Interaction between Fe and Cl2 in the bed of graphitized carbon black

Article abstract of DOI:10.1023/A:1013122313497

A possible route to remove Fe catalyst from graphitized carbon black synthesized in Boudouard's reaction is employment of gaseous chlorine in role of carrier. This process was explored by means of DTA method using the equipment designed in the laboratory. Obtained results demonstrated the complexity of processes occurring in systems containing Fe, C and Cl₂. Reactions in the system are highly influenced by the geometry of reacting solids. Process of FeCl₃ intercalation between graphite layers was observed analyzing DTA curves. The amount of Fe in the raw product of Boudouard's reaction was determined during the process of chlorination. Obtained results indicate that Cl₂ stream does not remove all the Fe even at high temperatures and prolonged chlorinating time.

Full text of DOI:10.1023/A:1013122313497

Journal of Thermal Analysis and Calorimetry, Vol. 66 (2001) 371� 37ꢀ
INTERACTION BETWEEN Fe AND Cl IN THE BED OF
2
GRAPHITIZED CARBON BLACK
J. Barkauskas, V. SamanaviŁiñtÅ and D. U�davinienÅ
Department of General and Inorganic Chemistry, Vilnius University, LT-2734 Vilnius, Lithuania
(
Received December 5, 2000; in revised form June 22, 2001)
Abstract
A possible route to remove Fe catalyst from graphitized carbon black synthesized in Boudouard’s re-
action is employment of gaseous chlorine in role of carrier. This process was explored by means of
DTA method using the equipment designed in the laboratory. Obtained results demonstrate the com-
plexity of processes occurring in systems containing Fe, C and Cl
highly influenced by the geometry of reacting solids. Process of FeCl
ite layers was observed analyzing DTA curves. The amount of Fe in the raw product of Boudouard’s
2
. Reactions in the system are
3
intercalation between graph-
reaction was determined during the process of chlorination. Obtained results indicate that Cl
2
stream
does not remove all the Fe even at high temperatures and prolonged chlorinating time.
Keywords: carbon black, chlorination, intercalation iron catalyst
Introduction
Graphitized carbon black (CB) is a product of nanocrystaline dispersity. Boudouard’s
reaction is often used for its synthesis [1]. The reaction occurs on the surface of a cat-
alyst. Among the other known catalysts iron can be used for this purpose. Therefore,
the raw product of Boudouard’s reaction contains a certain amount of Fe catalyst.
This catalyst has an influence on electrical conductivity, magnetic properties, and
surface activity of CB [2, 3]. Data concerning the removal of Fe catalyst from the
bulk of raw material are scanty [4–6]. Possible use of chlorine for this purpose is
worth an investigation, since this gas can be applied as carrier directly after the stage
of Boudouard’s reaction.
Materials and methods
Graphitized carbon black (CB) was synthesized:
Fe
2
CO(g) ← →C(gr) + CO2(g)
(1)
1
'
41ꢀ� 2ꢀ74ꢁ2001ꢁ $ 5.00
AkadØmiai Kiad� , Budapest
2001 AkadØmiai Kiad� , Budapest
Kluwer Academic Publishers, Dordrecht

3
72
3
BARKAUSKAS et al.: FeCl INTERCALATION BETWEEN GRAPHITE LAYERS
using carbonyl Fe catalyst equipment for synthesis is shown in Fig. 1. Synthesis was
executed in quartz tube (1) on 1 g carbonyl Fe catalyst (2) at 460°C. Carbon monox-
ide was produced in round bottomed flask (4) dehydrating formic acid [1]:
H3PO4
HCOOH →CO+H O
(2)
2
CO stream was flown through a condenser (7) where it loses the water and bub-
bled through flasks with KOH solution (9) where traces of formic acid are trapped.
Flask with Ba(OH) solution (10) served for indication of CO produced in the reac-
2
2
tion (1).
Fig. 1 Equipment for synthesis of CB. 1 – quartz tube; 2 – ceramic pan with Fe cata-
lyst; 3 – tube furnace SUOL 0,25.1.1/12; 4 – round bottomed flask with H PO
– separatory funnel with HCOOH; 6 – heater; 7 – condenser; 8 – tube for
shifting of the condensate; 9 – bubblers; 10 – flask with BaCl solution
3
4
;
5
2
Fig. 2 Construction of DTA apparatus. 1 – Al cover; 2 – tube furnace SUOL
,25.1.1/12; 3 – outer quartz tube; 4 – brass foil; 5 – inner quartz tube; 6 – cruci-
bles; 7 – micro pipes for gas support; 8 – thermo-couples (chromel–alumel);
– isolating blockage with built-in quartz tubes; 10 – quartz tubes serving as
holders; 11 – ceramic sleeve
0
9
J. Therm. Anal. Cal., 66, 2001

BARKAUSKAS et al.: FeCl
3
INTERCALATION BETWEEN GRAPHITE LAYERS
373
The necessity to apply equipment designed in the laboratory was conditioned by
using of gaseous chlorine that is extremely corrosive agent at higher temperatures.
Construction of that DTA apparatus is shown in Fig. 2. Bottoms of crucibles (6) were
–
1
–1
made of Al O ceramics that was of high thermal conductivity (~30 W K m ). Using
2
3
this construction chromel–alumel thermo-couples (8) were isolated from corrosive
environment in the reaction zone. Thermo-junctions were pressed to bottoms of cru-
cibles for better detection of heat transfer.
Temperature distribution in the reaction zone inside the furnace is uneven. It de-
pends on furnace geometry as well as on winding density. Brass foil in the construction
was used for the minimization the influence of uneven heat flow to crucibles. Tempera-
ture distribution in the profile of furnace quartz tube was determined using the same set
of differential thermo-couple. Temperature in the furnace depends on the clamp voltage.
Existing zone of approximately constant temperature is in the middle of tube furnace
(Fig. 3). Considering these data, working position of crucibles at altitude of 7 cm was
chosen for further experiments. Heating rate in all experiments was maintained
–
1
3.5±0.5°C min . DTA experiments were carried out in the atmosphere of slow chlorine
flow (flow rate 50 mL min ) maintained using PEM gas regulating equipment.
–1
Fig. 3 Temperature distribution in the profile of quartz tube inside the furnace. Clamp
voltages: 1 – 20 V; 2 – 30 V; 3 – 40 V; 4 – 50 V; 5 – 70 V
Fe concentration in the bed of CB was analyzed using two methods. The total
amount was determined by means of gravimetric method [7] after burning the
analyte. Using the photometric method the concentration of Fe on the surface of small
CB crystals was analyzed. Sulfosalicylic acid was chosen as a reagent for photomet-
ric Fe determination [8]. To weighed analyte in the beaker was added 10 mL of dis-
tilled water and 2 mL of HCl. After 10 min solution was filtered into 50 mL volumet-
ric flask, filter paper carefully washed with distilled water and analyzed according to
description.
Fe catalyst particle size distribution was established by means of sedimentation
analysis [9]. Obtained data are presented in Fig. 4. Particle size distribution in steel sam-
J. Therm. Anal. Cal., 66, 2001

3
74
3
BARKAUSKAS et al.: FeCl INTERCALATION BETWEEN GRAPHITE LAYERS
ple was determined using optical microscope AU-26; it was within the range 0.05 to
.5 mm.
0
Fig. 4 Particle size distribution of carbonyl Fe catalyst
Results and discussion
The system we have investigated consists of three chemical active components: Fe,
graphitized CB and gaseous chlorine. It is known that iron pieces without impurities
are resistant to corrosive action of gaseous chlorine at room temperature [10]. Fe re-
activity grows up significantly at higher temperatures as well as at finer dispersity of
the metal. Reaction product FeCl is volatile at higher temperatures; its sublimation
3
occurs at 317°C [11]. Graphitized CB is known as a substance that readily adsorbs
gaseous chlorine [12]. This adsorption can be amplified by various functional groups
attached on the surface of CB. Interaction between reaction products is also possible.
For example ferric chloride can dissolve gaseous chlorine and be intercalated be-
tween graphite layers [13, 14].
Fig. 5 DTA curves of analyzed systems in the atmosphere of Cl
IB – steel; IC – FeCl ; ID – purified CB; IIA – purified CB+carbonyl Fe;
IIB – purified CB+FeCl ; IIC – raw product of Boudouard’s reaction (Table 1)
2
. IA – carbonyl Fe;
3
3
J. Therm. Anal. Cal., 66, 2001

BARKAUSKAS et al.: FeCl
3
INTERCALATION BETWEEN GRAPHITE LAYERS
375
Having an objective to ascertain processes occurring in the system pure materi-
als, such as Fe, FeCl and graphitized CB were analyzed to start with, in the stream of
3
gaseous chlorine by means of DTA method. Combining these materials into mixtures
was made for locating interaction effects between components. Analyzed systems are
presented in Table 1.
Table 1 Systems analyzed by means of DTA
System
Materials and mixtures
A. Carbonyl iron
Method of preparation
Commercial product; producer P. O. B.
M-5168; purissimus
Commercial product; producer VNIISO;
sample No. 284-b. Composition (in mass%):
Fe – 96.7; Mn – 0.08; Si – 3.05; P – 0.0089;
S – 0.0028; Ni – 0.0066; Cu – 0.111
B. Steel
I (pure materials)
Synthesized in laboratory and sublimed in
chlorine stream at 400°C
C. Ferric chloride
D. CB
In Boudouard’s reaction with Fe catalyst
synthesized CB heated 45 min in the stream of
gaseous chlorine at 540°C. Residual Fe
concentration ~1%
Purified CB (with residual Fe concentration
~1%) mixed with carbonyl Fe in ratio 2:1 by
mass
A. CB with carbonyl Fe
II (mixtures)
B. CB with ferric
chloride
Purified CB (with residual Fe concentration
~1%) mixed with FeCl in ratio 2.5:1 by mass
3
CB synthesized by means of Boudouard’s
reaction with 37.74 mass% of the Fe catalyst
C. CB with Fe catalyst
DTA curves of these systems in the atmosphere of Cl are shown in Fig. 5. In the
2
reaction between carbonyl Fe and chlorine (system IA) at 90 and 265°C two exo-
thermal peaks of unregular shape appear. We assume those peaks indicate the forma-
tion of ferric chloride. At 90°C the reaction between Fe and Cl begins to occur lead-
2
ing to the formation of FeCl and resulting in a high narrow peak on the DTA curve.
Such shape of the peak is a sequel of the isolative effect of FeCl that covers all the
3
3
surface of Fe and cuts off the reaction. At higher temperatures chlorine becomes more
active; it can permeate through isolative layer of FeCl resuming the reaction (peak at
3
2
65°C). Later, at ~315°C small endothermal peak of FeCl sublimation is obtained. In
3
case when steel is taken to the reaction (system IB) observed processes are specific
and different from those in the system with carbonyl Fe. The peak at 90°C is much
smaller comparing it with the analogous one in the system IA. This can be explained
taking into account different dispersities of these two samples. Later, likewise as in
the system IA the reaction stops until 210°C due to the isolative effect of FeCl . At
this higher temperature resumed process differs from that in the system IA. Because
3
of more gross dispersity and impurities steel burning in Cl atmosphere stretches up
to 420°C and endothermal FeCl sublimation peak is disguised by the exothermal pla-
2
3
J. Therm. Anal. Cal., 66, 2001

3
76
3
BARKAUSKAS et al.: FeCl INTERCALATION BETWEEN GRAPHITE LAYERS
teau of FeCl formation. System IC consists of pure FeCl synthesized in the labora-
tory. In the DTA curve of this substance at 50°C an endothermal peak exists. At this
temperature it is possible to obtain the desorption of Cl from FeCl sample [14].
3
3
2
3
Later, an endothermal peak occurring at 150°C can reflect removal traces of humidity
adsorbed by hygroscopic FeCl . At 310°C an endothermal peak of FeCl sublimation
3
3
is observed. Exploring reactions of graphitized CB with residual Fe concentration
1% in the atmosphere of Cl (curve ID) no peaks in the system are observed. The
~
2
reason for this is the sample preparation (Table 1). Reactions which could occur are
exhausted at the stage of heating of CB in the stream of gaseous chlorine at 540°C.
In the system II (Table 1) containing mixtures peaks reflecting similar and even
more complex processes are observed. In the mixture IIA consisting of purified CB
and carbonyl Fe exothermal peak of FeCl formation appears at 60°C. It is indicative
of CB being an active media in the reaction between Fe and Cl . The similar effect is
3
2
seen at higher temperatures: in the presence of CB, the second exothermal peak ap-
pears at 210°C. Comparing the shape and structure of these peaks with those in the
system IA certain differences can be seen. The presence of CB not only decreases re-
action temperatures but also has an effect on the process. The first exothermal peak
appears more abruptly and its shape is more regular as it is in case with system IA.
The process at higher temperatures is more complex: several sharp isolated peaks in-
dicate FeCl formation. CB there can act as a mediator adsorbing gaseous chlorine
and intercalating FeCl produced in the system. Exploring the mixture IIB consisting
of purified CB and FeCl , in DTA curve series of specific small peaks in the range
3
3
3
150 to 300°C are observed. It is known that similar peaks originate in the process of
FeCl intercalation between graphite layers [15]. DTA curves of mixtures IIA and IIB
have small singular peaks at ~320°C where sublimation of FeCl occurs.
3
3
Mixture IIC consists of raw product of Boudouard’s reaction (1), i. e. from car-
bonyl Fe catalyst which particles are covered with graphitized CB [16]. In the DTA
curve of this mixture the peaks can be explained considering the information obtained
in previous experiments. At the beginning of the DTA experiment a peak at 60°C is
obtained. It is analogous to the similar peak in the system IIA, only its height is
smaller. Later, beginning from 150°C, complex series of small peaks are obtained on
the DTA curve. These indicate the simultaneous intercalation of FeCl between layers
of graphitized CB and the removal of moisture adsorbed by the raw product of Bou-
3
douard’s reaction. In this DTA curve no peaks indicating second step of FeCl forma-
tion are observed. Small peaks of FeCl intercalation cover the corresponding area.
3
3
Apparently, in Boudouard’s reaction dispersed carbonyl Fe catalyst reacts over in one
step until the temperature 150°C is reached. Moisture in the raw product of Bou-
douard’s reaction can appear keeping it not isolated in contact with air. At ~320°C
small endothermal peak of FeCl sublimation is observed.
Obtained results demonstrate the complexity of processes occurring in systems
3
containing Fe, C and Cl . Together with chemical properties and thermodynamical
parameters reactions in the system are influenced by the geometry of reacting solids.
2
Stages of FeCl formation are highly exothermal. At the same time this effect can be
considerably decreased in systems with highly dispersed Fe. There are some endo-
3
J. Therm. Anal. Cal., 66, 2001

BARKAUSKAS et al.: FeCl
3
INTERCALATION BETWEEN GRAPHITE LAYERS
377
thermal processes: FeCl sublimation and moisture removal. Process of FeCl interca-
lation being slightly expressed thermally is of high positive entropy [17].
3
3
Removal of Fe catalyst from the raw product of Boudouard’s reaction was carried
out in the stream of gaseous chlorine. The chlorination reaction was executed in a quartz
–
1
tube heated by a tube furnace. Cl flow rate was maintained 0.5 L min . Gravimetric and
2
photometric methods for determination of total and surface Fe concentration were used.
Results are presented in Figs 6 and 7. The total amount of Fe in graphitized CB before
chlorinating was 37.74 mass%, surface Fe concentration reached 0.08 mass%. This is in-
dicative of almost all Fe catalyst being capsulated by carbon. In the stream of gaseous
chlorine after 10 min total Fe amount is doubly reduced. At the same time surface Fe con-
centration increases considerably. These changes can be explained making the presump-
tion that gaseous chlorine penetrates through the carbon covering and reacts with Fe. The
reaction product FeCl is sublimed and carried out from the reaction zone. In that way,
the total amount of Fe decreases. Surface Fe concentration increases since the sublima-
tion of FeCl occurs through the surface of CB covering.
3
3
Fig. 6 Fe amount in graphitized CB at different temperatures of chlorination reaction.
Reaction time 45 min. 1 – total Fe; 2 – surface Fe concentration
Fig. 7 Fe amount in graphitized CB at different duration of chlorination reaction. Reac-
tion temperature 450°C. 1 – total Fe; 2 – surface Fe concentration
J. Therm. Anal. Cal., 66, 2001

3
78
3
BARKAUSKAS et al.: FeCl INTERCALATION BETWEEN GRAPHITE LAYERS
The reaction temperature exerts more influence upon efficiency of Fe removal in
comparison with the reaction time. Results obtained in the experiment indicate that
Cl stream does not remove all the Fe from CB even at high temperatures and pro-
longed chlorination. Residual Cl concentrations (~1%) are fixed after boiling of CB
2
2
(processed with 2 h at 590°C) in hydrochloric acid 0.5 h. The intercalation of FeCl3
can be the reason for this [18].
Conclusions
Interaction between Fe and Cl in the bed of graphitized carbon black was investi-
gated. For that purpose the DTA experiment using equipment designed in the labora-
tory was conducted. Pure materials, such as Fe, graphitized carbon black, FeCl , and
2
3
their mixtures were analyzed. Peaks on DTA curves show that processes occurring in
the system are complex. Together with chemical properties and thermodynamical pa-
rameters reactions are influenced by the geometry of solids. Experiments for remov-
ing of Fe from the bed of graphitized carbon black were done. Obtained results indi-
cate that Cl stream does not remove all the Fe even at high temperatures and
prolonged chlorinating time. The intercalation of FeCl can be the reson for this.
2
3
References
1
Handbuch der präparativen anorganischen Chemie, B. 2, G. Brauer (Herausg.), Ferdinand Enke
Verlag, Stuttgart 1975, S. 930.
2
3
4
5
6
V. M. Garamus and J. S. Pedersen, Colloid Surf. A, 132 (1998) 203.
A. Bezrijadin, R. M. Westervelt and M. Tinkham, Appl. Phys. Lett., 74 (1999) 2699.
S. Banjeri, S. K. Adhya and S. K. Ghosh, Carbon, 26 (1988) 461.
B. Pfritzlaff and H. Stahl, Carbon, 15 (1977) 399.
V. Ivanov, A. Fonseca, J. B. Nagy, A. Lucas, P. Lambin, D. Bernaerts and X. B. Zhang, Car-
bon, 33 (1995) 1727.
7
8
R. Kellner et al., Analytical Chemistry, Willey–VCH, Weinheim 1998, p. 916.
M. Radojevic and V. Bashkin, Practical Environmental Analysis, RSC Books, London 1999,
p. 466.
9
G. Bickert and W. Stahl, Particle and Particle Syst. Characterization, 14 (1997) 142.
1
1
0 A. Chambers and R. T. K. Baker, J. Phys. Chem. B, 101 (1997) 1621.
1 Encyclopedia of Chemical Technology, Kirk–Othmer Eds, John Wiley and Sons, New York
1
967, p. 36.
1
1
1
1
1
1
1
2 M. J. B. Evans, E. Halliop, S. Liang and J. A. F. Macdonald, Carbon, 36 (1998) 1677.
3 F. Kang, Y. Leng, T. Y. Zhang and B. S. Li, Carbon, 36 (1998) 383.
4 I. Gerard, D. Begin, G. Furdin and J. F. Mareche, Fuel, 77 (1998) 607.
5 H. Y. Zhang, W. C. Shen, Z. D. Wang and F. Zhang, Carbon, 35 (1997) 285.
6 M. Audier, M. Coulon and L. Bonnetain, Carbon, 21 (1983) 105.
7 D. Herein, T. Braun and R. Schlogl, Carbon, 35 (1997) 17.
8 E. Alain, D. Begin, J. Pajak, G. Furdin and J. F. Mareche, Fuel, 77 (1998) 533.
J. Therm. Anal. Cal., 66, 2001