Two-Stage SCR Catalyst for NOx Reduction with Propylene
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Solution Overview
Problem
Current methods for reducing nitrogen oxides (NOx) emissions from combustion processes, such as those in petroleum and petrochemical refining, are expensive and have limited efficiency, necessitating an improved selective catalytic reduction technique.
Innovation Solution
A method involving a two-stage catalytic process using a first catalyst with alumina loaded with silver and a second catalyst with zirconia loaded with metals like copper, cerium, or tungsten, where a low molecular weight hydrocarbon like propylene is used as a reductant to reduce NOx emissions, with operating conditions optimized for temperature and flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional SCR methods using ammonia or urea are used, then NOx reduction is achieved, but operating costs increase and efficiency is limited
Solution Approach 1:
The patent changes the chemical parameter by substituting the reductant from ammonia/urea to propylene, and changes the catalyst composition parameter by using alumina loaded with silver and zirconia loaded with metals. This parameter change achieves higher NOx removal efficiency (>90%) while reducing operating costs, as propylene is a byproduct in petroleum refining and the new catalyst system demonstrates superior activity
Solution Approach 2:
The patent employs composite catalyst materials: alumina loaded with silver and zirconia loaded with metals (such as copper, cerium, or tungsten). These composite materials work synergistically to achieve high NOx conversion efficiency, with the alumina-silver catalyst facilitating the primary reduction and the zirconia-metal catalyst enhancing the overall performance and stability
2Object-generated harmful factors
If conventional SCR methods using ammonia or urea are used, then NOx reduction is achieved, but operating costs increase
Solution Approach 1:
The patent enables the refining process to use its own byproduct (propylene) as the reductant for NOx removal. This self-service approach eliminates the need to purchase external reductants like ammonia or urea, thereby reducing operating costs while maintaining effective NOx control in petroleum refining operations
3Object-generated harmful factors
If a two-stage catalytic process is used, then NOx removal efficiency increases, but device complexity increases
Solution Approach 1:
The patent divides the NOx reduction process into two sequential catalytic stages: first stage using alumina loaded with silver, and second stage using zirconia loaded with metals. This segmentation allows each catalyst to perform its specific function optimally, achieving >90% overall NOx removal efficiency while maintaining manageable system complexity through modular design
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 achieves NOx reduction of greater than 90%, addressing the inefficiencies and costs of existing methods by effectively converting NOx to diatomic nitrogen and water.
Implementation Method 1
A portion of the exhaust stream and a reductant stream including a low molecular weight hydrocarbon are introduced to a first catalytic reactor, which comprises a first catalyst including alumina loaded with silver. The reductant stream and the portion of the exhaust stream being introduced to the first catalytic reactor are at suitable operating conditions to reduce the amount of NOx in the exhaust stream.
Implementation Method 2
The NOx-reduced exhaust stream from the first catalyst is then directed to a second catalyst including zirconia loaded with at least one metal.
Implementation Method 3
SCR is a catalytic technique to convert NOx to diatomic nitrogen, N2, and water, H2O. The low molecular weight hydrocarbon is propylene.
Implementation Method 4
The first catalytic reactor can be maintained at an operating temperature between about 300°C and 400°C by heating or cooling the exhaust stream.
Data Source
Figure 1
Figure 2A~2B
AI summary
Methods and systems are provided for selective catalytic reduction of NOx with a low molecular low molecular weight hydrocarbon, e.g., propylene, as a reductant using a catalyst system including two catalysts. An exhaust stream containing an amount of NOx from a combustion operation is provided. A portion of the exhaust stream and a reductant stream including a low molecular weight hydrocarbon is introduced to a first catalytic reactor, which comprises a first catalyst including alumina loaded with silver. The NOx-reduced exhaust stream from the first catalyst is then directed to a second catalyst including zirconia loaded with at least one metal.