Biopowered - vegetable oil and biodiesel forum
Biodiesel => Chemistry and process => Topic started by: Julian on May 25, 2018, 09:03:18 PM
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I tried a little experiment today. Processing a batch as normal, I took a sample just after the introduction of the methoxide on the first stage … you know, that gloopy mustard coloured stage that you pray will go away, and left it sitting in a sealed jar whilst the rest of the batch processed.
I left the batch processing for longer than normal (in all honesty I forgot about it), but 4 hr later I came back and the sample sitting in the jar looked, for all intents and purposes, like the sample I took from the processor. I did a 3/27 test on both with the following results ... "mixed" sample 0.8ml dropout and processed sample 0.52ml drop out.
Given that I'm processing with Frankinpump I'm thinking that the energy used to process for all that time (perhaps a little excessive in this case) wasn't worth the diferance in conversion.
Maybe less processing and three stages with a small additional amount of chemicals would be more economical. Or perhaps periodic mixing ... use the pump to draw in the chemicals and then run for 2 or 3 mins every hour ... this could quite easily be acheived on a plug in timer.
The batch was made with good quality glycerin washed oil starting at ambient temperature and, although Frankingpump took the processer up to 57°C, the "mixed" sample remained at 22°C.
I'll try and do some more tests using this idea and post up, but it would be great if others could have a play and see if they concur with my initial findings.
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The gloopy mustard stage you mention is when the mix is immicible due to oil and methanol being present (ie not enough biodiesel produced to act as a cosolvent) so it's a suprise that both results are similar.
However as you did a 3/27 both results show a large unconverted percentage. Mixed sample 26.7% unconverted and processed sample 17.3%
Did you use any heat at all Julian as the increase of 35degs from just the pump is high even for a 4 hour process.
Multistage processing certainly reduces chemical requirements, a few years ago I did a 7 stage on glyc washed oil and used only 3.5gms/litre KOH to get a clear 10/90
Interesting stuff, let us know how you go on.
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Dave, the heating effect of the pump will be proportional to the work it has to do. I have a small throat in my venturi and the pump runs around 2 bar on converted bio, so that temperature rise is not unusual for my system.
The second stage of the batch went fine resulting in a clear 3/27.
Had a look at a couple of plugin timers I've got and both are rated at 2 amps on an inductive load, so no good for Frankinpump, but I'll try manually running it for brief periods on the next batch.
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Use the timer to switch a SSR, that'll get around the amp rating.
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Yup, that or a relay.
I was just looking for a quick lash-up as an experiment initially.
On my super-doper £4.46 Ebay watch I have a timer, so to try out the idea I'll set that and switch the pump manually.
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Just a few thoughts here Julian, so hang in with me.
I suppose what you are saying is that when you have had so much conversion by only mixing for a short amount of time then the energy input (from mixing and heating) is disproportionally high to achieve a higher conversion when processing for an hour or so.
This all stems from the reaction being equilibrium. The only way I can see a process reaching completion in (say) 5 to 10 mins or so is to increase the chemicals. Doing this would leave the process open to possibly producing vast amounts of soap.
I remember several years ago doing 10/90's every 2 mins or so after the methoxide was added and I was surprised at the amount of conversion after just a few mins.
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Yes, that sums it up pretty well.
I've always suspected the bulk of the conversion happens right at the start of proceeding but have never investigated. Thoughts were to process over several hours (could even be days) using my normal 2 stage process, but only run Frankinpum say 5 mins in every hour.
Are you saying the process has to have vigorous and prolonged agitation to take it to completion? I'm in no shape or form a chemist, but I'd have thought the components only need to come into contact to react which periodic "mixing" would achieve.
Pub quiz tonight so seeing my mate with a PhD in chemistry. I'll see if he has any views.
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Anyone conducted any experiments on the effect of introducing methoxide into the dry oil at different rates?
I don't have any figures but I have a strong suspicion that dosing very slowly (15 litres over 30 mins) yields a significantly better reaction.
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I don't think your suspicions are correct neisel. Just look at the principal of the AAF method where all the methoxide has the oil added to it. My methoxide is added in about 15 seconds, I used to add it slowly but found there was no point.
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I don't think your suspicions are correct neisel. Just look at the principal of the AAF method where all the methoxide has the oil added to it. My methoxide is added in about 15 seconds, I used to add it slowly but found there was no point.
Yeah, I second that, Dave. JRL championed doing the reverse, hence the AAF method.
And whilst it may pain us to say .... "he ain't not normally not wrong".
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As I understand it the AAF method involves introducing oil to methoxide, not MO to oil.
I tried dumping 19 litres of MO into 145 litres of dry, hot oil once & had a very poor reaction. My last batch converted 145 litres of oil using just 19L of methanol (15 + 4) with 750 grms of KOH on the first stage & 140 grms of NaOH on the second, all introduced very slowly.
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Well, I asked the question and the answer was "That's chemical engineering not chemistry", so no definitive answer I'm afraid. But after perusing him, slow reactions in the lab are always stirred, and vigorous mixing is not necessary.
Best way is probably to try it and see what the results are.
Re speed of introduction, when I built my plant the accepted wisdom was to introduce the metoxide slowly, I've never deviated from that method and have found it quite satisfactory. It makes sense to me as the methoxide stream will be better mixed with the oil. At the end of the day I recon there probably isn't much difference between the two methods.
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One of my many processors that I tried over the years was a 400 litre plastic tank (the one with the dished bottom instead of a proper cone) it was fitted with one of those 110lpm yellow and black pumps (closed impeller)
I sometimes had to help the pump by running glycerol out of the bottom tap and pouring it back into the top. The methoxide was introduced over a 20 min period. I used to need 12 to 13 gms/litre KOH for full conversion with this set up. What a poor combination of tank and pump it was.
I then went small, 120 litre tank fitted with a puisi panther and 3/8 eductor; what a difference! Normal amounts of KOH needed, methoxide poured into the top (not to be recommended) in less than 10 secs. Those panthers are powerful little things, this is the set up I used when I did my 3.5gm experiment.
The trouble with adding methoxide slowly is that the last few % of methoxide is added when most of the reaction is complete and as such the glycerol in the mix will try to absorb the methoxide before it can do its job. This is why multistage processing is much more efficient as regards chemicals.
If you have ever done a S2 with a considerable amount of S1 glycerol in the mix you will know what I mean, a very poor reaction.
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I needed to do a process today, so thought I would give Julians idea a go.
196 litres of glyc washed oil that showed a conversion of 15% ( 8.5mls dropout using 10/90 )
I added the methoxide ( 700gms K + 1350mls ASM in 22 litres of methanol) and used the pump to mix for 5 mins only. Temp was 25degs.
10/90 showed 1.5mls dropout.
1 hour later I started the pump for another 5 mins then did another 10/90 which showed 0.5mls dropout.
1 hour later i started the pump again, just for 5 mins as before, after this the dropout was 0.25mls.
1 hour later I repeated this procedure and the dropout was 0.05mls,
After another cycle I got a clear pass with the 10/90
No heat was added and after the 5 hours the temp had risen to 30degs simply due to the hot sun shining on the side of the tank.
Off topic I know but tomorrow I'll do a stage 2 on this batch using about 0.3gms K/litre simply to convert the residual mono's that I know will still be there. Then I know it will water wash well with no emulsified layer.
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Beat me to it … I loaded the oil for the next batch yesterday and I've yet to do the glycerine wash!
Must have saved a lot of electrickery. So if I've got it right 25 mins total processing, single stage giving a clear 3/27. I've never acheived that with continious processing over several hours!
An interesting comparison would be to process for 25mins and let it sit for 5 hrs.
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I've saved at least 35 mins at 1.5 KW's You do seem to have 'hit' on something here Julian, in that the process seems to be continuing at a certain rate without mixing.
I'm doing a small S2 at the moment and keep stopping the pump and letting it rest for a while. Of course these S2's I do after I sometimes get a pass after S1 (ideally I like 0.3 mls d/o after S1 ) are something of a 'black art' in that processing
the mono's to completion are a bit of a guess.
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Could we be heading back to the bucket and stick method everyone used to poo poo!
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Strange you should say that. I've recently taken to processing the bio for the c/heating in a cubie, after adding the methoxide I shake it 3 times in the first half hour, then just leave it.
I normally don't bother testing for conversion but a couple of weeks ago I did a 10/90 which showed only 0.4mls d/o, I was amazed.
Recipe is 15lts oil (not my best stuff) 150gms K and 250mls methanol. This time of year when we only use the boiler for hot water this method is so much easier than a 'proper' process.
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Ok, so started the glycerine wash and I thought I'd try the start, stop trick with the glycerine. A 2min run of the pump seems to produce a homogeneous mix, so I'll try using 2mins as a basis for the whole batch.
I have a much smaller processor that you, only 80ltr batches, so with the same pump it shouldn't need such a long run to mix to a similar degree.
Just thinking about the oil glycerine mix, both are quite viscous (this is being done with no heat, current processor temperature is 22°C) and so should separate more slowly and hence need less mixing. Only issue may be separating the two at such low temperatures … any experience of this?
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Answer my own question here ... the sample I took during the first mix has separated quite clearly, so I don't think draining the glycerine will be a problem.
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As I glyc prewash in the IBC it is difficult to judge the separation time by the glycerol level, but by the colour of the oil getting lighter I would say it takes several days.
When I've done a prewash in the processor at low temperature it takes 3 days to get most of the glyc out.
From the outside (pre wash) IBC the oil is pumped into a 400 litre tank near the processor. It can sit there 3 to 6 weeks before being processed. Even then there is a few litres of glyc that has dropped to the bottom.
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I tried this on my last batch a week ago and got similar results:
Glyc washed 170L batch, very little conversion afterwards. I used 1600ml ASM and 650g Koh in 20 liters meth.Temp at start was 50c.
After getting in the methoxide I mixed for 5mins, 10/90 showed 1.7ml dropout, good glyc separation in the sample jar. Did another 10/90 on the same sample after 40 mins and this was 1.5ml dropout
1 hour later mixed for 5mins and 10/90 showed 1.2ml dropout
1 hour later mixed for 5mins and 10/90 showed 1.0ml dropout
After another hour and a 5 mins mix there was 1.0ml dropout so no further conversion, probably down to the chemicals needing adjusting upwards.
Carried on with a normal 2nd stage.
Interesting seeing the conversion after such a short overall mixing time as I normally process stage 1 for 45-60 mins for a similar final dropout.
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I'd be interested to see the conversion %s if you were to reduce the dosage of chems by 25%. I suspect there'd be not much difference.
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So, bio production is rather slow here at the moment … I'm just finishing off the batch I started a month or so ago!
I used my normal methanol and catalyst volumes and mixed for 2 mins, five times on the hour and ran two stages (with only an 80 ltr processor combined with Frankinpump I figured that should be sufficient mixing).
The result was a perfectly clear 3/27, so it seems to work. I wonder if more gentle mixing, something like a bubbler would work, certianly less energy than Frankinpump, although I have had issues with bubbling air into oil adding water from atmospheric humidity.
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A bio friend from the next village tried this a few weeks ago but it didn't work for him. He does however use a 105 that he says is worn out. From memory after his 1st 5 min mix his dropout was 6.5mls. The next two hours showed something like 5mls then 4.5mls. He didn't go any further and mixed for 1 hour to get a 2.0 dropout.
Julian, don't you think the methanol loss would be a problem if using a bubbler. I don't think R/H would be an issue.
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Interesting posts. Couple of ideas here:
1. The next person to try this "quick mix, then settle" regime, could try this:
After the settles, drain off X% of the glyc, before the next mix. As it might favour the glyc/bio equilibrium in a good way?
I've no idea what X might be...
2. Are we 'over-pumping' things? Remember the original GL plans used a CH pump!
They fell from favour, possibly due to the low flow rate not working too well with venturis? (can't remember if there was any other reason).
With three way valves, a CH pump could be plumbed in, in parallel to our pump of choice, and take over the donkey work of keeping things ticking over.
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A bio friend from the next village tried this a few weeks ago but it didn't work for him. He does however use a 105 that he says is worn out. From memory after his 1st 5 min mix his dropout was 6.5mls. The next two hours showed something like 5mls then 4.5mls. He didn't go any further and mixed for 1 hour to get a 2.0 dropout.
Julian, don't you think the methanol loss would be a problem if using a bubbler. I don't think R/H would be an issue.
Just a gut feeling, but I recon you want to turn the batch over two or three times to get reasonable mixing … that was the thinking behind running Frankinpum for only two minutes. Perhaps with a TAM 105 and a higher volume processor he may want to try running it for longer.
Good point, I didn't think about methanol loss. On the standard GL design you could run the condenser to collect it, but that's just adding complications I guess.
I tried drying either oil or bio (too many years ago to remember) in the processor. I made a connection low down to which I fitted a sintered brass air silencer and blew air from a small compressor through the hot bio/oil. As far as I could tell it had no drying effect at all and I put it down to atmospheric humidity (could well be wrong) … UK humidity apparently ranges between 70% and 90%.
Interesting posts. Couple of ideas here:
1. The next person to try this "quick mix, then settle" regime, could try this:
After the settles, drain off X% of the glyc, before the next mix. As it might favour the glyc/bio equilibrium in a good way?
I've no idea what X might be...
2. Are we 'over-pumping' things? Remember the original GL plans used a CH pump!
They fell from favour, possibly due to the low flow rate not working too well with venturis? (can't remember if there was any other reason).
With three way valves, a CH pump could be plumbed in, in parallel to our pump of choice, and take over the donkey work of keeping things ticking over.
Certainly worth a try, but I've always wondered where the bulk of the unused chemicals ends up. If they're in the glycerine it may be counter productive.
Some time back I had thoughts on trying to collect glycerine during processing. My sample point is a short vertical leg off the mian circulation pipwork. During processing glycerine collects in the leg, so when I take a sample the first slug is always settled glicerine ... thoughts were to have a drip feed off the leg, but not knowing where the chemicals were I never bothered trying.
At least with what you suggest you can lob the glycerine back into the mix if you don't get a good enough conversion.
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Interesting posts. Couple of ideas here:
1. The next person to try this "quick mix, then settle" regime, could try this:
After the settles, drain off X% of the glyc, before the next mix. As it might favour the glyc/bio equilibrium in a good way?
I've no idea what X might be...
IMB tried this some years ago and reported his results on infopop. Basically it didn't work. The very thing that hinders the reaction in the final stages ie glycerol is the medium that contains most of the Methanol and catalyst. It needs to stay in the mix until an equibrilium is reached.
Some years ago I did a process for some c/heating bio. It was mid winter and I processed at ambient which from memory was no more than 10degs C. Just as a test I heated it the next day and re-mixed with it's glycerol which I hadn't drained. To my suprise I got no further conversion (was about 10% unreacted)
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Just to add to this … I've tried leaving this batch circa 24hrs between two minute mixes on the last knockings of the second stage and the 3/27 test is showing an improvement each time.
Going to try both stages this way on the next batch. I'm starting to think that not continuously pounding the glycerine into the bio may be a distinct benefit.
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I gave this method another go a few days ago (one hour between 5min mixes)
Dropout results were; 1.0mls 0.5mls 0.3mls 0.1mls I then left it and carried on with S2 the next day.
I've held a cubie back from the water washing stage to try to dry at ambient with dried air from the turbo dryer. I'll post the results on the other thread.
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Can't believe it was a year ago that I started this topic. Returning to it, it looks like Dave had already looked at what I've been looking at on the last batch.
So, I've had it in my head for some years that the bulk of the conversion takes place when the methoxide is first introduced so I did a 3/27 test after the initial mix. Result was 0.7ml dropout. I usually do five mixes of around two minutes each, often over a period of days (depending on what's convenient for me) and did another 3/27 after the fifth mix. The result was exactly the same.
I ran the second stage and again tested after the initial mix and got a clear 3/27. I'm now wondering if multiple mixes are even necessary. Dave's results in the last post indicate that perhaps they are, but on the next batch I'm going to try just one mix on stage one and if the 3/27 test looks promising, go straight to stage two and test again.
I should add that the current oil is of good quality and glycerine washed. Both washing and mixing were done at ambient … currently circa 22°C. I'm using Frankinpump running against a new design of venturi ("design" is perhaps a misleading term!) which I think creates considerable turbulence and which I'll post more on when I can find some fittings to photograph.
If I get similar results on the next batch, I'll post up the details.
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Now that is an interesting read. Ambient processing and minimal mixing. I'm a couple of weeks away from my next brew.....guess what i'm going to do?
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The only issue I have with processing at ambient is the glyc drop out & separation after glyc washing. It takes too long & never looks (I have a glass panel in my processor) like the clean, sharp line of separation I get at >40 degrees.
I glyc wash twice, once with the stuff I used one time on the previous batch & once with the 'virgin' glyc made in the previous batch. At >40 it all drops out in an hour.
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Now that is an interesting read. Ambient processing and minimal mixing. I'm a couple of weeks away from my next brew.....guess what i'm going to do?
Nige, you probably know, but the ambient processing was Daves idea, not mine.
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The only issue I have with processing at ambient is the glyc drop out & separation after glyc washing. It takes too long & never looks (I have a glass panel in my processor) like the clean, sharp line of separation I get at >40 degrees.
I glyc wash twice, once with the stuff I used one time on the previous batch & once with the 'virgin' glyc made in the previous batch. At >40 it all drops out in an hour.
Never really seems to be a problem, but then I'm never in a rush to process these days. If it's done at ambient you're not trying to do things before the batch cools and with intermittent mixing you can leave the batch half way through for several days if needed.
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There is definitely something in this intermittent mixing. When I mix some for the central heating in a cubie, I mix it by shaking for no longer than 10 seconds and do that 3 times in the 1st half hour.
It then gets left for 4 days or so. This is all done outside and so in mid Winter the temp can be down to zero-ish.
When I do a 10/90 on the bio (just to see as the conversion doesn't really matter) you wouldn't know the difference if it had been pump mixed at temp for 1 hour.
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Just in the middle of the next batch.
i did a glycerine wash but much of the glycerine seemed to be retained in the oil. I ran stage one and very little glycerine dropped, so I gave it a second mix and then a 3/27 test and got a 1ml drop out. I drained the little glycerine that had dropped and ran stage two, just one mix. After a day or so to drop a very small amount of glycerine I did a 3/27 test and got a clear pass.
I'm struggling to believe this result but a pass is a pass in my books so I'll leave it to settle some more and start washing.
I'll try again on the next batch which hopefully will behave more normally!
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Does the intermittent mixing work with glyc washing too?
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I usually mix once with glycerine and then only for a brief period.
Using Frankinpump I think it has the capability of mixing so thoroughly that the glycerine tends to stay in suspension. I think that's what happened on the last batch.
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I did a second stage at 10C last week. Just sucked in the Meth for stage 2 and left it. This weekend, perfect pass!
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I usually mix once with glycerine and then only for a brief period.
Using Frankinpump I think it has the capability of mixing so thoroughly that the glycerine tends to stay in suspension. I think that's what happened on the last batch.
I found the same with my Frankenpump.
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I did a second stage at 10C last week. Just sucked in the Meth for stage 2 and left it. This weekend, perfect pass!
bet you don't want to calculate how much elec you could have saved after all these years brewing.