Barium sulphate catalyzed dehydration of lactic acid to acrylic acid

Article abstract of DOI:10.1039/c3gc42028k

Dehydration of lactic acid was performed over various metal sulphates. BaSO₄ was found to show an efficient activity for dehydration of lactic acid to acrylic acid due to the moderate acidity on its surface. Under the optimal conditions, 99.8% lactic acid conversion and 74.0% acrylic acid selectivity were achieved over the BaSO₄ catalyst.

Full text of DOI:10.1039/c3gc42028k

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Barium sulphate catalyzed dehydration of lactic acid
to acrylic acid†
Cite this: DOI: 10.1039/c3gc42028k
Received 29th September 2013,
Accepted 22nd October 2013
Jiansheng Peng,a Xinli Li,a Congming Tang*a and Wei Baib
DOI: 10.1039/c3gc42028k
www.rsc.org/greenchem
Dehydration of lactic acid was performed over various metal sul- salt in water with an appropriate acidity may be the ideal type
phates. BaSO4 was found to show an efficient activity for de- of catalyst for dehydration of lactic acid at high temperature.
hydration of lactic acid to acrylic acid due to the moderate acidity The Ca3(PO4)2–Ca2P2O7 (50 : 50 wt%) catalyst has been demon-
on its surface. Under the optimal conditions, 99.8% lactic acid con- strated to efficiently catalyze dehydration of methyl lactate.20
version and 74.0% acrylic acid selectivity were achieved over the The CaSO4–CuSO4 composite catalysts have a high activity for
BaSO4 catalyst.
dehydration of lactic acid or lactates.21,22 More recently,
Ghantani et al.23 reported that calcium hydroxyapatite cata-
lyzed the dehydration of LA to acrylic acid, achieving 100%
conversion of LA and 60% selectivity toward acrylic acid under
the optimal reaction conditions. To the best of our knowledge,
the highest yield (68%) of acrylic acid for the dehydration of
lactic acid was obtained for the CaSO4–Na2SO4 composite cata-
lysts.24 However, the knowledge of the relationship between
acidity of catalysts and the activity for dehydration of lactic
acid is still quite limited. Herein, we present a study on acidity
of metal sulphates and catalytic activity for dehydration of LA
to acrylic acid. Furthermore, other parameters such as calcina-
tion temperature, reaction temperature, lactic acid concen-
tration and reaction time are also discussed.
Preparation of bulk chemicals such as acrylic acid,1 propionic
acid,2 ethanol,3,4 pyruvic acid5 and ethylene glycol6 from
biomass has become an increasingly important subject in the
modern industrial society.7 Acrylic acid and acrylates are
widely used for the synthesis of polymers, dispersants,
adhesives and coatings.8 Acrylic acid from lactic acid (LA) is
viewed as a potential route due to the excessive depletion of
fossil resources like petroleum, coal, and natural gas for the
rapid development of the chemical industry.2,9–13 The modi-
fied NaY catalysts were demonstrated to show a high efficiency
for dehydration of LA to acrylic acid.1,14–17 It is well known
that the dehydration of LA is catalyzed by acid sites. Acidity is
a key factor in the process of dehydration of lactic acid. Strong
acidity is a great disadvantage for catalytic dehydration of LA,
while it favors decarbonylation and/or decarboxylation of LA to
acetaldehyde.15,18 In contrast, a catalyst with no acid sites or
with basicity will be inefficient for catalytic dehydration of LA.
Thus to adjust the acidity strength of a catalyst to an appropri-
ate degree is a crucial step for efficient catalytic dehydration. A
case in point is that several modifiers are used to change the
surface acidity of NaY zeolites to achieve a high catalytic per-
formance.14,19 But these modifiers16,17 are easily lost from the
surface of the catalyst under an atmosphere of water vapor
because they have an excellent solubility in water, resulting in
deactivation of the catalyst with time on stream. An insoluble
Initially, acidity of metal sulphates and catalytic activity for
dehydration of lactic acid to acrylic acid were investigated and
the results are given in Table 1. The data of the BET surface
Table 1 Catalytic activity of metal sulphates for dehydration of lactic acid to
acrylic acida
Sel.b [%]
Catalystc
LA conv. [%]
AA
AD
PA
5.5
9.3
12.5
6.2
9.4
7.6
24.1
PD
ACA
Al2(SO4)3
NiSO4
ZnSO4
MgSO4
BaSO4
CaSO4
Na2SO4
100
9.4
79.0
54.4
55.1
29.0
20.3
20.5
23.0
0.7
1.3
1.5
1.2
1.7
0.9
1.3
1.9
2.6
3.6
1.6
1.9
1.6
3.3
99.8
45.0
85.0
99.7
99.8
30.0
19.4
26.4
61.7
65.7
68.6
27.0
aChemical Synthesis and Pollution Control Key Laboratory of Sichuan Province,
China West Normal University, Nanchong, Sichuan 637002, P.R. China.
E-mail: tcmtang2001@163.com
a Conditions: calcination temperature 500 °C, reaction temperature
400 °C, catalyst: 0.50–0.60 g, particle size: 20–40 meshes, carrier gas
N2: 1 mL min−1, feed flow rate: 1 mL h−1, LA feedstock: 20 wt% in
water. b LA: lactic acid, AA: acrylic acid, AD: acetaldehyde, PA:
propionic acid, PD: 2,3-pentanedione, ACA: acetic acid. c Carbon
recovery is above 96% except for the Na2SO4 catalyst (85%).
bChengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu,
Sichuan 610041, P.R. China
†Electronic supplementary information (ESI)
available. See DOI:
10.1039/c3gc42028k
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area of metal sulphates are shown in the ESI (Table S1†). Con- with a pKa of +4.8 to display acidic colour, indicating that its
version of LA drastically changed depending on the type of H0 is above +4.8 and the acidity is the weakest. From the
metal sulphate. LA was almost fully converted in the process of results obtained for Na2SO4 including 30.0% conversion of
catalytic reaction using Al2SO4, NiSO4, CaSO4 and BaSO4. As lactic acid as well as 27.0% selectivity of acrylic acid, we can
for ZnSO4 and Na2SO4, the conversion of LA was less than conclude that the rare acidity on the surface of the catalyst is a
50%. Unlike the tendency of LA conversion to change depend- disadvantage for dehydration of LA. Therefore, the H0 charac-
ing on the type of metal sulphate, acrylic acid selectivity terizing the acidity strength of the catalyst lies between +3.3
increased from Al2(SO4)3 with only 9.4% to CaSO4 with 68.6%. and +4.8, favoring the conversion of LA to form acrylic acid.
Conversely, selectivity toward acetaldehyde decreased from
In a preliminary experiment, the stability of BaSO4 and
Al2SO4 with 79.0% to BaSO4 with only 20.3%. The formation of CaSO4 was firstly evaluated (seen in Fig. S6 and S7†). Although
other products such as propionic acid, 2,3-pentanedione and CaSO4 has an excellent initial activity, the catalytic perform-
acetic acid was also influenced by the type of metal sulphate. ance drastically decreased with an increase of reaction time.
In order to further understand the factors which affect the con- A possible reason is that the hydrothermal stability of CaSO4 is
version of LA to acrylic acid, the acidity strength and density of poor. Compared with CaSO4, the BaSO4 catalyst displays an
all catalysts were tested using the Hammett indicator method. excellent stability for catalytic activity due to the excellent
The results are given in Table 2. It is clearly seen that the order hydrothermal stability of BaSO4. In addition, it has no strongly
of acidity strength for metal sulphates is Al3+ > Zn2+ > Ni2+
>
acid sites for causing side reactions (e.g. coke deposition) and
Mg2+ > Ba2+ > Ca2+ > Na+. Although the conversion of lactic has only moderately acid sites favoring dehydration of lactic
acid fluctuated with the acidity strength of the catalyst, the acid to acrylic acid. Thereafter, we focused on the catalytic per-
selectivity toward acrylic acid decreased with an increase in the formance of the BaSO4 catalyst.
definite range of acidity strength of catalysts and the selectivity
Due to the moderate acidity on the surface of BaSO4 with
toward acetaldehyde increased with an increase in the definite the range of H0 between +3.3 and +4.8, it exhibited an efficient
range of acidity strength of catalysts. Strong acidity favored activity. It is generally believed that calcination can improve
decarbonylation or decarboxylation of LA to form acet- the acidity and the stability in the process of vapour phase
aldehyde. Among all metal sulphates, Al2(SO4)3 exhibits the catalytic reaction.20,23 The influence of calcination temperature
strongest acidity, and serious decarbonylation reaction occurs of BaSO4 on dehydration of LA was investigated and the results
to form acetaldehyde with a high selectivity of 79.0%. Similar are shown in Table 3. It is clearly seen that LA conversion
results were reported by Katryniok et al.18 In tested metal sul- increases with the increase of calcination temperature up to
phates, BaSO4, CaSO4 and MgSO4 have a moderate acidity, and 700 °C, and it slightly decreases with further increase to
more than 60% selectivity of acrylic acid has been achieved 900 °C. Interestingly, the surface acidity density of catalysts
over these catalysts. Compared with MgSO4, both BaSO4 and with different acidity distributions also increases with the
CaSO4 cannot make dimethyl yellow with a pKa of +3.3 to enhancement of calcination temperature (seen in Table 3). But
display acidic colour, suggesting that the acidity strength of it started to decrease at 900 °C. This result further demon-
BaSO4 and CaSO4 is weaker than that of MgSO4. Higher selecti- strated that an increase of the acid amount of the catalyst with
vity of acrylic acid was obtained over the BaSO4 and CaSO4 +3.3 < H0 < +4.8 favored the conversion of LA to acrylic acid.
catalysts. It seems as if it is an advantage for dehydration of LA Besides, the BaSO4 catalysts with different calcination temp-
to acrylic acid when the surface acidity of the catalyst becomes eratures were also characterized by FTIR spectra and powder
weaker. This prompted us to investigate a catalyst with weaker X-ray diffraction, and the results are shown in ESI (Fig. S2 and
acidity. Na2SO4 was chosen and it cannot make methyl red S3†). It is clearly seen that all characteristic peaks remain
Table 2 Acidity strength and density of metal sulphates characterized by the
Hammett indicators with standard pretreatmenta
Table 3 Effect of calcination temperature of the BaSO4 catalyst on dehydration
of lactic acid to acrylic acid as well as acidity distributiona
Acidity density of catalyst [mmol n-butylamine per g
catalyst]
Acidity distributiond [mmol
n-butylamine per g catalyst]
Calcination
temp. [°C]
LA conv.b
[%]
AA sel.c
[%]
+4.8(a)
4.0 < H0 < 4.8
+4.0(b)
3.3 < H0 < 4.0
+3.3(c)
1.5 < H0 < 3.3
+1.5(d)
H0 < 1.5
Catalystb
4.0 < H0 < 4.8
3.3 < H0 < 4.0
No
67.5
68.0
99.7
99.8
95.0
77.0
75.1
65.7
74.0
65.8
0.0038
0.0039
0.0042
0.0066
0.0033
0.0032
0.0101
0.0114
0.0163
0.0095
Al2(SO4)3
NiSO4
ZnSO4
MgSO4
BaSO4
CaSO4
Na2SO4
0.0063
0.0006
0.0180
0.0036
0.0042
0.0101
—
0.0271
0.0224
0.0130
0.0016
0.0114
0.0079
—
0.0065
0.0056
0.0100
0.0032
—
0.0025
—
—
—
—
300
500
700
900
—
—
—
—
a Conditions: reaction temperature 400 °C, BaSO4 catalyst: 0.57 g,
particle size: 20–40 meshes, carrier gas N2: 1 mL min−1, feed flow rate:
1 mL h−1, LA feedstock: 20 wt% in water. b LA: lactic acid. c AA: acrylic
acid. d Acidity distribution of the catalyst under different calcination
temperatures.
a Hammett indicators, a: methyl red, b: 4-phenylazo-1-naphthylamine, c:
dimethyl yellow, d: 4-(phenylazo)diphenylamine; “—”: non-acidic colour
for the indicator. b All catalysts were calcinated at 500 °C for 6 h.
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Fig. 1 Effect of reaction temperature on dehydration of LA with BaSO4. Con-
ditions: catalyst: 0.50–0.60 g, particle size: 20–40 meshes, carrier gas N2: 1 mL
min−1, feed flow rate: 1 mL h−1, LA feedstock: 20 wt% in water.
Fig. 2 Effect of lactic acid concentration. Conditions: catalyst: 0.50–0.60 g, par-
ticle size: 20–40 meshes, carrier gas N2: 1 mL min−1, feed flow rate: 1 mL h−1
,
reaction temperature: 400 °C.
unanimous with each other, but the peak intensity is different
for different calcination temperatures, indicating a change of
catalytic performance. Other characterizations such as SEM
and TG analysis are also given in ESI (Fig. S4 and S5†). Thus
the optimal calcination temperature should be around 700 °C.
At a fixed calcination temperature of 700 °C, the effect of the
reaction temperature on the dehydration of LA was further
investigated and the results are given in Fig. 1. From the
results presented in Fig. 1, this reaction is very sensitive to
temperature. LA conversion increased linearly in the range of
However, as for the BaSO4 catalyst, it has no crystal water.
Therefore, the effect of water on the acid strength of the BaSO4
catalyst is very limited. Subsequently, the effect of time on
stream on the catalytic performance was also investigated, and
the results are shown in Fig. S7.†
300–400 °C and LA was almost fully converted when the re- Conclusions
action temperature was above 400 °C. The selectivity to acrylic
In this work, we have presented a study on acidity of metal sul-
phates and the activity for dehydration of LA to acrylic acid.
The catalyst with a moderate acidity strength of +3.3 < H0
acid decreases with an increase in the reaction temperature.
For example, acrylic acid selectivity is higher than 70% when
the reaction temperature is lower than 400 °C, while it
decreases to 5.6% at 500 °C. In contrast, the selectivity of acet-
aldehyde increased with an increase of the reaction tempera-
ture, indicating that high temperature favors the
decarbonylation or decarboxylation to form acetaldehyde. Con-
sidering the conversion of LA and acrylic acid selectivity, the
optimal reaction temperature should be about 400 °C. In
addition, the effect of water is shown in Fig. 2. Conversion of
lactic acid as well as selectivity to acrylic acid were slightly
affected when the concentration of lactic acid was lower than
20 wt%. However, conversion of lactic acid as well as selectivity
to acrylic acid decreased with an increase of lactic acid concen-
tration. These results suggested that higher yield for acrylic
acid is achieved at low concentration of lactic acid. High con-
centration of LA favored coke on the surface of the catalyst,
resulting in a decrease of catalytic active sites (decrease of LA
conversion). 2,3-Pentanedione selectivity increased with an
increase of lactic acid concentration. It is known that the for-
mation of 2,3-pentanedione is via a Claisen condensation re-
action of two lactate moieties followed by decarboxylation and
dehydration steps. Thus, an increase of the lactic acid concen-
tration favors its condensation reaction to form 2,3-pentane-
dione. As is well known to all, changes of crystal water for the
catalysts with crystal water influenced the acid strength.
<
+4.8 exhibits an efficient activity. It is in agreement with the
basic principles of heterogeneous catalysis that larger amounts
of active sites (moderately acid sites) increase the catalytic
activity (conversion of LA). LA conversion and product distri-
bution are sensitive to reaction temperature. Low reaction
temperature favors the dehydration of LA to form acrylic acid,
while high temperature favors decarbonylation/decarboxy-
lation of LA to form acetaldehyde. BaSO4 was found to have an
excellent activity for dehydration of LA to acrylic acid. Under
the optimal reaction conditions, 99.8% LA conversion and
74.0% acrylic acid selectivity were achieved over the BaSO4
catalyst.
Acknowledgements
This work was supported by the Scientific Research Fund of
Chemical Synthesis and Pollution Control Key Laboratory of
Sichuan Province with project number of CSPC2012-7, the
Scientific Research Fund of China West Normal University
with project numbers of 10B004 and 12B019 and the
Nanchong Key Technology R&D Program of Sichuan, China
with project number of 11A0051.
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