Method of making modified activated carbon
A process for making modified activated carbon from an activated carbon substrate. The activated carbon substrate is pre-treated to make an exposed surface of the activated carbon substrate substantially hydrophilic, coated with a carbon precursor to form a coated activated carbon, and then the coated activated carbon substrate is heated to carbonize the carbon precursor to from the modified activated carbon. The modified activated carbon comprises a uniform porous carbon membrane formed on an exposed surface of the activated carbon substrate. The carbon membrane can mediate the absorption and/or adsorption kinetics of the activated carbon substrate. The modified activated carbon, which can be incorporated into one or more components of a cigarette, can selectively remove gaseous constituents from mainstream smoke during smoking.
1. A process for making modified activated carbon, said modified activated carbon comprising an activated carbon substrate and a uniform porous carbon membrane formed on an exposed surface of the activated carbon substrate, the process comprising:
(i) providing an activated carbon substrate;
(ii) pre-treating the activated carbon substrate to make an exposed surface of the activated carbon substrate substantially hydrophilic;
(iii) coating the pre-treated activated carbon substrate with a carbon precursor to form a coated activated carbon substrate; and
(iv) heating the coated activated carbon substrate in an oxidizing atmosphere and at a temperature of from about 150° C. to 400° C. to carbonize the carbon precursor to form the uniform porous carbon membrane,
wherein the carbon membrane has an average thickness having a standard deviation that is less than about 25% of the average thickness and the carbon membrane has an average thickness ranging from about 1 micron to 0.1 mm.
2. The process of claim 1 , wherein the activated carbon substrate is a substrate selected from the group consisting of beads, granules and fibers and/or the activated carbon substrate has an average particle size of from about 100 microns to 5 mm or from about 200 microns to 2 mm.
3. The process of claim 1 , wherein the activated carbon substrate has an average pore size of less than about 500 Angstroms, the activated carbon substrate has a pore size distribution comprising greater than about 20% micropores and fewer than about 80% mesopores and/or the activated carbon substrate has an average surface area of greater than 50 m 2 /g or greater than 200 m 2 /g.
4. The process of claim 1 , wherein the pre-treating comprises spraying the activated carbon substrate with and/or immersing the activated carbon substrate in a solution comprising from about 1 to 99 wt. % surfactant wherein the surfactant optionally comprises cetyltrimethylammonium chloride and/or the solution optionally comprises from about 1 to 25 wt. % surfactant.
5. The process according to claim 1 , further comprising drying the activated carbon substrate at a temperature of less than about 120° C. prior to coating and/or further comprising drying the coated activated carbon substrate at a temperature of less than about 120° C. prior to carbonizing.
6. The process according to claim 1 , wherein the coating comprises spraying the activated carbon substrate with and/or immersing the activated carbon substrate in a solution comprising the carbon precursor, the solution optionally comprising from about 1 to 99 wt. % carbon precursor or from about 20 to 60 wt. % carbon precursor.
7. The process according to claim 1 , wherein the carbon precursor is selected from the group consisting of saccharides, disaccharides, polysaccharides, fructose and ethyl cellulose.
8. The process of claim 1 , wherein the coating is carried out to provide from about 1 to 150% by weight of the carbon precursor in and/or on the activated carbon substrate or the coating is carried out to provide from about 20 to 80% by weight of the carbon precursor in and/or on the activated carbon substrate.
9. The process of claim 1 , wherein the coating is carried out without heating the activated carbon substrate or the coated activated carbon substrate is carbonized at a temperature of from about 150° C. to 400° C. to form the carbon membrane.
10. The process of claim 1 , wherein the modified activated carbon has an average surface pore size that is at least 10% less than or at least 25% less than the average surface pore size of the activated carbon substrate and/or the modified activated carbon has an average surface area of at least 50 m 2 /g or at least 200 m 2 /g.
11. The process of claim 1 , wherein the carbon membrane covers at least 80% of the exposed surface of the activated carbon substrate.
12. The process of claim 1 , wherein the modified activated carbon has an average surface pore size that is at least 10% less than the average surface pore size of the activated carbon substrate.
13. The process of claim 1 , wherein the pre-treating comprises spraying the activated carbon substrate with a solution comprising from about 1 to 25 wt. % cetyltrimethylammonium chloride.
14. The process according to claim 1 , further comprising drying the coated activated carbon substrate at a temperature of less than about 120° C. prior to carbonizing.
15. The process according to claim 1 , wherein the coating comprises spraying the activated carbon substrate with a solution comprising the carbon precursor, the solution comprising about 20 to 60 wt. % carbon precursor.
16. The process according to claim 1 , wherein the pre-treating consists of treating the activated carbon substrate with a solution or emulsion consisting of a surfactant and a solvent.