Compressed expanded graphite (CEG) was synthesized to improve upon the adsorption properties of Nyex particles. CEG was prepared by expanding and compressing Nyex particles, resulting in a higher surface area and pore volume than Nyex. This led to CEG having twice the adsorption capacity of Nyex for removing dye from wastewater. Both adsorbents showed over 100% regeneration efficiency through electrochemical regeneration and reduced power consumption compared to thermal regeneration methods. Future work involves characterizing Nyex attrition during regeneration and developing conductive polymer composites to further increase adsorption capacity.

1. TEMPLATE DESIGN © 2008
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DEVELOPMENT OF NOVEL ADSORBENTS FOR WASTEWATER TREATMENT
Raman Talwar
Supervisor: Dr. E.P.L Roberts
School of Chemical Engineering and Analytical Sciences, The University of Manchester
Introduction and Project Background
Wastewater treatment using
adsorbents is increasingly gaining
dominance owing to their
environment friendliness and cost-
effectiveness. After adsorbing
pollutants to their saturation
capacity, they lose their ability to
adsorb further and consequently
have to be regenerated.
Adsorbent Synthesis, Properties and Kinetics
Adsorbent Synthesis
The adsorbent (CEG) was prepared using the following scheme:
Adsorbent Properties
Stability of Nyex®Regeneration Characteristics
Experiments
Electrochemical regeneration was performed in a Y-cell (Figure 9):
Conclusions and Future Work
References
a) Sieving
Using a Sieve Tower to get
particles in the range of
250 – 425 microns
b) Expansion
Heating Nyex particles to
800 – 850 °C for 60
seconds
c) Compression
Compression in a hydraulic
press at 2500 kgf using a 4
cm2 die
d) Crushing
Crushing using a blender
at 18000 rpm
Figure 8: Adsorbate loading over time for Nyex and compressed expanded graphite (CEG).
The initial concentration of AV 17 was taken as 100 mg l-1 in both cases with 20 gm Nyex and
10 gm CEG. It can be seen that steady equilibrium is reached after 60 minutes for both the
adsorbents with about 50 – 60 % adsorption taking place within 20 minutes in both cases.
Figure 4: Surface morphology of Nyex® particles (left) at 100 times magnification. The non-
porous structure of Nyex® particles can be seen which leads to a low adsorption capacity. A
schematic (right) of the intercalated structure showing low inter-planar Van der Waals forces.
Figure 6: Procedure for adsorbent synthesis
1. Brown, N.W., et al., (2004). Electrochemical regeneration of a carbon-based adsorbent loaded with crystal violet
dye. Electro Acta, 49: 3269-3281.
2. Celzard, A., et al., (2002). Preparation, electrical and elastic properties of new anisotropic expanded graphite-
based composites. Carbon, 40: 557-566.
Figure 9: Y-cell equipment used for regeneration. Regeneration was performed for 40 minutes
at 1 A current for adsorbents (110 gm Nyex and 50 gm CEG) over 4 adsorption/regeneration
cycles. In each cycle, a fresh batch of AV 17 dye (500 mg l-1 for Nyex and 800 mg l-1 for CEG)
was taken and replaced after every adsorption cycle which lasted for 1 hour.
Adsorbent Kinetics
Adsorption experiments were performed in flasks using Acid Violet
17 (AV 17) dye solutions as the adsorbate loading. The saturation
adsorption capacity (Figure 8) for CEG (8 mg g-1) was found to be
twice that of Nyex® particles (4 mg g-1) due to a higher surface
area and pore volume of CEG particles (17 m2 g-1 and 0.07 cm3
g-1 respectively) as compared to Nyex particles (1 m2 g-1 and
0.004 cm3 g-1 respectively). This finding marked a significant
breakthrough in improving the adsorption properties of Nyex®.
Compression
Regeneration Efficiencies
The regeneration efficiencies (ratio of loaded capacity to fresh
capacity) for both CEG and Nyex® particles (Figure 10) were
found to be around 100%, suggesting that the synthesised
adsorbent (CEG) displayed good regeneration behaviour.
Figure 10: Regeneration efficiencies for both Nyex and CEG were found to be similar and
above 100% for theoretical charge passes (21.8 C g-1 for 110 gm Nyex and 48 C g-1 for 50 gm
CEG, implying 1 A for 40 minutes in each case) calculated using Faraday’s Laws. Marginal
decrease in efficiencies below 100% can be attributed to inefficient current passage through
the cell.
Cell Potentials
CEG bed required half the cell voltage (Figure 11) for the same
treatment time (40 minutes) over 4 cycles, leading to a lower
power consumption due to a higher electrical conductivity (1.6 S
cm-1) than Nyex® particles (0.8 S cm-1).
Figure 11: Cell potentials for the two adsorbent beds over 4 cycles. Values were recorded over
40 minutes and the error bars show the standard deviation of multiple readings from mean.
Methodology
Nyex® particles have been observed to break down in solution
during adsorption. To characterise this breakdown, turbidity
measurements were taken to account for the generation of fines.
Figure 12: Turbidimeter (left) used to assess Nyex® attrition and its working principle (right)
Figure 13: Turbidity values after adsorption/regeneration cycles (left) and with/without current
passage (right). Error bars show standard deviation of multiple readings from mean.
Turbidity Results
Adsorption and regeneration cycles were mimicked with Nyex®
and water solution in a Y-cell to study the fines generation upon
current passage (Figure 13). During regeneration, more fines
were produced and when current was passed, turbidity was
observed to be 30% higher.
Composite Development
The expanded graphite particles can be impregnated and
polymerised with a conductive furan based resin to obtain
composites (Figure 14) with a higher adsorption capacity, which
can be subsequently, carbonised and activated to increase micro-
porosity – a feature lacking in both Nyex® and CEG particles.
a) Sieving
Particles
b) Liquid
impregnation
c) Polymerise
on surface
d)
Carbonisation
e) Chemical
Activation and
final washing
Figure 7: Surface morphology of expanded graphite (left) and compressed expanded graphite
(CEG, right) at 200 and 100 times magnification respectively. The expansion of the graphite
layers can be observed in the morphology (SEM) of expanded graphite. The roughness of
edges which lead to enhanced adsorption can be observed on the surface of CEG particles.
Property Nyex® CEG
Activated
Carbon
BET Surface Area 1 m2 g-1 17 m2 g-1 2000 m2 g-1
Specific Pore Volume 0.004 cm3 g-1 0.07 cm3 g-1 0.70 cm3 g-1
Bulk Density 0.80 g cm-3 0.19 g cm-3 0.30 g cm-3
Electrical Conductivity 0.8 S cm-1 1.6 S cm-1 0.012 S cm-1
Project Objectives
a) Sieving
Particles
b) Expansion
of Nyex
c) Compression
of expansion
graphite (CEG)
d) Crushing of
CEG
Figure 2: Thermal regeneration drawbacks
Industrially, thermal regeneration is commonly practised but has
its drawbacks (Figure 2) whereas electrochemical regeneration is
an alternative technique which offers many advantages (Figure 3)
Figure 1: Activated Carbon, common
adsorbents for wastewater treatment
Thermal
Regeneration
Energy
and
Capital
Intensive
Environ-
mental
Issues
5 – 10%
Material
Losses
Electro-
chemical
Regeneration
Low
Energy
Usage
Environ-
mentally
Safe
No
Material
Losses
Figure 3: Electrochemical regeneration advantages
Earlier methods of electrochemical regeneration were less
efficient, made use of high charge passes and required long
treatment times. In 2004, using a non-porous graphite intercalated
compound called Nyex® (Figure 4), Brown et al.[1] achieved over
100% regeneration efficiencies within 20 minutes of treatment and
complete adsorption equilibrium within 60 minutes
Basic Methodology
Idea is to expand the Nyex structure by lowering the Van der Waals
forces between the layered structure, develop expanded graphite
and compress it to form compressed expanded graphite (CEG)[2].
Characterise the attrition behaviour of Nyex® particles as they have been
found to breakdown in solution during regeneration.
Increase the adsorption capacity of Nyex® particles whilst maintaining
similar regeneration efficiencies.
Figure 5: Scheme for the development of compressed expanded graphite
Conclusions
The synthesised adsorbent showed an increased adsorption
capacity due to a higher surface area and consumed lesser power
during regeneration due to a higher electrical conductivity.
Figure 14: Composite synthesis process
Material Modelling
Many options for the synthesis of composites can be screened
and explored by building a framework for material modelling of
intercalated compounds at a molecular level using molecular
dynamics (MD) and Monte-Carlo simulations.