Method for producing acrolein by means of dehydration
of glycerol
The present invention relates to an improved process
for the manufacture of acrolein by dehydration of
glycerol in the presence of acid gas additives.
Acrolein is the simplest of the unsaturated aldehydes.
It is also known as 2-propenal, acrylaldehyde or
acrylic aldehyde. Due to its structure, acrolein has a
high reactive power by virtue of the presence of its
two reactive functional groups, which are capable of
reacting individually or together. This is why acrolein
has numerous applications, in particular as synthetic
intermediate. It is in particular a key intermediate in
the synthesis of methionine, a synthetic amino acid
used as animal food supplement which is becoming
established as a replacement for fish meal. Acrolein is
a nonisolated intermediate in the synthesis of acrylic
acid in the industrial production of acrylic acid by
catalytic oxidation of propylene in the gas phase. The
importance of the chemistry of acrylic acid and of its
derivatives is known. Acrolein also results, by
reaction with methyl vinyl ether followed by
hydrolysis, in glutaraldehyde, which has numerous uses
in the tanning of leather, as, biocide in oil drilling
operations and during the treatment of cutting oils,
and as chemical disinfectant and sterilizing agent for
hospital equipment.
The most commonly used process for the production of
acrolein is based on the gas-phase catalytic oxidation
reaction of propylene with atmospheric oxygen.
The acrolein thus obtained can then be directly
incorporated in a process for the manufacture of
acrylic acid. When the acrolein is used as starting
material for the synthesis of methionine and/or acrylic
- 2 -
acid and/or acrylonitrile or for fine chemistry
reactions, a purification section makes it possible to
remove the reaction byproducts, mainly carbon oxides,
acrylic acid, acetic acid and acetaldehyde.
The production of acrolein is thus highly dependent on
the propylene starting material obtained by steam
cracking or catalytic cracking of petroleum fractions.
This starting material, of fossil origin, furthermore
contributes to increasing the greenhouse effect. It
thus appears necessary to have available a process for
the synthesis of acrolein which is not dependent on the
propylene resource and which uses another starting
material, preferably a renewable starting material.
This process would be particularly advantageous for the
synthesis of methionine and other products, which could
then be said to be "obtained from biomass". This is
because methionine, when used in animal food, is
rapidly metabolized and the carbon dioxide gas which
ends up in the atmosphere contributes to increasing the
greenhouse effect. If the acrolein is obtained from a
renewable starting material, for example obtained from
vegetable oil, the CO2 emissions no longer come within
the balance of the process as they compensate for the
carbon dioxide gas used by the biomass for its growth;
there is therefore no increase in the greenhouse
effect. Such a process then meets the criteria
associated with the new concept of "green chemistry" in
a broader context of sustainable development.
It is also known to synthesize aldehydes, such as
acrolein, by dehydration of a polyalcohol, such as
glycerol. Glycerol (also known as glycerin when it is
in the form of an aqueous solution) results in
particular from the methanolysis of vegetable and
animal oils at the same time as the methyl esters,
which are for their part employed in particular as
fuels in diesel oil and heating oil. This is a natural
product, available in large amounts; it can be stored
- 3 -
and transported without difficulty. It exhibits the
advantage of being a renewable starting material
meeting the criteria associated with the new concept of
"green chemistry".
Numerous recent studies have been devoted' to the
recovery in value of glycerol and in particular to the
preparation of acrolein. The process which is the
subject of these studies employs a reaction for the
dehydration of glycerol according to the consecutive
reactions:
CH2OH-CHOH-CH2OH -^ CH2OH-CH2-CHO+ H2O O CH2=CH-CH0 +
2H2O
which make it possible to obtain acrolein.
This reaction is an equilibrium reaction; as a general
rule, the hydration reaction is favored at low
temperatures and the dehydration is favored at high
temperatures. In order to obtain the acrolein, it is
thus necessary to employ a sufficient temperature
and/or a partial vacuum in order to displace the
reaction. The reaction can be carried out in the liquid
.phase or in the gas phase. This type of reaction is
known to be catalyzed by acids.
According to patent FR 69.5931, acrolein is obtained by
passing glycerin vapors at a sufficiently high
temperature over salts of•acids having at least three
acid functional groups, such as, for example, salts of
phosphoric acid. The yields shown are greater than 75%
after fractional distillation.
In patent US 2 558 520, the dehydration reaction is
carried out in the gas/liquid phase in the presence of
diatomaceous earths impregnated with phosphoric acid
salts, in suspension in an aromatic solvent. A degree
- 4 -
of conversion of the glycerol to give acrolein of 72.3%
is obtained under these conditions.
The process described in application WO 99/05085 is
based on complex homogeneous catalysis under a CO/H2
atmosphere under a pressure of 20/40 bar and in the
presence of a solvent, such as an aqueous sulfolane
solution.
Chinese patent application. CN 1394839 relates to a
process for the preparation of 3-hydroxypropanaldehyde
from glycerol. Acrolein, an intermediate reaction
product, is obtained by passing pure vaporized glycerol
over a catalyst of potassium sulfate or magnesium
sulfate type, and then the acrolein obtained is
rehydrated to give hydroxypropanaldehyde. The reaction
yields are not given.
Patent US 5 387 720 describes a process for the
production of acrolein by dehydration of glycerol, in
the liquid phase or in the gas phase, over solid acid
catalysts defined by their Haramett acidity. The
catalysts must have a Hammett acidity of less than +2
and preferably of less than -3. These catalysts
correspond, for example, to natural or synthetic
siliceous materials, such as mordenite, montmorillonite
or acid zeolites; supports, such as oxides or siliceous
materials, for example alumina (AI2O3) or titanium oxide
(Ti02) , covered with mono-, di- or triacidic inorganic
acids; oxides or mixed oxides, such as y-alumina or
ZnO-Al203 mixed oxide, or heteropolyacids. According to
that patent, use is made of an aqueous solution
comprising from 10 to 40% of glycerol and the operation
is carried out at temperatures of between 180 and 340°C
in the liquid phase and between 250 and 340°C in the
gas phase. According to the authors of that patent, the
gas-phase reaction is preferable as it makes it
possible to have a degree of conversion of the glycerol
of approximately 100%, which results in an aqueous
- 5 -
acrolein solution containing byproducts. A proportion
of approximately 10% of the glycerol is converted to
hydroxypropanone, which occurs as predominant byproduct
in the acrolein solution. The acrolein is recovered and
purified by fractional condensation or distillation.
For a liquid-phase reaction, a conversion limited to
15-25% is desired, in order to avoid an excessively
great loss in selectivity. Patent US 5 426 249
describes the same gas-phase process for the
dehydration of glycerol to give acrolein but followed
by hydration of the acrolein and by hydrogenation to
result in 1,2- and 1,3-propanediol.
The reaction for the dehydration of glycerol to give
acrolein is thus generally accompanied by side
reactions resulting in the formation of byproducts,
such as hydroxypropanone, propanal, acetaldehyde,
acetone, addition products of the acrolein with
glycerol (known as acetals), polycondensation products
of glycerol, cyclic glycerol ethers, and the like, but
also of phenol and polyaromatic compounds, which are
the cause of the formation of coke on the catalyst.
This results, on the one hand, in a reduction in the
yield and in the selectivity for acrolein and, on the
other hand, in a deactivation of the catalyst. The
presence of the byproducts in the acrolein, such as
hydroxypropanone or propanal, some being furthermore
difficult to isolate, requires separation and
purification stages which result in high costs for the
recovery of the purified acrolein. Furthermore, it is
necessary to regenerate the catalyst very often, so as
to regain a satisfactory catalytic activity.
The Applicant Company has attempted to solve these
problems by proposing, in the French patent published
under No. 2 882 052, to carry out the reaction for the
dehydration of glycerol in the presence of molecular
oxygen. It was observed on this occasion that,
surprisingly, the introduction of oxygen reduces the
- 6 -
formation of aromatic compounds, such as phenol, and of
byproducts resulting from a hydrogenation of dehydrated
products, such as propanal and acetone, but also of
hydroxypropanone. The formation of coke on the catalyst
is found to be reduced. This results in inhibition of
the deactivation of the catalyst and in continuous
regeneration of the catalyst. Some byproducts are found
to be present in markedly lower amounts, which
facilitates the subsequent purification stages.
Advantageous as they may be, these results are not
sufficient economically to move to an industrial scale.
Furthermore, the implementation of the process in the
presence of oxygen involves operational precautions in
order to prevent it from running away by proceeding as
far as combustion, with its risks of explosion. This
results, for example, in the use of an inert gas in
order to remain outside the flammability zone. The
nitrogen in the air can constitute a portion of this
inert gas but will often be in an insufficient amount
which will result in the use of additional inert gases,
such as recycle gases comprising, in addition to
nitrogen, which has not been able to react, the
combustion gases and rare gases, such as argon, but
also gases deliberately added, such as the abovementioned
gases but also methane and light alkanes. The
use of inert gases, which, by definition, do not
contribute to the reaction, involves the use of a large
reactor, in comparison with what is necessary for the
reactants alone. This results in an additional
expenditure. This is the reason why the Applicant
Company has continued its studies in order to improve
the selectivity for acrolein of the reaction by
focusing on the conditions of effectiveness and/or of
selectivity of the catalysts already known for being
used for the synthesis of acrolein from glycerol.
The Applicant Company has discovered with surprise that
the catalysts of acid type known for the catalysis of
- 7 -
the dehydration reaction which are solid homogeneous or
multiphase materials insoluble in the reaction medium
which, although acids, can also exhibit some
undesirable sites probably the cause of the formation
of the byproducts by reaction mechanisms which are
sometimes not easy to predict.
The aim of the present invention is to overcome these
disadvantages by implementing the process while adding,
to the gaseous reaction medium, a compound capable of
being attached, at least temporarily, to these sites
and by inhibiting them during the process to prevent
the formation of the byproducts.
A subject matter of the present invention is a process
for the synthesis of acrolein by dehydration of
glycerol in the presence of a solid acid catalyst,
characterized in that it is implemented in a reaction
medium comprising a gas phase comprising an acid
compound.
The term "acid compound" is understood to mean, within
the meaning of the present invention, a compound which,
in addition to that which will be specified below, will
exhibit, in solution with water, a pKa of less than
6.3. In particular, CO2 is not ah acid within the
meaning of the present invention.
The dehydration reaction is carried out, for example,
over solid acid catalysts, such as those described in
French patent FR 2 882 052.
The catalysts which are suitable are homogeneous or
multiphase materials which are insoluble in the
reaction medium and which have a Hammett acidity,
denoted Ho, of less than +2. As indicated in the patent
US 5 387 720, which makes reference to the paper by
K. Tanabe et al. in "Studies in Surface Science and
Catalysis", Vol. 51, 1989, Chap. 1 and 2, the Hammett
- 8 -
acidity is determined by amine titration using
indicators or by adsorption of a base in the gas phase.
The catalysts meeting the criterion of acidity Ho less
than +2 can be chosen from natural or synthetic
siliceous materials or acid zeolites; inorganic
supports, such as oxides, covered with inorganic acids
which are mono-, di- tri- or polyacids; oxides or mixed
oxides, iron phosphates or heteropolyacids.
Advantageously, the catalysts are chosen from zeolites,
Nafion® composites (based on sulfonic acid of
fluoropolymers), chlorinated aluminas, phosphotungstic
and/or silicotungstic acids and acid salts, and various
solids of the type comprising metal oxides, such as
tantalum oxide Ta205, niobium oxide NbaOs, alumina AI2O3,
titanium oxide Ti02, zirconia Zr02, tin oxide Sn02,
silica Si02 or silicoaluminate Si02/Al203, impregnated
with acid functional groups, such as borate BO3, sulfate
SO4, tungstate WO3, phosphate PO4, silicate Si02 or
molybdate M0O3. According to the literature data, these
catalysts all have a Hammett acidity Ho of less than +2.
The preferred catalysts are sulfated zirconias,
phosphated zirconias, tungstated zirconias, silica
zirconias, sulfated titanium or tin oxides, phosphated
aluminas or silicas, doped iron phosphates, or
phosphor- or silicotungstic acid salts.
These catalysts all have a Hammett acidity HQ of less
than +2; the acidity Ho can then vary to a large extent,
down to values which can reach -20 in the reference
scale with Hammett indicators. The table given on
page 71 of the publication on acid/base catalysis
(C. Marcilly), Vol. 1, in Editions Technip
(ISBN No. 2-7108-0841-2), illustrates examples of solid
catalysts within this acidity range.
The catalysts selected for this reaction are acid
solids. The acidity of the solids can be measured in
- 9 -
numerous ways and the Hammett method is only one of
them.
The work by C. Marcilly referred to above furthermore
lists various methods for measuring the acidity and the
basicity offthe solids.
Reference will be made to the publications by
Aline Auroux, where various methods for measuring the
acidity scales of solids are described, such as:
A. Auroux and A. Gervasini, "J. Microcalorimetric Study
of the Acidity and Basicity of Metal Oxide Surfaces",
Phys. Chem., (1990) 94, 6371-79, and L. Damjanovic and
A. Auroux, in "Handbook of Thermal Analysis and
Calorimetry", Vol. 5, Chapter 11, pages 387-485: Recent
Advances, Techniques and Applications, M.E. Brown and
P.K. Gallager, editors (2008 Elsevier B.V.).
Methods used to measure this acidity are described in
patents EP 1 714 696 [0038 and 0039] and EP 1 714 955
[0045 and 0046] where the cases where the solid is
white or not in color are distinguished.
These studies illustrate in particular that a solid is
rarely composed either of solely acidic sites or of
solely basic sites. Acid solids have most of the time
both acidic sites, which are predominant, but also some
basic sites. This dichotomy is illustrated in
particular in the paper by A. Auroux and A. Gervasini
on page 6377, where figure 13 shows that one and the
same oxide can simultaneously adsorb an acid compound,
such as CO2, and a basic compound, such as NH3. Without
wishing to be committed to any one theory, it is
believed that the latter compounds contribute to the
formation of the byproducts in the process.
The process is implemented in the presence of an acid
compound present in the gas phase of the reaction
medium which exhibits an affinity with the undesirable
- 10 -
basic sites constituting the catalyst. This compound
will be chosen from hard and soft acids as defined in
the "Pearson" classification illustrated in the
following, papers: R.G. Pearson, J. Am. Chem. Soc, 85,
3533 (1963); R.G. Pearson, Science, 151 (1966), 172;
R.G. Pearson, Chemistry in Britain, March 1967, 103;
R.G. Pearson, J. Chemical Education, Vol. 45, No. 9
(1968), 581, and Vol. 45, No. 10 (1968), 643; R.G. Parr
and R.G. Pearson, J. Am. Chem. Soc, (1983), 105, 7512.
It should be emphasized that, in the work by
C. Marcilly referred to above, the scale based on the
Pearson theory is used on pages 34 et seq.
These compounds can be gases under standard conditions
but they can be either liquids or even solids if they
are capable of passing into the gas phase of the
reaction medium under the operating conditions of the
process.
Preferably, the dehydration is carried out in the
presence of a gas phase comprising a minor fraction of
at least one acid compound within the meaning of the
Pearson classification.
This acid compound will be chosen in particular from
SO3, SO2, NO2, and the like. It would not be departing
from the scope of the invention if use were made of a
mixture of these compounds. According to the Pearson
theory, hard acids prefer to combine with hard bases
and soft acids with soft bases. Use may be made of a
mixture of compounds combining different acidities in
order to inhibit the different basic sites present on
the catalyst.
The content of acid compounds will depend on the nature
of the catalyst chosen for the dehydration reaction. It
will generally be between 1 and 3000 ppm of the gas
- 11 -
phase or, expressed as percentage by volume, from
0.0001 to 0.3%.
If the reaction is carried out in the liquid phase, the
acid compound can be in liquid form or even in solid
•form, provided that it is capable, under the reaction
conditions, of passing into the liquid phase to achieve
the above contents or, in the case of a solid compound,
of dissolving and then of passing into the liquid
phase, as was specified above.
It should be noted that patent EP 1 253 132 describes a
process for the synthesis of acrylic acid by oxidation
of alkanes or acrolein in the presence of a reducing
compound composed of organic acids (formic or oxalic
acid) or compounds comprising sulfur, such as SO2 or
H2S, SO2 being preferred. However, it may be emphasized
that it is not the same reaction with a different
catalyst and that the activity of said compound is to
stabilize the catalyst and not to increase its
selectivity. The reaction according to the invention
can be carried out in the gas phase or in the liquid
phase, preferably in the gas phase.
When the reaction is carried out in the gas phase,
different processing technologies can be used, namely
fixed bed process, fluidized bed process or circulating
fluidized bed process. In the first 2 processes, in a
fixed bed or in a fluidized bed, the regeneration of
the catalyst can be separated from the reaction.
It can be carried out ex situ, for example by
extraction of the catalyst and combustion under air or
with a gas mixture comprising molecular oxygen. In this
case, the temperature and the pressure at which the
regeneration is carried out, do not have to be the same
as those at which the reaction is carried out.
Preferably, the addition of the acid compounds within
- 12 -
the meaning of Pearson is carried out in the reactor
and not during the regeneration.
According to the process of the invention, it can be
carried out continuously in situ, at the same time as
the reaction, in view of the presence of a small amount
of molecular oxygen or of a gas comprising molecular
oxygen in the reactor. In this case, the regeneration
is similar to an inhibition of the deactivation and
takes place at the temperature and the pressure of the
reaction. Due to these specific conditions where the
regeneration takes place continuously, the injection of
the gaseous acid compound happens to be simultaneous
and preferably upstream of the catalytic bed, so that
the acid compounds are perfectly mixed in the reaction
mixture.
In the circulating fluidized bed process, the catalyst
circulates in two vessels, a reactor and a regenerator.
It is known that the dehydration reaction is
endothermic; it is therefore necessary to provide
energy to the first vessel, whereas the regeneration,
consisting of the combustion of the coke, is
exothermic; it is therefore necessary to remove the
heat from the second vessel. In the case of the
circulating fluidized bed, the two systems can cancel
each other out: according to the process of the
invention, the regeneration of the catalyst under a
stream of oxygen by combustion results in a reheating
of the catalyst and consequently provides the energy
necessary for the dehydration reaction when the
reheated catalyst returns to the reactor. The residence
time in each vessel depends on the rate of deactivation
of the catalyst and on the amount of coke formed on the
catalyst. Specifically, a minimum amount of coke is
desirable in order to be able to bring the solid back
to the favorable temperature and a maximum amount of
coke is necessary in order to prevent the solid from
deteriorating by sintering during the combustion. The
- 13 -
injection of the gaseous acid compound is preferably
carried out in the reactor.
The dehydration reaction is carried out in the gas
phase in the presence of a catalyst at a temperature
ranging from 150°C to 500°C, preferably of between
250°C and 350°C, and a pressure of between 1 and 5 bar.
The reaction is carried out in the liquid phase in the
presence of a catalyst at a temperature ranging from
150°C to 500°C, preferably of between 250°C and 350°C,
and a pressure of greater than 5 bar and preferably of
between 20 and 80 bar.
The following examples illustrate the process of the
present invention.
During the dehydration of glycerol in the presence of a
conventional acid catalyst, acrolein is obtained but
also byproducts, such as hydroxypropanone, propanal,
acetaldehyde, acetone, phenol, the addition products of
acrolein with glycerol, the polycondensation products
of glycerol, and cyclic or noncyclic glycerol ethers.
These examples illustrate the effect of the presence of
the acid compound on the selectivity of the reaction
with regard to the various known byproducts and in
particular hydroxypropanone, which is the most evident
compound and is thus representative of the
effectiveness of the process. They will also illustrate
the effects of the presence of acid compounds on the
deactivation of the catalyst.
Example 1
The reaction can be carried out under the following
conditions. Use is made of a Pyrex reactor containing a
catalyst bed held by a sintered glass. First of all a
catalyst, such as the tungstated zirconia dehydration
- 14 -
catalyst from Dailchi Kigenso KK, reference Z1044,
having a weight of approximately 6.6 g and reduced to a
particle size of 0,1-0.15 mm, diluted with 7 ml of
silicon carbide with a fine particle size (0.125 mm),
is charged. Subsequently, a series of beds of silicon
carbide with different particle sizes: 2 ml of
0.125 mm, 7 ml of 0.5 mm and, finally, 1.19 mm up to
the top of the reactor, is charged.
The reactor is subsequently placed in an oven connected
to the test installation. The temperature of the
catalyst is temperature regulated at 305°C, measured in
the "dehydration layer".
The reactor is fed via the top with a heliumk;
rypton/S02/water-glycerol gas mixture at a pressure of
1.3 bar absolute. The helium-krypton gas mixture
contains 4.92% of krypton, which acts as internal
standard. The water-glycerol mixture contains 30% by
weight of glycerol.
The composition of the injected mixture is as follows,
expressed as molar percentage:
he lium/krypt on/02/SO2/water/glycerol:
50/2. 6/3.4/0.02/40. 6/3.4.
The flow rate for introduction of the charging mixture
is such that the hourly space velocity (HSV) will be
2000 h"^
The hourly space velocity is equal to the ratio of the
total gas flow rate of the gas mixture, expressed in
standard liters per hour, to the bulk catalyst volume,
expressed in liters.
The effluents are trapped in water at the outlet of the
reactor with a trap cooled to 0°C, making it possible
to separate the liquid effluents from the
noncondensable effluents. The acrolein and the hydroxy-
15 -
propanone, as model compound for the byproducts other
than acrylic acid, are quantitatively determined by
chromatographic analysis.
The effluents are accumulated in the trap for a period
of 60 minutes. The noncondensable gases are analyzed
throughout the duration of the balance. The yield of
acrolein produced is 70 mol%, of acrylic acid 2 mol%
and of hydroxyacetone 0.5 mol%.
Example 2 (Comparative)
Example 1 will be repeated but in the absence of SO2.
The effluents are accumulated in the trap for a period
of 60 minutes. The noncondensable gases are analyzed
throughout the duration of the balance. The yield of
acrolein produced is 68 mol%, of acrylic acid 2 mol%
and of hydroxyacetone 2 mol%.
Example 3
Use is made of the same Pyrex reactor as in example 1,
It is charged with a tungstated zirconia dehydration
catalyst from Daiichi Kigenso Kagaku Kogyo, reference
Z1044 ring, ground and sieved to a particle size of
0.32 to 0.50 mm, with a volume of 7 ml and a weight of
9.18 g. The undiluted catalyst is placed between 2
layers of silicon carbide.
The reactor is placed in an oven which is regulated at
a temperature of 275°C. The reactor is fed with a gas
mixture at 275 °C of N2/02/S02/water/glycerol at a
pressure of 1.3 bar absolute. This gas mixture is
obtained by injecting, into an electric evaporator, on
the one hand, a stream of nitrogen and a stream of
oxygen which are controlled in flow rate by mass flow
regulators and, on the other hand, a liquid stream of a
mixture of glycerol (Prolabo), demineralized water and
- 16 -
sulfurous acid comprising 7.4% of SO2 (Sigma-Aldrich),
via a volumetric pump of HPLC type, the flow rate of
which is controlled by a balance.
The composition of the injected mixture is as follows,
expressed as molar percentages:
Nz/Oa/SOz/water/glycerol: 15.4/3.9/0.005/74.5/6.2.
The flow rate for introduction of the charging mixture
is such that the hourly space velocity (HSV) is
4200 h'After injecting the gas mixture over the catalyst for
3 hours, a material balance is carried out for
90 minutes in the same way as in example 1. The results
are given in table 1.
Example 4
The conditions of example 3 are repeated with a gas
mixture with the molar composition:
N2/02/S02/water/glycerol: 15.4/3.9/0.025/14. 5/6.2.
A balance is carried out after injecting the mixture
for 3 hours and for 24 hours.
The results are given in table 1.
Example 5 (Comparative)
The conditions of example 3 are reproduced with a gas
mixture with the molar composition:
N2/02/S02/water/glycerol: 15.4/3.5/0/74.5/5.2.
A balance is carried out after 3 hours and 24 hours.
The results are given in table 1.
Table 1
- 17 -
5
Example 3 4
(comparative)
Injection time
3 3 24 3 24
(hj
SO2 (mol%) 0.005 0.025 0.025' 0 0
Glycerol
100 100 87 100 69
conversion (%)
Acrolein yield
73 73 60 72 49
(%)
Hydroxypropanone
0.4 0.2 5.9 2.4 5.9
yield (%) | | | \ It is found that the addition of SO2 not only brings
about an improvement in the yield but also limits the
deactivation of the catalyst.

- 18 -
WHAT IS CLAIMED IS:
1. A process for the synthesis of acrolein by
dehydration of glycerol in the presence of a solid acid
catalyst, characterized in that it is implemented in a
reaction medium comprising a gas phase comprising an
acid compound.
2. The process as claimed in claim 1, characterized
in that the catalyst has a Hammett acidity of less than
+2.
3. The process as claimed in claim 2, characterized
in that the catalyst is chosen from zeolites, Nafion®
composites, chlorinated aluminas, phosphotungstic
and/or silicotungstic acids and acid salts, and solids
of the type comprising metal oxides, such as tantalum
oxide Ta205, niobium oxide Nb205, alumina AI2O3, titanium
oxide TiOa, zirconia ZrOs, tin oxide SnOa, silica Si02 or
silicoaluminate Si02/Al203, impregnated with acid
functional groups, such as borate BO3, sulfate SO4,
tungstate WO3, phosphate PO4, silicate Si02 or molybdate
M0O3.
4. The process as claimed in claim 3, characterized
in that the catalyst is chosen from sulfated zirconias,
phosphated zirconias, tungstated zirconias, silica
zirconias, sulfated titanium or tin oxides, phosphated
aluminas or silicas, doped iron phosphates, or
phosphor- or silicotungstic acid salts.
5. The process as claimed in one of claims 1 to 4,
characterized in that the dehydration is carried out in
the presence of a gas phase comprising a minor fraction
of at least one acid compound within the meaning of the
Pearson classification.
- 19 -
6. The process as claimed in claim 5, characterized
in that the acid compound is chosen from SO3, SO2 or
NO2.
7. The process as claimed in one of claims 1 to. 6,
characterized in that the content of acid compound in
the gas phase is between 1 and 3000 ppm.
8. The process as claimed in one of claims 1 to 7,
characterized in that the dehydration reaction is
carried out in the gas phase at a temperature of
between 150°C and 500°C, preferably of between 250°C
and 350°C, and under a pressure of between 1 and 5 bar.
9. The process as claimed in one of claims 1 to 7,
characterized in that the reaction is carried out in
the liquid phase at a temperature of between 150°C and
500°C, preferably of between 250°C and 350°C, and under
a pressure of greater than 5 bar and preferably of
between 20 and 80 bar.
Dated this 08/12/2010 \/ / /H
[lfeisHlK£SH\l^(yXHAip^^
\J ^ O? REMFRY^ SWGAR
ATTORNEY FOB 'THE APPLKCANTS.