Influence of catalyst and temperature on gasification performance of pig compost for hydrogen-rich gas production

The catalytic steam gasification of pig compost (PC) for hydrogen-rich gas production was conducted in a fixed-bed reactor. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 700–850 °C, for weight hourly space velocity (WHSV) in the range of 0.30–0.60 h⁻¹. The results indicate that the developed NiO on modified dolomite (NiO/MD) catalyst reveals better catalytic performance on the tar elimination and hydrogen yield than calcined MD or NiO/γ-Al₂O₃ catalyst. Meanwhile, the lower WHSV and higher reactor temperature can contribute to more hydrogen production and gas yield. Moreover, the char from catalytic steam gasification of PC has a highest ash content of 75.84% at 850 °C. In conclusion, pig compost is a potential candidate for hydrogen gas production through catalytic steam gasification technology.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

In-situ IR study for elucidating the adsorption cracking mechanism of toluene over calcined olivine catalyst

In order to improve the energy conversion efficiency of hydrogen production from biomass gasification and reduce environmental pollution, it is necessary to study the mechanism of tar catalytic cracking. In present work, in-situ infrared spectroscopy has been used to study the adsorption cracking of toluene on calcined olivine catalyst from room temperature to 500 °C. The experimental results indicate that there is no chemical adsorption of toluene on calcined olivine catalyst from room temperature to 200 °C. When the temperature is higher than about 300 °C, the toluene is chemically adsorbed on α-Fe₂O₃, which is the surface active site of the calcined olivine catalyst. The chemical adsorption occurs between the benzene ring and Fe³⁺, and it promotes the breakage of methyl from the benzene ring. With the increasing of reaction temperature, the delocalization large π bond in the benzene ring is destroyed by Fe³⁺, which makes the benzene ring easier to break into smaller products or intermediate products.     

Hydrogen production by biomass gasification in a fluidized-bed reactor promoted by an Fe/CaO catalyst

Biomass gasification for hydrogen production was performed in a continuous-feeding fluidized-bed with the use of Fe/CaO catalysts. The relationship between catalyst properties and biomass gasification efficiencies was studied. The findings indicated that only CaO was involved in the enhancement of char gasification, resulting in an increased hydrogen production. However, CaO was also easily deactivated by biomass tar. The characterization results indicated that when CaO was impregnated with Fe, Ca₂Fe₂O₅ formed on the surface of the support. Ca₂Fe₂O₅ decomposed polyaromatic tar but was not effective in char gasification. The synergistic effects between Fe and CaO that effectively enhanced biomass gasification mainly involved combustion and pyrolysis, and the biomass gasification products, i.e., char and tar, were further gasified, indicating that tailor-made Fe/CaO catalysts prevented CaO deactivation by tar, thus promoting biomass gasification and hydrogen production.     

Hydrogen production enhancement using hot gas cleaning system combined with prepared Ni-based catalyst in biomass gasification

This paper investigates the hot gas temperature effect on enhancing hydrogen generation and minimizing tar yield using zeolite and prepared Ni-based catalysts in rice straw gasification. Results obtained from this work have shown that increasing hot gas temperature and applying catalysts can enhance energy yield efficiency. When zeolite catalyst and hot gas temperature were adjusted from 250 °C to 400 °C, H₂ and CO increased slightly from 7.31% to 14.57%–8.03% and 17.34%, respectively. The tar removal efficiency varies in the 70%–90% range. When the zeolite was replaced with prepared Ni-based catalysts and hot gas cleaning (HGC) operated at 250 °C, H₂ contents were significantly increased from 6.63% to 12.24% resulting in decreasing the hydrocarbon (tar), and methane content. This implied that NiO could promote the water-gas shift reaction and CH₄ reforming reaction. Under other conditions in which the hot gas temperature was 400 °C, deactivated effects on prepared Ni-based catalyst were observed for inhibiting syngas and tar reduction in the HGC system. The prepared Ni-based catalyst worked at 250 °C demonstrate higher stability, catalyst activity, and less coke decomposition in dry reforming. In summary, the optimum catalytic performance in syngas production and tar elimination was achieved when the catalytic temperature was 250 °C in the presence of prepared Ni-based catalysts, producing 5.92 MJ/kg of lower heating value (LHV) and 73.9% tar removal efficiency.     

Hydrogen-rich gas production by air–steam gasification of rice husk using supported nano-NiO/γ-Al2O3 catalyst

The air–steam catalytic gasification of rice husk for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor with the newly developed nano-NiO/γ-Al₂O₃ catalyst. A series of experiments have been performed to explore the effects of catalyst presence, catalytic reactor temperature, the equivalence ratio (ER), and steam to biomass ratio (S/B) on the composition and yield of gasification gases. The experiments demonstrated that the developed nano-NiO/γ-Al₂O₃ catalyst had a high activity of cracking tar and hydrocarbons, upgrading the gas quality, as well as yielding a high hydrogen production. Catalytic temperature was crucial for the overall gasification process, a higher temperature contributed to more hydrogen production and gas yield. Varying ER demonstrated complex effects on rice husk gasification and an optimal value of 0.22 was found in the present study. Compared with biomass catalytic gasification under air only, the introduction of steam improved the gas quality and yield. The steam/biomass ratio of 1.33 was found as the optimum operating condition in the air–steam catalytic gasification.     

Hydrogen rich syngas production from biomass gasification using synthesized Fe/CaO active catalysts

Biomass gasification for hydrogen rich syngas production was investigated using the Fe/CaO catalysts in a fluidized bed reactor. The synthesized catalysts were prepared by an impregnation method with different Fe/CaO mass ratios (5%, 10%, 15%, 20%) for enhancing H₂ concentration and syngas yields and then characterized using X-ray diffraction (XRD), nitrogen adsorption and desorption isotherms test, scanning electron microscopy (SEM) and CO₂ absorption capacity test. The results showed that the Fe load had significant influences on the composition, textural properties and CO₂ adsorption capacity. Results of gasification experiments verified that the presence of Fe enhanced the concentration and yield of H₂. The highest syngas yield of 38.21 mol/kg biomass, H₂ yield of 26.40 mol/kg biomass, LHV values of 8.69 MJ/kg and gasification efficiency of 49.15% were obtained at an optimized mass ratio of Fe/CaO = 5%. In addition, the characterization results indicated that Ca₂Fe₂O₅ phase was formed. The Ca₂Fe₂O₅ had less CO₂ absorption capacity and effect on the gasification, but was considered to be a catalyst for tar cracking thus preventing the CaO deactivation.     

Hydrogen-rich gas from catalytic steam gasification of municipal solid waste (MSW): Influence of catalyst and temperature on yield and product composition

In the present study the catalytic steam gasification of MSW to produce hydrogen-rich gas or syngas (H₂ + CO) with calcined dolomite as a catalyst in a bench-scale downstream fixed bed reactor was investigated. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 750–950 °C, with a steam to MSW ratio of 0.77, for weight hourly space velocity of 1.29 h⁻¹. Over the ranges of experimental conditions examined, calcined dolomite revealed better catalytic performance, at the presence of steam, tar was completely decomposed as temperature increases from 850 to 950 °C. Higher temperature resulted in more H₂ and CO production, higher carbon conversion efficiency and dry gas yield. The highest H₂ content of 53.29 mol%, and the highest H₂ yield of 38.60 mol H₂/kg MSW were observed at the highest temperature level of 950 °C, while, the maximum H₂ yield potential reached 70.14 mol H₂/kg dry MSW at 900 °C. Syngas produced by catalytic steam gasification of MSW varied in the range of 36.35–70.21 mol%. The char had a highest ash content of 84.01% at 950 °C, and negligible hydrogen, nitrogen and sulphur contents.     

Catalytic gasification of pine-sawdust: Effect of primary and secondary catalysts

Pine sawdust steam gasification in a fixed double bed reactor and continuous flow was investigated. K₂CO₃ as primary catalyst and cobalt supported on γ-Al₂O₃ and SiO₂-Al₂O₃ as secondary catalyst was investigated. Thermal and catalytic steam gasification was compared. The effect of the support in tar yield and the H₂/CO ratio was pursued. It is noteworthy to observe that the primary catalyst increases the biomass gasification. It is also marked the total consumption of CH₄ species by the primary catalyst. The catalysts (K₂CO₃ and K₂CO₃-Co/γ-Al₂O₃) reduced tar formation from 11% in the thermal gasification to a value of 2.0% and 0.5% respectively. This tar yield reduction could be explained due to the action of potassium actives species of the primary catalyst combined with the lower acid strength of the support; high metal dispersion of cobalt species and the higher fraction of metallic cobalt species in Co/γ-Al₂O₃ catalyst. The catalysts decrease the formation of CO₂ from 21% in the thermal gasification to values on the order of 3%. The highest H₂/CO ratio with a value of 1.6 was obtained by K₂CO₃-γ-Al₂O₃ catalytic system. The presence of cobalt supported catalysts favored hydrogen consumption reactions such as reverse water gas shift reaction.     

Nickel-loaded red mud catalyst for steam gasification of bamboo sawdust to produce hydrogen-rich syngas

Ni/red mud (RM) catalysts were prepared by wet impregnation and used in the catalytic steam gasification of bamboo sawdust (BS) to produce hydrogen-rich syngas. The system was optimized in terms of the amount of added nickel (10%), reaction temperature (800 °C), and catalyst placement (separately behind the BS). The maximum H₂ yield was 17.3% higher than that using pure RM catalyst and 43.8% higher than that of BS gasification alone, and the H₂/CO ratio in the syngas reached 7.82. This Ni/RM catalyst also retained good activity after six cycles in a double-stage fixed bed reactor. Analysis using X-ray fluorescence, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and other methods revealed that the interaction of Ni, Fe, and Mg in Ni/RM produced bimetallic compounds containing active sites, such as NiFe₂O₄, MgNiO₂, and NiO. This explains the good catalytic performance in the tar conversion during the gasification process.     

Evaluation of modified Ni/ZrO2 catalysts for hydrogen production by supercritical water gasification of oil-containing wastewater

Supercritical water gasification (SCWG) technology is a clean and cost-effective conversion technology due to its unique chemical and physical properties. However, the unique properties also lead to instability and inactivity for the pure Ni/ZrO₂ catalyst in SCWG process. In this work, we investigated the effect of second metal addition on the catalytic performance by modifying Ni/ZrO₂ catalysts with different promoters (Co, Ce, La, Y, Mg), which prepared by a single-step sol-gel method. The analysis results of catalysts by XRD, SEM and automatic micropore & chemisorption analyzer showed that Ce, Y, La may be helpful promoters to stabilize the structure of ZrO₂. Compared to the non-catalytic experiment, all the catalysts showed significantly higher activities in the SCWG reaction. Among all catalysts, Ni-Co/ZrO₂ exhibited excellent activity, which achieved the highest carbon gasification efficiency (CE) and highest hydrogen yield. Additionally, two key factors, concentration and temperature, were also investigated for the optimum conditions, and the maximum carbon gasification efficiency (CE) of 98.8% was achieved at 600 °C with the Ni-Co/ZrO₂ catalyst.     

Improved yield parameters in catalytic steam gasification of forestry residue; optimizing biomass feed rate and catalyst type

The catalytic gasification (900 °C) of forestry industry residue (Eucalyptus saligna) was laboratory-studied. Biomass feed rate and type and amount of catalyst were assayed for their effect on the gasified product composition and the overall energy yield of the gasification reaction. The use of a calcined dolomite catalyst resulted in a combustible gas mixture of adequate calorific power (10.65 MJ m^?3) for use as fuel, but neither the product gas composition nor the energy yield varied significantly with widely different amounts of the catalyst (2 g and 20 g). The use of NiO-loaded calcined dolomite catalysts did not affect the product gas composition significantly but led to a 30% increase in the total product gas volume and to a reduction in the rate of tar and char formation. The catalyst loaded with the smallest amount of NiO studied (0.4 wt%. Ni/Dol) led to the highest energy yield (21.50 MJ kg^?1 on a dry-wood basis) based on the use of the gasified product as fuel. The gasified product was found to have an adequate H₂/CO molar ratio and H₂ content for use as synthesis gas source and partial source of H₂.     

Effect of metal addition to Ni/activated charcoal catalyst on gasification of glucose in supercritical water

Activated charcoal supported nickel-based catalysts such as Ni/AC, Ni-Y/AC, Ni-Fe/AC, and Ni-Co/AC were formulated and their catalytic activity for the gasification of glucose in supercritical water were investigated using a packed-bed reactor at 650 °C, 28 MPa. A set of glucose gasification experiments was also carried out without catalyst and with AC to provide baseline data. Loading of small amounts of Y to the Ni/AC catalyst appeared to increase both the extent of gasification and hydrogen yield while loading of Fe or Co metal to the Ni/AC catalyst did not give any positive effect on the gasification results. Effect of catalyst composition, temperature, reactant concentration, and reactor residence time on the glucose gasification with the Ni-Y/AC catalyst was examined. Catalyst analysis indicates that adding of Y into the Ni/AC catalyst inhibited carbon formation to a great extent, thereby maintaining catalytic activity of the Ni metal for H₂ formation reactions.     

Effects of catalyst preparation parameters and reaction operating conditions on the activity and stability of thermally fused Fe-olivine catalyst in the steam reforming of toluene

An iron-based olivine catalyst synthesized using thermal fusion (TF) was tested in a fixed bed reactor in the steam reforming of a biomass tar model compound. The effects of the catalyst preparation parameters (TF temperature, Fe precursor, Fe-loaded content and olivine support) and reforming reaction operating parameters (reaction temperature and steam to carbon (S/C) molar ratio) on the activity and stability of the TF-olivine catalyst were investigated. The physiochemical properties of the catalyst were analysed, using the following characterizations: X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, temperature program reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The results showed that a higher TF temperature (1400 °C) promoted the interactions between Fe and olivine supports, part of the Fe was fused into the olivine structure to reorganize a new (Mg, Fe) Fe₂O₄ phase, which resulted in a high H₂ yield and a strong resistance to carbon deposition. Fe₂O₃-olivine showed the best effect for toluene conversion, while Fe/Ni-olivine presented the best performance for carbon resistance. Fe-olivine showed a strong ability to combine hydroxyls, and the yield of H₂ increased with the Fe-loaded content. Toluene conversion increased with the reaction temperature. When the S/C ratio was 1.06, the selectivity of carbon could decrease to 2.71%; meanwhile, the H₂ yield decreased slightly with the increase in the S/C ratio. Finally, the stability of TF-olivine catalyst was tested, and no inactivation was observed in the 48-h continuous catalytic reforming experiment.     

Hydrogen-rich gas production by steam gasification of palm oil wastes over supported tri-metallic catalyst

The catalytic steam gasification of palm oil wastes for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor using the newly developed tri-metallic catalyst. The results indicated that the supported tri-metallic catalyst had greater activity for the cracking of hydrocarbons and tar in vapor phase and higher hydrogen yield than the calcined dolomite in catalytic steam gasification of palm oil wastes. A series of experiments have been performed to explore the effects of temperature, steam to biomass ratio (S/B) and biomass particle size on gas composition, gas yield, low heating value (LHV) and hydrogen yield. The experiments demonstrated that temperature was the most important factor in this process; higher temperature contributed to higher hydrogen production and gas yield, however, it lowered gas heating value. Comparing with biomass catalytic gasification, the introduction of steam improved gas quality and yield, the optimal value of S/B was found to be 1.33 under the present operating condition. It was also shown that a smaller particle size was more favorable for gas quality and yield. However, the LHV of fuel gas decreased with the increasing S/B ratio and the decreasing biomass particle size.     

Comprehensive experimental study on supercritical water gasification of oilfield sludge: Effect of operation parameters,and catalysts on the products

Supercritical water gasification (SCWG) was adopted to treat oilfield sludge and produce syngas. The effect of temperature (400–450 °C), reaction time (30–90 min) and catalyst addition on syngas production and residual products during SCWG of oilfield sludge was studied. When increasing SCWG temperature from 400 to 450 °C with reaction time of 60 min, the H₂ yield and the selectivity of H₂ increased significantly from 0.53 mol/kg and 75.53% to 0.98 mol/kg and 78.09%, respectively. It is noteworthy that when the reaction time was too long, CO₂ and CO were converted to CH₄ with the consumption of H₂ via methanation reaction. The addition of Ni/Al₂O₃ catalyst can substantially promote the production of high-quality syngas from SCWG of oilfield sludge. The H₂ yield and its selectivity at 450 °C and 60 min were as high as 1.37 mol/kg and 84.05% with 10Ni/Al catalyst. Moreover, the catalysts with bimetal loading (Fe–Ni, Rb–Ni or Ce–Ni) were found to be beneficial for improving gasification efficiency, H₂ yield, and the degradation of organic compounds. Among them, 5 wt% Rb on 10Ni/Al catalyst performed the best catalytic activity for SCWG at 450 °C and 60 min, which had the highest H₂ yield of 1.67 mol/kg and selectivity of 86.09%. More than 90% of total organic carbon in sludge was decomposed after the SCWG with all the catalysts. These findings indicated that catalytic SCWG is a promising alternative for efficiently dealing with oilfield sludge.     

Catalytic mechanism study on the gasification of depolymerizing slag in supercritical water for hydrogen production

Supercritical water gasification technology can realize efficient conversion of biomass, coal and other organics into hydrogen rich gas. But the efficiency of non-catalytic gasification at relative low temperature is not high. Besides, as for catalytic gasification, catalysis mechanism is complex. Thus how to improve efficiency and master the catalysis mechanism is a challenging issue. In this thesis, supercritical water gasification of depolymerizing slag experiments with the catalysis of different kinds of catalysts are conducted and the catalysis mechanism is analyzed. The results indicate that catalyst mechanism of K₂CO₃ is that it can promote the swelling and hydrolysis of lignocellulose and increase the amounts of phenolic intermediates. Ru/Al₂O₃ presents some different catalytic properties. It facilitates hydrogenation reaction of hydrolysis products, ring-opening reaction and the cleavage of carbon-carbon bonds then enhances gasification degree and increases gasification efficiency. Moreover, the binary catalyst displays a good synergic effect and the catalytic activity is higher than that of any single catalyst since these two catalysts promote various gasification stages. The gasification efficiency and hydrogen yield increase 13.22 mmol g^?1 and 66.46% respectively with the synergic catalyst of K₂CO₃ and Ru/Al₂O₃.     

Catalytic gasification of textile wastewater treatment sludge for hydrogen production in supercritical water with K2CO3/H2O2: Reaction variables,mechanism and kinetics

As the main by-product, sludge was generated during the process of textile wastewater treatment. Due to containing organic compounds, textile sludge has great potential to be effectively reused for production of clean energy. In this work, gasification of textile sludge in supercritical water for hydrogen production was investigated. In order to improve hydrogen production, H₂O₂ and K₂CO₃ were used as catalysts. Effects of reaction variables (including temperature, retention time, oxidation coefficient and alkali catalyst dosage) on hydrogen yield were studied. Experimental results indicate that hydrogen yield increases with rise of temperature. When reaction temperature reaches 500 °C, the maximum value of hydrogen yield being 10.6 mol/kg was obtained. When excessive H₂O₂ was added, decrease of hydrogen yield was achieved. However, the addition of K₂CO₃ is favor to hydrogen yield, which is about 1.5 times as much as that of without catalyst. Meanwhile, reaction mechanism and kinetics of textile sludge gasification in supercritical water were explored. Reaction activation energy and Arrhenius constants were obtained in the established kinetic model.     

Hydrogen generation via supercritical water gasification of lignin using Ni‐Co/Mg‐Al catalysts

In this study, a group of Ni‐Co/Mg‐Al catalysts was prepared for hydrogen production via supercritical water gasification of lignin. The effects of different supports and preparation methods were examined. All catalysts were evaluated under the operation conditions of 650 °C, 26 MPa, and water to biomass mass ratio of 5 in a batch reactor. The Cop.2.6Ni‐5.2Co/2.6Mg‐Al catalyst showed the best performance with highest gas yield (12.9 wt%) and hydrogen yield (2.36 mmol·g^?1). The results from catalyst characterization suggest that the properties of this type of catalyst are dependent on multiple factors including support Mg‐Al molar ratio and preparation method, and better coke resistance of the catalyst could be obtained by the preparation method of coprecipitation. Therefore, coprecipitation method should be applied for the preparation of Ni‐Co/Mg‐Al catalysts for hydrogen production via supercritical water gasification of lignin. Copyright © 2017 John Wiley & Sons, Ltd.     

Catalytic co‐pyrolysis of Eichhornia Crassipes biomaѕѕ and polyethylene using waste Fe and CaCO3 catalysts

A wild aquatic plant, Eichhornia Crassipes, and polyethylene have been converted into liquid product thermo‐catalytically and cost effectively through co‐pyrolysis using batch steel pyrolyzer. The Fe and CaCO₃ catalysts were obtained as wastes from various mechanical processes. The catalytic process was compared with non‐catalytic pyrolysis. The effect of various reaction conditions was investigated in order to find out the optimized process conditions. It was found that the favorable reaction conditions were 450 °C temperature and 1‐h reaction time at a heating rate of 1 °C/s and 0.4‐mm biomass particle size. The bio‐oil yield was found to be 34.4% and 26.6% using Fe and CaCO₃ respectively with catalysts particle size of 0.4 mm at the optimized reaction conditions and 5 wt% of biomass. The non‐catalytic and catalytic co‐pyrolysis using Fe as catalyst produced 23.9% and 28.7% oil respectively. Thus the efficiency of processes in terms of bio‐oil production was found in order of: Fe > CaCO₃ > non‐catalytic pyrolysis. The GC/MS analysis of n‐hexane extract of bio‐oil shows that Fe catalyst favors formation of aliphatic hydrocarbons while CaCO₃ and non‐catalytic pyrolysis favors formation of aromatic hydrocarbons. Mostly unsaturated aliphatic hydrocarbons were formed in case of co‐pyrolysis reactions. The calorific value of bio‐oil was also measured in order to find out the fuel properties of the products. Copyright © 2016 John Wiley & Sons, Ltd.