Cross-Linked Polyethylene Pipe Resin via Segmented Polymerization
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Solution Overview
Problem
The production of unimodal single-site resins using a single reactor results in incomplete polymerization, leading to increased risks of silica gel formation, reduced production rates, and unfavorable molecular weight distribution, which affects the cross-linkability and properties of polyethylene pipes.
Innovation Solution
A two-stage polymerization process using single-site catalysts in multiple reactors to produce a nominally unimodal ethylene polymer with improved molecular weight distribution and reduced silica gel formation, achieving higher yields and better cross-linkability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single reactor is used for polymerisation, then the process is simple and production rate is high, but incomplete polymerisation occurs leading to increased silica gel formation and poor molecular weight distribution
Solution Approach 1:
The polymerisation process is divided into two separate stages using two different reactors. The first reactor (gas phase) provides high production rate, while the second reactor (slurry phase) ensures complete polymerisation and removes silica gel formation. This segmentation allows each reactor to be optimized for its specific function, resolving the contradiction between productivity and reliability.
2Device complexity
If a single reactor is used for polymerisation, then the process complexity is low, but molecular weight distribution becomes broad and cross-linkability deteriorates
Solution Approach 1:
The polymerisation is segmented into two stages with different reactor types. The gas phase reactor produces polymer with certain MWD characteristics, while the slurry phase reactor further develops the molecular weight distribution to achieve narrowness. This two-stage approach enables precise control over MWD and cross-linkability while maintaining reasonable process complexity.
3Reliability
If residence time is extended to improve polymerisation completeness, then silica gel formation is reduced, but production rate decreases
Solution Approach 1:
The total residence time is segmented across two reactors. The gas phase reactor operates with shorter residence time for high productivity, while the slurry phase reactor provides extended residence time for complete polymerisation. This segmentation allows the system to achieve both high production rate and complete polymerisation without compromising either parameter.
4Manufacturing precision
If single site catalyst is used, then molecular characteristics are well defined, but silica gel particles still form due to short residence time
Solution Approach 1:
The use of single site catalyst is maintained in both reactors to preserve well-defined molecular characteristics. The harmful silica gel particle formation is eliminated by segmenting the process into two reactors, where the second slurry phase reactor provides sufficient residence time for complete polymerisation of any remaining monomer, preventing silica gel formation while maintaining the benefits of single site catalysis.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process results in ethylene polymers with enhanced cross-linkability, lower ash content, and improved pressure test performance, allowing for the production of more flexible and efficient polyethylene pipes with reduced energy requirements.
Implementation Method 1
polymerising ethylene and optionally at least one comonomer in a first stage in the presence of a single site catalyst
Implementation Method 2
polymerising ethylene and optionally at least one comonomer in a first stage in the presence of a single site catalyst; polymerising ethylene and optionally at least one comonomer in a second stage in the presence of the same single site catalyst
Data Source
Figure 1~2
AI summary
An ethylene polymer with a density of less than 955 kg/m3 obtained by polymerisation with a single-site catalyst and having a shear thinning index SHI2.7/210 of less than 5 wherein ethylene polymer comprises two components.