PG questions

[zadane]

I was wondering what the difference between the PG that suppliers sell and the PG that you can get on ebay like this one Propylene Glycol PG USP FCC grade 4 oz - eBay (item 260714623641 end time Jan-30-11 01:15:34 PST)

if there is even a difference

 

[aprioristic]

People seem to say that the source for VG makes it different, or even that the expensive VG is somehow more runny (which I am skeptical of). For PG though, I would think it is about all the same as long as it is USP.

You can get a better deal on PG at The Flavor Apprentice maybe. Instead of $7 on ebay for $10 +shipping you get 4 times as much, or even a better deal if you buy bigger, but that is up to you and you could get flavorings there too. There's probably even cheaper places then if you buy bigger sizes too.

 

[SethG]

Kind of along the same lines, there is this too. I've looked at a bottle of this at the local feed store and it states 100% USP Propylene Glycol. On another part of the bottle is says "For animal use only." Any ideas on how it can be USP and not be for human use? The only thing that I can figure is that the distributor didn't repackage the PG in a "food safe" facility and two probably doesn't have the insurance?
Amazon.com: Propylene Glycol, 1 Gal: Home Improvement

 

[aprioristic]

That's probably just bad labeling and they put "animals only" because it is the intended market. Maybe I am wrong and there is some other byproducts than in stuff without the animal warning, but I doubt it. USP just means 99%+ I think. Anything significantly closer to 100% would cost more. PG is a pretty well studied GRAS material so I wouldn't worry about vaping the animal only stuff personally.

It looks like there are various ways to produce PG, but my guess is that most is made in a similar way (i.e. the cheapest way):

Commercial production of propylene glycol is by hydration of propylene oxide. Di- and tripropylene glycols, as well as small quantities of higher glycols, are also produced in the reaction.

The reaction between propylene oxide and water takes place at a temperature of 200oC and 12 bar pressure. The amount of water is controlled to favour MPG production. The reaction mixture is dehydrated by evaporation and the various glycols separated by distillation.

There is a lot of interest in producing PG from renewable resources such as glycerine. Glycerine is a byproduct in biodiesel manufacture and with the boom in biodiesel projects, much effort is being made in finding new uses for glycerine. For example, a process for converting natural glycerine to PG has been developed by the University of Missouri. The conversion rate is claimed to be about 75% efficient.

A French biochemical company, Metabolic Explorer, has been awarded a French patent for a fermentation process based on renewable resources. Archer Daniels Midland (ADM) plans to build a plant using agricultural raw materials to produce pharmaceutical and industrial grade PG.

A carbohydrate-based route to PG could result from work at Michigan State University. It has demonstrated that crude aqueous (10%) lactic acid produced by fermentation of corn starch, dextrose or other carbohydrates can be readily hydrogenated to PG in 86% selectivity at 98% conversion.​

 

[zadane]

Thanks aprioristic, Really appreciate the info

 

[deback]

The PG from Tractor Supply is fine. It's also cheap at $20 for a gallon.

 

[Kurt]

aprioristic, thanks so much for the info! Glad someone else is paying close attention to chemical detail! I agree totally with your opinion about the USP/animal-only PG. Probably mislabeled, or because it is an animal feed store it might be they must label it that way, even if it claims USP.

I was only aware of the propylene oxide hydration process for PG production. Sounds like the other methods have good intent but are research-level only just yet, not general production.

I can't do PG much myself...I'm a VG guy. But I always enjoy chemistry discussions.

 

[aprioristic]

Thanks guys. I have no chemistry background but I am just good at finding info on the internet. I do get to bug my brother with questions though because he is a chemistry doctoral student. He also hooked me up with a sweet 50ml syringe and some other lab goodies! He isn't a smoker but would have cloves or a cig from time to time and he liked my PV when I saw him last. When I talked to him on the phone a few days ago, I thought it was funny that he seemed so happy I sort of knew what a racemix was.

I've not and still don't have much time right now to mess around with DIY stuff but later on I saw the wikipedia entry on PG and it is still throwing me off. Maybe you know Kurt.

So, a racemix or racemix mixture is two steroisomers. In The Flavor Apprentice's resource section (which I suggest all interested in DIY to read), She mentions in Part 1 that:

To continue, another very simple flavor is Spearmint. If you look at a GC/MS (you can google it!), you will find that it is mostly Carvone. What is really interesting about Carvone is that it has two “isomers” (mirror images) and each one smells and tastes completely different! L-Carvone (laevo) is the one that is spearmint, and D-Carvone (dextro) is caraway. Same shape molecule (just reversed) but our senses interpret them differently. Cool, huh!

So these are steroisomers as well. Then wikipedia says that:

[PG] is sometimes called α-propylene glycol to distinguish it from the isomer propane-1,3-diol HO-(CH2)3-OH, also called β-propylene glycol.​

Then it says:

Industrially propylene glycol is produced from propylene oxide. Different manufacturers use either non-catalytic high-temperature process at 200 °C (392 °F) to 220 °C (428 °F), or a catalytic method, which proceeds at 150 °C (302 °F) to 180 °C (356 °F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali.

Final products contain 20% 1,2-propanediol, 1.5% of dipropylene glycol and small amounts of other polypropylene glycols. Propylene glycol can also be converted from glycerol, a biodiesel byproduct.​

So the two stereoisomers I am going to shorten to 1,2-PG (this is the one called "propylene glycol" by wikipedia) then the other is 1,3-PG.

1,3-PG seems harmless from it's entry, but then it is saying that 1,2-PG only comprises 20% of "final products". So, is it possible that some of this stuff being sold (for animals/skincare) is only 20% 1,2-PG? It doesn't state what the other 78.5% in final products is...

Before that part it says "Pure optical isomers can be obtained by hydration of optically pure propylene oxide." That matches up with what I copied before. I just don't understand if what USP means is the pure 1,2-PG or if what can be sold as "100% PG" could be only 20% 1,2-PG. Maybe we should rethink if we want to vape that animal feed stuff.

 

[SethG]

@aprioristic The PG from the feed store also says "USP" which signifies that it was manufactured using the USP standard and should be consumable by humans and should be "as standard" as any other USP Propylene Glycol. My point is after the manufacture of it it had to be bottled, the company bottling the PG probably doesn't use FDA approved equipment to bottle the PG as it accounts for further expense in relation to sanitary conditions, sterilization of the bottles, approval documentation, licensing, inspection, insurance, and the list goes on....

Concerning the alpha and beta forms of propylene glycol, these are not the same thing at all. I think you may be confusing stereo-isomer (racemic) chemical structure with chemical formula. Chemically, if you count the number of atoms 1,2-PG and 1,3-PG are the same, but the structure of the molecules are different. The normal form of PG has a stereo-isomer nature, where the structure can be built with an exact "mirror" that matches the structure of the other.

There is an image here that may help visually show the stereoisomers of PG:
Fileropylene glycol stereoisomers v.1.png - Wikimedia Commons

Concerning the stereo-isomer nature of 1,2-propanediol (Propylene glycol), in some chemical structures left/right "spin" makes a difference, however it does not seem to make any difference in the case of PG. There has been some study done on them to see if one form is more easily absorbed by the human body than the other, however the manufacturing costs for getting the one type of "spin" is very high and is not worth the cost.

 

[SethG]

@aprioristic The PG from the feed store also says "USP" which signifies that it was manufactured using the USP standard and should be consumable by humans and should be "as standard" as any other USP Propylene Glycol. My point is after the manufacture of it it had to be bottled, the company bottling the PG probably doesn't use FDA approved equipment to bottle the PG as it accounts for further expense in relation to sanitary conditions, sterilization of the bottles, approval documentation, licensing, inspection, insurance, and the list goes on....

And I should go on to say, if the intended market is animal use they can avoid all of these headaches by stamping "not for human use" on the bottle. There is no mislabeling or misrepresentation here with this statement IMHO. The product they are selling isn't intended for human use and isn't treated as such.

If one were to call the bottler and ask about something, and the said manufacturer was to find out that you are using it for human use they would probably be very threatening to you. Possibly to the point of using their lawyers.

 

[SethG]

Reading back, I'm probably not being clear on the isomers issue. If I had a white board I would just draw it. Organic chemistry is nothing if not complex.

1,3-Propanediol (Common name Trimethylene Glycol)

1,2-Propanediol (Common name Propylene Glycol)

Now, to say that both of these are isomers of Propylene Glycol is false. However if one was to say that these are both Propanediol isomers is correct. The key to these chemicals is the organization of where the OH (alcohol) molecules are attached to the propane molecule which is designated by the preceding numbers in the formal chemical name.

Both of these molecules have stereoisomers. Stereoisomers are a common occurrence in organic chemistry and sometimes play a huge role in a chemists endeavors, other times none at all.

Does this help more?

 

[Numevexo]

Hi SethG,
Sorry to break in here, but I just recently saw the PG at Tractor Supply, also 100.0% Propylene Glycol. Looked at the label very closely and didn't see "animal use only".
I've talked to a couple of vaping friends and we're going to chip in and split up the $23.99/gal PG amongst ourselves to give it a try. Wish I had more chemistry background beside the basic 101 in college. If one of us kicks the bucket, we'll have the others post here.

 

[SethG]

Honestly, I'm guessing you'd be fine even if it did say for animal use only, I just wouldn't announce it to everyone. As previously stated, the other thing to make certain of is that it says USP.

What brand is it?

 

[Numevexo]

Sorry to take so long getting back to you. Had to find the paper I wrote it down on.
It's "Ideal Animal Health". Just thought I'd take a look around there after reading about it's availability at TSC and Farm & Fleet, elsewhere in the forum. Definitely states USP. "Propylene Glycol; USP".
The ingredients label read 100.0% Propylene Glycol. Also stated "used for prevention of Ketosis, I believe, which is a blood sugar glucose thing if I remember medical biology from way back.

 

[aprioristic]

Does this help more?

Yes, thanks. I do really need to learn a lot obviously. So much to do though. I still think wikipedia's article is bad then. It doesn't really explain why it is saying only 20% of what is sold as PG is PG.

Here's some stuff on PG from Dow Chem. They call it PG but also monopropylene glycol, to show it is the isolated isomer. The stuff about legal issues makes sense. Stupid regulations would force them to do it that way, even though it is chemically identical.

Here's some stuff from USP, but I didn't look through it much. I'm wondering if GRAS has caught on the increasing use of flavors to be inhaled. The science of that isn't identical to ingestion and many of these flavorings haven't been tested for inhalation AFAIK.

Regarding it's use to prevent ketosis in cows though I do not like. I guess it is supposed to be low glycemic index, but I wonder if there is anything else we can vape that isn't a "carbohydrate". I haven't even tried my Triacetin yet, but I think I read it is "the most simple form of oil except [something]".