Chromium Catalyst Flow Index Control
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Solution Overview
Problem
Chromium-based catalysts used in polyolefin production often fail to achieve the desired flow index response, leading to polymers with inappropriate molecular weights and distributions for specific applications, resulting in operational difficulties and suboptimal polymer properties.
Innovation Solution
A method involving the reduction of chromium-based catalysts with a reducing agent in a solvent, followed by controlled drying to adjust the flow index response, which includes varying the addition rate of the reducing agent, agitation rate, and drying temperature to achieve the desired molecular weight range and polymer properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chromium oxide-on-silica catalysts are used, then productivity is improved, but molecular weight distribution becomes narrower than desired
Solution Approach 1:
The patent applies parameter changes by controlling the oxidation state distribution of chromium atoms in the catalyst. Specifically, it adjusts the ratio of hexavalent chromium (Cr+6) to total chromium atoms to fall within 0.03 to 0.3, and controls the reduction potential parameters (Ep1 and Ep2) during polarization measurements. By precisely controlling these chemical parameters, the catalyst achieves both high productivity and broad molecular weight distribution simultaneously, resolving the contradiction between productivity and molecular weight distribution stability.
2Stability of the object's composition
If silyl chromate-based catalysts are used, then molecular weight characteristics are improved, but productivity decreases
Solution Approach 1:
The patent resolves this contradiction by changing the chemical parameters of the chromium catalyst, specifically controlling the oxidation state distribution and reduction potential characteristics. By adjusting the Cr+6 ratio to 0.03-0.3 and controlling the polarization parameters (Ep1, Ep2), the catalyst achieves both desirable molecular weight distribution (with high molecular weight shoulder) and high productivity, eliminating the need to choose between silyl chromate-based catalysts with good molecular weight but low productivity.
3Manufacturing precision
If flow index response is not controlled, then polymer properties become suboptimal, but controlling it adds process complexity
Solution Approach 1:
The patent applies preliminary action by pre-controlling the catalyst properties before polymerization. Instead of adjusting flow index during polymerization (which would add complexity), the method pre-adjusts the chromium oxidation state distribution and reduction potential parameters in the catalyst preparation stage. This preliminary control of catalyst parameters ensures the desired flow index response is achieved inherently, avoiding the need for complex process adjustments during operation.
Solution Approach 2:
The patent employs feedback mechanisms through polarization measurements to monitor and control the reduction potential parameters (Ep1, Ep2) of the catalyst. By using electrochemical feedback to adjust the catalyst's oxidation state distribution, the process achieves precise control over flow index response. This feedback-based control method provides manufacturing precision without requiring complex process adjustments during polymerization.
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 precise control of the flow index response, enabling the production of polyolefins with tailored molecular weights and distributions, improving catalyst productivity and polymer properties, and avoiding operational issues such as reactor shutdowns and polymer agglomeration.
Implementation Method 1
treating the resulting substance with a trialkylaluminum compound... contacting a chromium-based catalyst with a reducing agent in the presence of a solvent
Implementation Method 2
contacting a chromium-based catalyst with a reducing agent in the presence of a solvent
Implementation Method 3
evaporating the solvent at a drying temperature to dry the reduced chromium-based catalyst
Data Source
AI summary
A method including contacting a chromium-based catalyst with a reducing agent in a solvent to lower an oxidation state of at least some chromium in the chromium-based catalyst to give a reduced chromium-based catalyst, drying the reduced chromium-based catalyst at a temperature, and adjusting the temperature to affect the flow index response of the reduced chromium-based catalyst.