U.S. patent application number 13/003077 was filed with the patent office on 2011-05-19 for method for producing dialkoxy alkanes by partial oxidation of lower alcohols in the presence of a catalyst based on molybdenum and iron.
Invention is credited to Jean-Luc Dubois.
Application Number | 20110118507 13/003077 |
Document ID | / |
Family ID | 40328662 |
Filed Date | 2011-05-19 |
United States Patent
Application |
20110118507 |
Kind Code |
A1 |
Dubois; Jean-Luc |
May 19, 2011 |
METHOD FOR PRODUCING DIALKOXY ALKANES BY PARTIAL OXIDATION OF LOWER
ALCOHOLS IN THE PRESENCE OF A CATALYST BASED ON MOLYBDENUM AND
IRON
Abstract
The invention relates to a method for producing alkoxy alkanes
by direct partial oxidation of a lower alcohol with a catalyst
based upon mixed oxide containing molybdenum and at least one other
metal selected from the metals that can assume a trivalent
oxidation state such as Fe, Bi, Al, Cr, In, La, Sb, and/or a metal
selected from Ni, Co, Cu, V, W, Ti, Ta, Nb, Mn, Sn, P.
Inventors: |
Dubois; Jean-Luc; (Millery,
FR) |
Family ID: |
40328662 |
Appl. No.: |
13/003077 |
Filed: |
July 21, 2009 |
PCT Filed: |
July 21, 2009 |
PCT NO: |
PCT/FR2009/051456 |
371 Date: |
January 7, 2011 |
Current U.S.
Class: |
568/594 |
Current CPC
Class: |
C07C 41/50 20130101;
C07C 41/50 20130101; C07C 41/50 20130101; C07C 43/303 20130101;
C07C 43/30 20130101 |
Class at
Publication: |
568/594 |
International
Class: |
C07C 41/50 20060101
C07C041/50; C07C 41/58 20060101 C07C041/58 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 2008 |
FR |
FR 0854966 |
Claims
1. Method for producing a partial oxidation product of a light
alcohol, in the form of a dialkoxyalkane, comprising oxidizing a
light alcohol having from 1 to 4 carbon atoms by contact, in the
gas phase, with oxygen or a gas containing molecular oxygen in the
presence of a catalyst corresponding to the composition:
Mo.sub.12Fe.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.su-
p.5.sub.fO.sub.x in which X.sup.1=at least one element selected
from the group consisting of chromium, nickel, cobalt, manganese,
tin and copper; X.sup.2=at least one element selected from the
group consisting of bismuth, antimony, tellurium, indium, aluminium
and silicon, X.sup.3=at least one element selected from the group
consisting of phosphorus, tungsten, titanium, vanadium, tantalum
and niobium; X.sup.4=at least one element selected from the group
consisting of alkaline-earth metals, lanthanum and cerium; X.sup.5
is at least one element selected from the group consisting of
alkali metals; and a, b, c, d and e are indices whose values are
1.5.ltoreq.a.ltoreq.8; 0.ltoreq.b.ltoreq.4; 0.ltoreq.c.ltoreq.5;
0.ltoreq.d.ltoreq.2; 0.ltoreq.e.ltoreq.2; 0.ltoreq.f.ltoreq.2 and x
is a numerical value determined by the degree of oxidation of the
other elements, and characterized in that, the partial pressure of
alcohol is between 15 and 80% and the partial pressure of oxygen is
between 2 and 20%, the ratio of the O.sub.2/alcohol partial
pressures being less than or equal to 1, the remainder of the gas
phase comprising a gas that is inert towards the reaction.
2. Method according to claim 1, characterized in that the light
alcohol is selected from the group consisting of methanol, ethanol,
propanol, isopropanol, n-butanol and 2-butanol.
3. Method according to claim 1, characterized in that the molar
ratio of oxygen, calculated as O.sub.2, to the light alcohol is
between 0.5/6 and 1/l.
4. Method according to claim 1, characterized in that the reaction
is carried out at a temperature between 10 and 400.degree. C. and
under a pressure between 50 and 1000 kPa and with a space velocity
for introducing the reaction mixture between, 2000 and 100 000
h.sup.-1.
5. Method according to claim 1, characterized in that the light
alcohol is methanol or ethanol and the partial oxidation product is
methylal or acetal and the oxidation is carried out by contact in
the vapour phase at a temperature of 10 to 400.degree. C., and at a
pressure of 50 to 1000 kPa.
6. Method according to claim 5, characterized in that the
concentration of the light alcohol in the gas stream is between 25
and 40%, and that of the oxygen is such that the O.sub.2/alcohol
ratio is greater than 1.
7. Method according to claim 1, characterized in that X.sub.2 is
bismuth.
8. Method according to claim 1, characterized in that a catalyst is
selected from the group consisting of mixed oxides of formulae:
Mo.sub.12BiFe.sub.3.7Co.sub.4.7Ni.sup.2.6K.sub.0.09Sb.sub.1Si.sub.7.9O.su-
b.x,
Mo.sub.12BiFe.sub.3.7Co.sub.4.7Ni.sub.2.6K.sub.0.09Ti.sub.0.5S.sub.11-
9O.sub.x and MoO.sub.3--Fe.sub.2(MoO.sub.4).sub.3.
9. Method according to claim 5, characterized in that the space
velocity for introducing the gaseous mixture is from 2000-100
000h.sup.-1.
10. Method according to claim 1, characterized in that the
oxidation of the light alcohol is carried out in a fixed-bed
oxidation reactor containing the catalyst.
11. Method according to claim 10, further characterized in that an
effluent is obtained at an outlet of the reactor, and subjecting
said effluent to a separation step, to produce a top effluent of
light gases comprising the diluent gas or gases, CO, CO.sub.2,
nitrogen when air has been used as the gas containing molecular
oxygen, residual O.sub.2, and a bottom effluent of dialkoxyalkane
and water and further characterized in subjecting said
dialkoxyalkane and water to a distillation to separate the
dialkoxyalkane and the water.
12. The method according to claim 1 characterized in that the
partial pressure of alcohol is between 20 and 50%.
13. The method according to claim 1 characterized in that the ratio
of the O.sub.2/alcohol partial pressures is between 0.5/6 and
1.
14. The method according to claim 3 characterized in that the molar
ratio of oxygen, calculated as O.sub.2, to the light alcohol is
between 1.2/6 and 0.9/1.
15. The method according to claim 5 characterized in that the
oxidation is carried out by contact in the vapour phase at a
temperature of from 100 to 350.degree. C.
16. The method according to claim 5 characterized in that the
oxidation is carried out by contact in the vapour phase at a
temperature of from 200 to 300.degree. C.
17. The method according to claim 5 characterized in that the
oxidation is carried out by contact in the vapour phase at a
pressure of from 100 to 500 kPa.
18. The method according to claim 6 characterized in that the
O.sub.2/alcohol ratio is between 1.2/6 and 0.9/1.
19. The method according to claim 9 characterized in that the space
velocity for introducing the gaseous mixture is from 11 000-44 000
h.sup.-1.
Description
[0001] The present invention relates to a method of producing
dialkoxyalkanes by direct partial oxidation of a light alcohol with
a catalyst based on a mixed oxide containing molybdenum and
iron.
[0002] The dialkoxyalkanes from the method of the invention
correspond to the following general formula:
[0003] RR'CH--O--CRR'--O--CHRR' in which R and R' are either H, or
a CH.sub.3--(CH.sub.2).sub.n-- radical, n being between 0 and 2,
such that the total number of carbon atoms of the R and R' radicals
is .ltoreq.3.
[0004] These compounds are obtained by oxidation of light alcohols,
that is to say linear alcohols comprising from 1 to 4 carbon atoms.
These are primary alcohols such as methanol, ethanol, 1-propanol,
1-butanol or secondary alcohols such as 2-propanol (or isopropanol)
or 2-butanol.
[0005] When the synthesis reaction is carried out with primary
alcohols, the general formula of the dialkoxyalkanes is simplified:
RCH.sub.2--O--CHR--O--CH.sub.2R. This is the formula of the most
industrially sought-after dialkoxyalkanes, namely dimethoxymethane
(or methylal) and 1,1-diethoxyethane (or acetal).
[0006] The methods for oxidation of alcohols and especially light
monoalcohols have been well known for at least one century. This
oxidation can take two routes distinguished by the reaction
mechanism used. The first route is "simple" oxidation, which will
be the subject of the developments herein below, and the second
route is that of dehydrogenation.
[0007] This second route can be carried out in the form of
nonoxidizing dehydrogenation according to the following reaction
mechanism:
[0008] RCH.sub.2OH.fwdarw.RCHO+H.sub.2 with, therefore, production
of hydrogen (with a deficit of oxygen), or in the form of oxidizing
dehydrogenation(oxydehydrogenation) and with production of water by
oxidation of the hydrogen. These reactions are carried out in the
gas phase in the presence, for example, of a reduced copper
catalyst or a metallic silver catalyst at temperatures generally
between 600 and 700.degree. C. Reference may be made, on this
subject, to works such as that of the Institut Francais du Petrole
[French Institute of Oil], "Catalyse de Contact" [Contact
Catalysis] published by Editions Technip (1978) pages 385-393 or
the Catalyst Handbook by M. V. Twigg published by Wolfe Publishing
Ltd (1989) pages 490 to 503. These methods are generally used to
synthesize aldehydes (formol from methanol) or acids or esters.
[0009] As regards the first route of simple oxidation with oxygen,
it is well known that the oxidation of methanol in the presence of
catalysts results, at low temperature, in the production of a
mixture of various oxidized compounds such as, in particular,
formaldehyde, methyl formate or methylal(dimethoxymethane).
[0010] The various catalytic reactions then brought into play with
methanol may be illustrated by the following scheme:
##STR00001##
[0011] The same scheme may be transposed to ethanol and to other
light alcohols.
[0012] The conventional methods that target the production of the
aldehyde by a partial oxidation of the alcohol thus correspond to
the following reaction, in the case of primary alcohols:
2RCH.sub.2OH+O.sub.2.fwdarw.2RCHO+2H.sub.2O
[0013] The methods for complete oxidation of the light alcohols
make it possible to synthesize acids (then the corresponding
esters) according to the following overall reaction:
2RCH.sub.2OH+2O.sub.2.fwdarw.2RCOOH+2H.sub.2O
[0014] which is the result of the following two steps:
2RCH.sub.2OH+O.sub.2.fwdarw.2RCHO+2H.sub.2O
2RCHO+O.sub.2.fwdarw.2RCOOH,
[0015] followed by the esterification:
2RCOOH+2RCH.sub.2OH.fwdarw.2RCOO CH.sub.2R+2H.sub.2O
[0016] Unlike the methods of the second route, the methods of
partial oxidation of light alcohols also make it possible to form
dialkoxyalkanes according to the following overall reaction that
corresponds to primary alcohols:
6RCH.sub.2OH+O.sub.2.fwdarw.2RCH.sub.2ORCHOCH.sub.2R+4H.sub.2O
[0017] which is the result of two successive steps:
2RCH.sub.2OH+O.sub.2.fwdarw.2RCHO+2H.sub.2O
2RCHO+4RCH.sub.2OH.fwdarw.2RCH.sub.2ORCHOCH.sub.2R+2H.sub.2O
[0018] It is common practice to distinguish between, on the one
hand, total or deep oxidations which make it possible to form acids
or esters, and partial oxidations which stop at the aldehyde or
dialkoxyalkane stage.
[0019] The concomitance of these various reactions and the presence
of the various molecules in the medium are illustrated, for
example, by the articles by N. Pernicone et al. in "On the
Mechanism of CH.sub.3OH Oxidation to CH.sub.2O over
MoO.sub.3--Fe.sub.2 (MoO.sub.9).sub.3 Catalyst" published in
Journal of Catalysis 14, 293-302 (1969) and by Haichao Liu and
Enrique Iglesia published in J. Phys. Chem. B (2005), 109,
2155-2163 "Selective Oxidation of Methanol and Ethanol on Supported
Ruthenium Oxide Clusters at Low Temperatures".
[0020] Similar mechanisms are used in the oxidation reactions of
secondary light alcohols such as 2-propanol and 2-butanol.
[0021] The initial oxidation of the alcohol leads to a ketone of
formula CH.sub.3--CO--CH.sub.3 with isopropanol and
CH.sub.3--CO--C.sub.2H.sub.5 with 2-butanol. The following reaction
step of the ketone with the light alcohol leads to dialkoxyalkanes
of respective formulae
(CH3).sub.2CH--O--C(CH.sub.3).sub.2--O--CH(CH.sub.3).sub.2 and
(C.sub.2H.sub.5)(CH.sub.3)CH--O--C(CH.sub.3)(C.sub.2H.sub.5)--O--CH(CH.su-
b.3)(C.sub.2H.sub.5). The overall reaction for the oxidation to the
dialkoxyalkane 2,2-diisopropoxypropane from isopropanol is
summarized as follows.
##STR00002##
[0022] Research studies having an industrial objective have
therefore turned towards the study of the operating conditions,
temperature, liquid phase or gas phase and especially catalysts for
the method that makes it possible to obtain the "target" oxidized
compound, aldehyde, acid and/or ester or dialkoxyalkane. The
problem to be solved is to obtain, by direct oxidation of the
charge of alcohol, the desired "target" product with,
simultaneously, a high conversion and a high selectivity.
[0023] The conventional industrial methods for producing the
aldehyde by conventional oxidation (first route) correspond to the
following reaction:
2RCH.sub.2OH.sub.2.fwdarw.2RCHO+2H.sub.2O
[0024] This oxidation is carried out in the gas phase in the
presence of mixed oxide type catalysts at a temperature between 200
and 400.degree. C. In the latter case, the oxygen present within
the reaction medium is in excess but used in dilute form, the
substantially equal partial pressures of O.sub.2 and alcohol are
around a few %, therefore having an O.sub.2/alcohol molar ratio
>1, the main part of the reaction medium being composed of inert
compounds in order not to be under flammable conditions. The use of
a large stoichiometric excess of oxygen at a relatively high
temperature may result, if precautions are not taken, in complete
oxidation and therefore in the homologous acid of the alcohol (see
the preceding scheme) by oxidation of the aldehyde, the reaction
furthermore possibly continuing even further to result in the
"combustion" of the acid, producing carbon dioxide and water.
[0025] The manufacture of formol or formaldehyde was, and still is,
a particularly attractive sector, which explains the abundance of
literature on this subject, whereas the basic methods date back to
the start of the last century for the dehydration route and to 1931
for the oxidation route.
[0026] The aforementioned article by N. Pernicone at al. refers to
a method for the industrial synthesis of formaldehyde, the
Montedison process, catalysed by a mixed oxide based on molybdenum
and iron and cites a study on the reaction mechanism of this type
of reaction, including parasitic secondary reactions.
[0027] Mention may also be made of U.S. Pat. No. 7,468,341 which
describes a catalyst for oxidation of methanol to formaldehyde
consisting of a mixed Fe--Mo oxide associated with a mixed oxide
containing cerium or alternatively Application WO 99/52630 which,
in a method for oxidation of methanol to formaldehyde, is targeted
at the in situ regeneration of the iron molybdate catalyst. All of
the above illustrates the essential role that this type of catalyst
plays on the industrial scale in the manufacture of
formaldehyde.
[0028] The studies carried out for the synthesis of specific
(target) oxidation compounds of alcohols have mainly related to the
study of the types of catalysts suitable for the implementation of
such a specific oxidation. Note may be taken, regarding the
conventional synthesis of aldehydes, of the following studies:
[0029] For the complete oxidation resulting in formic acid or its
ester, methyl formate, Patent Application US 2005/0059839 A1 may be
cited which describes catalysts for the oxidation of methanol
composed of platinum-group metals (ruthenium) deposited on a
support. This patent application corresponds to the studies by H.
Liu and E. Iglesia targeted in the abovementioned publication.
Specific studies have been carried out on the methods for partial
oxidation of alcohols, for the synthesis of methylal, and relating,
in particular, to the catalysts to be used in this type of
method.
[0030] Mention may be made of the following documents.
[0031] U.S. Pat. No. 2,663,742 describes a method of producing
methylal by oxidation in the vapour phase of methanol in the
presence of a catalyst and a halogen or a hydrogen halide.
[0032] Several studies have focused on the use of rhenium-based
catalysts. U.S. Pat. No. 6,403,841 describes a process for
producing methylal by oxidation of methanol over a
rhenium-antimony-based catalyst (SbRe.sub.2O.sub.6). The reaction
is carried out with an excess of oxygen in the presence of a large
volume of inert gas (by volume: 5% methanol, 10% oxygen and 85%
helium, O.sub.2/methanol ratio=2). These studies carried out by Y.
Yuan, at al. have been the subject of several publications such as
Chem. Comm., 2000, 1421-1422, which describes catalysts based on
supported or unsupported rhenium and also in: J. Phys. Chem. B,
2002, 106, 4441; Topics in Catalysis, vol 22, No 1/2, January 2003;
Chemistry Letters 2000, 674 and J. Catal. 195 (2000) 51-61.
[0033] Other studies have been carried out on the use of
molybdenum-based catalysts.
[0034] US Application No. 2005/0154226 A1 describes a method for
producing methylal by oxidation of methanol and/or dimethyl ether.
The reaction is carried out over a heteropolyacid catalyst of
formula H.sub.3+nXV.sub.nMo.sub.12-nO.sub.40, where X represents
phosphorus or silicon, and n a value of 0 to 4. The best results
seem to be obtained with a H.sub.5PV.sub.2Mo.sub.10O.sub.40
catalyst on silica. These studies have also been published in J.
Phys. Chem. B 2003, 107, 10840-10847.
[0035] M. Fournier, C. Rocchicciolo-Deltcheff, et al. describe the
evaluation of catalysts of formula H.sub.3PMo.sub.12O.sub.40/silica
for the oxidation of methanol to methylal (J. Chem. Soc., Chem.
Common. 1994, 307-308). The same team describes the use, in the
same reaction, of a catalyst of formula
H.sub.4SiMo.sub.12O.sub.40/silica (J. Chem. Soc., Chem. Commun.
1998, 1260-1261).
[0036] The Applicant has filed a Patent Application WO 2007/034264
describing the use, in this type of method for partial oxidation of
a light alcohol, of a catalyst composed of a mixed oxide based on
molybdenum and vanadium combined, where appropriate, with other
metal elements. The preferred catalyst corresponds to the formula
Mo.sub.12V.sub.3W.sub.1.2Cu.sub.1.2Sb.sub.0.5O.sub.x, x being a
numerical value determined by the degree of oxidation of the other
elements. This type of catalyst makes it possible in particular to
obtain high yields of acetals over a wide range of methanol partial
pressures and over a wide range of O.sub.2/methanol ratio.
[0037] Furthermore, the Applicant has also filed a Patent
Application WO2007/128941 which describes a catalytic method for
partial oxidation of a light alcohol employing a light alkane as
inert gas for diluting the reaction medium. This type of method can
be used for the synthesis of methylal with the catalyst of Patent
Application WO2007/034264.
[0038] Furthermore, J. Sambeth, L. Gambaro and H. Thomas,
Adsorption Science Technology (1995) page 171, use vanadium
pentoxide for the oxidation of methanol, the methylal being one of
the products derived from the reaction.
[0039] None of the catalysts known for the preparation of a partial
oxidation product of a light alcohol in the form of a
dialkoxyalkane such as, for example, methylal by direct oxidation
of methanol gives complete satisfaction. The object of the present
invention is to overcome these drawbacks and to provide a method
for the synthesis of a dialkoxyalkane by direct partial oxidation
of a light alcohol that makes it possible to attain,
simultaneously, yields, productivities and selectivities that are
high in dialkoxyalkane.
[0040] The subject of the present invention is therefore a method
for producing a partial oxidation product of a light alcohol, in
the form of a dialkoxyalkane, in which a light alcohol comprising
from 1 to 4 carbon atoms is subjected to oxidation by contact in
the gas phase with oxygen or a gas containing molecular oxygen in
the presence of a catalyst corresponding to the following
composition:
Mo.sub.12Fe.sub.aX.sup.1.sub.bX.sup.2.sub.cX.sup.3.sub.dX.sup.4.sub.eX.s-
up.5.sub.fO.sub.x
[0041] in which Mo=molybdenum; O=oxygen; Fe=iron; X.sup.1=at least
one element chosen from chromium, nickel, cobalt, manganese, tin
and copper; X.sup.2=at least one element chosen from bismuth,
antimony, tellurium, indium, aluminium and silicon, X.sup.3=at
least one element chosen from phosphorus, tungsten, titanium,
vanadium, tantalum and niobium; X.sup.4=at least one element chosen
from alkaline-earth metals, lanthanum and cerium; X.sup.5 is at
least one element chosen from alkali metals; and a, b, c, d and e
are indices whose values are 1.5.ltoreq.a.ltoreq.8;
0.ltoreq.b.ltoreq.4; 0.ltoreq.c.ltoreq.5; 0.ltoreq.d.ltoreq.2;
0.ltoreq.e.ltoreq.2; 0.ltoreq.f.ltoreq.2 and x is a numerical value
determined by the degree of oxidation of the other elements, and
characterized in that, within the reaction medium, the partial
pressure of alcohol is between 15 and 80% and preferably between 20
and 50% and that of oxygen is between 2 and 20%, the ratio of the
O.sub.2/alcohol partial pressures being less than or equal to 1 and
preferably between 0.5/6 and 1, the remainder of the medium being
composed of a gas that is inert towards the reaction.
[0042] A light alcohol in the method of the present invention
denotes a linear alcohol having 1 to 4 carbon atoms, in other words
methanol, ethanol, propanol and butanol, the alcohol functional
group being placed at position 1 or 2 for the latter two.
[0043] In the catalyst, the Mo/Fe atomic ratio will be between 1.5
and 8 and preferably between 2.5 and 4.5 to give the industrial
catalyst a better service life and better stability.
[0044] In the method of the invention, use will be made of mixed
oxides of molybdenum and iron which could be associated with at
least one metal capable of adopting the degree of oxidation, three,
such as bismuth, aluminium, chromium, indium, antimony and
tellurium, and/or at least one metal chosen from phosphorus,
tungsten, vanadium, nickel, cobalt, copper, titanium, tantalum,
niobium, manganese, tin and silicon which in general plays more the
role of a binder than a component of the active phase of the
catalyst.
[0045] The preferred catalysts of the method of the invention will
be those which will combine, in the form of mixed oxides,
molybdenum and iron or molybdenum, iron and bismuth. Mention may be
made, for example, of the mixed oxides of formulae:
MoO.sub.3--Fe.sub.2(MoO.sub.4).sub.3,
Mo.sub.12BiFe.sub.3.7Co.sub.4.7Ni.sub.2.6K.sub.0.09Sb.sub.1Si.sub.7.9O.su-
b.x or Mo.sub.12BiFe.sub.3.7Co.sub.4.7Ni.sub.2.6K.sub.0.09
Ti.sub.0.5S.sub.119O.sub.x.
[0046] In order to carry out the oxidation of the light alcohol, a
gaseous starting charge composed of a mixture of the gaseous light
alcohol to be oxidized, molecular oxygen or a gas containing
molecular oxygen, such as air, and also, optionally, a diluent gas
(other than nitrogen from the air) is introduced into the reactor
containing the catalyst. In order to arrive at the composition
ranges defined above, use will preferably be made of diluted air or
an alcohol/air mixture while ensuring the presence of an excess of
oxygen relative to the stoichiometry of the reaction in order to
prevent degradation of the catalyst.
[0047] The gaseous charge will be composed of a mixture of a light
alcohol and oxygen generally in the presence of an inert gas,
usually nitrogen from the air, having a high alcohol content such
that the partial pressure of alcohol within the reaction medium is
greater than 15 and less than or equal to 80% and preferably
between 20 and 50% and that of oxygen is between 2 and 20%.
[0048] The concentration of the light alcohol in the gas stream,
expressed as a partial pressure, is advantageously between 25 and
40%, preferably between 30 and 37%. Use will preferably be made of
a mixture of air and the alcohol to be oxidized, in order to
simplify and optimize the operating conditions while avoiding as
much as possible the recycling of the co-products CO, CO.sub.2,
N.sub.2 of the reaction.
[0049] The molar ratio of oxygen (calculated as O.sub.2) to the
light alcohol is below 1 and preferably between 0.5/6 and 1/1. The
choice of the respective amounts of oxygen and of alcohol depends
on the type of implementation of the method, either seeking a
complete conversion, in which case it is necessary to be above the
stoichiometry of the reaction, or a partial conversion for which a
deficit of oxygen with respect to the stoichiometry suffices. Use
will preferably be made of a ratio of 1.2/6 to 0.9/1. The gas
containing molecular oxygen may be air or oxygen-enriched air.
Preferably, air is used as a mixture with the alcohol to be
oxidized.
[0050] The reaction carried out in the gas phase will generally be
carried out at a temperature between 10 and 400.degree. C. and
under a pressure between 50 and 1000 kPa and with a space velocity
for introducing the reaction mixture between, in particular, 2000
and 100 000 h.sup.-1.
[0051] The oxidation is carried out by contact in the vapour phase
at a temperature in particular of 10 to 400.degree. C., preferably
from 100 to 350.degree. C., and more preferably from 200 to
300.degree. C.
[0052] The oxidation is carried out by contact in the vapour phase
at a pressure generally between 50 and 1000 kPa, preferably between
100 and 500 kPa.
[0053] The space velocity for introducing the reaction mixture is
generally between 2000 and 100 000 h.sup.-1, preferably between 11
000 and 44 000 h.sup.-1.
[0054] The preferred dialkoxyalkanes which may be obtained
according to the method of the invention are dimethoxymethane, also
known as methylal or formaldehyde dimethyl acetal, and
1,1-diethoxyethane or acetal.
[0055] The present invention relates more particularly to the
preparation of these two alkoxyalkanes and especially of methylal
by direct (in one step) partial oxidation starting from methanol
(or ethanol) and oxygen or a gas containing oxygen, the
stoichiometry of the overall reaction being the following:
6CH.sub.3OH+O.sub.2.fwdarw.2CH.sub.3OCH.sub.2OCH.sub.3+4H.sub.2O
[0056] This reaction, applied to the oxidation of ethanol to obtain
acetal or 1,1-diethoxyethane, corresponds to:
6CH.sub.3CH.sub.2OH+O.sub.2.fwdarw.2CH.sub.3CH.sub.2OCH(CH.sub.3)OCH.sub-
.2CH.sub.3+4H.sub.2O
[0057] This is because the Applicant has surprisingly discovered
that catalysts based on a mixed oxide of molybdenum and iron,
widely used for the synthesis of formaldehyde starting from
methanol, make it possible to obtain, by direct oxidation of the
methanol, high yields (conversion and selectivity) of methylal and
that they also make it possible to synthesize 1,1-diethoxyethane
from ethanol. This is because the Applicant has surprisingly
observed, regarding catalysts dedicated to aldehyde synthesis, that
high yields of acetals could be obtained by using, in the presence
of catalysts such as defined in the general formula defined above,
an air/alcohol mixture with a high alcohol content greater than
15%, preferably containing from 30 to 40% alcohol. For example, use
will be made of an air/alcohol mixture having 35% alcohol, or a
ternary O.sub.2/N.sub.2/alcohol mixture having a composition close
to 13/52/35 and therefore an O.sub.2/alcohol ratio of 13/35.
[0058] Compared to the prior art, the advantages, apart from the
performance as regards yield and selectivity, are a greater
productivity and a lower consumption of energy since it is not
necessary to use a high flow rate or high concentration of diluent
inert gas to keep the reaction mixture outside of the flammability
zone of the alcohol/oxygen/inert gas mixture. In the case of the
use of inert gas(es) in sufficient amount(s) to remain outside of
the flammability limits, these will advantageously be chosen from:
nitrogen, CO.sub.2, H.sub.2O and CH.sub.4. It will be carried out
in the absence of halogens or hydrogen halides in order to prevent
the formation of halomethanes.
[0059] It may be noted that these conditions are highly different
from those described in U.S. Pat. No. 2,663,742, where the
MeOH/O.sub.2 molar ratio is greater than 12, but where the reaction
is carried out in the presence of chlorine. The conditions of the
present reaction are, in particular, an MeOH/O.sub.2 molar ratio
below 12 and preferably below 6, since it is desired, on the one
hand, to be outside of the flammability zone and, on the other
hand, to have enough O.sub.2 at the outlet of the reactor to
maintain the stability of the catalyst when working at a high
conversion.
[0060] The method may be carried out in any reactor technology
using a solid catalyst which makes it possible to effectively
eliminate the heat of reaction. Mention may be made, for example,
of multitubular fixed beds, circulating fluidized beds, or else
fluidized beds. The catalyst is then shaped according to the chosen
reactor technology, by techniques well known to persons skilled in
the art; for example, in the form of pellets, rings (hollow
cylinders), solid extrudates or else catalysts supported on an
inert material, for example beads of steatite, of alumina, of
silica, of silica-alumina or of silicon carbide in the case of a
fixed bed. In the case of a fluidized bed or a circulating
fluidized bed, the catalyst may be shaped, for example, by spraying
in the presence of a binder such as silica in order to give it the
necessary mechanical strength.
[0061] Preferably, a reactor with a fixed bed containing the
catalyst will be used.
[0062] It is then advantageously possible to carry out the
oxidation of methanol (or ethanol or another light alcohol) in a
fixed-bed oxidation reactor containing the catalyst in order to
obtain an effluent that is subjected to a separation step. Obtained
in this step is, on the one hand, at the top, an effluent of light
gases comprising, where appropriate, the diluent gas or gases, CO,
CO.sub.2, nitrogen from the air (N.sub.2) when air has been used as
the gas containing molecular oxygen, and residual O.sub.2 and, on
the other hand, at the bottom, the effluent of methylal (acetal or
dialkoxyalkane) and water which is subjected to a distillation step
to separate the desired dialkoxyalkane at the top and water at the
bottom. At least one part of said effluent of light gases may be
used in the boiler.
[0063] It is possible to use molecular oxygen or oxygen-enriched
air as an oxidant and methane as an additional diluent; an effluent
of light gases comprising CH.sub.4, CO, CO.sub.2, N.sub.2 and
residual O.sub.2 is then obtained which can, where appropriate, be
recycled to the inlet of the oxidation reactor and/or be subjected
to a purification step in order to separate a CO and/or CO.sub.2
and/or O.sub.2 effluent before recycling it to the inlet of the
oxidation reactor.
[0064] As has been indicated several times, all these methods for
oxidation of alcohols, and therefore of fuels, may be carried out
according to the choice of compositions of the ternary mixture
under flammability conditions of the alcohol/oxygen mixture. These
conditions are not an obstacle that nullifies an industrial
exploitation but they require operating precautions which, due to
their cost, must be avoided as much as possible. It is therefore
preferable to operate under strict safety conditions, that is to
say by being sure not to work in the flammability zone of the
alcohol/oxygen mixture.
[0065] In order to do this, it is possible to refer to certain
determinations of this zone in various cases taking into account
the components of the mixture, the operating temperature and the
pressure. The diagram from FIG. 1 illustrates this flammability
zone for a ternary methanol/oxygen/inert gas mixture at a
temperature of 25.degree. C. and at atmospheric pressure.
[0066] To determine the optimal reaction conditions outside of the
flammability zone, reference could be made to various publications
on the subject. Apart from the aforementioned "Catalyst Handbook"
page 498 and the work "Catalyse de Contact" [Contact Catalysis]
page 400, mention may be made of the article by Michael G.
Zabetakis "Flammability Characteristics of Combustible Gases and
Vapors", Bureau of Mines Bulletin 627, pages 66 to 68 and the
Technical report ISA-TR12.13.01-1999 "Flammability Characteristics
of Combustible Gases and Vapors" FIGS. 75 and 76 and Table 13.
[0067] The appended FIG. 1 is presented to better illustrate the
operability conditions, outside of the flammability zones, of the
method that is the subject of the present invention under standard
temperature and pressure conditions, 25.degree. C. and 1 atm.
[0068] In FIG. 1, the bold lines 1 and 2 specify the contents that
are respectively the lower (1) and upper (2) flammability limits.
They define, with the methanol-O.sub.2 axis, the flammability zone
of the mixture which substantially takes the shape of a triangle
(Zone 0), the apex of which is the maximum oxygen content (MOC).
The points denoted by LFL (Air) and UFL (Air) correspond to these
lower and upper limits in the case of using air as an oxidant.
Between these lines (1) and (2) the mixture is in the flammable
Zone 0. The parts located above these lines illustrate
non-flammable mixtures. The right-hand part, Zone 3, is that where
the concentration of alcohol is low and that of oxygen is larger or
smaller but always below the flammability threshold, whereas, in
the left-hand part, Zones 1 and 2 correspond to a low oxygen
content (above the flammability threshold). Lines 3, 4 and 5
correspond to the stoichiometries of the main oxidation reactions
of the alcohol, in this case methanol; a transposition to ethanol
could be easily carried out using the appropriate flammability
diagram. Line 3 corresponds to the combustion of methanol
(CH.sub.3OH+3/2O.sub.2.fwdarw.CO.sub.2+2H.sub.2O), line 4 to the
oxidation to formol
(CH.sub.3OH+1/2O.sub.2.fwdarw.CH.sub.2O+H.sub.2O), line 5 to the
synthesis of methylal
(3CH.sub.3OH+1/2O.sub.2.fwdarw.CH.sub.3OCH.sub.2OCH.sub.3+H.sub.2O)
and finally line 6 to air, that is to say the straight line joining
the methanol apex to the 80/20 N.sub.2 (inert)/O.sub.2 mixture.
[0069] Zone 1 corresponds to mixtures in which an oxygen content
below that of air is used (use of diluted air). It is located
entirely above line 6.
[0070] Zone 2 corresponds to mixtures in which an oxygen content
greater than that of air is used. It is located entirely below line
6.
[0071] Inside these two zones it is possible to provide some
information specific to the methylal formation reaction (line 5).
Specifically, if the straight line parallel to the left-hand axis
is plotted passing through the apex of the flammable zone (Zone 0):
line 7, zone 1 is delimited into two parts 1d and 1g on the one
hand and 1' on the other hand. In the Zone 1d/1g, the oxygen
content is still below the MOC and there is the guarantee of
therefore being outside of the flammability zone. In zone 1', there
is more oxygen than the MOC, but while still being outside of the
flammability zone. On either side of line 5 there are Zones 1g and
1d. In Zone 1g, there is less oxygen than the stoichiometry, which
mathematically will not make it possible to have 100% yield of
methylal. In zone 1d, there is more oxygen than the stoichiometry
for the synthesis of methylal; it is therefore possible to hope for
high conversions and yields. It is possible in each of Zones 1 and
2 to distinguish zones: 1d, 1g and 1' and 2d, 2g and 2'.
[0072] In Zones 1, the reaction may be carried out with air as an
oxidant.
[0073] In Zones 2d, 2g and 2', the reaction should be carried out
with an addition of molecular oxygen. Zone 3 is the zone delimited
by the lower flammability limit.
[0074] Zones 1d, 1g and 2g are delimited by the maximum oxygen
content (MOC). Below this oxygen content, there is the guarantee of
being outside of the flammability limits. It is therefore preferred
to work in this zone for safety reasons.
[0075] Zones 1', 1d and 1g and 2g, 2d and 2' are delimited by the
stoichiometry line for the methanol.fwdarw.methylal reaction
(6CH.sub.3OH/O.sub.2). To the right of this line, there is enough
oxygen to have a complete conversion of methanol to 100%
selectivity of methylal; on the left, there is not enough oxygen
and the conversion will only be partial. It is therefore preferred
to work in the zones 1', 1d and 2'.
[0076] In the method of the invention, the preferred zones are
Zones 1d, 1' and 1g in which it is possible to work with high
contents both of alcohols (30 to 40% or even 50 or 60% by volume)
and of oxygen, of around 15%, while still working with air as a
source of oxygen and being free from using a large source of inert
gas. It should be noted that the maximum content of O.sub.2 depends
on the alcohol and it rises with the number of carbons of the
alcohol.
[0077] It is preferred to use an oxidant gas that is rich in air in
order to reduce electricity consumption at the gas compressors. In
this configuration, it is not necessary to recycle oxygen-depleted
gases of the reaction in order to dilute the oxygen from the air of
reaction and therefore the method is simplified.
[0078] This ternary diagram may be transposed, on the one hand,
with the same constituents under different temperature and pressure
conditions and, on the other hand, to other alcohols, referring to
the publications cited above and especially that of Zebetakis.
Represented on page 67 of this publication is a table from which it
is possible to deduce the maximum oxygen contents according to the
alcohol used.
[0079] Methylal finds many applications in various fields due to
its remarkable properties: an exceptional solvating power; its
amphiphilic character: methylal is both hydrophilic and lipophilic;
a low viscosity; a low surface tension; and a particularly high
evaporation rate.
[0080] The fields of application for methylal are especially the
following: aerosols for cosmetic and technical applications; paints
and varnishes with methylal as a solvent; paint strippers; cleaning
and degreasing solvents; pharmaceutical products with methylal as a
support or as a reagent; in the synthesis of resins; quick-drying
adhesives; in the extraction of flavours, aromatic products and
fragrances; additives for diesel fuels; insecticides;
electrochemical cells, where methylal is a reactant in the
production of polyoxymethylene dimethyl ethers used as fuels in
fuel cells.
[0081] Diethyl acetal or acetaldehyde acetal, also known as
1,1-diethoxyethane, is an important raw material for the perfume
industries and pharmaceutical products. Added to perfumes, it
increases their resistance to oxidation and consequently their
lifetime, whereas it acts as a flavour enhancer in spirits. It also
has many applications in the chemical and pharmaceutical industry
where it is used as a solvent but also as an intermediate in
synthetic chemistry for protecting the carbonyl groups of ketones
and aldehydes. Furthermore, it is also a key molecule in the
synthesis of various chemical compounds such as alcohol vinyl
ethers (used as organic solvents for cellulose and its derivatives,
in perfumes and synthetic resins and also in adhesives) or else
N-vinylcarboxylic acid amides (raw materials for hydrophilic
polymers used in electronic compounds, televisions, motor vehicle
equipment and printers).
[0082] 1,1-diethoxyethane offers many advantages as a fuel additive
both in the formulation of petrols and in that of diesel fuels.
[0083] It may also be used as an oxygenated additive for diesel
fuel since it drastically reduces the emissions of particulates and
NO.sub.x whilst it maintains, or even increases, the cetane number
and thus facilitates the combustion of the final products without
reducing the ignition qualities. It should be noted that a high
cetane number indicates the ability of a fuel to ignite after
having been injected into the combustion cylinder of a diesel
engine. Furthermore, 1,1-diethoxyethane may also be used as an
intermediate to form glycerol acetals used in fuels.
[0084] The following examples further illustrate the present
invention without however limiting the scope thereof.
EXAMPLE 1
Evaluation of the Catalysts
[0085] The evaluation of the catalysts was carried out in a
fixed-bed reactor. The flow of helium and of oxygen was controlled
by mass flow meters. The gas stream passed into an
evaporator/saturator containing methanol. The evaporator was either
at ambient temperature or heated by heating tapes. The temperature
of the saturator was adjusted in order to control the partial
pressure of methanol. The temperature of the gas mixture was
controlled by a thermocouple at the top of the saturator. The gas
mixture was then sent to the reactor which was placed in an oven.
The reaction temperature was measured using a thermocouple which
was in the catalytic bed. The gaseous effluents were analysed by
in-line gas chromatography using a microGC equipped with 2 columns
(molecular sieve and Plot U).
[0086] The catalysts were milled and the 250 micron particle size
fraction was mixed with a double amount of silicon carbide of the
same particle size and placed in the glass reactors.
[0087] Calibration of the MicroGC was carried out with reference
gas mixtures, and calibration for the condensable products
(dimethoxymethane, methanol, methyl formate) was carried out using
the evaporator/saturator.
EXAMPLE 2
Oxidation Reaction of Methanol
[0088] 151 mg of an iron molybdate catalyst MFM3-MS supplied by
MAPCO and having an Mo/Fe atomic ratio of 2.5 were mixed with 300
mg of silicon carbide and charged into the reactor. MFM3-MS
catalyst: outer diameter=3.9 mm, inner diameter=1.85 mm,
height=4.04 mm.
[0089] The catalyst was first activated under a helium/oxygen
stream (48 Sml/min-12 Sml/min) at 340.degree. C. for 15 hours and
30 minutes. Next, the temperature was brought to 250.degree. C. and
the acquisition of data was started. After stabilization, the
performance of the catalyst was recorded. Next, the temperature of
the catalyst was increased in stages and at each level (260, 271
and 281.degree. C.) data were taken.
[0090] The flow rates of oxygen and helium were respectively 6.7
and 26.4 Sml/min and the concentration of methanol was adjusted to
37% (conditions: methanol/O.sub.2/inert gas: 37/13/50) for an HSV
of 22 000 ml.h.sup.-1.g.sup.-1.
[0091] The conversion and selectivity results obtained during the
catalytic oxidation of methanol are given in Table 1 (DMM=methylal;
F=formol; DME=dimethyl ether; ME=methyl formate; CO=carbon
monoxide; CO.sub.2=carbon dioxide).
TABLE-US-00001 TABLE 1 Temperature Conversion Selectivities (%)
Catalyst (.degree. C.) (%) DMM F DME MF CO CO.sub.2 Total MFM3-MS
250 25.3 94.3 0.1 4.9 0.6 -- -- 100 260 32.3 94.3 0.3 4.9 0.6 -- --
100 271 46.5 92.7 1.3 5.2 0.7 0.1 -- 100 281 55.7 89.8 4.2 5.3 0.6
0.1 -- 100
EXAMPLE 3
Oxidation Reaction of Methanol
[0092] The reaction was carried out with a commercial catalyst:
ACF-4S (bismuth-iron molybdate type) from Nippon Shokubai. 150 mg
of the commercial catalyst cited above were mixed with 300 mg of
silicon carbide, then charged into the reactor.
[0093] The catalyst was first activated under a helium/oxygen
stream (48 Sml/min-12 Sml/min) at 340.degree. C. for 15 hours and
30 minutes. Next, the temperature was brought to 236.degree. C. and
the acquisition of data was started. After stabilization, the
performance of the catalyst was recorded. Next, the temperature of
the catalyst was increased in stages and at each level data were
taken.
[0094] The flow rates of oxygen and helium were respectively 6.7
and 26.4 Sml/min and the concentration of methanol was adjusted to
37% (conditions: methanol/O.sub.2/inert gas=37/13/50 for an HSV of
22 000 ml.h.sup.-1.g.sup.-1. with DMM=methylal; F=formol;
DME=dimethyl ether; MF=methyl formate; CO=carbon monoxide;
CO.sub.2=carbon dioxide.
[0095] The conversion and selectivity results obtained are given in
Table 2 below:
TABLE-US-00002 TABLE 2 Temperature Conversion Selectivities (%)
Catalyst (.degree. C.) (%) DMM F DME MF CO CO.sub.2 Total ACF-4S
250 6.7 88.1 5.6 5.8 0.5 -- -- 100 from 259 9.1 87.9 5.8 5.6 0.6 --
-- 100 Nippon 271 13.0 88.5 5.5 5.3 0.6 -- 0.0 100 Shokubai "BiMo"
280 16.7 88.3 5.9 5.1 0.7 -- 0.0 100
EXAMPLE 4 (COMPARATIVE)
[0096] Methanol was oxidized, in accordance with the methods of the
prior art, with 150 mg of the commercial catalyst iron molybdate
MFM3-MS (MAPCO) which were mixed with 300 mg of silicon carbide,
then charged into the reactor.
[0097] The catalyst was first activated under a helium/oxygen
stream (48 Sml/min-12 Sml/min) at 340.degree. C. for 15 hours and
30 minutes. Next, the temperature was brought to 236.degree. C. and
the acquisition of data was started. After stabilization, the
performance of the catalyst was recorded. Next, the temperature of
the catalyst was increased in stages and at each level (255 and
265.degree. C.) data were taken.
[0098] The flow rates of oxygen and helium were respectively 4.7
and 47.6 Sml/min and the concentration of methanol was adjusted to
5% of the reaction medium (Methanol/O.sub.2/inert gas:
5/8.5/86.5).
[0099] The results are given in Table 3 below.
TABLE-US-00003 TABLE 3 CH.sub.3OH DMM Temperature conversion
selectivity DMM yield (.degree. C.) (%) (%) (%) 236 41 36 15 255 57
20 11 265 67 11 7
[0100] As can be seen by comparison between Tables 1 and 3, the
results obtained using a low partial pressure of methanol resulted
in much lower dimethoxymethane selectivities and yields than when
high partial pressures were used. These results are all the more
unexpected since the conversions may be kept at a high level.
EXAMPLE 5
Operating Conditions for the Selective Oxidation of Ethanol
[0101] The catalyst was tested in a fixed-bed reactor. The flow
rates of the helium and oxygen gases were regulated by a mass flow
controller. The gaseous mixture passed through an
evaporator/saturator filled with ethanol. The evaporator could be
at ambient temperature or heated by a heater cable. The temperature
of the saturator was adjusted and controlled in order to obtain the
desired partial pressure of ethanol. The temperature was measured
using a thermocouple at the outlet of the saturator.
[0102] The reaction mixture fed the reactor which was placed in an
oven. The temperature of the reaction was measured by a
thermocouple placed in the catalytic bed.
[0103] The gaseous effluents were analysed in line by a micro-GC
equipped with three columns (molecular sieve, Plot U and OV-1).
[0104] A stream of helium and oxygen passed through the
evaporator/saturator which were adjusted to the appropriate
temperatures making it possible to obtain the desired composition
of ethanol/oxygen/helium. The catalyst was mixed with a quadruple
amount of silicon carbide in the glass reactor.
[0105] The calibration of the micro-GC was carried out with
reference gas mixtures and the condensable products were calibrated
using the evaporator/saturator.
EXAMPLE 6 (COMPARATIVE)
[0106] 151 mg of the MFM3-MS catalyst (supplied by MAPCO) were
mixed with 600 mg of silicon carbide and were charged into the
reactor.
[0107] The catalyst was activated at a temperature of 340.degree.
C. under a helium/oxygen mixture (48 Sml/min/12 Sml/min) for 12
hours. Next, the temperature was decreased to 200.degree. C. and
the data were recorded. After stabilization, the efficiency of the
catalyst was tested. After acquisition of the data, the temperature
of the catalyst was increased to the following temperature:
228.degree. C. then 260.degree. C., where the data were
recorded.
[0108] The flow rates of oxygen and helium were respectively 12.7
and 51 Sml/min and the temperature of the saturator was adjusted to
obtain a molar fraction of ethanol of 2% (ethanol/O.sub.2/inert
gas=2/19.5/78.5).
[0109] The results as regards the conversions and selectivities
obtained during the catalytic oxidation of ethanol, expressed as
follows: A=acetaldehyde; DEE=1,1-diethoxyethane; EE=ethyl ether;
EA=ethyl acetate; AA=acetic acid; E=ethylene; CO=carbon monoxide;
CO.sub.2=carbon dioxide, are given in Table 4.
TABLE-US-00004 TABLE 4 Ethanol Temperature conversion Carbon
selectivities (%) (.degree. C.) (%) A DEE EE EA AA E CO CO.sub.2
200 31.2 92.5 6.5 1 -- -- -- -- -- 228 61.6 98.5 -- 1.5 -- -- -- --
-- 260 91.5 93.2 -- 0.9 1 -- 1.9 1.4 1.6
[0110] Under these operating conditions, the catalyst was very
selective to give acetaldehyde.
EXAMPLE 7
[0111] 150 mg of the MFM3-MS catalyst (MAPCO) were mixed with 600
mg of silicon carbide and were charged into the reactor.
[0112] The catalyst was activated at a temperature of 340.degree.
C. under a helium/oxygen mixture (48 Sml/min/12 Sml/min) for 12
hours. Next, the temperature was decreased to 200.degree. C. and
the data were recorded. After stabilization, the efficiency of the
catalyst was tested. After acquisition of the data, the temperature
of the catalyst was increased to the following temperature:
228.degree. C. then 260.degree. C., where the data were
recorded.
[0113] The flow rates of oxygen and helium were respectively 0.3
and 63.4 Sml/min and the temperature of the saturator was adjusted
to obtain a molar fraction of ethanol of 2% to obtain
EtOH/O.sub.2/inert gas=2/0.5/97.5.
[0114] The conversion and selectivity results obtained during the
catalytic oxidation of ethanol are given in Table 5.
TABLE-US-00005 TABLE 5 Ethanol Temperature conversion Carbon
selectivities (%) (.degree. C.) (%) A DEE EE EA AA E CO CO.sub.2
200 18.4 100 -- -- -- -- -- -- -- 228 41.4 97.5 -- 2.5 -- -- -- --
-- 260 63.5 95.7 -- 2.1 -- -- 2.2 -- --
[0115] Although the catalyst was fed with a stream that was less
rich in oxygen than in the case of the preceding example, it
remained very selective for the production of acetaldehyde.
EXAMPLE 8
[0116] 150 mg of the MFM3-MS catalyst (MAPCO) were mixed with 600
mg of silicon carbide and were charged into the reactor.
[0117] The catalyst was activated at a temperature of 340.degree.
C. under a helium/oxygen mixture (48 Sml/min/12 Sml/min) for 12
hours. Next, the temperature was decreased to 201.degree. C. and
the data were recorded. After stabilization, the efficiency of the
catalyst was tested. After acquisition of the data, the temperature
of the catalyst was increased to the following temperature:
231.degree. C. then 260.degree. C., where the data were
recorded.
[0118] The flow rates of oxygen and helium were respectively 4.6
and 41 Sml/min and the temperature of the saturator was adjusted to
obtain a molar fraction of ethanol of 30%
(Ethanol/O.sub.2/HE=30/7/63).
[0119] The conversion and selectivity results obtained during the
catalytic oxidation of ethanol are given in Table 6.
TABLE-US-00006 TABLE 6 Ethanol Temperature conversion Carbon
selectivities (%) (.degree. C.) (%) A DEE EE EA AA E CO CO.sub.2
201 5 62 36 2 -- -- -- -- -- 231 10.8 68.5 28.5 3 -- -- -- -- --
260 25.6 77.6 17.7 4.1 -- -- 0.6 -- --
[0120] Under these operating conditions, the catalyst produced
diethoxyethane which was not detected under the conditions of low
partial pressures of ethanol.
EXAMPLE 9
[0121] 75 mg of the MFM3-MS catalyst (MAPCO) were mixed with 300 mg
of silicon carbide and were charged into the reactor.
[0122] The catalyst was activated at a temperature of 340.degree.
C. under a helium/oxygen mixture (48 Sml/min/12 Sml/min) for 12
hours. Next, the temperature was decreased to 199.degree. C. and
the data were recorded. After stabilization, the efficiency of the
catalyst was tested. After acquisition of the data, the temperature
of the catalyst was increased to the following temperature:
230.degree. C. then 260.degree. C., where the data were
recorded.
[0123] The flow rates of oxygen and helium were respectively 4.6
and 41 Sml/min and the temperature of the saturator was adjusted to
obtain a molar fraction of ethanol of 30%
(Ethanol/O.sub.2/HE=30/7/63).
[0124] The conversion and selectivity results obtained during the
catalytic oxidation of ethanol are given in Table 7.
TABLE-US-00007 TABLE 7 Ethanol Temperature conversion Carbon
selectivities (%) (.degree. C.) (%) A DEE EE EA AA E CO CO.sub.2
199 2.4 26 72.7 1.3 -- -- -- -- -- 230 8.4 36.3 61.7 2 -- -- -- --
-- 260 17.2 55.9 40.4 3.3 -- -- 0.4 -- --
[0125] Under the conditions of high HSV (short contact time),
double that of Example 8, the catalyst proved to be selective for
diethoxyethane.
EXAMPLE 10
[0126] 150 mg of the MFM3-HS catalyst (MAPCO) were mixed with 600
mg of silicon carbide and were charged into the reactor.
[0127] MFM3-HS supplied by MAPCO is distinguished from the
preceding MFM3-MS in particular by its dimensions but also by its
activity: outer diameter=4.35 mm, inner diameter=1.85 mm,
height=4.44 mm.
[0128] The catalyst was activated at a temperature of 340.degree.
C. under a helium/oxygen mixture (48 Sml/min/12 Sml/min) for 12
hours. Next, the temperature was decreased to 198.degree. C. and
the data were recorded. After stabilization, the efficiency of the
catalyst was tested. After acquisition of the data, the temperature
of the catalyst was increased to the following temperature:
230.degree. C. then 260.degree. C., where the data were
recorded.
[0129] The flow rates of oxygen and helium were respectively 4.6
and 41 Sml/min and the temperature of the saturator was adjusted to
obtain a molar fraction of ethanol of 30%
(Ethanol/O.sub.2/HE=30/7/63). The conversion and selectivity
results obtained during the catalytic oxidation of ethanol are
given in Table 8.
TABLE-US-00008 TABLE 8 Ethanol Temperature conversion Carbon
selectivities (%) (.degree. C.) (%) A DEE EE EA AA E CO CO.sub.2
198 2.4 23.8 74.7 1.5 -- -- -- -- -- 230 7 37.2 60.4 2.2 -- -- 0.2
-- -- 260 17.1 57.9 37.9 3.7 -- -- 0.4 -- 0.1
[0130] Here too, the catalyst proved selective for
diethoxyoethane.
* * * * *