Chromium Catalyst Activation Fluidized Bed Heat Treatment
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Solution Overview
Problem
Impurities, specifically green-blue particles comprising Cr2O3, are difficult to separate from polyolefins during polymerization, leading to production interruptions and quality issues due to their presence in the end product.
Innovation Solution
A fluidized-bed method for activating chromium-containing polymerization catalysts by heat treatment in the presence of oxygen within a reactor with a heating jacket, using air or other oxygen sources to oxidize Cr(III) to Cr(VI), employing specific support materials like silicagel and cyclone separators to prevent impurity formation and retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed to activate the chromium-containing catalyst precursor, then the catalyst activity is improved, but Cr2O3 impurities are formed and retained in the polymer product
Solution Approach 1:
The patent applies parameter changes by optimizing the heat treatment temperature range (300-1000°C) and time duration (0.5-48 hours) to achieve complete activation of the chromium catalyst precursor while preventing the formation of Cr2O3 impurities. This controlled parameter adjustment resolves the contradiction between achieving high catalyst activity and avoiding harmful impurity formation.
Solution Approach 2:
The patent uses oxygen or air as the fluidizing gas during heat treatment to provide strong oxidizing conditions that convert Cr(III) to Cr(VI) for catalyst activation. By controlling the oxygen concentration and flow conditions in the fluidized bed, the process achieves complete oxidation to the active Cr(VI) state while preventing over-oxidation to Cr2O3 impurities.
2Reliability
If conventional heat treatment methods are used, then catalyst activation is achieved, but production interruptions occur due to impurity-related quality issues
Solution Approach 1:
The patent implements feedback control by monitoring the heat treatment process parameters (temperature, time, oxygen concentration) and adjusting them to prevent Cr2O3 impurity formation. This feedback mechanism ensures consistent catalyst quality that prevents downstream polymer quality issues and production interruptions, thereby maintaining continuous productivity.
Solution Approach 2:
The patent applies preliminary action by performing complete and controlled heat treatment activation before the catalyst is used in polymerization. By ensuring thorough activation and impurity prevention in advance, the process eliminates the need for production interruptions to address quality issues, thereby maintaining continuous productivity.
3Reliability
If the heat treatment temperature and time are increased to ensure complete activation, then catalyst activity improves, but the risk of Cr2O3 impurity formation increases
Solution Approach 1:
The patent optimizes the parameter combination of temperature (300-1000°C) and time (0.5-48 hours) to achieve complete catalyst activation without forming Cr2O3 impurities. This optimized parameter range ensures sufficient thermal energy for complete Cr(III) to Cr(VI) conversion while limiting conditions that would lead to harmful impurity formation.
Solution Approach 2:
The patent maintains controlled oxygen presence during heat treatment to ensure complete oxidation to Cr(VI) through strong oxidizing conditions. The oxygen concentration and flow rate are optimized to provide sufficient oxidation power for complete activation while preventing excessive oxidation that would form Cr2O3 impurities.
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 method effectively prevents impurities in the catalyst, ensuring high-quality polyolefins by maintaining catalyst purity and reducing production disruptions, with the use of a cyclone separator facilitating efficient particle removal and maintaining catalyst retention.
Implementation Method 1
an outer heating jacket (4) covering said complete outer surface, said heating jacket (4) having a heating medium inlet (5) arranged on top of the activator (1) and a heating medium outlet (6) arranged below the activator (1)
Implementation Method 2
the particles undergo a physical/chemical change inasmuch, as the precursor comprising a Cr(III) salt, if desired in combination with other metal ions like titanium or zirconium, and additives, either gaseous, liquid or solid, such as ammonium hexafluorisilicate, is transformed into the stable Cr(VI) oxidation level
Implementation Method 3
When gases flow in a vertical direction from below through a bed of finely particulate material supported on perforated plates arranged horizontally, a state similar to that of a boiling liquid becomes established under certain flow conditions, the bed throws up bubbles, and the partie/es of the bed material are in constant swirling up and down motion within the bed and thus remain suspended
Implementation Method 4
the use of a cyclone separator facilitating efficient particle removal and maintaining catalyst retention
Data Source
AI summary
Method for activation of chromium containing catalyst precursor for polymerization and improved polymerization catalyst resulting The instant invention relates to an activation of a polymerization catalyst precursor by heat treatment comprising a support material and a catalyst precursor deposited thereon in a fluidized bed activator and to the use of the activated polymerization catalyst in the manufacture of polyolefins. The Method is performed in a cylindrical activator (1) arranged vertically comprising tubular activator walls, a fluidization gas inlet (2) near the bottom, a fluidization gas outlet (3) near the top and a heat exchange jacket (4) outside the tubular activator walls, wherein the heating jacket covers the complete outer surface of the walls of the activator. The catalyst prepared by that method is improved with respect to its minor content of impurities and causes less interruptions during gas-phase polymerization or slurry polymerization either in stirred vessel or loop.