Process for reducing the sulphur content of anatase titania and the so-obtained product
20170348671 · 2017-12-07
Assignee
Inventors
Cpc classification
B01J21/063
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J21/06
PERFORMING OPERATIONS; TRANSPORTING
B01J37/03
PERFORMING OPERATIONS; TRANSPORTING
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.
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° C., preferably in the range of 800° to 1200° 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° C., preferably in the range of 800° to 1200° 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° C., preferably in the range of 800° to 1200° 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° to 1200° 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° C., preferably in the range of 800° to 1200° 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° 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
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° C. to complete reaction. Afterwards a hydrothermal aging was performed for 4 hours at 9.5-10 bar and 170-180° C. Finally the resulting reaction mixtures was filtered and washed with de-ionized water. The product was obtained after spray drying at 350° 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.2×8H.sub.2O were added and the temperature was raised to 50° 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° C. was reached. The white precipitate was filtered and washed with deionized water until the conductivity of the filtrate was below 100 μS/cm. The remaining filter cake was dried at 105° 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.2×8H.sub.2O and sodium silicate addition was changed. For example 4 first the Na.sub.2SiO.sub.3 solution and afterwards the ZrOCl.sub.2×8H.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° C., the solid was filtered and washed with deionized water to a filtrate conductivity of below 100 μS/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° C. The final pH was 6.2. After filtration the white solid was washed with de-ionized water to a filtrate conductivity <100 μS/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° 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° 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 μm 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° 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° 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.
[0081] 3. Low methan selectivity (S.sub.CH.sub.
[0082] 4. Low CO.sub.2 selectivity (S.sub.CO.sub.
[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° 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° C.) 70 <30 Anatase Example 3 (after 1 h 1000° C.) 77 <30 Anatase Example 4 (after 1 h 1000° 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.
[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.