Sciencemadness Discussion Board - benzene from crude oil at home lab

benzene from crude oil at home lab

nikotyna1939 - 26-9-2018 at 22:46

anybody knows ways to synthesize benzene from crude oil at home lab ?

Ubya - 27-9-2018 at 05:38

Extracting anything from crude oil is a hard task in an amateur setting, if you want to separate benzene using just distillation you'll need really long and efficient fractionation columns, then the purification steps to remove olefins and other aromatics from the fraction containing mostly benzene is hard. Not really an amateur experiment. If you just need benzene use other methods as described many times in this forum, but if you want to do it just for fun good luck

macckone - 27-9-2018 at 07:10

Not to burst a bubble but crude oil consists of less than 1% benzene.
Most benzene is made by hydrothermal cracking at high temperature and pressure.

But if you really want to try:

First step in refining crude oil is to get three fractions.
The stuff boiling below what you want <50C.
The stuff boiling in a range that contains your product 50C - 110C.
The stuff that boils higher >110C.

Throw out the flask coated with tar from the initial distillation or save it for the next run.
The first step is to get something you can work with as crude oil is horrible.
You may need some xylene to thin out the crude oil to get a workable mixture.
Light sweet crude is preferred as it is less viscous and contains less sulfur compounds as well as more aromatics.

Take the chosen fraction and rinse with water.
Then sulfuric acid to remove thiols and amines.
Then rinse with water again.
Then rinse with sodium hydroxide solution to remove acids.
Then rinse with water again.
Then dry it over magnesium sulfate.
Each of these steps requires shaking well.

Then use a packed column to distill the chosen fraction reflux is helpful.
You will want to collect from 70 to 85C in this stage.

The next stage you are going to want a packed column with 10 x reflux.

You will get three fractions of interest:
two azetropes:
cyclohexane - 45%/benzene 77.8C
n-heptane - 1%/benzene 80C
and benzene 80.1C

The first fraction is separable from the other two with just 10 x reflux.

Getting the cyclohexane and heptane out requires ethanol.
This also requires heavy reflux with a packed column to get good separation.

Then you get azetropes
ethanol - 45%, benzene - 68.2C
ethanol - 18%, benzene - 74% and water - 7% - 64C

The first fraction needs water added to get the second azetrope and mix the two and redistill.
This will give only the second azetrope and the benzene can be rinsed with water.
Then sulfuric acid then water again.
Then dried over calcium chloride.

And finally redistilled again.

This is a lot of work and if you don't have a 3 or 4 ft reflux column that can do 10 x reflux or better it is impossible. The good news is these columns are easy to build from copper which is a suitable metal.

Crude oil is very toxic as are the rinse solutions.
Please use appropriate precautions.
This is not easy for a home chemist.

Now for the real downside is the small amount of benzene you will get.

macckone - 27-9-2018 at 07:23

Now for other processing.
If you really want to process crude oil the first step is steam distillation with 300C steam.

This will hydrolyze a lot of the mix and distill off fractions boiling up to 300C as well as steam volatile compounds.

This is then fed into a cracking unit at 900C at about 7MPa (around 70 atmospheres).
This is separated into components.
Some components are hydrogenated.
Additional processing varies by component and factory.

But the short story is this isn't practical on a home scale.

JJay - 28-9-2018 at 04:18

I have wondered if this would be possible to do with something like a large, insulated sheet metal box with a lot of baffles that require vapors to snake a long, winding path. With one baffle per centimeter, a column only a meter high could have 100 baffles. I'm not exactly sure how many theoretical plates that would work out to, but it's surely a lot.

Code:



                    to condenser
                        ^
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
 ^
 
vapors in here

It wouldn't be particularly easy to put together such a column... you'd need to weld or otherwise place more than a hundred pieces of sheet metal. I'm not 100% sure it would work, but I don't see why it wouldn't.

Ubya - 28-9-2018 at 05:06

Quote: Originally posted by JJay

I have wondered if this would be possible to do with something like a large, insulated sheet metal box with a lot of baffles that require vapors to snake a long, winding path. With one baffle per centimeter, a column only a meter high could have 100 baffles. I'm not exactly sure how many theoretical plates that would work out to, but it's surely a lot.

Code:



                    to condenser
                        ^
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
|----------------------- |
| -----------------------|
 ^
 
vapors in here

to work every row should be insulated from all the others. in your design hot vapours travel horizontally, then up in the next row, and again horizontally but in the opposite direction. to work as a column there should be an equilibrium between liquid and vapour, and this thanks to the thermal equilibrium with the column. if the cooler vapour travels back where hot vapour is touching the walls it's going to warm again, so in the end the temperature will drop vertically, not horizontally, this would be like having a really wide condenser, not a tall one

[Edited on 28-9-2018 by Ubya]

JJay - 28-9-2018 at 06:25

Quote: Originally posted by Ubya

I don't think so, actually. I think what matters is the temperature at the condenser inlet and the reflux ratio. If some heat exchange occurs between vapor and liquid as it flows downwards, it could cause some vapors to condense and some liquids to evaporate. I believe that the apparatus would act quite similarly to a very long and well-insulated column. Then again, perhaps there is some reason that this apparatus wouldn't work as well as I think it would.

macckone - 28-9-2018 at 06:46

Congratulations, you have reinvented the (not theoretical) plate.

This is a plate column. Normally to improve retention there is a small lip on each plate. It needs to be well insulated and have a decent amount of reflux. A theoretical plate corresponds to one plate in this type of column.

macckone - 28-9-2018 at 06:52

Ps. the plate spacing needs to be a minimum of one inch (2.5 cm) from the lip to the next plate. With industrial units the spacing is generally higher. In an industrial plant the plates may have 10 inch (25 cm) spacing and 100 plates resulting in units that are a 100 ft (33M) tall as seen in a refinery.

[Edited on 28-9-2018 by macckone]

JJay - 28-9-2018 at 08:49

Why would the plate spacing need to be a minimum of one inch? For some reason, I highly doubt that physical plates would work out to theoretical plates exactly. I thought a plate column was more like a Snyder column...

Edit: Yes, this is a plate column. It's somewhat more complicated than a metal box with a bunch of simple baffles:

[Edited on 28-9-2018 by JJay]

macckone - 28-9-2018 at 09:22

Plate spacing is one inch for proper flow. cutting that in half yields a multiple for the resistance.
If you look at a chemical engineering handbook it should have the formula for resistance.
If you have a resistance of .01 atm for each plate, you will have a net pressure difference of 14.7 psi
from bottom to top with 100 plates. In commercial towers they actually make use of the pressure difference
and it is higher, but in a home environment that is a lot of pressure. You probably want less than .01 psi
pressure per plate. That would give 1 psi with 100 plates.

The theoretical plate is actually if you achieved 100% mixing of vapor and liquid at each stage with no heat loss.
The wiki article has a good explanation. But you are correct it will be less than one theoretical plate per plate.
https://en.wikipedia.org/wiki/Theoretical_plate

The bubble-cap plate as illustrated in the article provides close to the maximum theoretical. In that article they have a plate spacing 60 CM (24 in). That is for very high throughput. In the bubble-cap design the retention depth of the weir and the submersion of the bubble-caps determine the spacing and the pressure. One inch of submerssion on the bubble cap is about .03 psi which is 1.5 psi for a 50 plate tower which would exceed 100 ft.
In practice the bubble caps have more submerssion on industrial columns.

For a home rig you might consider off the shelf. This stuff exists.
https://moonshine-still.co/products/4-bubble-plate1?gclid=Cj...

Obviously you can make your own cheaper.
Honestly a three foot x 1" column with ring packing and 10x reflux
will separate azeotropic alcohol from 50%. The only complaint is backpressure is high.
a 2" column would be better.

happyfooddance - 28-9-2018 at 09:53

Quote: Originally posted by macckone

Obviously you can make your own cheaper.
Honestly a three foot x 1" column with ring packing and 10x reflux
will separate azeotropic alcohol from 50%. The only complaint is backpressure is high.
a 2" column would be better.

Or 3" or 4", depending on how much you're distilling. The great thing about a simple column as compared to these plate condensers, is that they can be easily adjusted to accomodate varying thoroughput by changing the column packing.

JJay - 28-9-2018 at 11:00

At this point, my most sophisticated column is two 30 cm Liebigs packed with broken glass. It's surely not sufficient for separating benzene from crude oil in a reasonable amount of time or volume.

Edit: deleted weird phantom image

[Edited on 28-9-2018 by JJay]

macckone - 28-9-2018 at 12:36

From my process, that should be sufficient for the first two stages. Since they are rough cutoffs. After that, your volume isn't going to be huge so you just need a way to do reflux. The first stage is a rough distillation. The second stage doesn't have to have reflux. But after that you are better off building a copper reflux column. You could use an air cooler condenser as the reflux section with glass but regulating the reflux may be difficult.