FORMALDEHYDE

Formaldehyde
The process is based on the continuous oxidation of pure methanol sprayed into an air stream (the methanol concentration must be under its the explosion limit) passing through an iron-molybdenum oxide catalyst bed.
The oxidation of methanol in the reactor (reaction temperature is 250 – 350°C) is almost complete and a water-formaldehyde solution of the desired strength can be obtained by simply adding water to the stream generated by the reaction.
In the same plant, changing the working conditions and feeding urea plus caustic soda solution to the absorption column, also a stable urea-formaldehyde condensate solution with a very low water content can be obtained (with a formaldehyde/water ratio up to 4:1).
This condensate solution is apt to be transformed in urea-based or in melamine-urea-based glues with low costs and without any need of distillation.

 

Methanol yield
More than 80% of the formaldehyde production cost is generally determined by the raw material consumption: therefore, the methanol yield is the most important parameter to be considered.
The methanol losses (namely the unconverted amount of methanol to formaldehyde and the amount of methanol which is oxidized to other chemical substances) are usually 7 – 8% of the feed.

 

Electric energy consumption
The formaldehyde production plant is not an electric energy intensive process (as a rough estimation, 70 kWh/t_37%w).

 

Catalyst
Under standard operative conditions, the metal oxide catalyst charge lasts 12 – 18 months.

 

Steam
The exothermic reaction of the production process generates a steam stream that can be exported from the production unit itself to be used somewhere else or to generate heat for other scopes (energy efficiency).

 

Plant capacity
Very small plants (up to 5.000 t/y at 37%w solution) are not economically worthwhile (high impact of the technology and equipment costs). Very large plants (over 100.000 t/y at 37%w solution) are almost unpractical due to the important size of the main ducts: over the specified size, it is better to install more than one production line. The ideal plant size is 40.000 – 60.000 t/y at 37%w solution.

 

Safety
The plant operates with a gas mixture outside the explosion limits. Additionally, safety can be increased by reducing the oxygen amount recirculating the inert/exhaust gas (good for energy savings too).

 

Main feature of the Alder process
The main identifying feature of the Alder process is the usage of molten salts as heat transfer medium to cool the reactor catalyst tubes: they are rather stable, they have a low cost and a quite long lifetime (they need a partial replacement every four or five years and the cost of such replacement is negligible).

In addition, compared to other processes:

• • Since the formaldehyde production cost is mostly determined by the raw material consumption (methanol), the methanol yield is the most important item to be considered: the Alder process is characterized by a very low level of methanol loss (< 8%);
• • The total amount of methanol present in the plant is much lower, so the intrinsic safety against fire and explosion is higher.