The catalytic conversion of methyl chloride to ethylene and propylene over phosphorus-modified Mg-ZSM-5 zeolites

Journal Article · Wed Sep 01 00:00:00 EDT 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1251· OSTI ID:5548126

Sun, Y; Campbell, S M; Lunsford, J H ^[1]; Lewis, G E; Palke, D; Tau, L M ^[2]

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1. Texas A M Univ., College Station, TX (United States)
2. Dow Chemical Co., Freeport, TX (United States)

A Mg-ZSM-5 zeolite modified with phosphorus is capable of catalyzing the reaction of CH[sub 3]Cl to C[sub 2]H[sub 4], C[sub 3]H[sub 6], C[sub 4]H[sub 8], and HCl at 500[degrees]C. At a WHSV of 20 h[sup [minus]1], an initial conversion level of 96% was achieved with combined C[sub 2]H[sub 4], C[sub 3]H[sub 6], and C[sub 4]H[sub 8] selectivities of about 80%. During the useful life of the catalyst the C[sub 3]H[sub 6] selectivity was 50-60%. The percent conversion decreased to 50% over a period of 20 h, but the catalyst could be regenerated by heating in flowing air. As the catalyst deactivated, the C[sub 3]H[sub 6] selectivity increased slightly and the C[sub 2]H[sub 4] selectivity decreased. Catalytic and spectroscopic results confirm that phosphorus, derived from trimethylphosphine, was responsible for a decrease in the strong Broensted acidity in the zeolite. For example, the phosphorus-modified zeolite was inactive for n-hexane cracking at 350[degrees]C, and the protonated amount of pyridine, added to the zeolite as a probe for acidity, decreased significantly. The catalyst, however, had sufficient acidity to crack hexene or octene at 500[degrees]C to propylene and ethylene in ratios that were very similar to those detected during the conversion of CH[sub 3]Cl. Without the strong Broensted acidity the PMg-ZSM-5 zeolite apparently is unable to convert the light olefins to paraffins and aromatics. A mechanism is proposed in which magnesium cations activate CH[sub 3]Cl to form HCl and a carbene intermediate. The latter is believed to be responsible for C-C bond formation via reaction with a surface methoxide species. Ethylene probably is the primary hydrocarbon, but it oligomerizes to a higher molecular weight olefin which cracks back to ethylene and propylene. 22 refs., 8 figs., 1 tab.

• OSTI ID: 5548126
• Journal Information: Journal of Catalysis; (United States), Vol. 143:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
10 SYNTHETIC FUELS
ETHYLENE
CHEMICAL PREPARATION
PROPYLENE
ZEOLITES
CATALYTIC EFFECTS
BROENSTED ACIDS
CATALYSTS
CATIONS
CRACKING
HETEROGENEOUS CATALYSIS
METHYL CHLORIDE
REACTION INTERMEDIATES
ALKENES
CATALYSIS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHLORINATED ALIPHATIC HYDROCARBONS
DECOMPOSITION
HALOGENATED ALIPHATIC HYDROCARBONS
HYDROCARBONS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IONS
MATERIALS
MINERALS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PYROLYSIS
SILICATE MINERALS
SYNTHESIS
THERMOCHEMICAL PROCESSES
400201* - Chemical & Physicochemical Properties
100200 - Synthetic Fuels- Production- (1990-)