Synthesis of Faujasite Zeolites from Kankara Kaolin Clay

Journal of Applied Sciences Research, 3(10): 1017-1021, 2007
© 2007, INSInet Publication
Synthesis of Faujasite Zeolites from Kankara Kaolin Clay
Atta, A.Y., Ajayi, O.A. and Adefila, S.S
Department of Chemical Engineering, Ahmadu Bello University, Zaria, Nigeria .
Abstract: The synthesis of zeolite X from locally available Kankara kaolin clay sourced in Nigeria has
been attempted. The beneficiated kaolin was converted to metakaolin at 600 0 C. Subsequently, the highly
reactive metakaolin was leached with sulphuric acid to achieve the required silica-alumina ratio for zeolite
X synthesis. Infrared spectra analysis suggest the presence of zeolite framework structure, hence the further
confirmatory characterization by x-ray diffraction method. Analysis by x-ray diffraction revealed a
composite crystalline phase consisting of zeolites X (32-36%) and Y (21-25%), unnamed zeolite (<1%),
quartz (2-5% ) and anatase (2-5%). In addition, an amorphous phase (>20%) was found present in the
synthesised zeolite. Furthermore, ion exchange capacity of the synthesised samples was found to be 4.724.94 meq/g. The structure was also observed to be stable up to a temperature of about 600 0 C.
Keywords: Kankara kaolin, metakaolin, dealuminated metakaolin, zeolites X and Y, x-ray diffraction,
infrared spectroscopy and ion exchange capacity.
INTRODUCTION
Catalytic cracking of gas oil fractions occurs over
many types of materials such as acidified clay,
alumina, silica, zeolites, etc. However, relatively higher
yields of desirable products are obtained with
zeolites [1 ] . In addition, zeolites are known to be stable
to physical impact, loading and thermal shocks and
withstand the action of carbon dioxide, air, nitrogen
compounds and steam. Zeolites, apart from their
major roles in the catalytic cracking of petroleum, are
also used in the filtration of drinking water, drying of
gases and liquids, gas purification of industrial effluents
and
emissions,
extraction
of
metals
from
complex solutions, etc.
Zeolites are crystalline, hydrated alumino-silicates
of groups É and ÉÉ elements [2 ]. Over 150 synthetic
zeolites and about 40 naturally occurring zeolites are
known [3 ]. Initially, only natural zeolites were used, but
more recently synthetic forms have been made on
industrial scale giving rise to tailor-made zeolites that
are highly replicable. Of these lots, only a few have
hitherto been exploited commercially either due to their
inaccessible pore structure or irreversible structural
collapse during dehydration. However, faujasite class of
zeolites (zeolite X and zeolite Y) are known for
remarkable stable and rigid structure with the large
void space [2 ]. This group of zeolites plays an important
role in the unprecedented gasoline yield commonly
obtained from the fluid catalytic cracking of gas
oil[4 ]. In addition, faujasite type zeolites have a regular
opening aperture of about 8Å, which is large enough
to
accommodate
typical
large
molecules
commonly found
in
gas
oil, during catalytic
cracking and refining operations [2 ].
Traditionally, zeolites are commonly produced from
the hydro gels of sodium aluminate and silicate [2 ].
However, production of zeolites from clay, as a source
of alumina and silica are being continuously
investigated, with positive results [2 ,5 ,6 ]. The critical
factors controlling zeolite-type synthesis are the silicaalum ina ratio, reaction time, hydrodynamics,
temperature and pH (alkalinity) [2 ].
Previous attempts to produce zeolite Y from
K a nka ra c la y re sulte d in the forma tion of
predominantly small pore sized zeolite D-type [6 ].
The presence of potassium ion in the clay, reagents and
leaching of the glasswares were believed to be
responsible for the hindered synthesis of the targeted
zeolite. In this research, synthesis of zeolite X from
Kankara kaolin clay was studied.
M ATERIALS AND M ETHODS
The beneficiation of the Kankara (a village in
Katsina State, Nigeria) kaolin was done in a manner
similar to that reported by Emofuriefa et al.,[7 ]. Clay
generally is unreactive in the natural form.
Subsequently, it was transformed to a more reactive
(amorphous) form by subjecting it to heating at 600 0 C
before using it as a reactant. Dealumination of
metakaolin was effected by leaching out the structural
alumina with sulphuric acid, to meet the silica–alumina
mole ratio (3-4) required for the targeted zeolite.
Corresponding Author: Atta, A.Y., Department of Chemical Engineering, Ahmadu Bello University, Zaria, Nigeria
E-mail: zeezoatta @yahoo.com, Tel: +234-8036253291
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J. Appl. Sci. Res., 3(10): 1017-1021, 2007
The chemical composition was determined using xray fluorescence (PW 1660 X Ray Analyser).
A gel from the dealuminated metakaolin and a
solution of sodium hydroxide was prepared based on
the recipe required for the synthesis of faujasite [2 ].
After this the gel was left to age for 3 days at room
temperature in a polypropylene container. The gel
sample was heated in an autoclave (W S2-84-64, model7101) set at 100 o C, for 24 hours. The post synthesis
treatment involved washing off the
excess
sodium hydroxide from the synthesised zeolite
and drying at 90 o C, for 3 hours. The dried sample was
later calcined at 300 0 C.
The analyses carried out on the synthesised
samples include; infrared spectroscopy (Genesis Series
FTIR), qualitative and quantitative x-ray diffractometry
(Siemens, D500) and ion exchange capacity as
described by Aderemi [6 ].
RESULTS AND DISCUSSIONS
Determination of the Elemental Composition of the
M aterials: Table 1 presents the elemental composition
of the raw kaolin, beneficiated kaolin, metakaolin and
gel from dealuminated metakaolin samples obtained
using XRF.
It is obvious from Table 1, that improvement on
the chemical composition of kaolin as result of
beneficiation was marginal. This is probably, not
unconnected with the small particle size nature of the
associated free silica (quartz) which were able to pass
through the mesh unscreened. The decrease in the
concentration of K + from 1.01 to 0.68 wt% shows that
raw water employed in the beneficiation washed off
some of the ions. Interestingly, calcination at 600 0 C
was able to bring this K + concentration down to a value
of 0.31 wt%.
The alumina content of the metakaolin was reduced
to 21.5% only after 15 minutes of the reaction with
sulphuric acid, as shown in Table 1. This meets the
requirement for faujasite zeolite synthesis. However,
SO 3 (3.50 wt%) was introduced significantly in the gel
from H 2 SO 4 during the dealumination step. Improved
washing technique for the dealuminated cake will
reduce the sulphate in the sample.
There was a noticeable increment in the Na 2 O
content from the metakaolin (0.04 wt%) to the gel
prepared from dealuminated metakaolin (10.50 wt%),
as presented in Table 1. This was a result of
introduction of sodium hydroxide into to the
dealuminated metakaolin to meet the condition of high
alkalinity required for zeolites synthesis.
Elem ental Com position Analysis of Raw Kaolin, Beneficiated Kaolin, M etakaolin and Dealum inated M etakaolin
W eight %
-----------------------------------------------------------------------------------------------------------------------------------------------------------Com ponent
Raw Kaolin
Beneficiated Kaolin
M etakaolin
G el from D ealum inated M etakaolin
SiO 2
47.30
46.50
50.60
54.30
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Al2 O 3
36.80
35.20
42.10
21.50
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------K 2O
1.01
0.68
0.31
0.20
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------N a2 O
0.05
0.07
0.04
10.50
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SO 3
0.06
0.09
0.08
3.50
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Fe 2 O 3
0.71
2.28
0.79
0.64
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------TiO 2
0.16
0.34
1.83
4.53
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------BaO
0.01
0.02
0.02
0.04
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------CaO
0.08
0.14
0.07
0.10
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------M gO
0.16
0.64
0.04
0.04
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------M nO
0.00
0.04
0.00
0.00
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SrO
0.00
0.00
0.01
0.01
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------P2O 5
0.02
0.02
0.09
0.02
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------LO I (1000 0 C)
14.81
13.49
2.13
1.94
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Total
101.11
99.49
98.13
97.34
Table 1:
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J. Appl. Sci. Res., 3(10): 1017-1021, 2007
Fig. 1: IR Spectrum of a Typical Synthesised Sample XRD analysis
The loss on ignition (LOI) was determined at
1000 0 C. The relatively large difference in the LOI
values between the beneficiated kaolin (13.49 wt%) and
metakaolin (2.13 wt% ) indicates that greater loss on
ignition took place during the calcination step. This is
largely due to the giving off of structural hydroxyl
water and volatile organic components. In the same
way, dealuminated metakaolin sample demonstrated low
LOI (1.94 wt%); most probably as result of lack of
structural water hitherto present in the beneficiated
kaolin matrix.
Product Characterization:
IR Analysis: Figure 1 is the IR spectrum of a
typical synthesised
zeolite
sample.
Based
on
Flanigen et al.,[8 ] the peak of transmittance frequency
of 1020.80 cm -1 corresponds to internal tetrahedron
asymmetrical stretch vibration found in zeolites, 574.19
cm -1 peak is related to the presence of double ring in
the framework structure of zeolites while the 720.88
cm -1 represent the tetrahedral atom. These peaks
suggest the synthesised samples to be zeolite in
the class of zeolitic A, X or Y due to auspicious
double ring vibrational peak.
XRD Analysis: The X RD
pattern represented in
Figure 2 shows successively synthesis of zeolite Y,
zeolite X and an unnamed zeolitic phase not picked by
the equipment. Along with these, anatase and quartz
were also observed which could have originated from
kaolin clay, indicating the inefficiency in either
pretreatment or dealumination procedure.
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J. Appl. Sci. Res., 3(10): 1017-1021, 2007
Fig. 2: XRD Analysis of a Typical Synthesised Zeolite Sampl
As shown in the footnote of Figure 2, titanium
oxide, quartz, zeolites X and Y and other unnamed
crystalline phases were identified. Anatase (TiO 2 ) and
quartz (SiO 2 ) identified as part of the crystalline phases
are undesired by-products as residual reactants from the
metakaolin. The elemental composition analysis of
Table 1 did not include TiO 2 ; this could have explained
further the presence of the oxide in the crystalline
phase. Most likely the free silica in the kaolin accounts
for the presence of quartz in the x- ray diffractogram.
This free silica and other unwanted materials observed
could be reduced further by improving on the
beneficiation technique of the kaolin.
From Figure 2, zeolite Y was synthesised as a byproduct of zeolite X synthesis. There are plausible
reasons for this observation: silica-alumina ratio,
alkalinity, aging of the gel, time of reaction and
temperature of reaction: all of which have close values
for zeolites X and Y syntheses and often these values
do overlap. For example zeolite X has been reportedly
synthesised from metakaolin at silica-alumina ratio of
3-5, while zeolite Y at values of 3 to 20. The
observation noted in Figure 2 corresponds to the work
reported by Chandrasekhar and Pramada [5 ,9 ]. Along this
line, the dealuminated metakaolin sample with
silica-alumina ratio of 3, could have been used as a
starting material for synthesis of zeolites X or Y. So,
the interference of zeolite Y on zeolite X could most
likely have been predicted from the silica-alumina ratio
of the reactant. This is in consonance with the work
by Chandrasekhar and Pramada [5 ] who reported the
Table 2: Q uantitative Analysis of a Typical Synthesised Zeolite
Com ponent
Q uantity (wt % )
Q uartz
2-5
Anatase
2-5
Zeolite X
32-36
Zeolite Y
21-25
U nnam ed zeolite
<1
Am orphous phase
>20
formation of multiphase (zeolites) crystalline products
from heterogeneous aluminosilicates as against the use
of soluble silicates and aluminates that often result in
formation of pure zeolite types.
Lack of proper mixing could also explain the
formation of zeolites X and Y in the same reaction
mixture. An inhomogeneous reaction mixture may
result with pockets of gel having different compositions
each pocket acting like a “mini-reactor” and generating
phases corresponding to the composition in that minireactor [1 0 ].
Furthermore, it is gratifying to record close to 60
% faujasite type yield (zeolite X: 34% and zeolite Y:
23 %) as shown in Table 2. This fraction is considered
more than enough in any known catalytic cracking or
reforming operations utilizing zeolite, as this seldom
exceeds 25% composition.
However, the high value of quartz (4%) and
anatase (4%) are speculated to lower number of days
employed for aging especially in the presence of
sodium ion. This is possibly responsible for sudden
collapse/drop in the ion exchange capacity of the
synthesised samples immediately the temperature rose
above 600 0 C (see Figure 4). This call for more
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J. Appl. Sci. Res., 3(10): 1017-1021, 2007
Fig. 3: Effect of T emperature on Ion Exchange
Capacity of Synthesised Zeolites Samples
Table 3: Ion Exchange Capacity of Synthesised Zeolite Sam ples (A,
B, C ) in Com parison to that of M etakaolin (M ), Standard
Zeolites X and Y (2)
Sam ple
Ion exchange capacity (m eq/g)
M
0.30-032
A
5.38-5.43
B
4.72-4.94
C
5.64-5.45
Zeolite X
6.4
Zeolite Y
5.0
phase. An amorphous phase (>20%) was also
confirmed to be present in the synthesised zeolite. The
level of the faujasite zeolites (about 60%) exceeds that
of zeolite (20%) in the matrix of a typical commercial
catalyst, for cracking, this suggest the need to dilute to
avoid over cracking. Additionally, an unnamed zeolite
was detected by the XRD machine.
The synthesised zeolite had an ion exchange
capacity of 4.72-4.94 meq/g with a stable structure
between 400 0 C and 600 0 C but collapsed above 600 0 C.
For the purpose of catalytic process, operating
condition seldom exceed 600 0 C, structural stability
regime of the samples.
However, further research effort will be geared
towards improving the purity of the faujasite zeolite as
well as reducing the level of the unconverted
amorphous material.
ACKNOW LEDGM ENT
The authors gratefully acknowledge the Petroleum
Technology Development Fund (PTDF), Abuja-Nigeria,
for supporting this research work.
stringent beneficiation of the clay targeted for zeolite
synthesis because their products are expected to be
used in high hydrothermal conditions.
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obviously higher than that of the starting materialmetakaolin (0.30-0.32 meq/g, 6), while it compared
favourably with that of zeolites X and Y, 6.4 and 5.0
meq/g respectively. This implies that the synthesised
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Figure 3 shows the variation of ion exchange
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while zeolite Y structure should remain firm up to
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Y (21-25%) and an unnamed zeolite (<1%). In
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