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Topic: Advantages and disadvantages of using TBD as a catalyst for transesterification  (Read 3657 times)

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Offline nick1124

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Hi all,

I'm doing my IB chemistry EE on transesterification, and I found out that TBD is another catalyst that could be used as a catalyst for this process-- thing is, I couldn't find any answers online as to how this particular process takes place, and some disadvantages of it (I've only seen good things being said about it as a catalyst for transesterification).

I'm just wondering why TBD isn't used in industrial productions instead of TBD since it doesn't form water that may potentially cause soap?

Thankssss

Offline Borek

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why TBD isn't used in industrial productions instead of TBD

What am I missing?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Babcock_Hall

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Would you please define your abbreviations?

Offline wildfyr

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Hi all,


... since it doesn't form water that may potentially cause soap?

Thankssss

Whats this bit about soap?

Also I assume TBD is triazabicyclodecene. Just in general, without a strong understanding of organic chemistry this is going to be a difficult question to boil down. It has to do with the unique electronics and acid/base properties of a bicyclicguanidine compound. It has the ability ability to form a sort of "activated" amide and be a fairly strong base at the same time.

Offline wildfyr

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I found this:

https://www.researchgate.net/publication/229772530_Organocatalytic_Depolymerization_of_Polyethylene_terephthalate/figures?lo=1

7th Figure (named Scheme 2). I personally prefer pathway a. This paper demonstrates evidence for a lower energy barrier for pathway b, which is based more on the hydrogen bonding characteristics and geometry of TBD.

Offline nick1124

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why TBD isn't used in industrial productions instead of TBD

What am I missing?

soz mate, I mean TBD instead of sodium hydroxide

Offline nick1124

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thanks mate, i'll have a look
« Last Edit: June 19, 2017, 05:27:27 AM by Arkcon »

Offline nick1124

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Soap formation in transesterification
« Reply #7 on: June 16, 2017, 11:43:01 PM »
Hi all,

I am doing a transesterification reaction, reacting canola oil and methanol with sodium hydroxide as the catalyst. The product that I make after leaving to settle for a day looks pretty good, with clear separation of the glycerol and biodiesel.

However, when i attempt to wash the biodiesel with water, a layer of soap forms under the biodiesel, and emulsions form as well between the biodiesel and water layer.

Is there a way I can wash the biodiesel to remove impurities, but not form the soap (or at least stop the formation of emulsions)??

Here is the link to my procedure: http://inside.mines.edu/~jobush/gk12/lessons/Biodiesel.pdf


Thanks <3

Offline Arkcon

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Hi nick1124:, I've merged your two threads on essentially the same topic, since you seem likely to reference them to each other, its best for everyone one to be on the same page.

To prevent soap formation in the production of biodiesel from methanol, its required to have everything scrupulously anhydrous.  That is, start with everything anhydrous, keep everything anhydrous before you start, keep the reaction tightly sealed while it progresses, and then ... dry everything before you start.  Then accept that there will still be some soap formed.  Sorry to be flippant, but this is the gist of what I've read.

I'm describing bench-top glassware biodisel production.  For industrial purposes, you want to apply industrial engineering concepts, that some people here can help you with.  But again, its tricky.

For production in a shed on a farm, our citizen chemists can try to combine the above concepts as best they can.

The final answer needs some info from you regarding scale:  are you paragraph one, two or three?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline nick1124

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Hey arkcon,

I believe i'm paragraph one from your descriptions.

Thing is, the sodium hydroxide tablets I use are fresh from the bottle, sealed and just opened, and the methanol that I use is also procured from a new bottle of methanol, so I believe in terms of the reactants, they should be pretty dry.

« Last Edit: June 19, 2017, 05:27:08 AM by Arkcon »

Offline phth

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Re: Soap formation in transesterification
« Reply #10 on: June 19, 2017, 01:31:53 AM »
Sodium hydroxide is not a catalyst! It is a stoichiometric reagent.  Methoxide is a catalyst.  Can you come up with a reason why??
Hi all,

I am doing a transesterification reaction, reacting canola oil and methanol with sodium hydroxide as the catalyst. The product that I make after leaving to settle for a day looks pretty good, with clear separation of the glycerol and biodiesel.

However, when i attempt to wash the biodiesel with water, a layer of soap forms under the biodiesel, and emulsions form as well between the biodiesel and water layer.

Is there a way I can wash the biodiesel to remove impurities, but not form the soap (or at least stop the formation of emulsions)??

Here is the link to my procedure: http://inside.mines.edu/~jobush/gk12/lessons/Biodiesel.pdf


Thanks <3

Offline nick1124

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Re: Soap formation in transesterification
« Reply #11 on: June 19, 2017, 01:59:43 AM »
Hey there,

Sodium hydroxide reacts with methanol to form methoxide, which makes a stronger base than just methanol due to its greater polarisability with a carbon atom next to the nucleophilic oxygen in methoxide compared to the oxygen next to the hydrogen in hydroxide
« Last Edit: June 19, 2017, 05:28:05 AM by Arkcon »

Offline phth

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Re: Soap formation in transesterification
« Reply #12 on: June 19, 2017, 11:43:23 PM »
Even if it does deprotonate methanol ( MeOH pKa > H2O pKa ) it still does not matter because the two things are in equilibrium (i.e. deprotonation is not the rate determining step).  What does matter is that once hydrolysis occurs due to hydroxide, then the alcohol will become irreversibly deprotonated forming RCOO- and R'OH; for this reason, the reaction has to be run dry.
Hey there,

Sodium hydroxide reacts with methanol to form methoxide, which makes a stronger base than just methanol due to its greater polarisability with a carbon atom next to the nucleophilic oxygen in methoxide compared to the oxygen next to the hydrogen in hydroxide

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