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Study of catalytic hydrogenation of N-ethylcarbazole over ruthenium catalyst
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Study of catalytic hydrogenation of N-ethylcarbazole over ruthenium catalyst Chao Wan, Yue An*, Guohua Xu, Wenjing Kong Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, PR China
article info
abstract
Article history:
Hydrogenation reaction of N-ethylcarbazole was investigated over ruthenium catalyst
Received 16 December 2011
supported by alumina powder. The catalytic conversion of 100% and selectivity of 98%
Received in revised form
towards N-perhydroethylcarbazole were achieved over 1 g catalyst. The effect of temper-
25 April 2012
ature, hydrogen pressure, stirring speed and the dosage of catalyst on the hydrogen
Accepted 25 April 2012
capacity of N-ethylcarbazole in liquid phase were studied, respectively. The optimum
Available online 26 May 2012
reaction condition was 6.0 MPa, 413 K, 1.0 gRu/g-Al2O3, 600rpm, and the corresponding hydrogen storage capacity reached 5.6 wt% approximately. The kinetics of hydrogenation
Keywords:
was also discussed and the apparent activation energy was 27.01 kJ/mol.
Hydrogen storage
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
N-ethylcarbazole Catalytic hydrogenation
1.
Introduction
Nowadays, the fossil fuels which are the primary energy sources are diminishing very rapidly; Besides, the production from their use have a bad effect on our environment and aggravate significantly global warming [1,2]. Thus, replacing fossil fuels with clean, sustainable energy sources are of paramount importance [3]. Hydrogen is considered as the promising and non-toxic environmentally benign energy carrier for its unique advantages like a high calorific value, wide variety of resource, clean and high efficient; However, a gap in hydrogen storage technology is one of the roadblocks to the development of largescale H2 use, especially vehicular fuel cells. Currently, studies in the area of hydrogen storage have been revealed for this category of materials including ammonia borane based compound [4e6], chemical and metal hydrides [7,8], and organic heteroaromatic compounds [9e15], among which, the latter use polyunsaturated organic compounds to store reversibly hydrogen with the organic molecules catalytically hydrogenating and dehydrogenating. The polyunsaturated organic
compounds (e.g. benzene, decalin) have been studied by a number of research groups [16e24]. Recently, a new kind of organic liquid hydrides named as N-ethylcarbazole has been found, and it is prospected that the temperature of hydrogenation and dehydrogenation can be reduced to a large extent due to the substitution of heteroatom in N-ethylcarbazole. Some studies have been reported on hydrogenation of N-ethylcarbazole as liquid carrier by Pez, Scott and Cheng from Air Product in their series of patent [25,26]. It is claimed that gravimetric capacities of up to 5.5wt%H2 and volumetric capacities of up to 69gH2/L can be achieved based on reversible catalytic hydrogenation over proprietary catalysts [27].
2.
Experimental section
2.1.
Materials
N-ethylcarbazole(purity 99.5%), ruthenium on alumina powder and ultra high purity hydrogen were purchased from
* Corresponding author. Tel./fax: þ86 571 87951742. E-mail addresses: [email protected], [email protected] (Y. An). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.04.123
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
13093
Shanghai Infine Chemicals Co Limited, Alfa aersar and minxing gas company, respectively. The composition of ruthenium is 5.16wt%, and the moisture is 1wt%. Hydrogen absorption measurement was carried out by an apparatus with an “in house” device which monitored continuously hydrogen absorption at different stable temperatures by measuring the pressure drop in the autoclave. The reactions were conducted in a 0.1 L FYX-D01 stainless autoclave with mechanical stirring, as seen in Fig. 1. The autoclave was filled with hydrogen from hydrogen reservoir with a certain capacity. So, the hydrogen absorption capacity can be calculated by measuring the hydrogen pressure in the autoclave.
2.2. Catalytic hydrogenation reaction of N-ethylcarbazole The catalytic hydrogenation of N-ethylcarbazole was conducted in the autoclave batch reactor with continuous monitoring and control of rotational speed, temperature and pressure. A certain amount of N-ethylecarbazole with desired catalyst was added into the autoclave which was sealed immediately afterwards and evacuated for about 15 min, hydrogen was then charged into autoclave to increase a desired pressure while the autoclave was heated to the designed reaction temperature. As the reaction proceeded, the experiment data was recorded by the computer including the hydrogen pressure decrease and the reaction time. The reaction mixture was analyzed using a Gas Chromatograph-Mass Spectrometer (HP6890/5973 GCeMS), by the end of the reaction; other experiments were carried out in parallel by following the same procedure.
3.
Results and discussion
3.1. Influence of temperature on the hydrogenation of N-ethylcarbazole Fig. 2 showes the hydrogen absorption curves of N-ethylcarbazole at various temperature under 1.0 g catalyst, 600rpm and 6.0 MPa reaction pressure condition. It can be seen that the initial reaction rate accelerates with increasing temperature from 368 K to 433 K, the reaction rate reaches maximum between 433 K and 453 K, and the hydrogen uptake of N-ethylcarbazole can reach the maximum value (5.6 wt%) between 368 K and 453 K. However, when the temperature further increases to 493 K, the hydrogen uptake decreased to 5.12wt%. The decrease of reaction rate may be caused by the drop of the catalyst activity at high temperature, furthermore, at high temperature the mass transfer of hydrogen might be restricted in this system, as reported in Ref [18]. The temperature have a little effect on the initial reaction rate from 453 K to 493 K, This may be explained by the fact that hydrogenation is a multiple reaction, the influence of temperature on every steps of multiple reaction is of difference, and the initial reaction is insensitive to the vary of temperature.
Fig. 1 e Scheme diagram of the experimental system 1－ hydrogen source; 2,6,10－connection valve; 3,8,14－ pressure gauge; 4,12－hydrogen reservoir; 5,11,13－ exhaust pipe valve; 7－stainless steel autoclave; 9-thermocouple temperature control; 15,16－pressure sensor; 17,18－detection apparatus; 19-computer.
3.2. Influence of hydrogen pressure on hydrogenation of N-ethylcarbazole The hydrogen absorption curves (Fig. 3) were measured under various pressures at 433 K to investigate the effect of the reaction pressure on the reaction rate. It is revealed that with the rise of the reaction pressure, the reaction rate increase; especially when the hydrogen pressure increase from 3.0 MPa to 5.0 MPa, the reaction rate increase significantly. Hydrogenation of N-ethylcarbazole is the reaction of volume reduced, the increment of hydrogen pressure benefit the shifting of reaction equilibrium to product direction; in the meantime improve hydrogen solubility in molten reactant, which can accelerate reaction rate. In addition, high hydrogen pressure has inhibitive effect on the carbon deposition on the catalyst, which is beneficial to the life of the catalyst.
Fig. 2 e Hydrogen absorption in N-ethylcarbazole measurements at different temperature (6.0 MPa H2, 600rpm, 1.0 g catalyst).
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
3.4. Influence of stirring speed on hydrogenation of N-ethylcarbazole Fig. 5 showes the effect of stirring speed on hydrogenation of N-ethylcarbazole. It is demonstrated that the rotational speed of reactor could influence the reaction rate to some extent. With the augment of rotational speed from 300, 450e600 rpm, the reaction time is shorted from 130, 60 to 32 min, therefore, it is indicated that the reaction rate is largely increased. But with the further rise of stirring speed from 600 to 1000 rpm, the reaction time remain 32 min, hence the stability of the reaction rate is attained. The reason of this phenomenon may be the weakening of the external diffusion which is caused by the resistance to mass transfer. When the rotational speed surpass 600 rpm, the increment of rotational speed have little effect on the reaction rate, the external diffusion was diminished. Fig. 3 e The influence of hydrogen pressure on the hydrogenation of N-ethylecarbazole (433 K, 600rpm, 1.0 g catalyst).
3.3. Influence of catalyst dosage on the hydrogenation of N-ethylcarbazole The hydrogenation of N-ethylcarbazole was carried out using a range of catalyst dosage from 0.3 g to 1.2 g at 433 K to determine the effect of catalyst concentration on reaction rate (Fig. 4). As shown in Fig. 4, when the dosage of catalyst increased from 0.3 g to 1.0 g, the hydrogen capacity is 2.5 wt%, 4.3 wt%, 5.4 wt% and 5.6 wt% within 25 min, respectively. It is revealed that the reaction rate is enhanced obviously. Nevertheless, the hydrogen reaction reaches the saturation with the increase of the catalyst from 1.0 g to 1.2 g. The hydrogen uptake curves over time at 433 K and 6.0 MPa demonstrate that the concentration of catalyst could influence the reaction rate to certain content. Therefore, the increase of the catalyst dosage would shorten reaction time, and have little effect on the hydrogen capacity, which can arrive at 5.6wt%.
Fig. 4 e Hydrogenation of N-ethylcarbazole measuring at diverse dosage of catalyst (6.0 MPa H2, 433 K, 600rpm).
4.
The kinetics of N-ethylcarbazole
In order to study the chemical kinetics for this reaction, the external diffusion need to be excluded. Since this reaction is catalytic hydrogenation reaction, according to Zievernek’s [28] study results, external diffusion mass transfer rate is higher than apparent reaction rate at least two orders of magnitude. From the discussion of 3.4, it is obtained that the external diffusion at the speed of 600 rpm has been excluded. As for the inner diffusion, according to weisz criterion, the influence of the inner diffusion can be neglected as a result of small size of catalyst particle. The analysis of the dynamics experiment manifest the hydrogenation of N-ethylcarbazole over ruthenium on alumina powder were described by a zero-order rate equation in N-ethylcarbazole concentration and first-order rate in H2 concentration [29]. Hydrogenation kinetics model could be expressed as [29]: dc r ¼ ¼ kPH2 dt
Fig. 5 e Hydrogen absorption in N-ethylcarbazole measurements at various speed (6.0MPaH2, 433 K, 1.0 g catalyst).
(1)
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
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concentration of N-ethylcarbazole. In the temperature range of 368e433 K, the apparent activation energy is only 27.01 kJ/mol, the kinetics model can be written as: 27010 PH2 r ¼ 5:9835exp RT
Acknowledgements This work is supported by the National High Technology Research& Development Program of China (2007AA05Z112) and National Basic Research Program of China (2007CB209700).
references
Fig. 6 e The hydrogenation of N-ethylcarbazole lnkw1/T curve.
Ea lnk ¼ þ lnk0 RT
(2)
r is the apparent reaction rate,mol/(min$g); c is N-ethylcarbazole concentration, mol/L; PH2 is hydrogen pressure, MP; R is gas constant, J/(mol$K); T is reaction temperature, K; Ea is apparent activation energy, J/mol; k is apparent reaction rate constant; k0 is apparent reaction pre-exponential factor. According to formula (1) and experimental result (Fig. 2), the reaction rate constant under different temperature could be obtained. A smooth straight line could be obtained by lnk verse 1/T plot,as shown in Fig. 6, and its linear correlation coefficient is 98.29%. According to the slope and intercept of the straight line, activation energy and pre-exponential factor of hydrogenation of N-ethylcarbazole over ruthenium on alumina powder were 27.01 kJ/mol and 5.9835 mol/ (min$g$MPa), respectively. Therefore, the kinetic equation is: 27010 PH2 r ¼ 5:9835exp RT
5.
Conclusions
(1) Ruthenium on alumina powder exhibited strong performance to the hydrogenation of N-ethylcarbazole .The reaction rate accelerated with the increase of temperature in a certain range, and the initial reaction reached the maximum when the temperature exceeded 433 K, and then the hydrogen uptake of N-ethylcarbazole reaches the maximum value (5.6wt%) at temperature between 368 K and 453 K. When temperature exceeded 453 K, the maximum of hydrogen uptake couldn’t be achieved. Especially at 368 K, the hydrogen uptake of the maximum also could get only 2 h later. (2) The hydrogen pressure, the stirring speed and the dosage of catalyst had influence on the hydrogenation of N-ethylcarbazole to some extent. (3) The apparent reaction rate was first order for hydrogen concentration in the liquid phase and zero order for the
[1] Duhamela LJ, Duhamela A, Carpentiera E, Payena FH. Hydrogen charging/discharging system with liquid organic compounds: a lacunar oxide catalyst to hydrogenate the unsaturated organic compound. Int J Hydrogen Energy 2007;32:2593e7. [2] Van den Berg AWC, Arean CO. Material for hydrogen storage: current research trends and perspectives. Chem Commun 2008;6:668e81. [3] Satyapal S, Petrovic J, Read C, Thomas G, Ordaz G. The U.S. Department of Energy’s National hydrogen storage project: progress towards meeting hydrogen-powered vehicle requirements. Catal Today 2007;120:246e56. [4] Schubert DM. Borax pioneer; 2001. p. 20. [5] Shore SG, Parry RW. The Crystalline compound ammonia borane, H3NBH3. J Am Chem Soc 1955;77:6084. [6] Yang JZ, Fu H, Song P, Zheng J, Li XG. Reversible dehydrogenation of Mg(BH4)2-LiH composite under moderate conditions. Int J Hydrogen Energy 2012;37:6776e83. [7] Breault RW, McClaine AW, Rolfe J, Konduri R, Miskolczy G. Proc Int Tech Conf Coal Util Fuel Sys 2000;25:751e61. [8] Li SL, Chen W, Luo G, Han XB, Chen DM, Yang K, et al. Effect of hydrogen absorption/desorption cycling on hydrogen storage properties of a LaNi3.8Al1.0Mn0.2 alloy. Int J Hydrogen Energy 2012;37:3268e75. [9] Clot E, Eisenstein O, Crabtree RH. Computational structureactivity relationships in H2 storage: how placement of N atoms affects release temperatures in organic liquid storage materials. Chem Commun 2007;22:2231e3. [10] Ichikawa M, Fukuoka A. Jpa Kokai TOKKYO koho A2(2001134141), 2002. [11] Huddleston JG, Visser AE, Reichert WM, Willauer HD, Broker GA, Rogers RD. Characterization and comparsion of hydrophilic and hydrophobic room temperature ionic liquid incorporating the imidazolium cation. Green Chem 2001;4: 156e64. [12] Hoenal M, Vierhapper FW. Selectivity of hydrogenations. Part 3. N-methylquinolinium, N-methylisoquinolinium, and 4-(3phenylpropyl)pyridinium salts. J Chen Soc Perkin Trans 1 1982;11:2607e10. [13] Dykstra SJ, Minielli JL. US3931195, January 6 1976. [14] Shukla A, Karmakar S, Biniwale RB. Hydrogen delivery through liquid organic hydrides: considerations for a potential technology. Int J Hydrogen Energy 2012;37:3719e26. [15] Sotoodeh F, Huber BJM, Smith KJ. Dehydrogenation kinetics and catalysis of organic heteroaromatics for hydrogen storage. Int J Hydrogen Energy 2012;37:2715e22. [16] Pande JV, Shukla A, Biniwale RB. Catalytic dehydrogenation of cyclohexane over Ag-M/ACC catalysts for hydrogen supply. Int J Hydrogen Energy 2012;37:6756e63.
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[17] Sotoodeh F, Smith KJ. Kinetics of hydrogen uptake and release from heteroaromatic compounds for hydrogen storage. Ind Eng Chem Res 2010;49:1018e26. [18] Eblagon KM, Rentsch K, Friedrichs O, Remhof A, Zuettel A, Ramirez-Cuesta AJ, et al. Hydrogenation of 9-ethylcarbazole as a prototype of a liquid hydrogen carrier. Int J Hydrogen Energy 2010;35:11609e21. [19] Hodoshima S, Nagata H, Saito Y. Efficient hydrogen supply from tetralin with superheated liquid-film-type catalysis for operating fuel cells. Appl Catal A Gen 2005;292:90e6. [20] Aparicio FP, Ramos IR, Ruiz AG. Pure hydrogen production from methylcyclohexane using a new high performance membrane reactor. Chem Commun 2002;18:2082e3. [21] Itoh N, Tamura E, Hara S, Takahashi T, Shono A, Satoh K, et al. Hydrogen recovery from cyclohexane as a chemical hydrogen carrier using a palladium membrane reactor. Catal Today 2003;82:119e25.
[22] Taube M, Taube P. A liquid organic carrier of hydrogen as a fuel for automobiles. Adv Hyd Energy 1981;2:1077e85. [23] Santa GV, Bustamante C, Swesi Y, Pitault I, Meille V, Heurtaux F. International Hydrogen Energy Congress and Exhibition 2005, IHEC2005, vol. 1. [24] Schwarz DE, Cameron TM, Hay PJ, Scott BL, Tumas W, Thorn DL. Hydrogen evolution from organic “hydrides”. Chem Commun 2005:5919e21. [25] Pez G, Scott A, Cooper AC, Cheng H. US Pat., 2857A1, 2005. [26] Pez G, Scott A, Cooper AC, Cheng H. US Pat., 7101530B2, 2006. [27] Cooper AC, Cambell KM, Pez G. WHEC proceedings. France: Lyon; 2006. [28] Levensplel O. Chemical reaction engineering. John Wiley&Sons; 1972. [29] Ye XF, An Y, Xu GH. Kinetics of 9-ethylcarbazole hydrogenation over Raney-Ni catalyst for hydrogen storage. J Alloys Compd 2011;509:152e6.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Study of catalytic hydrogenation of N-ethylcarbazole over ruthenium catalyst Chao Wan, Yue An*, Guohua Xu, Wenjing Kong Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, PR China
article info
abstract
Article history:
Hydrogenation reaction of N-ethylcarbazole was investigated over ruthenium catalyst
Received 16 December 2011
supported by alumina powder. The catalytic conversion of 100% and selectivity of 98%
Received in revised form
towards N-perhydroethylcarbazole were achieved over 1 g catalyst. The effect of temper-
25 April 2012
ature, hydrogen pressure, stirring speed and the dosage of catalyst on the hydrogen
Accepted 25 April 2012
capacity of N-ethylcarbazole in liquid phase were studied, respectively. The optimum
Available online 26 May 2012
reaction condition was 6.0 MPa, 413 K, 1.0 gRu/g-Al2O3, 600rpm, and the corresponding hydrogen storage capacity reached 5.6 wt% approximately. The kinetics of hydrogenation
Keywords:
was also discussed and the apparent activation energy was 27.01 kJ/mol.
Hydrogen storage
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
N-ethylcarbazole Catalytic hydrogenation
1.
Introduction
Nowadays, the fossil fuels which are the primary energy sources are diminishing very rapidly; Besides, the production from their use have a bad effect on our environment and aggravate significantly global warming [1,2]. Thus, replacing fossil fuels with clean, sustainable energy sources are of paramount importance [3]. Hydrogen is considered as the promising and non-toxic environmentally benign energy carrier for its unique advantages like a high calorific value, wide variety of resource, clean and high efficient; However, a gap in hydrogen storage technology is one of the roadblocks to the development of largescale H2 use, especially vehicular fuel cells. Currently, studies in the area of hydrogen storage have been revealed for this category of materials including ammonia borane based compound [4e6], chemical and metal hydrides [7,8], and organic heteroaromatic compounds [9e15], among which, the latter use polyunsaturated organic compounds to store reversibly hydrogen with the organic molecules catalytically hydrogenating and dehydrogenating. The polyunsaturated organic
compounds (e.g. benzene, decalin) have been studied by a number of research groups [16e24]. Recently, a new kind of organic liquid hydrides named as N-ethylcarbazole has been found, and it is prospected that the temperature of hydrogenation and dehydrogenation can be reduced to a large extent due to the substitution of heteroatom in N-ethylcarbazole. Some studies have been reported on hydrogenation of N-ethylcarbazole as liquid carrier by Pez, Scott and Cheng from Air Product in their series of patent [25,26]. It is claimed that gravimetric capacities of up to 5.5wt%H2 and volumetric capacities of up to 69gH2/L can be achieved based on reversible catalytic hydrogenation over proprietary catalysts [27].
2.
Experimental section
2.1.
Materials
N-ethylcarbazole(purity 99.5%), ruthenium on alumina powder and ultra high purity hydrogen were purchased from
* Corresponding author. Tel./fax: þ86 571 87951742. E-mail addresses: [email protected], [email protected] (Y. An). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.04.123
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
13093
Shanghai Infine Chemicals Co Limited, Alfa aersar and minxing gas company, respectively. The composition of ruthenium is 5.16wt%, and the moisture is 1wt%. Hydrogen absorption measurement was carried out by an apparatus with an “in house” device which monitored continuously hydrogen absorption at different stable temperatures by measuring the pressure drop in the autoclave. The reactions were conducted in a 0.1 L FYX-D01 stainless autoclave with mechanical stirring, as seen in Fig. 1. The autoclave was filled with hydrogen from hydrogen reservoir with a certain capacity. So, the hydrogen absorption capacity can be calculated by measuring the hydrogen pressure in the autoclave.
2.2. Catalytic hydrogenation reaction of N-ethylcarbazole The catalytic hydrogenation of N-ethylcarbazole was conducted in the autoclave batch reactor with continuous monitoring and control of rotational speed, temperature and pressure. A certain amount of N-ethylecarbazole with desired catalyst was added into the autoclave which was sealed immediately afterwards and evacuated for about 15 min, hydrogen was then charged into autoclave to increase a desired pressure while the autoclave was heated to the designed reaction temperature. As the reaction proceeded, the experiment data was recorded by the computer including the hydrogen pressure decrease and the reaction time. The reaction mixture was analyzed using a Gas Chromatograph-Mass Spectrometer (HP6890/5973 GCeMS), by the end of the reaction; other experiments were carried out in parallel by following the same procedure.
3.
Results and discussion
3.1. Influence of temperature on the hydrogenation of N-ethylcarbazole Fig. 2 showes the hydrogen absorption curves of N-ethylcarbazole at various temperature under 1.0 g catalyst, 600rpm and 6.0 MPa reaction pressure condition. It can be seen that the initial reaction rate accelerates with increasing temperature from 368 K to 433 K, the reaction rate reaches maximum between 433 K and 453 K, and the hydrogen uptake of N-ethylcarbazole can reach the maximum value (5.6 wt%) between 368 K and 453 K. However, when the temperature further increases to 493 K, the hydrogen uptake decreased to 5.12wt%. The decrease of reaction rate may be caused by the drop of the catalyst activity at high temperature, furthermore, at high temperature the mass transfer of hydrogen might be restricted in this system, as reported in Ref [18]. The temperature have a little effect on the initial reaction rate from 453 K to 493 K, This may be explained by the fact that hydrogenation is a multiple reaction, the influence of temperature on every steps of multiple reaction is of difference, and the initial reaction is insensitive to the vary of temperature.
Fig. 1 e Scheme diagram of the experimental system 1－ hydrogen source; 2,6,10－connection valve; 3,8,14－ pressure gauge; 4,12－hydrogen reservoir; 5,11,13－ exhaust pipe valve; 7－stainless steel autoclave; 9-thermocouple temperature control; 15,16－pressure sensor; 17,18－detection apparatus; 19-computer.
3.2. Influence of hydrogen pressure on hydrogenation of N-ethylcarbazole The hydrogen absorption curves (Fig. 3) were measured under various pressures at 433 K to investigate the effect of the reaction pressure on the reaction rate. It is revealed that with the rise of the reaction pressure, the reaction rate increase; especially when the hydrogen pressure increase from 3.0 MPa to 5.0 MPa, the reaction rate increase significantly. Hydrogenation of N-ethylcarbazole is the reaction of volume reduced, the increment of hydrogen pressure benefit the shifting of reaction equilibrium to product direction; in the meantime improve hydrogen solubility in molten reactant, which can accelerate reaction rate. In addition, high hydrogen pressure has inhibitive effect on the carbon deposition on the catalyst, which is beneficial to the life of the catalyst.
Fig. 2 e Hydrogen absorption in N-ethylcarbazole measurements at different temperature (6.0 MPa H2, 600rpm, 1.0 g catalyst).
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
3.4. Influence of stirring speed on hydrogenation of N-ethylcarbazole Fig. 5 showes the effect of stirring speed on hydrogenation of N-ethylcarbazole. It is demonstrated that the rotational speed of reactor could influence the reaction rate to some extent. With the augment of rotational speed from 300, 450e600 rpm, the reaction time is shorted from 130, 60 to 32 min, therefore, it is indicated that the reaction rate is largely increased. But with the further rise of stirring speed from 600 to 1000 rpm, the reaction time remain 32 min, hence the stability of the reaction rate is attained. The reason of this phenomenon may be the weakening of the external diffusion which is caused by the resistance to mass transfer. When the rotational speed surpass 600 rpm, the increment of rotational speed have little effect on the reaction rate, the external diffusion was diminished. Fig. 3 e The influence of hydrogen pressure on the hydrogenation of N-ethylecarbazole (433 K, 600rpm, 1.0 g catalyst).
3.3. Influence of catalyst dosage on the hydrogenation of N-ethylcarbazole The hydrogenation of N-ethylcarbazole was carried out using a range of catalyst dosage from 0.3 g to 1.2 g at 433 K to determine the effect of catalyst concentration on reaction rate (Fig. 4). As shown in Fig. 4, when the dosage of catalyst increased from 0.3 g to 1.0 g, the hydrogen capacity is 2.5 wt%, 4.3 wt%, 5.4 wt% and 5.6 wt% within 25 min, respectively. It is revealed that the reaction rate is enhanced obviously. Nevertheless, the hydrogen reaction reaches the saturation with the increase of the catalyst from 1.0 g to 1.2 g. The hydrogen uptake curves over time at 433 K and 6.0 MPa demonstrate that the concentration of catalyst could influence the reaction rate to certain content. Therefore, the increase of the catalyst dosage would shorten reaction time, and have little effect on the hydrogen capacity, which can arrive at 5.6wt%.
Fig. 4 e Hydrogenation of N-ethylcarbazole measuring at diverse dosage of catalyst (6.0 MPa H2, 433 K, 600rpm).
4.
The kinetics of N-ethylcarbazole
In order to study the chemical kinetics for this reaction, the external diffusion need to be excluded. Since this reaction is catalytic hydrogenation reaction, according to Zievernek’s [28] study results, external diffusion mass transfer rate is higher than apparent reaction rate at least two orders of magnitude. From the discussion of 3.4, it is obtained that the external diffusion at the speed of 600 rpm has been excluded. As for the inner diffusion, according to weisz criterion, the influence of the inner diffusion can be neglected as a result of small size of catalyst particle. The analysis of the dynamics experiment manifest the hydrogenation of N-ethylcarbazole over ruthenium on alumina powder were described by a zero-order rate equation in N-ethylcarbazole concentration and first-order rate in H2 concentration [29]. Hydrogenation kinetics model could be expressed as [29]: dc r ¼ ¼ kPH2 dt
Fig. 5 e Hydrogen absorption in N-ethylcarbazole measurements at various speed (6.0MPaH2, 433 K, 1.0 g catalyst).
(1)
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 3 0 9 2 e1 3 0 9 6
13095
concentration of N-ethylcarbazole. In the temperature range of 368e433 K, the apparent activation energy is only 27.01 kJ/mol, the kinetics model can be written as: 27010 PH2 r ¼ 5:9835exp RT
Acknowledgements This work is supported by the National High Technology Research& Development Program of China (2007AA05Z112) and National Basic Research Program of China (2007CB209700).
references
Fig. 6 e The hydrogenation of N-ethylcarbazole lnkw1/T curve.
Ea lnk ¼ þ lnk0 RT
(2)
r is the apparent reaction rate,mol/(min$g); c is N-ethylcarbazole concentration, mol/L; PH2 is hydrogen pressure, MP; R is gas constant, J/(mol$K); T is reaction temperature, K; Ea is apparent activation energy, J/mol; k is apparent reaction rate constant; k0 is apparent reaction pre-exponential factor. According to formula (1) and experimental result (Fig. 2), the reaction rate constant under different temperature could be obtained. A smooth straight line could be obtained by lnk verse 1/T plot,as shown in Fig. 6, and its linear correlation coefficient is 98.29%. According to the slope and intercept of the straight line, activation energy and pre-exponential factor of hydrogenation of N-ethylcarbazole over ruthenium on alumina powder were 27.01 kJ/mol and 5.9835 mol/ (min$g$MPa), respectively. Therefore, the kinetic equation is: 27010 PH2 r ¼ 5:9835exp RT
5.
Conclusions
(1) Ruthenium on alumina powder exhibited strong performance to the hydrogenation of N-ethylcarbazole .The reaction rate accelerated with the increase of temperature in a certain range, and the initial reaction reached the maximum when the temperature exceeded 433 K, and then the hydrogen uptake of N-ethylcarbazole reaches the maximum value (5.6wt%) at temperature between 368 K and 453 K. When temperature exceeded 453 K, the maximum of hydrogen uptake couldn’t be achieved. Especially at 368 K, the hydrogen uptake of the maximum also could get only 2 h later. (2) The hydrogen pressure, the stirring speed and the dosage of catalyst had influence on the hydrogenation of N-ethylcarbazole to some extent. (3) The apparent reaction rate was first order for hydrogen concentration in the liquid phase and zero order for the
[1] Duhamela LJ, Duhamela A, Carpentiera E, Payena FH. Hydrogen charging/discharging system with liquid organic compounds: a lacunar oxide catalyst to hydrogenate the unsaturated organic compound. Int J Hydrogen Energy 2007;32:2593e7. [2] Van den Berg AWC, Arean CO. Material for hydrogen storage: current research trends and perspectives. Chem Commun 2008;6:668e81. [3] Satyapal S, Petrovic J, Read C, Thomas G, Ordaz G. The U.S. Department of Energy’s National hydrogen storage project: progress towards meeting hydrogen-powered vehicle requirements. Catal Today 2007;120:246e56. [4] Schubert DM. Borax pioneer; 2001. p. 20. [5] Shore SG, Parry RW. The Crystalline compound ammonia borane, H3NBH3. J Am Chem Soc 1955;77:6084. [6] Yang JZ, Fu H, Song P, Zheng J, Li XG. Reversible dehydrogenation of Mg(BH4)2-LiH composite under moderate conditions. Int J Hydrogen Energy 2012;37:6776e83. [7] Breault RW, McClaine AW, Rolfe J, Konduri R, Miskolczy G. Proc Int Tech Conf Coal Util Fuel Sys 2000;25:751e61. [8] Li SL, Chen W, Luo G, Han XB, Chen DM, Yang K, et al. Effect of hydrogen absorption/desorption cycling on hydrogen storage properties of a LaNi3.8Al1.0Mn0.2 alloy. Int J Hydrogen Energy 2012;37:3268e75. [9] Clot E, Eisenstein O, Crabtree RH. Computational structureactivity relationships in H2 storage: how placement of N atoms affects release temperatures in organic liquid storage materials. Chem Commun 2007;22:2231e3. [10] Ichikawa M, Fukuoka A. Jpa Kokai TOKKYO koho A2(2001134141), 2002. [11] Huddleston JG, Visser AE, Reichert WM, Willauer HD, Broker GA, Rogers RD. Characterization and comparsion of hydrophilic and hydrophobic room temperature ionic liquid incorporating the imidazolium cation. Green Chem 2001;4: 156e64. [12] Hoenal M, Vierhapper FW. Selectivity of hydrogenations. Part 3. N-methylquinolinium, N-methylisoquinolinium, and 4-(3phenylpropyl)pyridinium salts. J Chen Soc Perkin Trans 1 1982;11:2607e10. [13] Dykstra SJ, Minielli JL. US3931195, January 6 1976. [14] Shukla A, Karmakar S, Biniwale RB. Hydrogen delivery through liquid organic hydrides: considerations for a potential technology. Int J Hydrogen Energy 2012;37:3719e26. [15] Sotoodeh F, Huber BJM, Smith KJ. Dehydrogenation kinetics and catalysis of organic heteroaromatics for hydrogen storage. Int J Hydrogen Energy 2012;37:2715e22. [16] Pande JV, Shukla A, Biniwale RB. Catalytic dehydrogenation of cyclohexane over Ag-M/ACC catalysts for hydrogen supply. Int J Hydrogen Energy 2012;37:6756e63.
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[17] Sotoodeh F, Smith KJ. Kinetics of hydrogen uptake and release from heteroaromatic compounds for hydrogen storage. Ind Eng Chem Res 2010;49:1018e26. [18] Eblagon KM, Rentsch K, Friedrichs O, Remhof A, Zuettel A, Ramirez-Cuesta AJ, et al. Hydrogenation of 9-ethylcarbazole as a prototype of a liquid hydrogen carrier. Int J Hydrogen Energy 2010;35:11609e21. [19] Hodoshima S, Nagata H, Saito Y. Efficient hydrogen supply from tetralin with superheated liquid-film-type catalysis for operating fuel cells. Appl Catal A Gen 2005;292:90e6. [20] Aparicio FP, Ramos IR, Ruiz AG. Pure hydrogen production from methylcyclohexane using a new high performance membrane reactor. Chem Commun 2002;18:2082e3. [21] Itoh N, Tamura E, Hara S, Takahashi T, Shono A, Satoh K, et al. Hydrogen recovery from cyclohexane as a chemical hydrogen carrier using a palladium membrane reactor. Catal Today 2003;82:119e25.
[22] Taube M, Taube P. A liquid organic carrier of hydrogen as a fuel for automobiles. Adv Hyd Energy 1981;2:1077e85. [23] Santa GV, Bustamante C, Swesi Y, Pitault I, Meille V, Heurtaux F. International Hydrogen Energy Congress and Exhibition 2005, IHEC2005, vol. 1. [24] Schwarz DE, Cameron TM, Hay PJ, Scott BL, Tumas W, Thorn DL. Hydrogen evolution from organic “hydrides”. Chem Commun 2005:5919e21. [25] Pez G, Scott A, Cooper AC, Cheng H. US Pat., 2857A1, 2005. [26] Pez G, Scott A, Cooper AC, Cheng H. US Pat., 7101530B2, 2006. [27] Cooper AC, Cambell KM, Pez G. WHEC proceedings. France: Lyon; 2006. [28] Levensplel O. Chemical reaction engineering. John Wiley&Sons; 1972. [29] Ye XF, An Y, Xu GH. Kinetics of 9-ethylcarbazole hydrogenation over Raney-Ni catalyst for hydrogen storage. J Alloys Compd 2011;509:152e6.