U.S. patent application number 09/971668 was filed with the patent office on 2002-06-20 for catalyst support.
Invention is credited to Krause, Helmfried, Lansink Rotgerink, Hermanus Gerhardus Jozef, Reidemann, Heike.
Application Number | 20020077246 09/971668 |
Document ID | / |
Family ID | 8170161 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020077246 |
Kind Code |
A1 |
Lansink Rotgerink, Hermanus
Gerhardus Jozef ; et al. |
June 20, 2002 |
Catalyst support
Abstract
A catalyst support consisting mainly of synthetic silica, with
0.5-10 parts by weight of one or more oxides or phosphates of the
elements of group IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides characterised in that the support
preparation method comprises mixing particulate synthetic silica
with particulate oxides or phospates of the elements of Groups IIA,
IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the
lanthanides, or with precursors thereof, a forming step and
calcination. The catalyst support is used together with phosphoric
acid in the production of alcohols from olefins by hydration.
Inventors: |
Lansink Rotgerink, Hermanus
Gerhardus Jozef; (Mombris-Mensengesass, NL) ;
Reidemann, Heike; (Mombris, DE) ; Krause,
Helmfried; (Rodenbach, DE) |
Correspondence
Address: |
VENABLE, BAETJER, HOWARD AND CIVILETTI, LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Family ID: |
8170161 |
Appl. No.: |
09/971668 |
Filed: |
October 9, 2001 |
Current U.S.
Class: |
502/214 ;
502/237; 502/242; 502/246; 502/250; 502/254 |
Current CPC
Class: |
B01J 21/063 20130101;
B01J 21/08 20130101; B01J 27/16 20130101; B01J 37/0018 20130101;
B01J 37/0009 20130101; B01J 21/066 20130101 |
Class at
Publication: |
502/214 ;
502/242; 502/246; 502/250; 502/254; 502/237 |
International
Class: |
B01J 027/182; B01J
021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2000 |
EP |
00 122 957.4 |
Claims
1. A catalyst support consisting mainly of synthetic silica, with
0.5-10 parts by weight of one or more oxides or phosphates of the
elements of group IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides characterised in that the support
preparation method comprises mixing particulate synthetic silica
with particulate oxides or phospates of the elements of Groups IIA,
IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the
lanthanides, or with precursors thereof, a forming step and
calcination.
2. A catalyst support according to claim 1 consisting mainly of
synthetic silica, with 0.5-10 parts by weight of titania and/or
zirconium dioxide characterised in that the support preparation
method comprises mixing particulate synthetic silica with
particulate titania and/or zirconium dioxide or with precursors
thereof, a forming step and calcination.
3. The catalyst support according to claim 1, wherein the content
of synthetic silica in the calcined support is at least 80%.
4. The catalyst support according to claim 1 or 2, wherein at least
50% of the titania and/or zirconium dioxide domains in the calcined
support are smaller than 2 .mu.m.
5. The catalyst support according to claim 1 or 2, wherein at least
50% of the titania and/or zirconium dioxide domains in the calcined
support are smaller than 1 .mu.m.
6. The catalyst support according to claim 1 or 2, wherein at least
50% of the titania and/or zirconium dioxide domains in the calcined
support are smaller than 0.8 .mu.m.
7. The catalyst support according to claim 1 or 2, wherein at least
90% of the titania and/or zirconium dioxide domains in the calcined
support are smaller than 0.8 .mu.m.
8. The catalyst support according to claim 1 wherein the synthetic
silica comprises pyrogenically produced silica.
9. The catalyst support according to claim 1 wherein the synthetic
silica consists entirely of pyrogenically produced silica.
10. The catalyst support according to claim 1 wherein the synthetic
silica comprises silica gel.
11. The catalyst support according to claim 1 wherein the titania
comprises pyrogenically produced titania.
12. The catalyst support according to claim 1 wherein the titania
consists entirely of pyrogenically produced titania.
13. The catalyst support according to claim 1 wherein the titania
comprises precipitated titania.
14. The catalyst support according to claim 1 wherein the titania
consists entirely of precipitated titania.
15. The catalyst support according to claim 1 wherein the zirconium
dioxide comprises pyrogenically produced zirconium dioxide.
16. The catalyst support according to claim 1 wherein the zirconium
dioxide consists entirely of pyrogenically produced zirconium
dioxide.
17. The catalyst support according to claim 1 wherein the zirconium
dioxide comprises precipitated zirconium dioxide.
18. The catalyst support according to claim 1 wherein the zirconium
dioxide consists entirely of precipitated zirconium dioxide.
19. A process for the preparation of a catalyst support according
to claim 1, which comprises mixing particulate synthetic silica
with 0,5 to 10 parts by weight of particulate oxides or phospates
of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB,
IIB, IIIA, IVA and the lanthanides, or with precursors thereof,
based on the total weight of the support, prior to the forming
step, a forming step and calcining the formed material between 400
and 1050.degree. C.
20. A process for the preparation of a catalyst support according
to claim 2, which comprises: mixing particulate silica, with 0.5 to
10 parts by weight of particulate titania and/or zirconium dioxide
or with precursors thereof, based on the total weight of the
support, prior to the forming step; a forming step and calcining
the formed material between 400 and 1050.degree. C.
21. A catalyst containing 5-55 wt.-% of phosphoric acid, based on
the total weight of the dried catalyst, supported on a catalyst
support according to claim 1.
Description
INTRODUCTION AND BACKGROUND
[0001] This present invention relates to catalyst supports and in
particular, to catalysts supported on such catalyst supports, for
use in processes for the hydration of olefins, e.g. in the
production of ethanol or isopropanol. The present invention also
relates to processes for the hydration of olefins, which employ
phosphoric acid supported on such catalyst supports to catalyse the
hydration reaction.
[0002] Hydration catalysts undergo ageing during operation, which
is discernible by a reduction in activity and/or selectivity.
Deactivation is frequently due to a reduction in the specific
surface area of the support brought about by elevated temperatures.
Specific surface area in the context of this application means the
BET surface according to well-known method of Brunauer, Emmett and
Teller determined by nitrogen adsorption according to DIN 66
132.
[0003] The specific surface area of support is closely related to
its pore structure. Moreover, solids having a high surface area
usually have a completely or predominantly amorphous structure,
which has a strong tendency to take on a thermodynamically stable
state by crystallite growth accompanied by a reduction in specific
surface area.
[0004] It has been found that catalyst supports containing silicon
dioxide are also subject to such ageing. Hydrothermal conditions
accelerate ageing. Hydrothermal conditions prevail in chemical
reactions in aqueous systems when the temperature is above the
boiling point of water and pressure is above standard pressure. It
is furthermore known that contaminants, in particular alkali
metals, promote the ageing of supports containing silicon dioxide
under hydrothermal conditions (c.f. for example R. K. Iler in The
chemistry of Silica, page 544, John Wiley & Sons (1979).
[0005] EP 0 578 441 B1 describes the use of a catalyst support for
the hydration of olefins. The active component, which is brought
onto the support by soaking, is phosphoric acid. This particular
support comprises of pellets of synthetic silicon dioxide having
high crush strength, high porosity and few metallic contaminants.
The purpose of the pores of the support is to accommodate the
active component. Pore volume is thus preferably greater than 0.8
ml/g. Average pore radius prior to use in the hydration process is
in the range between 1 and 50 nm.
[0006] In order to achieve optimum hydration performance, EP 0 578
441 B1 specifies a silicon dioxide content of the support of at
least 99 wt % with below 1 wt %, preferable below 0.3 wt % of
contaminants. This type of catalyst support has also been described
in EP 0 393 356 B1 and in U.S. Pat. No. 5,086,031
[0007] It has surprisingly also been found that the catalyst
supports based on synthetic pyrogenically produced silicon dioxide
described in EP 0 393 356 B1 are also subject to ageing under
hydrothermal conditions. Wherein small pores combine to yield
larger pores with loss of specific surface area. Initially, pore
volume remains virtually unchanged during such ageing. This ageing
is unexpected because the pyrogenic silicon dioxide of which the
supports consist has excellent temperature resistance according to
investigations with a scanning electron microscope, the morphology
of pyrogenic silicon dioxide does not change on heating to
temperatures of up to 1000.degree. C. for a period of 7 days
(Schriftenreihe Pigmente Nr. 11: Grundlage von Aerosil.RTM.;
Degussa publication, 5th edition, June 1993, page 20).
[0008] Klimenko (U.S. Pat. No. 3,311,568) has described the
positive influence of TiO.sub.2 on the lifetime of a phosphoric
acid loaded, naturally occurring siliceous support in the hydration
of unsaturated hydrocarbons. At that time it was believed that
natural siliceous deposits such as diatomite, kieselguhr or
diatomaceous earth were the most suitable supports for these
applications. However, naturally occurring siliceous materials
always contain impurities that have some adverse effects on the
catalytic properties. These adverse affects can be diminished, as
is demonstrated in a number of patents, e.g. DE 37 09 401 A1, EP 0
018 022 B1, DE 29 29 919, DE 29 08 491, DE 1 156 772. This,
however, requires a substantial number of additional steps in the
support/catalyst preparation.
[0009] In order to obtain a sufficient physical strength, Klimenko
had to calcine at a temperature from 1050 to 1350.degree. C., the
calcination time being between 5 and 24 hours.
[0010] Schluechter et al. (U.S. Pat. No. 5,208,195) recognise that
H3PO4 containing catalysts based on synthetic silica-gels supports
are highly active and possess a sufficient initial mechanical
strength. However, as they state, these supports have the remaining
disadvantage that the amorphous silica partially crystallises
during prolonged use under conditions of the hydration reaction.
This is associated with a sharp decrease in the specific surface
area and hence in catalytic activity and with a decrease in
mechanical strength. Because of these drawbacks, they prefer to
work with naturally based siliceous materials which require a large
number of preparation steps, e.g. treatment with acid in order to
decrease the alumina content, until they are fit to be used as a
support for hydration purposes.
[0011] Schluechter et al. describe the use of titanium dioxide in
order to increase the compressive strength of catalysts spheres
which are largely based on an essentially
montmorillonite-containing clay, hence, a natural occurring
material. The titanium dioxide is admixed with the acid treated
clay and finely divided silica gel, the TiO.sub.2 content is 1.5 to
2.5 parts by weight, the content of synthetically produced silica
gel is from 20 to 40 parts by weight. The mixture is optionally
shaped and calcined.
[0012] It is also known from the prior art that silica which is
modified by impregnation with a soluble Group IVB-compound, shows
improved stability, see e.g. EP 0 792 859 A2. Titanium is one of
the elements of Group IVB. The silica support is modified with the
stabilising element using the impregnation process, preferably by
pore volume impregnation.
[0013] Pore volume impregnation is performed by dissolving a
soluble compound of the stabilising element in a volume of solvent
which is equal to the pore volume of the catalyst support and then
distributing the solution, for example by spraying, over the
support, which may be rotated in a pill coater during spraying in
order to ensure uniform impregnation.
[0014] Both aqueous and organic solvents or mixtures thereof may be
used for impregnation. In industrial practice, water is generally
preferred as solvent. Selection of the suitable solvent, however,
is dependent upon the stabilising element compound to be used. An
organic titanium compound, such as for example tetrabutoxytitanium
(Ti(C.sub.4H.sub.9O).su- b.4, may also be used instead of aqueous
titanium(III)chloride. In this case, butanol is a suitable
solvent.
[0015] EP 0 792 859 (A2) shows that the degree of stabilisation of
pyrogenic silica increases with increasing Ti-content. However, the
addition of titanium leads to a decrease in pore volume, and,
hence, a lower activity of the catalyst. Therefore, the need exists
to keep the Ti-content as low as possible.
[0016] As is shown in the examples of the above mentioned patent
application, the impregnation with aqueous solutions of TiCl.sub.3
yields materials with only limited stabilisation. At a comparable
Ti-loading, the use of a Ti-alcoholate gave much better results.
These are thus clearly preferred as source for Ti. Since
Ti-alcoholates cannot be dissolved in water, organic solvents have
to be used in order to impregnate the stabilising element.
Appropriate and costly precautions must be taken to avoid any
explosion hazard in the manufacturing of the support.
[0017] The modification of supports by means of impregnation with a
stabilising element requires a substantial number of steps before
the finished stabilised support is obtained. First of all, the
support must be shaped, for instance by extrusion or by tabletting,
then dried and calcined. Next, the stabilising element needs to be
impregnated, then dried again. Finally, the treated supports are
calcined at temperatures of between 160 and 900.degree. C.
[0018] There is a need therefore for a less expensive and less
hazardous support preparation method which, at the same time, still
gives the required high degree of stabilisation and leads at the
same time to a highly active and selective catalyst.
SUMMARY OF THE INVENTION
[0019] An object of the present invention is accordingly to provide
catalyst supports consisting mainly of synthetic silicon dioxide
which, in combination with phosphoric acid, exhibit improved ageing
resistance when used under hydrothermal conditions and which, at
the same time, have excellent activity and selectivity for the
hydration of olefins to the corresponding alcohols.
[0020] A further object of the present invention are hydration
catalysts which are based on the improved supports according to the
invention and which have excellent activity and selectivity for the
hydration of olefins to the corresponding alcohols.
[0021] The above and other objects of this invention are achieved
by a catalyst support consisting mainly of synthetic silica, with
0.5-10 parts by weight of one or more oxides or phosphates of the
elements of group IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides characterised in that the support
preparation method comprises mixing particulate synthetic silica
with particulate oxides or phospates of the elements of Groups IIA,
IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the
lanthanides, or with precursors thereof, a forming step and
calcination.
[0022] The above and other objects of this invention are also
achieved by the supported phosphoric acid catalysts wherein the
catalyst support, consisting mainly of synthetic silica, is
modified by 0.5 to 10 parts by weight titanium dioxide and/or
zirconium dioxide based on the total weight of the calcined
support, and in which the silica and the titania and/or zirconium
dioxide are mixed, preferably, prior to the forming step.
[0023] Thus, according to one aspect, the present invention
provides a catalyst support consisting mainly of synthetic silica,
with 0.5-10 parts by weight of particulate oxides or phospates of
the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB,
IIB, IIIA, IVA and the lanthanides, or with precursors thereof,
preferred titania and/or zirconium dioxide characterised in that
the support preparation method comprises mixing particulate
synthetic silica with particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, or with precursors thereof,
preferred titania and/or zirconium dioxide, a forming step and
calcination.
[0024] In preferred embodiments of the invention, the catalyst
supports comprise silica, titania or zirconium dioxide.
[0025] By mixing particulate oxides or phospates of the elements of
Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and
the lanthanides, or precursors thereof, preferred titania and/or
zirconium dioxide with silica in this manner, the particulate
oxides or phospates of the elements of Groups IIA, IIIB, IVB, VB,
VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or
precursors thereof, preferred titania and/or zirconium dioxide form
domains within the structural framework of the calcined support,
and is not just a surface coating. Thus, according to another
aspect of the present invention, there is provided a catalyst
support comprising a structural framework of synthetic silica,
which framework contains domains of particulate oxides or phospates
of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB,
IIB, IIIA, IVA and the lanthanides, or of precursors thereof,
preferred titania and/or zirconium dioxide, wherein the particulate
oxides or phospates of the elements of Groups IIA, IIIB, IVB, VB,
VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or
precursors thereof, preferred titania and/or zirconium dioxide, in
said domains form 0.5 to 10 parts by weight based on the total
weight of the support.
[0026] The resulting support has an improved stability against
ageing and is substantially easier to produce than any of the
materials from the state of the art. Furthermore, it shows
excellent activity and selectivity in the hydration of olefins to
alcohols. Thus, according to a further aspect, the present
invention provides a process for the hydration of olefins, said
process comprising reacting an olefin with water in the presence of
phosphoric acid supported on one of the catalyst supports described
above.
[0027] Another object of the present invention is the preparation
method for these supports. Such a method comprises: mixing
particulate silica, with 0.5 to 10 parts by weight of particulate
oxides or phospates of the elements of Groups IIA, IIIB, IVB, VB,
VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or with
precursors thereof, preferred titania and/or zirconium dioxide,
based on the total weight of the support prior to the forming
step;
[0028] a forming step and
[0029] calcining the formed material between 400 and 1050.degree.
C.
[0030] The method of the present invention is not only much more
simple and easier to carry out than the existing manufacturing
technologies, but at the same time also gives materials with
improved activity and stability, with excellent selectivities.
DETAILED DESCRIPTION OF THE INVENTION
[0031] It has now been found, surprisingly, that the stability of
phosphoric acid catalysts based on synthetic silica can be
increased very substantially when the synthetic particulate silica
is physically admixed with particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, or with precursors thereof,
preferred particulate titania and/or zirconium dioxide prior to the
forming step.
[0032] The silicon dioxide used in accordance with the present
invention consists mainly of synthetic silica. Silica gels,
precipitated silica's, both produced by wet chemical methods, are
suitable synthetic materials. Synthetic silicon dioxide produced by
flame hydrolysis, so-called pyrogenic or fumed silicon dioxide, is
preferably used.
[0033] Fumed or pyrogenic silica is offered by Degussa-Huels under
the tradename AEROSIL.RTM..
[0034] To prepare AEROSIL.RTM., a volatile silicon compound is
sprayed into an oxyhydrogen gas flame consisting of hydrogen and
air. In most cases compounds like silicon tetrachloride or
SiMeCl.sub.3 are used. These substances hydrolyse under the effect
of the water produced in the oxyhydrogen gas reaction to give
silicon dioxide and hydrochloric acid. The silicon dioxide, after
leaving the flame, is introduced into a so-called coagulation zone
where the AEROSIL.RTM. primary particles and primary aggregates are
agglomerated. The product produced in this stage as a type of
aerosol is separated from the gaseous accompanying substances in
cyclones and then post-treated with moist hot air. As a result of
this process, the residual hydrochloric acid content drops to below
0.025%. Since the AEROSIL.RTM. at the end of this process is
produced with a bulk density of only about 15 g/l, a vacuum
compaction process follows, by means of which compacted densities
of about 50 g/l or above may be produced.
[0035] The particle sizes of the products obtained in this way may
be varied by varying the reaction conditions, such as for example
the flame temperature, the proportion of hydrogen or oxygen, the
amount of silicon tetrachloride, the residence time in the flame or
the length of the coagulation zone.
[0036] The titanium dioxide used in accordance with the present
invention can be of any source, for instance precipitated or fumed
titania. Fumed or pyrogenic titanium dioxide is also offered by
Degussa-Huels and is produced by flame hydrolysis of volatile
Ti-compounds, like e.g. TiCl.sub.4. The process to make pyrogenic
or fumed TiO.sub.2 is similar to the Aerosil.RTM. process described
above.
[0037] The titanium dioxide can consist of any of its crystalline
modification, e.g. anatase or rutile or it can be wholly or partly
amorphous. Mixtures of these different phases are also
possible.
[0038] The zirconium dioxide used in accordance with the present
invention can be of any source, for instance precipitated or fumed
zirconium dioxide.
[0039] Zirconium dioxide which can be used according to this
invention is for instance described in Ullmann's Encyclopedia of
Industrial Chemistry, 5.sup.th Edition, Vol. A28, 543-571 published
by VCH-Verlagsgesellschaft and in PhD Thesis from Patrick D. L.
Mercera, titled "Zirconia as a support for catalysts" Universiteit
Twente, the Netherlands (1991).
[0040] Instead of using particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, preferred particulate titania and/or
zirconium dioxide, it is also possible to use one or more of their
precursors, that upon calcination are transformed into the
corresponding oxide form. For instance, particulate Zr(OH).sub.4
can be used instead of or in addition to particulate zirconium
dioxide.
[0041] For use as support for phosphoric acid hydration catalysts,
the content of the particulate oxides or phospates of the elements
of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA
and the lanthanides, or precursors thereof, preferred titanium
dioxide and/or zirconium dioxide in the finished support is from
0.5 to 10 wt.-%, preferably from 1 to 9 wt.-%, most preferably from
2.6 to 8 wt.-%, based on the total weight of the support. Too high
concentrations lead to loss of activity caused by a reduction in
pore volume by formation of Ti- and/or Zr-phosphates. Too low
concentrations, on the other hand, lead to an insufficient
stabilisation of the catalyst and, hence, a too short lifetime.
[0042] The content of synthetic silica in the calcined support can
be at last 80%. The support preferably consists of particles with
dimensions between 0.8 and 10 mm, most preferably from 1.5 to 8 mm.
Too small particles lead to an unacceptable pressure drop over the
catalyst bed whereas too large particles result in diffusion
limitation and, hence, lower activity of the catalyst. The surface
area of the fresh unloaded support is mainly determined by the
starting compounds silica and the particulate oxides or phospates
of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB,
IIB, IIIA, IVA and the lanthanides, or precursors thereof,
preferred and titania and/or zirconium dioxide and can be anywhere
from 5 to 600 m.sup.2/g, preferably from 10 to 400 m.sup.2/g.
[0043] One of the most important properties of support materials to
be used in hydration catalysts is their pore volume. A higher pore
volume enables a higher uptake of phosphoric acid and thus leads to
a higher activity of the catalyst. The pore volume can be anywhere
from 0.5 to 1.8 ml/g, preferably from 0.8 to 1.5 ml/g, most
preferably from 0.9 to 1.5 ml/g.
[0044] The support can exist in form of tablets, extrudates,
spheres or beads. For extrudates and tablets the standard form is
cylindrical, but all other shapes known in the art, e.g. rings,
wagon wheels, trilobes, stars, etc. can be used as well. The front
and back end of such tablets can either be flat or capped.
[0045] The bulk density of the support is determined mainly by the
pore volume, the titania and/or zirconium dioxide content and by
the form and dimensions of the individual support particles. The
bulk density can thus vary within a broad range and can be anywhere
from 300 to 800 g/l.
[0046] Forming can consist of any forming technique. The preferred
forming methods for supports to be used in a fixed bed hydration
process are tabletting, compression or extrusion. In the process of
support preparation, particulate synthetic silica in a preferably
finely divided form is admixed with particulate oxides or phospates
of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB,
IIB, IIIA, IVA and the lanthanides, or with precursors thereof,
preferred titania and/or zirconium dioxide, also in a preferably
finely divided form, together with water and forming additives,
like lubricants and/or pore builders. Optionally, silica sol or
naturally occurring silica can be added, their maximum content is
10 parts by weight, based on the weight of the calcined support.
The mixture is then thoroughly mixed or kneaded. Optionally, the
mixture can be dried partially or completely before the forming
step, especially in the case of tabletting. The mixture is brought
into its final form by the chosen forming technique, e.g.
extrusion, tabletting or compression.
[0047] Finely divided in this respect means that the silica and the
particulate oxides or phospates of the elements of Groups IIA,
IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the
lanthanides, or precursors thereof, preferred titania and/or
zirconium dioxide, prior to the mixing or kneading step consist of
agglomerates preferably in the range of up to 100 .mu.m, more
preferably up to 50 .mu.m. Agglomerates that are in this range,
should be so loosely bound that they, in the mixing or kneading
step, are reduced in size to such an extent that the final support
comprises small domains of particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, or of precursors thereof, preferred
titania and/or zirconium dioxide.
[0048] Because the forming procedure includes physically admixing
particulate silica and particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, or precursors thereof, preferred
titania and/or zirconium dioxide, the finished support contains
domains of particulate oxides or phospates of the elements of
Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and
the lanthanides, or of precursors thereof, preferred titania and/or
zirconium dioxide. The size and the distribution of these domains
throughout the formed support are important with respect to the
stability. After the mixing or kneading procedure in conjunction
with the forming step, e.g. extrusion or tabletting, and
calcination, 50% or more of the domains of particulate oxides or
phospates of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB,
VIII, IB, IIB, IIIA, IVA and the lanthanides, or precursors
thereof, preferred titania and/or zirconium dioxide, in the
calcined support are smaller than 2 .mu.m in size. Preferably, at
least 50% of the domains of particulate oxides or phospates of the
elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,
IIIA, IVA and the lanthanides, or precursors thereof, preferred
titania and/or zirconium dioxide is smaller than 1 .mu.m and more
preferably, at least 50% of the domains of particulate oxides or
phospates of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB,
VIII, IB, IIB, IIIA, IVA and the lanthanides, or precursors
thereof, preferred titania and/or zirconium dioxide is in the range
below 0.8 .mu.m. Most preferably, at least 90% of the domains of
particulate oxides or phospates of the elements of Groups IIA,
IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the
lanthanides, or precursors thereof, preferred titania and/or
zirconium dioxide is in the range below 0.8 .mu.m.
[0049] Forming additives can be all aids known in the art, they may
for instance have a binding or a lubricating or a pore building
function. Examples are cellulose and its derivatives, polyethylene
glycol, wax, ammonia or ammonia releasing compounds,
polyvinylalcohols, starch, sugars, etc.
[0050] The contents of the different substances in the mixture is
to be adjusted such that the consistency of the mixture is suitable
for the chosen forming technique. Optionally, the mixture can be
dried partially or completely before the forming step.
[0051] After the forming step, the shaped bodies are optionally
dried and then calcined. Whereas drying is normally carried out at
temperatures below 200.degree. C., calcination takes place
preferably between 400 and 1050.degree. C., most preferably between
450 and 1000.degree. C. High calcination temperatures are no
problem since the support materials according to this invention
have surprisingly good thermal stability. The duration of the
calcination can be anywhere from 15 minutes to several hours,
depending on the type and size of kiln in which the calcination is
carried out. The calcination is preferably carried out in air.
[0052] The catalyst supports as described herein are particularly
advantageous for hydrating olefins to produce lower alkanols. For
the hydration of olefins, phosphoric acid is introduced into the
catalyst support as the active component. To this end, once the
stabilised support has been calcined, it may be loaded with an
aqueous solution of phosphoric acid. The phosphoric acid solution
may contain 15 to 85 wt. % of phosphoric acid relative to the total
weight of the solution, preferably from 30 to 65 wt.-%. Optionally,
the impregnated support is dried before use to form the dried
catalyst system. In the dried form, the catalyst may have a
concentration of phosphoric acid ranging from 5 to 55 wt.-%,
preferably from 20 to 50 wt.-% based on the total weight of the
dried catalyst system.
[0053] The phosphoric acid loading procedure can consist of any
appropriate technique, e.g. immersion in an excess phosphoric acid
solution, soaking, spray impregnation, dry impregnation, etc. The
amount of solution can be equal to, larger than or smaller than the
pore volume of the amount of support. Loading can be carried out at
any pressure. In order to facilitate the uptake of the rather
viscous phosphoric solution, the loading of the support might
advantageously be carried out at subambient pressure.
[0054] The catalysts according to the invention have a very good
stability against ageing under hydrothermal conditons, e.g. the
conditions that are encountered during olefin hydration. If
catalysts according to the invention are aged for approximately
40-45 hours at 350-370.degree. C. in the presence of 15-18 bar
water vapour, their pore size distribution is such, that the major
part of the pore volume is associated with pores with a diameter
smaller than 5 .mu.m.
[0055] Changes to the pore structure of catalyst supports
containing silicon dioxide under hydrothermal conditions are
investigated below. Conventional unstabilised and stabilised
supports are compared with the new stabilised supports.
[0056] As discussed above, the present invention also provides a
process for the hydration of olefins, said process comprising
reacting an olefin with water in the presence of a catalyst
comprising phosphoric acid supported on a catalyst support,
characterised in that said catalyst support comprises a structural
framework of synthetic silica, which frame work contains domains of
a particulate oxide or phosphate of at least one element selected
from the group consisting of Groups IIA, IIIB, IVB, VB, VIB, VIIB,
VIIIB, IB, IIB, IIIA, IVA and the lanthanide series of the Periodic
Table; said oxide or phosphate forming 0.5 to 10 parts by weight of
the total weight of the support. Preferably, the frame work of the
catalyst support contains domains of titania and/or zirconium
dioxide.
[0057] The olefins to be hydrated are suitably ethylene or
propylene. Where ethylene is employed, the alcohol produced is
ethanol. Where propylene is employed, isopropanol and n-propanol
are produced. Ethers corresponding to the olefin may also be formed
as by-products during the reaction. The hydration is preferably
carried out in the vapour phase, ie both the olefin and water are
in the vapour phase during the reaction.
[0058] The hydration reaction is typically carried out by placing
the catalyst impregnated support in a reactor, sealing the reactor
and then heating the supported catalyst to the reaction
temperature. The supported catalyst is preferably heated to a
temperature from 170 to 300.degree. C. depending upon the end
product desired. For instance, if the end product is ethanol from
ethylene, the supported catalyst is suitably heated from 225 to
280.degree. C., preferably from 230-260.degree. C., more preferably
from 235-245.degree. C. On the other hand, if the end product is
iso-propanol and n-propanol from propylene, the supported catalyst
is suitably heated from 180-225.degree. C., preferably from
185-205.degree. C.
[0059] When the supported catalyst bed has attained the desired
temperature, a charge of the olefin and water in the vapour state
may be passed through the reactor. The mole ratio of water to
olefin passing through the reactor may be in the range of from 0.15
to 0.50, preferably from 0.25 to 0.45, more preferably from
0.30-0.40. The space velocity of water vapour/olefin mixture
passing through the reactor may be subject to slight variations
depending upon whether the reactant olefin is ethylene or
propylene. For instance, in the case of ethylene, the space
velocity of the mixture thereof with water vapour is suitably from
0.010 to 0.100, preferably from 0.020 to 0.050 grams per minute per
cm 3 of the supported catalyst. In the case of a mixture of
propylene and water vapour, the space velocity is suitably in the
from 0.010-0.100, preferably from 0.02-0.07 g/min/cm3 of the
supported catalyst.
[0060] The hydration reaction may be carried out a pressure ranging
from 2000 to 24000 KPa. Within this range the hydration of ethylene
is suitably carried out at a pressure from 3000 to 10000 KPa,
whereas the hydration of propylene is suitably carried out at a
pressure from 2000-7600 KPa.
[0061] These and other aspects of the present invention will now be
described, by way of illustration, with reference to the following
Examples and accompanying Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 is a plot of differential intrusion vs. Pore diameter
for a pore structure of an unstabilised catalyst support after a
hydrothermal ageing test (comp. example 1);
[0063] FIG. 2 is a plot of differential intrusion vs. Pore diameter
for a pore structure of a catalyst support stabilised with 1.5% of
titanium, according to prior art, after a hydrothermal ageing test
(comp. example 2);
[0064] FIG. 3 is a plot of differential intrusion vs. Pore diameter
for a pore structure of a catalyst support stabilised with 4% of
titanium, according to prior art, after a hydrothermal ageing test
(comp. example 3);
[0065] FIG. 4 is a plot of differential intrusion vs. pore diameter
for a pore structure of a catalyst support stabilised with 5% of
titanium, according to prior art, after a hydrothermal ageing test
(comp. example 4);
[0066] FIG. 5 is a plot of differential intrusion vs. pore diameter
for a pore structure of a catalyst support stabilised with 5% of
titanium, according to prior art, after a hydrothermal ageing test
(comp. example 5);
[0067] FIG. 6 is a plot of differential intrusion vs. pore diameter
for a pore structure of a catalyst support stabilised with 3% of
titanium, according to this invention, after a hydrothermal ageing
test (example 6);
[0068] FIG. 7 is a plot of differential intrusion vs. pore diameter
for a pore structure of a catalyst support stabilised with 1.8% of
titanium, according to this invention, after a hydrothermal ageing
test (example 7);
[0069] FIG. 8 is a plot of differential intrusion vs. pore diameter
for a pore structure of a catalyst support stabilised with 1.8% of
titanium, according to this invention, after a hydrothermal ageing
test (example 8); and
[0070] FIG. 9 is a graph showing how the ethanol space time yield
(STY) of an olefin hydration process varies with time, depending on
the catalyst employed (Example 17).
[0071] FIG. 10 is a plot of differential intrusion vs. pore
diameter for a pore structure of a catalyst support stabilised with
5% of zirconia, according to this invention, after a hydrothermal
ageing test (example 22).
[0072] The pore size distribution curves shown in FIGS. 1 to 8 and
10 were determined using the well-known Hg porosimetry method. They
show the differential penetration (intrusion) of the mercury as a
function of pore diameter. Arbitrary units were selected for
differential intrusion and the curves were each expanded over the
available area of the diagram.
COMPARATIVE EXAMPLE 1
[0073] A state-of- the-art support was prepared according to
example 2 of EP 393 356 B1.
[0074] This support is thus made by mixing pyrogenic silica
(AEROSIL.RTM.200 from Degussa-Huels), magnesiumstearate,
methylcellulose and urea, and subsequent drying and tabletting. The
calcination procedure consists of two steps: a first calcination at
250.degree. C., and the final calcination at 750.degree. C. This
product is sold by Degussa-Huels under either of the names Degussa
350, Trger 350, Support 350 or Aerolys.TM. 350 and has the
following properties: specific surface area approx. 180 m.sup.2/g;
bulk density approx. 490 g/l; total pore volume approx. 0.8
cm.sup.3/g. It consists of tablets with a diameter of 6 mm, and a
height of 5.5 mm.
[0075] This support material was loaded with a 60 wt.-% phosphoric
acid solution and heated to 350.degree. C. in a high pressure
apparatus at a steam pressure of 15 bar for 41 hours.
[0076] The pore size distribution of the aged catalyst was
determined by Hg porosimetry. The measured pore size distribution
is shown graphically in FIG. 1.
[0077] The hydrothermally aged supports have a maximum in the pore
size distribution at pore diameters of between 20 and 30 .mu.m.
COMPARATIVE EXAMPLE 2
[0078] The catalyst support from comparative example 1 was modified
with 1.5 wt. % of Ti. In order to modify 100 g of support with 1.5
wt. % of Ti, 33 g of a 15% titanium(III)chloride solution
(TiCl.sub.3) were diluted with water to 80 ml, corresponding to the
pore volume of the support material. The support material was
impregnated with this solution.
[0079] After 30 minutes exposure to the solution, the support was
dried in a drying cabinet at 100.degree. C. for 3 hours and then
calcined in a furnace at 600.degree. C. for a period of 4 hours.
The support was then loaded with a 60 wt.-% phosphoric acid
solution and left in a high pressure apparatus at a steam pressure
of 15 bar at 350.degree. C. for 40 hours. The pore size
distribution of the aged catalyst was again determined by Hg
porosimetry. The pore size distribution is shown graphically in
FIG. 2.
[0080] The maximum of the pore size distribution is between 10 and
20 .mu.m. In comparison with the undoped catalyst used in
comparative Example 1, the catalyst doped with 1.5 wt. % of Ti has
a higher proportion of small pores of a diameter of below 10 .mu.m
after ageing.
COMPARATIVE EXAMPLE 3
[0081] The catalyst support as described in comparative example 1
was modified with 4 wt. % of Ti. In order to modify 100 g of
support with 4 wt. % of Ti, 85.93 g of a 15% titanium(III)chloride
solution were diluted with water to 80 ml and distributed over the
support to impregnate it.
[0082] After 30 minutes exposure to the solution, the support was
dried in a drying cabinet at 100.degree. C. for 3 hours and then
calcined in a furnace at 600.degree. C. for a period of 4 hours.
The support was then loaded with a 60 wt.-% phosphoric acid
solution and left in a high pressure apparatus at a steam pressure
of 15 bar at 350.degree. C. for 43 hours. The pore size
distribution of this specimen is very wide. The maximum of the pore
size distribution is approximately 2 .mu.m. In comparison with the
undoped catalyst used in Comparative Example 1, the catalyst doped
with 4 wt. % of Ti has a high proportion of pores of a diameter of
less than 10 .mu.m. In comparison with the undoped catalyst from
Comparative Example 1, the catalyst doped with 4 wt. % of Ti is
distinctly more stable and the enlargement of pore diameter is
distinctly less marked.
COMPARATIVE EXAMPLE 4
[0083] The catalyst support as described in Comparative Example 1
was modified with 5 wt. % of Ti. In order to modify 100 g of
support with 5 wt. % of titanium, 35.5 g of tetrabutoxytitanium
(Ti(C.sub.4H.sub.9O).sub- .4) were diluted to 80 ml with butanol
and distributed over the support. Special explosion-proof equipment
was used during impregnation and drying in order to avoid any risk
of explosion.
[0084] After 30 minutes exposure to the solution, the support was
dried in a drying cabinet at 100.degree. C. for 3 hours and then
calcined in a furnace at 600.degree. C. for a period of 4
hours.
[0085] The support was then loaded with phosphoric acid and heated
to 350.degree. C. in a high pressure apparatus at a steam pressure
of 15 bar for 41.5 hours. The pore size distribution of the aged
catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 4.
[0086] The maximum of the pore size distribution is approximately
0.7 .mu.m. There are virtually no pores with a diameter greater
than 3 .mu.m. In comparison with the undoped catalyst from
Comparative Example 1, the catalyst doped with 5 wt. % of Ti is
distinctly more stable. The average pore diameter for the catalyst
doped with 5 wt. % of Ti is smaller by a factor of 35 than in the
case of the undoped catalyst from Comparative Example 1.
[0087] The preparation method in this example is based on the use
of an organic solvent. Industrial production of this Ti-containing
support material requires the use of special explosion-proof
equipment and buildings. Furthermore, large amounts of organic
solvents have to be handled, and organic wastes have to be burned
or otherwise recycled. This material is thus difficult to produce
and, hence, expensive.
COMPARATIVE EXAMPLE 5
[0088] A similarly prepared catalyst support as described in
Comparative Example 1 with a higher pore volume of 1.0 ml/g was
modified with 5 wt. % of Ti by impregnation with titanylsulfate
(TiOSO.sub.4) which was dissolved in water that contained some
H.sub.2O.sub.2. This solution was distributed over the support.
[0089] After 30 minutes exposure to the solution, the support was
dried in a drying cabinet at 100.degree. C. for 3 hours and then
calcined in a furnace at 600.degree. C. for a period of 4
hours.
[0090] The support was then loaded with phosphoric acid and heated
to 350.degree. C. in a high pressure apparatus at a steam pressure
of 15 bar for 45 hours. The pore size distribution of the aged
catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 5.
[0091] In comparison with the undoped catalyst from Comparative
Example 1, the catalyst doped with 5 wt. % of Ti is distinctly more
stable.
EXAMPLE 6
[0092] A catalyst support in accordance with this invention was
prepared by mixing 1.0 kg of pyrogenic silica (Aerosil.RTM. 200 V
from Degussa-Huels, amorphous), 52.5 g of pyrogenic titania (P25
from Degussa-Huels, consisting of approx. 70-80% anatase and 20-30%
of rutile, surface area 50 m.sup.2/g, d.sub.503-4 .mu.m), 21 g of
methylcellulose, 50 g of wax, 5 g of polysaccharide, 10 g of a 30%
ammonia solution and 1.9 kg of water. The mixture was kneaded for
approx. 30 minutes and was subsequently extruded. After drying at
110.degree. C., the material was calcined in air at 750.degree. C.
for 3 hours. The obtained extrudates contain 5 wt.-% of TiO.sub.2
and 95% of SiO.sub.2. 5% TiO.sub.2 corresponds to a Ti-content of 3
wt.-%. The diameter of the extrudates is 4.0 mm, the surface area
is 175 m.sup.2/g, the pore volume is 0.99 ml/g, the bulk density
450 g/l and the crush strength 47 N.
[0093] The support of this example was analysed with transmission
electron microscopy (TEM). The titania domains are clearly visible
in the amorphous silica matrix. The titania domains have a maximum
size of approximately 0.3 .mu.m.
[0094] The support of this example was also analysed with XRD. No
peaks of crystalline silica were found. Titania peaks were present
for both anatase and rutile.
[0095] This support was loaded with phosphoric acid and heated to
370.degree. C. in a high pressure apparatus at a steam pressure of
15 bar for approx. 45 hours. The pore size distribution of the aged
catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 6. There are virtually no
pores of a diameter greater than 3 .mu.m, although the Ti-content
is only 3 wt.-%.
EXAMPLE 7
[0096] Another catalyst support in accordance with this invention
was prepared by mixing 970 g of pyrogenic silica, 30 g of pyrogenic
titania, 21 g of methylcellulose, 50 g of wax, 5 g of
polysaccharide, 10 g of a 30% ammonia solution and 1.9 kg of water.
The mixture was kneaded for approx. 30 minutes and was subsequently
extruded. After drying at 110.degree. C., the material was calcined
in air at 850.degree. C. for 3 hours. The obtained extrudates
contain 3% of TiO.sub.2 and 97% of SiO.sub.2. 3% TiO.sub.2
corresponds to a Ti-content of only 1.8 wt.-%. The diameter of the
extrudates is 3.5 mm, the surface area is 165 m.sup.2/g, the pore
volume is 1.0 ml/g, the bulk density 440 g/l and the crush strength
50 N.
[0097] This support was loaded with phosphoric acid and heated to
370.degree. C. in a high pressure apparatus at a steam pressure of
15 bar for approx. 43 h hours. The pore size distribution of the
aged catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 7. There are virtually no
pores of a diameter greater than 3 .mu.m. In comparative example 2,
the Ti-loading is 1.5 wt.-%, thus nearly identical to the Ti
content of the support in this example. Comparison of the
porosimetry data shows that the support of the present invention is
much better stabilised. Furthermore, the support of the present
invention is much easier to produce.
EXAMPLE 8
[0098] Another catalyst support in accordance with this invention
was prepared by mixing 970 g of pyrogenic silica, 30 g of
precipitated titania (anatase form), 21 g of methylcellulose, 50 g
of wax, 5 g of polysaccharide, 10 g of a 30% ammonia solution and
1.9 kg of water. The mixture was kneaded for approx. 30 minutes and
was subsequently extruded. After drying at 110.degree. C., the
material was calcined in air at 850.degree. C. for 3 hours. The
obtained extrudates contain 3 wt.-% of TiO.sub.2 and 97 wt.-% of
SiO.sub.2. 3 wt.-% TiO.sub.2 corresponds to a Ti-content of only
1.8 wt.-%. The diameter of the extrudates is 3.5 mm, the surface
area is 165 m.sup.2/g, the pore volume is 1.0 ml/g, the bulk
density 440 g/l and the crush strength 50 N.
[0099] This support was loaded with phosphoric acid and heated to
370.degree. C. in a high pressure apparatus at a steam pressure of
15 bar for 43 hours. The pore size distribution of the aged
catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 8. There are virtually no
pores of a diameter greater than 3.5 .mu.m. In comparative example
2, the Ti-loading is 1.5 wt.-%, thus nearly identical to the Ti
content of the support in this example. Comparison of the
porosimetry data shows that the support of the present invention is
much better stabilised. Furthermore, the support of the present
invention is much easier to produce.
EXAMPLE 9
[0100] The most frequently applied acid loading procedure consists
of soaking the support in an excess of approx. 60 wt.-% phosphoric
acid solution. After this soak procedure, the excess solution is
drained off and the catalyst is dried.
[0101] During the soaking operation some of the titania present in
the support might be dissolved. The loading procedure thus can lead
to an unwanted loss of titania.
[0102] In some of the examples described above, the drained-off
acid was analysed for the presence of titanium. Analysis was
carried out semi-quantitatively by adding some H.sub.2O.sub.2 to
the acid solution. In the presence of small amounts of titanium the
solution turns yellow, higher titanium concentrations give an
orange or red color.
1 Example Colour observed 1 (comparative), without Ti none 3
(comparative) yellow 4 (comparative) orange-red 5 (comparative)
orange 6 very slightly yellow 7 very slightly yellow
[0103] As can be seen from these results, the stabilised
state-of-the-art supports (examples 3, 4 and 5) suffer from
substantial Ti-loss during the acid loading. The supports according
to the invention do not lose any or only very little Ti. This is an
advantage from the supports according to the invention.
[0104] Other advantages have been demonstrated in the previous
examples: compared to the state of the art supports, they have a
better or equal hydrothermal stability after loading with
phosphoric acid, their method of preparation is much simpler and
their titania content is lower.
EXAMPLE 10
[0105] A catalyst support according to the present invention was
provided in the form of 3.5 mm cylindrical extrudates. The method
employed to prepare the catalyst support of this Example is
identical to that employed to prepare the catalyst support of
Example 6. The Ti content of the support was 3.9% wt/wt, as
measured by X-ray Fluorescence. The support had a bulk density of
480 g/l, a pore volume of 0.96 ml/g (by H.sub.2O absorption), a
crush strength of 45N (average of 50 crushed pellets, using
Mecmesin crush strength tester), and a pore size distribution
characterised by a sharp unimodal peak at 16 nm, as measured by Hg
porosimetry.
EXAMPLE 11
[0106] A catalyst was produced by impregnating 1 liter of the
support of Example 10 with phosphoric acid. This was achieved by
evacuating the pores of the support to approximately 35 mmHg, and
then submerging the evacuated support in a 55.3 wt/wt % solution of
orthophosphoric acid (H3PO4) .The support was then left to soak in
the solution at atmospheric pressure for 1 hour.
[0107] After soaking, the support was filtered free of excess acid,
and dried at 120.degree. C. for 24 hours. The bulk density of the
resulting catalyst was found to be 874 g/l. The acid loading of the
catalyst, as calculated by subtraction of the support's bulk
density, was 394 g/l.
[0108] The crush strength of the resulting catalyst was measured to
be 49N (average of 50 crushed pellets, using Mecmesin crush
strength tester).
EXAMPLE 12
[0109] The catalyst of Example 11 was used to catalyse an ethylene
hydration reaction.
[0110] The hydration reaction was carried out in a 1 liter
continuous flow pilot plant, designed to simulate the reaction
section of a gas phase ethylene hydration plant. The plant was
operated as follows:
[0111] Fresh ethylene gas was fed to the plant from a high pressure
ethylene compressor. Liquid water was fed to the plant by diaphragm
metering pump. The feeds were combined with recycled ethylene and
passed through a preheater/vaporiser, before being introduced to
the catalyst bed.
[0112] The catalyst was held in a copper lined tubular reactor,
which was also fitted with a central multipoint thermocouple for
accurately measuring catalyst temperatures at various (fixed)
depths down the catalyst bed. The gaseous reactor effluent was
cooled to ambient temperature using a simple shell and tube type
heat exchanger, and the mixture of liquid and gaseous products were
separated in a high pressure gas/liquid separator.
[0113] The gaseous product, still containing significant levels of
ethanol, was then further processed in a wash tower, where the
majority of the water soluble components was scrubbed out. The
liquid effluent from the wash tower was then mixed with the liquid
effluent from the gas/liquid separator to form the main product
stream. This stream was collected and analysed (by gas
chromatography).
[0114] The scrubbed gas from the wash tower was fed to a recycle
compressor and returned to the reactor. The recycle gas flow rate
was carefully controlled using a Coriolis meter to ensure that the
contact time through the catalyst bed was similar to that employed
in commercial ethanol plants. An on-line gas chromatograph was also
employed to analyse the recycle stream every 15 minutes in order to
determine the recycle gas composition.
[0115] The plant was operated at a pressure of 1000 psig (68 atm);
a reactor inlet temperature of 240.degree. C., a reactor exit
temperature of 260.degree. C.; a [water]: [ethylene] feed mole
ratio of 0.35- 0.36; a ethylene GHSV=1350 hr(-1); and a steam
GHSV=485 hr (-1).
[0116] The catalyst was kept on stream for 2 weeks, during which
time, the space time yields (STYs) of ethanol, ether and
acetaldehyde were measured. The results are shown in Table I
below.
COMPARATIVE EXAMPLE 13
[0117] A catalyst was prepared by impregnating a Degussa 350
support with phosphoric acid using an analogous method as that
described in Example 11. The Degussa 350 support has been described
in detail in comparative example 1.
[0118] The resulting catalyst was used to catalyse an ethylene
hydration reaction, using the 1 liter continuous flow pilot plant
described in Example 12 above.
[0119] Table I below compares the space time yields (STY) obtained
using a catalyst supported on the support of Example 10, with the
STYs obtained using the phosphoric acid catalyst supported on
Degussa 350 (Comparative Example 13).
2TABLE I ETHANOL ETHER ACETALDE- % STY STY HYDE STY SELECTIVITY
SUPPORT (g/Lcat/hr) (g/Lcat/hr) (g/Lcat/hr) TO EtOH Comparative 120
6.35 0.37 93.6 Example 13 Example 10 136 6.5 0.45 94.1
[0120] The results show that the catalyst supported on support of
Example 10 (i.e. the catalyst of Example 11) is more active and
selective towards ethanol than a catalyst supported on Degussa 350
(Comparative Example 13).
EXAMPLE 14
[0121] In this Example, the pore size distribution (PSD) of the
catalyst of Example 11 was measured before and after use. The fresh
catalyst was found to have a pore size distribution characterised
by a sharp unimodal peak at 16 nm, as measured by Hg porosimetry.
After use in the pilot plant as described in Example 12 above, the
catalyst was found to be bi-modal at 165 and 380 nm.
COMPARATIVE EXAMPLE 15
[0122] Example 14 above was repeated with a catalyst supported on
Degussa 350. The Degussa 350 support has been described in detail
in comparative example 1. The fresh catalyst was found to have a
pore size distribution characterised by a sharp unimodal peak at 17
nm, as measured by Hg porosimetry. After use, the PSD of the
catalyst was found to be bimodal, with peaks at 200 nm and 3000 nm.
By comparing the results of Example 14 and Comparative Example 15,
it can be seen that the PSD of the catalyst of the present
invention changes significantly less than the PSD of catalysts
supported on titania-free supports, such as Degussa 350.
EXAMPLE 16
[0123] A catalyst support according to the present invention was
provided in the form of 4 mm cylindrical extrudates. The method
employed to prepare the support of this Example is identical to
that employed to prepare the support of Example 6. The Ti content
of the support was 4% wt/wt, as measured by X-ray Fluorescence. The
support had a bulk density of 457.3 g/l, a pore volume of 1.01 ml/g
(by Hg porosimetry and H.sub.2O absorption), a crush strength of
44.8N (average of 50 crushed pellets, using Mecmesin crush strength
tester), and a pore size distribution characterised by a sharp
unimodal peak at 14.8 nm, as measured by Hg porosimetry.
EXAMPLE 17
[0124] A catalyst was produced by impregnating 8 liters of the
support of Example 16 with phosphoric acid. This was achieved by
evacuating the pores of the support to less than 40 mmHg, and then
submerging the evacuated support in a 52 wt/wt % solution of
orthophosphoric acid (H.sub.3PO.sub.4). The support was then left
to soak in the solution at atmospheric pressure for 2 hours.
[0125] After soaking, the support was filtered free of excess acid,
and dried at 120.degree. C. for 3 days. The bulk density of the
resulting catalyst was found to be 755.5 g/l. The acid loading of
the catalyst as calculated by subtraction of the support's bulk
density was 298.2 g/l.
[0126] The catalyst had a crush strength of 92.6N.
EXAMPLE 18
[0127] The catalyst of Example 17 was used to catalyse an ethylene
hydration reaction.
[0128] The hydration reaction was carried out in an 8 liter
continuous flow pilot plant, designed to simulate the reaction
section of a gas phase ethylene hydration plant. The plant was
operated as follows:
[0129] Fresh ethylene gas was fed to the plant from a high pressure
ethylene compressor. Liquid water was fed (by diaphragm metering
pump) into a "drip-feed" vaporiser, which converted the liquid
water into steam. The feeds were then combined with recycled
ethylene, and passed through the catalyst bed.
[0130] The catalyst was held in a copper lined tubular reactor,
which was also fitted with a central multipoint thermocouple for
accurately measuring catalyst temperatures at various (fixed)
depths down the catalyst bed. The gaseous reactor effluent was
cooled to ambient temperature using a simple shell and tube type
heat exchanger. The mixture of liquid and gaseous products were
separated in a high pressure gas/liquid separator. The gaseous
product, still containing significant levels of ethanol, was then
further processed by passing it through a wash tower. In the wash
tower, the majority of the water soluble components was removed
from the gaseous product.
[0131] The liquid effluent from the wash tower was then mixed with
the liquid effluent from the gas/liquid separator to form the main
product stream. This stream was collected and analysed (by gas
chromatography) on a regular basis to provide catalyst activity and
selectivity data.
[0132] The scrubbed gas from the wash tower was fed to a recycle
compressor and returned to the reactor. The recycle gas flow rate
was carefully controlled using a Coriolis meter to provide a
similar contact time through the catalyst bed as that encountered
in commercial ethanol plants. An on-line gas chromatograph was also
employed to analyse the recycle stream.
[0133] The plant was operated at a 1000 psig (68 atm) pressure, a
reactor inlet temperature of 240.degree. C., a reactor exit
temperature of 265.degree. C.; a [water]: [ethylene] feed mole
ratio of 0.28-0.30; a typical ethylene GHSV of 1250 hr.sup.(-1);
and a typical steam GHSV of 357.6 hr.sup.(-1).
[0134] The catalyst was kept on stream for 2 weeks, during which
time the ethylene STY of the process was measured 20 times, at
regular test intervals. The results are shown in FIG. 9 below.
[0135] As can be seen from the graph of FIG. 9, the catalyst of
Example 17 is significantly more active than prior art catalysts,
such as phosphoric acid supported on Degussa 350 (Comparative
Example 13).
[0136] In fact, the performance of Example 17 is comparable to that
of a catalyst supported on a conventional silica gel, such as Grace
57 in terms of spot productivity. However, as shown by the results
of Example 19 and Comparative Example 20 (below), the catalyst of
Example 17 is considerably superior to Grace 57 in terms attrition
resistance.
[0137] After use, the pellet crush strength of the catalyst was
found to have improved from 92.6N (fresh catalyst) to 169.4N (used
catalyst). This compares favourably to the crush strengths of
catalysts supported on Degussa 350, which have fresh and used crush
strengths of 77N and 148 N, respectively.
[0138] The pore size distribution (PSD) of the used catalyst of
Example 17 was also found to be different to that of the fresh
catalyst. After one pilot run, the used support was found to be
broad uni-modal at 171 nm. Although the PSD of the support had
opened up, this was not to the same degree as prior art supports
such as Degussa 350. After use, Degussa 350 supports were found to
be bimodal at 200 nm and 3000 nm.
EXAMPLE 19
[0139] Attrition resistance of the catalyst of Example 17 was
quantified by measuring the amount of dust/broken pellets (fines)
generated before and after use.
[0140] When the fresh catalyst was sieved through a 2 mm sieve, and
the collected fines weighed on an analytical balance, only 0.05%wt
fines were found to have been generated. After a 2 week run, the
catalyst was sieved through a 2 mm sieve. The collected fines were
weighed on an analytical balance. Only 0.6%wt fines had been
generated (some of which by the act of removing the catalyst from
the reactor, and not by the process).
COMPARATIVE EXAMPLE 20
[0141] In this Example, the attrition resistance of a phosphoric
acid catalyst supported on a silica gel (Grace 57) support was
measured using the process of Example 19.
[0142] After a 2 week run, the silica gel catalyst was sieved
through a 2 mm sieve. The collected fines were weighed on an
analytical balance. 10 wt % fines had been generated.
[0143] A comparison of the results of Example 19 and Comparative
Example 20 shows that the catalyst of Example 18 is considerably
superior to Grace 57 in terms of attrition resistance.
EXAMPLE 21
[0144] Since titanium is added to the catalyst support to stabilise
the support's physical structure, it is important that the titanium
is not lost from the support when subjected to process conditions.
Hence, samples of the used catalyst of Example 18 were analysed for
Ti content using X-ray Fluorescence. The results were compared to
the Ti content of the unused catalyst. It should be noted that the
used catalyst was subjected to Soxhlet extraction prior to analysis
in order to remove the orthophosphoric acid catalyst, and any
dissolved titanium.
[0145] The titanium content of the support has marginally decreased
from 4.0 to 3.8% wt/wt in the first run. However, the used catalyst
has retained ca. 3% phosphorus, and the bulk density of the support
changes as a result. When this is taken into account, there is no
evidence for any Ti loss from the support (to within the accuracy
of the XRF technique).
[0146] In addition, there was no evidence for Ti leaching during
catalyst preparation and operation.
EXAMPLE 22
[0147] A catalyst support in accordance with this invention was
prepared by mixing 1.0 kg of pyrogenic silica (Aerosil.RTM. 200 V
from Degussa-Huels, amorphous), 60 g of zirconium hydroxide, 20 g
of methylcellulose, 50 g of wax, 5 g of polysaccharide, 10 g of a
30% ammonia solution and 1.85 kg of water. The mixture was kneaded
for approx. 30 minutes and was subsequently extruded. After drying
at 110.degree. C., the material was calcined in air at 850.degree.
C. for 3 hours. The obtained extrudates contain 5 wt.-% of
ZrO.sub.2 and 95% of SiO.sub.2. wt.-%. The diameter of the
extrudates is 4.0 mm, the pore volume is 0.97 ml/g, the bulk
density 460 g/l and the crush strength 58 N.
[0148] This support was loaded with phosphoric acid and heated to
370.degree. C. in a high pressure apparatus at a steam pressure of
15 bar for approx. 45 hours. The pore size distribution of the aged
catalyst was determined by Hg porosimetry. The pore size
distribution is shown graphically in FIG. 10. Substantial part of
the pores has a diameter smaller than 5 .mu.m.
[0149] Further variations and modifications of the foregoing will
be apparent to those skilled in the art and are intended to be
encompassed by the claims appended hereto.
* * * * *