The objective of this review is to analyze potential technologies and their baseline performance of producing hydrogen from catalytic steam reforming of biodiesel byproduct glycerol. High oxygen ...content and high impurity level of biodiesel byproduct glycerol, as well as the complex intermediates and high coking potential in its thermal degradation, make the modeling, design, and operation of glycerol steam reforming a challenge. Thermal decomposition characterization of biodiesel byproduct glycerol was covered, and the recent developments and methods for high-purity hydrogen production from glycerol steam reforming were illustrated. The thermodynamics constraint of water gas shift reaction can be overcome by the sorption-enhanced steam reforming process, which integrated catalytic steam reforming, water gas shift reaction and in-situ CO2 removal at high temperatures in a single stage reactor. The effectiveness of both the enhanced H2 production and the use of CO2 sorbents have been demonstrated and discussed. The technical challenges to achieve a stable high-purity hydrogen production by the sorption-enhanced steam reforming process included extending operation time, selecting suitable sorbents, finding a way for continuous reaction-regeneration of catalyst and sorbent mixture and improving process efficiencies. The continuous sorption-enhanced steam reforming of glycerol was designed by a simultaneous flow concept of catalyst and sorbent for continuous reaction-regeneration using two slow moving-bed reactors for high-purity hydrogen production and CO2 capture, and in this process, catalyst and sorbent were run in nearly fresh state for H2 production. The sorption-enhanced chemical-looping reforming was also demonstrated. The paper discusses some issues and challenges, along with the possible solutions in order to help in efficient production of hydrogen from catalytic steam reforming of biodiesel byproduct glycerol.
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Sorption-enhanced chemical-looping steam reforming in an alternating fixed-bed reactor.
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•Efficient SE-CLSR was experimentally demonstrated in alternating fixed-bed reactor.•Sorbent to ...catalyst ratio dependencies during SE-CLSR were determined.•The superior molar ratio of Ca/Ni in OC and sorbent was to be 2.0–3.0 in SE-CLSR.•Alternating multiple cycles’ SE-CLSR demonstrated remarkable stability with 90% H2.
In this study, the effects of sorbent addition for in-situ CO2 removal on hydrogen production by sorption-enhanced chemical looping steam reforming (SE-CLSR) of ethanol have been evaluated in an alternating fixed-bed reactor using a mixture of NiO/Al2O3 oxygen carrier catalyst (OC) and CaO based sorbent at moderate operating conditions (T: 600 °C, P: 1.0 atm and S:C: 3.0). The experimental data were compared with chemical equilibrium analysis based on the minimization of Gibbs free energy. The results demonstrated that NiO component in the OC was first reduced by ethanol and the reduced OC was responsible of catalytic steam reforming and water gas shift (WGS) for hydrogen production. The CO2 produced was efficiently removed by CaO based sorbent, also resulting in the process intensification considerably. It appears that the superior molar ratio of sorbent to OC (Ca/Ni) is to be 2.0–3.0 and the highest hydrogen selectivity and feeding conversion were obtained at 3.0 of Ca/Ni ratio. Hydrogen production was inhibited using further high Ca/Ni ratio due to the OC particles were surrounded and diluted by sorbent. The exothermic reactions also provided the heat to raise the temperature of the reactor. In-situ CO2 removal by solid sorbent promotes ethanol dehydration and CC carbon bonds cleavage, and thus, the hydrogen production route of conventional CLSR is changed. Continuous high-purity hydrogen production was achieved by integrating the oxidization, steam reforming, WGS, and in situ CO2 capture in an alternating fixed-bed reactor.
The gas-solid reaction and breakthrough curve of CO(2) capture using calcium oxide sorbent at high temperature in a fixed-bed reactor are of great importance, and being influenced by a number of ...factors makes the characterization and prediction of these a difficult problem. In this study, the operating parameters on reaction between solid sorbent and CO(2) gas at high temperature were investigated. The results of the breakthrough curves showed that calcium oxide sorbent in the fixed-bed reactor was capable of reducing the CO(2) level to near zero level with the steam of 10 vol%, and the sorbent in CaO mixed with MgO of 40 wt% had extremely low capacity for CO(2) capture at 550°C. Calcium oxide sorbent after reaction can be easily regenerated at 900°C by pure N(2) flow. The experimental data were analyzed by shrinking core model, and the results showed reaction rates of both fresh and regeneration sorbents with CO(2) were controlled by a combination of the surface chemical reaction and diffusion of product layer.
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•New approach on continuous high-purity H2 produced auto-thermally with long time.•Low-cost NiO/NiAl2O4 exhibited high redox performance to H2 from glycerol.•Oxidation, steam ...reforming, WSG and CO2 capture were combined into a reactor.•H2 purity of above 90% was produced without heating at 1.5–3.0 S/C and 500–600°C.•Sorbent regeneration and catalyst oxidization achieved simultaneously in a reactor.
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.
The pyrolysis of the crude glycerol from a biodiesel production plant was investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy. The main gaseous products are ...discussed, and the thermogravimetric kinetics derived. There were four distinct phases in the pyrolysis process of the crude glycerol. The presence of water and methanol in the crude glycerol and responsible for the first decomposition phase, were shown to catalyse glycerol decomposition (second phase). Unlike the pure compound, crude glycerol decomposition below 500
K leaves behind a large mass fraction of pyrolysis residues (ca. 15%), which eventually partially eliminate in two phases upon reaching significantly higher temperatures (700 and 970
K, respectively). An improved iterative Coats–Redfern method was used to evaluate non-isothermal kinetic parameters in each phase. The latter were then utilised to model the decomposition behaviour in non-isothermal conditions. The power law model (first order) predicted accurately the main (second) and third phases in the pyrolysis of the crude glycerol. Differences of 10–30
kJ/mol in activation energies between crude and pure glycerol in their main decomposition phase corroborated the catalytic effect of water and methanol in the crude pyrolysis. The 3-D diffusion model more accurately reproduced the fourth (last) phase, whereas the short initial decomposition phase was poorly simulated despite correlation coefficients ca. 0.95–0.96. The kinetics of the 3rd and 4th decomposition phases, attributed to fatty acid methyl esters cracking and pyrolysis tarry residues, were sensitive to the heating rate.
•Advances in OCs for chemical-looping water splitting were critically reviewed.•Characteristics of different OCs were compared based on metal oxide redox reactions.•Effects of supports and additives ...on the performances of OCs were discussed.•Issues and challenges for development of OCs were analyzed.
Chemical looping water splitting (CLWS) process using metal oxides or perovskites as oxygen carriers (OCs), is capable of producing pure H2 in an efficient, simple, and flexible way. The OCs are first reduced by hydrocarbon fuels and then oxidized by steam in a cyclic way. After the condensation of the gaseous mixture of steam and H2 from the oxidation step, pure H2 is obtained. In recent years, great efforts for CLWS have been made to improve the redox activity and stability of OCs. In this paper, the development of the OCs for hydrogen production from CLWS were discussed. Effects of supports and additives on the performances of OCs were compared based on redox reactions in CLWS. Fe-based OCs with CeO2, Al2O3, ZrO2, CuO, MoO3, Rh etc. are very attractive for the CLWS process. Issues and challenges for the development of OCs were analyzed.
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In this study, the activity of Ni-Cu-Al based catalyst for renewable hydrogen production from glycerol steam reforming has been evaluated in a continuous flow fixed-bed reactor under atmospheric ...pressure at 500-600 degree C. The catalyst synthesized by the co-precipitation method with rising pH technique was characterized by the elemental analysis, Brenauer-Emmett-Teller (N2-BET) adsorption method, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and thermogravimetric analysis (TGA). The thermodynamic analysis for glycerol steam reforming was conducted by using a non-stoichiometric methodology based on the minimization of Gibbs free energy. The obtained results revealed that the great quantity of hydrogen is produced at excess water and the formations of CH4 and CO in the glycerol steam reforming were almost negligible. The deactivation of catalyst due to the formation of carbon residues was observed. The carbons removal was measured by TGA experiment during medium temperature oxidation conditions. The kinetics on glycerol steam reforming was described by means of the separability concept of reaction rate law and deactivation model, and the kinetic parameters were calculated.
CO2 flooding is used extensively as a commercial process for enhanced oil recovery. In this study, the visualization of CO2 flooding in immiscible and miscible displacements in a high-pressure ...condition was studied using a 400 MHz MRI system. For CO2 immiscible displacement, the phenomenon of CO2 channelling or fingering was obviously due to the difference in fluid viscosities and densities. Thus, the sweep efficiency was small, and the final residual oil saturation was 37.2%. For CO2 miscible displacement, the results showed that pistonlike displacement occurred, and the phenomenon of the miscible regions and CO2 front was obvious. The viscous fingering and gravity override caused by the low viscosity and density of the gas were restrained effectively, and the velocity of the CO2 front was uniform. The sweep efficiency was high, and the final residual oil saturation was 13.5%, indicating that CO2 miscible displacement could recover more oil compared with CO2 immiscible displacement. Finally, the average velocity of the CO2 front was evaluated by analyzing the oil saturation profile. A special core analysis method was applied to in situ oil saturation data to directly evaluate the effect of viscosity, buoyancy, and capillary pressure on CO2 miscible displacement.
•It is a discussion on the combination of hydrate-based gas capture and desalination.•3 Experimental procedures were used and evaluated to promote hydrate formation.•It is found that the primary way ...to avoid blockage is heating.•Taking the cost of pressure into account, 5.00MPa is a better value for application.
The purpose of this study was to obtain the characteristics of CO2 hydrate formation and dissociation by using different experimental modes and pressures with glass beads. From the experiments, it was found that hydrate forms rapidly in each cycle, especially at high pressure. Hydrate blockage rarely appeared during hydrate formation and dissociation when applying gas flow (Case 2); this approach was significantly better than the other two experimental modes. The maximum hydrate saturations for the three experimental modes were 28%, 24% and 67.5%. The overall hydrate saturation of Case 3 was significantly better than those of the other two cases. When a heating process was applied to induce hydrate dissociation, the rapid backpressure decrease led to migration of the pore solution during depressurization. The minimal residual water after hydrate formation resulted in consistent residual water saturation after hydrate dissociation for Case 2. Considering hydrate saturation and operating pressure, 5.00MPa is a better choice for hydrate-based desalination and CO2 capture. If the initial residual solution can be completely converted to hydrate, this technology has potential for industrial applications.
In this study, the continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production by a simultaneous flow concept of catalyst and sorbent for reaction and regeneration ...using two moving-bed reactors has been evaluated experimentally. A Ni-based catalyst (NiO/NiAl2O4) and a lime sorbent (CaO) were used for glycerol steam reforming with and without in-situ CO2 removal at 500 °C and 600 °C. The simultaneous regeneration of catalyst and sorbent was carried out with the mixture gas of N2 and steam at 900 °C. The product gases were measured by a GC gas analyzer. It is obvious that the amounts of CO2, CO and CH4 were reduced in the sorption-enhanced steam reforming of glycerol, and the H2 concentration is greatly increased in the pre-CO2 breakthrough periods within 10 min both 500 °C and 600 °C. The extended time of operation for high-purity hydrogen production and CO2 capture was obtained by the continuous sorption-enhanced steam reforming of glycerol. High-purity H2 products of 93.9% and 96.1% were produced at 500 °C and 600 °C and very small amounts of CO2, CH4 and CO were formed. The decay in activity during the continuous reaction-regeneration of catalyst and sorbent was not observed.
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•High-purity H2 from glycerol steam reforming with in-situ CO2 capture is evaluated.•New approach on continuous high-purity H2 production with long time is proposed.•Simultaneous flow of catalyst and sorbent for reaction-regeneration is feasible.•Catalyst and sorbent are always run in nearly fresh state for H2 production.•Same regeneration conditions of catalyst and sorbent does not lead to great decay.
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