Reduced Chromium Catalysts for Ethylene Polymerization Efficiency
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Solution Overview
Problem
Supported chromium catalysts used in olefin polymerizations often have limitations in reducing chromium to lower oxidation states, which affects the polymerization efficiency and product characteristics, particularly when exposed to light and specific reductants.
Innovation Solution
Reducing hexavalent chromium catalysts to a divalent form using CO at elevated temperatures and treating them with hydrocarbon or halogenated hydrocarbon compounds to form hydrocarbon-containing ligands, which are then used in olefin polymerization, allowing the incorporation of hydrocarbon moieties as terminal groups or chain ends in the polymer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If supported chromium catalysts are used in conventional oxidizing atmosphere calcining, then chromium is converted to hexavalent chromium, but chromium reduction to lower oxidation states is limited affecting polymerization efficiency
Solution Approach 1:
The patent changes the oxidation state parameter of chromium from the conventional +6 to lower states (+4, +3, or +2) to improve polymerization efficiency. This is achieved by modifying the calcining atmosphere from oxidizing to reducing conditions, allowing chromium to exist in lower oxidation states that are more active for olefin polymerization.
Solution Approach 2:
The patent uses a reducing atmosphere (inert or reducing environment) during calcining instead of the conventional oxidizing atmosphere. This creates the necessary conditions for chromium reduction while maintaining catalyst stability, resolving the contradiction between achieving low oxidation states and maintaining compositional stability.
2Productivity
If chromium catalysts are reduced to lower oxidation states, then polymerization efficiency improves, but catalyst preparation becomes more complex
Solution Approach 1:
The patent modifies the calcining atmosphere parameter from oxidizing to reducing conditions, which simultaneously achieves chromium reduction and maintains process simplicity. The reduction is accomplished during the standard calcining step itself, eliminating the need for separate reduction steps and keeping the preparation process straightforward.
3Adaptability or versatility
If conventional supported chromium catalysts are used, then catalyst structure is simple, but polymer product characteristics are limited
Solution Approach 1:
The patent changes the chromium oxidation state parameter to enable new polymer product characteristics including controlled molecular weight distributions, branching patterns, and density. The modified catalyst structure with lower oxidation state chromium provides enhanced adaptability for producing polymers with tailored properties while maintaining a relatively simple supported catalyst framework.
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 enhances catalyst activity and melt index potential, producing ethylene polymers with unique molecular weight distributions and branching patterns, improving the polymer's properties such as density and molecular weight range.
Implementation Method 1
Reducing hexavalent chromium catalysts to a divalent form using CO at elevated temperatures
Implementation Method 2
treating them with hydrocarbon or halogenated hydrocarbon compounds to form hydrocarbon-containing ligands
Implementation Method 3
using the reduced catalyst to polymerize olefins, such as ethylene alone or with an alpha-olefin comonomer
Data Source
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AI summary
Supported chromium catalysts with an average valence less than +6 and having a hydrocarbon-containing or halogenated hydrocarbon-containing ligand attached to at least one bonding site on the chromium are disclosed, as well as ethylene-based polymers with terminal alkane, aromatic, or halogenated hydrocarbon chain ends. Another ethylene polymer characterized by at least 2 wt. % of the polymer having a molecular weight greater than 1,000,000 g/mol and at least 1.5 wt. % of the polymer having a molecular weight less than 1000 g/mol is provided, as well as an ethylene homopolymer with at least 3.5 methyl short chain branches and less than 0.6 butyl short chain branches per 1000 total carbon atoms.