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EP-4735380-A1 - PROCESS FOR PREPARING CARBON XEROGELS

EP4735380A1EP 4735380 A1EP4735380 A1EP 4735380A1EP-4735380-A1

Abstract

The present invention refers to an efficient process for preparing a carbon xerogel.

Inventors

  • SCHMIDT, WOLFGANG
  • BILICAN, Abdurrahman

Assignees

  • Studiengesellschaft Kohle gGmbH

Dates

Publication Date
20260506
Application Date
20240625

Claims (14)

  1. 1. Process for the preparing a carbon xerogel, said process comprising the steps of: a) mixing a nucleophilic compound R, selected from melamin, melam, melem, ammeline, 4,6-amino-dihydroxy-1 ,3,5-triazine, aminophenol, diaminobenzene, preferably a mono- or polyhydroxy benzene and any combination thereof, and formaldehyde or an oligomer thereof as compound F in a molar ratio R / F of 0.1 to 1 , preferably of 1 : (1.5 to 2.5), more preferably of 1 : (1.8 to 2.2), and a catalyst in a solvent, being selected from water, a polar organic solvent, preferably a Ci- to C3- aliphatic alcohol, or a mixture thereof forming a reaction solution, where the mass of the nucleophilic compound and formaldehyde to the overall mass of the reaction solution is in the range of 1 to 60 % b.w., preferably in the range of 20 to 50%, and the said catalyst may be an acidic or basic catalyst, b) heating the mixture obtained in step a) in a sealed container to a temperature in the range of 50°C to 250°C, preferably 80°C to 160°C for a period of time in the range of 30 minutes to 24 hours whereby a stable gel is formed, c) heating the gel obtained in step b) for direct carbonisation to a temperature range of 500°C to 3000°C in an oxygen-free atmosphere with a heating rate of 1 to 100 °K/min, preferably 5 to 10 K/min, keeping the gel in said temperature range and atmosphere for a period of time in the range of 10 minutes to 2 hours, and d) bringing the product obtained in step c) to ambient temperature.
  2. 2. The process according to claim 1 wherein a nonpolar organic solvent is added to the reaction solution in step a) and the obtained mixture is stirred for forming an emulsion.
  3. 3. The process according to claim 1 or 2 wherein the sealed container in step b) is an autoclave which is optionally pressurized to 1 to 100 bar.
  4. 4. The process according to any one of claim 1 to 3, wherein the gel obtained in step b) is crushed to a particulate gel before step c)
  5. 5. The process according to any one of claim 1 to 4, wherein the gel obtained in step b) is directly transferred to a carbonization vessel without any further pre-treatment such as drying and/or solvent exchange.
  6. 6. The process according to any one of the preceding claims, wherein said oxygen-free atmosphere in step c) is nitrogen gas, argon gas, ammonia gas, or a mixture thereof.
  7. 7. The process according to any one of the preceding claims, wherein the polyhydroxy benzene is a dihydroxy benzene.
  8. 8. The process according to claim 7, wherein said dihydroxy benzene is selected from the group consisting of resorcinol, catechol, substituted resorcinol, substituted catechol and mixtures thereof.
  9. 9. The process according to claim 8, wherein said dihydroxy benzene is resorcinol.
  10. 10. The process of claim 8, wherein said dihydroxy benzene is a mixture of resorcinol and catechol.
  11. 11. The process according to any one of the preceding claims, wherein the molar ratio of said mono- or polyhydroxy benzene to said formaldehyde is in the range of the benzene compound to formaldehyde of (0.5 to 1) :1, preferably 1 :2.
  12. 12. The process according to any one of the preceding claims, wherein the polyhydroxy benzene to catalyst ratio is in the range of 0.1 to 100.000, preferably 10 to 10.000, and more preferably in the range of 100 to 5.000.
  13. 13. The process according to any one of the preceding claims, wherein said catalyst is sodium carbonate.
  14. 14. The process according to any one of the preceding claims, wherein said oxygen-free atmosphere is a nitrogen atmosphere.

Description

Process for Preparing Carbon Xerogels The present invention refers to an efficient process for preparing a carbon xerogel. Carbon Xerogels are porous carbon materials that lately found application in numerous fields, which are decisive for the ecological transformation of the global economy. The possess very high specific surface areas (SSA), high pore volumes and adjustable pore sizes with pore diameters in the micropore (< 2nm) and mesopore (2-50 nm) range. Their potential use was shown for electrochemical applications in fuel cells, supercapacitors or batteries, and for thermal insulation materials, catalyst supports, and adsorption materials. The high interest in these materials lies in the overall possibility to tune material properties of meso- and microporous carbon for individual applications. The synthesis of resorcinol and formaldehyde to an organic RF gel, as proposed by Pekala (Pekala et al., Journal of Materials Science, 1989, 24(9), 3221-3227), provides an opportunity to tailor the pore and particle sizes of a porous polymer by the variation of pH and dilution of the reaction solution. Such porous polymers can be further converted to conductive and high surface area carbon aerogels (CA) or carbon xerogels (CX) via pyrolysis. In the sol-gel chemistry, the known definition distinguishes gels and foams as follows. A gel is understood as an open-porous solid interpenetrating network whereas foam materials are materials in which one phase encloses a medium in another state of aggregation. Previous work on the field of sol-gel chemistry shows that the template-free sol-gel reaction proceeds either under acidic or basic conditions. Rey-Raap et al. (Rey-Raap et al., Microporous and Mesoporous Materials, 2014, 195, 266-275) showed that the porous properties of RF gels can be controlled by adjusting the pH and educt concentration of the reaction solution. It was shown that different synthesis parameters result in different specific surface areas, pore volumes, and pore size distributions. The formation of porous structures can also be driven by so-called nanocasting approaches where a porous template functions as a mold. After the reactands formed a solid inside the mold the template is removed by heat or by using a base or acid. The remaining solid is the obtained product. Protocols for the synthesis of resorcinol-formaldehyde-Gels using templates were also published. In Kong FM ET AL: "Low-Density Carbonized Resorcinol-Formaldehyde Foams Final Report" (DOE; USDOE, Washington, DC (United States), 4 July 1991 (1991-07-04), XP093109490, DOI: 10.2172/6108157) preparation of foams, based on various formulations of resorcinol-formaldehyde gels, polystyrene- RF gels is disclosed. Similar processes for preparing RF-foams are disclosed in KR 101 232 380 B1 and LI M ET AL: "Correspondence", CARBON, ELSEVIER OXFORD, GB, vol. 37, no. 10, 1 January 1999 (1999-01-01), pages 1645-1647. Since CA and CX are derived from organic polymeric gels with high porosity through a wetchemical sol-gel process, the solvent is still present in the pores after solidification of the sol in a gel. Thermal removal of the liquid phase causes high tension at the interface of the liquid and solid phase (capillary forces). The strong tension can result in collapse of the pore structure of the gel. In order to prevent shrinkage of the material and collapse of the pores, supercritical drying with CO2 or cryo-drying is often used to avoid the tension at the liquid-solid interface. Such processes are rather slow and the synthesis of respective carbon materials, denoted as CA, is very time-intensive. Even though CA are among the materials with highest known pore volumes and specific surface area, their broad application is restricted by their time- and labour-intensive synthesis. An alternative to CA are CX, where the organic precursor material is dried at ambient conditions. Even though significant parts of the porous properties of the gels can be deteriorated by the ambient drying method, CX still possess extraordinary porous properties and are thus promising material for several applications. Furthermore, the reduction of pore sizes upon drying can be counterbalanced by the adjustment of the synthesis parameters. The loss of porosity can be reduced by the use of additives or pore size modifiers. CX present a greater potential for commercial application than their supercitically dried counterparts, because of their simplified synthesis protocols. Nonetheless, the commercial use of CX is still challenged by following problems: 1 . High cost of monomers of the organic polymer 2. Still quire long synthesis times 3. Cost and energy intensive processes (Gelation, Curing, Drying, Carbonisation) Replacement of resorcinol by different phenolic compounds proved problematic as the different phenolic substituents were less reactive than resorcinol. Phenol shows a 15 times lower reactivity than resorcinol. Consequently, a stronger basic catalyst is