U.S. patent application number 10/752230 was filed with the patent office on 2004-11-18 for catalyst.
Invention is credited to Dugal, Markus, Heinen, Marie-Therese, Schmitt, Jorg, Wegener, Gerhard, Weisbeck, Markus.
Application Number | 20040230083 10/752230 |
Document ID | / |
Family ID | 7712158 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040230083 |
Kind Code |
A1 |
Weisbeck, Markus ; et
al. |
November 18, 2004 |
Catalyst
Abstract
The present invention provides hydro-oxidation catalysts for the
oxidation of hydrocarbons, containing an organic-inorganic hybrid
material as well as gold particles and/or silver particles, a
process for the production thereof, and the use thereof as a
catalyst.
Inventors: |
Weisbeck, Markus; (Koln,
DE) ; Heinen, Marie-Therese; (Langenfeld, DE)
; Schmitt, Jorg; (Grevenbroich, DE) ; Wegener,
Gerhard; (Mettmann, DE) ; Dugal, Markus;
(Koln, DE) |
Correspondence
Address: |
BAYER MATERIAL SCIENCE LLC
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7712158 |
Appl. No.: |
10/752230 |
Filed: |
January 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10752230 |
Jan 6, 2004 |
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10340289 |
Jan 10, 2003 |
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6770765 |
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Current U.S.
Class: |
568/959 ;
502/347 |
Current CPC
Class: |
B01J 23/48 20130101;
C07D 301/10 20130101; B01J 23/52 20130101; C07C 45/33 20130101;
C07C 45/34 20130101; C07C 47/22 20130101; B01J 37/033 20130101;
B01J 37/0211 20130101; B01J 37/0209 20130101; B01J 37/0215
20130101; C07C 45/33 20130101 |
Class at
Publication: |
568/959 ;
502/347 |
International
Class: |
C07D 301/03; C07C
027/00; B01J 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2002 |
DE |
10201241.5 |
Claims
1-7. (Cancelled)
8. A catalyst made by a process comprising, providing a support,
and impregnating the support with an organic-inorganic hybrid
material which is formed from the organic-inorganic hybrid solT
containing titanium in chemically bound form, and at least one of
gold particles and silver particles.
9. The catalyst according to claim 8, wherein the organic-inorganic
hybrid material is based on silicon oxide.
10. The catalyst according to claim 9, wherein the
organic-inorganic hybrid material contains terminal and/or bridging
organic groups on the silicon atoms of the organic-inorganic hybrid
material.
11. The catalyst according to claim 8, wherein the sum of the
contents of gold and silver in the organic-inorganic hybrid
material totals 0.001 to 15 % by weight.
12. The catalyst according to claim 11, wherein the content of gold
in the organic-inorganic hybrid material is 0.001 -2% by
weight.
13. The catalyst according to claim 11, wherein the content of
silver in the organic-inorganic hybrid material is 0.01 -15% by
weight.
14. The catalyst according to claim 8, containing gold particles
having a diameter less than 10 nm.
15. The catalyst according to claim 8, wherein the catalyst
comprises other extraneous oxides (promoters).
16-18. (Cancelled)
19. The catalysts according to claim 8, wherein the titanium is
present as titanium oxide and wherein the titanium oxide
concentration is 0.1 to 10 mol % with respect to the amount of Si
and Ti in the hybrid material.
20. (Cancelled)
21. The catalyst according to claim 8, wherein the support is
selected from the group consisting of oxides of silicon, oxides of
aluminium, oxides of zirconium, oxides of titanium, oxides of
boron, zeolites, clays, mixed oxides of the aforementioned oxides,
carbon, activated carbon, carbon black, graphite, monoliths,
knitted fabrics, cordierite monoliths, ceramic foams, alkali
carbonates, alkaline earth carbonates, carbides, silicon carbide,
silicon nitride, metals, glasses and mixtures thereof.
22. The catalyst according to claim 8, wherein the support is
selected from the group consisting of alumina, silicon oxide,
silicon carbide, carbon and cordierite monolith.
Description
FIELD OF THE INVENTION
[0001] The present invention provides hydro-oxidation catalysts,
for the oxidation of hydrocarbons, containing an organic-inorganic
hybrid material as well as gold particles and/or silver particles,
a process for the production thereof, and methods of use thereof as
a catalyst.
BACKGROUND OF THE INVENTION
[0002] Akylene oxides such as propene oxide, for example, can be
produced from alkenes such as propene. In this procedure, alkenes
are reacted, in the presence of catalysts, with oxygen and with a
reducing agent, e.g. hydrogen. This process is termed a
hydro-oxidation process and the catalysts used therein are termed
hydro-oxidation catalysts (abbreviated herein: HO catalysts).
[0003] Purely inorganic catalysts that contain titanium and gold
are known for the partial oxidation of hydrocarbons in the presence
of oxygen and hydrogen. Catalysts of this type are disclosed, for
example, in EP-A 0 709 360, EP-A 0 876 215, EP-A 0 827 779, WO
98/00414, WO 99/43431 and WO 99/52883.
[0004] Such catalysts are mainly powdered catalysts produced by
multi-stage processes. Suitable powdered support materials, which
are generally based on silicon oxide, are impregnated with a
titanium precursor, washed, dried and converted in a subsequent
process step into insoluble gold hydroxides in the liquid phase by
means of gold precipitation by deposition precipitation (soluble
gold precursors are converted into insoluble gold hydroxides, by
changing the pH from acidic to basic. This means that gold
hydroxides are precipitated on the support surface) with gold
precursors at a controlled pH.
[0005] These so-called precursors are precursor compounds (salts
and other compounds).
[0006] The powdered material which contains the Ti and Au and which
is obtained in this manner cannot yet be used in a fixed bed
reactor without a molding step.
[0007] Oxidation catalysts which contain noble metals and which are
based on organic-inorganic hybrid materials, and a process of
producing epoxides from olefins, oxygen and hydrogen using these
oxidation catalysts, are known from WO 01/41921. Powdered catalysts
are used. Organic-inorganic hybrid materials, which contain
titanium are produced by a sol-gel process. The gold content of
this hybrid process is imparted in a subsequent impregnation step.
This impregnation is termed incipient wetness. Incipient wetness is
an impregnation in which an accurately determined amount of solvent
is used which corresponds to the pore volume of the support. This
gives rise to a sponge effect, in which the support often remains
dry on a macroscopic scale.
[0008] Similar oxidation catalysts containing noble metals and
which are based on organic-inorganic hybrid materials are described
in DE-A 101 07 777, but differ from the systems described above in
that noble metal particles are deposited on to the finished hybrid
materials by spray-drying, namely in a subsequent step comprising a
sol-gel process which includes gel work-up. Catalysts which range
in size from powders to pellets are obtained (molding size<2 mm)
depending on the process.
[0009] DE-A 100 23 717 describes oxidation catalysts based on
organic-inorganic hybrid materials which have a content of noble
metals and which can be used for the production of epoxides from
olefins. In a subsequent step, these powdered catalysts are formed
into moldings, such as extrudates, granules, pellets, etc.
[0010] As an alternative to the molding process described in DE-A
100 23 717 (conversion of organic-inorganic hybrid materials which
contain gold and/or silver into moldings using binders, fillers and
molding apparatuses such as extrusion presses, extruders, etc.), a
route to HO catalysts is known in which an organic-inorganic hybrid
material which does not contain noble metals is deposited on the
inert moldings by impregnation, and the noble metal is deposited on
the impregnated molding in a subsequent step.
[0011] All the processes published heretofore have the disadvantage
that the catalysts disclosed therein are produced by multi-stage
syntheses, and are therefore associated with high manufacturing
costs.
[0012] For industrial processes, it is desirable to develop
catalysts which achieve service lives of industrial interest,
whilst exhibiting excellent selectivities and high productivities.
Moreover, a pressure drop across the catalyst bed that is as low as
possible is desirable. In order to produce catalysts on an
industrial scale (a tonnage scale), the process steps for the
preparation of the catalysts should be as reproducible and as
simple as possible. To achieve an economic process, the cost of
catalyst production should be very low.
SUMMARY OF THE INVENTION
[0013] Accordingly, the present invention provides catalysts
exhibiting low pressure drops for industrial processes, which
provide improved selectivities and productivities compared with the
prior art.
[0014] The present invention further provides a process of
producing these highly active catalysts.
[0015] The present invention also provides a process of producing
these highly active catalysts which is as reproducible as
possible.
[0016] The highly active catalysts of the present invention have a
high mechanical strength.
[0017] The present invention yet further provides a process of
catalyst production, the cost of which is as low as possible. This
is accomplished by having only a few preparation steps and the use
of simple apparatus.
[0018] The present invention still further provides a catalyst for
the oxidation of hydrocarbons.
[0019] The present invention greatly reduces or eliminates the
disadvantages of known powdered catalysts (high pressure drop in
tubular reactors, more rapid deactivation as a result of elevated
local catalyst concentration).
[0020] The present invention still further provides a
technologically simple, gas phase hydro-oxidation process for the
selective oxidation of hydrocarbons with a gaseous oxidizing agent
and in the presence of a reducing agent on said catalysts, which
results in high yields and low costs whilst achieving high catalyst
productivities, very high selectivities and catalyst service lives
of industrial interest.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention will now be described for purposes of
illustration and not limitation.
[0022] The present invention provides a process for producing a
catalyst comprising the provision of a support and impregnation of
the support with an organic-inorganic hybrid sol which contains
titanium and which contains gold and/or silver.
[0023] The process may preferably include modifying the surface of
the catalyst with silicon alkyl compounds, silicon aryl compounds
and/or SiH compounds.
[0024] In this respect, the support may preferably be selected from
the group consisting of oxides of silicon, oxides of aluminium,
oxides of zirconium, oxides of titanium, oxides of boron, zeolites,
clays, mixed oxides of the aforementioned oxides, carbon, activated
carbon, carbon black, graphite, monoliths, knitted fabrics,
cordierite monoliths, ceramic foams, alkali carbonates, alkaline
earth carbonates, carbides, silicon carbide, silicon nitride,
metals, glasses and mixtures thereof.
[0025] More preferably, the support is selected from the group
consisting of alumina, silicon oxide, silicon carbide, carbon and a
cordierite monolith.
[0026] Most preferably,.the support is a-alumina or silicon
carbide.
[0027] The process may also preferably include an annealing step at
temperatures in the range from 100 -1000.degree. C., particularly
from 200 to 600.degree. C.
[0028] The catalyst of the present invention comprises a support,
an organic-inorganic hybrid material which is formed from the
organic-inorganic hybrid sol, titanium in chemically bound form,
and gold particles and/or silver particles.
[0029] A preferred organic-inorganic hybrid material for the
catalyst of the present invention is based on silicon oxide.
[0030] In this respect, the organic-inorganic hybrid material may
preferably contain terminal and/or bridging organic groups on the
silicon atoms of the organic-inorganic hybrid material.
[0031] The catalyst preferably contains gold and silver in the
organic-inorganic hybrid material in an amount between 0.001 to 15%
by weight.
[0032] More preferably, the content of gold in the
organic-inorganic hybrid material is 0.001-2% by weight.
[0033] The catalyst may also preferably have a content of silver in
the organic-inorganic hybrid material between 0.01-15% by
weight.
[0034] The catalyst preferably may contain gold particles that have
a diameter less than 10 nm.
[0035] Furthermore, in one embodiment of the present invention the
catalyst that comprises other extraneous oxides (termed
promoters).
[0036] The method of the present invention also provides a process
for the selective, partial oxidation of hydrocarbons in the
presence of molecular oxygen and of a reducing agent, and in the
presence of the catalyst according to the invention.
[0037] One preferred process is a process of producing epoxides
from alkenes in the presence of molecular oxygen and of a reducing
agent and the catalyst according to the invention.
[0038] The process in which the epoxide is propene oxide and the
alkene is propene is preferred.
[0039] The catalyst of the present invention preferably has
titanium present as titanium oxide wherein the titanium oxide
concentration is 0.1 to 10 mol % with respect to the amount of Si
and Ti in the hybrid material.
[0040] A process in which silicon hydride units are added during
annealing is preferred.
[0041] Hereinafter, the support is also termed a molding material.
Catalysts according to the invention are hereinafter termed
catalyst moldings.
[0042] The catalyst moldings according to the invention, which
contain organic-inorganic hybrid materials and gold and/or silver
particles, have the advantage that moldings of high mechanical
strength are obtained. The catalysts which are thus produced are
hereinafter also termed hydro-oxidation catalysts (HO
catalysts).
[0043] Catalysts are described herein for the first time in which
the generation of catalytically active titanium and gold species is
achieved in a single process step.
[0044] The catalysts of the present invention have longer catalyst
lifetimes than the original powdered catalysts, whilst maintaining
high selectivities and productivities. Moreover, the catalysts
according to the invention enable very low pressure drops to be
achieved in industrially relevant reactors, such as fixed bed
reactors.
[0045] HO catalysts are described herein for the first time in
which the generation of catalytically active titanium and gold
species is achieved in a single process step.
[0046] The synthesis of these HO catalysts is surprising, because
the gold clusters in the catalyst synthesis according to the
invention do not agglomerate to form large, catalytically inactive
gold particles.
[0047] Further, according to the present invention the simultaneous
synthesis of the correct Ti and Au species is effected for the
first time on moldings which--optionally after thermal
treatment--can be used directly in reactors (e.g. fixed bed
reactors). It is thus possible to fulfill the requirement for HO
catalysts by efficiently providing catalytically active Ti and Au
species on suitable moldings in one process step.
[0048] The HO catalysts according to the invention enjoy a
considerable economic advantage compared with prior catalysts.
Moreover, the systems according to the invention provide a
considerably longer catalyst lifetime than that of conventional HO
catalysts.
[0049] The possibility, for the first-time, of depositing all the
requisite HO species by single or multiple impregnation (e.g. spray
impregnation, liquid phase impregnation, incipient wetness, etc) on
all possible surfaces opens up diverse new OH catalysis reaction
routes. Thus not only can palletized, inert moldings for fixed bed
reactors be impregnated with HO species, but large surfaces can
also be impregnated, such as those of monoliths for example.
[0050] The Organic-inorganic Gels are Described Below.
[0051] Organic-inorganic hybrid materials as used in the
description of the present invention are organically modified
glasses based on silicon oxide, which are preferably produced in
sol-gel processes by hydrolysis and condensation reactions of what
are generally compounds of low molecular weight, and which contain
terminal and/or bridging organic groups--preferably silicon
organosilicon groups--in their network, and which advantageously
contain free silicon hydride units. These are described in
Assignee's copending US applications, SN 10/149,056 and SN
10/019,997, which are hereby incorporated in their entireties in
the present application by reference.
[0052] The catalytically active organic-inorganic hybrid materials
which contain titanium and noble metals, and which are subsequently
deposited on moldings, preferably contain, with respect to silicon
oxide as the base component of the hybrid material, between 0.1 and
20 mol % titanium, preferably between 0.5 and 10 mol %, most
preferably between 0.8 and 7 mol %. The titanium is preferably
present in the form of an oxide and is preferably chemically
incorporated or bonded in the silicon oxide lattice via Si--O--Ti
and Si--O--Si bonds. Active catalysts of this type only comprise
subordinate Ti--O--Ti domains.
[0053] It is assumed that in active catalysts based on
organic-inorganic hybrid materials, titanium is bonded to silicon
via heterosiloxane bonds.
[0054] Apart from titanium, the catalysts can also contain other
extraneous oxides, which are termed promoters, namely those of
Group 1 of the IUPAC Periodic Table (1985), such as sodium,
potassium and caesium, of Group 2, preferably magnesium and
calcium, of Group 5, such as vanadium, niobium and tantalum,
preferably tantalum, of Group 6, preferably molybdenum and
tungsten, of Group 3, preferably yttrium, of Group 4, preferably
zirconium, of Group 8, preferably iron, of Group 9, preferably
iridium, of Group 12, preferably zinc, of Group 15, preferably
antimony, of Group 13, preferably aluminium, boron, thallium, and
metals of Group 14, preferably germanium.
[0055] The promoters, hereinafter denoted by M, are generally
present in dispersed form in the organic-inorganic hybrid material.
The chemical composition of these materials can be varied over wide
ranges. The proportion of the promoter element with respect to
silicon oxide preferably falls within the range from 0 to 10 mol %,
more preferably 0 to 3 mol %. As those skilled in the art will
appreciate, a plurality of different promoters can also be used.
The promoters are preferably used in the form of promoter precursor
compounds that are soluble in the respective solvent, such as
promoter salts and/or organic promoter compounds and/or
organic-inorganic promoter compounds.
[0056] These promoters are capable of increasing both the catalytic
activity of the organic-inorganic hybrid materials and the service
life of the organic-inorganic hybrid materials in catalytic
oxidation reactions of hydrocarbons.
[0057] If these promoters are incorporated in or added to
organic-inorganic hybrid materials which do not contain titanium
oxide species, compositions are obtained after thermal activation
which exhibit either no catalytic activity or a catalytic activity
which is less than that of systems which contain titanium.
[0058] The organic-inorganic hybrid materials which contain
titanium can be produced either by impregnating an
organic-inorganic silicon oxide matrix with a titanium precursor
compound, or, preferably, via sol-gel processes. Sol gel production
is effected, for example, by mixing suitable compounds, which are
usually of low molecular weight, after which the hydrolysis and
condensation reaction is initiated by adding water and optionally
catalysts (e.g. acids, bases and/or organometallic compounds,
electrolytes and/or ultrasound). Conducting sol-gel processes such
as these is known in principle to one skilled in the art (L. C.
Klein, Ann. Rev. Mar. Sci., 15 (1985) page 227, and S. J. Teichner,
G. A. Nicolaon, M. A. Vicarini and G. E. E. Garses, Adv. Colloid
Interface Sci., 5 (1976) page 245).
[0059] The HO catalysts according to the invention preferably
contain the following components on a suitable support: gold and/or
silver particles and organic-inorganic hybrid materials that
contain Ti and which optionally comprise Si-H groups. In their
thermally treated state, the active components can be approximately
described by the following empirical formula (I) (radicals formed
after modification on the surface and any incompletely reacted
groups are not taken into consideration here):
SiO.sub.x.Org.H.TiO.sub.y.MO.sub.z.E (I)
[0060] wherein SiO.sub.x represents silicon oxide, Org represents
the non-hydrolyzable organic constituents formed, preferably by a
sol gel process, from the organic-inorganic precursors, H
represents the molar proportion of "element"-H groups in the
network, wherein "element" does not represent carbon. M represents
a promoter, preferably K, Cs, Mg, Ca, Ta, Fe, Mo, Sb, V, Nb, Zr,
Al, B, Ti, Y, Ge or combinations thereof, E represents a noble
metal, preferably gold and/or silver, and x, y and z represent the
effective requisite number of oxygens to saturate the valencies of
the organic-inorganic compounds of the inorganic elements Si, Ti,
and M.
[0061] Composition (I) described above can be varied over a wide
range.
[0062] With respect to silicon oxide, the proportion of Org in mol
percent can range between 0 and 200%. It is preferably between 1
and 200%, more preferably between 10 and 100%. The molar proportion
of Si--H units with respect to silicon oxide can vary between 0 and
100 mol %. The proportion preferably ranges between 0.001 and 50%,
more preferably between 0.001 and 20 mol %. The proportion of
titanium oxide with respect to silicon oxide preferably ranges
between 0.1 and 10 mol %, more preferably between 0.5 and 8.0%,
most preferably between 0.5 and 7.0%. The proportion of MO with
respect to silicon oxide preferably ranges between 0 and 12 mol %.
The proportion of E with respect to the gold- and/or silver-free
active component composition preferably ranges between 0.001 and
15% by weight. For gold it is preferably between 0.001 and 2% by
weight, and for silver it is preferably between 0.01 and 15% by
weight.
[0063] Suitable precursor compounds for silicon, titanium and
promoter species are mixed organic-inorganic compounds that are
advantageously suitable for the sol-gel process, or are a
combination of corresponding mixed inorganic and organic-inorganic
compounds. As used in the description of the present invention, the
term "low molecular weight" refers to monomeric or oligomeric
compounds. Polymeric precursor compounds of silicon, titanium and
promoters are also suitable if they are sufficiently soluble.
[0064] The sol-gel process is based on the polycondensation of
hydrolyzed, colloidally dissolved mixed metal components (sol) to
form a network (gel).
[0065] Hydrolysis is effected by mixing hydrolyzable silicon and
titanium precursor compounds, optionally diluted in a solvent, with
water (simultaneously or in succession). Because under normal
conditions the hydrolysis of silicon precursor compounds is slow,
catalysts are generally required so that it proceeds more rapidly
and completely (J. Livage et al., Chemistry of Advanced Materials:
An Overview Edited by: L. V. Interrante et al., VCH, New York,
1998, pages 389-448). The resulting silanols condense to form
siloxane compounds. Dissolved polysiloxane networks are thus
formed. Branching and crosslinking continue until the polymer is
large enough for the gel transition to occur. The gel firstly
consists of a solid polymer network that is permeated by a solvent.
If the solvent is an alcohol, what are termed alcogels are formed.
After ageing, the compositions according to the invention can be
dried to form either xerogels, aerogels or cryogels. During drying,
e.g. of alcogels, the network shrinks with loss of the solvent,
whereupon a xerogel is formed. If the gel is dried under
supercritical conditions ("High-Temperature Supercritical Drying"
or "Low-Temperature Supercritical Drying"), the resulting network
product is termed an aerogel (A. Baiker et al., Catal. Rev. Sci.
Eng. 1995, 37, pages 515-556); cryogels are obtained when drying is
effected by freeze-drying.
[0066] The preferred solvents for the sol-gel process are alcohols
such as isopropanol, butanol, t-butanol, ethanol or methanol,
ketones such as acetone, and ethers such as THF or tert.-butyl
methyl ether, for example.
[0067] Suitable starting materials include all the soluble silicon
and titanium compounds that are known to those skilled in the art
and which can be employed as a starting material for the
corresponding oxides or hydroxides. Silicon and titanium compounds
of formula (II) are preferably used:
[R.sub.xM'(OR').sub.4-x] (II),
[0068] wherein
[0069] M' is selected from silicon and titanium,
[0070] R and R' independently represent C.sub.1-C.sub.12 alkyl and
C.sub.6-C.sub.12 aryl, wherein x=0,1, 2 or 3 and R' can also
represent H.
[0071] In the organically modified silanes, one or more
hydrolyzable groups may be replaced by terminal and/or bridged,
saturated (e.g. CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, . . . )
or unsaturated (e.g. C.sub.2H.sub.3, C.sub.6H.sub.5) R group(s).
Mixtures of different organically modified silanes or mixtures of
organically modified silanes with purely inorganic silicon network
formers, such as tetraalkoxysilanes, can also advantageously be
used. Polyfunctional organosilanes, e.g. polysilsesquioxanes
(polymethylsilsesquioxanes, polyvinylsilsesquioxanes, . . . )
silanols and alkoxides, can also be used. Silanes, which are
optionally organically modified, can also be reacted in the
presence of di- or polyhydric alcohols such as 1,4-butanediol, to
form organically modified polysiloxanes. In the present invention,
bridged R groups (alkylene radicals) are bridged structures such as
chain-like, star-shaped (branched), cage-like or ring-like
structural elements.
[0072] "Alkyl" is to be understood to represent all terminal and/or
bridged, linear or branched alkyl radicals comprising 1 to 12
carbon atoms which are known to those skilled in the art, such as
methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl,
n-pentyl, i-pentyl, neo-pentyl, hexyl and other homologes, which
themselves can be further substituted. Suitable substituents
include halogens, nitro, alkyl, hydroxide or alkoxy, as well as
cycloalkyl or aryl, such as benzoyl, tris-methylphenyl,
ethylphenyl, chloromethyl, chloroethyl and nitromethyl. Nonpolar
substituents are preferably used, such as methyl, ethyl, n-propyl,
i-propyl, n-butyl, i-butyl, t-butyl and benzoyl.
[0073] Higher molecular weight and/or oligomeric organic-inorganic
silicon and titanium precursors are also suitable, such as
gamma-glycidoxypropyltrimethoxysilane,
3,4-epoxycyclohexyl-ethyl-trimetho- xysilane,
1-(triethoxysilyl)-2-(diethoxymethylsilyl)-ethane,
tris(gamma)-trimethoxypropylsilyl isocyanurate, peralkylated
cyclosilo-xanes such as hexamethylcyclotrisiloxane,
octamethyltetrasiloxane or decamethylpentasiloxane.
Polyalkyl(aryl)siloxanes such as polydimethylsiloxane are also
suitable.
[0074] "Aryl" is to be understood to include all mono- or
polynuclear radicals comprising 6 to 12 carbon atoms which are
known to those skilled in the art, such as phenyl, naphthyl or
fluorenyl, which themselves may be substituted. Suitable
substituents here include a halogen, nitro, alkyl or alkoxyl, as
well as cycloalkyl or aryl, such as bromophenyl, chlorophenyl,
toloyl and nitrophenyl. Phenyl, fluorenyl, bromophenyl,
chlorophenyl, toloyl and nitrophenyl are preferred.
[0075] Even though salts such as halides, nitrates and hydroxides
can be used, the alkoxides of these elements are preferred, e.g.
the n-butoxides, t-butoxides, isopropoxides, n-propoxides,
ethoxides and methoxides thereof.
[0076] The titanium derivatives which are preferably used are those
such as tetralkoxytitanates comprising C.sub.1-C.sub.12 alkyl
groups such as iso-butyl, tert-butyl, n-butyl, i-propyl, n-propyl,
ethyl, etc., or titanium alkoxy complexes such as those described
in U.S. Pat. No. 6,090,961, e.g.
(.eta..sup.5-tetramethylcyclopentadienyl)
3-tert-butyl-5-methyl-2-phenoxy)-dimethylsilyl titanium
dimethoxides, other organic titanium species such as titanium
acetylacetonate, Ti(OSiPh.sub.3).sub.4, dicyclopentadienyltitanium
dihalides, titanium dihalogenodialkoxides, titanium
halogenotrialkoxides, or titanium siloxanes such as
diethoxysiloxane-ethyl titanate copolymer (available commercially
from Gelest Inc). Chlorine is the preferred halogen substituent.
Mixed alkoxides of titanium with other elements such as titanium
triisopropoxide-tri-n-butyltin oxide can also be used. The titanium
precursor compounds can also be used in the presence of
complex-forming components such as acetylacetone or ethyl
acetoacetate, for example.
[0077] The organic-inorganic silicon and titanium precursor
compounds can also be used in combination with inorganic network
formers such as tetraethoxysilane (Si(OC.sub.2H.sub.5).sub.4),
tetramethoxysilane (Si(OCH.sub.3).sub.4) or homologues thereof.
Instead of monomeric alkoxides, condensation products thereof can
also be used. Examples of the latter which are available
commercially include Si(OC.sub.2H.sub.5).sub.4 condensates, for
example. Moreover, oligomeric or polymeric systems such as
poly(diethoxysiloxane) can be used.
[0078] The aforementioned silicon and titanium precursor compounds
are reacted in a sol-gel process, preferably in combination with
silanes, and contain silicon hydride units. Most silanes that
contain silicon hydrides can be represented by formulae (IIIa) or
(IIIb):
[R.sub.xSiH.sub.y(OR').sub.4-(x+y)] (IIIa)
[R.sub.xSiH.sub.y(Hal).sub.4-(x+y)] (IIIb),
[0079] wherein
[0080] R and R' independently represent C.sub.1-C.sub.12 alkyl and
C.sub.6-C.sub.12 aryl, where x=0, 1, 2 or 3 and y=1, 2 or 3, and
where R' and R can also represent H.
[0081] The silanes containing Si--H can also be generated in situ,
e.g. from halosilanes in the presence of reducing agents such as
magnesium hydride.
[0082] The compounds of formulae (IIIa) and (IIIb) can be replaced,
wholly or in part, by other silicon precursor compounds comprising
proportions of Si--H units, such as 1,1,3,3-tetramethyldisiloxane,
1,3,5,7-tetramethylcyclotetrasiloxane, tri-n-hexylsilane or
triphenylsilane.
[0083] Examples of silanes include monoalkoxysilanes
(C.sub.1-C.sub.12), dialkoxysilanes (C.sub.1-C.sub.12),
trialkoxysilanes (C.sub.1-C.sub.12), dialkoxy-monohalogenosilanes
(C.sub.1-C.sub.12), monoalkoxy-dihalogenosil- anes
(C.sub.1-C.sub.12), methylhydro-cyclosiloxane, trihalogenosilanes,
dihalogen-silanes and monohalogenosilanes.
[0084] Apart from low molecular weight precursors, oligomeric and
polymeric precursors which contain silicon hydride can also be
used, such as poly(methylhydrosiloxanes).
[0085] The preferred trialkoxysilanes are those which comprise
C.sub.1-C.sub.12 groups, such as trimethoxysilane, triethoxysilane,
triisopropoxysilane, tripropoxysilane, triisopropoxysilane,
tributoxysilane, and those which comprise oligomeric or polymeric
SiH components, such as poly(methylhydrosiloxane).
[0086] The sequence of operations during sol-gel synthesis is not
fixed. The HO catalysts according to the invention are generated,
for example, by the simultaneous hydrolysis and/or condensation of
Si and Ti precursors or by the complete or partial reaction of
silicon precursor compounds with water or with catalytic amounts of
water and subsequent addition of the corresponding Ti
compounds.
[0087] In one embodiment of the present invention, the
organic-inorganic silicon precursor compound is placed in a vessel,
is initially or completely hydrolyzed with water with the addition
of a catalyst, and the Ti precursor compound is subsequently added.
The addition of silanes comprising free silane-hydride units is
likewise not a fixed procedure. The SiH species can be added either
before or after the addition of Ti.
[0088] According to the invention, gel formation is effected
directly on the support surface. One or more treatments of the
moist and/or already dried gel with an excess of water or water
vapor can optionally be effected in order to complete the
hydrolysis and condensation reactions.
[0089] The subsequent treatment of the "gel on support" system is
not fixed. It can be dried (e.g. at 20-150.degree. C. in an air
current or in other atmospheres) and then annealed (150 to
450.degree. C. in air, N.sub.2, H.sub.2, or in other atmospheres).
The freshly impregnated molding can also be annealed directly,
without drying.
[0090] The hydrophobic character of the organic-inorganic hybrid
materials according to the invention is essentially determined by
the number and type of terminal and bridging Si--C bonds. Compared
with other organic bonds, such as Si--O--C bonds for example,
terminal and bridging Si--C bonds have the additional advantage of
being substantially chemically inert, i.e. are insensitive to
hydrolysis and oxidation reactions.
[0091] The Noble Metals (Gold and/or Silver) are Described
Below.
[0092] In addition to the Si, Ti and possible promoter species, the
HO catalysts according to the invention additionally contain noble
metal clusters.
[0093] The noble metals are added in the form of precursor
compounds, such as salts, organic complexes or compounds, or as
colloids, preferably during the sol-gel process. Alternatively,
sol-gel-modified moldings can also be covered in a previous or
subsequent step with noble metal clusters (e.g. by precipitation,
impregnation in solution, incipient wetness, spray drying,
sputtering, colloids, CVD).
[0094] The noble metals are preferably gold and/or silver. In their
catalytically active form, the moldings contain gold and/or silver
particles which mainly have a particle size of <15 nm. In their
catalytically active state, the gold and/or silver mainly exist as
the elemental metals (analysis by X-ray absorption spectroscopy).
Small proportions of gold and/or silver can also be present in a
higher oxidation state. The gold and silver are preferably present
as gold and/or silver clusters on a nanometer scale.
[0095] The gold particles preferably have a diameter within the
range from 0.5 to 50 nm, more preferably 0.8 to 15 nm, and most
preferably 0.8 to 10 nm.
[0096] The silver particles preferably have a diameter within the
range from 0.5 to 100 nm, more preferably 0.5 to 40 nm, and most
preferably 0.5 to 20 nm.
[0097] It has been found that the selective hydro-oxidation
reaction described above is very sensitive to the structure of the
catalyst. In the presence of nano-dispersed gold and/or silver
particles in or on HO catalyst moldings, an advantageous increase
in productivity to form the selective oxidation product has been
observed.
[0098] With respect to the solid formed from the sol after
hydrolysis/condensation/annealing, the gold concentration in the
sol which contains silicon and titanium and with which the support
is treated is preferably within the range from 0.001 to 2% by
weight, preferably 0.001 to 1.5% by weight, and more preferably
0.005-1.0% by weight.
[0099] The silver concentration should fall within the range from
0.005 to 20% by weight, preferably 0.01 to 15% by weight, and more
preferably from 0.1 to 10% by weight of silver.
[0100] For economic reasons, the noble metal content should be the
minimum required to prolong the maximum catalyst activity.
[0101] The production of the noble metal particles in the
organic-inorganic hybrid sol that contains silicon and titanium or
on the molding which is treated with the hybrid sol that contains
noble metals is not restricted to one method.
[0102] The catalytically active noble metal clusters can be
generated either by reducing agents and/or by thermal
treatment.
[0103] Nano-scale gold particles may preferably be produced by
thermal treatment in the presence of reducing agents.
[0104] Nano-scale silver particles may preferably be produced by
thermal treatment in the presence of reducing agents.
[0105] It has surprisingly been found that the organic-inorganic
hybrid materials which contain proportions of hydrogen silanes are
particularly suitable for depositing metals such as gold and
silver, with a high degree of dispersion, on external and internal
surfaces. Ultrafine metal particles are generated in the course of
this procedure.
[0106] In contrast, on purely inorganic silica or
SiO.sub.2-TiO.sub.2 mixed oxide surfaces (analogous to WO98/00415,
WO-98/00414, WO-98/00413, EP-A 0 827 779), i.e. without organic
modification and/or without proportions of hydrogen silanes, it is
possible to synthesize nano-scale metal particles with a very
narrow particle size distribution, but in a much less selective
manner.
[0107] The Impregnation of the Support with the Sol is Described
Below.
[0108] The methods by which the organic-inorganic hybrid sol with a
content of noble metal precursors and/or noble metal colloids are
deposited on suitable supports are not subject to any
restrictions.
[0109] Different catalysts can be produced depending on the method
selected.
[0110] Impregnating the support in a liquid phase often results in
moldings which are impregnated homogeneously. Using dip coating
(immersion) or spray impregnation, systems can be generated which
cover the entire range from homogeneously impregnated to those
comprising shell-like impregnation.
[0111] The type of HO catalysts is also essentially determined by
the viscosity of the hybrid sol which contains noble metals. In
addition to the amount of solvent, the viscosity is also affected
by the ageing of the sol-gel. A liquid, low-viscosity sol-gel
system is preferably deposited on the molding.
[0112] Impregnation of the molding with the hybrid sol can be
effected as a single- or multi-stage process.
[0113] The amount of hybrid sol on the support is not fixed. In
many cases, the proportion of active ingredient after annealing
ranges from 1 to 80%, preferably 1 to 60%, most preferably 3 to
30%.
[0114] The further processing of the impregnated molding is not
fixed. Excess hybrid sol can be removed or gelled by a plurality of
routes, e.g. by drying, by vacuum treatment, in a centrifuge, in an
air current, or by similar routes.
[0115] Impregnation of the moldings with the hybrid sol can be
conducted not only in a single step, i.e. using hybrid sols
containing noble metals, but can also be conducted in two steps, by
firstly impregnating the moldings with HO hybrid sols which are
free from noble metals and subsequently covering them with noble
metals or noble metal precursors, or vice versa.
[0116] The catalytic activity of the HO catalysts according to the
invention is often increased by subsequent thermal treatment.
[0117] The Annealing Procedure is Described Below.
[0118] The HO catalysts according to the invention are
advantageously activated, before and/or after impregnation or
immersion with the hybrid sols containing noble metals, by thermal
treatment at temperatures within the range from 100-1000.degree. C.
in different atmospheres such as air, nitrogen, hydrogen, carbon
monoxide or carbon dioxide.
[0119] Thermal activation is preferably effected at temperatures
within the range from 150-400.degree. C. in gases which contain
oxygen, such as air, oxygen-hydrogen or oxygen-inert gas mixtures
or combinations thereof, or at temperatures within the range from
150-1000.degree. C. under inert gases such as nitrogen and/or
hydrogen and/or inert gases or combinations thereof. Activation of
the organic-inorganic hybrid materials is most preferably effected
under inert gases within the temperature range from 200-600.degree.
C.
[0120] It may also be advantageous, however, to impregnate the
moldings with hybrid sols which are free from noble metals, to
anneal them at temperatures within the range from 200-1000.degree.
C. and subsequently to cover them with noble metal. The thermally
activated (annealed) catalysts often exhibit a significantly higher
catalytic activity and a prolonged service life compared with known
catalysts.
[0121] The Supports are Described Below.
[0122] The selection of the support for the synthesis of the HO
catalyst moldings is subject to no particular restriction as
regards material, particle size, mechanical strength, size of
surface, pore structure, absorption capacity, chemical inertness,
etc., provided that it is possible effectively to impregnate said
sols with the HO hybrid sols which contain noble metals, and
provided that the support used does not give rise to secondary or
subsequent reactions of the desired products.
[0123] The preferred supports are mechanically stable, chemically
inert, commercially available in industrial quantities and
inexpensive. Particulate supports are particularly advantageous,
and are used in the form of spheres, cylinders, hollow cylinders,
saddles, extrudates, hollow extrudates, granules or rods, for
example.
[0124] Particulate catalyst moldings can be used in the form of a
fixed bed of loose material or in the form of a fluidized bed.
Instead of being deposited on a particulate support, the hybrid sol
that contains noble metals can be deposited on monolithic support
systems, for example. Examples thereof include ceramic honeycomb
bodies (such as cordierite honeycomb bodies), ceramic sponges,
knitted fabrics, etc.
[0125] The particle size depends on how the reaction is conducted,
e.g. in a fixed bed or fluidized bed, on the quantitative
throughput, and on the type and size of the reactor. If a fixed bed
reactor is used, a low pressure drop, good heat transfer and a low
diffusion barrier are attained for moldings of sizes 2-10 mm. In
fluidized bed processes, mechanically stable supports with a narrow
particle size distribution of 50-300 .mu.m are preferred.
[0126] All materials that form mechanically stable moldings and
which are inert or which only exhibit a slight activity with regard
to gas phase oxidation can be used as supports. Suitable examples
include oxides of aluminium (.alpha.-, .gamma.-, etc.), silicon and
zirconium. Carbon in various states, such as activated carbon,
carbon black or graphite, can also be used. Carbides such as
silicon carbide, or nitrides such as silicon nitride, are also
suitable. Glasses and metals of all types can also be used.
[0127] In principle, there is no restriction on the size and type
of the surface of these moldings. The specific surface is
advantageously 0.01-1000 m.sup.2/g, more advantageously 0.01-200
m.sup.2/g and most advantageously 0.01-100 m.sup.2/g.
[0128] The pore structure can be micro-, meso- and/or macroporous.
Both amorphous and crystalline molding systems can be selected.
[0129] In some situations, particularly in order to achieve
isothermal reaction conditions, it may be advantageous if the
catalyst material is diluted uniformly or in layers with an inert
or low-activity molding material. There is no restriction on the
choice of dilution materials such as these. Examples include oxides
of silicon, aluminum, zirconium, and materials made of glass such
as coarse powder, spheres, etc. Silicates, ceramics, carbon and
mineral particles are also suitable. By conducting the reaction
isothermally, hot spots are often reduced, which has a favorable
effect on the service life of the catalysts according to the
invention. Moldings that have good thermal conductivities, such as
graphite, carbon black and silicon carbide, for example, also
reduce hot spots.
[0130] The Modification of the Catalyst Surface is Described
Below.
[0131] The catalytic activity of the catalysts according to the
invention can often be increased by modifying the surface.
[0132] In the present invention, modification is to be understood
in particular as the provision of groups selected from
silicon-alkyl, silicon-aryl, silicon hydride, or alkyl or aryl
groups which contain fluorine, on the surface of the supported
composition, wherein these groups are often covalently or
coordinately bonded to the functional groups (e.g. OH groups) on
the surface. Any other surface treatment is also expressly included
in the scope of the invention, however.
[0133] The catalyst surface can be modified in many ways. The
moldings can be modified either before impregnation with HO-active
components or after impregnation. In some situations, modification
before impregnation is preferred.
[0134] Modification is preferably effected with organosilicon
compounds and/or with organosilicon compounds that contain fluorine
and/or with organic compounds which contain SiH, wherein
organosilicon compounds and compounds which contain SiH compounds
are preferred.
[0135] Suitable organosilicon compounds include all silylating
agents which are known to those skilled in the art, such as organic
silanes, organic silylamines, organic silylamides and derivatives
thereof, organic silazanes, organic siloxanes and other
organosilicon compounds, which of course can also be used in
combination. The term "organosilicon compounds" also expressly
includes compounds of silicon and partially fluorinated or
perfluorinated organic radicals.
[0136] Particular examples of organic silanes include
chlorotrimethylsilane, dichlorodimethylsilane,
chlorobromodimethylsilane, nitrotrimethylsilane,
chlorotrimethylsilane, iododimethylbutylsilane,
chlorodimethylphenylsilane, chlorodimethylsilane,
dimethyl-n-propylchloro- silane, dimethylisopropyl-chlorosilane,
t-butyldimethylchlorosilane, tripropylchlorosilane,
dimethyloctylchlorosilane, tributylchlorosilane,
trihexyl-chlorosilane, dimethylethylchlorosilane,
dimethyloctadecylchloro- silane, n-butyl-dimethylchlorosilane,
bromomethyidimethylchlorosilane, chloromethyldimethyl-chlorosilane,
3-chloro-propyldimethylchlorosilane, dimethoxymethylchlorosilane,
methylphenylchlorosilane, triethoxychloro-silane,
dimethylphenylchlorosilane, methyl-phenylvinylchlorosilane,
benzyldimethylchlorosilane, diphenylchlorosilane,
diphenyl-methylchlorosilane, diphenylvinylchlorosilane,
tribenzylchlorosilane and 3-cyano-propyldimethylchlorosilane.
[0137] Silanes which contain SiH, for example tri-, di- and
monoalkoxysilanes, poly(methylhydrosiloxane), etc., are also
suitable for surface modification.
[0138] Particular examples of organic silylamines include
N-trimethylsilyldiethylamine, pentafluorophenyldimethylsilylamine,
N-trimethylsilylimidazoles, N-t-butyidimethylsilylimidazole,
N-dimethylethylsilylimidazole, N-dimethyl-n-propylsilylimidazole,
N-dimethylisopropylsilylimidazole, N-trimethylsilyldimethylamine,
N-trimethylsilylpyrrol, N-trimethylsilylpyrrolidine,
N-trimethylsilylpiperidine and
1-cyanoethyl(diethylamino)dimethylsilane.
[0139] Particular examples of organic silylamides and derivatives
thereof include N,O-bistrimethylsilylacetamide,
N,O-bistrimethylsilyltrifluoro-ac- etamide,
N-trimethylsilyl-acetamide, N-methyl-N-trimethylsilylacetamide,
N-methyl-N-trimethylsilyl-trifluoroacetamide,
N-methyl-N-trimethylsilyl-h- eptafluorobutyramide,
N-(t-butyl-dimethylsilyl)-N-trifluoroacetamide and N,
O-bis(diethylhydrosilyl)trifluoroacetamide.
[0140] Particular examples of organic silazanes include
hexamethyl-disilazane, heptamethyldisilazane,
1,1,3,3-tetramethyidisilaza- ne,
1,3-bis(chloromethyl)tetramethyldisilazane,
1,3-divinyl-1,1,3,3-tetram- ethyl-disilazane and 1
,3-diphenyltetramethyldisilazane.
[0141] Examples of other organosilicon compounds are
N-methoxy-N,O-bistrimethylsilyltrifluoracetamide,
N-methoxy-N,O-bistrimet- hylsilyl carbamate, N,O-bistrimethylsilyl
sulphamate, trimethylsilyltrifluoro-methane sulphonate and
N,N'-bistrimethylsilylurea- .
[0142] The preferred silylation reagents are hexamethyldisilazane,
hexamethyldisiloxane, trialkoxysilanes,
N-methyl-N-(trimethylsilyl)-2,2,2- -trifluoroacetamide (MSTFA) and
trimethylchlorosilane.
[0143] The Process Parameters are Described Below.
[0144] The HO catalyst moldings are preferably used in gas phase
reactions for the partial oxidation of hydrocarbons in the presence
of oxygen and hydrogen.
[0145] The process parameters for this hydro-oxidation reaction can
be varied over wide ranges.
[0146] The catalyst moldings according to the invention are
employed in particular at temperatures of 100 to 300.degree. C.,
preferably 140 to 270.degree. C. and more preferably 160 to
250.degree. C.
[0147] For gas phase reactions, it is often advantageous for
economic reasons and for reasons relating to the construction of
the apparatus to operate under elevated reaction pressures. The
contact catalysts according to the invention exhibit particularly
high catalytic activities over the pressure range from normal
pressure to 70 bar. A pressure level of 2 to 50 bar is preferred,
more preferably from 3 to 30 bar.
[0148] The residence time can also be varied over a wide range. The
residence time is advantageously <70 seconds. The HO catalyst
moldings exhibit particularly high catalytic activities at
residence times <20 sec, for example at 0.001 to 10 seconds. The
present invention also expressly relates to extremely short
residence times of the order of milliseconds (<0.001
seconds).
[0149] The amount of feed gas or circulating gas, and thus the
catalyst loading, is not fixed. In particular, the catalyst loading
ranges from 1 to >1000 1 gas/(g active substance.times.h),
preferably from 4 to 600 1 gas/(g catalyst.times.h), more
preferably from 10-500 1 gas/(g active substance.times.h). The
present invention likewise expressly relates to extremely high
catalyst loadings, often associated with short catalyst contact
times.
[0150] The Feed Composition is Described Below.
[0151] HO catalyst moldings are preferably used in gas phase
reactions for the partial oxidation of hydrocarbons in the presence
of oxygen and hydrogen.
[0152] In reactions such as these, epoxides are obtained
selectively from olefins, ketones are selectively obtained from
saturated secondary hydrocarbons, and alcohols are selectively
obtained from saturated tertiary hydrocarbons.
[0153] The term "hydrocarbon" is to be understood to include
unsaturated or saturated hydrocarbons such as olefins or alkanes
which may also contain heteroatoms such as N, O, P, S or halogens.
The organic component to be oxidized can be acyclic, monocyclic,
bicyclic or polycyclic and can be monoolefinic, diolefinic or
polyolefinic. In organic components that contain two or more double
bonds, the double bonds may be conjugated or unconjugated. The
hydrocarbons which are preferably oxidized are those from which
oxidation products are formed at a partial pressure which is low
enough for the product to be continuously removed from the
catalyst. Unsaturated and saturated hydrocarbons are preferred
which contain 2 to 20, preferably 2 to 10 carbon atoms,
particularly ethene, ethane, propene, propane, isobutane,
isobutylene, 1-butene, 2-butene, cis-2-butene, trans-2-butene,
1,3-butadiene, pentene, pentane, 1-hexene, 1-hexane, hexadiene,
cyclohexene and benzene.
[0154] The molar amount of hydrocarbon used with respect to the
total number of moles of hydrocarbon, oxygen, hydrogen and dilution
gas, as well as the relative molar ratios of the components, can be
varied over wide ranges. An excess of hydrocarbon is preferably
used with respect to the oxygen used (on a molar basis). The
hydrocarbon content is typically greater than 1 mol % and less than
80 mol %. Hydrocarbon contents within the range from 4 to 90 mol %
are preferably used, and are more preferably within the range from
8 to 70 mol %.
[0155] Oxygen can be used in very different forms, such as
molecular oxygen, air, nitrogen oxide or hydrogen peroxide.
Molecular oxygen is preferred.
[0156] The mole fraction of oxygen with respect to the total number
of moles of hydrocarbon, oxygen, hydrogen and dilution gas can be
varied over a wide range. Oxygen is preferably used in a molar
deficit with respect to the hydrocarbon. Oxygen is preferably used
within the range of 1-30% oxygen by volume, more preferably 5-25%
oxygen by volume.
[0157] In the absence of hydrogen, the moldings according to the
invention only exhibit a slight activity and selectivity. In
general, the productivity in the absence of hydrogen is low up to
180.degree. C. At temperatures above 200.degree. C., larger amounts
of carbon dioxide are formed in addition to partial oxidation
products.
[0158] Any known source of hydrogen can be used, such as pure
hydrogen, cracker hydrogen, synthesis gas or hydrogen from the
dehydrogenation of hydrocarbons and alcohols. In another embodiment
of the invention, the hydrogen can also be produced in situ in an
upstream reactor, e.g. by the dehydrogenation of propane or
isobutane or of alcohols such as methanol or isobutanol. Hydrogen
can also be introduced into the reaction system as a complex-bonded
species, e.g. as a catalyst-hydrogen complex.
[0159] The mole fraction of hydrogen with respect to the total
number of moles of hydrocarbon, oxygen, hydrogen and dilution gas,
can be varied over a very wide range. Typical hydrogen contents are
greater than 0.1% by volume, preferably within the range from 4-80%
by volume, more preferably within the range from 5-75% by
volume.
[0160] A dilution gas such as nitrogen, helium, argon, methane,
carbon dioxide, carbon monoxide, or similar gases that mainly
exhibit inert behavior, can also optionally be used in addition to
the essential gaseous starting materials described above. Mixtures
of the inert components described above can also be used. Other
inert hydrocarbons, such as fluorinated hydrocarbons
(hexafluorethane, CF.sub.4, etc.) can also be used as components
for diluting the feed or circulating gas. The addition of an inert
component has a favorable effect on the transport of the heat
evolved from the exothermic oxidation reaction and is often
desirable for reasons of safety.
[0161] If the process according to the invention is conducted in
the gas phase, gaseous dilution components such as nitrogen,
helium, argon, etc. are preferably used.
[0162] When the invention is carried out in a liquid phase, an
inert liquid which is stable to oxidation and which is thermally
stable is advisedly used (e.g. alcohols, polyalcohols, polyethers,
halogenated hydrocarbons, silicone oils).
[0163] The catalysts according to the invention are also suitable
for the oxidation of hydrocarbons in the liquid phase. For example,
olefins are converted to epoxides in a highly selective manner on
the catalysts described above in the liquid phase, either in the
presence of organic hydroperoxides, in the presence of hydrogen
peroxide, or in the presence of oxygen and hydrogen.
[0164] It has surprisingly been found, compared with all the HO
catalyst systems which were known hitherto for the catalytic
partial oxidation of unsaturated and saturated hydrocarbons, that
the catalysts according to the invention often exhibit a catalytic
activity and a catalyst service life which are higher by several
orders of magnitude.
[0165] The catalysts according to the invention can be produced
inexpensively on an industrial scale, without process technology
problems.
[0166] Catalysts which may have become slightly deactivated after
months of use can often be regenerated either thermally or by
washing them with suitable solvents such as alcohols or water, or
by treating them with hot steam or dilute hydrogen peroxide
solutions (e.g. a 3-10% solution of H.sub.2O.sub.2 in
methanol).
[0167] The present invention is illustrated by the examples given
below. The present invention is not limited to these examples.
EXAMPLES
[0168] Procedure for Testing HO Catalyst Moldings (Test
Procedure)
[0169] A metal tube reactor was used which had an inside diameter
of 10 mm and a length of 20 cm, and which was heated at a
controlled temperature by means of a thermostat. The reactor was
supplied with the gaseous starting materials (propene, oxygen,
hydrogen) by a set of three mass flow controllers.
[0170] The reactor contained a HO catalyst molding (containing 0.5
g of a catalytically active HO component) at 180.degree. C. and 2
bar pressure. The gaseous starting materials were metered into the
reactor from above. The standard catalyst loading was 5 liters of
gas per gram of HO molding per hour.
[0171] A gas stream of the following composition (hereinafter
called the standard gas composition) was used for carrying out
oxidation reactions:
[0172] H.sub.2/O.sub.2/propene: 60/10/30% by volume.
[0173] The reaction gases were quantitatively analyzed by gas
chromatography. Separation by gas chromatography of the individual
reaction products was effected by a combined FID/TCD method in
which the gas flowed through three capillary columns:
[0174] FID: HP-lnnowax, 0.32 mm inside diameter, 60 m log, 0.25
.mu.m layer thickness.
[0175] WLD: A series arrangement of
[0176] HP-Plot Q, 0.32 mm inside diameter, 30 m long, 20 .mu.m
layer thickness
[0177] HP-Plot molecular sieve 5 A, 0.32 mm inside diameter, 30 m
long, 12 .mu.m layer thickness.
[0178] The abbreviations have the following meanings:
1 FID: flame ionization detector TCD: thermal conductivity detector
HP-Plot Q: gas chromatography column supplied by Hewlett Packard
(fused silica; PLOT = porous layer open tubular) HP-Plot molecular
sieve 5 A: gas chromatography column supplied by Hewlett Packard (5
Angstrom molecular sieve; PLOT = porous layer open tubular)
[0179] Preparation of Hybrid Sol-Gel Solution 1
[0180] 13.3 g methyltrimethoxysilane (98.1 mmol), 0.33 g
triethoxysilane (2 mmol) and 1.15 g tetrapropoxy-titanium (4 mmol),
dissolved in 7 g ethanol (absolute, analytical quality), were
placed in a vessel, mixed with 2.9 g of an 0.1 N solution of
p-toluenesulphonic acid in water and the mixture was stirred for 10
min. 2 g of a 1% solution of gold (HAuCl.sub.4.times.3 H.sub.2O in
ethanol) were then added with stirring.
[0181] Preparation of Hybrid Sol-Gel Solution 2
[0182] This preparation was effected analogously to the preparation
of hybrid sol-gel 1, except that 11.56 g methyltrimethoxysilane (85
mmol) and 1.97 g tetramethoxysilane (13 mmol) were used instead of
13.3 g methyltrimethoxysilane (98.1 mmol).
[0183] Preparation of Hybrid Sol-gel Solution 3
[0184] This preparation was effected analogously to the preparation
of hybrid sol-gel 1, except that 2 g of a 2% gold solution
(HAuC1.sub.4.times.3 H.sub.2O in ethanol) were used.
[0185] Molding Impregnation; Variant 1:
[0186] Preparation of an HO catalyst molding by impregnating
commercially available moldings with a hybrid sol-gel solution by
dip coating.
[0187] The hybrid-sol-gel was in placed in a 100 ml glass beaker.
15 g moldings--pelletised moldings were placed in a sieve with a
mesh aperture of 0.5 mm--were immersed for 30 seconds in a hybrid
sol-gel solution, excess sol-gel was removed in a centrifuge (when
monoliths were used, excess sol-gel was removed by means of
compressed air), dried for 1 hour at room temperature and
subsequently annealed for 4 hours at 400.degree. C. under nitrogen.
The molding contained about 3% by weight of HO-active
components.
[0188] To test the HO catalyst moldings by the procedure given
above, 16 g of the catalyst moldings obtained in this manner,
corresponding to about 0.5 g of HO-active substance, were used as a
fixed bed catalyst.
[0189] Molding Impregnation; Variant 2:
[0190] Preparation of a HO catalyst molding by spray-impregnating
commercially available moldings with a HO hybrid sol-gel
solution.
[0191] 15 g of palletized moldings were placed in a drum (made of a
plastics material, 15 cm diameter, inclined at 30.degree., 50 rpm).
The hybrid sol-gel solution was sprayed on to the rotating molding
particles by means of a fine nozzle. After drying for 1 hour at
25.degree. C., the material was annealed for 4 hours at 400.degree.
C. under nitrogen. The molding contained about 3% by weight of
HO-active components.
[0192] In order to test the HO catalyst moldings by the procedure
given above, 16 g of the catalyst moldings obtained in this manner,
corresponding to about 0.5 g of HO-active substance, were used as a
fixed bed catalyst.
[0193] The following Table gives the results obtained using the
catalysts according to the invention (no comparative tests are
given in the Table). (The supports were supplied by Condea, of
Hamburg)
2 Hybrid Molding PO Productivity Ex. sol-gel impregnation
selectivity gPO/(kg WS* .times. h) after No. Moldings method method
[%] 48 h 7 days 1 .alpha.-Al.sub.2O.sub.3 spheres, 1 1 95 200 183 2
mm spheres, supplied by Condea, Batch No. TKA 306 2
.alpha.-Al.sub.2O.sub.3 spheres, 1 2 95 250 230 2 mm spheres,
supplied by Condea, Batch No. TKA 306 3 .alpha.-Al.sub.2O.sub.3
spheres, 2 2 95 265 250 2 mm spheres, supplied by Condea, Batch No.
TKA 306 4 .alpha.-Al.sub.2O.sub.3 1 2 95 185 170 hollow extrudate,
3-4 mm extrudate, supplied by Condea, Batch No. M908 6
.alpha.-Al.sub.2O.sub.3 spheres, 1 2 95 140 120 2-4 mm spheres,
supplied by Procatalyse, Description SPH 512, 7
.alpha.-Al.sub.2O.sub.3 spheres, 3 2 95 180 140 2-4 mm spheres,
supplied by Procatalyse, Type SPH 512 8 SiC spheres, 1 2 96 230 220
3 mm spheres, supplied by Norton, Type XC 69374 9 SiC spheres, 3 mm
2 2 96 240 220 spheres, supplied by Norton, Type XC 69374 10
Cordierite 3 1 96 200 190 honeycomb body, supplied by Dow Corning
11 Metal wire grid 1 1 95 150 145 rings, 4 mm WS = HO-active
substance
[0194] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *