2
42
L. Harvey et al. / Applied Catalysis A: General 489 (2015) 241–246
coated alumina catalyst [5] was also produced in order to examine
the use of a product which would be highly characteristic of one
produced in an industrial process.
2.3. Analysis of reaction mixture
Fig. 1. Epoxidation of allyl alcohol to glycidol by hydrogen peroxide under TS-1
catalyst (R corresponds to a carbon chain generally of length 1–3).
The composition of the reaction mixture was monitored by
extracting aliquots of reactant material (∼0.03 g) through the
septum with a syringe which was then analysed by gas chromatog-
raphy. Quantification of species concentrations in the reaction
mixture was primarily obtained using an Agilent HP 5890 gas
chromatograph fitted with a Restek Stabilwax column and flame
the carbon double bond, rendering it less susceptible to attack by
an electrophilic oxidising agent such as hydrogen peroxide [17].
Furthermore, under certain reaction conditions the epoxide moiety
is susceptible to ring-opening reactions followed by nucleophilic
attack to yield either glycerol by hydrolysis or diols by solvolysis.
The primary focus of this study is to investigate the influence
of the purity of the allyl alcohol reactant mixture, in particular, the
effect of varying concentrations of impurities likely to be encoun-
tered in the production of allyl alcohol from waste glycerol derived
from biodiesel manufacture.
−
1
ionisation detector. Gas flows were carrier gas (N ): 30 mL min
,
2
−
1
−1
H : 40 mL min , air: 400 mL min and split ratio of 100:1. The
2
◦
◦
injector temperature was 130 C, detector temperature 270 C and
the temperature profile was to hold the oven at 35 C for 5 min,
ramping to 245 C over 10 min and holding at 245 C for 25 min.
Identification of any unknown species was performed using an Agi-
lent HP 6890 gas chromatograph fitted with a Restek CarboWax
silica capillary column and 5973 mass-selective detector. Carrier
gas used was helium, at a rate of 130 mL min with a split ratio
of 5:1. The injector temperature was 130 C, detector temperature
was 235 C and the temperature profile was to hold the oven at
5 C for 5 min, ramping to 220 C over 10 min and holding at 245 C
◦
◦
◦
2
. Experimental
−1
◦
2.1. Catalyst synthesis
◦
◦
◦
◦
3
The TS-1 used in all experiments was prepared as per Taramasso
et al. [11], where 37.99 g (0.182 mol) of tetraethylorthosilicate
for 30 min. The MSD filament was turned off during elution of the
solvent peak in order to protect the equipment. The data obtained
from these instruments was then used to calculate the conversion
and selectivity of reactant species. The fractional conversion of allyl
alcohol, XAA, and selectivity to glycidol, Sglc/AA (mol percent) were
calculated according to the following:
(
(
TEOS, Merck) and 0.61 g (0.003 mol) tetratethylorthotitanate
TEOT, Merck) were mixed at 35 C. The mixture was then cooled
◦
in an ice bath and 39.54 g (0.194 mol) of tetraethylammonium
hydroxide (TPAOH) template (40 wt% in water, Merck) was added
dropwise using a burette. Following addition of the template, the
◦
[AA] − [AA]
mixture was heated to 80 C in order to evaporate ethanol produced
0
t
XAA
=
(1)
(2)
[
AA]
0
by hydrolysis of TEOS. Distilled water was added to return the mix-
ture to its initial volume. The pH was found to be 12.7, close to
the published value of 12.2 [11]. The mixture was then transferred
to a PTFE-lined stainless steel autoclave fitted with a thermocou-
Sglc/AA = X [
glc] MWAA
t
× 100
[AA] MW
glc
AA
0
◦
ple, pressure gauge and pressure relief valve, and heated to 175 C
where [AA] is the concentration of allyl alcohol in the reaction mix-
ture (ppm) at times corresponding to the subscripts 0 (initially)
and t (at the time specified) and [glc] is the concentration of glyci-
dol in the reaction mixture (ppm). MWAA and MWglc corresponds
for two days. The solid product was collected by centrifuging three
times for 30 min each at 4000 rpm, washing with distilled water
between extractions. The centrifuged product was dried for 5 h at
◦
−1
1
20 C, yielding 11.47 g of fine white solid which was heated first in
to the molecular mass of allyl alcohol (AA, 58.08 g mol ) and glyci-
◦
−1
nitrogen at 450 C for 2 h, left to cool to ambient temperature and
subsequently calcined in air at 550 C for 20 h. The temperature
ramp rate for both heat treatments was 2 C min . X-ray diffrac-
dol (glc, 74.08 g mol ), respectively. The selectivity of allyl alcohol
◦
to its associated by-products was obtained in the same way as for
glycidol. In the case of by-products resulting from the oxidation of
an impurity, the conversion of that impurity was first calculated as
outlined in Eq. (1) and selectivity was calculated according to Eq.
(2). Allyl alcohol or glycidol concentration in Eq. (1) and (2) were
replaced with concentrations of impurity and oxidised impurity,
respectively.
◦
−1
tion using a Phillips X’pert Pro diffractometer with Cu K␣ incident
radiation (ꢀ = 1.5406 A˚ ) was used to characterise the catalyst and
compare it to samples synthesised elsewhere [18]. The surface area
was determined by nitrogen adsorption and found using Langmuir
2
−1
.
isotherm to be 563 m g
2.2. Epoxidation of allyl alcohol
3. Results
In a typical experiment, 0.25 g of TS-1, 2.90 g (0.05 mol) of allyl
alcohol (Sigma-Aldrich) and 22.5 mL of solvent were added to a
00 mL round bottomed flask fitted with a reflux condenser, ther-
mocouple and septum. The reactants were then heated to the
required temperature and 5.67 g of hydrogen peroxide (0.05 mol,
3.1. Catalyst synthesis
1
The X-ray diffraction pattern (Fig. 2) shows that the zeolite
synthesised is highly crystalline with a peak distribution corre-
sponding to the MFI zeolite structure and an average crystallite
size of ca. 62 nm. No significant quantity of amorphous material
was detected as indicated by the absence of a broad absorption at
3
0 wt% aqueous) were added. In particular, the effects of solvent
type, reaction temperature and the influence of impurities such
as acrolein (propenal) likely to be encountered when conducting
the reaction on a large scale were investigated. Molecular prop-
erties of the added impurities, in particular atomic charges and
dipole moment, were calculated using the B3LYP/6-31G* basis set
in density functional calculations in Spartan “10 [19].
◦
◦
approximately 2ꢁ = 10 –20 .
3.2. Effect of solvent type
◦
Ally alcohol was reacted with hydrogen peroxide at 60 C using
three different solvents; methanol, ethanol and ethyl acetate. The
results shown in Table 1 indicate that the highest conversion and
A mixture containing allyl alcohol produced in a fixed bed reac-
tor from the conversion of a 30 wt% solution of glycerol using Fe O3
2