Method for making methane from metal carbides

Methods for making mixtures of hydrocarbons including at least about 85% methane include hydrolyzing at least one metal pseudo-carbide that includes at least one metastable carbide-forming metal element and at least one stable carbide-forming metal element to release methane and the metals, then reforming the pseudo-carbides by reacting the recovered metals with a carbon source such as coal.

This invention relates to methods for making natural gas-type hydrocarbons 
from metal carbides that comprise at least one metastable and at least one 
stable carbide-forming metal element. 
Metal carbides consisting of a single metal such as calcium carbide, the 
binary metal carbide of calcium and magnesium, and methods of making these 
metal carbides are not new. Nor is it new to produce hydrocarbons from 
such carbides by reacting them with water in the presence of an acid or 
base catalyst. It is also known to make eutectic mixtures of alloys from 
metals that can form metal carbides. However, no one has adapted this 
knowledge to the production of natural gas-type hydrocarbons from 
carbonaceous materials such as coal using the binary, ternary and 
quaternary carbides of this invention. 
An object of this invention is to provide a method for making metal 
carbides that may be converted readily to natural gas-type hydrocarbons. 
Another object of this invention is to provide metal carbide products that 
can readily be hydrolyzed to form natural gas-type hydrocarbons and 
recoverable metal values that may be reconverted to the same or similar 
metal carbides. 
This invention provides a method for making a mixture of hydrocarbons 
comprising at least about 85% methane comprising reacting water with metal 
carbides which comprise at least one metastable carbide-forming metal 
element and at least one stable carbide-forming metal element, and which 
has the capacity to produce a mixture of gaseous hydrocarbons comprising 
at least about 85% methane. The metal values produced with the hydrocarbon 
mixture are substantially recovered and reconverted into these metal 
carbides which may again be hydrolized to form a hydrocarbon mixture 
comprising at least 85% methane. 
Metastable carbide-forming metal elements have a positive free energy of 
formation; they absorb energy upon formation of the carbides of this 
invention from oxides of such metals. Stable carbide-forming metal 
elements have a negative free energy of formation; they give off energy 
upon formation of the carbides of this invention from oxides of such 
metals. The metal carbides may be made by reacting sufficient carbon with 
a liquid metal alloy comprising at least one metastable carbide-forming 
metal element and at least one stable carbide-forming metal element. Where 
metastable and stable carbide-forming metal elements are not available in 
pure or relatively pure form, metal carbides used in the new process may 
be made from at least one compound of at least one metastable 
carbide-forming metal element and at least one compound of at least one 
stable carbide-forming metal element, usually from oxygen-containing 
compounds of such metals, by reducing these compounds with sufficient 
carbon to form such carbides, thus forming first a liquid metal alloy, and 
then a carbide comprising at least one metastable and at least one stable 
carbide-forming metal element each. Preferably, these two steps are 
effected in a single vessel at a temperature in the range of not more than 
about 2200.degree. F., and at pressures in the range of about 0.5 to about 
2 atmospheres, preferably about one atmosphere. 
At these temperatures and pressures, and with the employment of at least 
one stable carbide-forming metal element and at least one metastable 
carbide-forming metal element, true metal carbides of the kind set forth 
in Whitehead, U.S. Pat. Ser. No. 555,796, do not form. Thus, Whitehead's 
true carbides form at much higher temperatures than 2200.degree. F. 
Rather, the metastable/stable metal carbide complexes of this invention 
form. In such complexes, the carbon content is typically lower than that 
required to satisfy the sum of the valences of the metals therein, but is 
combined with the metals in a highly reactive form. Such complexes readily 
dissociate upon hydrolysis to form a gas mixture comprising at least about 
85% methane and compounds selected from the group consisting of oxides and 
hydroxides of the metastable metals and stable metals in the complexes. 
Because the heats of formation of these carbides are considerably lower 
than the sum of the BTU content of the gas mixtures formed upon hydrolysis 
and the heat released by the hydrolysis process itself, the method of this 
invention produces a natural gas substitute from carbonaceous materials 
such as coal at economically attractive costs. 
The carbides of this invention must contain at least one metastable, and at 
least one stable carbide-forming metal element each. Examples of the 
stable carbide-forming metal elements are aluminum, manganese, calcium, 
magnesium, beryllium, and boron. Examples of the metastable 
carbide-forming metal elements are cadmium, zinc, barium, copper, 
zirconium, titanium, chromium, iron and lead. Reacted with carbon, these 
metals may form binary, ternary or quaternary metal carbides, or a mixture 
of two or more of these carbides, provided at least one stable, and at 
least one metastable carbide-forming metal element is present in the 
combination. Typically, the stable metal or metals form higher mole 
percentages in these carbide complexes than do the metastable metal or 
metals. Typical binary combinations include: Aluminum-zinc 
(A1.sub.4.Zn.sub.2.C.sub.3), aluminum-zirconium 
(A1.sub.4.Zr.sub.2.C.sub.3), manganese-iron (Mn.sub.7.Fe.sub.7.C.sub.3), 
the calcium-zirconium (Ca.sub.2.Zr.sub.2.C.sub.4). Examples of ternary 
combinations are: Aluminum-beryllium-zinc 
(A1.sub.4.Be.sub.4.Zn.sub.2.C.sub.3), boron-zinc-aluminum 
(B.sub.2.Zn.sub.2.Al.sub.4.C.sub.3), aluminum-zinc-titanium 
(Al.sub.4.Zn.sub.2.Ti.sub.2.C.sub.3), aluminum-zinc-boron 
(Al.sub.4.Zn.sub.2.B.sub.2.C.sub.3) and beryllium-zinc-boron 
(Be.sub.4.Zn.sub.2.B.sub.2.C.sub.3). Examples of quaternary combinations 
are: Aluminum-zinc-beryllium-lithium 
(Al.sub.4.Zn.sub.2.Be.sub.4.Li.sub.2.C.sub.3), 
aluminum-zinc-titanium-magnesium 
(Al.sub.4.Zn.sub.2.Ti.sub.2.Mg.sub.2.C.sub.3), 
aluminum-zinc-titanium-lithium 
(Al.sub.4.Zn.sub.2.Ti.sub.2.Li.sub.2.C.sub.3), cadmium-lead-zinc titanium 
(Cd.sub. 4.Pb.sub.2.Zn.sub.2.Ti.sub.2.C.sub.3) and 
cadmium-zinc-titanium-beryllium 
(Cd.sub.4.Zn.sub.2.Ti.sub.2.Be.sub.4.C.sub.3). In the iron-manganese 
binary system, the manganese content may be from 3 to 23 atoms, the iron 
content, from 1 to 7 atoms, and the carbon content may be 2 or 3 atoms. As 
the number of manganese atoms in the system increases, the number of iron 
atoms in the system will also increase. 
The carbon used to form the metal carbides for this process may be obtained 
from any suitable carbonaceous source such as hydrocarbons and 
carbon-containing compounds such as coke, coals, and mixtures of any two 
of these sources. In the presently preferred embodiment, coal is the 
carbon source. 
In the process of this invention, the carbon potential of the carbides is 
converted to a hydrocarbon mixture comprising at least 85% methane by 
reaction with water. 
In a preferred embodiment, the metal carbide is fed to a hydrolyzer 
jacketed at least partially by water circulating pipes, and water is 
sprayed onto the carbide to form methane, other hydrocarbons and metal 
compounds. The reactant water may flow at a rate in the range of about 20 
to about 2,400 gallons per hour, and the metal carbides at a rate of about 
3,600 pounds to about 336,000 pounds per hour. The reaction is exothermic, 
and the hydrolyzer is maintained at a maximum temperature of about 
350.degree. F. by circulating water through the pipes jacketing the 
reactor. Thus, where the heat of reaction is as high as 1100.degree. F., 
the water coolant is converted to steam at a rate in the range of about 
500 to about 50,000 gallons per hour. This steam may be used as a heat 
source as such, or converted to other forms of energy in known ways. 
Hydrolysis of the metal carbides produces a mixture of hydrocarbons 
ocmprising at least about 85% and preferably about 90% methane, together 
with such other hydrocarbons as ethane, ethylene, propylene, and 
acetylene, and metal oxides and hydroxides of stable and metastable 
carbide-forming metal elements. These metal values may be recovered and 
used to make additional metal carbides. The hydrocarbonaceous gases 
produced may contain contaminants such as hydrogen sulfide which may be 
removed by well-known methods. Typically, the pressure of the 
hydrocarbonaceous gases produced in the hydrolyzer must be increased, say, 
from a pressure in the range of about 2 to about 8 pounds, to a pressure 
in the range of about 40 to about 1,500 pounds for industrial or 
commercial uses. These gases may also require dilution with active or 
inert diluents such as oxides of carbon and nitrogen, respectively, to 
bring the BTU gas value to conformance with delivered pipeline gases, 
normally 950 BTU/SCF. 
Because the preferred embodiment of this invention contemplates reduction 
of metal compounds such as hydroxides and oxides with carbon to form 
binary, ternary and quaternary liquid metal alloys and carbides, most 
impurities such as sulfur, sulfur compounds and silica may be readily 
removed as a slag which forms atop the liquid metal and alloys thereof so 
produced. Little oxides of sulfur is formed in this embodiment, precluding 
the need to prevent their escape or to effect their recovery, as is 
necessary in direct coal gasification processes. Thus, this invention is 
particularly suited to the gasification of coals that would produce more 
than say, 20 parts per million of sulfur dioxide upon combustion. Some 
hydrogen sulfide is formed, but is readily removed by scrubbing the 
hydrocarbons produced during formation of the metal carbides. 
Advantageously, all steps in the process are effected at pressures close 
to atmospheric. Moreover, except for the method for forming metal 
carbides, these processes are mildly or strongly exothermic, so that the 
overall consumption of energy used to produce hydrocarbons is 
substantially smaller than the energy value of the hydrocarbons produced. 
Most of the metal values used to make the metal carbides are recovered 
from the hydrolysis of the carbides, and may be reconverted to metal 
carbides.

Referring now to the drawing, which illustrates by block diagram the 
preferred practice of this invention, coal or other carbonaceous material 
from source 1 passes by line 2 to low-pressure crusher 3 where the 
carbonaceous material is reduced to sizes that may be handled efficiently. 
The crushed coal passes via line 4 to briquetter 5 where the coal is mixed 
with at least one metastable carbide-forming metal element, at least one 
compound of such an element, or a combination thereof, and at least one 
stable carbide-forming metal element, at least one compound of such an 
element, or a combination thereof, entering briquetter 5 from source 6 via 
line 7. The resulting mixture is formed into briquettes that contain at 
least a sufficient amount of carbon to reduce whatever stable and 
metastable compounds are present to the metal elements thereof, and to 
convert the metals to the carbides used in the process of the invention. 
These briquettes pass via line 8 to heating zone 9 where sufficient heat 
is supplied to expel a substantial portion, preferably substantially all, 
of the water from the briquettes. 
From heating zone 9, the relatively dry briquettes pass to 
reactor-synthesizer 10, which contains reactor zone 11 and synthesizer 
zone 12. Pellets enter reactor zone 11 via line 13, and are subjected 
there to a temperature in the range of about 1400.degree. F. to about 
2200.degree. F., and to near atmospheric pressure, and are reduced to a 
mixture of metastable and stable carbide-forming metal elements, together 
with some carbides of these metal elements. The liquid mixture passes 
below baffle 14 in reactor-synthesizer 10 into synthesizer zone 12, and 
carbon monoxide, hydrogen and other gases produced in reactor zone 11 pass 
above baffle 14 into synthesizer zone 12. In synthesizer zone 12, at least 
sufficient carbon, in the form of carbon monoxide or otherwise, is present 
to form a metal carbide comprising at least one metastable carbide-forming 
metal element and at least one stable carbide-forming metal element. That 
carbide, together with excess carbon, if any, passes to hydrolyzer 16 via 
line 15. 
In hydrolyzer 16, metal carbides are sprayed with water, with or without 
acid or base catalyst as an initiator of the reaction, entering hydrolyzer 
16 via line 17 from source 18. Coolant water passes through pipes (not 
shown) jacketing hydrolyzer 16, and heat of the hydrolysis reaction 
converts the water to steam which exits via line 19. Hydrocarbon gases 
produced pass via line 20 to scrubber 21 where hydrogen sulfide and other 
contaminants, if any, are removed, and then via line 23 to compressor zone 
25 where diluent, if desired, is added via line 26. Hydrocarbon gases of 
the proper pressure and concentration pass from zone 25 via line 27 to 
consumers. 
Metal compounds produced in the hydrolyzer 16 pass via line 24 to 
briquetter 5 where they are combined with makeup metal compounds and metal 
elements from source 6, and are reconverted to metal carbides as described 
above. 
Little metal value is lost in the preferred embodiment, and methane and 
other hydrocarbons are produced at low pressure, relative mild 
temperatures, and with no sulfur oxides emitted to the atmosphere. Minor 
attrition of metal values does occur, but only carbonaceous metarial is 
consumed in substantial quantities. Even the water used for cooling the 
hydrolyzer may be recovered and reused without any purification or other 
treatment. 
EXAMPLE I 
385 Grams of sugar were pyrolized at 350.degree. F. in a Kress furnace to 
produce carbon char. 13.9 Grams of the carbon char was mixed with 279.6 
grams of aluminum, 332.1 grams of zinc, and 343.1 grams of manganese, the 
mixture was placed in a Tercod crucible, and heated to 900.degree. C. 
under an Argon gas flow of about 2 to about 3 cubic feet per hour. The 
mixture was stirred with an aluminum rod to eliminate the formation of any 
wetting barrier during this heating step. 
The resulting carbide product was removed from the crucible after three 
hours holding time and allowed to cool. A 5.32 gram sample was prepared 
from the bulk product, crushed, and placed in an extraction thimble 
contained in the neck of a flask fitted with an air condenser. 50 Grams of 
mercury were added to the thimble, and the flask system was placed on a 
hot plate with an exhaust line venting the top of the condenser. The 
mercury was refluxed for a four hour period, and thereafter the system was 
cooled, and the sample weighed. The net weight of the sample was 4.07 
grams. The analysis of the carbide was as follows: zinc and 
manganese--27.6%, aluminum, 45.3%; combined carbon, 19.6% (by difference); 
and free carbon, 7.5%. The empirical formula of the carbide was: 
EQU Aluminum.sub.1.02 (Zinc+Manganese).sub.0.26 Carbon 
The 4.07 gram-sample was transferred to a hydrolysis container and treated 
with 200 milliliters of 5% HCl in water. The gas evolved was collected in 
an inverted cylinder on a water bath, and transferred to a 10 cc gas cell 
for infrared spectral analysis, 1.5 liters of gas evolved. 
The evolved gas was analyzed on a Beckman Acculab VI Spectrophotometer, and 
the product was seen to comprise methane as the principal constituent with 
traces of ethylene and carbon monoxide also present. The gas produced 
contained about 90% to about 95% methane and no acetylene. 
EXAMPLE II 
Carbon char was prepared from sugar as described in Example I above. 
Thereafter, 1,468 grams of the char were mixed with 1,508 grams of 
magnesium, 1,580 grams of iron, and 2,313 grams of manganese. The mixture 
was heated in the Kress furnace at 1100.degree. C. under an Argon flow at 
the rate of about 3 cubic feet per hour. During the heating, the mixture 
was stirred with a steel rod. Heating was continued for five hours, and 
thereafter the mixture was recovered and cooled. An analysis of the 
carbide showed the following: Iron, 33.6%; manganese plus carbon, 63.0%; 
free carbon, 3.4%; and magnesium, zero percent. Under the test conditions, 
magnesium fumed off and did not combine or alloy. 
A five gram sample of the carbide produced in this example was placed in 
the hydrolysis chamber, and treated with 200 milliliters of a 5% solution 
of hydrogen chloride in water. Approximately 2.3 liters of gas evolved, 
and were collected in an inverted cylinder in a water bath, as described 
in Example I above. 
The gas produced was analyzed on a Beckman Acculab VI Spectrophotometer, 
and observed to include at least about 85% methane, and lesser amounts of 
ethane, ethylene and carbon monoxide. Again, no acetylene was produced.