Process for enhancement of cycle life of zinc chromium based catalyst used in synthesis of 2-methyl pyrazine
A chromium-based catalyst, cycle life technology, applied in catalyst protection, organic chemistry methods, chemical instruments and methods, etc., can solve problems such as short cycle life
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example 1
[0035] 150 g of palladium sulphate promoted zinc-chromium catalyst at 1.5% by weight was charged to a fixed bed reactor having an internal diameter of 40 mm provided with a preheater of the same diameter. The liquid feed contained ethylenediamine and propylene glycol in a molar ratio of 1.1:1. The organic feed was mixed with an equal volume of water. The catalyst was reduced under hydrogen at 400°C for 4 hours and then slowly heated to and maintained at a reaction temperature of 410°C under flowing nitrogen. Liquid was introduced into the reactor and the performance of the catalyst was monitored hourly by analyzing the product on a gas chromatograph. The catalyst exhibited a gradual increase in conversion with increasing time flow for a period of time before beginning to taper off. From figure 1 It is evident that the catalyst has a cycle life of about 150 hours.
example 2
[0037] An additional 150 grams of fresh catalyst as used in Example 1 was charged to the reactor and the activation procedure as described in Example 1 was carried out. After reduction at 400°C for 4 hours, the catalyst was cooled to a reaction temperature of 320°C in a nitrogen stream, and the reaction continued with a liquid feed. Catalyst performance was monitored hourly. The reaction continued as long as the yield of 2-methylpyrazine was in the range of 70-80% and the level of pyrazine in the reaction effluent was below 10-12%. When the pyrazine level crossed the setpoint, the reaction temperature was stepped up and the production process continued. The performance of the catalyst is as figure 2 shown.
example 3
[0039] After testing the cycle life of the fresh catalyst for 500 hours as described in Example 2, the reaction was stopped to regenerate the catalyst. The catalyst was first treated in steam at 400° C. for 4 hours and calcined in air at the same temperature until there was no emission of carbon dioxide in the reactor effluent; then it was reduced in hydrogen at the same temperature for 4 hours. The reaction was again continued at 320°C with a staged temperature ramp strategy. The performance of the regenerated catalyst is as image 3 shown. The catalyst was even run at 380°C with the required performance parameters for over 500 hours, giving further scope for increased cycle life.
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