Adsorption using Activated Materials : Science behind the Activation

1. Role of Biomass in Activated
carbon Chemistry
Presented for the
DBT Sponsored One Day National Level Seminar on
Recent Trends and Challenges in
Phytochemistry and Biosorption (RTCPB -16)
March 04, 2016
Presented by
Dr. P. Sivakumar
Assistant Professor
PG & Research Department of Chemistry
Arignar Anna Govt Arts College
Namakkal – 637 002
1

2. India ranks 117 out of 158 nations on
global happiness index
• Switzerland now at the top
• The other countries in the top five are Iceland,
Denmark, Norway and Canada.
• What does it indicates?
• “The concepts of happiness and well-being are
very likely to help guide progress towards
sustainable development,”
2

3. 3
Where we are????????

4. 4
Sustainable Development
• Development that meets the needs of
the present without compromising
the ability of the future generations
to meet their own needs (World
Commission on Environment and
Development, 1987)

5. 5
Social
Economical
Environment
Any sustainable growth has to compromise
……

6. 6
Global Perspective
life supporting resources
declining
consumption of
life supporting resources
rising

7. 7
ROLE OF CHEMISTRY IN SUSTAINABLE
DEVELOPMENT
• Only research and innovation will allow the
development of economic and social networks
and processes that fulfill the requirements of
sustainability.

8. 8
GREEN TECHNOLOGY
• Basically, green technology is that in which the
technology is environmentally friendly and is
created and used in a way that conserves
natural resources and the environment.
• You may hear green technology being referred
to as environmental technology and clean
technology.

9. 9
Catalysis
Process
Intensification
Separation
Processes
Energy
Efficiency
Solvent
Replacement
Safer Reactions
& Reagents
Use of
Renewable
Feedstocks
Waste
Minimisation
Some Aspects of Green Chemistry
Green
Chemistry

10. Relevant to thematic background……………
• Role of Plant wastes for the Sorptive
Removal of Pollutants
• What is the special in this method?
10

11. Efficient techniques for the removal of highly toxic
organic compounds from water are….
• Coagulation
• Filtration with coagulation
• Precipitation
• Ozonation
• Ion exchange
• Advanced oxidation
• Reverse Osmosis
• Etc……….
• These methods have been found
to be limited, since they often
involve high capital and
operational costs.
• On the other hand ion exchange
and reverse osmosis are more
attractive processes because the
pollutant values can be recovered
along with their removal from the
effluents.
• Reverse osmosis, ion exchange
and advanced oxidation
processes do not seem to be
economically feasible because of
their relatively high investment
and operational cost.
11

12. Adsorption and its advantages …..
• Simple design
• Low investment
• Low operating cost
• Wide selectivity
– wastewater from organic and inorganic
pollutants
• Reusability
• Environmentally Sustainable
• Economically beneficial
• Meet the great attention from the researchers
12

13. Adsorption Phenomena….
Adsorption is a surface phenomenon with common mechanism
for organic and inorganic pollutants removal
• When a solution containing absorbable solute comes into contact with a
solid with a highly porous surface structure, liquid–solid intermolecular
forces of attraction cause some of the solute molecules from the solution
to be concentrated or deposited at the solid surface.
• The solute retained (on the solid surface) - Adsorbate
• The solid on which it is retained - Adsorbent.
• This surface accumulation of adsorbate on adsorbent is called
adsorption.
• This creation of an adsorbed phase having a composition
different from that of the bulk fluid phase forms the basis of
separation by adsorption technology.
13

14. 14

15. Basics to Understand the adsorption ………………
• Intermolecular Forces..(Weak & Strong)
• States of matter..(Solid, Liquid & Gases)
• Vapour pressure of liquids…
• Surface tension..
• Osmotic pressure ..
15

16. An explanation of why material accumulates at the interface
is based on the excess energy associated with particles at
interfaces (or Unbalanced Forces).
For example, in the case of pure water and air, the water
molecules at the air-water interface have higher energy than
water molecules in the interior of the water phase. (Vapour
Pr)
The reason that these surface molecules have higher energy
is that, unlike the interior molecules, they have an
unbalanced force component (on the airside of the
molecule).
Why Adsorption  (Surface Energy)
16

17. Hydrophobic molecules…..
In solutions certain particles tend to concentrate at the surface.
These particles are those that have low affinity for the water
(solvent).
Because they have low affinity for the solvent the can get to
the surface easily since they have low bond energy in the bulk
phase.
The water system prefers to have these molecules at the
surface because the placement at the surface requires less
energy than in the bulk.
17

18. Hydrophilic molecules..
On the other hand if a particle has a high affinity for the
solvent phase (hydrophilic) it will tend to remain in the
bulk solution because of its strong bond with water.
Hydrophilic molecules are preferred to stay at the bulk
rather than the surface.
As particles concentrate at surface there becomes a
"surface excess".
18

19. 19

20. Causes of Adsorption
• Dislike of Water Phase – ‘Hydrophobicity’
• Attraction to the Sorbent Surface
– van der Waals forces: physical attraction
– electrostatic forces (surface charge interaction)
– chemical forces (e.g., - and hydrogen bonding)
20

21. The surface of a solid shows a strong affinity for molecules that
come into contact with it.
Certain solid materials concentrate specific substances from a
solution onto their surfaces.
Adsorption Phenomenon
Physical adsorption (physisorption):
Physical attractive forces
(van der Waals forces)
e.g. Carbon ads, Activated aluminaAdsorption
Phenomenon
Chemical adsorption (chemisorption): the
adsorbed molecules are held to the surface
by covalent forces.
(little application in ww treatment)
21

22. Adsorbents in Natural & Engineered
Systems
• Natural Systems
– Sediments
– Soils
• Engineered Systems
– Activated carbon
– Metal oxides (iron and aluminum as coagulants)
– Ion exchange resins
– Biosolids
22

23. Engineered Systems - Removal Objectives
• Activated carbon (chemical functional groups)
– Adsorption of organics (esp. hydrophobic)
– Chemical reduction of oxidants
• Metal oxides (surface charge depends on pH)
– Adsorption of natural organic matter (NOM)
– Adsorption of inorganics (both cations & anions)
• Ion exchange resins
– Cations and anions
– Hardness removal (Ca2+, Mg2+)
– Arsenic (various negatively charged species), NO3
-, Ba2+
removal
23

24. Cost Comparison of Adsorbents..
24

25. Low cost adsorbents….
25

26. Activated Carbon …
• Activated carbon is a material with high
porosity consisting of hydrophobic graphene
layer as well as hydrophilic surface functional
groups making them beneficial for sorption
and catalytic applications.
26

27. Activated Carbon…
• The structure of a typical microporous activated carbon is
shown in Figure
27

28. Types of pores in AC
• Macroporosity  pores greater than 50 nm in
diameter.
• Flow through macropores is described by bulk
diffusion.
• Mesoporosity  refers to pores greater than 2 nm
and less than 50 nm in diameter.
• Microporosity  pores smaller than 2 nm in diameter.
Movement in micropores is activated by diffusion
28

29. Activated Carbon..
• In general, the structure
comprises of aromatic
sheets and strips.
• The voids and gaps of
molecular dimensions,
between such aromatic
sheets are regarded as
micropores.
• Again the microporosity is
dependent on the carbon
precursor as well as the
method of preparation
29

30. Advantages of Activated Carbon Systems………
• high specific surface
• tunable porosity
• design of the process is simple
• operation of the process developed or
adopted is easy
• carbon materials are resistant to corrosive and
toxic environments
• treated effluent is of high quality
30

31. The latest challenges for the researchers are……
Search for low-cost adsorbents that have
pollutant binding capacities
• Locally available materials such as
–Natural materials
–Industrial wastes
–Agricultural wastes
• Agricultural wastes have the advantage
• Renewable
• Clean and Green Precursor
31

32. Non conventional Activated carbon
• The demand for activated carbon is increasing owing to the
increased utility of the carbon materials in pollution control.
• As a result, cost of activated carbon is also growing depending
on the application.
• The production of activated carbon through economic ways is
the need of the hour.
• A range of low cost, easily available, carbon rich and low ash
precursors and sources are being explored for the production
of carbon materials.
32

33. Biomass carbon
• It is interesting to note that Carbon has come to
the rescue of even Thomas Alwa Edison, the
greatest inventor of modern times.
• In his backbreaking toilsome efforts to invent
high-resistance incandescent lamp, where in
either Pt or Pt-Ir alloy failed to provide an
antidote.
• To our surprise, the carbon filament that was
originally used was from biomass.
33

34. What is there in the biomass…
• In the biological lignocellulosic material, the
carbohydrate (holo cellulose and cellulose)
component is intimately bound to lignin.
• Lignin is a 3-dimensional cross linked aromatic
polymer with phenyl propane units.
• Lignin possesses a complicated chemical
structure with both phenolic (aromatic) as well as
alcoholic (aliphatic) hydroxyl groups being
present in the structure
34

35. Lignin…
• Lignin composed of phenylpropane units
• three main monomers are coumaryl alcohol,
coniferyl alcohol, and sinapyl alcohol.
• Syringyl lignin polymerized by syringyl propane
• Guaiacyl lignin polymerized by guaiacyl propane
• Hydroxy-phenyl lignin polymerized by hydroxy-phenyl
propane.
35

36. Cellulose….
• It is a “-1,4-linked linear polymer of glucose
units and is insoluble in water, dilute acidic
solutions, and dilute alkaline solutions at
normal temperatures.
36

37. Typical structural building units of Lignin and Cellulose
37

38. • The carbon precursor and the method of
preparation are the determining factors of the
textural and surface properties of carbon
materials.
• Taking into consideration some specific
properties like volatile matter, ash content and
fixed carbon content as well as the derivable
porosity, several researchers have studied the
possibility of producing carbon materials from
different lignocellulosic materials.
38

39. • Both cellulose and lignin contribute the
aromatic carbon content.
• But the precursors containing hexagonally
arrayed carbon, as those found in lignin,
would readily reform to stable graphitic
arrays.
• In the case of cellulose such structural
advantage is missing to some extent but the
Aldohexose Structure Favors the formation of
Aromatic Network.
39

40. Proposed mechanism for the transformation of cellulose to
aromatic carbon
40

41. 41

42. 42

43. Conceptual mechanism for the transformation of lignin to
aromatic carbon
a) structure of lignin
b) building block of Lignin
c) graphite like layer from the structural units formed
during pyrolysis 43

44. Suitable Lignocellulosic Materials for the production
of Activated Carbon Materials
• Wood materials with a coarse cellular structure with inherent
porosities greater than 35 % were found to be disadvantageous in
terms of poor mechanical strength of the activated carbon
derivable from such materials.
• Among the materials investigated, woods are found to be of highest
porosity (46 – 49 %) and nut shells and fruit stones were of lower
porosity.
• The coke yield increased with an increase in the lignin content of
the precursor.
• This is because lignin contains lower amount of structural oxygen
compared to hemicellulose or cellulose
44

45. • Cell structure (porosity) of the plant is an important
parameter in the choice of lignocellulosic materials.
• The morphology of the plant cell is the main factor
responsible for the hardness, density and the porosity
of the coke.
• Thus the morphology of the plant cell with peculiar
cross linking between cellulose, hemicellulose and
lignin determines whether a particular lignocellulosic
material is suitable for the production of activated
carbon.
• Also upon pyrolysis the ratio of mass loss (m) to
volume (V) shrinkage should be close to 1.
45

46. • Among the raw materials investigated the
order of suitability for the production of
activated carbon is as follows:
coconut shells > peach stones > plum stones >
hazel nut shells > walnut shells > cherry stones.
46

47. Methods of activation
• A multitude of activating agents has been extensively
employed for the production of activated carbon materials
with desired pore structure.
• The purpose of activation is to create and develop (volume
and size) porosity in the carbon material and there by
increase the adsorptive capacity.
• All the available methods of activation can be classified in
to two types, namely, physical activation or chemical
activation depending on whether a gaseous or solid
activating agent is used.
• Each of these methods has its own merits and demerits.
47

48. Chemical method of activation
• On the other hand, chemical activation is a
single step process for the preparation of
activated carbon where in carbonization of
organic precursor in the presence of chemical
agents.
• alkali and
• alkaline earth metal containing substances
• some acids
48

49. Functions of Chemical Activating Agents
• Function as dehydrating agents.
• Influence pyrolytic decomposition.
• Inhibiting the formation of tar and thereby
enhancing the yield of carbon.
• The temperatures used in chemical activation are
lower than that used in the physical activation
process.
• The development of a porous structure is better
in the case of chemical activation method
49

50. KOH as activating agent
• In general the chemical reaction between KOH
and carbon material can be written as follows:
• KOH reacts with disordered or amorphous
carbon at high temperatures to form K2CO3 as
well as the decomposition product K2O along
with the evolution of hydrogen.
50

51. • Considering the decomposition of KOH into K2O as well as the
reducing ability of carbon, additional reactions do take place during
the process of activation.
• The steam generated in (step 2) causes removal of amorphous
carbon as CO as shown in (step 3) leading to formation of
pores.
• Additional carbon is also consumed for reducing K+ to K as
shown in steps (7) and (8). All these carbon losses contribute
to the creation of porous network in the carbon material.
51

52. • The process of KOH activation of mesoporous carbon
material results in the generation of significant
amount of microporosity while keeping the
mesoporosity intact is depicted pictorially
52

53. Activation with ZnCl2
• The ability of ZnCl2 to activate (generate porosity)
carbon precursors is based on its dehydrating function.
• During the process of activation, ZnCl2 eliminates
hydrogen and oxygen atoms of carbon materials as
water rather than as oxygenated organic compounds,
thus leading to the generation of porosity as well as
enhancing the carbon content.
53

54. • Since by nature ZnCl2 is dehydrating agent, it
can alter the pyrolysis behaviour of carbon
precursor. ZnCl2 gets intercalated into the
carbon matrix by impregnation.
• Upon pyrolysis, the impregnated ZnCl2 causes
dehydration of the carbon precursor leading
to charring and aromatization along with the
creation of pores.
54

55. Activation with Conc. HNO3
• HNO3 treatment changes the surface chemistry of
carbon materials.
• Such oxidative treatment results in the formation of
oxygen containing surface functional groups (carbonyl
and carboxyl).
• The presence of such surface functional groups, in
most cases, enhances the adsorption capacity of
carbon materials.
• Thus upon nitric acid treatment C=O group is
generated on the adsorbent carbon surface
55

56. • Methods of activation of carbon materials have opened up a
new avenue to tune the structural, textural, morphological
and surface properties of carbon materials to suit to the
problem in hand.
• Activation methods based on environmentally benign
activating agents (for instance organic acids and the alkali
metal salts there of) with mild reaction conditions need to be
developed.
• The sphere of usefulness of carbon materials increases
manifold with the progress in the activation recipes.
56

57. Draw backs of Chemical Methods…
• Need for washing of the product
• The residual inorganic material
• Causes serious of pollution problem
• Suitable selection of chemical is essential
• Induces surface functionalities – (May be
desirable or may not be)
57

58. Physical method of activation
• Physical activation involves two steps,
• 1.  Carbonization - of the carbonaceous
precursor in an inert atmosphere
• 2.  Activation of the resulting char in the
presence of carbon gasification reactants
(gaseous) such as carbon dioxide, steam or air
or a suitable combination of the above
mentioned gaseous activating agents.
58

59. • Carbonization …
Material with carbon content is pyrolyzed at
temperatures in the range 600–900 °C,
usually in inert atmosphere with gases like
argon or nitrogen
• Activation …
• Raw material or carbonized material is
exposed to oxidizing atmospheres (oxygen or
steam) at temperatures above 250 °C, usually
in the temperature range of 600–1200 °C
59

60. • In the method of physical activation, the reaction
involved is between carbon atom and the
oxidizing gas.
• It is this reaction that gives rise to the pore
creation and development as some parts of the
char structure are reacted faster than the others.
• During this carbonization, enlargement of
opened micropores and the opening up of the
closed micropores takes place.
60

61. Pros and cons of physical activation..
• Since physical activation uses gaseous activation agents
and does not produce waste water this method is
considered to be an environmentally benign
technology.
• It takes long time and much energy for producing
microporous activated carbon.
• Also another inherent draw back of this method is that
large amount of internal carbon mass is eliminated to
obtain well developed pore structure.
• And thus one has to satisfy himself with limited carbon
yields if one were to go in this route.
61

62. Classification of AC
• Powdered activated carbon (PAC)
• powders or fine granules less than 1.0 mm in size
with an average diameter between 0.15 and
0.25 mm.
• The ASTM classifies particles passing through an 80-
mesh sieve (0.177 mm) and smaller as PAC.
• PAC is generally added directly to other process
units, such as raw water intakes, rapid mix basins,
clarifiers, and gravity filters.
62

63. Powder AC
63

64. • Granular activated carbon has a relatively larger particle
size compared to powdered activated carbon.
• .Presents a smaller external surface.
• These carbons are suitable for adsorption of gases and
vapors, because they diffuse rapidly.
• Granulated carbons are used for water treatment,
deodorization and separation of components of flow
system and is also used in rapid mix basins.
• GAC is designated by sizes such as 8×20, 20×40, or 8×30 for
liquid phase applications and 4×6, 4×8 or 4×10 for vapor
phase applications.
Granular activated carbon (GAC)
64

65. Granular AC
65

66. • Extruded activated carbon (EAC)
• Extruded activated carbon combines powdered
activated carbon with a binder, which are fused
together and extruded into a cylindrical shaped
activated carbon block with diameters from 0.8
to 130 mm.
• These are mainly used for gas phase applications
because of their low pressure drop, high
mechanical strength and low dust content.
• Also sold as CTO filter (Chlorine, Taste, Odor).
66

67. Extruded AC
67

68. • Bead activated carbon (BAC)
• Bead activated carbon is made from petroleum
pitch and supplied in diameters from
approximately 0.35 to 0.80 mm.
• Similar to EAC, it is also noted for its low pressure
drop, high mechanical strength and low dust
content, but with a smaller grain size.
• Its spherical shape makes it preferred for
fluidized bed applications such as water filtration
68

69. AC Beads
69

70. • Impregnated carbon
• Porous carbons containing several types of
inorganic impregnate such as iodine, silver,
cations such as Al, Mn, Zn, Fe, Li, Ca.
• Prepared for specific application in air pollution
control especially in museums and galleries.
• Due to its antimicrobial and antiseptic
properties, silver loaded activated carbon is
used as an adsorbent for purification of
domestic water.
70

71. • Polymer coated carbon
• This is a process by which a porous carbon can be
coated with a biocompatible polymer to give a
smooth and permeable coat without blocking the
pores.
• The resulting carbon is useful for hemoperfusion.
• Hemoperfusion is a treatment technique in
which large volumes of the patient's blood are
passed over an adsorbent substance in order to
remove toxic substances from the blood.
71

72. Polymer Bound AC
72

73. Qualities of a Good Activated Carbon…..
• Surface area in excess of 500 m2.
• Iodine number is the most fundamental
parameter used to characterize activated
carbon performance.
• Apparent density : The solid or skeletal
density of activated carbons will typically
range between 2.0 and 2.1 g/cm3
• Ash content : Ash reduces the overall activity
of activated carbon and reduces the efficiency
of reactivation.
73

74. • Carbon tetrachloride activity : Measurement of the
porosity of an activated carbon by the adsorption of
saturated carbon tetrachloride vapour.
• Particle size distribution :
• The finer the particle size of an activated carbon, the
better the access to the surface area and the faster the
rate of adsorption kinetics.
• In vapour phase systems this needs to be considered
against pressure drop, which will affect energy cost.
• Careful consideration of particle size distribution can
provide significant operating benefits.
Qualities of a Good Activated Carbon…..
74

75. SEM images of AC …
75

76. Activated Carbon from our research Group…
76
Euphorbia
Antiquorum L

77. Silk Cotton….
77

78. 78

79. Th. Neerifolia
79

80. XRD of AC
80

81. Raman
Spectra of
(a) various
non-
crystalline,
mainly
graphitic,
carbons
and
(b)
crystalline
graphites
81

82. Factors Affecting Adsorption……
The factors affecting the adsorption process
are:
• (i) surface area
• (ii) nature and initial concentration of
adsorbate (Hydrophillic and Hydrophobic)
• (iii) solution pH
• (iv) temperature
• (v) interfering substances
• (vi) nature and dose of adsorbent.
82

83. Removal of Emerging Compounds by
Adsorption
• The words ‘‘emerging compounds’’ encompass a
huge quantity of pollutants, including
• synthetically and naturally occurring hormones,
• industrial and household chemicals,
• nanomaterials
• disinfection by-products (DBPs),
• as well as their transformation products
83

84. 84

85. Reactivation and regeneration
• The reactivation or the regeneration of
activated carbons involves restoring the
adsorptive capacity of saturated activated
carbon by desorbing adsorbed contaminants
on the activated carbon surface.
• Thermal reactivation
• Other reactivations
85

86. Thermal reactivation
• Adsorbent drying at approximately 105 °C.
• High temperature desorption and
decomposition (500–900 °C) under an inert
atmosphere
• Residual organic gasification by an oxidising
gas (steam or carbon dioxide) at elevated
temperatures (800 °C)
86

87. Other regeneration techniques
• Chemical and solvent regeneration.
• Microbial regeneration.
• Electrochemical regeneration.
• Ultrasonic regeneration.
• Wet air oxidation.
87

88. Adsorbent cost
• Adsorbent cost is an important parameter to compare different materials.
• The adsorbent costs depend on
– availability,
– its source (natural, industrial/agricultural/domestic wastes or by-products or
synthesized products),
– treatment conditions,
– recycle and lifetime issues.
• The cost also depends on
– The adsorbents are produced in (or for) developed, developing, or
underdeveloped countries.
• The right cost evaluation is related to the application scale and, although
many studies about non-conventional low-cost adsorbents are available
in the literature, they are limited to laboratory scale.
• Thus, cost estimation is not strictly right and pilot-plant studies should
also be conducted utilizing low-cost adsorbents to check their feasibility
on commercial scale.
88

89. To Conclude..
• The economical and easily available adsorbent would certainly
make an adsorption- based process a viable alternative for the
treatment of wastewater containing pollutants.
• Selection of an appropriate adsorbent is one of the key issues to
achieve the maximum removal of type of pollutant depending upon
the adsorbent andadsorbate characteristics.
• The effectiveness of the treatment depends not only on the
properties of the adsorbent and adsorbate, but also on various
environmental conditions and variables used for the adsorption
process, e.g. pH, ionic strength, temperature, existence of
competing organic or inorganic compounds in solution, initial
adsorbate and adsorbent concentration, contact time and speed
of rotation, particle size of adsorbent, etc.
89

90. •Scope of AC is plenty….
•Needs to be Explored…
•To be Applied one….
90

91. Thank you….91