Lactic acid production from aqueous-phase selective oxidation of hydroxyacetone

Article abstract of DOI:10.1016/j.molcata.2015.02.005

Lactic acid is an important chemical with a wide range of application in food, pharmaceutical and chemical industries. Its worldwide demand has increased due to the ever-growing market of poly(lactic acid) - PLA. This present contribution aims at studying the catalytic transformation of hydroxyacetone toward lactic acid over heterogeneous systems. Commercial Pt/Al₂O₃ powder catalysts were used and their main features were analyzed as concerning their chemical composition (XRF), crystalline structure (XRD), morphology (TEM) and porosity (N₂ physisorption). Catalytic performance was evaluated in aqueous phase and the results showed that the catalytic activity and selectivity to lactic acid depends on the pH of the reaction medium, being mandatory to operate under strong alkaline conditions. Such reaction conditions promote both the initial oxidation of hydroxyacetone and the intramolecular disproportionation of the obtained aldehyde, which are fundamental steps to lactic acid formation. More importantly, this contribution reports the feasibility of alternatively using heterogeneous catalysts to produce lactic acid with high selectivity (>96%).q

Full text of DOI:10.1016/j.molcata.2015.02.005

Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Lactic acid production from aqueous-phase selective oxidation of
hydroxyacetone
Elise M. Albuquerquea,b, Luiz E.P. Borgesb, Marco A. Fragaa,b,∗
a Instituto Nacional de Tecnologia/MCTI, Divisão de Catálise e Processos Químicos, Av. Venezuela, 82/518, Centro, 20081-312 Rio de Janeiro, RJ, Brazil
b Instituto Militar de Engenharia, Prac¸ a Gen. Tibúrcio 80, Praia Vermelha, Urca, Rio de Janeiro, RJ, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2014
Received in revised form 4 February 2015
Accepted 7 February 2015
Available online 9 February 2015
Lactic acid is an important chemical with a wide range of application in food, pharmaceutical and chem-
ical industries. Its worldwide demand has increased due to the ever-growing market of poly(lactic acid)
– PLA. This present contribution aims at studying the catalytic transformation of hydroxyacetone toward
lactic acid over heterogeneous systems. Commercial Pt/Al2O3 powder catalysts were used and their main
features were analyzed as concerning their chemical composition (XRF), crystalline structure (XRD), mor-
phology (TEM) and porosity (N2 physisorption). Catalytic performance was evaluated in aqueous phase
and the results showed that the catalytic activity and selectivity to lactic acid depends on the pH of the
reaction medium, being mandatory to operate under strong alkaline conditions. Such reaction conditions
promote both the initial oxidation of hydroxyacetone and the intramolecular disproportionation of the
obtained aldehyde, which are fundamental steps to lactic acid formation. More importantly, this contri-
bution reports the feasibility of alternatively using heterogeneous catalysts to produce lactic acid with
high selectivity (>96%).
Keywords:
Acetol
Sustainable resources
Green chemicals
Biomass
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
degradation, only water and CO2 are produced, which are later
absorbed by plants and turned into biomass establishing the car-
Lactic acid is an important industrial product with a growing
market. It is present in several foods, both as an in situ fermentation
product (such as in yogurt, buttermilk and various other foods) or
naturally [1]. Lactic acid is non-volatile, odorless and is classified as
generally recognized as safe (GRAS) for use as food additive by the
Food and Drug Administration (FDA) in USA and other regulatory
agencies [2].
Besides the food industry, lactic acid is also used in many other
industrial sectors, particularly in textile, pharmaceutical and chem-
ical industries. As for the latter industrial segment, it is used as raw
material for the production of esters (lactates), propionic acid and
acrylic acid [3–5]. The growing interest in lactic acid, however, is
associated with its use in the production of the biodegradable poly
(lactic acid) or PLA.
bon cycle. Finally, PLA is also biocompatible, which motivates its
use in medicine as sutures (bio-absorbable), systems for control-
lable release of drugs in the blood stream and orthopedic implants
[8].
Lactic acid can be produced by a number of different routes,
which may be grouped as biochemical processes (fermentation)
[9,10], ordinary chemical synthesis with stoichiometric reagents
[11,12] and catalytic reactions based on either homogeneous
[13,14] or heterogeneous [15] catalysts. Each process, however,
relies on a different feedstock.
The biochemical synthesis corresponds to nearly 90% of the
worldwide production and reaches 95% yield on an industrial scale
[9,16]; C6 and C5 sugars (hexoses and pentoses) are the main sub-
strates used in this case [10] and a wide range of biocatalysts
may be applied. Nevertheless, the use of microorganisms requires
the mandatory control of the fermentation medium pH, which
must be kept between 5 and 7 [9]. Furthermore, a continuous
addition of nutrients in the reactor is demanded to maintain the
microorganisms activity and thus a profitable industrial run is only
accomplished within a few days [11,12].
PLA is a high resistant thermoplastic and is considered a
green plastic since it can be directly obtained from renewable
resources such as corn and sugar beet [6]. It is compostable, pre-
senting a degradation time from 6 months to 2 years [7]. Upon
There are few companies that produce lactic acid by chemical
synthesis and mostly the process is based on the hydrolysis of lac-
tonitrile [11,12]. In general terms, lactonitrile is firstly obtained
through the addition of hydrocyanic acid to acetaldehyde in the
∗
Corresponding author at: Instituto Nacional de Tecnologia/MCTI, Divisão de
Catálise e Processos Químicos, Av. Venezuela, 82/518, Centro, 20081-312 Rio de
Janeiro/RJ, Brazil. Tel.: +55 2121231152; fax: +55 2121231051.
E-mail address: marco.fraga@int.gov.br (M.A. Fraga).
http://dx.doi.org/10.1016/j.molcata.2015.02.005
1381-1169/© 2015 Elsevier B.V. All rights reserved.

E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
65
presence of a base at atmospheric pressure. After recovering and
purification by distillation, lactonitrile is then hydrolyzed to lactic
acid using a concentrated solution of hydrochloric acid or sulphuric
acid generating lactic acid and the corresponding ammonium salts
as by-products. The as-synthesized crude lactic acid is esterified
with methanol, generating the methyl lactate, which is recovered,
purified and finally hydrolyzed under acidic conditions to produce
a pure lactic acid. The sidestream methanol formed upon hydrolysis
is recycled to the process unit [1].
Other possible chemical routes to obtain lactic acid consist in the
reaction of acetaldehyde with CO and water at high temperatures
and pressures, chloropropionic acid hydrolysis and hydrolysis of
propylene with nitric acid [11,12]. All these routes require drastic
operation conditions and/or are based on harmful and toxic chem-
icals with potential environmental damage. As expected, they are
not economically viable either [11].
Homogeneous catalyzed reactions are also applied and they
make use of saccharides (cellulose, sucrose, frutose and glucose)
as the main feedstocks and the chemical processes are carried out
in aqueous solutions with metal salts [17,18]. The conversion of
glycerol to lactic acid with inorganic hydroxides as homogeneous
catalysts has also been reported [13,14]. This transformation occurs
under hydrothermal conditions, and thus the high pressure and
temperature are the main disadvantages.
Alternatively, lactic acid can also be obtained from renewable
sources (glucose and glycerol) using heterogeneous catalytic sys-
tems [19]. Glycerol is a relevant bio-renewable feedstock due to
its ever-growing availability as a consequence of the widespread
biodiesel production. Furthermore, it has been shown to be a
flexible starting material for many other intermediates. As a mat-
ter of fact the use of other organic compounds easily obtained
from glycerol may also be a promising alternative as they can
allow producing lactic acid under much milder conditions. 1,2-
propanediol, dihydroxyacetone and hydroxyacetone or acetol can
be listed amongst the most suitable glycerol intermediates [20–25].
Hydroxyacetone stands out as a key chemical for producing lac-
tic acid since it is not only obtained from glycerol [24,26] but also
from a wide variety of biomass-derived compounds [27,28]. Never-
theless, it has surprisingly been neglected and specific systematic
studies on hydroxyacetone transformation to lactic acid are rarely
found. It is quite clear though that studying its transformation may
also provide a better understanding of lactic acid formation from
other oxidative routes. As a matter of fact hydroxyacetone invari-
ably appears as a major intermediate in all processes, whether using
a ketone or glycols as starting materials.
using CuK␣ radiation (1.5406 Å), operating at 30 kV and 15 mA. The
diffraction patterns were obtained in the range 2–90◦ by increasing
2ꢀ with 0.01 steps.
Surface area, pore volume and average pore diameter were
determined from N2 physisorption at −196 ◦C according to BET and
BJH methods. Analyzes were conducted on an ASAP 2020 apparatus
from Micromeritics. Prior to analyzes the samples were treated at
300 ◦C under vacuum.
Chemical composition of the commercial catalysts was deter-
mined by X-ray fluorescence (XRF) in a S8 Tiger spectrometer from
Bruker. Powder samples were analyzed without any previous treat-
ment.
The morphology of the catalysts was identified by trans-
mission electron microscopy (TEM) that was conducted on
a
Tecnai 20 FEI microscope operating at 200 kV. The pow-
der samples were firstly ultrasonically dispersed in 2-propanol
and then deposited on a carbon-coated copper grid for TEM
examination.
2.3. Catalyst evaluation and analytical method
The catalytic tests were carried out in liquid phase in a glass
semi-batch reactor heated in an oil bath. Before the reaction, the
catalyst was reduced at 350 ◦C for 1 h under pure H2 flow at
50 mL/min. The reactions were performed at 40 ◦C and atmospheric
pressure, using 250 mL of an aqueous solution of hydroxyacetone
at 0.20 mol/L as starting material. A constant flow of synthetic
air (30 mL/min) was bubbled into the reaction medium through-
out the experiment and it was stirred at 1000 rpm to guarantee
that the reactor content was powerfully mixed, to favor gas
diffusion and to ensure kinetic control. Different alkaline condi-
tions were provided by continuous addition of a NaOH solution
into the reactor through an addition vessel attached to a reactor
mouth. The pH measurement was possible through a pH probe
placed into the reactor throughout the experiments. Unless indi-
cated otherwise, all catalytic runs were monitored for 6 h and
liquid aliquots (1 mL) were taken at every 30 min to determine
hydroxyacetone conversion and products formation. The samples
were analyzed by HPLC in a Waters Alliance equipment cou-
pled to a photodiode array detector (PDA) and a refractive index
detector (RID) operating at 50 ◦C. A Biorad Aminex HPX-87H ion
exchange column was used at 65 ◦C to separate all products; the
analyzes were performed in isocratic elution mode (0.7 mL/min),
using
a H2SO4 aqueous solution at 0.005 mol/L as mobile
The objective of this contribution is thus to assess the selec-
tive aqueous-phase transformation of hydroxyacetone to lactic acid
over a heterogeneous catalyst under mild conditions.
phase.
Initial reaction rates (rates at the zero conversion limit) were
determined by calculating the initial slope (dC/dt) from the time-
resolved profiles of hydroxyacetone concentration.
2. Experimental section
2.1. Materials
2.4. Characterization of used catalysts
Hydroxyacetone (Sigma–Aldrich 90%), d,l-lactic acid (Fluka
90%), pyruvic acid (Sigma–Aldrich 98%), pyruvic aldehyde (SAFC,
40% in water), sulphuric acid (Merck, 95–97%) and NaOH (Vetec, PA)
were the chemicals used in this work. 1 wt% and 5 wt% platinum-
supported on Al2O3 commercial powders (Sigma–Aldrich) were
used as oxidation catalysts and they were labeled 1Pt/Al2O3 and
5Pt/Al2O3, respectively.
The catalysts were recovered after liquid-phase reaction and
characterized as concerning the most critical points – porosity,
metal leaching and dispersion. BET surface area was determined
by N2 physisorption at −196 ◦C in a Micromeritics ASAP 2020
apparatus. Platinum loading was assessed by X-ray fluorescence
spectrometry (XRF) in a S8 Tiger spectrometer from Bruker while
its dispersion was estimated by hydrogen chemisorption at 35 ◦C
in Micromeritics AutoChem 2920 equipment. Platinum dispersion
was calculated by assuming a stoichiometry (H:Pt) of 1:1. Comple-
mentarily, after filtration to separate the solid catalysts, the liquid
phase was also analyzed by atomic absorption spectroscopy (AAS)
in a Varian 280FS equipment.
2.2. Characterization of fresh catalysts
Crystalline phases were identified by X-ray powder diffraction
(XRD) that was performed in a Rigaku Miniflex diffractometer

66
E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
Fig.1. Representative TEM images of the commercial 5Pt/Al2O3 powder fresh catalyst.
Table 1
The porosity of the catalysts was studied by collecting their
adsorption/desorption N2 isotherms (Fig. 2b). It was observed that
the commercial materials exhibit typical type IV isotherms accord-
ing to IUPAC nomenclature, indicating the presence of mesopores as
indeed observed in pore diameter distributions (Fig. 2c) [29]. Both
samples showed hysteresis type H1, which is associated with pores
with a cylindrical shape with open extremity and with a uniform
distribution [29]. Despite the differences in BET area (SBET) and pore
volume (Vp) both catalysts are high surface area solids as expected
for ␥-alumina based powders (Table 1). It should be recalled though
that those are commercial samples and differences in SBET and Vp
may not be straightly associated with metal loading since the cat-
alyst may have been produced from distinct ␥-alumina batches.
Anyway, the use of high-surface area materials presenting meso-
pores is certainly important when studying liquid-phase catalytic
processing.
Both commercial Pt/Al2O3 catalysts were evaluated in the
aqueous-phase oxidation of hydroxyacetone in alkaline medium,
which was provided by continuous addition of an aqueous solu-
tion of NaOH at 1 mol/L. Initially, some control experiments were
carried out in order to assess the relevance of the alkaline solution
in hydroxyacetone oxidation activity of Pt/Al2O3. For this purpose,
two comparative tests were conducted with and without the addi-
tion of NaOH into the reactor using only 5Pt/Al2O3 sample. In
former test, the pH of the reaction medium was adjusted to 10
and maintained at that value throughout the experiment. As for
the latter reaction, the test was performed without any adjustment
Specific surface area (SBET), pore volume (Vp), average diameter (dp) of the pores,
platinum content, metal dispersion (D) and Pt particle size (dPt) of the fresh com-
mercial catalysts used.
Catalyst
SBET (m2/g) Vp (cm3/g) dp (nm) Pt (wt%) D (%) dPt (nm)
1Pt/Al2O3 258
5Pt/Al2O3 97
0.43
0.24
5
7
1.2
4.9
95
25
1.2
4.6
3. Results and discussion
The commercial 1Pt/Al2O3 and 5Pt/Al2O3 catalysts used in this
work were characterized by XRF, XRD, BET and TEM to assess their
main physico-chemical features and the results are summarized in
Table 1. The actual platinum contents were confirmed by XRF while
TEM observation indicated that metal nanoparticles were well dis-
persed on the support surface as illustrated by the representative
images depicted in Fig. 1. As expected, the higher metal loaded sam-
ple presented bigger particles with average Pt size of 4.6 nm while
those examined in 1Pt/Al2O3 catalyst were 1.2 nm.
Typical XRD diffraction patterns of transition ␥-alumina were
collected for both samples as shown in Fig. 2a. As for 5Pt/Al2O3
catalyst, additional peaks at 39.8◦ and 81.5◦ can also be envisaged
and are associated with a Pt-containing phase, mostly likely PtO
(JCPDS no. 47-1171) and Pt0 (JCPDS no. 04-0802), whose accurate
distinction is delicate from such diffraction pattern.
Fig. 2. Diffraction patterns (a), N2 isotherms (b) and pore size distribution (c) of the commercial Pt/Al2O3 powder fresh catalysts.

E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
67
Table 2
of the reaction medium alkalinity, being carried out at the natu-
ral pH of the initial hydroxyacetone solution (pH 4.8; pH 7.7 after
adding the catalyst into the reactor). Hydroxyacetone conversions
achieved after 6 h reaction are shown in Fig. 3.
It is firstly observed that hydroxyacetone conversion is dramat-
ically affected by the pH medium. 5Pt/Al2O3 catalyst revealed to be
quite active, accomplishing 73% hydroxyacetone conversion within
the studied reaction period. On the other hand, the overall hydrox-
yacetone conversion in the reaction conducted without any pH
control (at the natural pH of the hydroxyacetone solution) was very
low (<5%).
Initial reaction rate (r0), selectivities to lactic acid (SLA) and pyruvic acid (SPA) and
yield of lactic acid (Y).
a
a
Entry Metal
catalyst
pH r0
(mol gPt−1 h−1
r0
SLA
SPA
Yb
)
(mol g−1 h−1
)
1
2
3
5Pt/Al2O3
5Pt/Al2O3
1Pt/Al2O3
10 152.6
142.1
10 113.9
7.5
7.0
1.4
96
42 58
100
4
60
16
37
8
–
a
Selectivities at isoconversion (∼30%).
b
Yields of lactic acid after 6 h reaction.
Fig. 5 (selectivity as a function of hydroxyacetone conversion) and
Table 2 (at isoconversion conditions).
The products distribution of the metal-catalyzed reaction in
alkaline conditions exhibited quite high selectivity to the aimed
acid with some pyruvic acid produced alongside as depicted in
Fig. 4. The formation of pyruvic acid as a secondary product may
be ascribed to the further oxidation of the obtained lactic acid as
already reported elsewhere [15,30]. Nevertheless, it is worth stress-
ing the high lactic acid yield (60%) accomplished in this test, which
is quite remarkable considering the use of a heterogeneous catalyst.
These previous results indicate that in the catalytic oxidation of
hydroxyacetone toward lactic acid both NaOH and Pt-based cata-
lyst are required, which is in close agreement with the extensive
literature regarding the selective oxidation of alcohols [31,32].
The critical role of alkali addition in determining lactic acid
selectivity observed in the initial tests, motivated a more detailed
evaluation of the influence of aqueous media pH. Therefore a
complementary run was carried out with 5Pt/Al2O3 at pH 8. The
conversion curve collected from this experiment is also shown in
Fig. 3 and the product distribution after 6 h is depicted in Fig. 4. A
comparison at isoconversion is also provided in Table 2.
Lactic acid is firstly formed at pH 8, but its selectivity decreases
sharply as the reaction proceeds. Such striking drop in lactic acid
selectivity is accompanied by the continuous increase in the selec-
tivity to pyruvic acid (Fig. 5a). These profiles suggest that the
formation of pyruvic acid occurs from the subsequent oxidation of
lactic acid initially formed and corroborate previous reports [15,30].
It should be noted, however, that lactic acid is the major product
at higher pH values (pH 10) and such noteworthy high selectivity
is maintained even at high hydroxyacetone conversions (Fig. 5b).
Under these conditions, pyruvic acid was only detected more sig-
nificantly for hydroxyacetone conversions above 60%. This behavior
indicates that an optimal hydroxyacetone:NaOH ratio must be
defined in order to accomplish the highest productivity. Indeed,
complementary runs were carried out by introducing in the reac-
tor the total amount of NaOH required for keeping the constant
pH values in the previously discussed tests. This amendment in the
experimental procedure did not cause any change in the catalyst
performance and rather similar results were obtained.
It can be observed that the catalyst global activity is somewhat
different when the reaction is carried out in alkaline medium, being
slightly lower when the pH is kept constant at 8. This trend is cor-
roborated by the respective reaction rates as summarized in Table 2.
As concerning the products formed at different pH conditions,
lactic and pyruvic acids were the only compounds detected. How-
ever, their selectivity patterns were fairly different as illustrated in
The influence of hydroxyacetone:Pt molar ratio was evalu-
ated by using a commercial sample with lower metal content
(1Pt/Al2O3). This reaction run was also performed at constant pH
(pH 10) and the time-resolved hydroxyacetone conversion is pre-
sented in Fig. 6. The results obtained with 5Pt/Al2O3 (Fig. 3) were
plotted again to allow a straightforward comparison.
It is noted that the global activity of the 5Pt/Al2O3 catalyst is
higher than that of the 1Pt/Al2O3 system, achieving, respectively,
Fig. 3. Hydroxyacetone conversion as a function of reaction time for the 5Pt/Al2O3
commercial powder catalyst at different pH. Reaction conditions: hydroxyacetone
(0.20 mol/L), 40 ◦C, atmospheric pressure, synthetic air at 30 mL/min. The reaction
at natural pH was carried out for 5.5 h.
Fig. 4. Conversion of hydroxyacetone and selectivity to lactic acid and pyruvic acid
over 5Pt/Al2O3 at pH 8 and pH 10. Reaction conditions: hydroxyacetone (0.20 mol/L),
40 ◦C, reaction time = 6 h, atmospheric pressure, synthetic air at 30 mL/min.

68
E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
Fig. 6. Evolution of hydroxyacetone conversion as a function of reaction time
for 1Pt/Al2O3 and 5Pt/Al2O3 commercial powder catalysts. Reaction conditions:
hydroxyacetone (0.20 mol/L), 40 ◦C, pH 10, atmospheric pressure, synthetic air at
30 mL/min.
aforementioned suggestion regarding the oxidation of lactic acid
initially formed to pyruvic acid.
The results reported herein reveal that the oxidation of hydrox-
yacetone is quite complex and both the metal catalyst and NaOH
play a role as catalyst/co-catalyst and selectivity directing agent.
The catalytic transformation is thus proposed to occur in a cascade
reaction whereby hydroxyacetone is oxidized to pyruvic aldehyde
on the metal catalyst and the aldehyde is then converted to lactic
acid through intramolecular disproportionation (Cannizzaro reac-
tion) promoted by the alkaline medium. However, it should be
stressed that no pyruvic aldehyde was detected in any experi-
ment whatsoever and thus further tests were carried out by using
a pyruvic aldehyde solution as starting substrate. It was found
that pyruvic aldehyde is very rapidly converted into lactic acid in
alkaline media. Complete conversion and 100% lactic acid yields
were accomplished within the very first minutes, corroborating
the occurrence of Cannizzaro reaction. This fashion is indeed in
close agreement with previous results reported elsewhere in the
literature [17,18,33].
Fig. 5. Selectivity to different products as a function of hydroxyacetone conversion
over 5Pt/Al2O3 at different pH: (a) 8 and (b) 10. Reaction conditions: hydroxyacetone
(0.20 mol/L), 40 ◦C, atmospheric pressure, synthetic air at 30 mL/min.
Taking such discussion into consideration, a general reaction
scheme for the catalytic synthesis of lactic acid from hydroxyace-
tone can be drawn, as depicted in Scheme 1.
73% and 37% conversion after a 6 h run. This trend is confirmed
by the reaction rate as normalized by the metal mass in each run
(Table 2).
Regardless the hydroxyacetone:Pt molar ratio used, lactic acid
was always the main product obtained over the monitored time
period. This is undeniably clear from the concentration curves
displayed in Fig. 7 and the selectivity values at hydroxyacetone
isoconversion summarized in Table 2.
It can be noted that lactic acid is the only product formed over
1Pt/Al2O3 (Fig. 7a), which is likely associated with the lower cata-
lyst global activity. This system would thus require a much longer
time to start the subsequent oxidation of the produced lactic acid to
pyruvic acid. This second oxidation step could indeed be observed
in the concentration profiles collected from the 5Pt/Al2O3 experi-
ments (Fig. 7b). Lactic acid is preferentially formed within the first
hours reaching the highest concentration after 2–3 h. Later its con-
centration is seen to drop steadily along with the increase of pyruvic
acid concentration. These concentration patterns corroborate the
The used catalysts were recovered after liquid-phase hydrox-
yacetone conversion and examined as regarding their textural
properties, chemical composition and metal dispersion and these
data are summarized in Table 3. Irrespective of reaction pH, no
significant change was seen on 5Pt/Al2O3 catalyst porosity since
the BET surface areas varied within an acceptable experimental
deviation. Likewise, no platinum leaching was observed in any reac-
tion condition tested, since metal loading was roughly the same as
examined by XRF. Accordingly, no appreciable amounts of platinum
Table 3
Specific surface area (SBET), platinum content and metal dispersion (D) of the used
catalysts.
Catalyst
SBET (m2/g)
Pt (wt%)
D (%)
5Pt/Al2O3 (pH 8)
5Pt/Al2O3 (pH 10)
115
100
4.9
4.5
15
16

E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
69
Fig. 7. Concentration curves of hydroxyacetone and its oxidized products as a function of reaction time for 1Pt/Al2O3 (a) and 5Pt/Al2O3 (b) commercial powder catalysts.
Reaction conditions: hydroxyacetone (0.20 mol/L), 40 ◦C, pH 10, atmospheric pressure, synthetic air at 30 mL/min.
Scheme 1. Reaction scheme for the catalytic transformation of hydroxyacetone into lactic acid.
(0.001%) or aluminum (<0.007%) were detected in the liquid phase
(reaction medium) after reaction by AAS. On the other hand, cata-
lyst dispersion significantly dropped after liquid-phase reaction at
either pH 8 or 10, indicating that those conditions may promote
particle agglomeration.
All in all, this contribution has reported the feasibility of lactic
acid production from hydroxyacetone aqueous solution, broad-
ening the current used feedstocks. The transformation of such
alternative renewable source, which may be provided as a glycerol-
derived product [24,26], would allow the process integration of
biofuels (biodiesel) and green chemicals production, matching the
nowadays widespread biorefinary concept.
that Pt-based heterogeneous catalyst has to mandatorily operate
under alkaline media in order to accomplish high lactic acid yields.
This study revealed that the transformation of hydroxyacetone
to lactic acid is based on a complex series of reaction involving
the initial oxidation of hydroxyacetone molecule followed by the
intramolecular disproportionation, both reactions being favored at
alkaline pH.
Acknowledgements
The authors thank CNPq for the financial support and fellow-
ships. They also thank Ms Nataly Amorim from CETENE and Dr.
A.M. Duarte de Farias for their valuable assistance in TEM exam-
ination. Mr. Alex de Aguiar Novo (INT) is also thanked for the
complementary AAS analyzes. EMA also acknowledges CAPES for
the scholarship.
4. Conclusion
This contribution reported the feasibility of lactic acid catalytic
synthesis from hydroxyacetone aqueous solutions. It was shown

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E.M. Albuquerque et al. / Journal of Molecular Catalysis A: Chemical 400 (2015) 64–70
[20] N. Dimitratos, J.A. Lopez-Sanchez, S. Meenakshisundaram, J.M. Anthonkutty,
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