Getting at the gasoline, part three

Crude oil contains many components, all of them useful. Gasoline is one of those things. These wonderful things are separated from each other by heating the crude oil to the various boiling temperatures of the components, then recovering them by cooling the vapors back to liquid state and collecting those new liquids.

Some of the components are very liquid, some are thicker, some are almost solid, or actually solid. The crud ones that are solid/almost solid require the highest boiling temperature to boil them.

Below is a list of the components of crude oil and show their boiling temperatures. Somewhere in this discussion I should work in an explanation of carbon chains, but I'm not going to do that right now. Here is a list (heavy on the bottom and the light stuff on the top.) Click to enlarge the chart:

You have most likely passed by an oil refinery and noticed the tall distilling towers. Basically, the crude oil supply is piped into the bottom of those towers up to a certain height and then heated (usually by steam). The bottom is hottest and so the lighter parts "boil" off and the vapors go upwards, of course. As the vapors get higher and higher in the tower, they get cooler and cooler since they are farther from the heat source at the bottom. When the various vapors get high enough (cool enough) they turn back into liquids. The various liquids are collected into trays at the various heights and drawn off out of the tower and piped to separate containers/holding tanks. One for gasoline. One for Diesel. One for kerosene. One for motor oil. And so forth. The "trays" at the various heights all have perforations ("bubble caps" like a soda pop bottle with a loose cap?) in them so the lighter components which are still vapor can keep going up higher into the tower until they too cool enough to liquify. Each catch tray is located at the height in the tower that is at the right temperature. See?

I will put up another picture to show this better. But the main thing to remember is that the entire crude oil is being boiled at the bottom of the tower and that means everything but the very heaviest components boil off and rise up the tower. When they cool enough to pass back through their boiling temperature, they liquify again, at different heights in that distilling tower. So thats how crude oil gets separated into the various parts we use for many different things.

Oil refinery distillation towers (columns) and holding tanks

You can go here to see an animation of the distillation process. (Go to the link and then scroll down toward the bottom of the page to see the flash animation.) Please do go look, because it will give you a much better understanding of the process than I can describe in words here. This is located at a very interesting site called "How Stuff Works". If you have an interest in more details of how crude oil is refined, stay on that site and read for hours! I can't tell you how much I like that website or how highly I commend it to you.

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Do you know what octane is? Do you know what "Cat Cracked" means? If you visit this space tomorrow, you will know these things and even more!

Getting at the gasoline, part two

Fractional distillation is a process that separates the individual components of a chemical mixture, by heating the mixture to the various boiling points of the components.

Gasoline is extracted from crude oil (petroleum) by fractional distillation.

If you have 5 gallons of water and a bottle of whiskey, it is easy to combine those chemicals: simply dump the whiskey into the water and stir.

But how do you get the alcohol back out again? Not quite so easy.

Not very hard either: simply heat the water until it is above the boiling point of the alcohol (174 degrees F.) and collect the alcohol vapor as it rises off the top of the mixture. Then, run the alcohol vapor through a tube whose other end is hanging over an empty contatiner, and BOOM! the alcohol will cool back to a liquid in the tube (assuming you made the tube long enough) and the liquid will drip into the empty container. The water will remain in the first container, since you didn't heat it enough for water to boil (212 degrees F.)

Actually, there is no BOOM! when this happens. I just threw that in there.

Neglecting little real-life details, such as you are unlikely to get all the alcohol out of the water the first go-around, that's basically how fractional distillation works.

Want a more practical example? OK:

1. Put some (human edible) carbohydrate into a kettle and add some water and yeast and mix it up. Put an airtight lid on the kettle. Run some coiled copper tubing from the airtight lid up to the ceiling and down the wall so the other end of the tube is hanging over an empty catch container. Put a little on-off valve in the copper tubing as it comes out of the kettle lid. Turn the valve to the "off" position.

2. Wait for about 2 weeks so your mix (let's call it "mash" or "wash") can ferment.

3. At the end of the 2 weeks, come back and turn the little valve in the copper tubing to "on" so the vapor can escape out of the kettle and build a fire under the kettle. Slowly heat the mixture. Not too hot. Hot enough. 174 degrees F. If you really do this, you will want to rig up a thermometer so you can see how hot it is inside the kettle.

4. Put the liquid that drips out of the other end of the copper tube into bottles. Or jugs.

5. Don't light a match while you put it in bottles.

This is fractional distillation. Alcohol (ethanol) is created by the action of your mash mixture fermenting, and heating the mixture separates the alcohol from the water and goop, as described at the top of this post.

Caveat: make sure the carbohydrate you use is edible by humans. Corn. Rye. Potato peelings. Cactus (agave.) ApplesPeachesPlumsCherriesBerriesPears. Molasses. Grapes. Sugar water. Like that.

Important: make sure your carbohydrate is clean and pure and edible by humans. Don't drink the stuff we talked about yesterday which was made by wood pyrolysis (destructive distillation.) That is methanol. Methyl alcohol. Wood alcohol. OK? Wood alcohol will make you drunk, but it will also make you blind. Stick to corn and other grains. Ethanol is the name of the alcohol you want to produce in this example. Not only can you get drunk on it, you can also burn it in your car (and probably already are). Unless you drive a diesel car.

We are sneaking up slowly on how we "make" gasoline. (Tomorrow)

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Disclaimers:

1. Don't do this.

2. Remember that pressure cookers can explode if they are not vented. An on-off valve is needed.

3. Remember that alcohol which is not still mixed with water is flamable.

4. Ethanol is made from EDIBLE carbohydrate. Clean. Not rotten. Pure.

5. It is not legal (in the U.S.) to distill spirits. It is especially not legal to sell the bounty of your mash. Unless you get a permit to do so from the government and put tax stamps on all your bottles. Good luck with that permit.

6. You CAN make up to 100 gallons of wine and 100 gallons of beer per person per household for personal consumption. You still can't sell it.

7. If you filter the fermented goop and drink the liquid (without distilling it) it is called wine. Or beer, if you use malt and add hops, I guess. But that has nothing to do with fractional distillation, so I don't know why I told you that.

8. Don't do this.