The steam reforming of naphthalene over a nickel–dolomite cracking catalyst

With naphthalene as a model compound, catalytic cracking experiments on biomass tar were made on Ni–dolomite catalysts. The performance of catalyst preparation, activity, coke formation and regeneration were analysed. The results showed that the ratio of the one-step conversion of naphthalene was 95% at space velocity 0.81 h⁻¹ and 700 °C; with saturated wet air as regeneration gas, the regeneration time was within 0.5 h; compared with thermal cracking at the same reaction temperature, the catalytic cracking was propitious to deep cracking of naphthalene.     

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.     

Numerical simulation on biomass-pyrolysis and thermal cracking of condensable volatile component

We studied the physical and chemical properties of the condensable volatiles of biomass pyrolysis products. We redefine the liquid product and divide the condensable volatiles into two categories, biomass oil and tar, the latter of which comes from the secondary pyrolysis or cracking reaction of the former. We further establish a kinetic model of biomass pyrolysis and secondary cracking. The chemical reaction kinetics equation and heat transfer equation are coupled to simulate the biomass pyrolysis process. For biomass solid particles, the model not only considers the initial reaction of biomass and secondary cleavage reaction of condensable gas, but also introduces a reaction mode in which biomass oil is converted into tar. When the pyrolysis temperature is below 500 °C, the pyrolysis products are essentially biomass oil. However, when the pyrolysis temperature exceeds 500 °C, the biomass oil gradually converts into tar. The model also considers characteristics of the reaction medium (porosity, intrinsic permeability, thermal conductivity) and the unsteady gas phase process based on Darcy's law of velocity and pressure, heat convection, diffusion, and radiation transfer. We analyze the relationships among the internal temperature of the particles, particle size and position, mass fraction of the reactants and products, the gas mixture, the production share of tar and biomass oil, and the relationship between gas pressure and time. The results show that the effects of the secondary cracking reaction and internal convective flow in the biomass pyrolysis process are coupled because the flow field in the porous medium determines the volatile residence time and thus species that affect the secondary cracking reaction. The rate of volatile formation in the initial and secondary cracking reactions affects the pressure gradient and gas diffusion. Additionally, the endothermic effect influences the temperature field of the pyrolysis reaction but has no apparent effect on small particles whose chemical reaction is the control mechanism. For large particles, heat transfer inside the particles is the diffusion control mechanism and the chemical reaction on the particle surface is the speed control mechanism. Two peaks are observed in the pyrolysis gas mass proportion curve, which result from the consumption of biomass oil and tar as they flow toward hot surfaces. The first peak is the decomposition of biomass oil into non-condensable volatile matter and tar, and the second peak is the further cracking of tar into gas and coke at high temperature.     

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.     

Experimental study on catalytic effect of biomass pyrolysis volatile over nickel catalyst supported by waste iron slag

The study aims to analyze catalytic tar destruction, evaluate the activity of the Ni‐based catalyst supported by waste iron slag, and obtain clean pyrolysis syngas. The effects of different nickel loadings, catalytic temperatures, and catalyst calcination temperatures on volatile were investigated in order to determine the optimal process condition. The analysis results showed that the iron slag Ni‐based catalyst had a relatively low specific surface area. However, it showed an excellent resistance performance to the coke deposition and displayed the high tar removal ability. Moreover, the tar conversion and the yield of syngas were significantly affected by nickel loadings. When the nickel loading reached 3%, the tar dew point was decreased by nearly 100 °C and the tar conversion reached 94.84%. The favorable reaction temperature was about 800 °C based on the consideration of energy consumption and the catalytic performance. Calcination temperature affected tar yield and syngas yield. The application of iron slag in nickel catalyst realized the reutilization of waste materials, indicating significant practical values. Copyright © 2017 John Wiley & Sons, Ltd.     

Preparation of NiO / PC catalyst with plasma for cracking tar to produce flammable gas

To increase the use of lignite, the tar was pyrolyzed with pyrolysis coke (PC) to produce more combustible gases such as H₂, CH₄, and CO. NiO/PC catalyst with plasma was prepared, and the influence of PC and NiO/PC catalyst on flammable gas was investigated in a two-stage fixed reactor. The catalysts were characterized by SEM, BET, XPS and XRD to analyze the tar cracking mechanism. The results were: (1) PC was prepared at different heating rates, and when the heating rate reached 20 °C/min, the amount of flammable gas was 5.4 L. (2) NiO/PC catalyst was modified with plasma in three background gases withO₂ being the best, mainly because of the increase of the oxygen functional groups. (3) PC was modified and calcined with plasma, and when the power reached 40 W, it produced the most combustible gas, and the volume could grow by 94.4%.     

Modeling of beech wood pellet pyrolysis under concentrated solar radiation

A two-dimensional, unsteady CFD (Computational Fluid Dynamics) single particle model was developed and used to simulate the solar pyrolysis process of beech wood pellets (10 mm in diameter and 5 mm in height). Pseudo-stoichiometric coefficients about the mass fraction of primary tar converted by the reaction into gas and secondary tar were determined at different temperatures and heating rates for the first time. The 2D model predictions were successfully validated with tests performed at 600 °C to 2000 °C final temperature, with 10 and 50 °C/s heating rates. The evolution of the final products and mass losses of pyrolyzed biomass are enhanced with temperature and heating rate. Moreover, the higher the temperature and heating rate, the higher the gas yield. This emphasizes the intra-particle tar secondary reaction into gas for pyrolysis of large size sample under high temperature and heating rate.     

High quality H2-rich syngas production from pyrolysis-gasification of biomass and plastic wastes by Ni–Fe@Nanofibers/Porous carbon catalyst

To produce the high quality H₂-rich syngas from biomass and plastic wastes, a two-stage pyrolysis-gasification system involving pyrolysis and catalytic gasification is considered as a suitable route. Generally, synthesis of highly active, low cost and coke-resistant catalyst for tar cracking is the key factor. A series of monometallic catalysts of Ni@CNF/PCs and Fe@CNF/PCs and the bimetallic Ni–Fe@CNF/PCs catalyst were prepared by a simple one-step pyrolysis approach for high quality syngas production from pyrolysis-gasification of biomass and plastic wastes. The results indicated that the bimetallic Ni–Fe@CNF/PCs catalyst appeared as the optimal catalyst in affording the best compromise between catalytic activity and stability with the existence of the excellent dispersibility of the Fe0.64Ni0.36 alloy nanoparticles and the carbon nanofibers/porous carbon composite structure. In addition, the optimal operation conditions of biomass/plastic ratio of 1/2 and gasification temperature of 700 °C were observed for the bimetallic Ni–Fe@CNF/PCs catalyst to play best roles in the H₂-rich syngas quality, with up to 33.66 mmol H₂/g biomass, and tar yields as low as 5.66 mg/g.     

Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm³/g_wood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm³/g_wood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.     

A novel nickel catalyst supported on activated steel slags for syngas production and tar removal from biomass pyrolysis

In this paper, a nickel-based steel slag catalyst prepared by wet impregnation was used to carry out a catalytic reforming experiment with the primary volatiles produced by pyrolysis of pine sawdust. The effects of nitric acid activation, acid-base activation, Fe promoter modification, and calcination/catalytic temperature on the catalytic performance were explored. A series of catalyst characterization methods were used to analyze the catalytic activity and coke deposition resistance. The analysis results showed that the 0.5M-Ni/SS-800 catalyst had the optimal catalytic effect. The tar conversion rate reached 97.61% and the gas yield was increased by 15.3%. The production of hydrogen was even increased by 20.23%. The elements such as Ni, Fe, Ca, and Mg in the catalyst had a synergistic catalytic effect and formed active centers such as Ni–Fe alloy, Ca₂Fe₂O_5, and MgFe₂O₄, which significantly improved the catalytic activity and coke deposition resistance.     

Hydrogen production via in-line pyrolysis-reforming of organic solid waste enhanced by steel slags

Steel slag derivates prepared from waste steel slag using acid leach method, are employed to promote hydrogen production from organic solid waste by in-line pyrolysis-steam reforming of Chinese medicine residues (CMR). The optimum pyrolysis conditions are determined during the fast pyrolysis experiment of CMR (T_prolysis = 800 °C, F_N2 = 200 mL_STP/min). During in-line pyrolysis-reforming of CMR with steel slag derivates, for example CaO(SS)-50 wt%LR compounds, as reforming catalyst, the hydrogen yield is profoundly increased from 7.57 mmol/g_CMR (pyrolysis operation) to 11.49 mmol/g_CMR, while tar yield has been reduced 30.50%. FeO_x in LR remarkably increases lattice oxygen and adsorption oxygen in NCA-LR or NCA-LR-CaO(SS) compounds, so tar and CO conversion are efficiently improved while coke deposition on catalyst surface is significantly reduced. LR is demonstrated to be able to act as or partially alternate nickel-based catalyst during steam reforming of pyrolysis gas, which would greatly reduce the cost of hydrogen production from OSWs.     

Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 °C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N₂ adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal efficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O-containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C–H and aliphatic C–H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring components. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH₄ cracking. AAEMs have a catalytic activity on CH₄ cracking. K is particularly effective in improving tar conversion and hydrogen production of biochar.     

Enhanced multi-cycle CO2 capture and tar reforming via a hybrid CaO-based absorbent/catalyst: Effects of preparation,reaction conditions and application for hydrogen production

A hybrid CaO-based absorbent/catalyst (Ca–Al–Fe) for calcium looping gasification (CLG) is prepared by a two-step sol-gel method. The effects of preparation and “carbonation-calcination” conditions on cyclic carbonation performance of Ca–Al–Fe are investigated. Calcination temperature of 900 °C and calcination time of 4 h are suitable parameters for absorbent preparation. The CaO conversion of Ca–Al–Fe increases with increasing carbonation temperature below 750 °C. Under severe calcination conditions such as high temperature, high CO₂ concentration and long-term up to 40 cycles, Ca–Al–Fe still shows good cyclic CO₂ capture reactivity. Moreover, the effect of Ca–Al–Fe on tar removal enhancement is investigated in comparison with three candidate absorbents (Ca、Ca–Fe and Ca–Al). During five toluene reforming cycles, Ca–Al–Fe presents the highest average H₂ yield and the least deposited coke with an average hydrogen concentration of about 68.8%. The average toluene conversion with Ca–Al–Fe is about 26.41% higher than that using conventional CaO.     

Coke formation in the co-production of hydrogen and phenols from pyrolysis-reforming of lignin

The phenolics derived from pyrolysis of lignin are important fractions of bio-oil, which could be reformed to generate hydrogen. Nevertheless, some phenolics are value-added chemicals and they might not have to be utilized as source of hydrogen. In this study, we have explored the concept of co-production of hydrogen and phenolics via a pyrolysis-reforming process at the low to medium temperatures of 450–650 °C over Ni/Al₂O₃ catalyst. The results indicated that, below 500 °C, pyrolysis of lignin was almost the exclusive reaction route to form phenolics of varied side chains. The effective reforming of the phenolics initiated at 600 °C and became remarkable at 650 °C. Meanwhile, cracking of the methoxy group and other side chains of the phenolics was also intense at these higher temperatures, producing phenol as the main phenolic compound. Polymerization of the phenolics on Ni/Al₂O₃ catalyst occurred from 450 to 650 °C, while the gasification of the precursors of coke accelerated at 650 °C, forming remarkably lower amount of coke together with enhanced yield of hydrogen. The coke formed from the phenolics was generally the polymeric type with abundant aliphatic structures like C–O–C, –OH and -C-H, low thermal stability, low carbon crystallinity, hydrophilic surface and amorphous morphology at 450–650 °C. The polymerization or cracking of the phenolics could form multiple carbon layers in the vicinity of nickel species, and also on alumina.     

Steam reforming of hot gas from gasified wood types and miscanthus biomass

The reforming of hot gas generated from biomass gasification and high temperature gas filtration was studied in order to reach the goal of the CHRISGAS project: a 60% of synthesis gas (as x(H₂)+ x(CO) on a N₂ and dry basis) in the exit gas, which can be converted either into H₂ or fuels. A Ni-MgAl₂O₄ commercial-like catalyst was tested downstream the gasification of clean wood made of saw dust, waste wood and miscanthus as herbaceous biomass. The effect of the temperature and contact time on the hydrocarbon conversion as well as the characterization of the used catalysts was studied. Low (<600 °C), medium (750°C–900 °C) and high temperature (900°C–1050 °C) tests were carried out in order to study, respectively, the tar cracking, the lowest operating reformer temperature for clean biomass, the methane conversion achievable as function of the temperature and the catalyst deactivation. The results demonstrate the possibility to produce an enriched syngas by the upgrading of the gasification stream of woody biomass with low sulphur content. However, for miscanthusthe development of catalysts with an enhanced resistance to sulphur poison will be the key point in the process development.     

稻壳连续热解特性研究

在自行研制的生物质连续热解反应装置上进行稻壳连续热解和二次裂解实验研究。随着稻壳热解温度的提高,炭产率降低,气体产率增加,液体产率先增加后减少;随着滞留时间的减少,炭产率、液体产率增加,气体产率减少。稻壳热解气以CO2和CO为主,且二者为竞争关系,热解温度提高,CO2产量降低,CH4、H2、C2H4、C2H6产量增加,CO的产率变化不大;滞留时间对热解气组分影响不大。二次裂解温度提高,裂解气中的H2、CH4、C2H4含量明显增加,二次裂解温度为800℃时,H2产率达到12%。稻壳500℃热解挥发物600℃二次裂解木醋液中醋酸含量高达49.44%,焦油中检测到的物质主要为丙酮和异丙醇。     

Effect of synthesis temperature on catalytic activity and coke resistance of Ni/bio-char during CO2 reforming of tar

Understanding how the synthesis parameters affect nickel particle distribution is critical to the synthesis of Ni/bio-char with excellent catalytic performance. In this work, the influence of synthesis temperature on catalytic activity and coke resistance of Ni/bio-char during CO₂ reforming of tar was explored. With the increase of synthesis temperature from 200 °C to 250 °C, the dispersion of nickel precursor into bio-char was promoted, resulting in an increase in crystallite size of metallic nickel particle from 51.98 nm to 62.45 nm. Besides, parts of the metallic nickel particles were oxidized to nickel oxides, providing more lattice oxygen to oxidize the coke deposited on the catalyst. However, further increasing the synthesis temperature to 300 °C would aggravate the oxidation of active nickel particles. The increase in crystallite size of nickel oxide particle from 23.25 nm to 43.38 nm could block the pore structure and hinder the access of reactants, resulting in a drop in the tar conversion rate from 40-51% to 13–27%.     

Experimental analysis of air-steam gasification of biomass with coal-bottom ash

Biomass gasification is an attractive option for producing high-quality syngas (H₂+CO) due to its environmental advantages and economic benefits. However, due to some technical problems such as tar formation, biomass gasification has not yet been able to achieve its purpose. The purpose of this work was to study the catalytic activity of coal-bottom ash for fuel gas production and tar elimination. Effect of gasification parameters including reaction temperature (700–900 °C), equivalence ratio, EQR (0.15–0.3) and steam-to-biomass ratio, SBR (0.34–1.02) and catalyst loading (5.0–13 wt %) on gas distribution, lower heating value (LHV) of gas steam, tar content, gas yield and H₂/CO ratio was studied. The tar content remarkably decreased from 3.81 g/Nm³ to 0.97 g/Nm³ by increasing char-bottom ash from 5.0 wt% to 13.0 wt%. H₂/CO significantly increased from 1.12 to 1.54 as the char-bottom ash content in the fuel increased from 5.0 wt% to 13.0 wt%.     

Mechanism of wet sewage sludge pyrolysis in a tubular furnace

The main objective of this work was to develop a preliminary mechanistic understanding of wet sewage sludge decomposition from starting constituents to final products, including intermediates formed during the pyrolysis process. Sewage sludge with a moisture content of 84.2 wt% was pyrolyzed at different temperatures in a tubular furnace, the pyrolysis products (hydrogen-rich fuel gas, tar and solid char) were detected by micro-GC, GC-MS, and FTIR, respectively. The high moisture content of wet sewage sludge generated a steam-rich atmosphere at high temperatures, leading to an in situ steam reforming of the volatile compounds and a partial gasification of the solid char, which contributed to the production of hydrogen-rich fuel gas. The pyrolysis process can be divided into two steps: at a relatively low temperature (<600 °C), the breaking of the C-H bonds of alkyl gave rise to the release of CH₄ and C₂ hydrocarbons, and a large amount of CO and CO₂ evolved as the result of CO decreasing, both processes indicated the decomposition of volatile compounds. The increasing absorbance amount of C-O and C-H_aromatic demonstrated the formation of tar. As temperature increased further, the diminishing IR absorbance of C-O and C-H_aromatic was accompanied by a significant reduction of tar yield and an increase of H₂. H₂ was considered as an indicator for the occurrence of tar cracking. The Diels-Alder reaction mechanism followed by dehydrogenation was employed to explain the PAHs formation.     

催化剂粒径与质量对生物质热解焦油催化裂化反应的影响

针对催化裂化条件对生物质热解焦油处理的影响,以秸秆热解产生的焦油为原料,在固定床焦油催化裂化反应试验台上研究了催化剂作用下焦油催化裂化的过程,并对催化剂粒径和质量等参数对焦油转化效果和催化裂化产物的影响进行了分析．结果表明：减小催化剂的粒径或者增加催化剂质量能促进燃气中高热值大分子气体转化为低热值的小分子轻质气体,从而有效促进焦油裂化,提高燃气产率,降低燃气热值．