Methane Conversion via Soft Oxidation to CS2
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Solution Overview
Problem
Current methods for converting methane to hydrocarbons face challenges such as over-oxidation, thermodynamic inefficiencies, and high capital and operating costs, particularly in producing C4+ hydrocarbons for transportation fuels and chemicals, due to complex processes and poor selectivity.
Innovation Solution
The process involves 'soft oxidation' of methane with sulfur-containing compounds, specifically using H2S as a reactant to convert methane to CS2, followed by hydrogenation/oligomerization, where methane partial pressure is managed to suppress re-formation and enhance selectivity and yield of C4+ hydrocarbons, allowing for continuous recycling of H2S and reduced equipment costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxidative coupling of methane is used to produce higher hydrocarbons, then hydrocarbon production is achieved, but over-oxidation occurs leading to substantial CO2 formation
Solution Approach 1:
The patent changes the oxidation parameter from oxygen-based oxidation to sulfur-based soft oxidation. This parameter change fundamentally alters the reaction pathway, preventing over-oxidation to CO2 while still enabling methane conversion to higher hydrocarbons through CS2 intermediate formation and subsequent hydrogenation/oligomerization reactions.
Solution Approach 2:
The patent introduces carbon disulfide (CS2) as an intermediary substance in the conversion process. Methane first reacts with H2S to form CS2, which then serves as a precursor for hydrogenation and oligomerization reactions to produce higher hydrocarbons. This intermediary approach avoids direct over-oxidation pathways that lead to CO2.
2Productivity
If Fisher-Tropsch or methanol-to-gasoline processes are used for natural gas conversion, then liquid fuels are produced, but process complexity and capital expenditure increase
Solution Approach 1:
The patent segments the conversion process into distinct functional stages: (1) soft oxidation of methane to CS2 using H2S, (2) hydrogenation of CS2 to hydrocarbons, and (3) oligomerization to form C4+ hydrocarbons. This segmentation allows each stage to be optimized independently and simplifies the overall process design compared to integrated FT or MTG processes.
Solution Approach 2:
The patent implements continuous recycling of H2S throughout the process. H2S consumed in the soft oxidation step is regenerated in the hydrogenation/oligomerization stages and continuously recycled back to the soft oxidation reactor. This continuous action eliminates the need for external H2S supply and maintains steady-state operation, reducing process complexity.
3Productivity
If oxygen is used as oxidant for methane conversion, then hydrocarbon production is achieved, but thermodynamic inefficiencies and exothermic reaction management problems occur
Solution Approach 1:
The patent changes the oxidant parameter from oxygen to sulfur (in the form of H2S). This parameter change transforms the highly exothermic oxidation reaction into a milder soft oxidation process with more favorable thermodynamics. The sulfur-based reaction pathway reduces energy losses and avoids the thermodynamic inefficiencies associated with oxygen-based oxidation and subsequent CO2 formation.
4Manufacturing precision
If H2S is used as reactant for soft oxidation of methane, then selectivity to C4+ hydrocarbons is improved, but H2S recycling system complexity increases
Solution Approach 1:
The patent designs the process so that H2S serves a dual function: it acts as a reactant in the soft oxidation of methane to CS2, and it is simultaneously regenerated as a product in the hydrogenation and oligomerization stages. This self-service characteristic means the system produces its own H2S, eliminating the need for external H2S supply systems and simplifying the recycling infrastructure.
Solution Approach 2:
The patent merges the H2S recycling function with the hydrocarbon production process itself. Rather than having a separate H2S recovery and recycling system, the H2S circulation is integrated into the reaction sequence where H2S is consumed in one stage and regenerated in subsequent stages. This merging of functions reduces equipment complexity while maintaining high selectivity to C4+ hydrocarbons.
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 approach increases the yield and selectivity of C4+ hydrocarbons, reduces carbon dioxide emissions, and improves process economics by minimizing material losses and recycling, making the production of hydrocarbon fuels more viable and environmentally friendly.
Implementation Method 1
the free energy losses associated with the counterpart reactions using S2 versus O2 as a reactant with methane, including over oxidation reactions, are significantly lower. This has led to the characterization of sulfur-based methane conversion as 'soft oxidation.'
Implementation Method 2
followed by hydrogenation/oligomerization, where methane partial pressure is managed to suppress re-formation and enhance selectivity and yield of C4+ hydrocarbons
Data Source
AI summary
Aspects of the invention are associated with the discovery of processes for converting methane (CH4), present in a methane-containing feedstock that may be obtained from a variety of sources such as natural gas, to higher hydrocarbons (e.g., C4+ hydrocarbons) such as gasoline, diesel fuel, or jet fuel boiling-range hydrocarbons, which may optionally be separated (e.g., by fractionation) for use as transportation fuels, or otherwise as blending components for such fuels. Particular aspects of the invention are associated with advantages arising from maintaining reaction conditions that improve the yield of C4+ hydrocarbons. Further aspects relate to the advantages gained by integration of the appropriate reactions to carry out the methane conversion, with downstream separation to recover and recycle desirable components of the reaction effluent, thereby improving process economics to the extent needed for commercial viability.