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16th International Environmental Project Olympiad

The Research of Optimal Mixing Ratio of

ACF (Activated Carbon Fiber) and AC (Activated Carbon)

for Removal of VOC (Volatile Organic Compound) s

in Crude Oil

Republic of Korea

Author
Dong-sung, Choi, Su-jin, Kim

Supervising Instructor

Chun-jeong, Lee
- Abstract -
A great amount of crude oil leaked in the ocean after a barge carrying a crane slammed into an oil

tanker in Tae-an, Chung-nam, Republic of Korea on December 7th, 2007. VOC (Volatile Organic

Compound) s from crude oil can caused people to have skin or respiratory problems. So it has become

necessary to develop an efficient method of adsorbing harmful gases in crude oil. What is especially

important is developing masks which have good absorption ability to VOCs. The purpose of this

study is to find the ways to reduce the harm of VOCs on people.

First, for the research, I developed a creative machine which can help measure the concentration of

gases and the efficiency of removal harmful gases easily. And I made experiments with the adsorption

of harmful gases using SEM and gas detectors. ACF (Activated Carbon Fiber) has large surface area

ratio, and its pores are exposed on the surface so it absorbed 25.4% of Benzene and 46.67% of

Toluene and this result shows that ACF have a better adsorption capacity for Benzene and Toluene

which have Benzene ring structure. However, ACF turned out to be a poor adsorbent of n-Hexane

which has a chain form structure. This research also shows that AC, which has a variety of pore sizes,

adsorbs 41.18% of n-hexane and this shows that AC adsorbs more n-hexane compared to other

adsorbents. According to approximate calculations of the molecular length of Benzene and n-Hexane,

the diameter of a Benzene ring is shorter than the molecular length of n-Hexane. It is analyzed in

probability aspect by comparing the molecular length of Benzene and n-Hexane that ACF which has

15 Å sized poles adsorb more Benzene than n-Hexane in the activated gas state. In the experiment

about the removal efficiency of harmful gases, results indicated that a mixture of ACF and AC has the

greatest synthetic removal efficiency of harmful organic gases which include both compounds which

have ring or chain form. According to the results, the optimal ratio of ACF to AC is 4:3.

Through this research, we developed a creative machine which can help measure the adsorption

ability of absorbents and we suggested an innovative way to reduce the damage of volatile organic

compounds.

-2-
- Contents -
Ⅰ. Introduction……………………………………………………………………5

1. Background reason for the research…………………………………………..…….…..…5
2. The purpose of the research……………………………………………………………..…5

Ⅱ. Theoretical Background………………………………………………...……6

1. The mechanism and classification of adsorption………………………………………….6
2. The structure of pores……………………………………………………………...………7
3. Adsorbents: ACF, AC, Zeolite 5A …………………………………………………….….7

Ⅲ. Experimental Procedure………………………………………………..……8

1. Measuring the concentration of gases in the instrument…………………………………..8
2. Analysis of the surface through Scanning electron microscope (SEM)……………….…10

Ⅳ. Results and Considerations………………………………………………...12

1. VOCs removal by cotton wool.…………………………………………………….…….12
2. VOCs removal by adsorbent (ACF, AC and Zeolite 5A)………………………………..13
3. Optimal ratio of ACF and AC for removing VOCs…………………………………..….17

Ⅴ. Conclusion and Suggestion…………………………………………………19

1. Conclusion.……………………………………………………………………………….19
2. Suggestion………………………………………………………………………………..20

Ⅵ. References……………………………………………………...…………..21

Ⅶ. Appendix………………………………………………………...…………21

-3-
-Figure contents-
Fig. 1 Satellite picture of oil in Tea-an……………………………………..…………………………..5
Fig. 2 Volunteers for removing oil…………………………..……………………………………...…..5
Fig. 3 Mechanism of adsorption………………………………………………………………………..6
Fig. 4 ACF………………………………………………………………………………………..…….7
Fig. 5 AC………………………………………………………………………………………….……7
Fig. 6 Variety sizes of pole in AC………………………………………………………………….…..7
Fig. 7 Zeolite…………………………………………………………………………………..……….8
Fig. 8 Instrument……………………………………………………………………………….….……8
Fig. 9 The experiment procedure for the VOCs adsorption………………………………….…….….10
Fig. 10 SEM…………………………………………………………………………………………...10
Fig. 11 The procedure of analyzing the surface with SEM…………………………………...………11
Fig. 12 SEM photo of cotton wool…………………………………………………………………….12
Fig. 13 Removal efficiencies of benzene by adsorbents………………………………..……………..13
Fig. 14 Removal efficiencies of toluene by adsorbents……………………………………………….14
Fig. 15 Removal efficiencies of n-hexane by adsorbents………………………………….………….14
Fig. 16 SEM photo of ACF……………………………………………………………………..…..…15
Fig. 17 SEM photo of AC…………….………………………………………………………….…....15
Fig. 18 SEM photo of Zeolite 5A………………………………………………………………....…..15
Fig. 19 Removal efficiencies of benzene by the mixed adsorbent……………………................……18
Fig. 20 Removal efficiencies of toluene by the mixed adsorbent……………………………………..18
Fig. 21 Removal efficiencies of n-hexane by the mixed adsorbent………………………...................18
Fig. 22 Average removal efficiency of all VOCs by the mixed adsorbent……………………………19
Fig. 23 Diagram of benzene ring…………………………………………………….………………..21
Fig. 24 Diagram of n-hexane……………………………………………………...……….………….22

-Table contents-
Table 1. Concentration of remained VOCs after adsorbing with cotton wool as time going…...…….12

Table 2. Concentration of remained VOCs and their removal efficiencies after adsorbing with
ACF, activated carbon and Zeolite 5A as time going………………………………….……..13
Table 3. Concentration of remained VOCs and their removal efficiencies after adsorbing with
the mixed adsorbent as time going…………………………………………………………...17
Table 4. Average removal efficiency of VOCs by adsorbing with the mixed adsorbent……...……...17

-4-
Ⅰ Introduction
.
1. Background reason for the research
A large amount of crude oil leaked in December 2007 due to the collision of an oil tanker and a
crane in Tea-An, Chung-Nam, Republic of Korea. Crude oil contained many organic compounds
some of which are volatile. These compounds can cause significant health problems. Although they
wore masks, people mobilized to clean up the spill reported experiencing headaches, vomiting, and
other acute symptoms. Scientists have discovered that VOC (Volatile Organic Compound) s can be
carcinogenic. Due to the harmful effects of VOCs on human beings it has become necessary to
develop an efficient method of adsorbing harmful gases in crude oil. What is especially important is
developing masks which can adsorb VOCs. It is also important to do research on ability of ACF
(Activated Carbon fiber), AC (Activated Carbon) and Zeolite 5A to adsorb VOCs.

Fig. 1 Satellite picture of oil in Tea-an Fig. 2 Volunteers for removing oil

2. The purpose of the research
We researched the optimum condition for efficient adsorption of volatile organic compounds
using ACF, AC and Zeolite 5A. The specific purposes of the research are explained below:

First, develop a machine which can easily measure the concentration of gases and have the
ability to conduct experiments under various parameters.
Second, compare the adsorption ability of ACF, AC and Zeolite 5A to Benzene, Toluene and n-
Hexane according to various properties of adsorption.
Third, crude oil is a mixture of volatile organic compounds, so research the optimum blending
ratio of ACF and AC to adsorb harmful gases.

The ultimate purpose of the research is to suggest ways to reduce damages to human health
caused by harmful volatile organic compounds in crude oil.

-5-
Ⅱ Theoretical Background
.
1. The mechanism and classification of absorption
A. Mechanism of adsorption
Adsorption is a phenomenon where gases stick to the surface of a solid through a physical or
chemical interaction. Materials which contain lots of pores to adsorb are called adsorbents. A
phenomenon where gases stick to around shaped hole is explained below.

a. Gases move to the surface of a pore in the adsorbent.

b. Gases approach the pore by molecular diffusion when close to the surface of a pore.

c. Gases pass through the spaces in the adsorbent by movement of the inner particles or
molecular diffusion and move towards an adsorption point.

d. Gases become fixed to the inner surface of an adsorbent.

In these adsorption processes, the last process is the Rate Limiting Step which can dominate the
speed of adsorption. Therefore adsorption is limited by the former process. Finally, adsorption rate
is determined by diffusion and the movement rate of molecules in the adsorbent.

Fig. 3 Mechanism of adsorption

B. Classification of adsorption
The main form of adsorption is classified in two ways; physical adsorption and chemical
adsorption. Physical adsorption occurs according to Van der Waals force which is relatively weak
in comparison to other bonds. Chemical adsorption occurs through ionic or covalent bonds. In
physical adsorption, there is no bond between the surface of the adsorbent and the gases, which
mean gases are in a temporary fixed state near the surface of the adsorbent. These molecules can
become separated easily by changes in pressure or concentration, therefore physical adsorption is
reversible. Most gas adsorption processes have similar characteristics. However, in chemical
adsorption, gases are caught on the surface of the adsorbent by covalent force so chemical
adsorption is irreversible.

-6-
2. Structure of pores
A pore is a space in a solid construction. There are two types of pores: space between particles and
space in particles. The structure of pore can be described by its shape, size and its connection state
to other pores. Compared to the size of molecules, pores are much larger. According to the size of
pores, if the size of the pore is larger than 50nm, it is called macro pore, if the size of the pore is
smaller than 2nm, it is called micro pore. Pores which are middle sized are called meso pores.
Although the activated point on the surface of an adsorbent can participate in the reaction, the effect
is very small since the total surface area of the outer surface of the adsorbent is much smaller than
that of the inner surface.

3. Adsorbents: ACF, AC, Zeolite 5A
A. ACF (Active Carbon Fiber)
ACF is an activated carbon which is made by manufacturing
during carbonized rayon. After heating rayon with deoxygenating,
the fixed carbon frame remains, and all other chemical elements
are eliminated. At that time, if we add water to it and oxidize it,
pores will form and it will turn into fiber form. ACF is very
efficient in adsorption because its pore size is 15 Å uniformly Fig. 4 ACF
and its pores are exposed on the outside more than activated carbon and other adsorbent.

B. AC (Activated Carbon)
AC, an aggregate of amorphous carbon which has many small
pores (and it has a large inner surface area because small pores
are made during activation), is classified into powder or lump
state by the size of the pores. The pores of AC are complex and
contain many capillaries which mean these pores have a large
surface area. Shown in Fig. 6, there are various sizes (micro pore
– meso pore - macro pore) the pores inside of activated carbon. Fig. 5 AC

Fig. 6 Variety sizes of pole in AC

-7-
C. Zeolite 5A
Zeolite is a general term used for crystallized aluminum silicate. The
synthesis Zeolite from nature is usually used Zeolite A, Zeolite X type
and Zeolite Y type are classified by the formation of the bonds and
Al2O3, SiO2. The front number of Zeolite A is classified with valid
pore's size.
Fig. 7 Zeolite

Ⅲ. Experimental Procedure

1. Measurement of the concentration of VOCs
A. Development of the standard instrument for removing VOCs
The commercial standard device for removing VOCs cannot be applied because it is difficult to
use this. Therefore, the standard device for removing VOCs was developed for this study. The
developed device was similar to one in the real field but the size was only small.

a. Instrument
The instrument for investigating the adsorption of VOCs was made out of acrylic (30 cm x 21
cm x 19 cm). This box was composed with a heating plate, fan, a gas detector hall and an
adsorbent column. The liquid pollutant was evaporated by the heating plate. The pollutant gas
flowed in the column by the fan. The gas detector hall had a valve for air tightness and the
various-sized detectors could be installed in the hall.

Fig. 8 Instrument

-8-
b. The gas detectors
The gas detector was the narrow glass column with the chemicals whose color was changed by
the reaction with VOCs. And this detector could measure the concentration of VOCs with the
length of the changed color in the column. This method is widely applied in the real field. The
concentration of Benzene, Toluene and n-Hexane in the instrument were measured with this gas
detector.

c. Pump
The gas in the instrument flowed into the gas detector column by the pump.

B. Experimental procedure
a. Fill the adsorbent in the column.
b. Lay a slide glass on the heating plate and drop some quantity of liquid VOCs on the slide glass
with a micro pipette.
c. After evaporating the liquid VOCs, remove the glass in the both side of the gas detector. And
put the detector into the pump.
d. Open the valve of the gas detector hall and turn on the pump for inhale the VOCs into the gas
detector.
e. If the color in the detector does not change, close the valve and measure the length of the
changed color in the column.

1. Fill the adsorbent in the column 2. Drop the liquid VOCs

-9-
3. Evaporate the liquid VOCs 4. Remove the glass in detector

5. Measure the VOCs 6. Measure the length of the color
Fig. 9 The experiment procedure for the VOCs adsorption

2. Analysis of surface with SEM
A. Scanning Electron Microscope (SEM)

Fig. 10 SEM
SEM is an instrument in which the specimen is examined point by point directly in a moving
electron beam, and electrons reflected by the specimen are used to form a magnified, three-
dimensional image on a television screen.

- 10 -
B. Analytical procedure
a. Fix a sample on the stove.
b. Coat the sample with platinum and prevent the sample in SEM.
c. Put the sample into SEM and turn on the vacuum pump.
d. Adjust the brightness and the focus and the position of the computer connected to SEM.
e. Capture the picture.

1. Prepare samples 2. Put the sample

Capture the picture

Fig. 11 The procedure of analyzing the surface with SEM

- 11 -
Ⅳ Results and Discussion
.
1. VOCs removal by cotton wool
People who were mobilized to remove crude oil in Tea-an wore masks and most of the masks are
made of cotton wool. But they experienced health problem because of VOCs from crude oil. First
of all, the adsorbent efficiency of cotton wool was investigated. The VOCs removal efficiency of
cotton wool is presented in Table 1.

Table 1. Concentration of remained VOCs after adsorbing with cotton wool as time going

Concentration (ppm)
Adsorbent VOCs
0 min 5 min 10 min 15 min

Benzene 60 58 59 58

Cotton wool Toluene 83 76 76 76

n-Hexane 190 190 190 190

X100 X1000

Fig. 12 SEM photo of cotton wool

As we can know that the inner formation of cotton wool is the tangled formation of fiber.
We could get these results through upper figures.

Table 1 show all VOCs were not almost removed by cotton wool. Cotton wool had sparsely
cellulose fiber and its pore was slightly developed (Fig. 12). Therefore, cotton wool could not
adsorb VOCs.

- 12 -
2. VOCs removal by adsorbent (ACF, AC and Zeolite 5A)
Three kinds of adsorbents were used in this study. Removal efficiencies of Benzene, Toluene and
n-Hexane were investigated as time going. The VOCs removal efficiency of ACF, AC and Zeolite
5A is presented in Table 2.

Table 2. Concentration of remained VOCs and their removal efficiencies after adsorbing with ACF, AC and
Zeolite 5A as time going

Concentration (ppm) Removal efficiency (%)
absorbent VOCs
0 min 5 min 10 min 15 min 0 min 5 min 10 min 15 min

Benzene 63 56 51 47 0.00 11.11 19.05 25.40
ACF Toluene 150 120 90 80 0.00 20.00 40.00 46.67

n-Hexane 190 170 150 140 0.00 10.53 21.05 26.32

Benzene 59 53 48 47 0.00 10.17 18.64 20.34

AC Toluene 72 54 50 48 0.00 22.22 30.56 33.33

n-Hexane 170 150 130 100 0.00 10.17 23.53 41.18

Benzene 63 58 55 53 0.00 7.94 12.70 15.87
Zeolite 5A Toluene 81 72 66 63 0.00 11.11 18.52 22.22

n-Hexane 200 190 180 170 0.00 5.00 10.00 15.00

The VOCs removal efficiency of ACF, AC and Zeolite 5A is presented in Fig. 13, Fig. 14, and Fig.
15. X axis of the graph presents time and y axis of the graph presents the removal efficiency.

Fig. 13 Removal efficiencies of benzene by adsorbents

- 13 -
Fig. 14 Removal efficiencies of toluene by adsorbents

Fig. 15 Removal efficiencies of n-hexane by adsorbents

As we can know in Fig. 13 and Fig. 14, ACF has the greatest total Benzene and Toluene removal
efficiency. However, in Fig. 15 AC has the greatest total n-Hexane removal efficiency.

We could get these results through upper figures.
- The removal efficiency of Benzene and Toluene with benzene ring by ACF was higher than
other adsorbents because ACF with the larger surface area had the high physical adsorption ability
of VOCs.

- 14 -
- These are the SEM pictures of absorbents.

X1000 X100, 0001

Fig. 16 SEM photo of ACF

X100 X1000

Fig. 17 SEM photo of AC

X100 X1000

Fig. 18 SEM photo of Zeolite 5A

1
We could not take the second picture of Fig. 16 because of the capacity of SEM. So we got that picture at a
specialty website which deals AFC.

- 15 -
Fig. 16 shows the pores of ACF were uniform (15 Å ) and exposed much. However, AC and
Zeolite 5A had the complex surface and multiform pores (Fig. 17 and 18). Therefore, ACF could
adsorb more VOCs because the pores of ACF were exposed more than of other adsorbents.

- However, more n-Hexane was removed by AC differently to other VOCs. While ACF had only
small pores, the pore size of AC was various (from micro pore to macro pore). According to
approximate calculation of length of Benzene and n-Hexane2, the length of Benzene (4.62 Å) is
shorter than the length of n-Hexane (9.08 Å). And in the probability aspect, gases molecular are in
activated state, so n-Hexane could not be adsorbed in AFC which has very small pores (15 Å) well
than Benzene and Toluene. On the other hand, although Zeolite 5A had various sized pores like
AC, the removal efficiency of n-hexane by this was lower than by ACF. This was why the surface
area of Zeolite 5A was smaller than of ACF. To conclude, n-Hexane was well removed by
adsorbent with large sized pore and the large surface area.

2
Calculation is in Appendix.

- 16 -
3. Optimal ratio of ACF and AC for removing VOCs
From previous experimental results, removals of Benzene and Toluene were dependent on the
surface area and the exposure of pores. And the removal of n-hexane was also dependent on the
diversity of pore size. In VOCs from crude oil, both chain and ring form compounds exist.
Therefore, in order to removal both chain form and ring form VOCs more efficiently, a mixed
adsorbent with ACF and AC was applied. This chapter studied the optimal mixing ratio of two
adsorbents according to comparing the average removal efficiency of all VOCs with variously
mixed adsorbents. The VOCs removal efficiency of absorbent which is mixed with ACF and AC is
presented in Table 3. And the average value of final VOCs removal efficiency is presented in table
4.

Table 3. Concentration of remained VOCs and their removal efficiencies after adsorbing with the mixed
adsorbent as time going

Mixing Ratio Concentration (ppm) Removal efficiency (%)
VOCs
(ACF : AC) 0 min 5 min 10 min 15 min 0 min 5 min 10 min 15 min

Benzene 68 64 58 54 0.00 5.88 14.70 20.60

2:5 Toluene 80 66 53 52 0.00 17.50 33.80 35.00

n-Hexane 179 143 136 114 0.00 20.11 24.02 36.31

Benzene 64 57 54 49 0.00 10.94 15.63 23.44

3:4 Toluene 80 72 61 46 0.00 10.00 23.75 42.50

n-Hexane 186 171 157 123 0.00 8.06 15.59 33.87

Benzene 63 56 50 46 0.00 11.11 20.63 26.98

4:3 Toluene 83 65 63 46 0.00 21.69 24.10 44.58

n-Hexane 233 180 179 157 0.00 22.75 23.18 32.62

Benzene 66 58 56 48 0.00 12.12 15.15 27.27

5:2 Toluene 92 68 56 50 0.00 26.09 39.13 45.65

n-Hexane 217 179 171 157 0.00 17.51 21.20 27.65

Table 4. Average removal efficiency of VOCs by adsorbing with the mixed adsorbent
Mixing Ratio
2:5 3:4 4:3 5:2
(ACF : AC)

Average 30.63 33.27 34.73 33.52

- 17 -
The VOCs removal efficiency of each mixed absorbents is presented in Fig. 19, Fig. 20, and Fig.
21. X axis of the graph presents time and y axis of the graph presents the removal efficiency.

Fig. 19 Removal efficiencies of benzene by the mixed adsorbent

Fig. 20 Removal efficiencies of toluene by the mixed adsorbent

Fig. 21 Removal efficiencies of n-hexane by the mixed adsorbent

- 18 -
The total VOCs removal efficiency of mixed adsorption is presented in Fig. 22. X axis of the
graph is ACF:AC, y axis of the graph presents averaged removal efficiency.

Fig. 22 Average removal efficiency of all VOCs by the mixed adsorbent

As we can see in Fig. 19 and Fig. 20, the mixing rate which has the greatest Benzene and Toluene
removal efficiency is 5:2. As we can see in Fig. 21, the mixing rate which has the greatest n-
Hexane removal efficiency is 2:5. The result has the same tendency that as the rate of ACF
increases, total Benzene and Toluene removal efficiency increases, and as the rate of AC increases,
total n-Hexane removal efficiency increases. As we can see in Fig. 22, the synthetic Benzene,
Toluene and n-Hexane removal efficiency is the greatest in ACF:AC=4:3

We could get these results through upper graphs.
- As previous results, the higher ratio of ACF, the higher removal efficiency of Benzene and
Toluene. And as the ratio of AC is high, removal efficiency of n-Hexane increases.
- The optimal mixing ratio of ACF:AC was 4:3 for the high removal efficiency of all VOCs.
- The mixed adsorbent included the both advantages of ACF and AC. Therefore this mixed
adsorbent could more efficiently remove the VOCs than each adsorbent.

Ⅴ Conclusion and Suggestion
.
1. Conclusion
This study was conducted for finding the optimal adsorbent for removing VOCs produced from
petroleum because the people had a headache by inhaling VOCs, who were cleaning up spilled oil
on the coast near Tae-an in Republic of Korea.
- Adsorption of VOCs by ACF, AC and Zeolite 5A was dependent on the surface area, the degree
of pore exposure and pore size of adsorbents.

- 19 -
- Because ACF had the larger surface area and its pores were more exposed than AC and Zeolite
5A, ACF had the good physical adsorption ability. Therefore, Benzene and Toluene could adsorb
on ACF well.
- Because the pore size of AC was various (from micro pore to macro pore), n-Hexane which has
long molecular length could be adsorbed on AC than on ACF with only small pores very well.
However, ACF could absorb more n-Hexane than Zeolite 5A which had various sized pore
because ACF had much larger surface area. Therefore, n-Hexane was well removed by adsorbent
with various sized pore and the large surface area.
- ACF and AC were better adsorbent for removing Benzene and Toluene, and n-Hexane,
respectively. Therefore, the mixed adsorbent with them was applied for removing VOCs and
could efficiently remove them. There was the optimal mixing ratio of ACF to AC (4:3).
Finally, this mixed adsorbent can be usefully applied in the oil spill accident in the ocean, a gas
station, an oil tank and so on.

2. Suggestion
A. In experiments, the VOCs removal efficiency of each adsorbent is under 50%. If we conduct
experiments until saturated physical adsorption state, we can get more credible VOCs removal
efficiency.
B. If we conduct experiments with compounds which is adsorbed by chemical adsorption such as
radical compound, Ammonia, we can find other factors which is related to adsorption mechanism
except large surface area, the size of pores and revealed degree of pores.
C. After conducting experiments which is about other VOCs such as Formaldehyde, we can apply
these results to another problems for instance Sick House Symptom.
D. ACF has a great amount of Benzene and Toluene adsorption ability since it has large surface
area and revealed pores. However, it cannot adsorb n-Hexane which has long molecular length
very well because its pores are so small. To replenish this disadvantage, AC which has variety size
of pores can be mixed with ACF so mixed adsorbent synthetically and efficiently adsorbs chain
and ring form VOCs. Therefore, the using possibility of mixed adsorbent is very high in crude oil
work place, house and gas station. And it is expected using its adsorption ability in many fields for
example impurities removal, moisture removal and separation of materials, etc.

- 20 -
Ⅵ References
.

1. Oxtoby, Gillis, Nachtrieb, Principle of modern chemistry, Thomson, 2003, pp.148-154

2. Peter Atkins, Julio de Paula, Physical Chemistry, Oxford, 7th Edition, pp. 1096-1115

3. Son Jae-Ik, An introduction of new carbon materials, KIER, 2000, pp. 94-96.

4. Dong Yang Carbon, Activated carbon, Dong-Yang Carbon, 1999, pp. 37~39.

5. Dae Dong A.C., Optimal design of activated carbon, p.11.

Ⅶ. Appendix

The calculation of molecular length

1. The length of Benzene Ring

Fig. 23 Diagram of benzene ring

Let’s put the covalent bond radius of Carbon, r. The angle of the benzene ring is 120°. So the length of

Benzene ring is
2  2r cos60  4r  6r .
r is 0.77Å. So the length of Benzene ring is 4.62 Å