Shell-and-Tube Reactor for Ethylene Production
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Solution Overview
Problem
Current oxidative dehydrogenation of ethane (ODHE) processes produce significant amounts of acetic acid as a by-product, limiting the application of ethylene production and requiring co-production with acetic acid, which is not always utilized efficiently, and existing optimizations have only led to limited improvements in ethylene yield.
Innovation Solution
A shell-and-tube reactor design with multiple catalyst beds of varying activity and a specific ratio of active catalyst mass to effective cooling surface, operated at higher linear velocities, achieving a significant increase in ethylene yield and process intensification while maintaining stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxidative dehydrogenation of ethane is carried out using conventional catalysts (MoVNbOx and MoVNbTeOx), then ethylene production is achieved, but significant amounts of acetic acid are formed as by-products
Solution Approach 1:
The patent applies local quality by creating different catalyst zones along the reactor length. The first catalyst zone has lower activity (higher selectivity to ethylene) while the second catalyst zone has higher activity (higher conversion). This spatial differentiation allows the process to optimize both ethylene yield and minimize acetic acid formation by matching catalyst properties to local process requirements.
Solution Approach 2:
The patent segments the catalyst bed into multiple zones with different activities. The first catalyst zone is positioned upstream with lower activity, while the second catalyst zone is positioned downstream with higher activity. This segmentation enables independent optimization of each zone's function, allowing high ethylene selectivity in the first zone and high conversion in the second zone.
2Productivity
If higher linear velocities are used to increase ethylene yield, then process intensification is achieved, but pressure loss increases
Solution Approach 1:
The patent changes the parameter of linear velocity to achieve process intensification. By operating at higher linear velocities (e.g., >500 cm/s), the patent increases ethylene yield and improves process intensity. The patent also adjusts other parameters such as temperature and catalyst activity distribution to manage the associated pressure loss.
3Productivity
If higher linear velocities are used to increase ethylene yield, then production output is improved, but thermal runaway risk increases
Solution Approach 1:
The patent implements feedback control through temperature monitoring and catalyst activity distribution. The lower activity first catalyst zone acts as a thermal buffer, while the higher activity second catalyst zone provides intensive conversion. This feedback mechanism allows the system to operate at high linear velocities for increased production while maintaining thermal stability through controlled heat generation zones.
Solution Approach 2:
The patent segments the catalytic function into two zones with different activities to manage thermal risks. The first catalyst zone with lower activity prevents excessive heat generation at the inlet, while the second catalyst zone with higher activity completes the conversion downstream. This segmentation allows high production output at high linear velocities while distributing thermal load to prevent thermal runaway.
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 design enhances ethylene yield and process intensification, allowing for higher production outputs with reduced reactor size and cooling surface, improving economic efficiency and avoiding thermal runaway, even at high ethylene yields.
Implementation Method 1
A plurality of catalyst beds are disposed in each of the reaction tubes... the plurality of catalyst beds are configured such that the plurality of catalyst beds in each of the reaction tubes have a different catalyst activity
Implementation Method 2
a ratio of active catalyst mass to effective cooling surface for the plurality of catalyst beds in each of the reaction tubes is in a range between 1.5 and 5 kg/m2
Data Source
AI summary
A process for producing ethylene by oxidative dehydrogenation of ethane using a shell-and-tube reactor having reaction tubes extending between a first end and a second end includes disposing one or more catalyst beds in each of the reaction tubes. In each of the reaction tubes, a ratio of a total length of the one or more catalyst beds between the first end and the second end to a diameter of each of the reaction tubes has a value between 150 and 400. The shell-and-tube reactor is operated at a linear velocity of 250 to 800 cm/s, and the one or more catalyst beds are configured such that a ratio of active catalyst mass to effective cooling area is in a range between 1.5 and 5 kg/m2.