Production of HDPE (1 Viewer)

[rheyn]

Hi,

I know that the production of LDPE involves initiation, propagation and termination.

However how is HDPE produced?

I know its through the Ziegler-Natta process and it use a catalyst which is a mixture of Titanium(III) Choride and a trialkylaluminium (e.g. triethylaluminium), but how is it initiated?

From what I've read it doesn't use an intiator molecule so how does the ethene monomer become a free radical (activated monomer) to propagate?

Also what happens to the organic peroxide radical in termination during LDPE production? Is it still present during termination? I read that it the peroxide radical becomes "engulfed in the reaction", what does that mean?

 

[Pwnage101]

from my experience doing 30+ past papers, all this is way more detail than you actually need to know

from my knowledge HDPE is initiated in the same way, but the zieghler natta cataclyst provides a surface for the polymerisation to occur with little branching - but i'm not completely sure of this

and that's all i'm sure enough to say because i think this is way too mu h detail for the syllabus

 

[rheyn]

Ok, so they will never ask you a question such as "Describe the process by which High Density Polyethylen is produced" and you will need to describe initation, propagation and termination?

 

[Pwnage101]

not even that, in past papers they have RARELY asked specifically for LDPE/HDPE in terms of production - they just ask how a polymer is produced in egneral

they want u to compare LDPE/HDPE in terms of their uses due to their properties, more often

 

[imoO]

If you really wanted to know, I believe HDPE is produced at higher(or lower, somebody help me here) temperatures, and high pressures <--I'm sure on pressure...not on temperature.

 

[Pwnage101]

isnt it low temperature, and relatively low pressure (lower than LDPE)?

http://www.ausetute.com.au/polythen.html
http://www.icis.com/v2/chemicals/9076153/polyethylene-high-density/process.html

 

[imoO]

isnt it low temperature, and relatively low pressure (lower than LDPE)?

Polythene: Production and Properties & Uses
Polyethylene - high density (HDPE) Production and Manufacturing Process

Hmm..I guess you're right. I swear I remember HDPE at higher pressures, but it seems you're right. I take it back, sorry

 

[rheyn]

Ok then thanks alot Pwnage101. You've helped heaps.

Can you also explain what happens to the initiator radical during LDPE production. Is it still part of the polymer after termination?

And what does "engulfed by the reaction" mean?

Thanks



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[H4rdc0r3]

Hi,

I know that the production of LDPE involves initiation, propagation and termination.

However how is HDPE produced?

I know its through the Ziegler-Natta process and it use a catalyst which is a mixture of Titanium(III) Choride and a trialkylaluminium (e.g. triethylaluminium), but how is it initiated?

From what I've read it doesn't use an intiator molecule so how does the ethene monomer become a free radical (activated monomer) to propagate?

Also what happens to the organic peroxide radical in termination during LDPE production? Is it still present during termination? I read that it the peroxide radical becomes "engulfed in the reaction", what does that mean?

HDPE is produced the same way as LDPE (initiation, propagation and termination) except that it uses a Ziegla-Natta catalyst which allows the process to be conducted under lower pressure and temperature (after all it is a catalyst). I'm pretty sure it uses the same free radical to open and combine with the first ethene double bond.

I guess the initiating organic peroxides just stays there because it just says that the polymerisation terminates when two free radical ethene chains join together. Either way it doesn't make a difference as it won't be tested, its just a random fact and its not in the syllabus.

where have you read this random stuff about engulfing?

 

[Pwnage101]

Ok then thanks alot Pwnage101. You've helped heaps.

Can you also explain what happens to the initiator radical during LDPE production. Is it still part of the polymer after termination?

And what does "engulfed by the reaction" mean?

Thanks



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1) u don't need to know this,a nd eveni don't know this with certainty but:

2) if u really have to know, it is my understanding the initiator radical is present after termination, as it is terminated :

a) NATURALLY - 2 acivated polymer chains join to terminate each other
b) ARTIFICIALLY - peroxide (initiator) molecules are released to terminate the chains

so yeh

never heard of "engulfed by the reaction", and this is not in any of the texbooks on the market i have read, so yeh

glad to help

 

[clintmyster]

I noticed you guys using the word catalyst. Just be careful of this because the initiator is consumed in the reaction and therefore not a catalyst.

 

[H4rdc0r3]

I noticed you guys using the word catalyst. Just be careful of this because the initiator is consumed in the reaction and therefore not a catalyst.

yo douche bag. read properly.

 

[Pwnage101]

I noticed you guys using the word catalyst. Just be careful of this because the initiator is consumed in the reaction and therefore not a catalyst.

uh we used the terms corectly - initiator is used in production of both LDPE and HDPE, but HDPE uses an additional catalyst (ziegler-Natta)