Selective conversion of dihydroxyacetone-ethanol mixture into ethyl lactate over amphoteric ZrO2-TiO2 catalyst

Article abstract of DOI:10.1016/j.catcom.2014.01.004

The conversion of dihydroxyacetone in ethanol solution into ethyl lactate over several acidic and amphoteric oxides at 100-160 C was studied. The formation of ethyl lactate with 80-90% selectivity was observed on amphoteric ZrO₂-TiO₂

Full text of DOI:10.1016/j.catcom.2014.01.004

Selective conversion of dihydroxyacetone-ethanol mixture into ethyl lactate
over amphoteric ZrO2–TiO2 catalyst
Artur M. Mylin, Svitlana.I. Levytska, Mykhailo E. Sharanda, Volodymyr V.
Brei
PII:
DOI:
Reference:
S1566-7367(14)00005-3
doi: 10.1016/j.catcom.2014.01.004
CATCOM 3774
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
5 November 2013
30 December 2013
2 January 2014
Please cite this article as: Artur M. Mylin, Svitlana.I. Levytska, Mykhailo E. Sha-
randa, Volodymyr V. Brei, Selective conversion of dihydroxyacetone-ethanol mixture
into ethyl lactate over amphoteric ZrO2–TiO2 catalyst, Catalysis Communications (2014),
doi: 10.1016/j.catcom.2014.01.004
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ACCEPTED MANUSCRIPT
Short Communication
Selective conversion of dihydroxyacetone-ethanol mixture into ethyl lactate over
amphoteric ZrO2–TiO2 catalyst
Artur M. Mylin, Svitlana. I. Levytska, Mykhailo E. Sharanda, Volodymyr V. Brei*
Institute for Sorption and Endoecology Problems of the National Academy of Science of Ukraine,
03164 General Naumov str.13, Kyiv, Ukraine
A B S T R A C T
The conversion of dihydroxyacetone in ethanol solution into ethyl lactate over several acidic and
amphoteric oxides at 100-160 C was studied. The formation of ethyl lactate with 80-90% selectivity was
observed on amphoteric ZrO2-TiO2 oxide whereas hemiacetal and acetal of pyruval were the main
products obtained over the acidic ZrO2-SiO2 catalyst and Amberlyst 15. Amphoteric ZrO2-3TiO2 oxide
provides 89% yield of ethyl lactate at 140 C and 1.0 MPa under the feed rate of 4 mmol C3H6O3/gcat/h.
Keywords: ethyl lactate, dihydroxyacetone, lactic acid, amphoteric catalyst
* Corresponding author. Tel.: 38 044 4520127; fax: 38 044 4525417.
E-mail address: brei@ukr.net

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1. Introduction
have been
from dihydroxyacetone and alcohols over solid acid catalysts. Dihydroxyacetone, obtained from
accessible glycerol, is considered as a low-cost precursor for the production of lactic acid and its
esters [3-10]. Dealuminated fauzasite (H-USY-6) [3], ion-exchanged Sn-montmorillonite [4],
and titanium-containing silicates (TS-1, Ti-MCM-41, TiSil-HPB-60) [5] were applied as
catalysts. The authors [3-5] supposed, that the acid B-sites [3, 4] or a combination of L- and mild
B-sites [5] provide the selective conversion of dihydroxyacetone to the lactates. We have studied
amphoteric ZrO2-TiO2 and ZrO2-Al2O3 oxides in the transformation of dihydroxyacetone -
ethanol mixture into ethyl lactate.
2. Experimental
2.1. Catalyst preparation and characterization
Sulforesin Amberlyst 15, acidic ZrO2-SiO2 oxide prepared according to [11], amphoteric
ZrO2-Al2O3 oxide obtained by the sol-gel method [12], and ZrO2-TiO2 mixed oxide were tested
as catalysts. The ZrO2-TiO2 samples with different molar ratios (0.17 ≤ Ti/Zr ≤ 6) were prepared
by a co-precipitated sol-gel method using ZrOCl2•8H2O and TiCl4. Calculated quantities of
ZrОCl2-water solution (209 Zr mg/g) and ~ 2.2 M TiCl4 water solution (103 Ti mg/g) were
mixed at stirring. Excess of hydrochloric acid was neutralized with ammonia solution (pH ~ 1.5).
Then, stoichiometrical quantity of urea was added and the solution was aged at 110°C for 24 h.
The obtained gel was washed and dried at 120 C. Finally, the samples were heated to 450 C for
2 h at 2 /min. Sample codes ZrTi2 and 2ZrTi mean that Ti4+ content in the catalysts is two times
higher or less than Zr4+ content correspondingly.

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Individual TiO2 and ZrO2 oxides were prepared from ZrOCl2 and TiCl4 water solutions in
the same way as ZrO2-TiO2 samples.
calculated from the adsorption-desorption
isotherms of nitrogen using the BET method
XRD patterns of samples were recorded with DRON-4-07 diffractometer (CuKα
radiation).
in
the presence of bromthymol blue indicator
2,4-dinitrophenol
correspondingly
[13]
ZrTi3 sample
2.2. Catalytic experiments
c

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C3H6O3/gcat/h
(LHSV = 2.2–0.9 h-1) using a Waters-590 pump. The experiments were performed in Ar flow
(15 cm3/min) at 1.0 MPa preventing liquid to gaseous phase transfer.
3. Results and discussion
The transformation of 1,3-dihydroxy-2-propanone into ethyl lactate, taking into account the
properties of hydroxy-aldehydes and hydroxy-ketones [15], could be described as follows.
Firstly, Lobry de Bruyn - Van Ekenstein rearrangement proceeds:
H+
OH
H
H
O
HO
OH
OH-
HO
O
In acidic medium, the equilibrium shifts to gliceral formation. Further, gliceral dehydration
occurs with the formation of pyruval+:
H+
OH
H
O
H2O
+
HO
O
H
O
H
Catalyst acidic sites catalyze this stage also. Pyruval is a key semiproduct. Methyl glyoxal easily
reacts with ethanol to form hemiacetal:
O
OH
O
H
+
O
OH
O
Hemiacetal can react with ethanol to form acetal in acidic medium:

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OH
O
O
O
H+
O
H2O
O
+
+
OH
However, the acetal formation is not a desirable process in our case. Alkali medium promotes the
isomerization of hemiacetal to ethyl lactate:
OH-
O
O
HO
O
OH
O
The obtained results confirm this scheme of dihydroxyacetone transformation. The
analysis of products obtained on typical solid acids Amberlyst 15 and ZrO2-SiO2 (Table 1) show
that at 100% dihydroxyacetone conversion the main products are acetal and hemiacetal (Table
2). Individual TiO2 and ZrO2 oxides (Table 1) also catalyze the transformation of
dihydroxyacetone into mainly acetals (Table 2). We have placed the product obtained on the acid
catalyst with 12% ethyl lactate content into an autoclave and added typical base catalyst –
Mg6Al2(OH)16CO3 hydrotalcite. After the reaction at 100 C, ethyl lactate content increased to
40% with corresponding decrease of the hemiacetal content. Thus, an amphoteric oxide with acid
and base surface sites can catalyze selective the transformation of dihydroxyaxetone-ethanol
mixture into ethyl lactate.
Table 2. Effect of catalyst on ethyl lactate synthesis
The mixed ZrO2-TiO2 and ZrO2-Al2O3 oxides were used as amphoteric catalysts. The mixed
oxides possess an ability to catalyze both dehydration of 2-methyl-3-butyn-2-ol (MBOH) test
substance to methyl-3-butene-1-in (m/e=66) over the acidic sites and the destruction of MBOH
to acetylene (m/e=26) and acetone (m/e=58) on the base sites. It has been determined earlier for
the mixed ZrO2-Al2O3 oxides [12]. The same situation is observed for the mixed ZrO2-TiO2
oxides with Zr/Ti< 1 (Fig. 1). However, the dehydration occurs at lower temperatures then

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MBOH destruction (Fig. 1). Usually, solid acids catalyze dehydration of MBOH, and solid bases
participate in MBOH destruction only.
Fig. 1. TPR profiles of 3-methyl-3-butene-1-in (66 a.u.m. ●), acetone (58 a.u.m. ▼) and acetylene (26 a.u.m. ■)
formation from 2-methyl-3-butyn-2-оl adsorbed on ZrTi3.
The presence of acid and base sites on ZrTi3 surface is confirmed by the IR spectra of
absorbed pyridine and pyrrole (Fig. 2). Namely, the bands at 1445, 1490 cm-1 and at 1540 cm-1
(Fig. 2 a) correspond to pyridine adsorbed on acidic L- and B-sites [13]. These acidic sites are
weak because the absorbed pyridine can be removed after evacuation at 150 C (Fig. 2 a).
Fig. 2. IR spectra of pyridine (a) and pyrrole (b) adsorbed on ZrTi3; a- after evacuation at 25 C (1), 100 C (2) and
150 С (3); b - thin film of liquid (1), adsorbed on ZrTi3 (2).
In IR spectrum of pyrrole absorbed on ZrTi3, a board band νN-H at 3410 cm-1 is observed
(Fig. 2 b). This band is shifted by 10 cm-1 comparing to liquid pyrrole (3420 cm-1, Fig. 2 b)
because of the absorbed pyrrole proton interaction with base sites on the ZrTi3 surface. Such a
small shift corresponds to weak base sites [16].
Employment of amphoteric ZrO2-TiO2 and ZrO2-Al2O3 oxides resulted in the ethyl
lactate content increase in the reaction products (Table 2). The best results were obtained on
catalysts with metal ratio Ti4+/Zr4+=3 (ZrTi3 sample). This sample has predominantly amorphous
structure, but weak anatase signals are registrated in the XRD pattern (Table 1). The weak-acid
sites (Н0 ≥+1.5; 0.7 mmol/g) and weak-base sites (Н– ≤ + 7.2; 0.5 mmol/g) were determined on
the catalyst surface using an indicator method.
13
In the C NMR spectrum of the products obtained on ZrTi3 at 120 С signals from both
ethyl hemiacetal of pyruval (202, 95, 63, 25, 15 ppm.), and ethyl lactate (176, (175), 67, 62, 20,
14 ppm.) were observed. Ethyl lactate content, obtained at different temperatures, passes over the

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maximum at 140 С (Fig. 3). At higher temperature, dark-colored products are formed as result of
aldol condensation of glyceral with dihydroxyacetone [15]. The ethyl lactate yield of 81% was
observed after 2 h reaction in a rotated autoclave at 140 C. For comparison, 48% and 93% ethyl
lactate yields were obtained using TiSil-HPB-60 (autoclave, 105 C, 6 h) [5] and Sn-
montmorillonite (autoclave, 150 C, 15 h) [4] correspondingly while processing 3% solutions of
dihydroxyacetone in ethanol.
Fig. 3. Conversion (X) of 1,3-dihydroxy-2-propanone and selectivity (S) towards ethyl lactate on ZrTi3 at different
temperatures (rotated autoclave).
The results of experiments performed in a flow reactor at 140 C are presented in Table 3.
At 100% conversion of dihydroxyacetone, raising its feed rate from 2 to 10 mmol C3H6O3/gcat/h
decreases the selectivity towards ethyl lactate from 90% to 70%. Ethyl lactate high yield (90%)
is observed at the load on a catalyst of up to 4 mmol C3H6O3/gcat/h (Table 3). The ZrTi3 catalyst
ensures the ethyl lactate space time yield in 3.6 mmol/gcat/h at 89% selectivity. The comparison
of the ethyl lactate yield values for the rotated autoclave (Table 2) with that for the flow
conditions (Table 3) shows that a higher yield could be achieved under the flow regime where
the liquid reaction mixture contact time with a catalyst is 0.25–0.5 h, being 2 h for the autoclave.
Table 3. Content of products (mol%) obtained at 140°C in flow reactor over ZrTi3 catalyst
Hemiacetal is the main by-product obtained under the flow conditions (Table 3). Water is
also formed according to the gross-reaction
C3H6O3 + C2H5OH = C5H10O3 + H2O,
and reacts with methyl glyoxal forming lactic acid as a co-product (Tables 2, 3). It should be
pointed out that the content of lactic acid increased when we employed 92% ethanol instead of
anhydrous one (Table 3).

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The ZrTi3 catalyst sustained 100% conversion of dihydroxyacetone during 7 h. However,
ethyl lactate selectivity decreased by 15% over the time.
4. Conclusions
The transformation of dihydroxyacetone into ethyl lactate in ethanol solution over acidic
and amphoteric catalysts in batch and flow regimes has been studied. It was shown that the
selective formation of ethyl lactate occurs on amphoteric ZrO2-TiO2 and ZrO2-Al2O3 oxides
whereas ethyl hemiacetal and acetal of pyruvic aldehyde are the main products obtained over
acidic Amberlyst-15 and ZrO2-SiO2 catalysts. The continuos process is preferable for ethyl
lactate synthesis than the batch process. 90 % selectivity towards ethyl lactate has been achieved
employing ZrO2-TiO2 catalyst under LHSV = 2.2–4.4 h-1 at 140 C and 1.0 MPa.
Acknowledgement
We thank Dr. G.Telbiz for the IR spectra recording.
References
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(2010) 1083-1089.

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[11] E.I. Inshina, D.V. Shistka, G.M. Telbiz, V.V. Brei, Chem. Phys. Technol. Surface, 3 (2012) 395-400.
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[13] Tanabe K. Solid acids and bases. Their catalytic properties, Acad. Press, New-York- London, 1970
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Figures and Tables captions
Fig. 1. TPR profiles of 3-methyl-3-butene-1-in (66 a.u.m. ●), acetone (58 a.u.m. ▼) and acetylene (26 a.u.m. ■)
formation from 2-methyl-3-butyn-2-оl adsorbed on ZrTi3.
Fig. 2. IR spectra of pyridine (a) and pyrrole (b) adsorbed on ZrTi3; a- after evacuation at 25 C (1), 100 C (2) and
150 С (3); b - thin film of liquid (1), adsorbed on ZrTi3 (2).
Fig. 3. Conversion (X) of 1,3-dihydroxy-2-propanone and selectivity (S) towards ethyl lactate on ZrTi3 at different
temperatures (rotated autoclave).
Table 2
Effect of catalyst on ethyl lactate synthesis*.
Table 3
Content of products (mol%) obtained at 140 C in flow reactor on ZrTi3 catalyst*.

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Fig. 1
20
15
10
5
0
40
80
120
160
200
T, °C
Fig. 2
1
10%
1490
2
1445
1455
1
1540
3410
3420
2
3
10%
1450
1500
1550
1600
, cm-1
3000 3200 3400
, cm-1
a
b

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Fig. 3
100
80
60
40
20
0
100
120
140
160
T, °C

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Total pore
BET surface
area, m2/g
Average pore
diameter, nm
Sample
XRD
volume,
сm3/g
0.35
0.35
0.26
0.26
0.23
0.37
0.44
0.06
0.53
0.82
ZrТі6
ZrТі3
ZrТі2
ZrТі
am. + anat. *
am. + anat.
am. + anat.
am.
170
260
295
300
270
310
315
30
8.3
5.4
3.5
3.4
2ZrТі
ZrAl2.5
ZrSi2
ZrO2
am.
3.4
am.
4.9
am.
5.6
m + t
8.3
TiO2
anat.
150
280
14.2
10.7
**
Al2O3

* am. – amorphous, anat. - anatase , m- monoclinic, t- tetragonal phase
**

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Table 2
Effect of catalyst on ethyl lactate synthesis*.
Catalyst
X, %
Selectivity, mol %
Т, С
EL
7
HAc
83
55
51
52
73
40
18
4
Ac
10
11
6
LA
-
NP
-
ZrTi6
ZrTi6
ZrTi6
ZrTi6
ZrTi3
ZrTi3
ZrTi3
ZrTi3
ZrTi3
ZrTi3
ZrТі2
ZrTi
100
120
130
150
100
120
130
140
150
160
130
100
100
100
130
100
130
140
100
130
130
100
85
100
100
100
84
23
33
25
14
38
61
81
72
69
46
13
8
11
10
9
-
-
13
13
9
1
-
-
100
100
100
100
100
98
13
15
10
11
11
14
5
-
6
-
5
-
6
9
2
3
-
10
31
67
65
38
30
35
16
4
7
9
65
12
16
42
16
45
40
45
84
26
12
-
3
8
9
10
8
-
2ZrTi
ZrAl2.5
ZrAl2.5
ZrSi2
49
3
52
11
44
12
39
42
-
-
82
-
69
-
ZrSi2
96
5
ZrSi2
100
100
66
3
6
5
5
-
Amberlyst15
ZrO2
11
57
47
71
-
7
5
TiO2
100
19
27
29
14
-
Al2O3
-
* reaction conditions: rotated autoclave; X, conversion of dihydroxyacetone; EL, ethyl lactate;
HAc and Ac, hemiacetal and acetal of pyruvaldehyde; LA, lactic acid; NP, non-specified products.

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Table 3
Load on a catalyst,
EL
HAc
Ac
LA
mmol C3H6O3/gcat/h
2
90
89
85
78
70
56
10
11
7
-
-
-
-
4
6
4
4
3
6
4
8
10
20
8
8
10
8**
7
30
* 100% conversion of dihydroxyacetone
** 20% dihydroxyacetone solution in 92% watered ethanol

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1
Graphical abstract
+
C2H5OH
H2C
HO
C
O
CH2
OH
H+
O
C
OH
CH3
CH
OC2H5
OH-
H+
O
O
C
OC2H5
OC2H5
CH3
CH
OH
C
CH3
CH
OC2H5

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Highlights

Ethyl lactate can be obtained with high selectivity from dihydroxyacetone in ethanol solution over
amphoteric ZrO2-TiO2 catalyst.


90% ethyl lactate yield was obtained at 140°C and 1.0 MPa.
Lactic acid is a co-product.