Process for heterogeneous exothermic synthesis of formaldehyde

Details Process for heterogeneous exothermic synthesis of formaldehyde Process for heterogeneous exothermic synthesis of formaldehyde

1997-12-01

1999-09-28

Kumar, Shailendra

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568448, 568487, 568422, 422196, 294011, C07C 4529

Patent

active

059591544

DESCRIPTION:

BRIEF SUMMARY
This is the us National stage Application of PCT/EP96/01516 filed Apr. 9, 1996 now WO96/32189 published Oct. 17, 1996.


DESCRIPTION

1. Field of Application
The present invention relates to a process for heterogeneous exothermic synthesis of formaldehyde in excess oxygen, in particular in synthesis reactors of the type comprising a plurality of adiabatic catalytic beds connected in series, with the process comprising the steps of: of said catalytic beds; methanol to partial oxidation.
The present invention also relates to a reactor for heterogeneous exothermic synthesis of formaldehyde.
In the description given below and in the following claims, the term: `adiabatic catalytic bed`, is understood to mean a bed containing catalyst in which the synthesis reaction takes place at a substantially constant pressure without heat removal.
In the field of heterogeneous exothermic synthesis of formaldehyde, the requirement on the one hand of increasing the productive capacity of the synthesis reactors and on the other hand of reducing the risks of explosion of the gaseous reagents comprising methanol and oxygen in excess, while holding down energy consumption and investment and maintenance costs, is increasingly felt.
2. Prior Art
For the purpose of meeting the above mentioned requirement, tubular reactors with heat removal by passage of a cooling liquid circulating outside the tubes have become increasingly accepted.
This type of reactor consisting of a plurality of small-diameter tubes filled with catalyst is very complicated to construct and has limited production capacity.
In the second half of the nineteen-eighties there was proposed by the Boreskov Institute of Catalysis of Novosibirsk, Russia, the adoption of a formaldehyde synthesis process in which the gaseous reagents comprising methanol and excess oxygen are reacted in a plurality of adiabatic catalytic beds connected in series.
The gaseous reagents cross the catalytic beds with axial flow. Between the outlet from a bed and the inlet to the following bed the gas flow is appropriately cooled by heat exchange in suitable heat exchangers.
The above mentioned process permits provision of reactors of large size and having a production capacity higher than that obtainable with the conventional tubular reactors, since it is possible to increase the reaction space and the flowrate of the gaseous reagents and it is possible to improve the selectivity of the oxidation reaction of the methanol.
If on the one hand this type of solution proves to be advantageous as compared with tubular reactors, on the other hand the production capacity of the synthesis reactor remains limited by the concentration of methanol contained in the gaseous reagents entering the reactor.
As known, this concentration must be held below certain values which generally do not exceed 6%-9% by volume depending on the oxygen concentration, which can vary between 5% and 21% by volume, to avoid the possible formation of explosive or inflammable mixtures with the oxygen.
A relatively low concentration of methanol is also preferable for limiting the amplitude of temperature variations in the catalytic mass. Indeed, at temperatures over 300.degree. C. there is the risk of deterioration of the catalyst with resulting reduction of its useful life and a drastic increase in the undesired secondary reactions which lead to direct degradation of the methanol or of the formaldehyde produced.
In addition, the embodiment of a large synthesis reactor with large gas flowrates of the type developed by the Boreskov Institute of Catalysis involves considerable technical difficulties, high investment costs and high energy consumption.
For the exothermic synthesis of compounds like ammonia or methanol, adiabatic reactors of the radial or axial/radial type are known. See for instance GB-A-2 722 702 or JP-A-60 770 328.


SUMMARY OF THE INVENTION

The technical problem underlying the present invention is to increase the production capacity of formaldehyde synthesis reactors while reducing the risks of explosion of the gas

REFERENCES:
patent: 2504402 (1950-10-01), Field
patent: 2512562 (1950-10-01), Cummings
patent: 4372920 (1983-02-01), Zardi
patent: 4755362 (1988-07-01), Zardi
patent: 4904453 (1990-02-01), Zardi
patent: 4952375 (1990-08-01), Zardi

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