Charge-Reversed Silica Sol via Decationization and Surface Modification
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Solution Overview
Problem
Conventional silica sols with high surface areas are unstable under low pH conditions, leading to aggregation and gelling, which limits their commercial viability in applications like water treatment and papermaking, where stability over several months is required.
Innovation Solution
A process involving decationization of an alkaline silica sol using an acidic cation-exchange solid followed by surface modification with elements in a +3 or +4 oxidation state to produce a charge-reversed silica sol with improved stability and reduced aggregation, maintaining low viscosity and effective flocculation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high surface area silica particles are used to improve drainage and retention properties in papermaking, then the performance in water treatment and papermaking applications is improved, but the sols become unstable under low pH conditions leading to aggregation and gelling
Solution Approach 1:
The patent changes the surface charge parameter of silica particles from negative to positive through chemical modification with cationic polymers or metal salts, enabling stability under low pH conditions where conventional negative charge silica sols would aggregate and gel
Solution Approach 2:
The patent creates composite silica particles by coating or modifying the surface of silica with cationic polymers or metal oxide layers, combining the high surface area benefits of silica with the charge-stabilization properties of the modifying agent
2Reliability
If silica sols are modified with aluminate to stabilize high surface area particles, then the stability is improved, but the particles retain negative charge and remain unstable under low pH conditions
Solution Approach 1:
The patent fundamentally changes the charge parameter from negative to positive by using cationic modifiers instead of aluminate, enabling the sols to remain stable under low pH conditions where aluminate-modified sols fail
3Productivity
If conventional silica sols are used in papermaking applications, then drainage and retention properties are achieved, but the sols require extreme dilution to avoid gel formation
Solution Approach 1:
The patent changes the surface charge parameter to positive, which fundamentally alters the interaction between particles, allowing them to remain stable at high concentrations without requiring extreme dilution to prevent gel formation
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 resulting charge-reversed silica sols exhibit enhanced stability and drainage properties, preventing gel formation for extended periods, making them suitable for applications in water treatment and papermaking without significant viscosity increase.
Implementation Method 1
contacting the slurry of (a) and the aqueous silica sol of (b); removing the acidic cation-exchange solid from the mixture resulting from (c) to leave a decationised aqueous silica sol
Implementation Method 2
contacting the decationised aqueous silica sol with one or more compounds comprising a modifying element that can formally adopt a +3 or +4 oxidation state, to produce a charge-reversed aqueous silica sol whose silica particles comprise such a modifying element on their surface
Data Source
AI summary
A process for producing a charge-reversed aqueous silica sol includes: (a) providing a slurry of an acidic cation-exchange solid in an aqueous liquid; (b) providing a starting aqueous silica sol with an alkaline pH and including a monovalent cation(s); (c) contacting the slurry with the starting sol; (d) separating the acidic cation-exchange solid from the mixture (c) to leave a decationised aqueous silica sol with an acidic pH and a reduced monovalent cation(s) content compared to the starting sol; and (e) contacting the decationised sol with a compound(s) including a modifying element(s) that can adopt a +3 or +4 oxidation state to produce a charge-reversed aqueous silica sol whose silica particles include the modifying element(s) on their surface. The S-value of the starting sol is from about 10 to about 50%, and the surface area of colloidal silica particles in the starting sol is at least about 500 m2 g−1.