| 摘要 |
1,148,280. Maleic anhydride. SOC. CHIMIQUE DES CHARBONNAGES. 21 March, 1968 [30 March, 1967], No. 13803/68. Heading C2C. Maleic anhydride is prepared by dehydration of maleic acid by a continuous process which comprises evaporating a saturated aqueous solution of maleic acid at a temperature of up to 125‹ C. for less than a minute to remove the water from the solution and to give a molten acid substantially free from water and fumaric acid, heating a mixture of maleic acid and maleic anhydride in which the ratio (acid)/ (anhydride) + (acid) is 20-40% to a temperature of up to 160‹ C. for less than a minute and condensing the maleic anhydride vapour. The heating processes may be carried out in the form of thin layers and at an absolute pressure of less than 760 mm. Hg, preferably 100-300 mm. Hg. Before the condensation step the anhydride vapour may be kept at a temperature of 150- 165‹ C. for a brief period and then subject to a first condensation at 110-130‹ C. and a second condensation at 50-62‹ C. |
