Production of animal feed grade biuret

Preparation of a composition particularly suitable for use as feedstock in the production of animal feed grade biuret by solid state pyrolyzation thereof in a recirculating oven, which composition comprises from about 37% to about 25% urea, from about 45% to about 60% biuret, and from about 3% to about 20% cyanuric acid, by weight, such preparation involving sparging air or other non-reactive gas through a urea charge at a temperature of from about 145.degree. C. to about 165.degree. C. and at a rate of between about two to about ten cu. ft. of gas/hr/lb of urea for a period of at least four hours, then cooling and comminuting the product.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the production of a partially pyrolyzed 
urea composition particularly suitable for use as the feedstock for the 
production of animal feed grade biuret, and containing controlled amounts 
of biuret, cyanuric acid, triuret, and other homologs. Production of such 
composition involves the controlled pyrolysis of urea at elevated 
temperatures above the melting point of urea and at a pressure above 
atmospheric while subjected to sparged air or other non-reactive gas at 
the rate of about two to about ten cubic feet of gas per hour pound of 
urea, and cooling and comminuting the resulting product. 
2. Description of the Prior Art 
Harmon U.S. Pat. No. 2,145,392 discloses a basic process for pyrolysis of 
urea wherein urea is heated in the temperature range of 
130.degree.-205.degree. C. while under partial vacuum in the absence of 
any catalyst to produce principally biuret, cyanuric acid, and other 
related compounds. Biuret is a useful chemical compound having 
considerable utility in prepared feeds for ruminant animals. Crude 
technical mixtures of urea, biuret, triuret, and cyanuric acid have long 
been used as cattle feed supplements. The United States Department of 
Agriculture, Food and Drug Administration has approved pyrolyzed urea 
compositions having not more than 15% urea, not less than 55% biuret, and 
not more than 30% of the sum of cyanuric acid, triuret, or other related 
compounds, and not more than 0.5% of oil, by weight, as a cattle feed 
additive. 
Garbo U.S. Pat. No. 2,525,049 discloses much the same process for producing 
biuret from urea as is disclosed by Harmon U.S. Pat. No. 2,145,392, with 
the added feature of accelerating the reaction by the use of one or more 
catalysts and in some instances use also of a hydrocarbon fluidizing 
medium such as naphthalene or kerosene. 
Olin U.S. Pat. No., 2,370,065 presents another teaching of use of an 
entraining agent such as toluene or naphtha to aid in the removal of 
ammonia when pyrolyzing urea to produce biuret. 
Kluge U.S. Pat. No. 3,150,177 presents a biuret production process similar 
to that disclosed by Harmon U.S. Pat. No. 2,145,392 coupled with the use 
of disodium phosphate or boric acid as a catalyst. 
Kamlet U.S. Pat. No. 2,768,895 presents a rather omnibus disclosure of use 
of biuret rich urea condensation products as animal feed. Kamlet U.S. Pat. 
No. 3,453,098 presents a variation of the process wherein biuret rich urea 
autocondensation products are dissolved in boiling water and then cooled 
to recrystallize the biuret products, which are then said to contain not 
less than 95% biuret and be characterized by complete removal of ammonium 
cyanate, the product thus being rendered suitable for use as a depot 
fertilizer without the phytotoxic consequences said to be characteristic 
of such a product when substantial ammonium cyanate is present. 
Colby et al, U.S. Pat. No. 2,861,886 presents another early disclosure of 
use of biuret rich compositions used as constituent ingredients of animal 
feed supplements. 
Great Britain Pat. No. 1,155,907 discloses the pyrolysis of urea to product 
a biuret rich reaction product, including the separation of a urea 
containing mixture from the reaction product, and recycling of the 
separated urea containing mixture to the reactor as a continuous process. 
Japan Patent Publication No. 47-41888 (1972) discloses the production of 
purified biuret. The English language abstract published with Japan Patent 
Publication No. 47-41888 states that this publication discloses a process 
for preparing purified biuret by treating urea decomposition products with 
hot water, filtering the obtained mixture, treating the filtrate with 
aqueous ammonia and cooling it to below 40.degree. C., separating the 
precipitated biuret, recovering ammonia from the supernatant liquor by 
evaporating water, and recycling residual urea after decomposing it by 
heating. Substantially pure biuret (separated from cyanuric acid and 
triuret) is obtained. Such abstract continues to give the following 
example. 100 grams urea is decomposed at 150.degree. C. while introducing 
22.0 l./min. air for 2 hours to give 38.8 grams biuret, 4.0 grams cyanuric 
aid, 3.8 grams triuret and 44.0 grams unreacted urea. The products are 
partly dissolved in 150 ml. water at 70.degree. C. The mixture is filtered 
and the filtrate is treated with 5 grams NH.sub.3 and cooled to 40.degree. 
C. The precipitate (24.1 grams; yield 98.8%) is biuret containing 1.2% 
urea and only traces of cyanuric acid and triuret. 
Formaini et al in U.S. Pat. No. 3,057,918 proposes a continuous process for 
the production of biuret wherein new urea plus recycled previously 
pyrolyzed urea is sparged with air while molten at elevated temperature to 
produce a feedstock for a pressure digestion step whereby a relatively 
pure biuret is separated from the mother liquor of the ammonia digestion 
step by a controlled vacuum crystallization and the unwanted byproduct is 
evaporated to give the solid recycle material added along with urea to 
make the feedstock for the initial pyrolysis step. The urea content of the 
typical feedstock entering the ammonia digestion step has the following 
analysis: 
______________________________________ 
Biuret 28-42% 
Urea 65-40% 
Cyanuric Acid 3-14% 
Triuret 5-7% 
______________________________________ 
This is to be contrasted with the typical analysis for the feedstock of the 
present invention which is: 
______________________________________ 
Biuret 45-60% 
Urea 37-25% 
Cyanuric Acid 3-20% 
Triuret 3-10% 
______________________________________ 
The pyrolysis of urea to produce biuret, triuret, cyanuric acid, ammelide, 
melamine and other homologs, is well known. When urea is pyrolyzed ammonia 
is always an accompanying byproduct. It was early established by Harmon in 
U.S. Pat. No. 2,145,392 that the pyrolysis of urea to produce biuret was 
aided by the application of controlled vacuum whereby the byproduct 
ammonia was effectively removed from the reactor thus lowering the partial 
pressure of ammonia and thereby driving the pyrolysis reaction toward 
higher biuret content. The use of volatile entraining agents such as 
toluene to sweep out byproduct ammonia in biuret manufacture was early 
suggested by Olin in U.S. Pat. No. 2,370,065. The use of gases such as 
nitrogen or air to sweep out byproduct ammonia formed during urea 
pyrolysis is suggested in U.S. Pat. No. 2,918,467 by Hibbitts et al in the 
production of a pyrolyzed urea feedstock used in the production of 
melamine. Formaini U.S. Pat. No. 3,093,941 uses air as the stripping gas 
to remove byproduct ammonia formed during urea pyrolysis in the production 
of a pyrolyzed urea feedstock used in the production of cyanuric acid. 
Formaini U.S. Pat. No. 3,057,918 uses air as the stripping gas to remove 
byproduct ammonia formed during continuous urea pyrolysis in the 
production of a pyrolyzed urea feedstock used in an extraction process to 
produce substantially pure biuret. 
SUMMARY OF THE INVENTION 
In the present invention air or like nonreactive gas is used as the 
stripping gas to remove byproduct ammonia formed during urea pyrolysis to 
produce a feedstock having a controlled fusion point which is attained by 
controlling the analysis of the feedstock in regard to the urea, biuret, 
triuret, and cyanuric acid content. A suitable feedstock product for use 
in the process claimed in our copending U.S. patent application Ser. No. 
265,550 is one that has the following characteristics: 
______________________________________ 
Chemical Analysis 
______________________________________ 
% Urea 37-25% 
% Biuret 45-60% 
% Cyanuric Acid 3-20% 
% Triuret 3-10% 
Melting Point 110-130.degree. C. 
______________________________________ 
Feed grade biuret is a mixture of nitrogen containing chemicals produced by 
the pyrolysis of urea. The Food and Drug Administration of the U.S. 
Department of Agriculture has promulgated a specification for feed grade 
biuret (see Code of Federal Regulations, Title 21, Section 573,220), as 
follows: 
______________________________________ 
Minimum biuret content 
55% 
Maximum urea content 
15% 
Maximum cyanuric acid, 
30% 
triuret, tetrauret, and 
others 
Maximum oil content 
0.5% 
______________________________________ 
In the two-stage process described in our aforesaid application Ser. No. 
265,550 partially pyrolyzed urea containing not over 25% cyanuric acid and 
more than 20% urea by weight is converted to animal feed grade biuret by 
subjecting the partially pyrolyzed urea feedstock in particulate form to a 
mild heat treatment in the substantially solid state with forced air flow 
through the particulate reaction mass. A product results having a high 
concentration of biuret and a product with a minimum of 55% biuret, a 
maximum of 15% urea, and a maximum of 30% cyanuric acid and similar urea 
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 
such process a feedstock consisting of partially pyrolyzed urea in dry 
particulate form and containing not over about 25% cyanuric acid is 
treated in an oven with forced air recirculation at a temperature at or 
slightly below the softening point of particles, e.g. at a temperature 
between about 100.degree. C. and about 140.degree. C., and preferably 
between 115.degree. C. and 125.degree. C. for a period of time of 
generally between about 15 hours to about 200 hours 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 substantially sublimation can occur as 
well as evolution of ammonia from the product. 
The ground 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, preferably upwardly through each tray. The 
temperature is preferably thermostatically controlled to within 
.+-.3.degree. C. within the oven. 
The comminuted feestock is placed in or on a container porous to air, such 
as a tray or other box-type container with a screen or like foraminous 
bottom and open top, which arrangements provide what may be generically 
termed a fixed 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 
consistent with the need to maintain substantially and continuing 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 air, the depth of the 
particle bed and the volume of air flow past the particles. Thus, for 
example, in a situation where a fixed bed, 2 feet in depth, is composed of 
particles having an average mesh size of 8 mesh, a pressure drop of 0.16 
psig per foot of bed has been found satisfactory for the operating 
condition where the air and particles are heated to a temperature of 
127.degree. C. 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 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. 
Regarding the powdered material added to expedite crystallization and 
cooling of the partially pyrolyzed reaction product to make the feedstock 
for the solid state heating stage of the process, other powdered or 
comminuted materials can be used as the additive if they do not 
substantially lower the melting point of the reaction mass during the 
solid state pyrolyzation and provided they are advantageous or at least 
not deleterious to the end of the final reaction product, such as for 
animal feed or the like. In the case of the end use being animal feed, for 
example, advantageous additives may be calcium carbonate or calcium 
phosphate or other known animal feed additive. 
However, the powdered 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 fines 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 it being heated during the solid 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. The second stage of the process involves the continued 
pyrolyzation of the 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 
treatment, some urea is sublimed as may also be a slight amount of biuret 
and possibly others. The effect of this sublimation in reducing the urea 
content of the product is substantial and is an improtant part of the 
process when one is attempting to produce FDA acceptable material having 
not more than 15% urea. 
In practicing the present invention, the pyrolysis of urea to give the 
desired feedstock is accomplished by heating urea above its melting point 
(132.6.degree. C.) but not over about 165.degree. C. and at an absolute 
pressure of between 16.5 psia to about 24.5 psia while simultaneously 
blowing air through the molten urea mass at the rate of from about 2 to 
about 10 cubic feet of air/hour/pound of molten urea. 
The progress of the pyrolysis may be followed by monitoring the 
disappearance of urea in the melt as well as by the liberation of 
byproduct ammonia. 
In carrying out this invention the raw material urea may be charged to the 
reactor in either liquid form or in the solid form as urea crystals or 
urea prills of commerce. When the solid form is charged to a reactor the 
reactor functions as a melter during the melt up stage and the temperature 
remains close to the melting point until all of the solid urea has melted. 
It is usually desirable to have some air sparging through the charge 
during the meltup stage in order to prevent any urea from fouling or 
plugging up the air sparger. The air sparger is suitably simply a tube 
which carries the air from a pressurized air supply to its point of 
release at or near the bottom of the reactor, well beneath the surface of 
the urea mass. When urea crystals or prills are charged to a combined 
melter/reactor due account should be taken of the fact that the bulk 
density of the solid urea is about 50#/cu.ft., whereas the density of the 
molten urea is about 80#/cu.ft. In other words, a reactor charged full of 
urea prills will be only approximately half full when melted down. A 
practical method of fully utilizing the working capacity of a 
melter/reactor is to repeatedly add urea either as liquid or prills to the 
reactor as the original charge of solid urea melts down. The temperature 
of the air sparged urea pyrolysis may vary between about 145.degree. C. 
and about 165.degree. C. with the preferred temperature range between 
about 155.degree. C. to 165.degree. C. Heat may be supplied to melt the 
urea and to initiate the biuret producing reaction by heat transfer 
through the walls of the melter/reactor. Conventional heat transfer 
systems such as steam, Dowtherm heat exchange fluid, electrical resistance 
heating, or the like, may be used. Electrical resistance heating has the 
advantage of easy thermostatic control and precise control of the end 
point of the reaction as a function of kilowatt input. A significant 
amount of energy may be transferred as contained heat in the sparged air 
as a result of the heat of compression of the air coming from a pressure 
blower; for instance a 150 horsepower blower producing air under a 
pressure of 10 psig will raise the temperature of the sparging air from 
21.degree. C. to 60.degree. C. when delivering air at the rate of 1680 
C.F.M. in the aeration of a charge of 18,000 lbs. of prilled urea in a 
2500 gallon reactor. Since the compression heated sparging air comes in 
contact with virtually all of the individual prills of urea, the heat 
transfer in the early stage of the heat-up period is markedly improved 
over compressed air from an air storage tank where the heat of compression 
has been lost to the surrounding atmosphere. Significant heat may be 
recovered by taking the hot off-gas existing from one batch reactor 
operating at 155.degree. C. and using this hot gas to heat up another 
batch reactor charged with urea prills and starting a melt-up and reaction 
cycle. 
The sparging gas delivery nozzle or nozzles can be directed downwardly or 
radially of the reaction vessel and can also be oriented to accomplish 
air-lift stirring, if desired, in a manner known per se. Separate 
mechanical stirring of a reacting urea batch undergoing air sparging may 
also be used but is not necessary. The heat transfer through the walls of 
a reactor is enhanced by the stirring of the molten urea by the sparging 
air. Where the hot off-gas from one reactor is used to heat up another, 
cold reactor, any sublimed urea or urea dust in the hot off-gas from one 
reactor is trapped in the bed of urea prills of the second reactor which 
acts thereby as a filter medium. 
An important function of sparging air through molten urea undergoing 
reaction to produce biuret according to the following equation: 
EQU 2 NH.sub.2 CONH.sub.2 .fwdarw.NH.sub.2 CONHCONH.sub.2 +NH.sub.3 .uparw. 
is that the removal of byproduct NH.sub.3 is facilitated. This is in 
contrast with the practice of Harmon in U.S. Pat. No. 2,145,392 which 
employs a vacuum to remove the byproduct NH.sub.3. Ammonia plus water 
vapor is by nature a corrosive system and it is necessary to protect the 
metal parts of any associated blower system. If one attempts to catch the 
off-gas ammonia in an aqueous trap operating under vacuum with the trap 
between the reactor and the vacuum source the amount of vacuum attainable 
is limited by the vapor pressure of the water and ultimately only a dilute 
ammonia water solution is produced. This severely limits the potentially 
attainable vacuum. When air sparging is used to hasten the removal of 
byproduct ammonia in the pyrolysis of urea the blower is never in contact 
with any ammonia released during the formation of biuret and the air 
passing through the reactor and containing the byproduct ammonia may be 
trapped in an aqueous trap without any corrosion of the blower parts. 
An important part of this invention is the recovery of byproduct ammonia as 
aqueous ammonia, also known in the trade as aqua ammonia, for use as 
agricultural fertilizer. This is accomplished by sparging air at a rate of 
from about 2 to about 10 cubic feet (measured at standard temperature and 
pressure) per hour per lb. of urea undergoing pyrolysis, and passing the 
hot off-gas containing sublimed urea and sublimed biuret through a water 
solution of ammonia in equilibrium with the ammonia in the off-gas and 
containing urea, biuret, and other pyrolysis reaction products in solution 
whereby any sublimed urea and biuret or any urea dust is trapped in the 
solution but the gaseous ammonia is not. In practice this urea and biuret 
particulate and sublimate scrubbing should proceed with the aqueous 
solution at a temperature corresponding to the wet bulb temperatures of 
the hot off-gas. The cooled and scrubbed gas existing from the scrubber is 
then admitted to the bottom of a counter-current absorber column in which 
water entering at the top of the absorber column is the makeup for the 
liquid phase. A relatively concentrated aqueous ammonia phase exits from 
the bottom of the absorber column. The counter-current absorber column has 
sufficient equivalent absorber plates to remove the ammonia in the gas 
stream to the desired degree.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Example I 
600 pounds of urea prills were charged into a 100 gallon 316 stainless 
steel reactor equipped with electrical resistance heaters rated at 36 
kilowatts. The 100 gallon reactor was 24" inside diameter in size and had 
conical heads top and bottom, each having a depth of 3.5". The height of 
the vertical side between the top and bottom heads was 48". The reactor 
was equipped with a top-mounted anchor type stirrer operating at 160 RPM. 
The upper head had one 8" flanged opening, one 4" flanged opening and 
three 2" flanged openings. The bottom head had one 2" flanged opening in 
the center which was used to introduce air into the urea mass from below 
and also to drain the molten product from the reactor. 600 pounds of urea 
amounts to 53.1 gallons when melted and filled the reactor to a depth of 
about 2.44' above the bottom drain. 
The charge of 600 pounds of urea was melted and heated to a temperature of 
152.degree. C. and held at that temperature for a period of 4.5 hours, 
during which time the evolved ammonia gas was removed by air introduced at 
15.82 psia and bubbled through the mass at the rate of 175 cubic feet per 
minute. The off-gas was run through a water trap. At the end of the 4.5 
hour pyrolyzation period, 520 pounds of molten pyrolysis product was 
recovered at a temperature of 149.degree. C., and upon analysis had the 
following composition; 33.7% urea, 14.8 cyanuric acid, 46.4% biuret, and 
5.1% other homologs, by weight, with a softening point of 128.degree. C. 
The molten pyrolysis product was mixed with 60 pounds of feed grade biuret 
powder analyzing 12% urea, 18.8% cyanuric acid, 63.3% biuret, and 5.9% 
other homologs, by weight, and then mixed with 123 pounds of powdered 
material analyzing 34.5% urea, 12.9% cyanuric acid, 47.9% biuret, and 5.5% 
other homologs, by weight, in order to provide crystallization centers to 
hasten crystallization, and was then allowed to cool to about 72.degree. 
C. This composite product was then comminuted to a product having a mesh 
size between 1 and 4 mesh and used as a feedstock in the oven pyrolyzation 
process of our patent application Ser. No. 265,550, noting particularly 
the solid state treatment thereof as set forth in the last portion of 
Example 5 of said application Ser. No. 265,550. Specifically, as stated in 
said Example 5, 600 lbs. of the comminuted feedstock material was placed 
in a 4'.times.4' steel box with a screen bottom and the box containing 
this bed of product, with a bed thickness of 11" was placed in a 
recirculating oven and heated to a temperature of 130.degree. C. by forced 
air recirculation upwardly through the bed at a rate of 6000 cubic feet 
per minute. After 24 hours of such recirculation of the heated air, the 
particles were slightly fused together and were manually broken apart by 
stirring with a shovel. The heating was then continued by further forced 
air recirculation at the same temperature for a total period of 40 hours, 
during which time some 28 lbs. of ammonia and some 22 lbs. of sublimate 
evolved. The final product, still in discrete particle form with only 
slight, readily broken surface fusion of the particles, analyzed 14.3% 
urea, 17.6% cyanuric acid, 62.7% biuret, and 5.4% other homologs, by 
weight. The aeration rate during this second phase of the process was 17.5 
cubic feet/hour/lb. of feedstock. As will be noted, the resultant product 
has a composition well within the feed grade biuret specification 
established by the Food and Drug Administration of the U.S. Department of 
Agriculture and may be used for this purpose without further treatment, 
except for further comminution of the product, if desired. 
Example II 
In the following example the reaction was carried out in a 750 gallon 
reactor made of 316 stainless steel having an internal diameter of 58" and 
dished heads top and bottom of radius 54". The height between the dished 
heads was 65". The upper dished head had an 18" manhole, one 10" centrally 
mounted flanged opening, two 8" flanged openings, and four 3" flanged 
openings. The bottom dish had one centrally mounted 2" flanged opening and 
two other 2" flanged openings. An air sparger line made of 5"O.D. pipe 
projected through one of the 8" flanged openings downward as far as 
possible and then made a right angle turn to support horizontally a closed 
end piece of 5" O.D. pipe having six 5/8" dia. holes and fourteen 1/2" 
dia. holes in its 56" length. All of the air at 645 C.F.M. was exhausted 
through these twenty holes and provided intimate contact of the air with 
the molten urea. The urea was charged through the 18" manhole in the upper 
head and compressed air at 25.7 psia was introduced through the sparger. 
The reactor was heated by electric resistance strip heaters attached to 
the outside shell. Heaters of 135 KW rating were placed on the vertical 
side wall and heaters of 15 K.W. rating were placed on the bottom dish for 
a total of 150 K.W. energy input. All of the heaters were thermostatically 
controlled responsive to a temperature probe immersed in the reaction 
mass. 
An initial charge of 4700 lbs. of urea prills was heated to 148.9.degree. 
C. in 2 hours 41 minutes while subjected to an airflow of 645 C.F.M. at 
which time the air flow was stopped and 1184 lbs. additional urea prills 
were added to give a total charge of 5884 lbs. urea. The temperature 
dropped to 128.9.degree. C. The airflow was then resumed and continued to 
the end of the reaction period. 1 hour and 4 minutes after the air flow 
was resumed, the temperature had risen to 150.5.degree. C. at which time a 
total of 534 KW hrs of electrical energy had been consumed. The 
temperature was maintained at 150.5.degree. C. for an additional 2 hours, 
after which the temperature varied between 150.5.degree. C. and 
156.1.degree. C. over a period of an additional 2 hours, at which time the 
product was removed from the reactor and cooled to a temperature of 
37.degree. C. and analyzed using the well known HPLC method. The resulting 
analysis was: urea 31.3%, cyanuric acid 14.0%, biuret 46.2%, triuret 8.5%, 
by weight. The heating up time to reaction temperature was 3 hours 44 
minutes. The reaction time was 4 hours making the total cycle time 7 hours 
44 minutes. This product was eminently suitable for conversion to feed 
grade biuret according to the procedure set forth in our copending U.S. 
patent application Ser. No. 265,550. The product was a tan cream color, 
was substantially odorless, and was easily comminuted into through 1 mesh 
particle size for the oven treatment to produce feed grade biuret. The air 
pressure on the reactor was 24.7 psia at the start during the meltup 
period and then declined to 21.7 psia during the reaction period. With 
5884 lbs. of urea prills charged and 645 C.F.M. of air sparged, the 
aeration rate was 6.58 cu. ft. of air/hour/lb. of urea, producing a 
product analyzing 31.3% urea. 
Example III 
A charge of 4800 pounds of urea prills was placed in the 750 gallon reactor 
described in Example II and heated from 22.degree. C. to 149.4.degree. C. 
in 3 hours during which time 175 C.F.M. of air was passed thru the molten 
urea. The temperature of the molten urea was then maintained at about 
150.degree. C. for an additional 8.0 hours. The product was then removed 
from the reactor and cooled. The product analyzed 44.3% urea and 37.85% 
biuret, by weight. This shows the effect of aeration at the rate of 2.19 
cubic feet of air/hour/lb. of urea on the disappearance of urea and 
production of biuret when the reaction is carried out at about 150.degree. 
C. During the run the air pressure in the reactor was 21.7 psia at the 
start and 20.7 psia at the conclusion. The off gas ammonia was absorbed in 
water. 
In carrying out the invention we have discoverd that the melting point of 
the crude urea pyrolysis product to be used as the feedstock for biuret 
producing oven pyrolyzation should preferably be between about 110.degree. 
C. and about 130.degree. C. and preferably as high as possible to prevent 
fusion during the oven treatment, since fusion interferes with heat 
transfer from the hot oven air and the sublimation of urea and byproduct 
ammonia gas removal. The melting point of the feedstock is affected mostly 
by the proportionate amounts of urea, biuret, and cyanuric acid. 
Generally, increased urea content lowers the melting point whereas 
increased cyanuric acid content raises the melting point and is a function 
of the phase diagram characteristic of all the urea pyrolysis products. 
For example, the M.P. of the lowest melting eutectic mixture of urea and 
biuret is 111.1.degree. C. and has the composition 30% urea and 70% 
biuret, by weight. For the feedstock of utility in our invention, it is 
considered that the urea analysis should be not over about 37% and may 
have any lower value down to about 25%, by weight. The cyanuric acid 
analysis of a feedstock of utility in our invention may vary from about 3% 
to 20%, by weight. The triuret analysis may vary from about 3% to 10%, by 
weight. 
Examples IV-IX 
The following reaction runs Nos. 4 through 9 were made in the equipment of 
Example II and following the same experimental procedure as in Example II. 
The results of the runs are tabulated in the following TABLE ONE together 
with the published results of the example given in Japan No. 47-41888. 
TABLE ONE 
__________________________________________________________________________ 
UREA TOTAL RATE OF 
CU. FT. 
REACTION 
REACTION 
CHARGED TO 
AIR AIR FLOW 
AIR 
RUN TEMP TIME IN 
REACTOR FLOW IN 
CU. FT. 
PER LB. 
NO. .degree.C. 
HOURS IN LBS. CU. FT. 
PER HR. 
UREA 
__________________________________________________________________________ 
4 152.degree. C. 
4 6160 154,800 
38,700 25.1 
5 151 4.22 6300 163,314 
38,700 25.9 
6 152 5.5 6800 212,850 
38,700 31.3 
7 151 7.65 6000 167,535 
21,900 27.9 
8 152 6 5000 131,400 
21,900 26.3 
9 151 9.83 7520 215,277 
21,900 28.6 
JAPAN 
150 2 0.22 93.2 46.6 423.6 
47-4188 
__________________________________________________________________________ 
CU. FT. POWER 
AIR ANALYSIS USAGE MELTING 
PER HR % KWHr POINT OF 
RUN PER LB. 
% % CYANURIC 
% PER LB. 
PRODUCT 
NO. UREA UREA BIURET 
ACID TRIURET 
UREA .degree.C. 
__________________________________________________________________________ 
4 6.28 31.1 45.1 14.2 9.6 0.1466 
-- 
5 6.14 31.8 46.8 13.1 8.3 0.1365 
120 
6 5.69 32.3 45.9 15.1 6.7 0.1326 
115 
7 3.65 36.0 40.6 15.2 8.2 0.1448 
122 
8 4.38 36.2 42.5 13.0 8.3 0.1424 
110 
9 2.91 37.4 41.8 16.6 4.2 0.1360 
116 
JAPAN 
211.8 
44.0 38.8 4.0 3.8 -- -- 
47-4188 
__________________________________________________________________________ 
An important part of our invention is the discovery that the rate of 
aeration in cubic feet of air/hour/lb. of urea, over a relatively narrow 
range (2-10 cu.ft/hr/lb. urea) is the major factor in controlling the 
physical and chemical properties of the feedstock product which render it 
suitable for solid state pyrolysis to produce feed grade biuret. 
As will be readily understood by those skilled in the art, variations and 
modifications are possible in practice of the present invention. Thus, 
simply by way of further example, while air has been the primary sparging 
gas referred to in the foregoing Examples and is believed preferable for 
practice of the invention because of economic considerations, it is 
considered technically possible to utilize other gases or mixtures of 
gases for sparging purposes in the process, so long as the gas or mixture 
of gases is nonreactive in relation to the pyrolysis reactions. Another 
example of such a nonreactive gas is nitrogen and also the class of gases 
known as inert gases.