Method of producing formaldehyde directly from methane

Details Method of producing formaldehyde directly from methane Method of producing formaldehyde directly from methane

1999-09-09

2001-09-25

Padmanabhan, Sreem (Department: 1621)

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

Organic compounds

Oxygen containing

C568S449000, C568S470000, C568S493000

Reexamination Certificate

active

06294701

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of producing formaldehyde, particularly to a novel catalyst that permits producing formaldehyde directly from methane at a high yield and a method of producing formaldehyde by using the novel catalyst.
Formaldehyde is produced by partial oxidation reaction of methanol. Half the methanol produced in an amount of one million tons in a year is used as a raw material for the production of formaldehyde. The produced formaldehyde is used as a raw material of synthetic resins such as phenolic resins and urea resins or as a raw material of various medicines.
Methanol is synthesized from hydrogen and carbon monoxide obtained by water vapor reforming reaction of methane. The conventional process of producing formaldehyde is as given below:
Methane→H
2
/CO→Methanol→Formaldehyde
The reaction for preparing H
2
/CO from methane is an endothermic reaction using a large amount of high temperature water vapor, which is one of typical processes consuming a large amount of energy. On the other hand, the reaction for synthesizing methanol from H
2
/CO is an exothermic reaction. In order to prevent the reaction heat from being generated excessively, the CO conversion rate must be suppressed to about 10% in operating the process unit. Also, the conversion rate of methanol must be suppressed in operating the process unit in the production of formaldehyde by partial oxidation of methanol in order to suppress formation of carbon dioxide and carbon monoxide. In short, the conventional process of producing formaldehyde is a process consuming a large amount of energy and requiring a very complex operation of the process unit.
In order to avoid the large energy-consuming process in the production of formaldehyde, it is necessary to develop a new producing process that permits producing formaldehyde without involving the step of water vapor reformation of methane to produce H
2
/CO.
It is considered theoretically possible to produce methanol and formaldehyde by partial oxidation of methane, i.e., direct synthesis from methane, as suggested by chemical reaction formulas given below:
CH
4
+1/2O
2
→CH
3
OH, CH
4
+O
2
→HCHO+H
2
O
Therefore, vigorous researches are being made over more than these 50 years on the method of directly synthesizing methanol or formaldehyde from methane in research institutes over the world. Since a catalyst is required for the reactions given above, the major portion of these researches has been concentrated on the development of an effective catalyst. For example, catalysts having molybdenum oxide, vanadium oxide, chromium oxide, etc. supported by silica are reported in, for example, “Chemistry Letter, 1997, p31-32” and “Catalyst Today, 45, p29-33(1998)”.
However, the yield of methanol or formaldehyde is very low, i.e., less than 1% in general, even in the presence of these catalysts. It is said among the researchers in this field that it is difficult for the yield of methanol or formaldehyde to exceed 4%. In other words, the yield of 4% is said to be a wall that cannot be broken in the direct synthesis of methanol or formaldehyde from methane. Further, the methane conversion rate of at least 10% is required for putting the process to practical use. In conclusion, a process for direct conversion from methane into formaldehyde with a practical yield of formaldehyde has not yet been developed.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to produce formaldehyde with a high yield directly from methane by a process that does not involve a water vapor reforming step of methane, which is a step consuming a large amount of energy, and that does not bring about an air pollution or water contamination problem. To achieve the object, the present invention provides a novel catalyst and a method of producing formaldehyde by using the novel catalyst.
The present inventors have conducted an extensive research on a catalyst excellent in its activity of partially oxidizing methane and on the conditions of the reaction carried out in the presence of the particular catalyst, and found that a silica-supported 12-molybdosilicic acid catalyst, in which 12-molybdosilicic acid is supported on silica, is excellent in its activity of partially oxidizing methane and, thus, is very effective when used as a catalyst in the synthesis of formaldehyde directly from methane. The formaldehyde yield is markedly improved if the reaction for direct synthesis of formaldehyde from methane is carried out under a water vapor atmosphere in the presence of the particular catalyst.
According to the present invention, there is provided a silica-supported 12-molybdosilicic acid catalyst, comprising a silica carrier and at least 10% by weight, based on the silica amount, of 12-molybdosilicic acid supported on the carrier.
It is desirable for the silica carrier to have a specific surface area of at least 500 m
2
/g.
The present invention also provides a method of directly producing formaldehyde from a mixed gas of methane and oxygen in the presence of a catalyst, wherein the catalyst comprises a silica carrier and at least 10% by weight, based on the silica amount, of 12-molybdosilicic acid supported on the carrier.
It is desirable for the volume ratio of methane to oxygen of the mixed gas to fall within a range of between 9/1 and 4/6 and to carry out the reaction in the presence of the catalyst at 550 to 650° C.
It is also desirable to supply water vapor into the mixed gas of methane and oxygen in an amount of 40 to 80% by volume of the total volume of the mixed gas and water vapor.
The present invention makes it possible to synthesize formaldehyde directly from methane at a high yield. This suggests that the conventional process consuming a large amount of energy need not be employed for the production of formaldehyde, leading to a prominent energy saving in the chemical industries.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.


REFERENCES:
Chemical Abstracts, vol. 128, AN 61300, 1997.
Chemical Abstracts, vol. 126, AN 48569, 1996.
Chemical Abstracts, vol. 126, AN 77111, 1995.
Chemical Abstracts, vol. 123, AN 209732, 1995.
Chemical Abstacts, vol. 118, AN 46556, 1992.
Chemical Abstracts, vol. 117, AN 236244, 1992.
Chemical Abstracts, vol. 108, AN 204092, 1987.
Derwent Abstracts, AN 95-355203/46, JP 07 242578, Sep. 19, 1995.
Derwent Abstracts, AN 80-80026, JP 55 125119, Sep. 26, 1980.
S. Kasztelan, et al. “The Oxidation of Methane on Heteropolyoxometalates”, Journal of Catalysis, vol. 106, 1987, pp. 512-524.
C. Rocchiccioli-Deltcheff, et al. “Structure and Catalytic Properties of Silica-Supported Polyoxomolybdates”, Journal of Catalysis, vol. 125, 1990, pp. 292-310.
M. Banares, et al. “Genesis and Stability of Silicomolybdic Acid on Silica-Supported Molybdenum Oxide Catalysts: In Situ Structural-Selectivity Study on Selective Oxidation Reactions”, Journal of Catalysis, vol. 155, 1995, pp. 249-255.
C. Rocchiccioli-Deltcheff, et al. “Catalysis by 12-Molybdophosphates”, Journal of Catalysis, vol. 164, 1996, pp. 16-27.
M. Ohmae, et al. “Effects of Water Vapor upon Partial Oxidation of Methane over Highly-dispersed MoO3/SiO2”, Chemistry Letters, 1997, pp. 31-32.
K. Aoki, et al. “Direct Conversion of Methane into Methanol over MoO3/SiO2Catalyst in an Excess Amount of Water Vapor”, Catalysis Today, vol. 45, 1998, pp. 29-33.

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