Title of Invention

CATALYST FOR OXIDATION OF METHANOL TO FORMALDEHYDE

Abstract Catalysts for oxidation of methanol to formaldehyde, comprising a catalytic mixtures Fe2(MoO4)3 / MoO3, wherein the Mo/Fe atomic ratio ranges from 1.5 to 5, and cerium molybdate in a quantity from 0.1 to 10% by weight expressed as cerium.
Full Text CATALYST FOR OXIDATION OF METHANOL TO FORMALDEHYDE
The present invention relates to a catalyst for oxidation of methanol
to formaldehyde, to the method for preparing the catalyst, and to its use in
processes for preparing formaldehyde.
Catalysts used industrially in processes for oxidation of methanol to
formaldehyde (commonly termed iron molybdates, since Fe2(Mo04)3 is one
of the main active components), comprise both Fe2(Mo04)3 and
molybdenum trioxide (M0O3), uniformly distributed within the mass of the
catalyst.
In fresh catalysts, the Fe/Mo ratio is generally higher than 1.5 and not
higher than 5; however, it is subject to changes during oxidation due to
losses of M0O3, which occur mainly at the inlet of the fresh reagents in the
catalytic bed and in hot spot temperature regions (maximum temperature
inside the reactor).
The loss of M0O3 determines decreases in the performance of the
catalyst. This requires, after a more or less long period of use, the
replacement of the catalyst, which is a long and expensive operation.
The loss of M0O3 causes, in addition to a reduction in the
performance of the catalyst, the collapse of the catalytic bed and the
consequent increase in load losses.
The need is therefore felt for a catalyst capable of providing constant
performance for sufficiently long periods of time.
A catalyst has now been unexpectedly found which meets the above
cited requirements and comprises, in addition to the Fe2(Mo04)3/Mo03
mixtures (hereinafter termed "basic catalyst"), in which the Mo/Fe atomic
ratio is higher than 1.5 and does not exceed 5, also a compound of cerium,
molybdenum and oxygen (hereinafter cerium molybdate) in a quantity of
0.2-10% by weight expressed as cerium. Preferably, the basic catalyst has a
composition Fe2(Mo04)3 2Mo03, and cerium molybdate is present in
quantities from 0.2 to 5% by weight as cerium.
The cerium molybdate is added as molybdate of cerium in which
cerium can be tri- and/or tetravalent. During the activation of the catalyst
and/or during use, the starting cerium molybdate can undergo
transformations.
An X-ray diffractogram recorded on the finished catalyst in high-
resolution conditions (using a high signal-to-noise ratio, a 40-KV copper
tube, 40 microamperes, with CuKa=1.540 598A, range of 2 theta angle of 5
to 125, step 0.01 and collection time of 15 seconds/step) shows, at relatively
low cerium concentrations (3000 ppm), diffraction lines at lattice distances
d=8.44A, d=6.69A and d=4.79A, which do not appear in the diffractogram
of the catalyst without cerium, and, at higher cerium concentrations (17000
ppm), lines which appear at shorter lattice distances and specifically at
distances d=4.7A, d=4.29A, d=3.37A, d=3.04A, and d=2.75A, while the
lines observed at concentrations of 3000 ppm shift to higher lattice
distances, i.e., d=8.53A, d=6.74A and d=4.82A.
The addition of cerium molybdate has the effect of lowering
significantly the hot spot temperature with respect to a catalyst without
cerium molybdate, thus increasing the stability of the catalytic bed and
therefore its life. The other catalyst performances, such as conversion of
methanol and selectivity to formaldehyde, remain practically unchanged.
The catalyst is prepared starting from an aqueous suspension which
contains the base catalyst, obtained according to known methods such as for
example precipitation from a solution of a soluble ferric salt (FeCl3,
Fe(NO3)3 and similar soluble salts), mixed with a solution of a soluble
molybdate, such as a molybdate of an alkaline metal and/or ammonium
(suspension 1) and from a suspension of cerium molybdate (suspension 2)
obtained by reacting, while hot, an aqueous mixture of molybdenum trioxide
(M0O3) and cerium carbonate with a cerium title of 42% by weight, with a
Mo/Ce molar ratio of 1.5 to 3, preferably 1.6-2.1, until the generation of CO2
) ceases.
As an alternative, the suspension 2 can be obtained by mixing a
suspension of a molybdate of an alkaline metal and/or of ammonium with a
solution of a soluble trivalent cerium salt using a Mo/Ce ratio of 1.5 and
washing with water the resulting suspension until the undesired ions (NIV,
Na+ and the like) disappear.
The cerium molybdate can also be prepared and added to in the base
catalyst as tetravalent cerium molybdate by reacting a cerium salt and a
molybdate in an aqueous solution.
Suspensions 1 and 2 are then mixed together and the final product is
dried by spray drying so as to obtain a powder suitable to form pellets,
generally in the form of cylinders with a through bore or cylinders with a
three-lobed cross-section, provided with through bores at the lobes, which
have axes that are parallel to the axis of the granule, or having other shapes.
The granules have a height of generally 2 to 7 mm.
The granules are then activated by calcination in an oxidizing
atmosphere (air) at temperatures from 450° to 600 °C, preferably from 480°
to 580 °C.
Calcination lasts generally four or more hours.
The final catalyst has a specific surface (BET) of 1-7 m2/g, preferably
3-6 m7g.
It is also possible, but it is not one of the preferred methods, to mix
uniformly a powder of tri- and/or tetravalent cerium molybdate with a
powder or slurry of the base catalyst.
It has been found, and this is an additional aspect of the catalysts
according to the present invention, that said catalysts, particularly those
having a specific surface of 3-6 m2/g, can be used conveniently to form the
layer of the catalytic bed wherein the hot spot temperature is reached which
is in contact with the fresh reagents. Use of this layer allows to reduce
significantly the hot spot temperature in the catalytic bed.
The oxidation of the methanol is performed according to known
methods.
The gas mixtures comprise methanol in concentrations from 6 to 10%
by volume and oxygen in concentrations from 9 to 13% by volume, the
remainder being inert gas (for example nitrogen).
The reactor is of the bundle-tube type and the reaction heat is
removed by a cooling liquid, which circulates outside the pipes.
The linear velocity of the gases is comprised from 1 to 2 Nm/sec; the
temperature of the bath is from 250 to 320 °C.
Preferably, the gas mixture is fed into the reactor at a temperature
comprised from 120 to 160 °C.
The following examples are given to illustrate but not to limit the
scope of the invention.
EXAMPLES
A pilot plant used for catalytic tests of methanol oxidation to
formaldehyde is constituted by a tubular reactor immersed in a molten salt
bath. The reactor is 1950 mm long and has an inside diameter of 20.4 mm.
The catalyst is placed in the central part of the reactor so as to ensure
maximum isothermicity.
The supply gases are introduced from the top of the reactor. The air
and nitrogen are dosed by mass-flow and methanol is dosed by means of a
constant-flow pump and is first sent to an evaporator.
The stream exiting the reactor and the gases after the purging column
are analyzed by gas chromatography.
Example 1
Preparation of cerium molybdate
Reagents:
418.6 g cerium carbonate (Ce=42%)
271.0 g molybdenum trioxide
In a reactor with a capacity of approximately 10 liters, provided with
efficient mechanical agitation, temperature measurement and control
system, gas inlet and exit tube, the necessary demineralized water
(approximately 4 liters) and the molybdenum trioxide are loaded. Heating is
performed under agitation up to the temperature of 70 °C; cerium carbonate
is added over approximately 60 minutes and agitation and heating are
continued for approximately 5 hours. A dense and voluminous yellow
precipitate is formed. The amount of the obtained cerium molybdate is
sufficient to prepare approximately 58.6 kg of catalyst containing
approximately 0.3% cerium.
Example 2
Preparation of cerium molybdate
Reagents
2.5 kg cerium carbonate (Ce=42%).
1.62 kg molybdenum trioxide
In a reactor with a capacity of approximately 20 liters, equipped with
efficient mechanical agitation, temperature control and measurement
system, gas inlet and exit tube, the necessary demineralized water
(approximately 12 liters) is loaded together with the molybdenum trioxide.
Heating is performed under agitation up to the temperature of 70 °C; cerium
carbonate is added over approximately 60 minutes and agitation and heating
continue for approximately 5 hours. A dense and voluminous yellow
precipitate is formed. The resulting quantity of cerium molybdate is
sufficient to prepare approximately 61 kg of catalyst containing
approximately 1.7% cerium.
Comparison example 1
Preparation of a catalyst which does not contain cerium
Reagents:
23.8 kg molybdenum trioxide
40.0 kg sodium molybdate dihydrate
35.2 kg ferric chloride hexahydrate
In a container with a capacity of approximately 2.5 m3, equipped with
a mechanical agitator, a temperature measurement and control system,
approximately 1 m3 of demineralized water, the molybdenum trioxide and
the sodium molybdate are loaded. Heating is performed to 60 °C until the
solids dissolve completely.
The solution of ferric chloride, prepared separately (approximately
0.5 m3), is added over 90 minutes, keeping the reaction temperature constant
at 60 °C.
Once the addition of the ferric chloride has ended, agitation is
continued for 10 minutes, the mass is brought to the volume of 2 m3 with
demineralized water, agitation is stopped and cooling is allowed until room
temperature is reached.
After decantation of the precipitated solid, the supernatant clear liquid
is made to overflow and then the solid is filtered on a fabric filter, and
washed with demineralized water to eliminate the chlorides that are present.
The resulting filtration cake is poured into an appropriate tank and
converted into a slurry by mechanical agitation.
The slurry is then fed to a spray-dryer, to convert it into dry powder.
The resulting powder is converted, after lubrication, into pellets having the
shape of a perforated cylinder. Calcination of the pellets at 500 °C for 4
hours leads to the formation of the catalyst used in the oxidation of
methanol to formaldehyde.
Example 3
Preparation of a catalyst containing cerium
Reagents
23.8 kg molybdenum trioxide
40.0 kg sodium molybdate dihydrate
35.2 kg ferric chloride hexahydrate
In a container with a capacity of approximately 2.5 m3, equipped with
a mechanical agitator, and with temperature measurement and control
system, approximately 1.0 m3 of demineralized water, the molybdenum
trioxide and the sodium molybdate are loaded. Heating is performed up to
the temperature of 60 °C until the solids dissolve completely.
The solution of ferric chloride prepared separately (approximately 0.5
m3) is added over a period of 90 minutes, keeping the reaction temperature
constant at 60 °C.
Once the addition of the ferric chloride has ended, agitation is
continued for 10 minutes, the mass is brought to the volume of 2 m3 with
demineralized water, agitation is stopped and cooling is allowed until room
temperature is reached.
After decantation of the precipitated solid, the supernatant liquid is
overflowed and then the solid fraction is filtered on a fabric filter, and
washed with demineralized water to eliminate the chlorides that are present.
The resulting filtration cake is poured into an appropriate tank and
converted into a slurry by mechanical agitation. The resulting slurry is
added with the suspension of cerium molybdate prepared according to
Example 1. After vigorous agitation for at least 30 minutes, the resulting
suspension is fed to a spray dryer, to obtain a dry powder. The resulting
powder is converted, after lubrication, into cylindrical pellets which have a
three-lobed cross-section and are provided with through bores at the lobes.
The calcination of the pellets at 500 °C for four hours leads to the formation
of the catalyst containing 0.3% by weight of cerium (from chemical
analysis), in the form of cerium molybdate.
Preparation of a catalyst containing cerium
Reagents:
23.8 kg molybdenum trioxide
40.0 kg sodium molybdate dihydrate
35.2 kg ferric chloride hexahydrate
In a container with a capacity of approximately 2 m3, provided with a
mechanical agitator, temperature measurement and control system,
approximately 1 m3 of demineralized water, the molybdenum trioxide and
the sodium molybdate are loaded. Heating is performed up to the
temperature of 60 °C, until complete dissolution of the solids is achieved
with consequent formation of sodium dimolybdate.
The solution of ferric chloride prepared separately (approximately 0.5
m3) is added over a period of 90 minutes, keeping the reaction temperature
constant at 60 °C.
Once the addition of the ferric chloride has ended, agitation is
continued for 10 minutes, the mass is brought to the volume of 20 m3 with
demineralized water, agitation is stopped, and cooling to room temperature
is allowed.
After decantation of the precipitated solid, the supernatant clear liquid
is overflowed and then the solid is filtered on a fabric filter and washed with
demineralized water to eliminate the chlorides that are present. The resulting
filtration cake is poured into an appropriate tank and converted into a slurry
by mechanical agitation.
The resulting slurry is added with the suspension of cerium
molybdate prepared according to Example 2.
The two products are mixed uniformly by vigorous agitation for at
least 30 minutes and then fed to a spray dryer, which allows to obtain a dry
powder.
The resulting powder is converted, after lubrication, into three-lobed
pellets of the type prepared in Example 3.
Calcination of the pellets at 500 °C for four hours leads to the
formation of the catalyst, which contains approximately 1.56% by weight of
cerium, (from chemical analysis) in the form of cerium molybdate.
Comparison example 2
The preparation of Comparison example 1 is repeated with the only
difference that together with the molybdenum trioxide and the sodium
molybdate, 418.6 kg of cerium carbonate and the corresponding quantity
(271 g) of molybdenum trioxide are loaded.
The cerium present in the powder after calcination is only 20% of the
cerium present in the starting cerium compound.
Example 5
Catalytic tests
A catalytic bed is used which is constituted by two layers: an upper layer of
400 mm of ceramic rings and a lower layer of 700 mm of catalyst.
The total inlet gas flow-rate is 1765 Nl/hour. The O2 content of the
mixture at inlet is 9.5%.
The results of the test by using the catalyst of Comparison example 1
are given in the following table:
therefore the test was interrupted and repeated at 6% methanol in order to
evaluate the catalyst degradation.
The results of the test using the catalyst of Example 3 are given in the
following table:
WE CLAIM
1. Catalysts for oxidation of methanol to formaldehyde, comprising a
catalytic mixtures Fe2(Mo04)3 / Mo03, wherein the Mo/Fe atomic
ratio ranges from 1.5 to 5, and cerium molybdate in a quantity from
0.1 to 10% by weight expressed as cerium.
2. The catalysts according to claim 1, wherein cerium molybdate is
present in a quantity from 0.2 to 5% by weight as cerium.
3. The catalysts according to claims 1 and 2, wherein the catalytic
mixture has a composition Fe2(Mo04)3 2Mo03
4. The catalysts according to anyone of claims 1 to 3, wherein cerium
is in the form of tri- and/or tetravalent cerium.
5. The catalysts according to any one of claims 1 to 4, having a
surface area from 1 to 7 m2/g.
6. The catalysts according to claim 5, wherein the surface area is 2-6
m2/g.
7. The catalysts according to claim 5, wherein the surface area is 3-5
m2/g.
8. The catalysts according to anyone of claims 1 to 7, in the form of
cylindrical granules provided with a through bore or of cylindrical
granules with a three-lobed cross-section, provided with a through
bore at the lobes and with the axes of the bores which are parallel
to the axis of the granule.
9. Granules according to claim 8, wherein the granules have a height
from 2 to 7 mm.
10. A multiplayer catalytic bed, wherein the layer in contact with the
mixture of the fresh reagent gases is formed by a catalyst
according to anyone of claims 1 to 4 having a surface area from 3
to 6 m2/g.
11. A process for preparing catalysts having the characteristics set
forth in anyone of claims 1 to 9, comprising the steps of a) mixing a
suspension obtained by precipitating a mixture Fe2(Mo04)3 / Mo03,
wherein the Mo/Fe atomic ratio is comprised from 1.5 to 5, from a
solution of a soluble ferric salt mixed with a solution of a molybdate
of an alkaline metal or of ammonium with an aqueous suspension
obtained by reacting, while hot, molybdenum trioxide and a
carbonate of trivalent cerium in a Mo/Ce atomic ratio from 1.5 to 2.1
until the generation of CO2 ceases, b) dilution, decantation, filtration
and washing of the precipitate thereafter converted into a slurry by
agitation before mixing with the suspension of the product of
reaction of molybdenum trioxide with cerium carbonate c) shaping
of the dried mixture or a paste thereof in the form of granules and
d) calcination the granules at a temperature from 450 to 600°C.
12. The process according to claim 11, wherein the calcination is
performed at a temperature from 480 to 580°C.
13. A process for oxidation of methanol to formaldehyde, wherein a
gaseous mixture of methanol at a concentration of 6 to 10% by
volume and of oxygen at a concentration from 9 to 13% by volume,
the remainder being inert gas, is fed into a bundle-tube reactor in
which the catalyst inside the pipes is a catalyst according to anyone
of claims 1 to 9, using linear velocities of 1-2 Nm/s and temperatures
of the bath that circulates outside the pipes comprised from 250°C to
320°C.
14. The process according to claim 13, wherein the layer of the catalyst
that is in contact with the fresh reagent gases is formed by a
catalyst according to claim 10.
15. The process according to anyone of claims 13 and 14, wherein the
reagent gases are fed to the catalytic bed at a temperature from
120to160°C

Catalysts for oxidation of methanol to formaldehyde, comprising a catalytic mixtures Fe2(MoO4)3 / MoO3, wherein the Mo/Fe atomic ratio ranges from 1.5 to 5, and cerium molybdate in a quantity from 0.1 to 10% by weight expressed as cerium.

Documents:

1142-KOL-2005-FOR ALTERATION OF ENTRY.pdf

1142-KOL-2005-FORM-27-1.pdf

1142-KOL-2005-FORM-27.pdf

1142-kol-2005-granted-abstract.pdf

1142-kol-2005-granted-claims.pdf

1142-kol-2005-granted-correspondence.pdf

1142-kol-2005-granted-description (complete).pdf

1142-kol-2005-granted-examination report.pdf

1142-kol-2005-granted-form 1.pdf

1142-kol-2005-granted-form 18.pdf

1142-kol-2005-granted-form 2.pdf

1142-kol-2005-granted-form 26.pdf

1142-kol-2005-granted-form 3.pdf

1142-kol-2005-granted-form 5.pdf

1142-kol-2005-granted-priority document.pdf

1142-kol-2005-granted-reply to examination report.pdf

1142-kol-2005-granted-specification.pdf

1142-kol-2005-granted-translated copy of priority document.pdf


Patent Number 233995
Indian Patent Application Number 1142/KOL/2005
PG Journal Number 18/2009
Publication Date 01-May-2009
Grant Date 29-Apr-2009
Date of Filing 14-Dec-2005
Name of Patentee SUD-CHEMIE CATALYSTS ITALIA S.R.L.
Applicant Address VIA G. FAUSER 36/B, 28100 NOVARA
Inventors:
# Inventor's Name Inventor's Address
1 ESTERINO CONCA VIA MONTE GRAPPA, 8, 28100 NOVARA
2 CARLO RUBINI VIA DE CRISTOFORIS, 21, 22020 SAN FERMO DELLA BATTAGLIA
3 MARCELLO MARCHI VIALE ALLEGRA, 11, 28100 NOVARA
PCT International Classification Number B01J 23/88, 35/10
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 MI2004A002456 2004-12-22 Italy