Producing methacrylic acid (MAA) by the use of isobutylene or t-butyl alcohol as a raw material via intermediate methacrolein (MAL) is one of the advanced routes for MAA preparation. There are a number of patents concerning the catalysts for producing MAA by MAL oxidation. All of the catalysts disclosed are heteropolymolybdophosphoric acid compounds (CN 100490973C, U.S. Pat. No. 4,256,914, U.S. Pat. No. 4,347,163, etc.). However, low degradation is the deficiency of these catalysts. Being subjected to an increased for an extended time, the catalyst may break down, with MoO3 being generated, resulting in deteriorated activity.
Various approaches on the regeneration of the catalyst for recovering the catalytic activity have been studied in order to extend the lifespan of the catalyst. For example, U.S. Pat. No. 4,471,062 provided a method for the regeneration of the catalyst without discharging same, comprising the steps of sweeping the catalyst with an inert gas first, and then directly feeding an oxynitride at a of from about 100° C. to 400° C.
Chinese patent CN1451478A provided an online activation method comprising a step of feeding a gas mixture of oxygen, steam and nitrogen at a of from 290 to 400° C. once every half year or once a year.
Japanese Patent Publication JP 58-156351 disclosed a process to recover the catalytic activity by heat treatment, which process comprises a step of feeding an air flow containing at least 10% of steam by volume to the deactivated catalyst at a temperature of from 70 to 240° C.; however, such a process is ineffective with a catalyst with a destroyed structure.
U.S. Pat. No. 4,814,305 provides a method for regenerating a deactivated catalyst comprising the steps of dispersing the deactivated catalyst in water, adding a certain amount of aqueous ammonia at 50° C. and stirring for 1 hour, adding pyridine after drying and stirring the mixture obtained at 90° C. for 30 minutes, drying, and then calcining to produce a regenerated catalyst.
Japanese patent JP-A-2001-286763 provides a method for the regeneration of a deteriorated catalyst, comprising the steps of dispersing the deteriorated catalyst into water, adding a nitrogen-containing heterocyclic compound, ammonium nitrate and nitric acid at 70° C. to obtain a mixture, drying the mixture and then calcining the dried mixture.
Chinese patent CN101554593A discloses a method for the regeneration of a deactivated catalyst, comprising the steps of heat treating the deactivated catalyst at 350° C., mixing same with water, nitrate ions and ammonium ions, heat treating at 100° C., drying the mixture, and then calcining the dried mixture twice to obtain a regenerated catalyst.
Chinese patent CN100490975 discloses a method for the regeneration of a deactivated catalyst, comprising the steps of mixing the deactivated catalyst with water, nitrate ions and ammonium ions, aging same at 70° C. for 5 hours, and drying, molding and calcining the dried mixture to obtain a regenerated catalyst.
However, all these conventional methods for regeneration are cumbersome, time-consuming, and incapable of obtaining a regenerated catalyst having satisfactory catalytic activity.