Higher Syngas Yield Research Articles

Obtaining high H2-rich syngas yield and carbon conversion efficiency from biomass gasification: From characterization to process optimization using machine learning with experimental validation

Gasification, among the other thermochemical processes, stands as a promising method for sustainable waste management while generating valuable H2-rich syngas. In the last few years, there has been a significant surge in the adoption of machine learning (ML) techniques for modelling biomass as well as gasification and pyrolysis of waste. The present study unveiled the supremacy of Gaussian Process Regression (GPR) algorithm as compared to other ML models, in predicting syngas yield [Ysyn (Nm3/kg of biomass)] and carbon conversion efficiency[ηCarbon(%)] respectively, with a high prediction accuracy of R2 > 0.9 in both the cases. The necessary datasets were collected from experimental trials, at reaction conditions of temperature (T): 550–1000 °C, air flow rate (AFR): 0.02–0.04 L/min, and reaction time of 2 h, in a two-stage fixed bed reactor, which were identified on the Basis of thermodynamic as well as stoichiometric analysis. Additionally, the models were employed in Bayesian optimization within a weighted multi-objective framework to obtain the optimal operational parameters, focusing on maximizing both yield and conversion simultaneously. Finally, this result was validated experimentally to check the sanctity of the data-driven optimization.

Solution Combustion Synthesis of Ce‐based Composite Oxygen Carriers for Chemical Looping Reforming of Methane

AbstractEfficient activation and the conversion of methane to value‐added products have long attracted interest. Chemical looping reforming has become a competitive technology to transform methane into syngas that can act as raw material for various chemicals. In this paper, the methane chemical looping reforming reactivity of the Ce−Co composite oxygen carriers fabricated with different preparation methods, including solution combustion, ball‐milling, hydrothermal, and co‐precipitation method, are investigated on a fixed‐bed. Various bulk/surface characterizations (TEM, XRD, BET, XPS, Raman, etc.) were applied to reveal the effect of preparation methods on the properties of these oxygen carriers. The results indicate that the oxygen carrier prepared by the solution combustion method exhibits excellent methane conversion, high syngas yield, and desirable H2/CO ratio, as well as stable regenerability because of its relatively small crystal size, large specific surface area, high oxygen vacancy concentration and Ce3+/Ce4+ ratio. This work may be helpful in the preparation of highly active and stable oxygen carriers for chemical looping reforming reaction of methane.

High-reactive and coke-resistant polyhedral NiO/Fe2O3 oxygen carrier for enhancing chemical looping CH4–CO2 dry reforming

Chemical looping dry reforming of methane (CL-DRM) is a promising technology for syngas production and efficient CH4 and CO2 utilization to provide appropriate H2/CO ratio in the reducer for Fischer-Tropsch synthesis. The crucial issue in CL-DRM is to find a highly reactive oxygen carrier (OC) with good stability. Polyhedral NiO/Fe2O3 composite oxygen carriers were successfully fabricated via a hydrothermal and calcination method based on different solubility product constants of nickel carbonate (NiCO3) and ferrous carbonate (FeCO3) in aqueous solution. The physicochemical properties of the OCs were characterized by XRD, XRF, SEM, TEM, TG/DTA, XPS, H2-TPR and Raman spectroscopy. The performance of NiO/Fe2O3 OCs was measured in a fixed-bed reactor. The experimental results indicated that the Fe2O3-0.6Ni OC has the highest syngas yield up to 90.25% with ideal H2/CO mole ratio (approximately 2) in the reducer at 750 °C. In addition, in reducing atmospheres, the Ni3Fe alloy was formed instead of metallic Ni and Fe, thus significantly improves coke resistance. Density functional theory (DFT) calculations demonstrated that the energy barrier of rate determining step of dehydrogenation process (CH3 releases H to form CH2) is 2.64 eV with OC of pure Fe2O3, which is higher than that of the condition with OC of NiO/Fe2O3 composite (2.21 eV). Therefore, the addition of NiO to Fe2O3 favors the CH4 dehydrogenation process on the surface of OCs. This study provides guidance for the design of oxygen carriers for chemical looping dry reforming of methane with the better coke-resistant property.

Enhancement of H2 production via catalytic steam gasification of food waste as feedstock and its ash as a support and promoter for Ni catalyst

A novel Ni-based catalyst was prepared with 5% and 10% loading of Ni on food waste ash, and then it was characterized using various physico-chemical methods. Thereafter, the steam gasification experiments were conducted at 850 °C and a steam flow rate (SFR) of 0.75 mL/min in a downdraft fixed bed gasifier. The gasification results showed that a 5% Ni-loaded catalyst was more effective than 10% in enhancing the syngas production with a high hydrogen fraction. It was found that the use of this catalyst increased the syngas yield significantly to 1.8 m3/kg on increasing the catalyst content in feedstock to 50%. Additionally, the hydrogen fraction in syngas increased to 71% which, together with higher syngas yield, increased the hydrogen yield by almost 100%. Furthermore, the performance parameters for gasification, such as carbon conversion efficiency (CCE) and cold gas efficiency (CGE), were also found to be highest at 50% catalyst content of 5% Ni-loaded catalyst in the feedstock.

Crystalline phase transformation of Sr-Fe based oxygen carriers modulate the cyclic performance for syngas and CO coproduction in chemical looping ethanol reforming coupled with CO2 splitting

The chemical looping reforming coupled with CO2 splitting (CLR-CS) offers a promising solution for syngas production and simultaneous decomposition of CO2. In this study, the Sr-Fe based oxygen carriers (OCs) were evaluated in CLR-CS using ethanol as fuel. The presence of Sr significantly improved the oxidation performance of iron oxides. The Sr element in fresh Sr-Fe based OCs mainly formed two crystal phases, including SrFe12O19 and Sr4Fe6O13. Increasing the amount of Sr element made it easier to form Sr4Fe6O13 crystal phase. The Sr4Fe6O13 was favorable for syngas production, due to the higher surface oxygen vacancy formation energy with a range of 3.13–3.37 eV. However, the lower oxygen transfer capacity (OTC) of Sr4Fe6O13 resulted in a lower CO yield in the of stage of CO2 decomposition. Compared with Sr4Fe6O13, SrFe12O19 exhibited the higher OTC and the higher reactivity of lattice oxygen, which was preferable to produce more CO2 in the stage of ethanol reforming in fuel reactor. During the cycle tests, the crystalline phase of SrFe12O19 didn’t regenerate under the CO2 atmosphere but transformed into Sr4Fe6O13. It was attributed to the lower energy barrier of CO2 oxidation on the oxygen defect surface of Sr4Fe6O13. The phase transformation of SrFe12O19 accompanied the formation of Fe3O4. The excessive Fe3O4 had poor stability and inactivated easily due to sintering and agglomeration in Sr1Fe4 and Sr1Fe6 samples. The Sr1Fe2, namely the molar ratio of SrO to Fe2O3 of 1:2, exhibited the better performance for syngas (0.291 Nm3/kg OC) and CO (0.141 Nm3/kg OC) coproduction at 800 °C. Additionally, the Sr1Fe2 presented an excellent cyclic stability in 30 cycles due to the suitable proportion of Sr4Fe6O13 and iron oxides formed, which maintained a high syngas yield and avoided sintering of iron oxides. Overall, the Sr1Fe2 is a promising OC candidate in CLR-CS process.

Gasification Performance of Barley Straw Waste Blended with Lignite for Syngas Production under Steam or Carbon Dioxide Atmosphere

The gasification performance of lignite/barley straw mixtures for syngas production was investigated. The experiments were carried out under a steam or carbon dioxide atmosphere, in fixed-bed and thermogravimetric–mass spectrometry systems. The thermal behavior, reactivity, conversion, product gas composition, liquid and gaseous by-products and interactions between fuels were determined and correlated with the structural characteristics and inherent minerals in ashes, which were analyzed via mineralogical, chemical and fusibility tests. Devolatilization of the materials up to 600 °C resulted in the carbon enrichment of chars and a 30–90-fold increase in the specific surface area. Gaseous and liquid by-products with higher heating values of 5–7 MJ/m3 and 20–28 MJ/kg could offer valuable energy. Upon steam gasification up to 1000 °C, product gas was enriched in hydrogen and carbon monoxide. The syngas yield and heating value of the gas mixture were higher for barley straw fuel (0.77 m3/kg, 11.4 MJ/m3), which, when blended with the lignite, produced upgraded products. Upon carbon dioxide gasification up to 1000 °C, barley straw char exhibited a 3-times higher rate than the lignite, as well as higher conversion (94.5% vs. 62.9%) and a higher syngas yield (0.84 m3/kg vs. 0.55 m3/kg). Lignite/barley straw blends showed synergistic effects and presented higher gasification reactivity and conversion in comparison to lignite. The overall performance of lignite was improved with the steam reagent, while that of barley straw was improved with the carbon dioxide reagent.

Carbon dioxide-steam reforming gasification of carbonized biomass pellet for high syngas yield and TAR reduction through CFD modeling

Experimental and numerical evaluation of steam and carbon dioxide gasification on torrefied palm kernel shell in an updraft fixed bed gasifier is studied. Euler-Lagrangian two-dimensional model with 15 kinetic reactions is developed to investigate tar formation in relation to torrefaction temperature, gasification temperature, and steam-to-carbon-dioxide ratio (S-CO2-R). The combination of steam and CO2 had considerable effect on the tar reduction and also influenced the gaseous composition significantly when the varying parameters were compared. The results show that increasing both gasification temperature and S-CO2-R do enhance the H2 production whiles drastically reducing the tar formation. The tar concentration reduced by 21.4 % and 20.5 % by changing the S-CO2-R from 0.4 to 2.0 and gasification process temperature from 973 and 1173 K respectively. An increase in hydrogen is also observed, from 55.5 % to 60.84 %, when the S-CO2-R is increased to 1.2. Similarly, 29.1 % increase is observed in gasification efficiency as compared to the raw-PKS.

Coke formation pathway under various reaction conditions during the production of syngas in a dielectric barrier discharge plasma environment using CeO2 nanorods supported Ni catalysts

Plasma-assisted dry reforming of methane (DRM) was investigated using CeO2 nanorods (NR) supported Ni catalysts in a fixed-bed coaxial dielectric barrier discharge (DBD) reactor. This study individually examined the catalyst support, packing material, and 10 wt% Ni-CeO2 NR catalyst under pure thermal and plasma-assisted thermal DRM environments to explore the plasma-thermal synergy. Support and packing material displayed no discernible reactivity under thermal DRM within 450 °C; however, the catalyst exhibited reactivity beginning around 350 °C. Alternatively, plasma-assisted DRM experiments revealed a distinct reaction occurrence at significantly lower temperatures across all sample types. Introducing plasma demonstrated a significant enhancement in CH4 conversion compared to CO2 conversion. The 10 wt% Ni-CeO2 NR catalyst in plasma-assisted DRM testing showed increasing conversions of CH4 and CO2 with rising temperatures, peaking at 52.1 % and 46.1 %, respectively, at 450 °C. The catalyst’s improved performance in the plasma environment can be attributed to the enhanced metal-support interaction between NiO and the CeO2 NR support, a consequence of the rich surface oxygen vacancy concentration. However, this increase in conversion was accompanied by an escalation in carbon deposition. Considering contributions from the thermal DRM process, the optimal operating temperature was determined as 350 °C. Increasing plasma power at this temperature led to enhanced conversion. However, beyond a threshold of 23.8 W power, the reaction path altered, resulting in reduced syngas output. Increasing the CH4:CO2 feed gas flow ratio, while maintaining constant plasma power and temperature, elevated H2/CO generation. Moreover, increasing the total flow rate under identical conditions, with a constant feed gas flow ratio, reduced both conversions due to decreased chemical residence time. Consequently, under a constant feed gas ratio, a higher syngas yield is achievable with lower overall flow rates.

Improving bio aviation fuel yield from biogenic carbon sources through electrolysis assisted chemical looping gasification

The second-generation bio aviation fuel production via Chemical Looping Gasification (CLG) of biomass combined with downstream Fischer-Tropsch synthesis is a possible way to decarbonize the aviation sector. Although CLG has a higher syngas yield and conversion efficiency compared to the conventional gasification processes, the fraction of biogenic carbon which is converted to biofuel is still low (around 28%). To increase carbon utilization and biofuel yield, incorporation of two types of electrolyzers, Polymer Electrolyte Membrane (PEM) and Molten Carbonate Electrolysis Cell (MCEC), for syngas conditioning has been investigated. Full chain process models have been developed using an experimentally validated CLG model in Aspen Plus for Iron sand as an oxygen carrier. Techno-economic parameters were calculated and compared for different cases. The results show that syngas conditioning with sustainable hydrogen from PEM and MCEC electrolyzers results in up to 11.5% higher conversion efficiency and up to 8.1 % higher biogenic carbon efficiencies in comparison to the syngas conditioning with water gas shift reactor. The study shows that the lowest carbon capture rates are found in the configurations with the highest biogenic carbon efficiency which means up to 14% more carbon ends up in FT crude compared to the case with conventional WGS conditioning. Techno-economic analysis indicates that syngas conditioning using PEM and MCEC electrolyzers would result in an increase of the annual profit by a factor of 1.4 and 1.7, respectively, when compared to using only WGS reactors.

Evaluation of Engineered Biochar-Based Catalysts for Syngas Production in a Biomass Pyrolysis and Catalytic Reforming Process

Biochar, originating from biomass pyrolysis, has been proven a promising catalyst for tar cracking/reforming with great coke resistance. This work aims to evaluate various engineered biochar-based catalysts on syngas production in a biomass pyrolysis and catalytic reforming process without feeding extra steam. The tested engineered biochar catalysts include physical- and chemical-activated, nitrogen-doped, and nickel-doped biochars. The results illustrated that the syngas yields were comparable when using biochar and activated biochar as catalysts. A relatively high specific surface area (SSA) and a hierarchical porous structure are beneficial for syngas and hydrogen production. A 2 h physical-activated biochar catalyst induced the syngas with the highest H2/CO ratio (1.5). The use of N-doped biochar decreased the syngas yield sharply due to the collapse of the pore structure but obtained syngas with the highest LHVgas (18.5MJ/Nm3). The use of Ni-doped biochar facilitated high syngas and hydrogen yields (78.2 wt % and 26 mmol H2/g-biomass) and improved gas energy conversion efficiency (73%). Its stability and durability test showed a slight decrease in performance after a three-time repetitive use. A future experiment with a longer time is suggested to determine when the catalyst will finally deactivate and how to reduce the catalyst deterioration.

Pyrolysis-gasification of biomass and Municipal Plastic Waste using transition metal modified catalyst to investigate the effect of contaminants

Pyrolysis and gasification are one of the possible solutions for the recycling of polymer waste. This work focussing to the combined pyrolysis-gasification of different wastes to investigate the effect of raw materials, temperature, and contaminants. To enhance the pyrolysis reactions different transition metal-containing catalysts were used: Ni/ZSM-5, Ce/Ni/ZSM-5, La/Ni/ZSM-5, Ce/La/ZSM-5. Different sourced biomasses, municipal plastic wastes and municipal solid waste had been used as raw materials with different amount of contaminants. Regarding biomass, the effect of nitrogen and sulphur were investigated to the product yields and composition, while that nitrogen and chlorine in case municipal plastic waste. The pyrolysis-gasification experiments had been performed in a two zones batch reactor in horizontal layout, where 500 °C were used in the pyrolysis step, while the gasification reactions were investigated at 500 and 800 °C in the presence of steam. The composition of gases were measured by GC-FID and GC-TCD, while that of the hydrocarbon oils by GC-FID and HPLC. It was found, that the raw material significantly affected the product yields; e.g. in addition hydrocarbon products, aqueous products found only in case of biomass and municipal solid waste, while municipal plastic waste pyrolysis-gasification resulted hydrocarbon gases, hydrocarbon oil and solid char. Significant amount of carbon monoxide and carbon dioxide can be obtained in case, when raw materials contained cellulose, hemicellulose or lignin in their main structure, however, the concentration of carbon monoxide can be increase at 800 °C in case of municipal plastic waste. The highest syngas yield can be found in case of plastic waste. The ratio of hydrogen/carbon monoxide, that of carbon bon monoxide and carbon dioxide and the structure of aromatic hydrocarbons can be also significantly affected by the raw materials and the contaminants.

Two-Step Gasification of Cattle Manure for Hydrogen-Rich Gas Production: Effect of Gasification Temperature, Steam Flow Rate, and Catalysts

Highlights Steam gasification parameters of cattle manure char were optimized. Effects of slow heating and fast heating modes on char gasification were analyzed. 1.92 m3/kg syngas yield and 88.72% C-conversion efficiency were obtained at 850 °C, with fast heating, 1.66 g/min of steam flow rate, and K2CO3 catalyst. Abstract. This study investigated the hydrogen-rich gas production from cattle manure char by steam gasification. The characteristics of char were studied by proximate analysis, ultimate analysis, thermogravimetric analysis, and XRD analysis. The effects of temperature, heating mode, steam flow rate, and catalyst on syngas yield, hydrogen yield, gas composition, heating value, and carbon conversion efficiency were explored. The results showed that the fixed carbon content in cattle manure char was 34.46%, an increase of 2.24 times compared with that of cattle manure, and the cattle manure char had a high fixed carbon content and thermal stability. The steam gasification indicated that the high temperature and fast heating could obtain high syngas and hydrogen yields. The steam flow rate played an important role in the char and steam reforming reactions. The SiO2 and ash catalysts had an inhibitory effect on the steam gasification of char. However, the K2CO3 catalyst improved the syngas and hydrogen yields. The optimal parameters in this study were 850 °C, fast heating, 1.66 g/min of steam flow rate, and K2CO3 catalyst. By comparison, the syngas and hydrogen production of char were better than those of biomass. As a result, the steam gasification of char was a promising method for producing hydrogen-rich gas. Keywords: Catalysts, Cattle Manure Char, Hydrogen, Steam Flow Rate, Steam Gasification.

Experimental microwave-assisted air gasification of biomass for syngas production

Syngas production from biomass is a clean way to supply energy for our economy and society. In this study, a microwave-assisted air gasification system was developed and the preliminary results of syngas yields, syngas compositions, syngas lower heating values (LHVs), carbon conversion efficiencies, and cold gas efficiencies obtained from corn stover (CS) gasified at varied air flow rates (200, 400, and 600 mL/min), gasification temperatures (500, 600, and 700 °C), and retention times (10, 20, and 30 min) were reported for the first time. The results showed that the increase in air flow rate increased the syngas yield and carbon conversion efficiency, decreased the syngas LHV whereas first increased then decreased the cold gas efficiency. Higher gasification temperature favored the syngas yield, syngas LHV, carbon conversion efficiency and cold gas efficiency. Longer retention time favored the syngas yield and carbon conversion efficiency whereas lowered the syngas LHV and cold gas efficiency. Syngas yield of 38.90–76.14 wt% and LHV of 4.95–6.34 MJ/m3 were observed for the syngas at air flow rate of 200–600 mL/min, gasification temperature of 500–700 °C and retention time of 10–30 min. The most significant contribution of this study is the high syngas yield, which is even higher than that from a microwave-assisted pyrolysis process at a high temperature of 900 °C.

Experimental microwave-assisted air gasification of biomass in fluidized bed reactor

Microwave-assisted heating is an effective heating method for thermochemical conversion of biomass. In this study, experimental syngas production from microwave-assisted air gasification of biomass in a fluidized bed reactor at different gasification temperatures, equivalence ratios and silicon carbide loads, was studied and reported. The results showed that the highest syngas yield (78.2 wt%), higher heating value (6.3 MJ/Nm3) and cold gas efficiency (81.8 %) were obtained at gasification temperature of 900 °C, equivalence ratio of 0.35 and silicon carbide load of 30 g, and the gasification temperature had significant influence on the syngas production. Microwave-assisted heating showed positive effect on tar reduction, i.e., the tar content at 900 °C (2.1 wt%) in this study was even lower than the tar content (3.2 wt%) from catalytic electrical air gasification of rice husk at 950 °C. Generally, the introduction of microwave-assisted heating showed positive effect on biomass gasification.

Enhancement of the production of aromatics and bio-syngas from microwave ex-situ pyrolysis based on Zn/Zr modified biochar and multi-catalysts

The main purpose of this work was to explore the effect of metal modified biochar and multi-catalysts on improving the quality of products by microwave pyrolysis (MVP) of biomass. Single-component catalysts and multi-catalysts were prepared by Zn/Zr impregnation methods. The prepared catalysts were evaluated by XRD, BET, FT-IR and SEM. The properties, composition and product distribution of bio-oil and bio-syngas were analyzed. The results showed that ZSM-5 obtained more bio-oil (42.16 wt%) at the expense of gas product yield, and BC obtained the highest gas yield (43.10 wt%). Zn promoted the selectivity of aromatic hydrocarbons in bio-oil, Zr could effectively improve the yield of syngas and upgrading bio-oil, respectively. Zr-modified multi-catalyst was prepared, and the highest syngas yield (91.54 vol%) and aromatic hydrocarbon products were obtained. Among them, the selectivity of monocyclic aromatic hydrocarbons (MAHs) reached 21.82%. The mechanism of MVP of biomass under the effect of Zn/Zr modified different catalysts was proposed. The study has successfully demonstrated an approach for producing high-value bio-oil and bio-syngas from microwave multi-catalyst pyrolytic system.

Valorization of sludge using microwave pyrolysis for green bio-energy: Combined effects of key parameters on the directional optimization of high-quality syngas

To directionally convert sludge into the high-quality syngas, the effects of various parameters on the biogas produced by the sludge microwave pyrolysis are explored, and the syngas generation mechanism under the synergistic effect of parameters is revealed. The results showed that the pyrolysis final temperature, reaction time, and the amount of the microwave absorber were the key factors that affected the biogas yield. A response surface analysis was used to explore the synergistic effect of each key parameter on the yield and the lower heating vale (LHV) of syngas. The pyrolysis temperature was the key to driving syngas generation. Properly prolonging the reaction time decreased the formation of tar by-products and increased the syngas yield. The addition of a microwave absorber increased the heating rate by enhancing the conversion efficiency of microwave energy, and this contributed to accelerating the dehydrogenation and the Boudouard reactions to promote the generation of H2 and CO. Under high temperature conditions (900 °C), a higher syngas yield (10.25–34.31 mol/kgDS) and LHV (4.85–14.53 MJ/kgDS) were obtained in a shorter period time by synergistically optimizing the amount of microwave absorbers (8–10 g) and the reaction time (28–40 min). As the pyrolysis temperature increased, the H2 content gradually rose to the peak, while the content of CO continued to increase. By analyzing the evolution of the specific pyrolysis products, the secondary pyrolysis of bio-oil at high temperatures and the Boudouard reaction were found to be the primary pathways that promoted syngas generation. This research provides strategic guidance for producing high-quality syngas using the microwave pyrolysis of waste biomass, thereby minimizing the exploration cost of basic experiments and providing directional control of the syngas quality.

Evaluation of Different Oxygen Carriers for Chemical Looping Reforming of Toluene as Tar Model Compound in Biomass Gasification Gas: A Thermodynamic Analysis

A thermodynamic study on a toluene chemical looping reforming process with six metal oxides was conducted to evaluate the product distribution for selecting an appropriate oxygen carrier with thermodynamic favorability towards high syngas yield. The results show that a suitable operation temperature for most oxygen carriers is 900 °C considering syngas selectivity and solid C formation whether the toluene is fed alone or together with fuel gas. The syngas selectivity of all oxygen carriers decreases with the increasing equivalence ratio, but the decrease degrees are quite different due to their different thermodynamic natures. With the increasing amounts of H2 and CO, the syngas selectivity for various oxygen carriers correspondingly decreases. The addition of CO2 and H2O(g) benefits reducing the solid C formation, whereas the addition of CH4 leads to more solid C being produced. Under the simulated gasification gas atmosphere, a synergetic elimination of solid C and water–gas shift reactions are observed. In terms of syngas selectivity, Mn2O3 possesses the best performance, followed by CaFe2O4 and Fe2O3, but NiO and CuO exhibit the lowest performance. BaFe2O4 presents a high H2 selectivity but a very poor CO selectivity due to the formation of BaCO3, which has a high thermodynamic stability below 1200 °C. Nevertheless, Mn2O3 is more likely to form solid C than feeding toluene alone and has a lower melting point. Considering syngas selectivity, carbon deposit and melting point, CaFe2O4 exhibits the highest performance concerning the tar chemical looping.

Comparative evaluation of microwave and conventional gasification of different coal types: Experimental reaction studies

Effects of gasifier conditions (microwave or conventional) on the gasification characteristics of four different types of coal are evaluated by analysis of gaseous species generated during pyrolysis and gasification reactions. Four different coal samples are tested: a lignite (Mississippi), a low-ash subbituminous (Wyodak), a high-ash subbituminous (Usibelli), and a low volatile bituminous (Pocahontas #3). Gas composition, overall yields, carbon conversion efficiency, and cold gas efficiency are evaluated to compare gasification reactivity of the different coal types under microwave and conventional heating. During microwave pyrolysis (Ar atmosphere), greater selectivity of syngas species (H2 + CO) and greater overall non-condensable gas yields are observed, compared to conventional pyrolysis for all coals tested. The high yield of syngas during microwave pyrolysis is attributed to primary pyrolysis gases subsequently gasifying the char of the same sample to produce greater amounts of H2 and CO. During microwave gasification (CO2 atmosphere), selective heating and formation of hotspots within the coal enable the reverse Boudouard reaction to occur at a low bulk gasification temperature of 700 °C, which is less favorable under thermal gasification at this temperature. Yields of syngas are much higher under microwave gasification of all coals. Carbon conversion is found to have a linear correlation with volatile matter of the parent coal. Carbon conversion and cold gas efficiency are highest for coals gasified under microwave irradiation, and gasification reactivity of the four coals was determined to be dependent on the coal type.

Porous coal char-based catalyst from coal gangue and lignite with high metal contents in the catalytic cracking of biomass tar

In this study, coal gangue and lignite with high metals-containing are used to prepare porous coal char-based catalysts for biomass tar decomposition via a simple pyrolysis method under CO2 atmosphere. The CO2 etching during the preparation process of the catalysts helps to improve the porosity of the coal char, and the metals in coal are exposed on the surface of the catalyst, thus enhancing the adsorption of the catalysts to the reactants and contact possibility of the reactants with the metals. The activity of the catalysts is influenced by the metals content and preparation temperature, and the coal gangue char prepared at 800 °C (CG-800) exhibits the highest catalytic activity in this work. At a reforming temperature of 700 °C, the conversion efficiency of biomass pyrolysis tar reaches 91.2% using CG-800 as the catalyst with a high total syngas yield of 516 mL/g. Moreover, part of the metal oxides in the catalysts can be reduced by the reducing gases during the tar reforming process, which can further help the catalysts maintain high catalytic activity in the recycling process. During the five-time reuse, the catalysts exhibit excellent stability with only a slight loss in tar conversion and total gas yield.

Upgrading waste plastic derived pyrolysis gas via chemical looping cracking–gasification using Ni–Fe–Al redox catalysts

A novel chemical looping cracking–gasification process was investigated to produce separate H2 and syngas from plastic-derived pyrolysis gas over synthetic Ni–Fe–Al redox catalysts. The non-condensable pyrolysis gas was catalytically cracked at 800 °C, followed by catalyst regeneration with steam. The highest activity was obtained over NiFeAl (molar Ni:Fe:Al = 1:1:1), producing concentrated H2 (83.1 vol%, 0.46 mol g(Ni+Fe)−1) and coke intermediate (232.1 wt%) from cracking. During the steam gasification stage, coke removal efficiency of 96% was obtained with a high syngas yield of 0.89 mol g(Ni+Fe)−1. With equimolar Ni/Fe, increasing Al/(Ni+Fe) ratio led to decreased catalyst activity due to enhanced metal–support interaction. Plausible reaction mechanisms were proposed to interpret the catalytic effects on tuning the morphologies, chemical structure and activity of the coke deposits. This work demonstrates the important role of Ni–Fe–Al catalysts on the production of H2 and syngas via chemical looping cracking–gasification process.