Polyolefin Melt Index Control via Monomer Pressure Adjustment
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Solution Overview
Problem
In polyolefin production via gas-phase fluidized bed polymerization, the use of induced condensing agents (ICAs) increases production rates but adversely affects the melt index of the polyolefin, which is undesirable as it deviates from the specified range required for downstream applications, and the use of hydrogen to counteract this effect is not preferred with certain catalyst systems.
Innovation Solution
Adjusting the monomer partial pressure and potentially altering the catalyst ratio in a multimodal catalyst system to maintain the polyolefin melt index within the desired range, thereby mitigating the need for hydrogen addition and minimizing the use of additional catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If induced condensing agents (ICAs) are added to increase production rates, then productivity increases, but the melt index of the polyolefin deviates from the specified range
Solution Approach 1:
The patent changes operating parameters (monomer partial pressure, reactor temperature, ICA concentration) to maintain melt index within specifications while operating at higher production rates with ICAs present. This allows the system to achieve higher productivity without sacrificing product quality.
Solution Approach 2:
The patent introduces hydrogen as an intermediary substance that mediates between the ICA's effect on productivity and the melt index specification. Hydrogen acts as a chain transfer agent that adjusts molecular weight and melt index while allowing the ICA to maintain its productivity-enhancing role.
2Manufacturing precision
If hydrogen is added to counteract the melt index change caused by ICAs, then melt index control is improved, but catalyst system compatibility is compromised
Solution Approach 1:
The patent changes the approach from adding hydrogen to adjusting other parameters such as monomer partial pressure, reactor temperature, and ICA concentration. This allows melt index control through parameters that are compatible with the specific catalyst system being used.
Solution Approach 2:
The patent extracts the hydrogen addition step from the process for catalyst systems where it is incompatible, and replaces it with alternative parameter adjustments that achieve the same melt index control objective without using hydrogen.
3Manufacturing precision
If additional catalysts are used to maintain melt index, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses parameter changes (temperature, pressure, concentration) to control melt index instead of adding additional catalysts. This maintains manufacturing precision while avoiding the complexity and cost associated with multiple catalyst systems.
Solution Approach 2:
The patent extracts the additional catalyst addition step and replaces it with parameter adjustments, thereby simplifying the catalyst system while maintaining melt index control within specifications.
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 increased polyolefin production rates while maintaining the melt index within acceptable limits, eliminating the need for hydrogen and reducing catalyst costs, thus optimizing polymer properties for downstream processing.
Implementation Method 1
Cooling of the recycle stream to a temperature below the gas dew point temperature produces a two-phase gas/liquid mixture
Implementation Method 2
The liquid phase of this two-phase gas/liquid mixture in condensed mode operation is generally entrained in the gas phase of the mixture
Implementation Method 3
Vaporization of the liquid occurs only when heat is added or pressure is reduced. Generally, the vaporization occurs when the two-phase mixture enters the fluidized bed, with the resin providing the required heat of vaporization
Implementation Method 4
since the polymerization reaction is exothermic, the amount of polymer produced in a fluidized bed polymerization process is related to the amount of heat that can be withdrawn from the reaction zone
Implementation Method 5
Generally, the recycled gas stream is heated in the reactor by the heat of polymerization. This heat may be removed in another part of the cycle (e.g., by a cooling system external to the reactor such as a heat exchanger)
Implementation Method 6
In a typical gas-phase fluidized bed polymerization process, a gaseous stream containing one or more monomers is continuously passed through the fluidized bed under reactive conditions
Data Source
AI summary
The use of induced condensing agent (ICA) in fluidized bed gas phase reactor systems enables higher production rates but can affect the resulting polyolefins melt index. The effect the increased ICA concentration may have on a melt index may be counteracted, if necessary, by altering the concentration of olefin monomer within the reactor system.