Manufacture of a metal impregnated carbon from peat material

There is provided a novel process for preparing a carbon supported metal catalyst which comprises impregnating a peat material selected from finely divided peat, ammoniated peat and humic materials derived from peat with an aqueous solution of a metallic salt, drying the impregnated peat and pyrolyzing same in an inert atmosphere to yield a carbon supported metal and/or metal oxide.

The present invention relates to a method for preparing a metal impregnated 
carbon from peat. 
PRIOR ART 
Three different methods have been generally used for the preparation of 
metal supported carbon catalysts: 
In liquid phase impregnation, finely ground carbon or activated carbon is 
mixed with a solution containing the impregnating metal salt. This step is 
followed by filtration and drying. The method has the disadvantage of poor 
impregnation of the micropore surfaces. High internal surface area carbons 
cannot then be used, the method being nevertheless universal for high 
external surfaces area carbon blacks. 
In vapor phase impregnation, the carbon particles are contacted with the 
vapor of a volatile salt of the metal. In this way the micropores can be 
reached and high metal loadings (about 10% wt) are achieved. The method is 
limited to metals which can form volatile salts, thus becoming a rather 
expensive way of preparation. 
A third method consists of loading suitable synthetic resins having 
ion-exchange properties via liquid phase exchange. Filtration and drying 
are followed by high temperature carbonization of the mixture 
(500.degree.-800.degree. C.). Highly dispersed metals are thus prepared 
with metal loadings as high as 12.2% wt. The main disadvantage of the 
method lies on the initial cost of the synthetic resins normally used in 
this preparation. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided method for 
preparing a metal supported carbon catalyst which comprises impregnating a 
peat material selected from finely divided peat, ammoniated peat and humic 
materials derived from peat with an aqueous solution of a metallic salt, 
reducing the water content of the impregnated peat material and pyrolyzing 
same to yield a metal and/or metal oxide supported on carbon. If desired 
the metal supported carbon can be activated to yield a metal supported 
activated carbon. The metal and/or metal oxide supported carbon can be 
pelletized before or after activation. Alternatively, the impregnated peat 
material can be mixed with a binder and extruded in the form of pellets 
before pyrolyzing. 
ADVANTAGES 
One of the important features of the present invention is that a metal 
and/or metal oxide supported carbon catalyst substantially free of sulfur 
is obtained in opposition to prior art carbon catalysts which contain high 
amounts of sulfur which are usually present in the original meterial from 
which activated carbon is made. It should be appreciated the peat material 
used in accordance with the present invention has a low sulfur content 
which rarely exceeds 0.2% dry weight basis and thus a substantially sulfur 
free catalyst is obtained. 
The method of the present invention is simple and economical since only one 
pyrolysis and only one activation step is required in opposition to those 
methods of the prior art where these steps have already been performed on 
the starting charcoal or activated charcoal and which are usually repeated 
after their impregnation with an aqueous metal salt solution. 
The novel method of the present invention also provides versatility in the 
wide range of metals and amounts of each metal which can be supported 
because of the presence of reactive sites of the humic acids present in 
the starting peat material in opposition to carbon or activated carbon 
used in the prior art where the concentration of reactive sites is 
difficult to control because of the substantial absence of any reactive 
sites. 
Finally, the method of the present invention appears to allow the physical 
characteristics of certain deposited metals such as platinum to be 
controlled as to their crystallite size which seem to be a problem with 
most known platinum carbon catalyst particularly when prepared by the 
vapor phase impregnation process. 
PEAT MATERIAL 
The term "peat" used herein is intended to cover peat which is the layer 
found below the layer of peat moss in a peat bog and normally has an ash 
content of less than 2% on a dry weight basis. The term peat material is 
intended to include peat, ammoniated peat and humic acids derived from 
peat. 
Ammoniated peat is obtained by first drying peat on the field to a moisture 
content of about 35% by weight. Subsequently, the moisture content is 
reduced to 10-15% by weight by further drying in a storage room and then 
the peat is ammoniated with NH.sub.3 either in batches or in a fluidized 
bed at a temperature of between 50.degree. or 80.degree. C. in presence of 
air or inert gas or mixtures thereof. 
The humic acids contained in peat are obtained by extraction with a 4% 
sodium hydroxide solution. The extract is acidified with hydrochloric acid 
thereby to cause a floc to precipitate. The floc containing the humic 
acids is recovered by filitration and dried. 
The particle size of the peat material is preferably between the range of 
from 42 to 60 U.S. Tyler mesh. 
Peat material is available in various degrees of humification which is 
measured for example by the humic acid content. The humic acid content is 
a measure of the degree of humification (degree of decomposition of 
organic matter in the peat) of the starting peat and since the reaction 
with the metal salts is in a large extent due to the reactive sites of the 
humic acid it should be appreciated that other factors will intervene for 
optimum results. A weakly humified peat is one normally containing from 20 
to 30% by weight of humic acid and a large amount of cellulose and lignin, 
while a well humified peat is one where the humic acid is usually in 
excess of 60% by weight with a lower content of cellulose and lignin. 
Accordingly peat with a high humic acid content might require slightly 
different conditions than those indicated herein for a low humic acid 
content. 
METAL CATALYST 
The metals which can be supported on carbon in accordance with the present 
invention are those which are available in water soluble salt form. As an 
example of such metals there may be mentioned platinum, ruthenium, 
chromium manganese, molybdenum, vanadium, iron, nickel, copper and the 
like which may be desirable as a catalyst for any specific purpose. There 
is no restriction as to the metals available, provided that one of the 
salts of the selected metals in relatively water-soluble. The more soluble 
the metal salt is the more metal can eventually be deposited on the 
carbon. 
IMPREGNATION OF PEAT MATERIAL 
Impregnation of the peat material is carried out by stirring the peat 
material with an aqueous solution of the metallic salt. Usually the ratio 
of peat/liquid is about 1:20 (gr/cc). The amount of metal salt which can 
be impregnated is determined by the equilibrium conditions applicable to 
each metal/peat system and is determined easily by drawing an adsorption 
or ion-exchange isotherm as is well known to one skilled in the art. Once 
the isotherm has been established a choice can then be made as to how much 
metal is to be used per weight of peat and consequently how much metal 
will eventually be supported on the carbon. 
The pH of the metal solution during impregnation is not critical, but 
better results can be obtained when the pH of the metal solution is made 
less acid keeping in mind that the acidity cannot be reduced to a point 
where precipitation of the impregnating metal salt will occur. 
The stirring of the peat material and the aqueous solution of the selected 
metal salt is preferably carried out `in vacuo` in order to eliminate any 
occluded air thus facilitating penetration of the metal salt inside the 
pores of the peat material where most of the reactive sites are found. 
The impregnated peat is then dried at about 105.degree. C. for a period of 
about 48 hours before proceeding to the pyrolysis or carbonization step. 
PYROLYSIS OR CARBONIZATION 
The carbonization step, also referred to as controlled pyrolysis is carried 
out in an appropriate furnace at a temperature range of from 500.degree. 
to 800.degree. C. with a preferred range of from 500.degree. to 
600.degree. C. in an inert atmosphere. The inert atmosphere can be 
provided either by supplying an inert gas such as nitrogen to the 
pyrolysis chamber or the inert atmosphere can be built up `in situ` by the 
pyrolysis gases. Nitrogen is supplied to the system at an appropriate flow 
rate. For example, about 981 cc/min can be used for a linear velocity of 
about 103 cc/min. The impregnated peat material is fed into the oven so 
that the temperature profile increases regularly at a rate of about 
10.degree. C./min up to the selected carbonization temperature which is 
usually maintained for about 30 minutes. 
Depending on the type of metal supported carbon catalyst desired, the dried 
impregnated peat can be converted to a metal supported carbon by 
controlled pyrolysis or carbonization and, if desired, the metal supported 
carbon could be converted to a metal supported activated carbon by further 
activation as is well known in the art. Alternatively, both the 
carbonization and activation steps can be carried out in the same reactor. 
The yield of carbonization is determined by using the amount of impregnated 
peat material before carbonization and of impregnated coke after 
carbonization. The amount of metal or metal oxide on the coke can be 
accurately determined by digestion and analysis by atomic absorption 
spectrometry.

EXAMPLE 1 
A water solution of chloroplatinic acid (having a Pt concentration of 1409 
mg of Pt/l of solution) is prepared by adding 3.73 g. of H.sub.2 
PtCl.sub.6.2H.sub.2 O to 1000 c.c. of water. The pH of the resulting 
solution is 1.75. 
Peat samples containing about 10% moisture are finely ground and sieved 
(42/60 U.S. Tyler mesh). 22 g. of the peat powder thus obtained are mixed 
at room temperature with 400 c.c. of the platinum solution above 
described. No pH adjustment is made in this preparation. Stirring of the 
slurry is carried out under vacuum to eliminate occluded air. Once the 
evolution of bubbles has ended the slurry is filtered out also under 
vacuum conditions. The yellow liquid solution which results from this 
operation is analyzed by atomic absorption spectrophotometry in order to 
determine the residual concentration of metal ions. 
The filtered residue is dried in oven at 105.degree. C. for a period of 48 
hrs. A small fraction of the resulting peat is digested in a hot 
concentrated acid solution in order to determine its metal content. The 
remaining impregnated material is put into a displaceable holder and 
carbonized in a 3 inch diameter laboratory furnace at 540.degree. C. for 
30 min. under a nitrogen atmosphere (flow rate = 103 cm/min). The 
temperature profile is such that the heating rate is of approximately 
10.degree. C./min up to the hold temperature of 540.degree. C. 
Measurments of the surface area pore volume and platinum dispersion can be 
carried out following established procedures. 
The results are shown in Table 1. 
TABLE 1 
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IMPREGNATION OF SPHAGNUM PEAT WITH PLATINUM 
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Impregnating salt H.sub.2 PtCl.sub.2 . 2H.sub.2 O 
pH of salt solution 1.75 
pH adjustment none 
Metal ion concentration 
in liquid (ppm) 1274.0 -Metal concentration 
mg. metal/g peat 2.7 
Moles of metal/g peat 
(.times. 10.sup.4) 0.14 
moles of metal/g coke 
(.times. 10.sup.4) 0.42 
Metal concentration 
mg. metal/g coke 8.1 
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EXAMPLES 2-10 
In a manner similar to the one described for Example 1, impregnation with 
other metals was also tried from solutions of different metal salts at 
varying concentrations as determined from isotherms. Other compounds could 
also be used since the procedure is not limited in any way to the metals 
and salts listed. In Example 3-10 the pH was adjusted where indicated with 
hydrochloric acid. 
The results after carbonization at 540.degree. C. are shown in Table 2. 
TABLE 2 
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IMPREGNATION OF SPHAGNUM PEAT WITH METAL IONS 
pH Metal ion 
Metal concen- 
Moles of 
of equlibrium 
tration mg. 
metal/g 
Moles of 
Metal concen- 
metal concentration 
metal/g of 
of peat 
metal/g 
tration mg. 
Metal 
Impregnating 
salt pH in liquid 
peat (m.a.f.) 
of coke 
metal/g of 
Ex. 
ion salt solution 
adjusted 
(ppm) (m.a.f.) 
(.times. 10.sup.4) 
(.times. 10.sup.4) 
coke 
__________________________________________________________________________ 
2 Rh.sup.3+ 
RhCl.sub.3 . 4H.sub.2 O 
2.30 none 1700 9.9 0.97 3.23 32.9 
3 Cr.sup.3+ 
Cr(NO.sub.3).sub.3 . 9H.sub.2 O 
2.80 4.10 1450 15.0 2.88 9.60 50.0 
4 Mn.sup.2+ 
MnCl.sub.2 . H.sub.2 O 
5.30 7.20 1516 16.0 2.91 9.33 51.3 
5 Mo.sup.5+ 
MoCl.sub.5 
1.40 none 550 22.0 2.29 7.63 73.3 
6 Ru.sup.3+ 
RuCl.sub.3 . 3H.sub.2 O 
1.80 none 1460 4.3 0.42 1.40 14.3 
7 V.sup.3+ 
VCl.sub.3 
1.97 3.40 1150 11.5 2.25 7.55 38.5 
8 Fe.sup.3+ 
FeCl.sub.3 . 6H.sub.2 O 
2.13 2.45 1120 11.4 2.04 6.02 33.6 
9 Fe.sup.2+ 
FeSO.sub.4 
4.50 6.50 625 5.8 1.04 3.12 17.4 
10 Ni.sup.2+ 
Ni(NO.sub.3).sub.2 . 6H.sub.2 O 
6.00 7.15 400 5.4 0.92 3.16 18.6 
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EXAMPLES 11-13 
Finely ground peat (48/60 U.S. Tyler mesh) and having a moisture content of 
10% by weight is contacted with NH.sub.3 -air-N.sub.2 mixtures in a 
fluidized bed reactor (21/2 in. in diameter and 19 in. height provided 
with stirrer). The ammoniation proceeds exothermally and as a result the 
bed is heated up to 45.degree. C. 
Fluidization conditions are: 
Gas Flow Rate: 30 liters/min. 
Gas composition: 10% NH.sub.3, 30% air, 60% N.sub.2 
Sold residence time: &gt;30 sec. 
Stirrer speed: 300 rpm 
The ammoniated material undergoes then the same procedure than the one 
described in Example 1. Ammoniation results in quite a large increase in 
the amounts of metal fixed as it is shown in Table 3. 
TABLE 3 
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IMPREGNATION OF AMMONIATED SPHAGNUM PEAT WITH METALS 
pH Metal ion 
Metal concen- 
Moles of 
of equilibrium 
tration mg. 
metal/g 
Moles of 
Metal concen- 
metal concentration 
metal/g of 
of peat 
metal/g 
tration mg. 
Metal 
Impregnating 
salt pH in liquid 
peat (m.a.f.) 
of coke 
metal/g of 
Ex. 
ion salt solution 
adjusted 
(ppm) (m.a.f.) 
(.times. 10.sup.4) 
(.times. 10.sup.4) 
coke 
__________________________________________________________________________ 
11 Fe.sup.3+ 
FeCl.sub.3 . 6H.sub.2 O 
2.13 2.45 1120 48.6 8.7 25.7 143.4 
12 Fe.sup.2+ 
FeSO.sub.4 
4.50 6.50 625 48.7 8.7 26.1 146.4 
13 Ni.sup.2+ 
Ni(NO.sub.3).sub.2 . 6H.sub.2 O 
6.00 7.15 400 50.4 8.6 29.5 173.6 
__________________________________________________________________________ 
It will be observed that starting with ammoniated peat results in a greater 
ion exchange capacity between the metal salt and the peat which cannot be 
explained only by the fact that NH.sub.4 sites have been incorporated in 
the form of COO.sup.- NH.sub.4.sup.30 groups on the reactive sites of the 
peat. It is believed that ammoniation causes important structural changes 
in the peat itself, probably due to the fact that the saturation values in 
the case of ammoniated peat are nearly identical on a molar basis which 
would not appear to be the case of unsaturated peat, as can be seen in 
Table IV. 
TABLE IV 
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COMISON OF ION EXCHANGE CAITY 
OF UNTREATED AND AMMONIATED PEAT 
Metal ion 
equilibrium Saturation values 
conc. in liquid (mg ion/g sphagnum peat) 
Metal Ion 
p.p.m. Untreated peat 
Ammoniated peat 
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Fe.sup.3+ 
1120 11.4 47.5 - 48.6 
Fe.sup.2+ 
625 5.8 47.2 - 48.7 
Ni.sup.2+ 
400 5.4 48.3 - 50.4 
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