ES2221782B1 - CARBON BASED MONOLITIC SUPPORTS AND A PROCEDURE FOR PREPARATION. - Google Patents

Abstract

Carbon-based monolithic supports and a procedure for their preparation. Carbon-rich monoliths prepared by a method similar to that used with ceramic-type pastes. These carbon-based monoliths can be used as active phase supports in environmental catalysis such as those used in the control of emissions of polluting gases derived from combustion processes. The invention comprises obtaining a paste of carbon-rich composition, capable of being extruded and the preparation of carbon-based monoliths using a method normally used for ceramic pastes. The carbon monoliths obtained are excellent potential supports for environmental catalysis by combining the interesting intrinsic properties of coal (high chemical inertia and adsorption capacity) with its goodness to achieve high dispersions of the phases typically active in decontamination reactions.

Description

Carbon-based monolithic supports.

Mastery of the technique

The invention is applicable in development commercial of monolithic carbon filters and catalysts used for the purification of polluting gases generated in industrial activities that involve processes of combustion.

Prior state of the art

The catalysts in the form of monoliths with honeycomb structure of square cells have come using for the control of polluting emissions of sources caused by the burning of fossil fuels for energy transformation (electrical, motor and automotive) in fixed or mobile installations (see, for example, Jannsen, F.J. in Handbook of Heterogeneous Catalysis Vol. 4; G. Ertl, H. Knözinger and J. Weitkamp, editors; P. 1633; Wiley-CCH, Germany, 1997). The purification of flue gases has been the strategy mostly used to satisfy legislation which regulates the limits of substances such as carbon monoxide, nitrogen oxides and unburned hydrocarbons that can be air spills. Currently, catalysts are marketed that incorporate noble metals (rhodium, platinum, palladium) and oxides of  elements such as vanadium, chrome, copper or titanium, among others. These elements are capable of catalyzing the transformation of polluting substances to others of less toxicity, or reduce its concentration to the limits of tolerance. Normally, the active components are deposited on supports in order to obtain well dispersed phases that maintain great accessibility to The substances to be purified.

In relation to the supports, and in front of others more conventional designs such as bed-based ones particles, longitudinal monolithic structures are characterized by a minimum pressure drop in gaseous flows with high spatial velocity, raising the performance of catalysts Additionally, monolithic designs minimize weight and space requirements for filters and catalytic converters Currently the necessary technology for the manufacture of ceramic monoliths and metallic, and this type of products are being manufactured by Various commercial houses. In the case of metal monoliths, the excellent mechanical properties of stainless steels employees allow to obtain the required design from the union thin sheets (around 0.05 mm thick) flat and corrugated In the case of ceramic materials, they can be obtain monoliths from the extrusion of pastes containing a typical composition of 14% w / w MgO, 36% w / w Al 2 O 3 and 50% SiO2.

Various investigations have revealed the interest of using coal as a base material to build monolithic catalysts with or without deposited active phase (see, for example, Schlögl, R. in Handbook of Heterogeneous Catalysis Vol. 1; G. Ertl, H. Knözinger and J. Weitkamp, editors; P. 138; Wiley-CCH, Germany, 1997). The texture of carbonaceous materials allow, on one hand, their use in selective adsorption processes, and other facilitate dispersion of active phases according to the possibility of obtaining high surface areas In particular, coal presents interesting properties in relation to the processes of removal of nitrogen oxides by being insensitive to metals  heavy as lead and mercury present in gaseous effluents to debug. Additionally, the surfaces of carbonaceous materials exhibit a high capacity for self-regeneration in oxidizing and reducing environments, so they avoid catalyst destruction due to compositional changes of the gases generated in combustion. Finally, and from a point Technologically speaking, coal is relatively cheap and can Obtained in large quantities.

However, the plastic properties of coal they are not suitable for extrusion, so obtaining monolithic elaborated fundamentally with this material is a complicated task. Currently, the catalysts that contain coal are prepared in the form of beds of pulverized material or granulated. Along these same lines, it is significant that no company Spanish have in its catalogs monoliths manufactured with this material.

Therefore, it is of interest to obtain media honeycomb-shaped coal monolithic for development commercial of filters and catalysts related to systems anti pollution

Explanation of the invention.

The invention comprises the development of a methodology that allows obtaining carbon monoliths in honeycomb shape. These monoliths allow development subsequent commercial of catalysts and filters, with or without the incorporation of active phases.

The monoliths are rectangular, and their dimensions, section geometry, number of cells, the arrangement of these, the thickness of the walls and the surface hollow, in section, of each longitudinal cell, depend on the nozzle and extruder used.

The monoliths are obtained by extrusion of a paste mostly made of coal. The plastic characteristics of carbon make the stage of extrusion does not lead to satisfactory results if it is not they satisfy certain rheological properties (plasticity, thixotropy, density, exudation, segregation of solid / liquid phases, etc.). In In the case of coal it is necessary to incorporate additives (binders, emulsifiers, plasticizers, lubricants, etc.) that make viable The extrusion of the mixture.

The proposed methodology involves the measurement of a series of characteristic parameters of the paste in relation only to its plastic properties; that is, related to the percentage of humidity that it has. The measures of the Plasticity of ceramic materials are based on the works by Atterberg and Casagrande (see, for example, Gippini, E. in Ceramic Pastes; P. 48; Spanish Ceramic Society, Spain, 1979).

The Liquid Limit (LL) is the crossing point of the liquid state to the plastic, and is measured by the amount of water that the material contains at the moment the fluidity of a dense liquid It is expressed as a percentage by weight (%) of moisture content To calculate it, use a spoon Big house. The work procedure is standardized and its specifications are included in the UNE standard 103-103-94.

The plastic limit (LP) is the crossing point of the plastic state to semi-solid, and is measured by the amount of water that a material contains at the time when It loses plasticity and ceases to be moldable. It is expressed as percentage by weight (%) of moisture content. For its calculation it follow the UNE standardized procedure 103-104-93.

The plasticity index (IP) is defined as the difference between the liquid limit and the plastic limit:

IP = LL - LP

According to Casagrande's studies (see, for example, Gippini, E. in Ceramic Pastes; P. 52; Society Spanish Ceramics, Spain, 1979), any composition paste ceramic whose liquid limit is between the 40-60%, and, simultaneously, the plasticity index is between 10-30%, is suitable for extrusion Our methodology extends the validity of this procedure developed for ceramic pastes in the case of pastes mainly composed of coal. This method allows, by therefore, obtain monoliths of carbonaceous material by extrusion procedures

The methodology described here is applicable to active and coking carbons. In the case of the latter, it is necessary to include a final stage of carbonization and activation, after the common stage of drying the green monolith. The carbonization process allows: (1) Eliminate waste contained in natural carbon and additives added for the extrusion process; and (2) it provides the monolithic support with good mechanical properties, which it lacks after the drying stage. In relation to activation, this stage provides carbon with textural properties (fundamentally, it creates a pore distribution) that allows it to be used as a specific adsorbent and support for very dispersed active phases.
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This methodology is valid even for mixtures of carbon-clay with higher carbon content at 80% To these mixtures, and depending on the nature of both charcoal like clay, different amounts of additives comprised between 0.2-3.5 g of methyl cellulose; 1.5-5.5 g of glycerin; up to 2 g of aluminum stearate; and up to 3 g of aluminum phosphate diluted in o-phosphoric acid in amounts between 5-75 ml (all amounts refer to 100 g of the mixture coal-clay).

The monolithic supports obtained by means of described procedure are useful as active phase supports in environmental catalysis These monolithic supports are therefore of application in the manufacture of filters and catalysts for control of polluting atmospheric emissions.

Embodiment of the invention Examples of preparation of carbonaceous pastes that allow their extrusion Example 1

Using coal as the main element active, a paste has been formulated that, fulfilling the requirements included in the Explanation Section of the invention, it has Good properties for extrusion. In the elaboration of this 90 g of commercial powdered active carbon have been used, and 10 g of a clay that has as plastic properties a Limit Liquid of 65%, a Plastic Limit of 27% and therefore an Index Plasticity of 38%. To this mixture were added the following additives in the following quantities: 0.5 g of methyl cellulose; 4.3 ml glycerin; 1 g of aluminum stearate; and 2.5 g of aluminum phosphate diluted in 70 ml of o-phosphoric acid. The properties plastic turned out to be 44% of Liquid Limit and 11% of Index of Plasticity.

After the extrusion stage, the drying stage at 80 ° C using a stove.

Example 2

Meeting the requirements contained in the Section of Explanation of the invention, a paste was formulated composed of 90 g of a coking natural carbon (with the Features: 75% vitrinite phase, 30% volatile, and less 6% of ashes), and 10 g of clay that it has as properties plastic a Liquid Limit of 65%, a Plastic Limit of 27% and therefore a Plasticity Index of 38%. This base will be They added the following additives in the following quantities: 2 g of methyl cellulose; 2.4 ml glycerin; and 0.3 g of aluminum phosphate diluted in 10 ml of acid o-phosphoric Its plastic properties resulted be 47% of Liquid Limit and 24% of Plasticity Index.

After the extrusion stage, the dried at 80 ° C using a stove. In this case, and after the stage drying, carbonization processes were performed (by heating at 850 ° C, for 30 minutes, in an inert atmosphere of argon), and activation (by heating at 890 ° C, for 150 minutes, in an atmosphere of argon saturated with water vapor at 90 ° C), at in order to provide the monolithic support with good mechanical properties and textural.

The textural properties of the monolith obtained (BET specific surface area equal to 411 m2 / g) resulted be ideal for the deposition of catalytic phases or use as a selective adsorption agent.

Claims (10)

1. Carbon-based monolithic supports, characterized in that they are obtained by extrusion of a paste mainly composed of coal. 2. Carbon-based monolithic supports, according to claim 1, characterized in that their composition is based on coal-clay mixtures. 3. Carbon-based monolithic supports, according to claims 1 and 2, characterized in that their carbon content is greater than 80%. 4. Carbon-based monolithic supports, according to claims 1, 2 and 3, characterized in that, depending on the nature of both the coal and the clay, different amounts of additives comprised between 0.2-3.5% of methyl are added. cellulose; 1.5-5.5% glycerin; up to 2% aluminum stearate; and up to 3% aluminum phosphate diluted in o-phosphoric acid in concentrations between 0.05-0.35 M (all percentages refer to the coal-clay mixture). 5. Carbon-based monolithic supports, according to claims 1 to 4, characterized in that they are constructed in the form of a honeycomb. 6. Procedure for the manufacture of supports carbon-based monolithic according to claims 1 to 5, which includes the application to carbonaceous pastes of the methodology developed for ceramic pastes. 7. Carbon-based monolithic supports, according to claims 1 to 5, characterized in that for its manufacture a defined methodology for ceramic pastes is used following the procedures set forth in standards UNE 103-103-94 and UNE
103-104-93. 8. Use of carbon-based monolithic supports, according to claims 1 to 5, for emission control atmospheric pollutants 9. Use of carbon-based monolithic supports, according to claims 1 to 5, for the manufacture of filters and catalysts 10. Use of monolithic base supports carbonaceous according to claims 1 to 5, as phase supports active in environmental catalysis.