production of PE... (1 Viewer)

[lepton_index]

The dot point: Outline the steps in the production of polyethylene as an example of a commerically and industrially important polymer

I find some information but they are very inconsistent in terms of temperature, pressure, etc... And I'm not sure what we should include in the answer. Should it be about initiation, propagation and termination, or should it be about temperature, pressure, etc...?

Please help. Thanks alot.

 

[tina_goes_doo]

I went to this tutoring workshop in the hols and the tutor said all you really needed was the basics on initiation, propagation and termination. I'm not too sure on the reliability of that though.

Honestly what i would do is talk about the three steps (remember the dot point only says OUTLINE), then compare the different temperatures and pressures when producing LDPE and HDPE. Probably don't need the actual numbers, just a "very high" or "low" would do. As you said, they are inconsistent and different industries use different conditions anyway.

I hope that ramble helped.

 

[xiao1985]

gas phase polymerisation - 1000 - 3000 atm 700 k temperature... peroxide/oxygen initiator... end product bein LDPE (significant chain branchin)

zeigler natta process - few atm (2-3) 60C... trialkyl aluminium and titanium tri cloride catalyst... HDPE, less chain branchin...

 

[tina_goes_doo]

gas phase polymerisation - 1000 - 3000 atm 700 k temperature... peroxide/oxygen initiator... end product bein LDPE (significant chain branchin)

zeigler natta process - few atm (2-3) 60C... trialkyl aluminium and titanium tri cloride catalyst... HDPE, less chain branchin...

I have the conditions for LDPE as 300C and >3000atm.
HDPE (ziegler-natta) as 80C - 100C and 20atm.

So yeah, all the conditions are different. They won't be too picky, just pick one if you really want to use numbers. As long as the conditions seen correct in terms of high/low pressure etc, then they can't mark you down.

 

[za]

c how in the production of LDPE a catalyst such as aperoxide is used, is it removed later onwards or does it reamin part of the polymer.

wat im trying to ask ask is whetheror not there is still any peroxide in the polyehtene once the process has been terminated.

 

[BlackJack]

The answer is no. Remember that catalysts do not end up inside the product.

The peroxide serves to take an electron from the ethene double bond, and does not take part in the other steps of the polymerisation. In the end you have chains, and what is left from the peroxide separately.

 

[lepton_index]

Thanks very much. I got the specific temperature and pressure.

 

[za]

The answer is no. Remember that catalysts do not end up inside the product.

dont worry, my mistake. I misunderstood the picture on p.25 of the Contextx book.

thnx

 

[xiao1985]

The answer is no. Remember that catalysts do not end up inside the product.

The peroxide serves to take an electron from the ethene double bond, and does not take part in the other steps of the polymerisation. In the end you have chains, and what is left from the peroxide separately.

have to disagree black jack...

peroxide is an initator, and it is build into the polymer chain... tho only 1 per polymer chain(which is more than thousands of monomer units) it strictly speakin not a catalyst...

 

[mr EaZy]

peroxide decomposes to be a radical and breaks down an ethene monomer double bond. id say it is a polymer

 

[green_appletini]

The answer is no. Remember that catalysts do not end up inside the product.

The peroxide serves to take an electron from the ethene double bond, and does not take part in the other steps of the polymerisation. In the end you have chains, and what is left from the peroxide separately.

i was just reading about it in the Conquering Chemistry text book when i saw this thread haha, it says that the initiator is PEROXIDE and that it's not strictly a catalyst b/c it gets incorporated into the actual polymer formed (low density polyethylene).

-marilia- xoxo

 

[Li0n]

gas phase polymerisation - 1000 - 3000 atm 700 k temperature... peroxide/oxygen initiator... end product bein LDPE (significant chain branchin)

zeigler natta process - few atm (2-3) 60C... trialkyl aluminium and titanium tri cloride catalyst... HDPE, less chain branchin...

the point asks for steps, not conditions required.
So id rather talk about initiation propagation and termination along with the use of peroxide and say what happens in each step.

 

[tennille]

green_appletini is right. It is an INITIATOR, not a catalyst. Yes, a catalyst doesn't get incoporated into the product but an initiator does. There is one initiator molecule per 2000-3000 monomer units of ethylene. So yes, the peroxide molecule is incorporated in LDPE.

 

[green_appletini]

the point asks for steps, not conditions required.
So id rather talk about initiation propagation and termination along with the use of peroxide and say what happens in each step.

but don't you sort of have to put in the conditions if you're doing steps??

also, how detailed are the steps? cos in the text book it seems to be really brief and just says an initiator blah blah is used to help join the monomers, so what are the actual steps? thanks!

-marilia- xoxo

 

[Li0n]

but don't you sort of have to put in the conditions if you're doing steps??

also, how detailed are the steps? cos in the text book it seems to be really brief and just says an initiator blah blah is used to help join the monomers, so what are the actual steps? thanks!

-marilia- xoxo

Thats detailed enough i think.

The only different conditions are that for LDPE which is high pressure high temp [somehow] causes the branches to be long which doesnt allow close packing, whilst the HDPE Ziegler natta along with the titanium chloride catalyst or something [somehow] causes the brances to be very short and linear which allows for close packing.

 

[nit]

If you're accounting for linearity for HDPE, then all you need to do is talk about the rxn as occuring on the surface of the catalyst, while backbiting occurs in the polymerization of ethene to LDPE.

As for the organic peroxide (eg benzoyl peroxide), it will certainly be contained in the final product - there's no elimination reaction that will remove an RO group from the end product, unless you have something like an acid floating around...and you certainly don't have that in this system....

 

[steph@nie]

Thats detailed enough i think.

The only different conditions are that for LDPE which is high pressure high temp [somehow] causes the branches to be long which doesnt allow close packing, whilst the HDPE Ziegler natta along with the titanium chloride catalyst or something [somehow] causes the brances to be very short and linear which allows for close packing.

catalyst also has a trialkylaluminium cpd doesnt it?

 

[tennille]

has titanium (III) chloride and a triakylaluminium compound.

 

[Li0n]

i cbf memorising or stating the other one and i will be doing the same in the hsc, i got shit loads of more important stuff to remember ^_^