Cyclohexylbenzene Production via Hydroalkylation and Dehydrogenation
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Solution Overview
Problem
Current processes for producing phenol through benzene hydroalkylation suffer from low selectivity to cyclohexylbenzene and high production of unwanted by-products, including cyclohexane, which leads to inefficiencies and increased costs due to the need for additional hydrogen and catalyst aging issues.
Innovation Solution
A process where benzene is contacted with hydrogen in the presence of a hydroalkylation catalyst to produce cyclohexylbenzene, and then cyclohexane is dehydrogenated to recycle additional benzene, with hydrogen pre-contacting the dehydrogenation catalyst to extend catalyst life and improve selectivity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If benzene is contacted with hydrogen in the presence of a hydroalkylation catalyst to produce cyclohexylbenzene, then cyclohexylbenzene is formed, but significant quantities of unwanted by-products including cyclohexane are produced
Solution Approach 1:
The process is divided into two separate catalytic steps: (1) hydroalkylation of benzene to cyclohexylbenzene, and (2) dehydrogenation of cyclohexane by-product back to benzene. This segmentation allows each catalyst to be optimized for its specific function, improving overall selectivity and reducing unwanted by-products.
Solution Approach 2:
Instead of discarding the cyclohexane by-product, the process recycles it by dehydrogenating it back to benzene using a dehydrogenation catalyst. This recovered benzene is then fed back into the hydroalkylation reactor, improving atom economy and reducing waste.
2Productivity
If cyclohexane is produced as a by-product, then benzene conversion is achieved, but the cyclohexane builds up in the benzene recycle stream displacing benzene and increasing by-product production
Solution Approach 1:
The cyclohexane by-product is continuously removed from the recycle stream through dehydrogenation back to benzene. This prevents cyclohexane accumulation and maintains high benzene concentration in the recycle stream, ensuring sustained productivity.
Solution Approach 2:
The dehydrogenation step creates a feedback loop where cyclohexane is converted back to benzene and returned to the hydroalkylation reactor. This feedback mechanism maintains the balance of reactants and prevents by-product accumulation that would otherwise reduce productivity.
3Duration of action of stationary object
If hydrogen is co-fed with cyclohexane to the dehydrogenation process to control catalyst aging, then catalyst life is extended, but the amount of hydrogen consumed in hydroalkylation far outweighs hydrogen produced in dehydrogenation requiring fresh hydrogen introduction
Solution Approach 1:
Hydrogen is introduced into the system before the dehydrogenation step, allowing it to contact the dehydrogenation catalyst and suppress unwanted side reactions. This preliminary action protects the catalyst and extends its life without requiring excessive hydrogen consumption during the main reaction.
Solution Approach 2:
Hydrogen acts as an intermediary substance that facilitates the dehydrogenation reaction while protecting the catalyst from aging. By introducing hydrogen upstream, it mediates between the need for catalyst protection and the overall hydrogen balance of the process.
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 useful life of catalysts, reduces by-product formation, and enhances the recycling of benzene, leading to improved selectivity and efficiency in phenol production.
Implementation Method 1
contacting benzene with hydrogen in the presence of a hydroalkylation catalyst under hydroalkylation conditions effective to form a first effluent stream comprising cyclohexylbenzene
Implementation Method 2
benzene undergoes partial hydrogenation to produce a reaction intermediate such as cyclohexene which then alkylates the benzene starting material
Implementation Method 3
contacting at least a portion of the cyclohexane from the first effluent stream with hydrogen in the presence of a dehydrogenation catalyst under dehydrogenation conditions effective to convert at least some of the cyclohexane into benzene
Implementation Method 4
cyclohexane is dehydrogenated to recycle additional benzene
Data Source
AI summary
In a process for producing cyclohexylbenzene, benzene is contacted with hydrogen in the presence of a hydroalkylation catalyst under hydroalkylation conditions effective to form a first effluent stream comprising cyclohexylbenzene, cyclohexane, and benzene. At least a portion of the cyclohexane from the first effluent stream is then contacted with hydrogen in the presence of a dehydrogenation catalyst under dehydrogenation conditions effective to convert at least some of the cyclohexane into benzene contained in a second effluent stream. At least some of the hydrogen is supplied to the process so as to contact the dehydrogenation zone (e.g., the dehydrogenation catalyst) before contacting the hydroalkylation catalyst.