Nano-silica?PVC-bonded N-ethyl sulfamic acid as a recyclable solid catalyst for the hydroxyalkylation of phenol with formaldehyde to bisphenol F

Article abstract of DOI:10.1246/bcsj.20190081

Sulfamic acid functionalized PVC-coated nano-silica (NS) catalyst (NS?PVC-EDA-SO₃H) was prepared via multi-step treatment processes and characterized by FT-IR, N₂ adsorption-desorption, TGA/DTG, XRD, TEM, STEM-EDS, as well as acid-base back-titration. The hydroxyalkylation of phenol with formaldehyde to bisphenol F was employed to evaluate in detail its acid catalysis performances. The results indicated that the newly constructed NS?PVC-EDA-SO₃H possessed richer short mesoporous to macroporous channels and highly exposed sulfamic acids and could exhibit excellent hydroxyalkylation activity and reusability owing to fast mass transfer and reaction rates for the conversion of substrates, as well as excellent structural and chemical stabilities. This new solid acid was obviously superior to the conventional homogeneous concentrated sulfuric acid and heterogeneous sulfonated resin catalysts in catalytic activity and reusability, which could achieve a remarkable formaldehyde conversion (99.9%) and selectivity of bisphenol F (94.5%) under optimal hydroxyalkylation conditions. Furthermore, it could also be recovered easily and used repeatedly at least nine times without an obvious decrease in activity.

Full text of DOI:10.1246/bcsj.20190081

Advance Publication Cover Page
Nano-silica@PVC-Bonded N-Ethyl Sulfamic Acid as a Recyclable Solid Catalyst for the
Hydroxyalkylation of Phenol with Formaldehyde to Bisphenol F
Dabo Jiang, Shuolin Zhou, Zaihui Fu,* Qiong Xu, Jiafu Xiao, Min Zheng, Wenzhou Zhong,
Xianxiang Liu, Steven Robert Kirk, and Dulin Yin*
Advance Publication on the web June 1, 2019
doi:10.1246/bcsj.20190081
© 2019 The Chemical Society of Japan
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Publication manuscripts.

Nano-silica@PVC-Bonded N-Ethyl Sulfamic Acid as a Recyclable Solid Catalyst for
the Hydroxyalkylation of Phenol with Formaldehyde to Bisphenol F
Dabo Jiang,1 Shuolin Zhou,1,2 Zaihui Fu,*1 Qiong Xu,1 Jiafu Xiao,1 Min Zheng,1,3 Wenzhou Zhong,1 Xianxiang Liu,1
Steven Robert Kirk,1 and Dulin Yin*1
1
National & Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources, College of
Chemistry and Chemical Engineering, Hunan Normal University Changsha 410081 (China).
2 Educational Scientific Institute, Changsha Normal University, Changsha Hunan 410100 (China)
3 Educational Scientific Institute, Hunan First Normal University, Changsha Hunan 410205 (China)
E-mail: < fzhhnnu@126.com, dulinyin@126.com>
Zai hui Fu
Zai hui Fu, is a professor at the Institute of Fine Catalytic Synthesis, Hunan Normal University. His research interests
involve molecular design of new catalytic materials, green catalytic oxidation and enzyme-like catalytic conversion.
Related research achievements are published in many domestic and foreign academic journals.
Abstract
Sulfamic acid functionalized PVC-coated nano-silica (NS)
functionalized molecular sieves[10], clay[11] and H-beta zeolite
[12]
.
Phosphotungstic acid encapsulated in metal-organic
catalyst (NS@PVC-EDA-SO3H) was prepared via multi-steps
treatment processes and characterized by FT-IR, N2
adsorption-desorption, TGA/DTG, XRD, TEM, STEM-EDS, as
well as acid-base back-titration. The hydroxyalkylation of
phenol with formaldehyde to bisphenol F was employed to in
details evaluate its acid catalysis performances. The results
indicated that the newly constructed NS@PVC-EDA-SO3H
possessed richer short mesoporous to macroporous channels
and highly exposed sulfamic acids and could exhibit excellent
hydroxyalkylation activity and reusability owing to it’s fast
mass transfer and reaction rates for the conversion of substrates,
as well as its excellent structural and chemical stabilities. This
new solid acid was obviously superior to the conventional
homogeneous concentrated sulfuric acid and heterogeneous
sulfonated resin catalysts in catalytic activity and reusability,
which could achieve a remarkable formaldehyde conversion
(99.9%) and selectivity of bisphenol F (94.5%) under optimal
hydroxyalkylation. conditions. Furthermore, it could also be
recovered easily and used repeatedly at least nine times without
an obvious decrease in activity.
frameworks PTA@MIL-100 (Fe or Cr) (β) was also reported as
an efficient solid catalyst for synthesis of BPF by Chen et. al.
and showed high yield (92.1%) and selectivity (93.0%) for the
hydroxyalkylation of phenol with formaldehyde to BPF.
Unfortunately, not only are the synthesis routes of these
catalysts complex, but their stability is also poor[13]. An
aluminum-grafted MCM-41 molecular sieve used as a catalyst,
also having higher yield (93.2%) and selectivity (91.1%) for the
reaction, was reported by Suman K. J et. al.[14], who suggested
that these catalysts possess high surface areas which can
accelerate the progress of the reaction. The reaction conditions,
however (phenol/formaldehyde up to 30 mol·mol-1, catalyst
concentration of 15 wt.%, reaction temperature of 90 and
reaction time of 4 h), were relatively harsh in terms of energy
consumption for the industrial BPF process, and no evidence
was provided for the reuse and stability of the catalysts.
Short-channeled mesoporous Zr-Al-SBA-15, as an efficient
catalyst for hydroxyalkylation of phenol with formaldehyde,
was reported by Wei et. al:[15] in this case, a maximum BPF
yield of 96.1% was obtained. But the reusability of these
catalysts is poor: the catalyst can only be recycled four times,
with an accompanying marked decline in catalytic performance.
The use of DTP (H3PW12O40)-impregnated fumed silica
(DTP/SiO2) as an effective catalyst for the reaction was
reported by Garade et. al.[16], giving a higher selectivity
(90.1%) to BPF. But the low yield (34.2%) and poor reusability
(two times) severely restricted its application for the
hydroxyalkylation of phenol with formaldehyde to BPF.
Herein, relying critically on the fulfillment of certain
green chemistry principles such as the ease-inexpensiveness,
environmental friendliness, high efficiency, we report an
efficient method for the preparation of NS-coated PVC bearing
sulfamic acid (NS@PVC-EDA-SO3H) as a stable and robust
heterogeneous catalyst for the hydroxyalkylation of phenol
with formaldehyde to BPF. As shown in scheme 1, NS-coated
PVC material (NS@PVC) was prepared via a simple
impregnation method; And then the sulfonation sites were
introduced on NS@PVC by N-alkylation of ethylenediamine
with PVC, yielding the EDA grafted NS@PVC material
(NS@PVC-EDA) and the latter was finally converted to the
Keywords: Solid acid catalyst, Sulfamic Acid,
Hydroxyalkylation
1. Introduction
The synthesis of bisphenol F (BPF) has been given
extensive attention due to the increasing demand and
applicability in plastics, resins and rubber industries[1,2]
.
Conventionally, the method for the preparation of BPF is based
on the condensation reaction of phenol and formaldehyde using
a liquid protonic acid such as phosphoric acid, hydrochloric
acid, sulfuric acid or other inorganic acids etc. as catalyst,
owing to their high activity and low cost[3-6]
. These
homogeneous catalysis systems, however, suffer from several
drawbacks such as high toxicity, hazards of handling, corrosion
of equipment and difficulty in separation and recovery [7, 8]. It is,
therefore, of great practical importance to develop easily
separable and reusable solid catalysts having high activity for
the synthesis of BPF. Recently, a series of works have been
reported to replace the conventional liquid protonic acids by
solid acid catalysts, such as heteropolyacid catalysts[9], acid

Scheme 1. Synthetic routes to NS@PVC-EDA-SO3H catalyst with inset corresponding photograph.
goal catalyst through grafting chlorosulfonic acid (LHS). Series
2.3 Catalytic performance tests: The hydroxyalkylation
of phenol with formaldehyde to BPF was performed in a
magnetically stirred glass reactor fitted with a reflux condenser
and an arrangement for temperature control. In a typical
procedure, 0.2 mol of phenol, 0.01 mol of formaldehyde and
catalyst (0.02 g, 0.25 mol%, based on the acid density of the
catalyst) were added into the reactor. No other solvent was
needed. The reaction mixture was heated to 70oC. After 1 h, the
reaction was stopped and cooled down to room temperature,
then the solid catalysts were separated by filtration, washed
with aqueous ethanol, and then was dried overnight at 60oC in a
of characterizations have confirmed that the newly constructed
solid acid has richer short mesoporous to macroporous
channels and highly exposed and stable sulfamic acids and can
remarkably accelerate the diffusion and conversion of
substrates on it[17-20], thus showing excellent hydroxyalkylation
activity and reusability in the synthesis of BPF.
2. Experimental
2.1 Materials: Polyvinyl chloride (polymerization degree
1580~1780, PVC), Silicon dioxide (99.5%, 20±5 nm),
Tetrahydrofuran (≥99.0%, THF), ethanol (≥99.0%),
ethylenediamine (≥99.0%, EDA), dichloromethane (≥99.5%),
phenol (≥99.0%), formaldehyde solution (38.2%) were
purchased from Sinopharm Chemical Reagent Co., Ltd;
(Shanghai, China) and used without further purification.
Methanol was purchased from TEDIA (HPLC grade, USA).
Chlorosulfonic acid (≥99.0%, LHS) was purchased from Xiya
Chemical Co., Ltd (Chengdu, China). Water used in the
laboratory was prepared by a Millipore Milli-Q ultrapure
water-purification system.
vacuum
drying
oven
for
reuse.
The unreacted formaldehyde was determined using an
UV-2450 spectrophotometer (Shimadzu, Kyoto, Japan)
using an acetylacetone spectrophotometric method [23,24]. The
compositions of the hydroxyalkylated products were
determined on an Agilent 1100 HPLC (Agilent, USA) with an
external standard method[14,15] and the specific operation
conditions were as follows: 4.6×250 mm of Agilent SB-C 18
chromatographic column, methanol/water 65:35 (v/v) of mobile
phase, 1.0 ml/min of flow rate, the UV detector 270 nm,
column temperature 30oC, injection volume 20 μL. The activity
of catalyst was evaluated in terms of formaldehyde conversion
and the selectivity of bisphenols F, which were calculated as
follows:
2.2 Preparation of the catalyst:
NS@PVC: For the preparation of NS@PVC, the phase
inversion method was used [21]. The activated NS powder of 10
g was added to 100 mL of tetrahydrofuran (THF) solution and
then dispersed to form a stable suspension solution under an
ultrasound treatment for 30 min. The obtained suspension
solution was mixed with 4 g PVC dissolved in 100 mL THF
and then stirred at room temperature for 24 h. Finally, this
mixed solution was evaporated to obtain NS@ PVC material at
40oC.
NS@PVC-EDA: 5 g NS@PVC was mixed with an
excess of ethylenediamine (40 mL) in a reaction vessel
equipped with a condenser. The resulting mixture was refluxed
at 80oC for 8 h under stirring. The reaction mixture was then
cooled to room temperature and filtered through a vacuum
glass filter. The filter-cake was washed sequentially with a
large excess of ethanol and dried under vacuum overnight at
60oC to give the desired product NS@PVC-EDA, as a yellow
powder.
moles of reacted formaldehyde
Conversion (%) =
× 100%
moles of formaldehyde
moles of bisphenols F
Selectivity (%) =
× 100%
∑ moles of all products
2.4 Characterization of catalyst: X-ray diffraction
spectroscopy (XRD) was performed with a Bruker D8-Advance
X-ray diffractometer, under the following conditions: Cu target
K αray (λ=1.54187 Å); scanning voltage 40 kV, scanning
current 40 mA; scanning speed 0.2 s, scanning step 0.02 °. The
materials were identified using the ICDD/JCPDS database.
FT-IR spectra of the samples were tested by the KBr pellet
technique on a Nicolet Avata 370 Fourier-transform infrared
spectrophotometer in the range 400~4000 cm-1. N2
adsorption-desorption isotherms were recorded with an ASAP
2400 physisorption instrument made by Micromeritics
Corporation (UNITED STATES). Prior to measurement, all
samples were dried under vacuum at 60oC for 24 h. The
specific surface area was calculated by BET method. Pore size
distribution was calculated by BJH method. Thermogravimetric
analyses (TG) were performed with a NETZSCH-STA 409 PC
thermoanalyzer at a heating rate of 10oC/min under oxygen
atmosphere. The morphology of the NS@PVC-EDA-SO3H
NS@PVC-EDA-SO3H: Referring to the preparation of
CoFe2O4
nanoparticle
immobilized
N-propyl
diethylenetriamine sulfamic acid catalyst [22], chlorosulfonic
acid (10 ml) was added dropwise to a magnetically stirred
mixture of NS@PVC-EDA (2.5 g) in CH2Cl2 (20 ml) at 0oC
over a period of 2 h. Upon completion of the reaction, the
mixture was stirred for 24 h and then filtered. The filter-cake
was washed with a large excess of ethanol and dried under
vacuum overnight at 60oC to afford the desired product,
NS@PVC-EDA-SO3H, as a brown powder.

catalyst was determined using High-resolution transmission
electron microscopy (HR-TEM; JEM 2100, JEOL, Japan). The
EDS was measured using a JEOL JSM-2000EM scanning
electron microscope. Referring to the literature[25]
, The
measurement for the -SO3H groups of catalyst was described as
follows: a catalyst (0.05 g) was treated with 0.005 mol·L-1 of
NaOH solution (20 mL) for 1 h at 20~50°C under ultrasonic
vibration. After the removal of catalyst, the resulting filtrate
was titrated with 0.005 mol·L-1 of HCl solution. The acid
density was calculated as follows:
푉
(푁푎푂퐻)푐(푁푎푂퐻) − 푉(퐻퐶푙)푐(퐻퐶푙)
푄푒 =
푤
Where c(NaOH) and c(HCl) are the concentrations of the standard
aqueous NaOH and HCl solution, respectively. V(HCl) is the
volume (mL) of the standard aqueous HCl used in the titration,
V(NaOH) is the volume (mL) of the standard aqueous NaOH
solution (20 mL), and w is the sample weight (g), Qe is the acid
density of catalyst.
Figure 1. FT-IR spectra of NS, PVC, NS@PVC,
NS@PVC-EDA, NS@PVC-EDA-SO3H samples.
N2 adsorption-desorption: Figure 2 is the physical
adsorption-desorption isotherms of N2 at -196oC and pore size
distributions for the above samples and the calculated porous
parameters including the BET surface area, pore volume and
BJH pore size are listed Table 1. As shown in Figure 2(a), the
raw material PVC presents a typical non-porous feature in its
adsorption-desorption isotherms. While NS support exhibits
typical type III adsorption-desorption isotherms with a BET
surface area of 147 m2g-1 and a porous volume of 1.08 cm3g-1,
its BJH curve presents a broad pore size distribution from 10 to
100 nm, indicating that NS, NS@PVC, NS@PVC-EDA,
NS@PVC-EDA-SO3H samples contains richer mesoporous to
microporous channels, whereas the observed pores (Figure 2b)
are mostly due to the gap between those particles. In addition,
the materials that NS is combined with PVC and its
3. Results and Discussion
3.1 Characterization：
FT-IR: Figure
1
gives the FT-IR spectra of
NS@PVC-EDA-SO3H and its precursors. The FT-IR spectrum
of PVC shows its some characteristic peaks, including two
peaks at 2912 and 1429 cm−1 respectively attributed to the
stretching and wagging vibrations of C-H from CH2 groups,
three peaks at 2968, 1331 and 1254 cm-1 respectively
originating from the stretching and deformation of C-H of
CHCl groups, as well as two peaks at 690 cm−1 and 613
cm−1assigned to C-Cl bond stretching[26,27]
. The FT-IR
spectrum of NS exhibits two peaks at 798 and 1110 cm−1,
which are initiated by Si-O-Si symmetric and asymmetric
stretching vibrations, respectively. NS@PVC also shows the
above characteristic peaks belonged to PVC and NS in its
FT-IR spectrum, supporting that this material is composed of
PVC and NS. Comparing with NS@PVC, NS@PVC-EDA
shows a new peak at 1652 cm-1 due to the bending vibration of
N-H bond and a disappearance of the C-Cl peak at 615 cm-1 is
found in its FT-IR spectrum, and the peak at 3420 cm-1 is larger
than NS@PVC, perhaps because the graft of the N-H bond
results in the absorption peak being stronger after N-alkylation,
indicating that EDA is successfully grafted on the carbon chain
of PVC loaded NS via N-alkylation. The FT-IR spectrum of
NS@PVC-EDA-SO3H shows the peak at about 1110 cm−1 is
attributed to the typical symmetric stretching vibration of
functionalized derivatives also show
a
similar III
adsorption-desorption isotherm and BJH pore size distribution
to pure NS (Figure 2b), but their BET surface areas and pore
volumes decrease to some extent, along with an increase of
their average pore sizes. Moreover, the change of these porous
parameters is becoming more and more prominent with the
continuous functionalization of PVC by successively grafting
EDA and LHS (Table 1). This supports that the impregnation of
PVC partly occurs in the macropores and especially mesopores
of NS and its further functionalization can remarkably increase
its ratio to enter the pores of NS.
Table 1. The specific surface areas (SBET), pore volume (Vg)
and average pore size (D) of PVC, NS, NS@PVC,
NS@PVC-EDA, NS@PVC- EDA-SO3H.
-
Si–O–Si and the vibration bands of SO3 stretching of
supported SO3H group. However, the peak cannot be resolved
due to its overlap with the absorbance of Si–O–Si stretch in the
970–1310 cm-1. And the peak at 1380 cm-1 may be attributed to
the O=S=O stretching band of sulfamic group, whereas the
N–S stretch was present at 691 cm-1, confirming the successful
Samples
PVC
SBET (m2/g)
Vg (cm3/g)
0.01
D (nm)
22
3
NS (support)
NS@PVC
147
123
88
1.08
36
grafting of chlorosulfonic acids on NS@PVC-EDA [28-31]
.
1.13
39
NS@PVC-EDA
NS@PVC-EDA-SO3H
1.08
44
48
0.57
50

Figure 3. TG thermograms and derivative thermogravimetric
(DTG) curves of PVC, NS, NS@PVC, NS@PVC-EDA,
NS@PVC-EDA-SO3H samples.
Figure 2. N2 adsorption-desorption isotherms and pore size
distributions of PVC, NS, NS@PVC, NS@PVC-EDA,
NS@PVC-EDA-SO3H samples.
XRD: Powder X-ray diffraction (XRD) spectra of these
samples are shown in Figure 4. An amorphous structure
character of NS support is clearly observable in its XRD
spectrum, consistent with previous reports[36,37]. The amorphous
structure of PVC is also indicated by the broad peak appearing
in the region of 15~30o. In addition, the XRD spectra of
NS@PVC, NS@PVC-EDA, NS@PVC-EDA-SO3H samples
are very similar to that of NS, which suggests an amorphous
structure for these samples.
TG/DTG: The thermal decomposition behavior of the
above samples under oxygen atmosphere was investigated by a
thermal gravimetric analysis (TGA) technique and the obtained
TG and differential TG (DTG) curves are shown in Figure 3. It
is seen from the TG and DTG curves of two raw materials that
NS support itself has no obvious weight loss process during the
temperature range examined, indicating its high thermal
stability. While pure PVC shows two significant weight loss
peaks at 298 and 511°C in its DTG curve, respectively
corresponding to the dehydrochlorination of PVC and the
further oxidation degradation of its dehydrochlorinated
residues[32-34]. When PVC was loaded on NS, its two weight
loss peaks can still be found in the DTG curve of NS@PVC
sample although they are weakened remarkably in intensity.
And the estimated PVC loading from the TG curve of
NS@PVC is about 22.8%. From the TG and DTG curves of
NS@PVC-EDA, it can be seen that the weight loss attributable
to the dehydrochlorination of PVC is weakened after PVC
grafting EDA. In addition, a new weight loss occurs about
100oC, which is likely due to the evaporation of the adsorbed
water. These findings indicate that most C-Cl bonds of PVC
have been successfully substituted by C-N bonds via
N-alkylation and such substitution can increase hydrophilicity
of NS@PVC-EDA. After NS@PVC-EDA further grafting LHS,
its weight loss peak for the adsorbed water is slightly
strengthened owing to the grafting of polar LHS. In addition, a
weight loss between 150-400oC could be assigned to removal
of organic motif (ethylenediamine and sulfamic acid) from the
Figure 4. XRD pattern for PVC, NS, NS@PVC,
NS@PVC-EDA, NS@PVC-EDA-SO3H samples.
TEM: The morphology of NS@PVC-EDA-SO3H catalyst
was characterized by high resolution transmission electron
microscopy (HRTEM) and its three HRTEM micrograph are
given in Figure 5. Figure 5(c, d) demonstrates that NS has an
average diameter of 15–20 nm, however most of the NS
particles have an agglomerated appearance. This catalyst
structure of NS@PVC-EDA-SO3H [35]
.

presents an irregular spherical structure in morphology and
most of its nanoparticles are located in 20 to 30 nm (Figure 5a,
b). In addition, the PVC film coated on the surface of NS can
also be clearly discerned from its high resolution HRTEM
images and the thickness of this coated film is estimated to be
5–10 nm. By the way, some the naked NS particles and
uncoated PVC films, which are marked in the red and green
regions, respectively, are also found in its HRTEM images,
indicating that at least a portion of the PVC derivative is not
coated on the NS.
Figure 6. Elemental mappings and energy-dispersive
spectroscopy analyses of NS@PVC-EDA-SO3H catalyst.
3.2 Catalytic performance of NS@PVC-EDA-SO3H
Effects of average particle size of NS support: The
effect of average particle size of NS support on the acid density
and hydroxyalkylation performance of NS@PVC-EDA-SO3H
catalyst was studied and the results are listed in Table 2. It can
be seen from Table 2 that the acid density of catalyst,
formaldehyde conversion and BPF selectivity increase with
decreasing silica’s average particle size from 60 to 0.02 μm.
This is probably because the catalyst prepared using the small
size of NS not only has higher sulfamic acid sites but also its
short pore channels are conducive to improve the exposure of
the acid sites and accelerate the diffusion of the reactants to the
acid sites, thus leading to it showing excellent formaldehyde
conversion activity (98.1%) and BPF selectivity (92.2%).
Effect of activation temperature of NS: The effect of
NS’s activation temperature on the acid density and
hydroxyalkylation performance of NS@PVC-EDA-SO3H
catalyst was studied and the results are shown in Figure 7. The
results indicate that the acid density of the catalyst and the
formaldehyde conversion over it gradually increase with
elevating the activation temperature, respectively achieving the
highest 1.26 mmol·g-1 and 99.6% at 200°C. After that, its acid
density and the conversion are gradually reduced to 0.83
mmol·g-1 and 74.6%, accompanied by BPF selectivity
decreased by 16%. The above effects of the activated
temperature likely originate from its regulation on the surface
properties of NS, the low activated temperature hardly
completely remove the physically absorbed water on NS
surface[38,39],while the high activated temperature significantly
reduces the silanols on NS surface via dehydration[40], a large
amount of adsorbed water or low density of silanols may
reduce the loading efficiency of PVC on the NS carrier, thus
leading to a significant decrease in the acid sites and
hydroxyalkylated activity of catalyst. Here, 200°C was selected
as the preferred activation temperature of NS for the
preparation of an excellent catalyst.
Figure 5. HRTEM images NS@PVC-EDA-SO3H catalyst.
STEM-EDS: The distribution and content of this
catalyst’s surface elements were further investigated using high
resolution scanning transmission electron microscopy
(HRSTEM) equipped with a high-angle annular dark field
(HAADF) and energy-dispersive spectroscopy (EDS) detectors.
As shown in Figure 6 (a, c-e), an overlay and single elemental
mappings for the surface Si and
C
elements of
NS@PVC-EDA-SO3H show relatively uniform distributions in
the regions marked with the green circles but are an obvious
inhomogeneities in the unmarked other regions, which can well
correspond to its HRTEM images. Notably, the distributions of
N and especially S elements in the two mappings (Figure 6f, h)
are very similar to that of C element, supporting that EDA and
LHS can be homogeneously grafted on the PVC in successive.
The Cl element presents an obviously sparse distribution in its
mapping (Figure 6g), further supporting that most C-Cl bonds
of PVC have been substituted by C-N bonds via N-alkylation.
Furthermore, the real content of loading PVC measured via
high temperature combustion method approximately accounts
for 72.3% of the loading PVC (31.5%, calculated according to
carbon element measured via energy-dispersive spectroscopy,
which indicated that PVC covers successfully the surface of the
NS. Notably, the amount of SO3H groups on
NS@PVC-EDA-SO3H calculated from EDS analysis of Figure
6 (b) is 1.12 mmol•g-1, which closes to the acid density
measured via chemical analysis (1.26 mmol•g-1), indicating that
most of the -SO3H groups are exposed on the surface of the
catalyst, only a small amount of SO3H groups are enclosed in
the dense layer of the NS@PVC-EDA-SO3H.

Table 2. Effects of NS’s average particle size on catalyst performance of NS@PVC-EDA-SO3H catalyst a
BPF isomer distribution (%)
NS’s
particle size (μm)
average Acid density
HCHO
conv. (%)
BPF
sel. (%)
(mmol·g-1)
4,4’-BPF
2,4’-BPF
2,2’-BPF
60
0.52
77.9
73.6
55.2
33.4
11.4
20
0.69
0.81
86.9
98.1
88.2
92.2
39.6
34.7
41.8
44.6
18.6
20.7
0.02
a
Reaction conditions: silica average particle size, 60 μm, 20 μm, 0.02 μm; Activation conditions, 200oC, 5 h; wt.%=
m(PVC)/m(silica), 20%. 10 mmol formaldehyde, mole ratio of phenol/formaldehyde, 20; Catalyst concentration, 3.0 wt.%; Reaction
time, 1 h; Reaction temperature, 70oC.
Figure 8. Effect of PVC loading on catalyst performance of
Figure 7. Effect of activation temperature on the performance
NS@PVC-EDA-SO3H catalyst a
of NS@PVC-EDA-SO3H catalyst a
a
Reaction conditions: silica average particle size, 0.02 um;
a
Reaction conditions: silica average particle size, 0.02 um;
Activation conditions, 200oC, 5 h; wt.% = m(PVC)/m(silica),
Activation conditions, 100~500oC,
5
h; wt.%
=
10~50%. 10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 3.0 wt.%;
Reaction time, 1 h; Reaction temperature, 70oC.
m(PVC)/m(silica), 40%. 10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 3.0 wt.%;
Reaction time, 1 h; Reaction temperature, 70oC;
Effects of reaction temperature ： The influence of
reaction temperature on hydroxyalkylation was examined under
catalysis of the best NS@PVC-EDA-SO3H. As shown in
Figure 9, this catalyst shows a good low temperature activity
and can provide 78.8% formaldehyde conversion and 81.4 %
BPF selectivity at 45oC. As reaction temperature is elevated to
70oC, the conversion and selectivity continuously and
remarkably increase to 99.6 and 93.9%, respectively. After that,
the enhanced effect of temperature on hydroxyalkylation is
almost invalid. The distribution of three isomers in bisphenol F
products varies obviously in the range of 45–60°C and the
selectivity for 2,4’- and 2,2’-isomers is improved with
elevating the temperature, further supporting that
Effect of PVC loading: Considering the close relationship
between PVC loading and acid sites on the surface of catalyst,
a series of NS@PVC-EDA-SO3H catalysts were prepared using
10 to 50 wt.% PVC dosages and their catalysis performances
were evaluated by the hydroxyalkylation of phenol with
formaldehyde to BPF. As shown in Figure 8. The acid density
increases from 0.61 to 1.26 mmol·g-1 and the formaldehyde
conversion increases from 82.1 to 99.4%, with PVC loading
consequently increasing from 10 to 40%. The reason for this
result may be the amount of amino groups increases with the
increase in PVC loading, and the larger PVC loading on the
surface of silica, the more amino groups are grafted on the
carbon chain, so a large number of SO3H groups can be
obtained after chlorosulfonation. However, the acid density,
formaldehyde conversion and selectivity to BPF shows no
significant increase upon further increases in PVC loading.
Therefore, a solid acid catalyst with high catalytic performance
was obtained when the PVC loading is 40 wt.%.
2-hydroxybenzyl alcohol has
a
lower activity than
4-hydroxybenzyl alcohol and needs a higher temperature to
accelerate its conversion to such two isomers.

Such catalyst exhibits an outstanding acceleration effect on
hydroxyalkylation, which can afford 38.5% formaldehyde
conversion and 82.3% BPF selectivity at 5 min. When the time
is prolonged from 5 to 60 min, the conversion and selectivity
further increase to 98.3 and 94.0%, respectively. At the same,
the 2,4’- and 2,2’- BPF isomers gradually increase from 38.1%
to 45.7% and 16.9% to 21.6%, respectively. This may be
because the intermediate 4-hydroxybenzyl alcohol is rapidly
and mainly converted to 4,4’-isomer in the early reaction
period, while the rate of another intermediate 2-hydroxybenzyl
alcohol being converted to 2,4’- and 2,2’-isomers is not so fast.
Hence the amount of 4,4’-isomer is dominant in the initial
period. As the reaction proceeds, the intermediate
2-hydroxybenzyl alcohol could be converted to 2,4’- and
2,2’-isomers more quickly. So, the selectivity of 2,4’- and
2,2’-isomers increases obviously, whereas the distribution of
4,4’-isomer decreased relatively. Therefore, the optimal
reaction time is 1 h.
Figure 9. Effect of reaction temperature on the
hydroxyalkylation of phenol with formaldehyde a
a
Reaction conditions: 10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 0.25% mol;
Reaction temperature, 45-70oC; Reaction time, 1 h.
Effects of catalyst concentration: The effect of catalyst
concentration on hydroxyalkylation was also checked using the
optimal NS@PVC-EDA-SO3H as a catalyst. As shown in
Figure 10. The activity and selectivity of catalyst continuously
and markedly increase with
a gradual increase of its
concentration, which can achieve 97.5% formaldehyde
conversion and 93.0% BPF selectivity at 0.1 mol % catalyst
concentration. Upon further increase in catalyst concentration,
the formaldehyde conversion and selectivity to BPF only show
a minor change. Thus, 0.1% mol is selected as the suitable
catalyst concentration. Notably, the distribution of three
isomers in BPF products is influenced by catalyst concentration,
as the concentration of catalyst is enhanced from 0.025 to
0.050% mol, 2,4’- and 2,2’-isomers increase from 41.2 to
45.8% and from 17.2 to 21.6%, respectively, along a significant
decrease in 4,4’-isomer from 41.6 to 32.7%. This is perhaps
because an increase in the acid amount relied on catalyst
concentration can accelerate the conversion of the intermediate
2-hydroxybenzyl alcohol to 2,4’- and 2,2’-isomers.
Figure 11. Effect of reaction time on the hydroxyalkylation of
phenol with formaldehyde a
a
Reaction conditions:10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 0.1% mol;
Reaction time, 5~120 min; Reaction temperature, 70oC.
Compared with existing homogeneous and
heterogeneous catalysts: The catalytic hydroxyalkylation
performance of NS@PVC-EDA-SO3H was compared to those
of two reference catalysts (the existing concentrated sulfuric
acid (H2SO4) and sulfonic acid resin) and the results are shown
in Figure 12, NS@PVC-EDA-SO3H catalyst exhibits an
outstanding hydroxyalkylation activity, which can achieve 92.9%
formaldehyde conversion and 93.1% BPF selectivity. While
homogeneous H2SO4 and heterogeneous sulfonated resin
catalysts only provide 53.4 and 12.9
% formaldehyde
conversions under the same reaction conditions, respectively.
Furthermore, its BPF selectivity (93.1%) is also higher than
those of H2SO4 (89.9%) and especially sulfonated resin
(74.7%). As
a
heterogeneous solid acid catalyst,
NS@PVC-EDA-SO3H has an absolute advantage over
concentrated sulfuric acid in the reusability. With a higher
dispersibility, NS@PVC-EDA-SO3H shows a better catalytic
activity than sulfonic acid resin. These compared data support
that NS@PVC-EDA-SO3H, as a newly constructed solid acid
catalyst, has an overwhelming advantage in hydroxyalkylation
performance compared to the two existing reference catalysts,
expecting that it has extensive application prospects in acid
catalysis reactions, especially including hydroxyalkylations.
Figure 10. Effect of catalyst concentration on the
hydroxyalkylation of phenol with formaldehyde a
aReaction conditions: 10 mmol formaldehyde, mole ratio of
phenol/formaldehyde,
20;
Catalyst
concentration,
0.025~0.500% mol; Reaction time, 1 h; Reaction temperature,
70oC.
Effects of reaction time: The influence of reaction time
on hydroxyalkylation was examined under catalysis of the best
NS@PVC-EDA-SO3H and the results shown in Figure 11.

a
Reaction conditions:10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 0.1% mol;
Reaction time, 1 h; Reaction temperature, 70oC.
Reusability of the catalyst: Finally, the stability of
NS@PVC-EDA-SO3H was tested by performing a recycle
experiment and the testing results are presented in Figure 14.
The performance of the catalyst shows no significant reduction
even after nine successive runs, still achieving 97.6%
formaldehyde conversion and 93.5% BPF selectivity,
Furthermore, the distribution of the isomers in BPF products
only varies slightly in all the recycle experiments. Thus,
NS@PVC-EDA-SO3H is considered to be an excellent and
stable recyclable solid acid catalyst for the current
hydroxyalkylation.
Figure 12. The catalytic performance of different catalysts in
the synthesis of BPF a
a
Reaction conditions:10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 0.1% mol (10
mg concentrated sulfuric acid, 60 mg NS@PVC-EDA-SO3H
catalyst, 20 mg sulfonic acid resin); Reaction temperature,
60oC; Reaction time, 1 h. b Re-prepared catalyst.
Comparison of catalytic activity of NS, NS@PVC,
NS@PVC-EDA, NS@PVC-SO3H and PVC-EDA-SO3H
catalyst: The catalytic hydroxyalkylation performance of
NS@PVC-EDA-SO3H was compared to NS, NS@PVC,
NS@PVC-EDA, NS@PVC-SO3H and PVC-EDA-SO3H
catalysts and the results are shown in Figure 13. It can be seen
that NS@PVC-EDA-SO3H catalyst exhibits an outstanding
superiority in catalytic activity compared to those catalysts,
which can achieve 99.6% formaldehyde conversion and 93.3%
BPF selectivity. While NS, NS@PVC, NS@PVC-EDA
catalysts show a poor hydroxyalkylation activity, which obtains
a extremely low formaldehyde conversion. It is worth
mentioning that NS@PVC-SO3H and PVC-EDA-SO3H
Figure 14. Reusability of catalyst study a
Reaction conditions:10 mmol formaldehyde, mole ratio of
phenol/formaldehyde, 20; Catalyst concentration, 0.25% mol;
Reaction temperature, 70oC; Reaction time, 1 h.
a
The plausible mechanism for formation of bisphenol F:
A plausible mechanism of condensation of phenol and
formaldehyde to BPF is presented in scheme 2. A carbocation
CH2OH+ is formed by protonation of formaldehyde with H+
released by -SO3H in NS@PVC-EDA-SO3H. An electrophilic
substitution reaction occurs on phenol with the formation of
two intermediates I(a) and I(b) as the first step, then the
short-lived intermediates I (b) and I (a) deprotonates fast to
form II (a) 2-hydroxybenzylalcohol and II (b) 4-hydroxybenzyl
The protonation of alcohol II (a) and II (b) initially produced
form the carbocation III (a) and III (b) respectively. A
complexation of the electrophile carbocation III (a) and III (b)
with the π electron system of another phenol molecule
generates three intermediates IV(a), IV(b) and IV(c): these
unstable intermediates then eliminate a proton, resulting in final
formation of BPF (V(a) 2,2'-BPF, V(b) 2,4'-BPF and V(c)
4,4'-BPF).
catalysts also has
a remarkable catalytic activity for
hydroxyalkylation, provide 77.4 and 85.9 % formaldehyde
conversions under the same reaction conditions, respectively.
However, NS@PVC-EDA-SO3H has a greater advantage in
hydroxyalkylation. This may be due to the fact that the
NS@PVC-EDA-SO3H catalyst has
a
mesoporous to
macroporous structure that can accelerate the diffusion and
conversion of substrates.
Figure 13. Comparison of catalytic activity of NS, NS@PVC,
NS@PVC-EDA, NS@PVC-SO3H and PVC-EDA-SO3H
catalyst a

Scheme 2. Plausible mechanism of condensation of phenol and formaldehyde to BPF
4. Conclusion
14. S. K. Jana, T. Kugita and S. Namba, Appl. Catal. A Gen.
In summary, NS@PVC-EDA-SO3H catalyst with richer
short mesoporous to macroporous channels has been
successfully synthesized via multi-steps treatment processes
and this newly constructed solid acid catalyst offers several
promising advantages in the hydroxyalkylation of phenol with
formaldehyde to BPF, including excellent catalytic activity and
selectivity, as well as easy recovery and good recyclability.
With such kind of renewable solid acid in hand, we are
interested in further exploring its potential applications to other
important acid-catalyzed reactions in industry, such as
esterification, alkylation, hydrolysis and so on .
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Acknowledgement
This research is financially supported by the National Natural
Science Foundation of China (Nos. 21546010, 21576078,
21676079, 21606082, 21776068), the National & Local United
Innovation Platform (No. 20123098), and the Natural Science
Foundation of Hunan Province (Grant No. 2016JJ2081). Hunan
2011 Collaborative Innovation Center of Chemical Engineering
& Technology with Environmental Benignity and Effective
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