Conversion of dimethyl ether to formaldehyde

A process is disclosed for oxidizing dimethyl ether to formaldehyde using naturally occurring manganese nodules as a catalyst.

FIELD OF THE INVENTION 
This invention relates to a process for converting dimethyl ether to 
formaldehyde utilizing as a catalyst naturally occurring manganese 
nodules. 
BACKGROUND OF THE INVENTION 
Manganese nodules have been found on both ocean floors and in fresh water. 
These nodules have been noted as a valuable mineral resource of the 
future. Many investigations have been made on the mining of these nodules 
and the extraction of valuable minerals therefrom. These manganese nodules 
generally certain 30 kinds of metals or more, in the form of oxides or 
hydroxides. The principal metallic components are primarily manganese and 
iron, although silicas are present in significant amounts. Manganese 
nodules have been found suitable for use as oxidation catalysts in 
converting carbon monoxide to carbon dioxide. (P. B. Weisz, Journal of 
Catalysis, 10, 407-408 (1968)). They have been utilized as catalysts for 
the decomposition of isopropyl alcohol (Matsuo et al, Journal of 
Catalysis, 54, 446-449 (1978)). In this reference isopropyl alcohol is 
converted to acetone, carbon dioxide and water. Chang et al (Ind. Eng. 
Chem., Process Des. Dev., Vol. 15, No. 1, 166-164 (1976)) illustrates a 
use of manganese nodules for the demetalation of petroleum residues. 
Manganese nodules have also been noted to carry out the reduction of 
nitric oxide with ammonia (Wuu et al, Atmos. Environ., 6, 303 (1972)). 
Formaldehyde is a chemical used extensively as a reagent, preservative, 
embalming agent, antiseptic and deodorant and industrially, in large 
quantities in the synthesis of many substances such as plastics. A process 
that would convert a readily available syngas chemical such as dimethyl 
ether to a more valuable substance like formaldehyde could be of 
commercial interest. Known commercial catalysts for converting dimethyl 
ether to formaldehyde are stannic phosphate (V. D. Mezhov, M. M. Levkovich 
& G. M. Sychera, U.S.S.R. Pat. No. 294465, "Method of Production of 
Formaldehyde", Nov. 1, 1977) and tungstic acid (H. Tadenuma, T. Murakami 
and H. Mitsushima, U.S. Pat. No. 3,655,771, "Process for Producing 
Formaldehyde", Apr. 11, 1972). 
SUMMARY OF THE INVENTION 
The instant invention comprises a process for oxidizing dimethyl ether to 
formaldehyde by contacting dimethyl ether and oxygen with a catalyst which 
comprises naturally occurring manganese nodules. These nodules typically 
contain from about 5 to about 40 percent by weight of manganese and from 
about 1 to about 40 percent by iron in the form of an oxide or a hydroxide 
thereof. The use of these manganese nodules provides for a significant 
yield of formaldehyde from dimethyl ether. These manganese nodules are 
readily available, comparatively inexpensive and provide an ease of use 
not exhibited by other commercial catalysts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The manganese nodules utilized as catalysts in the instant process are 
those naturally occurring manganese nodules that are found on ocean floors 
and in fresh water. They comprise primarily oxides and hydroxides of the 
manganese and iron with silica present in lesser amounts and with various 
transition metal and rare earth metal oxides and hydroxides also present 
in small amounts. Typically, the catalysts useful in the instant process 
will contain from about 5 to about 40 percent by weight of manganese 
(measured as a metal) and from about 1 to about 40 percent by weight of 
iron (measured as a metal). Smaller amounts of silica present in these 
modules can range up to 30 percent by weight. The silica is essentially 
inert in the process of the instant invention and can be considered as 
acting as an inert support for the active metals, such as iron and 
manganese. The manganese nodules useful as catalysts have relatively high 
surface areas. Typically surface areas will range from about 100 to about 
300 m.sup.2 /gm, preferrably from about 150 to about 250 m.sup.2 /gm. 
Table 1, taken from Chang et al, Ind. Eng. Chem., Process Des. Develop., 
Vol. 13, No. 3, 315-316 (1974) illustrates typical properties and metal 
analyses of nodules which would be suitable as catalysts in the instant 
process and which were taken from the Pacific Ocean, the Atlantic Ocean 
and Lake Michigan. 
TABLE 1 
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TYPICAL PROPERTIES OF MANGANESE NODULES 
Pacific Atlantic Lake 
Nodule Source Ocean Ocean Michigan 
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Surface area, m.sup.2 /g 
230 226 233 
Particle density, g/cm.sup.2 
1.52 1.43 1.49 
Average pore diameter, A 
69 73 81 
Pore volume, cm.sup.3 /g 
0.40 0.41 0.41 
Real density, g/cm.sup.3 
3.80 3.53 3.75 
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Metals analysis 
wt. % 
______________________________________ 
Mn 28.5 18.8 9.2 
Fe 13.9 12.3 35.4 
Ni 1.21 0.72 0.01 
CoO 0.23 0.46 0.04 
MoO.sub.2 0.1 0.10 0.08 
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The manganese nodules are used in a fashion typical of that used for 
heterogeneous catalysts. They may be used in fixed beds, and fluidized 
beds or in reactors. Typical reaction temperatures range from about 
250.degree. C. to about 500.degree. C. Typical reaction pressures range 
from atmospheric to about 500 bars, preferably from atmospheric to about 
200 bars. Typical feed rates include gaseous hourly space velocities 
ranging from about 500 to about 25,000 l/l/hr. 
The formaldehyde is prepared by oxidizing the dimethyl ether with oxygen. 
Generally, the oxygen is provided diluted with an inert gas such as 
nitrogen. Air provides a suitable oxygen-containing feed gas. Suitable 
precautions should be taken to avoid the hazards of explosive 
oxyyen-hydrocarbon mixtures. 
The manganese nodules may be utilized in the form in which they are mined. 
For example, they may be loaded into a tubular reactor in the nodule form. 
In many cases, however, it is desirable to crush and sieve the nodules to 
certain selected size ranges. 
The process of the instant invention is further described below by the 
following illustrative embodiments which are provided for illustration and 
are not to be construed as limiting the invention. 
ILLUSTRATIVE EMBODIMENTS 
Manganese nodules were obtained from Kennecott Copper Company and their 
physical and chemical properties were analyzed. These properties are 
illustrated in Table II below. 
TABLE II 
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PROPERTIES OF NODULES OBTAINED 
FROM KENNECOTT 
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Analysis (wt %) 36.1 Mn 
0.4 Ba 
6.7 Si 
0.9 K 
3.7 Fe 
44.0 O 
1.0 Ca 
1.0 Ti 
Trace amounts of 
Ni, Cu, Zn, La, Ce, Sr, Y, Rb, Pb, Sb, Zr, Co 
Surface Area 168 m.sup.2 /gm 
Pore Volume .612 cc/gm 
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The manganese nodules, as received, were ground and sieved to 20-30 mesh 
particle size. The particles were loaded into a quartz tube and were 
tested in a flow reactor isolated in a barricade cell. The reactor was 
operated at atmospheric pressure with a volume concentration of dimethyl 
ether in air of 4.6-5.5%. The results for a series of runs in which the 
reactor temperature and catalyst volume (hence gas hourly space velocity) 
were varied are tabulated in FIG. 2. 
FIGURE 2 
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Gas Hourly 
Reactor 
Dimethyl Ether 
Formaldehyde 
Formaldehyde 
Run 
Space Velocity 
Temp. (.degree.C.) 
Conversion (%) 
Selectivity (%) 
Yield (%) 
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1* 
4000 450 37 0 0 
2* 
7600 450 92 0 0 
3 16000 450 17 37 6 
4 16000 400 13 38 5 
5 16000 350 18 49 9 
6 8000 300 6 69 4 
7 8000 350 21 38 8 
8 5300 350 86 3 2 
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*100% selectivity to carbon dioxide. 
The above results for formaldehyde selectivity and yield are plotted in 
FIG. 1 and FIG. 2. The data from run 1 was inexplicably inconsistent with 
the rest of the data and was omitted. As demonstrated by FIG. 1, the 
catalyst is more selective for formaldehyde production at lower dimethyl 
ether conversion. From FIG. 2, it can be seen that the maximum 
formaldehyde yield using these particular manganese nodules will be about 
10% at conversions of less than about 30%.