Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/58—Fabrics or filaments
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/18—Carbon
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/132—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group
  • C07C29/136—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH
  • C07C29/14—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of a —CHO group
  • C07C29/141—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group of >C=O containing groups, e.g. —COOH of a —CHO group with hydrogen or hydrogen-containing gases
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
  • D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
  • D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
  • D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
  • D01F9/16—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from products of vegetable origin or derivatives thereof, e.g. from cellulose acetate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
  • B01J23/46—Ruthenium, rhodium, osmium or iridium
  • B01J23/462—Ruthenium

Definitions

• the present invention relates to activated carbon catalyst supports, more particularly catalyst supports comprising an activated carbon fiber substrate.
• activated carbons in the form of grains, powders or extrusions.
• Their use poses a certain number of problems: microporosity sometimes difficult to access, need for sorting of particle size by sieving, filtration for elimination of fines, risk of crushing the grains piled up in a reactor which leads to the choice of precursors which give carbon hard (coconut, olive kernels) but not always optimal porosity, creation of preferential paths for liquids through a bed of carbon grains which results in an incomplete exploitation of the useful surfaces.
• Document FR 2 521 873 A thus discloses the use of an activated carbon or activated carbon felt on which a metal catalyst can be deposited, such as ruthenium or a combination of ruthenium and palladium, and envisages the use of the catalyst support obtained for the catalytic conversion of glucose to sorbitol.
• a metal catalyst such as ruthenium or a combination of ruthenium and palladium
• the object of the invention is to provide a process allowing simple preparation of catalyst supports comprising a substrate made of activated carbon fibers and particularly suitable for use for catalytic reactions in fine chemistry which require high selectivity.
• a process for producing a catalyst support comprising the production of a carbon fiber texture with a large specific surface and the fixing of a catalyst to the texture is characterized in that the a carbon fiber texture with a precursor rayon is used.
• the production of the carbon fiber texture with a large specific surface area comprises: the carbonization of a rayon texture which, during a final phase, is carried out at a temperature included between 1000 ° C and 1300 ° C, for a period between 0.7 min and 1, 3 min, and
• the carbonization of the rayon texture comprises a precarbonization phase carried out at a temperature between 350 ° C and 420 ° C, and the activation is carried out at a temperature between 850 ° C and 950 ° C, for example under carbon dioxide atmosphere.
• the production of the carbon fiber texture with a large specific surface area comprises:
• the impregnation composition can contain a constituent chosen from phosphoric acid, zinc chloride, potassium sulphate, potassium hydroxide, diammonic phosphate and ammonium chloride.
• the heat treatment comprises a rise in temperature at a speed of between 1 and 15 ° C / min followed by a plateau at a temperature between 350 ° C and 500 ° C.
• the first or the second mode of implementation of the method make it possible to obtain a texture of carbon fibers having a specific surface greater than 800 m 2 / g, and even at 1200 m 2 / g.
• the use of carbon fibers with a precursor rayon offers other particularly important advantages.
• such fibers have a microstructure promoting the formation of surface functions, or active sites and, thereby, the attachment of catalyst, without necessarily requiring specific surface oxidation as is most often the case with grains of active carbon.
• the carbon fibers with a radiated precursor may have, after activation, a porosity having an average dimension of between 0.3 nm and 3 nm, for filaments with a diameter of between approximately 5 ⁇ m and 20 ⁇ m, and with a rate total volume porosity from 30% to 50%. This favors a large dispersion of the catalyst in the form of fine particles, the size of which does not exceed 3 nm, hence great efficiency during catalytic reactions.
• Another advantage consists in the high purity of the carbon fibers obtained: a carbon content greater than 99%, an ash content less than 0.3% and an alkaline impurity content less than 1500 ppm.
• the fibers allow the production of substrates particularly suitable for receiving metallic catalysts such as, in particular, ruthenium, platinum, rhenium, palladium, iridium, nickel or a combination of these metals, for use in the field of fine chemistry, the purity of the carbon support being favorable to confer the necessary selectivity.
• the carbon from the radiating precursor is hydrophilic and consequently promotes exchanges with the liquid phases, in particular aqueous media.
• the catalyst support is used in an oxidizing medium at a temperature higher than that of the starting oxidation of carbon
• a protective coating against oxidation for example a silicon carbide skin. This can be formed by reaction between the carbon of the fibers and the silicon and / or a silicon compound such as silica.
• the production of the carbon fiber texture with a large specific surface comprises:
• the texture obtained having a specific surface which can be greater than 10 m 2 / g and reach a few tens of m 2 / g, allowing the deposition of catalysts used in an oxidizing medium.
• Various known methods of fixing the catalyst to the texture of activated carbon fibers can be used, such as cation exchange or liquid impregnation. They are advantageously produced continuously by scrolling the texture in one or more baths.
• the carbon fiber texture is essentially a two-dimensional texture, the shaping of which is carried out after fixing the catalyst so that the latter is distributed in a substantially uniform manner throughout the support.
• This shaping is carried out so as to produce a support adapted to the volume of a reactor to be occupied. It includes, for example, winding, winding or even needling operations for layers so as to give cohesion to the shaped support.
• FIG. 1 indicates the successive stages in the preparation of a catalyst support according to a first embodiment of the invention
• FIG. 2 indicates the successive stages in the preparation of a catalyst support according to a second embodiment of the invention
• FIG. 3 indicates the successive stages in the preparation of a catalyst support according to a third embodiment of the invention
• FIGS. 4A-AB very schematically illustrate a cation exchange process
• FIG. 5 schematically illustrates a continuous process for fixing a catalyst to a fabric by impregnation
• FIG. 6 schematically illustrates a continuous process of fixing a catalyst on a fabric by impregnation.
• a first embodiment of a method according to the invention is indicated in FIG. 1.
• a first step 10 consists in developing a carbon fiber texture in the form of a fabric, a knitted fabric, a braid, of a felt, of a unidirectional ply, of several superimposed unidirectional plies, preferably in different directions and linked to one another by light needling, or of any other essentially two-dimensional similar texture.
• the carbon fiber texture is obtained directly from carbon threads or fibers from rayon threads or fibers by heat treatment or, preferably, from a texture from rayon threads or fibers, the heat transformation treatment of the rayon then being produced after shaping the texture.
• the heat treatment for transforming rayon into carbon comprises a precarbonization phase at a temperature between 350 ° C and 420 ° C, preferably at around 400 ° C, followed by a final carbonization phase at a temperature between 1000 ° C and 1300 ° C, preferably at about 1200 ° C, under a nitrogen atmosphere and for a period of between 0.7 min and 1.3 min.
• the final carbonization is preferably carried out under pressure reduced, for example between 5 Pa and 60 Pa, which promotes the elimination of impurities entrained with the gaseous effluents and the migration of alkaline impurities on the surface of the fibers from where they can be eliminated by simple rinsing with water. demineralized water, without the need for acid washing.
• High purity carbon fibers are then obtained, the carbon content being greater than 99%, the ash content less than 0.3% and the alkaline impurity content less than 1500 ppm.
• the fibers obtained are also remarkable in that they consist structurally of a large number of very small cristailites having an average height L c of approximately 1 nm and an average lateral size L a of approximately 3 nm.
• These cristailites offer a large number of active sites at the edge of the graphene planes which promote the formation of functional surface groups during the re-exposure of the texture after carbonization, without the need for any specific treatment of 'oxidation. Subsequent activation considerably amplifies the rate of surface functions.
• Activation is carried out by heat treatment of the carbon fiber texture under an oxidizing atmosphere, such as water vapor or preferably carbon dioxide or a mixture of carbon dioxide and water vapor.
• the heat treatment temperature is preferably between 850 ° C and 950 ° C and its duration is preferably between 50 min and 300 min depending on the specific surface desired.
• Continuous activation can be achieved by scrolling through the carbon fiber texture in a heat treatment area of an oven in which an oxidizing gas flow is maintained. Such a method is described for example in document FR-A-2,741,363.
• the specific surface is greater than 800 m 2 / g, and even 1,200 m 2 / g.
• the porosity is characterized by pores with an average diameter between 0.3 nm and 3 nm and an overall porosity rate between 30% and 50%. This is measured by the known technique of X-ray scattering at small angles (or DPAX technique). It consists in exposing the fibers to an X-ray beam under conditions such that there is electron density contrast between the voids (pores) and the material (carbon), therefore a diffusional intensity linked to the total porosity rate of the carbon fibers.
• An optional third step 30 consists in providing the activated carbon fiber texture with a surface coating for protection against oxidation, in order to allow the use of the catalyst support in an oxidizing atmosphere.
• the surface coating consists, for example, of a skin of silicon carbide (SiC). This can be reactively formed, by depositing a dispersion of a mixture of silicon (Si) and silica (SiO 2 ) or silica alone, for example in the form of powder suspended in water and in performing a heat treatment at a temperature for example between 1300 ° C and 1700 C C.
• a fourth step 40 consists in depositing the catalyst on the activated texture of carbon fibers obtained. Due to the fact that it comes from a radiated precursor, it has a microporosity and a functional surface grouping rate (active sites) which make it suitable for fixing, in the form of very small particles, a metal catalyst, such as that, in particular, ruthenium, platinum, rhenium, palladium, iridium, nickel, or other metals or combinations of metals known as catalysts, for applications in the field of fine chemistry.
• the carbon fibers with a ray precursor have a residual oxygen content such that it promotes the presence of active sites and does not require a surface oxidation treatment for this purpose.
• the rate of functional surface groups obtained is thus high.
• Surface chemistry characterized by the Boehm method, results in acid functional groups up to 0.3 to 0.8 meq / g (millimole / g), of which 0.02 to 0.06 meq / g carboxylic functions.
• the deposition of the catalyst can be carried out by cation exchange or by liquid impregnation, examples of the implementation of such processes being given below.
• the porosity and surface chemistry characteristics allow a dispersion of the metal catalyst in the form of fine particles, of average size between about 1 nm and 3 nm, with an exceptionally high dispersion rate, between 0.3 and 0.7 .
• the dispersion rate represents the ratio between the number of surface metal atoms and the total number of metal atoms. It is measured by hydrogen chemisorption.
• a last step 50 consists in shaping the catalyst support, for example to adapt it to the volume to be occupied inside a reactor.
• This shaping can be carried out by winding or winding the activated texture on which the catalyst is fixed, or even by superposition of strata cut from this texture. In the latter case, the strata can be linked together by needling.
• FIG. 2 indicates a second mode of implementation of a method according to the invention, which differs from the first mode of implementation in that steps 10 and 20 of obtaining an activated carbon fiber texture are replaced by a step 60, the following steps 30 to 50 being unchanged.
• Step 60 consists of starting with a texture of rayon fibers and of impregnating the latter with a composition making it possible, after carbonization, to directly obtain an activated texture of carbon fibers.
• the impregnation is carried out with a composition containing a mineral constituent which promotes dehydration of the rayon, such as a constituent chosen from phosphoric acid, zinc chloride, potassium sulphate, potassium hydroxide, phosphate. diammonic and ammonium chloride.
• a composition containing phosphoric acid so that the mass of acid fixed on the texture is between 10 and 22% of the mass of the dry texture.
• the heat treatment comprises a rise in temperature at a speed of between 1 ° C / min and 15 ° C / min, followed by a level preferably carried out at a temperature between 350 ° C and 500 ° C under an inert atmosphere or under atmosphere containing a reaction activator such as carbon dioxide or water vapor.
• the texture is then preferably washed.
• a carbon fiber texture with a large specific surface is obtained having similar characteristics of purity, porosity, active surface sites as that obtained with steps 10 and 20 of the method described with reference to FIG. 1, therefore a texture particularly suitable for use as a catalyst support for catalytic reactions in the field of fine chemistry.
• FIG. 3 shows a third embodiment of a method according to the invention, making it possible to obtain a catalyst support made of carbon fibers coated with silicon carbide, for use in an oxidizing medium.
• a first step 10 consists in making a fabric of carbon fibers as described with reference to FIG. 1.
• the carbon fibers obtained with rayon precursor exhibit a structural disorganization favorable to obtaining fibers with a carbon core, skin of silicon carbide (SiC) and high specific surface using the following process.
• a second step 70 consists in impregnating the fabric with carbon fibers with a sol-gel of a SiC precursor in a mixture of ethanol, water and hydrochloric acid.
• the precursor is for example an ethyl silicate such as tetraethoxysilane (TEOS).
• step 80 a heat treatment is carried out at a temperature of around 900 ° C. under argon, leaving a film of silica on the carbon fibers.
• the silica is transformed into silicon carbide by carbothermy at a temperature of around 1550 ° C. under argon (step 90).
• This process makes it possible to coat the carbon fibers with a thin film of SiC protecting against oxidation, without consuming carbon from the fibers to form the SiC coating, therefore without affecting the mechanical properties of the texture.
• the texture finally obtained has a relatively high specific surface, of approximately
• Steps 40 and 50 of depositing the catalyst and shaping the support can then be carried out in the same way as in the other embodiments of the process.
• Example 1 (cation exchange) A rayon fabric consisting of a multifilament viscose obtained from yarns of 190 tex woven in 15x15 texture (15 threads per cm in warp and weft) is used. After desizing, the fabric is charred by being brought to a temperature of approximately 400 ° C. for approximately 12 h. then at a final temperature of approximately 1200 ° C. for approximately 1 min under nitrogen at a pressure of 30 Pa. The activation of the carbon fabric obtained is carried out by passing the fabric through a heat treatment zone of an oven under an atmosphere made up of 100% carbon dioxide.
• This zone is materialized, as well as zones of rise and fall in temperature by a muffle in the form of tunnel along which the fabric is advanced continuously.
• the heat treatment is carried out at a temperature of approximately 920 ° C., and the residence time at this temperature is approximately 1 hour.
• the activated carbon fabric obtained has a microporosity of average size approximately equal to 0.6 nm, an overall porosity of 40% (relative to the apparent volume of the fabric) and a carbon content of 99%.
• a sample of activated carbon tissue having an initial mass of 11.06 g is kept in suspension by stirring in 100 ml of 1 N ammonia where nitrogen is bubbled through. 30 ml of a molar ammonia solution in which a mass of 0.44 g of ruthenium salt Ru (NH 3 ) 6 Cl 3 is slowly added. We let the balance take place for 1 hour. In an ammoniacal medium, protons are removed from the anchoring sites as illustrated in FIG.
• Passivation is carried out at 25 ° C Before release to air, the catalyst is passive to avoid deep oxidation of the metal. Passivation is carried out at 25 ° C. under a flow of 6 l / h of a mixture of oxygen O 2 and nitrogen N 2 in which the percentage by volume of oxygen is equal to 1%. At the end of these operations, 12.6 g of carbon tissue in perfect condition is collected, carrying 0.5% by weight of fixed ruthenium, the ruthenium being in the form of particles of average size equal to about 1 nm and having a dispersion rate of approximately 0.7.
• the process for fixing ruthenium by cation exchange described above can advantageously be carried out continuously using an installation as illustrated diagrammatically in FIG. 5.
• the fabric 100 in activated carbon fibers is continuously unwound from a storage roller 102. It passes along a tortuous path in a bath 104 containing ammonia and a dissolved mass of salt Ru (NH3) 6Cl3 in a molar ratio from 1 to 0.01, respectively, with nitrogen bubbling.
• a bath 104 containing ammonia and a dissolved mass of salt Ru (NH3) 6Cl3 in a molar ratio from 1 to 0.01, respectively, with nitrogen bubbling.
• the fabric is directed to a washing bath 106 containing demineralized water.
• the fabric On leaving the bath 106, the fabric is dried by passing through a tunnel 108 at a temperature of approximately 120 ° C. under nitrogen and then is admitted into a hydrogenation oven 110 where the reduction of ruthenium takes place.
• the fabric passes into a passivation compartment 112 under a mixture of nitrogen and oxygen (with a volume rate of 1% of O 2), before being collected on a storage reel 114.
• the length of the fabric paths in the baths 104, 106 and the running speed are chosen to have residence times of approximately 1 h and 30 min in the baths 104 and 106.
• the heating in the oven 110 and the length thereof are chosen, in relation to the speed of movement of the fabric, in order to respect the speed of temperature rise and the duration of the plateau necessary for the reduction of the ruthenium.
• ruthenium Although the case of ruthenium has been considered here, the process of fixing a metal catalyst M by cation exchange can be used with metals other than ruthenium, which can be present in the form of a cationic salt of the type [M (NH 3) x ] y + , y CI " , for example platinum.
• Example 2 liquid impregnation
• 25 ml of a molar hydrochloric solution containing 0.3 g of RUCI3XH2O are slowly added and the impregnation is allowed to take place for 30 min.
• the fabric is washed for approximately 1 h with demineralized water and then dried at approximately 120 ° C. under nitrogen.
• the fabric 200 in activated carbon fibers is continuously unwound from a storage roller 202. It passes at ambient temperature following a tortuous path in a bath 204 containing a molar hydrochloric solution of RUCI3XH2O, with 1 mole of HCl for 4.10 "3 mole of RUCI3.
• the impregnated fabric is reduced by passing to room temperature in two consecutive baths 206, 208 containing 37% formalin and 30% potash, following two tortuous paths.
• the speed of movement of the fabric and the length of the paths in the baths 204, 206, 208 are chosen to have an impregnation duration of approximately 30 min and a total reduction duration of approximately 10 h.
• the fabric is admitted into a bath 210 to be washed with demineralized water for approximately 1 h. used for other metallic catalysts M, using the corresponding anionic complex MCI ⁇ in an acid medium.
• the efficiency of the catalyst supports is estimated from the glucose conversion rate C, the selectivity S to sorbitol and the initial specific activity A s (number of moles of glucose converted per hour and per gram of ruthenium).
• the table below gives the results obtained.
• the catalytic properties with the catalyst supports TCA1 and TCA2 are comparable to those of the reference Ru / CA. It is noted that the conversion of glucose is practically total (at least equal to 98%), and that the selectivity to sorbitol is excellent (greater than 99%), while retaining initial specific activities similar to that obtained according to the state of the technique. In addition, the post-reaction separation phases are simplified, in particular due to the absence of fine particles which are usually encountered with catalyst supports using grains of activated carbon.
• the catalyst support according to the invention is notably remarkable for the very high selectivity that it allows, and is therefore particularly interesting for applications in the field of fine chemistry.

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• Textile Engineering (AREA)
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• 1997
  • 1997-11-24 FR FR9714704A patent/FR2771309B1/fr not_active Expired - Fee Related
• 1998
  • 1998-11-24 US US09/555,037 patent/US6383972B1/en not_active Expired - Fee Related
  • 1998-11-24 EP EP98955728A patent/EP1034034A1/de not_active Withdrawn
  • 1998-11-24 WO PCT/FR1998/002506 patent/WO1999026721A1/fr not_active Application Discontinuation
  • 1998-11-24 JP JP2000521915A patent/JP2001523568A/ja active Pending

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