Supported Chromium Catalyst Particle Size Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Improper particle size features of supported chromium catalysts lead to operational difficulties and inconsistent properties during ethylene/α-olefin polymerizations in loop slurry reactors, resulting in polymer defects and heterogeneity.
Innovation Solution
Developing supported chromium catalysts with controlled particle size distributions, specifically with a solid oxide comprising 0.1 to 15 wt.% chromium, where the particle size greater than 100 μm is less than 3 wt.% and the particle size span is between 0.5 to 1.4, and using these catalysts in loop slurry polymerization processes to produce ethylene polymers with improved properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If supported chromium catalysts with improper particle size features are used, then catalyst activity may be maintained, but operational difficulties and inconsistent polymer properties occur
Solution Approach 1:
The patent applies parameter changes by precisely controlling the particle size distribution parameters of the supported chromium catalyst. Specifically, it limits particles greater than 100 μm to ≤3 wt.% and controls the particle size span (d90-d10)/d50 to 0.5-1.4, which resolves the contradiction between maintaining catalyst activity and achieving consistent polymer properties.
2Ease of manufacture
If catalysts with broad particle size distribution are used, then catalyst loading is simplified, but polymer heterogeneity and gel defects increase
Solution Approach 1:
The patent applies local quality by implementing different particle size constraints for different catalyst particle populations. It specifically targets and limits the problematic size ranges (particles >100 μm and particles <10 μm) while allowing the majority of particles to fall within the optimal 10-100 μm range, thus achieving homogeneous polymer composition without requiring complete uniformity across all particles.
3Productivity
If fine catalyst particles (<10 μm) are present in high amounts, then catalyst surface area increases, but polymer fines and operational difficulties increase
Solution Approach 1:
The patent applies partial action by not completely eliminating fine particles (<10 μm) from the catalyst, but rather limiting them to ≤10 wt.%. This partial control allows sufficient surface area for catalyst activity while preventing the excessive fine particle content that would generate harmful polymer fines and cause operational difficulties in loop slurry reactors.
Data Source
AI summary
Supported chromium catalysts containing a solid oxide and 0.1 to 15 wt. % chromium, in which the solid oxide or the supported chromium catalyst has a particle size span from 0.5 to 1.4, less than 3 wt. % has a particle size greater than 100 μm, and less than 10 wt. % has a particle size less than 10 μm, can be contacted with an olefin monomer in a loop slurry reactor to produce an olefin polymer. Representative ethylene-based polymers produced using the chromium catalysts have a HLMI of 4 to 70 g/10 min, a density from 0.93 to 0.96 g/cm3, from 150 to 680 ppm solid oxide (such as silica), from 1.5 to 6.8 ppm chromium, and a film gel count of less than 15 catalyst particle gels per ft2 of 25 micron thick film and/or a gel count of less than or equal to 50 catalyst particles of greater than 100 μm per five grams of the ethylene polymer.