Tar Cracking Research Articles

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.

Experimental study on catalytic pyrolysis of oily sludge for H2 production under new nickel-ore-based catalysts

Oily sludge (OS) from steel mills contains a large number of heavy components and has high viscosity. In this paper, the preparation of high value-added gas from the pyrolysis of OS catalyzed by calcined olivine (C-OL), xiuyan jade (C-XY), iddingsite (C-ID) and their nickel carrier was investigated. ICP-OES, SEM, EDX, XRF, and XRD were applied to characterize the catalysts. The effect of the catalyst on the pyrolysis of OS and the regulation mechanism of gas product quality were investigated. Thermogravimetric results showed that all the six catalysts could improve the total weight loss of OS, among which the addition of C-OL(Ni) increased by 11.58 wt%. Compared with the pyrolysis of OS, the production of H2 increased by 82.65 and 23.49 mL after C-OL and C-XY were added at 900 °C, respectively. Ni ore-based catalysts can promote tar cracking, thereby producing more pyrolysis gas, in which the production of H2 is significantly increased. The addition of C-XY(Ni) increased the production of H2 by 239.29 mL. After nickel was loaded, the catalysts showed better catalytic activity at a high temperature. Results show that the nickel-loaded natural ore as catalyst can promote the pyrolysis of OS and can obtain pyrolysis gas with high added value.

Hydrogen-Rich Gas Production from Two-Stage Catalytic Pyrolysis of Pine Sawdust with Nano-NiO/Al2O3 Catalyst

Hydrogen production from biomass pyrolysis is economically and technologically attractive from the perspectives of energy and the environment. The two-stage catalytic pyrolysis of pine sawdust for hydrogen-rich gas production is investigated using nano-NiO/Al2O3 as the catalyst at high temperatures. The influences of residence time (0–30 s) and catalytic temperature (500–800 °C) on pyrolysis performance are examined in the distribution of pyrolysis products, gas composition, and gas properties. The results show that increasing the residence time decreased the solid and liquid products but increased gas products. Longer residence times could promote tar cracking and gas-phase conversion reactions and improve the syngas yield, H2/CO ratio, and carbon conversion. The nano-NiO/A12O3 exhibits excellent catalytic activity for tar removal, with a tar conversion rate of 93% at 800 °C. The high catalytic temperature could significantly improve H2 and CO yields by enhancing the decomposition of tar and gas-phase reactions between CO2 and CH4. The increasing catalytic temperature increases the dry gas yield and carbon conversion but decreases the H2/CO ratio and low heating value.

Computational fluid dynamics modeling of biomass catalytic fast pyrolysis in bubbling fluidized reactor: Effects of catalyst parameters on process performance

AbstractIn this study, a computational fluid dynamics mathematical model has been developed for catalytic fast pyrolysis (CFP) of biomass based on multiphase flow, transfer process, and biomass pyrolysis reactions in a bubbling fluidized bed reactor. The multiphase fluid flow, and the inter‐phase momentum and energy transfer processes are modeled with Eulerian multiphase formulas, representing the flows of gases and solids (catalyst and biomass) within the reactor. The biomass CFP reactions are described by using a two‐stage, semi‐global model. Specified secondary tar catalytic cracking process, which considers both intrinsic reaction rates and mass‐transfer process, is embedded to the developed model by user‐defined function. The model simulation results of pyrolysis product yield and distribution are compared with the experimental data with close agreement. The model is then employed to investigate the effects of structural properties of catalyst, such as specific internal area, average size of active sites, pore diameter, and tortuosity, on products yields and composition. The tar cracking process by the selected catalyst is proposed and the influences of adsorption capability of tar molecule on catalyst surface and external film mass transfer are also analyzed. The developed model can be solved with short computational time and thus it can be employed for further research and engineering designs of the catalytic pyrolysis of carbonaceous materials.

In-situ catalytic upgrading of tar from integrated process of coal pyrolysis with steam reforming of methane over carbon based Ni catalyst

In order to improve the tar quality by decreasing the heavy tar content and ensuring high tar yield, in-situ catalytic upgrading of tar from the integrated process of coal pyrolysis coupled with steam reforming of methane was conducted over carbon (KD-9) based Ni catalyst. The results show that at 650 °C, the tar yield of CP-SRM over 5Ni/KD-9 is 24.4%, which is a little lower than that of without catalyst, while the light tar yield (i.e., 18.9%) is 1.4 times higher than that of without catalyst, and the content of C2, C3 and C4 alkyl used as a substitute for benzene significantly increases tar yields by 0.5, 0.6 and 4.0 times, respectively. The content of phenols and naphthalenes in tar also increases dramatically after upgrading. Isotope tracer approach combined with the mass spectra of typical components was employed in exploring the mechanism of the upgrading process. The results show that 5Ni/KD-9 catalyzes coal tar cracking and SRM at the same time. Small free radicals such as ·CHx, ·H and ·OH generated by SRM can combine with free radicals from tar cracking, thus avoiding excessive cracking of tar.

Pyrolysis of RDF and Catalytic Decomposition of the Produced Tar in a Char Bed Secondary Reactor as an Efficient Source of Syngas

One of the technical limitations of refuse-derived fuel (RDF) pyrolysis is the high content of tar in its gas products. In order to resolve this problem, a two-stage RDF pyrolysis with a catalyst based on char from RDF pyrolysis is proposed. This paper presents the results of municipal waste pyrolysis beginning in an oven heated to 480 °C and ending with catalytic tar cracking carried out in the temperature range from 800 to 1000 °C. Thermal and catalytic pyrolysis with a char catalyst containing a minimum of 6% Fe resulted in increases in the CO and H2 contents in gas products and decreases in CO2 and CH4. At 1000 °C, the mass ratio of gaseous products to liquids was greater than 6. The residence time of the gases in the catalytic zone was about 3–5 s. The reactor was a good source of hydrogen and carbon monoxide.

Catalytic processing of the acid tars

Acid tars are wastes from the processing of coal, petroleum, and petrochemicals (oil refining, benzene refining and petroleum fractions refining and alkylation of isobutane with butenes). Acid tar compositions include resinous substances, organic matter, and polymerization products of unsaturated hydrocarbons. The presence of free sulfuric acid in acid tars often reaches 70 % by weight. Almost all metals from oil are concentrated in tars, and the content of vanadium and nickel can reach 0.046 and 0.014 %, respectively. A lot of countries keep acid tar in the open air in spent quarries, storage ponds, barns, lagoons or near landfills. It poses a risk or even potential threat to people and to the environment nearby due to soil, water, and air pollution. Thus, disposal of the acid tars is a very important ecological and industrial task. In this study, we have researched catalytic cracking and distillation as the utilization methods for acid tar. Anhydrous AlCl3 was used as a catalyst during the cracking of petroleum residues to obtain volatile gasoline fractions due to its catalytic activity in many organic reactions. The catalyst ratios (0.15 g/g of tar or 0.1 g/g of tar) had a very significant influence on the number of volatile fractions and boiling temperature in the acid tar cracking process. According to the results of 1H NMR research, the main components of volatile fractions in the case of catalytic cracking were alkanes CH3-(CH2)n-CH3. The compositions of these fractions were similar to the compositions of gasoline and diesel fuel. A series of distillation experiments (distillation of previously deacidified and centrifuged tar, acid tar without deacidification and centrifugation, and previously deacidified tar without centrifu-gation) gave different results for each type of material. Aliphatic hydrocarbons were the main components of volatile fractions (~ 80, ~ 60 and ~ 90 %, respectively) and the contents of aliphatic S-organic compounds were also significant (~ 10, ~ 30 and ~ 8 %). Thus, both for catalytic cracking and for tar distillation, aliphatic hydrocarbons were the main component of volatile fractions. Deacidification of tar increased the yield of aliphatic hydrocarbons during tar distillation and decreased production of S-organic compounds due to its reactions with calcium carbonate. It is perspective in the context of fuel production.

Structure, Surface Nature, Thermal Stability, and Biomass Gasification Process of NiO/SiO2 and NiO‐Pr2O3/SiO2 Nanocomposites Obtained through Facile Deposition Precipitation Method

Recently, composites of metal matrix attracted many researchers in mechanical, biomedical, chemical, and electrical fields due to its structure, thermal, and some interesting chemical properties. Nanocomposites of NiO/SiO2 and NiO‐Pr2O3/SiO2 considered much interest due its wide range of applications in medical, engineering, physics, chemistry, and material science. In the present work, synthesizing of NiO/SiO2 and NiO‐Pr2O3/SiO2 nanocomposites was carried out using simple and low‐cost deposition precipitation technique. Structural features represent that the prepared samples found to be nanocrystalline nature. Surface morphology showed that there is formation of particle with spherical in shape. Transmission electron microscopy supported that the structure of composite with size is in the range of nanometer. The Brauner‐Elmer‐Teller method showed the surface area of the synthesized nanoparticles. The pore volume present in the nanoparticle was determined by Barrett–Joyner–Halenda method. Thermogravimetric analysis revealed that the thermal stability of the synthesized nanocomposite is up to 1000°C. The hydrogen enrichment in the producer gas was evident by the tar cracking activity of the synthesized NiO/SiO2 and NiO‐Pr2O3/SiO2 nanocomposites.

Catalytic conversion of gaseous tar using coal char catalyst in the two-stage downer reactor

The effect of catalyst height (0–50 mm) and catalyst temperature (600–900 °C) on the catalytic cracking of gaseous tar is investigated using a two-stage down reactor. Results show that the utilization of catalyst promotes the removal of coal tar. The yield of coal tar at the pyrolysis temperature of 900 °C is 7.14% and tar is composed of aromatics and high-carbon-number aliphatics. The coal char prepared by fast coke-making method at 900 °C is directly used as a catalyst in the catalytic cracking of coal tar. When the catalyst temperature and the catalyst height are 900 °C and 50 mm, the tar produced by coal pyrolysis is connected with high-temperature coal char for a short time, reducing the tar yield from 7.14% to 4.26%. Among them, aliphatic hydrocarbons with carbon number of C10 and C11 and aromatics are the main components of coal tar. Similarly, compared with the pyrolysis, the content of CH4 and H2 obtained with the addition of the catalyst increase from 0.56 to 0.97 to 1.64%g/g coal and 1.02%g/g coal, respectively. Moreover, GC/MS results show that the increment of catalyst height and catalyst temperature increases aromatics content and facilitates the conversion of high-carbon-number component to low-carbon-number ones.

Comparison of Tar Samples from Reaction Zone and Outlet in Ex-Situ Underground Coal Gasification Experiment

Tar remaining in the gasification cavity during underground coal gasification (UCG) is an important pollution source, while the reported studies only focus on the tar behavior at the outlet. The present work aims to compare the tar properties from the reaction zone and the outlet, analyze the tar evolution during gasification, and discuss possible measures to control tar pollution. Tar was sampled with a self-developed equipment from an ex-situ underground coal gasification experimental system and analyzed by GC-MS. The gas composition, temperature, and PM10 were also compared for the reaction zone and the outlet. Compared with the tar from reaction zone, the tar from outlet has a smaller percentage of high boiling point content, PAHs, C, O, N, S, Cl, Si, and a larger percentage of H. The PAHs percentage in tar at the outlet in this work is closer to the field data than the lab data from literature, indicating the experimental system gives a good simulation of tar behavior in underground coal gasification. Condensation due to a fast temperature drop is one of the main reasons for PAHs decreasing. Tar cracking and soot formation also cause the decrease of heavy tar, proven by the light gas and particulate matter results.

Simulation of air gasification of Napier grass using Aspen Plus

In this research, a thermodynamic equilibrium model was developed using Aspen Plus for parametric study of syngas composition and product yield from air gasification of Napier grass in a fluidized bed gasifier. Operating conditions of gasification encompassing temperature, pressure, equivalence ratio (ER), and moisture content were manipulated and studied with further validation against experimental data. Tar cracking reaction was considered with M-cresol and heptane as represented species. Conversion of homogenous reactions was empirically correlated in MATLAB and further utilized to adjust the composition of CO, H2 and CH4 for prediction of experimental data with better accuracy, where the average mean error ranges from 0.20 to 0.25. Maximum lower heating value (LHV) was attained at 750 °C, contributed by the highest CH4 composition. ER change had limited effect on bioliquid yield but showed a significant contribution in lowering biochar yield. Lowering moisture content improved syngas quality significantly through the promotion of CO, H2 and CH4 production, with minimum biochar and bioliquid yield. The optimized LHV were 7.69 MJ/Nm3 at T = 750 °C, ER = 0.2 and moisture content of 4.5 wt%.

Thermocracking of a heavy fraction of the oil residue in a mixture with shale

The process of tar thermal cracking in a mixture with crushed oil shale to obtain components of motor fuels and raw materials for the process of thermal cracking is investigated in this paper. The optimization results of technological parameters (shale concentration, temperature, and duration) are presented and the material balance (mass.%) of the process is made. It was found that during single-stage processing under relatively mild conditions (5 MPa, 425C, feed space velocity of 1.0 h-1), a deep destruction of tar is achieved (the yield of the gasoline fraction from boiling point to 200C is ~12 wt.%; medium distillates with boil. point 200370C-43-44 mass.%; raw materials for thermal cracking with boil. point above 370C ~15-16 wt.% on per the original tar). The generating coke-like products and the V and Ni contained in the raw materials are deposited on the mineral part of the shale and removed from the reaction zone with the liquid products of the process.

Non-thermal plasma removal of naphthalene as tar model compound from biomass gasification

Gasification of biomass is an industrial process utilized to produce product gas that can be used in electrical power generation with internal combustion engines. However, there remain huge challenges with regards to tar and other pollutants, thus their removal before further use is necessary. Non-thermal plasma method can be considered as a novel and efficient way for treatment of tar from product gas. In this work, a laboratory-scale, reverse vortex flow gliding arc plasma reactor was developed and tested for the removal of tar model compound using naphthalene as surrogate. Effects of total gas feed rate in the range of 20–60 L/min, applied voltage in the range of 50–220 V, hence, power input in the range of 300–460 W with initial naphthalene concentration of 610 ± 50 mg/m3 on removal and energy input were investigated. It was found the tar removal efficiency increased with increasing applied voltage. Maximum naphthalene removal efficiency of 85% was achieved at applied high voltage of 15 kV and specific energy input of 0.13 kWh/m3 with energy utilization efficiency of about 4.60 g/kWh. From the findings, non-thermal plasma technology appeared to offer great potential in the removal of biomass tar from gasification. The technology may be promising for possible application to real biomass tar cracking and upgrading of product gas from gasification.

A novel system of biomass for the generation of inherently separated syngas by combining chemical looping CO2-gasification and steam reforming process

The utilization of biomass and CO2 has become very important for solving environmental problems all over the world. In this study, a novel Fe-based CO2-gasification (FCG) process of biomass which combining chemical looping CO2 gasification and steam reforming process is proposed. The effects of experimental parameters including biomass/oxygen carrier (B/OC) ratio and initial CO2 concentration on the performance of the gas, liquid and solid products were analyzed in detail. The results show that CO2 has an opposite effect on the oxygen transfer capacity (OTC) of OC and carbon conversion rate, which results in an inflection point of initial CO2 concentration at around 20%: larger than this value, only a little hydrogen is generated, and once the concentration lower than this value, the yield of hydrogen dramatically increases. Moreover, the carbon conversion rate encountered a slight decline at the inflection point. As for the generation of tar, CO2 and OC have a synergetic effect on tar cracking: CO2 promotes the cracking of heavy tar and OC reduces the production of light tar effectively, and thus a better effect of tar cracking can be obtained when both OC and CO2 exist. This process can generate inherently separated syngas (CO-rich gas and high purity of H2), reduce the amount of undesired tar, utilize CO2 and Fe-containing solid waste, and thus this process is expected to have an extensive prospect for industrial application.

Waste tire derived char supported Ni‐Fe catalyst for catalytic thermochemical conversion of wet municipal solid waste

Thermochemical conversion technology (pyrolysis/gasification) has been extensively employed for biomass, fossil fuels, and MSW feedstock to transform them into valuable products (gas, oil, and char). Since the practical application of waste tire derived char (WTC) faces uncertainty, the exploitation of WTC's high-value application would significantly impact the overall economy of the waste tire pyrolysis process. Therefore, in this study, WTC was utilized as a support material for developing Ni-Fe-based catalysts (Ni-WTC, Fe-WTC, and Ni-Fe-WTC). The catalyst performance for wet MSW catalytic conversion was studied in a fixed-bed reactor. The results affirmed that the application of catalysts considerably boosted the H2 concentration (29.26% to 38.24%-42.15%), dry gas yield (0.73 to 1.04-1.16 Nm3/kg MSW), and H2 yield (212 to 396-487 mL/g MSW). Meanwhile, the tar content reduced significantly from 9.11% (without catalyst) to 2.15%, (Ni-WTC), 2.83% (Fe-WTC), and 2.47% (Ni-Fe-WTC). The tar analysis indicated that the chemical composition significantly transformed with the application of catalysts. This work successfully suggested that WTCs can be used as an effective and inexpensive support material for developing Ni-based catalysts that can offer greater opportunity toward tar and hydrocarbons catalytic cracking and reforming during MSW conversion.

Study of mayenite produced from waste eggshell as support for Ni–Co catalysts for biomass tar cracking

Ultrasonication-promoted synthesis was applied to produce mayenite (M-CES) with properties similar to mayenite produced with commercial reagents, using calcined eggshell waste as a calcium source. Monometallic 10Ni/M-CES (10 wt.% Ni) and 10Co/M-CES (10 wt.% Co) and bimetallic 5Ni5Co/M-CES (5 wt.% Ni and 5 wt.% Co) catalysts were synthesized by the wet impregnation method. Catalyst 10Co/M-CES showed a noticeably lower metal dispersion when compared to the Ni-containing catalysts. 5Ni5Co/M-CES bimetallic catalyst showed the highest metal dispersion, and XRD analysis proved the Ni–Co alloy formation. The performance of Ni–Co catalysts for hydrocarbon cracking was evaluated by methane and propane catalytic decomposition. The alloy formation between Ni and Co in the bimetallic catalyst provided a reduction in the start temperature of the cracking reaction of approximately 80 °C and 110 °C for methane and propane, respectively, when compared to monometallic catalysts. A synergistic effect was also observed by a decrease in carbon deposition and an increase in the catalytic activity of 5Ni5Co/M-CES. The use of eggshell waste to produce mayenite support for tar cracking catalysts has proved to be attractive to add value to the eggshell waste.

Study on chemical kinetics and catalytic cracking of tar from gasification of rice straw using various catalysts

Study on chemical kinetics and catalytic cracking of tar from gasification of rice straw using various catalysts

Utilization of Modified Zeolite as Catalyst for Steam Gasification of Palm Kernel Shell

Syngas from biomass gasification is being developed for alternative feedstock in the chemical industry. Palm kernel shell which is generated from palm oil industry can be potentially used as raw material for gasification process. The purpose of this study was to investigate the use of modified natural zeolite catalysts in steam gasification of palm kernel shells. Mordenite type zeolite was modified by acid leaching to be used as a tar cracking catalyst. Steam gasification was conducted at the temperature range of 750–850 °C and the steam to biomass ratio was in the range of 0–2.25. The result showed that steam gasification of palm kernel shell with the addition of zeolite catalyst at 750 °C and steam to biomass ratio 2.25 could reduce tar content up to 98% or became 0.7 g/Nm3. In this study, gasification of palm kernel shells produced syngas with the hydrogen concentration in the range of 52–64% and H2/CO ratio of 2.7–5.7. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

The effect of steam concentration on hot syngas cleaning by activated carbons

Activated carbons are recognised as inexpensive, easily available, and efficient catalysts for tar cracking reactions at high temperatures. Their use in hot syngas cleaning is limited by the rapid deactivation resulting from the coke deposition, and the consequent masking phenomenon over the activated carbon surface. This study contributes to a better understanding of the problem and sheds light on possible solutions, by investigating how the temperature (750 °C–850 °C) and the steam concentration (0%–10%) can affect the extent of the water-gas and reforming reactions occurring between steam and the coke covering the catalyst surface. The activated carbons have been fully characterised before and after the tests utilizing naphthalene as a tar model compound, to study the evolution of their structure after long duration tests. Steam positively affects the naphthalene conversion efficiency, preserving the characteristics of the material. For example, at a temperature of 800 °C and a steam concentration of 7.5%, a naphthalene conversion of over 90% is achieved even after 7 h of testing. XRD and Raman spectroscopy analyses suggest that naphthalene cracking produces a coke layer that is more amorphous and, above all, more reactive towards the water gas reaction than the original activated carbon structure.

Hydrogen-rich gas production via steam gasification of food waste over basic oxides (MgO/CaO/SrO) promoted-Ni/Al2O3 catalysts

Food waste, a renewable resource, was converted to H2-rich gas via a catalytic steam gasification process. The effects of basic oxides (MgO, CaO, and SrO) with 10 wt% Ni/Al2O3 on the gasification properties of food waste were investigated using a U-shaped gasifier. All catalysts prepared by the precipitation method were analyzed by X-ray diffraction, H2-temperature-programmed reduction, NH3-temperature-programmed desorption, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The Ni/Al2O3 catalyst was reduced incompletely, and low nickel concentrations were detected on the surface of the alumina. The basic oxides minimized the number of acid sites and suppressed the formation of nickel-aluminate (NiAlxOy) phase in catalyst. In addition, the basic oxides shifted nickel-aluminate reduction reaction to lower temperatures. It resulted in enhancing nickel concentration on the catalyst surface and increasing gas yield and hydrogen selectivity. The low gas yield of the Ni/Al2O3 catalyst was attributed to the low nickel concentration on the surface. The maximum gas yield (66.0 wt%) and hydrogen selectivity (63.8 vol%) of the 10 wt% SrO- 10 wt% Ni/Al2O3 catalyst correlated with the highly dispersed nickel on the surface and low acidity. Furthermore, coke deposition during steam gasification varied with the surface acidity of the catalysts and less coke was formed on 10 wt% SrO- 10 wt% Ni/Al2O3 due to efficient tar cracking. This study showed that the steam gasification efficiency of the Ni/Al2O3 catalyst could be improved significantly by the addition of SrO.