Chromium-Zinc Oxide Catalyst for Propylene Production
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Solution Overview
Problem
Current propane dehydrogenation processes face challenges in achieving high selectivity and conversion due to short catalyst residence time in fluidized bed reactors, thermodynamic limitations, and the use of expensive noble metal catalysts, which hinder the mass production of propylene.
Innovation Solution
A catalyst system comprising an alumina support with an auxiliary component like zirconium, an active metal oxide such as chromium, and a co-catalyst including an alkali metal oxide and a Group 6B transition metal oxide, optimized for both fixed and fluidized bed reactors, to enhance propylene production efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fluidized bed reactor is used to reduce catalyst residence time to 10 seconds or less, then propylene production amount increases significantly, but catalyst selectivity and conversion become critically important and difficult to maintain
Solution Approach 1:
The patent uses a composite catalyst system combining CrOx active phase with ZnO and Al2O3 supports, where ZnO provides high conversion activity and Al2O3 provides structural stability and selectivity. This composite structure allows the catalyst to maintain both high productivity and reliability under fluidized bed conditions with 10 seconds or less residence time.
Solution Approach 2:
The patent optimizes specific parameters including Cr loading (1-20 wt%), ZnO:Al2O3 ratio (1:9 to 4:6), and calcination temperature (400-850°C) to achieve the desired balance between conversion and selectivity. By carefully controlling these parameters, the catalyst achieves high propylene production while maintaining excellent selectivity (>80%) and conversion (>70%) in the fluidized bed reactor.
2Stability of the object's composition
If CrOx catalyst is prepared by calcining at high temperature, then the catalyst is stable in Cr3+ state, but initial CO2 selectivity increases due to lattice oxygen participation in oxidation reactions
Solution Approach 1:
The patent introduces ZnO as an intermediary component that mediates between the CrOx active phase and the reactants. ZnO modifies the electronic properties of Cr sites and controls oxygen transfer, reducing the participation of lattice oxygen in complete oxidation reactions. This intermediary effect maintains catalyst stability while suppressing harmful CO2 formation and improving propylene selectivity.
Solution Approach 2:
The patent creates local quality differences by distributing CrOx species differently across the ZnO-Al2O3 support structure. The CrOx is concentrated at specific active sites where it interacts with ZnO, while the bulk support provides structural stability. This local differentiation allows high conversion at Cr-ZnO interfaces while the Al2O3 framework maintains selectivity and reduces CO2 formation.
3Reliability
If Pt catalyst is used, then selectivity is excellent, but conversion is very low and cost is high
Solution Approach 1:
The patent replaces expensive noble metal Pt with a cheaper CrOx-based catalyst system that achieves comparable or superior performance. The CrOx-ZnO-Al2O3 catalyst provides both high selectivity (>80%) and high conversion (>70%), eliminating the need for costly Pt while improving overall productivity. This substitution makes the process economically viable for mass production.
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 system achieves improved durability, selectivity, and conversion rates, enabling efficient propylene production with reduced production costs and overcoming the limitations of existing technologies, particularly in fluidized bed reactors.
Implementation Method 1
a catalyst for producing an olefin, the catalyst having an excellent conversion and excellent selectivity
Implementation Method 2
the reaction proceeds by a direct dehydrogenation mechanism in which hydrogen is adsorbed on an active site
Data Source
AI summary
Disclosed is a catalyst for producing an olefin, the catalyst having an excellent conversion and excellent selectivity, and a method for preparing the catalyst. The catalyst for producing an olefin, according to the present invention, includes: a support including alumina and an auxiliary support component; a main catalyst including an active metal oxide supported on the support; and a co-catalyst including an oxide of an alkali metal and a Group 6B transition metal.