Sorption-Enhanced Steam Reforming of Glycerol for Hydrogen

Oct 28, 2015 - University of Technology, Guangzhou, Guangdong 510006, People's Republic of China. ‡. Artie McFerrin Department of Chemical Engineeri...
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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

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Guangdong University of Technology, Guangzhou 510006, China;

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§

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;

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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