I have studied that formaldehyde stored at temperature lower than room temperature convert into 1,3,5-oxane. So, it's not stored at colder temperatures.
But my question is - Can a similar degrading reaction happen if methanal is stored at temperature higher than room temperature?
Trimerization of formaldehyde can happen at high temperatures, but appear to require catalysts. There is a patent for synthesizing 1,3,5-trioxide at high temperature. This patent uses phosphoric acid catalysts. According to the patent:
The process of the invention is advantageously carried out at reaction temperatures of from 80 to 160° C., preferably from 90 to 145° C., at an inlet partial pressure of the formaldehyde of from 0.5 to 5 bar absolute, preferably from 0.5 to 2 bar, and at an inlet concentration of formaldehyde of from 1 to 100% by volume, preferably from 20 to 100% by volume
There is also an early study which explored the kinetics of the reaction but for a different catalyst. In "Vapour-phase trimerization of formaldehyde to trioxane catalysed by 1-vanado-11-molybdophosphoric acid" by Kern and Emig, they use a molybdophosphoric acid catalyst. They used a tube reactor and varied the temperature from 102.5 to 110° C. According to their study:
The conversion observed increases extremely with decreasing temperature.
However, they comment that
the temperature dependence cannot be attributed to thermodynamic effects only. It has to be related to the properties of the heteropoly compound.
Another study is "Synthesis of Trioxane Using Heteropolyacids as Catalysts" by Mazamoto et al. Their process uses heteropolyacids as catalysts and they were able to obtain a conversion % of 22.9 at 110° C. Where $$\text{Conversion %}=\frac{3[\text{trioxane}]+2[\text{methyl formate}]+[\text{methylal}]}{[\text{feed formaldehyde}]}\cdot 100$$
