Tar Model Compound Research Articles

Coking and Regeneration of Nickel Catalyst for the Cracking of Toluene As a Tar Model Compound

The coking and regeneration of Ni/γ-Al2O3 for the cracking of toluene as a tar model compound were investigated. Special attention has been paid on the effect of coke nature, especially filamentous coke, on the regeneration performance. The catalyst was deactivated by cracking toluene at 700 °C for 0.5 h. The deactivated catalyst was then regenerated by calcination in air at 600 °C for 3 h. The cracking–regeneration cycle usage was carried out up to four times. The results showed that the toluene conversion decreased slowly from 28.2% by fresh catalyst to 22.6% by the third regenerated catalyst and then decreased quickly to 16.3% by the fourth regenerated catalyst. The increase of NiO crystal size from 12.8 to 18.0 nm and the decrease of Brunauer–Emmett–Teller (BET) surface area from 97.7 to 86.9 m2/g caused by sintering and remaining coke were the major reasons for the loss of catalytic activity of Ni catalyst after cycle usage. The cycle usage made the deposited coke more graphitized by slightly enhanci...

Iron Oxide over Silica-Doped Alumina Catalyst for Catalytic Steam Reforming of Toluene as a Surrogate Tar Biomass Species

An iron oxide over silica-doped alumina catalyst was successfully synthesized using one-pot, solvent-deficient method. The prepared Fe2O3/SiO2–Al2O3 catalyst was characterized using TGA/DTG, XRD, N2 adsorption isotherm, NH3-TPD, and SEM. The TGA/DTG and XRD results show that the presence of Si enhances the stability of γ-Al2O3 support at high temperatures. The prepared Fe2O3/SiO2–Al2O3 catalyst was obtained by calcination at 950 °C, with a high BET specific surface area (49 m2/g). The NH3-TPD showed that Fe addition can significantly increase catalyst acidity. SEM images confirmed the textural properties of the catalysts in term of surface morphology. The catalytic activity of Fe2O3/SiO2−Al2O3 catalysts was examined in a CREC fluidized riser simulator using toluene as model compound for biomass tar. Experiments with this catalyst yielded high toluene conversions. Composition of gases produced (H2, CO, CO2, and CH4) were close to chemical equilibrium at 25 s and 600 °C. These results indicate that the Fe2O...

Novel treatment of a biomass tar model compound via microwave-metal discharges

Electrical discharges triggered by microwave-metal interactions are important phenomena in microwave heating processes with the generation of plasma. In this study, microwave-metal (MW-m) discharge was developed for tar destruction. Toluene was used as a tar model compound. Uniform tungsten electrodes was adopted and optimized to provide a fast-ignition, relatively-stable and sustainable discharge process. The conversions of toluene were investigated at different gas flow rates and preliminary tests were conducted to in-situ eliminate the generation of solid carbon. Microwave-tungsten discharge can effectively destruct toluene into useful gases (H2, C2H2 and CH4) and solid carbon, with a high conversion efficiency of more than 90%. The generated solid carbon can be effectively eliminated by introducing water steam into the discharge reaction to achieve a comparable toluene conversion efficiency of 92.3% and a production of syngas (H2 to CO ratio is around 1.6). This work can offer important reference for developing a new technology for tar cracking in a biomass gasification process.

Steam reforming of tar model compounds over ni supported on CeO2and mayenite

AbstractNi‐CeO2, Ni/Co‐CeO2, and Ni‐Ca12Al14O33were synthesized by the auto‐combustion method and tested as catalysts in the steam reforming of tar model compounds in a fixed bed reactor. Toluene, phenol, andn‐heptane were chosen as representative of the different classes of organic compounds that can be found in tar. The catalysts were characterized by X‐ray diffraction (XRD) and temperature‐programmed reduction (TPR). From XRD analysis it was observed in all the synthesized catalysts the presence of two phases, NiO and CeO2or Ca12Al14O33. A stronger interaction of NiO with mayenite structure, compared to that of NiO with CeO2, was also shown by TPR analysis. The best performances in terms of conversion and stability were obtained when Ni supported on mayenite was used, confirming the higher redox properties of this support that confers to the catalyst a better resistance to deactivation by carbon deposition. The lower performances observed for Ni supported on CeO2in terms of conversion and activity were substantially improved by partial substitution of Ni with Co, confirming its ability to increase the Ni catalytic activity and to enhance the reforming of oxygenated species. The apparent kinetic parameters calculated for all the catalysts and the model compounds confirm the obtained experimental results.

Anchoring effect and oxygen redox property of Co/La0.7Sr0.3AlO3-δ perovskite catalyst on toluene steam reforming reaction

To elucidate specific functions of supports, we investigated steam reforming of toluene as a model compound of biomass tar over Co catalyst supported on perovskite-type oxide. Co-supported La0.7Sr0.3AlO3-δ catalyst showed the highest activity among various Co-supported catalysts. STEM measurements and XPS measurements revealed the coexistence of La cation and lattice oxygen defect produces an anchoring effect to Co particles. The lattice oxygen release rate on each catalyst was measured with H218O steady-state isotopic transient kinetic analysis (SSITKA). The anchoring effect, higher dispersion of Co and redox property, are important for the high catalytic performance of Co/La0.7Sr0.3AlO3-δ catalyst on toluene steam reforming.

34.活性炭を用いた軽質タールモデル物質の吸着除去(1)

34.活性炭を用いた軽質タールモデル物質の吸着除去(1)

Perovskite-based catalysts for tar removal by steam reforming: Effect of the presence of hydrogen sulfide

One of the greatest problems in biomass gasification processes is the conditioning of the produced synthesis gas, which contains various contaminants, including tar and hydrogen sulfide. Nickel catalysts, designed for steam reforming of aliphatic hydrocarbons (natural gas and nafta), are usually deactivated by coke deposition and sulfur poisoning. In this work, nickel and/or manganese catalysts derived from perovskites were prepared by the citrate method and characterized by X-ray diffraction, N2 physisorption and temperature programmed reduction. The catalysts were evaluated in the steam reforming of toluene, used as tar model compound, in the absence of H2S at 700 °C and in the presence of 50 ppm H2S at 800 °C. LaNi0.5Mn0.5O3 catalyst showed higher activity and stability in the absence of H2S. LaMnO3 catalyst, although less active in the absence of H2S, showed increased stability in the presence of H2S, with conversion of about 60%. H2 production was only observed in the absence of H2S.

Toluene Oxidation in the Absence and Presence of CO, CO2, Water and H2 over ZrO2‐Based Gasification Gas Clean‐Up Catalysts

AbstractGasification of biomass is an environmentally friendly way to produce electricity and syngas when combined with effective gas cleaning. ZrO2‐based catalysts have been proven to remove undesired tar molecules when a convenient amount of oxygen is added. However, high activity in the tar oxidation is not the only requirement for the catalyst performance. The valuable gasification gas components, such as CO and H2, must be protected while passing the complex gasification gas over the catalyst. Oxidation of toluene as a tar model compound was addressed by applying temperature‐programmed surface reaction (TPSR) experiments with continuous feed of toluene, oxygen and one main gasification gas component (CO, CO2, H2 or water) over pure and doped zirconias. The most water tolerant catalyst was pure ZrO2 and the least was SiO2‐ZrO2. A new indicator called ‘Preferentiality’ was introduced and it expresses in one single quantity how well the catalyst is performing in tar conversion while protecting the valuable components of the gas. At 600 °C, the highest preferentiality of toluene oxidation over both CO and H2 oxidation was achieved over pure ZrO2.

Steam reforming of different biomass tar model compounds over Ni/Al2O3 catalysts

This work focuses on the removal of the tar derived from biomass gasification by catalytic steam reforming on Ni/Al2O3 catalysts. Different tar model compounds (phenol, toluene, methyl naphthalene, indene, anisole and furfural) were individually steam reformed (after dissolving each one in methanol), as well as a mixture of all of them, at 700°C under a steam/carbon (S/C) ratio of 3 and 60min on stream. The highest conversions and H2 potential were attained for anisole and furfural, while methyl naphthalene presented the lowest reactivity. Nevertheless, the higher reactivity of oxygenates compared to aromatic hydrocarbons promoted carbon deposition on the catalyst (in the 1.5–2.8 wt.% range). When the concentration of methanol is decreased in the feedstock and that of toluene or anisole is increased, the selectivity to CO is favoured in the gaseous products, thus increasing coke deposition on the catalyst and decreasing catalyst activity for the steam reforming reaction. Moreover, an increase in Ni loading in the catalyst from 5 to 20% enhances carbon conversion and H2 formation in the steam reforming of a mixture of all the model compounds studied, but these values decrease for a Ni content of 40%. Coke formation also increased by increasing Ni loading, attaining its maximum value for 40% Ni (6.5 wt.%).

Performance of nickel supported catalysts in steam reforming of toluene as a tar model compound for use in hot-syngas clean-up

Performance of nickel supported catalysts in steam reforming of toluene as a tar model compound for use in hot-syngas clean-up

A highly carbon-resistant olivine thermally fused with metallic nickel catalyst for steam reforming of biomass tar model compound

The Ni/olivine catalyst prepared by thermal fusion showed high catalytic activity and carbon deposition resistance during toluene steam reforming.

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.

Catalytic cracking mechanisms of tar model compounds

B3LYP/6-31G(d, p) method was used to investigate the catalytic cracking mechanism of biomass tar model compound. Phenol, toluene and benzene were selected as the tar model compounds and CaO was selected as the catalyst. The pathways of tar compound radical absorbed by CaO were determined firstly through comparing enthalpy changes of the absorption, and then Mulliken population changes were analyzed. The results show that the absorption of tar model compound radical and CaO is an exothermic reaction. Formation of C—O—Ca is more easily than that of C—Ca—O and formation of Caromatic—Caromatic—Ca—O is more easily than that of Caromatic—C(O)—Ca—O. The C—C bond Mulliken populations in tar model compound radicals are reduced by 11.9%, 10.5% and 15.5% in the case of a hydrogen atom removed, and those are 15.7%, 14.3% and 16.3% in the case of two hydrogen atoms removed through the absorption of CaO. Catalytic ability of CaO acting on the tar model compound is in an order of phenol>benzene>toluene.

Promotive effect of Ba addition on the catalytic performance of Ni/LaAlO3 catalysts for steam reforming of toluene

Ba addition to supported Ni catalysts was investigated on steam reforming of toluene, as a model compound of biomass tar. Ba addition showed drastic promotive effects on catalytic activity and tolerance against oxidation. Various catalytic tests and characterization were conducted, including pressure dependence, Arrhenius plots, STEM and XAFS observations, dispersion of supported Ni, and temperature programmed reduction. Results revealed that the electron donation from Ba to Ni enabled high catalytic performance of Ba/Ni/LaAlO3 perovskite catalyst.

No.2-13 鉄担持触媒によるタールモデル化合物の分解

No.2-13 鉄担持触媒によるタールモデル化合物の分解

Fe-Ca interactions in Fe-based/CaO catalyst/sorbent for CO2 sorption and hydrogen production from toluene steam reforming

After biomass gasification, tar can be removed by steam reforming and additional hydrogen production. This latter can be enhanced by CO2 sorption using the global process known as sorption enhanced hydrogen production (SEHP). Toluene was studied as tar model compound and its reforming was carried out at a compromise temperature (700°C) to permit simultaneous activation of iron based catalyst and CO2 sorption on CaO based sorbent.Fe-Ca interactions on Fe-based/CaO catalyst/sorbent performances occur during steam reforming of toluene. In order to determine the specific conditions for the formation of the different iron species, Fe-based/CaO bi-functional materials have been prepared following three different methods with various calcium and iron precursors. The characterizations (XRD, Mossbauer spectroscopy, TGA, TPR, SEM, and BET/BHJ) performed before and after steam reforming of toluene provide information about the evolution of the iron species and Fe-Ca interactions during catalytic tests. The results suggest that the activity of Fe/CaO materials depends not only on the presence of Fe2O3 but also on the stability of the interactions between iron and calcium under reaction conditions.The bi-functional material prepared from iron acetate and calcium acetate by mechanical mixing (FeAc/CaO (M)) has properties (large specific surface area, appropriate sorption capacity at 700°C, and the lowest deactivation) that play an important role for CO2 capture. Moreover, the presence of the α-Fe2O3 phase, precursor of the active phase in steam reforming of tar, reducible at 700°C, intervenes in the hydrogen production rate by enhancing the Water Gas Shift reaction. Finally, its higher availability of iron (Fe2O3) limit the selectivity towards undesirable products such as benzene.

Catalytic Cracking of Toluene as a Tar Model Compound Using Sewage-Sludge-Derived Char

The catalytic cracking of model tar species (toluene) using sewage sludge char (SSC) was investigated. The effects of typical syngas components from municipal solid waste (MSW) gasification on toluene conversion ratio, cracking product distribution, and characteristics of the SSC catalyst were studied. Deposited coke significantly decreased the Brunauer–Emmett–Teller (BET) surface area from 74.213 to 51.782 m2/g in a N2 atmosphere. CO2 and steam slowed the decrease of the BET surface area. Hydrogen chloride (HCl) showed a negative effect on the pore structure by the formation of low-melting-point chlorides, which melted above 750 °C and blocked the pores. The cracking efficiency in different reaction atmospheres was ordered as CO2/H2O/N2 > H2/CO/H2O/N2 > H2/CO/H2O/HCl/N2 > N2. The conversion ratios were all above 65% at 750 °C, which reached more than 93% at 950 °C. The highest conversion ratio of 97.1% was achieved at 950 °C when CO2 and steam were presented. CO2 and steam significantly increased the tar...

Effects of oxygen species from Fe addition on promoting steam reforming of toluene over Fe–Ni/Al2O3 catalysts

A series of Fe-modified Ni/Al2O3 (FNA) catalysts with different Fe/Ni ratios (Fe/Ni = 0.5, 2, 3) was investigated during steam reforming of toluene as a model compound of biomass tar. The percentages of hydrogen in the product gas reached about 65% over prepared catalysts. The addition of Fe remarkably increased the toluene conversion and reduced the amount of coke. According to X-ray photoelectron spectrometer and pulse injection experiments, the addition of Fe increased the amount of lattice oxygen and adsorbed oxygen on the surface of FNA. The Fe in alloy was easily oxidized to FeOx by steam. The lattice oxygen in FeOx could oxidize the carbon deposited or intermediates on adjacent Ni atoms to produce CO. Meanwhile, the more adsorbed oxygen promoted the further reaction with the intermediates during the steam reforming of toluene. Both the adsorbed oxygen and lattice oxygen from the addition of Fe played important roles in the steam reforming of toluene. For the two types of cokes (amorphous/paraffinic and graphitic/filamentous), the formation of graphitic/filamentous carbon was remarkably suppressed due to the oxidization property of oxygen species from the addition of Fe.

Steam reforming of toluene as biomass tar model compound in a gliding arc discharge reactor

Non-thermal plasma is considered a promising and attractive approach for the removal of tars from biomass gasification to deliver a clean and high quality syngas (a mixture of H2 and CO). In this study, an AC gliding arc discharge (GAD) reactor has been developed for the conversion of toluene as a tar model compound using nitrogen as a carrier gas. The presence of steam in the plasma reaction produces OH radicals which open a new reaction route for the conversion of toluene through a stepwise oxidation of toluene and intermediates, resulting in a significant enhancement in both the conversion of toluene and the energy efficiency of the plasma process. The effects of steam-to-carbon (S/C) molar ratio, toluene feed rate and specific energy input (SEI) on the performance of the plasma steam reforming of toluene have been investigated. The optimal S/C molar ratio was found to be between 2 and 3 for high toluene conversion and energy efficiency. The maximum toluene conversion of 51.8% was achieved at an optimal S/C molar ratio of 2, a toluene feed flow rate of 4.8ml/h and a SEI of 0.3kWh/m3, while the energy efficiency of the plasma process reached a maximum (∼46.3g/kWh) at a toluene feed flow rate of 9.6ml/h and a SEI of 0.19kWh/m3. H2, CO and C2H2 were identified as the major gas products with a maximum syngas yield of 73.9% (34.9% for H2 and 39% for CO). Optical emission spectroscopy (OES) has been used to understand the role of steam on the formation of reactive species in the plasma conversion of toluene. The possible reaction pathways in the plasma conversion of toluene have also been proposed by combined means of the analysis of gas and liquid samples and OES diagnostics.

Steam reforming of phenol as biomass tar model compound over Ni/Al2O3 catalyst

Catalytic steam reforming of phenol over Ni/Al2O3 catalyst with 10wt% of Ni loading was carried out in a fixed bed reactor. The effect of temperature (650–800°C), reaction time (20–80min) and catalyst amount (0–2g corresponding to 0–4.5gcathgphenol−1) on carbon conversion, H2 potential and catalyst deactivation was studied. High efficiency of Ni/Al2O3 catalyst in steam reforming of phenol is observed at 750°C for a reaction time of 60min when 1.5g of catalyst (3.4gcathgphenol−1) is used, with carbon conversion and H2 potential being 81 and 59%, respectively. An increase in temperature enhances phenol reforming reaction as well as coke gasification, minimizing its deposition over the catalyst. However, at high temperatures (800°C) an increase in Ni crystal size is observed indicating catalyst irreversible deactivation by sintering. As catalyst time on stream is increased the coke amount deposited over the catalyst increases, but no differences in Ni crystal size are observed. An increase in catalyst amount from 0 to 1.5g increases H2 potential, but no further improvement is observed above 1.5g. It is not observed significant catalyst deactivation by coke deposition, with the coke amount deposited over the catalyst being lower than 5% in all the runs.