Abstract: A process for producing a methacrylic ester which comprises catalytically oxidizing isobutylene, tert-butanol, methacrolein or isobutyl aldehyde in a vapor phase; removing light-boiling substances form the resulting reaction product by distillation or stripping; extracting methacrylic acid from the resulting methacrylic acid aqueous solution using a saturated chain aliphatic hydrocarbon having 6 to 9 carbon atoms as a solvent; recovering the solvent from the obtained solvent solution of methacrylic acid; esterifying the resulting methacrylic acid by the reaction of it with a lower aliphatic alcohol or a lower alicyclic alcohol having 1 to 12 carbon atoms using a porous strongly acidic cation exchange resin as a catalyst for esterfication; and then subjecting the thus obtained esterification reaction product to a purification step.

Abstract: A method of collecting pyromellitic anhydride, which comprises introducing a high-temperature gas containing pyromellitic anhydride together with an inert cooling gas into an empty column-type collecting device whose wall temperature is maintained at 150.degree. to 200.degree. C., effecting heat exchange between the high-temperature gas and the cooling gas in the collecting device to lower the temperature of the high-temperature gas to 150.degree. to 200.degree. C., thereafter passing the gaseous mixture through the collecting device at an average linear gas velocity of 0.05 to 0.5 m/sec with an average residence time to 5 to 60 seconds, and recovering needle-like crystals of pyromellitic anhydride from the bottom of the collecting device.