Note: Descriptions are shown in the official language in which they were submitted.
245~
DESCRIPTION
BIURET PRODUCTION BY CONTROLLED
PYROLYSIS OF UREA
--
Tech~ical Field
This invention relates to a process for the
production of animal feed grade biuret and more specifically
to the pyrolyzation of urea and its reaction products in two
stages, the first stage of the reaction proceeding with the
urea in molten form and resulting in a reaction product which
comprises about 20~ to 60% unreacted urea, and the second
stage of which involves further pyrolyzation of the product
in dry, particulate, solid form to reduce the urea content
and increase the biuret content without substantial further
increase in cyanuric acid content.
Backqround Art
As is well-known, an animal feed shortage e~ists
worldwide. Feed which has a high protein analysis is in
par~icularly short supply. ~istorically, cattle have been
fed with grass hay, and the raising of such hay for winter
feeding is a well-established traditional procedure.
Grass hay contains up to 20~ protein if harvested
in the early summerO However, there is a decline in the
protein content as the summer progresses, making later
cuttings of hay less valuable for cattle growth.
After July 1st, the intermountain natural grazing
area of th~ United Sta~es produces a natural hay which has a
protein content below 10% on the dry basis. When hay has a
protein content below this level, the ruminant animal eating
such hay does not gain weight at a satisfactory rate.
Consequently a great deal of research effort has
been devoted to the establishment of diets and feeding
schedules for ruminant animals which will maximize the
profit to be realized in raising such animalsO It was
discovered early that protein-rich leguminous hay produced
not only better quality meat, but also more pounds of meat
per acre. This discovery has led to the use of protein-rich
agricu]tural by~products as additives to hay to enrich the
diet of the animals when hay of low protein analysis is fed.
Such agricultural products as cottonseed meal,
soybean meal, peanut meal, flax seed meal, etc. are widely
used along with the hay in order to upgrade the average
protein analysis of the resulting feed mixture. At the
present time, escalating costs of farming and ranching make
it imperative that any mixed feed fed to the cattle be of
lowest cost and the search for readily available, economic
fe~ding additives of consistent quality continues.
It was discovered may years ago that it is not
necessary to feed protein per se to ruminant animals in
order to increase the protein cont nt of the animal. The
animal itself has the ability to con~ert non-protein
materials into protein.
Thus, it was discovered about 1920 that inorganic
nitrogen in the form of ammonium salts could be used to
supplant protein in part of the diet of a ruminant animal.
The ammonia content of the ammonium salts is converted by
the animal ints muscle tissue. Ruminants have multiple
5~
stomachs and ammonium salts release their ammonia content in
the rumen, where it is converted into protein by the
bacteria occurring naturally thereO When the
bacteria produced protein passes into another stomach of the
ruminant, it is digested just like any other feed protein.
Ammonia and ammonium salts are an inexpensive
source of non-protein nitrogen utilizable in this manner.
Unfortunately, there is a limit to the amount of ammonia
which can be included in the diet of the animal without
causing the occurrence of adverse reactions. These adverse
reactions are believed to be caused by the absorption of
unconverted ammonia in the digestive system of the animal.
Such absorption results in ammonolysis, a
condition wherein the ammonia in the digestive system of the
animal causes toxic effects and possible death.
Consequently the amount of free a~monia which can be
tolerated by an animal is very small. The use of ammonium
salts as a source of non-protein nitrogen in mixed feeds,
therefore, has not been a commercial success.
Urea is used widely today in limited amount as a
non-protein nitrogen additive to mixed feeds for ruminants.
The economic incentive to use urea as a source of
non-protein nitrcgen is great. ~t has its basis in the fact
that urea is 46% nitrogen by weight, whereas hay analyzing
10~ protein is only 1.6% nitrogen. In other words, the
addition of 20 pounds of urea (1% of the dry weight) to a
ton of 10% protein hay produces 2,020 pounds of hay having a
protein equivalent of approximately 13%o It would require
the addition of only 74.77 pounds of urea to bring the
protein equivalent of the hay up to 20%~
s~
With hay having a current market value of $75.00
per ton and urea of $165.00 per ton, the economic advantages
of adding urea to hay is obvious.
However, the u5e of urea is generally restricted
to between 1/2~ and 1% of the dry weight of the mixed feed
because of the toxicity which develops when the urea is
overfed. This toxicity is due to the hydrolysis of the urea
by the enzyme urease generally present in the stomach of the
ruminant animal. when urea is hydrolyzed by urease, it
gives off free ammonia and the toxicity which results in the
animal is in reality the earlier recognized toxicity due to
free ammonia.
Because of the restriction due to ammonolysis on
the use of urea, the search continued for an alternate hay
additive. This search has led to the discovery that biuret,
a compound which can be made from urea, can also be used by
ruminant animals in the synthesis of protein.
Biuret is not readily hydrolyzed by the enzyme
urease and consequently can be included in the diet of
ruminants without danger of toxicity. Biuret which is
unused as a symbiotic feed for the ruminant passes through
the digestive tract unchanged. This makes it virtually
impossible ~or toxic symptoms to develop when feeding biuret
as a diet supplement. U.S. Patents 2,~68,895 and 2,861,886,
fox example, describe the use of biuret in animal feeds.
It is not necessary to use pure biuret in the
supplementation of animal feeds. A technical grade product
analyzing as little as 55% biuret maybe used satisfactorily.
The commercial standard for feed-grade biuret adopted by the
U.S. Food and Drug Administration is a mixture having a
minimum analysis for biuret of 55%, a maximum of 15% urea~
and not more than 30% of the group consisting of cyanuric
acid and other urea derivatives, by weightO
These materials result from the conversion of urea
to biuret by heating the urea to a temperature above its
melting point. Thereupcn ammonia gas is evolved and there
results a reaction mixture comprising in varying amounts the
following products:
Unreacted urea
~mmonium cyanate
Cyanuric acid
B iur et
Triuret
I'etrauret
lS Higher homologs
In carrying out this pyrolytic reaction, it is not
possible to achieve a yield of biuret over about 60% when
operating at a temperature above the melting point of urea
and at any partial pressure between 10 and 60 mm wlth a
reaction time of from 30 minutes to 16 hours. The longer
the reaction time, the greater the yield of cyanuric acid,
which a~ter a reaction time of about 12 hours is generated
in ever increasing amounts at the expense of the desired
biuret product.
~he pr3duction of biuret by pyrolysis of urea
under elevated temperatures is well-known and a considerable
art has developed as shown by following the United States
patents showing various methods of biuret manufacture.
2~145,392 to Harmon - 3anuary 31, 1939
2,370,065 to Olin - February 2Q, 1945
2,524,049 to Garbo - October 3, 1950
2,768,895 to Kamlet ~ October 30, 1956
2,861,886 to Colby - November 25, 1958
3,057,918 to Formaini et al. - October 9, 1962
4~,055,598 to Lee - October 25, 1977
All of these patented processes involve the
pyrolysis of urea in l~he molten sta~e or liquid phase, in a
single step, which may be under vacuum, to facili~ate the
removal of by-product ammonia which oceurs according to the
following chemistry:
NH2CO NH2 NH3 ~ HOCN
Urea Ammonia Cyanic Acid
NEI~CO NH2 ~ HOCN NH2CONHCONH2
Urea Cyani.c Acid Biuret
Biuret and cyanic acid also may react to form
cyanuric acid as :Eollows:
NH2coN~lcoNH2 ~ HOCN (HOCN)3 ~ NH3
Biuret Cyanic acid Cyanuric acid Ammonia
The formation of cyanuric acid is enhanced by
elevated temperatures and reduced pressures and retarded by
lower reaction temperatures.
~eretofore, purification and concentration of the
biuret product has been necessary in order to produce a
feed-grade biuret meeting Food and Dru~ Administration
requirements.
This is difficult because cyanuric acid and urea
canno~ be separated with ease from biuretO Ordinary
routines of fractional crystallization do not lead to the
production o a pure, crystalline, dry biuret product. They
lead rather to the formation of a wet, sticky, clay-like
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filter cake which contains urea in various amounts.
Also if an appreciable amount of cyanuric acid is
present, the reaction mixture is viscous and sticks to the
reaction and refining vessels, making it hard to handle. In
addition, the cyanuric acid tends to combine with the
unreacted urea compound of the reaction mixture so that it
becom~s virtually impossible to separate the urea by
filtration, as is normally required to produce the FDA
approved low-urea biuret product.
The precise mechanism by which this occurs is not
Icnown. However, urea may form an insoluble complex with
cyanuric acid in the nature of a secondary valence compound.
Alternatively, the urea may simply be strongly occluded by
any cyanuric acid present so that in the mixed precipitate
oE urea, biuret, biuret homologsr and cyanuric acid, the
urea is not readily removed by washing with an aqueous
solvent for urea. Where a pyrolyzed urea product contains
cyanuric acid in excess of 10~, and unreacted urea in excess
of 35%, it is not practical t.o lower the urea analysis to
below 15~, even by multiple recrystallizations.
The disclosure of Lee U.S. Patent No. 4,005,598
includes a good summarization of various prior art processes
for pyrolyzing urea to produce reaction products which are
principally biuret. The contribution to the art offered by
the Le~ patent disclosure is that of a process for producing
biuret wherein the extent of pyrolytic conversion of urea to
biuret is increasedr with less than normal amounts of
cyanuric acid, triuret and o~her biuret homolog produc~s
being formed, the reaction involving a starting material
made up of a low urea, high biuret seed material mixed with
a high urea, low biuret feedstock material, which mixture
has a total urea content not exceeding 20% by weight, such
mi~ture being heated to a range of from about 100C. to
about 150C. and preferably from about 115C~ to about
125C. while dispersed as a slurry in an alkane series
hydrocarbon carrier having from 8 to 12 carbon atoms and a
boiling point at or above the reactior. temperature. In the
Lee process, heating of the mixture of low urea seed
material and high urea feedstock material proceeds with the
mixture in slurry form in the liquid hydrocarbon carrier,
with by-product ammonia being removed by evolution of
hydrocarbon carrier vapor. This process, although
assertedly achieving the objective of permitting the
reaction to proceed at relatively low temperature in order
to minimize the formation of cyanuric acid and other
undesired autocondensation products, has mani~est practical
disadvantages in that it requires an essentially liquid
phase reaction environment and the toleration of potentially
dangerous reaction conditions since the reaction is carried
out in the presence of a heated liquid hydrocarbon carrier
which inherently presents an explosion or fire hazard.
The Lee process is severely limited in production
capacity in that the urea content of the reaction mass is
limited to a maximum of 20%. This limitation in the Lee
process is dictated by the fact that the Lee reaction
product will gum up and not remain a slurry in the liquid
medium and in the processing equipmen~ if the urea content
exceeds 20%. In contrast, applican~'s dry, solid state
pyrolvzation process is operable with up to about 60~ urea
content by weight in the heated reaction mass, which
2~S~
correspondingly increases production capacity insofar as the
amount of urea which can be converted to a reaction product
suitable for use as feed grade biuret in a given amount of
~ime.
A further disadvantage of the Lee process is that
its end product is oil contaminated in the sense of the
product retaining some residual alkane hydrocarbon, which
detracts from its palatability when used as animal feed.
There is also the possibility that residual pyrolyzed
hydrocarbon may render the product unsuitable for animal
consumption and indirectly human consumption in view of
possible carcinogenic risk. Furthermore, a residual oil
content in the end product in this type of process may
inter~ere or complicate use of the product or portions
thereof in water solution. As a related consideration, the
use of an oily, hydrophobic carrier as the reaction medium
can complicate evolved ammonia by-product recovery in
aqu~ous solution since the by-product is then recovered in
what amounts to an oil-in-water emulsion.
Disclosur _o~ Invention
According to the present invention, partially
pyrolyzed urea containing not over 25% cyanuric acid and
more than 20% urea by weight maybe converted to animal feed
grade biuret b~ subjecting the partially pyrolyzed urea
feedstock in particulate form to a mild heat treatment in
the substantially ~olid sta~e with forced air flow ~hrough
the particulate reaction mass. A product results having a
high concentration of biuret and a product with a minimum of
55% biuret, a ma~imum of 15% urea, and a maximum of 30%
--10--
cyanuric acid and similar ~rea pyrolysis by-products is
easily produced. Such product is hydrocarbon-free and
eminently suitable as a feed additive -For cattle and needs
no additional separation step to remove excess urea and
cyanuric acid.
In carrying out this invention, a feedstock
consisting of partially pyrolyzed urea in dry particulate
form and containing not over about 25% cyanuric acid which is
treated in an oven wîth forced air recirculation at a
temperature at or slightly below the softening point of
particles, e.g. at a temperature between about 100C. and
about 140C., and preferably between 115C. and 125C. for a
period of time of generally between about 15 hours to about
200 hour~ and preferably from about 24 hours to 180 hours.
During this stage of pyrolyzation it is essential that the
feedstock be in an essentially solid state with at most only
incipient surface fusion of particles, as distinguished from
the molten, i.e. liquid state so that substantial
sublimation can occur as well as evolution of ammonia from
the product.
~ typical feedstock for this process may be
prepared, for example, by reacting urea at 157C. and 160mm
Hg for 3.5 hours to give a product having an analysis by
wei~ht of urea 37.5%, biuret 41~6% and cyanuric acid 16.1~,
cooling the autoclave product below its melting point, and
comminuting it. One method o accomplishing this is to
drain the molten product into trays and allow it to cool
naturally and solidify before comminuting, preferably with
preformed biuret powder addition to provide crystallization
"seed" and improve cooling rate~
It is advantageous in carrying out the process of
the invention to have the feedstock comminuted to a mesh
size of about 1 mesh and smaller (i.e. where the diameter
of the particles is 1 inch and smaller, and preferably about
4 mesh and less).
~he groun~ feedstock is suitably placed in trays
or the like to a bed depth of between 1/2 inch and 3 feet
or more, and placed in a forced air circulating oven or the
like with hot air circulated through the particulate mass in
each tray, preferablv upwardly through each tray. The
temperature is preferably thermostatically controlled to
within ~3C. within the oven.
The comminuted feedstock is placed in or on a
container porous to air, such as a tray or other boxtype
container with a screen or like foraminous bottom and open
top, which arrangements provide what may be generically
termed a ~ixed bed. Alternatively, the feedstock bed may be
arranged on a wire screen or like foraminous conveyor, or in
a fluidizing chamber, which arrangements provide what may be
generically termed a movable bed.
The depth of the bed of the particulate material
can be any desired depth consis~ent with the need to
maintain substantial and continuiny forced air flow in
contact with the material surfaces, and considering also
that under a given operating condition, a given total amount
of contact of moving air with the surfaces of the particles
is necessary to achieve the result of substantial urea
sublimation and urea conversion to biuret, which
considerations involve several interrelated factors such as
average mesh size of the particles, the temperature of the
~2~
air, depth of the particle bed and the volume of air flow
past the particles. Thus/ for example, in a situation where
a fixed bed, two feet in depth, is composed of particles
having an average mesh size of 8 mesh, a pressure drop of
O.lS psig per foot of bed has been found satisfactory for
the operating condition where the air and particles are
heated to a temperature of 127C. and for 36 hours.
Correspondingly, however, when the average particle size is
4 mesh, an optimized pressure drop through a bed 2 feet
thick to accomplish a similar end product at the same
temperature has been found to be 0.13 psig per foot of bed,
and the heating should continue for a period of 50 hours.
Comminution of the solidified and broken up
pieces of the partially pyrolyzed reaction product
lS resulting from the first stage of reaction of urea and the
addition thereto of feed grade biuret powder to increase the
melting point and expedite cooling of the reaction product,
can be carried out in any appropriate mechanical
disintegrator such as a jaw crusher or rotary crusher, or
hammermill or the like.
The powdered material added to expedite
crystallization and cooling of the partially pyrolyzed
reaction product to mak-e the feedstock for the solid state
heating stage of the process, other powered and comminuted
materials can be used as the additive if they do not
substantially lower the meltiny point of the reaction mass
during the solid sta~e pyrolyzation and provided they are
advantageous or at least not deleterious to the end use of
the final reaction product, such as for animal feed or the
llke~ In ~he case of the end use being animal feedr for
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~2~ 5~
example, advantageous additives may be calcium carbonate or
calcium phosphate or other known animal feed additive.
~owever, the powered or comminuted additive
introduced to the partially pyrolyzed reaction product in
making up the feedstock is preferably feed grade biuret such
as readily available by product fînes from earlier sizing
processing, and offers the advantage of increasing the
melting point of the reaction mass during the solid state
pyrolyzation (since the proportion of biuret and its
homologs is thereby increased in the mass) which in turn
permits its being heated during the sold state pyrolyzation
to a somewhat higher temperature without melting, thus
accelerating the heat conversion.
We have found that the two stage pyrolyzation
technique described results in a product which when
comminuted needs no further processing before use as animal
feed grade biuret. In general, the initial stage of the
reaction process is carried out at a temperature above the
melting point of urea, forming a partially pyrolyzed
reaction product comprising urea, cyanuric acid and biuret.
~he second sta~e of the process involves the continued
pyrolyzation of ~he reaction product in particulate,
essentially solid state, with forced hot air flow
interstitially through the particles; the net effect of
which is to reduce the urea content and enhance the biuret
content of the reaction mass, while only slightly increasing
the cyanuric acid, triuret and other by-product content.
During the solid state heat treatmen~, some urea is sublimed
as may also be a slight amount of biuret and possibly
o~hers. The effect of this sublimation in reducing the urea
~Z~ 5~
content of the product is substantially and is an important
part of the process when one is attempting to produce FDA
acceptable material hav.ing not more than 15% urea.
Investigation has revealed that carrying out the
final pyrolysis reaction at a low temperature at or slightly
below about the softening point of feed material retards the
conversion of the biuret into cyanuric acid, but permits
effective further conversion of urea into biuret and the
lowering of the urea content, and that such pyrolysis can be
dona with the reaction mass in a dry, particulate state.
When molten urea is heated first at atmospheric
pressure and thereafter under vacuum, there is a rapid
evolution of ammonia upon the application of the ~acuum.
~lhis indicates the presence of a substantial quantity of
biuret precursor moieties generated during the pyrolysis at
atmospheric pressure. These active bodies then react under
the influence of reduced pressure to give enhanced yields of
biuret without excessive production of cyanuric acid~
It accordingly is evident that the pyrolytic
conversion of urea to various products is highly sensitive
to the reaction condikions of time, temperature and
pressure. It is the essence of the first pyrolysis reaction
that the conditions of high temperature pyrolysis at
temperatures exceeding the melting point of urea are
controlled and used for only a brief, first portion of our
process in order to produce a feedstock for the second
reaction which is controlled in composition; with the
conversion of urea to biuret being then continued at a lower
temperature with the reaction mass in the substantially solid
skate to react the feed.
~z~s~
Acceptable elevated temperature pyrolysis to
prepare the partially reacted feedstock for the solid state
pyrolyzation are the following, wherein tha percentages are
given in percent by weight:
Constituent General LimitsOptimum Limits
Cyanuric acid 0 - 25% 0 - 20g
Biuret 20 - 60% 35 - 60%
Urea 20 - 60% 20 - 45~
In a manner known per se in the art, pyrolysis
products having compositions within the foregoing ranges are
obtainable, for example, by adjusting the pyrolysis
variables of time, temperature an~ pressure to within the
following limits, with time and temperature being genera:Lly
inversely related:
Parameter General Limits Optimum Limits
Time (hours) 0.25 - 24 1.0 - 4.0
Temperature (C) 200 - 135 175 - 135
Pressure (mm) 0 - 1520 0 - 200
A feed-grade biuret can readily be obtained by
reacting the intermediate feedstock prepared in the above
manner, with or without seed material addition during
cooling, by adjusting the reaction variables of time,
temperature and pressure to within the following limits,
with time and temperature being generally inversely related:
Parameter General Limits Optimum Limits
Time 5hours) 5 - 200 12 - 180
Temperature (C~ 140 - 100 130 - 110
Pressure
(mm.~g.ABS.) 10 - 1520 50 - 760
The process may be carried out under atmospheric
~16-~
~2~Z~
pressure or such slight negative pressure as may be required
to recover the by-product ammonia~ While higher pressure
than atmospheric pressure may be used, there is no
particular advantage in its use. where the heat treatment
is carried out under vacuum, ît has been found that the
reaction proceeds faster.
The foregoing parameters may be varied as desired
so long as the second stage of the pyrolyzation reaction
results in an acceptable level of the constituents in the
final product, notably a high level of biuret and a cyanuric
acid and urea concentration within the prescribed
composition parameters as set forth below:
Gomponent~ General Limits Optimum Limits
Cyanuric acid less than 50% less than 30%
Biuret 30 - 70% 40 - 60%
Urea less than 40~ less than 15%
In a given run, when the feed material for the
further pyrolyzation of the product in solid form i~ at hand
and a determination is to be made as to the temperature at
which the further, second stage pyroly~ation is to proceedr
a sample of the f~ed material can be analyzed for softening
point, such as by analysis on a Fisher Johns melting point
detector, as marketed by the Fisher Scientific Company.
During such analysis, as the temperature of the sample is
raised progressively r and as it reaches the point where the
sample starts to soften, its color change from a white dry,
particulate appearance to a duller, greyish moist, shiny
appearance. Further increase in temperature then causes
such moist appearance to changes ~o a glistening appearance
and finally to a puddled, melted s~age which is defini~ely a
melting point. The temperature at which the first change in
appearance from softening occurs is the temperature at or
slightly below which the final pyrolyzation of the product
should start. However, as the further pyrolyzation reaction
proceeds~ and ~he urea content of the reaction mass is
further reduced with the biuret content thereof
progressively increasing, the sotening point of the mass
will progressively increase somewhat because of the changing
con~tituency of the reaction mass. This progressive
increase in softening point can permit a somewhat progressive
increase in the temperature at which the reaction proceeds
in the course o the run.
It has also been found that the feed material, being
a mixture oE several compounds, i.e. urea, biuret, cyanuric
acid and other homologs, apparently demonstrates an eutectic
action, i.e~ the softening point is at a temperature
somewhat less than the melting point oE the urea and
considerably less of course than the melting points of the
other constituents, principally biuret and cyanuric acid.
The melting point of urea itselE is 132C. but the initial
softeniny point at least at the start of the second stage
pyrolyzation oftentimes is somewhat less, e.g. 1~3C.,
particularly in the instance where there has been no or
minimal seed material addition of the type where the seed
material has a relatively high biuret content and relatively
low urea content as compared with the constituency of the
intermediate reaction product obtained from the first stage
pyrolyzationO Interestinglyp the melting point of the final
product, i.e. feed grade biuret, is at around 190C. if in
Eact it even melts. The phenomenon involved apparently is
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that of disintegration of the biuret to cyanuric acid at the
higher temperature~
The :Einal reaction product is sized as in a
hammermill to 16-20 mesh and fines resulting from the
comminution which are considered too small for the final
product can readily be recycled to the first phase reaction
product as the seed material or part of the seed material
added during cooling thereof.
Best Mode of carrYi~ Out The Invention
Example_l
A charge of commercially available technical grade
urea was placed in an autoclave set at 157.~C. ~2C. The
autoclave was evacuated to a pressure of 160 mm Hg Abs. The
charge as held in the autoclave at the foregoing conditions
for 3.5 hours. The in~ermediate product resulting from the
initial autoclave reaction has the following composition:
Constituent% By Weiqht
Urea 37.5
Biuret 41.6
Cyanuric acid 16.1
Other Pyrolysis
Products 4~8-
100 .0
A solid comminuted intermediate feedstock
consisting of 591 grams of the above product was placed in
an aluminum tray to a depth of 1.5 inches and given a heat
treatment in a circulating oven at 112-122C. for 42 hours
with forced air flow across the tray, during which time the
material which had 2 size distribution of between Eour and
-19-
twenty mesh was allowed to remain undisturbed. At the end
of the heat treatment, the analysis of a uniform sample was:
14.3% urea, 60.0% biuret, 24.5% cyanuric acid, and 1.2% other
related by-products.
During the 42 hour treatment at 112-122C., the
urea content dropped from 37.5% urea to 14.3% urea. The
biuret content increased from 41.6% biuret ~o 60.0% biuret,
and the cyanuric acid increasing from 16.1% to 24.5%. The
gaseous ammonia given off during the oven treatment was
checked and found to be stoichiometric with the formation of
biuret and cyanuric acid.
Example 2
A feed stock of 591 grams of a parkially pyrolyzed
urea product consistiny of particles substantially 1/8" to
1/4" in diameter and having an analysis of 38.4% urea, 42.8%
biuret, and 14.1% cyanuric acid, formed by the feedstock
preparation process described in Example 1, was placed in an
aluminum tray to a depth of 1.5 inches and heated in a
Farberware Turbo oven or 50 hours at 118-122C., with
forced air flow across the tray. The material in the tray
was turned over once every 10 hours to aid in uniformizing
the reaction. At the conclusion of the heating period, the
product analyzed 10.5% urea, 57.8% biuret, 19.4% of cyanuric
acid, and 12.3% other urea pyrolysis products.
Example 3
A feedstock comprising 591 grams of a partially
pyrolyzed urea product as in Example 1 and analyzing 37.5%
urea and 1611% cyanuric acid, was placed in an aluminum tray
-20
~z~
to a depth o 1.75 inches and heated in a Farberware Turbo
oven for 33 hours total heating time, with forced air flow
across the tray. At the end of the first 16 hours of
heating, during which the oven temperature was between
116-122C., the product analyzed 29.0% urea, 46.7% biuret,
20.0% ~yanuric acid and 3.3% others. The temperature o the
oven was adjusted slightly upwards to 126-130C. for another
17 hours of heating, at the conclusion of which the product
analyzed 16.8~ urea~ 31.9% biuret, and 42.5% cyanuric acid.
This e~emplifies a mode of operation, i.e. a total
33 hours of heating between 116-130C., which produces a
product higher in cyanuric acid and in urea than the current
U.S. Food and Drug Administration specification for animal
feed grade biuret but which has utility in other feed grades
or for other purposes.
Example 4
As a further example o~ practice of the present
invention, on a larger scale and with greater efficiency in
term~ of volume of production of animal feed grade biuret,
900 pounds of urea was charged to a 100 gallon autoclave
reactor, and melted by heating to a temperature of 149QC~,
with a partial pressure of 70 mm Hg applied to remove
evolved ammonia. The molten urea was thus pyrolyzed for a
period of four hours at a temperature ranging from 146C. to
157Co with the temperature in general progressively
increasing during this period. At the end of the four hour
period the molten crude partially pyrolyzed reaction product
was discharged into a barrel trough equipped with an auger
for stirring. At this point in the process~ the reaction
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5~L
product weighed about 750 pounds and was a white, creamy
fluid material with an analysis as follows: urea 35%,
biuret 48%, cyanuric acid 14%, others 3~, by weight, with a
softening point of 123C.
To prepare feedstock for the second stage of
pyrolyzation of the molten crude reaction product from the
foregoing reaction, while the mass was still fluid and being
stirred by the auger, there was added thereto 83 pounds of a
pre~formed powered biuret reaction product from a previous
process, analyzing 12% urea, 58% biuret, 2Q~ cyanuric acid,
and, 10~ related homologs, by weight. As will be noted, the
amount of such pre-ormed powdered biuret reaction product
added was approximately 10% by weight of the mol~en crude
product. It has been determined that the amount oE this
powder addition, when employed, should be from about 5% to
about 25% relative to the weight of the molten crude
reaction product, depending upon availability and need from
the point of view of expediting the cooling of the crude
product. In this instance, after the approximately 10% by
weight powder addition, the resulting mixture analyzed as
follows: 32.9% urea~ 48.9% biuret, 1~.5% cyanuric acid, and
3.6% other homologs, with a softening point of 135C. As
will be understood by those skilled in the art to which the
invention is addressed, the proportionate reduction in urea
content and slight increase in content of the other
constituents also functions to raise the softening point o
the mixture somewhat, which in turn permits a somewhat
higher reaction temperature during the following stage of
pyrolyzation, consistent with the requirement that the
sub~equent stage of pyrolyzation occur with the reaction
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mass in particulate, essentially ~olid state, i~e. at a
temperature at or slightly below the softening point of th~
reaction mass.
Stirring of the crude intermediate reaction
product with powdered feed grade biuret added, was
continued, with the mixture becoming increasingly thicker
and attaining a cookie-dough like character when the
temperature reached about 110C. At this point the auger
was removed from the trough and material spread out on a
cement floor and allowed to fur~her cool. The material
while still dough-like was cut and chopped into chunks with
rakes and shovels and these discrete particles assumed a
rigid character and became hard at about 90~C. Upon cooling
of the particles to essentially room temperature, they were
passed through a hammermill and comminuted to a particle
size of 1 mesh and smaller (1 inch in diameter and smaller).
Comminuted particles in the 1 mesh to 4 mesh range were then
~egregated and placed in a 4' x 4' steel box with a fine
mesh screen in the bottom and the box was placed in a
circulating oven, with a product bed in the box having a
depth of about 22 inches. Particles smaller than 4 mesh
resulting from the comminution step were set aside for
remelting in the crude reactivn product of a subsequent
batch, and may be conveniently added thereto at the same
time as the feed grade biuret powder addition to the molten
crude product.
Then particulate reaction mass contained in the
box was then heated by a duct heater and forced air flow
upwardly through the box, to a temperature of 130C., the
air flow through the box being at about 6000 cubic feet per
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~2~
minute. Such heating and forced air flow was continued for
a period of 24 hours~ during which the reaction mask
particles retained their shape but become slightly soft with
some degree of surface fusion, which was easily broken by
stirring with the particles retaining their discrete
character. Heating was continued for a total period of 40
hours and at the end of this time the product, which
continued to be e~sentially free flowing irregular
particles, was removed from the oven and emptied from the
steel box, and analy~ed 14~ urea, 58% biuret, 17% cyanuric
acid and llg other homologs. Upon cooling the reaction
product was comminuted to powder form, in a hammermill, to a
particle size of 16-20 mesh, and was deemed suitable for use
as feed grade biuret withou~ further treatment.
ExamPle 5
600 pounds of urea was charged to a 100 gallon
reactor equipped with a 36 RW heater. q~he charge was heated
to a temperature of 152C. and the molten reaction mass held
at this temperature for a period of 4.5 hours, during which
time evolved ammonia gas was removed by air bubbled out
through the mass at the rate of 175 cubic feet per minute.
At the end of the 4.5 hour pyroly~ation period, 520 pounds
of molten pyrolysis produ~t were recovered from the reactor,
analyzing 33.7% urea, 14.8% cyanuric acid, 46.4~ biuret and
5.1% other homologs, with a softening point of 128C. The
temperature of the ~olten product as recovered from the
reactor was 149C. While stirring the product with a ribbon
auger in an open barrel trough~ 60 pounds of feed grade
biuret powder at 13C. and analyzing 12% urea, 18.8
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2~
cyanuric acid, 63.3% biuret, and 5.9% other homologs were
blended into the molten mass. An additional 123 pounds of
powdered material analyzing 34.5~ urea, 12.9% cyanuric acid,
47.9% biuret, and 5O5% other homologs (and obtained as fines
resulting from the comminution of the partially pyrolyzed
reaction product from a previous run) was also added to the
molten mass. These powder additions brought the temperature
of the whole mixture down to 115C., at which point the
mixture had a very thick dough-like consistency. This
material was next allowed to cool to about 72C. at which
point it was run through a hammermill and ground to 1 mesh
to 4 mesh particle size. The mixing, cooling and grinding
required a total of 45 minutes time. It is notable in this
respect that, without addition of powdered seed material in
lS the form of feed grade biuret powder and/or fines from a
previous comminution of partially pyrolyæed reaction
product, it can take as much as 16 hours for the molten
partially py.rolyzed reaction product as discharged from the
autoclave reactor to cool to the point where it is
solidified and may be comminuted~ It is thus apparent that
the powdered material addition acts as seed material or what
may be termed crystallization centers to materially improve
the solidification rate of the product and to provide a more
crystallin~ product, in contrast to the nature of the cooled
product wi~hout any seed ma~erial addition~ which is more
amorphous and gummy in character.
600 pounds of the comminuted feedstock material of
1 meæh to 4 mesh size was placed in a 4' x 4' s~.eel box with
a screen bottom and the box containing this bed o~ product,
with a bed thickness of 11 inches, was placed in a
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24~5~L
recirculating oven and heated to a temperature of 130C. by
forced air recirculation upwardly through the bed at a rate
of 6000 cubic feet per minute. After 2~4 hours of such
recirculation of the heated air, the particles were slightly
fused together and were manually broken apart by stirring
with a shovel. Heating was then continued by further forced
air recirculation at the same temperature for a total period
of 40 hours, during which time some ~8 pounds of ammonia and
some 22 pounds of sublimate evolved. The final product,
still in discrete particle form with only slight, readily
broken surface fusion of the particlesr analyzed 14.3% urea,
17.6% cyanuric acid, 62.7% biuret, and 5.4~ other homologs~
E~ample 6
900 pounds of urea was charged to a 100 gallon
reactor equipped with a 36 KW heater and melted and heated
to a temperature of 152C. for 2 1/2 hours, with a partial
pressure of 70 mm Hg being maintained, the evolved ammonia
b~ing captured in a water trap. Heating was continued for
an additional 4 hours. During this time 110 pounds of
ammonia was released and 30 pounds of the reaction mass was
lost as sublimate. 760 pounds of molten reaction product
was recovered from the reactor, and analyzed 34.2% urea,
12.3% cyanuric acid, 51.5% biuretr and 2% other homologs,
with a softening point o~ 127C. To this product was added
70 pounds of feed grade biuret analyzing 12.0% urea, 18.8%
cyanuric acid, 63.3% biuret, and 5.g% other homologs, and
the mixture when cooled was comminuted to particles of 1
mesh ~ize and less, as in Example 1. This comminuted
feedstock and some additional feedstock from a previous
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~24~
batch, making up a feed~tock mix weighing 1281.5 pounds with
a softening point of 141C., was loaded into the box and
oven described in Example 5, the depth of the material bed
after such loading being 22 inches. Heated air was then
blown through ~he bed by an upward recirculation by means of
a 6000 cubic feet per minute blower, with the air maintained
at a temperature of 132C. for a total heating time in the
oven of 56.75 hours, and the resulting product yield weighed
1079 pounds and analyzed 17~1% urea, 17.6% cyanuric acid,
54.1% biuret~ and 11.2% other homologs. In this instance the
particulate product bed in the box was not disturbed for the
entire period of heating. Although in this instance the
urea content of the final reaction product is somewhat high
and the biuret content slightly lower than specification
requirements for feed grade biuret, it will be recognized
that 3uch product can be mixed with other reaction products
such as that resulting in Example 4 or Example 5 to provide
a product mix which meets feed grade specifications, .if
desired~
Example-7
Feedstock for solid state pyrolyzation according
to the present invention was prepared as in Example 6 but
without any feed grade biuret powder addition. This
feedstock was comminuted to an average particle size of 4
mesh and analyzed 37.1% urea, 12.9% cyanuric acid, 47.8%
biuret, and 2.2% other homologs, with a softening point of
123C. The feedstock was placed in the 4~ x 4' steel box
with bottom screen and in the oven for forced air
recirculation as in Example 4 and the material was heated by
-27~
the recirculating forced air at a volume of 6000 cubic feet
per minute and at a temperature cf 132Co In 24 hours the
product had fused into a solid mass so that most of the
particle distinction had been lost and it was evident that
ammonia had been entrapped in the mass in the process, since
the blower was not able to drive air through the mass at
this point and the material after such heating analyzed
31.1% urea, 14.1% cyanuric acid, 50.2~ biuret and 4.6~ other
homologs.
Example 8
A further quantity of the same feedstock as in
Example 6 was arranged in a bed of 11 inches depth in the
same steel box and heated in the oven by recirculating air
lS as in Example 6 but with the temperature o the
recirculating air maintained at 121C., for a period of 72
hours. During this heating the product in the bed remained
in discrete particles, ammonia by-product evolved in the
approximate amount of 28 pounds r and the final reaction
product on cooling and recomminution analyzed 13.0% urea,
15.1~ cyanuric acid, 59.4% biuret, and 12.5% other homologs.
It will be understood that the foregoing examples
are merely illustrative of the invention and that variations
will readily occur to those skilled in the art to which the
invention is addressed as to the equipment and processing
conditions under which pyrolysis reactions characteristic of
the present invention proceed, within the scope of the
following claims.
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