WO2021111019A1

WO2021111019A1 - Method for obtaining integral carbon monoliths and carbon monoliths obtained

Info

Publication number: WO2021111019A1
Application number: PCT/ES2020/070731
Authority: WO
Inventors: Miguel Ángel CENTENO GALLEGO; José Luis SANTOS MUÑOZ; José Antonio ODRIOZOLA GORDON; José de Jesús DÍAZ VELÁSQUEZ; Yazmin Yaneth AGÁMEZ PERTUZ; Nicolás RODRÍGUEZ RIAÑO
Original assignee: Consejo Superior De Investigaciones Científicas (Csic); Universidad De Sevilla; Universidad Nacional De Colombia
Priority date: 2019-12-02
Filing date: 2020-11-24
Publication date: 2021-06-10
Also published as: ES2829958B2; ES2829958A1; CO2020006437A1

Abstract

The present invention relates to a method for preparing integral carbon monoliths, which uses a synthetic resorcinol–formaldehyde polymer together with a polymer of natural origin, such as soluble starch, as a binding agent of carbon materials of different natures. Thus, a process is achieved that allows structured carbon monoliths to be obtained, with and without mineral matter, encompassing a wide range of carbon sources and multiple geometries, by implementing the design and production of extrusion moulds using 3D printing.

Description

PROCEDURE FOR OBTAINING INTEGRAL CARBON MONOUTES AND

CARBON MONOLITHES OBTAINED

DESCRIPTION

TECHNICAL SECTOR

The present invention relates to the preparation of integral carbon monoliths starting from carbonaceous materials of different nature that can be used as supports in fixed bed catalytic reactions.

STATE OF THE ART

After alumina and silica, carbonaceous materials are interesting since they have advantages such as:

- high thermal resistance and acid or alkaline media, the possibility of modifying its structure at the meso, micro and / or nano level, thus forming the option of manipulating its surface chemistry, generating solids of different porosity and surface area in a controlled way, the possibility of modifying Their chemical nature to obtain hydrophobic, hydrophilic or amphoteric structures, are materials that are mostly inexpensive, inert to most unwanted reactions.

However, these materials are not the most used due to their great variety in their properties due to preparation and / or modification methods, thus hindering the reproducibility in the synthesis, due to the existence of unwanted metals in trace-level concentrations present, such as, for example, the mineral matter in mineral coals. Currently, carbonaceous materials free of mineral matter are prepared, synthesized from organic polymers that allow the control of their structural and surface characteristics. These include carbon nanotubes and nanofibers, vitreous carbons, and carbon aerogels and xerogels.

The main use of carbonaceous materials has been in processes aimed at controlling environmental pollution, water purification, selective NOx hydrogenation, catalyzed oxidation of volatile organic compounds, biodiesel synthesis, methane reforming, among others. . It is well known in these processes that Pressure in packed systems does not allow to take full advantage of the porosity of the materials and, in addition, they present problems of mechanical and thermal resistance at relatively high temperatures. To solve the problem, a process for the preparation of supports and catalysts based on carbonaceous materials free of inorganic components (excluding the active phase in the case of catalysts) with geometry, porosity and / or fully defined resistance has been investigated since the geometry, chemical structure and surface structure of the solid are determining factors.

There are different manufacturing processes for these materials. The main differences are the variation of the carbonaceous precursor, which is usually an activated carbon, the inclusion of different binders such as hydrolyzed cellulose or polyfurfuryl alcohol, and plasticizers; the so-called extrusion method being the most common synthesis.

Tennison (Applied Catalysis A: General, 1998. 173 (2): p. 289-311.) Developed a route of preparing carbons derived from phenolic resins for use as catalyst supports and adsorbents. The route is to use the commercial phenol-formaldehyde mixture (Novolak) as the carbonaceous precursor. The formation of the materials developed by Tennison is based on a 5-stage process on which it bases its study, with an emphasis on activation and extrusion processes. Coals can be produced from simple granules to large monolithic structures. Tenisson refers to the carbonization of a natural material to obtain charred or pitches which are extracted with the help of oil pitches and subsequent activation. The extrusion product is limiting in the physical forms that can be obtained since it is very weak against mechanical stress. In the process of the present invention, the formation of a binding agent under specific conditions is included in its initial stages, which consists of a synthetic polymer of resorcinol-formaldehyde together with one of natural origin such as soluble starch, to bind in an improved way to the carbonaceous materials used, in order to avoid the stages most investigated by said author such as activation and extrusion. The limitation of weakness in the face of mechanical stress and the obtaining of different physical forms is overcome by the process of the present invention where the stage of mixing a synthetic polymer with one of natural origin is combined together with the implementation of the design and manufacture of extrusion molds using 3D printing; achieving structured carbon monoliths, with and without mineral matter. Gadkaree, et al., (Carbon, 2000. 38 (7): p. 983-993) present in their work the preparation of beehive-type monoliths combining activated carbon with different organic and inorganic additives such as cordierite powder, cellulose fibers and acetate of cobalt to generate a paste that is subsequently extruded, charred and activated. It was found that the purity of the phenolic resin directly influences the microporosity of the material and that the presence of metallic catalysts significantly changed the final structure of the material, mainly affecting the meso and macroporosity. In Gadkaree's work undesirable inorganic compounds are included in integral carbon monoliths. They also studied commercial resins and the manufacturing method was made by extrusion after carbonization, obtaining materials with a fraction of about 50% of inorganic material. In this document it is stated that the objective of the work is to study the development of porosity in beehive-like structures as a function of the activation level and the extrusion composition. Therefore, its purpose is far away from the object of the present invention, which does not include the activation and extrusion steps, which are expensive given the severity of the treatment. On the contrary, in the present invention it is possible to obtain structured carbon monoliths, with and without mineral matter, reducing costs through structuring in multiple geometries by implementing the design and manufacture of extruder molds using printing.

3D.

Gatica et al. (Catalysis Today, 2015. 249: p. 86-93) prepared beehive-like monoliths with a cell density of 13.7 units / cm ² combining carbonaceous precursors (a commercial activated carbon and a natural carbon supplied by the National Carbon Institute in Spain). They were based on the methodology that states that any ceramic paste with a 'liquid limit' between 40-60% and a plasticity index between 10-30% can be extruded. To prepare the monoliths, different additives were used as binders to achieve the carbonaceous paste; These include methylcellulose, starch, polyvinyl alcohol, hydroxymethylcellulose, and potato starch dextrin; as plasticizers polyethylene glycol, and glycerin; as deflocculants ammonium polyacrylate and oleic acid; as lubricants aluminum stearate and stearic acid; as dispersant aluminum phosphate hydrated and dissolved in o-phosphoric acid and, as humidifiers, ethanol and kerosene. In this work, results are revealed with different carbonaceous materials and different binders, but the responsibility of the mechanical properties is attributed to the ceramic resin. In this way, monoliths with an unwanted mineral charge are obtained, as has been mentioned. US Patent No. 4677086 to Me Cue et al. reveals the preparation of an activated carbon from wood with pores smaller than one (1) micron in diameter and a higher bulk density. The process of the invention consists of grinding the granular activated carbon until obtaining a fine powder, which is mixed with a selected liquid that can be water or another polar solvent and bentonite. The mixture is then shaped and the shaped activated carbon is dried to remove the liquid present. Finally, a heat treatment is performed to calcine or fix the clay binder. The use of bentonite as a binder to shape activated carbon obtained from wood introduces inorganic matter into the final form obtained and significantly increases its density, two unwanted characteristics in integral carbon monoliths. As mentioned above, integral carbon monoliths are applied as catalytic supports or as a catalyst itself, in which the inorganic matter present can catalyze unwanted side reactions, promote poisoning of the active phase, or even inhibit the reactions of interest. .

U.S. Patent No. 4124529 presents the procedure to obtain shaped adsorbents from the pyrolysis of different carbonaceous sources such as mineral coal, oxidized mineral coal, charcoal, lignites or low temperature cokes with different binding agents such as butadiene-acrylonitrile or butadiene-styrene and materials thermoplastics such as polyvinyl alcohol, polypropylene, or a mixture thereof. In this patent, strong emphasis is placed on the pyrolysis and activation conditions by employing a temperature range of 673-1273 K and heating rates of 5 to 10 K / min. The use of binders, thermosetting materials, high carbonization temperatures and activation with carbon dioxide significantly increase production costs compared to other processes that use fewer precursors and fewer steps to obtain the final product.

US Patent No. 5389325 discloses a process for manufacturing shaped activated carbons using a solid phenolic resin of phenol formaldehyde between 5-35%, an organic binder between 4-10% such as cellulose ether, cellulose ether derivatives and combinations . The extrusion method is used to form a beehive-like structure and the resin is dried at 363 K. In this procedure, when working with an unpyrolyzed phenolic polymer resin, the use of the carbonaceous structure is restricted, since in the vast majority of catalytic reactions in which structured monoliths arouse interest are carried out at temperatures between 453 - 1173 K, very high temperatures at which these types of resin would undergo decomposition reactions due to their thermal stability.

Patent CA 2442243 reveals the manufacture of spherical shaped activated carbon using a cellulose polymer as a binder such as sodium carboxymethylcellulose or starch, an organic compound that favors extrusion, increases mechanical resistance and generates the formation of spheres of activated carbon, but whose cost can triple that of other organic binders such as soluble starch. The improvement is attributed to the crosslinking reaction that is generated between activated carbon and sodium carboxymethylcellulose. In addition, two advantages are pointed out: the production of the spheres at a very low temperature (543 K), and better properties such as lower density, lower ash content and greater stability in water, the latter when comparing the materials obtained with materials from the same dimensions prepared with clay as a binder. The procedure reveals the use of water as a solvent, a urea-formaldehyde resin, and a carboxymethylcellulose or starch binder. This invention uses commercial polymers that, when pyrolyzed at the given temperatures, generate little or no surface area in the monoliths.

Patent CA 2639955 reveals the manufacture of carbon monoliths from the carbonization and activation of resole beads as the only carbonaceous source, which are polymers obtained by the condensation of phenol and formaldehyde with a basic catalyst NH ₄ OH, in water, ethanol and methanol in different proportions as solvents and a colloidal stabilizer and / or binders such as sodium carboxymethylcellulose and sodium dodecyl sulfate. Abundant and available carbonaceous materials such as mineral coals, commercial activated carbons, another type of low-cost carbonaceous source or another material of a different nature are not covered in this work. In addition, a post-carbonization activation is required in the final process.

However, there is no process in the state of the art for the manufacture of integral carbon monoliths that includes the specific sequence of the six (6) steps that comprise the preparation of the organic solution of the resordnol-formaldehyde (DP) polymer together with the starch, the stabilization of the binding agent, the grinding of the carbonaceous source, the packaging of the same in a mold, the curing of the polymer and the carbonization of the material. Much less exists in the state of the art a process for structuring carbonaceous materials into carbon monoliths, with and without mineral matter, reducing costs through obtaining multiple geometries. for the implementation of the design and manufacture of extrusion molds using Printing

3D.

EXPLANATION OF THE INVENTION The main object of the present invention is to provide a process for the preparation of integral carbon monoliths, which includes: the use of carbonaceous materials of different nature (commercial activated carbon, pyrolyzed mineral carbon, synthetic carbonized, among others) , the inclusion of a synthetic polymer based on the polycondensation of resorcinol and formaldehyde with an inorganic catalyst prepared in aqueous and organic solvents, and the insertion of a low-cost natural polymer that modifies in a controlled way the structural and surface properties of the monoliths.

The implementation of the synthetic resin resorcinol formaldehyde as a binder of carbons of different nature and the combination with a synthetic polymer of natural origin coupled with the implementation of the design and manufacture of extruder molds using 3D printing allows to obtain a novel process for the preparation of structured monoliths of carbon, with and without mineral matter.

These monoliths have defined and controlled surface characteristics, due to the contribution of the two carbonaceous sources, both the resin and the carbonaceous material. In this way, the possible use of any carbonaceous material for the manufacture of monoliths is expanded. In one embodiment of the invention the use of different solvents provides the advantage of working with carbonaceous materials with hydrophilic, hydrophobic or amphoteric character for the production of monoliths. Likewise, the incorporation of the low-cost binder improves the structural properties of the monoliths, generating microporosity in them in a controlled manner and increasing the crosslinking of phenolic rings when reacting with the synthetic polymer. A further aspect of the invention is the manufacture of integral carbon monoliths using different heating rates during the pyrolysis process.

BRIEF DESCRIPTION OF THE FIGURES Figure 1. a) Molds used for the preparation of monoliths, b) Monolith obtained in example 1.

Figure 2. Diffractograms of the monoliths obtained using different solvents. Figure 3. Diffractograms of the monoliths obtained using different heating rates in the pyrolysis stage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention refers to a process for obtaining integral carbon monoliths using carbonaceous materials of different nature, which comprises the following steps: a) Preparation of a precursor solution (DP) of the resorcinol-formaldehyde polymer using a basic catalyst and a starch polymer of natural origin b) Stabilization of the precursor solution of step a); c) Grinding and sieving of the carbonaceous material; d) Packing of the carbonaceous material previously ground and sieved together with the precursor solution, in a mold previously designed and manufactured using 3D printing; e) Gelling and curing of the packaged material in step d) at a temperature between 335 K and 345 K; f) Carbonization of the mold with the cured material in step e) under temperature conditions between 900 and 1200 K heating at a speed between 5 and 15 K / min. The process of the present invention makes it possible to obtain structured materials with fully defined geometries and preserving properties of the carbonaceous source. The carbonaceous material is selected from an activated carbon, a carbonizate of a mineral coking carbon, and a synthetic carbonizate such as an airgel or carbon xerogel. The process of the present invention is summarized in: - PD is prepared by dissolving resorcinol in a solvent (water, ethanol, polyethylene glycol or polyethylene glycol with 1% by weight of polyvinyl alcohol - PVA) in a proportion of 2 mL of solvent per gram of resorcinol , sodium carbonate (Na ₂ CO ₃ ) as polymerization catalyst in 1: 300 molar ratio resorcinol / catalyst, starch as binder between 1 and 15%, preferably 5%, by weight relative to the amount of initial resorcinol and formaldehyde in relation 1: 2 molar relative to resorcinol (step a). - the DP is left to stabilize for 24 h at temperatures between 280 and 310 K (stage b). The sources used are activated carbon, coke obtained from the carbonization of a low volatile bituminous mineral coal and a carbon airgel or xerogel obtained from the pyrolysis of DP in the absence of another carbonaceous source. The carbonaceous source must be at a particle size less than 600 μm.

- the carbonaceous sample is ground and sieved until the whole is at the indicated particle size (step c).

- the molds are designed with FreeCAD software version 0.16. In figure 1a an example of the mold that can be used is observed. In one embodiment of the invention packing can be carried out by adding the carbonaceous source into the mold up to a height of 1 cm. The DP is then slowly dripped until the carbonaceous material is completely wetted (step d). This procedure is repeated until the height of the mold used is completed, filling the multilayer mold. The amount of DP used varies according to the carbonaceous source. In another embodiment of the invention, packing is carried out with the assistance of ultrasound, pouring a suspension of the carbonaceous source and the DP into the mold filling it up to 95% of its height. In another embodiment of the invention, packaging is carried out by introducing into the mold, the entire carbonaceous source, followed by a dropwise impregnation to pore volume with the precursor solution of synthetic polymer and natural polymer assisted by ultrasound.

- The mold with the carbonaceous source already packed gels and cures by placing it in a completely sealed container with a lid to avoid evaporation of the solvent. This, in turn, is brought into an oven at a temperature that can be selected between 335 and 345 K and is left for a selected time between 72 and 144 h (step e). - for carbonization, the mold is introduced into a tubular oven under a nitrogen atmosphere at a flow of 100 mL / min and the pyrolysis process is carried out at a heating rate selected between 2 and 15 K / min up to 1073 K; once said temperature is reached, it is maintained for 2 h (stage f). The pyrolysis conditions used make it possible to eliminate the mold and obtain the formed monolith or carbonaceous material.

Another object of the present invention is a carbon monolith obtained by the process as described above, which has:

- surface areas between 60 and 590 m ² / g micropore volumes between 0.001 and 0.160 cm ³ / g micropore areas between 1 and 430 m ² / g external areas between 60 and 300 m ² / g total pore volumes between 0.084 and 1.350 cm ³ / g heights of crystallite between 13 and 18 Å diameters of crystallite between 23 and 57 Å

The application and specific configuration of this process to obtain a carbon monolith make it different from those disclosed in the state of the art and it becomes an effective alternative in the technology of the carbonaceous materials manufacturing industry. The sequence and the conditions under which each one of the stages of the process of the present invention are carried out allows to mold a great variety of carbonaceous materials of particular interest and to work in a wide framework of controlled experimental variables, obtaining ideal surface characteristics for the preparation of catalysts. supported on carbonaceous materials, which are of great interest due to their thermal stability in non-oxidizing atmospheres, the possibility of modifying their surface chemistry, low cost and low density compared to typical inorganic materials such as silica and alumina, among others.

MODE OF EMBODIMENT OF THE INVENTION Example 1

Preparation of monolith with commercial activated carbon

DP is prepared to carry out the polycondensation reaction between resorcinol and formaldehyde (1: 2 molar ratio), using sodium carbonate as a catalyst and water, 96% ethanol, polyethylene glycol or polyethylene glycol + 1% PVA as solvents. 9.91 g of resorcinol are dissolved in 18.8 mL of solvent and 13.5 mL of formaldehyde stabilized in 96% ethanol. 0.036 g of sodium carbonate (resorcinol / catalyst molar ratio 300), 0.496 g of starch (5% with respect to the amount of resorcinol) are added under constant stirring and maintained until the pH of the solution stabilizes (pH = ~ 6.5). The mold used was made with a WANHAO DUPLICATOR i3 PLUS printer and PVA as raw material. For the template shown in figure 1a, 1.5 g of activated carbon and 6 mL of DP were used. The mold with activated carbon already packed together with the DP is placed in a sealed container and kept for 24 h at 273K. Then it is introduced into a 343 K oven and after 120 h it is removed from it. At this time the monolith curing occurs. The carbonization process is carried out in a reactor horizontal tube at 1073 K for 2 h with a heating rate of 10 K / min in a N ₂ flow of 100 mL / min.

Figure 1b shows the monolith obtained. The carbonaceous source used is a commercial Darco Sigma-Aldrich activated carbon with a BET area of 892 m ² / g, a pore volume of 0.73 cm ³ / g, micropore area of 470 m ² / g (52.7 % of the total area) and an external area of 422 m ² / g. The total micropore volume is 0.215 cm ³ / g and the average pore size is 0.8 nm. Monolith 1 (m1 Darco / CX-ETOH) obtained using 96% ethanol has a BET surface area of 301 m ² / g, with a pore volume of 0.40 cm ³ / g, a micropore area calculated by the t-method of 171 m ² / g (56.8% of the total area) and an external area of 130 m ² / g (the difference between the BET area and the micropore area). The total micropore volume of 0.078 cm ³ / g and the average pore size obtained by the Density functional theory (DFT) model using a non-localized function is 0, 5 nm, indicating that the majority of pores are in the micropore region.

Monolith 2 (m2 Darco / CX-PEG) obtained using polyethylene glycol has a BET surface area of 213 m ² / g, with a pore volume of 0.24 cm ³ / g, a micropore area calculated by the t-method of 132 m ² / g (56.8% of the total area) and an external area that mainly represents the mesopore area of 81 m ² / g (the difference between the BET area and the micropore area). The total micropore volume of 0.065 cm ³ / g and the average pore size obtained by the DFT using a non-localized function is 0.7 nm, indicating that the majority of pores are in the micropore region.

Monolith 3 (m3 Darco / CX-PVA) obtained using PVA has a BET surface area of 381 m ² / g, with a pore volume of 0.39 cm ³ / g, a micropore area calculated by the t-method carbon-black of 223 m ² / g (58% of the total area) and an external area of 166 m ² / g (the difference between the BET area and the micropore area). The total micropore volume of 0.103 cm ³ / g and the average pore size obtained by the DFT using a non-localized function is 0.5 nm, indicating that the majority of pores are in the micropore region.

Figure 2 shows the diffactograms obtained for commercial activated carbon and the 3 monoliths made with different solvents. All diffractograms exhibit the characteristic features of amorphous carbonaceous materials: the (002) and (100) planes at 25 ° and 44 ° 28 respectively. The peak (002) is due to the ordering of aromatic rings and the (100) is attributed to the degree of condensation of aromatic rings. The sharp peaks located at 21 °, 23 °, 27 °, 36 ° and 51 ° 2θ correspond to the inorganic matter present in commercial activated carbon and correspond to calcium and silicon oxides. A summary of the structural parameters obtained from the X-ray diffraction is shown in table 1. The value of the interplanar distance of the materials practically remains constant. Only in m1 Darco / CX-ETOH a significant change in crystallite height is observed, with a value of 18.1 Å, this with respect to the values of commercial activated carbon and the other two monoliths. The crystallite diameter values show significant changes with respect to commercial activated carbon for the monolith m1 Darco / CX-ETOH which is reduced by about 14 Å and for the monolith m3 Darco / CX-PVA increases 13

TO.

Table 1. Structural parameters obtained for commercial activated carbon monoliths varying the type of solvent.

Taking into account the above, it is established that with the process of the present invention and using different solvents it is possible to obtain monoliths with values of pore volumes, surface area and diameter of crystallite totally defined and different and specific compared to the carbonaceous starting material.

Example 2

Preparation of pellet-type carbon monoliths with carbon xerogels. Pellet-type monoliths obtained from the carbonization of the polycondensation of resorcinol-formaldehyde in water as a solvent were prepared following the methodology set forth in Example 1 for the preparation of the DP. The DP was mixed with the carbonaceous source. The curing time is the same. The carbonization process is carried out in a horizontal tubular reactor at 1073 K for 2 h, varying the heating rates in a flow of N ₂ of 100 mL / min. The range of heating speed worked was between 2 and 15 K / min. Table 2 contains a summary of the monoliths obtained at different heating rates during the pyrolysis stage. The BET surface area values vary between 432 and 590 m ² / g. The micropore volume presents values between 0.12 and 0.16 cm ³ / g and a slight tendency is observed when reducing this respect increases the heating rate. The micropore area percentages of the series of monoliths are between 50 and 70%, the monolith manufactured with a heating rate of 5 K / min being the one with the highest percentage. The external area, mainly a consequence of the existence of mesopores and macropores in the monoliths, varies between 130 and 301 m ² / g and the pore volume between 0.59 and 1.35 cm ³ / g. Obtaining materials with defined surface characteristics of materials that present micro and mesoporosity are emphasized, attractive characteristics for different catalytic processes that prefer non-homogeneous pore distributions with the presence of pores lower and higher than 2 nm on the same support.

Table 2. Textural parameters calculated for PELLET TYPE monoliths obtained by varying the heating rate in the pyrolysis stage.

Figure 3 shows the diffractograms obtained for the pellet-type monoliths obtained by varying the heating rate in the pyrolysis stage. All diffractograms are typical of amorphous carbonaceous materials with typical peaks in the (002) and (100) planes. The total absence of any other type of signal is noted, thus indicating the production of fully organic, integral monoliths with high carbon content, understood by the pyrolysis conditions.

Table 3 shows the structural parameters obtained for the monoliths manufactured at different heating rates during carbonization. As can be seen in Table 1 of Example 1, the interplanar height remains close to the same value, 3.7 Å for the monoliths made with different solvents and 3.8 Å for the monoliths obtained with different heating rates in the pyrolysis stage. The crystallite height has values between 13.1 and 15.4 Å. The crystallite diameter shows values between 23.7 and 31.2 Å.

Table 3. Structural parameters obtained for the monoliths obtained by varying the heating rate in the pyrolysis stage.

Example 3

Monoliths with carbonized mineral coal and carbon xerogels.

In this example the preparation of monoliths is enunciated using as carbonaceous materials: a) carbon xerogel produced by the polycondensation between resorcinol and formaldehyde, using water and ethanol as solvents and b) a coke obtained from the carbonization of a medium volatile bituminous carbon that is used in the metallurgical industry in the production of steel. Table 4 shows a summary of the textural parameters calculated for the coke and carbon xerogel (CX5 10 K / min) used as raw materials and the monoliths defined as m4 CX5 / CX-WATER and m6 CX5 / CX-ETOH . The monolith prepared with coke is defined as m5 Coke / CX-ETOH and is not included in the table as it did not show development of textural properties. It is observed that coke is a mesoporous material with a very low surface area and carbon xerogel a porous material with a contribution of microporosity in the BET area close to 50%. In the m4 CX5 / CX-WATER monolith practically all the microporosity of the CX5 10 K / min disappears and the surface decreases to one tenth, thus defining the obtention of a clearly mesoporous monolith with an average pore diameter of 6.59 nm .

Table 4. Textural parameters calculated for monoliths obtained from coke and carbon xerogel (CX5 10 K / min)

Table 5 shows the parameters calculated for the coke, the carbon xerogel and the 3 monoliths prepared. The height and diameter of the coke crystallite present high values compared with the materials previously characterized in tables 1 and 3 since this is a material characterized by presenting a high degree of reordering of graphonic layers in its structure. In the monolith m5 Coke / CX-ETOH it is observed that the crystallite height remains the same and the crystallite diameter decreases a little due to the presence of the resorcinol formaldehyde char in the structure of the material. In the monoliths prepared with CX5 10 K / min, m4 CX5 / CX-WATER and m6 CX5 / CX-ETOH, both the crystallite height and the crystallite diameter present the same values, differing from the carbon xerogel in the value of the diameter crystal, which in the latter is smaller. Table 5. Structural parameters obtained for the monoliths obtained from coke and carbon xerogel (CX5 10 K / min)

Claims

1. Procedure for obtaining integral carbon monoliths using carbonaceous materials of different nature, characterized in that it comprises: a) Preparation of a precursor solution of the resorcinol-formaldehyde polymer using a basic catalyst and a starch polymer of natural origin b) Stabilization of the precursor solution of step a); c) Grinding and sieving of the carbonaceous material; d) Packing of the carbonaceous material previously ground and sieved together with the precursor solution in a mold previously designed and manufactured using 3D printing; e) Gelling and curing of the packaged material in step d) at a temperature selected between 335 K and 345 K; f) Carbonization of the mold with the cured material in step e) under temperature conditions between 900 and 1200 K heating at a speed between 5 and 15 K / min.

2. Process according to claim 1, characterized in that in step a) the preparation of the precursor solution is carried out by mixing resorcinol / formaldehyde in a 1: 2 molar ratio, resorcinol / catalyst (Na ₂ CO ₃ ) in a 1: 300 molar ratio , 2 mL of solvent per gram of resorcinol and 5% soluble starch as a natural polymer, allowing it to stabilize for 24 h at temperatures between 280 and 310 K.

3. Process according to claims 1 or 2, characterized in that in step a) water, ethanol, polyethylene glycol and polyethylene glycol with 1% by weight of polyvinyl alcohol are used.

4. Process according to any one of claims 1 to 3, characterized in that in step c) a commercial activated carbon, a mineral carbon coke and a carbon airgel or xerogel obtained from the pyrolysis of the precursor solution are used in absence of another carbonaceous source.

5. Process according to any one of claims 1 to 4, characterized in that in step d) the packaging is carried out by introducing the entire carbonaceous source into the mold, followed by an impregnation at pore volume drop by drop with the precursor solution synthetic polymer and natural polymer assisted by ultrasound.

6. Process according to any one of claims 1 to 5, characterized in that in step d) the packaging is carried out by adding the carbonaceous source inside the mold up to a height of 1 cm, then slowly dripping the precursor solution until it is wetted in its the entire carbonaceous material and repeating the procedure until completing the height of the mold used, filling the mold in multilayer.

7. Process according to any one of claims 1 to 5, characterized in that in step d) the packaging is carried out by pouring a suspension of the carbonaceous source and the DP into the mold, filling it up to 95% of its height, assisting the packaging with ultrasound.

Process according to any one of claims 1 to 7, characterized in that in step e) the gelling and curing of the monoliths is carried out in sealed containers at temperatures between 335 - 345 K and times between 72 and 144 hours.

9. Process according to any one of claims 1 to 8, characterized in that in step f) the carbonization of the monoliths is carried out at 1073 K for 2 hours in a tubular reactor with a flow of N ₂ of 100 mL / min and using different speeds heating between 2 and 15 K / min.

10. Carbon monolith obtained by the process as defined in claims 1 to 9, characterized in that it has surface areas between 60 and 590 m ² / g.

Carbon monolith according to claim 10, characterized in that it has micropore volumes between 0.001 and 0.160 cm ³ / g.

12. Carbon monolith according to claims 10 or 11 characterized in that it has micropore areas between 1 and 430 m ² / g.

13. Carbon monolith according to any one of claims 10 to 12, characterized in that it has external areas between 60 and 300 m ² / g.

14. Carbon monolith according to any one of claims 10 to 14, characterized in that it has total pore volumes between 0.084 and 1.350 cm ³ / g.

Carbon monolith according to any one of claims 10 to 14, characterized in that they have crystallite heights between 13 and 18 Å.

16. Carbon monolith according to any one of claims 10 to 15, characterized in that it has crystallite diameters between 23 and 57 Å.