CATALYTIC CONVERSION OF GLYCEROL INTO AROMATIC HYDROCARBONS
2453
Table 3. Composition of liquid products, wt %
Catalyst Н-ZSM-5 SAPO-34 H-Beta
Hydrocarbon part of catalysate
well as tert-butyl glycerol ethers (mono-, di-, and tri-
TBGs) without specifying their contents in detail.
H-BETA zeolite exhibits slightly lower activity and
selectivity for liquid products. The glycerol conversion
at 340°C is 70.5%; the yield of the liquid catalysate is
only ~72%, and increased formation of gaseous hydro-
carbons С1–С4 was observed. The selectivity for high-
octane ArHs (36.7%) and oxygenates (42.3%) is slightly
lower (by 4–6%), but comparable to the values
obtained for zeolite H-ZSM-5. Among the products of
the reaction on zeolite H-BETA, acrolein, which is the
product of the thermal decomposition of glycerol, was
present in much greater amounts than on H-ZSM-5.
An analysis of the product distribution in the organic
and aqueous parts of the catalysate for these acid cata-
lyst samples with high surface concentration of Brøn-
sted acid centers shows (Table 3) that xylenes and ethyl-
benzene are dominant among ArHs formed on
H-BETA and heavier alkyl aromatics С9+ prevail on
H-ZSM-5.
Methanol
Acrolein
Aliphatic hydrocarbons C5+
5.6
16.0
4.8
0.2
48.0
7.4
4.8
26.8
0.8
Aromatic hydrocarbons,
73.6
44.4
67.6
including:
Benzene
Toluene
Xylenes + ethylbenzene
Alkylaromatics С9+
2.5
9.8
20.6
40.7
0.5
6.6
20.4
16.9
5.0
25.3
20.7
16.6
Aqueous part of catalysate
Methanol
Acrolein
10.2
2.1
0.5
6.5
4.0
3.0
Methyl glycerol ethers
tert-Butyl glycerol ethers
ethers was observed in the aqueous part of the cataly- Unidentified
12.0
3.4
2.8
–
0.2
6.4
2.5
11.8
2.0
Active formation of branched tert-butyl glycerol
sate among the products obtained on zeolite
H-BETA; in contrast, methyl glycerol ethers formed
on H-ZSM-5 (Table 3). This is consistent with the
data of [11], which reported the use of wide-pore zeo-
lites as effective catalysts of glycerol etherification with
isobutylene and tert-butyl alcohol; zeolite ZSM,
which also has satisfactory acidity, showed lower activ-
ity because of narrower pores, which is certainly a very
important factor in view of the bulkiness of TBG mol-
ecules. This also agrees with the data of [12], which
showed that H-BETA had low activity in glycerol
etherification with monohydric alcohols such as
methanol.
An indirect evidence for glycerol alkylation on
H-ZSM-5 and H-BETA formed in the reaction with
isobutylene is its low concentration in the hydrocar-
bon gas of the reaction, not exceeding 0.2 wt %; on
zeolite SAPO-34, on which TBG does not form, the
concentration of isobutylene in the hydrocarbon gas-
eous reaction products reaches 6.9 wt % (Table 2).
According to Table 2, acrolein is the main product
of the reaction on SAPO-34. At low conversion of
glycerol (12.5%), the selectivity of its formation is
63.1%, with only trace amounts of glycerol ethers
formed (Table 2). The absence of MG among the
products, in our opinion, is explained by the fact that,
as is known [13], SAPO-34 is an effective catalyst of
methanol conversion into С2–С3 olefins. This is con-
firmed by the fact that ethylene and propylene form in
maximum amounts (33.3 and 26.8%, respectively) in
the hydrocarbon gaseous products of the reaction on
Glycerol (unchanged)
Water
Total
19.9
49.5
100.0
70.0
16.4
100.0
44.7
31.9
100.0
active formation of acrolein on acid catalysts, i.e.,
high-silica zeolite with deposited silicotungstic acid;
acrolein is an important petrochemical product used
as a starting material for the synthesis of acrylonitrile,
pyridine, β-picoline, and amino acids (methionine,
proline) in chemical and pharmaceutical industry.
To summarize, in addition to acrolein, the prod-
ucts of the reaction on all catalysts included ArHs and
oxygenates (methanol and various glycerol ethers),
which are promising fuel additives that can be used in
compounding of gasolines for increasing its octane
number. In contrast to glycerol itself, the trisubstituted
glycerol ethers obtained in small amounts in the reac-
tion on the sample do not contain –OH polar groups;
due to this, the stability of the resulting high-octane
gasoline increases. Further prospects for the develop-
ment of effective catalysts of the conversion of glycerol
and other polyhydric alcohols are associated with the
search for nanosized catalysts with molecular sieve
properties [15–17] and hybrid nanomaterials [18–21].
ACKNOWLEDGMENTS
This study was financially supported by the Minis-
try of Education and Science of the Russian Federa-
SAPO-34, as compared to other catalysts (Table 2). tion (project no. RFMEFI57617X0089).
Also, methanol was found in a low concentration in
the aqueous phase of the catalysate (Table 3).
Our results obtained with the use of SAPO-34 do
not contradict the data of [6, 14], which indicated
REFERENCES
1. S. K. Tanugula, PhD Thesis (2010).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 92 No. 12 2018