CC BY
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AZ9RBAYCAN KIMYA JURNALI № 1 2016
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UDK 547.262
THE ACTIVITY OF THE ZINC-COBALT OXIDE SYSTEM IN THE REACTION
OF ETHANOL STEAM REFORMING
F.Z.Abuzarli, V.L.Baghiyev
Azerbaijan State Oil and Industry University vagif_bagiev@yahoo.com Received 28.10.2015
Reaction of ethanol steam reforming to hydrogen over binary zinc-cobalt oxide catalysts of different compositions has been studied. It is found that at low temperatures the reaction products are acetaidehyde and acetone, whereas at high - hydrogen and carbon dioxide. It is shown that in the reaction of formation of hydrogen the most active samples are composition Zn:Co = 2:8 and 9:1. The highest yield of hydrogen over studied catalysts reaches 74.3% at ethanol conversion equal 95%.
Keywords: hydrogen, steam reforming, ethanol, binary catalysts, zinc oxide.
Introduction
As it is known, a promising method for the production of hydrogen is the steam reforming of ethanol [1-3]. From the periodical literature it is known that catalysts based on cobalt oxide are active in the reaction of ethanol steam reforming [4-6]. In this case, we have previously studied the effect of iron oxide additives on the activity of cobalt oxide [7]. It has been found that the iron-cobalt oxide catalysts exhibit high activity in the conversion reaction of ethanol vapor. This work is a continuation of this research and is devoted to the study of reaction of ethanol steam reforming to hydrogen over binary zinc-cobalt oxide catalysts of different composition.
Experimental
Zinc-cobalt oxide catalysts of various compositions was prepared by coprecipitation from aqueous solutions of zinc nitrate and cobalt carbonate. The obtained mixture was evaporated and dried under 100-1200C then decomposed to complete release of nitrogen and carbon oxides at 2500C, and then calcined at a temperature 5500C for 10 hours. Thus, the nine catalysts were synthesized from the atomic ratio of elements Zn:Co=9:1 to Zn:Co=1:9. Activity of synthesized catalysts were studied in flow unit at hourly volume space velocity 1200 h-1 in the temperature range 250-7000C. The quartz reactor was charged with 5 ml of the catalyst grained 1.0-2.0 mm and studied its activity in the reaction of the steam reforming of ethanol into hydrogen. Outputs of hydrogen, methane and CO were determined on a chromatograph with column 2 m filled with
activated carbon. The yields of ethylene, acetal-dehyde, acetone and the amount of unreacted ethanol were determined on a chromatograph with a flame ionization detector and 1 m column packed with polisorb.
Results and discussion
The main product of the reaction of steam reforming of ethanol over zinc-cobalt oxide catalysts are hydrogen and carbon dioxide. As the byproducts are also formed, ethylene, acetal-dehyde, acetone, carbon monoxide and methane. At low temperatures, the main products of the reaction are acetone, acetaldehyde, while at temperatures above 4000C the direction of the reaction changing toward the formation of hydrogen. For comparative evaluations, we studied also the catalytic activity of cobalt and magnesium oxides. Results of ethanol steam reforming reaction over cobalt oxide are shown in Table 1.
As seen from Table ethanol steam reforming reaction begins at 25 00C. At this temperature, acetaldehyde is formed only in an amount of 5%. Further increasing of temperature leads to the formation and other reaction products. Formation of acetone is observed only at 350 and 4000C, and the largest amount of it is 20.8%. Formation of carbon monoxide and hydrogen are observed, since the temperature 3000C. Increasing of temperature leads to an increase of hydrogen yield until 63.6% at 6000C. The yield of carbon monoxide is increased throughout the studied temperature range and at 7000C is 25%. Output of methane passes through a maximum with increasing reaction temperature.
Table 1. Catalytic activity of cobalt oxide in the reaction of ethanol steam reforming
Output of reaction products
Temperature 0C (N X О О 5 CH3CHO 3 H3 C О О 3 H3 C Conversion, %
200 0 0
250 0 0 5 5
300 1.4 1.2 8.1 0 10.6
350 3.9 2.2 8 11.9 26
400 13.2 5.5 0 2 20.8 41.5
450 29.2 11.1 8.4 0 0 56.7
500 45.9 14.9 12.8 77.6
550 58.2 17.9 16.2 93.3
600 63.6 20.3 14.7 98.6
650 62.6 23.7 10.4 97.7
700 63.7 25.6 5.4 95.7
The highest yield of methane was 16.2% at 5500C. From Table 1 it can be seen that ethanol conversion over cobalt oxide reaches 98%.
Table 2 shows the dependence of products yields of the reaction from temperature over zinc oxide. As seen, steam reforming of ethanol over zinc oxide also starts at temperature 250 0C.
Table 2. Catalytic activity of zinc oxide in the reaction of ethanol steam reforming
Output of reaction products
Temperature (N X О О 5 CH3CHO 3 H3 C О О 3 H3 C Conversion, %
200 0 0
250 0 1.5 0 1.5
300 3.5 2.5 2.8 8.8
350 6.3 5.5 7.2 21.9
400 11.2 0 7.6 21.5 43.3
450 20.7 1.1 0 10.5 30 66.3
500 27.7 2.2 6.7 13.5 27.5 78.6
550 34.3 3.3 12.3 19.9 15.2 85
600 40.4 7.7 19.4 16 4.3 87.8
650 44.4 11.1 24.4 7 1.8 89.7
700 45.5 16.1 29.6 0 0 91.2
At this temperature, 1.5% acetaldehyde formed. Further increasing of temperature leads to a monotonic increasing of acetaldehyde yield up to 19.9% at 7000C. With increasing temperature, in the reaction mixture are also present and other products. The outputs of the acetone also passes through a maximum with increasing reaction temperature.
The maximum yield of acetone was observed at 4500C and it is equal to 30%. Outputs of hydrogen, carbon monoxide and methane increases with increasing reaction temperature. The maximum yield of hydrogen over zinc oxide is 45.5% at 7000C. The highest yields of carbon monoxide and methane was observed also at 7000C and are respectively 16.1 and 29.6%. The conversion of ethanol over studied catalyst reaches 91.2%.
Results of the study of the reaction of etha-nol steam reforming over catalyst Zn:Co= 1:9 are shown in Figure 1. The reaction of steam reforming of ethanol starts at 2000C. At this temperature, a small amount of acetaldehyde (2.1%) is formed. With increasing of temperature, the yield of acetaldehyde passes through a maximum at 3500C (18.2%) and at 6000C in the reaction mixture formation of acetaldehyde is not observed.
-10
i;;0 200 250 300 350 400 450 500 550 600 650 700 750
Temperature. °C
Figure 1. Catalytic activity of catalyst Zn:Co=1:9 in the reaction of ethanol steam reforming: 1 -conversion, 2 - H2, 3 - CO, 4 - CH4, 5 -CH3CHO, 6 - CH3COCH3.
As seen from Figure 1, a further increasing of temperature leads to the formation of other reaction products. Formation of acetone was observed only in small amounts (up to 5.7%) in the temperature range 300-4500C. The formation of hydrogen, methane and carbon monoxide begins at 400-4500C and above 5000C the main directions of the reaction of steam reforming of ethanol is formation of hydrogen. As can be seen from Figure 1, the maximum yield of hydrogen over the catalyst Zn:Co = 1:9 reaches 55% at temperatures above 6000C. From the picture also it can be seen that with incre-
F.Z.ABUZARLI, V.L.BAGHIYEV
37
asing of temperature, the outputs of hydrogen and carbon monoxide rising, while the yield of methane passes through a maximum at 5000C. The conversion of ethanol over studied catalyst reaches up to 90%.
Provided studies have shown that the activity of cobalt-zinc oxide catalysts depends also from atomic ratio of zinc to cobalt. Figures 2 and 3 show the effect of the atomic ratio of zinc to cobalt to the reaction of the steam reforming of ethanol into hydrogen at 500 and 7000C.
Number of atoms of zinc
Figure 2. Effect of the atomic ratio of zinc to cobalt on the reaction of steam reforming of ethanol into hydrogen at 5000C: 1 -conversion, 2 - H2, 3 - CH4, 4 - CO.
120
0 -
0 2 4 6 8 10
Number of atoms of zinc
Figure 3. Effect of the atomic ratio of zinc to cobalt on the reaction of steam reforming of ethanol into hydrogen at 7000C: 1 - conversion, 2 - H2, 3 - CO.
It is seen that in a hydrogen formation reaction the most active sample composition are catalysts Zn:Co=2:8 and 9:1, and their activity is more pronounced at lower temperatures. Apparently, this is because these catalysts are solid solutions while other samples represents of mechanically mixed of zinc and cobalt oxides.
Based on the foregoing, it can be said that the binary cobalt-zinc oxide catalysts have relatively high activity and selectivity in the reaction of steam reforming of ethanol into hydrogen and these catalysts are promising for further modification.
References
1. Sonia Abello, Evgeniy Bolshak, Daniel Montane. Ni-Fe catalysts derived from hydrotalcite-like precursors for hydrogen production by ethanol steam reforming // Appl. Catal., A: General. 2013. No 450. P.261-274.
2. Gabriella Garbarino, Paola Riani, Mattia Alberto Lucchini, Fabio Canepa, Shrikant Kawale, Guido Busca. Cobalt-based nanoparticles as catalysts for low temperature hydrogen production by ethanol steam reforming // Int. J. Hydrogen Energy. 2013. No 38. P. 82-91.
3. Jaime Gallego, Fanor Mondragon, Catherine Batiot-Dupeyrat. Simultaneous production of hydrogen and carbon nanostructured materials from ethanol over LaNiO3 and LaFeO3 perovskites as catalyst precursors // Appl. Catal., A: General. 2013. No 450. P. 73-79.
4. FumihiroHaga, Tsuyoshi Nakajima, Hidemaru Miya and Shozi Mishima. Catalytic properties of supported cobalt catalysts for steam reforming of ethanol, Catal. Lett. 1997. No 48. P. 223-227.
5. Simonetta Tuti, Franco Pepe. On the Catalytic Activity of Cobalt Oxide for the Steam Reforming of Ethanol //Catal. Lett. 2008. No 122. P. 196-203.
6. Grzegorczyk, A. Denis, W. Gac, T. Ioannides, A. Machocki. Hydrogen formation via steam reforming of ethanol over Cu/ZnO catalyst modified with nickel, cobalt and manganese. // Catal. Lett. 2009. No 128. P. 443-448.
7. Герайбейли С.А., Алиева С.М., Абузерли Ф.З., Багиев В.Л. О реакции паровой конверсии этанола в водород на Fe-Co-O-катализаторах // Изв. высш. технич. учебных заведений Азербайджана. 2014. № 5. С. 31-34.
ETANOLUN BUXAR KONVERSÍYASI REAKSÍYASINDA SÍNK-KOBALT OKSÍD SÍSTEMÍNÍN AKTÍVLÍYÍ
F.Z.Abuzarli, V.L.Bagiyev
Taqdim olunan i§da etanolun hidrogena buxar konversiyasi reaksiyasinda müxtalif tarkibli binar sink-kobalt oksid katalizatorlarinin aktivliyi 0yranilmi§dir. Müayyan edilmi§dir ki, algaq temperaturlarda reaksiya mahsullari asetaldehid va aseton, eyni zamanda yüksak temperaturlarda hidrogen va karbon qazi hesab edilir. Góstarilmiíjdir ki, hidrogenin amala galmasi reaksiyasinda Zn:Co=2:8 va 9:1 tarkibli nümunalar yüksak aktivlik nümayi§ etdirir. Tadqiq edilmi§ katalizator üzarinda hidrogenin giximi 74.3% etanolun isa konversiyasi 95%-dir.
Agar sozlar: hidrogen, buxar konversiyasi, etanol, binar katalizatorlar, sink oksid.
АКТИВНОСТЬ ЦИНК-КОБАЛЬТ-ОКСИДНОЙ СИСТЕМЫ В РЕАКЦИИ ПАРОВОЙ
КОНВЕРСИИ ЭТАНОЛА
Ф.З.Абузерли, В.Л.Багиев
Изучена реакция паровой конверсии этанола в водород на бинарных цинк-кобальт-оксидных катализаторах различного состава. Установлено, что при низких температурах продуктами реакция являются ацетальдегид и ацетон, в то время как при высоких - водород и углекислый газ. Показано, что в реакции образования водорода наибольшую активность проявляют образцы составов Zn:Co=2:8 и 9:1. Наибольший выход водорода на изученных катализаторах достигает 74.3% при конверсии этанола, равной 95%.
Ключевые слова: водород, паровая конверсия, этанол, бинарные катализаторы, оксид цинка.
