(314a) Strategies for H2 Production By Steam Reforming of Ethanol with Pressure Swing Adsorptive Reactor

Strategies for H₂ Production by Ethanol Steam
Reforming

with Pressure Swing Adsorptive Reactor

Yi-Jiang
Wu¹, Ping Li¹,
Jian-Guo Yu¹ and Alirio E. Rodrigues²*

1
School of Chemical Engineering, East
China University of Science and Technology,

Shanghai
200237, China

2
Laboratory of Separation and Reaction Engineering, Associated Laboratory
LSRE/LCM,

Department of Chemical Engineering, Faculty of Engineering, University of
Porto,

Rua Dr. Roberto Frias s/n, Porto 4200-465, Portugal

Tel. 0086-021-64252171          
Email: wuyijiang@ecust.edu.cn

Ethanol, which can be produced from
renewable biomass resources, is an ideal feedstock for H₂
production, and the overall reaction of ethanol steam reforming can be
described as:

CH₃CH₂OH(g)+3H₂O(g)↔6H₂(g)+2CO₂(g)
(¦¤H⁰_298K = +173.3 kJ∙mol^-1)   (1)

However, the product
stream always contains a large amount of CO₂, and other undesired
products from side reactions. By using an adsorptive reactor, where steam
reforming reaction with in-situ CO₂ adsorption taking place,
the thermodynamic equilibrium can be shifted towards the product side, which is
known as sorption-enhanced reaction process (SERP) (Hufton
et al., 1999). Most researches have focused on the reaction stage where SERP
was performed with different catalysts and adsorbents, while the cyclic
operation process for H₂ production from SERP with ethanol as
feedstock is yet to be developed and improved.

In this work, a
two-dimensional reactor model developed in our previous work (Wu et al., 2014a)
has been employed, since the temperature gradient in radial direction is found
able to affect the H₂ production performance comparing with the
one-dimensional reactor model (Wu et al., 2014b) where the effect of radial
temperature difference is ignored. A model considering multi-compound and
overall mass balance, Ergun relation for pressure drop, energy balance for the
bed-volume element, and nonlinear adsorption equilibrium isotherm coupled with
reactions to describe coupled mass, momentum and heat transport phenomena
within the adsorptive reactor. Numerical solution of model equations for the
cyclic process was obtained by orthogonal collocation with finite elements
method. Besides, Ni-based hydrotalcite (Wu et al.,
2013b) has been used as the reforming catalyst and the high temperature CO₂
adsorbent employed is the K-promoted hydrotalcite (Wu
et al., 2013a), as shown in Fig.1.

Figure
1 2D reactor model used in this work

The
effect of different operating strategies on the performance of cyclic pressure
swing sorption-enhanced ethanol steam reforming for high-purity H₂
production has been investigated. The feasibility and effectiveness of
conventional pressure swing SERP operating procedure and the use of reactive
regeneration (with 10% of H₂ in the feed during the regeneration
step) instead of direct steam purge developed by (Xiu
et al., 2002) have been investigated. A schematic diagram is illustrated in the
following Figure 2.

Figure
2 Schematic diagram of the cyclic operation
for sorption-enhanced ethanol steam reforming

The
simulation of a cyclic pressure swing process has been constructed accordingly
with the following steps:

l  Reaction
(co-currently to feed). Sorption-enhanced reaction process at p_H;

l  Depressurization
(counter-currently to feed).  Pressure of the column is reduced to
atmospheric pressure (p_L);

l  Regeneration
(counter-currently to feed). Regenerating the CO₂ sorbent by steam
(y_H2O = 100%) or steam with hydrogen (y_H2O = 90% and y_H2
= 10%) at p_L;

l  Purge
(counter-currently to feed). Purging the column with H₂ and steam
gas-mixture (y_H2 = y_H2O = 50%) with a pressure increase
to p_H before the next cycle.

Finally, the effects of
operating conditions (reaction temperatures, pressures, length of each step,
feeding flow rate as well as the used of reactive regeneration) on the hydrogen
purity, productivity and energy efficiency have been investigated by numerical
simulation. High purity H₂ product (> 99 mol%,
dry basis) with traces of CO content (< 30 ppm) can be produced directly
from the pressure swing adsorptive reactor.

References

Hufton,
J.R., Mayorga, S., Sircar,
S., 1999.
Sorption-enhanced reaction process for hydrogen production.
AIChE J. 45, 248-256.

Rohland, B., Plzak, V., 1999. The PEMFC-integrated CO oxidation °ª a
novel method of simplifying the fuel cell plant. J. Power Sources 84, 183-186.

Wu,
Y.-J., Li, P., Yu, J.-G., Cunha, A.F., Rodrigues, A.E., 2013a. K-Promoted Hydrotalcites for CO2 Capture in Sorption Enhanced
Reactions. Chem. Eng. Technol. 36, 567¨C574.

Wu,
Y.-J., Li, P., Yu, J.-G., Cunha, A.F., Rodrigues, A.E., 2013b. Sorption-enhanced
steam reforming of ethanol on NiMgAl multifunctional
materials: experimental and numerical investigation. Chem. Eng. J. 231, 36-48.

Wu,
Y.-J., Li, P., Yu, J.-G., Cunha, A.F., Rodrigues, A.E., 2014a. Sorption-enhanced
steam reforming of ethanol For Continuous High-Purity Hydrogen Production: 2D
Adsorptive Reactor Dynamics and Process Design. Chem. Eng. Sci. 118, 83-93.

Wu,
Y.-J., Li, P., Yu, J., Cunha, A.F., Rodrigues, A.E., 2014b. High-Purity Hydrogen
Production by Sorption-Enhanced Steam Reforming of Ethanol: A Cyclic Operation
Simulation Study. Ind. Eng. Chem. Res. 53, 8515¨C8527.

Xiu,
G.-h., Li, P., E. Rodrigues, A., 2002. Sorption-enhanced
reaction process with reactive regeneration. Chem.
Eng. Sci. 57, 3893-3908.