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Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

Paper ID Volume ID Publish Year Pages File Format Full-Text
43737 45986 2007 8 PDF Available
Title
Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables
Abstract

It has been demonstrated that it is possible to produce p-xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p-xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p-xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p-xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p-xylene isomer, under optimised conditions.

Graphical abstractIt has been demonstrated that it is possible to produce p-xylene with >99.9% selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p-xylene on the external acid sites of the catalyst by controlling the contact time. Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Toluene alkylation; ZSM-5 zeolite catalyst; Boron; Magnesium; Methanol; p-Xylene
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Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 316, Issue 1, 2 January 2007, Pages 53–60
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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Any Questions? feel free to contact us