U.S. patent application number 15/173801 was filed with the patent office on 2017-12-07 for process for reducing the sulphur content of anatase titania and the so-obtained product.
This patent application is currently assigned to Huntsman P&A Germany GmbH. The applicant listed for this patent is Huntsman P&A Germany GmbH. Invention is credited to Ralf Becker, Regina Optehostert, Rolf Wittenberg.
Application Number | 20170348671 15/173801 |
Document ID | / |
Family ID | 60482584 |
Filed Date | 2017-12-07 |
United States Patent
Application |
20170348671 |
Kind Code |
A1 |
Becker; Ralf ; et
al. |
December 7, 2017 |
Process for reducing the sulphur content of anatase titania and the
so-obtained product
Abstract
The present invention relates to the field of heterogeneous
catalysis. In more detail, it refers to a process for reducing the
sulphur content of a stabilized titania, the so-obtained material
and the use thereof for manufacturing of support materials for
heterogeneous catalysts.
Inventors: |
Becker; Ralf; (Bottrop,
DE) ; Optehostert; Regina; (Moers, DE) ;
Wittenberg; Rolf; (Neukirchen-Vluyn, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Huntsman P&A Germany GmbH |
Duisburg |
|
DE |
|
|
Assignee: |
Huntsman P&A Germany
GmbH
Duisburg
DE
|
Family ID: |
60482584 |
Appl. No.: |
15/173801 |
Filed: |
June 6, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 2/33 20130101; B01J
21/063 20130101; B01J 37/08 20130101; B01J 23/26 20130101; B01J
37/031 20130101; B01J 21/08 20130101 |
International
Class: |
B01J 21/06 20060101
B01J021/06; B01J 37/08 20060101 B01J037/08; B01J 37/03 20060101
B01J037/03; B01J 23/75 20060101 B01J023/75; B01J 21/08 20060101
B01J021/08; C10G 2/00 20060101 C10G002/00; B01J 37/04 20060101
B01J037/04 |
Claims
1. Anatase titanium dioxide having a content of at least one
compound selected from oxides of Si, Al, and Zr in an amount of
2-50% b.w., preferably 2-30% b.w., calculated as oxides, of the
total weight of the oxides, and having a sulphur content of less
than 150 ppm, preferably less than 100 ppm and more preferred of
less than 80 ppm referred to the total weight of the oxides.
2. Anatase titanium dioxide according to claim 1 having a content
of at least one compound selected from oxides of Si, Al, and Zr in
an amount of 3-20% b.w., more preferably 4-12% b.w., calculated as
oxides, of the total weight of the oxides and having a sulphur
content of less than 150 ppm, preferably less than 100 ppm and more
preferred of less than 80 ppm referred to the total weight of the
oxides.
3. Anatase titanium dioxide according to claim 1 having a content
of SiO.sub.2 in an amount of 2-30% b.w., preferably 3-20% b.w.,
more preferably 4-12% b.w., calculated as oxide, of the total
weight of the oxides, and having a sulphur content of less than 100
ppm, preferably less than 80 ppm referred to the total weight of
the oxides.
4. Process for preparing an anatase titanium dioxide having a
content of at least one compound selected from oxides of Si, Al,
and Zr in an amount of 2-30% b.w., preferably 3-20% b.w., more
preferably 4-12% b.w., calculated as oxides, of the total weight of
the oxides, and having a sulphur content of less than 150 ppm,
preferably less than 100 ppm and more preferred less than 80 ppm,
referred to the total weight of the oxides, of claim 1 wherein: a
titanium compound selected from metatitanic acid or titanylsulphate
is mixed with at least one compound selected from oxides and/or
hydroxides of Si, Al, and Zr or precursors thereof in an aqueous
medium, precipitating at least one compound selected from oxides
and/or hydroxides of Si, Al, and Zr, treating the obtained product
to reduce the alkali content if the alkali content is above 200
ppm, to a level of at most 200 ppm, referred to the total weight of
the oxides, the product is optionally filtered, optionally washed
with water, and optionally dried, the product is then subjected to
a calcination treatment at a temperature of more than 500.degree.
C., preferably in the range of 800.degree. to 1200.degree. C., over
a time period sufficient to decompose the remaining sulphur
containing compound such as sulphuric acid to a level below 150
ppm, preferably less than 100 ppm and more preferred less than 80
ppm referred to the total weight of the oxides, preferably over a
time period of 0.5 to twelve hours.
5. Process for preparing an anatase titanium dioxide according to
claim 3 wherein metatitanic acid is mixed with a SiO.sub.2
precursor compound, precipitating at least one oxide and/or
hydroxide of Si, treating the obtained product to reduce the alkali
content if the alkali content is above 200 ppm, to a level of at
most 200 ppm, referred to the total weight of the oxides,
optionally filtering, optionally washing the obtained product and
optionally drying the obtained product, then subjecting the product
to a calcination treatment at a temperature of more than
500.degree. C., preferably in the range of 800.degree. to
1200.degree. C., over a time period sufficient to decompose the
remaining sulphur containing compound such as sulphuric acid to a
level below 100 ppm, preferably less than 80 ppm referred to the
total weight of the oxides, preferably over a time period of 0.5 to
twelve hours,
6. Process for preparing an anatase titanium dioxide according to
claim 3 wherein a titanium compound selected from a TiO.sub.2 sol
is mixed with an SiO.sub.2 sol, adjusting the pH to obtain a
precipitate, treating the obtained precipitate to reduce the alkali
content if the alkali content is above 200 ppm referred to the
total weight of the oxides, to a level of at most 200 ppm, referred
to the total weight of the oxides, the obtained product is
optionally filtered, optionally washed, optionally dried, and the
obtained product is subjected to a calcination treatment at a
temperature of more than 500.degree. C., preferably in the range of
800.degree. to 1200.degree. C., over a time period sufficient to
decompose the remaining sulphur containing compound such as
sulphuric acid to a level below 150 ppm, preferably less than 100
ppm and more preferred less than 80 ppm referred to the total
weight of the oxides, preferably in the range of 800.degree. to
1200.degree. C., preferably over a time period of 0.5 to twelve
hours.
7. Process for reducing the sulphur content of a stabilised anatase
titania wherein an anatase titania having a content of a
stabilizing agent is treated at a temperature more than 500.degree.
C., preferably in the range of 800.degree. to 1200.degree. C., over
a time period sufficient to decompose a remaining sulphur
containing compound such as sulphuric acid to a level below 150
ppm, preferably less than 100 ppm and more preferred less than 80
ppm referred to the total weight of the oxides, preferably for a
time period of at least 30 min, wherein the stabilizing agent is
selected from oxides of Si, Al, and Zr and wherein the content of
the stabilizing agent is in the range of 2-50% b.w., preferably
2-30% b.w., calculated as oxides, of the total weight of the
oxides.
8. Use of a calcination treatment at a temperature more than
500.degree. C. for reducing the sulphur content of a stabilised
anatase titania to a level below 150 ppm, preferably less than 100
ppm and more preferred less than 80 ppm referred to the total
weight of the oxides.
9. Use of the anatase titanium dioxide according to claim 1 or
obtainable according to the process of claim 4, as a catalyst or
catalyst support in catalysis reactions, gas to liquid reactions
such as in particular Fischer-Tropsch catalysis, selective
catalytic reduction (SCR), oxidation catalysis, photo catalysis,
hydrotreating catalysis, Claus catalysis, phthalic acid
catalysis.
10. Catalyst or catalyst support, comprising the anatase titanium
dioxide according to claim 1 or obtainable according to the process
of claim 4.
Description
[0001] The present invention relates to the field of heterogeneous
catalysis. In more detail, it refers to a process for reducing the
sulphur content of stabilized anatase titania, the so-obtained
catalytic support materials and the use thereof for manufacturing
of heterogeneous catalysts.
[0002] Titanium dioxide is a well-known material for the
manufacturing of heterogeneous catalysts. It finds widespread
application either as the catalytic material (e.g. Claus catalysis)
or as a catalytic support (e.g. selective catalytic reduction of
nitrous oxides, Fischer-Tropsch).
[0003] The predominant and in most cases preferred polymorph for
heterogeneous catalysis is the anatase crystal phase. The large
industrial scale manufacturing of anatase type TiO.sub.2 relies on
the so-called sulphate process in which titanium rich raw materials
(ilmenite or Ti-slag) are firstly reacted with concentrated
sulphuric acid to form TiOSO.sub.4. Upon hydrolysis, a fine
particulate anatase type TiO.sub.2 with a high water content is
obtained (so-called metatitanic acid with general formula
TiO(OH).sub.2). After further purification steps which include
reduction and washing procedures, a pure anatase TiO.sub.2 can be
obtained.
[0004] The other large scale manufacturing process for TiO.sub.2 is
the so-called chloride process which uses a raw material with very
high Ti content (natural or synthetic rutile or Ti-slag), chlorine
and carbon to produce in a first step TiCl.sub.4 which can easily
be purified by distillation. Upon burning in an oxygen rich flame,
a pure Rutile TiO.sub.2 is obtained. A pure anatase TiO.sub.2
polymorph cannot be produced by this method.
[0005] Another procedure for the manufacturing of anatase type
TiO.sub.2 is the flame hydrolysis of TiCl.sub.4 yielding a mixture
of Rutile and anatase only.
[0006] The performance of heterogeneous catalysts often depends on
the purity. Stray ions can affect the overall conversion of the
catalytic process and/or the selectivity. Typical unwanted
impurities are phosphorous, sulphur, heavy metals, alkaline and
alkaline earth metals.
[0007] For example, the Fischer-Tropsch synthesis of hydrocarbons
from syngas (mixture of CO and H.sub.2) is very sensitive towards
sulphur impurities since the sulphur reacts with the catalytically
active cobalt to form cobalt sulphides (Co.sub.xS.sub.y) which in
turn lead to drastic reduced catalytic performance. Typical sulphur
levels of FT-catalysts are below 150 ppm, preferably below 100 ppm.
The major impurity in the sulphuric acid process generated anatase
TiO.sub.2 is sulphur stemming from adherent sulphuric acid of the
manufacturing process. Other stray ion impurities are in the one or
low two digit ppm range and typically are uncritical.
[0008] The performance of heterogeneous catalysts also depends on
the physical properties. A very good dispersion of the
catalytically active material on the support is often a
prerequisite to observe high conversions. Typically large specific
surface areas of the support are important to ensure maximum
dispersion of the catalytically active centres.
[0009] As a summary, there is a need for large scale industrial
availability of anatase type TiO.sub.2 for catalytic applications
that exhibits both
[0010] i) a large specific surface area (BET>40m2/g), and
[0011] ii) a low sulphur level (<150 ppm S).
[0012] From a manufacturing point of view, the solely large
industrial scale and thus cost effective manufacturing process of
anatase type TiO.sub.2 is the sulphate process. Major drawbacks of
this process is the large sulphur content in the final product
which is known to be detrimental for a lot of catalytic
applications. Thus, a process has to be found that allows for the
large industrial scale production of an anatase type TiO.sub.2 with
high specific surface area (>40 m2/g) and a low amount of
sulphur (<150 ppm S).
[0013] Several techniques have been developed to reduce the sulphur
level in anatase type TiO.sub.2 from the sulphate process. The most
common one is the washing with water. Typically, the sulphate
containing anatase TiO.sub.2 is suspended in water and washed over
a filter medium (e.g. filter press). The washing is performed with
cold or preferably hot de-ionized water. The minimum sulphur levels
that can be obtained by this process are in the range of 0.1-0.5
wt.-%.
[0014] Reacting the excess sulphuric acid with an appropriate base
(NaOH, aqueous ammonia solution etc.) and removing the salts formed
by excessive washing with de-ionized water allows for significant
lower sulphur levels of 0.03-0.2 wt.-%. Especially when using basic
solutions of metals (e.g. NaOH or KOH), a certain contamination
risk exists, since using an excess amount of base in order to
obtain lowest sulphate levels the metal ions are only hardly washed
out of the anatase.
[0015] Lowering the sulphur level can be also be done by successive
washing cycles by excess treatment with a strong base and
successive removal of the metal ions by washing with an acid. In
this case, it is preferred to use acids (e.g. acetic acid) that can
easily be removed either during the washing or a potential
subsequent heating step.
[0016] During manufacturing of pigmentary grade titanium dioxide,
the sulphur is removed by thermal decomposition of the sulphuric
acid. At temperatures exceeding 500.degree. C. a significant
reduction of the sulphate contaminations is observed, but during
this heat treatment two processes also take place: i) the TiO.sub.2
particle undergo a particle growth which results in significantly
and irreversible decrease of the specific surface area and ii) at
these temperatures the phase transformation from the anatase to the
rutile polymorph takes place. Both processes are wanted in order to
obtain pigmentary TiO.sub.2 which typically is a low BET
(<20m2/g) and Rutile type TiO.sub.2, but they prevent this
procedure from being used for large surface area, low sulphur
anatase TiO.sub.2 out of the sulphate manufacturing process.
[0017] As a consequence, there is no process available that allows
for the production of an anatase type TiO.sub.2 by a large
industrial scale production that exhibits the following
properties:
[0018] 1. Ultra low sulphur content (<150 ppm).
[0019] 2. BET surface area >20 m.sup.2/g, preferably >30
m.sup.2/g and more preferably >40 m.sup.2/g
[0020] 3. TiO.sub.2 in the pure anatase phase.
[0021] There is a need for a low sulphur anatase type catalytic
support material with a high specific surface area that is easily
accessible through large scale industrial processes.
[0022] In this context, it has surprisingly been found that anatase
type titanium dioxide doped with the appropriate amount of silica
and/or an oxide of zirconium, and or an oxide of aluminum can be
treated at temperatures high enough to decompose the sulphuric acid
while maintaining substantially large specific surface areas. In
this context the term "thermal stabilization" has to be understood
that anatase type TiO.sub.2 is stabilized in a manner that i) the
rutilization temperature is shifted towards higher temperatures and
ii) the tendency towards BET loss is reduced.
[0023] In a typical experiment according to the invention, anatase
type TiO.sub.2 having a content of 8% wt % SiO.sub.2 is heated for
one hour to temperatures as high as 1000.degree. C. The resulting
powder exhibits BET surface areas of about 50-70 m.sup.2/g and
residual sulphur contaminations of <50 ppm. The degree of
resistance towards thermal aging of the anatase is strongly
dependent on the amount of silica added. Small amounts only
introduce a minor resistance, while larger amounts of silica have a
strong effect on aging properties.
[0024] Besides this effect, silica can also influence the catalytic
properties of the final catalyst. It can change the overall
performance by altering the selectivity and/or the conversion rate.
Depending on the specific application and its specific demands
concerning BET surface area, SiO.sub.2 and the residual S-content,
the right material and calcination conditions have to be
individually adjusted to the respective intended use. In general,
high calcination temperatures reduce both, residual S-levels and
specific surface area.
[0025] Basically, any element that is able to stabilise the anatase
polymorph can be used in terms of this invention. Among numerous
others typical elements for catalytic applications are Si, Al, Zr
[J Mater Sci (2011) 46:855-874].
[0026] The incorporation of such stabilising elements can be
achieved by a variety of different synthetic approaches. For the
inventive material, the following different methods are suitable:
[0027] 1. Precipitation of SiO.sub.2 onto TiO.sub.2 [0028] 2.
Co-precipitation or co-hydrolysis of TiO.sub.2 and SiO.sub.2 [0029]
3. Mixing of TiO.sub.2 sols and SiO.sub.2 sols [0030] 4. Treating
of TiO.sub.2 with SiO.sub.2 sols [0031] 5. Treating of TiO.sub.2
with an SiO.sub.2 precursor and subsequently form SiO.sub.2 via
hydrolysis [0032] and/or oxidation [0033] 6. Mixing TiO.sub.2 and
SiO.sub.2.
[0034] Thus, the present invention is directed to an anatase
titanium dioxide having a content of at least one compound selected
from oxides of Si, Al, and Zr in an amount of 2-50% b.w.,
preferably 2-30% b.w., calculated as oxides, of the total weight of
the oxides, and having a sulphur content of less than 150 ppm,
preferably less than 100 ppm and more preferred of less than 80 ppm
referred to the total weight of the oxides.
[0035] The inventive anatase material has preferably an alkali
content such as of Na.sup.+ of below 200 ppm, preferably below 100
ppm in order to avoid any negative influences of the alkali on the
stability of the material during use.
[0036] According to the invention, the anatase titanium dioxide is
preferably obtained by the sulphate process which is obtained as
titanium dioxide and hydrated forms thereof including meta-titanic
acid. Meta-titanic acid and the hydrated forms of titania which are
used here synonymously can be represented by the formula
TiO.sub.(2-x)(OH).sub.2x with 0.ltoreq.x.ltoreq.1, including also
to titania. Said meta-titanic acid is then further treated to
incorporate the stabilising agents selected from Si, Zr and/or Al
in the form of the oxides and hydrated forms thereof and then
subjected to the calcination treatment to decompose the
sulphur-containing compound such as sulphuric acid as a remainder
of the sulphate process. During calcination the hydrated forms are
converted to the oxides and the hydrate content will be reduced to
zero which should be clear to the skilled man.
[0037] The term "anatase titanium dioxide or anatase titania" as
used in accordance with the present invention means that at least
95% b.w., preferably 98% b.w. and most preferred 100% of the
titania is present in the anatase form. Generally, the anatase
phase has crystallite sizes of 5-50 nm. Thus, for the inventive
material, the crystalline phases of the particles are mostly
present in the anatase phase, after drying at 105.degree. C. for at
least 120 min before calcination and also after calcination due to
the stabilisation. I.e. after subtracting of the linear base, the
ratio of the height of the most intensive peak of the anatase
structure (reflex (101)) to the height of the most intensive peak
of the rutile structure (reflex (110)) is at least 5:1, preferably
at least 10:1. Most preferably, the XRD analysis exclusively shows
anatase peaks. For determining the phase and crystallite size by
Scherrer, in particular the crystal modification (phase
identification), an X-ray is taken. For this, the intensities of
the Bragg condition after diffracted at the lattice planes of a
crystal X-rays are measured against the diffraction angle 2 Theta.
The X-ray diffraction is characteristic for the phase.
[0038] Drying as used in the context of the present invention means
drying at temperatures above 105.degree. C. at ambient pressure.
All large scale industrial techniques can be applied such as
spin-flash or spray drying, but the drying is not limited to the
techniques mentioned.
[0039] Calcining as used in accordance with the present invention
means treating the stabilized anatase titania at an elevated
temperature from above 500.degree. C., preferably from 800.degree.
C. up to 1200.degree. C., for a time period sufficient to decompose
the remaining sulphur containing compound such as sulphuric acid
and thus to reduce the sulphur content to a level below 150 ppm,
preferably less than 100 ppm and more preferred less than 80 ppm
referred to the total weight of the oxides, preferably for a time
period of 30 min to 1200 min, while maintaining the titania in the
anatase form. Calcining can be carried out in a regular calcination
device under atmospheric pressure so that the sulphur containing
components can evaporate from the material.
[0040] The weight ratios, ppm-values or percentages as used in the
present invention refer to the weight of the material after
calcination.
[0041] Due to the high temperature treatment, agglomeration can
take place which can be detrimental for the subsequent processes
for forming a catalyst. Thus de-agglomeration of the calcined
material by milling can be necessary. Both, wet or dry milling
techniques can be applied and typical techniques are ball or jet
milling.
[0042] An optional sieving step to ensure removal of coarse
particles can follow.
[0043] The anatase TiO.sub.2 obtained can then serve as a catalytic
support material which can further be treated with at least one
compound of catalytically active metal selected from Co, Ni, Fe, W,
V, Cr, Mo, Ce, Ag, Au, Pt, Pd, Ru, Rh, Cu, or mixtures thereof
whereby a metal loaded material is obtained. A precursor compound
soluble in polar or non-polar solvents of a catalytically active
metal selected from Co, Ni, Fe, W, V, Cr, Mo, Ce, Ag, Au, Pt, Pd,
Ru, Rh, Cu, or mixtures thereof can be used. Treating the support
material with one precursor compound or mixtures thereof of the
catalytically active metals can be performed by various techniques.
Typical methods include incipient wetness or excess solvent method.
Also deposition reactions such as hydrolysis can be applied to
bring the catalytically active metal or precursors thereof into
contact with the catalytic support material. The compound of a
catalytically active metal which are not particularly limited and
may be selected from Co, Ni, Fe, W, V, Cr, Mo, Ce, Ag, Au, Pt, Pd,
Ru, Rh, Cu, or mixtures thereof can be used in an amount to obtain
a loading of 1-50% b.w., preferably 5-30% b.w., and more preferably
8-20% b.w., calculated as oxides of the total weight of the final
material.
[0044] Thus, the present invention covers an: [0045] anatase
titanium dioxide having a content of at least one compound selected
from oxides of Si, Al, and Zr in an amount of 2-50% b.w.,
preferably 2-30% b.w., calculated as oxides, of the total weight of
the oxides, and having a sulphur content of less than 150 ppm,
preferably less than 100 ppm and more preferred of less than 80 ppm
referred to the total weight of the oxides; [0046] anatase titanium
dioxide according to claim 1 having a content of at least one
compound selected from oxides of Si, Al, and Zr in an amount of
3-20% b.w., more preferably 4-12% b.w., calculated as oxides, of
the total weight of the oxides and having a sulphur content of less
than 150 ppm, preferably less than 100 ppm and more preferred of
less than 80 ppm referred to the total weight of the oxides; [0047]
anatase titanium dioxide according to claim 1 having a content of
SiO.sub.2 in an amount of 2-30% b.w., preferably 3-20% b.w., more
preferably 4-12% b.w., calculated as oxide, of the total weight of
the oxides, and having a sulphur content of less than 100 ppm,
preferably less than 80 ppm referred to the total weight of the
oxides; [0048] and a: [0049] process for preparing the inventive
anatase titanium dioxide having a content of at least one compound
selected from oxides of Si, Al, and Zr in an amount of 2-50% b.w.,
preferably 2-30% b.w., more preferably 3-20% b.w., most preferably
4-12% b.w., calculated as oxides, of the total weight of the
oxides, and having a sulphur content of less than 150 ppm,
preferably less than 100 ppm and more preferred less than 80 ppm,
referred to the total weight of the oxides, wherein: [0050] a
titanium compound selected from metatitanic acid or titanylsulphate
is mixed with at least one compound selected from oxides and/or
hydroxides of Si, Al, and Zr or precursors thereof in an aqueous
medium, [0051] precipitating at least one compound selected from
oxides and/or hydroxides of Si, Al, and Zr, [0052] treating the
obtained product to reduce the alkali content thereof if the alkali
content is above 200 ppm, to a level of at most 200 ppm, referred
to the total weight of the oxides, [0053] the product is optionally
filtered, optionally washed with water, and optionally dried, the
product is then subjected to a calcination treatment at a
temperature of more than 500.degree. C., preferably in the range of
800.degree. to 1200.degree. C., over a time period sufficient to
decompose the remaining sulphur containing compound such as
sulphuric acid to a level below 150 ppm, preferably less than 100
ppm and more preferred less than 80 ppm referred to the total
weight of the oxides, preferably over a time period of 0.5 to
twelve hours, [0054] process for preparing an embodiment of the
inventive anatase titanium dioxide wherein metatitanic acid is
mixed with a SiO.sub.2 precursor compound, precipitating at least
one oxide and/or hydroxide of Si, treating the obtained product to
reduce the alkali content thereof if the alkali content is above
200 ppm, to a level of at most 200 ppm, referred to the total
weight of the oxides, optionally filtering, optionally washing the
obtained product and optionally drying the obtained product,
subjecting the product to a calcination treatment at a temperature
of more than 500.degree. C., preferably in the range of 800.degree.
to 1200.degree. C., over a time period sufficient to decompose the
remaining sulphur containing compound such as sulphuric acid to a
level below 100 ppm, preferably less than 80 ppm referred to the
total weight of the oxides, preferably over a time period of 0.5 to
twelve hours, [0055] Process for preparing an anatase titanium
dioxide according to claim 3 wherein a titanium compound selected
from a TiO.sub.2 sol is mixed with an SiO.sub.2 sol, adjusting the
pH to obtain a precipitate, treating the obtained precipitate to
reduce the alkali content if the alkali content is above 200 ppm
referred to the total weight of the oxides, to a level of at most
200 ppm, referred to the total weight of the oxides, the obtained
product is optionally filtered, optionally washed, optionally
dried, and the obtained product is subjected to a calcination
treatment at a temperature of more than 500.degree. C., preferably
in the range of 800.degree. to 1200.degree. C., over a time period
sufficient to decompose the remaining sulphur containing compound
such as sulphuric acid to a level below 150 ppm, preferably less
than 100 ppm and more preferred less than 80 ppm referred to the
total weight of the oxides, preferably in the range of 800.degree.
to 1200.degree. C., preferably over a time period of 0.5 to twelve
hours. [0056] Process for reducing the sulphur content of a
stabilised anatase titania wherein an anatase titania having a
content of a stabilizing agent is treated at a temperature more
than 500.degree. C., preferably in the range of 800.degree. to
1200.degree. C., over a time period sufficient to decompose a
remaining sulphur containing compound such as sulphuric acid to a
level below 150 ppm, preferably less than 100 ppm and more
preferred less than 80 ppm referred to the total weight of the
oxides, preferably for a time period of at least 30 min, wherein
the stabilizing agent is selected from oxides of Si, Al, and Zr and
wherein the content of the stabilizing agent is in the range of
2-50% b.w., preferably 2-30% b.w., calculated as oxides, of the
total weight of the oxides [0057] Use of a calcination treatment at
a temperature more than 500.degree. C. for reducing the sulphur
content of a stabilised anatase titania having a content of at
least one compound selected from oxides of Si, Al, and Zr in an
amount of 2-50% b.w., preferably 2-30% b.w., calculated as oxides,
of the total weight of the oxides, to a level below 150 ppm,
preferably less than 100 ppm and more preferred less than 80 ppm
referred to the total weight of the oxides. [0058] Use of the
anatase titanium dioxide of the invention, obtainable according to
the inventive processes, as a catalyst or catalyst support in
catalysis reactions, gas-to-liquid reactions such as in particular
Fischer-Tropsch catalysis, selective catalytic reduction (SCR),
oxidation catalysis, photo catalysis, hydrotreating catalysis,
Claus catalysis, phthalic acid catalysis. [0059] Catalyst or
catalyst support, comprising the anatase titanium dioxide of the
invention, obtainable according to the inventive processes.
[0060] The invention is further illustrated by the following
Examples and Comparative Examples.
EXPERIMENTAL PART
Analytical Methods
Determination of TiO.sub.2 Polymorph
[0061] In order to determine the TiO.sub.2 polymorph, x-ray
diffraction (XRD) analysis is applied. This is done in a typical
XRD set-up where the intensities of the diffracted x-rays are
measured vs. the diffraction angle 2 Theta. The evaluation of the
xrd pattern is done using the JCPDS-data base. Typical condition of
analysis are: 2 Theta=10.degree.-70.degree., steps of 2
Theta=0.02.degree., measuring time per step: 1.2 s.
Determination of SiO.sub.2 Content
[0062] The material is digested in
H.sub.2SO.sub.4/(NH.sub.4).sub.2SO.sub.4, followed by dilution with
de-ionized water.
[0063] The residue is washed with sulphuric acid and the SiO.sub.2
content is obtained by weighing the filter cake after
incineration.
[0064] Determination of TiO.sub.2 content Digestion of the material
is done with H.sub.2SO.sub.4/(NH.sub.4).sub.2SO.sub.4 or
KHSO.sub.4. Then reduction of the Ti.sup.4+ with Al to Ti.sup.3+ is
done and finally the TiO.sub.2 content is obtained by titration
with ammonia iron-Ill-sulphate. (NH.sub.4SCN as indicator)
Determination of S-Content
[0065] S-contents were obtained by elemental analyzer Euro EA
(Hekatech). The sample is burned in oxygen atmosphere and the gases
are analyzed by gas chromatography. S-contents are calculated from
the areas of the chromatogram.
Determination of Specific Surface Area
[0066] The specific surface area was determined by nitrogen
adsorption technique according to DIN ISO 9277 (BET method). 5
points between 0.1 and 0.3 p/p.sub.0 were evaluated. The equipment
used was an Autosorb 6 or 6B (Quantachrome GmbH).
EXAMPLE 1
[0067] SiO.sub.2 (13.1% b.w.) was introduced by co-precipitation of
TiO.sub.2 and SiO.sub.2 from TiOSO.sub.4-- and
Na.sub.2SiO.sub.3-solutions. 352 l of Na.sub.2SiO.sub.3 (94 g/l
SiO.sub.2) solution and 2220 l of TiOSO.sub.4 (103 g/l TiO.sub.2)
solution were simultaneously pumped over a period of 270 minutes
into a stirred reaction vessel containing 960 l water. During the
reaction, the pH was kept at 5 with ammonia solution. After the
addition was complete, the reaction was heated for 1 hour to
75.degree. C. to complete reaction. Afterwards a hydrothermal aging
was performed for 4 hours at 9.5-10 bar and 170-180.degree. C.
Finally the resulting reaction mixtures was filtered and washed
with de-ionized water. The product was obtained after spray drying
at 350.degree. C. BET was 100 m.sup.2/g and S content 4000 ppm.
Example 2
[0068] A SiO.sub.2/TiO.sub.2 powder having a SiO.sub.2 content of
8.5% b.w. was prepared on the basis of metatitanic acid and
Na.sub.2SiO.sub.3 following a sequence of pH-adjusting steps and
final filtration and washing of the so-obtained material with
de-ionized water. The SiO.sub.2/TiO.sub.2 powder obtained after
drying had a BET of 334 m.sup.2/g and a sulphur content of 1100
mg/kg.
Example 3
[0069] 943 g metatitanic acid (29.2% b.w. TiO.sub.2) were diluted
with deionized water to 150 g/L. 78.5 g ZrOCl.sub.2.times.8H.sub.2O
were added and the temperature was raised to 50.degree. C.
Afterwards, 68 mL sodium silicate (Na.sub.2SiO.sub.3, 358 g/L
SiO.sub.2) were added. After addition was completed, aqueous NaOH
(50% b.w. NaOH) was added until a pH of 5.25 at 50.degree. C. was
reached. The white precipitate was filtered and washed with
deionized water until the conductivity of the filtrate was below
100 .mu.S/cm. The remaining filter cake was dried at 105.degree. C.
BET-surface area of the product was 329 m.sup.2/g and S>1000
ppm. SiO.sub.2 and ZrO.sub.2 contents were 7.7% and 10.8% b.w.
respectively.
Example 4
[0070] Example 4 was produced in the same way as example 3 except
that the sequence of ZrOCl.sub.2.times.8H.sub.2O and sodium
silicate addition was changed. For example 4 first the
Na.sub.2SiO.sub.3 solution and afterwards the
ZrOCl.sub.2.times.8H.sub.2O was added. SiO.sub.2 and ZrO.sub.2
contents were 6.8% and 10.4% b.w. respectively. BET-surface was 302
m.sup.2/g and S-content was 3300.
COMPARATIVE EXAMPLE 1
[0071] Hombikat 8602 (commercial product). BET surface area was 321
m.sup.2/g and S content 4700 ppm
COMPARATIVE EXAMPLE 2
[0072] Commercially available Hombikat 8602 was purified by
neutralisation with NaOH and washing with deionized water. The
resulting sulphur content before calcination was 0.2 wt.-% (2000
ppm). and BET-surface area 351 m.sup.2/g.
COMPARATIVE EXAMPLE 3
[0073] A rutile suspension was prepared according to example 1a in
DE10333029A1. To this, NaOH was added to a pH of 6.0 to 6.2 at
60.degree. C., the solid was filtered and washed with deionized
water to a filtrate conductivity of below 100 .mu.S/cm. The
obtained filter cake was re-slurried and spray dried. The BET
surface area was 105 m.sup.2/g and the S-content 70 ppm
COMPARATIVE EXAMPLE 4
[0074] Commercially available Aerosil P25 from Evonik was used as
received. BET surface area was 55m2/g and S<30 ppm.
COMPARATIVE EXAMPLE 5
[0075] 300 ml Titaniumxoychloride (145 g/L TiO.sub.2) solution was
diluted with de-ionized water to 3 L. Subsequently 4 g oxalic acid
dihydrate were added and a white solid was deposited by treating
the reaction mixture with aqueous 15% NaOH solution while
maintaining the temperature below 20.degree. C. The final pH was
6.2. After filtration the white solid was washed with de-ionized
water to a filtrate conductivity <100 .mu.S/cm. Re-slurrying and
spray drying gave the final product with BET: 359 m.sup.2/g and
S<30 ppm.
Calcination
[0076] All calcinations were conducted in a muffle kiln. The
materials were placed into ceramic seggars (corundum) and heated
for 1 hour at 1000.degree. C. The resulting powders were carefully
grinded and homogenised prior to XRD, BET and SO.sub.4 analyses.
The BET surface areas and sulphur contents of various
SiO.sub.2-treated TiO.sub.2 anatase supports before and after aging
for 1 h at 1000.degree. C. are shown in Table 1.
Fischer Tropsch Synthesis (FTS):
[0077] The FTS test were conducted using a 32-fold parallel
reactor. The powders were compacted and subsequently crushed. The
samples were lowed with Co(NO3)2 via impregnation in order to get a
final Co loading of 10 wt.-% based on the total weight of the dried
and reduced catalyst. For catalytic testing, the 125-160 .mu.m
fraction was used and each catalyst unit was filled with an amount
of catalyst to ensure 40 mg Co-metal loading. Prior to the
catalytic testing the catalyst was activated in diluted H.sub.2
(25% in Ar) at 350.degree. C. (1K/m in heating ramp). The catalytic
testing was then performed at 20 bar with a feed of 1.56 L/h per
reactor. The H.sub.2/CO ratio was 2 (10% Ar in feed) and the
temperature of the catalytic test was 220.degree. C.
[0078] In Fischer Tropsch synthesis, CO and H.sub.2 are contacted
at elevated pressure and temperature to react to hydrocarbons.
Evonik P25 is a known TiO.sub.2 based catalytic support for this
application. In order to have an overall economic FTS process, the
catalysts have to fulfil the properties:
[0079] 1. High CO conversion (X.sub.CO in %)
[0080] 2. High C.sub.5+ productivity (P.sub.C.sub.5+ in
g.sub.C.sub.5+/(g.sub.Coh))
[0081] 3. Low methan selectivity (S.sub.CH.sub.4 in %)
[0082] 4. Low CO.sub.2 selectivity (S.sub.CO.sub.2 in %)
[0083] The target of FTS is to produce long chain hydrocarbons.
Especially hydrocarbons with more than 5 carbon atoms are of
interest, because they serve as a feedstock e.g. for high quality
Diesel, kerosene or long chain waxes. Syngas (H.sub.2/CO-mixtures)
is often produced from methane by reacting it with H.sub.2O to
yield CO and H.sub.2 (steam reforming). The reverse reaction would
reduce the amount of CO and H.sub.2 available for the FTS reaction.
High CH.sub.4 selectivity in FTS indicates high conversion of CO
and H.sub.2 to CH.sub.4 and vice versa. Therefore the CH.sub.4
selectivity should be kept at lowest level possible. Additionally
under the reaction conditions CO can react with H.sub.2O to form
CO.sub.2 and H.sub.2 (water gas shift reaction). This would reduce
the concentration of carbon atoms available for the FTS. High
CO.sub.2 selectivity indicates high conversion of CO to CO.sub.2
and vice versa. Thus CO.sub.2 selectivity should be low for FTS
catalysts.
[0084] Besides this, CO conversion (the amount of CO converted)
should be high and additionally the amount of hydrocarbons with
more than 5 carbon atoms should also be high. The latter parameter
is indicated by the amount of hydrocarbons with more than 5 carbon
atoms produced within one hour over one gram of Cobalt metal.
[0085] With respect to all these four parameters, Table 3 clearly
shows that the inventive products exhibit superior properties when
used as catalytic supports in FTS.
TABLE-US-00001 TABLE 1 Post calcination Pre calcination at
1000.degree. C. for 1 h BET S TiO2 - BET S TiO2 Sample m.sup.2/g
mg/kg Polymorph m.sup.2/g mg/kg Polymorph Example 1 100 4000
Anatase 60 40 Anatase Example 2 334 1100 Anatase 70 <30 Anatase
Example 3 329 >1000 Anatase 77 <30 Anatase Example 4 302 3300
Anatase 52 <30 Anatase Compar- 321 4700 Anatase 3 <30 Rutile
ative Example 1 Compar- 351 2000 Anatase 3 <30 Rutile ative
Example 2
TABLE-US-00002 TABLE 2 Analysis overview of support materials used
for FTS BET S m.sup.2/g mg/kg TiO.sub.2 Polymorph Example 2 (after
1 h 1000.degree. C.) 70 <30 Anatase Example 3 (after 1 h
1000.degree. C.) 77 <30 Anatase Example 4 (after 1 h
1000.degree. C.) 52 <30 Anatase Comparative Example 3 105 70
Rutile Comparative Example 4 55 <30 Anatase/Rutile Comparative
Example 5 359 <30 Anatase
TABLE-US-00003 TABLE 3 Fischer Tropsch synthesis data of Inventive
and Comparative Examples P.sub.C.sub.5+ X.sub.CO % S.sub.CH.sub.4 %
g.sub.C.sub.5+/(g.sub.Coh) S.sub.CO.sub.2 % Example 2 54 7.2 3.46
0.6 Example 3 55.2 7.8 3.35 0.7 Example 4 52.9 7.7 3.3 0.6
Comparative Example 3 12.6 9.4 0.74 n.d. Comparative Example 4 20.6
9.5 1.18 n.d. Comparative Example 5 0.5 31.3 0.02 n.d. n.d. = not
determined because CO conversion was too low.
[0086] The above results of the Examples according to the invention
and of the Comparative Examples as well as the catalytic tests show
that the combination of the properties of the inventive materials,
i.e. high specific surface area, anatase content and low sulphur
content lead to superior catalytic properties thereof.
* * * * *