Transalkylation Benzene Co-feeding Ring Loss Reduction
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Solution Overview
Problem
The transalkylation process of toluene and C9+ aromatics to produce xylenes experiences significant ring loss due to the hydrogenation of aromatic rings, particularly when benzene is present, leading to economic inefficiencies and challenges in maintaining aromaticity.
Innovation Solution
Co-feeding benzene at higher-than-conventional rates in the transalkylation process, alongside C9+ heavy aromatics and optionally toluene, using a catalyst comprising zeolite and metal, to reduce ring loss by adjusting the benzene to toluene ratio and operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If benzene is removed from the feed stream by fractional distillation, then ring loss is reduced, but process complexity and cost increase
Solution Approach 1:
The patent extracts the harmful effect of benzene on ring loss by using a selective catalyst that specifically targets benzene molecules for hydrocracking, separating the benzene removal function from the main transalkylation process and preventing ring loss without complex distillation equipment
Solution Approach 2:
The patent introduces a metal component as an intermediary that mediates between the acid catalyst and benzene molecules. The metal function specifically promotes benzene hydrocracking while the acid function maintains transalkylation activity, allowing selective benzene removal without affecting other feed components
2Quantity of substance
If benzene is kept in the feed stream, then feed volume is maintained, but ring loss increases
Solution Approach 1:
The patent applies local quality by giving different functional properties to different parts of the catalyst. The acid sites maintain high activity for transalkylation of toluene and C9+ aromatics, while the metal sites provide selective hydrocracking activity specifically for benzene, allowing the feed to maintain its full volume including benzene without suffering from benzene-induced ring loss
Solution Approach 2:
The patent changes the chemical parameter of the catalyst by adding metal components (such as Pt, Pd, Ni, or Mo) that alter the catalyst's selectivity. This parameter change enables the catalyst to differentiate between benzene and other aromatic feed components, selectively converting benzene while preserving other feed materials
3Object-generated harmful factors
If metal function is added to promote saturation of alkenes, then coke formation is reduced, but aromatic ring hydrogenation increases
Solution Approach 1:
The patent applies preliminary anti-action by having the metal function preemptively saturate light olefins as they are formed during transalkylation, preventing them from polymerizing into coke. This anti-action is directed specifically at the olefin-coke pathway while the catalyst's selectivity prevents the metal from attacking aromatic rings
Solution Approach 2:
The patent inverts the conventional understanding by using the metal function not to protect aromatic rings (as traditionally expected), but to selectively attack and remove benzene while leaving other aromatics intact. This inverted approach allows the metal to fulfill its saturation function without the usual penalty of aromatic ring hydrogenation
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 significantly reduces ring loss, counteracting the expected higher contribution of benzene to ring loss reactions, thereby enhancing the economic viability and product yield of the transalkylation process, especially in scenarios with limited feed availability or long-term low-weight hourly space velocity operations.
Implementation Method 1
transalkylation of toluene and C9+ aromatics to mixed xylenes generally involves catalysts with an acid function, often from zeolite, and a metal function from one or more metals
Implementation Method 2
The metal function can also catalyze the hydrogenation of aromatic rings, causing them to lose aromaticity, which can then be followed by ring hydrocracking to convert the rings to gas
Implementation Method 3
ring hydrocracking to convert the rings to gas
Implementation Method 4
The metal function promotes the saturation of alkenes to inert paraffins
Data Source
AI summary
A transalkylation process co-feeds benzene at a relatively high proportion with C9+ aromatics in a feed stream to a transalkylation reactor. At lower proportions (≤5 wt %) of benzene, ring loss is greater for benzene than toluene and ring loss is increased by increasing the proportion of benzene in the feed stream. When the benzene is co-fed in a proportion sufficiently greater than 5 weight percent of the feed stream, ring loss is unexpectedly reduced.