SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai
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Tailored Hydrotalcite as Hybrid Material for Sorption-Enhanced Reforming of Ethanol
Karan D. Dewoolkar, Prakash D. Vaidya
Department of Chemical Engineering, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai-400019
Email: dewoolkarkaran@gmail.com, pd.vaidya@ictmumbai.edu.in
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1. Introduction:
Hydrogen (H2), a potential energy carrier, has several applications in the chemical and energy industries. Sorption-enhanced
reforming process (SERP), which combines reaction (steam reforming) and product separation (CO2 adsorption), is a
candidate technique for producing pure H2 at temperatures lower than those used in steam reforming [1,2]. In SERP,
mixtures of a reforming catalyst and a chemisorbent are employed; alternately, multifunctional hybrid materials which
possess the properties of the catalyst and the adsorbent may be used [3]. Such materials are advantageous, due to the fact
that they offer low diffusion resistance and improved access to the adsorbent sites. Hydrotalcites, which are layered double
hydroxides, represent useful intermediate-temperature sorbents. These materials are durable and easily regenerable;
however, they have low adsorption capacity. In the present work, several cationic modified hydrotalcite-based hybrid
materials were investigated for SERP using ethanol as feedstock. Ethanol, which can be produced from agricultural products
and residues, is a renewable resource for H2; thus, the entire process is very attractive.
2. Materials and Methods:
Four hybrid materials, which differed in the cation (Mg, Ca, Cu and Zn) present in the hydrotalcite structure, were
synthesized by using co-precipitation technique. Cations, which increase the inter-layer spacing, and hence, the CO2 uptake,
were selected for this study. Activity trials for ethanol conversion were performed in a vapour-phase reactor. Product gases
were analyzed online using a gas chromatograph (GC) unit equipped with a thermal conductivity detector (TCD). The
analysis of the liquid phase was accomplished using flame ionization detector (FID). Further, sorption studies were
performed using the hybrid materials. The influence of reaction variables on performance of the investigated materials was
studied so: temperature, 573 to 773K, steam/ethanol ratio, 3 to 15 mol/mol, and sorbent mass fraction, 0.085 to 0.25 kg
h/mol.
3. Results and Discussion:
Ethanol conversion expectedly increased with a rise in temperature, due to the endothermic nature of the reforming reaction
(Fig. 1). It was observed that high-purity H2 is produced, even at low reaction temperature. The hybrid material NiCuHTc
offered the highest adsorption capacity at 573 K (see Table 1). The product composition was strongly dependent on
temperature. Assuming first-order kinetics, it was found that the copper-based hybrid material exhibited the lowest
activation energy (44.5 kJ/mol). A reaction pathway for H2 production from ethanol over the selected hybrid materials was
suggested. Cyclic stability tests are currently underway.
1
100
XEtOH (mol %)
80
60
NiMgHTc
40
NiCaHTc
20
NiCuHTc
NiZnHTc
0
550
600
650
700
Temperature (K)
750
800
Figure 1: Dependence of ethanol conversion on temperature
(Reaction pressure = 0.1 MPa, steam/carbon ratio = 9 mol/mol, GHSV = 3600 mL/(g h), time on stream = 3h)
Table 1: Dependence of the adsorption capacity on temperature
(Reaction pressure = 0.1 MPa, steam/carbon ratio = 9 mol/mol, GHSV = 3600 mL/(g h), time on stream = 3 h).
Temperature
(K)
Qads
(mol CO2/ kg sorbent)
NiMgHTc (HM1)
NiCaHTc (HM2)
NiCuHTc (HM3)
NiZnHTc (HM4)
0.43
0.09
0.92
0.58
0.31
0.19
0.79
0.7
0.15
0.42
0.74
0.42
0.12
0.53
0.25
0.1
0.06
0.69
0.1
0.04
573
623
673
723
773
4. Conclusions:
In the present investigation, a comparative assessment of cation-modified hydrotalcite-based hybrid materials on SERP of
ethanol was performed. These hybrid materials resulted in high adsorption capacities and longer breakthrough times at
much lower temperatures. Thus, such multifunctional hybrid materials are promising candidates for sustainable and
economical H2 production.
References
[1] Y. Ding, E. Alpay, Chem. Eng. Sci., 55, 2000, 3929-3940.
[2] S. G. Mayorga, J. R. Hufton, S. Sircar, T. R. Gaffney, Sorption Enhanced Reaction Process for Production of Hydrogen.
Phase I Final Report, DOE/GO/10059-T1, 1997.
[3] K. D. Dewoolkar, P. D. Vaidya, Energy Fuels, 29(6) 2015, 3870-3878.
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