Molybdenum Oxide Catalyst Particle Size Distribution for Hot Spot Suppression
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Solution Overview
Problem
Catalytic gas-phase oxidation processes for producing acrolein or acrylic acid face challenges with localized high temperature spots (hot spots) in catalyst layers, leading to reduced yield and catalyst deterioration, particularly when using molybdenum-containing catalysts, especially under high space velocity or gas concentration conditions.
Innovation Solution
A catalyst with a specific particle size distribution, characterized by a relative standard deviation of 0.02 to 0.20, is used in a fixed bed shell-and-tube reactor to uniformize and enlarge voids between catalyst particles, suppressing hot spots without reducing productivity, and maintaining high acrolein or acrylic acid yield over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high space velocity or high starting gas concentration is used to improve productivity, then productivity of acrolein or acrylic acid is improved, but hot spots are enhanced and catalyst deterioration is accelerated
Solution Approach 1:
The patent applies local quality by creating a non-uniform catalyst layer structure where the catalyst concentration varies through the layer thickness. The catalyst-containing slurry is applied to form a layer with specific solid content concentration distribution, resulting in higher catalyst concentration at certain regions and lower concentration at others. This local variation in catalyst density prevents uniform hot spot formation throughout the layer, thereby maintaining catalyst stability even under high productivity conditions.
2Productivity
If molybdenum is used as catalytic component, then catalytic activity is improved, but sublimation of molybdenum at high temperatures causes changes in catalyst composition and large deterioration
Solution Approach 1:
The patent addresses molybdenum sublimation by creating a non-uniform catalyst layer where molybdenum-containing catalyst is distributed unevenly through the layer thickness. This local quality variation ensures that regions with higher molybdenum concentration are positioned where temperature conditions are more favorable, while regions with lower molybdenum concentration are positioned to minimize sublimation losses. This spatial distribution strategy maintains both high catalytic activity and composition stability.
Solution Approach 2:
The patent applies beforehand cushioning by pre-distributing the catalyst with non-uniform concentration before the reaction begins. The catalyst-containing slurry is applied to form a layer with predetermined solid content concentration distribution, which acts as a buffer against molybdenum sublimation during high-temperature reactions. This pre-established non-uniform distribution cushions the system against composition changes that would otherwise occur under high-temperature conditions.
3Ease of manufacture
If uniform catalyst particle size is used, then catalyst filling is simple, but voids between particles are not uniformized and hot spots occur
Solution Approach 1:
The patent applies parameter changes by deliberately controlling the particle size distribution of the catalyst to achieve a specific relative standard deviation range (0.05 to 0.20). This parameter optimization creates a balance: the particle size distribution is narrow enough to maintain relatively uniform filling characteristics, yet broad enough to generate uniform void spaces between particles. The resulting uniform void distribution prevents localized heat accumulation and hot spot formation while keeping the filling process simple.
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 catalyst effectively stabilizes acrolein or acrylic acid production by preventing hot spots, ensuring long-term high productivity and catalyst longevity, even under high-load reaction conditions, by maintaining uniform voids and adequate catalytic component loading.
Implementation Method 1
the relative standard deviation of particle size... is at least 0.05 and no more than 0.20... uniformize and enlarge voids between catalyst particles
Implementation Method 2
high temperatures at hot spots accelerate sublimation of the molybdenum to cause changes in the catalyst's composition
Implementation Method 3
catalytic gas-phase oxidation of propylene... catalytic gas-phase oxidation of acrolein... using an oxidation catalyst
Implementation Method 4
This catalytic gas-phase oxidation reaction is a highly exothermic reaction, and hence locally extraordinarily high temperature spots are formed
Data Source
AI summary
The invention provides a process which enables, in preparation of acrolein by catalytic gas-phase oxidation of propylene in the presence of molecular oxygen or a molecular oxygen-containing gas or in preparation of acrylic acid by catalytic gas-phase oxidation of acrolein in the presence of molecular oxygen or a molecular oxygen-containing gas, using single kind of catalyst, to suppress occurrence of localized extraordinarily high temperature spots (hot spots) in the catalyst layer and can stably maintain high acrolein or acrylic acid yield for a long time. The process is characterized by use of an oxide catalyst containing molybdenum as an essential component and having relative standard deviation of its particle size in a range of 0.02 to 0.20.