Coking, microbalance system

Figure 5. Schematic of microbalance system for coking studies under flowing...

Deposition was performed using a vacuum system [1]. Before deposition of the alkoxlde, the sample was evacuated at 673 K for 2 hr, and the temperature was then lowered to 593 - 293 K for the deposition of silicon methoxlde. S1(0CH3)4 vapor was then admitted to the dried zeolite at a vapor pressure of 2.5 Torr. The resultant Increase of weight was measured by the quartz microbalance. After the deposition, the decatlonlzed zeolite was calcined Iji situ by oxygen at 673 K to remove the coke residue, while the Na-type mordenlte was treated with water vapor at 593 K. The amount of SI deposited was... 

Details can be found in Bdlare (ref. 3). The experimental equipment consists of a cumene reservoir, a thermogravimetric analyzer (TGA) and a gas chromatograph (GC). The hdium-cumene mixture enters the TGA, a Cahn System 113DC with a Cahn 2000 Recording Electrobalance, a quartz tubular reactor, and an external split-shell furnace. The catalyst is placed in the sample pan of the microbalance inside the quartz reactor, kept at a controlled temperature in the center of the split-shell furnace. The incremental weight due to coke deposition on the catalyst is monitored by an IBM PC. The reactor exit stream is injected into a Varian 3700 GC using FID. 

Catalyst deactivation in the form of coking, during the hydrodechlorination of 1,2-dichloropropane (12DCP) over Pt-Cu/C catalysts, has been investigated with a novel microbalance-TEOM. The amount of coke deposition on both fresh and spent catalysts has been continuously measured. The activity and selectivity to propene decreases with an increase in the coke formation. The catalyst deactivation is mainly attributed to coke deposition. The TEOM technique with a well-defined gas-phase system, a good mass resolution, and a long-term stability is uniquely suitable to study simultaneous adsorption, reaction, and coke deposition. 

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