What factors contribute to high yield?

[gwalker Senior Member Find all posts View Profile Close gwalker]

In a given quantity of VO to be reacted with KOH, what causes better or worse yields?

eg, Does adding more catalyst optimise the yield and conversely, does being a bit short reduce the yield?

The same goes for Methanol.

Will 25% give a better result than 22%?

Will 18% produced more glycerol and less biodiesel than 20%?

If you want to err on the side of getting maximum yield:

would 25% Methonal and a couple of extra grams per litre of KOH (ie base + titration +2) be a good policy?

George

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello George
In a single stage method the main things that affect yield are titration and water content.
It has been my experience that high conversion results in lower yield and low conversion will maximise yield.

[gwalker Senior Member Find all posts View Profile Close gwalker]

Re: What factors contribute to high yield?

Hello George
In a single stage method the main things that affect yield are titration and water content.
It has been my experience that high conversion results in lower yield and low conversion will maximise yield.

Tilly,
I must be confused with the term 'high conversion'. What I thought it meant was: more biodiesel and less glycerine.
George

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello george

You can think of conversion as what percent of the oil has been turned into Methyl esters.
Yield is how much fuel you have from each litre of oil reacted, this includes methyl esters as well as mono di and tri glycerides and whatever else might be in the fuel.
Less glycerine would = lower conversion.

[marki Senior Member Find all posts View Profile Close marki]

Re: What factors contribute to high yield?

Hello george

You can think of conversion as what percent of the oil has been turned into Biodiesel.
Yield is how much fuel you have from each litre of oil reacted..
Less glycerine would = lower conversion.

I think you're getting a bit mixed up there Tilly. Your definitions of conversion and yield are the same......

[TroyH Senior Member Find all posts View Profile Close TroyH]

Re: What factors contribute to high yield?

yeah a little confusing there, however I think what Tilly is getting at is that you can get a high conversion of oil without it all being converted to product (i.e. making lots of soap). I'm not so sure about the whole high conversion = low yield thing. You would need higher conversion to have higher yield, unless you had less soap made.

However, in a true catalytic reaction, the yield is not affected, only the rate. This is because they affect the forward and reverse reactions equally, so equilibrium is not altered.
In our case, where there are alternate reactions going on, that use the catalyst as an actual reagent, then things get a bit more complicated. So more catalyst should only affect yield due to the amount of soap formed, no actual direct affect on the transesterification.

[gwalker Senior Member Find all posts View Profile Close gwalker]

Re: What factors contribute to high yield?

So more catalyst should only affect yield due to the amount of soap formed, no actual direct affect on the transesterification.

So, are you saying that once there is enough catalyst, you don't need or want any more?

What about Methanol? Does more Methanol (eg 25%) convert more VO to BD producing less Glycerine?
George

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello Marki

I think you're getting a bit mixed up there Tilly. Your definitions of conversion and yield are the same......

Conversion is what percent of your oil is converted into Biodiesel (methyl esters) or probably more correctly what percent of the fuel you are testing is methyl esters.
Some of the oil will not be converted into methyl esters but will still be present and considered part of the yield.
I have changed the word biodiesel to Methyl esters in my post above as I can see that it could be confusing.

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello Troy

yeah a little confusing there, however I think what Tilly is getting at is that you can get a high conversion of oil without it all being converted to product (i.e. making lots of soap).

Conversion is how much of your fuel is methyl esters.
Yield is how much fuel you have at the end of the reaction. The fuel will consist of methyl esters and mono, di and Triglycerides + other assorted things.
Conversion and yield are different.

I'm not so sure about the whole high conversion = low yield thing. You would need higher conversion to have higher yield, unless you had less soap made.
However, in a true catalytic reaction, the yield is not affected, only the rate. This is because they affect the forward and reverse reactions equally, so equilibrium is not altered.
In our case, where there are alternate reactions going on, that use the catalyst as an actual reagent, then things get a bit more complicated. So more catalyst should only affect yield due to the amount of soap formed, no actual direct affect on the transesterification.

Exactly, if you add enough NaOH/KOH to drive the reaction to very high conversion you make extra soap and reduce yield.
Most people either wash or settle the soap out of the biodiesel so is usually not considered a part of the yield

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello George
Yes, if you use excess Catalyst to what is required for very high conversion you will make more soap.
Within reason, increasing methanol or NaOH/KOH will increase conversion. One test I performed suggested that increasing NaoH/KOH will produce more soap and so lower yield than increasing methanol does. But I would need to do more testing to be sure.

So, are you saying that once there is enough catalyst, you don't need or want any more?
What about Methanol? Does more Methanol (eg 25%) convert more VO to BD producing less Glycerine?
George

Typically we call the byproduct layer glycerine. It mainly consists of glycerine, soap, Methanol and NaOH/KOH
Higher conversion will produce more actual glycerine.
The titration has an effect on how much soap is produced, and there is a side reaction that is also producing soap. The more methanol used in the reaction the more that will end up in the "byproduct layer"
Adding excess NaOH to what is required will make extra soap and lower yield, but it does not lower conversion.

[gwalker Senior Member Find all posts View Profile Close gwalker]

Re: What factors contribute to high yield?

Let me approach 'yield' a different way.
I've just reacted and separated 1 litre of VO.
After adding a 5% pre-wash, the BD layer is 66% of the total volume with the glycerol by-product layer 33%.
Is this result what others normally achieve or is 80%BD 20% by-product or better achievable?
George

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello George

Measure how many ml of biodiesel is in the jar on top of the by product.
Because you started with 1000ml of oil, Divide this amount by 1000.
Then multiply this result by by 100.
Your answer is the yield in percent not counting a bit more methanol and soap that might wash out in later washes.

So, if you have 893 ml of fuel on top of the by product layer that is:
893/1000= 0.893
0.893X 100= 89.3
Your yield would be 89.3%

[TroyH Senior Member Find all posts View Profile Close TroyH]

Re: What factors contribute to high yield?

lol I think it's more confusing now than it was before.

generally if you were talking about a conversion percentage, you would be referring to the conversion of one thing, into another (that is, one overall reaction. eg: transesterification). In this case, conversion and yield would be the same thing, because yield would refer to the total amount of ester formed, compared to if all the limiting reagent (oil) had been converted to product. Since neither mono or di-glycerides (or soap and triglycerides for that matter) are what we desire as product, they do not make up yield, and aren't part of the total conversion percentage (as they are incompletely reacted). Potentially they could be considered desired product, and then would be considered part of the yield. Soap reduces yield of esters, and thus conversion TO esters, but obviously is part of the conversion products if you are referring to conversion OF the oil.

They are subjective terms, but usually you would be talking in terms of amount of desired product obtained as yield, and total oil turned into product as conversion.

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: What factors contribute to high yield?

Hello Troy, welcome to home-brew biodiesel termonology

If I react 100 litres of oil and at the end of the reaction I have 92 litres of fuel I have a Yield of 92%
I have no way of determining what my conversion is so that is something I can not check. Most people never actually have their fuel GC tested.
Most people are concerned about how much fuel they make.

Did you actually join the forum other than to criticize the way people do things?

[TroyH Senior Member Find all posts View Profile Close TroyH]

Re: What factors contribute to high yield?

Not at all. I'm sorry you think that. Do you come on this forum and expect noone to ever disagree with you or tell you you've made a mistake? I know I dont, I make them all the time.

Anyway, what you are saying there is fine. I did mention in my last post, that if you consider all the bits that end up in the top layer, to be product, then your yield includes all of them. However your first post (now edited) was completely confusing (and wrong). If you are going to use terms (that often have been derived from science and engineering) perhaps you should use them correctly.

Have you ever heard the joke about the blonde asking the mechanic where to put the oil? He tells her to put it in the cap that says 'OIL" on the top. She cant find it anywhere so he points it out to her. "Oh, you meant the 710 cap".

edit:

Yield (chemistry) - Wikipedia, the free encyclopedia
Conversion (chemistry) - Wikipedia, the free encyclopedia