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EP-3752549-B1 - LIGNIN-BASED CARBON FOAMS AND COMPOSITES AND RELATED METHODS

EP3752549B1EP 3752549 B1EP3752549 B1EP 3752549B1EP-3752549-B1

Inventors

  • CAI, ZHIYONG
  • YAN, QIANGU
  • LI, JINGHAO

Dates

Publication Date
20260506
Application Date
20180214

Claims (2)

  1. A method of making a carbon foam, the method comprising: (a) providing a compressed precursor composition by subjecting a precursor composition comprising an amount of at least partially decomposed kraft lignin and an amount of raw kraft lignin to a first pressure in the range of from greater than 0 MPa to 50 MPa for a first time, optionally, while heating the precursor composition to a first temperature, wherein the precursor composition has a mass ratio of raw kraft lignin to at least partially decomposed kraft lignin in the range of from 5:1 to 1:5, further wherein the raw kraft lignin is kraft lignin which has not been exposed to a temperature greater than its T d and/or chemicals capable of facilitating the decomposition of the kraft lignin and the at least partially decomposed kraft lignin has been formed by heating raw kraft lignin to an elevated temperature in a range of from 200 °C to 500 °C under an inert atmosphere and for a time of from 0.5 to 5 hours, and further wherein step (a) is a cold press step and the first time is in the range of from 5 sec to 60 sec or step (a) is a hot press step and the first temperature is in the range of from 150 °C to 300 °C, suitably wherein the first time is in the range of from 5 min to 30 min; (b) providing a porous, decomposed precursor composition by heating the compressed precursor composition to a second temperature in the range of from 450 °C to 700 °C for a second period of time in the range of from 30 min to 60 min while subjecting the compressed precursor composition to a second pressure in the range of from 1 Pa to 10,000 Pa to further decompose the at least partially decomposed kraft lignin and the raw kraft lignin to generate pores within the compressed precursor composition; and (c) providing a carbon foam by heating the porous, decomposed precursor composition to a third temperature for a third time to carbonize, and optionally, to graphitize, the porous, decomposed precursor composition.
  2. The method of claim 1, wherein the at least partially decomposed kraft lignin comprises carbon-encapsulated metal nanoparticles, graphene-encapsulated metal nanoparticles, a graphene-based material, or combinations thereof, optionally, wherein the precursor composition further comprises one or more additives selected from carbon particles, carbon nanoparticles, metal, metal oxide, metal carbide, and combinations thereof.

Description

BACKGROUND Carbon foam is a carbon structure containing open macropores (cells) which are interconnected through carbon walls. Carbon foams have several desirable properties, such as large geometric surface area, low density, high corrosion resistance to chemicals and fire, strong mechanical strength, ultra-high service temperatures, low coefficient of thermal expansion, hydrophobic surfaces, and high thermal and electrical conductivities. There are two categories of carbon foams, graphitic and non-graphitic. Graphitic carbon foams tend to have high thermal and electrical conductivity, but relative lower mechanical strength as compared to non-graphitic carbon foams. Non-graphitic carbon foams are generally higher in mechanical strength, can serve as thermal insulators, and cost far less to manufacture. Several preparation processes have been developed for carbon foam production including blowing carbon precursors followed by carbonization, template carbonization of carbon precursors, compression of exfoliated graphite, and assembly of graphene nanosheets. Blowing of carbon precursors can be divided into two methods including pyrolysis under pressure and adding chemicals (blowing agents) to generate gases. In the pyrolysis technique, the decomposition gases from precursors (like pitches) are kept in a closed vessel, followed by a sudden release of the pressure. For example, a pitch may be heated up to its softening temperature (Ts) in an autoclave and kept for a certain time. The precursor pitch will decompose and release gases or volatile components during heating, resulting in a build-up of pressure of up to a few MPa pressure. After being kept under pressure at a high temperature, the product is cooled down to room temperature and then the pressure is released quickly. Template carbonization is a technique used to control the pore structure of the carbon foam and can create micropores, mesopores and macropores. Polyurethane (PU) foams are usually used as the template in this method. Currently, carbon foams are generally produced by blowing carbon precursors. This is a high cost method requiring high temperature/high pressure reactor systems and is limited in the scope of the size and properties of the carbon foam it can produce. Various feedstocks have been used as the precursors for carbon foam production including various pitches, asphalts, foamed synthetic plastics, coals, and coal extracts. The properties of the carbon foams depend on both the raw material characteristics and the selected process conditions. For example, carbon foams from pitches show good thermal conductivity and low density but poor mechanical strength; coal-based foams have good mechanical strength and higher density, but lower thermal/electrical conductivity. Some carbon foams have been formed from ligninsulfonates and ligninsulfonate/polymer compositions. However, such carbon foams exhibited low density and very low mechanical strength. US2005/085372 discloses a process for the production of an open-cell carbon foam from a metallic salt of a lignosulfonate. The process includes heating the metallic salt of a lignosulfonate from ambient temperature to a maximum temperature, greater than about 250° C., at a rate sufficiently slow as to provide for essentially uniform heating of the lignin derived material. The resultant carbon foam can subsequently be optionally subjected to carbonization or graphitization temperatures as desired. The resultant carbon foam has a regular open-cell structure. "Carbon foam: preparation and application" (Inagaki Michio et al., Carbon, Elsevier Oxford, GB, vol. 87, 9 February 2015, pages 128-152, XP029204866) discloses carbon foams with regular pores and a compressive strength from 13.1 to 98.3 MPa. "A graphite foam reinforced by graphite particles" (Zhu et al., Carbon, Elsevier Oxford, GB, vol. 45, no. 13, 20 October 2007, pages 2547-2550, XP022308237) discloses that additives such as graphite particles can be used to help strengthen carbon foam. SUMMARY Provided are methods for making lignin-based carbon foams. Also provided are the carbon foams and composites made from the carbon foams. In one aspect, methods for making carbon foams are provided comprising: Step (a): providing a compressed precursor composition by subjecting a precursor composition comprising an amount of at least partially decomposed kraft lignin and an amount of raw kraft lignin to a first pressure in the range of from greater than 0 MPa to 50 MPa for a first time, optionally, while heating the precursor composition to a first temperature. The precursor composition has a mass ratio of raw kraft lignin to at least partially decomposed kraft lignin in the range of from 5:1 to 1:5. The raw kraft lignin is kraft lignin which has not been exposed to a temperature greater than its Td and/or chemicals capable of facilitating the decomposition of the kraft lignin and the at least partially decomposed kraft lignin has been formed by heating