Production of carbon foam from coals
Methods for the production of carbon foam from swelling coals that do not require the use of high process pressures, oxidized coal, devolatized coal, or high-strength, foam expansion confining molds are described. In some embodiments, a comminuted swelling bituminous coal is heated to a first elevated temperature sufficient to result in the coal particles softening and melting together to form a substantially homogeneous open cell plastic carbon material. The substantially homogeneous open cell plastic carbon material may then be heated to a second elevated temperature at a slow rate to form carbon foam. In some embodiments, the resulting carbon foam may be heated to a higher third elevated temperature. The resulting carbon foam may be subsequently heated to elevated temperatures as great as 3200° C. or more.
1. A method for producing carbon foam, the method comprising the steps of:
heating comminuted coal that has not been devolatized or subjected to oxidizing pre-treatment to a first elevated temperature sufficient to form a substantially homogeneous, plastic, open cell carbon material, wherein said comminuted coal forms a coke when heated to about 510° C. at a rate of about 2° C./min; and
heating said substantially homogeneous, plastic, open cell carbon material to a second elevated temperature sufficient to form a carbon foam, wherein the carbon foam is substantially free to expand in at least one direction during formation, and wherein said method is conducted at about 0 psig.
2. The method of claim 1 , wherein said heating is conducted in a substantially non-oxidizing atmosphere.
3. The method of claim 1 , wherein said second elevated temperature is a temperature at which the carbon foam has expanded to an essentially maximum volume and formed an open cell, nonplastic, carbon foam.
4. The method of claim 1 , further comprising the step of heating of said carbon foam to a third elevated temperature, wherein said third elevated temperature is a temperature greater than said second elevated temperature.
5. The method of claim 4 , wherein said third elevated temperature is a temperature greater than about 450° C. and less than about 700° C.
6. The method of claim 4 , wherein said third elevated temperature is a temperature greater than about 700° C.
7. The method of claim 4 , further comprising the step of heating of said carbon foam to a temperature greater than said third elevated temperature.
8. The method of claim 1 , wherein said first elevated temperature is above about 340° C.
9. The method of claim 1 , wherein said second elevated temperature is at least about 20° C. greater than said first elevated temperature.
10. The method of claim 1 , further comprising the steps of:
placing comminuted coal in a container to form a coal bed; and
positioning a coal cover on a top surface of the coal bed.
11. A method for producing carbon foam, the method comprising the steps of heating comminuted coal that has not been devolatized or subjected to oxidizing pre-treatment to a temperature and at a rate sufficient to form carbon foam having a density ranging from about 0.1 to about 0.8 g/cc, wherein said heating is conducted in an essentially inert atmosphere having a pressure of about 0 psig, wherein said comminuted coal forms a coke when heated to about 510° C. at a rate of about 2° C./min, and wherein said carbon foam is substantially free to expand in at least one direction during formation of carbon foam.