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Tubular Process
In the tubular process polymerization takes place in a long tube (>1000 m) at high pressure. The free radical initiator is introduced at different zones to optimize productivity and performance optimization.
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Heat from the reaction is evacuated by cooling the reaction wall. The reaction temperature profile is controlled by the amount and nature of the initiators.
Initiators are:
- Formerly oxygen
- Combinations of oxygen and peroxides
- Cocktails of peroxides in mono or multi-injection along the tube
(mix 3 - 4 initiators to sustain reaction over large T gradient)
The benefits of peroxide initiation, compared to O2 are:
- Lower initiation temperatures
- Extended cooling zones preventing max peak lagging and as a consequence
- Increased conversion rate of ethylene + 20 %
- More efficient use of reactor length - 10 %
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The addition of organic peroxide in various steps increases the conversion rate of ethylene (+ 20 %) and the use of a reactive transfer agent (ie. propanal) maintains good optical properties.
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When the change in temperature is too great to be sustained by a single initiator:
- Short half life peroxides (Luperox® 26) alone provide fast light-off, but lower peak temperature.
- Long half-life peroxides (Luperox® P) alone provide high peak temperature, but long light-off.
Cocktail (e.g. Luperox® 26 + Luperox® P) permits low light off and high peak temperature. In order to maximize productivity, peroxides "cocktails" are needed.
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