We produced biodiesel from soy oil with 0.9% FFA. Our process is simple tranesterification with methanol and sodium methylate. Once biodiesel is produced we found the Acid number to be 1.5 mg KOH/g. So its not meeting the ASTM standard along with the cetane number and cold soak filterability test.
Can anybody tell what could be the possible reason for the increase in Acid number? As we are not adding any acid during the water wash process.
I've seen this before. That time, the FFA had to be neutralized prior transesterification with sodium methylate before it would pass for AN.
A dry wash might fix your current product. Biodiesel Magazine online says water in biodiesel can cause hydrolysis to produce ffa. I didn't write down the article title or date but I found it by doing a google search on the key words Acid Number Biodiesel. But hydrolysis has a rate associated with it. Thanks
Are you using a dry wash with ion exchange or do you have a lot of copper tubing/fittings on the process? Although for that big of a difference you should be able to see a noticible colour change in the bio if it is copper (will turn green).
If you are water washing your drying might be a little to extended/strong. Or the bio is simply being stored too long. Failed Cetane number and cold soak are odd though. What type of oil is it made from?
A low melting point oil ie: Canola shouldn't fail the cold soak test. That's an indication you have something in your bio you need to filter out
What process steps are you carrying out on the oil.
Are you doing a single step reaction? or a two step?
What next, are you water washing, demething or just settling?
How are you removing the soaps from your biodiesel?
Are you water washing or dry washing?
Quite a common problem with a starting point at 0.9% FFA is that there will be a little soap created but not a huge amount but they have to go somewhere, if you don't take them out completely in a demething or washing step and then you neutralize or pass them through some form of acidic resin, the Soaps crack and turn back to FFA making the fuel fail the ASTM test for acid value.
It's a single step transeterification reaction with sodium hydroxide and sodium methylate. We are washing with water and letting it to sit for 30 minutes. The settled water is the drained from the water. Biodiesel is sent to centrifuge for further removal of water. Then its passed through filter (5 micron)from there its sent to storage tank.
We are water washing twice and letting it to sit for 30 minutes and then draining the water after which we are centrifuging to remove additional water. The bio made from soy oil is not stored long its the fresh batch results.
Alright so excessive heat oxidization is out of the question. What about copper or other 'red/earth' metal does it come into contact with them anywhere in the process? This will cause an increase in acid # as well. Otherwise I'm not seeing much that could cause it. Have you tried testing acid # at different stages to see where it jumps? Also assuming you aren't using citric acid to neutralize catalyst anywhere?
Also where do you get your wash water?
Do you mean your biodiesel also does not meet ASTM cetane or cold Soak?
@ Dr Dixieland
Yes the cetane number was 47 which is the minimum and the cold soak is >720. So, both tests failed along with acid number. Also the distillation temperature, 90% recovered test failed. It says 370C but has to be 360C.
But wouldn't that water would be reflected in water and sediment ASTM D2709 test. Because that test shows that we have water and sediment <0.025.
Many questions to answer.First have you done a complete test on the water being used. Also one wash may not be enough depending on your method.In the begininig we used water matching the temprature of the fuel 120F tp 140F and used two agitation washes.We then switched to dry wash process to get rid of water disposal issues and go to methanol recovery.Try taking a sample of fuel from reactor before washing and settling then let it settle in an open beaker for 48 hrs. Pull a sample after 48hrs and water wash that sample a couple times and dry, submitt for testing. If you pass then the issue is in your wash process.
this might be a dumb question..
your adding Naoh to sodium methylate?? WHY!!!!!! shouldn't you be adding more methylate to methanol it increase Na density depending on titration
I don't think that's quite right..
sodium methylate..methanol with elemental Na added..not the same as NaOH added to methanol.
with sodium methylate..there is not water created..unlike mixing NaOH with methanol.
off the soap box..
so what are you using?
did I miss it your you did mention
does it pass 27/3 first??
a single/double water wash isn't enough..what are you soap numbers?
are you washing with soft or hard water? di water?
what about your drying process..does the CF remove all the water? have you tested?
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