Catalyst for melamine production

Article abstract of DOI:10.1023/A:1022247111693

A novel electrolytic method for preparing the catalyst (active aluminum oxide) for melamine synthesis and a process for catalytic synthesis of melamine from urea are proposed.

Full text of DOI:10.1023/A:1022247111693

Russian Journal of Applied Chemistry, Vol. 75, No. 11, 2002, pp. 1883 1884. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 11,
2002, pp. 1920 1921.
Original Russian Text Copyright
2002 by Moiseeva, Kurylev, Pomerantsev, Tubolkin.
BRIEF
COMMUNICATIONS
Catalyst for Melamine Production
I. D. Moiseeva, A. Yu. Kurylev, V. M. Pomerantsev, and A. F. Tubolkin
Novomoskovsk Institute, Mendeleev Russian University of Chemical Engineering, Novomoskovsk,
Tula oblast, Russia
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received February 5, 2002
Abstract A novel electrolytic method for preparing the catalyst (active aluminum oxide) for melamine
synthesis and a process for catalytic synthesis of melamine from urea are proposed.
Melamine (1,3,5-triamino-2,4,6-triazine) is a valu-
able precursor in production of plastics, lacquers, and
adhesives exhibiting high mechanical strength, sta-
bility in hot water and in organic solvents, low elec-
trical conductivity, and high thermal stability. These
materials based on melamine formaldehyde resin are
widely used in various branches of industry [1, 2].
method for preparing Al(OH) from pure metallic
3
aluminum by electrolytic precipitation. The precipitate
was molded in grains by a sol gel process and then
was thermally treated to obtain granulated -Al O [3].
2
3
Two electrodes (200 120 15-mm plates) made
from metallic aluminum (99.9 wt % Al) were placed
parallel to each other at a distance of 10 15 cm in a
glass vessel filled with distilled water containing 2
4 wt % NH NO as an electrolyte; dc electrolysis was
To synthesize melamine from urea, we developed a
catalyst, active aluminum oxide with the specific sur-
4
3
2
1
face of about 300 400 m g .
performed at I = 27 A and U = 65 V.
A goal of this work was to develop a low-waste
procedure for preparing the catalyst, by ensuring
stable conditions of granule formation and improved
quality of the target product.
A gel-like Al(OH) precipitate was formed on the
3
anode. The pulp was separated at the solid : liquid
ratio of 1 : 8 by centrifuging, and a substance with the
solid : liquid ratio of 1 : 4 and pH 7 was obtained.
Concentrated chemically pure grade HCl was added to
decrease pH to 3 4. A transparent thixotropic colloid
of basic aluminum chloride (BAC) was thus obtained
by the reaction [4]
We improved a process for production of Al(OH)
3
and -Al O to increase the melamine content in the
2
3
target product from 80 to 96 98%. Initially we took
commercial aluminum hydroxide with the specific sur-
2
1
face area of 80 120 m g . Impurities present in it
(up to 0.1 wt % Na O, 0.1 SiO , and 0.4 Fe O )
2Al(OH)3 + HCl
Al2(OH)5Cl + H2O
3
(1)
2
2
2 3
adversely affected the quality of the -Al O obtained
2
3
with the Al O content of 50 g dm ; it was aged at
2
3
(the melamine yield was about 80%). To remove
room temperature for 12 24 h.
them, commercial aluminum hydroxide was reprecipi-
A drop-oil method was used to mold granules.
A molding mass was poured in a cone-shaped vessel
and fed through a pipette 1.5 mm in diameter at a rate
tated from chemically pure grade HNO , washed to
3
remove ammonia, molded, dried, and calcined. The
thus prepared -Al O provided the melamine yield of
2
3
1
up to 88.5% and had the specific surface area of 160
of 2 3 drops s into a molder, a cylinder filled with
2
1
170 m g , which is insufficient for commercial pro-
duction of melamine.
a two-phase liquid (3 4-cm layer of kerosene to form
drops and 25% aqueous solution of urea to form three-
dimensional gel structure; the layer thick was suf-
ficient for neutralization of granules for 3 4 min).
In the first stage, granules were dried for 1 day in air.
In the second stage, they were dried in a vacuum drier
for 2 3 days at 40 C. Then the temperature was ele-
Nevertheless, the above study showed that purifica-
tion of alumina increases the process selectivity.
However, the above purification procedure is unaccep-
table, because the increase in the number of reprecipi-
tation stages complicates the technology and increases
the washwater amount. Therefore, we developed a
1
vated at a 10 deg h rate to 150 C, and at this tem-
1070-4272/02/7511-1883$27.00 2002 MAIK Nauka/Interperiodica

1884
MOISEEVA et al.
A mixture of cyanic acid and ammonia is fed to
the catalyst bed, where melamine is formed by the
reaction
6HNCO
C3H6N6 + 3CO2
(3)
at a pressure of 0.1 0.2 MPa.
The reaction products are sublimed in vessel 3 at
180 200 C. Melamine as a white finely dispersed
powder is unloaded through hatch 4. An NH + CO
3
gas mixture from the sublimer is bubbled through
water in vessel 5, where ammonia partially dissolves.
The urea conversion amounts to 97 98%, and the
yield of the target product is 98% [5].
To atmosphere
CONCLUSION
Melamine
The developed procedure for preparing granulated
-Al O provides high specific surface area of the
catalyst (up to 300 400 m g ) and elevated selec-
tivity with respect to the target product, melamine
(yield 96 98%).
2
3
Scheme of the pilot setup for melamine production from
urea: (1) melter, (2) catalytic reactor, (3) sublimer with
packings for collecting product, (4) hatch for unloading
the target product, (5) bubbler with ammonia water,
(6, 7) rotameters, (8, 9) ammonia heaters, (10 12) valves,
and (13) injector.
2
1
REFERENCES
perature the granules were kept for 4 h. In the third
stage, granules were calcined in a muffle furnace ac-
cording to the following schedule: heating at a rate of
1. Hermann, D.F., Nitrogen, 1973, no. 83, pp. 49 50.
2. Haines, W., Nitrogen, 1966, no. 40, pp. 32 34.
1
1
20 deg h from 150 to 200 C, 50 deg h from 200
3. Moiseev, I.D.,, Kurylev, A.Yu., and Pomerantsev, V.M.,
Abstracts of Papers, Konferentsiya molodykh uchenykh,
Novomoskovskii institut Rossiiskogo khimiko-tekhnolo-
gicheskogo universiteta im. D.I.Mendeleeva (Conf. of
Young Scientists, Novomoskovsk Inst., Mendeleev
Russian Univ. of Chemical Engineering), Novomos-
kovsk: NI RKhTU, 2001, pp. 200 201.
1
to 500 C, 100 deg h from 500 to 900 C; keeping at
900 C for 4 h; and gradual cooling and sampling.
Production of the catalyst was tested in a pilot setup
1
(see figure).
The urea melt is fed from a melter 1 at 140 160 C
under a pressure of 0.8 MPa into the reactor 2. Am-
monia heated to 350 500 C is also fed at the melt to
gas wt ratio of 1 : (7 9). In the reactor, the melt is
entrained with the gas and decomposes by the reaction
4. Sychev, M.M., Neorganicheskie klei (Inorganic Adhe-
sives), Leningrad: Khimiya, 1974.
5. Moiseev. I.D., Kurylev, A.Yu., and Pomerantsev, V.M.,
Abstracts of Papers, XIV Mezhdunarodnaya konferen-
tsiya Uspekhi v khimii i khimicheskoi tekhnologii
(XIV Int. Conf. Progress in Chemistry and Chemical
Technology), Moscow: RKhTU, 2001, pp. 20 23.
CO(NH2)2
HNCO + NH3.
(2)
1
The pilot setup was developed in Novomoskovsk Institute,
Mendeleev Russian University of Chemical Engineering.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 11 2002