Rapid, non-pyrolytic method of making activated carbon
High-speed formation of char, useful as a precursor to activated carbon, is produced by a combination of cellulosic material and an acid solution both preheated close to the steam temperature and then mixed. The rapid endothermic reaction rapidly chars the cellulosic material driving excess water away as steam and minimizing tar formation.
1. A method of carbonizing cellulosic materials comprising the steps of:
(a) granulizing the cellulosic material;
(b) heating the cellulosic material to above the steam point;
(c) combining the heated cellulosic material with a heated liquid acid solution in a weight ratio of at least 0.5:1 liquid acid to cellulosic material to create a mixture at a temperature above a steam point to strip hydroxyl groups from the cellulosic material in a catalytic reaction with the heated acid and to outgas resulting water as steam to produce a low water content char; and
(d) washing the char to separate out a liquid acid solution and concentrating the solution for use again in step (c).
2. The method of claim 1 further including the step of activating the char at high temperatures to produce activated carbon.
3. The method of claim 1 wherein the heated liquid acid solution is heated to temperatures no less than 80 degrees Celsius.
4. The method of claim 3 wherein the cellulosic material at step (b) is heated to no less than 120 degrees Celsius.
5. The method of claim 1 wherein the heated liquid acid solution includes sulfuric acid and water.
6. The method of claim 5 wherein the heated liquid acid solution further includes phosphoric acid.
7. The method of claim 6 wherein the acid of the heated liquid acid solution is 70 to 90 percent by volume sulfuric acid and 10 to 30 percent by volume phosphoric acid.
8. The method of claim 5 wherein the heated liquid acid solution further includes a metallic salt.
9. The method of claim 1 wherein the granularizing provides particles having at least one dimension of substantially less than four millimeters.
10. The method of claim 1 further including the step of trapping the steam in a condenser for reuse in the step of washing.
11. The method of claim 1 wherein step (c) is conducted in a vessel freely communicating with the atmosphere.
12. The method of claim 1 further including the step of activating the char using steam or carbon dioxide to form activated carbon.
13. The method of claim 12 wherein the step of activating the char heats the char with microwave energy.
14. The method of claim 1 wherein the liquid acid solution at step (d) is sent to a reclaimer unit to recover the liquid acid solution to be heated at step (c).
15. A method of carbonizing cellulosic materials comprising the steps of:
(a) granulizing the cellulosic material;
(b) heating the cellulosic material to above the steam point; and
(c) combining the heated cellulosic material with a heated liquid acid solution in a weight ratio of at least 0.5:1 liquid acid to cellulosic material to create a mixture at a temperature above a steam point to strip hydroxyl groups from the cellulosic material in a catalytic reaction with the heated acid and to outgas resulting water as steam to produce a low water content char;
wherein the heated liquid acid solution includes sulfuric acid, water and a metallic salt.