Catalytic dehydration of lactic acid to acrylic acid over dibarium pyrophosphate

Article abstract of DOI:10.1016/j.catcom.2013.10.009

Barium phosphate catalysts were prepared by a precipitation method. The catalysts were calcined at 500 C for 6 h in air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by N₂ sorption for specific surface area, by TPD-NH₃ for acidity and by TG for thermal stability. The dibarium pyrophosphate catalyst was found to have the best catalytic performance, ascribing to weak acidity on the surface. Under the optimal reaction conditions, 99.7% of the lactic acid conversion and 76.0% of the selectivity to acrylic acid were achieved over the dibarium pyrophosphate catalyst.

Full text of DOI:10.1016/j.catcom.2013.10.009

Catalysis Communications 43 (2014) 231–234
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Catalytic dehydration of lactic acid to acrylic acid over
dibarium pyrophosphate
a
a
a
a
b
Congming Tang a, , Jiansheng Peng , Guoce Fan , Xinli Li , Xiaoli Pu , Wei Bai
⁎
a
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong, Sichuan 637002, PR China
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, Sichuan 610041, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 July 2013
Received in revised form 5 October 2013
Accepted 10 October 2013
Available online 24 October 2013
Barium phosphate catalysts were prepared by a precipitation method. The catalysts were calcined at 500 °C
for 6 h in air atmosphere and characterized by SEM for morphological features, by XRD for crystal phases, by
N2 sorption for specific surface area, by TPD–NH3 for acidity and by TG for thermal stability. The dibarium
pyrophosphate catalyst was found to have the best catalytic performance, ascribing to weak acidity on the
surface. Under the optimal reaction conditions, 99.7% of the lactic acid conversion and 76.0% of the selectivity
to acrylic acid were achieved over the dibarium pyrophosphate catalyst.
Keywords:
Dehydration
Lactic acid
© 2013 Elsevier B.V. All rights reserved.
Acrylic acid
Dibarium pyrophosphate
Biomass
1. Introduction
surface acidity of NaY zeolites to achieve a high catalytic performance
[18,19]. But the modifiers [12,20] are easily lost from the surface of
The utilization of renewable resources for substitution of fossil
resources like petroleum, natural gas and coal, is a key project in the
modern industrial society [1–9]. For some industrial applications, bio-
mass has already been proven to be a promising candidate compared
to fossil reactants [2,10]. Lactic acid and its esters as platform molecules,
can be converted into many chemicals such as acrylic acid [11–14],
propionic acid [15], acetaldehyde [10], and 2,3-pentanedione [16]. In
these processes, catalytic dehydration of lactic acid to acrylic acid has
been viewed as the most important sustainable process. It is well
known that the dehydration of the hydroxyl group in lactic acid
molecule is catalyzed by acid sites. Ordinarily, as for aliphatic alcohol,
dehydration reaction for formation of ether bond requires low temper-
ature due to substitution mechanism, while dehydration reaction for
formation of olefinic bond through elimination mechanism requires
high temperature. Therefore, dehydration of lactic acid to form α,β-
unsaturated acid occurs only at high temperature. Under high tempera-
ture, acid plays a crucial role in the process of dehydration for lactic acid.
Strong acidity is a great disadvantage for catalytic dehydration of lactic
acid, while it favors for decarbonylation and/or decarboxylation of lactic
acid to acetaldehyde [10,17]. On the contrary, the catalyst without acid
performance or with a basicity has no efficiency for catalytic dehydra-
tion of lactic acid. Thus to adjust or choose the acidic strength of catalyst
to appropriate degree is a crucial step for efficient catalytic dehydration.
A case in point is that all kinds of modifiers are used to change the
the catalyst under the atmosphere of water vapor because they have
an excellent solubility in water, resulting in deactivation of catalyst
with time on stream. Insoluble salts in water with appropriate acid
may be an ideal type of catalysts for dehydration of lactic acid at
high temperature. Ca3(PO4)2–Ca2P2O7 (50:50 wt.%) catalyst has been
demonstrated to efficiently catalyze dehydration of methyl lactate
[15]. However, the knowledge on the use of the alkaline earth metal
phosphates for dehydration is still quite limited. In the present work,
the dehydration of lactic acid to acrylic acid using an efficient Ba2P2O7
catalyst is reported.
2. Experimental
2.1. Materials
Lactic acid (analytic grade) was purchased from Chengdu Kelong
Chemical Reagent Co. and was used for the dehydration reaction of
lactic acid without further purification. Sodium pyrophosphate, sodium
phosphate, barium chloride, acrylic acid, propionic acid, acetic acid,
acetaldehyde, 2,3-pentanedione and n-butanol, together with hydro-
quinone were obtained from Sigma-Aldrich.
2.2. Preparation of catalysts
The method about catalyst preparation in this work was similar to
that described previously [15,21]. 1) Ba2P2O7: Under the condition of
continuous stirring at 55 °C, 0.09 mol BaCl2·2H2O in 100 mL distilled
⁎
Corresponding author. Tel.: +86 817 2568081.
E-mail address: tcmtang2001@163.com (C. Tang).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.10.009

232
C. Tang et al. / Catalysis Communications 43 (2014) 231–234
Table 1
Screening of catalysts.
Catalysts
Conversion of lactic acid/%
Selectivity/%
Acrylic acid
Acetaldehyde
Propionic acid
2,3-Pentanedione
Acetic acid
Ba2P2O7
Ba3(PO4)2
Ba2P2O7–Ba3(PO4)2 (50:50 wt.%)
99.7
99.5
81.0
76.0
18.5
54.0
14.1
7.9
11.2
2.8
7.4
3.9
2.1
1.0
1.1
1.1
1.1
1.3
Conditions: Reaction temperature 400 °C, catalyst 0.57 g, carrier gas 1 mL/min, feed flow rate 1 mL/h, LA feedstock 20 wt.%.
water was dropwisely added to 0.035 mol sodium pyrophosphate in
200mL distilled water to form a white precipitate of barium pyrophos-
phate. Subsequently, the white precipitate was rinsed at least three
times to remove sodium pyrophosphate using distilled water and
dried at 120 °C in the air circulating oven for 6 h. 2) Ba3(PO4)2: The
method of preparation of Ba3(PO4)2 was similar to that of Ba2P2O7. 3)
Ba3(PO4)2–Ba2P2O7 (50:50 wt.%): It was prepared by mixing barium
phosphate together with barium pyrophosphate in the agate mortar
for 20 min. Prior to activity evaluation and characterization, the above
catalysts were calcined at 500 °C for 6 h.
conversion was obtained by Ba2P2O7–Ba3(PO4)2 (50:50 wt.%). The selec-
tivity toward acrylic acid changed drastically and the best result was
achieved by Ba2P2O7. Considering the conversion of lactic acid and selec-
tivity to acrylic acid, Ba2P2O7 catalytic performance is far better than that
of Ba2P2O7–Ba3(PO4)2 (50:50 wt.%), indicating that no synergistic effect
existed in Ba2P2O7–Ba3(PO4)2. The selectivities toward acrylic acid and
acetaldehyde decreased in the order of Ba2P2O7, Ba2P2O7–Ba3(PO4)2
(50:50wt.%), and Ba3(PO4)2. Propionic acid was formed from hydrogena-
tion of lactic acid and/or acrylic acid with hydrogen generated from
decarboxylation/decarbonylation of lactic acid. Analysis of tail gas
shows that hydrogen, CO2 and CO existed in the process of catalytic
reaction, indicating occurrence of decarboxylation/decarbonylation
of lactic acid. It is not astonishing that the highest selectivity to
propionic acid was observed from Ba3(PO4)2. The reason is that the
alkalinity of catalyst favors for the hydrogenation reaction and
under the steam atmosphere Ba3(PO4)2 has the strongest alkalinity.
Therefore, Ba2P2O7 is an excellent catalyst for formation of acrylic
acid from dehydration reaction of lactic acid although plenty of acet-
aldehyde was also produced in the catalytic process.
2.3. Catalyst characterization
Powder X-ray diffraction measurement was conducted on a Dmax/
Ultima IV diffractometer operated at 40 kV and 20 mA with Cu-Ka
radiation. The FTIR spectra of the catalysts were recorded in the range
of 500–4000 cm−1 on a Nicolet 6700 spectrometer. The particle
size and the morphology of the catalysts were examined using SEM
(JSM-6510). TG analysis was used with Netzsch STA449 F3 analyzer.
TPD–NH3 analysis was used with Autochem II2920, and the specific
surface areas and pore volumes of catalysts were measured with TriStar
3000.
3.1.2. Catalyst stability
The stability of catalyst with time on stream was studied at 400 °C
over the Ba2P2O7 catalyst calcinated at 500 °C. From Fig. 1, the conver-
sion of lactic acid decreased slightly from 99.8% to 93.5% with time on
stream. The selectivity to acrylic acid increased from 69.1% to 76.9% at
the primary stage of reaction and gradually decreased from 76.9% to
about 55% with further increase of reaction time. Compared with that
of the modified NaY catalyst [11], this result is far better. In the former,
the conversion of lactic acid decreased from 80% to 60% while the selec-
tivity to acrylic acid drastically decreased from 73% to 40%. The possible
reason is that the modified NaY catalyst has stronger acid on its surface
than that of the Ba2P2O7 catalyst. It is known that stronger acid favors
2.4. Catalyst evaluation
The dehydration of lactic acid to acrylic acid over the catalysts
was carried out in a fixed-bed quartz reactor with a 4mm inner diame-
ter operated at atmospheric pressure. The catalyst (0.50–0.60 g, 20–
40 meshes) was placed in the middle of the reactor and quartz wool
was placed in both ends. Before catalytic evaluation the catalyst was
pretreated at the required reaction temperature (400 °C) for 1.0 h
under high purity N2 (0.1 MPa, 1.0 mL/min). The feedstock (20 wt.%
solution of lactic acid) was then pumped into the preheating zone
(lactic acid aqueous solution flow rate, 1.0 mL/h) and driven through
the catalyst bed by nitrogen. The liquid products were condensed
using ice-water bath and analyzed off-line using an SP-6890 gas chro-
matograph with a FFAP capillary column connected to an FID. Quantita-
tive analysis of the products was carried out by the internal standard
method using n-butanol as the internal standard material. GC–MS
analyses of the samples were performed using Agilent 5973N Mass
Selective Detector attachment.
100
80
95
90
85
80
75
70
70
60
50
40
30
20
3. Results and discussion
Conversion of lactic acid
3.1. Evaluation of catalyst
Selectivity toward acrylic acid
3.1.1. Screening of catalysts
Barium phosphate catalysts were utilized to catalyzed dehydration of
lactic acid, and the results were shown in Table 1. Ca3(PO4)2–Ca2P2O7
(50:50wt.%) catalyst has been found a high catalytic performance for de-
hydration of methyl lactate due to a synergistic effect between Ca3(PO4)2
and Ca2P2O7 [15]. It is known that achieving high selectivity for dehydra-
tion reaction is more difficult for lactic acid than that of lactates [22].
From Table 1, the conversion of lactic acid decreased in the order of
Ba2P2O7, Ba3(PO4)2, and Ba2P2O7–Ba3(PO4)2 (50:50 wt.%) and the lowest
0
5
10
15
20
25
Run time/h
Fig. 1. The performance of catalyst with time on stream. Conditions: Reaction temperature
400 °C, Ba2P2O7 catalyst 0.57 g, carrier gas 1 mL/min, feed flow rate 1 mL/h, LA feedstock:
20 wt.%.

C. Tang et al. / Catalysis Communications 43 (2014) 231–234
233
Table 2
B4
Physical properties of catalysts.
Catalyst
Surface area/m2/g
Pore volume/cm3/g
Pore size/nm
B3
B2
Ba2P2O7
Ba3(PO4)2
Ba2P2O7–Ba3(PO4)2
(50:50 wt.%)
1.58
12.64
2.18
0.0047
0.0624
0.0051
12
20
8
B1
the carbon deposition, resulting in deactivation of catalyst. In addition,
the modified components such as alkaline Na2HPO4 encountered a los-
ing, leading to an increase of acidity of NaY catalyst. Therefore, a drastic
decrease of catalyst performance was observed with time on stream.
However, the similar disadvantage cannot exist for the Ba2P2O7 catalyst.
Besides, effects of other parameters such as reaction temperature, lactic
acid concentration and LHSV were also investigated (seen in supporting
information, Table S1, Table S2 and Table S3.)
500
1000
1500
2000
2500
3000
3500
Wavenumber/cm-1
Fig. 2. FT-IR of catalysts. B1—Fresh Ba2P2O7 catalyst, B2—used Ba2P2O7 catalyst, B3—
Ba2P2O7–Ba3(PO4)2 (50:50 wt.%), B4—fresh Ba3(PO4)2.
3.2. Characterization of catalysts
appear in the Ba2P2O7–Ba3(PO4)2 (50:50 wt.%) catalyst and no new dif-
fraction peak occurs, suggesting that physical mixture of two components
exists in the Ba2P2O7–Ba3(PO4)2 (50:50 wt.%) catalyst. Besides, both used
Ba2P2O7 and fresh Ba2P2O7 catalysts remain constant in the XRD. Fig. S2
presented the TG of fresh Ba2P2O7 catalyst. Slight mass decrease of the cat-
alyst was observed in the temperature programming process. Thus the
characterizations of XRD and TG further demonstrated that the structure
of catalyst is very stable in the catalytic process. Fig. S3 shows the mor-
phological features of fresh Ba2P2O7 catalyst.
3.2.1. Physical properties and TPD–NH3
It is clearly seen from the results presented in Table 2 that Ba2P2O7
and Ba3(PO4)2 have low specific surface areas of 1.58 and 12.64 m2/g,
respectively. The specific surface area and pore volume of Ba2P2O7–
Ba3(PO4)2 (50:50wt.%) lie in between two pure components, indicating
that a physical mixture exists between Ba2P2O7 and Ba3(PO4)2. The sim-
ilar result was observed by Hong et al. [15]. The Ba3(PO4)2 has the low-
est activity although it has a relatively high specific surface area,
compared to that of others. This suggests that as for the tested catalysts,
surface area of catalyst is not a crucial factor for activity. TPD–NH3 was
performed and the results were given in Fig. S1 and Table 3. From the
results obtained from TPD–NH3, Ba2P2O7 has the lowest acid strength
and lowest acid density (total acid amount 5.59 μmol NH3/g) while
Ba3(PO4)2 has the highest acidity and acid density (total acid amount
13.88 μmol NH3/g). Low amounts of acid sites favor the dehydration
of lactic acid to acrylic acid. In the presence of water, for Ba3(PO4)2
hydrolytic reaction occurs resulting in alkalinity of its surface (seen
effect of water on acidity–alkalinity of the catalysts in ESI). Therefore,
hydrogenation of lactic acid or acrylic acid to propionic acid over the
Ba3(PO4)2 catalyst was promoted. However, for Ba2P2O7 hydrolytic
reaction hardly occurs. Thus, propionic acid selectivity is very low for
Ba2P2O7 catalyst. It is concluded that Ba2P2O7 displays an excellent cat-
alytic performance owing to weak acidity and hydrothermal stability.
4. Conclusions
Dehydration of lactic acid to acrylic acid was carried out over the
barium phosphate catalysts at various conditions. Dibarium pyrophos-
phate was found to have an effectively catalytic performance due to
weak acidity. The dibarium pyrophosphate catalyst retained an excel-
lent stability for catalytic dehydration of lactic acid because strong
acidity is absent on the surface of the catalyst which caused carbon
deposition, resulting in deactivation of the catalyst. Furthermore the
dibarium pyrophosphate catalyst remained the hydrothermal stability
due to very low solubility of Ba2P2O7 and no hydrolytic reaction in the
water. Under the optimal reaction conditions, 99.7% of the lactic acid
conversion and 76.0% of the selectivity to acrylic acid were achieved
over the dibarium pyrophosphate catalyst.
3.2.2. FT-IR, XRD and SEM
FT-IR spectra of catalysts were shown in Fig. 2. It can be seen that all
characteristic peaks of both Ba2P2O7 and Ba3(PO4)2 appear in the spectra
of Ba2P2O7–Ba3(PO4)2 (50:50 wt.%) except for peak intensity decreases
and no new peak appears, indicating that no reaction occurs between
Ba2P2O7 and Ba3(PO4)2. In addition, all the specific adsorption bands of
used Ba2P2O7catalyst are identical with those of fresh Ba2P2O7catalyst, in-
dicating high stability of catalyst structure with time on stream. The wide-
angle X-ray diffraction (XRD) was performed and the results were shown
in Fig. 3. All the specific diffraction peaks of both Ba2P2O7 and Ba3(PO4)2
B4
B3
B2
B1
Table 3
TPD–NH3 results of catalysts.
Catalyst
Acidity amount/μmol/g
Weak Medium
Total acid
amount/μmol/g
Strong
(100–200 °C) (200–400 °C) (400–600 °C)
10
20
30
40
50
60
70
80
90
Ba2P2O7
Ba3(PO4)2
Ba2P2O7–Ba3(PO4)2 0.47
(50:50 wt.%)
0.71
1.72
2.02
4.92
2.15
2.86
7.24
5.22
5.59
13.88
7.84
2Theta(degree)
Fig. 3. XRD of catalysts. B1—Fresh Ba2P2O7 catalyst, B2—used Ba2P2O7 catalyst, B3—
Ba2P2O7–Ba3(PO4)2 (50:50 wt.%), B4—fresh Ba3(PO4)2.

234
C. Tang et al. / Catalysis Communications 43 (2014) 231–234
[5] R.D. Cortright, M. Sanchez-Castillo, J.A. Dumesic, Appl. Catal. B Environ. 39 (2002)
Acknowledgments
353–359.
[6] C.M. Tang, Y. Zeng, X.G. Yang, Y.C. Lei, G.Y. Wang, J. Mol. Catal. A Chem. 314 (2009)
15–20.
[7] C.M. Tang, Y. Zeng, P. Cao, X.G. Yang, G.Y. Wang, Catal. Lett. 129 (2009) 189–193.
[8] C.M. Tang, X.L. Li, G.Y. Wang, Korean J. Chem. Eng. 29 (2012) 1700–1707.
[9] J.M. Lee, D.W. Hwang, Y.K. Hwang, S.B. Halligudi, J.S. Chang, Y.H. Han, Catal.
Commun. 11 (2010) 1176–1180.
[10] B. Katryniok, S. Paul, F. Dumeignil, Green Chem. 12 (2010) 1910.
[11] J. Zhang, Y. Zhao, M. Pan, X. Feng, W. Ji, C.-T. Au, ACS Catal. 1 (2010) 32–41.
[12] P. Sun, D.H. Yu, K.M. Fu, M.Y. Gu, Y. Wang, H. Huang, H.H. Ying, Catal. Commun. 10
(2009) 1345–1349.
This work was supported by Scientific Research Fund of Chemical
Synthesis and Pollution Control Key Laboratory of Sichuan Province
with project number CSPC2012-7, Scientific Research Fund of China
West Normal University with project numbers 10B004, and 12B019
and the Nanchong Key Technology R&D Program of Sichuan, China
with project number 11A0051.
[13] Z.Q. Zhang, Y.X. Qu, S. Wang, J.D. Wang, Ind. Eng. Chem. Res. 48 (2009) 9083–9089.
[14] V.C. Ghantani, S.T. Lomate, M.K. Dongare, S.B. Umbarkar, Green Chem. 15 (2013)
1211–1217.
Appendix A. Supplementary data
[15] J.H. Hong, J.-M. Lee, H. Kim, Y.K. Hwang, J.-S. Chang, S.B. Halligudi, Y.-H. Han, Appl.
Catal. A Gen. 396 (2011) 194–200.
[16] D.C. Wadley, M.S. Tam, P.B. Kokitkar, J.E. Jackson, D.J. Miller, J. Catal. 165 (1997)
162–171.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2013.10.009.
[17] P. Sun, D.H. Yu, Z.C. Tang, H. Li, H. Huang, Ind. Eng. Chem. Res. 49 (2010) 9082–9087.
[18] J. Yan, D. Yu, H. Li, P. Sun, H. Huang, J. Rare Earths 28 (2010) 803–806.
[19] J. Yan, D. Yu, P. Sun, H. Huang, Chin. J. Catal. 32 (2011) 405–411.
[20] H.J. Wang, D.H. Yu, P. Sun, J. Yan, Y. Wang, H. Huang, Catal. Commun. 9 (2008)
1799–1803.
References
[1] J.C. Serrano-Ruiz, J.A. Dumesic, Chemsuschem 2 (2009) 581–586.
[2] B. Katryniok, S. Paul, M. Capron, F. Dumeignil, Chemsuschem 2 (2009) 719–730.
[3] M.S. Holm, S. Saravanamurugan, E. Taarning, Science 328 (2010) 602–605.
[4] P. Gallezot, Chem. Soc. Rev. 41 (2012) 1538–1558.
[21] G.C. Fan, C.M. Tang, X.L. Li, J. Mol. Catal. (China) 26 (2012) 506–514.
[22] J.F. Zhang, J.P. Lin, P.L. Cen, Can. J. Chem. Eng. 86 (2008) 1047–1053.