Versatile boiler ash containing potassium silicate for the synthesis of organic carbonates

Article abstract of DOI:10.1039/c5ra26286k

In this study, boiler ash containing potassium silicate (BA 900) and potassium silicate (K₂SiO₃) were proven to be feasible Lewis acid catalysts for the synthesis of different organic carbonates (glycerol carbonate, ethylene carbonate, and propylene carbonate) from different polyol (glycerol, ethylene glycol, and propylene glycol) feedstocks. In addition, the developed catalytic reaction has the ability to produce propylene carbonate at milder reaction temperatures. BA 900 and K₂SiO₃ were reusable for three consecutive reaction cycles without the loss of activity. The reusable characteristics of catalysts were confirmed through several characterisation techniques, i.e. XRD, FTIR, XRF, N₂ physisorption, FESEM-EDX, and Hammett test. All organic carbonates synthesised had a similar synthetic mechanistic pathway, which involved decomposition of intermediate carbamates into their respective carbonates.

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Versatile Boiler Ash Containing Potassium Silicate for the
Synthesis of Organic Carbonates
Vidhyaa Paroo Indrana, Anisah Sajidah Haji Dauda, Gaanty Pragas Maniama,b, Mashitah Mohd.
Yusoffa, Yun Hin Taufiq-Yapc and Mohd Hasbi Ab. Rahim*a,d
Received 00th December 2015,
Accepted 00th December 2015
DOI: 10.1039/x0xx00000x
In this study, boiler ash containing potassium silicate (BA 900) and potassium silicate (K2SiO3) were proven to be a feasible
Lewis acid catalysts for the synthesis of different organic carbonates (glycerol carbonate, ethylene carbonate, propylene
carbonate) from different polyol (glycerol, ethylene glycol, propylene glycol) feedstock. Additionally, the developed
catalytic reaction has the ability to produce propylene carbonate at milder reaction temperature. BA 900 and K2SiO3 were
reusable for three consecutive cycles of reaction without the loss of activity. The reusable characteristics of catalysts were
confirmed through several characterisation techniques, i.e. XRD, FTIR, XRF, N2 physisorption, FESEM-EDX, and Hammett
Test. All organic carbonates synthesised had similar synthesis mechanistic pathway, which involved decomposition of
intermediate carbamates into their respective carbonates.
www.rsc.org/
for conversion to occur.6 Another way of synthesising glycerol
carbonate is through the use of glycerol and dimethyl carbonate
(DMC) with the aid of catalyst. Even though this synthesis route is
Introduction
In our previous report, it was found that the boiler ash from palm
oil industry was introduced as catalyst for the synthesis of glycerol
carbonate (GC) from glycerol and urea as
highly employed by many, the reaction requires higher ratio of DMC
to glycerol and it also causes shift in chemical equilibrium.7 Recent
synthesis proposes the use of glycerol and urea as feedstock for the
synthesis of glycerol carbonate.8,9 The use of relatively cheaper bio-
renewable feedstock and catalyst derived from industrial waste has
gain our interest to conduct the study. On the other hand, previous
study conducted by our group using gypsum in glycerolysis reaction
with urea to produce glycerol carbonate also suggest proper
utilisation of industrial waste.10Though there have been studies
reported on the use of catalyst containing K-zeolite derived from fly
ash for the transesterification reaction of glycerol with DMC, the
catalyst preparation involved deposition of synthetically derived
potassium ions involving several pre-treatment stages.11 Therefore,
waste boiler ash is deduced herein as a catalyst for a greener and
cost effective reaction operation. Hence, similar to glycerol used as
a feedstock,1 the cyclisation of ethylene glycol and propylene glycol
to form their respective carbonate was possible through the use of
boiler ash as catalyst and it was reported for the first time herein.
a bio-renewable
feedstock.1 In present study, the feasibility of the catalyst to
synthesise ethylene carbonate (EC) and propylene carbonate (PC) is
discussed. This specific carbonates were chosen due to their
adverse use in many industries. Ethylene carbonate and propylene
carbonate have variety of applications in many major industries
such as polymers, gas separation membranes, paints,
agrochemicals, batteries as well as supercapacitors.2-4 Apart from
that, previously identified element in boiler ash, i.e. potassium
silicate (K2SiO3), which was responsible for the catalytic behaviour
of boiler ash is also introduced as a new catalyst for the synthesis of
glycerol carbonate. There are various routes of synthesising glycerol
carbonate. One of the very common and known routes is through
direct carbonylation of glycerol using carbon dioxide.5 The reaction
was conducted at higher temperature of 180 °C with the pressure
of 5 MPa. However, this catalytic process is less feasible due to low
conversion of glycerol as well as poor yield of glycerol carbonate
due to the stability of CO2. Besides, the direct carbonylation
reaction requires very high energy input and very effective catalyst
Results and discussion
Catalytic Mechanism of Potassium Silicate Contained in Boiler Ash
for the Synthesis of Glycerol Carbonate
Based on our previous study, potassium silicate (K2SiO3) contained
in boiler ash was found to be the major element which influenced
the catalytic behaviour of boiler ash in synthesising glycerol
carbonate from glycerol and urea. The presence of potassium
silicate in boiler ash was verified using XRD analysis1 as well as
through X-Ray Fluorescence (XRF) data, which is reported herein.
Therefore, the detailed catalytic mechanism of potassium silicate
contained in boiler ash for the synthesis of glycerol carbonate is
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proposed. It can be inferred that the K+ ion acts as a weak Lewis characteristic through analysis conducted using FTIR, XRD, FESEM
acid by activating the carbonyl group of urea. On the other hand, and N2 physisorption.
SiO32- acts an effective conjugate basic site to activate the hydroxyl
group of glycerol. Based on scheme 1, the activation of carbonyl
group of urea grounds the carbonyl group to become positively
charged and further acting as an electrophile. In contrast, the
activated hydroxyl group of glycerol acts as a nucleophile. In step 1,
100
80
the nucleophilic attack of hydroxyl group towards the electrophilic
carbonyl of urea formed the carbamate intermediate while
releasing ammonia gas. It is believed that the second step is the
most anticipated reaction phase where the selectivity towards
desired product formations is evidently observed due to the
influence of the catalyst. The cyclisation is complete by the loss of
more ammonia gas, followed by ring formation and rearrangement
of the carbonyl double bond to form glycerol carbonate.
60
40
20
0
1st
2nd
3rd
Conversion (%)
Selectivity (%)
Yield (%)
Fig. 1 Reusability study of glycerol carbonate using K2SiO3
100
80
60
40
20
0
1st
2nd
3rd
Conversion (%)
Selectivity (%)
Yield (%)
Fig. 2 Reusability study of glycerol carbonate using BA 900
However, unobserved FTIR peaks at range of 1200-1500 cm-1 for
spent catalyst was found due to the presence of glycerol moiety
that remained intact on the catalyst, which then interfered and
broadened the FTIR signal (Fig. 3). For record, the spent catalyst
was subjected to washing with deionised water, thus remaining
glycerol is expected. In the meantime, a slight difference in XRD
pattern as shown in Fig. 4 is due to dominant presence of SiO2 in
spent catalyst as an evident from EDX analysis (Table 1). More
dominant amorphous SiO2 is expected to be present due to the loss
of some potassium ion, thus the XRD diffractogram will closely
Scheme 1 Catalytic mechanisms of glycerol carbonate synthesis
using K2SiO3
Reusability study of BA 900 and K2SiO3
In any fine chemical synthesis industry, the reusability of catalyst is
one of the crucial parameters of concern. Thus, both boiler ash (BA
900) and K2SiO3 were subjected to reusability test that is being
carried out under standard reaction conditions. As depicted in Fig. 1
and 2, the conversion, selectivity and yield were significantly
comparable and showed optimum performance in all three cycles
12
resemble the diffraction pattern of pure SiO2.
Based on the analysis being carried out using N2 physisorption, it
was found that the BET surface area of both fresh and spent K2SiO3
were comparable to each other (Table 2). However, spent catalyst
contains larger pore volume and pore size. This scenario is expected
to occur due to the loss of some potassium ion embedded to the
silicate that allows larger pore of silicate to be present. As
for both tested catalysts
. The reusability of K2SiO3 catalyst is
anticipated since the fresh and spent catalyst exhibits comparable
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mentioned, it was found that potassium ion and silicate ions Table 1: Element and composition in weight percent of Fresh and
majorly plays an important role in the catalytic mechanism. Spent K2SiO3
Therefore, the variation of catalyst surface area, porous structure
and morphology (Fig. 5) are less significant. The presence of K2SiO3
predominantly in calcined boiler ash (BA 900) was verified using XRF
analysis (Table 3). It was also found that at higher heat treatment
under static air environment, KCl that exist in dried boiler ash is
later transformed into K2SiO3 where the loss of chlorine ion can be
expected as reported by our group1 (ESI 1). The presence of other
elements such as MgO, CaO, Al2O3, Fe2O3, P2O5, ZrO2 are at minor
level that do not significantly affect the catalytic activity of boiler
ash. Additionally, the presence of SiO2 also does not affect the
catalytic activity of boiler ash and gives the yield of glycerol
carbonate amount to be comparable to uncatalysed reaction1.
Indeed, it was found that potassium ion along with its conjugated
basic site (i.e. KCl, KOH and K2SiO3) acted as the most effective
metal element of interest. Apart from that, the XRF analysis
conducted is in agreement with the ICP-MS and FESEM-EDX analysis
reported earlier in which the dominant metal element detected in
all three analysis was potassium.1
Element
wt% (Fresh)
wt% (Spent)
O
Si
56.11
26.01
17.88
100.00
57.27
28.47
14.26
100.00
K
Totals
Table 2: BET Surface area, pore size and pore volume of fresh and
spent K2SiO3.
Catalyst
BET
Surface area
(m2/g)
Pore Volume
(cm3/g)
Pore Size
(Å)
Fresh
Spent
2.50
0.003
0.021
45.14
2.54
342.06
Fig. 3 FTIR spectrum of fresh and spent K2SiO3
(a)
Fig. 4 XRD of fresh and spent K2SiO3
(b)
Fig. 5 FESEM morphology of (a) fresh K2SiO3 (b) Spent K2SiO3.
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Table 3: X-Ray Fluorescence of BA 900 (metal oxides)
over frequency (TOF) of K2SiO3 is 125.6 mmol/ g.cat.h-1, which do
not ideally deviate from the TOF value of BA 900, which were 126.5
mmol/ g.cat.h-1.
Analyte
K2SiO3
SiO2
Mass %
43.53
33.14
7.17
8.98
2.41
1.93
1.89
0.73
0.22
100
K2O
CaO
MgO
Al2O3
Fe2O3
P2O5
ZrO2
Total
Even though K2SiO3 demonstrated reusable property, only
56.3 wt % of catalyst was recovered after the third cycle. The
partial recovery of the catalyst might be due to the
delocalisation of potassium ions during reaction and washing
procedure as well as contribution from systematic and random
error during experimental work. Indeed, the minor amount of
metal leached was confirmed through Energy Dispersive X-Ray
(EDX) analysis of spent catalyst and ICP-MS analysis of reaction
solution, where 2.4 % K and 18.21 % of Si were lost.
Fig. 6: FTIR spectrum of spent K2SiO3 and BA 900
In similar trend to K2SiO3, only 31.7 wt % of catalyst was
recovered after the third cycle. The higher weight percent of
catalyst loss was observed from BA 900 compared to K2SiO3 that
can be attributed to the loss of other present element in boiler ash
as previously reported1 apart from leaching of potassium ion. It is
also notable that the FTIR spectrum (Fig. 6) of spent BA 900 and
spent K2SiO3 showed almost similar patterns. This qualitative data
indicated that major composition of boiler ash is predominantly
existed in potassium silicate phase. Besides, there is also no
significant difference between the FTIR spectrums (Fig. 7) of fresh
BA 900 and spent BA 900. Moreover, Hammett test from Table 4
also indicate the basic property of all fresh and spent BA 900 as well
as K2SiO3 as confirmed by changed in colour of phenolphthalein Fig. 7: FTIR spectrum of fresh and spent BA 900
indicator. Hence, the activity of reusable boiler ash is expected to
be comparable as the reusable K2SiO3. Indeed, the calculated turn
Table 4: Hammett test of fresh and spent catalyst
Catalyst
Methyl Red
(H_=4.8)
Phenolphthalein
(H_=8.2)
2, 4 – Dinitroaniline
(H_=15)
4 – Nitroaniline
(H_=18.4)
Fresh BA 900
Spent BA 900
Fresh K2SiO3
Spent K2SiO3
No changes
Colourless to pink solution
No changes
No changes
No changes
No changes
No changes
Colourless to pink solution
Colourless to pink solution
Colourless to pink solution
No changes
No changes
No changes
No changes
No changes
No changes
4 | RSC Advances., 2015, 00, 1-8
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Catalyst Feasibility Study in Synthesis of Ethylene Carbonate (EC) transcarbonylation reaction to be equal. Apart from that, reaction
and Propylene Carbonate (PC)
involving the use of K2SiO3 alone instead of boiler ash produced
almost similar yield of respective carbonates of EC (79.9 ± 0.3 %)
and PC (72.8 ± 0.7 %). Thus, it is suggested that the catalytic activity
was due to the presence of K+, which acted as a weak Lewis acid to
Waste boiler ash (BA 900) was used as the catalyst for a greener
and cost effective reaction operation. Similar to glycerol as a
feedstock,1 the cyclisation of ethylene glycol and propylene glycol
to form their respective carbonate was made possible through the
use of boiler ash catalyst and it was reported for the first time
herein. It was found that potassium silicate (K2SiO3) contained in
boiler ash could aid in the selective carbonylation of ethylene glycol
and propylene glycol to their respective carbonates. As shown in
Table 5, the optimum yield of ethylene carbonate of 80.1 ± 0.6 %
was obtained at 8 h reaction time while at 10 h, the yield of
propylene carbonate was 73.8 ± 0.7 %. It is important to note that
catalytic activity for both ethylene carbonate and propylene
carbonate shows almost identical turn over frequency (TOF)
indicating that the amount of active species responsible for the
2-
activate urea while the conjugate basic site SiO3 activated the
hydroxyl group of the polyols to form the respective carbonates.
Moreover, the current study proposes better yield of ethylene
carbonates than previously reported study.13,14 Besides, previous
study reported the synthesis of propylene carbonate being
o
operated at higher temperature (170 C and 180 oC), which could
15-17
contribute to relatively non cost effective process.
Indeed, the
use of higher temperature, which is more than 150 °C was not
favoured due to the reported decomposition of urea into isocyanic
acid.18 It is worth to note that there is no available study being
reported on the use of potassium as an active catalyst for the
cyclisation of polyols with the aid of urea.
Table 5: Reaction conditions and yield of ethylene carbonate and propylene carbonate
No.
1
Reaction/
Catalyst
Temperature
(°C)
Molar ratio of
Polyol to Urea
Conversion of
polyol
Duration
(h)
Yield % of
Organic
Carbonate
TOF
(mmol/ g
cat.h-1)
Ethylene
carbonate
Blank
BA 900
K2SiO3
Propylene
carbonate
Blank
BA 900
K2SiO3
1.5:1
Ethylene glycol:
Urea
150
150
60.5
92.7
92.7
8
8
8
17.9
80.1
79.9
-
120.2
119.8
2
4:1
Propylene glycol:
Urea
78.4
89.2
89.4
10
10
10
36.3
73.2
72.8
-
117.1
116.5
Reaction conditions: Catalyst mass, 0.25 g; gas, N2; standard stirring rate, 340 rpm; TOF: calculated based on the yield of
carbonate multiplied by mmol of initial polyols per gram catalyst per total reaction time (h). Quantitative analysis was carried out
using Agilent Technologies A7890 Gas Chromatography-Flame Ionised Detector (GC-FID) equipped with DB-WAX (60m, 0.25mm,
0.25µm) column).
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Proposed Mechanistic Pathway of EC and PC using Boiler Ash
as Catalyst
The cyclisation pathway of ethylene glycol and propylene glycol
along with their by-products formation using boiler ash as a catalyst
is proposed in Scheme 2 and 3. The mechanistic pathway for both
ethylene carbonate and propylene carbonate through respective
carbamate intermediate was confirmed via time online study
monitored by ATR-FTIR (Fig. 8 and 9) and 13C NMR (ESI 2). Both FTIR
spectra showed the presence of C=O (1715 cm-1) group of 2-
hydroxyethyl carbamate and 2-hydroxypropyl carbamate, which
later on transformed into carbonate compounds. There was also no
sign of N-C-O stretching of isocyanic acid in peak observation at
2210 cm-1, which indicates that the reaction is solely dependent on
carbamate as an intermediate compound. In Fig. 8, the band at
1801 cm-1and 1788 cm-1 indicate the symmetrical C=O stretching of
EC.19 The ring stretching peak of EC and PC were visible as duration
or reaction is increased and was present at range of 770-785 cm-1.
In case of TOL of PC, the methyl group was also observed to be
formed at 1352 cm-1 and 1380 cm-1. The decomposition of urea
from 0 h to 10 h is visible from being consumed in the reaction
where the peak for urea is labelled in Fig. 8 and Fig. 9 that gradually
disappeared.
Fig.
carbonate synthesis
8
ATR-FTIR time online analysis study of ethylene
Based on TOL analysis conducted using ATR-FTIR and 13C NMR,
the mechanistic pathway for both EC and PC corresponds to
the similar pathway observed for glycerol carbonate, where
the formation of glycerol carbonate is originated through
selective
transformation
of
respective
carbamate
intermediate. Even though similar route was observed in
related literature,15,20 a slight difference was perceived with
boiler ash as catalyst whereby the conversion of carbamate
into respective carbonate occurred in an accelerated manner.
However, some of the by-products detected in prior-art
experiments were not detected in this study such as biuret
which is also known as carbamylurea.13 Similar finding on the
reaction pathway involved decomposition of intermediate
carbamate into EC.13,20 On the other hand, Wang and co-
researchers in 2014 proposed the formation of propylene
carbonate that was due to decomposition of intermediate 2-
hydroxypropyl carbamate, which was similar to the current
findings.14 However, they also reported the presence of
isocyanic acid, which later forms the intermediate compound.
This scenario is expected since the reaction was carried out at
temperature higher than 150 °C, thus increasing the possibility
of urea to decompose into isocyanic acid. Scheme 2 and
Fig. 9 ATR-FTIR time online analysis study of propylene
carbonate synthesis
Scheme
3 illustrate the reaction pathway of ethylene
carbonate and propylene carbonate using BA 900 containing
potassium silicate as catalyst.
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Experimental
Materials
Glycerol (99.5%) and Urea (AR Grade) were purchased from
Friendemann Schmidt Chemical. Waste boiler ash used as the
catalyst was collected from a palm oil mill located in Lepar Hilir,
Pahang, Malaysia. The boiler ash used is the ash obtained from
incineration of palm fruits, palm kernel, palm shells and palm fibre.
Potassium Silicate (K2SiO3) ≥99.9% used was purchased from Sigma-
Aldrich.
Catalyst Preparation
Raw boiler ash was dried at 110 ˚C for overnight and then
powdered using mortar and pestle. Then, the ash was sieved using
a 200 µm sized sieve. Next, 2 g of the sieved ash was loaded on the
combustion boat and calcined under static air at the temperature of
900 ˚C for 4 h in a horizontal tube furnace at temperature ramping
of 5 ˚C/ min. The catalysts were later denoted as BA 900. Potassium
silicate was directly used without any prior pre-treatment.
Catalytic Testing
The reaction of ethylene carbonate and propylene carbonate
synthesis was carried out using a three-neck round bottom flask
attached to a cycle condenser with water cooling system. The
reaction parameters are as described in Table 5. For the reaction
involving synthesis of ethylene carbonate, 18.6 g of ethylene glycol
was allowed to heat up to 150 ˚C for 10 h under the flow of
nitrogen gas for 20 min before adding urea and catalyst while the
temperature and stirring rate was controlled using IKA@DTS-5
temperature controller. When the temperature reached 150 ˚C,
12.0 g urea and 0.25 g catalyst were added to the reaction and it
was stirred using a magnetic stirrer under 340 rpm of stirring rate.
The molar ratio of ethylene glycol to urea used was (1.5:1). For the
reaction involving synthesis of propylene carbonate, 30.4 g of
propylene glycol was allowed to heat up to 150 ˚C for 10 h under
the flow of nitrogen gas for 20 min before adding urea and catalyst
while the temperature and stirring rate was controlled using
IKA@DTS-5 temperature controller. When the temperature reached
170 ˚C, 6.0 g urea and 0.25 g catalyst were added to the reaction
and stirred using magnetic stirrer under 340 rpm of stirring rate.
The molar ratio of propylene glycol to urea used was (4:1).
Sampling was done from 0 h to 10 h with the time interval of 1 h. 50
µl of sample was transferred in 1450 µl of deionised water. The
experiment was repeated three times for repeatability study.
Scheme 2 Proposed reaction pathway of ethylene carbonate
synthesis using BA 900 containing K2SiO3
The reaction setup was similar to the reaction of EC and PC for the
reusability study of potassium silicate (K2SiO3). Glycerol was heated
up to 150˚C for 20 min under the flow of nitrogen gas before adding
urea and catalyst. The molar ratio of glycerol to urea was (1:1.5)
and 0.5 g catalyst (K2SiO3) was added to the reaction and the
sampling was done at 4 h. 50 µL of sample was transferred in 1450
µL of deionized water. The reaction mixture was immediately
placed into a 100 mL centrifuge tube and centrifuged for 1 h at
8000 rpm. The catalyst deposited as residue at the bottom of the
centrifuge tube was carefully transferred into a clean 100 mL
centrifuge tube and washed with deionized water. The water was
removed from the centrifuge tube after 30 min of centrifugation.
Scheme 3 Proposed reaction pathway of propylene carbonate
synthesis using BA 900 containing K2SiO3.
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This step was repeated for 4 times. The final catalyst was filtered FESEM-EDX, JEOL (JSM-7800f) with a spatial resolution up to 1 nm
and dried overnight at 110 ˚C and the synthesis of glycerol was used to study the surface morphology and elemental analysis
carbonate using dried catalyst was repeated for the second cycle. of the fresh and spent K2SiO3.
The same procedure was again repeated until the third cycle.
The Hammett test were carried out on spent and fresh catalyst of
BA 900 as well as K2SiO3 where phenolphthalein, 2, 4-dinitroaniline,
4-nitroaniline and methyl red were used as indicators to determine
the qualitative acidic as well as basic properties of the catalyst. 25
mg of catalysts were weighed and prepared in three batches and 5
ml of methanol was added to the catalyst. Then, 1 ml of the
indicator was added to 4 ml of methanol with the final volume of 5
ml indicators were added separately to the catalysts weighed in
batches. The mixture was then let to equilibrate for 2 h and the
colour changes were observed and noted.
Product Analysis
GC-FID Agilent Technologies 7890A equipped with DB-WAX (60m,
0.25mm, 0.25µm) was used to analyse the product of ethylene
carbonate and propylene carbonate. Helium gas was used as the
carrier gas with a flow of 1.5 mL/min. The temperature of the
injector and the detector were 225 °C and 250 °C respectively. The
temperature of the column was programmed to have a 2 min initial
hold at 80 °C and then 15 °C/min ramp from 80 °C to 250 °C at 5
min holding time. The split ratio was 1:10 and the injection volume
was 1 µl.
Turn Over Frequency (TOF)
ATR-FTIR Perkin Elmer USA was used to study the functional group
present in the online time analysis of the product from 0 min to 10
h, which could attribute to the product and by product that is also
present in the reaction mixture as a validation. A single drop of
reaction mixture was placed on the liquid holder and the
Equation 1
ꢀ
ꢁ
Turnover Frequency, TOF
Mols of Polyol used × yield % of Organic carbonate
ꢀ
ꢁ
Mass of catalyst × 100
ꢀ ꢁ
transmission data were collected in the range of 4000–700 cm−1
.
=
Duration of reaction h
NMR, BRUKER Ultra Shield Plus 500 MHz was also used to study the
13C NMR of the products formed.
Inductive Coupled Plasma-Mass Spectrometer (ICP-MS) Agilent Conclusions
7500c was used to study the potassium and silicate content in the
reaction
mixture
using
in-house
method
of
In brief, boiler ash containing K2SiO3 (BA 900) and commercially
available K2SiO3 demonstrates high selectivity and yield toward
glycerol carbonate formation with no loss of activity up to three
consecutive cycles. Besides, it is proven that boiler ash containing
potassium silicate can act as an attractive catalyst to selectively
convert polyols, ethylene glycol and propylene glycol into their
desired cyclic organic carbonates. Therefore, the catalyst can serve
CHEMITEL/WI/CHEMTM/001 that was based on AOAC999.10.
Catalyst Characterisation
XRD Rigaku Miniflex II was used to analyse the XRD pattern of the
fresh and spent K2SiO3. Diffraction patterns were recorded with Cu
Kα radiation (λ=1.5406 A), which was operated at 40kV and 30mA
over the range of 3 degree to 80 degree at 2 Theta (θ) for crystalline
phase determination at scan speed of 0.04 degree/s. The catalysts
samples in powder form were then loaded individually on a glass
sample holder for measurement.
as
a Lewis acid catalyst for the synthesis of cyclic organic
carbonates. In short, the catalyst derived from waste boiler ash can
serve as an economical catalyst for the synthesis of GC, EC and PC.
Acknowledgements
The authors would like to thank Universiti Malaysia Pahang,
Universiti Putra Malaysia and the Ministry of Higher Education for
Research Acculturation Collaborative Effort grant (RACE,
RDU121301) and Universiti Malaysia Pahang for Internal Grants
Scheme (RDU120363).
FTIR transmission data were collected for pressed catalyst disk
made with KBr with ratio of (1:10) catalyst to KBr in the scanning
range of 4000–400 cm−1 for fresh and spent BA 900 as well as
K2SiO3.
Shimadzu X-Ray Fluorescence 720 was used to analyse metal oxide
content in boiler ash and it was conducted based on acceptable
calibration range at CuKa 8.00-8.05 while the instrument was
operated at 50 Kv and 30 µA.
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