Pseudoplastic Washcoat Composition for Monolith Substrate Coating
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Solution Overview
Problem
Existing washcoat compositions for substrate monoliths face challenges in achieving even distribution and retention of liquid components within the monolith channels, particularly due to non-Newtonian rheology that prevents plug flow, leading to excess liquid and losses of precious metals.
Innovation Solution
A washcoat composition incorporating polysaccharide rheology modifiers such as Scleroglucan, guar gum, and hydroxyethyl cellulose, which impart pseudoplastic properties, allowing for plug flow and retention within the monolith channels, even at low pH and high temperatures, reducing the need for intermediate drying steps and enhancing the stability of precious metal salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional washcoat compositions are applied to substrate monoliths, then coating is achieved, but non-Newtonian rheology prevents plug flow leading to excess liquid and poor distribution
Solution Approach 1:
The invention changes the rheological parameters of the washcoat composition by adding pseudoplastic agents (such as hydroxyethyl cellulose, carboxymethyl cellulose, or xanthan gum) to transform the non-Newtonian fluid into a pseudoplastic fluid. This parameter change enables the liquid to exhibit shear-thinning behavior, allowing it to flow uniformly under pressure and achieve even distribution within the monolith channels without excessive liquid retention.
2Productivity
If pressure is applied to transfer liquid component into monolith, then coating is achieved, but non-pseudoplastic rheology causes excess liquid and losses
Solution Approach 1:
By modifying the rheological parameters to create pseudoplastic behavior, the invention enables the washcoat composition to be transferred efficiently into the monolith under pressure while controlling liquid retention. The pseudoplastic properties ensure that the liquid flows smoothly during pressure application and then stabilizes within the channels, preventing excess liquid from being forced through and reducing precious metal losses.
Solution Approach 2:
The pseudoplastic agents act as intermediary substances that mediate between the applied pressure and the liquid component. These agents (hydroxyethyl cellulose, carboxymethyl cellulose, or xanthan gum) modify the flow characteristics of the washcoat, allowing pressure to be applied effectively for coating while preventing uncontrolled liquid flow that would cause precious metal losses.
3Manufacturing precision
If intermediate drying steps are used in coating process, then coating quality is improved, but process complexity and time increase
Solution Approach 1:
The invention extracts or removes the intermediate drying step from the coating process by using pseudoplastic washcoat compositions that maintain their position and distribution within the monolith channels without requiring drying between applications. The pseudoplastic properties and controlled rheology allow the liquid to be retained evenly in the channels, eliminating the need for intermediate drying operations and simplifying the overall process.
4Manufacturing precision
If washcoat composition is retained within monolith channels, then even distribution is achieved, but rheology control is difficult
Solution Approach 1:
The invention simplifies rheology control by making specific parameter changes to the washcoat composition - adding pseudoplastic agents at controlled concentrations (0.1-5% by weight). These parameter changes create predictable pseudoplastic behavior that can be easily controlled during manufacturing, allowing the liquid to be retained uniformly within monolith channels through simple pressure application without complex rheology management.
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 pseudoplastic washcoat composition ensures efficient coating with reduced viscosity under applied shear stress, allowing complete retention within the monolith channels, minimizing precious metal losses and streamlining the coating process by eliminating intermediate drying steps, while maintaining stability and viscosity over time.
Implementation Method 1
the rheology of the washcoat composition is pseudoplastic
Implementation Method 2
A washcoat composition incorporating polysaccharide rheology modifiers such as Scleroglucan, guar gum, and hydroxyethyl cellulose, which impart pseudoplastic properties
Implementation Method 3
allowing for plug flow and retention within the monolith channels
Data Source
AI summary
A method of coating substrate monoliths is disclosed. The method comprises locating a containment means on top of the first end face of the monolith; and dosing a predetermined quantity of washcoat composition comprising a liquid phase, at least one polysaccharide rheology modifier and at least one of (i) a suspension of metal oxide particles into the containment means; and (ii) at least one metal salt solute in the liquid phase. The locating step may occur before or after the dosing step. Pressure is applied to the washcoat composition to generate shear stress and to transfer an entirety of washcoat composition into the channels of the monolith by plug flow. Substantially all of the predetermined quantity is retained within the monolith. The part-coated monolith is then rotated so that the second end face is located at the top, and the first three steps are repeated without drying the part-coated monolith.