CHAPTER VII
Steam reforming
of
Ethyl acetate
Steam reforming of ethyl acetate over metal supported catalyst
7.1. Introduction
Ethyl acetate (EA) is generally produced from the esterification of acetic acid and
ethanol. Ethyl acetate represents ester group which is present in bio-oil. A systematic and
detailed comparison of steam reforming of ethyl acetate was performed in this study. The
steam reforming reaction of ethyl acetate was carried out over Ni/Al 2 O 3 , Ru/Al 2 O 3 ,
Ru/C, Pt/C and Pd/C catalyst and the influence of the reaction parameters such as
reaction temperature, steam to carbon ratio (S/C), and reaction time were investigated.
The coke formation tendency of the catalysts in the presence and absence of steam was
analyzed in detail. EA is a colourless liquid having a characteristic sweet smell (similar
to pear drops) and finds its application in surface coatings, pharmaceuticals, flavours,
flexible packaging and other miscellaneous applications like adhesives, cleaning fluids,
inks, nail-polish removers and silk, coated papers, explosives, artificial leather,
photographic films & plates, decaffeinating tea and coffee, and cigarettes.
Hu and Lu. (2009) have studied steam reforming of EA over 30% Ni/Al 2 O 3 catalyst
and reported that EA showed high tendency to form coke deposit whether in the presence
or absence of steam, due to their instability or high tendency of polymerization at
elevated temperature. Carbon precursor formed during EA reforming are generally due to
ethylene (C 2 H 4 ), acetone and CO. Coke formation is a serious problem in steam
reforming of EA. Nevertheless, promotion of steam reforming through optimizing
reaction variables or employing active and coke-resistant catalyst may effectively
suppress polymerization of the feedstock and the production of the carbon precursors,
resulting in the elimination of coke deposit. Present study focuses on efficiency of
various metal supported catalysts in production of H 2 via steam reforming of EA.
7.2. Experimental
7.2.1 Catalytic Activity Testing
The desired catalyst was placed inside a fixed bed reactor by means of a glass wool.
Initially, the catalyst was reduced at 773 K for 1 h in the presence of H 2 (50 cm3/min).
The aqueous feed was charged from a liquid reservoir using an HPLC pump, vaporized in
a pre-heater (573 K) and contacted with the catalyst inside the reactor. The product
vapours leaving the reactor were passed through a condenser, back-pressure regulator and
a gas-liquid separator. The non-condensable gases and condensate were analysed by
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Steam reforming of ethyl acetate over metal supported catalyst
using gas chromatography technique. The system pressure was maintained at 0.1 MPa.
The reproducibility of results was checked by repeating one experiment at T=773 K and
W/F O = 49.1 g h/mol. Ethyl acetate has very low solubility i.e., only 8.3 g/100 mL of
water, hence the experiment was performed at lower concentration of EA (1 & 5 wt %).
Catalyst performance of steam reforming of EA was calculated on the basis of %
conversion to gas phase and H 2 , CO, CO 2 and CH 4 selectivity were defined by Eqs. 4.44.6 in Chapter IV.
7.2.2 Product Analysis
The concentrations of H 2 , CO, CO 2 , CH 4 and C 2 H 4 were analyzed by thermal
conductivity detector (TCD) with Hayesep DB column. From a comparison with the
analysis of calibration gas mixtures, we found that concentrations of C 3 hydrocarbons in
the reformed gas were negligible. The condensate was collected at regular intervals and
analyzed by using flame ionization detector (FID) with SE-30 column. Acetaldehyde and
ethanol and acetone were by-product identified during steam reforming of EA.
7.2.3 Catalyst Characterization
BET specific surface area, total pore volume and average pore diameter were
determined using a SMART SORB 93 device. To accomplish this, N 2 adsorptiondesorption isotherms were obtained at 78.5 K over a wide range of relative pressures on
samples previously out gassed at 573 K for 1 h. Physiochemical properties of the
investigated catalysts are represented in Table 6.1.
7.3. Results and Discussion
7.3.1 Reactions in Ethyl acetate Reforming
The reactions describing the reforming process are ethyl acetate reforming and water
gas shift:
C4 H8 O2 + 2H2 O → 4 CO + 6 H2
CO + H2 O ↔ CO2 + H2
(7.1)
∆H298 K = −41 kJ/mol
(7.2)
∆H298 K = 320.1 kJ/mol
(7.3)
The overall reaction, which is the sum of reactions represented by Eqs. 7.1 and 7.2, is
given by:
C4 H8 O2 + 6 H2 O → 4 CO2 + 10 H2
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Steam reforming of ethyl acetate over metal supported catalyst
Eq. 7.3 represents an endothermic reaction, wherein the number of moles is increased.
Consequently, it is facilitated at high temperature and low pressure. The reverse reaction
in Eq. 7.2, which results in CO formation, is favoured at high temperature. Because of the
methanation of CO and CO 2 , the H 2 yield may be reduced:
CO + 3 H2 ↔ CH4 + H2 O
CO2 + 4 H2 ↔ CH4 + 2 H2 O
∆H298 K = −206 kJ/mol
∆H298 K = −165 kJ/mol
(7.4)
(7.5)
The reverse reaction in Eq. 7.4, which denotes steam methane reforming, is
thermodynamically limited. CO 2 may react further with methane as follows:
CO2 + CH4 ↔ 2 CO + 2 H2
∆H298 K = 247 kJ/mol
(7.6)
7.3.2 Catalytic Steam Reforming of Ethyl acetate
EA reforming was investigated without using a catalyst at T=773 K and 5 wt% EA.
The liquid feeding rate was 1 mL/min, whereas the total volumetric flow rate, Q O , was
1290 cm3/min (303 K, 0.1 MPa). We found that H 2 selectivity and conversion to gasphase products after 1 h time-on-stream were 1.4 and 36.2 %, respectively. Ethyl acetate
decomposes to ethylene and C 2 H 4 selectivity was found to be 74.7 %.
The effect of temperature on product selectivity and carbon to gas phase conversion
using Ni/Al 2 O 3 is represented in Table 7.1. The H 2 selectivity increases with increase in
temperature from 623 to 773 K while CH 4 selectivity decreases with increase in
temperature. Carbon to gas phase conversion at 623 K is 58.5% while that of 773 K is
76.3%.
A comparison of the efficacy of the selected catalysts is shown in Table 7.2. When
Ni/Al 2 O 3 and Ru/Al 2 O 3 catalysts were used at W/F O =49.1 g h/mol, % H 2 selectivity
(70.8 and 49.2) and conversion (76.3 and 69.1) were much higher. CH 4 selectivity was
determined (23.02 and 20.7 %). Also, C 2 H 4 formation was observed over Ru/Al 2 O 3 and
Ni/Al 2 O 3 . When catalysts with C support were used, H 2 selectivity (maximum 36.4 %)
decreased in the order Ru > Pt > Pd. Then again, the activity of Pd was the lowest
(conversion 48%). Ru/C showed the highest conversion (61%). CO 2 selectivity was
29.9%, whereas CH 4 selectivity was 34.2% when Ru/C was used.
Conversely, Hu and Lu. (2009) reported low EA conversion at prolonged reaction
time (12 h) using 30 % Ni/Al 2 O 3 at 873 K. They reported conversion of 89.1% and H 2
selectivity of 47.7% (see Table 7.3). They reported the formation of ethylene and acetone,
which are major coke precursors. Among the C-supported catalysts, used in this work,
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Steam reforming of ethyl acetate over metal supported catalyst
both Ru/C and Pd/C demonstrated stable operation; however, the Pt/C catalyst exhibited
deactivation during time-on-stream. For example, EA conversion to gas-phase products
decreased from 51% (after 1 h of operation) to 49% after 3 h in its presence. The present
work deals with 20 % Ni/Al 2 O 3 and maximum gas phase conversion was 76.3% with H 2
selectivity of 70.8% at 773 K.
In EA reforming high CO selectivity was observed at 773 K implying low efficiency
of Ni/Al 2 O 3 catalyst for EA reforming at low temperatures. Large amount of CO are
produced from decomposition of EA since cracking of acetyl and ethoxy groups gave CO
intermediate (Shin et al., 2001; Farkas and Solymosi, 2008). Decomposition of ethyl
acetate at lower temperature (623 K) may be responsible for CH 4 generation at low
temperature since, at low temperature the efficiency of steam reforming is less.
Methanation of carbon oxides was speculated the main reason for sharp increase of CH 4
amounts at lower temperature (623 K), since Ni catalyst presented high efficiency for
methanation of carbon oxide Hu et al. (1997) and Czekaj et al. (2007), and furthermore,
the high concentration of H 2 and CO 2 in effluent gas associated with mild temperature
favoured methanation reaction.
Increasing steam-to-carbon (S/C) ratio remarkably promoted the efficiency of steam
reforming and the amount of by-product decreases. This is because at high S/C the high
partial pressure of steam promoted the adsorption of steam on the active sites, and
consequently suppressed the decomposition and degradation of the ethyl acateate.
Moreover, the high steam pressure also promoted the water gas shift reaction to remove
CO intermediate, resulting in high H 2 selectivity.
7.3.3 Reaction Mechanism over Ni/Al 2 O 3
In the presence of a metal catalyst, Ethyl acetate is dehydrogenated into an
intermediate species that is adsorbed on the metal surface either by the formation of
metal-carbon and/or metal-oxygen bonds. In steam reforming process, ethyl acetate
degrades to acetyl and ethoxy groups that then react with the activated steam, as in the
case of steam reforming of dimethyl ether. Fig. 7.1 represents reaction mechanism of
steam reforming of ethyl acetate over Ni/Al 2 O 3 catalyst. By now, there exists no
information in the literature on the mechanistic features of ethyl acetate steam reforming,
and thus, further work is essential.
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Steam reforming of ethyl acetate over metal supported catalyst
7.4. Conclusions
Catalytic steam reforming of ethyl acetate was investigated in a fixed-bed reactor
at 773 K. Reactions involved in the reforming process was highlighted. Ni/Al 2 O 3 and
Ru/Al 2 O 3 showed stable conversion for at least 6 h. Ni/Al 2 O 3 was stable for steam
reforming of EA and gave maximum % conversion to gas phase at 773 K which was
determined as 76%. Among the C-supported catalysts, both Ru/C and Pd/C demonstrated
stable operation; however, the Pt/C catalyst exhibited deactivation during time-on-stream.
It was found that H 2 selectivity decreases in the order Ru > Pt > Pd, when C-supported
catalysts are used. The effects of reaction variables on the efficacy of Ni/Al 2 O 3 were
investigated. Wide ranges of temperature (573-773 K) and W/F O (49.11-245.57 g h/mol)
were examined over Ni/Al 2 O 3 catalyst. The increase in temperature and W/F O ratio
facilitated H 2 production. The performance of Ni/Al 2 O 3 was enhanced at high S/C ratio.
Ethyl acetate decomposes to form ethoxy and acetyl compounds. At 773 K, H 2 selectivity
(70.83%) and EA conversion (76.28%) were maximized using W/F O = 49.1 g h/mol.
Finally, a plausible reaction pathway for EA steam reforming was proposed.
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Steam reforming of ethyl acetate over metal supported catalyst
Figure 7.1: Reaction Pathway for ethyl acetate reforming over Ni/Al 2 O 3 catalyst
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Steam reforming of ethyl acetate over metal supported catalyst
Table 7.1: Effect of temperature over conversion and product selectivity over
Ni/Al 2 O 3
Temp.
Carbon to
(K)
gas phase
Product Selectivity
conversion
(%)
(%)
H2
CO 2
CH 4
CO
C2H4
623
58.45
22.18
17.25
66.07
13.83
2.85
673
67.94
36.76
26.95
45.63
19.91
7.51
723
71.66
49.31
38.03
32.59
21.27
8.11
773
76.28
70.83
42.44
23.02
25.90
8.63
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Steam reforming of ethyl acetate over metal supported catalyst
Table 7.2: Performance of alumina supported catalyst at 773 K and 0.1MPa pressure
over time-on-stream data (1, 2 & 3h data)
Catalyst
Carbon to
Selectivity
gas phase
(%)
conversion
H2
CO 2
CO
CH 4
C2H4
69.10
49.19
39.68
32.02
20.76
7.54
68.69
46.26
38.15
32.09
22.07
7.68
65.87
42.76
36.95
31.25
24.51
7.29
76.27
70.83
42.44
25.90
23.02
8.63
76.69
61.99
41.17
26.18
22.59
10.05
76.20
57.47
40.62
25.58
23.87
9.92
61.04
36.37
29.93
25.43
34.17
10.47
59.85
33.92
29.44
25.42
34.49
10.65
57.87
32.36
29.01
24.99
34.84
11.16
51.14
17.16
26.87
56.05
17.07
0.00
50.34
16.51
26.30
56.10
17.60
0.00
49.55
15.81
27.41
55.48
17.11
0.00
48.07
9.31
23.49
49.43
27.07
0.00
47.27
8.47
25.87
52.63
21.50
0.00
44.14
8.33
24.70
54.54
20.77
0.00
(%)
Ru/Al 2 O 3
Ni/Al 2 O 3
Ru/C
Pt/C
Pd/C
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Steam reforming of ethyl acetate over metal supported catalyst
Table 7.3: Comparison of our results with those reported by Hu and Lu (2009)
% Ni
Temp. Conv.
H2
CO
Sel. % Sel. %
CO 2
CH 4
Sel. %
Sel. %
Ref.
content
K
%
20
773
76.3
70.8
25.9
42.8
23.0
This work
30
873
89.1
47.7
33.4
41.8
9.6
Hu and
Lu.( 2009)
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