Sciencemadness Discussion Board - Isolation of short-chain hydrocarbons from gasoline via fractional distillation

Isolation of short-chain hydrocarbons from gasoline via fractional distillation

Endimion17 - 25-9-2011 at 08:32

Has anyone tried to do this?

Last year I was interested in fossil fuels so I began with some distillations. I was searching for easily accessible petroleum ether for chromatography and general dissolving, but the only one readily available was the one sold in pharmacies in small bottles (it says "pentane and hexane mixture"). It's ridiculously expensive.
So I tried to use Eurosuper (octane rating 95) gasoline.

The procedure can be quite dangerous, you can imagine why.
I used a fully ground glass apparatus with silicone grease seals and a boiling water heating bath (tried it without bath, just heating pad and few asbestos pieces as a flask resting spot; distillation proceeds great, but the danger is too big, so don't do it). Tap water went through the Liebig condenser. Receiving flask was immersed into an ice-water bath.
At first I thought the amount of dissolved butane will be small so I vented it through the window, but when I realized there's a considerable amount of it, I started collecting it in a U-tube immersed in ice and salt bath. Any residual butane was vented out for the first few minutes. After that I tested it on residual air and upon a negative result, ignited the tip. It was like a small oil refinery.

There were numerous halts on the thermometer during the distillation, indicating a rich variety of all kinds of hydrocarbons. I don't have the notes here with me, but there were halts indicating several branched hydrocarbons. What can I say? It was loads of fun. I used less than 250 ml of gasoline, so the halts were probably not very accurate. I couldn't really collect all those fractions separately, but it was nevertheless interesting.

As I've said, I used a boiling water bath, but as I let the heat escape through the column, the last fraction had a boiling point close to 45 °C and that was it. So I've collected all of them in one receiving flask. It was truly remarkable. It's completely transparent, leaves no stains upon evaporation, has a great smell (it's essentially what makes gasoline smell nice in small concentrations) and it's a great solvent. Evaporates very fast, kind of like diethyl ether. Cools hands and dissolves the fat like it, too.
No matter if stored in a cool place, there'll be a hissing sound every time you open the bottle cap.

The part left in the flask had a terrible smell. Choking and disgusting. Its color was of gasoline, only more intense.

Over the next few days, I've tried to use an oil bath, close to 200 °C. I've managed to collect some more distinct fractions with increasingly bad odors, density and viscosity. The remaining liquid had an even more disgusting smell. I'm sure it would induce vomiting after a few seconds.

The only disadvantage of this process, if done on a larger scale, is that you essentially get larger amounts of short-chain depleted gasoline that wouldn't work alone in cold weather. I don't know about summer, but it would certainly fail during the winter season.
Small scale doesn't pose problems, as the depleted fuel can be dilluted with the original stock. There shouldn't be any difference if you mix half liter of it with a 20 liter canister. So I've returned the depleted mixture with no consequences.

Advantages are - cheap source of petroleum ether and clean apparatus. You don't even have to wash it, not even the column. :cool:

I doubt I'll do this with diesel fuel. I simply know the smell would be too bad, and the thought of cleaning the remaining fluid doesn't appeal to me.

Unfortunately, I don't have any photos of the finished setup as I was too busy.

Diesel

pip - 25-9-2011 at 11:07

I don't see why the leftovers from a larger batch can't be mixed with diesel fuel as long as you don't go crazy and try to mix it 50/50.

Are you looking to do somthing useful with the leftovers or are you considering it pure waste?

You can build a waste oil burner which is a good excuse to get some (white) phosphorus which is darn near impossible to get easily unless your willing to pay $10+ per gram to make it (red) from lialh4, triphenylphosphate, carbitol.

Phosphorus halides are hard to get and valuable enough to go through the effort. By value I mean scientific do not try to sell any as any legal problems arn't worth the money.

Carbon disulfide needs a furnace of one type or another to make and the example in the cs2 thread can be modified to use a waste oil burner furnace.

You can make a waste oil burner kiln if time is taken to design it properly.

[Edited on 25-9-2011 by pip]

Magpie - 25-9-2011 at 12:16

Quote: Originally posted by Endimion17

The procedure can be quite dangerous, you can imagine why.
I used a fully ground glass apparatus with silicone grease seals and a boiling water heating bath (tried it without bath, just heating pad and few asbestos pieces as a flask resting spot; distillation proceeds great, but the danger is too big, so don't do it). Tap water went through the Liebig condenser. Receiving flask was immersed into an ice-water bath.

I understand that distilling gasoline can be quite dangerous, but this applies to other flammable solvents as well. And organic chemists remove and purify these solvents by distillation routinely.

When I needed ether I made it first by the dehydration of ethanol using sulfuric acid and then likely purified by distillation. I have also recovered ether from starting fluid in which it was dissolved in hexane, also by distillation. The propellant was propane so that was coming off too. I'm sure that ether is every bit as dangerous as gasoline.

I'm not trying to downplay the dangers, just saying that for organic chemists this is somewhat routine. Due precautions must be taken. I used a steam bath and have a well ventilated hood. Without that equipment I would not do it.

Endimion17 - 25-9-2011 at 12:21

pip, I'm not interested in leftovers and most certainly don't have the time to throw myself into the construction of a kiln.
My goal was to isolate the lightest fractions of gasoline and see what's inside, but didn't have the time for the latter. I never did any tests for nonsaturated hydrocarbons.
My batch was everything with boiling points below ~45 °C, and that can be a number of things. Alkanes, cycloalkanes, branched or not, alkenes, etc...

I encourage others to try the same because it seems like a really cheap way of getting alkanes and alike.

Quote: Originally posted by Magpie

Yeah, I've distilled ether a number of times, but small amounts, during the preparation of other organic compounds.

But this is about obtaining larger amounts of petroleum ether or whatever it is. My next goal is using a 1 liter flask in boiling water bath. I want that solvent.

[Edited on 25-9-2011 by Endimion17]

pip - 25-9-2011 at 21:59

It does seem to be a easy to get pet. ether but I'd hate to go through all that effort and not make max use of the effort.

Do you plan to test your home made pet ether for unsaturated hydrocarbons and what are your thoughts about consistacy of gas from one region to another.

Endimion17 - 26-9-2011 at 05:36

Considering that by raising the temperature the distilling flask is left with a quite complex mixture, including antidetonators, aromatic compounds, not to mention all kinds of heavy isomers of aliphatic compounds, it would seem quite a waste of time to pick through that garbage, except one had a strict procedure and the knowledge of what's inside.

It's much easier to sift through the lowest fraction because there's not too much inside. It is a rich variety, as I've said, but remains simple. I'm definitively doing this again and checking for unsaturated compounds. There should be some pentene isomers. I don't know about alkynes.

There can't be any appreciable amount of n-hexane inside, as it boils at 69 °C. There could be some neohexane. Isomers of pentane should be the primary ingredient, as they all boil below 50 °C. Isomers of butane should be the primary reason why this mixture is so volatile.

No, I didn't have any opportunity to check out the differences...

Dr.Bob - 26-9-2011 at 11:07

Nice way to get pet. ether. I would doubt that gasoline has many alkynes, and the amount of alkenes should be low, as they would make gas go bad faster. (That is why biodiesel has a short shelf life.) You will get far more low BP hydrocarbons in the winter gas blends, however, as during the summer the EPA limits the amount of pentanes in gasoline so it outgases less, thus less smog in theory.

The residuals should be fine to dilute with more gas to burn in a car or lawn mower, but you are right that it will work better in summer. I would not add them to diesel, as even the higher fractions of gasoline are too low a BP for a diesel engine. But most cars can burn higher BP gasoline fine, as that should improve the octane rating somewhat. You should fine very little n-hexane, or other n-alkanes, but lots of branched hexanes, heptanes, and octanes. Isooctane should be one of the constituents, especially in higher octane gas.

Distilling diesel would not give much of anything at the lower end, as low BP hydrocarbons would destroy a diesel engine. It is mostly C12-C18 fractions, primarily C16, as best as I can recollect.

Have fun and don't catch fire.

Bob

fledarmus - 27-9-2011 at 11:11

The major difference between gasoline and diesel is the amount of branching in the carbon chains. Increasing the amount of branching for hydrocarbons having the same molecular formula will decrease the tendency of the hydrocarbon to ignite when it is compressed. For a gasoline engine, you don't want it to ignite when it is compressed - you want it to wait until you supply a spark with the spark plug. Diesel engines, on the other hand, don't have spark plugs, and the diesel fuel is ignited by compression. Consequently, fuels that are good for gasoline engines are terrible for diesel engines, and vice versa.

The standards for measuring these qualities reflect this trend. Gasoline quality is measured by the octane number, which is a comparison of the fuel mixture to pure iso-octane (2,2,4-trimethylpentane). Iso-octane has an octane number of 100, while n-heptane, which has no branching, has an octane number of 0.

Truck diesel has a higher overall molecular weight than gasoline, and the standard for diesel fuel is the cetane number. Cetane is n-hexadecane, and is rated 100 on the cetane scale. Zero on that scale is isocetane, which is 2,2,4,4,6,88-heptamethylnonane. Note - cetane has no branches, iso-cetane has a lot!

So I wouldn't mix any portion of gasoline into diesel fuel, or vice versa.

peach - 30-9-2011 at 16:17

Interesting!

Perhaps you could try it with a salt ice trap and see what you can get out really low. I'm tempted to give it a go too.

Quote:

I understand that distilling gasoline can be quite dangerous, but this applies to other flammable solvents as well. And organic chemists remove and purify these solvents by distillation routinely.

Yep. Although I'd say that's a fair description he's using. The flash point of petrol is pretty low at -43C (ethanol is 13 to 14C, hexane -23.3C and ether is -45C). So it's going to push it's self well into the atmosphere at room temperature; I absolutely love the smell!

It has obviously been engineered to ignite in commonly encountered outdoor environments. E.g. leaving your car out in winter where it hits hard.

I would expect there to be manipulated azeotropes and very close BP's to ensure it's all well mixed in the vapour phase and won't extinguish.

They are leaving really low fractions in there, or adding things (e.g. ethers), to get it going really low.

Here are some ethers added to petrol. They're antiknocks but also added to alter the cloud properties, among others, of the fuel;

MTBE
TAME
ETBE

Amazing bit of trivia, the lowest temperature recorded on Earth is from the Russian Vostok station in Antarctica. -89.2C, cold enough to solidify the CO2 in my breath.

Quote:

Even with a simple fractional distillation, a graph can be really useful as they take a long time and seeing the temperature changes in the minds eye can be misleading. If I believe something is there, I will want to believe I've got it.

Drawing a graph reveals a lot.

Distilling petrol, with all that stuff in there, I bet it'd be a mess.

Unless you have a datalogging thermometer, that means a piece of paper, a pencil and sitting watching it all the way through.

Here's an example of one I drew this afternoon; mit pencil and paper, and then converted for your digital pleasure.

This was a distillation of about 75ml I think and it took an hour. I recorded the temperature once every minute.

The two major components are toluene and benzaldehyde, under vacuum in a vacuum jacketed vigreux column with a standardised mercury thermometer; can you predict the pressure from that graph?

The first thing to note is that this is a 'dot to dot' line, because the variations in the line are not measurement errors, they are actual temperature changes occurring in the still, due to the fact that is it not a perfect system. If I included the dots, it'd be covered in them.

The line starts low and curves up to the BP of toluene under that pressure, because there are traces of cyclohexane (a lower BP) in it. The sloped line indicates that a possible azeotrope is coming past; this is not the kind of thing I want to see in a distillation, there is no pure split here.

The temperature then does a vertical climb to the BP of the benzaldehyde, a near vertical line shows that a new band has appeared. Another good sign is that the temperature slightly dips before the new band, showing that the last has been pushed out and the flask is now warming to the new BP, whilst the thermometer cools between the two.

The benzaldehyde band runs horizontal for a while and then tapers off very gradually over a long period, showing nothing else is coming through, despite the heat still being on and high.

The line here is wobbling up and down because the benzaldehyde left in the column is going round in a circle, unable to come over as a true stream.

Tedious to do, but very satisfying and interesting to see a graph of after standing there for an hour.

I've spent longer than that watching distillations. Far, far longer.

Get a digital kitchen timer, set it to 1 minute and open a book.

[Edited on 1-10-2011 by peach]

Endimion17 - 1-10-2011 at 05:59

I actually have been monitoring the entire process for a couple of hours. I have the patience, that's not the problem.
Pencil, piece of paper and the night ahead. Old school style. Quite used to it... :-/

I really have to repeat this starting with almost 1 liter and adding a better jacket around the column. Glass wool and aluminium foil should do it.

But what to do with the petroleum ether after analysis? I was thinking about chlorinating it somehow, and then redistilling with temperature monitoring, that could be interesting. The experiment might yield a different, but similar graph line, indicating which hydrocarbons were initially inside.

I love graphs. I really do.

[Edited on 1-10-2011 by Endimion17]

fractional distillation

leu - 1-10-2011 at 12:26

The attachment, US 2009814 invented by Walter Podbielniak describes the fractional distillation apparatus for analyzing petroleum :cool:

Attachment: 2009814_METHOD_AND_APPARATUS_FOR_ANALYZI.pdf (478kB)
This file has been downloaded 587 times

Panache - 6-10-2011 at 04:24

Quote: Originally posted by leu

The attachment, US 2009814 invented by Walter Podbielniak describes the fractional distillation apparatus for analyzing petroleum :cool:

That's a bit of fractionating legend you are referring to there. Story goes he used to get his young children to sleep at night with a gently running synder column distilling milk and honey.

pip - 11-11-2011 at 17:25

Anyone do anything like this recently, how can I test for saturation in a safe manor?

watson.fawkes - 11-11-2011 at 17:45

Quote: Originally posted by pip

Anyone do anything like this recently, how can I test for saturation in a safe manor?

(1) Get rich like Bruce Wayne. (2) Buy a large manor house in the country. (3) Fortify it. (4) Build a secret underground laboratory.

As to a safe manner to test for saturation, I'd recommend looking up olefin tests, common for characterizing petroleum products. Negative results to these tests give you a reasonable measure for saturation.