I was wondering how many people here use waste restaurant/kitchen oil for their biodiesel feedstock. We have made fuel out of our kitchen oil, but a lot of the kitchen oil is more than 2 years old and even though it has mid to low ffa levels, we are concerned about failing sulfur.

Has anyone here had a problem with failing sulfur for their biodiesel made from waste vegetable oil? If so, how much did you fail by and what means are there to correct it? Are there any means to screen for sulfur in the feedstock, other than using XF or FTIR methods?

Are there any adsorbents or something you can use to remove sulfur currently available on the market? Can you blend it with virgin feed, if so what kind of success do people have with blending?

Thanks all!

I'm not familiar with sulfur being a problem, but then again theres alot I'm not familiar with.

Where would the sulfur come from?

Perhaps refried beans.

I think sulfated ash is an ASTM spec. Never heard it to be a problem with WVO. They use sulfur in oil refineries, but that has been reduced due to the EPA & environmentalists. I think most if not all of the sulfur in sulfuric acid goes out with the byproduct layer.

Apparently it is a fairly common problem with waste restaurant oil, Eurocab, b/c we failed sulfur even after passing everything else.

Sulfur in waste vegetable oil, from what I understand, comes from the bacterial degradation of the oil over time. It's apparently particularly bad with animal based fats, which inevitably are in many of our restaurant's cooking oil. I'm not sure if there is a relationship b/w free fatty acid degradation and sulfur formation from bacterial degradation.

We made two batches, one from virgin oil and one from our grease, and while we were able to get both to pass free and total glycerol, we failed sulfur from our biodiesel made from grease. The virgin one got 2 ppm, but the wvo biodiesel got 32 ppm and the spec is 15 ppm.

Arrg. So we pretty much have to cut it in half with virgin, which is incredibly expensive and difficult to obtain, that's the only way I can think of for dealing with the sulfur issue.

Pretty aggravating, since 32 ppm is still very low, and since the spec used to be 500 ppm (or thereabouts). I read a couple of years ago that the guy who developed the spec was being investigated for fraud (apparently he didn't even have a phd). If that's true, you'd think they'd change the spec back.

Anyway, any suggestions with cutting down sulfur? Do any water softener based technologies work well?

Bacteria, fungi, and other microbes need water to survive. Dewater the VO and microbial degradation won't occur.

quote:

Bacteria, fungi, and other microbes need water to survive. Dewater the VO and microbial degradation won't occur

That should work on future oil, but the stock is already 2 years old.

If the spec was reduced from 500ppm to 15ppm then I doubt you would have any problems burning it. Now if you are selling it...

You could do a two stage AE/BT on it and maybe the sulfur will hang out with the sulfates in the byproduct layer. I am sure someone else will come up with a better solution.

Yeah, unfortunately 2 years ago we didn't have the means to separate the water from the oil (other than gravity), so we're well aware of what causes it and how we can prevent it in the future, how we deal with it now though is another kettle of fish b/c we've already made thousands of gallons of biodiesel from waste feedstock. You need to remove the water anyway to process the fuel, but when it's been sitting there awhile it's likely going to be somewhat higher in sulfur over time. Now that we're set up to remove water immediately, we're in somewhat better shape.

AE is an option, but to AE everything we need a lot more methanol to do that which may offset the cost to benefits.

I can see I'm not going to get much further here. Thanks so much for the input, though.

How about a centrifuge? Sulfur should be heavier than the oil and perhaps spinning it out will work.

The problem with Sulfur is there are different types and different sources within the same oil. My understanding is that a large amount in animal fats are tied up with amino acids.

There are some which are high boiling point which can be removed in a Methyl Ester distillation step which is added at the end of the process. This involves high temperatures and vacuum but can pretty much be guaranteed to get the Sulfur levels down from around 50ppm to <10ppm which is the EN specification level.

You can blend either the feedstock or the finished product to achieve similar results but as you say that could be expensive especially if you have high levels of sulfur.

We did find some samples that where up above 50ppm in the feedstock (tallow) which came down only a few ppm even in Esterification and Transesterification so that does not tend to reduce it from what I have seen.

As far as raising the standard back to 500ppm, that is highly unlikely in fact I would not be suprised if it was not reduced to <10ppm to match what the rest of the world typically works to. Also I am not familiar with the story of the guy without the pHD "who developed the spec" being investigated for fraud. Can you post a link to that I would be interestd to read about it.

quote:

I think sulfated ash is an ASTM spec. Never heard it to be a problem with WVO

Eurocab
Sulfated ash is a test which looks for ash forming contaminants such as abrasive solids, un removed catalyst and metalic soaps. As far as I am aware it has nothing to do with detecting levels of Sulfur. The test for Sulfated Ash is D874 whereas the test for Sulfur is D5453.
The problem with Sulfur is quite well known in biodiesel produced fromanimal fats as Emily e mentions. Quite a few plants have distillation columns for this reason.

I suspect that if you separate out the high melt point fats and PHO from the used VO with something like cold upflow, then most of the sulfur will separate out with them. Have you tried making a batch with only clear dry oil off the top which likely won't contain much fats and PHO?

quote:

Originally posted by john galt:
I suspect that if you separate out the high melt point fats and PHO from the used VO with something like cold upflow, then most of the sulfur will separate out with them. Have you tried making a batch with only clear dry oil off the top which likely won't contain much fats and PHO?

I guess it depends upon the percentage high melting fats, if it is an animal fat then it is all high melting point so that would not work. If it is a liquid oil with animal fats only from the cooking process then your suggestion may work but then the yield would be down and there could be a disposal issue both are likely to affect the cost/ benefit.

Fuzznag, or Emily
are the sulfates/sulfides that are contributing to the high sulfur levels able to be washed out with water washing of the fuel?

quote:

Originally posted by Double D:
Fuzznag, or Emily
are the sulfates/sulfides that are contributing to the high sulfur levels able to be washed out with water washing of the fuel?

No, not from results I have seen. The sample I mentioned earlier that only reduced a few ppm through the whole process was washed in various different ways but still it did not reduce. Not until it was distilled.

To reduce metals content (sulfur is one) in commercial oils, it is recommended in one of my books to do an alkali wash (caustic stripping), converting them to soaps that can be washed out. In some cases a phosphoric acid pretreatment is used to denature the phosphatides, so they can be removed in the caustic stripping stage. "The phosphoric acid acts as a sequestering agent by combining with metal ions in the oil, retarding their catalytic poential for oxidizing the neutral oil and facilitating their removal during subsequent processing." (p248, Oil Crops of the World, 1989)
I don't know enough chemistry, or about your oils, to predict if this would work for you.
Cheers,
JohnO

quote:

Originally posted by johno:
To reduce metals content (sulfur is one) in commercial oils, it is recommended in one of my books to do an alkali wash (caustic stripping), converting them to soaps that can be washed out. In some cases a phosphoric acid pretreatment is used to denature the phosphatides, so they can be removed in the caustic stripping stage. "The phosphoric acid acts as a sequestering agent by combining with metal ions in the oil, retarding their catalytic poential for oxidizing the neutral oil and facilitating their removal during subsequent processing." (p248, Oil Crops of the World, 1989)
I don't know enough chemistry, or about your oils, to predict if this would work for you.
Cheers,
JohnO

JohnO
My understanding is that you are right, however it all depends upon the source and type of sulfur in the original oil. Yes, some can be washed out by adding an acid wash of the feedstock oil up front of the caustic refining step or even just in the caustic refining without the acid wash. However that does not work for all sulfur compounds in all oils especially animal fats. It is also known that some sulfur compounds (lower boiling point) can come overhead in the deodoriser and out with the fatty acid distillate.

The problem is that a lot still end up passing through all of the pretreatment and biodiesel production and end up in the finished biodiesel. At the end of the day you only need to be a single ppm over the 15ppm limit (10ppm over on this side of the pond) for the fuel to fail ASTM or EN tests. That is why there are distillation columns at the end of a lot of animal fat based biodiesel plants around the world.

If they are deep frying onion rings this will increase sulfur levels too

Canola oil (rape seed) can also cause you to fail the sulfur test. Since it's in the mustard family, it needs a fair amount of sulfur in the soil and ends up with a fair amount of sulfur in its proteins.

HTH,


troy