Comparative study of shape-selective toluene alkylations over HZSM-5
- The Weizmann Institute of Science, Rehovot (Israel)
The alkylation of toluene with methanol, ethanol, and 2-propanol was studied in a comparative manner using medium-port HZSM-5-type zeolite catalysts differing in crystal size and morphology and in the presence of an amorphous silica-boria phase. For comparison with large-port zeolites, propylation was also performed on H-mordenite (HM) and HY. A typical small-crystal HZSM-5 sample is non-para-selective in methylation and ethylation but exhibits substantial para-selectivity in propylation. When the catalyst is a large-crystal HZSM-5, para-selectivity is established in the case of methylation and ethylation and improves in the case of propylation; it is further enhanced with a large-crystal sample containing the amorphous phase. In contrast with HM and HY, which in toluene propylation produce only cymene, the HZSM-5 samples also catalyze the production of n-propyltoluene whose concentration in the product mixture can be twice as high as that of cymene. Cymene becomes the preferred product (up to {approximately} 10:1 ratio) upon increasing space velocity or time on stream. It is proposed that in the case of C{sub 3} and perhaps also larger ring substituents, skeletal isomerization is operative in ZSM-5 in addition to positional isomerization. Shape selectivity as revealed in the above comparison can be explained by assuming both internal and external catalytic activity in HZSM-5, as opposed to the essentially exclusively internal activity of HM and HY. It is further postulated that the proposed external effect is shape-selective, discriminating between molecules at a range in between that of the medium-port 10-ring channels as found in HZSM-5 and that of the large=port 12-ring channels characterizing HM and HY.
- OSTI ID:
- 7014295
- Journal Information:
- Journal of Catalysis; (USA), Vol. 118:1; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
TOLUENE
ALKYLATION
ZEOLITES
CATALYTIC EFFECTS
AMORPHOUS STATE
COMPARATIVE EVALUATIONS
CRYSTAL STRUCTURE
CYMENE
ETHANOL
GRAIN SIZE
ISOMERIZATION
METHANOL
METHYLATION
MORPHOLOGY
PROPANOLS
SYNTHESIS
ALCOHOLS
ALKYLATED AROMATICS
AROMATICS
CHEMICAL REACTIONS
HYDROCARBONS
HYDROXY COMPOUNDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MICROSTRUCTURE
MINERALS
ORGANIC COMPOUNDS
SIZE
020400* - Petroleum- Processing