CO2 Hydrogenation to Aromatics via Composite Catalyst
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Solution Overview
Problem
The existing methods for carbon dioxide hydrogenation have low selectivity for aromatic hydrocarbons, high selectivity of side products CO and methane, and low CO2 utilization rate, making it challenging to efficiently produce aromatic hydrocarbons.
Innovation Solution
A method involving a composite catalyst composed of an iron-based low-carbon olefin synthesis catalyst and modified or non-modified molecular sieves, which converts a mixed gas of carbon dioxide and hydrogen into aromatic hydrocarbons, with specific reaction conditions and catalyst preparation processes, to produce high-value-added products like toluene, ethylbenzene, and xylene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional Fischer-Tropsch synthesis is used for CO hydrogenation, then hydrocarbon production is achieved, but product selectivity is limited by ASF rule with maximum C5-C11 selectivity of only 45%
Solution Approach 1:
The patent changes the feedstock from CO to CO2, fundamentally altering the reaction pathway and product distribution. CO2 hydrogenation follows different kinetics and surface adsorption behavior, enabling selectivity outside the ASF limitation while maintaining high productivity through direct conversion to aromatic hydrocarbons.
Solution Approach 2:
The patent employs a composite catalyst system combining Fe-Zn-Zr/HZSM-5 with Cu-Zn-Al methanol synthesizing catalyst. This composite structure integrates multiple functional components: Fe-based catalyst for CO2 conversion, Zr modification for chain growth control, HZSM-5 molecular sieve for aromatization, and Cu-Zn-Al for methanol synthesis. The synergistic effect of these components resolves the selectivity-productivity contradiction by coordinating multiple reaction pathways.
2Manufacturing precision
If CO2 hydrogenation is used to prepare long-chain hydrocarbons, then aromatic hydrocarbon production is targeted, but CO2 conversion efficiency is low with high side product selectivity (CO >50%, methane high)
Solution Approach 1:
The patent segments the catalytic system into distinct functional zones: Fe-based catalyst for initial CO2 hydrogenation and syngas generation, Cu-Zn-Al catalyst for methanol synthesis intermediate step, and HZSM-5 molecular sieve for final aromatization. This segmentation allows each component to optimize its specific function, improving overall CO2 conversion efficiency while minimizing side products through coordinated reaction stages.
Solution Approach 2:
The patent introduces methanol as an intermediary substance in the reaction pathway. CO2 is first converted to syngas, then to methanol on Cu-Zn-Al catalyst, and finally to aromatic hydrocarbons on HZSM-5. This intermediary step acts as a buffer that directs carbon flow toward desired products while reducing direct formation of CO and methane side products, thereby improving both selectivity and conversion efficiency.
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 increased selectivity and yield of aromatic hydrocarbons, reduces side product formation, and enhances CO2 utilization, enabling efficient production of aromatic hydrocarbons through a one-step process with reduced energy consumption and equipment investment.
Implementation Method 1
CO2 is subjected to reversed water gas shift reaction to produce CO
Implementation Method 2
CO is subjected to Fischer-Tropsch synthesis to form the hydrocarbon compounds
Implementation Method 3
with the catalysis of a composite catalyst to produce aromatic hydrocarbons
Implementation Method 4
the second component is one or more than two of metal modified or non-modified molecular sieves which are mainly used for olefin aromatization
Implementation Method 5
because CO2 is slow in absorption on a catalyst surface
Implementation Method 6
CO2 hydrogenation to directly produce liquid hydrocarbons
Data Source
AI summary
A method for preparing aromatic hydrocarbons with carbon dioxide hydrogenation, comprising: directly converting a mixed gas consisting of carbon dioxide and hydrogen with the catalysis of a composite catalyst under reaction conditions of a temperature of 250-450° C., a pressure of 0.01-10.0 MPa, a feedstock gas hourly space velocity of 500-50000 mL/(h·gcat) and a H2/CO2 molar ratio of 0.5-8.0, to produce aromatic hydrocarbons. The composite catalyst is a mixture of a first component and a second component. The first component is an iron-based catalyst for making low-carbon olefin via carbon dioxide hydrogenation, and the second component is at least one of metal modified or non-modified molecular sieves which are mainly used for olefin aromatization. In the method, CO2 conversion per pass may be above 33%, the hydrocarbon product selectivity may be controlled to be above 80%, the methane content is lower than 8%, C5+ hydrocarbon content is higher than 65% and the proportion of the aromatic hydrocarbons in C5+ hydrocarbons may be above 63%.