GB1453766A - Production of concentrated aqueous solutions of formaldehyde - Google Patents

Abstract

1453766 Formaldehyde BASF AG 20 Feb 1974 [21 Feb 1973] 7650/74 Heading C2C In a process for the manufacture of a concentrated aqueous solution of formaldehyde by oxidative dehydrogenation of methanol with pure oxygen or a gas containing free oxygen in the presence of a silver catalyst and in the presence of steam at an elevated temperature and subsequent absorption of the formaldehyde thus produced in absorption apparatus, the reaction is effected with a starting mixture in the vapour state at a temperature from 650‹ to 780‹ C., which mixture contains from 0À44 to 1À8 moles of water per mole of methanol, the resulting reaction mixture, which is in the vapour state, is cooled and absorbed in two stages, the ratio of the length or number of plates of the absorption column(s) of the second absorption stage to that of the absorption column of the first absorption stage being from 1À1 : 1 to 8 :1, the reaction mixture being treated in the first absorption stage at a temperature of 45‹ to 80‹ C. and using a throughput of 2 to 5 tonnes of reaction mixture per hour per square meter of column cross-section (measured at the column inlet) in countercurrent with an absorption mixture which contains from 47 to 60% by weight of formaldehyde, from 35 to 52% by weight of water and from 0À5 to 5% by weight of methanol, based on the absorption mixture, the throughput of absorption mixture being 20 to 50 tonnes per hour per square meter of column cross-section (measured at the point of entry into the column), and the off-gas from the first absorption stage being treated in the second absorption stage at a temperature of 40‹ to 65‹ C. and using a throughput of 4 to 8 tonnes of off-gas per hour per square meter of column cross-section (measured at the point of entry into the first column of the second absorption stage) in countercurrent with a second absorption mixture which contains, measured in the first column of the second absorption stage from 10 to 40% by weight of formaldehyde, from 55 to 89% of water and from 0À5 to 5% by weight of methanol, based on the absorption mixture, using a throughput of 12 to 30 tonnes of the second absorption mixture per hour per square meter of column cross-section (measured at the point of entry into the first column of the second absorption stage), and formaldehyde, in the form of the solution thus produced, is withdrawn from both stages. The absorption liquids are suitably recirculated formaldehyde solutions from the particular stage, additional water being added as required. The second stage may use a multiplicity of columns, absorption liquid being passed from the bottom of one column to the top of the preceding column.