Isabel P.P. Cansado, Manuela Ribeiro Carrott, Peter J.M. Carrott, João M.V. Nabais, and Filipa...
1
Isabel P.P. Cansado , Manuela Ribeiro Carrott, Peter J.M. Carrott, João M.V. Nabais, and Filipa A.M.M. Gonçalves Centro de Química de Évora e Departamento de Química, Universidade de Évora, Colégio Luís António Verney, 7000-671 Évora, PORTUGAL [email protected] Conclusions Two series of carbonaceous materials were prepared from granulated PEEK by physical activation with CO 2 at different temperatures and for different activation times. In the series prepared at 1173K, the mean pore size varies from 0.88 to 2.17nm, and the micropore volume varies from 0.33 to 1.27 cm 3 g -1 . All AC present a very high temperature resistance which is a major advantage when considering gas adsorption processes at high temperatures or when the adsorbent regeneration is crucial to ensuring that the adsorption process will be economical. The collective results confirm that, PEEK is an excellent precursor for preparing activated carbon with a high carbonisation yield, a high micropore volume and surface area and finally, a very high resistance to elevated temperature. Samples V s / cm 3 g -1 A ext / m 2 g -1 V DR / cm 3 g -1 E o / kJ mol -1 d p / nm PK-6-0 -- -- -- -- -- PK-8-5 0.15 9.9 0.14 19.10 1.41 PK-9-12 0.33 8.3 0.31 23.65 0.88 PK-9-33 0.46 31.5 0.46 19.94 1.27 PK-9-55 0.89 34.5 0.79 17.41 1.80 PK-9-65 1.07 72.4 0.85 17.34 1.82 PK-9-74 1.27 38.6 0.99 16.39 2.17 Abstract A series of activated carbons (AC) with high surface areas and micropore volumes were prepared from granulated PEEK by physical activation with CO 2 at different temperatures. As the activation temperature increased, between 873 and 1173K, the burn off, the BET surface area, the micropore volume and the mean pore size increased too. The AC prepared at 1173K, with 74% burn off presented a high micropore volume of 1.27 cm 3 g -1 and a mean pore size of 2.17nm, which are characteristics very important for aqueous phase applications. The thermogravimetric analysis allowed us to conclude that the AC obtained from PEEK are thermo resistant. PEEK polymer has never previously been used before as a precursor for AC production, maybe because of its high cost. However, the collective results confirm that, PEEK is an excellent precursor for preparing activated carbon with a high carbonisation yield, a high micropore volume and surface area and finally, a very high resistance at elevated temperature. Introduction A proper choice of precursor, method of activation and control of processing conditions allows production of activated carbons with precise textural or chemical properties. As AC applications become more specific, a better control of pore size distribution is required and the challenge is to prepare tailored ACs with optimised properties, such as surface area, micropore volume, pore size distribution and surface functionality. The formation of the porous structure by physical activation is achieved by elimination of a large amount of internal carbon mass and high-porosity carbons can be obtained only at high extents of char burn-off. An important advantage of the chemical process is that the yield tends to be greater since carbon burn-off is not required. In this work the carbonisation yield at different temperatures was always higher than 50%. For some applications the activated carbon shape and the grain size distribution of the particles, for example, are very important, but for others the high temperature resistance remains the most important property of the adsorbent used. Due to its high temperature stability, activated carbon can be reactivated and reused, and it is a logical choice for gas-phase adsorption applications [1]. Table 1: Textural characteristics of the AC prepared by physical activation with CO2 at 1173 K References [1] Ania CO, Menendez, JA, Parra JB and Pis JJ. Microwave-induced regeneration of activated carbons polluted with phenol. A comparison with conventional thermal regeneration. Carbon, Carbon 2004;42:1383-1387. [2] Carrott PJM, Mourão PAM, Carrott MMLR. Controlling the micropore size of activated carbons for the treatment of fuels and combustion gases Appl. Surf. Sci. 2006;252:5953-56. [3]Van der Vegt AK. From Polymers to Plastics. Delft: VSSD, 2006. p. 255-63. [4] http://www.zeusinc.com/pdf/Zeus_PEEK.pdf , PEEK vs. Metal: Why Plastic is Better? Acknowledgements This work was supported by the Fundação para a Ciência e a Tecnologia (Portugal) with national and European funding (FEDER) (Plurianual Finance Project Centro de Química de Évora (619)).The authors are grateful to the Fundação para a Ciência e a Tecnologia (Portugal) and Flupol APL-Técnicas de Polímeros Fluorados Lda,- Portugal for the provision of the granulated PEEK. 0 5 10 15 20 25 30 35 40 45 0 0,5 1 1,5 2 2,5 3 a s n a / mmol g -1 PK-9-12 PK-9-33 PK-9-55 PK-9-65 PK-9-74 Figure 1: N 2 adsorption isotherms on AC prepared at 1173K for different activation times 0 5 10 15 20 25 30 35 40 45 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 p/p o n a / m m ol g -1 PK -900 PK-9-12 PK-9-33 PK-9-55 PK-9-65 PK-9-74 Figure 2: Alfa-s representation for the N 2 adsorption isotherms on the AC prepared at 1173K Results and Discussion A series of carbonaceous materials was prepared from granulated PEEK by physical activation with CO 2 at different temperatures. In the temperature range between 873 to 1173K, the carbonisation yields were higher than 50% and as the temperature increased, two hours activation provided a burn-off increasing from 0 to 12%. Also a series off AC with different burn-offs (from 12 to 74%) was prepared at 1173K. Two hours off activation at 1173K provide an AC with a micropore volume of 0.33cm 3 g -1 , which is already a comparatively high value for an AC with narrow micropores only[2]. That with 9 hours activation (74% burn off) presents a micropore volume of 1.27cm 3 g -1 which is an extremely high value. PEEK is referred to as one of the few polymers that can be considered for use as a true metal replacement for high temperature applications [3,4]. The study of the thermal stability of the two precursors used in our laboratory, PET and PEEK are presented in figure 3. PET degradation started at a temperature around 673K and PEEK degradation started only at 823K. Figure 4 illustrates the thermograms obtained on the AC, with different burn-off, prepared at 1173K. At a lower temperature the mass loss is around 5%, then the mass of all the AC remains almost stable until a temperature higher Experimental AC from PEEK TGA N 2 adsorption at 77K Tf = 117 3K 2 g PEEK Results presented in table 1 N 2 = 90cm 3 min -1 CO 2 = 90cm 3 min -1 10Kmin -1 0 20 40 60 80 100 120 0 200 400 600 800 1000 Tem p /ºC Weight lost (%) PK-9-12 PK-9-33 PK-9-55 PK-9-65 PK-9-74 Figure 3: Thermograms off PEEK and PET polymers Figure 4: Thermograms of the AC with different burn off prepared from PEEK by physical activation with CO 2 at 1173K 0 20 40 60 80 100 120 0 200 400 600 800 1000 Tem p /ºC Weight lost (%) PET PEEK
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Transcript of Isabel P.P. Cansado, Manuela Ribeiro Carrott, Peter J.M. Carrott, João M.V. Nabais, and Filipa...
Isabel P.P. Cansado, Manuela Ribeiro Carrott, Peter J.M. Carrott, João M.V. Nabais, and Filipa A.M.M. Gonçalves Centro de Química de Évora e Departamento de Química, Universidade de Évora,Colégio Luís António Verney, 7000-671 Évora, [email protected]
Conclusions
Two series of carbonaceous materials were prepared from granulated PEEK by physical activation with CO2 at different
temperatures and for different activation times. In the series prepared at 1173K, the mean pore size varies from 0.88 to
2.17nm, and the micropore volume varies from 0.33 to 1.27 cm3g-1.
All AC present a very high temperature resistance which is a major advantage when considering gas adsorption
processes at high temperatures or when the adsorbent regeneration is crucial to ensuring that the adsorption process
will be economical.
The collective results confirm that, PEEK is an excellent precursor for preparing activated carbon with a high
carbonisation yield, a high micropore volume and surface area and finally, a very high resistance to elevated
temperature.
Samples Vs / cm3g-1 Aext / m2g-1 VDR / cm3g-1 Eo / kJ mol-1 dp / nm
PK-6-0 -- -- -- -- --
PK-8-5 0.15 9.9 0.14 19.10 1.41
PK-9-12 0.33 8.3 0.31 23.65 0.88
PK-9-33 0.46 31.5 0.46 19.94 1.27
PK-9-55 0.89 34.5 0.79 17.41 1.80
PK-9-65 1.07 72.4 0.85 17.34 1.82
PK-9-74 1.27 38.6 0.99 16.39 2.17
Abstract
A series of activated carbons (AC) with high surface areas and micropore volumes were prepared from granulated
PEEK by physical activation with CO2 at different temperatures. As the activation temperature increased, between 873
and 1173K, the burn off, the BET surface area, the micropore volume and the mean pore size increased too. The AC
prepared at 1173K, with 74% burn off presented a high micropore volume of 1.27 cm3g-1 and a mean pore size of
2.17nm, which are characteristics very important for aqueous phase applications. The thermogravimetric analysis
allowed us to conclude that the AC obtained from PEEK are thermo resistant. PEEK polymer has never previously
been used before as a precursor for AC production, maybe because of its high cost. However, the collective results
confirm that, PEEK is an excellent precursor for preparing activated carbon with a high carbonisation yield, a high
micropore volume and surface area and finally, a very high resistance at elevated temperature.
Introduction
A proper choice of precursor, method of activation and control of processing conditions allows production of activated
carbons with precise textural or chemical properties. As AC applications become more specific, a better control of pore
size distribution is required and the challenge is to prepare tailored ACs with optimised properties, such as surface
area, micropore volume, pore size distribution and surface functionality. The formation of the porous structure by
physical activation is achieved by elimination of a large amount of internal carbon mass and high-porosity carbons can
be obtained only at high extents of char burn-off. An important advantage of the chemical process is that the yield tends
to be greater since carbon burn-off is not required. In this work the carbonisation yield at different temperatures was
always higher than 50%.
For some applications the activated carbon shape and the grain size distribution of the particles, for example, are very
important, but for others the high temperature resistance remains the most important property of the adsorbent used.
Due to its high temperature stability, activated carbon can be reactivated and reused, and it is a logical choice for gas-
phase adsorption applications [1].
Table 1: Textural characteristics of the AC prepared by physical activation with CO2 at 1173 K
References [1] Ania CO, Menendez, JA, Parra JB and Pis JJ. Microwave-induced regeneration of activated carbons polluted with phenol. A comparison with conventional thermal regeneration. Carbon, Carbon 2004;42:1383-1387.[2] Carrott PJM, Mourão PAM, Carrott MMLR. Controlling the micropore size of activated carbons for the treatment of fuels and combustion gases Appl. Surf. Sci. 2006;252:5953-56.[3]Van der Vegt AK. From Polymers to Plastics. Delft: VSSD, 2006. p. 255-63.[4] http://www.zeusinc.com/pdf/Zeus_PEEK.pdf, PEEK vs. Metal: Why Plastic is Better?
AcknowledgementsThis work was supported by the Fundação para a Ciência e a Tecnologia (Portugal) with national and European funding (FEDER) (Plurianual Finance Project Centro de Química de Évora (619)).The authors are grateful to the Fundação para a Ciência e a Tecnologia (Portugal) and Flupol APL-Técnicas de Polímeros Fluorados Lda,- Portugal for the provision of the granulated PEEK.
0
5
10
15
20
25
30
35
40
45
0 0,5 1 1,5 2 2,5 3
as
na / mmo
l g-1
PK-9-12
PK-9-33
PK-9-55
PK-9-65
PK-9-74
Figure 1: N2 adsorption isotherms on AC prepared at 1173K
for different activation times
0
5
10
15
20
25
30
35
40
45
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
p/po
na / m
mol
g-1
PK-900PK-9-12PK-9-33PK-9-55PK-9-65PK-9-74
Figure 2: Alfa-s representation for the N2 adsorption isotherms on the AC prepared at 1173K
Results and Discussion
A series of carbonaceous materials was prepared from granulated PEEK by physical activation with CO2 at different
temperatures. In the temperature range between 873 to 1173K, the carbonisation yields were higher than 50% and as
the temperature increased, two hours activation provided a burn-off increasing from 0 to 12%. Also a series off AC with
different burn-offs (from 12 to 74%) was prepared at 1173K. Two hours off activation at 1173K provide an AC with a
micropore volume of 0.33cm3g-1, which is already a comparatively high value for an AC with narrow micropores only[2].
That with 9 hours activation (74% burn off) presents a micropore volume of 1.27cm3g-1 which is an extremely high
value. PEEK is referred to as one of the few polymers that can be considered for use as a true metal replacement for
high temperature applications [3,4]. The study of the thermal stability of the two precursors used in our laboratory, PET
and PEEK are presented in figure 3. PET degradation started at a temperature around 673K and PEEK degradation
started only at 823K. Figure 4 illustrates the thermograms obtained on the AC, with different burn-off, prepared at
1173K. At a lower temperature the mass loss is around 5%, then the mass of all the AC remains almost stable until a
temperature higher than 873K and at 1273K, all AC lost only between 10 and 20% of the initial mass.
Experimental
AC from PEEK
TGAN2 adsorption
at 77K
Tf = 1173K
2 g PEEK
Results presented in table 1
N2 = 90cm3min-1
CO2 = 90cm3min-1
10Kmin-1
0
20
40
60
80
100
120
0 200 400 600 800 1000
Temp / ºC
Weigh
t lost
(%)
PK-9-12
PK-9-33
PK-9-55
PK-9-65
PK-9-74
Figure 3: Thermograms off PEEK and PET polymers Figure 4: Thermograms of the AC with different
burn off prepared from PEEK by physical
activation with CO2 at 1173K
0
20
40
60
80
100
120
0 200 400 600 800 1000
Temp / ºC
Weigh
t lost
(%)
PET
PEEK
