Note: Descriptions are shown in the official language in which they were submitted.
1t~3~ 7
This invention relates to nitrogenous fertilizers and in
particular to processes for preparing the same.
Research has indicated that the properties of coal humus
are similar.to those of soil humus in that both consist of dark
brown complex'organic colloidal compounds which are soluble in an
alkali medium but not in water. In addition, both have a high
base exchange capacity and contain acidic oxygen-containing func-
tional groups. In view of these similarities and because coals of
low rank, for example brown coal (lignite), contain a higher pro-
portion of humus than other coals, it was considered that if coalsof 1GW rank could be subjected to a suitable treatment to extract
the humus content, it might well be possible to produce a nitro-
genous fertilizer having all or most of the desirable properties
of known fertilizers and at appreciably less cost.
With this consideration in mind, it has now been dis-
~overed that by treating a coal of low rank with a suitable hydro-
tropic solvent to dissolve at least a substantial amount of the
humus content of the coal, subjecting the thus formed solution
to;oxidising conditions, adding ammonia or a like nitrogen-donat-
ing compound to the oxidised solution so as to form a gel, anddrying the gel, such a fertilizer may be obtained.
Thus, the present invention provides a process for the pre-
paration of a nitrogenous fertilizer, which process comprises treat-
. , ing a coal of low rank with a suitable hydrotropic solvent which
is an aqueous solution of a nitrogen-conferring material which
acts as a weak base to dissolve at least a substantial amount of
.. . .
the humus content of the coal, which content is otherwise sparing-
ly soluble in water, subjecting the thus formed solution to-oxidi-
sing conditions, adding a nitrogen-donating compound to the oxi-
dised solution so as to form a gel, and drying the gel.
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The expression "hydrotropic solvent" as used throughout
the specification, including the claims, refers to an aqueous
soluti~n containing a nitrogen-conferring material - the hydro-
tropic mate~rial - which acts as a weak base to facilitate solubi-
lization of the humus content of a coal of low rank, which con-
tent is otherwise sparingly soluble in water. The aqueous solu-
tion may ~e formed in situ, the hydrotropic material dissolving
in water present in the coal. In fact, in coals of very low rank
with a hlgh water content, in situ formation i~ decidedly preferr-
ed; this may involve milling of the hydrotropic material and the
coal.
The actual amount of coal employed in the process will be
dependent upon the type of coal, since the proportion of humus
present varies from coal to coal. This amount can be readily de-
termined by simple experiment. A pre~erred range, however, is 60%
to 80% by weight, based on the overall weight of reactants.
By this process it is possible to provide a fertilizer ex-
hibiting the following properties: -
1) It permits a slow release of combined nitrogen,
thus avoidin~ the high initial yield and following
rapid fall-off in efficiency, characteristic of
chemical fertilizers such as ammonium sulphate.
2) It permits a retention of essential plant nutrients,
such as phosphorus and iron, in an easily available
form.
3) It improves the water retention and heat absorbing
capacity of the soil.
4) It constitutes a buffer which prevents rapid changes
in the acidity or alkalinity of soils.
Though any coal of low rank may be used, brown coal is
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preferred, usually in amounts of from 60% to 80% by weight, based
on the overall weight of reactants. Certain peats or peat coals
may also be put to good use.
Simple experiment will determine the types of hydrotropic
materials suitable for the present invention. Of the materials
capable of conferring nitrogen to the fertilizer, urea is especi-
ally suitable, preferably in amounts of from 18 to 22% by weight,
based on the overall weight of reactants. Other suitable hydro-
tropic materials include urea nitrate, urea peroxide, sugar, biu-
ret and thiourea.
Oxidation may be carried out by means of conventional oxi-
dants. For example, nitric acid, preferably concentrated commer-
cial nitric acid, or hydrogen peroxide may be employed The
amounts of nitric acid preferably range from 1.7 to 3% by weight
and the amounts of hydrogen peroxide from 0.5 to 2.0 by weight.
~ Sodium hydroxide or potassium hydroxide are desirably introduced
; into the solution following or before addition of the oxidant,
usually in amounts ranging from 0.4 to 1% by weight.
Ammonia is the preferred nitrogen-donating compound. 880
ammonia, namely concentrated (about 36%) ammonium hydroxide solu-
tion having a density of 0.880 in amounts of from 5 to 7~ by weight
are more preferred.
Oxidation establishes functional groups such as phenolic,
; carbonyl and carboxylic groups, which are capable of readily com-
bining with the nitrogen-donating compound, preferably ammonia, to
form a gel. On drying to a granular consistency, the gel is found
to be slowly peptised in water. Analysis of the product reveals
a nitrogen content of the order of 23 to 25%.
The invention will now be further illustrated by reference
to the following examples.
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EXAMPEE I
.
301b. of brown coal from the Morwell-Yallourn area of
Victoria, Australia, was dissolved in a concentrated aqueous solu-
tion of urea containing 91b. of urea. 12 02. of concentrated com-
mercial nitric acid was then added to the solution followed by
30z. of sodium hydroxide. 31b. of ammonia (s.g. 0.88~ was then
introduced into the solution and the resulting gel filtered off
and dried to a granular consistency.
EXAMPLE II
lOlb. of brown coal from the Morwell-Yallourn area of
Victoria, Australia, was dissolved in an aqueous solution of urea
containing 31b. of urea. 102. of sodium hydroxide was then added
to the solution followed by 1-40æ. of H202 (100) Vol. llb. of
ammonia was then pumped into the solution and the resulting gel
dried to a granular consistency.
The products of Examples I and II were shown to exhibit
all the abovementioned four properties, as well as being chemic-
ally ~table in the dry state, thereby permitting normal packag-
ing for transport purposes.
Apart from providing a process of preparing such fertilizers,
' the present invention also provides a fertilizer whenever prepar-
ed by such a process.
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SUPPLEMENTARY DISCLOSURE
Additional aspects of the invention described and claimed
in the principal disclosure are hereinafter described.
In general, low rank coals such as lignite are known to
enhance the desired formation of crumb structures of soil parti-
cles and to impart porosity, aeration and water-absorption. How-
ever, these coals may be so acidic that they can hardly be
applied as they are without having detrimental effects upon plant
life. Treatment of the coals is therefore necessary to render
them satisfactory for purposes of addition to soil. - -
One classical method for obtaining humates or humic acid
involves treating coal with an aqueous sodium hydroxide extrac-
tant. Humates are dissolved in the extracting solution and sepa- ;~
rated from insoluble tailings. The extractant may then be acidi- ~ -
fied and humic acid precipitated. U.S. patent Specification No.
1~ 2,992,093 to E. M. Burdick discloses on~such treatment.
The aqueous caustic extraction system, though ef~fective,
; has been found to be objectionable because of the low concentra-
tions of humic acid which are dissolved in the aqueous caustic
extraction liquor. The maximum amount of humic acid which can be
dissolved in the extraction liquor is about 8% by weight, and --
this occurs only in strongly caustic solutions. In practice, be-
cause of the low concentration of humic acid salts in the ex-
tracting solution, large quantities of sodium hydroxide and water
are necessary to recover humic acid in commercial operations.
In an effort to obtain more efficient recovery of the
humic acid, other extraction systems have been attempted, such as
flotation processes using a non-polar medium such as carbon tet-
rachloride, and organic solvent extraction systems using ac~tone
and water extracting mediums. While these processes are
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effective, they are expensive to operate and require complicated
purification techniques.
Humic acid itself contains carbon, hydrogen and oxyten
atoms only, and finds use as a soil conditioner but not as a fer-
tilizer because of the absence of any essential plant nutrients
such as nitrogen, potassium or phosphorus. In preparing the
humates, however, if ammonium hydroxide or potassium hydroxide
are used as the extractant in place of sodium hydroxide, nitrogen
or potassium becomes available for supply to plants. Here again,
though, ammonium or potassium hydroxide are not particularly good
extractants, being no better than sodium hydroxide in quantity of
humus dissolved, which in turn means that little nitrogen or po-
tassium is available for plant supply. Moreover, at least in the
case of nitrogen, this is present predominantly in a form which
is released at a fairly rapid rate. The nitrogen bearing compo-
nents of the composition are rather easily dissolved in water.
Ammonium humates are thus not suitable where the aim is to pro-
vide a fertilizer which will permit the slow release of nitrogen.
Coals have also been subjected to treatment with nitric
acid, this giving rise to a compound commonly referred to as
nitro humic acid. As with the aqueous caustic extractant, nitric
acid is not a particularly effective extractant unless high con-
centrations of nitric acid and high extraction temperatures are
employed, and even then the maximum amount of humic acid ex-
tracted is not very high. Nitro humlc acid contains little ni-
trogen - generally little more than about 2% by weight, based on
the overall weiyht of the acid- and the bulk of whatever nitrogen
is available in water-soluble and in quick-release form.
In an endeavour to improve the fertilizer characteristics
of nitro humic acid, the acid has been treated with such compounds
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as gaseous ammonia or urea. There is, however, no chemical reac-
tion between the acid and the additive, and the resultant product
is merely a physical admixture of the two components. The addi- ~- -
tive serves to boost the overall nitrogen content, but yet again
most of the nitrogen is in a water-soluble form available for
quick release. In the case of the addition of ur~a, this addi-
tive suffers the same failures as soluble nitrates, that is to
~l' say, it is too easily washed out of soil.
In contrast to the above extraction techniques - alkaline,
organic and acidic - and their attendant disadvantages, it has now
been found that coals of low rank may be extracted with an aque-
ous urea solution, which is substantially neutral, with surpri-
singly good results.
More particularly, one aspect of the present invention
provides a process for the preparation of a nitrogenous composi- --
tion suitable for use as a fertilizer, which process comprises
treating a coal of low rank with a suitable hydrotropic solvent
which is an aqueous solution of a nitrogen-conferring material
which acts as a weak base to facilitate dissolution of the humus
~0 content of the coal; subjecting at least a portion of the thus-
formed composition to oxidizing conditions; adding to at least a
portion of the composition, either before or after the step of
` subjecting to oxidizing conditions, a member selected from the
group of a nitrogen-donating compound, an alkali, and a mixture
of the two; and removing water from the oxidized composition to
form the nitrogenous composition.
- Another aspect of the invention provides a process for
the preparation of a nitrogenous compound suitable for use as a
` fertilizer and a soil conditioner comprising the steps of:
30 treatlng a coal of low rank with an aqueous urea solution at
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about room temperature, at least a part of the aqueous urea solu-
tion being formed in situ by virtue of the initial moisture con-
tent of the coal; subjecting the composltion thus formed to oxi-
dizing conditions; introducing an alkali into the composition;
and removing the water from the oxidized composition to form the
nitrogenous compound.
It is of importance to note that in the dissolution of
the humus content of the coal in the aqueous urea solution there
is no reaction of the urea and humus to form a soluble salt. The
aqueous urea solution acts in the capacity of an extractant
rather than reactant and in so doing renders the humus more amen-
able to oxidation. Furthermore, the extract is acidic, the de-
gree of acidity depending upon the initial pH of the coal to be
treated.
As the rank of coal goes down so does the water content
go up, and with coals of low rank the water content is generally
within the range of 50% to 80% by weight, based on the total
weight of coal. Thus, aqueous urea solution may be ormed in
situ by the mixing of the low rank coal with dry urea. In some
instances, where the water content of the low rank coal is low,
say of the order of 50 to 55% by weight, it may be desirable to
add ~ater to the coal and urea to boost the water content to
about 60% by weight and so effect maximum dissolution.
The insoluble fraction of the coal is not generally sepa-
rated from the soluble fraction, though it may be. Where there
is no separation~ the insoluble fraction is carried through to ;~
the end product and, as far as can be established, has no adverse
effects on that product.
The actual amount of coal employed in the process will be
~ 30 dependent upon the type of coal, since the proportion of humus
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present varies from coal to coal. This amount can be readily de-
termined by simple experiment. A preferred range, however, is
60% to 80~ by weight, based on the overall weight of reactants.
By this process it is possible to provide a fertilizer
exhibiting the following properties~
(1) It permits a slow release of combined nitrogen, thus avoid-
ing the high initial yield and following rapid fall-off in
efficiency, characteristic of chemical fertilizers such as
ammonium sulphate and prior humus extracts.
(2) It permits a retention of essential plant nutrients, such as
phosphorus and iron, in an easily available form.
(3) It improves the water retention and heat absorbing capacity
of the soil.
(4) It constitutes a buffer which prevents rapid changes in the
acidity or alkalinity of soils.
Though any coal of low rank may be used, brown coal is
preferred, usually in amounts of from 60~ to 80% by weight, based
on the overall weight of reactants. The amount of coal may, of
course, vary considerably, even outside of this range, and will
depend on the amounts of the other reactants used. These latter
amounts are set out hereinafter. Certain peats or peat coals may
also be put to good use.
The coal should be in particulate form to facilitate dis-
solution in the aqueous urea solution, and as might be expected
the smaller the average particle size the less the time required
for effecting dissolution.
The treat is preferably carried out at room temperature
for the simple reason that elevated temperatures are only margin-
ally better in terms of overall efficiency.
The urea is preferably present in an amount greater than
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about 15% by weight based on the overal weight of the coal, added
water (if any) and urea. Extraction is to a degree proportion-
ately related to the amount of urea and the relative amounts of
urea and water present, and in some instances amounts of urea
less than 15~ by weight may give rise to an inferior end product
because of incomplete dissolution. Preferably, the amount of
urea is less than about 30% by weight since higher amounts in-
crease cost without enhancing extraction efficiency and may re-
sult in the presence o~ some unreacted urea in the final product.
It is found that urea is most preferably present in amounts of
from about 18 to 22% by weight. This range appears to give opti- -
mum extraction, bearing in mind cost and efficiency factors.
Oxidation may be carried out by means of conventional
oxidants, although generally speaking solid and liquid oxidants
are preferred to gaseous oxidants because of ease of handling.
By way of example, there is mentioned urea peroxide, sodium pero- ;~
xide, nitric acid and hydrogen peroxide. Needless to say, the
oxidant should not be one having one or more elements which are
toxic to basic plant life. Nitric acid, particularly concentra-
ted commercial nitric acid, and hydrogen peroxide are most pre-
ferred.
The amounts of nitric acid preferably range from about
1.5 to 5% by weight, based on the overall weight of reactants.
Oxidation will proceed with amounts below about 1.5% by weight, ~,
but it may with some coals be incomplete so that not all of the
humus content is utilized in the process. There is little advan-
tage in using more than about 5% by weight of nitric acid when
increased efficiency is balanced against increased material
costs. A range of 1.7 to 3% by weight is generally quite satis-
factory.
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The amounts of hydrogen peroxide preferably range from
about 0.5 to 3.0~ by weight, based on the overall weight of reac-
tants, the upper and lower limits being determined by the same
factors as mentioned above in relation to nitric acid. Generally,
up to 2% by weight will suffice.
Oxidation establishes functional groups such as phenolic,
carbonyl and carboxylic groups on the humic acid molecules, which
are capable of readily combining simultaneously with the NH
groups which are a product of the oxidation of the urea, and the
ammonia, if present, to form a gel. On drying to an effectively
dry granular consistency suitable for packaging and shipping, the
gel is found to be slowly peptised in water.
The alkali is preferably selected from the group consist-
ing of sodium hydroxide, potassium hydroxide and ammonia, and is
introduced after the dissolving step and either before or after
the step of subjecting the solution to oxidizing conditions. The
amount of alkali will be largely dictated by the amount of oxi-
dant, but usually the alkali is added in an amount ranging from
0.4 to 1~ by weight when either sodium hydroxide or potassium
hydroxide, and from 5 to 7% by weight when ammonia. With ammonia
there is the additional benefit of a compound which is able to
confer further nltrogen to the end product. In some instances, -s
ammonia and either of the alkali metal hydroxides may be added.
The amount of total nitrogen and fixed nitrogen in the
end product is a function of the nature of the coal used as the
starting material and the amount of functional groups provided by
that coal. Where ammonia is used, however, the final product
will usually contain from about 15 to 25~ by weight of nitrogen
of which about 4 to 6% is essentially water-insoluble and avail-
able for slow release. Where ammonia is not used, the final
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product may still contain upwards of about 10% by weight of ni-
trogen, 4 to 6% being essentially water-insoluble and available
for slow release. When the oxidant is nitric acid, the alkali
preferably is added after the oxidant, whereas the reverse is the
case where hydrogen peroxide is employed as the oxidant.
~ he invention will now be further illustrated by refer-
ence to the following examples.
EXAMPLE I
a 30-lb sample of brown coal from the Morwell-Yallourn
area of Victoria, Australiaf in finely-divided form, was mixed
with 9 lb of dry urea powder in a mill. No additional water was
necessary. Following dissolution, 12 oz of concentrated commer-
cial nitric acid ~7as added to the mixture followed by 3 oz of
sodium hydroxide dissolved in a small amount of water. 3 lb of
aqueous ammonia solution (s.g. 0.880) was then introduced into
the mixture and the resulting gel dried to a granular consis-
tency. There was no separation of the soluble and insoluble
fractions following dissolution. The gel and dried product
analysed as follows:
Ge Z 52.7% moisture
47.3% total solids
11.85% total nitrogen
9.0 pH
Dried Prod~ct (subjected to washing)
4.1% fixed nitrogen (residue)
13.26% soluble nitrogen (filtrate)
A second 30-lb sample from the same area was treated in
the same manner and ~he gel and dried product analysed as
follows:
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~eI 50.5% moisture
49.5% total solids
15.38% total nitrogen
9.21 pH
DYied Product 4.46% fixed nitrogen -
12.51% soluble nitrogen
EXAMPLE II .
Example I was repeated, except that no aqueous ammonia
solution was introduced at the end. The gel and dried product
analysed as follows:
; Ge ~ 49 .1% moisture ~ ;
50.9~ total solids
10.91% total nitrogen ~;
6.92 pH
Dried Product 4. % fixed nitrogen
11.09% soluble nitrogen
EXAMPLE III
10 lb of brown coal from the Morwell-Yallourn area of
Victoria, Australia, in finely-divided particulate form, was
mixed with 3 lb of dry urea powder in a mill. No additional
water was necessary. Following dissolution, l oz o sodium hy-
droxide dissolved in a small amount of water was added to the
mixture followed by 4 oz of H2O2 (100) Vol. 1 lb of aqueous
i ammonia solution (s.g. 0~880) was then introduced into the mix-
ture and the resulting gel dried to a granular consistency.
~, There was no separation of the soluble and insoluble fractions
'~ following dissolution. The gel and the dried product analysed
as follows:
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Ge ~ 4g . 8% moi~ture
50.2% total solids
11.38% total nitrogen
9.01 pH
Dried Product 3.95% fixed nitrogen
12.05% soluble nitrogen
EXAMPLE IV
Example III was repeated, except that no ammonia was in-
troduced at the end. Analyses of the resulting gel and dried
product were similar to those above. -
The products of Examples I to IV were shown to exhibit
all the above-mentioned four properties, as well as being chemi- - ;
cally ~table in the dry state, thereby permitting normal packag-
ing for transport purposes.
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