| 摘要 |
Formaldehyde is polymerized by distilling a formaldehyde-methanol solution through a distillation column containing a catalyst, as defined below, the methanol-formaldehyde solution being maintained at constant pressuretemperature conditions so that the methanol is removed as distillate. Methanolic formaldehyde is continuously added and polyoxymethylene continuously removed. The catalysts which may be used are organic or inorganic bases having a pKb value at 25 DEG C. greater than 5,15 or a metal salt of an acid having a pKa value at 25 DEG C. greater than 3,0. Suitable catalysts are, for example, amines; hydroxides of sodium, potassium and barium; acetates, butyrates, and borates of various metals and basic ion exchange resins.ALSO:The concentration of alcohol in alcohol-formaldehyde solutions is reduced by distilling the solution through a distillation column containing as catalyst an organic or inorganic base having a pKb value at 25 DEG C. of greater than 5,15 or a metal salt of an acid having a pKa value at 25 DEG C. of greater than 3,0 and removing a distillate having a materially higher alcohol concentration than the solution, an alcohol-formaldehyde solution having a higher concentration of formaldehyde than the original solution being left in the distillation column. The process may be used for concentrating solutions of formaldehyde in, for example, methanol, ethanol, n-propanol, isopropanol, n and secbutanols and n-, sec- and tert-amyl alcohols. Suitable catalysts are, for example, aliphatic, cycloaliphatic and heterocyclic mono-amines which may be primary, secondary or tertiary; triethylene diamine; the acetates of sodium, magnesium, aluminium, chromium, cobalt, lead, manganese and zinc; the propionate, tetraborate, citrate, formate and hydroxide of sodium; potassium butyrate, barium hydroxide and potassium hydroxide; and basic ion exchange resins; the amines being preferred. The process may be carried out in the presence of water and in this case the distillate contains water as well as alcohol. In a modification the process may be incorporated as part of a process for polymerising formaldehyde in methanol. |
