G Model
CATTOD-8889; No. of Pages10
ARTICLE IN PRESS
N. Alonso-Fagúndez et al. / Catalysis Today xxx (2014) xxx–xxx
3
Thermogravimetric (TGA) analysis of the different solids were
conducted with a Mettler Toledo TGA/SDTA 851e instrument upon
heating the samples in synthetic air from room temperature to
respectively. Further details of the chromatographic analysis are
given in Supplementary data section.
1073 K at a heating rate of 5 K min−1
.
2.3.3. Selective oxidation with H2O2 of furfural to C4 diacids
The reaction was carried out in batchwise mode in a glass flask
reactor (50 mL) with three necks for the thermocouple, for a con-
denser and for sampling through a septum. The second neck was
also used for addition of reactants. The required amounts of catalyst
and of a 30% H2O2/H2O solution (Sigma-Aldrich) were incorpo-
rated into the reactor that was heated to the reaction temperature
by immersion in an oil bath. The reaction started when a known
amount of a furfural dissolved in water, previously heated at the
reaction temperature, was poured into the reactor. This mixture
was vigorously agitated at 800 rpm. Different aliquots were sam-
pled at different reaction time to determine the concentration of
organic compounds by HPLC and the H2O2 concentration by iodom-
etry. Further details of the analyses are given in Supplementary data
section.
The 1H and 13C NMR spectra were recorded in a AV-400-WB
Bruker spectrometer equipped with a triple channel probe. Pow-
der samples were finely grounded and dried for several days at
373 K in an oven and then rapidly transferred to ZrO2 rotors (4 mm)
and capped with Kel-F caps to prevent the hydration of the poly-
mer. Frequencies used were 400.13 and 100.32 MHz for 1H and 13
C
nuclei, respectively. Samples were spun at 10 kHz. 1H MAS-NMR
spectra were obtained after direct irradiation at a spectral width of
35 kHz, a relaxation delay of 5 s and pulses of ꢀ/3 at 40 kHz. The
CP-MAS 1H–13C spectra were recorded by using a spectral width of
35 kHz, excitation pulse for 1H of 3.4 s, contact time of 3.5 ms and
a relaxation time of 4 s, with 1H tppm15 decoupling at 80 kHz. The
number of scans was 1024 for 13C spectra and 256 for 1H. 13C chem-
ical shift is referenced to the adamantane CH2 signal (29.5 ppm) as
secondary reference relative to the TMS as a primary reference. 1
H
is referred to H2O as a secondary reference (4.77 ppm) relative to
TMS as primary reference.
3. Results and discussion
Viscosities were measured at 25 0.05 ◦C using an Ubbelohde
viscometer (purchased from Schott-Gerate, Germany) with the
diameter of their capillary of 1.03 mm (Nm. 525.20II). Aqueous
solutions of PSSA samples in 0.1 M CH3COOH/0.2 M NaCl were pre-
pared at concentration about 2.4 g dL−1. All solutions were filtered
to 0.45 m using a cellulose type filter prior to use. Six dilutions
with corresponding pure solvent were used, the flow time mea-
surements were repeated three times, and the average values were
used to calculate the intrinsic viscosity [ꢁ] for that solution.
Two different liquid phase routes to sulphonate PS waste were
selected as they are frequently used procedures in sulphonation of
commercial PS [11,12]. Gas phase sulphonation is not very effective
in extensive sulphonation. Moreover liquid phase routes involve
the dissolution and re-precipitation of the polymer molecules that
can help in removing additives present in waste PS that may inter-
fere in the final product. Three different types waste PS were
selected: CD covers (CD) and yoghurt (Y) and expanded polystyrene
packaging (EPS).
2.3. Measurements of the catalytic activity
The sulphur content of different WTC-PSSA catalysts deter-
mined by elemental analysis and the amount of acid sites
determined by acid–base titration are summarized in Table 1. Sul-
phur content and the amount of acid sites are not exactly the same
in the different samples. Sulfone bridges and acidic groups other
than –SO3H groups (e.g. –COOH) might have been created by oxi-
dation of the polymer backbone during the sulfonation process and
may explain the misfit between these two magnitudes. In the first
case the acid content should be smaller than the S content, whereas
in the second case acid content should be larger. However we have
to consider that the differences between these two parameters are
close to experimental error so we can assume that the presence of
sulfones and other acidic groups are not very relevant, regardless
the type of PS waste and the method of sulfonation
The degree of sulfonation (DS), or the percentage of aromatic
rings that are substituted by sulphonic groups, was very high in all
the catalysts (Table 1). The values are equivalent to the substitution
of ca. 90% of the aromatic rings, which indicates that almost all of
the aromatic rings were substituted. The high degree of sulphona-
tion reached for all samples was an objective of the preparation
2.3.1. Conversion of vegetable oil to biodiesel
To evaluate the catalytic activity in the production of biodiesel, a
pressure glass tube reactor with a capacity of 15 mL from Ace Glass,
Inc. was used. A given amount of catalyst (the resulting amount
after drying 200 mg at 373 K overnight, aprox. 4 wt% referred to
oil mass) was dissolved in 3.5 g of methanol (Scharlau, >99.8% GC,
H2O <0.005%) previously incorporated in the reactor. Once dis-
solved, 4 g of Cynara cardunculus oil (with an acidity index of 9.7%)
was added (methanol/oil mol ratio = 24). Then, the reaction started
when the reactor was introduced into an oil bath maintained at the
selected reaction temperature (403 K). Both the oil in the bath and
the reaction mixture were vigorous stirred at 1000 rpm by magnetic
stirrers. The reaction was halted by stopping the agitation taking
the reactor out the oil bath. The analysis of the reaction mixture
was conducted by HPLC (tri, di and monoglycerides (TG, DG, MG),
free fatty acids (FFA), fatty acid methyl esters and methanol) and
GC for glycerol. Further details of the chromatographic analysis are
given in Supplementary data section.
2.3.2. Dehydration of xylose to furfural
Table 1
To evaluate the catalytic activity in the dehydration of xylose to
furfural, 150 mg of D-xylose (SigmaUltra, >99%), a known amount
of catalysts, deionised water (1.35 mL) and 3.5 g of organic solvent
(cyclopentyl methyl ether (CPME)) (Sigma-Aldrich ≥99.9%), were
poured into an Ace Glass pressure glass tube reactor (capacity
of 15 mL). The reaction started when the reactor was introduced
into an oil bath maintained at the selected reaction temperature
(443 K). Both the oil in the bath and the reaction mixture were
vigorous stirred at 1000 rpm by a magnetic stirrer. The reaction
was halted by stopping the agitation taking the reactor out the oil
bath. The concentrations of xylose and furfural in both aqueous
and organic phase were determined by HPLC and GC analyses,
Sulphur content, number of acidic sites and sulfonation degree, referred to g of dry
catalyst for different WTC-PSSA catalysts.
S content
[mmol S gcat
Acid sites
Degree of
−1
−1
]
]
[mmol H+ gcat
sulfonationa
Y-SUL
5.2
4.9
5.0
5.2
5.0
5.0
4.9
4.3
5.4
5.4
5.4
5.4
93.4
84.5
87.4
93.4
87.4
87.4
CD-SUL
EPS-SUL
Y-ACET
CD-ACET
EPS-ACET
a
Calculated from the S content determined by chemical analysis according with
the equation proposed by Bekri-Abbes [8].
Please cite this article in press as: N. Alonso-Fagúndez, et al., Poly-(styrene sulphonic acid): An acid catalyst from polystyrene waste for