WO2010029201A1

WO2010029201A1 - Composition of a material having a porous structure, method for preparing same, and use of said composition

Info

Publication number: WO2010029201A1
Application number: PCT/ES2009/070332
Authority: WO
Inventors: Roberto Dos Santos
Original assignee: Desarrollos Tecnicos Mc, S.L.
Priority date: 2008-09-15
Filing date: 2009-08-03
Publication date: 2010-03-18
Also published as: BRPI0804104A2; UY32122A; AR073299A1

Abstract

The invention relates to adsorbent materials having porous structures suitable for use in the elimination of contaminating compounds in the dynamic regime. Said novel adsorbents are produced by shaping pastes prepared in an aqueous medium with mixtures of carbon powder and natural clay powders with a disaggregated particle size of less than 20 μm in 90% thereof. Once shaped and dry, said materials are subjected to a single heat treatment in the presence of water vapour and carbon dioxide in order to obtain adsorbents with a wide pore size distribution. The structure of said materials contains micropores corresponding to those in the activated carbon obtained during activation of the carbon, and likewise contains the mesopores corresponding mainly to the clays used, and the macropores formed from the interparticulate spaces.

Description

COMPOSITION OF A MATERIAL WITH POROUS STRUCTURE, METHOD TO PREPARE THE SAME AND USE OF A COMPOSITION

SECTOR OF THE TECHNIQUE

The invention relates to new materials with wide distribution of pore sizes and to their industrial use in the elimination of contaminating compounds by means of adsorption systems in dynamic regime.

STATE OF THE TECHNIQUE

The elimination of undesirable compounds existing in gaseous and liquid effluents has been the subject of numerous studies and technological developments in order to avoid their emission to the environment.

Among them, physical adsorption is one of the most used techniques in the control of contaminants present in industrial effluents.

As described by M. Yates, J. Blanco and M.A. Martín, Studies in Surface

Science and Catalysis, 569-576 (2002), the values of the micropore volume, the external surface (corresponding to the area not associated with the micropores) and the threshold diameter (defined as the average diameter of the pores that due to its greater size, cause the first signal in the mercury intrusion porosimetry analysis) are the data that determine the adequacy of the texture of the adsorbent material for use in the different adsorption processes in dynamic regime.

In general, the micropores (diameters from 0 to 2 nm) confer the storage capacity, while the mesopores (diameters from 2 to 50 nm) and the macropores (diameters from 50 to 10,000 nm), responsible for the surface values external and of the internal diameter of the material, favor the adsorption rate by allowing the rapid diffusion of the adsorbate molecules on the inner surface of the solid.

The design of adsorbents for these industrial units therefore requires textures with a wide distribution of pore sizes that include interconnected macro, meso and micropores in order to enable and facilitate the collection, diffusion and storage of undesirable molecules.

In numerous industrial processes, the adsorption is carried out with activated carbons generally prepared with coconut shell, some types of hardwoods and most of the mineral carbons. During the physical activation process, the mineral coal or carbonized material of plant origin reacts partially and in a controlled manner with an oxidizing compound such as carbon dioxide, water vapor or mixture of both at temperatures above 800 ⁰ C, with Ia consequent creation of the desired porosity (F. Rodríguez and M. Molina, Chemistry and Industry, 563-571, 1998). These materials have a high specific surface area, derived from the numerous micropores they contain but in practice have an absence of larger pores, so that their use, in a dynamic regime, has severe limitations in terms of diffusion.

On the other hand, certain clays are known that have plastic properties, that is, sufficiently moist, that are deformable when light pressure is applied while maintaining the shape and that they become rigid again when dried and vitreous when subjected to high temperatures. In general, they are natural phyllosilicates composed of small particles or crystals, generally of colloidal size, which give rise to textures based on mesoporosity and, therefore, with limited storage capacity in physical adsorption processes due to the absence of micropores.

Most plastic clays can incorporate other materials in powder form as fillers. Thus, for example Larsson BK et al. (J. Amer. OiI Chem. Soc. 64365-70, 1987) describe the preparation of mixtures of calcium montmorillonite with activated carbon for the elimination of benzopyrene present as an impurity in edible oils; With this same objective in US Patent 5,218,132 a smectite is used that contains activated carbon formed by carbonization of previously adsorbed oil within its texture. EP-0978313 describes a hive-shaped adsorbent compound consisting of α-sepiolite that incorporates activated carbon homogeneously dispersed in the silicate structure; The industrial application of these compounds is limited by their low resistance to abrasion and their ability to crumble in the presence of water or water vapor.

In the patent PE-200600187, the material described above is treated at temperatures between 830 and 125O ⁰ C in an inert or reducing atmosphere for at least 2 hours to significantly improve its physical properties by transforming the α-sepiolite into a new phase crystalline called enstatite (Grim, RE, 1968 Clay Mineralogy MacGraw-Hill, pp. 596); However, the preparation of these materials implies a high energy cost derived from a first heat treatment in a controlled atmosphere to manufacture activated carbon and a second treatment, also at high temperature and in an inert or reducing atmosphere, for the generation of the enstatite . The high cost of manufacturing and the complexity of the preparation of these adsorbent materials can certainly discourage its use in a large number of possible industrial applications.

DESCRIPTION OF THE INVENTION

The present invention relates to new adsorbent materials, with predetermined porous structure, with wide distribution of pore sizes, and their use in the elimination of existing pollutants in industrial effluents.

The present invention relates to a composition of adsorbent material characterized by the fact that it includes activated carbon and enstatite, prepared by a single heat treatment in a controlled atmosphere from carbon and sepiolite and which, eventually, can incorporate aluminum silicates and oxides of alkaline earth elements as additives.

The said composition can be formed into granules, pellets, spheres, solid cylinders, hollow cylinders, plates or in a structure of channels parallel to the length of the longitudinal axis in a number greater than 2 and less than 25 channels per square centimeter of cross section generally called monolith or hive.

Preferably, the composition takes the form of hollow cylinders that can be smooth or striated, of any shape and size with a length of approximately 0.5 cm to about 10 cm and a wall thickness between 0.02 cm and 0.5 cm approximately. The passage of the fluid to be purified through the adsorbent material arranged in the form of a hollow cylinder, results in a dynamic fluid that combines a turbulent regime caused by the flow that passes between the cylinders with a laminar regime that takes place in the passage of the fluid through the interior of the hollow cylinders; This situation implies a unique behavior that significantly improves the effectiveness of the adsorption phenomenon in dynamic operations.

According to a preferred embodiment, the final composition includes only enstatite and activated carbon in the weight ratios corresponding to predetermined distributions of pore sizes.

The present invention further relates to a method for preparing the compositions indicated above. For the preparation of the materials object of this invention, sepiolite powder and selected carbon powder and, eventually, alumina powder and bentonite powder, with a determined weight ratio, are mixed dry and homogeneously. subsequently, the mixture is kneaded with water in a high shear kneader. When sepiolite particles are adequately kneaded in an aqueous medium (or in any other polar solvent), a pseudoplastic mass is produced that easily incorporates the carbon particles. The mass obtained after kneading is molded or extruded to obtain the desired shape and then preferably dried at room temperature for at least 2 hours and 80- 25O ⁰ C for at least four hours; subsequently the material is subjected to heat treatment between 500 and 600 ⁰ C in an inert atmosphere for at least 2 hours and finally activated at 800 ° C-1000 ⁰ C for at least 2 hours under carbon dioxide and water. According to a preferred embodiment of the method, this comprises the following phases:

a) mixing sepiolite and coal powders until a homogeneous powder mixture is obtained, b) kneading the homogeneous powder mixture obtained with the addition of water to obtain a wet paste, c) forming the wet paste in the desired way to obtain a piece, d) Dry the shaped piece in air and at room temperature during

2 hours and between 80 and 25O ⁰ C for 4 hours, e) subject the piece to heat treatment at temperatures between 500 ° and 600 ⁰ C, in an inert atmosphere for at least 1 hour, preferably 2 hours and at temperatures between 800 ° and 1000 ⁰ C for 1 hour, preferably 2 hours, in an atmosphere of carbon dioxide and water vapor.

According to this embodiment, preferably in step a), sepiolite and carbon are mixed in a sepiolite / carbon weight ratio of 0.5 to 3 and more preferably 0.8 to 2. The carbon content determines the total micropore volume , while the sepiolite content determines the total volume of mesopores in the final product.

The composition that includes enstatite and activated carbon is obtained by forming pastes prepared in aqueous medium with a mixture of sepiolite and carbon powders without any other additive or component and by means of a unique heat treatment in a controlled atmosphere.

The appearance of macropores in the pieces subjected to heat treatment is due to the consolidation of the interparticle spaces of the previously formed pastes and it was verified that the particle size of the carbon used when conditioning the average volume of the interparticle spaces determines the average size of the macropores in the final product. Therefore, in this invention, the total volume and average size of the macropores can be predetermined by manipulating the quantity and particle size of the coal used as raw material, which has a great importance, since the adsorption speed in dynamic regime will depend on these parameters.

The natural sepiolite used as raw material in this invention is α-sepiolite in a compact micronized form and was supplied by Tolsa S.A., under the name Pansil. It is a hydrated magnesium silicate, whose typical weight content of impurities is as follows:

AI ₂ O ₃ : 2.6%; Fe ₂ O ₃ : 0.3%; K ₂ O: 0.6%; CaO: 0.9%; Na ₂ O: 0.1%. The open zeolitic channels on the surface of the α-sepiolite create a network of pores of different sizes and dimensions and confer a specific surface

BET of 200-300 m ² g ^"1. The texture has a total pore volume of

0.35-0.45 cm ³ g ^"1 with a development based on mesoporosity. The disintegrated particle size of this material is 90% less than 1 μm.

In this invention, any mineral or vegetable coal can be used, with the exception of coking coals, with particle sizes disintegrated so that 90% are less than 20 μm. As indicated above, the particle size of the carbon used determines the volume of the interparticle spaces responsible for the macroporosity of the finished product. Thus, for example, similarly prepared adsorbent materials using the same carbon they contain with two different particle sizes at 90% less than 20 μm and less than 4 μm gave rise to products with macropore volume of 0.517 mlg ^"1 and of 0.317 mlg ^"1 respectively.

According to a preferred embodiment of the method of the present invention, in step a), the mixture of dry sepiolite and carbon powders also contains, as additives, bentonite powder and alumina powder in discrete amounts. Thus, a weight percentage of bentonite can be between 1 and 3% and alumina between 1 and 6%, in relation to the total weight of the dry powder mixture. The particle sizes disintegrated in both powders must be 90% less than 50 μm. The bentonite contributes to the plasticity of the wet mass to form and improves the mechanical properties of the final product while, as observed by the X-ray diffraction, the alumina reacts in part with the magnesium oxide present in the surface of the sepiolite forming a spinel (MgCAI ₂ O ₃ ) that also contributes to improve the hardness of final product (J. Blanco, M. Yates, P. Avila and A. Bahamonde, Journal of Materials Science, 5927-5933, 1994).

The bentonite used as raw material in this invention was supplied by Oil-Dry Corporation under the name of Bentonite of Paraná. It is an aluminum silicate whose weight content of impurities is as follows: Fe ₂ O ₃ : 5.9%; K ₂ O: 1, 8%; MgO: 1.6%; CaO: 0.5%; Na ₂ O: 0.8%, with a BET specific surface area of 95 m ² g ^"1 , a total pore volume of 0.17-0.18 cm ³ g ^{" 1} , based on mesoporosity.

The alumina that is eventually used as an additive in the preparation of the materials object of this invention, mostly has a gamma-like crystalline structure. The raw material used was supplied by Condea with the name of Pural SB; This conveniently dehydrated material has a specific BET surface area of 264 m ² g ^"1 , a total pore volume of 0.40-0.45 cm ³ g ^{" 1} , similarly based on mesoporosity.

The use of raw materials, with particle sizes greater than those indicated in the preparation of these new adsorbents, gives rise to difficult extrusion pastes and excessively soft materials. The particle size required for each and every one of the raw materials used in the preparation of these new materials also enables and characterizes this invention.

The structure of these new materials typically has a micropore volume of 0.1 to 0.2 cm ³ g ^"1 corresponding to the activated carbon that is formed during the heat treatment, which confers adsorbate storage capacity, also contains a volume of mesopores around 0.2 cm ³ g ^"1 derived mainly from the clays used and a macropore volume that typically ranges between 0.3 and 0.6 cm ³ g ^{" 1} formed from the interparticle spaces that provide external surface and threshold diameter values around 100 m ² g ^"1 and 1700 nm respectively, which guarantee high adsorption speeds in units operating in a dynamic regime. The present invention also relates to the use of a composition, as defined and described above, as adsorbent material for liquids, gases and vapors in units operating in a dynamic regime.

The size classification - micro, meso and macro - used in this document is the one adopted by the IUPAC "Manual of Symbols and Terminology of Physicochemical Quantities and Units" E. Butterworths. London (1972). The values of the volumes of pores and specific surface of the materials are determined by the intrusion of mercury and by adsorption of nitrogen following the BET method. The disintegrated particle size is calculated from data obtained in mercury intrusion tests.

EXAMPLES OF EMBODIMENT OF THE INVENTION

The following non-limiting examples further illustrate the present invention.

Example 1

Mineral powder with a particle size of less than 15 μm in 90% and sepiolite powder with a particle size of less than 0.3 μm in 90% are used as raw materials.

The coal, lignite type, without appreciable porosity, supplied by MPX. Santa Catarina (Brazil), has a calorific value of less than 9.6 MJ / Kg., An ash content of 45% and a total humidity of 14% by weight. Sepiolite, supplied by TOLSA SA (Spain) when dried at 200 ⁰ C in air for 3 hours, has a surface area of 182 m ² g ^"1 and a mesopore volume of 0.42 ^{mlg" 1} without significant presence of micropores (0.02 mlg ^"1 ) and absence of macropores.

Dry 1 kg of dried sepiolite powder with 1 kg of coal powder dry. Once a homogeneous mixture is obtained, it is taken to a double sigma kneader and kneading is started by slowly adding deionized water; after the addition of water, kneading is maintained During 4 hours. The mass obtained in this way is formed by an extruder to obtain cylinders 10 mm long, 4.5 mm outside diameter and 2.5 mm inside diameter. Shaped parts, air dried at room temperature for 24 hours and then at 200 ⁰ C for 24 hours in air atmosphere and treated at 500 ⁰ C for 1 hour in nitrogen at 85O ⁰ C for 1 hour under of carbon dioxide and water vapor.

The hollow cylinders obtained in this way have a specific surface area of 420 m ² g ^"1 , an outer surface of 87 m ² g ^{" 1} , a micropore volume of 0.125 mlg ^"1 , a mesopore volume of 0.228 mlg ^{" 1} , a macropore volume of 0.453 mlg ^"1 and threshold diameter of 1700 nm.

The mechanical properties of the cylinders obtained are suitable for industrial use; similarly, its structure proved to be perfectly stable to water or water vapor. The static adsorption capacity of the material obtained was determined with different adsorption at temperatures of 22-24 ⁰ C. The values obtained in the corresponding tests were 0.24 g of orthodichlorobenzene, 0.30 g of toluene, 0.31 g of trichlorethylene and 0.36 g of acetone per gram of adsorbent.

Example 2

To prepare the adsorbent material, the procedure described in Example 1 is followed, although the dry powder mixture contains alumina and bentonite powder as additives with a weight ratio carbon / sepiolite / alumina / bentonite of 40/52/6/2 . The disintegrated particle size of alumina and bentonite powders is 90% less than 40μm.

The cylinders thus obtained have a specific surface area of 390 m ² g ^"1 , an external surface area of 99 m ² g ^{" 1} , a micropore volume of 0,120 mlg ^"1 , a mesopore volume of 0.207 mlg ^{" 1} , a volume of macropores of 0.517 mlg ^"1 and a threshold diameter of 1700 nm.

The mechanical properties of the cylinders obtained are appropriate for industrial use, and also their structure remains perfectly stable to water or water vapor.

The evaluation of the adsorption capacity in dynamic regime of this material was carried out in a 10 mm reactor. of internal diameter at a pressure of 0.94 kg cnrϊ ² and at 3O ⁰ C temperature. The cylinders were cut to lengths less than 3 mm. to introduce them into the reactor where they were previously dried at ¹⁵ ° C in air flow for 12 hours. The reactor temperature was then lowered to 3O ⁰ C and maintaining this temperature, an air flow with a content of 10 ppm of o-dichlorobenzene was fed at a linear velocity of 0.32 ms ^"1 (measured under normal conditions). The concentration of the organic compound at the inlet and outlet of the reactor was measured with a sensitivity of ± 0.1 ppm by means of a flame ionization detector, the break-up time elapsed until the concentration of the o -dichlorobenzene at the outlet reaches the value of 0.3 ppm The amount of o-dichlorobenzene adsorbed in the solid cylinders was 0.14 grams per gram of adsorbent If the density of the liquid o-dichlorobenzene, under the test conditions , is 1, 305 g mi ^"1 , the adsorbed volume of liquid o-dichlorobenzene will be 0.107 millimeters per gram, very close to the corresponding volume of the micropores of the material.

In another experiment, water contaminated with dioxins and furans is passed through these cylinders at a linear velocity of 0.2 ms ^"1 , with a spatial velocity of 250 h ^{" 1} and at a temperature of 60-70 ⁰ C. At the end of the 15 days that the test lasted, the total concentration of dioxins and furans in the water expressed in international toxic equivalents was 280 pg ITEQ I ^"1 at the entrance and 67 pg ITEQ I ^{" 1} at the exit.

Claims

1. Composition of a material with porous structure characterized by the fact that it includes activated carbon and enstatite, which were obtained in a single heat treatment in a controlled structure.

2. Composition of a material according to claim 1, characterized in that the sepiolite powder has a particle size of 90% less than 1 µm, preferably less than 0.3 µm and carbon dust it has a particle size disintegrated in 90% less than 20 μm, preferably less than 7 μm.

3. Composition of a porous structure material according to claims 1 and 2 characterized in that it was prepared from mixtures of coal and sepiolite powders, with sepiolite / carbon weight ratios of 0.5 to 3, and more preferably from 0.8 to 2.

4. Composition of a material according to claims 1 to

3, characterized by the fact that the material is formed into granules, pellets, spheres, solid cylinders, hollow cylinders, plates or a hive structure with channels parallel to the length of the longitudinal axis in a number greater than 2 and less than 25 channels per square centimeter of cross section, in which this material preferably adopts the shape of hollow smooth or striated cylinders, with a length between 0.5 and 10 cm and a wall thickness between 0.02 cm and 0.5 cm.

5. Composition of a material according to claims 1 to 3, characterized in that the material typically has a micropore volume of 0.1 to 0.2 cm ³ g ^"1 , a mesopore volume close to 0 , 2 cm ³ g ^"1 and a macropore volume that typically ranges between 0.3 and 0.6 c mm ³³ gg ^""1 with values of outer surface and threshold diameter around 100 m ² g ^{" 1} and 1700 nm respectively.

6. Method for preparing the composition according to claims 1 to 4 characterized in that it comprises the following phases:

a) mix sepiolite and coal powders until a homogeneous powder mixture is obtained,

b) knead the homogeneous mixture of powders obtained with the addition of water to obtain a wet paste,

c) drying the shaped piece in air and at room temperature for at least 2 hours, preferably 24 and between 80 and 25O ⁰ C for at least 2 hours, preferably 4 hours,

e) subject the piece to heat treatment at temperatures between 500 ⁰ C and 600 ⁰ C, in an inert atmosphere for at least 1 hour, preferably 2 hours, and at temperatures between 800 and

1000 ⁰ C for at least 1 hour, preferably 2 hours, in an atmosphere of carbon dioxide and water vapor.

7. Method according to claim 6, characterized in that in step a), the mixture of sepiolite and carbon powders also contains as additives bentonite powder and alumina powder with a particle size of less than 50 μm in 90%, the weight content of bentonite is 1 to 3% and that of alumina is comprised between 1 and 6% in relation to the total weight of the dry powder mixture.

8. Use of a composition according to claims 1 to 5, characterized in that it is used as an absorbent material for liquids, gases and vapors in units operating in a dynamic regime.