Catalytic Tar Removal Research Articles

Machine learning-driven optimization of Ni-based catalysts for catalytic steam reforming of biomass tar

Biomass gasification is a promising process for producing syngas, which is widely used in various industrial processes. However, the presence of tar in syngas poses a significant challenge to biomass gasification due to the difficulties in its removal and potential downstream issues, such as clogging, slagging, and corrosion. Extensive efforts have been made to address this challenge through catalytic tar removal using various catalysts, generating a vast amount of experimental data. Processing this large dataset and gaining new insights into process optimization requires the development of efficient data analysis methods. In this study, a comprehensive database was built, encompassing a total of 584 data points and 14 input parameters collected from literature published between 2005 and 2020. Machine learning algorithms were then trained using this dataset to predict and optimize the catalytic steam reforming of biomass tar. The predicted results were found to agree well with the experimental data. The results show that the reaction temperature is the most important process parameter, with the highest relative importance of 0.24, followed by the support (0.16), additive (0.12), nickel (Ni) loading (0.08), and calcination temperature (0.07), among the 14 input parameters. This work has proposed optimal ranges for the reaction temperature (600–700 °C), Ni loading (5–15 wt%), and calcination temperature (500–650 °C). Furthermore, it was found that a larger specific surface area and higher Ni dispersion are two critical factors for selecting additives and supports. This study provides insights into key parameters for optimizing the catalytic steam reforming of biomass tar, enabling enhanced efficiency and effectiveness in biomass gasification processes.

La0.7(Ca, Sr)0.3Ni0.6Mn0.5O3 perovskites for photothermal catalytic reforming of toluene: The role of oxygen species in the photothermal synergistic effect

Photothermal steam reforming (PTR) has emerged as an attractive approach for catalytic tar removal, due to the excitation of the photothermal synergistic effect. However, the role of oxygen species in PTR is still unclear. In this paper, the effect of alkaline earth metals (Ca and Sr) A-site-substitution on perovskite LaNi0.6Mn0.5O3 was investigated to reveal the role of oxygen species in PTR. The substitution of alkaline earth metals into perovskite lattice affected the dispersion of nickel and significantly adjusted the active oxygen species content on the catalyst surface. Oxygen species are crucial to the carbon deposition behavior of catalysts in PTR. La0.7Ca0.3Ni0.6Mn0.5O3 was rich in reactive oxygen species, which effectively inhibited the deposition and graphitization of coke, resulting in its good coke resistance and catalytic stability in PTR. Ultraviolet–visible light (UV–vis) supported the formation of oxygen vacancies and the dissociation of H2O to hydroxyl radicals through the photochemical reaction, which ultimately increased the surface adsorbed oxygen contents. Meanwhile, UV–vis promoted the migration and reaction of lattice oxygen. The photoactivation of oxygen species by UV–vis effectively enriched active oxygen species and improved the coke resistance, which resulted in enhanced catalytic stability of PTR at low-temperature.

Novel nickel ceramic filter for hot gas cleanup of tars from syngas

Tars, defined as hydrocarbons having molecular weights above that of benzene, have been considered to be one of the major impurities in syngas preventing largescale commercialization of biomass gasification. Catalytic tar removal has shown the most promise in reforming/eliminating tars compared to physical and thermal techniques. Nickel based catalytic filter was developed using porous ceramic support, which acts both as a particulate filter and tar reformer, resulting in process intensification. The relatively high surface area of the ceramic filter (100 m2/g) makes it an ideal catalyst support. Nickel based ceramic catalysts were prepared using incipient wetness method and evaluated for tar removal effectiveness using naphthalene as a tar simulant. Influence of nickel loading, steam/carbon ratios, and temperatures on steam reforming activity of the catalyst was performed. Promising results were obtained with naphthalene conversions of 76% using a 15 wt% nickel filter over 2 h with very minimal pressure drop across the catalytic filter, offering a promising potential of using catalytic ceramic filters for integrated tar and particulate removal applications.

Photothermal steam reforming: A novel method for tar elimination in biomass gasification

Tar elimination is the bottleneck which hinders the industrial application of gasification due to the risks of corrosion and blockage in downstream components. Tar production decreases the energy efficiency of gasification systems. The steam reforming is attractive for tar treatment, but the high reaction temperature limits its applications. Photothermal catalysis has the potential to decompose organic pollutants, and it is expected to improve tar removal and reduce the reaction temperature. So, the photothermal steam reforming of toluene was performed to evaluate the toluene conversion. The effects of the toluene concentration, the temperature, the steam to carbon ratio, and the ultraviolet light intensity were investigated. The results showed that, compared with the thermal steam reforming, the photothermal steam reforming could significantly improve the conversion of toluene and promote the formation of gaseous products, especially H2. At 600 °C, the conversion of toluene in the photothermal steam reforming was 90.1%, which was 16.3% higher than that in the thermal steam reforming. Moreover, the mechanisms of the photothermal steam reforming were revealed. The introduction of the ultraviolet irradiation could strongly promote the toluene decomposition and alter the reaction pathways. The carbon deposition and agglomeration of the catalyst were inhibited in photothermal steam reforming. Meanwhile, the toluene removal performance and the energy consumption were compared in photothermal and thermal steam reforming. The potential applications of photothermal catalytic tar removal were also described. These findings proposed a novel approach for low-cost but high-efficiency biomass tar removal, thus promoting the clean utilization of biomass energy.

Seashell waste-derived materials for secondary catalytic tar reduction in municipal solid waste gasification

Catalytic tar removal from producer gas is critical for the economic feasibility of Municipal Solid Waste (MSW) gasification in the waste-to-energy(WtE) approach. Nickel- and noble-metal catalysts have the highest tar cracking activities, but they increase costs, use scarce materials, and generate dangerous byproducts. To overcome these drawbacks, naturally occurring materials should be used for tar cracking. In this paper, two nanomaterials, synthesized from oyster and mussel waste shells respectively, are used to clean syngas from MSW in a secondary tar cracking unit. We observed that they reform class 1 tar (heavy tars that condense at high temperatures at very low concentrations) into class 3 tar (light hydrocarbons that are not important in condensation) and benzene. Although both catalysts’ composition and textural properties were identical, crystallite size and especially specific surface area variation was enough to generate a change in product selectivity. A larger crystallite size and SSA shows a soot yield reduction of 95% with respect to the non-catalytic case, simultaneously increasing the H2/CO at 1000 °C.

Application of Dolomite for tar mitigation in downdraft gasifiers: An experimental analysis

The biomass gasifiers have been adopted to generate producer gas widely across the globe. The producer gas finds application in automotive sectors in spark and combustion ignition engines. Furthermore the producer gas is used in power production and thermal applications. Inspite of the wide applications of biomass gasifiers it is not broadly employed due to its inherent disadvantages. The formation of tar along with the producer gas is a major bottleneck in applying producer gas as a viable alternative fuel. The tar mitigation methods viz., physical, thermal and catalytic tar removal methods has been employed to refine the producer gas. From published literature it is evident that many bulk and nano catalysts have been investigated for tar cracking. The dolomite mineral is a potential material for tar cracking in producer gas but has not been investigated widely. In this study the tar cracking capability of dolomite has been investigated in a downdraft gasifier. Two important tar cracking influencing parameters viz., dolomite tar cracking temperature and dolomite quantity required for tar cracking has been investigated. From the experimental study it is eviden that the optimum dolomite operating temperature is 700 °C and the optimum dolomite quantity is 200 g.

Thermal and Catalytic Cracking of Toluene Using Char from Commercial Gasification Systems

Tar formation hinders the development of biomass gasification technologies. The use of pyrolytic char as a catalyst for removing tar has been widely investigated; its large specific surface area and pores distribution make it a good candidate for the cracking of heavy hydrocarbons. The present work assesses the catalytic activity of char from a commercial gasifier. Thermal degradation tests in N2 and in CO2 proved that the char is suitable for high-temperature applications (catalytic cracking) and showed release of CO and H2, which might affect the catalytic performance of the char when used for tar removal applications. For inspecting the potential of the char for tar removal, toluene was chosen as model tar. Through GC-FID, toluene removal efficiency and the amount of benzene produced from its decomposition were evaluated. Tests up to 1273 K resulted in tar removal efficiencies as high as 99.0%, and empty reactor tests allowed for discerning the effects of thermal and catalytic cracking. The catalytic activity of the char was more pronounced at 1173 K, as char increased the toluene removal efficiency from 39.9% (empty reactor) to 60.3%. The results confirmed that gasification char, like pyrolytic char, has a high potential for catalytic tar removal applications.

Impact of Char Properties and Reaction Parameters on Naphthalene Conversion in a Macro-TGA Fixed Char Bed Reactor

Catalytic tar removal is one of the main challenges restricting the successful commercialization of biomass gasification. Hot gas cleaning using a heterogeneous catalyst is one of the methods used to remove tar. In order to economically remove tar, an efficient low-cost catalyst should be applied. Biomass char has the potential to be such a catalyst. In this work, the reactor parameters that affect the conversion of a model tar component “naphthalene” were investigated employing an in situ thermogravimetric analysis of a fixed bed of biomass char. The following reactor and catalyst parameters were investigated: bed temperature (750 to 900 °C), gas residence time in the char bed (0.4 to 2.4 s), char particle size (500 to 1700 μm), feed naphthalene concentration, feed gas composition (CO, CO2, H2O, H2, CH4, naphthalene, and N2), char properties, and char precursor. It was found that the biomass char has a high activity for naphthalene conversion. However, the catalytic performance of the biomass char was affected by the gasification reactions that consumed its carbon, and the coke deposition that reduced its activity. Furthermore, high ash and iron contents enhanced char activity. The results of this work will be used in the design of a process that uses biomass char as an auto-generated catalyst in the gasification process.

Catalytic tar removal using TiO2/NiWO4-Ni5TiO7 films

One-dimensional nickel catalysts are more promising than nickel powders for catalytic tar removal from biomass gasification, originating from their unique morphologies and higher specific surfaces. Herein, we demonstrate the application of a Ti supported multilayer system, namely a TiO2/NiWO4-Ni5TiO7 film, for catalytic tar removal. This film is synthesized via plasma electrolytic oxidation (PEO) combined with subsequently impregnation and annealing. The surface morphology and the size of as-synthesized Ni5TiO7 nanowires are determined mainly by used electrolytes during PEO processes. For catalytic tar removal, a fixed bed reactor is utilized and naphthalene is chosen as a model tar. This TiO2/NiWO4-Ni5TiO7 film exhibits higher efficiency than thermal cracking as well as long-term stability towards catalytic steam reformation of naphthalene. A naphthalene conversion rate of 63% is achieved at 800 °C with a short residence time of 0.34 s and a high tar load of 75 g mN−3. Such a TiO2-NiWO4/Ni5TiO7 film is thus promising for future tar removal from biomass gasification in the industry.

Catalytic Tar Removal from Bio‐Syngas via Oxidation on Metal Oxide Catalysts

AbstractTo diversify energy sources and to address the impacts of global warming, the transformation of biomass, a renewable energy source, into fuels and chemicals is becoming increasingly necessary. The gasification technology is an efficient way of converting biomass via syngas into sustainable fuels. By‐products, especially tar, are formed during the gasification process and need to be removed before further downstream processing. Mo/V/W‐mixed oxides were found to be applicable for the catalytic tar oxidation in CO/H2 atmosphere by adding a stoichiometric amount of oxygen. In temperature‐programmed experiments the reactivity of different tar model compounds during the selective oxidation on Mo/V/W‐mixed oxides as well as the catalytic performances of V2O5, WO3, and MoO3 during the tar oxidation were investigated.

Modified Mo/V/W‐Mixed Oxides for Catalytic Tar Removal from Biosyngas via Oxidation

AbstractIn view of the growing energy demand and the current climate problems, renewable energy sources are becoming increasingly popular. The so‐called biosyngas obtained from the gasification of dry biomass can be used to synthesize fuels and basic chemicals. Besides gaseous by‐products and salts, this gas contains tar which needs to be removed before downstream processing. Catalysts like Mo/V/W‐oxides were found to be inert towards the oxidation of CO and H2 but are able to activate the tar model compound naphthalene highly selective. Unfortunately, besides the total oxidation, the partial oxidation to the undesired intermediates phthalic acid anhydride and maleic acid anhydride takes place. Modification of the catalyst with bases leads to synergetic effects on the catalyst surface, the total oxidation is promoted, and the formation of intermediates decreases.

Fundamentals of Catalytic Tar Removal over in Situ and ex Situ Chars in Two-Stage Gasification of Coal

Intrinsic fundamentals of catalytic tar removal over coal char were studied in a laboratory two-stage gasification facility. The in situ char from coal pyrolysis (without cooling) exhibited higher activity for tar removal than the char experiencing its slow cooling in N2 to room temperature. The tar content in dry producer gas can be as low as 100 mg/Nm3 over the in situ char in 1.2 s of gas residence time inside the char bed at 1100 °C. Brunauer–Emmett–Teller surface area results showed that the in situ char has a larger specific surface area and more micropores than the ex situ char, while X-ray diffraction analysis clarified that the ordering of the carbon crystallite structure in the char increased with raising the temperature of tar removal. The latter is considered to be due to the facilitated secondary pyrolysis occurring to the ex situ char at increased temperatures. The secondary pyrolysis of the ex situ char also decreased its specific surface area and the amount of micropores. Severe coke deposition on the surface of spent char was observed, especially at temperatures above 1000 °C. The tar coking ratio defined as the mass ratio of coked tar over the totally converted tar reached as much as 0.7 when the temperature was 1100 °C and the gaseous tar residence time was 1.2 s. The coke formed on the char surface reduced the difference of structural properties between the in situ and ex situ chars and, in turn, decreased the difference in their performances for cracking tar.

Co-gasification of Plastics and Biomass in a Dual Fluidized-Bed Steam Gasifier: Possible Interactions of Fuels

Co-gasification of biomass and plastics was investigated in a 100 kW dual fluidized-bed pilot plant using four types of plastic material of different origins and soft wood pellets. The proportion of plastics was varied within a broad range to assess the interaction of the materials. The product gas composition was considerably influenced by co-gasification, whereas the changes were nonlinear. More CO and CO2 were measured in the product gas from co-gasification than would be expected from linear interpolation of mono-gasification of the materials. Less CH4 and C2H4 were formed, and the tar content in the product gas was considerably lower than presumed. With the generation of more product gas than expected, co-gasification of wood and plastic materials also had other beneficial effects. Because of the fuel mixtures, more radicals of different types were available that interacted with each other and with the fluidization steam, enhancing the reforming reactions. Wood char had a positive effect on polymer decomposition, steam reforming, and tar reduction. As a result of the more active splash zone during co-gasification of wood and plastics, contact between gas and bed material was enhanced, which is crucial for catalytic tar removal.

Catalytic tar removal from bio syngas—Catalyst development and kinetic studies

One of the most demanding areas of current energy research is related to the production, use and integration of fuels from renewable, i.e. CO 2 neutral, primary energy sources. The generation of biofuels of the second generation requires the gasification of biomass. Thereby considerable amounts of tar are formed in the crude gas. These impurities must be removed before further processing via Fischer–Tropsch or methanol synthesis [1]. For energy efficiency reasons of the whole process, the catalytic hot-gas-cleaning is a promising method. The operating temperature range from 450 to 700 °C results from the outlet temperature of the gasification process and the working temperature of the following synthesis steps. By means of selective, oxidative tar removal on Mo/V/W-mixed oxide catalysts tar compounds can be removed systematically, without converting the synthesis gas components hydrogen and carbon monoxide [2,3]. Therefore, stationary and transient kinetic experiments were performed with naphthalene as tar model compound on Mo/V/W-catalysts [4]. In the temperature range of interest Mo/V/W-mixed oxides show the required performance [5]. That way the total conversion of 2500 ppm naphthalene with an oxygen-feed of 3% (L L −1) is already obtained at 425 °C. At the same time no conversion of CO and H 2, and, therefore no disturbance of the synthesis gas yield takes place. It turned out that the selective oxidation of the tar ingredients in crude synthesis gas on mixed oxide catalysts is a promising alternative for the tar removal in the required temperature range.

Performance of a catalytically activated ceramic hot gas filter for catalytic tar removal from biomass gasification gas

Silicon carbide-based filter elements were catalytically activated to provide filter elements for catalytic tar removal from biomass-derived syngas. The filter element support was coated with CeO2, CaO–Al2O3 and MgO with a specific surface of 7.4, 15.9 and 21.9m2/g synthesized by exo-templating with activated carbon. Doping of a MgO coated filter element with 60wt% NiO has led to an increase of the specific surface from 0.15 to 0.21m2/g, whereas in case of a MgO–Al2O3 coated filter element a decrease from 1.18 to 0.91m2/g was found. An increase of the NiO loading from 6 to 60wt% on a MgO coated filter element resulted in an increase of the naphthalene conversion from 91 to 100% at 800°C and a face velocity of 2.5cm/s at a naphthalene concentration of 5g/Nm3 in model biomass gasification gas. In case of a MgO–Al2O3 coated filter element with 60wt% NiO in addition to complete naphthalene conversion in the absence of H2S, a higher conversion of 66% was found in the presence of 100ppmv H2S compared to 49% of the MgO–NiO coated filter element. After scaling up of the catalytic activation procedure to a 1520mm long filter candle, which shows an acceptable differential pressure of 54.9mbar, 58 and 97% naphthalene conversion was achieved in the presence and absence of H2S, respectively. The calculated WHSV value of 209.6Nm3h−1kg−1 indicates the technical feasibility of a further increase of the catalytic performance by an increase of the NiO loading.

Toluene Decomposition in the Presence of Hydrogen on Tungsten-Based Catalysts

Removal of NH3, tars, and H2S from biomass gasification gas represents a significant step in the commercial use of biomass gasification as a source of hydrogen, syngas, and electricity. This paper reports the results of an investigation into the use of W-based catalysts [tungsten carbide (WC), tungstated zirconia (WZ), and platinum supported on tungstated zirconia (PtWZ)] for catalytic tar removal. In this study, toluene was used as a model compound for tars. In the case of WZ, the effect of calcination temperature on the activity of toluene decomposition was also investigated. The toluene decomposition reaction was conducted at 1 atm, in the temperature range of 300−800 °C, and in the presence of 10% H2. CH4 and benzene were the only detectable products of toluene decomposition on all the catalysts. Incorporation of 5 wt % Pt with WZ was found to give the most effective catalyst considering initial rates of product formation. WC, WZ, and PtWZ each showed an initial partial deactivation for both CH4 and benzene formation due to coke deposition on active sites. Pt incorporation had a significant effect on the steady-state activity of WZ for toluene decomposition at temperatures below 600 °C; however, at temperatures above 700 °C, the effect was nullified. All W-based catalysts showed comparable performance to that of a commercial cracking catalyst (ultra-stable Y zeolite) above 700 °C.

Ni-olivine catalysts prepared by thermal impregnation: Structure, steam reforming activity, and stability

Abstract Ni-olivine catalysts prepared by thermal impregnation are candidate materials for in-bed catalytic tar removal during fluidized bed biomass gasification. The present work examined the structure and surface properties of the Ni-olivine catalysts prepared by thermal impregnation following preparation, during reduction by in-situ techniques, and following naphthalene-steam reforming in simulated biomass derived syngas. Catalysts were characterized by BET surface area, laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). During the preparation, secondary phases containing Mg (i.e., (Mg,Fe)3Si2O5(OH)4 and MgFe2O4) reacted to form an olivine phase enriched in Mg and either MgO or Mg-enriched (Mg,Ni)O. The presence of excess steam in the naphthalene-steam reforming appeared to limit coking and also caused behavior to be different than was observed under reducing conditions. Post-reaction characterization indicated the loss of a metallic phase through a possible alloying process and the exchange of Fe for Mg in the olivine structure. Either can potentially explain the high coke resistance of the Ni-olivine catalysts prepared by thermal impregnation compared to Ni-olivine catalysts prepared by incipient wetness impregnation or the olivine support. Finally, the properties of the olivine catalysts with and without Ni were compared through activity for methanol- and ethylene-steam reforming.

Highly efficient sulfur and coking resistance catalysts for tar gasification with steam

Ni-on-dolomite catalysts were found to be effective catalysts for coking resistance and promising sulfur tolerance for steam reforming of tar. Experiments were carried out in a fixed bed reactor at 730–850 °C with a short contact time ( W/ F: 0.55 g h/mol) and under atmospheric pressure. Toluene and naphthalene were selected as the model component of tar. The process variables such as calcination temperature, reaction temperature and the content of nickel had substantial influence on promising sulfur tolerance in catalytic tar removal by Ni/Dolomite catalysts. Results were compared with the Ni/Al 2O 3, Ni/SiO 2 as a representative of commercial catalysts. The novel 15%Ni/Dolomite almost gasified tar component even at 770 °C and the presence of 100 ppm H 2S in the feed. The poisoning effect of H 2S was discovered to be reversible. The suppression of the catalytic activity by adding H 2S was much lower for Ni/Dolomite than Ni/Al 2O 3. The TGA–DTA analysis of used catalysts revealed that Ni/Dolomite exhibited high resistance to coke deposition over those of the Ni/Al 2O 3, Ni/SiO 2.

99/01160 Commercial steam reforming catalysts to improve biomass gasification with steam-oxygen mixtures. 2. Catalytic tar removal : Aznar, M. P. et al. Ind. Eng. Chem. Res., 1998, 37, (7), 2668–2680

99/01160 Commercial steam reforming catalysts to improve biomass gasification with steam-oxygen mixtures. 2. Catalytic tar removal : Aznar, M. P. et al. Ind. Eng. Chem. Res., 1998, 37, (7), 2668–2680

99/00307 Commercial steam reforming catalysts to improve biomass gasification with steam-oxygen mixtures. 2. Catalytic tar removal

99/00307 Commercial steam reforming catalysts to improve biomass gasification with steam-oxygen mixtures. 2. Catalytic tar removal