Tapering Reactor for Alkane Dehydrogenation
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Solution Overview
Problem
Current alkane dehydrogenation processes in circulating fluidized-bed reactors face challenges such as low conversion per pass, high energy consumption, and catalyst deactivation due to back-mixing and local high temperatures, which affect alkene selectivity and catalyst regeneration efficiency.
Innovation Solution
A reaction device with a tapering section and integrated catalytic dehydrogenation-cracking reactor, where reactants and catalysts flow upwards, reducing back-mixing and local high temperatures, and a catalyst regeneration device with a diameter-expanding regenerator for uniform temperature distribution and efficient combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a circulating fluidized-bed reactor is used for alkane dehydrogenation, then continuous reaction and regeneration can be achieved, but back-mixing occurs causing reduced alkene selectivity and conversion per pass
Solution Approach 1:
The reactor is divided into multiple sections with different flow patterns: a fluidized bed reaction section for continuous processing and a tapering section for reducing back-mixing. This segmentation allows the system to maintain continuous operation while improving alkene selectivity by preventing product mixing with reactants.
Solution Approach 2:
Instead of using a conventional cylindrical reactor that promotes back-mixing, the patent employs a tapering reactor design where the cross-sectional area decreases in the flow direction. This inverted geometry utilizes gravity and flow dynamics to reduce back-mixing effects, thereby improving alkene selectivity while maintaining continuous operation.
2Productivity
If high temperature is applied to increase equilibrium conversion ratio, then dehydrogenation conversion improves, but local high temperatures cause thermal reactions reducing selectivity
Solution Approach 1:
The reactor design creates different thermal zones: a fluidized bed section for uniform heat distribution and a tapering section for controlled cooling. This local quality variation allows high temperatures to be maintained in the reaction zone for improved conversion while preventing excessive temperatures that would cause unwanted thermal reactions and reduce selectivity.
Solution Approach 2:
The tapering section acts as an intermediary zone between the high-temperature fluidized bed reaction section and the discharge point. It provides a transition region where temperature is gradually reduced, allowing the system to benefit from high-temperature conversion while avoiding the negative effects of localized high temperatures on selectivity.
3Productivity
If catalyst circulation rate is increased to improve conversion, then reaction efficiency increases, but energy consumption increases due to hydrogen circulation requirements
Solution Approach 1:
The patent extracts and eliminates the requirement for hydrogen circulation by using a catalyst circulation system that operates without hydrogen makeup gas. The dehydrogenation reaction produces hydrogen that is separated and removed from the system, allowing catalyst circulation to drive conversion without the energy penalty of hydrogen compression and circulation.
Solution Approach 2:
Instead of using expensive Pt-based catalysts that require hydrogen circulation for stability, the patent employs cheaper Cr-based catalysts that can be circulated continuously. The catalyst is regenerated in situ by burning off coke deposits, eliminating the need for expensive hydrogen circulation and reducing energy consumption while maintaining high conversion per pass.
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 solution enhances alkene selectivity and conversion per pass, reduces energy consumption, and prolongs catalyst life by minimizing back-mixing and thermal reactions, while ensuring safe and efficient catalyst regeneration.
Implementation Method 1
alkane catalytic cracking (such as Superflex), heavy oil catalytic cracking (such as TMP and DCC) and heavy oil catalytic pyrolysis (such as CPP). And It is also an important technical route to prepare alkene and dialkene via the alkane catalyzed dehydrogenation.
Implementation Method 2
the catalysts need frequent coke-burning regeneration or oxychlorination regeneration
Implementation Method 3
circulating-fluidized-bed (FBD) reaction-regeneration devices
Data Source
AI summary
A reaction-regeneration device for catalytic dehydrogenation or/and catalytic cracking of alkanes comprises a reaction device and a regeneration device. The reaction device comprises a reactor and a disengager, and the disengager is located at an upper part of the reactor. The reactor comprises a tapering section, and diameters of cross sections of the tapering section gradually decrease from bottom to top. Secondary conversion of alkenes caused by back-mixing is reduced, and thus the yield and selectivity to alkenes are increased.