Catalyst for preparing lactone and a method for preparing lactonePatent US6323347
AbstractThe present invention relates to a catalyst for preparing a lactone, which is prepared by supporting a cupric compound, a zinc compound and at least one alkaline earth metal compound on the supporter. The present invention also relates to a method for preparing a lactone, which comprises a dehydrocyclization reaction of a diol under a gas phase in the presence of the aforementioned catalyst after activating said catalyst. The catalyst for preparing lactone of the present invention is quite economic because of its high activity, long lifetime and high selectivity of products.The catalyst of the present invention used for preparing a lactone is prepared according to the following method. The supporter is immersed in the above aqueous cupric salt and zinc salt solutions, and the value of pH is adjusted between 8 and 11 using ammonia water, while the hydroxides of copper and zinc are precipitated on the supporter. The precipitate is washed with water and dried. The precipitate is immersed in the above aqueous salts solution selected from one or two alkaline earth metal compound(s) consisting of magnesium, calcium and barium, and then calcined for 3 to 5 hours at 400-500°C.
In such resultant catalyst, each metal component exists in the form of oxide. Therefore, before the dehydrogenation reaction of diol, the catalyst must be reduced and be activated at a temperature ranging from 180-250°C for 6-20 h with hydrogen gas wherein the ratio of hydrogen gas to nitrogen gas starts between 5-10% by volume, then gradually adjusts to all hydrogen gas.In the dehydrocyclization reaction of the method for preparing lactone such as gamma-butyrolactone used in the present invention, the reaction temperature usually ranges from 160-280°C., preferably 180-250°C. If the reaction temperature is too low, the conversion of 1,4-butylene glycol may be decreased. Although the higher temperature may increase the conversion of 1,4-butylene glycol, the selectivity of gamma-butyrolactone may be substantially decreased.
In the dehydrocyclization reaction of the method for preparing lactone such as gamma-butyrolactone used in the present invention, the reaction pressure usually ranges from 0-10 atm., preferably from 1-5 atm. However, the higher reaction pressure may easily carry out an undesired reaction, decreasing the yield.
Reference Example 1 -
Activation of the catalystA commercially available copper-chromium catalyst (30 ml) (copper oxide 42% and chromium oxide 28% by weight, 5 mm diam.) was packed in the stainless steel reactor having an inside diameter of 23.5 mm. After the temperature was elevated to 150°C with nitrogen gas, the mixed gas of 10 vol % hydrogen gas was passed into the reactor, then the catalytic reduction reaction was initiated. The temperature and the concentration of hydrogen gas were gradually elevated until the reduction temperature of catalyst was 200°C. and the concentration of hydrogen gas was 100 vol %. When the temperature of catalyst bed was confirmed to be the same as that of the heating equipment, the reduction reaction was terminated.