Hydrogenation of acetic acid over PtSn/Al2O3 catalyst: Effect of shaping method, kinetics and stability

Article abstract of DOI:10.14233/ajchem.2015.17635

The hydrogenation of acetic acid to ethanol is a promising technology for the mass production of ethanol. Two series of PtSn/Al₂O₃ catalysts with commercial size were prepared and shaped by different method and tested in the hydrogenation of acetic acid at 275 °C, 2 MPa, LHSV (liquid hourly space velocity) = 0.6 h^-1 and n(H₂)/n(CH₃COOH) = 12.5. The effect of operation conditions on the performance of one of the catalysts, which shows the highest selectivity of ethanol, was also investigated. After checking the catalyst internal and external diffusion resistance, kinetics of the powdered catalyst was carried out at the following conditions: catalyst 1 g (100-120 mesh), temperature 235-275 °C, pressures 0.5-4.5 MPa, LHSV 0.73-2.18 h_-1 and n(H₂)/n(CH₃COOH) 2.5-12.5. After that, a 30-days stability test was performed. Kinetics equations derived from a Langmuir-Hinshelwood-type mechanism were established and turn out to be reliable for the hydrogenation of acetic acid over PtSn/A_l2O₃ catalyst.

Full text of DOI:10.14233/ajchem.2015.17635

Asian Journal of Chemistry; Vol. 27, No. 4 (2015), 1293-1298
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17635
Hydrogenation of Acetic Acid Over PtSn/Al
2
3
O Catalyst:
Effect of Shaping Method, Kinetics and Stability
*
KE ZHANG, HAITAO ZHANG , HONGFANG MA, WEIYONG YING and DINGYE FANG
Engineering Research Center of Large Scale Reactor Engineering and Technology of the Ministry of Education, State Key Laboratory of
Chemical Engineering, East China University of Science and Technology, Shanghai 200237, P.R. China
*
Corresponding author: Tel/Fax: +86 21 64252151; E-mail: zht@ecust.edu.cn; zhangke0124@163.com
Received: 20 March 2014; Accepted: 27 May 2014; Published online: 4 February 2015;
AJC-16778
The hydrogenation of acetic acid to ethanol is a promising technology for the mass production of ethanol. Two series of PtSn/Al
O
2 3
catalysts with commercial size were prepared and shaped by different method and tested in the hydrogenation of acetic acid at 275 °C,
-1
2
MPa, LHSV (liquid hourly space velocity) = 0.6 h and n(H
2
)/n(CH COOH) = 12.5. The effect of operation conditions on the performance
3
of one of the catalysts, which shows the highest selectivity of ethanol, was also investigated. After checking the catalyst internal and
external diffusion resistance, kinetics of the powdered catalyst was carried out at the following conditions: catalyst 1 g (100-120 mesh),
-1
temperature 235-275 °C, pressures 0.5-4.5 MPa, LHSV 0.73-2.18 h and n(H
2
)/n(CH COOH) 2.5-12.5. After that, a 30-days stability test
3
was performed. Kinetics equations derived from a Langmuir-Hinshelwood-type mechanism were established and turn out to be reliable
for the hydrogenation of acetic acid over PtSn/Al
O
2 3
catalyst.
Keywords: Acetic acid hydrogenation, PtSn/Al
2
O
3
catalyst, Kinetics, Stability.
oil while the disadvantage of latter route is its low energy-
INTRODUCTION
efficiency caused by the energy-intensive distillation steps
involved in the production of high purity ethanol.
Nowadays, there is a growing demand for alternatives to
petroleum-derived fuels and chemicals due to the consideration
The catalytic conversion of syngas (CO + H ), which
2
1,2
of improving air quality and increasing energy security . In
this context, the research of novel technologies for the produc-
tion of synthetic fuels and chemicals is gaining attention.
Ethanol is being considered as a promising alternative synthetic
fuel because it can be produced from biomass and can be used
to fuel automobiles or as a potential source of hydrogen for
derived from the gasification of biomass or coal, could produce
ethanol in large quantities. Both homogeneous and hetero-
3
geneous catalytic processes have been reported . The homo-
geneous catalytic processes are in need of expensive catalyst,
high operating pressure and tedious workup procedures for
catalyst separation and recycling while the heterogeneous
catalytic processes exhibit low yield and poor selectivity. Thus,
this process remains challenging and no commercial process
has been reported though the research on this topic has been
proceeding for about a century. However, the production of
methanol and its further homogeneous carbonylation to acetic
3
fuel cells . Apart from this, ethanol is also applied in many
other fields, such as in the synthesis of a variety of industrial
chemicals and polymers, as solvent and antiseptic.
Traditionally, ethanol is mainly produced by two routes:
(
i) fermentation of biomass, especially sugars that containing
7
six carbons and (ii) hydration of ethylene, which based on
acid are mature technologies . For this reason, the catalytic
3,4
petroleum industry . The ethylene hydration process, which
is carried out by reacting ethylene with steam at 300 °C, 6-7
hydrogenation of acetic acid to ethanol is a promising route,
especially suitable for countries with limited farm land and
abundant in coal resources, like China.
5
MPa over a solid catalyst,can get industrial-grade pure ethanol .
The fermentation process is not suitable for woody biomass
and sugars derived from lignocelluloses and the crude product
only contains about 14 % ethanol . From the point of industrial
view, both processes are uncompetitive for large-scale ethanol
production. The challenge for the former route confronted is
the rising of crude oil price and the dependence on imported
The study of acetic acid hydrogenation has been con-
8-12
ducted by several authors . Our former research showed that
PtSn catalysts supported on alumina is a good candidate for
the production of ethanol from acetic acid hydrogenation and
we have studied the role of Sn addition and the effect of Pt/Sn
6
13
ratio on the performance of the catalysts . The kinetics of

1
294 Zhang et al.
Asian J. Chem.
acetic acid hydrogenation is indispensable for the sizing of
reactor and the research on this topic is few. Rachmady and
China) hydrogenation is a fixed-bed reactor with an inner
diameter of 14 mm, combined with a separation unit and an
analysis system. Commonly, 2.8 g catalyst was loaded in the
9-11
Vannice have conducted experiments to explore the reaction
mechanism of acetic acid hydrogenation, both on TiO suppor-
2
isothermal region of the reactor and reduced in pure H (100
2
-1
ted Pt and PtFe catalysts and similar kinetics were obtained
based on a Langmuir-Hinshelwood-type model, which involve
the dissociation of hydrogen on Pt sites along with the
adsorption and activation of acetic acid on oxide phases to
create surface acyl species. Catalysts used in commercial process
should have appropriate pellet dimension so as to maintain a
good physical strength and a suitable pressure drop. In this
paper, we compared the performance of two groups of catalysts
with commercial size and studied the kinetics of acetic acid
hydrogenation over alumina supported PtSn catalyst, as well
as its stability.
mL min ) at 350 °C for 2 h, then the catalyst bed was cooled
down to the reaction temperature in 0.5 h. After that, acetic
acid was pumped and transported by H into the system and
2
preheated to maintain gas phase before entering the reactor.
After passing through the condenser and the liquid-vapor
separator, the liquid was stored in a tank and the effluent was
lead to the analysis system. Compositions of the tail gas were
determined on-line and the products in the liquid phase were
detected off-line byAgilent 7890A GC (Agilent Technologies,
Santa Clara) with a thermal conductivity detector (TCD) and
a flame ionization detector (FID). The TCD is furnished with
a molecular sieve 5A packed column and a Hayesep Q packed
column while the FID is coupled with an HP-PLOT/Q capillary
column and an HP-INNOWAX capillary column. Particularly,
the acetic acid in the liquid was determined by titration. The
performance of the catalysts was tested at a selected condition:
t = 275 °C, P = 2 MPa, LHSV (liquid hourly space velocity) =
EXPERIMENTAL
Catalysts preparation and characterization: Two
groups of catalysts with commercial size and a given loading
(
1 wt. % Pt and 1 wt. % Sn) were prepared by co-impregnation.
Alumina spheres with a diameter of 3-5 mm were used as
support and H PtCl .6H O and SnCl .5H O were used as
-1
0
.6 h and Rm (n(H
2
)/n(CH COOH)) = 12.5. The effect of
3
2
6
2
4
2
operation conditions, such as temperature, pressure, LHSV
and Rm, on the performance of 1Pt1Sn-T3 was also evaluated.
Acetic acid conversion and product selectivity were determined
after carbon balance (within ±5 %) was achieved. The
calculation of acetic acid conversion and product selectivity
was the same as previously described .
Kinetics study and stability: Kinetics measurements
were carried out under the following conditions: catalyst 1 g
precursors for the PtSn catalysts. One group of the catalysts
was prepared as follows. After being ground and sieved to
1
00-120 mesh and calcined at 550 °C for 12 h (in order to
remove the organic contaminants), the support was impreg-
nated with aqueous solution of H PtCl .6H O and SnC1 .5H O,
then the slurry was subject to drying and calcination as
2
6
2
4
2
13
13
described . The catalyst powder was shaped by a tablet press
with replaceable moulds and tablets of different size can be
obtained. The tablet catalysts were labeled as 1Pt1Sn-T3,
(
100-120 mesh), temperature 235-275 °C, pressures 0.5-4.5
-1
MPa, LHSV 0.73-2.18 h and Rm 2.5-12.5, based on the four-
factor and five-level orthogonal experimental design. Both the
internal and external diffusion effects were eliminated on these
kinetics experiments. Stability of the catalyst was tested after
the kinetics experiments.
1
Pt1Sn-T4 and 1Pt1Sn-T5 where 3, 4, 5 refer to the diameter
of the catalysts (mm) and the height of the catalysts is 3 mm.
The other group of the catalysts was prepared through the direct
impregnation of Al
SnC1 .5H O solution when other steps were the same. Accor-
dingly, the catalysts were labeled as 1Pt1Sn-S3, 1Pt1Sn-S4,
Pt1Sn-S5 where 3, 4, 5 represent the diameter (mm) of the
spheres.
X-Ray diffraction (XRD) of the catalysts was recorded
on a Rigaku D/Max 2550VB/PC (Rigaku, Tokyo, Japan, CuK
radiation). The textural properties of the catalysts were mea-
sured by N physisorption operated at -196 °C using an ASAP
020 instrument (Micromeritics, Atlanta, GA). Prior to the
adsorption-desorption measurements, the samples were
2
O
3
spheres with H
2
PtCl
6
.6H
2
O and
4
2
RESULTS AND DISCUSSION
1
Catalysts characterization: The BET surface area (SBET),
pore volume (V
catalysts and Al
p
) and average pore diameter (D
p
) of the
α
2
O
3
support are listed in Table-1. The tablet
catalysts show a relative higher surface area and a smaller pore
diameter, which may be caused by the crush of pores with big
diameter during the process of catalyst shaping. On the XRD
spectrum (Fig. 1), characteristic diffraction peaks centered at
37.5°, 45.7° and 66.9° are clearly observed, which can be
2
2
degassed at 200 °C in a N
and other adsorbates.
2
flow for 16 h to remove the moisture
14
ascribed to γ-Al
2
O phase (JCPDS 04-0858) . The absence of
3
Activity testing: The setup used for the evaluation of
Pt, Sn and PtSn alloy phases in our samples may be ascribed
to the low loading of Pt, Sn or that Pt and Sn are so highly-
acetic acid (99.95 %, Sinopharm Chemical Reagent Co., Ltd,
TABLE –1
RESULTS OF N PHYSISORPTION
2
2
-1
3
-1
Catalysts
Surface area (m g )
Pore volume (cm g )
Average pore diameter (nm)
1
Pt1Sn-T3
Pt1Sn-T4
Pt1Sn-T5
Pt1Sn-S3
Pt1Sn-S4
Pt1Sn-S5
185.2
172.9
159.8
174.7
156.9
133.6
0.42
0.41
0.41
0.40
0.39
0.38
7.7
7.4
7.8
10.0
9.6
9.4
1
1
1
1
1

Vol. 27, No. 4 (2015)
Hydrogenation of Acetic Acid Over PtSn/Al
2
3
O Catalyst 1295
and detrimental to the product of ethanol. The enhancement
of acetic acid conversion is due to the promotion of reaction
rate caused by the rise of temperature while the changes of
product selectivity can be attributed to the difference of
activation energy.
1Pt1Sn-T3
100
xHOAc
sAH
80
60
40
20
0
1
Pt1Sn-S3
sEtOH
sEtOAc
20
40
60
80
2
θ
(°)
Fig. 1. XRD pattern of the catalysts
dispersed on the alumina support that the size of the crystallite
is too small to be detected by XRD characterization .
1
3
Performance of the catalysts: The performance of the
commercial-sized catalysts is summarized in Table-2. On
one hand, on both catalyst series, the conversion of acetic acid
decreased as the diameter increased, which is caused by the
decrease of surface area and the selectivity of aldehyde is minor
compared to that of ethanol and ethyl acetate, which is because
aldehyde is the initial product and can be further hydrogenated.
On the other hand, the catalysts directly impregnated with
alumina spheres not only show higher acetic acid conversion,
180
200
220
240
260
280
Temperature (°C)
Fig. 2. Effect of temperature on the performance of catalyst 1Pt1Sn-T3
Effect of pressure: The influence of pressure on the
conversion and product selectivity over catalyst 1Pt1Sn-T3 is
present in Fig. 3. The conversion of acetic acid rose along
with the increase of pressure, which is result from the enhanced
density of active acetate surface species and the improved
collision probability of reactants and catalyst.At the same time,
the selectivity of ethanol increased while that of ethyl acetate
decreased. The reduction of acetic acid to ethanol and the
but also lead to the production of CH
originate from the decomposition of acetic acid and the hydro-
genation of the ethanol . Both phenomena can be explained in
4
and C
2
H , which
6
9
terms of the different metal distribution behaviour caused by
the preparation procedure. For catalysts impregnated with
alumina spheres, the distribution of metals is inhomogeneous,
being eggshell-typed, i.e. the concentration of metals is
gradually decreased from the outer layer to the core of the
1
00
xHOAc
sAH
8
0
sEtOH
sEtOAc
15
alumina sphere . However, the distribution of metal precursors
is homogeneous on the tablet catalysts. For industrial catalysts,
the appearance of by-product should be prevented and suitable
operating conditions are indispensable. Consequently, 1Pt1Sn-
T3 was selected to investigate the effect of operating conditions
on the performance of acetic acid hydrogenation.
60
4
0
0
0
Effect of temperature: The effect of temperature on
acetic acid conversion and product selectivity over catalyst
2
1
Pt1Sn-T3 is shown in Fig. 2, where HOAc represents acetic
acid, AH aldehyde, EtOH ethanol and EtOAc ethyl acetate. It
is evident that the rise of temperature is beneficial to the
conversion of acetic acid and the selectivity of ethyl acetate
1
2
3
4
5
Pressure (MPa)
Fig. 3. Effect of pressure on the performance of catalyst 1Pt1Sn-T3tec
TABLE-2
PERFORMANCE OF THE CATALYSTS
Selectivity (%)
C H OCOCH
Sample
Conversion (%)
CH CHO
C H OH
CH4
C H6
2
3
2
5
2
5
3
1
1
1
1
1
1
Pt1Sn-T3
Pt1Sn-T4
Pt1Sn-T5
Pt1Sn-S3
Pt1Sn-S4
Pt1Sn-S5
51.4
39.9
30.9
52.2
47.5
44.9
1.9
1.8
2.1
1.6
1.5
1.4
47.7
42.0
37.7
39.9
39.7
38.4
50.4
56.2
60.1
53.2
50.7
51.3
-
-
-
7.5
7.8
7.2
-
-
-
1.6
1.5
1.6

1
296 Zhang et al.
Asian J. Chem.
esterification of acetic acid and ethanol to ethyl acetate are
two consecutive reactions in the system. The former one is a
molecules reduced reaction while the latter one is an
equimolecular reaction. Thus, the increase of pressure is ben-
eficial to the production of ethanol.
Effect of liquid hourly space velocity (LHSV): Fig. 4
displays the effect of LHSV on the conversion of acetic acid
and product selectivity. The changes caused by the rise of
LHSV are minor: the conversion of acetic acid and selectivity
of ethyl acetate saw a slight decline while the selectivity of
ethanol was prompted a bit. The higher the LHSV, the shorter
the contact time between the reactants and the catalyst surface.
Consequently, the above-mentioned behaviour was observed.
as the initial product, which can either desorb or be hydro-
genated to ethanol. Subsequently, the formed ethanol can
desorb or react with the adsorbed acetic acid molecule to form
ethyl acetate. These surface reactions and reversible desorption
steps are depicted by eqns. 7-14 and the rate-determining steps
of reaction 1 and 2 are eqn. 7 and 13, respectively.
K
H2
H2(g) + 2* YZ ZZ ZZ XZZ 2H*
(3)
K
sp
H* YZ ZZ ZZXZ H
(4)
(5)
(6)
(7)
(8)
sp
K
Ac
ZZZX
CH COOH + 2* YZZZ CH COO* + H*
3
(g)
3
KHOAc
ZZZZX
CH COOH +SYZZZZ CH COOH-S
3
(g)
3
'
1
k
1
00
CH COOH-S + H →CH COOH -S
xHOAc
sAH
3
sp
3
2
90
80
70
60
50
40
30
20
10
0
k'
2
CH COOH -S+H →CH CHO-S+H O
3
2
sp
3
2
(g)
sEtOH
sEtOAc
k3
'
ZZZX
CH CHO-SYZZZCH CHO + S
3
'
-
3
(g)
(9)
k
3
'
4
k
CH CHO-S + H →CH CHOH-S
(10)
3
sp
3
k'
5
(
11)
CH CHOH-S + H →CH CH OH-S
3
sp
3
2
K
EtOH
CH CH OH-S ZZZZX CH CH OH + S
(12)
3
2
YZZZZ
3
2
(g)
'
6
k
CH CH OH − S+ CH COOH − S →
3
2
3
0
.4
0.5
0.6
0.7
LHSV (h )
Fig. 4. Effect of LHSV on the performance of catalyst 1Pt1Sn-T3
0.8
0.9
1.0
1.1
CH CH OCOCH − S + H O + S (13)
–1
3
2
3
2
(g)
k'
7
CH CH OCOCH -SZZ ZX CH CH OCOCH + S
3
2
3
YZ
'
ZZ
3
2
3(g)
(14)
k-7
The hydrogenation activity is determined by the rate of
acetic acid disappeared to form hydrogenated products, i.e.
the overall formation rate of acetaldehyde, ethanol and ethyl
acetate.Applying the steady-state approximation to the surface
intermediates, the final rate expressions can be written as 15-
17.
Kinetics of hydrogenation of acetic acid
9
Kinetics model assumptions: Rachmady and Vannice
had studied the kinetics of hydrogenation of acetic acid over
Pt/TiO catalysts and a final rate expression was obtained. The
2
experiments were carried out at a low acetic acid conversion
and the products they considered were aldehyde, ethanol and
ethane. In present case, the acetic acid conversion is in the
range of 5-65 % and the selectivity of aldehyde is about 1 %
while the selectivity of ethyl acetate is considerable. Thus, the
reactions we considered are the hydrogenation of acetic acid
to ethanol and the esterification of ethanol with acetic acid to
ethyl acetate.
'
1
r = k θHOAcCH
(15)
1
'
6
r = k θHOAcθEtOH
(16)
(17)
2
rHOAc = r
1
+ r
2
where θ
subscript HOAc and EtOH represents the acetic acid and
ethanol molecules adsorbed on the oxide respectively and C
is the concentration of hydrogen atoms at this site on the oxide
surface. The total number of active sites are incorporated in k
and k
i
is the fractional surface coverage of species i, the
H
CH COOH + 2H = C H OH + H O
(1)
3
2
2
5
2
1
CH COOH + C H OH = C H OCOCH + H O (2)
3
2
5
2
5
3
2
6
.
The elementary steps involved in reaction 1 are eqn. 3-12
while the elementary steps related to eqn. 2 are eqn. 13 and
The dissociative adsorption of hydrogenation and acetic
acid on the Pt surface are quasi-equilibrated and can be expre-
ssed as:
1
4. Briefly, eqn. 3-5 in the reaction sequence represent the
dissociative adsorption of hydrogen on Pt surface, followed
by the migration of H atoms from the metal to the oxide surface,
as well as the dissociative adsorption of acetic acid, where * is
an active site on the Pt surface, sp denotes the transfer of H
atoms from the metal to the oxide surface. Eqn. 6 depicts the
molecular adsorption of acetic acid, where S represents a site
on the oxide surface. After a series of irreversible surface
reactions, i. e. the consecutive addition of adsorbed hydrogen
atoms to the adsorbed acetic acid molecule, aldehyde is formed
2
H
2
*
K = θ /P θ
(18)
(19)
H
H
2
2
2
K
Ac = θAc
θ
H
/PHOAc
θ
*
where subscripts * and Ac represent vacant sites and acetate
on the Pt surface, respectively, while P and K are the partial
i
i
pressure and adsorption equilibrium constant of species i,
respectively. The quasi-equilibrium expressions for acetic acid
and ethanol adsorption and H atom concentration at the oxide
surface site are written as

Vol. 27, No. 4 (2015)
Hydrogenation of Acetic Acid Over PtSn/Al
2
O
3
Catalyst 1297
(36)
K
K
K
HOAc = θHOAc/PHOAc
θ
S
(20)
(21)
(22)
w
r
x =
dw
EtOH = θEtOH/PEtOH
θ
S
∫0
NHOAc,0
sp = C
H
/θ
H
The production rate of ethyl acetate is
where sp represents the migration of adsorbed H from Pt sites
to the surface of oxides. Based on the following assumptions:
adsorbed hydrogen atoms (H*) and adsorbed acetate species
dNEtOAc
dw
N
HOAc,0d(xHOAc (1− sEtOH ))
r2 =
=
=
2dw
(
CH COO*) are the predominant surface species on Pt and
3
NHOAc,0 (1 −sEtOH )dxHOAc − xHOAcdsEtOH
(37)
(
)
molecular acetic acid and ethanol are the significant surface
intermediates on the oxide surface sites, the expressions can
be obtained.
2
dw
where s represents selectivity. After a simple algebraic trans-
formation, eqn. 37 can be write as:
θ = 1/( K P + K P
/ K P )
(23)
*
H
H
AC HOAc
H
H
2
2
2
2
dsEtOH (1− sEtOH )r1 − (1+ sEtOH )r2
=
(
38)
θs = 1/(1 + KHOAcP
HOAc
+ KEtOHPEtOH
)
(24)
dw
xHOAcNHOAc,0
After resolving equation group (13-22), the final rate
expressions are obtained
Acetic acid conversion and the selectivity of ethanol in
the reactor outlet can be obtained by integrating eqns. 36 and
3
8. Discrimination of the kinetic model was performed by
k1PHOAc PH2
r1 =
fitting the experimental data to the kinetics eqns. 25 and 26.
The estimation of the values of the kinetics parameters through
best-fit methods was determined with a multivariable nonlinear
regression method, using the Levenberg-Marquardt algorithm.
The objective function was to minimize the sum of the square
of residuals corresponding to the differences between the
experimental data and those calculated data for the kinetic
model. It was found that the kinetics equations fit well to the
experimental data.
(25)
(
1+K P
+K P )(K1 P +K P
/ P )
HOAc H
2
3
HOAc
4
EtOH
H
2
2
k2 P
HOAc
PEtOH
r2 =
2
(26)
(1+K P
+K P
)
3
HOAc
4
EtOH
where
'
1
k = k KHOAcKsp KH2
(27)
(28)
1
'
6
k = k KHOAcKEtOH
2
Estimation of the kinetics parameters: Since the reaction
rate was tested in an isothermal integral fixed bed reactor, the
process taking place inside the catalyst bed was described by
K = KH2
(29)
1
K = K / KH2
(30)
16
2
AC
the pseudo-homogeneous fixed bed reactor model . The
K
K
and k
3
= KHOAc
= KEtOH
(31)
(32)
activation energy of the reactions and other kinetics parameters
can be obtained using the Levenberg-Marquardt algorithm and
the results are represented in Table-3.
4
2
k
1
are reaction rate constants and the temperature
dependence of the rate constants is expressed by theArrhenius'
law,
TABLE-3
ESTIMATED KINETICS PARAMETERS
ki = k0,i exp(-E /RT)(i = 1,2)
(33)
a,i
Parameter
Estimated value
3.43
while
-1
-1
k1,0 (mol g cat h )
-
1
K = exp(a + b /RT)(i = 1, 2, 3, 4)
(34)
E
1,a (J mol )
-78429.5
744.52
-35805.5
50.39
-57663.3
-153.82
55877.24
-80.58
50471.95
-154.49
111185.1
i
i
i
-
1
-1
k2,0 (mol g cat h )
The reaction rate was tested in the isothermal integral
fixed bed reactor. Preliminary tests were carried out to check
the catalyst internal and external diffusion resistance. The
influence of the internal diffusion was investigated by
performing experiments on catalyst of different pellet sizes in
identical working conditions. To check for external diffusion
resistance, several tests were carried out at different acetic acid
-
1
E2,0 (J mol )
a1
b1
a2
b
2
a3
b3
a
4
b4
16
flow rates, keeping constant the catalyst weight . The acetic
acid conversion showed that, during the working domain, the
influence of external diffusion on process kinetics is not
obvious. Finally, the kinetic study was performed under the
following condition: catalyst 1 g (100-120 mesh), temperature
Verification of the model: It is stated that the kinetics
model is suitable when F > 10 × F0.05, ρ > 0.9. Statistic results
2
-1
in Table-4 shows that kinetics eqns. 25 and 26 meet the
requirements above. The parity plot of all the data compared
to the model estimations with the use of the kinetics eqns 25,
26 are given in Fig. 5. The distribution of the points in this
diagram indicates a reasonably good quality of fitness of our
experimental data, by the kinetics eqn 25, 26. Therefore, the
kinetics eqn. 25 and 26 are suitable for this experiment.
2
35-275 °C, pressures 0.5-4.5 MPa, LHSV 0.73-2.18 h and
Rm 2.5-12.5. Reaction rate can be obtained as follows:
dNHOAc
d(NHOAc,0 (1-xHOAc ))
dxHOAc
=
-
=NHOAc,0
(35)
dw
dw
dw
Acetic acid conversion in the reactor outlet can be
expressed as follows:

1
298 Zhang et al.
Asian J. Chem.
TABLE-4
60
50
STATISTIC RESULTS OF THE KINETICS MODEL
2
Equation
Mp
M-Mp
ρ
F
F0.05 × 10
(
(
25)
26)
10
6
15
19
0.997
0.997
497.81
992.91
25.4
25.1
40
30
20
10
0
xHOAc
sALD
sEtOH
sEtOAc
(A)
0.6
0.4
0.2
0
0
10
20
30
Time (day)
Fig. 6. Stability plot of the catalyst
1
Pt1Sn-T3 was analyzed and the results exhibit that tempe-
rature and pressure had significant effect on the conversion of
acetic acid and the selectivity of ethanol and ethyl acetate while
LHSV and molar ratio had minor impact on the performance
of the catalyst under the laboratory conditions. The kinetics
eqns. 25 and 26 derived from a Langmuir-Hinshelwood-type
mechanism are reliable for acetic acid hydrogenation over
0
0.2
0.4
0.6
xHOAc, exp.
0
0
0
0
.7
(B)
PtSn/Al
2
3
O catalyst. At the same time, the catalyst also
displayed a quite good stability. During the 30 days experiment,
the acetic acid conversion dropped from 25.1 to 20.6 % while
the product selectivity fluctuated slightly.
.6
ACKNOWLEDGEMENTS
This work is financially supported by the National Science
and Technology Supporting Plan (2006BAE02B02).
.5
.4
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.
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=
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1
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1
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1
Conclusion
(
Two groups of commercial-sized PtSn/Al
2
O
3
catalysts
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Commun., 12, 895 (2011).
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1
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1
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(CH
4
+ C
2
6
H ) under the selected reaction condition. The effect
of operation conditions on the performance of the catalyst