Peripheral Pd Crust Catalyst for Selective C3 Hydrogenation
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Solution Overview
Problem
Current catalysts for selective hydrogenation of C3 hydrocarbon cuts from steam cracking and catalytic cracking suffer from activity defects and loss of selectivity due to intragranular material transfer, leading to incomplete hydrogenation and early deactivation, particularly when palladium-based catalysts with high dispersion are used.
Innovation Solution
A palladium catalyst with a porous alumina support, where at least 80% of the palladium is distributed in a crust at the periphery with a thickness between 25-500 µm, and a metal dispersion of less than 20%, prepared through a process involving dry impregnation and hydrothermal treatment, enhancing selectivity and reducing total hydrogenation of mono-olefins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If palladium-based catalysts with high dispersion are used, then catalytic activity is improved, but selectivity is lost and intragranular mass transfer problems occur
Solution Approach 1:
The patent applies local quality by creating a crust structure where palladium is concentrated at the periphery of the catalyst granules (within 250 μm from the surface) rather than being uniformly distributed throughout. This peripheral concentration ensures that reactions occur primarily at the external surface, avoiding intragranular mass transfer issues while maintaining high catalytic activity through optimized palladium positioning in the region where reactants actually access the catalyst.
2Productivity
If palladium content is increased to improve activity, then hydrogenation efficiency increases, but total saturation and formation of alkanes increases
Solution Approach 1:
The patent concentrates palladium in a peripheral crust rather than distributing it uniformly throughout the granule. This localized positioning ensures that hydrogenation reactions occur at the surface where reactant concentration can be controlled, enabling efficient conversion of acetylenes and diolefins to alkenes while preventing over-hydrogenation to alkanes by limiting the active catalyst sites to the peripheral region accessible to reactants.
3Reliability
If intragranular mass transfer is improved, then activity defects are reduced, but catalyst complexity increases
Solution Approach 1:
The patent extracts the active palladium phase from the interior of the catalyst granules and concentrates it in a peripheral crust within 250 μm from the surface. This extraction eliminates intragranular mass transfer problems by ensuring all active sites are accessible from the external surface, while maintaining relative structural simplicity by using a straightforward impregnation and controlled sintering process to create the crust structure.
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 achieves significant selectivity in hydrogenating acetylenic and diolefins while limiting total hydrogenation of mono-olefins, reducing polymerization reactions and extending catalyst life, thereby improving propylene yield and maintaining high performance over time.
Implementation Method 1
The selective hydrogenation process allows the transformation of polyunsaturated compounds from petroleum fractions by converting the most unsaturated compounds to the corresponding alkenes while avoiding total saturation and therefore the formation of the corresponding alkanes
Implementation Method 2
a specific hydrothermal treatment step, resulting in sintering of the catalyst, which has the effect of reducing the metallic dispersion of palladium within the catalyst
Data Source
AI summary
A catalyst comprising an active phase made of palladium, and a porous support comprising at least one refractory oxide selected from the group consisting of silica, alumina and silica-alumina, wherein: - the palladium content in the catalyst is between 0.0025 and 1% by weight relative to the total weight of the catalyst; - at least 80% by weight of the palladium is distributed in a crust at the periphery of the porous support, the thickness of said crust being between 25 and 500 µm; - the specific surface area of the porous support is between 1 and 50 m2/g; - the metallic dispersion D of the palladium is less than 20%.