Thermal conversion efficiency of producing hydrogen enriched syngas from biomass steam gasification

This paper presents the results from an experimental study on the energy conversion efficiency of producing hydrogen enriched syngas through uncatalyzed steam biomass gasification. Wood pellets were gasified using a 100 kW_th fluidized bed gasifier at temperatures up to 850 °C. The syngas hydrogen concentration and cold gas efficiency were found to increase with both bed temperature and steam to biomass weight ratio, reaching a maximum of 51% and 124% respectively. The overall energy conversion to syngas (based on heating value) also increased with bed temperature but was inversely proportional to the steam to biomass ratio. The maximum energy conversion to syngas was found to be 68%. The conversion of energy to hydrogen (by heating value) increased with gasifier temperature and gas residence time, but was found to be independent of the S/B ratio. The maximum conversion of all energy sources to hydrogen was found to be 25%.     

High hydrogen content syngas for biofuels production from biomass air gasification: Experimental evaluation of a char-catalyzed steam reforming unit

This work investigates the performance of a reformer reactor for the upgrading of syngas and char derived from a pilot-scale air gasifier. The proposed setup represents a circular approach for the production of hydrogen-rich syngas from air gasification. Specifically, the reforming-unit was operated under a range of temperatures (from 700 °C to 850 °C) and steam flow rates and for each the improvement in producer gas composition and reducing species yield is evaluated. The results highlight that an increase in hydrogen concentration is obtained at higher temperature, moving from 16.2% to 21.3%, without using steam, and to 45.6%, with steam injection on the char-bed, while CO concentration did not follow a monotonic behavior. Moreover, the gas quality index, defined as a ratio between reducing species and inert species, delivered the highest values at the highest temperatures and steam flow rates. These results provide a guide for future gas quality optimization studies.     

Steam reforming of n-heptane for production of hydrogen and syngas

Simultaneous production of hydrogen and syngas from the catalytic reforming of n-heptane in circulating fast fluidized bed reactors (CFFBR) and circulating fast fluidized bed membrane reactors (CFFBMR) is investigated. This paper presents modeling and simulation approach for the analysis of these reformers. Complete conversion of heptane (100%) is attained at high steam to carbon feed ratios and shorter reactor lengths by both configurations. However, the CFFBMR is very efficient in hydrogen production and can produce exit hydrogen yield up to 473.14% higher than the CFFBR. It was found that operating the CFFBMR at the optimal conditions results in a minimum value of hydrogen to carbon monoxide ratio (H₂/CO) within the recommended practical range for the syngas used as a feedstock for the gas to liquid processes (GTL). The results of the sensitivity analysis conducted for the CFFBMR has shown that the reaction side pressure and the feed temperature have significant effects on increasing the heptane conversion (up to 100%) and the temperature effect is stronger than the reaction side pressure effect. Considerable improvement in the hydrogen to carbon monoxide ratio (H₂/CO) has been achieved by increasing the reaction side pressure, while the high feed temperature has negative effect on this ratio. It seems that the practical range of H₂/CO ratio can be achieved by controlling the reformer length and the right combinations of the operating conditions.     

Process simulation and optimization of groundnut shell biomass air gasification for hydrogen-enriched syngas production

In this study, a detailed steady-state equilibrium simulation model was designed using ASPEN Plus software to analyze and assess the efficiency of the groundnut shell biomass air gasification process. The developed model includes three general stages: biomass drying, pyrolysis, and gasification. The predicted results are quite similar to those found in the literature, which is consistent with simulation results being validated against experimental data. The effect of different operating parameters, like the gasification temperature, gasification pressure, and the equivalence ratio (ER), on the syngas composition and H₂/CO ratio is investigated using sensitivity analysis. The findings of the sensitivity analysis revealed that raising the temperature preferred H₂ and CO production, whereas increasing the pressure has favored CO₂ and CH₄ production. Increasing the ER value also boosted CO and CO₂ yield. Moreover, in an effort to optimize the amount of H₂ generated within the process, the sensitivity analysis was used to evaluate the simultaneous effect of operational parameters on the molar fraction of H₂. To maximize H₂ as a desired product, the following operating parameters were achieved: gasification temperature of 894 °C, gasification pressure of 1 bar, and ER of 0.05, resulting in an H₂ molar fraction of 0.64.     

Liquid phase reforming of woody biomass to hydrogen

This work concentrates on the production of H₂ directly from raw biomass through liquid phase reforming in the presence of a liquid base and a solid catalyst. Both precious metal and base metal catalysts were found to be active for the liquid phase hydrolysis and reforming of wood. Pt-based catalysts, particularly Pt–Re, were shown by atomistic modeling to be more selective toward breaking C–C bonds, resulting in a higher selectivity to hydrogen versus methane. Ni-based catalysts were found to prefer breaking C–O bonds, favoring the production of methane. The results showed that at a constant wood concentration, increasing the concentration of base (base to wood ratio) in the presence of Raney Ni catalysts resulted in greater selectivity toward hydrogen. The amount of wood converted to gas was lower due to increased production of undesirable organic acids from the wood at higher base concentrations. It was shown that by modifying Ni-based catalysts with dopants, it was possible to reduce the base concentration while maintaining the selectivity toward hydrogen and increasing wood conversion to gas versus organic acids.     

Hydrogen and/or syngas production by combined steam and dry reforming of methane on nickel catalysts

Two alumina supported Ni catalysts with pore sizes of 5.4 nm and 9 nm were synthetized, characterized and tested in the Combined Steam and Dry Reforming of Methane (CSDRM) for the production of hydrogen rich gases or syngas. The reaction mixture was designed to simulate the composition of real clean biogas, the addition of water being made in order to have molar ratios of H₂O:CO₂ corresponding to 2.5:1, 7.5:1 and 12.5:1. Structural and functional characterization of catalysts revealed that Ni/Al₂O₃ with larger pore size shows better characteristics: higher surface area, lower Ni crystallite sizes, higher proportion of stronger catalytic sites for hydrogen adsorption, and higher capacity to adsorb CO₂. At all studied temperatures, for a CH₄:CO₂:H₂O molar ratio of 1:0.48:1.2, a (H₂+CO) mixture with H₂:CO ratio around 2.5 is obtained. For the production of hydrogen rich gases, the optimum conditions are: CH₄:CO₂:H₂O = 1:0.48:6.1 and 600 °C. No catalyst deactivation was observed after 24 h time on stream for both studied catalysts, and no carbon deposition was revealed on the used catalysts surface regardless the reaction conditions.     

Two-step steam pyrolysis of biomass for hydrogen production

In this study, different char based catalysts were evaluated in order to increase hydrogen production from the steam pyrolysis of olive pomace in two stage fixed bed reactor system. Biomass char, nickel loaded biomass char, coal char and nickel or iron loaded coal chars were used as catalyst. Acid washed biomass char was also tested to investigate the effect of inorganics in char on catalytic activity for hydrogen production. Catalysts were characterized by using Brunauer–Emmet–Teller (BET) method, X-ray diffraction (XRD) analyzer, X-ray fluorescence (XRF) and thermogravimetric analyzer (TGA). The results showed that the steam in absence of catalyst had no influence on hydrogen production. Increase in catalytic bed temperature (from 500 °C to 700 °C) enhanced hydrogen production in presence of Ni-impregnated and non-impregnated biomass char. Inherent inorganic content of char had great effect on hydrogen production. Ni based biomass char exhibited the highest catalytic activity in terms of hydrogen production. Besides, Ni and Fe based coal char had catalytic activity on H₂ production. On the other hand, the results showed that biomass char was not thermally stable under steam pyrolysis conditions. Weight loss of catalyst during steam pyrolysis could be attributed to steam gasification of biomass char itself. In contrast, properties of coal char based catalysts after steam pyrolysis process remained nearly unchanged, leading to better thermal stability than biomass char.     

Comparison of several glycerol reforming methods for hydrogen and syngas production using Gibbs energy minimization

This paper focuses on the comparison of different glycerol reforming technologies aimed to hydrogen and syngas production. The reactions of steam reforming, partial oxidation, autothermal reforming, dry reforming and supercritical water gasification were analyzed. For this, the Gibbs energy minimization approach was used in combination with the virial equation of state. The validation of the model was made between the simulations of the proposed model and both, simulated and experimental data obtained in the literature. The effects of modifications in the operational temperature, operational pressure and reactants composition were analyzed with regard to composition of the products. The effect of coke formation was discussed too. Generally, higher temperatures and lower pressures resulted in higher hydrogen and syngas production. All reforming technologies demonstrated to be feasible for use in hydrogen or synthesis gas production in respect of the products composition. The proposed model showed good predictive ability and low computational time (close to 1 s) to perform the calculation of the combined chemical and phase equilibrium for all systems analyzed.     

Oxidative steam reforming of vacuum residue for hydrogen production

A two-step process for production of hydrogen from vacuum residue has been developed. In the first step, which has already been communicated [18], the residue is reacted with ozone to get oxidized and cracked products. Next, the catalytic oxidative steam reforming of the product obtained after ozonation over a Pt catalyst supported on La₂O₃-CeO₂-γ-Al₂O₃ was carried out. Effects of the operating conditions: the temperature, the steam to carbon ratio and the oxygen to carbon ratio on oxidative steam reforming were investigated. The oxidative steam reforming was efficient at the molar ratio of O₂/C = 0.5, S/C = 4 at 1173 K. Pt catalyst deactivated with time due to coke formation. The catalyst could be regeneration by blowing oxygen through the catalytic bed. Catalysts were characterized by XRD, N₂ adsorption–desorption and thermo gravimetrically to understand the microstructures.     

Structural and catalytic studies of Mg1-xNixO nanomaterials for gasification of biomass in supercritical water for H2-rich syngas production

Nowadays, catalytic supercritical water gasification (SCWG) is undoubtedly used for production of H₂-rich syngas from biomass. The present study reported the synthesis and characterisation of Mg_1-xNi_xO (x = 0.05, 0.10, 0.15, 0.20) nanomaterials that were obtained via self-propagating combustion (SPC) method, and catalysed the SCWG for the first time. It had found that increased the nickel (Ni) content in the catalyst reduced the crystallite size, thus, increased the specific surface area, which influenced the catalytic activity. The specific surface area followed the order of Mg_0.95Ni_0.05O (36.2 m² g⁻¹) < Mg_0.90Ni_0.10O (58.9 m² g⁻¹) < Mg_0.85Ni_0.15O (63.6 m² g⁻¹) < Mg_0.80Ni_0.20O (67.9 m² g⁻¹). From the Rietveld refinement, the Ni that was successfully partial substituted in the cubic crystal structure of MgO resulting in a cell contraction which ascribed the reduction of crystallite size. Increased the amount of Ni also narrowed the pore size distribution ranging between 4.17 nm and 6.23 nm, as well as increased the basicity active site up to 5741.0 μmol g⁻¹ at medium basic strength. All the synthesised nanocatalysts were catalysed the SCWG of OPF (oil palm frond) biomass. Among them, the mesoporous Mg_0.80Ni_0.20O nanocatalyst exhibited the highest total gas volume of 193.5 mL g⁻¹ with 361.7% increment of H₂ yield than that of the non-catalytic reaction.     

Production of renewable hydrogen by steam reforming of tar from biomass pyrolysis over supported Co catalysts

Co catalyst supported on BaAl₁₂O₁₉ (BA) showed higher activity in the steam reforming of tar from the pyrolysis of biomass than those supported on Al₂O₃, ZrO₂, SiO₂, MgO, and TiO₂. Characterization results indicate that the Co metal particles supported on BA had high dispersion, although the surface area of Co/BA was small. High dispersion of Co metal particles on BA can account for the high steam reforming activity, and this high dispersion is related to the strong basicity of the BA surface. Strong basicity of BA and high dispersion of Co metal particles on BA are connected to high H₂O reactivity to form H₂, probably at the interface between Co metal and BA. In addition, the Co/BA catalyst exhibited higher reusability through the coke combustion and the subsequent reduction treatment than the Co/Al₂O₃ catalyst. This is attributed to the suppression of the solid reaction between the oxidized Co and BA.     

Oxidative catalytic steam gasification of sugarcane bagasse for hydrogen rich syngas production

Reactive Flash Volatilization (RFV) is an emerging thermochemical method to produce tar free hydrogen rich syngas from waste biomass at relatively lower temperature (<900 °C) in a single stage catalytic reactor within a millisecond residence time. Here, we show catalytic RFV of bagasse using Ru, Rh, Pd, or Re promoted Ni/Al₂O₃ catalysts under steam rich and oxygen deficient environment. The optimum reaction conditions were found to be 800 °C, steam to carbon ratio = 1.7 and carbon to oxygen ratio = 0.6. Rh–Ni/Al₂O₃ performed the best, resulting in highest hydrogen concentration in the synthesis gas at 54.8%, with a corresponding yield of 106.4 g-H₂/kg bagasse. A carbon conversion efficiency of 99.96% was achieved using Rh–Ni, followed by Ru–Ni, Pd–Ni, Re–Ni and mono metallic Ni catalyst in that order. Alkali and Alkaline Earth Metal species present in the bagasse ash and char, that deposited on the catalyst, was found to enhance its activity and stability. The hydrogen yield from bagasse was higher than previously reported woody biomass and comparable to the microalgae.     

Optimization of hydrogen production from steam reforming of biomass tar over Ni/dolomite/La2O3 catalysts

Industrially, the endothermic process of steam reforming is carried out at the lowest temperature, steam to carbon (S/C) ratio, and gas hourly space velocity (GHSV) for maximum hydrogen (H₂) production. In this study, a three-level three factorial Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was applied to investigate the optimization of H₂ production from steam reforming of gasified biomass tar over Ni/dolomite/La₂O₃ (NiDLa) catalysts. Consequently, reduced quadratic regression models were developed to fit the experimental data adequately. The effects of the independent variables (temperature, S/C ratio, and GHSV) on the responses (carbon conversion to gas and H₂ yield) were examined. The results indicated that reaction temperature was the most significant factor affecting both responses. Ultimately, the optimum conditions predicted by RSM were 775 °C, S/C molar ratio of 1.02, and GHSV of 14,648 h⁻¹, resulting in 99 mol% of carbon conversion to gas and 82 mol% of H₂ yield.     

Dry reforming of model biomass pyrolysis products to syngas by dielectric barrier discharge plasma

Biomass is frequently used to produce CO and H₂ together with undesirable by-products containing CO₂ and liquid tar by pyrolysis and gasification. This leads to decreased energy efficiency and increased maintenance costs. This study investigated the reforming of biogas and tar, respectively, using non-thermal plasma featuring dielectric barrier discharge (DBD). The gas surrogates studied were CH₄ and CO₂, and toluene was used as a substitute for tar. During reforming of biogas, CO or H₂ was added to the CH₄ and CO₂ to investigate their effects on CH₄ and CO₂ conversion. Both the discharge power and gas components influenced the conversion of CH₄ and CO₂. The conversion efficiency of CH₄ and CO₂ and the selectivity of H₂ and CO both increased with the discharge power while reforming the mixture of CH₄ and CO₂. The maximum conversion efficiency of CH₄ and CO₂ and selectivity of CO and H₂ were obtained with a CH₄:CO₂ ratio of 1:2. During reforming of toluene, the conversion efficiency of toluene reached a maximum value of 90% and the production yields of H₂, CO, and CO₂ reached respective maximums of 0.79, 2.24, and 1.51 mol/mol-toluene at a discharge power of 90 W and temperature of 300 °C. Higher temperatures of 400–500 °C did not favour toluene destruction due to the thermal breakdown of the quartz dielectric and the rapid decrease in the discharging intensity. In addition, reaction mechanism for reforming of both biogas and toluene was proposed to improve our understanding of the reforming process in DBD plasma.     

Zirconia-supported tungsten oxides for cyclic production of syngas and hydrogen by methane reforming and water splitting

ZrO₂-supported tungsten oxides were used for cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation). The reduction characteristics of WO₃ to WO₂ and WO₂ to W were examined at various temperatures (1073–1273 K) and reaction times. Significant portions of the tungsten oxides were also reduced by the produced H₂ and CO. The extent of reduction by H₂ varied greatly depending on temperature and WO₃ content and also on the reduction of either WO₃ or WO₂, while that by CO was consistently low. When the overall degree of reduction became sufficiently high, methane decomposition started to proceed rapidly, resulting in considerable carbon deposition and H₂ production. Consequently, the H₂/(CO + CO₂) ratio varied from around 1 to higher than 2. During the repeated cyclic operations with a proper reduction time at a given temperature, the syngas and hydrogen yields decreased gradually while the H₂/(CO + CO₂) ratio remained nearly constant and the carbon deposition was negligible.     

Numerical investigation of a multichannel reactor for syngas production by methanol steam reforming at various operating conditions

A novel multichannel reactor with a bifurcation inlet manifold, a rectangular outlet manifold, and sixteen parallel minichannels with commercial CuO/ZnO/Al₂O₃ catalyst for methanol steam reforming was numerically investigated in this paper. A three-dimensional numerical model was established to study the heat and mass transfer characteristics as well as the chemical reaction rates. The numerical model adopted the triple rate kinetic model of methanol steam reforming which can accurately calculate the consumption and generation of each species in the reactor. The effects of steam to carbon molar ratio, weight hourly space velocity, operating temperature and catalyst layer thickness on the methanol steam reforming performance were evaluated and discussed. The distributions of temperature, velocity, species concentration, and reaction rates in the reactor were obtained and analyzed to explain the mechanisms of different effects. It is suggested that the operating temperature of 548 K, steam to carbon ratio of 1.3, and weight hourly space velocity of 0.67 h⁻¹ are recommended operating conditions for methanol steam reforming by the novel multichannel reactor with catalyst fully packed in the parallel minichannels.     

Thermodynamic analysis of steam reforming of ethanol and glycerine for hydrogen production

In the past few years there has been a growing interest in environmentally clean renewable sources for hydrogen production. In this context new technologies have been developed for ethanol and glycerine reforming. Hydrogen production varies significantly according to the operating conditions such as pressure, temperature and feed reactants ratio. The thermodynamic analysis provides important knowledge about the effects of those variables on the process of ethanol and glycerine reforming. The present work was aimed at analyzing the thermodynamic steam reforming of ethanol and glycerine, using Gibbs free energy minimization using actual temperature and pressure data found in the literature. The nonlinear programming model was implemented in GAMS^® and the CONOPT2 solver was used to solve the equations. The ideality in gaseous phase and the formation of solid carbon was considered. The methodology used reproduced the most relevant papers involving experimental studies and thermodynamic analysis.     

Biomass to hydrogen-rich syngas via catalytic steam reforming of bio-oil

Hydrogen-rich syngas production from the catalytic steam reforming of bio-oil from fast pyrolysis of pinewood sawdust was investigated by using La_1−xK_xMnO₃ perovskite-type catalysts. The effects of the K substitution, temperature, water to carbon molar ratio (WCMR) and bio-oil weight hourly space velocity (W_bHSV) on H₂ yield, carbon conversion and the product distribution were studied in a fixed-bed reactor. The results showed that La_1−xK_xMnO₃ perovskite-type catalysts with a K substitution of 0.2 gave the best performance and had a higher catalytic activity than the commercial Ni/ZrO₂. Both high temperature and low W_bHSV led to higher H₂ yield. However, excessive steam reduced hydrogen yield. For the La_0.8K_0.2MnO₃ catalyst, a hydrogen yield of 72.5% was obtained under the optimum operating condition (T = 800 °C, WCMR = 3 and W_bHSV = 12 h⁻¹). The deactivation of the catalysts mainly was caused by coke deposition.     

Steam reforming of gasification-derived tar for syngas production

In this study, the steam reforming of tar was catalyzed by dolomite, Ni/dolomite, and Ni/CeO₂ for syngas production under different reaction temperature and weight hourly space velocity (WHSV, h⁻¹). The tar was the major side product from the biomass gasification.     

Stepwise production of syngas and hydrogen through methane reforming and water splitting by using a cerium oxide redox system

Stepwise production of syngas and hydrogen from ZrO₂-supported CeO₂ through methane reforming and water splitting was investigated in order to find proper operating conditions under which carbon deposition could be minimized. Recommendable operating temperature and time were 1073 K and 30 min for both the methane reforming and the water splitting. Even though the H₂/CO ratio during the methane reforming was maintained close to the desired ratio of 2, undesirable methane cracking occurred to a small extent and further reduction of Ce₂O₃ to metallic Ce by CH₄ and H₂ occurred to some extent. When the methane reforming-water splitting cyclic operations were repeated, the yields of syngas and hydrogen decreased considerably from the first cycle to the second cycle, but from the second cycle to the fifth cycle the gas yields were maintained nearly constant. As the CeO₂ content in the sample increased, the gas yields per mole of CeO₂ decreased but the gas productions per gram of sample increased.