Catalyst for self ignition of fuels

A catalyst for self ignition and combustion of a fuel such as the lower alcohols namely methanol, ethanol and isopropanol and comprises a small pellet body, preferably of gamma alumina which is integrated with a metal of the platinum family. The metal is present in amounts from 16% to 60% of the weight of the body. With such concentration, the pellet is effective to self-ignite the alcohol above and below normal ambient temperatures and humidity.

BACKGROUND OF THE INVENTION 
The present invention relates to heating systems in which a mixture of a 
fuel vapor and air are burned flamelessly on the surface of a catalyst. 
The invention relates particularly to the rapid and efficient starting of 
the combustion of the fuel when both the fuel and the catalyst are 
initially cold; i.e., at a temperature near room temperature or lower. 
The catalytic oxidation of hydrocarbons, alcohols, and other chemicals at 
elevated temperatures has been practiced efficiently for many years in 
industrial processes, and more recently in such applications as small 
space heaters fueled by propane. A characteristic of such applications is 
that they operate steadily for relatively long periods, and are started 
from an initially cold state only infrequently. Thus, the catalytic space 
heater can be ignited with matches, and large industrial catalytic systems 
can be brought slowly up to operating temperature by auxiliary heaters. 
Such systems would be more conveniently started by a self igniting 
catalyst. 
For certain applications which might be most advantageously served by 
catalytic heaters, however, the heating periods are very short and the 
system must be heated frequently from a cold start; hence very rapid and 
efficient initiation of combustion is mandatory, and an auxiliary heating 
system for starting combustion is unacceptable. One such application is 
the heating of shave foam or cosmetics dispensed from an aerosol can, 
where a few grams of material must be heated about 50.degree. to 
80.degree. F in a period of 10 to 20 seconds, or less. In this case the 
heating system must be small and inexpensive, but capable of developing 
high heating intensities very quickly, and also capable of completely 
burning the fuel without production of noxious combustion products. It is 
also imperative that the system be highly efficient in converting and 
transferring the heating value of the fuel into the fluid which is to be 
heated. 
Experience has shown, however, that suitable fuels, such as hydrocarbons 
and alcohols, when vaporized and mixed with air, will not start to burn 
spontaneously when brought into contact with catalysts of the types 
commonly used, unless the catalyst or the fuel, or both are preheated. 
A further difficulty encountered in the use of conventional catalyst 
results from the fact that the catalytically active metal, for example 
platinum black, is most effective when supported upon highly porous base 
materials such as gamma alumina or silica gel, which are highly 
hydroscopic. Of the known catlyst compositions a mulled mixture of 
platinum and silica found in a small pellet may exhibit self ignition of 
methanol, but the reliability of such a pellet after exposure to high 
humidity is questionable. Commercially available pellets of alumina 
impregnated with small amounts, that is, less than 1%, of platinum family 
metal will not self ignite lower alcohols except at temperatures well 
above even high ambient temperatures. Thus, between heating periods when 
the system is cool, the catalyst support material absorbs moisture from 
the ambient air which greatly reduces the activity of the catalyst. This 
will completely block the spontaneous oxidation of preferred fuels such as 
methanol on the surface of the catalyst when both catalyst and fuel are 
initially cold. U.S. Pat. No. 3,191,659 to G. Weiss describes 30 mesh 
grains of alumina impregnated with 1/2 to 10% platinum by weight. The 
platinum concentration is then diminished by deposition on a fibrous 
sheet, but in any case my experience has shown that even a 10% 
concentration of platinum on alumina is ineffective to self ignite the 
lower alcohols at ambient temperatures after several days of exposure to 
an expectable range of natural humidity. 
Accordingly it is the object of the present invention to provide a catalyst 
which will rapidly and reliably cause spontaneous ignition of lower 
alcohol fuels at hyper- and sub-normal temperature and humidity. 
STATEMENT OF THE INVENTION 
According to the invention a catalyst for combustion of a hydrogenous fuel, 
such as a lower alcohol comprises a body of porous, fuel absorbent alumina 
integrated with one or more metals of the platinum family in an amount 
effective to self ignite the fuel in less than 8 seconds after the 
catalyst has been exposed to hyper normal humidity. Preferably the porous 
body is gamma alumina. The amount of the metal should be sufficient to 
provide a ratio of about 16 and 60% by weight of the integrated portion of 
the porous body.

DESCRIPTION 
Two-Phase Fuel Combustion -- FIG. 1 
Fuels 
Catalysts -- FIGS. 2 and 3 
Two-Phase Fuel Combustion -- FIG. 1 
The catalytic combustion apparatus of FIG. 1 comprises a tubular metal 
casing 1 having an upper fuel inlet 2 and a lower combustion product 
outlet 3 covered by screens 4. Surrounding the combustion chamber within 
the casing 1 is a coil of metal tube 6 with an entrance 7 and exit 8 for a 
fluid to be heated. The remaining volume within the chamber is filled with 
a bed of catalyst pellets 10 of three types 10A, 10B, 10C as shown in 
FIGS. 2 and 3. 
Fuel is supplied to the combustion chamber 1 from a pressurized container 
11 holding a hydrogenous fuel in liquid phase volume 12 and vapor phase 
volume 13. Fuel from the liquid volume is fed to a conduit 14 through a 
metering valve 16 whose rotating plug 17 has a space 18 for holding a 
predetermined amount of fuel which is released into the conduit upon 45 
counter clockwise rotation of the plug from the position shown in FIG. 1. 
The metering valve plug 17 is coordinated with the plug 22 of a vapor 
valve 21 by a mechanical coupling 19. The vapor valve plug 22, upon 
90.degree. rotation from the position shown, connects the vapor volume 13 
with a vapor conduit 24. 
The liquid fuel conduit 14 leads to an atomizing nozzle 26 within an air 
aspirator 27, the nozzle spraying the metered amount of liquid fuel in 
fine droplets toward the fuel inlet 2 to the combustion chamber 1. 
Immediately inside the inlet is a mass of catalyst pellets 10A with a high 
concentration of catalyst in the platinum family described more fully 
hereinafter. A hydrogenous fuel such as methanol will spontaneously ignite 
in flameless combustion on contact with a high platinum family 
concentration. Simultaneously with, or shortly after ignition fuel in 
vapor phase is supplied through conduit 24 to a nozzle 20 with an orifice 
25 which meters the continuous flow of vapor and directs it in a jet 28 
through the convergence 29, throat 31 and divergence 32 of the aspirator 
toward the fuel inlet 2 to the combustion chamber. The vapor jet entrains 
air and draws it through openings 32 adjacent the metering nozzle 20, 
mixing the fuel and air as they approach the combustion chamber so that 
flameless catalytic combustion is sustained by continued flow of the fuel 
in its vapor phase. 
Heat from the combustion is exchanged with fluid flowing through the coil 
6, which fluid may be a gas such as air or a liquid such as water, either 
of which can be circulated through radiators or other apparatus. 
A catalytic heater of the type described above and having a double helical 
coil as shown in FIG. 4 was tested to determine its characteristics as a 
water heater. For this purpose, the inlet was connected to a water source 
which provided a constant water flow rate of 1.38 grams per second. The 
measured temperature rise of the water was 12.8.degree. C. The total 
volume of the catalytic heater, i.e. the catalyst bed, was 8.05 cubic 
centimeters. The heating intensity of this system was thus 2.2 calories 
per second per cubic centimeter or in other units 890,000 BTU per hour, 
per cubic foot. The importance of this high heating intensity can be 
visualized in terms of a familiar application such as a house heater which 
might typically have a capacity of 150,000 BTU per hour. The catalytic 
heater described above scaled to a capacity of 150,000 BTU per hour would 
occupy a volume of only 0.169 cubic foot. Along with this remarkable heat 
intensity the heater operates with high efficiency and fuel economy, and 
low pollution in its combustion products. 
Fuels 
Of the many available fuels only four are known to ignite spontaneously and 
safely in the presence of a suitable catalyst at normal ambient 
temperature, that is 40.degree. to 100.degree. F. Other fuels such as 
formaldehyde, formic acid and hydrazine hydrates will oxidize 
spontaneously but are toxic, inconvenient and dangerous to handle. Thus, 
safe spontaneously igniting fuels are hydrogen and the three lower 
alcohols, methanol, ethanol and isopropanol; methanol being preferred. 
While other hydrocarbons such as natural gas or the lower alkanes may be 
used as a primary fuel after ignition they will not start catalytic 
combustion spontaneously. Thus either in industrial processes using 
primary fuels after ignition or in intermittently started catalytic 
combustion apparatus using the starting fuel as an operating fuel also the 
lower alcohols are useful. 
Whereas primary fuels are delivered from a pressurized system, smaller 
apparatus run on the starting fuel requires fuel pressurization by air or 
a self pressurizing fuel. For catalytic combustion the lower ethers, 
dimethyl and methyl ethyl ether, and lower alkanes and alkenes have been 
found to be most suitable as a pressurizer when mixed with the lower 
alcohols. The mixture of methanol and dimethyl ether as a catalytic fuel 
is mentioned generally in U.S. Pat. No. 2,764,969 to Weiss. Such a fuel 
mixture has, however, been found to have a rather critical range of 
alcohol ether proportion, particularly in small fuel containers used in 
portable or compact selfigniting combustion units such as are described 
herein. While the ether is a fuel, the alcohol which is essential to start 
combustion has a substantially lower vapor pressure, so that as fuel is 
withdrawn from the vapor space of a fuel container the concentration of 
ether in the liquid phase drops resulting in a drop of vapor pressure. 
When the pressure is reduced to the point that the heating rate is below 
the useful limit a residue of unusable fuel remains in the container. When 
the pressure drops to atmospheric the liquid residue is substantially all 
alcohol. I have found that if the alcohol is is excess of 25% by volume of 
the initial alcohol-ether mixture an unusable residue of fuel in excess of 
35% of the original fuel volume will result in substantial economic waste. 
On the other hand a proportion of approximately 5% alcohol by volume is 
required to insure spontaneous ignition. Within the range of 5 to 25% 
alcohol (e.g. methanol) to 95 to 75 % ether (e.g. dimethyl ether) 10% 
alcohol and 90% ether is preferred. 
Although the loss of pressure and waste of alcohol could be avoided by 
withdrawing fuel from the liquid volume 12 of the container 11, the liquid 
fuel would be evaporated in the aspirator 27 or in the mass 10 of catalyst 
pellets. Such fuel evaporation produces a refrigeration effect which will 
reduce or inhibit ignition or continue combustion. However, according to 
one aspect of the invention, metering only a small amount of alcohol-rich 
liquid fuel does not inhibit spontaneous ignition, and subsequently 
supplying fuel preevaporated in the fuel container 11 isolates the 
combustion chamber 27 from the refrigeration effect. The fuel container 
can absorb and dissipate the refrigeration remotely from the combustion 
chamber. Further the fuel container has sufficient mass and external heat 
transfer surface to prevent excessive chilling of the fuel therein. 
While the alcohol-ether pressurizer mixture described above has been found 
to be a reliable starting and running fuel, particularly in a single fuel 
container delivering the fuel in liquid and vapor phase, several 
advantages have been found in the use of lower alkane, alkene and cyclo 
hydrocarbons with less than five carbon atoms as a pressurizer for the 
alcohols and as a primary, separately supplied fuel for continued 
catalytic combustion after spontaneous ignition with a lower alcohol-fuel 
mixture. Thus the preferred fuels for use in the present apparatus and 
method comprise not only ethers with less than four carbon atoms including 
dimethyl and methyl ethyl ether, but also the lower alkane and alkene 
hydrocarbons with a boiling point below nominal room temperature including 
methane, ethane, propane including cyclo propane, butane including 
n-butane and isobutane, ethylene, propylene, butene-1 and -2, butadiene 
and butylene including isobutylene. 
As a pressurizing constituent of the lower alcohol starting mixture the 
lower hydrocarbons mentioned may comprise as little as 5% of the fuel 
mixture with 95% of the mixture rich in alcohol. As previously noted the 
alcohol may be as low as 5% by volume, but higher concentrations 
approaching 95% by volume are preferred because catalytic combustion will 
start spontaneously more rapidly and reliably, particularly in humid 
weather, if the starting fuel is rich in alcohol. A mixture of 60% 
methanol and 40% isobutane, for example, affords reliable starting in 
ambients of 90% relative humidity, and at temperatures below 40.degree. F. 
Catalysts -- FIGS. 2 and 3 
A platinum family catalyst is necessary for spontaneous ignition of the 
previously mentioned hydrogenous fuels. The platinum family includes the 
platinum group of metals platinum, iridium and osmium, and the palladium 
group of palladium, ruthenium and rhodium. Preferably the platinum family 
catalyst is supported on a catalytically active porous body composed of 
one or more of the porous forms of alumina. The porous catalytic supports 
are relatively inexpensive whereas platinum family metals are very 
expensive. Therefore, prior catalytic bodies have very little platinum 
family metal. Porous catalytic pellets with a platinum content of 
approximately 0.05 to 0.2% by volume are used in industrial processes 
which are brought to combustion temperature but which cannot initiate 
spontaneous ignition. Similarly the above named porous bodies cannot alone 
initiate spontaneous combustion, and are, moreover, powerful adsorbers of 
atmospheric moisture and fuel at ordinary temperatures. For example, a bed 
of 0.1% platinum black supported on the surface of small (1/8 inch) 
spherical pellets of highly porous gamma alumina, after several hours of 
exposure in a combustion chamber to air of normal humidity, will not 
catalyse the oxidization of an air-methanol fuel at room temperature. Nor 
will such a catalytic body initiate spontaneous combustion of liquid or 
vapor phase fuel mixture of 5 to 25% methanol in dimethyl ether. 
I have found that the ignition inhibiting effect of adsorbed moisture is 
overcome by substantially increasing the platinum family content of the 
porous catalytic body to at least about 16% and in a range up to 60% of 
the initial weight of the porous body. 
Below approximately 16% spontaneous ignition does not occur and an 
undesirably high amount of formaldehyde is produced and above 60% the time 
for combustion to start begins to increase. Within the range of 16 to 60% 
platinum, the fastest starting of spontaneous ignition is assured even 
after the catalyst has been exposed to extreme, naturally expectable 
humidity. 
Catalytic bodies with such a high platinum family content are, of course, 
relatively costly but I have further found that only a small proportion of 
the catalyst bed 10 within the combustion chanber 27 need consist of the 
enriched or highly concentrated 16 to 60% platinum family bodies 10A, 
symbolized by cross hatched areas in FIG. 2, and that less costly 
platinized porous bodies 10B with under 16% platinum family concentration 
(preferably under 2% platinum) symbolized by unshaded areas in FIG. 2, may 
be used as the major portion of the catalytic mass 10. 
The preferred form of enriched catalytic pellet is a porous support of 
gamma alumina with over 16 to 60% platinum black or palladium integrated 
with the alumina as shown in FIG. 3. Alumina and silica with less than 16% 
platinum is not reliable for starting under unfavorably high humidity 
which will normally occur under natural conditions. Gamma alumina 
integrated with between about 16% and 60% by weight of platinum family 
metal will reliably start spontaneous ignition within 1 to 8 seconds under 
natural hyper humidity and even extreme artificial hyper humidity. 
In special applications where starting is desired in all cases in 1 or 2 
seconds, it may be preferable to use the enriched pellets strung as beads 
10D, as in FIG. 4, or otherwise supported integrally with a resistively 
heated wire 40 of nichrome stainless steel or the like. 
The lower (under 2%) platinum family concentration bodies 10B may consist 
of platinum applied to the surface of gamma alumina pellets. Herewith the 
catalytic activity of the metal is augmented by the catalytic activity of 
the gamma alumina, which together cause complete oxidization of methanol 
with little or no formaldehyde production. 
The unplatinized catalytic pellets 10C are also preferably porous gamma 
alumina. 
The bodies 10A of high catalytic concentration are disposed at the fuel 
inlet 22 to the combustion chamber 1 where they will initiate spontaneous 
combustion dispite the fuel refrigeration effect and the presence of 
adsorbed moisture. 
Starter pellets 10A, although exposed to humid air for days will ignite 
catelytic combustion within a few seconds when exposed to methanol. 
Combustion will then dry the less enriched pellets and spread through the 
bed. 
EXAMPLE 
Slightly more than 125 grams of gamma alumina pellets were baked at 
125.degree. C. for about 3 hours to remove water. Exactly 125 grams were 
measured and immersed in a 10% by weight solution of chloroplatinic acid. 
The pellets were then heated in a pyrex dish overnight at 125.degree. C. 
followed by a reduction in a flowing stream of hydrogen for 1 hour at 
125.degree. C. The dried and reduced pellets weighed 144.5 gm. (15.6% by 
weight Pt.). 
The pellets were then treated for a second and a third time in the same 
manner as above and weighed. They weighed 182 gm. (45.6% by weight Pt.) 
following the third treatment. 
To test the pellets for catalytic activity, theywere disposed in a stream 
of isopropane at which point they began to glow bright red, and heat was 
produced. 
It should be understood that the present disclosure is for the purpose of 
illustration only and that this invention includes all modifications and 
equivalents which fall within the scope of the appended claims.