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ENVIRONMENTAL ENGINEERING
Introduction
Technological development has increased the human impact on our environment and
the ecosystem, but a new technology has also emerged simultaneously to solve
environmental pollution problems. This discipline of science is environmental
engineering, in which new methods of purification and recirculation of pollutants are
developed and attempts are made to change existing technology to reduce pollution.
Environmental technology involves the application of engineering principles to devise
methods and processes to solve problems in air, water and solid waste pollution. The
role of this technology is changing in two important areas: sustainable development
which deals primarily with global problems, and preventive technology which is
designed to reduce the environmental effects of processes, operations and products.
Environmental engineering is one of the key research areas that the staff in the
Thermal and Fluids Engineering Division, School of Mechanical and Aerospace
Engineering, are pursuing in. Most of the equipment and facilities in this area are
housed in the Thermal and Fluids Research Laboratory.
Research and Development
One of the leading research areas in environmental engineering currently engaged in
is the development of activated carbons from biomass waste materials. Substantial
research has already been carried out to prepare activated carbons from oil-palm
shells to be used in the gaseous adsorption of pollutant gases such as sulphur dioxide,
ammonia and nitrogen oxides.
Traditionally, palm-oil mills generate a large amount of wastes which have to be
disposed of in an environmentally friendly way. When oil is extracted from the fruit, a
large amount of waste is generated as the shells and pulp fibres are left behind. For
instance, in Malaysia which is the largest producer of palm oil, 6 million tonnes of
waste fibre and 2.4 million tonnes of shell are generated annually.
The technique first grinds the shells and fibres into smaller sizes of a few millimetres.
These raw materials are heated in an inert atmosphere in a process called pyrolysis to
release the volatile matters, thereby leaving rudimentary pores inside the char. The
char is subsequently activated by burning some of the carbon contents to create a well
developed network of pores of nanometre sizes. These highly porous structures yield
a large pore surface area for trapping pollutants. One gram of this activated carbon
has a pore area of 1,950 sq m, which is equivalent to 18 five-room Singapore Housing
Board flats.
Activated carbon is used in various industries and treatment plants to filter the air of
poisons such as hydrogen sulphide, sulphur dioxide, nitrogen oxides and ammonia by
an adsorption process. It can also be used to remove organics such as phenol and
benzene; and heavy metals such as lead, cadmium and arsenic from raw water in the
purification of drinking water. Activated carbons can also be used in gas masks to be
worn by pump attendants in petrol stations to prevent them from inhaling noxious
petrol vapours, which are suspected to be carcinogenic. They can also be put into gas
masks in times of chemical or biological warfare to trap nerve agents (such as sarin)
or viruses.
Fig. 1 shows the progression of the oil-palm fruits to the final activated carbons. Oil is
being squeezed out from the mesocarp (pulp) and the kernel of the fruit, producing
waste residues of fibre and shell. The fibres and shells are carbonised in inert
atmosphere to form chars which are then activated in a gas stream of CO2 to produce
the final activated carbons.
Fig. 1 Photographs of the oil-palm fruits, fibres, shells, chars and activated carbons
The adsorptive capacity of activated carbon is related to its specific pore surface area,
pore volume and pore size distribution. Generally, as the pore surface area of the
activated carbon increases, its adsorptive capacity will also increase. These surface
areas are generated gradually during the activation process. Activation temperature is
an important parameter for the process. Figure 2 shows the effects of activation
temperature on the pore surface area of activated carbons prepared from oil-palm
shells pre-treated with different impregnating solutions for 24 hours. In spite of
different impregnating solutions used, the pore surface area versus the activation
temperature showed a similar trend. Increasing the activation temperature from 500oC
up to an optimum value increased the pore surface area, beyond which the surface
area decreased. For oil-palm shells impregnated with 20% ZnCl2, the largest pore
surface area was obtained at 750oC while a higher temperature of 800oC was required
for those impregnated with 40% H3PO4 and 10% KOH. For temperatures beyond
these optimum values, the pore surface area decreased with increasing temperature.
2000
BET Surface Area, m2/g
1700
1400
1100
20% ZnCl2
800
40% H 3PO 4
10% KOH
500
500
600
700
800
900
o
Activation Temperature, C
Fig. 2 Pore surface areas of activated carbons prepared at different activation
temperatures for 1 hour from oil-palm shells pre-treated with different impregnating
solutions for 24 hours.
The amount of gaseous pollutant adsorbed onto the activated carbon is a function of
its pore surface area. Figure 3 shows the amounts of SO2 (a common gaseous
pollutant) adsorbed onto the oil-palm-shell activated carbon versus the pore surface
area. For the various SO2 concentrations shown, the amount of SO2 adsorbed
increased progressively with increasing pore surface area.
Amount of SO2 Adsorbed (mg/g)
80
SO2 : 500 ppm
64
SO2 : 1000 ppm
SO2 : 2000 ppm
48
32
16
0
500
700
900
1100
1300
1500
BET Surface Area (m 2/g)
Fig. 3 Amount of SO2 adsorbed for different SO2 concentrations versus the pore
surface area of the oil-palm-shell activated carbon.
Another biomass material that is also studied to be used as a precursor for preparing
activated carbon is pistachio-nut shell. It is reported that the world production of
pistachio nuts is 0.21 million tonnes and therefore a huge amount of nut shells are
generated as waste materials. The raw shells first undergo a pyrolysis or carbonisation
process, and thereafter the chars are impregnated with KOH solution and activated in
N2 atmosphere. Figure 4 shows the effects of activation temperature on the pore
surface area and pore volume of the chemically activated carbons. Increasing the
temperature from 500 to 8000C progressively increased both the pore surface area and
micropore volume. However, for further temperature increase from 800 to 9000C,
both the pore surface area and micropore volume decreased due to excessive carbon
“burn-off”, resulting in the widening of pores as could be seen in the increases in the
non-micropore volume at 800 and 9000C.
Non-micropore volume
BET surface area
Micropore volume percentage
Micropore volume
Micropore volume(cm3/g)
0.7
BET surface area(m2/g)
2000
0.6
1800
1600
0.5
1400
1200
0.4
1000
(a)
800
600
500
600
700
90
0.6
80
0.5
0.4
70
0.3
60
0.2
50
0.1
(b)
0.3
800
900
o
Activation temperature( C)
0.0
500
600
700
800
40
900
o
Activation temperature( C)
Fig. 4 Effects of activation temperature on the (a) pore surface area and micropore
volume, and (b) non-micropore volume and micropore volume percent of chemically
activated carbons.
Another research area in environmental engineering is the development of carbon
molecular sieve membranes for gas separation. These membranes consist of thin
carbon films with pore sizes similar to those of gas molecules. They are prepared
either by the carbonization/pyrolysis of polymeric substrates or the carbonization of
polymeric films deposited on porous supports. In a particular study, a commercial
polyimide film, Kapton 100HN from DuPont, was used to prepare the carbon
membranes. The effects of carbonization parameters, such as the carbonization
atmosphere, the final temperature, the heating rate and the thermal soak time at the
final temperature, on the permeation rates of He, CO2, O2 and N2 were studied. The
permselectivities of the membranes for the gas pairs of He/ N2, CO2/N2, O2/N2 and
CO2 /CH4 were also measured.
Micropore volume pecentage(%)
2200
Non-micropore volume(cm3/g)
0.7
Permeability (Barrer)
1200
He
CO2
O2
N2
900
600
300
0
CM1 CM2 CM3 CM4 CM5 CM6 CM7 CM8
Sample ID
Figure 5. Effect of the carbonisation parameters on the transport properties of the
Kapton® based carbon membranes.
Figure 5 compares the average gas permeabilities for He, CO2, O2 and N2 for the
various carbon membranes obtained at different preparation conditions. Samples
CM1, CM5 and CM6 show large differences in the permeabilities of the different
penetrating gases while samples CM2, CM3, CM4, CM7 and CM8 yield small
permeability variations. Hence, the processing parameters during carbonization will
determine the pore structure and characteristics of the membranes.
Facilities
The equipment available include the ultra-pycnometer (Fig. 6) to measure the solid
density of sample, thermogravimetric analyser (Fig. 7) to determine the proximate
analysis of sample, accelerated surface area and porosimeter (Fig. 8) to measure pore
surface area and pore volume of porous material, a mercury intrusion porosimeter to
measure the apparent density and pore surface area of porous material, SO2 and NOx
analysers, and electrical furnaces.
Fig. 6 Ultra-Pycnometer
Fig. 7 Thermogravimetric Analyser
Fig. 8 Accelerated surface area and porosimetry system
Other equipment in the laboratory include gas chromatograph – mass spectrometry
system, ion chromatograph and various gas analyzers.
Publications
1.
A.C. Lua and J. Guo, Preparation and characterization of chars from oil palm
waste, Carbon, Vol 36, No 11, U.K., 1998, pp 1663-1670.
2.
J. Guo and A.C. Lua, Characterization of chars pyrolyzed from oil palm stones
for the preparation of activated carbons, Journal of Analytical and Applied
Pyrolysis, Vol 46, No 2, The Netherlands, 1998, pp 113-125.
3.
A.C. Lua and J.Guo, Activated carbons prepared from extracted-oil palm fibers
for nitric oxide reduction, Energy & Fuels, An American Chemical Society
Journal, Vol 12, No 6, U.S.A., 1998, pp 1089-1094.
4.
A.C. Lua and J. Guo, Chars pyrolyzed from oil palm wastes for activated carbon
preparation, Journal of Environmental Engineering, American Society of Civil
Engineers, Vol 125, No 1, U.S.A., 1999, pp 72-76.
5.
J. Guo and A.C. Lua, Textural and chemical characterisations of activated carbon
prepared from oil-palm stone with H2SO4 and KOH impregnation, Microporous
and Mesoporous Materials, Vol 32, The Netherlands, 1999, pp 111-117.
6.
J. Guo and A.C. Lua, Kinetic study on pyrolysis of extracted oil palm fiber:
Isothermal and non-isothermal conditions, Journal of Thermal Analysis and
Calorimetry, Vol 59, The Netherlands, 2000, pp 763-774.
7.
J. Guo and A.C. Lua, Effect of heating temperature on the properties of chars and
activated carbons prepared from oil palm stones, Journal of Thermal Analysis
and Calorimetry, Vol 60, The Netherlands, 2000, pp 417-425.
8.
J. Guo and A.C. Lua, Textural characterization of activated carbons prepared
from oil-palm stones pre-treated with various impregnating agents, Journal of
Porous Materials, Vol 7, The Netherlands, 2000, pp 491-497.
9.
J. Guo and A.C. Lua, Effect of surface chemistry on gas-phase adsorption by
activated carbon prepared from oil-palm stone with pre-impregnation, Separation
and Purification Technology, Vol 18, The Netherlands, 2000, pp 47-55.
10. A.C. Lua and J. Guo, Activated carbon prepared from oil palm stone by one-step
CO2 activation for gaseous pollutant removal, Carbon, Vol 38, U.K., 2000, pp
1089-1097.
11. J. Guo and A.C. Lua, Preparation of activated carbons from oil-palm-stone chars
by microwave-induced carbon dioxide activation, Carbon, Vol 38, U.K., 2000, pp
1985-1993.
12. J. Guo and A.C. Lua, Adsorption of sulfur dioxide onto activated carbons
prepared from oil-palm shells impregnated with potassium hydroxide, Journal of
Chemical Technology and Biotechnology, Society of Chemical Industry, Vol 75,
U.K., 2000, pp 971-976.
13. J. Guo and A.C. Lua, Preparation and characterization of adsorbents from oil
palm fruit solid wastes, Journal of Oil Palm Research, Vol 12, Malaysia, 2000, pp
64-70.
14. A.C. Lua and J. Guo, Preparation and characterization of activated carbons from
oil-palm stones for gas-phase adsorption, Colloids and Surfaces A:
Physicochemical and Engineering Aspects, Vol 179, Ireland, 2001, pp 151-162.
15. J. Guo and A.C. Lua, Experimental and kinetic studies on pore development
during CO2 activation of oil-palm-shell char, Journal of Porous Materials, Vol 8,
The Netherlands, 2001, pp 149-157.
16. J. Guo and A.C. Lua, Kinetic study on pyrolytic process of oil-palm solid waste
using two-step consecutive reaction model, Biomass & Bioenergy, Vol 20, U.K.,
2001, pp 223-233.
17. A.C. Lua and J. Guo, Adsorption of sulfur dioxide on activated carbon from oilpalm waste, Journal of Environmental Engineering, American Society of Civil
Engineers, Vol 127, U.S.A., 2001, pp 895-901.
18. A.C. Lua and J. Guo, Microporous oil-palm-shell activated carbon prepared by
physical activation for gas-phase adsorption, Langmuir, American Chemical
Society, Vol 17, U.S.A., 2001, pp 7112-7117.
19. J. Guo and A.C. Lua, Microporous activated carbons prepared from palm shell by
thermal activation and their application to sulfur dioxide adsorption, Journal of
Colloid and Interface Science, Vol 251(2), UK, 2002, pp 242-247.
20. J. Guo and A.C. Lua, Characterization of adsorbent prepared from oil-palm shell
by CO2 activation for removal of gaseous pollutants, Materials Letters, Vol 55(5),
Ireland, 2002, pp 334-339.
21. J. Guo and A.C. Lua, Textural and chemical characterizations of adsorbent
prepared from palm shell by potassium hydroxide impregnation at different
stages, Journal of Colloid and Interface Science, Vol 254(2), UK, 2002, pp 227233.
22. J. Guo and A.C. Lua, Adsorption of sulphur dioxide onto activated carbon
prepared from oil-palm shells with and without pre-impregnation, Separation and
Purification Technology, Vol 30(3), Ireland, 2003, pp 265-273.
23. J. Guo and A.C. Lua, Textural and chemical properties of adsorbent prepared
from palm shell by phosphoric acid activation, Materials Chemistry and Physics,
Vol 80(1), Ireland, 2003, pp 114-119.
24. J. Guo and A.C. Lua, Surface functional groups on oil-palm-shell adsorbents
prepared by H3PO4 and KOH activation and their effects on adsorptive capacity,
Transaction IChemE: Chemical Engineering Research & Design, Vol 81, Part A,
UK, 2003, pp 585-590.
25. T. Yang and A.C. Lua, Characteristics of activated carbons prepared from
pistachio-nut shells by physical activation, Journal of Colloid and Interface
Science, Vol 267(2), USA, 2003, pp 408-417.
26. T. Yang and A.C. Lua, Characteristics of activated carbons prepared from
pistachio-nut shells by potassium hydroxide activation, Microporous and
Mesoporous Materials, Vol 63(1-3), Netherlands, 2003, pp 113-124.
27. A.C. Lua and T. Yang, Properties of pistachio-nut-shell activated carbons
subjected to vacuum pyrolysis conditions, Carbon, Vol 42(1), UK, 2004, pp 224226.
28. A.C. Lua and T. Yang, Effect of activation temperature on the textural and
chemical properties of potassium hydroxide activated carbon prepared from
pistachio-nut shell, Journal of Colloid and Interface Science, Vol 274(2), USA,
2004, pp 594-601.
29. A.C Lua and T. Yang, Effects of vacuum pyrolysis conditions on the
characteristics of activated carbons derived from pistachio-nut shells, Journal of
Colloid and Interface Science, Vol 276(2), USA, 2004, pp 364-372.
30. A.C. Lua, T. Yang and J. Guo, Effects of pyrolysis conditions on the properties
of activated carbons prepared from pistachio-nut shells, Journal of Analytical and
Applied Pyrolysis, Vol 72(2), Ireland, 2004, pp 279-287.
31. J. Guo, W.S. Xu, Y.L. Chen and A.C. Lua, Adsorption of NH3 onto activated
carbon prepared from palm shell impregnated with H2SO4, Journal of Colloid and
Interface Science, Vol 281(2), USA, 2005, pp 285-290.
32. A.C. Lua and T. Yang, Characteristics of activated carbon prepared from
pistachio-nut shell by zinc chloride activation under nitrogen and vacuum
conditions, Journal of Colloid and Interface Science, Vol 290(2), USA, 2005, pp
505-513.
33. A.C. Lua and J.C. Su, Isothermal and nonisothermal pyrolysis kinetics of Kapton
polyimide, Polymer Degradation and Stability, Vol 91(1), UK, 2006, pp 144-153.
34. A.C. Lua, F.Y. Lau and J. Guo, Influence of pyrolysis conditions on pore
development of oil-palm-shell activated carbons, Journal of Analytical and
Applied Pyrolysis, in press.
35. J.C. Su and A.C. Lua, Influence of carbonization parameters on the transport
properties of carbon membranes by statistical analysis, Journal of Membrane
Science, in press.
36. T. Yang* and A.C. Lua, Textural and chemical properties of zinc chloride activated
carbons prepared from pistachio-nut shells, Materials Chemistry and Physics, Vol 100(2-3),
Ireland, 2006, pp 438-444.
37. A.C. Lua and J.C. Su*, Effects of carbonisation on pore evolution and gas permeation
properties of carbon membranes from Kapton polyimide, Carbon, Vol 44(14), UK, 2006,
pp 2964-2972.
38. J. Guo, Y. Luo, A.C. Lua, R.A. Chi, Y.L. Chen, X.T. Bao and S.X. Xiang, Adsorption of
hydrogen sulphide (H2S) by activated carbons derived from oil-palm shell, Carbon, Vol
45(2), UK, 2007, pp 330-336.
39. A.C. Lua and Q.P. Jia*, Adsorption of phenol by oil-palm-shell activated carbons,
Adsorption, Vol 13, USA, 2007, pp 129-137.
40. J.C. Su* and A.C. Lua, Effects of carbonisation atmosphere on the structural
characteristics and transport properties of carbon membranes prepared from Kapton
polyimide, Journal of Membrane Science, Vol 305, Ireland, 2007, pp 263-270.
41. Q.P. Jia* and A.C. Lua, Concentration-dependent branched pore kinetic model for aqueous
phase adsorption, Chemical Engineering Journal, Vol 136(2-3), Ireland, 2008, pp 227-235.
42. J. Guo, B. Gui, S.X. Xiang, X.T. Bao, H.J. Zhang and A.C. Lua, Preparation of activated
carbons by utilizing solid wastes from palm oil processing mills, Journal of Porous
Materials, Vol 15(5), 2008, pp 535-540.
43. Q.P. Jia* and A.C. Lua, Effects of pyrolysis conditions on the physical characteristics of
oil-palm-shell activated carbons used in aqueous phase phenol adsorption, Journal of
Analytical and Applied Pyrolysis, Vol 83(2), Ireland, 2008, pp 175-179.
44. A.C. Lua and T. Yang*, Theoretical analysis and experimental study on SO2 adsorption
onto pistachio-nut-shell activated carbon, American Institute of Chemical Engineers
(AIChE) Journal, Vol 55(2), USA, 2009, pp 423-433.
45. A.C. Lua and J.C. Su*, Structural changes and development of transport properties during
the conversion of a polyimide membrane to a carbon membrane, Journal of Applied
Polymer Science, Vol 113(1), USA, 2009, pp 235-242.
46. A.C. Lua and Q.P. Jia*, Adsorption of phenol by oil-palm-shell activated carbons in a
fixed bed, Chemical Engineering Journal, Vol 150(2-3), Ireland, 2009, pp 455-461.
47. J.C. Su* and A.C. Lua, Experimental and theoretical studies on gas permeation through
carbon molecular sieve membranes, Separation and Purification Technology, Vol 69,
Ireland, 2009, pp 161-167.
48. A.C. Lua and T. Yang*, Theoretical and experimental SO2 adsorption onto pistachio-nutshell activated carbon for a fixed-bed column, Chemical Engineering Journal, Vol 155,
Ireland, 2009, pp 175-183.
49. Y. Shen* and A.C. Lua, Effects of membrane thickness and heat treatment on the gas
transport properties of membranes based on P84 polyimide, Journal of Applied Polymer
Science, Vol 116(5), USA, 2010, pp 2906-2912.
50. J. Guo, G. Hu, A.C. Lua and M.J. Heslop, Separation of ethane gas by adsorption onto
various biomass-derived activated carbons, Advanced Materials Research, Vols 113-114,
Switzerland, 2010, pp 1896-1899.
51. Y. Shen* and A.C. Lua, Structural and transport properties of BTDA-TDI/MDI copolyimide (P84)-silica nanocomposite membranes for gas separation, Chemical
Engineering Journal, Vol 188, Ireland, 2012, pp 199-209.
52. Y. Shen* and A.C. Lua, Preparation and characterization of mixed matrix membranes
based on poly(vinylidene fluoride) and zeolite 4A for gas separation, Polymer Engineering
and Science, Vol 52, Issue 10, USA, 2012, pp 2106-2113.
53. Y. Shen* and A.C. Lua, Preparation and characterization of mixed matrix membranes
based on PVDF and three inorganic fillers (fumed nonporous silica, zeolite 4A and
mesoporous MCM-41) for gas separation, Chemical Engineering Journal, Vol 192, Ireland,
2012, pp 201-210.
54. A.C. Lua and Y. Shen*, Preparation and characterization of asymmetric membranes based
on nonsolvent/NMP/P84 for gas separation, Journal of Membrane Science, Vol 429,
Ireland, 2013, pp 155-167.
55. A.C. Lua and Y. Shen*, Preparation and characterization of polyimide-silica composite
membranes and their derived carbon-silica composite membranes for gas separation,
Chemical Engineering Journal, Vol 220, Ireland, 2013, pp 441-451.
56. A.C. Lua and Y. Shen*, Influence of inorganic fillers on the structural and transport
properties of mixed matrix membranes, Journal of Applied Polymer Science, Vol 128,
Issue 6, USA, 2013, pp 4058-4066.
Contact Person
Dr. Lua Aik Chong
Associate Professor
School of Mechanical and Aerospace Engineering
Nanyang Technological University
50 Nanyang Avenue
Singapore 639798
Tel: (65)-67905535 Fax: (65)-67924062
E-mail: maclua@ntu.edu.sg