PROCESS FOR THE PREPARATION OF A POROUS CARBONACEOUS MATERIAL, POROUS CARBONACEOUS MATERIAL, AND A CATALYST MADE OF THE MATERIAL

Abstract

Known processes for preparing a porous carbonaceous material require lengthy polymerization and washing steps involving solvents or neutralizing agents. The use of high quantities of pore formers leads to a lower carbon yield and higher costs, and use of sulphuric acid leads to sulphur contamination of the final material, but also to corrosion and corrosive by-products and a more complicated handling of the process. In order allows the manufacturing of a porous carbonaceous material with a high pore volume and avoiding the disadvantages of the known methods, a process is provide that comprise the steps of a) providing at least one carbon source and at least one amphiphilic species, b) combining at least the carbon source and the amphiphilic species to obtain a precursor material, c) heating the precursor material to a temperature in the range between 300° C. and 600° C. for at least 15 min so as to obtain a porous carbonaceous material, which is then cooled so as to form the porous carbonaceous material having a modal pore size and a pore volume and a skeleton density.

Claims

1. The process for the preparation of a porous carbonaceous material comprising: a) providing at least one carbon source and at least one amphiphilic species, b) combining at least the carbon source and the amphiphilic species to obtain a precursor material, c) heating the precursor material to a temperature in the range between 300° C. and 600° C. for at least 15 min so as to obtain the porous carbonaceous material, and d) cooling the porous carbonaceous material having a modal pore size and a pore volume and a skeleton density e) comminuting the porous carbonaceous material so as to obtain crushed porous carbonaceous material particles, and f) heating the crushed porous carbonaceous material particles to a temperature in the range from 700-1500° C.

2. The process according to claim 1, wherein during heating step c) the precursor material is heated to a temperature in the range between 350° C. and 550° C., and even more preferred between 450 and 500° C., for at least 15 min.

3. The process according to claim 1, wherein the crushed porous carbonaceous material has a medium particles size (D.sub.50 value) of less than 10 mm, preferably less than 5 mm, and most preferred less than 3 mm.

4. The process according to claim 1, characterized in that the heating of the precursor material in heating step c) comprises an oxidation phase in which the precursor material is heated in an oxidizing atmosphere.

5. The process according to claim 4, characterized in that the oxidizing atmosphere during heating the precursor material during the oxidation phase is an oxygen-containing atmosphere, preferably an atmosphere with an oxygen content of less than 25% by volume, particularly preferably air.

6. The process according to claim 4, characterized in that the heating of the precursor material during the oxidation phase is carried out in a temperature range between 150° C. and 470° C., preferably between 200° C. and 400° C.

7. The process according to claim 4, characterized in that the oxidation phase has a duration in the range of 60 to 360 minutes, preferably in the range of 120 to 300 minutes.

8. The process according to claim 1, wherein the carbon source is selected from the group consisting of Novolac type phenolic-formaldehyde resins, especially a Novolac type resorcinol-formaldehyde resins or in the alternative Novolac type phenol-formaldehyde resins, hydrolysable tannic acid, lignin, cellulose resins.

9. The process according to claim 1, wherein the at least one amphiphilic species is selected from the group consisting of block co-polymers and/or surfactants, preferably least one amphiphilic species comprises an amphiphilic compound, the amphiphilic compound comprising two or more adjacent ethylene oxide based repeating units, preferably 5 or more, more preferably 7 or more, more preferably 20 or more, or 30 or more, or 50 or more, and up to 1000 adjacent ethylene oxide based repeating units.

10. The process according to claim 9, wherein the block-copolymer is selected from the group consisting of triblock copolymers with the structure polyoxyethylene-polyoxypropylene-polyoxyethylene or polyoxypropylene-polyoxyethylene-polyoxypropylene, emulsifiers such as polyethylene-polypropylene glycol, surfactants such as polyethylene glycol monoalkyl ether and other modified polyethylene glycols.

11. A porous carbonaceous material obtainable by the process according to claim 1 having a skeletal density in the range from 1.2 g/cm.sup.3 to 1.8 g/cm.sup.3, preferably from 1.3 g/cm.sup.3 to 1.7 g/cm.sup.3, and further comprising pores including open interconnected pores.

12. A porous carbonaceous material according to claim 11, wherein the pores have a modal pore size is in the range from 50 to 280 nm.

13. A porous carbonaceous material according to claim 11, wherein the pores have a monomodal pore size distribution.

14. A porous carbonaceous material according to claim 11, wherein the porous carbon material is present as a monolithic body or as a powder.

15. A catalyst comprising a catalyst support having a surface area on which metal particles are distributed, wherein the catalyst support is made from a porous carbonaceous material according to claim 11.

Description

SHORT DESCRIPTION OF THE FIGURES

[0094] The invention is now further elucidated with reference to the figures. The figures and figure descriptions are exemplary and are not to be considered as limiting the scope of the invention.

[0095] FIG. 1 shows a diagram of a thermal gravimetric analysis of a sample,

[0096] FIG. 2 shows a diagram of the pore size distribution of a first sample,

[0097] FIG. 3 shows a diagram of the pore size distribution of second sample,

[0098] FIG. 4 shows a diagram of the pore size distribution of third sample,

[0099] FIG. 5 shows a diagram of the pore size distribution of a fourth sample,

[0100] FIG. 6 shows a diagram with the pore size distribution of a comparative example

[0101] FIG. 7 shows a diagram of skeletal densities form several samples, and

[0102] FIG. 8 shows the result of a thermogravimetric analysis (TGA) of a specific precursor material heated up to 1000° C. in both argon and in synthetic air.

EXAMPLES

[0103] In the preferred embodiment the porous carbon material is produced by combining an aqueous resorcinol-formaldehyde resin (Novolac resin) or solid pellets of resorcinol-formaldehyde/phenolic-formaldehyde resin (Novolac types) and an amphiphilic molecule (either a block copolymer or a surfactant or a (non-ionic) emulsifier or a combination of amphiphilic molecules). The components are mixed to obtain a homogenous precursor material and filled into a crucible. The crucibles are put into an oven for heat treatment.

[0104] The heat treatment of this is performed in one-step in a nitrogen atmosphere by heating from room temperature to a higher temperature in the range from 300 to 600° C. The heating program is as follows:

[0105] From 25° C. to 250° C. with 1K/m in, hold at 250° C. for 60 min, from 250 to 400° C., with 0.5K/min, hold at 400° C. for 60 min, then (in cases where 400° C. is not the final treatment temperature) heating up to the final temperature with 1 K/min and a 30 or 60 minute hold at the final temperature. The thus obtained porous carbonaceous material is cooled down, removed from the oven, and mechanical crushed/milled to the desired particle size.

[0106] Table 1 lists the tested recipes and the conditions of the heat treatment.

TABLE-US-00001 TABLE 1 Heat Treatment Weight ratio Final temperature Recipe Carbon Amphiphilic Carbon source/ (° C.)/ No source species Amphiphile Dwell time (min) 1 Liquid Genapol 5:3 400/60 Askofen PF20 779 W 50 2 Pellets Synperonic 5:9 500/60 Alnovol L62 PN320 3 Pellets Genapol 5:9 500/30 Penacolite X-080 B-16S 4 Liquid Genapol 5:3 600/30 Askofen PF20 779 W 50 5 Liquid Genapol 5:3 500/30 Askofen PF20 779 W 50 6 Tanex 20 Synperonic 1:1 500/30 F127

[0107] The ‘ weight ratio’ indicated in the fourth column refers to the ratio of the total masses of the respective substances. The 779 W 50 Askofen resin, for example, is an aqueous resorcinol-formaldehyde resin of the Novolac type. and contains 50 wt. % solid resin and 50 wt. % liquid phase. Therefore, 5 parts by weight of this substance correspond to 2.5 parts by weight of the resin.

[0108] A multiple of experiments was made for each recipe to see the reproducibility of the results.

Comparative Example According U.S. Pat. No. 8,227,518 B2

[0109] Mixture of 100 g Askofen 779 W 50 and 60 g Ethylene glycol; heat treated to 500° C. under nitrogen atmosphere. Instead of using an amphiphilic species as pore generating agent, the non-amphiphilic molecule ethylene glycol (CAS: 107-21-1) was used.

[0110] Commercial sources for the materials employed are presented in Table 2.

TABLE-US-00002 TABLE 2 Product name Material type Genapol ® PF20  Amphiphilic molecule Genapol ® X-080 Amphiphilic molecule Synperonic ™ PE/L62  Amphiphilic molecule Synperonic ™ PE/F127 Amphiphilic molecule Alnovol ® PN 320 Phenolic-formaldehyde resins of the Novolac type Penacolite B-16S Resorcinol-Formaldehyde Novolac resin ASKOFEN 779 W 50 Aqueous resorcinol- formaldehyde resin of the Novolac type (50% solids) Tannic Acid Tanex 20 Hydrolysable tannic acid Ethylene Glycol Ethylene glycol (CAS: 107-21-1)

[0111] The diagram of FIG. 1 show results of a thermal gravimetric analysis in argon up to 1000° C. of a carbonaceous material produced according to recipe 1 (thermal treatment at 400° C.). The lost in weight Δm (in %) of the sample is plotted on the primary ordinate as a function of the heating time t (in min). The temperature in the measuring chamber is plotted on the secondary ordinate axis and shows the constant heating rate (5° C./min) until the end temperature of 1000° C. is reached following which an isotherm of 30 minutes is held.

[0112] Curve A in FIG. 1 shows the mass loss of the sample, curve B shows the heating temperature and curve C the mass flow of argon flushing. Accordingly, the porous carbonaceous material loses at most about 10% of its initial weight upon treatment up to 500° C. At higher temperatures a remarkable loss of weight occurs showing the low temperature stability of the material. This can be explained by a continuing carbonization process of the porous carbonaceous material. On the other hand, the low stability of the porous carbonaceous material allows for faster secondary temperature treatments.

[0113] The diagrams of FIGS. 2 to 6 show the pore size distribution of the porous carbonaceous materials (FIG. 2 for sample 1; FIG. 3 for sample 2; FIG. 4 for sample 3 and FIG. 5 for sample 4; FIG. 6 for the comparative example according U.S. Pat. No. 8,227,518 B2).

[0114] The cumulative pore volume V.sub.c in [cm.sup.3/g] is plotted on the left ordinate and the derivative dV/d(log D) on the right ordinate against the pore diameter D in [nm]. It can be seen that all samples according to the invention have a unimodal pore size distribution with a maximum of the pore size in the macropore range of about 50 nm to 280 nm. There are also some larger pores with D values of up to about 10,000 nm, which are interpreted as interparticle pores and which do not belong to the pore structure of the particles.

[0115] In contrast to this, the resulting carbonaceous material of the comparative example does not exhibit a suitable porosity in the desired range as shown in FIG. 6. The pore size distribution shows a small pore volume of about 0.002 cm.sup.3/g, i.e. the material is non-porous. Curve D in the figure shows the cumulative pore volume, then two curves E and F show the pore size derivative as a function of pore size (curve F is a smoothed curve of the measured data points). These are all obtained in one measurement on one material.

[0116] Table 3 lists the carbonaceous material properties obtained from Nitrogen adsorption, Hg Porosimetry, and Helium Pycnometry

TABLE-US-00003 TABLE 3 Modal Pore Skeletal Recipe BET.sub.Micropore BET.sub.Total Pore Size Volume Density No. (m.sup.2/g) (m.sup.2/g) (nm) (cc/g) (g/cc) 1 31 177 132 1.65 1.46 2 440 583 221 0.99 1.39 3 392 575 80 1.3 1.34 4 508 639 141 1.6 1.51

[0117] Depending on the individual type and ratio of the respective precursors used for the synthesis of the carbonaceous material, skeletal densities between 1.3 g/cm.sup.3 and up to 1.7 g/cm.sup.3 can be achieved. This is illustrated in FIG. 7. The distribution on x-axis is simply a scatter to show the individual data points. The grouping corresponds to a class of materials. The group of points designated by reference sign “1” is based on 20 measurements with the carbon source “Askofen 779 W 50”. The calculated mean value of the skeletal density is 1.47 g/cm.sup.3. The group of point “2” is based on 23 measurements with the carbon source “Alnovol PN320”. The calculated mean value of the skeletal density is 1.34 g/cm.sup.3. The group of points “3” is based on 4 measurements with the carbon source “Penacolite B-16S”. The calculated mean value of the skeletal density is 1.37 g/cm.sup.3. The grey-colored band “4” corresponds to skeletal densities values measured for precursor materials that have been treated at a high temperature of 900° C. The values there are given for the skeletal density range of the whole 47 samples (not the mean of values).

[0118] Table 4 lists material additional properties obtained from Nitrogen adsorption, Hg porosimetry, helium pycnometry, thermogravimetry and x-ray photoelectron spectroscopy for sample Nos. 4 and 5.

TABLE-US-00004 TABLE 4 Oxygen content on Recipe Mass loss (%) surface (in at.-%) 1 35 16.3 4 12  5.1

[0119] In column “Mass loss” the mass loss is listed when the porous carbonaceous material was heated to 1000° C. under inert gas.

[0120] The oxygen content on the surface is a measure of the specific surface area of the material. The oxygen content is measured using the XPS method.

[0121] As it is shown in Tables 3 and 4, the macroporosity in the carbonaceous material is already established at a final synthesis temperature as low as 400° C. and does not change significantly with increasing the temperature to 600° C. (Comparing Recipe 1 and 4). The main difference with increasing the final synthesis temperature to 600° C. is an increase in the specific surface area, and conversely a decrease in the oxygen content on the surface. The properties of the carbonaceous material can therefore be tuned depending on the desired specifications of the material. Furthermore, in dependence on the temperature at which the materials are firstly obtained, the mass loss upon heating even further and up to 1000° C. under inert gas atmosphere, can be influenced. This allows for an addition adjustment of the material properties depending on the desired post-processing after the synthesis, i.e. it allows for example to reduce the off-gassing from the material during such a posttreatment depending on the synthesis temperature (e.g. 400° C. or 600° C.). This means that for example by using a synthesis temperature of 600° C., a higher throughput can be achieved during a post-treatment step than compared to a material that was obtained at 400° C.

[0122] Table 5 lists additional material properties obtained from Nitrogen Adsorption, Hg porosimetry, helium pycnometry and thermogravimetry for sample of recipe No 6.

TABLE-US-00005 TABLE 5 Modal Pore Pore Skeletal Mass Oxygen content BET.sub.Micro BET.sub.Total Diameter Volume Density Loss on surface Recipe (m.sup.2/g) (m.sup.2/g) (nm) (cc/g) (g/cc) (%) (at.-%) 6 325 407 114 1.4 1.62 14 5.7

[0123] As it is shown in Table 5, the macroporosity in the carbonaceous material can also be achieve with a hydrolysable tannic acid carbon precursor. The properties of the carbonaceous material can therefore be tuned also via the choice of carbon source depending on the desired specifications of the material.

[0124] Also, the carbonaceous materials described herein do not conduct electrical current, i.e. they are electrical insulators. Such porous insulators are well suited to act as separators for example in electrochemical energy storage devices. Also, these materials could be used as thermal insulators at a low ambient pressure or under vacuum.

[0125] The precursor material mixture typically contains a novolac resin and an amphiphilic surfactant. An example for the novolac resin is Alnovol PN320 (Allnex) and for the surfactant Genapol PF20 (Clariant) or Synperonic PE/L64 (Croda). The ratio of the resin to surfactant is in general 5:(1.5-9).

[0126] FIG. 8 shows the result of a thermogravimetric analysis (TGA) carried out with a mixture of Alnovol PN320 with the Genapor PF20 Synperonic PE/L64 with the ratio of 5:5, where said mixture was separately heated up to 1000° C. in both argon (curve 81) and synthetic air (curve 82) atmospheres. Similar as in FIG. 1, the remaining mass compared to the original sample mass Δm (in %) of the sample is plotted on the ordinate as a function of the heating temperature T (in ° C.). The heating temperature is a function of the heating rate which is 3° C./min until a temperature of 600° C. is reached and 5° C./min until the end temperature of 1000° C. Until about 400° C. the TGA curves 81, 82 of the samples heated in different atmospheres have rather similar profiles. At 400° C. the argon pyrolyzed sample (81) shows a larger mass loss and its slope decreases afterwards. The air pyrolyzed sample (82) has a plateau in the temperature range from about 400 to 450° C., where the mass loss of carbon is about 10 wt. % lower than the mass loss of the argon pyrolyzed sample (81). The mass loss however strongly increases when oxidation takes place at temperatures higher than 450° C. The difference in the carbon yields at 450° C. is indicated by the distance bar 83.

[0127] Similar thermogravimetric analysis results were revealed for a precursor material made from Alnovol PN445 and Genapol PF20 (5:5) mixture. At a temperature of 450° C., the mass loss of the sample crosslinked in argon atmosphere was almost 15 wt. % larger compared to the sample crosslinked in synthetic air.

[0128] Based on these thermogravimetric results, an experiment was designed to prove that the increase of the carbon yield (the reduction of the carbon mass loss) during the pyrolysis can be transferred to the synthesis of the porous carbon material by the process of the invention. A mixture of Alnovor PN320 and Genapor PF20 with the ratio of 5:5 was crosslinked and pyrolyzed up to 600° C. with the following heating ramp profile: 20-350° C.: on average 0.5° C./min.fwdarw.350-450° C.: 1° C./min.fwdarw.450-600° C.: 2° C./min. At a temperature of 450° C. the decomposition of the amphiphile is sufficiently complete and the atmosphere is changed from containing the oxidizing agent to one with inert gas only. This temperature (450° C.) is at the same time the maximal temperature of the oxidation phase in which the precursor material is heated in an atmosphere containing an oxidizing agent and the “first temperature” of the low temperature treatment.

[0129] In the first trial the mixture was pyrolyzed in nitrogen atmosphere. In the second trial the mixture was heated in an open retort in order to ensure an atmosphere containing an oxidizing agent (air) during pyrolysis until 450° C. As soon as that temperature was reached, the retort was closed, and the nitrogen flow was turned on in order to protect the carbonaceous material from further oxidation by air at higher temperatures (450-600° C.). Table 6 shows a comparison of the yields of the porous carbon material after the pyrolysis in nitrogen and in air (until 450° C.).

TABLE-US-00006 TABLE 6 Yield at Yield at 600° C. 900° C. Atmosphere Precursor mixture in % in % Nitrogen Alnovol ® PN320 30.3 26.3 Genapol ® PF20 Air until 450° C. Alnovol ® PN320 32.7 29.7 (and afterwards N.sub.2) Genapol ® PF20

[0130] The sample treated in nitrogen has a yield of 30.3 wt. % at 600° C., while the air crosslinked sample has a higher yield of 32.7 wt. %. The statistical error of the yield is typically 0.5 wt. %. In fact, the yield of the carbonized air crosslinked sample is 3.4 wt. % larger compared to the nitrogen crosslinked sample. This improvement is even larger than the yield gain of 2.4 wt. % found at 600° C. This implies that oxygen stabilizes the polymeric network and this improvement can be preserved. In this first experiment the air was replaced by nitrogen at a temperature of 470° C. By other experiments it could be shown that even a higher carbon yield might be obtained by process optimization, e.g. by switching to an inert atmosphere at a temperature of 400° C. and lower.

[0131] The crosslinking and pyrolysis of the precursor material mixtures result in a macroporous carbon with a cumulative pore volume above 0.4 cm.sup.3/g and with a modal pore size in the range between 50-280 nm.