Catalytic decomposition of tar derived from biomass pyrolysis using Ni-loaded chicken dropping catalysts

The Ni-loaded chicken droppings (Ni/CD) and chicken dropping ash (Ni/CDA) were prepared by the impregnation method and applied as catalysts for biomass tar decomposition at low temperature (450 °C) under N₂ and steam/N₂ conditions. The prepared samples and the supports were characterized by N₂ adsorption measurements, X-ray diffraction, H₂ temperature-programmed reduction, and X-ray photoelectron spectroscopy. The results reveal that Ni/CD and Ni/CDA showed higher catalytic activity for tar decomposition, in terms of producing hydrogen-rich gas, relative to commercial Ni/Al₂O₃ under N₂ conditions. This higher activity was caused by lower interactions of Ni with the support and the presence of additional reduced Ni. In the case of steam reforming, Ni/CDA also showed higher hydrogen yield and a lower amount of carbon deposition than Ni/Al₂O₃. This result indicates that a hydrophilic hydroxyapatite in the CDA support promoted the water–gas shift reaction to suppress carbon deposition and increase hydrogen yield.     

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

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

Tar removal from biomass pyrolysis gas in two-step function of decomposition and adsorption

Tar content in syngas pyrolysis is a serious problem for fuel gas utilization in downstream applications. This paper investigated tar removal, by the two-step function of decomposition and adsorption, from the pyrolysis gas. The temperature of the tar decomposition process was fixed at 800 °C both with and without steam, with air as the reforming agent. Both steam and air had a strong influence on the tar decomposition reaction. The reduction of the gravimetric tar mass was 78% in the case of the thermal cracking, whereas, it was in the range of 77–92% in the case of the steam and air forming. Under conditions of tar decomposition, the gravimetric tar mass reduced, while the yield of the combustible gaseous components in the syngas increased. Synchronously, the amount of light tars increased. This should be eliminated later by fixed-bed adsorption. Three adsorbents (activated carbon, wood chip, and synthetic porous cordierite) were selected to evaluate the adsorption performance of light tars, especially of condensable tar. Activated carbon showed the best adsorption performance among all light tars, in view of the adsorption capacity and breakthrough time. On the other hand, activated carbon decreased the efficiency of the system due to its high adsorption performance with non-condensable tar, which is a combustible substance in syngas. Synthetic porous cordierite showed very low adsorption performance with almost all light tars, whereas, wood chip showed a high adsorption performance with condensable tar and low adsorption performance with non-condensable tar. When compared with other adsorbents, wood chip showed a prominent adsorption selectivity that was suitable for practical use, by minimizing the condensable tar without decreasing the efficiency of the system.     

Biomass thermochemical conversion: A review on tar elimination from biomass catalytic gasification

Biomass is promising renewable energy because of the possibility of value-added fuels production from biomass thermochemical conversion. Among the thermochemical conversion technology, gasification could produce the H₂-rich syngas then into value-added chemicals via F-T (Fischer-Tropsch) synthesis. However, a variety of difficulties, such as tar formation, reactors impediment, complex tar cracked mechanism, etc. make it difficult to develop for further application. This paper sheds light on the developments of biomass thermochemical conversion, tar classifications, tar formation, and elimination methods. Secondly, we provide a comprehensive the state-of-the-art technologies for tar elimination, and we introduce some advanced high activity catalysts. Furthermore, many represent tar models were employed for explanation of the tar-cracked pathway, and real tar-cracked mechanism was proposed. Following this, some operational conditions and effective gasified models were concluded to give an instruction for biomass catalytic gasification.     

Catalytic reforming of biomass primary tar from pyrolysis over waste steel slag based catalysts

Steel slag (SS) contains high amounts of metal oxides and could be applied as the catalyst or support material for the reforming of biomass derived tar. In this research, steel slag supported nickel catalysts were prepared by impregnation of a small amount of nickel (0–10 wt%) and calcination at 900 °C, and then tested for the catalytic reforming of biomass primary tar from pine sawdust pyrolysis. The steel slag after calcination was mainly composed of Fe₂O₃ and MgFe₂O₄, and granular NiO particles was formed and highly dispersed on the surface of nickel loaded steel slag which lead to a porous structure of the catalysts. The steel slag showed good activity on converting biomass primary tar into syngas, and its performance can be further enhanced by the loading of nickel. The yield of H₂ increased significantly with the increase of nickel loading amount, while excessive nickel loading resulted in the decrease in CO and CH₄ yields and significant increase in CO₂ yield. The presence of steam contributed to enhancing the tar steam reforming as well as reactions between steam and produced gases, while decrease the contact probability between the reactants and the active sites of catalysts, leading to a little decrease in tar conversion efficiency but significant increase in syngas yield. The iron and nickel oxides were reduced by the syngas (CO and H₂) from the biomass pyrolysis, and stable and porous structure was formed on the surface of the nickel loaded catalysts during tar reforming.     

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.     

Co-gasification of biomass and coal for methanol synthesis

In recent years, a growing interest has been observed in the application of methanol as an alternative liquid fuel, which can be used directly for powering Otto engines or fuel cells achieving high thermodynamic efficiencies and relatively low environmental impacts. Biomass and coal can be considered as a potential fuel for gasification and further syn-gas production and methanol synthesis. In the near future, the economy of methanol production through coal and biomass gasifications can be achieved by their linking with modern gas-steam power systems. The essence of linking is the full utilisation of the capacity of coal/biomass gasification installations. The up-to-date experience of coal and biomass gasification, including gas processing towards syn-gas and methanol production, is described and discussed. A conceptual flow diagram of pressurized and oxygen feeded co-gasification of biomass and coal integrated with combined cycle and parallel methanol production is evaluated. The effect of methanol production rate on the economy of power production is assessed.     

Synthesis and evaluation of biochar-derived catalysts for removal of toluene (model tar) from biomass-generated producer gas

Challenges in removal of contaminants, especially tars, from biomass-generated producer gas continue to hinder commercialization efforts in biomass gasification. The objectives of this study were to synthesize catalysts made from biochar, a byproduct of biomass gasification and to evaluate their performance for tar removal. The three catalysts selected for this study were original biochar, activated carbon, and acidic surface activated carbon derived from biochar. Experiments were carried out in a fixed bed tubular catalytic reactor at temperatures of 700 and 800 °C using toluene as a model tar compound to measure effectiveness of the catalysts to remove tar. Steam was supplied to promote reforming reactions of tar. Results showed that all three catalysts were effective in toluene removal with removal efficiency of 69–92%. Activated carbon catalysts resulted in higher toluene removal because of their higher surface area (∼900 m²/g compared to less than 10 m²/g of biochar), larger pore diameter (19 A° compared to 15.5 A° of biochar) and larger pore volume (0.44 cc/g compared to 0.085 cc/g of biochar). An increase in reactor temperature from 700 to 800 °C resulted in 3–10% increase in toluene removal efficiency. Activated carbons had higher toluene removal efficiency compared to biochar catalysts.     

A novel utilized method of tar derived from biomass gasification for fabricating binder-free all-solid-state hybrid supercapacitors

As an industrial pollutant, tar derived from biomass gasification is used as the precursor for fabricating a novel carbon-metal hydroxides composite electrode. A slurry (the mixture of tar, KOH and melamine) is daubed uniformly onto the nickel foam, which is directly carbonized to form NPC@LDH electrode material. This electrode is further coated with NiCo-LDH nanosheets using an electrodeposition method to form NF@NPC@LDH. The newly made NF@NPC@LDH electrode exhibits a high specific capacity of 9.6 F cm⁻² at a current density of 2 mA cm⁻² and good rate performance (55.3% retention). Furthermore, a hybrid NF@NPC@LDH//NF@PC all-solid-state supercapacitor is fabricated, and the device exhibits high energy density of 1.28 mWh cm⁻³ at a power density of 8.04 mW cm⁻³, low resistance and good cycling stability.     

Thermodynamic analysis of combined unit of biomass gasifier and tar steam reformer for hydrogen production and tar removal

A combined unit of biomass gasifier and tar steam reformer (CGR) was proposed in this study to achieve simultaneous tar removal and increased hydrogen production. Tar steam reforming calculations based on thermodynamic equilibrium were carried out by using Aspen Plus software. Thermodynamic analysis reveals that when selecting appropriate operating conditions, exothermic heat available from the gasifier could sufficiently supply to the heat-demanding units including feed preheaters, steam generator and reformer. The effects of gasification temperature (T_gs), reforming temperature (T_ref) and steam-to-biomass ratio (S:BM) on percentages of tar removal and improvement of H₂ production were investigated. It was reported that the CGR system can completely remove tar and increase H₂ production (1.6 times) under thermally self-sufficient condition. The increase of H₂ production is mainly via the water–gas shift reaction.     

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.     

Iron and nickel doped alkaline-earth catalysts for biomass gasification with simultaneous tar reformation and CO2 capture

The tar reforming catalytic activity of iron and nickel based catalysts supported on alkaline-earth oxides CaO, MgO and calcined dolomite [a (CaMg)O solid solution] has been investigated in a fixed bed reactor operating at temperatures ranging from 650 to 850 °C; toluene and 1-methyl naphthalene were used as model compounds for tar generated during biomass gasification. The CO₂ absorption capacities of Fe/(CaMg)O and Ni/(CaMg)O were also investigated at the lower temperature condition (650 °C) at which the sorption process is thermodynamically favoured. It was found that iron and nickel may be optimised in the substrate particles to enhance both the catalytic activity and the carbon deposition resistance during catalytic tests, at the same time reducing critical limitations on CO₂ capture capacity.     

Environmental effects of coal gangue and its utilization

Coal gangue has accumulated huge coal gangue piles, occupying lots of land as well as having striking influence on the neighboring environmental effects. This paper seeks a new way of coal gangue treatment in which the coal gangue blended with shale and sludge was sintered in rotary kiln to form lightweight aggregates. The results show that the optimum mixture ratio of coal gangue, shale, and sludge is 50, 40, and 10 wt% and the corresponding indicators of aggregates obtained are: (a) bulk density of 658 kg/m³, (b) granule strength of 643N, (c) 1 h absorption water to be 13.8%.     

Catalytic decomposition of biomass tars: use of dolomite and untreated olivine

Although biomass is getting increased attention as a renewable energy source, one of the remaining problems still to be solved is the reduction of the high level of tar present in the product gas from gasification of biomass. The purpose of the present work is to study the activity of olivine and dolomite for tar destruction. Some researchers investigated olivine as bed material for biomass gasification. But it is not yet known how tars behave in the presence of olivine and whether olivine has some activity towards tar destruction. A slipstream from a lab-scale atmospheric bubbling-fluidised-bed gasifier (located at ECN) is passed through a secondary fixed-bed reactor where the additives are placed. For easy understanding, the results are represented in terms of the following tar classes; GC-undetectable tars (class 1), heterocyclic compounds (class 2), aromatic compounds (class 3), light polyaromatic compounds (class 4), heavy polyaromatic compounds (class 5). The general observation is that the conversion of all tar classes increases as the temperature was raised from 800 to 900 °C for both additives. The water-soluble heterocyclic compounds can be easily converted by thermal treatment. At the temperature of 900 °C, the water-soluble heterocyclic compounds are completely converted. A 48% decrease in heavy PAHs is observed with pure sand. Addition of 17 wt% olivine to the sand leads to a 71% decrease of PAHs at 900 °C, whereas addition of 17 wt% (pre-calcined) dolomite converted 90%. Also improvement in conversion of other tar classes is observed when olivine and dolomite are added during hot gas cleaning. A total tar amount of 4.0 g m₀⁻³ could be reduced to 1.5 and 2.2 g m₀⁻³ using dolomite and olivine, respectively, at a temperature of 900 °C. Inspite of this reduction in total tar concentration, a limited impact on the tar dewpoint is observed.     

Experimental study on high temperature catalytic conversion of tars and organic sulfur compounds

A 400 cpsi noble metal catalyst was used to test the conversion of tars and sulfur containing hydrocarbons in the presence of steam, hydrogen sulfide and ethene. In order to reproduce producer gas from biomass gasification, higher molecular hydrocarbons (toluene, naphthalene, phenanthrene, pyrene) and sulfur containing hydrocarbons (thiophene, benzothiophene, dibenzothiophene) were added to a syngas. The syngas consisted of H₂, CH₄, H₂O, CO, CO₂ and N₂. The catalyst was operated at temperatures between 620 °C and 750 °C and at gas hourly space velocity (GHSV) of 9000 h⁻¹ and 18,000 h⁻¹.     

A novel process simulation model for hydrogen production via reforming of biomass gasification tar

Process modeling and simulation are very important for new designs and estimation of operating variables. This study describes a new process for the production of hydrogen from lignocellulosic biomass gasification tars. The main focus of this research is to increase hydrogen production and improve the overall energy efficiency of the process. In this study, Aspen HYSYS software was used for simulation. The integration structure presented in this research includes sections like tar reforming and ash separation (Ash), combined heat and power cycle (CHP), hydrogen sulfide removal unit (HRU), water-gas shift (WGS) reactor, and gas compression as well as hydrogen separation from a mixture of gases in pressure swing adsorption (PSA). It was found that the addition of CHP cycle and the use of the plug flow reactor (PFR) model, firstly, increased the overall energy efficiency of the process by 63% compared to 29.2% of the base process. Secondly it increased the amount of hydrogen production by 0.518 kmol (H2)/kmol Tar as compared with 0.475 of the base process. Process analysis also demonstrated that the integrated process of hydrogen production from biomass gasification tars is carbon neutral.     

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.     

Evolution characteristics of different types of coke deposition during catalytic removal of biomass tar

The evolutions of different types of coke deposition, including amorphous carbon, carbon networks (CNWs) and carbon nanotubes (CNTs), were clarified on Ni-based catalyst during catalytic cracking and reforming of biomass tar. Different from the changing of total coke, the amount of amorphous carbon gradually increased at the decreasing rate, while the amount of graphite carbon (CNWs and CNTs) firstly increased and then decreased after 60min reactions. The formation of amorphous carbon was prior to that of graphite carbon, and it was proved that a part of amorphous carbon converted to graphite carbon. After the 60min reaction, the proportion of graphite carbon and graphitization degree of coke decreased. The graphite carbon underwent the aging process in which the graphite structure would be destroyed to amorphous carbon. In cracking reaction, CNWs was the main type of graphite carbon which encapsulated the Ni particles with graphitic layers. After the addition of steam, the toluene conversion and coke amount remarkably increased in reforming reaction. Plenty of CNTs grew on the surface of catalysts and the amount of CNTs reached the maximum of about 200mg/g-cata at 60min. These research results are important for understanding the formation mechanism of coke and optimization the produced CNTs.     

Structure and catalytic properties of Ni/MWCNTs and Ni/AC catalysts for hydrogen production via ammonia decomposition

The structure and catalytic properties of nickel catalysts supported on multi-wall carbon nanotubes (MWCNTs) and on three different types of activated carbon (AC) were studied. The surface areas of AC carriers were defining the size of supported nickel particles. Large surface area of AC led to small Ni nanoparticles and high Ni dispersion. Turnover frequency (TOF_NH3) of ammonia decomposition decreased with decreasing of Ni particle size. The highest degree of ammonia conversion was observed on Ni/AC prepared by using of AC support with largest surface area. The catalytic activity of Ni/MWCNTs was much higher than catalytic activity of the studied Ni/AC catalysts. The synergic nickel-support interaction and special electronic conductivity properties of MWCNTs were responsible for high catalytic activity of Ni/MWCNTs catalyst.     

In situ generation of nickel/carbon catalysts by partial gasification of coal char and application for methane decomposition

Catalytic methane decomposition (CMD) has a good potential to develop environmentally friendly hydrogen economy, and the catalyst plays a vital role on its applications. In this work, a novel strategy was proposed to fabricate efficient and effective nickel/carbon catalysts for CMD by introducing some additional nickel and K₂CO₃ into partial steam gasification of coal char. The gasification process is conducive to in situ synthesize nickel crystallites with high reduction degree (the value of Ni⁰/(Ni⁰+Ni²⁺) up to 76%–81%) on the catalyst surface, and it is competent for co-generation of hydrogen-rich gas and nickel/carbon hybrids with large surface areas (around 86–149 m²/g after washing off the residual potassium salts). The nickel/carbon hybrid as the gasification residue could serve as the catalyst for CMD, showing high and stable methane conversion (up to 80%–87%) at 850 °C. It is observed that co-production of hydrogen and filamentous carbons can be achieved in the 600-min process of CMD, thanks to the positive effect of K₂CO₃ on formation and activity improvement of the nickel/carbon catalyst.