Pyrolysis waste char supported metallic catalyst for syngas production during catalytic reforming of benzene

Waste rice husk char supported Fe and Ni were synthesized to prepare the monometallic and bimetallic catalysts for removing the tar model compound benzene in a laboratory dual-stage reactor. The prepared catalysts were examined by microstructure and textural characterization to analyse catalytic performance and stability. The molar proportions of CO, H₂, CO₂ and CH₄ in the generated gas and the influence of residence time (τ) and the steam-to-carbon ratio (S/C) on the catalytic reaction were investigated. The results show that the rice husk char-based catalysts showed excellent catalytic activity for syngas production and benzene conversion. Under optimized conditions, the benzene conversion can reach 95.2%, and the mol% of syngas in the generated gas is greater than 93.0%, of which 91.0% is H₂. The experimental results show that the influence of residence time on catalytic performance is greater than that of the steam-to-carbon ratio, and that excessive τ or S/C values will have no more positive effect on the performance of the catalyst. The stable active sites on the catalyst surface can guarantee the catalytic activity in the reaction. Ultimately, rice husk char-based catalysts can be used to remove tar and produce syngas.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Hydrogen-rich syngas production by catalytic cracking of polypropylene over activated carbon based monometallic and bimetallic Fe/Ni catalysts

The aim of this study is to efficiently produce hydrogen-rich syngas. The thermal conversion experiment of polypropylene was carried out in a two-stage pyrolytic-catalytic device. Activated carbon based catalyst was developed, the catalytic performance of monomial and bimetallic catalysts was explored, and the influence of metal addition ratio in bimetallic catalysts on hydrogen production performance was analyzed. The microscopic morphology and structural characterization of the unreacted and spent catalyst were analyzed, and the effect of active substance in catalyst on the reaction performance was described. Under optimized reaction conditions, bimetallic catalyst 5Fe–10Ni had excellent catalytic activity, large hydrogen yield (136.32 mmol/g_PP) and high carbon deposition quality. For this high performance catalyst, the catalyst stability was verified by 10 cycles of recycling experiments. The method of hydrogen production from waste plastic cracking in this paper will provide new ideas for high value utilization of plastic and hydrogen production.     

Hydrogen production by catalytic supercritical water gasification of nitriles

Supercritical water gasification (SCWG) of nitriles was studied in a tubular flow reactor at different temperatures. This article focuses on the product distributions and corresponding reaction pathways influenced by addition of Na₂CO₃ catalyst. Results showed that gas yield for both acetonitrile and acrylonitrile can be greatly enhanced by adding Na₂CO₃ catalyst. Especially, H₂ gasification efficiency can reach 55.4% and 123.3% at 550 °C, respectively. But the catalytic effect on the gas yield of benzonitrile was relatively insignificant. Na₂CO₃ can also accelerate the hydrolysis of cyanogen and amido as a base catalyst. Benzene and acetic acid were the primary intermediate products during the SCWG of benzonitrile and acetonitrile, respectively. The conversion of acrylonitrile was more complicated because of the activity of double bond. It is possible that 3,3′ iminodipropionitrile was formed by Na₂CO₃ catalyzed in the range of 490–520 °C, which dominated two thirds of pathways for the subsequent formation of acetic acid. Ammonia-nitrogen content in the liquid effluent was limited by the hydrolysis degree of cyano-group and the possible polymerization reaction of intermediate products. There was no obvious trend to reveal that NH₃ was converted into nitrogen under our experimental conditions.     

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.     

Hydrogen-rich syngas production by gasification of Urea-formaldehyde plastics in supercritical water

Supercritical water is a promising medium to convert plastics into hydrogen and other recyclable products efficiently. In previous research, supercritical water gasification characteristics investigations focus on thermoplastics instead of thermoset plastics due to its chemical, thermal and mechanical stability. Urea-formaldehyde (UF) plastics were selected as a typical kind of thermoset plastics for investigation in this paper and quartz tubes were used as the reactor in order to avoid the potential catalytic effect of metal reactor wall. Conversion characteristic were studied and the influence of different operating parameters such as temperature, reaction time, feedstock mass fraction and pressure were investigated respectively. The molar fraction of hydrogen could reach about 70% in 700 °C. Products in gas phase and solid phase were analyzed, and properties, chemical structures and inhibition mechanism of thermoset plastics was analyzed after comparing with polystyrene (PS) plastics. The result showed that increase of high temperature and long reaction time could promote gasification process, meanwhile the increase in the feedstock mass fraction would result in suppression of the gasification process. Finally, kinetic study of UF was carried out and the activation energy and pre-exponential factor of the Arrhenius equation were calculated as 30.09 ± 1.62 kJ/mol and 0.1199 ± 0.0049 min⁻¹, respectively.     

Hydrogen-rich syngas production through coal and charcoal gasification using microwave steam and air plasma torch

In the present study, microwave plasma gasification of two kinds of coal and one kind of charcoal was performed with various O₂/fuel ratios of 0–0.544. Plasma-forming gases used under 5 kW microwave plasma power were steam and air. The changes in the syngas composition and gasification efficiency in relation to the location of the coal supply to the reactor were also compared. As the O₂/fuel ratio was increased, the H₂ and CH₄ contents in the syngas decreased, and CO and CO₂ increased. When steam plasma was used to gasify the fuel with the O₂/fuel ratio being zero, it was possible to produce syngas with a high content of hydrogen in excess of 60% with an H₂/CO ratio greater than 3. Depending on the O₂/fuel ratio, the composition of the syngas varied widely, and the H₂/CO ratio necessary for using the syngas to produce synthetic fuel could be adjusted by changing the O₂/fuel ratio alone. Carbon conversion increased as the O₂/fuel ratio was increased, and cold gas efficiency was maximized when the O₂/fuel ratio was 0.272. Charcoal with high carbon and fixed carbon content had a lower carbon conversion and cold gas efficiency than the coals used in this study.     

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.     

Biomass to hydrogen-rich syngas via tar removal from steam gasification with La1-XCeXFeO3/dolomite as a catalyst

Biomass gasification produces hydrogen, which is a clean and promising technology. One of the most important aspects of the biomass gasification process is choosing the right catalyst. In this study, 10% La_1-XCe_XFeO₃/Dolomite (X = 0,0.2,0.4,0.6,0.8) synthesized using the sol-gel method was used as a catalyst in biomass gasification for the production of hydrogen-rich syngas. Gasification tests were carried out in a fixed bed reactor. The effects of an elemental substitution in LaFeO₃, temperature on the product were examined. Ce-substitution boosted the activity of LaFeO₃/DOL according to the data. Among the prepared catalysts, La_0.8Ce_0.2FeO₃/DOL performed the best, yielding a greater H₂ production and tar with a higher naphthalene concentration. As the temperature rises, so does the H₂ yield, at 850 °C, the highest H₂ yield is 0.69Nm³/Kg. Furthermore, the aromatization of phenols in tar is more likely to occur at high temperatures.     

Supercritical water gasification of wastewater sludge for hydrogen production

The use of hydrogen as clean fuel gas in the power generation sector becomes essential to reduce the environmental issues related to conventional fuel usage. By avoiding biomass drying process, supercritical water gasification is considered the most efficient technology in hydrogen production from wastewater sludge. Wastewater sludge is difficult to disposal in its received form since it is often produced with high moisture content, contribute to numerous environmental issues and direct contact with this waste can result in health concerns. The assessment of the treatment and conversion of this material into fuel gas at condition beyond supercritical state (374°C and 22.1 MPa) is required. This paper is discussed the degradation routes of wastewater sludge in supercritical water. Furthermore, it is reviewed the influence of the main operation parameters role in the hydrogen production, which includes reaction temperature, pressure, residence time, feed concentration and catalysts. The development in reactor design and setup for maximum hydrogen production is highlighted. The technical challenges encountered during the conversion process and its solutions are also discussed. In addition, future prospective to optimal and standardization of the supercritical water gasification process is reviewed.     

Hydrogen production from catalytic gasification of switchgrass biocrude in supercritical water

Biomass can be liquefied to produce biocrude for ease of transportation and processing. Biocrude contains oxygenated hydrocarbons of varying molecular structure and molecular weights, including lignin derived products, sugars and their decomposition products. In this work several catalysts were screened for hydrogen production by gasification of switchgrass biocrude in supercritical water at 600 °C and 250 bar. Nickel, cobalt, and ruthenium catalysts were prepared and tested on titania, zirconia, and magnesium aluminum spinel supports. Magnesium aluminum spinel was seen to be an inappropriate support as reactors quickly plugged. Ni/ZrO₂ gave 0.98 mol H₂/mol C, the highest hydrogen yield of all tested catalysts; however, over time, increase in pressure drop lead to reactor plugging with all zirconia supported catalysts. Titania supported catalysts gave lower conversions, however they did not plug during the course of the study. Charring of all catalysts was seen to occur at the entrance of the reactor as the biocrude was heated. All support materials suffered significant surface area loss due to sintering.     

Review of catalytic supercritical water gasification for hydrogen production from biomass

Hydrogen is defined as an attractive energy carrier due to its potentially higher energy efficiency and low generation of pollutants, which can replace conventional fossil fuels in the future. The governments have invested huge funds and made great efforts on the research of hydrogen production. Among the various options, supercritical water gasification (SCWG) is a most promising method of hydrogen production from biomass. Supercritical water (SCW) has received a great deal of attention as a most suitable reaction medium for biomass gasification because it is safe, non-toxic, readily available, inexpensive and environmentally benign. However, high temperature and pressure are required to meet the minimum reaction condition. Therefore, the high operating cost has become the biggest obstacle to the development of this technology. To overcome this bottleneck, many researchers have carried out intensive research work on the catalytic supercritical water gasification (CSCWG). Based on the previous studies stated in the literature, the authors try to give an overview (but not an exhaustive review) on the recent investigations of CSCWG. Besides, the physicochemical properties of SCW and its contributions in subcritical and supercritical water reaction are also summarized.     

Hydrogen production from catalytic supercritical water reforming of glycerol with cobalt-based catalysts

Glycerol reforming under catalytic supercritical water at temperatures in the range of 723–848 K using Co catalyst deposited on various supports including ZrO₂, yttria-stabilized zirconia (YSZ), La₂O₃, γ-Al₂O₃, and α-Al₂O₃ was investigated. An increase in operating temperature promoted the continued increase in glycerol conversion; however, carbon formation causing system operation failure was observed for γ-Al₂O₃ and α-Al₂O₃ at high operating temperatures (i.e. 748–798 K). Co supported on YSZ provided the most efficient performance for hydrogen production. 10 wt.% Co loading on YSZ support was an optimum amount to enhance the reaction. The increase in glycerol conversion and reduction of the amount of liquid products were observed for lower weight hourly space velocity (WHSV), higher operating temperature or higher cobalt loading. On Co/YSZ catalyst, glycerol conversion of 0.94 and hydrogen yield of 3.72 was obtained with WHSV of 6.45 h⁻¹at 773 K.     

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.     

Study on solid waste pyrolysis coke catalyst for catalytic cracking of coal tar

Low value solid waste pyrolysis coke was used as a catalyst to catalytically crack gas-phase tar to improve tar yield and gas production. Pyrolysis coke with different pyrolysis final temperature and pyrolysis time were prepared, the effect of tar cracking products was studied, and the optimal pyrolysis coke were screened. The pyrolysis coke catalyst was characterized by BET, FTIR, SEM. The results show that the optimal preparation final temperature of pyrolysis coke is 750 °C, and the optimal preparation pyrolysis time is 2 h. Compared with the pyrolysis of raw coal, the tar cracking rate increased by 9.3%, after added the pyrolysis coke catalyst, the gas increased by 23.2%, and the light component increased to 36.6%. And the OH, C–N and C–O–C functional groups present on coke are the factors that affect the catalytic cracking.     

Hydrogen production by catalytic gasification of coal in supercritical water with alkaline catalysts: Explore the way to complete gasification of coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) was carried out in a micro batch reactor with various alkaline catalysts: Na₂CO₃, K₂CO₃, Ca(OH)₂, NaOH and KOH. H₂ yield in relation to the alkaline catalyst was in the following order: K₂CO₃ ≈ KOH ≈ NaOH > Na₂CO₃ > Ca(OH)₂. Then, hydrogen production by catalytic gasification of coal with K₂CO₃ was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal × 100%) and H₂ yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 °C when the weight ratio of K₂CO₃ to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.     

Review of methane catalytic cracking for hydrogen production

Methane catalytic cracking is a process by which carbon monoxide-free hydrogen can be produced. Despite the fact that hydrogen produced from methane cracking is a pure form of hydrogen, methane cracking is not used on an industrial scale for producing hydrogen since it is not economically competitive with other hydrogen production processes. However, pure hydrogen demand is increasing annually either in amount or in number of applications that require carbon monoxide-free hydrogen. Currently, hydrogen is produced primarily via catalytic steam reforming, partial oxidation, and auto-thermal reforming of natural gas. Although these processes are mature technologies, CO is formed as a by-product, and in order to eliminate it from the hydrogen stream, complicated and costly separation processes are required. To improve the methane catalytic cracking economics, extensive research to improve different process parameters is required. Using a highly active and stable catalyst, optimizing the operating conditions, and developing suitable reactors are among the different areas that need to be addressed in methane cracking. In this paper, catalysts that can be used for methane cracking, and their deactivation and regeneration are discussed. Also, methane catalytic cracking kinetics including carbon filament formation, the reaction mechanisms, and the models available in the literature for predicting reaction rates are presented. Finally, the application of fluidized beds for methane catalytic cracking is discussed.     

Hydrogen production by coal gasification in supercritical water with a fluidized bed reactor

The technology of supercritical water gasification of coal can converse coal to hydrogen-rich gaseous products effectively and cleanly. However, the slugging problem in the tubular reactor is the bottleneck of the development of continuous large-scale hydrogen production from coal. The reaction of coal gasification in supercritical water was analyzed from the point of view of thermodynamics. A chemical equilibrium model based on Gibbs free energy minimization was adopted to predict the yield of gaseous products and their fractions. The gasification reaction was calculated to be complete. A supercritical water gasification system with a fluidized bed reactor was applied to investigate the gasification of coal in supercritical water. 24 wt% coal-water-slurry was continuously transported and stably gasified without plugging problems; a hydrogen yield of 32.26  mol/kg was obtained and the hydrogen fraction was 69.78%. The effects of operational parameters upon the gasification characteristics were investigated. The recycle of the liquid residual from the gasification system was also studied.     

Catalytic supercritical water gasification mechanism of coal

Catalytic supercritical water gasification (SCWG) for H₂ production is a hopeful way of coal conversion to replace the traditional coal utilization mode. At present, the detailed catalytic mechanism in the process remains unknown. Herein, a comprehensive catalytic SCWG mechanism of coal is proposed by establishing a novel catalytic kinetic model. It shows that catalysts (K₂CO₃) break up the coal matrix by a cyclic redox reaction to produce plenty of mesopores, accelerating steam reforming of fixed carbon and coal pyrolysis. Water-gas shift reaction is facilitated by K₂CO₃ via formation of formate, which then promotes steam reforming of CH₄ at high temperature (≥700 °C) due to the decreasing CO. The proposed mechanism provides important insights in catalytic SCWG process of coal.     

Hydrogen-rich syngas production from municipal solid waste gasification through the application of central composite design: An optimization study

This study aims to investigate the influence and interaction of experimental parameters on the production of optimum H₂ and other gases (CO, CO₂, and CH₄) from gasification of municipal solid waste (MSW). Response surface method in assistance with the central composite design was employed to design the fifteen experiments to find the effect of three independent variables (i.e., temperature, equivalence ratio and residence time) on the yields of gases, char and tar. The optimum H₂ production of 41.36 mol % (15.963 mol kg-MSW⁻¹) was achieved at the conditions of 757.65 °C, 0.241, and 22.26 min for temperature, ER, and residence time respectively. In terms of syngas properties, the lower heating value and molar ratio (H₂/CO) ranged between 9.33 and 12.48 MJ/Nm³ and 0.45–0.93. The predicted model of statistical analysis indicated a good fit with experimental data. The gasification of MSW utilizing air as a gasifying agent was found to be an effective approach to recover the qualitative and quantitate products (H₂ and total gas yield) from the MSW.