CO2 Injection in Isosynthesis Catalyst for Carbon Efficiency
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Solution Overview
Problem
Hybrid catalysts for converting methane to gasoline-range hydrocarbons face challenges due to excessive steam pressure, leading to CO conversion to CO2, making them unsuitable for GTL applications where carbon is the limiting element and efficient oxygen rejection is necessary.
Innovation Solution
Operating in a 'dry gas' recycle mode with a moderate CO2 recycle ratio and inlet CO2 content to balance the water gas shift reactions, maintaining high liquid hydrocarbon productivity while controlling CO2 production, and optimizing temperature and pressure ranges to prevent catalyst aging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high single pass conversion is used, then productivity is improved, but steam pressure buildup causes CO to convert to CO2, worsening carbon efficiency
Solution Approach 1:
The patent extracts and removes water from the recycle stream using a water removal unit (condenser, separator, or molecular sieve). By removing water before recycling the gas, the system prevents steam pressure buildup that would otherwise drive the unwanted CO to CO2 conversion, thereby maintaining carbon efficiency while allowing high productivity operation.
Solution Approach 2:
The patent implements a recycle mode where unreacted synthesis gas is recycled back to the reactor inlet. This feedback loop allows the system to maintain high single pass conversion while managing CO2 production through controlled water removal, balancing productivity and carbon efficiency through continuous process adjustment.
2Loss of substance
If CO2 is added to balance water gas shift reactions, then net CO2 production is reduced, but reactant gases are diluted, worsening methanol synthesis rates
Solution Approach 1:
The patent carefully controls the CO2 concentration parameter in the synthesis gas, maintaining it within the range of 5-15 vol%. This parameter optimization balances the need to suppress CO to CO2 conversion through water gas shift equilibrium while minimizing the dilution effect on methanol synthesis rates. The water removal unit further fine-tunes the composition to achieve optimal performance.
3Productivity
If high pressure and high conversion are used, then productivity is improved, but catalyst aging accelerates, worsening catalyst life
Solution Approach 1:
The patent removes water from the recycle stream to prevent water-induced catalyst aging. By extracting water before the gas is recycled and reused, the system maintains high pressure and conversion conditions for improved productivity while protecting the catalyst from degradation, thereby extending catalyst life.
4Loss of substance
If recycle ratio is increased to control CO2 production, then carbon efficiency is improved, but compressor costs increase, worsening operating costs
Solution Approach 1:
The patent implements water removal in the recycle loop to enable effective CO2 control at moderate recycle ratios. By extracting water before recycling, the system achieves good carbon efficiency without requiring excessively high recycle ratios that would impose prohibitive compressor costs, thus optimizing the balance between carbon efficiency and operating costs.
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
Achieves net CO2 consumption with high liquid hydrocarbon productivity, extending catalyst life and enabling efficient operation in GTL applications by balancing water gas shift reactions and controlling CO2 production.
Implementation Method 1
Hybrid catalysts for conversion of methane through a synthesis gas pathway to gasoline-range hydrocarbons, (mainly isoparaffins) and LPG, comprising a ZnO—Cr2O3 methanol catalyst with a ZSM-5 type zeolite
Implementation Method 2
At high single pass conversions, the buildup of steam pressure causes conversion of CO to CO2. Without control, this makes these 'isosynthesis' catalysts unsuitable for GTL applications
Implementation Method 3
introducing CO2 from another source into the feed gas, so that the reverse water gas shift reaction is in balance with the forward water gas shift reaction and net production of CO2 is avoided
Data Source
AI summary
A process of form hydrocarbons boiling to the gasoline range and reducing or eliminating net CO2 production during isosynthesis over a ZnO—Cr2O3 plus ZSM-5 catalyst by adding from about 5% to about 15% CO2 to the synthesis gas mixture prior to contact to with catalyst.