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.degree. 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.
Process for preparing high-concentration gaseous formaldehyde having a molar CH.sub.2O:H.sub.2O ratio of .gtoreq.0.6 from an aqueous formaldehyde solution by evaporation of at least part of the solution, in which the aqueous formaldehyde solution is heated to a vaporization temperature T and the gas phase formed is taken off, wherein the evaporation temperature T obeys the relationship: T[.degree. C.].gtoreq.T'.sub.min[.degree. C.] where T'.sub.min(c)=A+B.times.(c/100)+C.times.(c/100).sup.2+D.times.(c/100).sup- .3 and A=+68.759, B=+124.77, C=-12.851, D=-10.095, where c is the instantaneous CH.sub.2O content of the aqueous formaldehyde solution during the evaporation in percent by weight and is from 20 to 99% by weight.
