Facile synthesis of dodecatungstophosphoric acid @ TiO2 pillared montmorillonite and its effectual exploitation towards solvent free esterification of acetic acid with n-butanol

Article abstract of DOI:10.1007/s10562-011-0684-1

An acid activated montmorillonite, treated with organic cationic surfactant, i.e. cetyltrimethylammonium bromide (CTAB), was used as a template to prepare TiO₂ pillared montmorillonite taking titanium ethoxide as titania precursor in hydrochloric acid environment. The pillared montmorillonite was further promoted by dodecatungstophosphoric acid impregnation. The as prepared materials were characterized by various spectroscopic and analytical characterization techniques. The catalyst was employed towards a solvent free esterification of acetic acid with n-butanol. The catalyst showed excellent results with 88% conversion and 100% butyl acetate selectivity. It can be recovered and reused readily, making product isolation and catalyst reuse simple.

Full text of DOI:10.1007/s10562-011-0684-1

Catal Lett (2011) 141:1476–1483
DOI 10.1007/s10562-011-0684-1
Facile Synthesis of Dodecatungstophosphoric Acid @ TiO2
Pillared Montmorillonite and Its Effectual Exploitation Towards
Solvent Free Esterification of Acetic Acid with n-Butanol
•
G. Bishwa Bidita Varadwaj K. M. Parida
Received: 1 July 2011 / Accepted: 8 August 2011 / Published online: 18 August 2011
ꢀ Springer Science+Business Media, LLC 2011
Abstract An acid activated montmorillonite, treated with
organic cationic surfactant, i.e. cetyltrimethylammonium
bromide (CTAB), was used as a template to prepare TiO2
pillared montmorillonite taking titanium ethoxide as titania
precursor in hydrochloric acid environment. The pillared
montmorillonite was further promoted by dodecatungsto-
phosphoric acid impregnation. The as prepared materials
were characterized by various spectroscopic and analytical
characterization techniques. The catalyst was employed
towards a solvent free esterification of acetic acid with
n-butanol. The catalyst showed excellent results with 88%
conversion and 100% butyl acetate selectivity. It can be
recovered and reused readily, making product isolation and
catalyst reuse simple.
syntheses, demand of the day for a cleaner environment has
attracted considerable attention to replace these homoge-
neous, polluting, and corrosive systems with environmen-
tally benign heterogeneous acid catalysts.
Among numerous solid acid systems, heteropoly acids
(HPA) having Keggin anion structures have received the
most attention due to their high acidity, low volatility and
low corrosiveness. One member of this HPA family is, do-
decatungstophosphoric acid (DTP) which is the most studied
because of its super acidity. Even though heteropoly acids
display promising surface and catalytic properties, their
application is limited by their low surface area, rapid deac-
tivation and relatively poor stability. Attempts to improve
the efficiency and stability of HPAs have been made by using
various supports including mesoporous silica [3], mesopor-
ous aluminosilicates [4], alumina and carbon [5, 6], and
zirconia [7]. Because of their basic nature, alumina and zir-
conia tend to decompose HPAs, resulting in deformation of
the parent Keggin structure, thereby reducing the overall
activity [7]. In this context we have chosen a suitable acidic
support i.e. titania pillared montmorillonite. Literature
review reveals the occurrence of many successful acid cat-
alyzed reactions using HPA supported acid activated mont-
morillonite catalysts [8, 9]. But the presence of acid centres
on the surface of their layers as well as on the pillars of the
pillared montmorillonites enhances their acidic activity than
the virgin clay [10, 11]. Since clay minerals are the focus of
renewed interest owing to their use as supports, titania pil-
lared montmorillonite constitutes a very promising surrogate
for DTP dispersion than other solid acid systems.
Keywords Esterification ꢀ Acetic acid ꢀ n-Butanol ꢀ
n-Butyl acetate ꢀ Montmorillonite
1 Introduction
As a versatile solvent, extractant and dehydrator, n-butyl
acetate has extensive applications in the industry and
esterification reaction is the most viable route for produc-
ing this value added product [1, 2]. Catalysts are key fac-
tors of esterification. Traditional industry esterifications are
catalyzed by use of mineral acids such as H2SO4, HCl, HF,
H3PO4, and ClSO2OH. Although mineral acids display a
high catalytic effectiveness in conventional industrial
It is known that presence of more Bronsted acidity in the
catalyst promote the esterification reaction more effec-
tively. As far as the acidity is concerned, the acid activated
montmorillonite is much more useful in increasing the total
and the Bronsted acidity of the pillared material [12].
G. Bishwa Bidita Varadwaj ꢀ K. M. Parida (&)
Colloids and Materials Chemistry Department, Institute of
Minerals & Materials Technology (CSIR), Bhubaneswar
751013, Orissa, India
e-mail: paridakulamani@yahoo.com
123

Facile Synthesis of Dodecatungstophosphoric Acid
1477
Therefore in this work we have chosen acid activated
montmorillonite for pillaring purpose. Here CTAB sur-
factant is used as a gallery expanding agent in order to
control the size of the pillars, as a result of which the
surface area of the material increases as compared to the
conventional pillared montmorillonite prepared without
using surfactant. This high surface area pillared montmo-
rillonite offers more DTP dispersion. The DTP supported
titania pillared montmorillonite possessing high Bronsted
acidity proved to be very active towards solvent free
esterification of acetic acid with n-butanol.
prepared by a cation exchange mechanism using a proce-
dure described elsewhere [13]. 1 g MMT was dispersed in
120 mL distilled water at room temperature, followed by
the subsequent addition of CTAB under constant stirring.
The quantity of CTAB added was 0.5 times of the clays
cation exchange capacity. This reaction mixture was stirred
for 10 h at 80 ꢁC. The reaction product was separated by
centrifugation and washed with distilled water to make it
free of bromide. It was then dried at 80 ꢁC for 48 h.
2.2.3 Preparation of Titania Pillared Montmorillonite
(Ti-PILM)
2 Experimental
To 1 wt% suspension of surfactant modified montmoril-
lonite, pillaring solution was added drop wise in order to
obtain 1 mmol of Ti/g of clay. This suspension was stirred
for 3 h at room temperature followed by filtration, drying
and calcination at 450 ꢁC for 4 h, which resulted in the
formation of Ti-PILM (Scheme 1).
2.1 Materials
For pillaring purpose, the parent montmorillonite (Main-
burg, Germany) was acid activated (hereafter designated as
MMT) prior to use according to a previously reported
procedure [12]. The cation exchange capacity was deter-
mined to be 67 meq/100 g clay. Chemicals like sulphuric
acid, hydrochloric acid, titanium ethoxide (titania precur-
sor) and CTAB surfactant (swelling agent) were purchased
from Merck and DTP from Aldrich.
2.2.4 Preparation of DTP Impregnated Titania Pillared
Montmorillonite
A series of catalysts having 5, 10, 15 and 20 wt% of DTP
loading on Ti-PILM surface were prepared by incipient
wetness impregnation method. These are designated further
as wt% DTP @ Ti-PILM.
2.2 Synthetic Procedures
2.2.1 Preparation of Pillaring Solution
2.3 Analytical Methods
Titanium ethoxide was added to a 5 M HCl solution to
obtain HCl/Ti molar ratio 2.5. The resulting solution was
aged for 3 h at room temperature in order to get a clear
titania sol solution.
Low angle X-ray powdered diffraction pattern was recor-
ded on a Rigaku D/Max III VC diffractometer with Cu Ka
radiation at an accelerating voltage of 40 kV and a current
of 40 mA scanned in the range of 2h = 3–10ꢁ. Thermo-
gravimetric/differential thermal analysis (TG/DTA) was
performed under air with a Toledo-Mettler TG/DTA/851e
system at a heating rate of 5 ꢁC min-1. FT-IR Spectra of
the samples were recorded with a Perkin-Elmer (model
Paragon 500) FT-IR spectrometer in KBr matrix in the
2.2.2 Preparation of Surfactant Modified Montmorillonite
The main intention of using CTAB is to expand the clay’s
interlayer space. Surfactant modified montmorillonite was
Scheme 1 Preparation of Ti-PILM
123

1478
G. Bishwa Bidita Varadwaj, K. M. Parida
range 4000–400 cm-1. The surface acidities of the cata-
lysts were investigated by means of a FT-IR study of
pyridine adsorption. Pyridine chemisorbed samples were
obtained by passing pyridine vapour over the catalysts at
373 K for 1 h in the flow system. After which each sample
was stabilised in a N2 flow for 30 min, then allowed to
cool to room temperature and subsequently used for IR
analysis. SEM images were obtained using HITACHI
3400N microscope. The BET surface areas of the samples
were measured by N2 adsorption measurements at 77 K
by means of ASAP 2020 (Micromeritics). Prior to the
adsorption measurements the samples were outgassed at
150 ꢁC for 2.5 h. The UV–vis DRS spectra of the samples
were recorded in a Varian spectrophotometer fitted
with Carry 100 software in the wavelength range of
200–800 nm in BaSO4 phase.
Fig. 1 XRD spectra of (a) MMT, (b) Ti-PILM, (c) 20 wt% DTP @
Ti-PILM and (d) Reused catalyst
2.4 Catalysis Testing
˚
layer is 9.6 A). The calcined Ti-PILM shows an intense
The catalytic activities of the samples were tested in the
esterification reaction involving acetic acid and n-butanol,
performed in a flask with a condenser at the reflux tem-
perature of 100 ꢁC. The mole ratio of acid to alcohol was
2:1, the catalyst taken was 0.1 g, and the reaction time was
6 h. After reaction, the products were analyzed by offline
GC (Shimadzu, GC-2010) equipped with capillary column
(ZB-1, 30 m length, 0.53 mm ID and 3.0 l film thickness).
The filtered catalysts were washed, dried and reused for
further experimentations. The conversion and selectivity
were calculated as follows:
˚
peak at 4.8ꢁ corresponding to a d value of 18.38 A. The
shifting of the characteristic d001 peak towards a lower
diffraction angle suggests the intercalation of the pillaring
precursor. The layer structure is retained in the 20 wt%
DTP @ Ti-PILM material which shows a well-defined
˚
XRD peak with a d spacing value of 18.38 A. The retention
of the intense peak at the same position as in case of
Ti-PILM indicates that the layer structure of the Ti-PILM
is retained in the 20 wt% DTP @ Ti-PILM catalyst.
3.1.2 TG-DTA
Substrate conversionð%Þ
Figure 2 describes the TG-DTA profiles of DTP, Ti-PILM,
and 20 wt% DTP @ Ti-PILM. The typical endothermic
peak (at about 100 ꢁC) for DTP is attributable to the
removal of water adsorbed by the solid. Moreover, an
exothermic peak at about 627 ꢁC is evident, due to the
complete DTP decomposition in WO3 crystals and P2O5
that sublimates.
¼ ½Substrate converted (moles)=Substrate used (moles)ꢁ
ꢂ 100:
Product selectivityð%Þ
¼ ½Product formed (moles)=Substrate converted (moles)ꢁ
ꢂ 100:
In case of Ti-PILM, the main weight losses occurred in
two steps: 30–150 and 500–725 ꢁC. The first step corre-
sponds to the loss of physically adsorbed or occluded
water. The dehydroxylation of the interlayer pillars as well
as the organic combustion began to occur at 150 ꢁC and
caused a continuous weight loss up to 500 ꢁC. After
500 ꢁC, the weight loss is attributed to both clay and pillars
dehydroxylation.
3 Results and Discussion
3.1 Characterization
3.1.1 Low Angle XRD
The low angle X-ray diffraction patterns of MMT,
Ti-PILM and 20 wt% DTP @ Ti-PILM in the 2h range of
3–10ꢁ are shown in Fig. 1. The parent clay shows a broad
and intense reflection at 2h value of 6.5ꢁ corresponding to a
In case of 20 wt% DTP @ Ti-PILM, the broad exo-
thermic DTA peak persists as in Ti-PILM, but no promi-
nent weight losses for DTP was observed. Therefore we
may say that the decomposition peaks of DTP may got
overlapped with the above mentioned exothermic peak of
Ti-PILM.
˚
d value of 13.58 A. The interlayer spacing of the clay
˚
material is found to be 3.98 A (since thickness of each
123

Facile Synthesis of Dodecatungstophosphoric Acid
1479
3.1.3 FT-IR
Generally DTP shows characteristic vibrations in the range
800–1100 cm-1. The characteristic bands found at 1080
and 984 cm-1, are assigned to the symmetric stretching of
P–O in central tetrahedral and terminal W=O respectively.
Bands at 894 and 801 cm-1 are associated with the
asymmetric vibrations (W–O–W) of the Keggin polyanion.
In 20 wt% DTP @ Ti-PILM, the characteristic Keggin
band at 891 cm-1 was observed and all other bands were
merged up with the Ti-PILM bands (Fig. 3).
3.1.4 Surface Acidities
The nature of Bronsted and Lewis acidic sites in our catalyst
was investigated using FT-IR spectrums of adsorbed pyri-
dine. As depicted in Fig. 4, the bands at 1640 and
1540 cm-1 correspond to pyridinium ion bonded to Bron-
sted sites. Band observed at 1490 cm-1 is associated to both
Bronsted and Lewis acid sites, whereas the band at
1445 cm-1 is assigned to the vibrational mode of Lewis site
co-ordinated pyridine [14]. We can observe both the types of
acidities in our catalyst. However, the band intensities of
Bronsted acid sites are stronger than those of the Lewis acid
sites. The relative peak heights corresponding to the Bron-
sted acid sites are increasing in the order of 20 wt% DTP @
Ti-PILM [ Ti-PILM [ MMT. From these facts, we can
conclude that Bronsted acidity is increasing in the pillared
montmorillonite prepared from acid activated clay, which is
again increasing in the 20 wt% DTP impregnated sample.
An attempt has been made to estimate quantitatively the
ratio of the Bronsted to Lewis (B/L) site for MMT,
Ti-PILM and 20 wt% DTP @ Ti-PILM. As can be seen
from Table 1, the B/L ratio of MMT was found to be 0.46
Fig. 2 TG-DTA profile of (a) DTP, (b) Ti-PILM and (c) 20 wt%
DTP @ Ti-PILM
Fig. 3 FT-IR spectra of (a) DTP, (b) Ti-PILM, (c) 20 wt% DTP @
Ti-PILM and (d) reused catalyst
123

1480
G. Bishwa Bidita Varadwaj, K. M. Parida
Table 1 B/L ratio of different
samples
Sample
B/L ratio
MMT
0.46
0.71
1.19
Ti-PILM
20 wt% DTP @
Ti-PILM
there are many small and aggregated particles and the
plates become relatively flatter. In case of the 20 wt% DTP
@ Ti-PILM, fine particles of DTP are found to have
adhered on the surface of Ti-PILM.
3.1.6 UV–vis DRS
Figure 6 shows the UV–vis diffuse reflectance spectra of
MMT, Ti-PILM and 20 wt% DTP @ Ti-PILM. The parent
MMT displays a characteristic broad band centred at about
250 nm. This band is assigned to charge transfer band for
the structural iron present in the octahedral layer of the clay
mineral [15]. MMT was almost transparent in the wave-
length range longer than 350 nm [16]. In case of Ti-PILM,
the broad absorption feature extending towards higher
wavelength is because of the presence of TiO2 pillars.
Generally neat DTP shows absorption bands at 254 and
315 nm which are attributed to oxygen-tungsten charge
transfer absorption bands for the Keggin anion [17–19]. In
case of 20 wt% DTP @ Ti-PILM, we cannot detect the first
peak for DTP because of overlapping with the peak due to
the support. But the second peak due to charge transfer
Fig. 4 FT-IR pyridine adsorption spectra of (a) MMT, (b) Ti-PILM
and (c) 20 wt% DTP @ Ti-PILM
which gradually increased on pillaring and subsequent DTP
loading onto its surface.
3.1.5 SEM
Figure 5 shows representative SEM photographs of the
MMT, Ti-PILM and 20 wt% DTP @ Ti-PILM samples. It
can be seen that the original MMT consists of corn flake
like particles with fluffy appearance revealing its fine platy
structure. However, the clay introduced by Ti polycations
and organic surfactant shows significant changes in the
morphology. Compared with the morphology of the MMT,
Fig. 5 SEM micrographs of
(a) MMT, (b) Ti-PILM and
(c) 20 wt% DTP @ Ti-PILM
123

Facile Synthesis of Dodecatungstophosphoric Acid
1481
aforementioned studies by our group, a high alcohol to acid
molar ratio had been taken for the reaction. But in this
study, taking 2:1 acid to alcohol molar ratio (since acid is
less expensive than alcohol) and using 20 wt% DTP @ Ti-
PILM we got appreciable results. During a comparative
analysis with other DTP loaded catalysts, we found 0.25 g
of 30% 12-tungstophosphoricacid loaded neutral alumina
prepared by Sharma et al. [24] showed 88% butyl acetate
yield taking alcohol to acid molar ratio 1:4.4. In another
study, Bhorodwaj et al. [25] obtained 88% acid conversion
within 12 h of reaction time with 100% butyl acetate
selectivity. But in this study we got the same % of con-
version and selectivity in just 6 h of the reaction period.
This may presumably because of the presence of high
Bronsted acid sites in our catalyst which is facilitating the
reaction more effectively in a lesser time period.
Fig. 6 UV-Vis DRS spectra of (a) MMT, (b) Ti-PILM and (c) 20
wt% DTP @ Ti-PILM
Hence we can say, due to its easy preparation, possible
processability and good environmental stability, 20 wt%
DTP @ Ti-PILM is proving itself to be an environmentally
benign alternative to the corrosive mineral acids as well as
other solid acids reported till date.
between oxygen-tungsten (where W atoms are located in
between the corner sharing WO6 octahedra in the Keggin
structure) appears as a shoulder peak.
As shown in Scheme 2, the mechanism of esterification
can be explained as follows
3.1.7 Surface Area
•
•
•
Protonation at the carbonyl oxygen of acetic acid by
acid catalyst: carbocation production;
The surface area and pore volume of Ti-PILM and different
wt% of DTP on Ti-PILM are given in Table 2. The
decrease in surface area with increase in DTP loadings was
due to the better dispersion of DTP on Ti-PILM which
partially blocks some of the pores of Ti-PILM surface;
making the pores inaccessible to N2 [20].
Attack at positive carbon by alcohol (n-butanol):
nucleophilic attack by hydroxyl group;
Removal of a proton from the unstable intermediate
results in n-butyl acetate production.
The activities of different catalysts are given in Table 3.
It can be concluded from the table that 20 wt% DTP @ Ti-
PILM showed highest catalytic activity. i.e. 88% acid
conversion with 100% product selectivity.
3.2 Analysis of Esterification Reaction
3.2.1 Catalytic Testing
To explore the generality and scope of the 20 wt% DTP
@ Ti-PILM catalyzed esterification, we examined the
reaction varying various experimental parameters.
The standard experimental condition used in the reaction
reported was fixed to 2:1 acetic acid to n-butanol molar
ratio. We explored two conditions with higher and lower
The esterification of acetic acid with n-butanol is an elec-
trophilic substitution reaction. The reaction is relatively
slow and needs activation either by high temperature or by
a catalyst to achieve equilibrium conversion to a reasonable
amount. In this context several reports have been published
by our group [21–23]. However, for economic reasons the
reactant that is usually less expensive of the two should
be taken in excess for n-butyl acetate production. In
O
C
O
O
C
Catalyst
+
+
H2O
CH3
OH + H+
C
+
O
H
CH3
O
CH3
H
O
Table 2 Surface area and pore volume of different samples
..
+
C
+
CH3-CH2-CH2-CH2-O-C-CH3
CH3-CH2-CH2-CH2-OH + CH3
..
Catalyst
Surface area
(m2/g)
Pore volume
(cm3/g)
H
O
O
Ti-PILM
325
263
235
221
0.38
0.23
0.19
0.16
+
+ H+
CH3-CH2-CH2-CH2-O-C-CH3
CH3-CH2-CH2-CH2-O-C-CH3
10 wt% DTP @ Ti-PILM
20 wt% DTP @ Ti-PILM
30 wt% DTP @ Ti-PILM
H
Scheme 2 Mechanism of esterification of acetic acid with n-butanol
123

1482
G. Bishwa Bidita Varadwaj, K. M. Parida
The effect of reaction temperature on the conversion and
selectivity over the catalyst was studied in the temperature
range 60–150 ꢁC (Fig. 8). The figure suggests that the
increase in reaction temperature increased the conversion
to a significant level up to 100 ꢁC, after which the con-
version increased marginally. High temperature may be
required to reduce intermolecular association of the alcohol
for dispersed adsorption and to avoid the clustering of
alcohols around the Bronsted acid sites by hydrogen
bonding [26].
Table 3 Effect of different catalysts on esterification of acetic acid
with n-butanol
Catalyst
Acid
conversion (%)
Selectivity
of n-butyl
acetate (%)
MMT
41
56
59
67
72
88
75
99
Ti-PILM
99
5 wt% DTP @ Ti-PILM
10 wt% DTP @ Ti-PILM
15 wt% DTP @ Ti-PILM
20 wt% DTP @ Ti-PILM
25 wt% DTP @ Ti-PILM
99.5
100
100
100
99
We have also tried the reaction by varying the catalyst
amount from 0.02 to 0.3 g. The obtained results are plotted
in Fig. 9. An increase in the catalytic activity was observed
on increasing the catalyst amount from 0.02 to 0.1 g. After
that also the activity is increasing but to a marginal extent
up to 0.3 g.
Conditions: catalyst: 0.1 g, time: 6 h, temp.: 100 ꢁC, acetic acid:
n-butanol (2:1)
In order to know the stability of the catalyst during the
course of the reaction, the low angle XRD and FT-IR
spectra of the fresh and recycled samples are compared.
The low angle XRD spectrum suggests no delamination of
the clay layer during the progress of the reaction had taken
place which is confirmed by the retention of the d001 peak
at the same position as in the fresh catalyst (Fig. 1d). The
IR spectrum (Fig. 3d) for the recycled sample that was
repeatedly used for four times was consistent with that of
the fresh one, indicating good structural stability of the
catalyst. However, the peak intensities decreased to some
extent, which might be indicative of the slight deactivation
of the recovered catalyst.
acid: alcohol molar ratios. Since the selectivity was 100%
in all the cases the effect of molar ratio of the substrates
was studied in order of conversion only. At 100 ꢁC when
the reaction was carried out for 6 h with a lower acid to
alcohol molar ratio i.e. 1:1, the conversion achieved was
74%. At a molar ratio of 3:1, the conversion achieved was
80% which is again lower than the conversion achieved at
2:1 molar ratio. Increasing the ratio to 3:1, a decrease in
conversion was observed which may be due to the leaching
of DTP in polar medium.
The effect of reaction time was studied which is illus-
trated in Fig. 7. As can be seen from the figure, there was a
gradual increase in conversion with an increase in the time
period. The selectivity on the other hand remains almost
100% up to 6 h. Further increasing the time period to 8 h,
there was increase in conversion but decrease in selectivity
because of the formation of butene as the by product.
Hence 6 h is taken as the optimum time period for the
reaction.
3.2.2 Leaching Test
Quantitative analysis of heteropoly acids can be done by its
treatment with a mild reducing agent such as ascorbic acid,
which results in the development of a heteropoly blue
Fig. 7 Effect of time period on esterification of acetic acid over 20
wt% DTP @ Ti-PILM. Conditions: catalyst: 0.1 g, temp.: 100 ꢁC,
time: 6 h, acetic acid: n-butanol (2:1)
Fig. 8 Effect of reaction temperature on esterification of acetic acid
over 20 wt% DTP @ Ti-PILM. Conditions: catalyst: 0.1 g, time: 6 h,
acetic acid: n-butanol (2:1)
123

Facile Synthesis of Dodecatungstophosphoric Acid
1483
Ti-PILM is found to be an excellent catalyst for the
esterification of acetic acid with n-butanol in absence of
any solvent. The simple procedure for catalyst preparation,
easy recovery and reusability of the catalyst are expected to
contribute its utilization for the development of benign
chemical process and products. Hence the present hetero-
geneous catalytic system can be a potential candidate not
only for laboratory practice but also for commercial
applications.
Acknowledgment The authors are thankful to Prof. B. K. Mishra,
Director, Institute of Minerals and Materials Technology (CSIR),
Bhubaneswar, India, for the constant encouragement and permission
to publish this paper.
Fig. 9 Effect of catalyst amount on esterification of acetic acid over
20 wt% DTP @ Ti-PILM. Conditions: time: 6 h, temp.: 100 ꢁC,
acetic acid: n-butanol (2:1)
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As it is very convenient to recover the catalyst at the end of
the reaction, the solid catalyst left could be readily reused for
the next run without any regeneration steps and it was found
that the catalyst could be reused for four times without any
appreciable loss of its catalytic activity as can be seen from
Table 4.
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4 Conclusions
In summary, we have successfully prepared various wt% of
DTP loaded Ti-PILM. In our methodology 20 wt% DTP @
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