Chromium Catalyst Activation Cycles for High Melt Index, Low-Gel Polymers
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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 to activate chromium catalysts, including specific temperature ranges and hold times, producing an activated chromium catalyst suitable for olefin polymerization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional activation methods are used to activate supported chromium catalysts, then the activation process is simple, but the conversion to Cr(VI) is low and the production of high melt index polymers with low film gel content is inefficient
Solution Approach 1:
The activation process is divided into multiple sequential steps with distinct functions: Step 1 (heating to 1000-1400°F in inert atmosphere) removes impurities and prepares the surface, Step 2 (oxidizing atmosphere exposure) converts chromium to Cr(VI), and Step 3 (cooling and stabilization) ensures proper catalyst formation. This segmentation allows each step to optimize for its specific purpose, achieving high Cr(VI) conversion while maintaining process control
Solution Approach 2:
The invention employs systematic changes in temperature parameters (from 500-700°F during oxidation to 1000-1400°F during inert heating) and atmospheric composition (switching between oxidizing and inert gases) to control the activation process. These parameter changes enable precise control over chromium oxidation state and catalyst structure, achieving high Cr(VI) conversion and improved polymer properties
2Productivity
If conventional activation methods are used, then the process is straightforward, but the melt index potential and film gel content of the resulting polymer are poor
Solution Approach 1:
The catalyst support undergoes preliminary treatment in an inert atmosphere at high temperature (1000-1400°F) before chromium oxidation occurs. This preliminary action removes surface impurities, creates active sites, and prepares the support structure to maximize chromium activation efficiency. As a result, the activated catalyst produces polymers with high melt index potential and low film gel content
Solution Approach 2:
The activation process maintains continuous control over atmospheric composition and temperature throughout all steps, ensuring that chromium conversion to Cr(VI) proceeds efficiently and uniformly. The continuous monitoring and adjustment of process parameters ensure consistent catalyst quality, leading to reliable polymer production with desired melt index and gel content specifications
3Manufacturing precision
If high conversion to Cr(VI) is achieved through extended oxidation, then catalyst activity improves, but the process time and energy consumption increase
Solution Approach 1:
The invention achieves rapid Cr(VI) conversion by optimizing the oxidation temperature range (500-700°F) and atmospheric composition. The controlled parameters enable complete chromium activation in a shorter time compared to conventional methods, reducing both process time and energy consumption while maintaining high conversion efficiency
Solution Approach 2:
The activation process uses periodic cycling between inert and oxidizing atmospheres with controlled duration. This periodic action allows sufficient time for complete chromium oxidation to Cr(VI) while preventing over-oxidation or degradation. The optimized cycle timing achieves maximum conversion efficiency in minimal time
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 yields chromium catalysts with high Cr(VI) content and high melt index potential, enabling the production of ethylene polymers with low film gel levels and improved extrusion processability.
Implementation Method 1
the first oxidizing atmosphere causes an exothermic increase in temperature from T2 to T3
Implementation Method 2
heating the pre-catalyst in a third inert atmosphere to a temperature T4 in a range from 1000° F. to 1400° F. (538° C. to 760° C.) and holding the pre-catalyst at T4
Implementation Method 3
cooling the pre-catalyst in a fourth inert atmosphere to a temperature T5 in a range from 900° F. to 1200° F. (482° C. to 649° C.)
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.