Note: Descriptions are shown in the official language in which they were submitted.
10618~3
New Dehydration Catalysts and a
Processlor their Prepara-tion and ~pplication
The present invention relates to new catalysts for
the dehydration of organic compounds. More particularly, it
relates to ca-talysts for the dehydration of diols, including
vicinal diols, and/or olefinic alcohols.
The description which follows deals, more particularly,
with the application of the catalysts of the invention to the
dehydration of methyl-2,3-butanediol because of the importance
which it has assumed. As is known, the dehydration of methyl-
~ 2,3-butanediol leads to isoprene, a monomer that is very much
10~ in demand for the manufacture of both synthetic rubbers and a
wide range of high polymers. However, this particular appli-
cation should not be construed as a limitation of the inven-
tion, which may be applied to other compounds as well - for
example, to the dehydration of 2,3-butanediol to give butadiene.
~- 15 The usual dehydration catalysts, such as thoria or
alumina, cannot be used in the dehydration of methyl-2,3-buta-
nediol or of vicinal diols generally. They result in excessive
amounts of by-products such as methyl isopropyl ketone and
trimethyl acetaldehyde or, more generally, carbonyl compounds.
On the other hand, the application of lithium orthophosphate,
Li3P04, which is known to be a catalyst for the isomerization
` and dehydration of 2-methylepoxy-2,3-butane to isoprene, in
the dehydration of methyl-2,3-butanediol gives only a low iso-
prene yield when the lithium phosphate is prepared without
; 25 special precautions.
In French patent 2,087,011 (priority equivalent to
U.S. patent 3,781,222), the applicants and a co-worker have
., _1, ,
10~ 3
described new dehydration catalysts, particularly for diols,
which are formed, partly or wholly, of at least one pyrophos-
phate, whether mixed or not, of at least one metal from the
group consisting of lithium, sodium, strontium and barium.
These patents further describe catalysts containing, in addition,
at least one neutral orthophosphate of at least one metal from
the group consisting of lithium, sodium, strontium and barium.
Canadian Patent No. 1,023,767 describes and claims the further
advantageous process for preparation of said catalysts which
consists in using as starting materials at least one acid ortho-
phosphate of at least one metal from the aforesaid group and at
least one pyrophosphate from the same group; mixing the ortho-
phosphate and the pyrophosphate in powder form; extruding the
mixture in appropriate form; and drying and calcining the
extruded mass in air so as to convert the acid orthophosphate to
pyrophosphate. Note also the improved catalysts of the afore-
mentioned type incorporating chromium in combined form or a basic
additive as disclosed in U.S. patent 3,862,964.
These catalysts have proved particularly effective and
worthwhile in the dehydration of methyl-2,3-butanediol to isoprene
and/or to olefinic alcohols, which are intermediate products in
the dehydration of methyl-2,3-butanediol to isoprene.
An object of the present invention is to provide a
dehydration catalyst, particularly for diols, whether vicinal
or not, which is as selective and as active as the catalysts
mentioned above, and preferably using less expensive starting
materials.
In pursuing their investigations, the applicants have
found that solids based on calcium pyrophosphate also make very
- 2 -
., . . ~ : '
.
106~03
good catal~sts for dehydra-tion, especially of diols to dienes,
specifically including vicinal diols.
Thus a preferred embodiment o~ the present invention
is a dehydration catalyst, particularly for diols, which is ,'
formed partly or wholly of calcium pyrophosphate.
Another preferred embodiment of the present invention
is a dehydration catalyst, particularly for diols, formed of a
mixture of calcium pyrophosphate and at least one neutral
orthophosphate of at least one metal from the group consisting
of lithium, sodium, strontium, barium and calcium.
Still another preferred embodiment of the present
invention is a dehydration catalyst, particularly for diols,
formed of a mixture of calcium pyrophosphate and at least one
pyrophosphate, whether mixed or not, of at least one metal
- 15 from the group consisting of lithium, sodium, strontium and
barium, and possibly at least one neutral orthophosphate of at
least one metal from the group consisting of lithium, sodium,
I strontium, barium and calcium.
` Lastly, a further preferred e~bodiment of the
present invention is a process for preparation of a dehydration
catlyst from calcium pyrophosphate and at least one acid
orthophosphate of at least one metal from the group consisting
of lithium, sodium, strontium and barium, said process con-
sisting in mixing the pyrophosphate and the acid orthophosphate;
extruding or pelletizing the mixture; and drying and then cal-
cining tne granules or pellets at a temperature between 300 and
600~C, and preferably between 350 and 500~C, so as to convert
the acid orthophosphate to pyrophosphate.
-3-
-
' ' ''
.:
1061~03
The applicants have found that these calciu~-b~sed
catalysts are as advanta~eous as the catalysts discovered
earlier. A further advantage is that the calcium-based com-
pounds -- for example, calcium chloride, CaC12 -- necessary ,
for the manufacture of the catalyst are cheaper than lithium-
based compounds, for example, and this translates into a
substantial cost saving.
- The applicants have found,m~reover, that calcium-
- based catalysts exhibit better thermal stability than the
catalysts used up to now. When used alone, calcium pyro-
phosphate has a melting point of a~out 1300C. ~en used in
admixture with another pyrophosphate, the catalysts obtained
will not undergo a deleterious thermal change until an
elevated temperature is reached. For example, when a calcium
pyrophosphate is used in admixture with sodium pyrophosphate
prepared from sodium acid orthophosphate, the catalytic mass
obtained will not under~o a thermal change up to 780C,
which is approximately the melting temperature of sodium
pyrophosphate. In the course of their work, the applicants
have further found that the thermal degradation which occurs
manifests itself in a frittering of the catalyst, and this
shortens its service cycle. Moreover, since these catalysts
are employed mainly in the dehydration of diols to diolefins,
the diolefins produced may polymerize on the catalyst. It
follows that to regenerate the catalyst the latter has to be
; brought to an elevated temperature to burn off the polymers
deposited on its surface, which quite often have already been
converted to coke. A catalyst based on calcium pyrophosphate
.. - ' :
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1061t:~(33
there~ore undergoes less alteration during regeneration than
other catalysts since the temperature at which it begins to
sustain a thermal change is higher than that at which other
catalysts undergo alteration.
However, when used alone, calcium pyrophosphate
has rather mediocre mechanical properties for a catalyst.
It is therefore preferable to mix it with a pyrophosphate,
whether mixed or not, of at least one of the metals of the
group consisting of lithium, sodium, strontium and barium,
obtained from the corresponding acid orthophosphate. For
example, the calcium pyrophosphate may be mixed with sodium
acid orthophosphate, which then i~ converted to neutral pyro-
phosphate.
Several processes for the preparation of caIcium
pyrophosphate are known. One of these is the so-called "dry"
route whereby the pyrophosphate is obtained by calcination
of mixtures of salts of calcium, such as the oxide, CaO, the
hydroxide, Ca(0H2), the carbonate, CaC03, and so forth, and
of phosphoric acid (ammonium phosphate, phosphoric acid, etc.).
For example, the applicants have run tests with ammonium
phosphate and calcium carbonate.
Another of these processes might be called the "wet"
route. Calcium pyrophosphate being insoluble in water, it may
be precipitated by double decomposition between a solution of
calcium salt and a solution of a pyrophosphate. The starting
- materials may be an inorganic or organic calcium salt, for
.: .
- example, the chl~ide or the acetate of calcium, and sodium
pyrophosphate, Na4P2O7.1OH2O; calcium pyrophosphate, Ca2P2O7
``` ~061~1~3
:`
thus being precipitated.
Lastly, still another possible rou-te is the calcination
of the phosphate Ca~IPO4, which may be preceded by the precipita-
~ tion of the dicalcium orthophosphate.
; 5 However, the applicants have found in the courseof
their tests that the calcium pyrophosphate produced by the
"dry" route is a compact, scarcely divided, often heterogenous
solid. The porosity therefore is low, which is detrimental for
a dehydration catalyst. The other two metnods, on the other
10 hand, yield solids which hold promise for the manufacture of
catalysts.
- To improve the mechanical properties of the catalyst,
the applicants prefer to employ theprocess of preparation des-
cribed in what follows. The process consists in mixing cal-
' 15l cium pyrophosphate, prepared either by the "wet" route or by
calcination of dicalcium orthophosphate, with disodium acid
orthophosphate, for example; extruding or pelletizing the
mixture so obtained; drying it at about 100 or 120C, and
calcining it so as to convert the acid orthophosphate to
pyrophosphate. To facilitate the mixing of the powders, water(from 0 to 150~ of the total weight of the powders) may be
~!~, added. Of course, i~ one of the powders is sufficiently
' moist, there will be no need to add water durlng mixing.
` However, water must be added if the powders are dry. In fact,
a paste must be obtained which then is dried, ground, screened
. and pelletized. The catalyst so produced has good mechanical
properties in addition to good catalytic properties. Good
catalysts are obtained also by mixing or coprecipitating
"
-
1061~(~3
calcium pyrophosphate, and possibly at least one neutral ortho-
phosphate of at leas-t one metal from the group consisting of
lithium, sodium, strontium, barium and calcium, with at leas-t
one pyrophosphate, whether mixed or not, of at least one metal
from the group consisting of lithium, sodium, strontium and
barium. The neutral orthophosphate acts as a bonding agent
which improves the mechanical properties of the catalysts,
and particularly its resistance to crushing, without affecting
its original catalytic properties.
;: 10 In all of the mixtures referred to above, the calcium
. pyrophosphate is preferably present in a proportion of from 40;~
~ to 80 wt.
; ~ :
.. . .
The catalytic dehydration of diols, whether vicinal
or not, may be effected either in the liquid state or in the
-t15 vapor state. However, it is preferably carried out in the .
vapor phase and at a temperature comprised between 250 and
.600C, and preferably between 300 and 500C, and a space
velocity per hour (v/v/hr) -- which specifies the volume of
diol, measured in the liquid state, passlng over a unit volume
.20 of catalyst in one hour -- generally comprised between 0.1
,........... . .
~and 5, and preferably between 0.5 and 2.5 v/v/hr.
The diol may be pure or diluted in an inert gas
such as nitrogen, or mixed with olefinic alcohols. The de-
hydration of the diol directly to diene is carried out with
.25 production of intermediates such as the aforesaid olefinic
;alcohols, which essentially are ~-olefinic alchols. For
example, in the dehydration of methyl-2,3-butanediol,
. 2-methyl-1-butene-3-ol is formed which may readily be re-
cycled in the dehydration reactor, since the catalysts in
accordance with the invention will dehydrate said olefinic
alcohols just as effectively to dienes~
':
. -7-
-.
. - .
: . :
106~U;~
A catalyst in accordance with the invention may be
employed industrially in one or more dehydration reactors in
the manner which is well known in the field of catalytic
reactions. However, the catalyst is preferably used in a ,'
fixed bed.
The examples which follow are in no wise limitative.
They relate to the preparation of the catalysts and their
application to the dehydration of a diol to dlene.
EXAMPLE I
This example relates to the preparation of pure
; 10 calcium pyrophosphate. 200 cc of a solution containing 31.6 g
, of (CH3COO)2Ca is poured into a solution of 100 cc of
~ ! I
Na4P2O7lOH2O containing 44.7 g of that salt. The solutions
are hot. A precipitate of calcium pyrophosphate is obtained
, which is filtered, washed, and dried at 110C.
~, 15 The precipitate is calcined in two portions. One
~ portion is calcined at 500C for 2 hours while the other portion
i' is calcined at 725C, also for 2 hours.
eonventional macroporosity and apparent-density
measurements are then made on the two portions of catalyst.
; 20 The results thereof are presented in Table 1 be~ow.
The catalytic tests are carried out as follows:
Methyl-2,3-butanediol carried by a nitrogen stream is passed
over 4.5 cc of catalyst at 1 v/v/hr.
~ The results of the catalytic tests are also presented
in Table '. It should be noted that the calcium ~rophosphate
here used is in the form of a powder which has good activity
and good selectivity but would be difficult to use on an
industrial scale.
-8-
. .
- 6 - ~06~L~V3
~ ~ o ~r
; ~ ~ a ~ ~ ~
~ Q D ~1 0 (~ 00
`' C) ~ 0(~ ~ 1
~ ~ ~ .
.' . ~ 0~ ~ 00
H P~ _. _ __ ._ _
~ h
E~ ~,0 o 1~
~ ...... _ _ . _ . __ ._
H ~ 1` Q) O
'~ P~ Q~ ~ \ ~1 3
, p:; ~ O ~ O
. _ - ___
'S 0 ~
H X O t) ~ 1
. __ __
~00
' ~ O
~'~ 0~ oCJ C~
.: ~ ~ O U~
15~ 1~
. ._ I
~q._
, ~
~ '
~0611~
In that Tahle -
- the conversion represents the ratio of number of
molecules of diol consumed to number of molecules of diol in-
troduced;
- the selectivity is equal to the sum of the mole ,
percentages,in the converted fraction, of isoprene and isoprene
precursors (mainly the olefinic alcohols produced along with
the isoprene but also, to a small extent, 2-methy~poxy-2,3-
butane); and
- the macroporosity of the catalysts designates,
in cc/g, the pore volume of one gram of catalyst for pores
having a radius comprised between 80 to 100 R and 75000 A.
It is determined by means of a well-known apparatus, the
~ mercury penetration porosimeter. -
It is apparent that raising the temperature of
calcination has a deleterious effect on diene production,
as for a temperature increase of about 200C the mole percen-
tage of isoprene, the desired diene, is roughly halved.
EXAMPLE II
In this example, the same method of preparation is
employed as in Example I, but only up to the drying step. A
calcium pyrophosphate that has been dried at 110 is then at
hand.
To 52 g of dried precipitate, 34.7 g of decahydrated
disodium phosphate, Na2HPO4 lOH2O ~weight ratio, 60%:~0%), is
added, and then 87 cc of water to form the paste, which is
dried at 120C, ground, and screened so that only particles of
--10--
124246
1)3
a size comprised between 0.5 and 1 mm are retained for the
catalytic test. Lastly, these particles are calcined for 2 hours
at 500C. In the course of this operation, the water present
in the catalytic particles is eliminated and the disodium ortho-
phosphate is converted to sodium pyrophosphate. The catalyst
, so prepared has a macroporosity of 0.876 cc/g and an apparent
density of 0.46 g/cc.
Three catalytic tests are then made which consist in
passing methyl-2,3-butanediol in the vapor phase at 1 v/v/hr
over 4.5 cc of catalyst as in Example I. Three tests are run
~at different temperatures (350, 400 and 450C, respectively),
` ~the results of which are reported in Table II.
~;
,~ TABLE II ¦
.,, .~' C:~:~ --- . . ,
. 1 v/v/hr i
. , _ . ........... . ~ .
15 -Test Con- Iso- Olefinic Carbonyl ~isc. Selec-
temp. version prene alcohols_ compounds tivity
350C 77.716.4 68.4 12.6 3.1 85.5
. . . ..
400C 10079.2 2.6 15.0 3.3 81.8
, -_ __ . _ _ .
450C _ _81 1 0 ~ 15.3 3 0 8
It is apparent from this table that catalysts con-
20 taining calcium pyrophosphate and sodium pyrophosphate are good
dehydration catalysts. Above 400C, the mole percentage of iso-
prene is substantial, being nearly 80% in relation to the diol
converted land hence to the diol entering, as conversion is
100%).
--11--
,
., : - ~ . .
lUG1~03
E~AMPL~ III
In this example, two hot solutions (about 90C) are used
as starting materials, one of fi46 grams/liter of the pyrophos-
phate Na4P207 10H20 (a molar solution), the other of 22 grams/
liter of calcium chloride (hence a 2x molar solution), both in
distilled water. The latter solution is poured into the former
with agitation. It is found that calcium pyrophosphate pre-
cipitates in accordance with the reaction.
aC12 + Na4P207 Ca2P207 ~ 4NaCl
The precipitate obtained is filtered and washed with
5 liters of distilled water and then dried at about 110C. 302.3
grams of a solid having the approximate formula Ca2P207.3H20 is
obtained.
298.7 g of this precipitate and 128 g of disodium acid
orthophosphate, Na2HPO4-10H20, are mixed ln a weight ratio of
70:30% with the addition of 395 cc of water so as to facili-
tate mixing in the form of a paste. The pasteis dried at 110C,
followed by grinding and screening so as to retain only particles
of a size comprised between 0.5 and 1 mm. The catalyst so
obtained has a macroporosity of 1.177 cc/g and an apparent den-
sity of 0.37 g/cc. In this operation, the fine particles may
be recovered with -~ater, redried and reground.
A catalytic test is performed in accordance with
exampleSl or 2 at 400C, methyl-2,3-butanediol being passed over
the catalyst at 1 v/v/hr. Conversion of the diol is 98.1%.
The molar distribution in the converted fraction is as follows:
,,
-12-
12~2~
~()61~33
Isoprene 51.4%
Olefinic alcohols 28.3%
Carbonyl compounds 16.6%
Miscellaneous 3.7%
The selectivity is 80.2%.
EXAMPLE IV
The procedure used in Example III is followed in pre-
paring the catalyst, except that here potassium pyrophosphate is
used to precipitate the calcium salt:
K4P207 + 2CaC12 ~ Ca2P207
, ,
Two cold solutions, one containing 33 g of potassium pyrophos-
phate per 100 cc of distilled water, the other containing 22.2 g
of calcium chloride per 100 cc of distilled water, are mixed.
Calcium pyrophosphate is thus precipitated, and the precipitate
is filtered and washed with 500 cc of water and then dried at
100 C .
12 g of the dried precipitate is then mixed with 8 g of
disodium acid orthophosphate (weight ratio, 60:40%) with the
addition of 25 cc ~ water. The paste obtained, dried at about
120C, is ground and screened to separate the particles between
0.5 and 1 mm. The particles separated by screening are then
calcined at 500C for 2 hours.
The catalyst so obtained has a macroporosity of 0.698
cc/g and an apparent density of 0.51 g/cc.
A catalytic test comparable in all respects to that of
Example II is then made. The results are as follows:
Diol conversion 98.æ%
Product distributi.on (mole percentages) in the converted fraction: .
, .
-13-
. .
1(J6~ 3
Isoprene 53.2%
Olefinic alcohols28.5%
Carbonyl compounds13.3%
Miscellaneous 4.9%
The selectivity is 82.5%
In this example, potassium pyrophosphate was used in
the preparation of the catalyst. This pyrophosphate offers the
advantage of being far more readily soluble than sodium pyro-
phosphate, whose solubility in water is not pronounced below
80C. The calcium pyrophosphate may therefore be precipitated
cold.
EXAMPLE V
Calcium pyrophosphate is prepared in the same manner
as in Example III. However, the weight ratio of the calcium
; ~ pyrophosphate and the disodium acidcrthophosphate used in the
15 ` preparation of the catalyst is 50:50%.
The catalytic mass obtained after drying is subjected
to two mechanicl treatments, namely:
The first portion is pelletized in admixture with 5%
~ of didecyl adipate and 5% of naphthalene, used as lubricants.
-i 20 The pellets are calcined in a nitrogen stream at 500C. The
catalyst so produced has a macroporosity of 0.266 cc/g and an
apparent density of 0.99 g/cc.
The second portion is ground and screened to give
granules of a size comprised between 0.5 and 1 mm. The catalyst
so produced has a macroporosity of 0.344 cc/g and an apparent
density of 0.78 g/cc.
-14-
~ .
. .
1061~()3
TABLE III _ _
CATALYTIC TEST
400C - 1 v/v/hr
.. . ......... . ..
Con- Iso- Olefinic Carbonyl Misc. Selec-
Catalystversion prene alcohols compounds tivity
Pelletized100 81.8 0.9 14.7 2.782.7
Granulated95.3 40.5 41.2 14.3 3.982.5
_.__ .... . _ . ..... . . ...
EXAMPLE VI
In this example, calcium pyrophosphate is prepared by
calcination if dicalcium orthophospha*e, CaHPO4.
First CaHP04 is prepared by precipitation. To an 0.1 N
acid solution of calcium chloride, a solution is gradually added,
i the operation being performed cold. This preparation is described
in "Nouveau Traite de-Chimie Minerale", by P. Pascal, on page 462
of volume IV~ The precipitate obtained, which is washed with
water and dried at 110C,is identified by its powder pattern. It
is dicalcium orthophosphate, CaHPO4 2H20.
50.9 g of this precipitate is mixed with 39.4 g of
15 Na2HPO4 10H20 with the addition of 120 ml of water. (Weight
ratio, 56.3:43.7%) The paste obtained is dried at about 120C,
ground, and screened to give a particle size between 0.5 and 1 mm.
: This is followed by calcination for 2 hours at 500C, which con-
verts the orthophosphate CaHP04 lOH20 to sodium pyrophosphate.
A test is then run which is identical to those of
Example V. The results obtained are as follows:
- ~ .
1()61~(~3
Diol conversion 99.1
Molar distribution:
Isoprene78.8%
Olefinic alcohols 3.9%
Carbonyl compounds 15.1%
Miscellaneous 1.6
The selectivity is 83.3%
Thus the catalyst so prepared is a very good catalyst
for the dehydration of diols and olefinic alcohols to dienes
EXAMPLE VII
In this example, calcium pyrophosphate is prepared by
calcination of dicalcium orthophosphate, CaHP04, obtained by
precipitation from a mixture of calcium chloride and diammonium
, phosphate by the method described in Example VI. The dicalcium
- orthophosphate precipiate is dried at 110C.
A portion of the precipitate is calcined at 500C for
2 hours for the purpose of analysis. It is found that the weight
per cent of the calcium (32.5~ as determiend by atomic absorption)
and of the phosphorus (23.7, as determined by x-ray fluorescenae)
correspond to an atomic ratio of calcium to phosphorus of 1.06,
20 which confirms that during calcination dicalcium phosphate,
, .
CaHP04, readily converts to pyrophosphate, Ca2P207.
Another portion of the dried precipitate is mixed with
disodium orthophosphate in a weight ratio of 50:50%. The paste
i obtained is ground and screened so as to retain for the cata-
~.,
lytic test only particles of a size bet~een 0.5 and 1 mm. These
particles are calcined at 500C for 2 hours. The catalyst
ultimately obtained has a macroporosity of 1.313 cc/g and an
- apparent density of 0.36 g/cc. A catalytic test is then run
-16-
. , .
1061~(~3
with methyl-2,3-butanediol as in the preceding exa~ples (at 350C
and 1 v/v/hr). Conversion of the diol is 84.6~.
The molar distribution in -the conver-ted fraction is
as follows:
Isoprene 42.7%
Olefinic alcohols41.9
Carbonyl compounds 12.7~
Miscellaneous 2.6%
EXAMPLE VIII
; Described in this example is the use of a cat~yst pre-
10 pared from the following mi~ture:
25 wt. % of calcium pyrophosphate, Ca2P207
25 wt. % of mixed pyrophosphate, Li3NaP207
: 50 wt. % of acid orthophosphate, Na2HP04 OH20
This mixture is prepared in the form of a paste which
15 is treated to give catalyst granules that are dried overnight at
J 75C and calcined for 2 hours at 400C. The catalyst so obtained
has a macroporosity of 1.088 cc/g and an apparent density of
0.365 g/cc.
Methyl-2,3-butanediol is then dehydrated over this
20 catalyst at 350C and 1 v/v/hr by the procedure described in the
preceding examples. Diol conversion is 36.9%. The molar dis-
tribution in the converted fraction is as follows:
- Isoprene 10.2%
Olefinic alcohols 73.8
Carbonyl compounds 13.6
Miscellaneous 2.4~
; The se~ctivity (84~) is good. Conversion, on the
oth~ hand, is low but can readily be increased by reducing the
space velocity per hour or by raising the test temperature,
and this does not constitute a limitation of the catalyst so
prepared. It is also seen that the mole percentage of olefinic
alcohols is high, but this is not a drawbacl~ as they can be re-
-17-
v~
cycled over the ca-talyst, which then will dehyclrate them to
isoprene.
EX~MPLE IX
This example relates to the simultaneous preparation of
calcium pyrophosphate and tricalcium orthophosphate. A mixture
of calcium chloride (1/2 mole) and disodium acid orthophosphate,
Na2HP04 10H20 (1 mole), is the starting material. The procedure
used in the preceding examples is followed. (A solution con-
taining 1/2 mole of CaC12 and a solution containing 1 mole of
Na2HP04 10H20 are mixed.) In this way, a solid is precipitated
which is dried overnight at 75C and then calcined for 2 hours
at 400C.
An analysis made of the dried precipitate (by atomic
absorption in the case of the calcium and by ~-ray fluorescence
for the phosphorus) gives 32.1 wt. % of calcium and 18.5 wt. %
of phosphorus. The atomic ratio of Ca/P thus is 1.35, which
places it between that of pyrophosphate (for which this ratio
is 1) and that of tricalcium phosphate, Ca3(P04)2 (for which
the ratio is 1.5). The x-ray diagram of the solid shows that
these two constituents are present in the solid obtained by
calcination, which gives good results in the dehydration of
~f
2-methyl-2,3-butanediol, carried out as in the preceding ex-
amples (at 350C and 1 v/v/hr). Conversion of the diol is 100%,
and the molar distribution in the converted fraction is as
follows:
Isoprene 69.7
Olefinic alcohols 0%
Carbonyl compounds 29.7
Miscellaneous 0.6%
The catalyst prepared and used in this test has a
macroporosity of 1.46 cc/g and an apparent density of 0.315 g/cc.
-18-
10~1803
Another test run with a catalyst prepared frorn 0.8 mole
of calcium chloride and 1 mole of disodium orthophosphate under
the same conditions as the one above, and which upon analysis was
found to contain 37% of calcium and 20.6~ of phosphorus, which
- 5 corresponds to an atomic ratio of Ca/P of 1.39, gave the follow-
ing results:
Diol conversion: 100%
Molar distribution:
Isoprene 69.7%
10 Olefinic alcohols 15.3%
Carbonyl compounds 13.5%
Miscellaneous 1.5%
The catalyst used in this test has a macroporosity of
0.812 cc/g and an apparent density of 0.455 g/cc.
15~ Thus the above two catalystS formed of calcium pyro-
phosphate and tricalcium orthophosphate, are equally good cata-
lysts for the dehydration of diols to dienes and/or olefinic
alcohols.
.,
~i EXAMPLE X
This example relates to a dehydration test on 2-methyl-
-~;
2,3-butanediol with a magnesium pyrophosphate as catalyst.
More precisely, this test is intended to show that not
every alkaline-earth metal issuited for dehydration of a vici-
nal diol and/or of olefinic alcohols to diolefins and/or ole-
' finic alcohols.
Two identical tests are run in parallel over 5 cc each
of catalyst, one a calcium pyrophosphate catalyst, the other
a magnesium pyrophosphate catalyst. Tle methyl butanediol is
-19-
,:
,
, - . ,
~()61~
introduced over the catalysts in the presence of nitrogen (in
a ratio of 1/3 diol to 2/3 nitrogen) at 400C and 1 v/v/hr
(measured in the liquid state). The test duration is 1 hour.
The results are summarized in Table IV.
TABLE IV
.. . _ .... . _ . _ .. .... _ _ . ..
CatalystSelectivityActivity
used ~ mole/g/hr*
.. _ . _ . . .. _ . .. . . . _ . . . . ...
Caleium pyrophospate 85.3 0.0644 '`
.- 'Magnesium pyrophosphate 34.1 0.0159
.. . ... ~
.
*) The aetivity is measured in moles of diol dehydrated
. per gram of eatalyst per hour. -
These results show that a magnesium-base catalyst is
, not a good catalyst for dehydration of vincinal dids. In faet,
Y 'it will facilitate isomerization reactions, which is not con-
. dueive to good seleetivity for diolefins as it leads to pro-
15 duetion of earbonyl eompounds
For the dehydration of vicinal diols it is important
that the eatalyst not be aeidie.
,
~'
-20-
