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Sorption-enhanced steam reforming of glycerol for hydrogen production over NiO/NiAl2O4 catalyst and Li2ZrO3 based sorbent Chao Wang, Ying Chen, Zhengdong Cheng, Xianglong Luo, Lisi Jia, Mengjie Song, Bo Jiang, and Binlin Dou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01941 • Publication Date (Web): 28 Oct 2015 Downloaded from http://pubs.acs.org on October 29, 2015
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Sorption-enhanced steam reforming of glycerol for hydrogen
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production over NiO/NiAl2O4 catalyst and Li2ZrO3 based sorbent
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Chao Wang*,†, Ying Chen†, Zhengdong Cheng†, , Xianglong Luo†, Lisi Jia†,
‡
§
Mengjie Song†, Bo Jiang , Binlin Dou
4 5
†
6
Guangdong University of Technology, Guangzhou 510006, China;
7 8 9 10
‡
§
Guangdong Provincial Key Laboratory on Functional Soft Condensed Matter, School of Materials and Energy,
Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122,
USA; §
School of Energy and Power Engineering, Key Laboratory of Ocean Energy Utilization and Energy Conservation
of Ministry of Education, Dalian University of Technology 116023, Dalian, China;
11 12
Abstract: This paper describes the synthesis and application of NiO/NiAl2O4 catalyst
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and Li2ZrO3 based sorbent in sorption enhanced glycerol steam reforming.
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NiO/NiAl2O4 catalyst was prepared by incipient wetness impregnation and
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co-precipitation method using rising pH technique, the NiAl2O4 crystalline spinel in
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the catalyst was formed under high calcination temperature of 900oC. The K doped
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Li2ZrO3 sorbent was prepared by solid state method. The synthesized catalyst and
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sorbent were evaluated for H2 production and CO2 removal, respectively. Sorption
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enhanced reforming (SER) hydrogen production possessing high initial H2 purity with
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CO2 removal was carried out during multicycle reaction/regeneration process under
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550oC and steam-to-carbon ratio of 3. CO2 sorption capacity of Li2ZrO3 sorbent was
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decreased with increasing cycle number in SER. A kinetic model was proposed to
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understand the isothermal kinetics for multicycle SER CO2 sorption over K-Li2ZrO3
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sorbent, and the breakthrough curves for each cycle were fitted based on the derived
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kinetic parameters.
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Keywords: Glycerol steam reforming; Hydrogen production; NiO/NiAl2O4 catalyst;
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Li2ZrO3 sorbent; In-situ CO2 removal.
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1. Introduction
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With the diminishing reserves of conventional fossil fuels, it is an urgent to
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develop sustainable energy resources. An increasing biodiesel production all over the
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world from the last decade has led to a great increment of glycerol production. In
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general, for every kilogram of biodiesel produced, about 10wt% of crude glycerol is
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produced.1 Various methods for disposal and utilization of this produced glycerol have
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been attempted, including combustion, composting, anaerobic digestion, animal feeds,
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and thermo-chemical/biological conversions to value-added products. Especially in
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the case of large-scale production, the use of glycerol as a source of hydrogen
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provides a possible solution for the dilemma.2 A widely established technology, such
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as, steam reforming of glycerol would be most likely adopted for its wide use and
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economic feasibility.3 The gaseous products from the reforming reactor, after
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condensation, go to the purification processes such as a pressure swing adsorption
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(PSA) process to produce high purity H2. Actually, there is significant amount of CO2
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in the equilibrium composition of the conventional reforming reactor. Steam
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reforming of glycerol can produce up to 3mol of CO2 per mole feed glycerol
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theoretically according to the stoichiometric coefficient in the chemical reaction.4
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The thermodynamic limitations of the conventional glycerol steam reforming
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reaction can be circumvented by the ‘‘sorption enhanced’’ method. The sorption
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enhanced reforming (SER) concept was proposed based on the Le Chatelier’s
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principle, and this process combines a reversible gas phase reaction with selective
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removal of certain reaction product from the gas phase of the reaction zone, thereby,
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driving the reaction more to the product side.5 For this method, a selected CO2 sorbent
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is installed together with the catalyst to achieve in-situ CO2 removal. In this way, it is
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possible to obtain products containing higher purity H2 (dry basis) than that of
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conventional steam reforming method.6 This (SER) process has the potential to
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decrease the cost by reducing the operational complexity and the severity of the
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operating conditions for hydrogen purification.7
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For producing high purity hydrogen, SER process involves two main steps including glycerol steam reforming (R1), and CO2 sorption (R2): energy C 3 H 8O 3 + H 2O ← → H 2 , CO 2 , CO , CH
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+ Others
(R1)
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XO + CO2 XCO3 (X: Misadivalent metal: Ca, Mg, Fe etc.)
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By separating CO2 from the products, the equilibrium of the reforming reaction
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(R1) could more favor hydrogen production.8 The SER process has been
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experimentally demonstrated in fixed bed reactor, and several experiments have been
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carried out in fixed bed reactors either with natural or synthetic sorbents.9, 10 It has
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been demonstrated that the solid/gas contact in the reaction bed allows for equilibrium
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compositions in gas product using CO2 sorbent and a reforming catalyst in a certain
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ratio. Dou et al.11 reported hydrogen production from catalytic steam reforming of
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glycerol with in-situ CO2 removal in a fixed-bed reactor over a commercial Ni-based
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catalyst and dolomite as CO2 sorbent, and the results suggested an optimal
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temperature of 500-600oC and S/C (steam to carbon ratio) of 3. He et al.10 achieved
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high-purity hydrogen production by sorption-enhanced steam reforming of glycerol
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with Co-Ni catalysts derived from hydrotalcite-like material and dolomite as CO2
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sorbent at atmospheric pressure, 575oC with S/C of 3.
(R2)
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In fact, the development of SER relies on the performance of the involved
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sorbent and catalyst. To be applied in SER process, the catalyst candidates should be 3 ACS Paragon Plus Environment
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in
multiple
reaction/regeneration
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stable
cycles
(corresponding
to
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carbonation/calcination steps for the sorbent). In our previous studies, Ni based
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catalysts have been investigated to be effective for hydrogen production by glycerol
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steam reforming.12 Ni acting as an active phase has been generally proposed to be
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used in glycerol reforming due its high activity and low price.13,14 Although, Al2O3 is
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commonly used for the catalyst support, carbon deposition or possible reaction
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between Ni and Al2O3 support could cause catalyst deactivation problems during
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steam reforming process.15 Besides, the Ni catalyst exposed to the CO2 sorbent
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regenerating step under high regeneration temperature could make its life time shorter.
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Nickel aluminate spinel (NiAl2O4) is almost inverse spinel with the nickel ion
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preferentially distributing over the octahedral site and it has been proposed to be the
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catalyst support because of its low reactivity with the active phase and its high
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resistance to high temperatures and acidic or basic atmospheres. Some have achieved
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for hydrogen production from glycerol steam reforming using Ni over NiAl2O4 in
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SER process.16
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Considering CO2 sorption, the sorbent candidates should be with an adequate
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CO2 carrying capacity and fast kinetics for CO2 sorption/regeneration. They should
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also be stable with carbonation/calcinations cycles in order to reduce purge
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requirements in the system. Lithium zirconate based sorbents have received much
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attention due to their ability to retain good CO2 chemisorption capacity at high
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temperature.17 Nair et al.18 synthesized Li2ZrO3 using sol-gel method and studied its
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high-temperature CO2 sorption properties. Their results showed this material can store
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significant quantities of CO2 at high temperature, and the reacted sorbent can be
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regenerated by thermal cycling. Rusten et al.19 studied sorption-enhanced steam
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methane reforming with both experiment and simulation method using Li2ZrO3 as
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CO2-acceptor, their results showed that more than 87 mol% of hydrogen purity could
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be produced at a temperature of 848 K with a pressure of 10 bar. From a
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thermodynamic perspective, Li2ZrO3 sorbents are appropriate CO2 sorbent for SER
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process of glycerol steam reforming, since they are able to react at moderate
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temperatures of 450-650oC with low CO2 partial pressures.20 However, the published
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works on hydrogen production in SER process using Li2ZrO3 sorbents are very
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limited.21,22
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As shown, the forward reaction pathway (R3) describes sorption of CO2, whereas
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the reverse reaction path expresses regeneration of the Li2ZrO3 sorbent. Temperature
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swing approaches would be able to change the direction of the reaction:23 o
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o
450 C
