Silica-Coated Alumina Chromium Catalysts for Higher Olefin Activity

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Solution Overview

Problem

Hexavalent chromium/silica-coated alumina catalysts exhibit poor catalytic activity and produce polymers with excessive molecular weight, making them inferior to traditional chromium/silica catalysts.

Innovation Solution

Preparation of chromium/silica-coated alumina catalysts with high silica content (greater than 30 wt.%) and calcination at high temperatures (at least 650 °C) to form supported chromium catalysts, which are used in olefin polymerization processes without a co-catalyst.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If chromium on silica gel is treated with strong acids or bases to remove siloxane dimers, then the polymerization activity is improved, but the catalyst stability deteriorates due to leaching of chromium into the aqueous phase

Engineering Contradiction:

Improvepolymerization activityVSAvoidcatalyst stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the chemical parameters of the treatment process by using buffered solutions with controlled pH (pH 4-6) instead of strong acids or bases. This parameter modification allows removal of siloxane dimers while maintaining chromium stability in the catalyst structure, preventing leaching into the aqueous phase.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces buffered solutions as intermediary substances between the chromium catalyst and the siloxane dimers. These buffers act as mediators that enable the removal process without creating the harsh conditions that cause chromium leaching, thus resolving the contradiction between activity improvement and stability maintenance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If conventional strong acid or base treatment is used to remove siloxane dimers, then polymerization activity increases, but harmful factors increase due to chromium leaching into the aqueous phase

Engineering Contradiction:

Improvepolymerization activityVSAvoidchromium leaching

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potentially harmful strong acid or base treatment into a beneficial buffered treatment. By using buffers, the harmful chromium leaching is prevented while still achieving the desired removal of siloxane dimers, thus transforming a harmful process into a beneficial one that improves activity without creating pollution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

Buffered solutions serve as intermediary substances that enable the removal of siloxane dimers without causing chromium to leach into the aqueous phase. This intermediary approach eliminates the harmful effects while preserving the beneficial outcomes of the treatment process.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If chromium is deposited on silica gel followed by strong acid/base treatment, then polymerization activity is enhanced, but device complexity increases due to multiple processing steps

Engineering Contradiction:

Improvepolymerization activityVSAvoidprocessing steps

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent merges the siloxane dimer removal step with the chromium stabilization step into a single buffered treatment operation. This combination eliminates the need for separate strong acid/base treatment steps, reducing processing complexity while maintaining the activity enhancement benefits.

Inventive Principle:

Principle #5Merging (Combining)

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 catalysts demonstrate excellent catalytic activity, producing olefin polymers with a high molecular weight, narrow molecular weight distribution, and low rheological Carreau-Yasuda breadth, surpassing traditional chromium/silica catalysts.

Implementation Method 1

supported chromium catalysts... polymerization activity... polyethylene and copolymer

Methodology Applied

Scientific EffectCatalysis: Catalysis

Data Source

PatentEP3856796B1Methods for making supported chromium catalysts with increased polymerization activity

Publication Date: 2026.05.06 CHEVRON PHILLIPS CHEMICAL COMPANY LP

Figure 1

AI summary

Methods for making a supported chromium catalyst are disclosed, and can comprise contacting a silica-coated alumina containing at least 30 wt. % silica with a chromium-containing compound in a liquid, drying, and calcining in an oxidizing atmosphere at a peak temperature of at least 650 °C to form the supported chromium catalyst. The supported chromium catalyst can contain from 0.01 to 20 wt. % chromium, and typically can have a pore volume from 0.5 to 2 mL/g and a BET surface area from 275 to 550 m2/g. The supported chromium catalyst subsequently can be used to polymerize olefins to produce, for example, ethylene-based homopolymers and copolymers having high molecular weights and broad molecular weight distributions.