Sciencemadness Discussion Board

What's the difference between cracking and distilling?

gnitseretni - 16-11-2010 at 08:23

After reading that one can get a diesel like fuel from Waste Motor Oil (WMO), I build a crude setup to heat WMO and yesterday I tried it for the first time. But what I got looks like new motor oil and has about the same viscosity as new motor oil as well. I think what I did was simply distilling WMO and ended up with new motor oil instead of what I wanted to do which was "cracking" the WMO and getting a diesel like fuel. So I distilled it instead of "cracking" it. Why? What exactly is "cracking"? I'm talking about non-catalytic cracking. I've researched the non-catalytic cracking process and I don't see how its different from distilling. The only thing I can think of is that maybe cracking requires more heat. Is that what it is?

One more thing... can you also get gasoline from WMO? Probably not as I couldn't find any info on it but thought I'd ask just to make sure.

gsd - 16-11-2010 at 08:31

cracking is a chemical reaction ; in case of WMO it is thermal decomposition of long carbon chain to 2w or more chains having lesser number of carbon atoms.

Distillation is a physical separation of different chemical species which is based on the difference in boiling points (and relative volatility) of those species. If any of the species you are trying to distill-off is having higher boiling point than its decomposition temperature then you will first have cracking of that species and then distillation of the resulting products.

gsd

gnitseretni - 16-11-2010 at 08:36

Ok, so I need more heat then, to decompose it instead of distilling.

ScienceSquirrel - 16-11-2010 at 09:24

The beginner's guide to cracking;

http://en.wikipedia.org/wiki/Fluid_catalytic_cracking

gnitseretni - 16-11-2010 at 10:32

I quoted the text below from here http://multi-science.metapress.com/content/b85595646p38843j/

They say the aim of their study is to get a gasoline like fuel from waste motor oil by catalytic pyrolysis, and under acceptable processes they listed distillation.

So distillation will work if I add 10% by weight of perlite to the waste engine oil? Hmm... I might try that, perlite is cheap and easy enough to get.
Quote:

The aim of this study is to obtain gasoline like fuel from waste engine oil by catalytic pyrolysis which can be used in internal-combustion engines. Petroleum based waste engine oil can be converted into reusable products such as gasoline and diesel fuel. The aims of waste engine oil processing are upgrading via recycling and re-refining processes of the petroleum based wastes by converting them into reusable products such as gasoline and heavy oil. <b>Possible acceptable processes are distillation, cracking and pyrolysis. </b>The pyrolysis liquid products of waste lubricant oil can be used as alternative engine fuel. The yields of liquid products, they were called as "waste oil gasoline" increase increasing temperature and catalyst amount. To investigate the effects of catalysts on the yields of distillation the purified oil samples were blended as mass basis of 2.5%, 5.0 %, and 10.0 with catalysts known as perlite and wood ash. The highest yield of liquid product was 92.5% which can be obtained from the pyrolysis with 10% perlite. The yields of liquid products from pyrolysis of waste lubricant oil in the presence of perlite are higher than those of wood ash catalytic runs.

12AX7 - 16-11-2010 at 12:01

Cracking occurs at higher temperatures or harsher conditions than distillation. For instance, in the presence of catalysts, hydrogen, steam, pressure and heat.

In lieu of high pressure distillation apparatus, you might be better off boiling the oil and directing the vapors through a heated catalyst tube, where cracking occurs.

Tim

gnitseretni - 16-11-2010 at 16:13

Quote: Originally posted by 12AX7  

In lieu of high pressure distillation apparatus, you might be better off boiling the oil and directing the vapors through a heated catalyst tube, where cracking occurs.
Tim


What is this heat catalyst tube made of, do you know? Or does the material even matter, I thought it was the heat that actually does the cracking? If it's the heat, than do you think passing the vapor through a tube, that's heated externally, filled with steel wool would work?

not_important - 16-11-2010 at 17:35

You could get away with that. When I was fairly young I had a home experiments in chemistry book that including an example of cracking (we're talking the late 1950s, goys and birls); a longer test tube had some motor oil placed in it, some steel wool stuck in a bit down from the top, the section with the wool heated and then the bottom heated as well. The ascending oil vapours cracked on the steel wool, giving rise to a mixture of gases and lower boiling liquids.

The problem with this simple form is that it suffers from non-selectivity and carbon build-up. With a simple acyclic alkane C<sub>N</sub>H<sub>2+2N</sub>, it breaks down giving shorter chains of alkanes and alkenes and carbon left when, the hydrogen one boded to the carbon fills out the smaller alkanes. To avoid rapid carbon build up hydrogen and/or steam is added, the steam reacting through the water gases family of reactions to give H2 and carbon oxides.

The difference between cracking and pyrolysis is blurry. Pyrolysis generally being the simple heat driven decomposition, while cracking employs steam/H2 and catalysts to favour the formation of hydrocarbons over carbon and/or to help shape the product distribution. The catalytic processes generally still suffer from carbon buildup and need periodic treatment to remove it.

So, yeah, a steel tube stuff with steel wool and heated would work. However there'd be little selectivity in the products formed, and it would soon become less active as carbon coated the steel.


Sedit - 16-11-2010 at 19:07

Cracking is heating the shit out of a hydrocarbon until it breaks into two pref with a catalyst of some sort. As you distill heat your factioning gear with a torch.... this would equate cracking in a sence.....

Please dont try the above until you understand it.

12AX7 - 16-11-2010 at 20:05

Some other options besides iron include copper (brillo pads??), silica gel, alumina, or any of the various popular catalysts, like Pt or Pd on glass wool. Or just glass wool, probably anything with a lot of surface area would work.

Tim

gnitseretni - 16-11-2010 at 21:14

If it gets coated with carbon quickly, I'd probably want to use whatever's cheapest.

Btw, anyone have any idea what exactly the perlite does that they talked about in the text I quoted earlier?

watson.fawkes - 16-11-2010 at 21:40

Quote: Originally posted by gnitseretni  
Btw, anyone have any idea what exactly the perlite does that they talked about in the text I quoted earlier?
It's got analogous activity to zeolites, a family of commercial catalysts for cracking hydrocarbons. Both minerals are alumino-silicates. See the link posted above by Science Squirrel.

gnitseretni - 17-11-2010 at 13:04

Picture of my setup:
Full size: http://img99.imageshack.us/img99/2189/mysetup003.jpg




Here's a rough drawing of how I would make it if I were to use a catalyst:
Full size: http://img808.imageshack.us/img808/5092/catalyticcracking.jp...



With my current setup, the vapor goes right to the condenser (black arrows). The red arrows show how I would do it if I were to use a catalyst. The vapor would go from the top, down the side of the barrel and then entering the barrel a third from the bottom or so, then going through the tube with the catalyst, and then exiting on the other side and from there it would have to travel up to the condenser. The tube with the catalyst would get nice and hot being right over the hot coals.

Whatcha think? Yes no maybe?

not_important - 17-11-2010 at 13:05

Note that small scale cracking is a low yield process, more energy goes into it than is recovered as useful fuels. Small scale is good for demonstration of the process, and diddling around with catalysts in attempts to control what products are formed.

Sense - to perceive (I sense a draft of cold air), or to be logical (it makes sense to me)

cents - a small denomination coin, common in the USA

scents - odors, in particular those intended to be pleasant.

gnitseretni - 23-11-2010 at 10:17

I changed my setup. Now it looks exactly like my drawing 2 posts up.

The first time I did it, I had to stop early because I noticed a leak. But the little bit that came over had about the same viscosity as gasoline and would light just as easily as gasoline as well.

I fixed the leak and tried again. What I got at first, again had about the same viscosity as gasoline and would light just as easily as gasoline, but this didn't last long. As the fire got hotter I guess the catalyst stopped working because what was coming over was new motor oil.

Does anyone have any idea what might have happened? If the steel wool got oxidized, would that prevent it from cracking the oil?

gnitseretni - 23-11-2010 at 15:45

Ok, I think I know the answer. The steel wool got too hot. I placed some more steel wool in the tube, I placed it at the very end on both sides which is just outside of the barrel but still plenty hot, just not as hot as the steel wool in the middle which is inside the barrel. I'm now getting something resembling gasoline again. Low viscosity, catches fire easily. It does smoke a little though, there's probably some diesel or something in there or perhaps uncracked motor oil.

not_important - 26-11-2010 at 10:55

Yeah, a simple rig such as yours is not going to give near complete conversion, and generally fractional distillation (more properly fractionating columns) is used to pull off the desired fractions will heavies are recycled and lights often are collected to use as heating fuel for the processes.

gnitseretni - 27-11-2010 at 05:40

I'm going to distill the gasoline out and recrack the heavies. I wish I could do that in one step but that would make it too complicated not to mention too expensive. I know everybody's thinking I'm wasting my time here, and I probably am, but for the moment I'm still interested in this so I'll keep on going for a little while longer. Actually, I'm going to try it with waste plastic also.

gnitseretni - 27-11-2010 at 11:39

Argh, it's like the steel wool is only good for one use!
I'm cracking more motor oil as we speak. In the beginning I got a gasoline like liquid, but soon after that nothing but motor oil.

Not_important, you mentioned the catalyst would need periodic cleaning due to carbon buildup. But after just one use? Isn't that a little fast? Perhaps my steel wool is being poisoned another way?
I know, I know.. lots of questions, and I suppose the answer could be anything considering my crude setup. Oh well.

bquirky - 27-11-2010 at 11:54

prehaps its not hot enough.. and the steel wool is being cooled down by the oil.. or the steel wool cant conduct enough heat from the walls of the tube.

I cant help but feeling you'd be better off running some kind of steam engine and just plain old burning your waste oil and plastic, a well designed boiler chould probobly get close to complete combustion.

I know that some guys that are into running back yard metal founderys use used motor oil as a cheap fuel for there furnaces