Loop Reactor Volume Balance for Multimodal Polyethylene
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Solution Overview
Problem
In multiple reactor systems for olefin polymerization, achieving an ideal size profile and catalyst activity balance between reactors is challenging due to varying catalyst types and cooling requirements, making it difficult to produce multimodal polyethylene efficiently.
Innovation Solution
Using two loop reactors of approximately the same size, with a volume difference of less than 10%, to maintain consistent polymerization processes and reduce construction costs, while optimizing catalyst activity and cooling capacities to produce multimodal polyethylene with a desired block ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the second and subsequent loop reactors are made larger to handle polymer from previous reactors, then the ability to handle polymer transfer is improved, but the flexibility to operate different catalyst types and optimize cooling requirements deteriorates
Solution Approach 1:
The patent merges the functions of handling polymer transfer and optimizing catalyst operations by making all loop reactors the same size. This uniform design allows each reactor to be equally capable of handling polymer from previous reactors while maintaining flexibility for different catalyst types and cooling requirements, eliminating the need to prioritize one function over the other.
Solution Approach 2:
By designing all loop reactors with identical dimensions, the patent creates a universal reactor configuration that can perform multiple functions: handling polymer transfer, supporting different catalyst types (Ziegler-Natta, chromium, metallocene), and accommodating varying cooling requirements. This universal design eliminates the trade-off between polymer handling capacity and catalyst flexibility.
2Productivity
If loop reactors of different sizes are used to optimize polymer handling, then polymer transfer capability is improved, but construction costs and process complexity increase
Solution Approach 1:
The patent combines the advantages of different reactor sizes by making them all the same size, thereby achieving both efficient polymer transfer and cost-effective construction. The uniform design allows standardization of reactor components and simplifies the overall system architecture, reducing construction costs while maintaining effective polymer handling capability across all reactors.
3Adaptability or versatility
If reactors of the same size are used, then construction costs are reduced and flexibility is improved, but the ability to handle increasing polymer volumes from upstream reactors becomes limited
Solution Approach 1:
The patent applies universality by designing all reactors with identical dimensions, creating a system where each reactor has the same capacity to handle polymer volumes. This uniform design ensures that polymer transfer between reactors of the same size is efficient, while simultaneously maintaining flexibility for different catalyst types and operating conditions, thus achieving both goals without compromise.
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
This approach allows for a wide range of polymerization processes using different catalysts, achieving high space-time yields and minimizing the need for recompression in flash tanks, thus enhancing efficiency and reducing costs.
Implementation Method 1
the slurry in the reactor will comprise the particulate polymer, the hydrocarbon diluent(s), (co) monomer(s), catalyst, chain terminators such as hydrogen and other reactor additives
Implementation Method 2
The heat of polymerisation is typically removed using indirect exchange with a cooling medium, preferably water, in jackets surrounding at least part of the tubular loop reactor
Implementation Method 3
optionally using concentrating devices such as hydrocyclones or settling legs to minimise the quantity of fluids withdrawn with the polymer
Implementation Method 4
optionally using concentrating devices such as hydrocyclones or settling legs to minimise the quantity of fluids withdrawn with the polymer
Data Source
AI summary
Process for producing a multimodal polyethylene in at least two loop reactors connected in series. In the process 20-80 wt % of a high molecular weight (HMW) polymer is made in suspension in a first reactor and 20-80 wt % of a low molecular weight (LMW) polymer is made in suspension in a second reactor, one polymer being made in the presence of the other in either order. The ratio of the average activity in the LMW reactor to the average activity in the HMW reactor is from 0.25 and 1.5, where average activity in each reactor is defined as the rate of polyethylene produced in the reactor (kgPE/hr)/[ethylene concentration in the reactor (mol %)×residence time in the reactor (hours)×feed rate of catalyst into the reactor (g/hr)], residence time being defined as the mass of the polymer in the reactor (kg)/the output rate of polymer from the reactor (kg/hr), and the volumes of the two reactors differ by less than 10%.