----- Original Message -----
From: "t_watchornnz" <[EMAIL PROTECTED]>
Sent: Wednesday, February 27, 2002 5:30 PM
Subject: [biofuel] Re: Biodiesel,Glycerine pretreat
Trevor, please excuse delay in replying>
> I have gone on to process upper layer (eg top 2 layers mixed!)
> Titration of oil was 0.6 mil. I normally get 1.8 to 2.5 mil form my
> one supply.
Titration of upper layer would suggest that there was not enough residual
caustic in glycerine to neutralise FFA in oil. Therefore not enough excess
for transesterification.
> I normally use about 17% methanol.
17% methanol wouldn't leave much methanol in the glycerine.
Would hardly be worth the trouble of recovery.
Rate of conversion of WVO would also be low, generally agreed that 20 to 25%
methanol required for high rate of conversion WVO to ester.
At that use rate methanol recovery becomes worthwhile.
Options 1/. Distillation
2/. Mix fresh WVO with glycerine
3/. Add glycerine to next batch, use lower % of methanol.
4/. Can anyone suggest another method?
Whilst option 1 is well established options 2 and 3 are as far as I know
experimental.
2 would require higher than normal levels of NaOH so that enough was carried
over in the glycerine to both neutralise the FFA in the WVO and catalyse the
reaction. This in turn produces its own problems.
The mixture of WAF and glycerine did not turn out as planed.
Had hoped that upon cooling thjree layers would form. BD,solid unreacted WAF
and glycerine. Result was two levels, semi-liquid fat above glyverine.
>So tried 3 test batches of 250
> mils. Used 0.5 to 0.6 grams of caustic in all batches. Mixed in
> blender for 10 minutes at 30 to 40 deg C.
> Test 1, 20 mil (8%) methanol
> Test 2, 25 mil (10%) methanol
> Test 3, 32 mil (13%) methanol
Have not had much success with such low levels of methanol,they are all
below the ammount required by the reaction and an excess is usually required
to push the reaction towards completion.
With the variable and poor quality feedstocks that I use experienced a lot
of failures before moving up from 15% methanol.
> In all the stuff I have read re-titration of oil it says to add 3
> to 3.5 grams to the resulting mils and use this as your grams per
> litre. With test batches I find I only need to add 1.4 grams to
> titration result to give good result. Have double checked my caustic
> solution and method and think everything is correct. I this a common
> result??
With good quality oil the result may appear satisfactory but I would suspect
that the reaction has not gone to completion without the 3.5g to act as
catalyst.
A fair guide would be the ammount of glycerine. Its volume should
approximate the ammount of methanol used (given that enough methanol was
used to ensure complete reaction).
With well used WVO/WAF I find that more than the titrated ammount of NaOH is
required for satisfactory reaction/stability of product.
Look forward to reading further results,
Paul Gobert.
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