washers than ever before. As some have eluded, I reintroduce a small amount of stage one glyc to the raw bio prior to introducing 7% water. This prevents any chance of an emulsion occuring and leaves a good amount of dry glyc for a glyc wash on the next batch. Others use different, and I dare say, equally effective methods to acheive the same results.

The benefits of a 7% water prewash are huge. The soap reductions are massive. (Documented on this forum in a soap testing thread somewhere)

I don't think that there is a reduction in popularity....just a tweaking of how, when and why the water is intruduced.

[willbuild]

makes sense