Integrated P-Xylene Production via Dealkylation and Disproportionation
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Solution Overview
Problem
Existing processes for producing p-xylene have low concentration levels, leading to high energy consumption and large circulation quantities, resulting in a low overall yield and inefficient use of aromatic hydrocarbon resources.
Innovation Solution
An integrated process involving dealkylation of C9+ aromatic hydrocarbons, toluene selective disproportionation, and combined adsorption and crystallization separation methods to increase p-xylene concentration, reduce unit scales, and lower energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If toluene selective disproportionation process is used, then p-xylene concentration is improved, but benzene by-product increases resulting in lower overall yield
Solution Approach 1:
The process segments the C8 aromatic hydrocarbon stream into different fractions based on boiling point and composition. The C8A stream is separated into toluene-rich fraction, xylene-rich fraction, and other fractions, allowing selective processing to maximize p-xylene yield while minimizing benzene by-product.
Solution Approach 2:
The process performs preliminary separation of C8 aromatic hydrocarbons from the reaction mixture before the disproportionation reaction. By removing C8A from the feedstock and recycling it separately, the process prevents unwanted side reactions and maximizes the conversion of toluene to p-xylene, thereby improving overall yield.
2Productivity
If conventional Tatoray process is used, then C9A conversion is improved, but p-xylene concentration remains low resulting in high energy consumption
Solution Approach 1:
The process changes the operational parameters by using a modified ZSM-5 catalyst with specific pore structure and composition. This catalyst modification enables selective disproportionation at lower temperatures and pressures, reducing energy consumption while maintaining high C9A conversion and producing high concentration of p-xylene.
Solution Approach 2:
The process employs a composite catalyst system combining ZSM-5 molecular sieve with metal components (Pt, Pd, Ni, or Co). This composite catalyst structure provides both the shape-selective properties of ZSM-5 and the active sites needed for efficient disproportionation, achieving high conversion with lower energy input.
3Manufacturing precision
If toluene selective disproportionation is used, then p-xylene concentration is improved, but feedstock selection is restricted resulting in resource waste
Solution Approach 1:
The process makes the disproportionation unit universal by accepting multiple feedstock types including toluene, C9 aromatic hydrocarbons, and their mixtures. The modified ZSM-5 catalyst and process conditions are designed to handle various aromatic hydrocarbon compositions, allowing the same unit to process different feedstocks and maximize p-xylene production from available resources.
Solution Approach 2:
The process recovers and recycles C8 aromatic hydrocarbons from the reaction mixture back to the disproportionation unit. By recovering these valuable intermediates and feeding them back into the process, the system maximizes the utilization of aromatic hydrocarbon resources and reduces waste, enhancing overall adaptability to different feedstock compositions.
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 process significantly increases p-xylene concentration, decreases energy consumption, and reduces equipment investment, achieving a higher overall yield and more efficient production of p-xylene.
Implementation Method 1
feeding the stream of C9 and higher aromatic hydrocarbons from step A) to a C9 and higher aromatic hydrocarbon dealkylation unit, where dealkylation reaction occurs in the presence of hydrogen
Implementation Method 2
toluene undergoes selective disproportionation over a modified ZSM-5 catalyst to produce benzene and C8A with a high concentration of p-xylene
Implementation Method 3
a majority of p-xylene can be separated through only a simple step of freezing separation
Implementation Method 4
feeding both the first C8 aromatic hydrocarbon stream and the second C8 aromatic hydrocarbon stream to an adsorption separation unit
Implementation Method 5
feeding the third C8 aromatic hydrocarbon stream to a crystallization separation unit
Data Source
AI summary
A process of making p-xylcne comprising processing a mixed feedstock containing benzene, toluene, C8 aromatic hydrocarbons, C9 and higher aromatic hydrocarbons, and non-aromatic hydrocarbons through a series of operations and various units, including a C9 and higher aromatic hydrocarbon dealkylation unit, a toluene selective disproportionate unit, an adsorption separation unit, an isomerization unit, and a crystallization separation unit.