Abstract: In a process for preparing formaldehyde from methanol by dehydrogenation in a reactor in the presence of a catalyst at a temperature in the range from 300 to 1000° C., a circulating gas stream comprising by-products of the dehydrogenation is passed through the reactor.

Abstract: Process for the nonoxidative preparation of formaldehyde from methanol The invention relates to a process for preparing formaldehyde from methanol by dehydrogenation in a reactor at temperatures in the range from 300 to 1000° C. in the presence of a catalyst which is introduced into the reactor with the aid of a carrier gas to give a product gas mixture, wherein the formaldehyde is separated from the product gas mixture and at least part of the remaining product gas mixture is recirculated to the reactor in a circulating gas stream and the carrier gas used is a carbon-free gas or gas mixture.

Abstract: Abstract A process for purifying formaldehyde in which the formaldehyde is scrubbed with alcohol in an absorption unit and in the course of this reacted virtually completely to form the hemiformal and is simultaneously separated off from gaseous impurities in a first purification step. In a desorption unit, the residual impurities are then converted into a gaseous state and separated off from the liquid hemiformal, whereupon the purified hemiformal is thermally cleaved into alcohol and formaldehyde in a pyrolysis unit. The formaldehyde thus prepared is suitable, for example, for preparing oligomers, polymers, dyestuffs and fertilizers, as well as for the treatment of seeds.

Abstract: The invention relates to a method for separating a gaseous mixture comprising formaldehyde and trioxane, wherein at least some of the formaldehyde and the trioxane are dissolved from the mixture in a alcohol-containing liquid and the trioxane is crystallized from the solution thus obtained and is separated.