Patent GB-635220-A (GB)
Title: Improvements in or relating to the manufacture of formaldehyde
IPC: C07C45/33
Filed: 1946-08-28
Abstract: <PICT:0635220/IV (b)/1> Formaldehyde is obtained by heating a mixture of methane and air with nitrogen dioxide to a temperature above 1100 DEG  F., thereby causing the mixture to react and form formaldehyde and then immediately after said reaction has occurred and before any substantial decomposition can take place cooling the vaporized product by direct contact with a cool formaldehyde solution.  The cool formaldehyde solution may suitably be of the same concentration as the formaldehyde solution resulting from the condensation of the reacted gas mixture.  The air gas mixture used may comprise 30 to 50 parts methane with 70 to 50 parts of air. In the Figure, a furnace 10 contains a series of horizontal two-pass reactors each of which may comprise a lower tube 11 of alloy steel connected outside the furnace to a tube 13 of silica. A mixture of natural gas and air, introduced through a pipe 14, is forced by a blower 16 to the tube 11 and oxides of nitrogen from a catalytic ammonia combustion unit 19 are drawn into the blower and forced into the air-gas mixture and then through the reactor tubes.  The furnace is heated by natural gas fuel and to this may be added waste gases from the stack 23.  The steel tube is preferably maintained at below 1100 DEG  F., e.g. at 900 DEG  F., and the silica tube at a temperature above 1100 DEG  F., e.g. about 1200 DEG  F. The gaseous reaction products pass through a manifold, not shown, and are then immediately cooled by a spray of cool formaldehyde solution supplied by a spray head 26.  The cool formaldehyde solution is supplied to the spray head from a storage tank 40 by a pump 29 and the spray head has return connections to a second pump 35 by which the formaldehyde solution heated by contact with the vaporized product in the spraying operation is delivered to a hot solution cooler 36 and thence to the storage tank 40.  The uncondensed vaporized product passes through the condenser 25 and the formaldehyde solution condensed therein is delivered to the tank 40. The uncondensed vapours pass through a refrigerated condenser 44 and the formaldehyde solution condensed also passes to the tank 40.  The gases still uncondensed are discharged through the stack 23 or returned through the connection 22 for fuel.  A portion of the formaldehyde pumped to the spray head is deflected by a connection 47 through a series of tubular coolers 46 and then passes to the top of the tower 25 where it passes downwardly in counterflow to the ascending vapours.  The refrigerating medium for the condenser 44 is provided by an ammonia refrigerating unit 50.  The liquefied ammonia passes to the condenser 44 and expanding into the condenser is returned to the unit 50 via compressor 54.  Cooling water for the unit 50 is drawn from a cooling tower 56 and this cooling water is also forced by a pump 58 to the main solution coolers 46 and is then delivered via pipe 62 to the hot solution cooler 36 from which it returns to the top of the cooling tower 56.  Cooling water is also taken through pipe 67 to a condenser 68 connected to the top of a rectifying column 70 and is returned to the tower 56 via the connection 82.  The formaldehyde solution collected in the tank 40 contains some formic acid and acetaldehyde and the former is removed or neutralized by boiling with caustic alkali in a boiler 73 and the solution then passed through a condenser 75 and delivered to the centre of the column 70.  The formalin solution collected at the bottom of the column is finally delivered to a storage tank 79.  An alternative form of furnace (Fig. 2, not shown), is of the vertical type (see Group XII), and comprises a circular refractory body having an outlet stack and having its interior ringed with a double bank of vertical tubes, the inner series being of alloy steel and connected outside the top of the furnace to the outer tubes which are preferably of silica.  The air-gas-nitrogen dioxide mixture is supplied to the alloy steel tubes through an annular gas inlet manifold located below the body of the furnace.