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]
Abstract
45
40
40
35
35
and 1173K, the burn off, the BET surface area, the micropore volume and the mean pore size increased too. The AC
20
allowed us to conclude that the AC obtained from PEEK are thermo resistant. PEEK polymer has never previously
-1
-1
15
/ mmol g
25
a
2.17nm, which are characteristics very important for aqueous phase applications. The thermogravimetric analysis
n / mmol g
prepared at 1173K, with 74% burn off presented a high micropore volume of 1.27 cm3g-1 and a mean pore size of
PK-900
PK-9-12
PK-9-33
PK-9-55
PK-9-65
PK-9-74
30
30
25
PK-9-12
20
PK-9-33
a
PEEK by physical activation with CO2 at different temperatures. As the activation temperature increased, between 873
45
n
A series of activated carbons (AC) with high surface areas and micropore volumes were prepared from granulated
15
PK-9-55
been used before as a precursor for AC production, maybe because of its high cost. However, the collective results
10
10
PK-9-65
confirm that, PEEK is an excellent precursor for preparing activated carbon with a high carbonisation yield, a high
5
5
PK-9-74
micropore volume and surface area and finally, a very high resistance at elevated temperature.
0
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
p/po
3
2,5
2
1,5
1
0,5
0
1
as
Figure 1: N2 adsorption isotherms on AC prepared at 1173K
Figure 2: Alfa-s representation for the N2 adsorption
isotherms on the AC prepared at 1173K
for different activation times
Introduction
carbons with precise textural or chemical properties. As AC applications become more specific, a better control of pore
100
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
120
PET
100
PEEK
80
Weight lost (%)
120
Weight lost (%)
A proper choice of precursor, method of activation and control of processing conditions allows production of activated
60
40
80
PK-9-12
60
PK-9-33
40
PK-9-55
20
20
0
0
PK-9-65
PK-9-74
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.
0
200
400
600
800
0
1000
400
600
800
1000
Temp / ºC
Temp / ºC
Due to its high temperature stability, activated carbon can be reactivated and reused, and it is a logical choice for gas-
Figure 4: Thermograms of the AC with different
Figure 3: Thermograms off PEEK and PET polymers
phase adsorption applications [1].
200
burn off prepared from PEEK by physical
activation with CO2 at 1173K
Experimental
Table 1: Textural characteristics of the AC prepared by physical activation with CO2 at 1173 K
10Kmin-1
AC from PEEK
N2 = 90cm3min-1
CO2 = 90cm3min-1
TGA
Samples
Vs / 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
N2 adsorption
at 77K
Conclusions
Two series of carbonaceous materials were prepared from granulated PEEK by physical activation with CO2 at different
Results presented in table 1
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.
Results and Discussion
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
A series of carbonaceous materials was prepared from granulated PEEK by physical activation with CO2 at different
will be economical.
temperatures. In the temperature range between 873 to 1173K, the carbonisation yields were higher than 50% and as
The collective results confirm that, PEEK is an excellent precursor for preparing activated carbon with a high
the temperature increased, two hours activation provided a burn-off increasing from 0 to 12%. Also a series off AC with
carbonisation yield, a high micropore volume and surface area and finally, a very high resistance to elevated
different burn-offs (from 12 to 74%) was prepared at 1173K. Two hours off activation at 1173K provide an AC with a
temperature.
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
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?
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.
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.