Titanium dioxide-based fibrous solids
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- AXENS SA
- Filing Date
- 2024-05-29
- Publication Date
- 2026-04-15
AI Technical Summary
Existing catalysts for sulfur compound hydrolysis, such as COS and CS2, require high residence times and large reactors to achieve sufficient sulfur yields and comply with atmospheric emission standards, but increasing catalytic performance often compromises mechanical resistance and increases costs or pressure loss.
A solid material comprising 75-95% titanium dioxide mixed with 1-20% fibrous mineral binder, predominantly silica fibers with specific dimensions, enhancing porosity and mechanical strength while maintaining high catalytic performance.
The resulting solid exhibits increased open porosity and mechanical resistance, achieving higher catalytic activity for sulfur and nitrogen compound hydrolysis without the drawbacks of prior art, such as reduced mechanical resistance or increased pressure loss.
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Abstract
Description
[0001] Titanium dioxide-based fibrous solids
[0002] Technical field
[0003] The present invention relates to titanium dioxide-based solids useful as catalysts or as supports for the preparation of heterogeneous catalysts, and their use in processes for converting H2S into sulfur, in particular the modified Claus process. In this process, large quantities of COS and CS2 can be formed and the use of catalysts active towards their hydrolysis towards H2S is then necessary to ensure sufficient sulfur yields and to ensure compliance with standards for emissions of sulfur compounds into the atmosphere. Titanium dioxide-based catalysts are among the catalysts conventionally used for these hydrolyses thanks to their very high performance.
[0004] These solids can also be used for the hydrolysis of COS and HCN in synthesis gas purification processes from natural gas, oil, coal or biomass, but are also useful for the selective reduction of nitrogen oxides to nitrogen in the treatment of fumes from the combustion of nitrogen derivatives, for example during the production of nitric acid.
[0005] The invention also relates to the preparation of fibrous solids based on titanium dioxide.
[0006] Prior art
[0007] Existing catalysts have average performances requiring long residence times and therefore large reactors to transform sulfur compounds such as COS or CS2 and thus limit atmospheric emissions. Increasing catalytic performance often involves adding elements that increase the cost of catalysts or reducing dimensions such as the diameter of the catalysts, but the pressure drop generated then increases significantly. Increasing the porosity of catalysts also improves catalytic performance, but the mechanical resistance then becomes too low to allow loading into industrial units, especially when the catalyst drop height becomes significant.Document EP 38741 is known in the state of the art, which describes solids based on titanium dioxide TiO2 which are prepared from the mixing of a TiO2 powder in order to obtain a paste, which is then shaped and finally heat-treated in air between 200 and 900°C. When preparing the solid, a shaping additive (up to 30% by weight) can be added during the mixing step, which can be chosen from silica, alumina, clays, silicates, titanium sulfate, ceramic fibers. It is further disclosed that the following may also be used as shaping additives: cellulose, carboxymethylcellulose, carboxyethylcellulose, tall oil, xanthan gums, surfactants, flocculating agents such as polyacrylamides, carbon black, starches, stearic acid, polyacrylic acid, polyvinyl alcohol, biopolymers, glucose, polyethylene glycol.
[0008] The publication by Knapp et al. focuses on the synthesis of TiC>2-sepiolite supports comprising 30 to 95% TiCh, but sepiolite is described as decreasing the amount of titanium on the surface and increasing the titanium content leads to a decrease in the BET surface area below 100 m 2 / g, whether the shaping is done in water or in the presence of acid. Both aspects are indicated as detrimental to catalytic activity (Phase distribution in titania-sepiolite catalyst supports prepared by different methods - Knapp et al. J. Mater. Chem., 1997, 7(8), 1641-1645).
[0009] Summary of the invention
[0010] Surprisingly, the Applicant noted that the use of titanium dioxide at a content of between 75 and 95% by weight, mixed with 1 to 20% of a fibrous mineral binder comprising 70 to 100% silica and fibers with a median diameter of between 5 and 50 μm and an average length of between 50 and 1000 μm, made it possible to obtain a solid material having an open porosity greater than known solids while maintaining optimal mechanical strength, allowing its use as a catalyst, in particular in the Claus process, or as a heterogeneous catalyst support.
[0011] Unless otherwise indicated, the contents in percentage by weight are expressed on an anhydrous basis, i.e. taking as a basis the weight of the material deprived of water. The invention relates to a solid with a specific surface area SBET greater than 100 m 2 / g, preferably greater than 120 m 2 / g, including:
[0012] - 75 to 95% by weight of titanium dioxide TiCh, limits included, relative to the total weight of the anhydrous solid;
[0013] - 1 to 20% by weight of a mineral compound in the form of fibers, limits included, relative to the total weight of the anhydrous solid, said fibers comprising from 70 to 100% by weight of silica and said fibers having a median diameter of between 5 nm and 50 pm and an average length of between 50 nm and 1000 pm.
[0014] The solid according to the invention may comprise from 80 to 90% by weight of titanium dioxide TiCh, limits included, relative to the total weight of the anhydrous solid.
[0015] The solid according to the invention may comprise from 2 to 10% by weight of a mineral compound in the form of fibers, limits included, relative to the total weight of the anhydrous solid.
[0016] The solid according to the invention may comprise a total pore volume of pores with a diameter of between 3.7 nm and 10 pm measured according to standard ASTM D4284-12 greater than 0.35 ml / g, preferably greater than 0.5 ml / g.
[0017] The mineral compound can be chosen from fiberglass and sepiolite.
[0018] Preferably, the mineral compound is sepiolite.
[0019] The solid according to the invention may have a grain-to-grain EGG crushing strength greater than or equal to 1 daN / mm and a rate of breakage generated after an impact against a steel plate of less than 15% by volume.
[0020] The invention also relates to a process for preparing a solid according to any one of the variants described comprising the following steps: i) A source of titanium dioxide comprising 90 to 100% by weight of titanium dioxide TiCh, a mineral compound in the form of fibers, a thickening organic compound and water are mixed in the presence of a base or an acid in order to obtain a paste, in the proportions required to obtain the solid described above; ii) The kneaded paste obtained in step i) is shaped, preferably by extrusion or granulation; iii) The paste shaped in step ii) is dried at a temperature of between 100 and 200°C in order to obtain a dried product; iv) The dried product is calcined at a temperature of between 300 and 600°C.
[0021] The thickening compound may be chosen from a polysaccharide compound such as, for example, starch, cellulose, carboxymethylcellulose, carboxyethylcellulose, agar-agar, or a polysaccharide compound obtained by fermentation by bacterial fermentation or fungal fermentation, such as xanthan gum, succinoglycan gum, scleroglucan gum or heteropolysaccharides S-194.
[0022] The source of titanium dioxide can be introduced at a content of between 50 and 65% by weight, the mineral compound in the form of fibers can be introduced at a content of between 1 and 8% by weight, the thickening compound can be introduced at a content of between 0.5 and 2% by weight, relative to the total mass of the mixture in step i).
[0023] The invention also relates to a process for hydrolyzing sulfur or nitrogen compounds contained in a gaseous feedstock, preferably chosen from H2S, COS, CS2 and / or HCN, by bringing said gaseous feedstock into contact with water and a solid according to any one of the variants described or prepared according to the preparation process according to any one of the variants described.
[0024] The gaseous feedstock may be a gaseous effluent from a Claus H2S treatment process.
[0025] The gaseous feedstock can be a synthesis gas.
[0026] The invention finally relates to the use of the solid according to any one of the variants described or prepared according to the preparation process according to any one of the variants described, as a catalyst or as a heterogeneous catalyst support.
[0027] List of figures
[0028] Figures 1 and 2 illustrate the invention without limitation. Figure 1 shows an image obtained by scanning electron microscopy of a catalyst according to example 1 containing 90% titanium dioxide and 10% sepiolite clay in the form of very fine fibers (diameter of 10 nm for an average length of 300 nm).
[0029] Figure 2 shows an image obtained by scanning electron microscopy of a catalyst according to Example 5 containing 85% titanium dioxide and 5% glass fibers (diameter of 14 pm for a length of 200 pm).
[0030] Description of the embodiments
[0031] Terminology
[0032] Throughout this text, groups of chemical elements are described according to the new IUPAC classification. For example, groups 9 or 10 correspond to the metals in columns 9 and 10 according to the IUPAC classification or to the last two columns of group VIIIB according to the CAS classification (CRC Handbook of Chemistry and Physics, CRC editor press, editor-in-chief DR Lide, 81st edition, 2000-2001). Similarly, group 6 corresponds to the metals in column 6 according to the IUPAC classification or to the metals in columns VIB according to the CAS classification.
[0033] Throughout this text, the total pore volume VPT is obtained by mercury intrusion porosimetry according to the ASTM D4284-12 method and expressed as the pore volume generated by pores with a diameter of 37 Å at 10 pm.
[0034] The SBET specific surface area is a surface area measured by the BET method, i.e. the specific surface area determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical The Journal of the American Chemical Society, 6Q, 309 (1938).
[0035] Hourly volumetric flow rate (HV) is the ratio of the volumetric flow rate of the feed at the reactor inlet in m 3 / h at 0°C, 1 atm, divided by the catalyst volume in m 3 contained in the reactor.
[0036] The median diameter of mineral fibers, particularly glass or sepiolite fibers, is obtained by measuring the diameter of at least 10 fibers observed on a scanning electron microscope. The average length is obtained by measuring the length of at least 10 fibers also observed on a scanning electron microscope.
[0037] The grain-to-grain crushing (GTC) value is obtained via a standardized test (ASTM D4179-01 standard) which consists of subjecting a millimetric object, such as a support in extruded form in the case of the present invention, to a compressive force generating rupture. This test is used to indirectly measure the resistance of the material. The analysis is repeated on a certain number of particles taken individually and typically on a number of particles between 50 and 200, preferably between 100 and 200. The average of the measured lateral crushing rupture forces constitutes the average GTC which is expressed in the case of spheroidal particles in force units (N).
[0038] The impact-generated breakage rate is obtained on a dedicated installation that allows the extrudates to be projected against a steel plate. One liter of millimeter-sized extrudates are fed into a 30 mm diameter and 50 mm long tube subjected to 3 bars of compressed air, which projects the extrudates one by one against the plate located at a distance of 220 mm from the tube outlet. The sample is then recovered and the dimensions of the objects obtained are characterized by laser diffraction. The impact-generated breakage rate is then expressed as the volumetric rate of extrudates that have been broken (whose diameter is smaller than that of the initial extrudates) by the impact against the steel plate.
[0039] Unless otherwise indicated, weight percentages (% weight) correspond to mass percentages expressed in relation to the total mass of the components of the formulation or the final solid.
[0040] Detailed description of the invention
[0041] The present invention relates to a solid material comprising from 75 to 95% by weight of titanium dioxide relative to the total weight of the anhydrous material and from 1 to 20% by weight of a mineral compound preferably comprising from 70 to 100% of silica, the mineral compound being in the form of fibers, relative to the total weight of the anhydrous material. The fibers are advantageously in the form of needles with a median diameter between 5 nm and 50 pm and an average length between 50 nm and 1000 pm. The solid according to the invention advantageously has a total pore volume greater than 0.35 ml / g (ASTM D 4284-12, volume of pores with a diameter between 3.7 nm and 10 pm). The BET specific surface area (measured according to standard ASTM D3663-78) of the solid is at least 100 m 2 / g, preferably at least 120 m 2 / g.
[0042] The titanium dioxide used for the manufacture of the solid is preferably crystallized (anatase or rutile structure). "Poorly crystallized" means titanium dioxide with an X-ray spectrum showing halos in place of the main lines of well-crystallized titanium dioxide. "Amorphous" means titanium dioxide whose X-ray spectrum shows no diffraction lines.
[0043] According to the invention, the mineral compound may advantageously be chosen from fiberglass, sepiolite, rock fiber, asbestos fiber. Preferably, the mineral compound is sepiolite or fiberglass.
[0044] The addition of a mineral binder in the form of fibers in a catalyst or support manufacturing process consisting mainly of titanium dioxide and involving the use of an organic thickening additive unexpectedly makes it possible to significantly improve the catalytic performance of the product. This gain is possible because the product thus obtained has a large pore volume without negatively impacting its mechanical resistance to crushing or breakage by impact.
[0045] Preparation process
[0046] The catalyst can be manufactured from a source of titanium dioxide, mixed with a mineral binder in the form of fibers advantageously in the form of needles and containing between 70 and 100% silica. The manufacturing process comprises in particular the formation of a paste by kneading the source of titanium dioxide and the mineral binder in the form of fibers to which an acid or basic solution and an additive of the type of thickening organic compound such as xanthan gum are added. The solid is shaped by any technique known to those skilled in the art, then dried and calcined to form a support. Preferably, the solid is shaped by extrusion or granulation.
[0047] Advantageously, the method for preparing the support according to the invention may comprise the following steps: - a step i) of preparing a paste from a mixture comprising water, 50 to 65% by weight of a source of titanium dioxide containing 90 to 100% by weight of TiO2, 1 to 8% by weight of the mineral compound in the form of fibers, preferably sepiolite clay or fiberglass and 0.5 to 2% by weight of a thickening organic compound, such as xanthan gum, in the presence of an acid preferably (HCl, HNO3, H2SO4, organic acid (acetic acid, citric acid, maleic acid, etc.) or a base (KOH, NaOH, Ca(OH)2Mg(OH)2, tetraethylammonium hydroxide);
[0048] - a step ii) of shaping the paste, for example by extrusion or granulation of said paste;
[0049] - a step iii) of drying between 100 and 200°C, preferably for 1 to 24 hours;
[0050] - a step iv) of calcination between 300 and 600°C preferably for 1 to 24 hours and preferably in air and possibly humid.
[0051] The preparation of the paste can be carried out in an acidic or basic medium, preferably the pH of the suspension from step i) is less than 3 or greater than 11.
[0052] The thickening organic compound is preferably a polysaccharide compound such as, for example, starch, cellulose, carboxymethylcellulose, carboxyethylcellulose, agar-agar, a polysaccharide compound obtained by bacterial fermentation or fungal fermentation. As polysaccharide compounds obtained by bacterial fermentation suitable for the invention, mention may be made of xanthan gums, succinoglycan gums or heteropolysaccharides S-194 described in particular in patent EP 77680.
[0053] Xanthan gums are obtained by fermentation of a carbohydrate under the action of microorganisms and more particularly bacteria belonging to the genus xanthomonas, such as those described in Bergey's manual of determinative bacteriology (8th edition - 1974 - Williams N. Wilkins C degrees Baltimore) (Xanthomonas begoniae, Xanthomonas campestris, Xanthomonas carotae, Xanthomonas hederae, Xanthomonas incanae, Xanthomonas malvacearum, Xanthomonas papavericola, Xanthomonas phaseoli, Xanthomonas pisi, Xanthomonas vasculorum, Xanthomonas vesicatoria, Xanthomonas vitians, Xanthomonas pelargonii).Other microorganisms capable of producing polysaccharides include bacteria belonging to the genus Arthrobacter, and more particularly the species Arthrobacter stabilis, Arthrobacterviscosus; to the genus Erwinia; to the genus Azotobacter, and more particularly the species Azotobacter indicus; to the genus Agrobacterium, and more particularly the species Agrobacterium radiobacter, Agrobacterium rhizogenes, Agrobacterium tumefaciens.
[0054] Suitable polysaccharide compounds obtained by fungal fermentation include scleroglucan gums synthesized by fermentation of a carbohydrate using fungi belonging to the genus Sclerotium and more particularly to the species Sclerotium glucancium and Sclerotium rolfsii.
[0055] The catalyst or support according to the invention can advantageously be in all the usual known forms: powder, beads, extruded and crushed materials. Beads and extrudates are preferred. The size of the beads is advantageously between 0.5 and 10 mm, preferably between 0.7 and 8 mm. The extrudates can be cylindrical or polylobed, solid or hollow; their size is advantageously between 0.5 and 6 mm, preferably between 2 and 5 mm.
[0056] The product thus obtained has a total pore volume greater than 0.35 ml / g, preferably greater than 0.5 ml / g (ASTM D 4284-12), a BET specific surface area (ASTM D 3663-78) greater than 100 m 2 / g, preferably greater than 120 m 2 / g, very preferably between 120 and 150 m 2 / g, a catalytic activity 50% higher than the prior art and a resistance to impact breakage at least equivalent to the prior art.
[0057] In addition to the aforementioned components, the final solid may include possible impurities introduced by the preparation process, in particular by the source of titanium dioxide, for example impurities chosen from: aluminum oxide or sulfate, iron oxide or sulfate, niobium oxide or sulfate, other aluminum, ferric, ferrous, or niobic impurities.
[0058] The final solid advantageously has a loss on ignition (PAF, expressed in % by weight relative to the total weight of the solid) of between 0.5 and 5% by weight. Applications
[0059] The solid according to the invention is advantageously used as a catalyst for the hydrolysis of COS and CS2 contained in the gases treated in the Claus processes, the composition of which is generally that indicated in Table 1 below: Table 1
[0060] In the case of the hydrolysis of COS and HCN for the purification of synthesis gas, for example obtained by gasification or pyrolysis of biomass, the composition is typically that indicated in Table 2 below:
[0061] Table 2 The hydrolysis of the compounds COS, CS2 and HCN with the solid according to the invention is generally carried out at a pressure of between 0.1 and 5 MPa, preferably between 0.5 and 3 MPa), at a temperature of between 100 and 400°C, preferably between 150 and 250°C, and with a WH (ratio between the volume flow rate of the feed at the reactor inlet in m3 / h at 0°C, 1 atm and the volume of catalyst in m 3 contained in the reactor) between 1000 and 8000 h-1, preferably between 500 and 8000 h-1, very preferably between 1000 and 6000 h-1. The hydrolysis is carried out in the presence of water, the content of which is generally between 5 and 50% volume relative to the volume of gas to be treated.
[0062] Advantages of the invention
[0063] The solid according to the invention has an open porosity superior to the prior art and a resistance to breakage by impact against a preserved metal plate. In fact, the solid according to the invention has a catalytic activity for the conversion of sulfur or nitrogen compounds such as CS2, COS and HCN superior to the prior art.
[0064] Examples
[0065] Comparative Example A is a catalyst comprising 90% by weight of TiO2, in anatase form. This catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid and an anatase powder such as G2 from Tronox, which contains 10% by weight of calcium sulfate and 90% by weight of TiO2 on a dry basis. The paste thus obtained contains 8% by weight of nitric acid and its loss on ignition is then 43.5%.
[0066] The paste is extruded through a die with cylindrical holes 4 mm in diameter. The extrudates are then dried for two hours in an oven at 140°C and then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air.
[0067] This catalyst is conventionally used in the first converter of the process
[0068] Claus to convert CS2 and COS by hydrolysis into H2S and possibly HCN.
[0069] A titanium dioxide catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid, xanthan gum, sepiolite clay and an anatase M211 powder, marketed by Venator, which contains at least 98% by weight of TiO2 on a dry basis. The paste is obtained by mixing the powders and an acidified solution in the following proportions:
[0070] - 0.88% xanthan gum by weight
[0071] - 2.76% by weight of nitric acid
[0072] - 52.23% weight of anatase powder M211
[0073] - 6.32% by weight of sepiolite clay
[0074] - The rest in water
[0075] The loss on ignition of the pulp is then 48.5%. The loss on ignition (LAI) is measured as the weight loss corresponding to the ratio:
[0076] PAF (%) = (Po-Pi) / Po,
[0077] Po = Initial weight of the raw material
[0078] Pi = Weight of this raw material after calcination for 2 hours at 1000°C and cooling to room temperature in an anhydrous enclosure
[0079] The quantity of sepiolite clay is targeted to obtain 10% by weight of sepiolite clay relative to the weight of the final product. Sepiolite clay is in the form of very fine needle-shaped fibers with a median diameter of approximately 10 nm and an average length of approximately 300 nm.
[0080] The paste is extruded through a die with cylindrical holes 4 mm in diameter. The extrudates are then dried for two hours in an oven at 140°C, then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air.
[0081] A titanium dioxide catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid, xanthan gum, sepiolite clay (fibers with a median diameter of 10 nm and an average length of approximately 300 nm), and anatase G2 powder from Tronox, which contains 10% by weight of calcium sulfate and 90% by weight of TiO2 on a dry basis. The paste is obtained by mixing the powders and an acidified solution, according to the following proportions:
[0082] - 0.94% xanthan gum by weight
[0083] - 3.15% by weight of nitric acid
[0084] - 56.31% weight of anatase G2 powder
[0085] - 6.50% weight of sepiolite clay
[0086] - the rest in water
[0087] The quantity of sepiolite clay is targeted to obtain 10% weight of sepiolite clay relative to the weight of the final product. The loss on ignition of the paste is then 46.8%.
[0088] The paste is extruded through a die with cylindrical holes 4 mm in diameter. The extrudates are then dried for two hours in an oven at 140°C and then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air.
[0089] A titanium dioxide catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid, xanthan gum, needle-shaped glass fibers with a median diameter of 14 μm and an average length of 200 μm, and an anatase G2 powder marketed by Tronox. The paste is obtained by mixing an aqueous solution containing, relative to the weight of the mixture:
[0090] - 0.93% xanthan gum by weight
[0091] - 3.29% by weight of nitric acid
[0092] - 58.50% weight of anatase G2 powder
[0093] 3.20% weight of glass fiber, the rest in water The quantity of glass fibers is targeted to obtain 5% weight of glass fibers relative to the weight of the final product. The loss on ignition of the paste is then 47.7%.
[0094] The paste is extruded through a die with cylindrical holes 4 mm in diameter.
[0095] The extrudates are then dried for two hours in an oven at 140°C and then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air.
[0096] A titanium dioxide-based catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid, xanthan gum, sepiolite clay in the form of a needle with a median diameter of 10 nm and an average length of approximately 300 μm, and anatase G2 powder from Tronox.
[0097] The paste is obtained by mixing an aqueous solution which contains, relative to the weight of the mixture:
[0098] 0.92% xanthan gum by weight
[0099] 3.38% by weight of nitric acid
[0100] 60.0% weight of anatase G2 powder
[0101] 1.60% by weight of sepiolite clay, the remainder in water
[0102] The quantity of sepiolite clay is targeted to obtain 2.5% by weight of sepiolite clay relative to the weight of the final product. The loss on ignition of the paste is then 47.7%.
[0103] The paste is extruded through a die with cylindrical holes 4 mm in diameter.
[0104] The extrudates are then dried for two hours in an oven at 140°C, then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air. Example 5 (according to the invention)
[0105] A titanium dioxide catalyst is produced by preparing a paste in a Z-arm mixer from water, nitric acid, agar-agar, needle-shaped glass fibers (median diameter of 14 pm and average length of 200 pm) and anatase G2 powder from Tronox.
[0106] The paste is obtained by mixing an aqueous solution which contains, relative to the weight of the mixture:
[0107] - 0.92% weight of agar-agar
[0108] - 3.26% by weight of nitric acid - 58.0% by weight of anatase G2 powder
[0109] - 3.17% by weight of fiberglass
[0110] - the rest in water
[0111] The quantity of glass fibers is targeted to obtain 5% by weight of glass fibers relative to the weight of the final product. The loss on ignition of the paste is then 48.2%. The paste is extruded through a die with cylindrical holes 4 mm in diameter. The extrudates are then dried for two hours in an oven at 140°C and then calcined for 2 hours at a temperature of 450°C in humid air containing 40 g of water per kg of dry air.
[0112] The characteristics of the extruded catalysts obtained are listed in Table 3 below:
[0113] Table 3
[0114] The catalysts of the invention therefore have open porosities (in particular total pore volume VPT) measured by mercury intrusion significantly higher than conventional catalyst A while maintaining sufficient mechanical strengths with an EGG > 1 daN / mm and a rate of breakage generated after an impact of less than 15% by volume. This example illustrates the application of the catalysts of the invention for the hydrolysis conversion of CS2 under conditions simulating the first converter of the Claus process. This reaction is considered as a model for evaluating the performance of a catalyst under these conditions, because the reaction rate is much lower than the hydrolysis of COS:
[0115] Chem 1
[0116] The following gas mixture is sent into a reactor maintained at 320°C:
[0117] - 3% vol H2S
[0118] - 2% vol SO2
[0119] - 1000 ppmv CS2
[0120] - 30% vol H2O
[0121] - Balance (100% vol supplement) N2
[0122] The reactor contains 30 g of the catalysts according to the invention. The total gas flow rate is adjusted to achieve WHs of 4000 and 6000 h 1 reported to the volume of catalyst in the reactor. The WHs of this example are deliberately chosen to be much higher than the WHs of industrial Claus processes to discriminate the activity of the catalysts to convert CS2.
[0123] The conversions to CS2 recorded during the implementation of the extruded catalysts obtained are gathered in Table 4 below:
[0124] Table 4
[0125] It therefore appears that the catalysts of the invention, thanks to a much higher open porosity, can achieve conversions into CS2 under the conditions simulating the first converter of the Claus process much higher than those observed on conventional catalysts such as that of comparative example A.
Claims
Claims 1) Solid with a specific surface area SBET greater than 100 m 2 / g including: - 75 to 95% by weight of titanium dioxide TiCh, limits included, relative to the total weight of the anhydrous solid; - 1 to 20% by weight of a mineral compound in the form of fibers, limits included, relative to the total weight of the anhydrous solid, said fibers comprising from 70 to 100% by weight of silica and said fibers having a median diameter of between 5 nm and 50 pm and an average length of between 50 nm and 1000 pm. 2) Solid according to claim 1 comprising from 80 to 90% by weight of titanium dioxide TiCh, limits included, relative to the total weight of the anhydrous solid. 3) Solid according to one of claims 1 or 2 comprising from 2 to 10% by weight of a mineral compound in the form of fibers, limits included, relative to the total weight of the anhydrous solid. 4) Solid according to one of claims 1 to 3 comprising a total pore volume of pores with a diameter of between 3.7 nm and 10 pm measured according to standard ASTM D4284-12 greater than 0.35 ml / g, preferably greater than 0.5 ml / g. 5) Solid according to one of claims 1 to 4 in which the mineral compound is chosen from fiberglass and sepiolite. 6) Solid according to claim 5 in which the mineral compound is sepiolite. 7) Solid according to one of the preceding claims having a grain-to-grain crushing strength EGG greater than or equal to 1 daN / mm and a rate of breakage generated after an impact against a steel plate less than 15% by volume. 8) A method for preparing a solid according to one of the preceding claims comprising the following steps: i) A source of titanium dioxide comprising 90 to 100% by weight of titanium dioxide TiO2, a mineral compound in the form of fibers comprising 70 to 100% by weight of silica, said fibers having a median diameter of between 5 nm and 50 pm and an average length of between 5 nm and 1000 pm, a thickening organic compound and water are mixed in the presence of a base or an acid in order to obtain a paste; ii) The kneaded paste obtained in step i) is shaped, preferably by extrusion or granulation; iii) The paste shaped in step ii) is dried at a temperature of between 100 and 200°C in order to obtain a dried product; iv) The dried product is calcined at a temperature of between 300 and 600°C. 9) Process for preparing a solid according to claim 8 in which the thickening compound is chosen from a polysaccharide compound such as for example starch, cellulose, carboxymethylcellulose, carboxyethylcellulose, agar-agar, or a polysaccharide compound obtained by fermentation by bacterial fermentation or fungal fermentation, such as xanthan gum, succinoglycan gum, scleroglucan gum or heteropolysaccharides S-194. 10) Process for preparing a solid according to claim 8 or 9 in which the source of titanium dioxide is introduced at a content of between 50 and 65% by weight, the mineral compound in the form of fibers is introduced at a content of between 1 and 8% by weight, the thickening compound is introduced at a content of between 0.5 and 2% by weight, relative to the total mass of the mixture in step i). 11) Process for the hydrolysis of sulfur or nitrogen compounds contained in a gaseous feedstock, preferably chosen from H2S, COS, CS2 and / or HCN, by bringing said gaseous feedstock into contact with water and a solid according to one of claims 1 to 7 or prepared according to any one of claims 8 to 10. 12) Hydrolysis process according to claim 11, in which the gaseous feedstock is a gaseous effluent from a Claus treatment process of FhS. 13) Hydrolysis process according to claim 11, in which the gaseous feedstock is a synthesis gas. 14) Use of the solid according to one of claims 1 to 7 or prepared according to one of claims 8 to 10 as a catalyst or as a heterogeneous catalyst support.