Aqueous formaldehyde solutions with a low tetroxane content

A process for forming an aqueous-formaldehyde solution comprising, continuously,

• in a 1st absorption stage
• forming a part-formaldehyde-loaded aqueous solution II and a formaldehyde-depleted gas stream II having decreased formaldehyde content, by conducting a part-formaldehyde-depleted gas stream I and a part formaldehyde-loaded aqueous solution I in countercurrent through an absorption zone I, to partially absorb said part-formaldehyde-depleted gas stream I in said part-formaldehyde-loaded aqueous solution I,
• removing said formaldehyde-depleted gas stream II and said part-formaldehyde-loaded aqueous solution II from said absorption zone I,
• dividing said part-formaldehyde-loaded aqueous solution II into 2 partial streams I and II,
• passing said partial stream I into said absorption zone I together with an aqueous solution W which comprises no formaldehyde or smaller amounts thereof than said part-formaldehyde-loaded aqueous solution I to form said part-formaldehyde-loaded aqueous solution I,
• and in a further upstream absorption stage 2
• forming a formaldehyde-loaded aqueous solution IV, wherein said formaldehyde-loaded aqueous solution IV is an aqueous solution comprising,
• a) from 10 to 75% by weight of formaldehyde,
• b) from 0 to 500 ppm by weight of tetroxane,
• c) from 50 to 400 ppm by weight of formic acid, based on the formaldehyde absorbed;
• and
• d) from 0.2 to 5.0% by weight of methanol, based on the formaldehyde absorbed;
• and said part-formaldehyde-depleted gas stream I by conducting a formaldehyde-loaded gas stream III and a part-formaldehyde-loaded aqueous solution III in countercurrent through an absorption zone II, to partially absorb said part-formaldehyde-depleted gas stream I in said part-formaldehyde-loaded aqueous solution I,
• removing said formaldehyde-loaded aqueous solution IV and said part-formaldehyde-depleted gas stream I from said absorption zone II,
• dividing said formaldehyde-loaded aqueous solution IV into 2 partial streams III and IV,
• producing a partial stream V by adding from 0.001 to 0.01% by weight of a Brönsted base to said partial stream III per part by weight of formaldehyde which is passed into said absorption zone II in the form of said formaldehyde-loaded gas stream III and
• forming said part-formaldehyde-loaded aqueous solution III by passing said partial stream V and said partial stream II together into said absorption zone II.