GELLED COMPOSITION FOR AN ORGANIC MONOLITHIC GEL, USES THEREOF AND PROCESS FOR PREPARING SAME

Abstract

The invention relates to a gelled carbon-based composition forming an organic polymeric monolithic gel which is suitable for forming an aerogel by drying, to uses and to a process for preparing this carbon-based composition. The invention applies especially to the production of such gels having a very low density and a very low heat conductivity, a very high specific surface area and a satisfactory compression strength, for their use as thermal superinsulators or as carbon-based electrode precursors of supercondensers.

A composition according to the invention comprises a resin at least partly derived from polyhydroxybenzenes H and from formaldehyde(s) F, said polyhydroxybenzenes comprising at least one unsubstituted poly-hydroxybenzene R and at least one polyhydroxybenzene substituted with one or two alkyl groups.

This composition is such that said polyhydroxybenzenes comprise several said unsubstituted polyhydroxybenzenes R and R and in that the composition comprises a water-soluble cationic polyelectrolyte P.

Claims

1. A gelled carbon-based composition forming an organic polymeric monolithic gel which is capable of forming an aerogel by drying and a porous carbon monolith by pyrolysis of said aerogel, the composition comprising a resin derived at least partly from polyhydroxybenzenes H and from formaldehyde(s) F, said polyhydroxybenzenes comprising at least one unsubstituted polyhydroxybenzene R and at least one polyhydroxybenzene substituted with one or more alkyl groups, characterized in that said polyhydroxybenzenes comprise several said unsubstituted polyhydroxybenzenes R and R and in that the composition comprises a water-soluble cationic polyelectrolyte P.

2. The gelled composition as claimed in claim 1, characterized in that the composition has a heat conductivity of less than or equal to 40 mW.m.sup.1.K.sup.1.

3. The gelled composition as claimed in claim 1, characterized in that the composition comprises a product of a mixing reaction, in an aqueous solvent: of a first said unsubstituted polyhydroxybenzene R, and of a premix H comprising: in minor amount by mass, a second said unsubstituted polyhydroxybenzene R, which is identical to or different from said first unsubstituted polyhydroxybenzene, and in major amount by mass, said at least one substituted polyhydroxybenzene.

4. The gelled composition as claimed in claim 3, characterized in that, in said product of the mixing reaction, said premix H is present in equal or major amount by moles relative to said first unsubstituted polyhydroxybenzene R.

5. The gelled composition as claimed in claim 4, characterized in that said premix H comprises, in a mass fraction of less than 10%, said second unsubstituted polyhydroxybenzene R, and, in a mass fraction of greater than 80%, several said substituted polyhydroxybenzenes.

6. The gelled composition as claimed in claim 3, characterized in that said first and second unsubstituted polyhydroxybenzenes R and R are each a resorcinol, and in that the composition comprises several said substituted polyhydroxybenzenes comprising in major amount by mass methyl resorcinols and in minor amount by mass dimethyl resorcinols and an ethyl resorcinol.

7. The gelled composition as claimed in claim 6, characterized in that said methyl resorcinols comprise in major amount by mass 5-methyl resorcinol and in minor amount by mass 4-methyl resorcinol and 2-methyl resorcinol, in that said dimethyl resorcinols comprise 2,5-dimethyl resorcinol and 4,5-dimethyl resorcinol, and in that said ethyl resorcinol is 5-ethyl resorcinol.

8. The gelled composition as claimed in claim 1, characterized in that the composition has for said aerogel a density of less than or equal to 0.20 and a compression strength, defined for compression of a plate formed from said aerogel with a thickness equal to 9 mm along 50% of said thickness, which is greater than or equal to 0.15 MPa, or even 2 MPa.

9. The gelled composition as claimed in claim 1, characterized in that it comprises the product of a polymerization reaction in an aqueous solvent W of said polyhydroxybenzenes R and H and formaldehyde(s) F, in the presence of said cationic polyelectrolyte P dissolved in the solvent and of an acid catalyst C, the product of the polymerization reaction comprising said cationic polyelectrolyte in a mass fraction of between 0.2% and 2%.

10. The gelled composition as claimed in claim 1, characterized in that said water-soluble cationic polyelectrolyte P is an organic polymer chosen from the group consisting of quaternary ammonium salts, poly(vinylpyridinium chloride), poly(ethyleneimine), poly(vinylpyridine), poly(allylamine hydrochloride), poly(trimethylammonium ethylmethacrylate chloride), poly(acrylamide-co-dimethylammonium chloride), and mixtures thereof.

11. The gelled composition as claimed in claim 10, characterized in that said water-soluble cationic polyelectrolyte P is a salt comprising units derived from a quaternary ammonium chosen from poly(diallyldimethylammonium halides) and is preferably poly(diallyldimethylammonium chloride) or poly(diallyldimethylammonium bromide).

12. The use of a gelled composition as claimed in claim 1 for the heat insulation of a building or for forming a carbon-based electrode precursor of a supercapacitor.

13. A process for preparing a gelled composition forming an aerogel as claimed in claim 1, characterized in that it comprises: a) a polymerization at room temperature in an aqueous solvent W of said polyhydroxybenzenes R and H and formaldehyde(s) F, in the presence of said cationic polyelectrolyte P dissolved in the solvent and of an acid catalyst C, to obtain a solution comprising said resin, b) gelation of the solution obtained in a) to obtain a hydrogen of said resin, and c) drying of the hydrogel obtained in b) to obtain said aerogel.

14. The preparation process as claimed in claim 13, characterized in that step a) is performed: a1) by dissolving in said aqueous solvent consisting of water said polyhydroxybenzenes R and H and said cationic polyelectrolyte P, which is used in a mass fraction in the composition of between 0.2% and 2%, and then a2) by adding to the solution obtained said formaldehyde(s) F and then said acidic catalyst C.

15. The preparation process as claimed in claim 13, characterized in that it comprises, before step a), a step a0) comprising mixing of a first said unsubstituted polyhydroxybenzene R and of a premix H, in that said premix H comprises, in minor amount by mass, a second said unsubstituted polyhydroxybenzene R, which is identical to or different from said first unsubstituted polyhydroxybenzene, and, in major amount by mass, said at least one substituted polyhydroxybenzene, and in that, in step a0), said premix H is used in equal or major amount by mass relative to said first unsubstituted polyhydroxybenzene R.

16. The preparation process as claimed in claim 15, characterized in that said premix H comprises, in a mass fraction of less than 10%, said second unsubstituted polyhydroxybenzene R, and, in a mass fraction of greater than 80%, several said substituted polyhydroxybenzenes.

17. The preparation process as claimed in claim 15, characterized in that said first and second unsubstituted polyhydroxybenzenes R and R are each a resorcinol, and in that said premix H comprises several said substituted polyhydroxybenzenes comprising: in a mass fraction of between 60% and 70%, methyl resorcinols which comprise in major amount by mass 5-methyl resorcinol and in minor amount by mass 4-methyl resorcinol and 2-methyl resorcinol, and in a mass fraction of between 20% and 30%: dimethyl resorcinols, which comprise 2,5-dimethyl resorcinol and 4,5-dimethyl resorcinol, and an ethyl resorcinol, which is 5-ethyl resorcinol.

18. The preparation process as claimed in claim 13, characterized in that step c) is performed by drying in humid air, for example in an oven, without solvent exchange or drying with supercritical fluid, to obtain said aerogel.

Description

EXAMPLES OF PREPARATION OF A CONTROL AEROGEL G0, OF THREE AEROGELS G1, G2, G3 ACCORDING TO THE INVENTION AND OF AN AEROGEL G4 NOT IN ACCORDANCE WITH THE INVENTION

[0068] The examples that follow illustrate the preparation: [0069] of a control organic monolithic gel G0 exclusively derived from a resorcinol R as polyhydroxybenzene precursor, like the aerogel obtained in the abovementioned patent application in the name of the Applicant, PCT/IB2013/059 208, [0070] of three organic monolithic gels G1 to G3 according to the invention which are each derived from a resorcinol precursor R mixed with a premix H based on resorcinol and on resorcinols substituted with alkyl groups, as polyhydroxybenzene precursors, and [0071] of an organic monolithic gel G4 not in accordance with the invention, exclusively derived from this premix H based on resorcinol and on resorcinols substituted with alkyl groups, as polyhydroxybenzene precursors, as in the abovementioned article Preparation of Low-density Aerogels From Technical Mixture of Diphenolic Compounds by A. L. Peikolainen et al.

[0072] The following starting reagents were used: [0073] resorcinol (R) from Acros Organics, 98% pure, [0074] formaldehyde (F) from Acros Organics, 37% pure, [0075] an acid catalyst (C) consisting of hydrochloric acid, [0076] poly(diallyldimethylammonium chloride) (P), 35% pure (dissolved in water W), and [0077] Honeyol (H), sold by the company VKG (Viru Keemia Grupp), which is, in a known manner, a premix of resorcinol R and of alkyl resorcinol derivatives and whose formulation is detailed in table 1 below (the molar mass M of this premix H was determined using the mass fractions of its main ingredients, and a molar mass M of about 121 g/mol.sup.1 was thus obtained).

TABLE-US-00001 TABLE 1 Constituents of the premix H Molar mass Mass fractions named Honeyol (g .Math. mol.sup.1) (%) methyl resorcinols: 124 64.1 4-methyl resorcinol 2.8 5-methyl resorcinol 59.6 2-methyl resorcinol 1.7 dimethyl resorcinols: 138 16.0 2,5-dimethyl resorcinol 8.4 4,5-dimethyl resorcinol 7.6 5-ethyl resorcinol 138 9.8 resorcinol R 110 5.7 monohydroxybenzenes 0.8 not identified 3.6

[0078] These gels G0 to G4 were prepared as follows. Resorcinol R and/or the premix H (R alone for gel G0 not derived from H, R+H for gels G1, G2, G3 and H alone for gel G4 not derived from R) and also the polyelectrolyte P were, in a first stage, dissolved in a container containing water W. Next, after total dissolution of R and/or H and of P, formaldehyde F was added. Each polymer solution obtained was adjusted to the appropriate pH with the acid catalyst C, it being pointed out that all of these operations were performed at room temperature (at about 22 C.).

[0079] In a second stage, each solution obtained was transferred into Teflon molds, which were then placed in an oven at 90 C. for 24 hours to effect the gelation.

[0080] Drying of each hydrogel obtained in a humid chamber at 85 C. with a humidity content of 90% for 24 hours was then performed, followed by drying at 105 C. for 24 hours.

[0081] Table 2 below shows the following ratios for each gel G0 to G4, in addition to the pH measured for each polymer solution obtained by adding the catalyst C: [0082] (R+H)/F is the mole ratio of the resorcinol precursor(s) R and/or premix H (with R+H=R for the aerogel G0 and R+H=H for the aerogel G4) on the formaldehyde precursor F, [0083] H/(R+H) is the mole ratio of the premix precursor H to the resorcinol precursor(s) R and/or premix H (with H=0 for the aerogel G0 and R=0 for the aerogel G4), [0084] (R+H)/W is the mass ratio of the resorcinol precursor(s) R and/or premix H to the water W, and [0085] P denotes the mass fraction of the cationic polyelectrolyte in each aerogel composition G0 to G4.

TABLE-US-00002 TABLE 2 Amounts of reagents/process G0 G1 G2 G3 G4 H/(R + H) 0 0.5 0.5 0.7 1 (R + H)/F 0.5 0.38 0.5 0.38 0.5 (R + H)/W 0.03 0.03 0.03 0.03 0.03 P 0.4% 0.4% 0.4% 0.4% 0.4% pH 1.8 1.8 1.8 1.8 1.8

[0086] As may be seen in table 2, the H/(R+H) mole ratio of the aerogels according to the invention advantageously satisfies 0.5H/(R+H)<1, i.e. HR.

[0087] Table 3 below collates the densities of the aerogels G0 to G4 obtained, their resistances measured at a relative compression of 50% and their heat conductivities measured at 22 C. (with a Neotim conductimeter) according to the hot wire technique.

[0088] The mechanical properties in compression of plates consisting of the aerogels G0 to G4 were measured at 23 C. using a DY35 No.I_62 dynamometer equipped with a 1 kN sensor (I62_02) at a rate of 5 mm/min, up to a maximum deformation of 50% (i.e. for a maximum compression corresponding to 50% of the initial thickness of each plate). Plates 9 mm thick were used for these measurements, which were cut using a cutter so that they had dimensions of about 13 mm13 mm. The real dimensions of each plate were measured with a steel ruler for the calculation of the stresses by means of the Testworks software.

TABLE-US-00003 TABLE 3 Properties of the aerogels G0 G1 G2 G3 G4 Density 0.08 0.11 0.12 0.18 Strength at 50% of 0.14 0.15 0.3 >2 compression (MPa) Heat conductivity 24 24 26 28 (mW .Math. m.sup.1K.sup.1)

[0089] This table 3 shows that the three aerogels according to the invention G1, G2 and G3 prepared from mixtures of resorcinol R and of the premix H containing resorcinol R and resorcinol derivatives have, firstly, thermal superinsulating properties close to that of the aerogel G0 obtained from resorcinol R alone, and, secondly, a better compression strength than that of this control aerogel G0, which makes these aerogels of the invention even better suited to heat insulation in buildings in which they are subjected to high mechanical stresses.

[0090] In particular, the gel G3 according to the invention, which is especially characterized by H/(R+H) and (R+H)/F mole ratios of between 0.6 and 0.8 and between 0.30 and 0.45 approximately, respectively, advantageously has simultaneously a low heat conductivity (less than 30 mW.m.sup.1K.sup.1) and excellent compression strength that is very markedly better than that of the control aerogel G0 (see the ratio close to 15 between the respective strengths of G3 and of G0).

[0091] It should be noted that the aerogel G4 not in accordance with the invention, due to the fact that it was obtained without resorcinol R, broke on drying and could therefore not be characterized, either as regards its density, its compression strength or its heat conductivity.

[0092] It will be noted that the aerogel compositions included in the context of the present invention are not limited to those tested in the three abovementioned examples of gels G1, G2 and G3, but that they may more generally be extended to aerogels derived from a formaldehyde precursor F and from a first unsubstituted polyhydroxybenzene precursor R (e.g. resorcinol or catechol) combined with a premix of a second unsubstituted polyhydroxybenzene precursor R and of alkyl derivatives thereof.