Chromium Catalyst Activation Cycles for High Melt Index, Low Gels
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Solution Overview
Problem
Commercial activation of supported chromium catalysts results in low conversion to Cr(VI) and inefficient production of high melt index polymers with low film gel content.
Innovation Solution
A multi-step process involving controlled temperature cycles of inert and oxidizing atmospheres is used to activate chromium catalysts, including stages of heating, cooling, and purging, to produce activated chromium catalysts with high Cr(VI) content and improved melt index potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional activation methods are used, then the process is simple, but conversion to Cr(VI) is low and productivity is poor
Solution Approach 1:
The activation process is divided into multiple sequential steps with different atmosphere conditions (inert and oxidizing) and temperature ranges. This segmentation allows controlled conversion to Cr(VI) while preventing gel formation, achieving high productivity without excessive complexity
Solution Approach 2:
The activation method employs periodic cycling between inert and oxidizing atmospheres at different temperatures. This periodic action enables progressive Cr(VI) formation while managing heat release and preventing harmful gel formation, resolving the contradiction between conversion efficiency and process complexity
2Productivity
If high conversion to Cr(VI) is achieved, then melt index potential improves, but film gel content increases
Solution Approach 1:
The activation method changes multiple parameters including temperature, atmosphere composition, and time duration across different steps. By carefully controlling these parameters, the process achieves high Cr(VI) conversion and melt index potential while maintaining low film gel content through suppressed gelation reactions
Solution Approach 2:
The method converts the potentially harmful exothermic oxidation reactions into beneficial Cr(VI) formation by controlling the oxidation process in staged atmosphere cycles. This transforms what would normally cause gel formation into a controlled pathway for achieving high melt index potential with low gel content
3Productivity
If activation temperature is increased, then conversion to Cr(VI) improves, but gel formation increases
Solution Approach 1:
The temperature profile is segmented into different ranges corresponding to inert and oxidizing atmosphere steps. This segmentation allows the system to achieve necessary Cr(VI) conversion temperatures while avoiding sustained high temperatures that would promote gel formation
Solution Approach 2:
Temperature is controlled through periodic atmosphere cycling, where oxidizing steps provide necessary heat for Cr(VI) formation followed by inert atmosphere cooling periods. This periodic temperature control achieves conversion while limiting gel formation
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 produces ethylene polymers with high melt index, low film gel levels, and improved extrusion processability, suitable for applications like blown film and pipe production.
Implementation Method 1
the first oxidizing atmosphere causes an exothermic increase in temperature from T2 to T3
Implementation Method 2
activation of supported chromium pre-catalysts and to the use of the activated chromium catalysts to polymerize olefins... convert at least a portion of lower valence chromium to an oxidation state of +6 (hexavalent chromium)
Data Source
AI summary
Processes for producing activated chromium catalysts such as titanated chromium/silica catalysts are disclosed, and these processes utilize a multistep process involving exposure to inert and oxidizing atmospheres at specific temperature conditions. The resulting activated chromium catalysts have unexpectedly high melt index potential and can produce ethylene-based polymers with lower gel counts in addition to higher melt indices.