Polymer-monolith pre-oxidation to improve shape retention during subsequent heat treatment, and monolith produced
High purity carbon sorbent monoliths, particularly effective for the removal of trace-contaminants such as ammonia, formaldehyde, and methyl mercaptan from a gas flow, are fabricated by 3D-printing polymer monoliths, pre-oxidizing them in a flow of air at a temperature below the melting point of the polymer precursor, carbonizing them, and subsequently activating them to a weight loss of about 20 percent. The pre-oxidation step effectively prevents polymer-monolith swelling and melting during carbonization.
1. A method for the production of a carbon sorbent monolith for removing at least one gas from a gaseous environment in which the at least one gas is contained, comprising the steps:
(a) producing a shaped polymer monolith using 3-D printing of a polymer precursor consisting essentially of polyether ether ketone (PEEK);
(b) pre-oxidizing said shaped polymer monolith in a flow of an oxidizing gas at a temperature below the melting point of said polymer precursor for a time sufficient to preserve the shape of said polymer monolith during a subsequent carbonizing step;
(c) carbonizing said pre-oxidized shaped polymer monolith of step (b) so as to produce a carbon sorbent monolith by exposure to elevated temperatures in a non-oxidative atmosphere;
and
(d) optionally, activating said carbon sorbent monolith of step (c) by exposure to an oxidizing environment under conditions sufficient to cause a carbon weight loss in said carbon sorbent monolith of at least about 1 weight percent and thereby producing a microporous sorbent monolith with a surface area of at least about 100 m 2 /g, with the majority of pores being smaller than about 2 nm.
2. The method of claim 1 , wherein said pre-oxidizing step (b) is carried out at a temperature at least 3° C. below said melting point of said polymer precursor.
3. The method of claim 1 , wherein said pre-oxidizing step (b) is carried out at a temperature at least 5° C. below said melting point of said polymer precursor.
4. The method of claim 1 wherein said sorbent monolith has a honeycomb cell structure.
5. The method of claim 4 , wherein the walls that define the cells of said honeycomb structure are about 0.10 mm to 1.0 mm thick.
6. The method of claim 1 , wherein said polymer precursor includes reinforcement in the form of fibers, at a fiber content of about 1-20 weight percent, for improved shape retention during said carbonizing step (c) and for enhanced strength.
7. The method of claim 6 , wherein said fibers are carbon fibers.
8. The method of claim 1 , wherein said pre-oxidizing step (b) is carried out in a flow of air.
9. The method of claim 1 , wherein said pre-oxidizing step (b) is carried out at a temperature at least 1° C. below said melting point of said polymer precursor.
10. The method of claim 1 , wherein said time in step (b) sufficient to preserve the shape of said polymer monolith during subsequent carbonizing step (c) is at least about 3 hours.
11. The method of claim 1 , wherein said oxidizing environment in step (d) is selected from the group consisting of air, oxygen, carbon dioxide, steam, ozone, hydrogen peroxide, nitric acid, and mixtures thereof.
12. The method of claim 1 , wherein said oxidizing environment in step (d) comprises air at a temperature in the range of 150° C. to 400° C.
13. The method of claim 12 , wherein said temperature range in step (d) is 250° C. to 325° C.
14. The method of claim 1 , wherein said carbon weight loss of at least about 1 weight percent in said step (d) is at least about 5 weight percent.
15. The method of claim 1 , wherein said carbon weight loss of at least about 1 weight percent in said step (d) is at least about 20 weight percent.