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1 | P a g e
1. INTRODUCTION
It is well-known that sulphur compounds are undesirable in the fuels.
Elemental sulphur is not toxic, but many simple sulphur derivates are very
toxic, such as sulphur dioxide (SO2) and hydrogen sulphide. Combustion of
sulphur-containing compounds in fossil fuels emits sulphur oxides, which can
cause adverse effects on health, environment and economy.
Globally sulphuric substances can have the following effects on human
health: Disturbance of blood circulation, Heart damage, Effects on eyes and
eyesight, Reproductive failure, Damage to immune systems, Stomach and
gastrointestinal disorder, Damage to liver and kidney functions, Hearing
defects, Disturbance of the hormonal metabolism, Dermatological effects,
Suffocation and lung embolism and, Neurological effects and behavioural
changes
Need for Desulfurization:
Presence of sulphur in crudes is a menace because it causes many difficulties
like-corrosion of metals, in processing of oils, and also environmental pollution
as a result of burning of high sulphur fuels that are processed from crudes
having high sulphur content. In brief, presence of sulphur in crudes causes [1]:
1. Problems of corrosion and odour
2. Pollution problems
3. Cost of waste treatment is a punitive for all refiners with high- sulphur
crudes
4. Sulphur containing residums when cracked leaves cross-linked structures
that resemble the phenomenon of vulcanization of rubber and offer
perennial problems
5. It desists the effects of additives
2 | P a g e
6. Its presence in different fractions complicates the refining and treatment
methods
Types of sulphur compounds in various fuels
Table 1.1 below gives us an idea of the type of sulphur compounds that are
present in various fuels. Although sulphur concentrations in gasoline and diesel
fuel are moving to progressively lower levels, additional steps to remove the
remaining sulphur are still required.
Table 1.1 Type of sulphur compound
BOILING RANGE SULPHUR
COMPOUNDS
GASOLINE 25 – 225 *C Mercaptans, sulphides,
disulphides, thiophene
and its alkylated
derivatives,
Benzothiophene
JET FUEL/ KEROSENE 130-300 *C Mercaptans,
benzothiophene,
alkylated Benzothiophene
DIESEL 160-380*C Alkylated
benzothiophene, di-
benzothiophene,
alkylated
dibenzothiophene
3 | P a g e
2. LITERATURE REVIEW
Li et al[1] in 2008 had worked on desulphurization of fuel using CuNaY
zeolites that were prepared by microwave irradiation and also studied about the
influence of aromatics on thiophene adsorption. The zeolites are prepared by
Solid phase ion exchange (SPIE) or liquid phase ion exchange (LPIE). LPIE is
quite common. In contrast to the usual process of heating the exchange
suspension through an oil or water bath, microwave irradiation is used. On
analysing the X-Ray powder Diffraction patterns of Na-Y and Cu-ion
exchanged zeolite samples, recorded at 2θ values between 5ᵒ and 60ᵒ, Li showed
that the irradiation technique is a better option because the characteristic peaks
for Cu ion-exchanged zeolite samples are similar to those of Na-Y and no shift
in the peak positions and no significant diffraction lines assigned to any new
phase were observed. They observed the effects of the microwave irradiating
power, duration time and the copper ion concentration in aqueous solutions on
the ion exchange level and the structure of copper ion-exchanged zeolite
samples with the help of atomic absorption spectrophotometer, X-ray powder
diffraction, N2 adsorption and scanning electron microscope and X-ray
photoelectron spectroscopy and showed that microwave irradiation was a more
attractive zeolite preparation method.
Xiao et al [2] in 2008 worked on the adsorption of benzo-thiophene (BT)
and di-benzo-thiophene (DBT) on transition metal ion impregnated activated
carbons and ion exchanged Y- zeolites. A total of 10 samples were prepared
where 5 of them were transition-metal ions (Ag+, Ni
2+, Cu
2+, Zn
2+, and Fe
3+)
separately loaded on the ACs by the impregnation method and the other five
included Y-type zeolites separately containing Ag+, Ni
2+, Cu
2+, Zn
2+, and Fe
3+,
prepared by the liquid ion-exchange method. They compared the Isotherms of
BT and DBT on original activated carbon, with, the effects of different ions on
isotherms of BT and DBT, and concluded that the adsorbing capacity depended
on the concentration of BT, where, at high concentration of BT, activated
4 | P a g e
carbon was a better sorbent and at low concentration, Y-zeolite was a good
adsorbent. It was observed that the pore surfaces of the ACs have stronger
interactions with adsorbate DBT compared to BT because the size of DBT is
larger than that of BT. This was the reason why, there was no adsorption of
DBT on Na(I)/Y zeolites. They showed that (1) the adsorption of BT by
Ag(I)/Y was the highest, while that by Na/Y was the lowest and (2) the Ag
(I)/AC was the highest, while that on Fe (III)/AC was the lowest.
David L. King et al [3], worked on removal of sulfur components from
low sulfur gasoline using copper exchanged zeolite Y at ambient temperature.
Copper-exchanged zeolite Y has been shown to be an effective material for
removal of a variety of sulfur species from hydrocarbon streams, and both
monovalent (Cu(I)) and divalent (Cu(II)Y) materials have been claimed to be
effective. In their work, they discussed about experiments aimed at providing a
direct performance comparison between the two copper-containing materials.
Cu(I)Y zeolite is somewhat more effective than Cu(II)Y in removing thiophene
from various fuel blends. Capacity of both materials for thiophene diminishes
markedly when aromatics and/or olefins are present, and Cu(I)Y immediately
turns dark on exposure to such feeds. Both materials demonstrate ability to
convert thiols to disulfides at ambient temperature.
AnkurSrivastav et al [4], there study shows that the alumina could be
used as adsorbent for the desulfurization of liquid fuels. There studies were
performed to understand the mechanism of DBT adsorption onto alumina.
Presence of DBT on the surface of alumina was confirmed by comparing EDX
of DBT loaded alumina. Equilibrium between the DBT in the solution and on
the alumina surface was practically achieved in 24 h. The adsorption processes
was well described by his amulti-stage diffusion model. The DBT up take was
found to be controlled by external mass transfer at earlier stages and by intra-
particle diffusion at later stages The adsorption of DBT onto alumina was found
5 | P a g e
to be endothermic in nature with the heat of adsorption being 19.5 kJ/mol. His
experiments best represents the equilibrium adsorption data at all temperatures.
Babich et al [5] ,they discussed about the technologies of sulfur removal
from refinery streams leads to a better research topic. There several topics have
the character of demonstration better removal of sulfur. Some of the integrated
approachs are catalyst selection, reactor design, process configuration will lead
to efficient desulfurization processes that will produce fuels with zero sulfur
emission. There other approaches to sulfur removal, such as extractive
desulfurization, look less attractive since the involvement of an additional phase
leads to large plants and limited efficiency. The same applies for oxidative
extraction, in which in addition to the solvent an oxidant is required in addition
to the solvent, although recycling might reduce the amounts consumed.
Blanco-Brieva et al [6],worked to improve the adsorption capacity and
sorbent regeneration in areas such as increasing specific desulfurization activity,
hydrocarbon phase tolerance, sulfur removal at higher temperature, and
development of new porous substrates for desulfurization of a broader range of
sulphur compounds. There work comprehensively describes the adsorption of
organo-sulfur compounds present in liquid fuels on metal-organic framework
(MOF) compounds. They has been demonstrated that the extent of
dibenzothiophene (DBT) adsorption at temperatures close to ambient (304 K) is
much higher on MOF systems than on the benchmarked Y-type zeolite and
activated carbons. In addition, the DBT adsorption capacity depends strongly on
the MOF type as they illustrated by the much higher extent of adsorption
observed on the Cu-(C300) and Al-containing (A100) MOF systems than on the
Fe-containing (F300) MOF.
6 | P a g e
Chetan Borkar et al [7], worked on several experiments on adsorption of
VOC, namely, dichloromethane,on activated carbon by a flow-through
gravimetric technique using a thermo-gravimetric analyser. They took the
measurements which were performed at three different temperatures, namely,
(303.15, 318.15, and 353.15) K. They compared the results to already available
data for the adsorption of dicholoro-methane on activated carbon.Although
higher partial pressures can readily be obtained, he measured the isothermsup to
partial pressures of about 1 kPa; higher partial pressureswould be rarely
encountered in industry. The isotherms werefit using virial and Langmuir
models. It was observed that thebest description of experimental data is
obtained using a virialisotherm across all of the temperatures. The limiting
enthalpyof adsorption obtained using the virial model was -41 kJ ·mol-1.
I.HilalGübbük et al [8],conducted several experiments on synthesis,
characterization, and sorption properties of silica gel-immobilized Schiff base
derivative. Theyderivatized the Silica gel from benzophenone 4-
aminobenzoylhydrazone (BAH), a Schiff base derivative, after silanization of
silica by 3-chloropropyltrimethoxysilane (CPTS) by using a reported method.
The mean sorption energy (E) of benzophenone 4-aminobenzoylhydrazone
(BAH) immobilization onto silica gel was calculated from D–R isotherms,
indicating a chemical sorption mode for four cations. He also calculated the
thermodynamic parameters, like _G, _S, and _H for the system. They observed
_H values were found to be endothermic: 27.0, 22.7, 32.6, and 34.6 kJmol−1 for
Cu(II), Ni(II), Co(II), and Zn(II) metal ions, respectively and _S values were
calculated to be positive for thesorption of the same sequence of divalent
cations onto sorbent. They observed negativeG-values, which indicate that the
sorption process for these three metal ions onto immobilized silica gel is
spontaneous.This study indicated that the immobilized silica gel surface using
BAH after CPTS, as precursor silylating agent, could be used as effective
adsorbent material for the purification of water. The sorption of four metal ions,
7 | P a g e
from aqueous solution onto an immobilized silica gel, was studied in his work.
The order of sorption capacities order was “Zn >Cu >Co >Ni”. Immobilized
silica gel may be used as an inexpensive, effective, and alternative sorbent for
removal of four metal ions from aqueous solutions.
Chunshan Song et al [9], worked on deep desulfurization for ultra-clean
gasoline, diesel fuel and jet fuel. It was clear that deep reduction of gasoline
sulfur (from 330 to 30 ppm) must be made without decreasing octane number or
losing gasoline yield. The problem is complicated by the high olefins contents
of FCC naphtha which contributes to octane number enhancement but can be
saturated under HDS conditions. Deep reduction of diesel sulfur (from 500 to
<15 ppm sulfur) is dictated largely by 4,6-dimethyldibenzothiophene, which
represents the least reactive sulfur compounds that have substitutions on both 4-
and 6-positions. The deep HDS problem of diesel streams is exacerbated by the
inhibiting effects of co-existing polyaromatics and nitrogen compounds in the
feed as well as H2S in the product. The approaches to deep desulfurization
include catalysts and process developments for hydro-desulfurization (HDS),
and adsorbents or reagents and methods for non-HDS-type processing schemes.
His research on Desulfurization should also take into consideration of the fuel-
cell fuel processing needs, which will have a more stringent requirement on
desulfurization (e.g., <1 ppm sulfur) than IC engines.
Kyu-Sung Kim et al [10], have worked on removal of sulphur
compounds in FCC raw C4 using activated carbon impregnated with
CuCl and PdCl2 . They studied on several activated carbon(AC) based
adsorbents were to develop a more efficient adsorbent for
removal of mercaptans and sulfides during the FCC refinery
process. The adsorbents were prepared by impregnating AC with
CuCl and PdCl2 .Kyu-Sung Kim evaluate the degree of metal halide
impregnation into the activated carbon support, and each adsorbent
was characterized by N2 adsorption, elemental analysis (EA) and XRF.
8 | P a g e
After repeating the experminent several times he stated the sulfur
adsorption capacities of adsorbents decreased in the following order :
AC impregnated PdCl2, AC impregnated CuCl and non-impregnated
AC (NIAC). The saturated adsorbents were regenerated by toluene
treatmentand reactivated at 130 °C under a vacuum.
Hisham S. Bamuflehet al [11], conducted several experiments on single
and binary sulfur removal components from model diesel fuel using granular
activated carbon. Sulfur compounds in diesel comprise mainly of alkylated
benzothiophene (BT), dibenzothiophene (DBT) and its derivatives. They
conducted several studies to desulfurize diesel fuel and opted
Hydrodesulfurization process (HDS) at high temperature (320–380 8C) and
high pressure (3–7 MPa) over CoMo or NiMo catalysts is which is currently a
major process in petroleum refineries to reduce the sulfur in diesel fuel.
Activated carbon surface structure and properties can be controllable to propose
better adsorbents. They chose activated carbon was for refractory compounds
desulfurization of liquid fuels such as fuel oil straight run gas oil and it showed
high adsorptive capacity and selected the refractory sulfur compounds such as
4,6-DMDBT. Selective adsorption of 4,6-DMDBT using activated
carbonactivated prepared by ZnCl2 activator and prepared at differentconditions
from dates’ stone is feasible, promising and worthfurther studying. The studies
of dynamics desulfurizationby adsorption of DBT and 4,6-DMDBT from model
andcommercial diesel in fixed bed adsorbers of activated carbon.
Rosaset al [12], have done several experiments on desulfurization of
low sulfur diesel by adsorption using activated carbon by adsorption isotherms
.Diesel fuels with ultralow sulfur content (15 ppmw) can be contaminated when
they are transported. Experiment conducted desulfurization of diesel fuel with
72 ppmw of sulfur in a batch system using four activated carbons at 303.15 K,
atmospheric pressure, and magnetic stirring during 18 h was performed.
Theycorrelates better the experimental behavior of this adsorbent. For sulfur
9 | P a g e
removal of diesel from a total sulfur concentration of 72-15 ppmw, and
recommended to process less than 4.2 g-D/g-A with the used activated carbons.
Also, Celia Marin-Rosas recommended to make additional test to study the
selectivity and competitively between the sulfur compounds and the rest of the
organic compounds present into diesel fuel, such asaromatics, paraffins,
isoparaffins, naphthenes, and olefins.
Yang et al [13], have worked on Desulfurization of Liquid Fuels by
Adsorption via ð Complexation with Cu(I)-Y and Ag-Y Zeolites. Fixed-bed
adsorption using different ð-complexation adsorbents for desulfurization of
liquid fuels was investigated. Cu(I)-Y (autoreduced Cu(II)-Y), Ag-Y, H-Y, and
Na-Y zeolites were used to separate low-concentration thiophene from mixtures
including benzene and/or n-octane, all at room temperature and atmospheric
pressure. Sulfur-free (i.e., below the detection limit of 4 ppmw sulfur) fuels
were obtained with Cu(I)-Y, Ag-Y, and H-Y but not Na-Y. Breakthrough and
saturation adsorption capacities obtained for an influent concentration of 760
ppmw sulphur (or 2000 ppmwthiophene) in n-octane follow the order Cu(I)-Y >
Ag-Y > H-Y > Na-Y and Cu(I)-Y > H-Y > Na-Y > Ag-Y, respectively.
10 | P a g e
3. THEORY
3.1 Adsorption and types of adsorption:
Adsorption is a process that occurs when a gas or liquid solute
accumulates on the surface of a solid or a liquid (adsorbent), forming a
molecular or atomic film (the adsorbate). It is different from absorption, in
which a substance diffuses into a liquid or solid to form a solution. The term
sorption encompasses both processes, while desorption is the reverse process.
Adsorption is operative in most natural physical, biological, and chemical
systems, and is widely used in industrial applications such as activated charcoal,
synthetic resins and water purification. Similar to surface tension, adsorption is
a consequence of surface energy. In a bulk material, all the bonding
requirements (be they ionic, covalent or metallic) of the constituent atoms of the
material are filled. But atoms on the (clean) surface experience a bond
deficiency, because they are not wholly surrounded by other atoms. Thus it is
energetically favourable for them to bond with whatever happens to be
available. The exact nature of the bonding depends on the details of the species
involved, but the adsorbed material is generally classified as exhibiting
physisorption or chemisorption.
Physisorption or physical adsorption is a type of adsorption in which the
adsorbate adheres to the surface only through Vander Waals (weak
intermolecular) interactions, which are also responsible for the non-ideal
behaviour of real gases.
Chemisorption is a type of adsorption whereby a molecule adheres to a
surface through the formation of a chemical bond, as opposed to the Van der
Waals forces which cause physisorption.
11 | P a g e
Adsorption is usually described through isotherms, that is, functions
which connect the amount of adsorbate on the adsorbent, with its pressure (if
gas) or concentration (if liquid). One can find in literature several models
describing process of adsorption, namely: Freundlich isotherm, Langmuir
isotherm, BET isotherm, etc.
Table 3.1 Comparison between Physisorption and Chemisorption
Physisorption Chemisorption
Low heat of adsorption usually in the
range of 20-40 kJ mol-1
High heat of adsorption in the range
of 40-400 kJ mol-1
Force of attraction are Van der Waal's
forces
Forces of attraction are chemical
bond forces
It usually takes place at low temperature
and decreases with increasing
temperature
It takes place at high temperature
It is reversible It is irreversible
It is related to the ease of liquefaction of
the gas
The extent of adsorption is generally
not related to liquefaction of the gas
It is not very specific It is highly specific
It forms multi-molecular layers It forms monomolecular layers
It does not require any activation energy It requires activation energy
12 | P a g e
Factors affecting adsorption: The extent of adsorption depends upon the
following factors:
• Nature of adsorbate and adsorbent.
• The surface area of adsorbent.
• Activation of adsorbent.
• Experimental conditions. E.g., temperature, pressure, etc.
3.2 Applications of adsorption:
The principle of adsorption is employed,
1. In heterogeneous catalysis.
2. In gas masks where activated charcoal adsorbs poisonous gases.
3. In the refining of petroleum and decolouring cane juice.
4. In creating vacuum by adsorbing gases on activated charcoal.
5. In chromatography to separate the constituents' of a mixture.
6. To control humidity by the adsorption of moisture on silica gel.
13 | P a g e
Important Adsorbents and their Uses:
� Silica Gel:
• Drying of gases, refrigerants, organic solvents, transformer oils
• Desiccant in packings and double glazing
• Dew point control of natural gas
� Activated Alumina:
• Drying of gases, organic solvents, transformer oils
• Removal of HCl from hydrogen
• Removal of fluorine in alkylation process
� Carbons:
• Nitrogen from air
• Hydrogen from syngas
• Ethene from methane and hydrogen
• Clean-up of nuclear off-gases
• Water purification
� Zeolites:
• Oxygen from air
• Drying of gasses
• Removing water from azeotropes
• Sweetening sour gases and liquids
• Purification of hydrogen
• Separation of xylenes and ethyl benzene
� Polymers and Resins:
• Water purification
• Recovery and purification of steroids, amino acids
• Separation of fatty acids from water and toluene
14 | P a g e
3. 3. Methods for Desulfurization
Hydrodesulphurization process (HDS) at high temperature (320–380 8C)
and high pressure (3–7 MPa) over CoMo or NiMo catalysts was a major process
in petroleum refineries to reduce the sulphur in diesel fuel. The major sulphur
compounds existing in current commercial diesel are the alkyl di-
benzothiophenes (DBTs) with one or more alkyl groups at 4 or/and 6 positions
which have been considered to be refractory sulphur compounds in the fuel due
to the steric hindrance of the alkyl groups in HDS. This process is highly
efficient for the removal of thiols, sulfides, and disulfides.However, it is
difficult to reduce sulphur levels to an ultra low level using the HDS process
because of the very low reactivity of the HDS catalysts towards sulphur
compounds and also towards refractory sulphur-containing compounds such as
dibenzothiophene and its derivatives especially 4,6-dimethydibenzothiophene
(4,6-DMDBT). An increase in the reactor size and hydrogen consumption is
required to achieve high levels of desulphurization.
Other methods, such as oxidative desulphurization and bio-
desulphurization, have shown good potential for removing refractory sulphur
under mild conditions. This process is based on the well known propensity of
organic sulphur compounds to be oxidized; it consists of an oxidation followed
by the extraction of the oxidized products. The greatest advantage of oxidative
desulphurization and bio-desulphurization, compared with the conventional
HDS technology, is that they can be carried out in the liquid phase under very
mild conditions near room temperature and under atmospheric pressure.
The advantage of BDS is that it can be operated in conditions that require
less energy and hydrogen. BDS operates at ambient temperature and pressure
with high selectivity, resulting in decreased energy costs, low emission, and no
generation of undesirable side products. Over the last two decades several
15 | P a g e
research groups have attempted to isolate bacteria capable of efficient
desulphurization of oil fractions.
ODS offers several advantages compared with HDS. For example, the
refractory-substituted dibenzothiophenes (DBTs) are easily oxidized under low
temp and pressure conditions so expensive hydrogen is not required and,
therefore, the capital requirement for an ODS unit is significantly less than that
for a deep HDS unit.Currently, the main obstacles to the industrial application
of ODS are (1) their low-oxidation activity and their low selectivity for the
sulfides present in fuel oils, (2) the difficulties in separation and recovery of the
catalysts after the reactions, (3) the low utilization efficiency of H2O2, and (4)
the introduction of other components to the oxidation systems.
Desulphurization of commercial fuels by selective adsorption has been
reported as an alternative technology for the current HDS method. Yang and co-
workers reported using zeolites for selective adsorption under ambient
conditions for the desulphurization of commercial fuels [6-10]. Metal ion-
exchange Y zeolites have also been shown to effectively remove sulphur
compounds under ambient conditions. However, the sulphur adsorption capacity
depends on the composition of the fuel. Adsorptive removal of sulphur
compounds from liquid commercial fuels has been widely investigated using
various different adsorbents. Ag-Y and Cu-Y zeolites have been shown to have
a particularly high adsorption capacity and selectivity for thiophene and its
derivatives. The advantages of using absorbents, such as the low-energy
demands of the process, potential to regenerate the spent adsorbent, and broad
availability of adsorbents, have made adsorption processes an attractive area of
research.
16 | P a g e
Figure 3.1 Methods for Desulfurization
3.4 Gas Chromatograph
Gas chromatography is used to identify and quantitate individual components in
a mixture. Quantitation uses chromatographic data to determine the amount of a
given component in a mixture and the data can be in the form of either peak
height or peak area which is obtained from an integrated chromatogram.
Methods available for De-
decompostion of sulphur compounds
with hydrocarbon
return
•conventional HDS
•HDS with octane recovery
•selective oxidation
•reactive adsorption
•bio-desulfurization
.1 Methods for Desulfurization
Gas Chromatography:
Gas chromatography is used to identify and quantitate individual components in
a mixture. Quantitation uses chromatographic data to determine the amount of a
given component in a mixture and the data can be in the form of either peak
which is obtained from an integrated chromatogram.
Methods available for -sulfurization
seperation of S-compounds without S
elimination
•alkylation
•extraction
•oxidation to sulfones
•precipitation
•adsorption
combinationseperation
+decomposition
• catalytic distillation
Gas chromatography is used to identify and quantitate individual components in
a mixture. Quantitation uses chromatographic data to determine the amount of a
given component in a mixture and the data can be in the form of either peak
which is obtained from an integrated chromatogram.
Methods available for
combination-seperation
+decomposition
catalytic distillation
17 | P a g e
Figure 3.2 Schematic Layout of GC
Quantitative Methods
The most common methods used are Area percent, Single point external
standard,Multiplepoint external standard, Single point internal standard and
multiple point internal standards. Among those:
Area Percent Method: This method provides a rough estimate of the amounts
of analytes present and for calculating area percent take the area of an analyte
and divide it by the sum of areas for all peaks. This value represents the
percentage of an analyte in the sample.
Single Point External Standard: Analyze a sample containing a known
amount of analyte or analytes and record the peak area.
Then calculate a response factor.
Response factor = (Peak area / sample amount)
after getting the response factor we can calculate the amount of unknown
analyte of the sample
Amount of analyte=(Peak area / response factor)
18 | P a g e
Procedure:
When a sample is injected into the correct column, a carrier gas sweeps the
sample through the column. If necessary, an oven heats the system to vapourize
the sample and speed its passage through the column. The different components
of the sample will be separated by the column because each of the components
sticks to the liquid coating that on the column packing differently. The greater
the stickiness the longer it takes for a substance to pass through the column.
When a substance leaves the column, it is sensed by a detector. The detector
generates a voltage that is proportional to the amount of the substance. The
signal from the detector is then displayed by a chart recorder and/or fed into a
computer.
Modern gas chromatograph’s are connected to a computer which displays the
peaks of all the substances in the sample. This is called the chromatogram.
The time that it takes a substance topass through the instruments from injection
to detection is called retention time. The retention time is measured from the
injection point topeak height. The amount of substance in a sample is
proportional to the area under the peak of that substance and that proportionality
constant is different for each substance and detector.
Chromatography(GC) is a method of separating “volatile” compounds so that
they may detected individually in complex mixtures. Compounds are separated
based on differences in their vapour pressures and their attraction to solid
materials inside the instruments. Because the vapour pressure of a given
compound is a function of intermolecular forces between molecules, GC takes
advantages in differences in at least one of the properties of matter
In GC, the sample is injected into the instrument using a small syringe. The
sample is swept into the instrument using a carrier gas where the sample is
separated into its individual chemical components, called analytes. Separation is
19 | P a g e
achieved by both attraction to the stationary phase and differences in vapour
pressure. Because vapour pressure varies with temperature, the temperature of
the instrument is often adjusted during the chromotoraphic run. A detector,
which is designed to sense analyte molecules as they exit the GC, is at the exit
of the column.
Because the analyte molecules bind differently to the stationary phase, they
travel through the GC column at different rates. That is, they have different
retention times on the column. As an analyte appears in the detector, its
presence is signaled by a peak. Thus, a gas chromatogram consists of a series of
peaks,one for each of the components of the sample. The chromatogram is
displayed on a chart recorder or computer screen.
Gas chromatography is an instrumental method for the separation and
identification of chemical compounds. Chromatography involves a sample
being dissolved in a mobile phase. The mobile phase is then forced through an
immobile, immiscible stationary phase. The phases are chosen such that
components of the sample have differing solubilites in each phase. A
component that is quite solute in the stationary phase will take longer to travel
through it than a component that is not very soluble in the stationary phase but
very soluble in the mobile phase. As a result of these differences in mobilities,
sample components will become separated from each other as they travel
through the stationary phase. After the separation of the compounds, Flame
Ionization Detector(FID) is used to identify each of them and determine their
mass.
The effluent from the column is mixed with hydrogen and air, and ignited.
Organic compounds burning in the flame produce ions and electrons that can
conduct electricity through the flame. A large electrical potential is applied at
the burner tip, and a collector electrode is located above the flame. The current
resulting from the pyrolysis of any organic compounds is measured. FID s are
20 | P a g e
mass sensitive rather than concentration sensitive; this gives the advantage that
changes in mobile phase flow rate do not affect the detectors response. The FID
is a useful general detector for the analysis of organic compounds; it has high
sensitivity, a large linear response range, and low noise. It is also robust and
easy to use, but it destroys the injected sample.
After detection, a signal is sent to the recording device. Each analyte in a
sample will have different retention time. The time taken for the mobile phase
to pass through the column is called tM.
A GC can separate the compounds, but cannot identify them itself. By
calibrating GC you can find out at what time various organic compounds are
being detected. The area under the curve may be expressed in terms of
concentration of the pollutant, by running some calibration standards at known
concentration.
Calculating the Area: The area of a peak is proportional to the amount of the
compound that is present. The area can be approximated by treating the peak as
a triangle. The area of a triangle is calculated by multiplying the height of peak
times its width at half height.
21 | P a g e
4. EXPERIMENTAL PROCEDURE
Adsorbent properties:
1. cbv-3020 (H-ZSM-5)
Si/Al = 33
Pore size = 0.54 mm
Pore Volume = 0.19 ml/gm
2. cbv 20A: (Hmodermite-c)
Si/Al =20
Surface Area =420 m2/gm
Nominal Cation form = H2
Ag-Y Zeolite Adsorbent Preparation:
As Na in Na-Y zeolite is less active towards sulphur, it is better to replace
the Na with Cu or Ag(which are more active towards sulphur). To prepare 0.2M
Ag-Y Zeolite adsorbent , take 60ml distilled water in a 250ml conical flask and
add 2gms of Na-Y zeolite and 2gms of AgNO3(Silver Nitrate). Keep this
solution away from sunlight by keeping in a dark room for 48 hours. After 48
hours filtrate the solution by using filter papers and dry it. Later wash the dried
filtrate with distilled water. Again filter the solution and dry it. The required
Ag-Y Zeolite is prepared[9].
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Procedure:
Take 3 conical flasks of 50 ml volume. Fill these conical flasks with 10
ml toluene in each with the help of burette. To make a 500 ppm of sulphur
content, add 5 milligrams of Thiophene in each flask. Measure the Thiophene
peaks of each flask with the help of Gas Chromatography Equipment for one of
the adsorbent. And then add available adsorbents like zeolites, activated carbon
etc. Before adding the adsorbents, they have to be activated at 110 °C in heater.
After activating the adsorbents, add 1gm of each adsorbent in each
conical flask. After adding adsorbents, keep these flasks in shaker for 24hours.
After 24 hours of shaking, filtrate the solutions and measure the sulphur content
in each flask with the help of Gas Chromatography Equipment. The percentage
of suphur removal and the amount of sulfur adsorbed onto the adsorbent were
measured using the expressions
Percentage sulfur removal = 100*(C0−Cf)/C0
Amount of adsorbed sulfur per gram of solid =(C0−Cf)/m
where,
C0 is the initial sulfur concentration (mg/l),
Cf is final sulfur concentration (mg/l) and
mis the adsorbent dose in grams per litre of solution
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Table 4.1 Gas Chromatography Operating Conditions:
COLUMN USED ZB WAX PLUS
INJECTION TEMPERATURE 250°C
COLUMN TEMPERATURE 120°C
FID TEMPERATURE 250°C
SPLIT RATIO 100
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5. RESULTS AND DISCUSSION
Table 5.1: Percentage of sulphur removal
Adsorbent INITIAL CONC FINAL CONC % REMOVED
cbv-3020 500 97 80
cbv-720 500 337.2 33.56
Hβ-zeolite 500 207.3 58.5
Ag-Y 500 148.5 70.3
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Figure 5.1: The amount of sulphur adsorbed in mmol/gm on different
adsorbents
Figure 5.2: The percentage of sulphur removal on four adsorbents.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
Cbv 3020 zeolite Hbeta zeolite Cbv 720 zeolite Ag-y zeolite
Amount of sulfur
adsorbed mmol/gm
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
Cbv 3020 zeolite Hbeta zeolite Cbv 720 zeolite Ag-y zeolite
% sulfur removed
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Table 5.1shows the initial and final concentrations of the thiophene-toluene
solutions onto the different zeolites. Figure 5.1 shows the amount of sulphur
adsorbed in mmol by the various adsorbents for 1gm of sample solution
taken.While Figure 5.2 shows the percentage of sulfur removed by various
adsorbents and all the experiments were carried out at normal atmospheric
conditions ie., room temperature. The amount of thiophene adsorbed onto the
cbv-3020 is 4.78 mmol/gm and it can be seen that the cbv-3020 zeolite is a very
efficient zeolite for desulfurization. Whereas Xiao et al suggested that Ag-Y
zeolite interaction towards thiophene is more compared to Na-Y zeolite. So in
our laboratory we attempted to synthesize the modified Zeolite ie.,replacing the
Na+ metal ion in Na-Y zeolite with Ag+ metal, and we observed the amount of
thiophene adsorption is higher than the Na-Y zeolite.
On interpreting the results we find that the cbv-3020 zeolite is having higher
adsorption, due to its large surface area and pore size. The pore size of cbv-3020
zeolite adsorbent is 0.54mm which is higher than the other adsorbents and
allowing more thiophene molecules to accommodate in its pores. Whereas Hβ
zeolite, due to its low surface area and pore size cannot adsorb sulphur
efficiently.
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6. CONCLUSION
Conventional HDS process is highly efficient for the removal of thiols, sulfides,
and disulfides. However, it is difficult to reduce sulphur levels to an ultra- low
level because of the very low reactivity of the HDS catalysts towards sulphur
compounds and also towards refractory sulphur-containing compounds such as
di-benzothiophene and its derivatives. Adsorption is also another method
available for the removal of sulfur at ambient temperature and pressure and this
process can be worked out without using hydrogen. The reactivity order of
sulfur components is Thiophene > Benzothiophene > Dibenzothiophene.
Initially our experiments carried out on thiophene removal on different zeolites
at room temperature in order to understand the interaction of thiophene
molecule with different metal ions in zeolites. The adsorption capacity increases
in the order of cbv 3020>AgY>Hβ zeolite>cbv 720. The larger adsorption is
due to stronger interaction towards metal ion. The adsorbent cbv-3020 was very
effective in removal of sulphur and we also observed that Ag-Y zeolite was
effective in removing sulphur from toluene-thiophene solution, however, due to
the presence of unavoidable impurities and experimental errors, resulted in
significantlycompromised adsorption performance in our tests.
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7. REFERENCES
[1] David L. King *, Liyu Li “Removal of sulfur components from low sulfur gasoline
usingcopper exchanged zeolite Y at ambient temperature”Catalysis Today 116 (2006) 526–529
[2] Jing Xiao, Zhong Li,* Bing Liu, Qibin Xia, and Moxin Yu “Adsorption of
Benzothiophene and Dibenzothiophene on Ion-Impregnated Activated Carbons and Ion-
Exchanged Y Zeolites”
Energy & Fuels 2008, 22, 3858–3863
[3]David L. King *, Liyu Li “Removal of sulfur components from low sulfur gasoline using
copper exchanged zeolite Y at ambient temperature”Catalysis Today 116 (2006) 526–529
[4] AnkurSrivastav, Vimal Chandra Srivastava “Adsorptive desulfurization by activated
alumina”Journal of Hazardous Materials 170 (2009) 1133–1140
[5]I.V. Babich*, J.A. Moulijn “Science and technology of novel processes for deep
desulfurization of oil refinery streams: a review”Fuel 82 (2003) 607–631
[6] G.Blanco-Brieva, J.M.Campos-Martin, S.M.Al-Zahrani† “REMOVAL OF
REFRACTORY ORGANIC SULFUR COMPOUNDS IN FOSSIL FUELS USING MOF
SORBENTS” Global NEST Journal, Vol 12, No 3, pp 296-304, 2010
[7] ChetanBorkar, DheerajTomar, and Sasidhar Gumma* “Adsorption of Dichloromethane
on Activated Carbon”J. Chem. Eng. Data 2010, 55, 1640–1644
[8] I.HilalGübbük, RamazanGüp, Mustafa Ersöz† “Synthesis, characterization, and sorption
properties of silica gel-immobilizedSchiff base derivative”Journal of Colloid and Interface Science 320
(2008) 376–382
[9] ChunshanSong“An overview of new approaches to deep desulfurization forultra-clean
gasoline, diesel fuel and jet fuel”Catalysis Today 86 (2003) 211–263
[10] Kyu-Sung Kim, Sun Hee Park, Ki Tae Park, Byung-Hee Chun, and Sung Hyun Kim†
“Removal of sulfur compounds in FCC raw C4 using activated carbon impregnated with
CuCl and PdCl2”Korean J. Chem. Eng., 27(2), 624-631 (2010)
[11] Hisham S. Bamufleh” Single and binary sulfur removal components from model diesel
fuel using granular activated carbon from dates’ stones activated by ZnCl2”Applied Catalysis A:
General 365 (2009) 153–158
[12] CeliaMarı´n-Rosas,*,† Luis F. Ramı´rez-Verduzco,† Florentino R. Murrieta-Guevara,†
Gonzalo Herna´ndez-Tapia,† and Luis M. Rodrı´guez-Otal‡ “Desulfurization of Low Sulfur
Diesel by Adsorption Using Activated Carbon:Adsorption Isotherms”Ind. Eng. Chem. Res. 2010, 49,
4372–4376
[13] Arturo J. Herna´ndez-Maldonado and Ralph T. Yang “Desulfurization of Liquid Fuels
by Adsorption via ð Complexationwith Cu(I)-Y and Ag-Y Zeolites”Ind. Eng. Chem. Res. 2003, 42, 123-
129
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8. APPENDIX
SAMPLE1
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SAMPLE 1 (AFTER ADDING ADSORBENT :CBV-3020)
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SAMPLE: 2
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SAMPLE 2( AFTER ADDING ADSORBENT:CBV 720)
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SAMPLE 3
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SAMPLE3 (AFTER ADDING ADSORBENT :Hβ ZEOLITE)
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SAMPLE 4:
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SAMPLE 4(AFTER ADDING ADSORBENT: AG-Y ZEOLITE)