Method for producing activated carbon

Abstract

A method is for producing activated carbon. The method includes: a) mixing a carbonaceous precursor with chemically activating agents to obtain a feedstock mixture; b) producing activated carbon by heating the feedstock mixture under the atmosphere of a physically activating gas; and c) performing suitable post-activation treatment of the produced activated carbon. Step a) includes in sequence the sub-steps of: i. addition of a first chemically activating agent to obtain an impregnated precursor; and ii. addition of a second chemically activating agent to obtain the feedstock mixture. An activated carbon species is obtainable by the method. The activated carbon species may thus be tuned to have a pore size distribution optimized for use in a carbon electrode.

Claims

1. A method for producing activated carbon, said method comprising the steps of: a. mixing a carbonaceous precursor with chemically activating agents to obtain a feedstock mixture; b. producing activated carbon by heating the feedstock mixture under the atmosphere of a physically activating gas; and c. performing post-activation treatment of the produced activated carbon via at least one of washing, drying or grinding, wherein step a) comprises in sequence the sub-steps of: i. addition of a first chemically activating agent to obtain an impregnated precursor; and ii. addition of a second chemically activating agent to obtain the feedstock mixture; wherein the first chemically activating agent is selected from the group consisting of MgCl.sub.2, AlCl.sub.3, CaCl.sub.2, FeCl.sub.3, ZnCl.sub.2, H.sub.3PO.sub.4, P.sub.2O.sub.5 and H.sub.2SO.sub.4, and wherein the second chemically activating agent is selected from the group consisting of K.sub.2CO.sub.3, Na.sub.2CO.sub.3, Li.sub.2CO.sub.3, KHCO.sub.3, NaHCO.sub.3, LiHCO.sub.3, KOH, NaOH, LiOH and benzyl potassium (C.sub.7H.sub.7K).

2. The method according to claim 1, wherein a mass ratio of the carbonaceous precursor to the first chemically activating agent ranges from 1:10 to 1000:1.

3. The method according to claim 1, wherein the carbonaceous precursor and the first chemically activating agent are mixed with assistance of a solvent.

4. The method according to claim 1, wherein the mass ratio of the impregnated precursor and the second chemically activating agent ranges from 1:10 to 1000:1.

5. The method according to claim 1, wherein the feedstock mixture is introduced into a reactor through a batch feed process.

6. The method according to claim 1, wherein the feedstock mixture is introduced into a reactor through a continuous feed process.

7. The method according to claim 1, wherein the physically activating gas is selected from the group consisting of H.sub.2O, H.sub.2, O.sub.2, CO.sub.2, SO.sub.2, SO.sub.3, and NH.sub.3.

8. The method according to claim 1, wherein the physically activating agent is introduced into the activation reactor after heating of said activation reactor.

9. The method according to claim 1, wherein heating is carried out at a temperature ranging from 400 to 1500° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

(2) FIG. 1 Shows a diagram of the pore size distribution (presented as dV/dD, i.e. the total volume per unit mass of pores having a characteristic pore size) of the produced activated carbon of example 1 with H.sub.3PO.sub.4 and C.sub.7H.sub.7K as chemically activating agents and ammonia as physically activating agent according to the invention;

(3) FIG. 2 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 2;

(4) FIG. 3 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 3;

(5) FIG. 4 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 4;

(6) FIG. 5 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 5;

(7) FIG. 6 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 6;

(8) FIG. 7 Shows a diagram of the pore size distribution of the produced activated carbon from the method described in example 7; and

(9) FIG. 8 Shows a charge/discharge curve of a supercapacitor fabricated using activated carbon produced according to the invention as electrode and ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate as electrolyte.

DETAILED DESCRIPTION OF THE DRAWINGS

Examples

(10) In example 1, 10 g pine wood sawdust as carbonaceous precursor is impregnated with 30 ml 1 M H.sub.3PO.sub.4 aqueous solution as a first chemically activating agent, followed by drying at 120° C. for 12 hours in an oven to form an impregnated precursor. Afterwards, 2 g C.sub.7H.sub.7K as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 900° C. at a heating rate of 5° C./min, and dwelled for 2 hours under an ammonia atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the activated carbon is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2000 m.sup.2/g) and favourable pore size distribution, dominated by small micropores and small mesopores as seen in FIG. 1. A symmetrical supercapacitor fabricated by using this activated carbon as electrode materials and ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF.sub.4) as electrolyte shows a high specific capacitance of about 190 F/g (calculated from the charge-discharge curve shown in FIG. 8).

(11) In example 2, 10 g pine wood sawdust as carbonaceous precursor is impregnated with 30 ml 1 M ZnCl.sub.2 aqueous solution as a first chemically activating agent before drying at 120° C. for 12 hours in an oven to form an impregnated precursor. Afterwards, 10 g KOH as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 900° C. at a heating rate of 10° C./min, and dwelled for 1 hour under a CO.sub.2 atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2000 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores as seen in FIG. 2).

(12) In example 3, 10 g waste newspaper as carbonaceous precursor is impregnated with 30 ml 0.5 M ZnCl.sub.2 aqueous solution as a first chemically activating agent before drying at 120° C. for 12 hours in an oven to form an impregnated precursor. Afterwards, 5 g NaOH as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 800° C. at a heating rate of 10° C./min, and dwelled for 1 hour under an ammonia atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2200 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores seen in FIG. 3).

(13) In example 4, 10 g waste newspaper as carbonaceous precursor is mixed with 20 g P.sub.2O.sub.5 as a first chemically activating agent by physical grinding to form an impregnated precursor. Afterwards, 5 g KOH as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 750° C. at a heating rate of 5° C./min, and dwelled for 2 hours under a CO.sub.2 atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2000 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores seen in FIG. 4).

(14) In example 5, 10 g pine wood sawdust as carbonaceous precursor is impregnated with 30 ml 1 M ZnCl.sub.2 aqueous solution as a first chemically activating agent before drying at 120° C. for 12 hours in an oven to form an impregnated precursor. Afterwards, 5 g K.sub.2CO.sub.3 as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 900° C. at a heating rate of 10° C./min, and dwelled for 2 hours under a CO.sub.2 atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2000 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores seen in FIG. 5).

(15) In example 6, 10 g polyaniline powder as carbonaceous precursor is mixed with 5 g P.sub.2O.sub.5 as a first chemically activating agent by physical grinding to form an impregnated precursor. After drying for 12 hours at 120° C., 5 g K.sub.2CO.sub.3 as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a tube furnace, heated to 900° C. at a heating rate of 10° C./min, and dwelled for 2 hours under a steam atmosphere as a physically activating agent, after which the tube furnace is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2300 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores seen in FIG. 6).

(16) In example 7, 10 g graphene oxide as carbonaceous precursor is mixed with 20 g ZnCl.sub.2 as a first chemically activating agent by physical grinding to form an impregnated precursor. After drying for 12 hours at 120° C., 10 g KOH as a second chemically activating agent is grinded physically and homogeneously with the impregnated precursor to form a feedstock mixture. The feedstock mixture is thereafter introduced into a microwave oven and heated at a power of 600 W for 20 min under an ammonia atmosphere as a physically activating agent, after which the material is cooled down to ambient temperature under N.sub.2 atmosphere. The activation is operated under atmospheric pressure. As post-activating treatment, the obtained product is washed with 1 M HCl and hot water, and then dried in an oven. The obtained activated carbon exhibits a high specific surface area (>2200 m.sup.2/g) and favourable pore size distribution (dominated by small micropores and small mesopores seen in FIG. 7).

(17) In example 8, an optimised electrode, based on activated carbon produced by the activation method disclosed within this application, is fabricated by combining the activated carbon with conductive carbon black as a conductive additive and polytetrafluoroethylene (PTFE) as a binder. A powder mixture comprising 60-90 wt % activated carbon, 5-20 wt % carbon black, and 5-20 wt % PTFE is rolled and pressed to form a carbon-based electrode with a thickness in the range of about 40-400 micrometers. A supercapacitor is assembled by using the carbon-based electrode as electrode and ionic liquid as electrolyte. The charge-discharge performance of a supercapacitor produced by this method is shown in FIG. 8.

(18) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

(19) The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.