Wednesday, August 8, 2012

Anonymous said: Hi! I stumbled upon your tumblr, and I'd like to start off by saying how amazing it is, and thank you for making this tumblr! Moreon to my issue, i'm currently studying crude oil in Chemistry. Could you please help me understand"cracking" in terms of crude oil? From what I understand, 'cracking' is the CHEMICAL process of breaking down large molecules into smaller ones. And they 'crack' crude oil to refine it into petroleum; fractional distillation being a PHYSICAL process. More info please?

It sounds like you’re a bit confused between fractional distillation and cracking. It’s true that cracking is a chemical process and fractional distillation is a physical process, but by saying that I mean to show you that they’re two entirely different processes.

When crude oil is first extracted from the ground, is made up of a variety of different hydrocarbons (chemical compounds that only consist of carbon and hydrogen), some very short (ethene) and some long (decane), and is entirely useless in this state.  Hydrocarbons can be separated into two groups: alkanes and alkenes. An alkane is saturated, meaning it holds as many hydrogen atoms as possible, whereas an alkene is unsaturated and contains a double carbon bond. 

Fractional distillation serves to separate the longer hydrocarbons from the shorter hydrocarbons by their boiling points. This works because the longer the hydrocarbon, the higher the boiling point and viscosity and the lower the flammability.

Fractional distillation takes place as follows:

  1. Crude oil is vapourised and fed into the bottom of the fractionating column.
  2. As the vapour rises up the column, the temperature falls.
  3. Fractions with different boiling points condense at different levels of the column and can be collected.
  4. The fractions with high boiling points (long chain hydrocarbons) condense and are collected at the bottom of the column
  5. Fractions with low boiling points (short chain hydrocarbons) rise to the top of the column where they condense and are collected.

To see a diagram of the fractional distillation process, click here.

Cracking on the other hand, breaks long alkanes down into shorter, more useful alkane and alkene molecules. It requires a catalyst (a substance that causes or accelerates a chemical reaction without itself being affected) and a high temperature. This is done mainly to assuage the high industrial demand for the shorter molecules. The alkenes are typically converted into polymers (plastics) while the alkanes are sought after as a fuel source. Cracking is an example of a thermal decomposition reaction.

I hope that helps clear up some of your confusion.

Friday, October 14, 2011
Going superfluid!
A liquid goes superfluid when it suddenly loses all internal friction and gains near infinite thermal conductivity. The combination of zero viscosity but nonzero surface tension allows a superfluid to creep up walls and back down the outside to drip from the bottom of open containers, or to completely cover the inner surface of sealed containers. Lack of viscosity also allows a superfluid to leak through a surface that is porous to any degree, because the molecules can slip through even microscopic holes. Superfluids furthermore exhibit a thermo-mechanical effect where they flow from colder to warmer temperatures, exactly the opposite of heat flow as stated by the laws of thermodynamics! That implies the remarkable property of superfluids of carrying zero entropy. Because of this, a perpetual fountain can be set up by shining light on a superfluid bath just below a vertical open capillary tube, causing the fluid to shoot up through and beyond the tube until its  contact with the air causes it to cease being a superfluid and fall back  down into the bath, whereby it will cool back into the superfluid state  and repeat the process.
So how does superfluidity work, exactly?
Makings of a superfluid
Physicists first got the inkling of something stranger than the norm when, around 1940, they cooled liquid helium (specifically, the 4He isotope) down to 2.17 K and it started exhibiting the above-mentioned properties. Since the chemical makeup of the helium didn’t change (it was still helium), the transformation to a superfluid state is a physical change, a phase transition, just like ice melting into liquid water. Perhaps for cold matter researchers, this transition to a new phase of matter makes up for the fact that helium doesn’t solidify even at 0 K except under large pressure - whereas ALL other substances solidify above 10 K.
[Phase diagram of 4He, source]
Helium is truly the only substance that never solidifies under its own vapor pressure.
Instead, when the temperature reaches the transition or lambda point, quantum physics takes hold and a fraction of the liquid particles drop into the same ground-energy quantum state. They move in lock-step, behaving identically and never getting in each others’ way. Thus we come to see that superfluidity is a kind of Bose-Einstein condensation, the general phenomenon of a substance’s particles simultaneously occupying the lowest-energy quantum state.
Read more:”This Month in Physics History: Discovery of Superfluidity, January 1938”. APS News: January 2006
Based on a project by Barbara Bai, Frankie Chan, and Michele Silverstein at Cornell University.

Going superfluid!

A liquid goes superfluid when it suddenly loses all internal friction and gains near infinite thermal conductivity. The combination of zero viscosity but nonzero surface tension allows a superfluid to creep up walls and back down the outside to drip from the bottom of open containers, or to completely cover the inner surface of sealed containers. Lack of viscosity also allows a superfluid to leak through a surface that is porous to any degree, because the molecules can slip through even microscopic holes. Superfluids furthermore exhibit a thermo-mechanical effect where they flow from colder to warmer temperatures, exactly the opposite of heat flow as stated by the laws of thermodynamics! That implies the remarkable property of superfluids of carrying zero entropy. Because of this, a perpetual fountain can be set up by shining light on a superfluid bath just below a vertical open capillary tube, causing the fluid to shoot up through and beyond the tube until its contact with the air causes it to cease being a superfluid and fall back down into the bath, whereby it will cool back into the superfluid state and repeat the process.

So how does superfluidity work, exactly?

Makings of a superfluid

Physicists first got the inkling of something stranger than the norm when, around 1940, they cooled liquid helium (specifically, the 4He isotope) down to 2.17 K and it started exhibiting the above-mentioned properties. Since the chemical makeup of the helium didn’t change (it was still helium), the transformation to a superfluid state is a physical change, a phase transition, just like ice melting into liquid water. Perhaps for cold matter researchers, this transition to a new phase of matter makes up for the fact that helium doesn’t solidify even at 0 K except under large pressure - whereas ALL other substances solidify above 10 K.

[Phase diagram of 4He, source]

Helium is truly the only substance that never solidifies under its own vapor pressure.

Instead, when the temperature reaches the transition or lambda point, quantum physics takes hold and a fraction of the liquid particles drop into the same ground-energy quantum state. They move in lock-step, behaving identically and never getting in each others’ way. Thus we come to see that superfluidity is a kind of Bose-Einstein condensation, the general phenomenon of a substance’s particles simultaneously occupying the lowest-energy quantum state.

Read more:
This Month in Physics History: Discovery of Superfluidity, January 1938”. APS News: January 2006

Based on a project by Barbara Bai, Frankie Chan, and Michele Silverstein at Cornell University.