Formaldehyde as a liquid solution of 37 wt%–55 wt% is primarily used in the production of synthetic resins in the wood industry and as feedstock for a wide variety of industrially important chemical compounds.
Formaldehyde solutions are produced by the oxidation of methanol with air. In the UIF process, the reaction occurs on the surface of a silver- crystal catalyst at temperatures of 620°C– 680°C, where the methanol is dehydrated and partly oxidized: CH3OH t CH2O + H2 ?h = 84 kJ/mol CH3OH + ½ O2 t CH2O + H2O ?H = –159 kJ/mol The methanol/water mixture, adjusted for density balance and stored in the preparation tank, is continuously fed by pump to the methanol evaporator (1). The required process air is sucked in by a blower via a filter and air scrubber into the methanol evaporator. From here, the methanol/water/air mixture enters the reactor (2) where the conversion of methanol to formaldehyde occurs. Because the reaction is exothermic, the required temperature is self-maintained once the ignition has been executed.
The reaction gases emerging from catalysis contain formaldehyde, water, nitrogen, hydrogen and carbon dioxide, as well as unconverted methanol. They are cooled to 150°C in a waste-heat boiler directly connected to the reactor. The amount of heat released in the boiler is sufficient for heating the methanol evaporator. The reaction gases enter a four-stage absorption tower (3), where absorption of formaldehyde occurs in counter-flow to an aqueous formaldehyde solution and cold demineralized water. The final formaldehyde solution is removed from the first absorption stage.
Waste gas from the absorption tower, with a heating value of approximately 2,000 kJ/m3, is burned in a post-connected thermal combustion unit. The released heat can be used to produce high-pressure steam or thermal oil heating.
By recycling a part of waste gas to the reactor, formaldehyde concentrations up to 52 wt% in the final solution can be reached. To produce urea/formaldehyde precondensate, an aqueous urea solution, in place of absorption water, is fed into the absorption tower.
Licensor: Uhde Inventa-Fischer
