OCM Catalyst Composition for High C2+ Selectivity
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Solution Overview
Problem
The oxidative coupling of methane (OCM) process struggles to achieve high selectivity for C2+ hydrocarbons like ethylene, as produced C2+ hydrocarbons are more reactive and tend to oxidize to carbon oxides, resulting in selectivity below commercial requirements, and attempts to improve selectivity often compromise methane conversion and yield, leading to reduced process efficiency and increased costs.
Innovation Solution
A catalyst composition represented by the formula (AMzAEaRE1bRE2cATdOx) is developed, where AM is an alkali metal or alkali metal tungstate, AE is an alkaline earth metal, RE1, RE2, and RE3 are rare earth elements or a redox agent, with specific molar ratios and calcination processes, forming an unsupported catalyst that enhances C2+ hydrocarbon selectivity and methane conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional catalysts are used to oxidatively couple methane, then C2+ hydrocarbons are produced, but selectivity towards C2+ hydrocarbons remains below commercial requirements (below 80%) due to further oxidation to COx
Solution Approach 1:
The patent employs a composite catalyst system comprising multiple metal oxides (alkali metal oxide, alkaline earth metal oxide, rare earth metal oxides, and transition metal oxide) in specific weight ratios. This composite structure creates synergistic effects that enhance C2+ hydrocarbon selectivity while suppressing COx formation through distributed active sites with different functions.
Solution Approach 2:
The patent optimizes specific parameters including the weight ratios of different metal oxides (e.g., alkali metal oxide 10-30 wt%, rare earth metal oxides 40-70 wt%), calcination temperature (700-900°C), and catalyst composition formulas. These parameter adjustments tune the catalyst's electronic and geometric properties to achieve >80% ethylene selectivity.
2Manufacturing precision
If catalyst modifications are attempted to increase C2+ hydrocarbon selectivity, then selectivity may improve, but methane conversion and C2+ hydrocarbon yield decrease, leading to reduced process efficiency
Solution Approach 1:
The catalyst is designed with segmented functional zones through the combination of different metal oxides: alkali metal oxides (Na2O, K2O) provide one function while rare earth metal oxides (La2O3, CeO2, Pr6O11) and transition metal oxides (MnO2, Co3O4, NiO) provide complementary functions. This segmentation allows simultaneous optimization of selectivity and activity without mutual interference.
Solution Approach 2:
The composite catalyst performs multiple functions simultaneously: activating methane C-H bonds, facilitating C-C coupling, suppressing over-oxidation to COx, and maintaining structural stability at high temperatures. The multi-functional design enables the catalyst to achieve both high selectivity (>80%) and high conversion/yield performance.
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 composition achieves C2+ hydrocarbon selectivity ranging from 82% to 93% and improved methane conversion, reducing carbon oxide byproducts and increasing overall process efficiency and yield, thereby addressing the limitations of existing OCM processes.
Implementation Method 1
oxidative coupling of methane (OCM)... in presence of certain methane coupling catalysts... The catalyst composition achieves C2+ hydrocarbon selectivity ranging from 82% to 93% and improved methane conversion
Implementation Method 2
with specific molar ratios and calcination processes, forming an unsupported catalyst
Data Source
AI summary
The invention relates to a composition containing a catalyst suitable for producing ethylene and other C2+ hydrocarbons at high selectivity while improving both methane conversion and product yield. Particularly, the catalyst contains mixed metal oxides having at least one alkali earth metal and at least one rare earth metal along with an alkali metal promoter in the form of an alkali metal or in the form of an alkali metal tungstate. The invention further provides a method for preparing such a composition, using a calcination process to calcine the alkali metal promoters together with mixed metal oxides. Additionally, the invention further describes a process for producing C2+ hydrocarbons, using such a composition.