GRANULES D'UREE ENDUITS DE POUDRE DE MELAMINE

UREA GRANULES COATED WITH MELAMINE POWDER

Abrégé anglais

Abstract
Urea granules coated with a powder in order to
prevent clumping, where the powder coating comprises from
0.01 to 0.6 % by weight of melamine, based on the total
weight of the urea granules.

Revendications

-4-
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follow:
1. Urea granules coated with powder in order to
prevent clumping, characterized in that the powder
coating comprises from 0.01 to 0.6 % by weight of
melamine, based on the total weight of the urea granules.
2. Urea granules according to claim 1,characterized
in that the powder coating comprises from 0.02 to 0.4 %
by weight of melamine, based on the total weight of the
urea granules.
3. Urea granules according to claim 1, characterized
in that the powder coating comprises impure mother liquor
melamine produced in the melamine synthesis process.
4. Use of the urea granules according to claim 1 in
the melamine synthesis.
O.Z. 970
10.03.1992

Description

2 0 9 1 1 2 9
t.
~rea granule~ coated with ~elamine powder
The invention relates to urea granules coa~ed
with melamine powder in order to prevent clumping.
Many granuLated or crystalline indu~trial
products, including urea, tend to clump on extended
storage or during transportation. This property generally
has an adverse effect on the quality, removal from
storage, scattering pxoperties, grain stability, int~r
alia.
In order to protect these products again~t
clumping, it i8 known to coat them with a dust. Suitable
~usts are finely divided lime, kieselguhr, talc, clay~
and the like. Furthermore, DE-A-2,039,599 discloses that
urea, mixed with biuret, ha~ virtually no tendency toward
clumping. However, in order to reduce clumping, these
agents must be added in larqe amounts in order to achieve
a satisfactory action.
Furthermore, US Patent 3,837,835 discloses that
granular substance~, such as, for example, fertilizers
based on ammonium nitrata, can be trea~ed with s-~ri-
azines which are substituted by relatively lon~ alkyl
chains or by ether groups. However, substituted s-tri-
azin~s of this type are relatively complex compounds
which~ in addition, have an in~er~ering effect during any
~5 further conversion o~ the urea granules into melamine.
It has now been found, unexpectedly, that clump-
ing of urea granule~ can be reduced to a large extent by
admixiny melamine powder with the urea granules.
The invention therefore relates to urea granules
~hich haYe been coated with a powder in order to preYent
clumping, which are char~cterized in that the po~der
coating comprises from 0.01 to 0.6 percent by weight of
melamine, ba~ed on the total w2ight of the urea granules.
Melamine can be employed here as a commercially
available, purified product. However, it is also possible
~o use Lmpure melamine from the melamine syn~hesis
process~ known as mother liquor melamine, since the small

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amounts of impurities, for example, ammelinP or a~melide,
do not have any interfering effect during any further
conversion of the urea granules into melamine, since
the~e impurities are for the moat part re~converted into
melamine in the melamine process.
Even if the urea granules coated with mother
liquor melamine are usedt for example in the fertilizer
or feeds industries, no disadvantage arises due to the
small amounts of impurities. The mel~mine in powder form
is admixed with the urea granules in powder drum~,
vibration channels or other suitable devic~s at room
t~mperature. In order to ~implify distribution onto the
urea granules and in order to achieve a uniform action
with the greatest possible e~fect u~ing the smalle3t
possible amount of additive, melamine i8 used in the most
finely divided form possible. The duration of the mixi~g
operation depends on the choice of mixing unit and on the
desired throughput. The amount of melamine is from 0oO1
to 0.6 % by weight, preferably from about 0.02 to 0.4 ~
by weight, based on the total weight of the urea
granules.
The reduction in clumping of urea due to admix-
ture of melamine was determined by determining the hear
force by the method of Jenike (for example Chem. Tech-
nologie, Winnacker-K~chlex, 4th Edition, Volume 1, page
120). In thi~ determination, the s~mple8 were in each
CaBe loaded for 23 hours at room temperature with a
piston having a surface area of 22.9 cm2 or a diameter of
5.4 cm. ~he pre~ure exerted was 15.5 N/c~2.
The experiments carried out show that, after
admixture of 0.1 ~ by weight or 0.035 ~ by weight of pure
melamlne or of 0.1 ~ by weight of mother liquor melamine;
the shear force was reduced by up to in excs~s of 50 %,
wherea~ ~ig~ificantly larger amounts, for example 5 % by
weight, had to be added to achieve the ~ame action in the
case of dust~ alrea~y known from the lit~rature, such a ,
for example, biuret.

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~xample 1:
1000 g of urea granule~ having a water content of
0.26 %, determined by the method of Karl-Fischer, were
mixed with 1 g (0.1 % by weight) or 2 g ~0.2 % by weight)
of melamisle having a water content of 0.13 ~ ~y weight
for lS minutes by means of a laboratory mixer. Admixture
of only 0.1 ~ of melamine reduced th~ shear force from
43.7 N by half (22 N~. Admixture of 0.2 % of melamine
achieved a reduction in the ~hear force to 16.8 N.
~xample 2:
1000 g of urea granules having a water content of
0O25 % ~y weight, were mixed with 1 g (0.1 % by weight~
of mother liguor melamine having a water content of 1.3
by weight for 15 minute~ in a laboratory mixer. A reduc-
tion in the shear force from 24.2 N to 14.0 N wa8
achieved.
~xample 3:
37,500 g of urea granules having a water content
of 0.30 ~ were mixed with melamine having a water content
of 0. 06 ~ for 15 minutes in a concrete mixer. Addition o
13 g (0.035 % by weight) of melamine, ba~ed on the urea
granule~, reduced the shear force by mora than hal~, from
52.2 N to 22.5 N.
Bxample 4: Comparative ~xample
1000 g of urea granule~ having a wat0r content of
0.26 % were mixed with biuret, p.a. grade from Merck,
having a water content of 2.9~ % for 15 minute~ in a
laboratory mixer. Only on admixture of 53 g (5 % by
weight) of biuret was an approximate halving of the shear
force from 50 N to 29 N achieved.