Fixed-bed Reactor Catalyst Segmentation for Acrylic Acid Yield
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Solution Overview
Problem
Industrial-scale production of acrolein and acrylic acid by catalytic gas-phase oxidation of propylene in fixed-bed multitubular reactors faces challenges in maintaining high yield and catalyst life.
Innovation Solution
Filling the reaction tubes of a fixed-bed multitubular reactor with at least two catalysts differing in pore size distribution, comprising molybdenum, iron, and bismuth, with specific ratios of D1/D2, to create axial reaction zones, where the catalysts are either molded or supported on inert carriers, enhancing the production of acrolein and acrylic acid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single type of catalyst is used in the fixed-bed multitubular reactor, then the device complexity is low, but the yield and catalyst life of acrolein and acrylic acid are insufficient
Solution Approach 1:
The catalyst bed is segmented into multiple layers with different pore size distributions (D1/D2 ratios). The first layer has a smaller D1/D2 ratio (0.05-0.5) while the second layer has a larger D1/D2 ratio (0.5-2.0), allowing different regions to optimize for different aspects of the reaction, thereby improving overall yield without excessive complexity
Solution Approach 2:
Different portions of the catalyst bed are given different local properties through varying pore size distributions. The inlet region uses catalyst with smaller pores (lower D1/D2) for better diffusion control, while the outlet region uses catalyst with larger pores (higher D1/D2) for enhanced activity, optimizing performance at each location
2Productivity
If catalyst layers are added to extend reaction zones, then the productivity increases, but the device complexity increases
Solution Approach 1:
The catalyst bed is divided into multiple layers with distinct pore size characteristics. Each layer is optimized for specific reaction conditions, enabling extended reaction zones that maintain stable continuous operation while keeping the structural complexity manageable through systematic design
3Productivity
If the reactor operates under heavy load conditions, then the productivity increases, but the catalyst life decreases
Solution Approach 1:
The pore size distribution parameters (D1/D2 ratios) are optimized to balance activity and stability. By controlling the pore structure parameters, the catalyst maintains high productivity under heavy load conditions while extending catalyst life through reduced deactivation
Solution Approach 2:
The catalyst system uses composite materials with different pore size distributions combined in layered structures. This composite approach allows the system to achieve both high productivity and extended catalyst life by leveraging the complementary properties of different catalyst materials
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
This method achieves a high yield and stable catalyst performance over a long period, even under heavy load conditions, with improved acrolein and acrylic acid production.
Implementation Method 1
catalytic gas-phase oxidation reaction of propylene
Implementation Method 2
catalytic gas-phase oxidation reaction of propylene with molecular oxygen
Implementation Method 3
pore size distribution... D1 denoting the proportion of the total pore volume of pores whose pore diameter falls within the range of at least 0.03 μm and less than 0.3 μm
Data Source
AI summary
This invention provides a method for producing acrolein and/or acrylic acid by catalytic gas-phase oxidation, which method makes it possible to carry out a continuous operation steadily for a long period of time while a high yield is maintained. This method is characterized by comprising filling each of reaction tubes of a fixed-bed multitubular reactor with at least two species of catalysts each of which essentially comprises, as catalytically active components, oxide of molybdenum, oxide of bismuth and oxide of iron and/or composite oxide of at least two of said elements, said at least two species of catalysts being different in the ratio of D1/D2, D1 denoting the proportion of the total pore volume of pores whose pore diameter falls within the range of at least 0.03 µm and less than 0.3 µm to the total pore volume of the whole pores, and D2 denoting the proportion of the total pore volume of pores whose pore diameter falls within the range of at least 0.3 µm and at most 3 µm to the total pore volume of the whole pores, in such a manner that at least two reaction zones are formed axially in each of the reaction tubes.