Chromium Catalyst Flow Index Control via Reduction
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Solution Overview
Problem
Current chromium-based catalysts lack the ability to adjust and predictably control the flow index response, which is crucial for producing polyolefins with varying molecular weights and distributions suitable for different applications.
Innovation Solution
The process involves concurrently contacting a supported chromium-based catalyst with a reducing agent at a selected feed rate over a specific time period and agitating it at a selected rate to produce a catalyst composition with a tailored flow index response, allowing for the production of polyolefins with desired molecular weight ranges.
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 modifying the oxidation state distribution of chromium species in the catalyst. Specifically, it controls the ratio of Cr(VI) to Cr(III) species through controlled reduction of Cr(VI) during catalyst preparation. This parameter adjustment transforms the catalyst's polymerization behavior to produce broader molecular weight distributions while maintaining high productivity, thus resolving the contradiction between productivity and molecular weight distribution breadth.
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 employs composite materials by creating a hybrid chromium catalyst system that combines features of both chromium oxide and silyl chromate catalysts. The catalyst contains a mixture of Cr(VI) and Cr(III) species on a silica support, effectively composite-ing the desirable productivity of chromium oxide catalysts with the desirable molecular weight distribution characteristics of silyl chromate catalysts, thereby resolving the productivity-molecular weight distribution contradiction.
3Device complexity
If chromium-based catalysts lack flow index response control, then catalyst simplicity is maintained, but adaptability to different applications decreases
Solution Approach 1:
The patent applies dynamics by introducing a controllable variable (reduction level of Cr(VI) to Cr(III)) that allows the catalyst's flow index response to be dynamically adjusted. By controlling the extent of reduction during catalyst preparation, the catalyst can be tailored to produce polymers with specific flow indices suitable for different applications (injection molding, blow molding, etc.), thus providing adaptability without requiring multiple different catalyst systems.
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 enables the production of polyolefins with tailored flow index responses, enhancing the flexibility and efficiency of polymerization processes, allowing for the creation of polymers with specific properties suitable for various applications while avoiding operational difficulties and cost increases.
Implementation Method 1
concurrently contacting a supported chromium-based catalyst with a reducing agent fed at a selected feed rate over a selected time period
Implementation Method 2
agitating the chromium-based catalyst at a selected agitation rate
Data Source
AI summary
Embodiments disclosed herein generally relate to olefin polymerization catalysts, and more specifically to chromium-based catalysts and methods of use of chromium-based catalysts for the production of polyolefins, and even more specifically to methods for controlling or tailoring the flow index response of chromium-based catalysts through the controlled addition of a reducing agent to the catalysts under controlled mixing conditions.