Industrial Production Of Polyethylene
Raw Material:
The first polyethylene plant built by ICI used ethylene produced by dehydration of ethanol. Modern ethylene production plants are based on the thermal cracking of hydrocarbon feed stock at 800-900°C The polymerization grade ethylene is 999 vol% pure The main impurities of importance to free radical polymerization are oxygen and water. Oxygen could cause inhibition of low temperature initiators, or uncontrolled initiation of reaction at higher temperatures Water can form ethylene hydrate in the cooler parts of high-pressure process, completely blocking the pipes. Hydrogen is poison only for Phillips catalyst.
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The main types of processes used to manufacture polyethylene are:
1.High-pressure autoclave.
2.High pressure tubular
3.Gas-phase fluidized bed
4.plurry phase autoclave/loop
5.Solution autoclave
Modern polyethylene production processes offer the possibilities of a versatile range of products. High-pressure processes can produce LLDPE in addition to the normal range of LDPEs and ester copolymers. As well as HDPE some low-pressure plants can also produce LLDPE and VLDPE
Following Table gives the technical applicability of processes for polyethylene manufacture.
+ Suitable; 0 Technically feasible with some limitations; – Unsuitable
From the above Table following conclusions can be drawn.
1. LDPE, EVA and Acrylate copolymers can be manufactured only by high-pressure processes.
2. HDPE is preferably manufactured by low-pressure catalytic process.
3. LLDPE can be manufactured by both processes.
4. Gas-phase fluidized bed is the most popular process.
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