Chemical Looping Steam Reforming Research Articles

Effect of support on hydrogen production from chemical looping steam reforming of ethanol over Ni-based oxygen carriers

The Ni-based oxygen carriers (OCs) with different supports including alloy Ni/Al2O3, lamellar Ni/MMT, mesoporous Ni/Al-MCM-41 and mesoporous Ni/SBA-15 were synthesized. The effect of support on hydrogen production from chemical looping steam reforming (CLSR) of ethanol was investigated in a fixed-bed reactor. The oxygen carriers were characterized by some techniques, including N2 adsorption–desorption, XRD, TEM, ICP-OES, H2 pulse chemisorption, H2-TPR, and TG-DTG. It was observed that Ni/SBA-15 exhibited most efficient confinement effect followed by Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3 via: 1) small nickel particle size and high dispersion as well as strengthened metal-support interaction; 2) sintering resistance due to spatial restriction of support; 3) anti-coke capability derived from small nickel particles and ordered diffusion routes for reactants and products. In addition, the silica supported OCs were conductive to promote water gas shift (WGS) reaction but the supports containing Al atoms were prone to coke deposition due to the formation of acid sites. The ‘dead time’ and oxygen transfer capacity reflected that the redox performance of oxygen carriers was listed in the following order: Ni/SBA-15, Ni/Al-MCM-41, Ni/MMT and Ni/Al2O3. Ni/Al-MCM-41 exhibited excellent activity in initial cycle of CLSR but the collapse of the Ni/Al-MCM-41 structure for its weak thermo stability leaded to the deactivation and sintering of active phase. The Ni/SBA-15 and lamellar Ni/MMT OCs exhibited superior activity and stability but the performance of Ni/Al2O3 OCs was mediocre.

Hydrogen production from chemical looping steam reforming of glycerol by Ni based Al-MCM-41 oxygen carriers in a fixed-bed reactor

This paper describes the synthesis of a series of Ni based Al-MCM-41 oxygen carriers with and without Ce promoter and their application in chemical looping steam reforming of glycerol. The Al-MCM-41 is derived from montmorillonite. The oxygen carriers were prepared by direct-synthesis and post-synthesis method. A variety of technologies including N2 adsorption-desorption, X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), H2 temperature-programmed reduction (H2-TPR), and transmission electron microscopy (TEM) were conducted to characterize the fresh and used oxygen carriers. The results show the direct-synthesis oxygen carrier possesses excellent textual properties, such as high Ni loading, small particle size, large pore volume, and uniform pore size. The incorporation of Ce could effectively control particle size via strong metal support interaction, promote the homogeneous distribution of Ni, and enhance oxygen mobility capability and water gas shift reaction. And thus shorten ‘dead time’ during the fuel feed step. The CeNi/Al-MCM-41 displayed the superior activity and excellent long-term stability, which could be due to the strengthened anti-sintering and coke capability.

Renewable hydrogen production from chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers in a fixed-bed reactor

Chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers was carried out at 650 °C under atmospheric pressure in a fixed-bed reactor. The mesoporous support SBA-15 was synthesized via hydrothermal method and the xCeNi/SBA-15 oxygen carriers were prepared by encapsulating CeO2 and NiO nanoparticles in SBA-15 using surfactant-assisted iso-volumetric impregnation method. Some techniques were conducted to characterize the oxygen carriers, including N2 adsorption–desorption, XRD, TEM, H2-TPR, ICP-OES, and DSC-TGA. It was observed that all the oxygen carriers exhibited high specific surface area (>435 m2/g) and large pore volume (>0.64 cm3/g). Small NiO particle size (e.g. 3.2 nm for 12CeNi/SBA-15), high dispersion and strengthened metal-support interaction were achieved by the CeO2 promotion. The ceria promoter not only inhibited the coke formation but facilitated the removal of coke deposition, and the coke deposition could be further eliminated in the air feed step, both of which resulted in long-term stability. Meanwhile, superior redox performance and shorter ‘dead time’ (e.g. 30 s for 12CeNi/SBA-15) were achieved on account of easier reducibility of NiO particles with increasing amount of CeO2. The oxygen carriers exhibited superior sinter resistance capacity and high activity and stability in CLSR process. The highest ethanol conversion (90.0%) and hydrogen selectivity (84.7%) were obtained for 12CeNi/SBA-15 even after 14 cycle stability test.

Hydrogen production by chemical looping steam reforming of ethanol using NiO/montmorillonite oxygen carriers in a fixed-bed reactor

Hydrogen production by chemical looping steam reforming of ethanol using oxygen carriers was carried out in a fixed-bed reactor. NiO/montmorillonite prepared by ultrasound assisted cation exchange impregnation method was used as oxygen carriers. The synthesized NiO/montmorillonite was characterized by N2 adsorption–desorption, inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), H2 pulse chemisorption, temperature-programmed reduction (TPO) and thermal gravimetric analysis (TGA). The characterization results showed the particle size, metal-support interaction, nickel dispersion interrelated with cation exchange capability and confinement effect of montmorillonite’s lamellar structure. Activity and stability tests were conducted at 550°C with a steam to carbon ratio of 4. The results showed that 20Ni–MMT possessed the best performance due to its strong sintering and coking resistance, and also presented the shortest ‘dead time’ due to its larger active surface area. Moreover, 20Ni–MMT exhibited the excellent coke elimination ability in the air feed step.

Hydrogen production by chemical looping steam reforming of methane over Mg promoted iron oxygen carrier: Optimization using design of experiments

In the chemical looping reforming (CLR) process, methane is converted to hydrogen and carbon monoxide through cyclic reduction–oxidation reactions of fuel with active lattice oxygen (O2−) of an oxygen carrier. In this research, Mg promoted iron based oxygen carrier was used in the process. The response surface method (RSM) based on Box–Behnken design was applied to examine the operating conditions of chemical looping steam methane reforming process. Independent variables including reaction temperature (550–750°C), Mg loading (0–10%) and oxygen carrier preparation method (co-impregnation and sequential impregnation methods) were selected for investigation and optimization of methane conversion, hydrogen production yield and CO/CO2 molar ratio using RSM. The characterization of samples was accomplished by means of X-ray diffraction (XRD), N2 adsorption–desorption (BET test) and transmission electron microscope (TEM). The Design expert software suggested several optimized solutions; among them, the best choice was 15Fe/5Mg/Al2O3 oxygen carrier synthesized with sequential impregnation method at reaction temperature of 650°C. However, 15Fe/5Mg/Al2O3 oxygen carrier is consistently stable in chemical looping reforming with high hydrogen producing capacity over redox cycles.

Hydrogen production from chemical looping steam reforming of glycerol by Ni-based oxygen carrier in a fixed-bed reactor

Hydrogen production from chemical looping steam reforming (CLSR) of glycerol was studied by Ni-based oxygen carrier in a fixed-bed reactor. For the fixed-bed reactor configuration, solid Ni-based oxygen carrier is stationary and alternatively exposed to reducing and oxidizing conditions by periodically switching the feed gases. The Ni-based oxygen carrier was prepared by a liquid-state co-precipitation method with rising pH technique and the characterization was performed by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption–desorption. Gaseous products and temperature variety during CLSR process by Ni-based oxygen carrier in a fixed-bed reactor were measured, and the thermodynamic equilibrium calculation was also carried out. The results showed that the Ni-based oxygen carrier synthesized has a dual function and can efficiently convert glycerol and steam to H2 by redox reactions. The coexisting reactions of glycerol oxidization (or NiO reduction) and steam reforming occurred before the steady stage of hydrogen production in the fuel feed step, and the conversion of NiO to Ni was obtained. Alternating reduction and oxidation reactions enabled Ni-based oxygen carrier to produce H2 with a concentration of 85% of the equilibrium value at 600°C, and glycerol conversion was up to 99%. The increase of temperature related to the exothermic reactions by Ni-based oxygen carrier in CLSR process was observed in redox cycles.

Hydrogen production by enhanced-sorption chemical looping steam reforming of glycerol in moving-bed reactors

The continuous high-purity hydrogen production by the enhanced-sorption chemical looping steam reforming of glycerol based on redox reactions integrated with in situ CO2 removal has been experimentally studied. The process was carried out by a flow of catalyst and sorbent mixture using two moving-bed reactors. Various unit operations including oxidation, steam reforming, water gas shrift reaction and CO2 removal were combined into a single reactor for hydrogen production in an overall economic and efficient process. The low-cost NiO/NiAl2O4 catalyst efficiently converted glycerol and steam to H2 by redox reactions and the CO2 produced in the process was simultaneously removed by CaO sorbent. The best results with an enriched hydrogen product of above 90% in auto-thermal operation for reforming reactor were achieved at initial temperatures of 500–600°C and ratios of steam to carbon (S/C) of 1.5–3.0. The results indicated also that not all of NiO in the catalyst can be reduced to Ni by the reaction with glycerol, and the reduced Ni can be oxidized to NiO by air at 900°C. The catalyst oxidization and sorbent regeneration were achieved under the same conditions in air reactor.

Hydrogen enrichment of fuels using a novel miniaturised chemical looping steam reformer

Experiments were conducted on the Fe 3O 4/FeO metal oxide system under pure methane and pure steam environments in a thermogravimetric analyser (TGA) and a prototype-miniaturised micro-reactor. Experimental results show that during a typical fuel oxidation step the concentration of methane in the product gas stream gradually decreases while Fe 3O 4 is being reduced to FeO. However, on or about a fractional conversion of 60% the slope of the CH 4 plot sharply increases due to catalytic effects of FeO on methane decomposition. Similarly, the H 2 plot associated with steam reforming step picks up rapidly and reaches a maximum of 98% at a fractional conversion of 30%. The conversion times of steam and fuel in the micro-reactor were generally shorter than conversion times obtained in the TGA system. The experimental results provided two vital pieces of information: (i) the chemical looping steam reforming cycle is technically viable, and (ii) the performance of the process at micro-scales needs to be further understood before high throughput miniaturised reformers could be designed and built.

Waste Lubricating Oil as a Source of Hydrogen Fuel using Chemical Looping Steam Reforming

Initial results are presented for the production of hydrogen from waste lubricating oil using a chemical looping reforming (CLR) process. The development of flexible and sustainable sources of hydrogen will be required to facilitate a 'hydrogen economy'. The novel CLR process presented in this paper has an advantage over hydrogen production from conventional steam reforming because CLR can use complex, low value, waste oils. Also, because the process is scalable to small and medium size, hydrogen can be produced close to where it is required, minimising transport costs. Waste lubricating oil typically contains 13-14% weight of hydrogen, which through the steam reforming process could produce a syngas containing around 75 vol% H , representing over 40 wt% of the fuel. The waste oil was converted to a hydrogen rich syngas in a packed bed reactor, using a Ni/ Al O catalyst as the oxygen transfer material (OTM). An oil conversion rate based on carbon species (CO, CO and CH 4) of up to ~95% was achieved. The steam to hydrogen conversion of 53%, accounted for 63% of the total H produced, compared to the theoretical ideal of 67.4%. The syngas composition was initally >65 vol% H , 15 vol% CO, 15 vol% CO , and <5 vol% CH . Deterioration of the reactants conversion, specifically steam, was observed over repeated cycles indicating fouling of the catalyst. This was not by carbonaceous deposits, which were eliminated during the cycle's alternated oxidation steps, but could be by trace additives within the lubricating oil. Further work is planned in order to overcome this issue.

Hydrogen Production via Chemical Looping Steam Reforming in a Periodically Operated Fixed-Bed Reactor

Chemical-looping steam reforming (CLSR) is a chemical-looping combustion (CLC) derived technology in which air is replaced by steam as oxidant. CLSR combines the inherent CO2 capture of CLC with the production of PEMFC-ready hydrogen streams without further purification steps. CLSR thus results in strong process intensification in hydrogen production. Here, we present results from a proof-of-concept study of CLSR of synthesis gas which combines thermodynamic screening for carrier selection, with synthesis and reactive test of highly active and high-temperature stable nanostructured oxygen carriers, and a reactor modeling study in order to demonstrate the feasibility of CLSR in a periodically operated fixed-bed reactor.