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The conversion of chloromethane to light olefins over SAPO-34: The influence of dichloromethane addition

Paper ID Volume ID Publish Year Pages File Format Full-Text
42427 45925 2009 9 PDF Available
Title
The conversion of chloromethane to light olefins over SAPO-34: The influence of dichloromethane addition
Abstract

The effect of CH2Cl2 impurities on the conversion of CH3Cl to olefins over SAPO-34 has been investigated. CH3Cl was co-reacted with CH2Cl2 in a 10:1 ratio at 400 °C, WHSV = 8 h−1, p(CH3Cl) = 620 mbar and p(CH2Cl2) = 65 mbar, over a typical SAPO-34 catalyst with (Al + P)/Si = 11. It was observed that CH2Cl2 promotes the formation of aromatic compounds and leads to rapid deactivation of the catalyst for the CH3Cl to olefins reaction. The induction period, which is typically observed as an increase in activity before maximum conversion is reached is, however, significantly shortened by the addition of CH2Cl2. Feeding a mixture of 12CH3Cl and 13CH2Cl2 in a 10:1 ratio led to formation of olefins with about 5% 13C, which was indistinguishable from the 13C content in the aromatic hydrocarbons (reaction intermediates and coke) retained inside the SAPO-34 crystals in the same experiment. This shows that CH2Cl2 takes part in the reactions leading to both products, including the formation of aromatic reaction intermediates, and deactivation. Hypothesized reaction steps for the incorporation of carbon atoms from CH2Cl2 into both gas phase products and coke were found to be plausible by studying the reactions of xylene/CH2Cl2 mixtures and of 2,5-dimethylbenzyl chloride alone. The intimate mechanistic links between the desired conversion of CH3Cl to olefins and the detrimental effects of CH2Cl2 addition imposes restrictions on the purity of the CH3Cl feedstock in a commercial SAPO-34 based CH3Cl to olefins application.

Graphical abstractThe conversion of chlormethane is an alternative route for the production of light olefins from natural gas. Dichloromethane, which is formed during chlorination of methane, has been shown to deactivate the chloromethane conversion, following a similar mechanism as for the chloromethane conversion itself. This suggests that separation of the over-chlorinated products before conversion of chloromethane is necessary.Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Methane conversion; Chloromethane to olefins; Dichloromethane; Reaction mechanism; SAPO-34; Hydrocarbon pool; MTH
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 367, Issues 1–2, 1 October 2009, Pages 23–31
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
Online Support
Any Questions? feel free to contact us