Note: Descriptions are shown in the official language in which they were submitted.
11~1369
The present invention relates to the production
of catalysts such as can be used, for example, in the
manufacture of isoprene from isobutylene and formaldehyde,
and more particularly to a method of preparing a calcium boron
phosphate catalyst usable for the decomposition into isoprene
of 1,3-dioxanes and, in particular, 4,4 dimethyl-1,3-dioxane
(hereinafter referred to as DMD), as well as for alcohol
dehydration reactions.
It has been known in the prior art to prepare
phosphates of metals of Group II of the Periodic Table,
usable as catalysts for selective cleavage of ` C-0-bonds in
organic compounds, and, specifically, for converting 4,4
dimethyl-1,3-dioxane into isoprene, as well as for dehydration
of alcohols, by precipitating tertiary phosphates of Group
II metals from aqueous solutions of their salts taken in
conjunction with water-soluble salts of phosphoric acid,
followed by separating the precipitate, washing the paste
obtained, and shaping it into catalyst granules (cf. U.S.
Pat. No. 3,872,216).
Catalysts prepared by the above technique, however,
are characterized by low selectivity, equal to 78 to 82 mole %,
low activity resulting in DMD space velocities as low as
0.7 h 1, and high operating temperatures equal to about
375C
Selectivity is defined herein as the ratio of the
amount in moles of isoprene formed to the amount in moles of
DMD converted. Selectivity is expressed in percent.
Selectivity is quantitatively dependent upon
catalyst composition and structure, as well as upon the
process conditions under which the catalyst operates.
1369
Increased selectivity will lead to reduced DMD
consumption rates per unit of finished product. The
relatively low selectivity of the catalyst obtainable by the
aforesaid prior art technique would result in high feed-
stock consumption rates in isoprene production, varying
between ca. 2.10 and 2.25 kg of DMD per 1 kg of isoprene.
The activity of catalysts is dependent upon their
acidity which is determined by the number and efficiency of
the active centres and can be characterized by the DMD
conversion degree.
DMD conversion degree is defined herein as the ratio
of the amounts of DMD converted to DMD used, expressed in
percent.
Known in the art is a method of preparing calcium
phosphate catalysts, comprising the steps of reacting
calcium salts with phosphoric acid salts in aqueous ammonia,
followed by separating the resulting precipitate from the
reaction mixture, washing, drying and heat treating it with
the use of super-heated steam or a mixture of steam and
air at high temperatures (cf. U.S. Pat. No. 3,846,338).
The catalysts obtained by this prior art technique
are relatively low in activity.
Furthermore, calcium phosphate catalysts prepared
by said technique are lacking in efficiency, which is as
low as 0.3 to 0.4 ton/h of isoprene per cubic meter of
catalyst.
The efficiency of a catalyst depends on its
activity and selectivity as well as on the feedstock space
velocity.
In the prior art technique, heat treatment of the
ll~i3~i9
catalyst is carried out at high temperatures, which involves
overheating of the heat carrier to temperatures as high as
650 to 800C and high process power inputs, as well as the
use of special heat-resistant materials for the reactors
adapted to produce the catalyst.
Furthermore, the catalyst obtained by the aforesaid
technique has a relatively short useful life of 250 hours.
The catalyst life depends on many factors including
catalyst composition and structure, catalyst activity,
operating temperatures, and coke deposition. Coke deposition
is understood to denote coke depositing on the catalyst in
the process of DMD decomposition. It is determinable as the
ratio of the amount in moles of coke deposited to the amount
in moles of DMD converted, expressed in percent.
In spite of the advantages inherent in the prior
art techni~ues for preparation of calcium phosphate catalysts,
no commercial process for converting DMD into isoprene based
thereon has been developed so far, since there is no catalyst
as yet with selectivity and stability such as to permit a
commercial process with a high yield of the desired product.
It is an object of the present invention to provide
a method of preparing a high-activity calcium boron phosphate
catalyst usable at low operating temperatures, lower than or
equal to 300C.
Another object of the present invention is to
provide a method of preparing a calcium boron phosphate
catalyst that would yield a catalyst with good stability at
low operating temperatures.
A further object of the invention is to provide
a method of preparing a high-efficiency calcium boron
catalyst.
13~i9
A still further object of this invention is
to provide a method of preparing a high-selectivity
calcium boron phosphate catalyst.
With these and other objects in view, there is
provided a method of preparing a calcium boron phosphate
catalyst, comprising the steps of reacting calcium salts
with phosphoric acid salts in aqueous ammonia, separating
the resulting precipitate from the reaction mixture, suitably
shaping said precipitate, drying it, and heat treating at an
elevated temperature in the presence of steam, or a mixture
of steam and an inert gas, in which method, according to the
invention, heat treatment is carried out in the presence of
steam mixed with boric acid or boric and phosphoric acids.
The heat treatment thus performed yields a
caLcium boron phosphate catalyst with good stability at low
operating temperatures less than or equal to 300C.
It is advisable that the heat treatment procedure
be carried out in the presence of 0.01 to 0.~/O by mass of
boric acid, this permitting a calcium boron phosphate
catalyst featuring high activity at low operating
temperatures.
The heat treatment procedure is preferably effected
in the presence of boric acid taken in the amount of 0.02 %
by mass.
The best results can be achieved with the heat
treatment carried out using boric acid in the aforesaid
amount.
It is also advisable that heat treatment be
carried out using boric and phosphoric acids in a molar
ratio of between 0.1:1 and 10:1.
3~9
Using boric and phosphoric acids in the above
range of molar ratios results in enhanced stability of
calcium boron phosphate catalysts.
It is desirable that heat treatment be carried out
with boric and phosphoric acids taken in an equimolar ratio.
An equimolar ratio of boric and phosphoric acids
can give the best results in so far as stability is
concerned.
The reaction of calcium salts with phosphoric
acid salts is preferably carried out in aqueous ammonia
with the starting reactants taken in the molar ratio of
1.5:1.
Reacting the above components under conditions as
described above will yield a calcium boron phosphate
catalyst featuring low coke deposition characteristics.
It is also advisable that the reaction of
calcium salts with phosphoric acid salts in aqueous ammonia
be carried out with the starting reactants taken in a molar
ratio of between 1.5:1 and 5:1, and the resultant reaction
mixture treated with a phosphoric acid solution to pH of
from 5.0 to 7Ø
The range of molar ratios for the starting
reactants and the pH range of the reaction mixture as
specified above are consistant with obtaining ~ calcium
boron phosphate catalyst of desired structure and
composition.
The reaction mixture is preferably to be treated
with a phosphoric acid solution to p~ of from ~.5 to 6Ø
With the proposed method, a catalyst can be
obtained featuring high selectivity (87.2 to 88 mole %),
11'~1369
high activity at low operating temperatures lower than or
equal to 300C, low coke deposition, and high stability. The
DMD conversion remains practically invariant during 100 hours
of operation.
The aforesaid and other objects and additional
features of the present invention are set forth in the
appended claims, and the present invention will be more
fully apparent from the detailed description of embodiments
thereof presented hereinunder.
The proposed method of preparing a calcium boron
phosphate catalyst can be realized as follows.
The starting reactants to be used are solutions
of calcium salts such as calcium chloride and those of
phosphoric acid salts such as diammonium phosphate, disodium
phosphate, etc. A suitable amount of ammonia solution is
added to the phosphoric acid salt solution before reacting
it with the calcium salt solution for pH control of the
medium.
The solutions of calcium and phosphoric acid salts
are gradually introduced into a vessel fitted with a stirrer,
with the resulting slurry being continuously stirred. The
reaction is carried out with the calcium salts and phosphoric
acid salts taken in the molar ratio of 1.5:1. However
the reaction is realizable with the startiny reactants
having a molar ratio anywhere within the range of 1.5:1 to
5.0:1, preferably 2.5:1. In cases such as these the reaction
mixture formed is to be treated with a phosphoric acid
solution to pH of from 5.0 to 7.0, preferably to pH of from
5.5 to 6Ø
The range of molar ratios for calcium salts and
13t;9
phosphoric acid salts and the pH range of the reaction
mixture as specified above are consistant with producing
catalysts of desired structure and composition.
The resulting precipitate is separated by
filtration or any other conventional technique, washed with
distilled water to remove calcium salt anions, shaped into
granules by a suitable conventional technique, and dried at
a temperature between 110 and 140~ to obtain a raw calcium
phosphate which is then loaded into a reactor for further
treatment.
The reactor is a quartz tube of 20 to 26 mm in
diameter, and is placed into an electrically heated oven
for the catalyst enclosed in the reactor to undergo heat
treatment at a temperature of between 400 and 600C,
using steam with boric acid or with boric and phosphoric
acids.
Where a calcium boron phosphate catalyst is
obtained without pretreatment of the reaction mixture with
phosphoric acid solution, heat treatment is preferably
performed at 400C.
However, when the process of calcium boron
phosphate catalyst preparation comprises the step of treating
the slurry~with phosphoric acid to provide the pH value of
the reaction mixture within the range of 5.0 to 7.0, the
heat treatment temperature should preferably be 450C.
Heat treatment can also be carried out using
steam mixed with an inert gas such as nitrogen, argon, etc.
Steam is fed in at a space velocity of 1.0 to
2.0 h 1, Boric acid content in the steam is 0.01 to O.~h
~y mass, preferably 0.02% by mass.
11~1369
When the catalyst heat treatment is performed in
the presence of a mixture of boric and phosphoric acids,
the boric acid content in the steam ranges from 0.001 to
0.02 %, by mass and that of phosphoric acid 0.0015 to 0.03 %
by mass, preferably 0.002 % by mass of boric acid and 0.003 %
by mass of phosphoric acid.
In the course of heat treatment the molar ratio of
boric to phosphoric acids is maintained within 0.1:1 to
10:1, preferably at 1:1.
Heat treatment times are within 2 to 50 hours,,
preferably between 20 and 30 hours.
The calcium boron phosphate catalyst thus obtained
has the following characteristics: DMD conversion over 100
operating hours being substantially constant (ca. gOo/O),
selectivity 87.2 to 88 mole %, coke deposition below 1 mole %.
The following typical examples will further
illustrate certain aspects of the present invention,
deliniating more clearly the features and advantages
specific to it.
Example 1
The starting reactants used for the preparation of
a raw calcium phosphate catalyst are 1.78 4 of an aqueous
calcium chloride solution containing 101.892 g of calcium
chloride per 1~ of the solution, and 1.608 ~ of an aqueous
diammonium phosphate solution containing 51.08 g of
diammonium phosphate per 1 ~ of the solution. An ammonia
solution with a concentration of 152.15 g/l is added to
the diammonium phosphate solution on the bases of having
2.33 moles of ammonia per 1 mole of diammonium phosphate.
The starting reactants are gradually poured into a
11~13~9
vessel fitted with a stirrer, the molar ratio of calcium
chloride to diammonium phosphate being kept at 2.5:1.
The pouring procedure continues for 2 hours, the resulting
reaction mixture in the form of a slurry being continuously
stirred all the while. The pH value of the slurry is
found to be 9.0+0.05. The slurry is treated with 150 ml of
phosphoric acid concentrated to 281.26 g/l, in order to reduce
the pH value to 5.75. The resulting precipitate is separated
from the reaction mixture by filtration, washed with distilled
water to remove chlorine ions, shaped into granules in a
press, and dried at 120C.
The raw calcium phosphate catalyst thus obtained
is loaded, in an amount of 24 cm3, into a reactor which has
the form of a quartz tube of 20 to 26 mm in diameter. The
reactor is placed into an electrically heated oven, and steam
mixed with 0.01 % by mass of boric acid is used for heat
treatment of the raw calcium phosphate catalyst at 450C
for 20 hours.
The catalyst thus prepared is test run in a DMD
decomposition reaction in an atmosphere of steam, followed
by regeneration which consists in burning out the coke
deposit after every 2 hours of catalyst operation.
The DMD deccmposition reaction is carried out at
atmospheric pressure and at an average temperature of 280C
for the duration of 2 hours. DMD is fed in at the rate of
24 cm3/h, and water, at 48 cm3/h, which gives a DMD space
velocity of 1.0 h 1 and a DMD to steam dilution ratio of 1:2.
The DMD decomposition cycle is followed up by a
regeneration cyc~e using a temperature of 425C and feed
rates of 48 cm3/h for water and 16.800 cm3/h for air.
~i4~369
The duration of the test is 100 hours.
The products of the reaction are analysed using
gas-liquid chromatography techniques. The quantity of coke
deposited is determined by a conventional method.
The catalyst test results are presented below in
Table 1.
Example 2
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
The calcium phosphate catalyst thus obtained is
subjected to heat treatment at 450C for 20 hours with the
use of steam mixed with 0.8 % by mass of boric acid. The
calcium boron phosphate catalyst so prepared is test run
as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 3
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst
thus obtained is performed using steam mixed with 0.02 % by
mass of boric acid, at 450C for 20 hours.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 4
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst
-- 10 -
1141369
thus obtained is performed at 450C for 20 hours, using steam
mixed with 0.02% by mass of boric acid and 4800 cm3/h of
nitrogen, equivalent to a nitrogen space velocity of 200 h 1.
The resulting calcium boron phosphate catalyst is
test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 5
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phophaste thus obtained
is carried out at 450C for 20 hours, using steam mixed with
0.02 % by mass of boric acid and 4800 cm3/h of air, equivalent
to an air space velocity of 200 h 1,
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 5
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is carried out at 400C for 20 hours, using steam
mixed with 0.02 % by mas~ of boric acid.
The resulting calcium boron phos~hate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 7
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
-- 11 --
~.~
1141369
Heat treatment of the raw calcium phosphate catalyst thus
obtained is carried out at 600C for 20 hours, using steam
mixed with 0.02 % by mass of boric acid.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below
in Table 1.
Example 8
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is performed at 450C for 20 hours, using steam
mixed with 0.002 % by mass of boric acid and 0.003 % by mass
of phosphoric acid.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below
in Table 1.
Example 9
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is performed at 400C for 20 hours, using steam
mixed with 0.002 % by mass of boric acid and 0.003 % by mass
of phosphoric acid.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 10
The procedure used to prepare the raw calcium
1369
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is carried out at 600C for 20 hours, using water
steam mixed with 0.002 % by mass of boric acid and 0.003 % by
mass of phosphoric acid.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 11
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of raw calcium phosphate catalyst thus obtained
is carried out at 450C for 20 hours, using steam mixed with
0.02 % by mass of boric acid and 0.003 % by mass of
phorphoric acid.
The resulting calcium boron phosphate catalyst
is test run as described in Example 1~
The catalyst test results are presented below in
Table 1.
Example 12
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is carried out at 450C for 20 hours, using steam
mixed with 0.002 % by mass of boric acid and 0.03 % by mass
of phosphoric acid.
The resulting calcium boron phosphate catalyst is
test run as described in Example 1.
The catalyst test results are presented below
- 13 -
~l~i369
in Table 1.
Example 13
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of the raw calcium phosphate catalyst thus
obtained is carried out at 450C for 20 hours, using steam
mixed with 0.002 % by mass of boric acid, 0.003 % by mass of
phosphoric acid, and 4800 dm3/h of nitrogen, equivalent to a
nitrogen space velocity of 200 h 1,
The resulting calcium boron phosphate catalyst
is test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 14
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 1.
Heat treatment of calcium phosphate catalyst thus obtained
is carried out at 450C for 20 hours, using steam mixed
with 0.002 % by mass of boric acid, 0.003 % by mass of
phosphoric acid, and 4800 cm3/h of air, equivalent to
an air space velocity of 200 h 1,
The resulting calcium boron phosphate catalyst is
test run as described in Example 1.
The catalyst test results are presented below in
Table 1.
Example 15
The starting reactants used for preparation of
a raw calcium phosphate catalyst are 1.18 ~ of a calcium
chloride solution containing 99.8 g/l of calcium chloride
and 2.0~ of a disodium phosphate solution containing
- 14 -
1141369
50.21 g/l of disodium phosphate. An ammonia solution with a
concentration of 130 g/l is added to the disodium phosphate
solution immediately prior to-the reaction, on the basis of
having 1.3 moles of ammonia per 1 mole of disodium phosphate.
The calcium chloride and disodium phosphate solutions are
gradually poured into a vessel fitted with a stirrer. The
pouring procedure continues for 2 hours, the resulting slurry
being continuously stirred all the while. Reaction is
carried out with the solutions used at a constant volume
ratio to ensure a calcium chloride to disodium phosphate
molar ratio of 1.5:1 and the slurry pH value of 9.0+0.05.
The resulting precipitate is separated by filtration, washed
with distilled water to remove chlorine ions, shaped into
granules, and dried at a temperature of 120C. Heat treatment
of the calcium phosphate obtained is performed at 400C for
20 hours, using steam mixed with 0.02 % by mass of boric acid.
The ca~cium boron phosphate catalyst thus obtained
is test run as described in Example 1.
The test results for the calcium boron phosphate
catalyst are presented below in Table 1.
Example 16
The procedure used to prepare the raw calcium
phosphate catalyst is the same as described in Example 15.
Heat treatment of the calcium phosphate obtained
is carried out at 400C for 20 hours, using water vapour
mixed with 0.002 % by mass of boric acid and with 0.003 % by
mass of phosphoric acid.
The calcium boron phosphate catalyst thus obtained
is test run as described in Example 1.
The test results for the calcium boron phosphate
- 15 -
1369
catalyst are presented below in Table 1.
Although the present invention has been described
herein with reference to the preferred typical embodiments
thereof, it will be apparent to those skilled in the art
that there may be minor modifications made in the procedures
comprised in the proposed method for preparation of calcium
phosphate catalysts without departing from the spirit of the
invention.
All such modifications and variations are
contemplated to be embraced in the spirit and scope of the
invention, as defined in the appended claims.
- 16 -
~4~ 369
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