Steam Reforming Of Tar Research Articles

Catalytic steam reforming of real tar under high-efficiency Ni/USY catalyst for H2 production

A series of Ni/USY catalysts were developed by incipient wetness impregnation and applied for catalytic steam reforming of coal tar in a two-stage reactor. The reforming conditions, including Ni loading amount (5–20 wt%) and reaction temperature (600–900 °C), were studied. It was found that Ni/USY catalyst showed a superior catalytic activity in terms of tar conversion (81.3%) and H2 yield (87.2 mmol/g) when the Ni loading amount was 15 wt% (i.e. 15NiY) and reaction temperature was 800 °C. The performance of 15NiY in terms of tar conversion decreased slightly after 180 min of reaction and could be recovered easily. According to N2 adsorption-desorption analysis, as-prepared catalysts exhibited excellent porosity and the special surface area was higher than 450 m2/g. Ascribed to the high porosity and special structure of Ni/USY, Ni nanoparticles with a size of 10–50 nm were well dispersed, which was observed by XRD and FE-SEM/EDS. H2-TPR demonstrated the strong metal-support interation of Ni/USY catalysts. The XPS spectra demonstrated that the surface of Ni/USY catalysts were enriched with surface adsorbed oxygen species and the value of Ni0/Ni2+ reached the highest for 15NiY, which facilitated the extent of reaction. In addition, a kinetic model was applied for calculation of apparent activation energy and pre-exponential factor, which were 57.6 kJ/mol and 8.76 × 103 m3 kg−1catalyst h−1, respectively, indicating the effectiveness of Ni/USY catalyst.

Comparative evaluation of tar steam reforming over graphitic carbon supported Ni and Co catalysts at low temperature

The development of cheap and highly dispersed nano-catalyst is one of the key technologies for low temperature steam reforming (SR) of biomass tar. This work used acid-washed and oxidized Shengli lignite char (OXAWSL) as carbon precursor to load Co (Co/OXAWSL) and Ni (Ni/OXAWSL) via ion exchange method to SR of toluene and biomass tar. The Co/OXAWSL was more active and stable than Ni/OXAWSL during the 30 h test with a final toluene conversion of 85% at a relatively low temperature of 450 °C and steam to carbon ratio (S/C) of 3.4, which resulted from its small particle size (5.6 nm) and high dispersion (12.3%) of Co. The relatively high H2 production (42.59 mmol/g-biomass) over Co0.1/OXAWSL (450 °C, S/C = 3.4) in SR of tar was also obtained. A low Ea (22.0 kJ/mol) value of Co/OXAWSL and good affinity to oxygen for Co explained its excellent performance. The low-temperature tar cracking process can provide theoretical and technical support for the large-scale industrial utilization of biomass pyrolysis and gasification.

Nickel supported over MCM-41 coated ceramic membrane for steam reforming of real tar

A novel catalyst, Nickel supported over MCM-41 coated ceramic membrane (NMC), was developed using coating method and deposition-precipitation method and applied for steam reforming of real tar in fixed bed. The effects of reaction conditions such as Ni loading amount, reaction temperature and mass ratio of steam to tar were also studied. The good dispersion of Ni nanoparticles and the strong interaction between Ni particles and the support were identified by BET, XRD, H2-TPR and SEM/EDS, resulting in the excellent performance of NMC catalysts. Maximum tar conversion of 96.4% and H2 yield of 98.7 mmol g−1 were obtained using 20NMC with a mass ratio of steam to coal tar of 2 at 800 °C. Moreover, 20 NMC exhibited a good stability in 10 h of lifetime test and the resistance of graphitic carbon formation prone to easier regeneration of catalysts illustrated by Raman spectroscopy. It indicates that the utilization of NMC catalysts for tar steam reforming is a promising way.

Advanced approach for catalytic decomposition of tar: Electrically heated catalyst system

The catalytic steam reforming of tars was conducted using the electrically heating catalyst (EHC) system, having a fast start-up and shutdown advantages as an advanced approach. A compact EHC unit was prepared by the washcoating method using a NiO/MgO/γ-Al2O3 (NMA) catalyst slurry on thermally treated Fe-Cr alloy monolithic substrates. The catalyst slurry (0.0252 g of NMA) was successfully deposited on the substrate's unit gram. The desired reaction temperature (700 – 750 ̊C) could be reached within 20 sec by supplying about 200 – 300 watts (70 – 80 A) to the EHC unit. Carbon conversion in benzene steam reforming (BSR) was 102%, and the gas productivity was 89.3 % in the EHC system at 750 ̊C. The EHC system is one of the effective ways for the BSR in controlling coke formation, compared with the results of the BSR in the conventional fixed-bed system. It is also suggested that some parts should be modified and further investigated to scale up the EHC system successfully.

Tar steam reforming during biomass gasification: kinetic model and reaction pathway

In this study, the steam reforming of naphthalene and pyrene as heavy tar model compounds was investigated experimentally in a horizontal tube reactor and theoretically using the CHEMKIN simulation. The experimental results revealed that the reactivity of naphthalene was higher than that of pyrene in the presence of steam. The carbon content converted to soot is a little more than that converted to light gas during tar steam reforming. The kinetic parameters of the overall reaction were determined, and the pre-exponential factor and activation energy were calculated using the experimental data. The comparison of the numerical simulation with the experimental findings exhibited an excellent agreement for the prediction of the light gas products and soot after eliminating the influence of the water–gas shift. Further, the reaction schemes including the reaction pathway and associated kinetics were determined for the steam reforming of these model compounds. Both naphthalene and pyrene exhibited a similar performance during the reaction in the presence of steam. Benzene and naphthalene, representing the precursors of the light gas product, were confirmed to be the dominant intermediate components of naphthalene and pyrene, respectively. The consecutive reactions of these intermediates subsequently resulted in the generation of the light gaseous products.

Effect of boron doping on the performance of Ni/Biochar catalysts for steam reforming of toluene as a tar model compound

Biochar-supported nickel (Ni/BC) catalysts have potential applications in steam reforming of tar during biomass gasification. However, the industrial application of Ni/BC catalysts is restricted by their rapid deactivation caused by the gasification of biochar support and deposition of carbon on the active Ni metal. In this study, the effect of boron doping was explored on the performance of Ni/BC catalysts in steam reforming of toluene as a tar model compound. A series of Ni/BC and boron-doped Ni/BC catalysts were prepared by impregnating Ni salts on raw and acid-washed biomass as the starting materials and used in steam reforming of toluene as the tar model compound. It was found that boron doping significantly prolonged the lifetime of Ni/BC catalysts by interacting with Ni and the biochar support simultaneously. It is believed that boron doping lowered the gasification consumption rate of the biochar support in three ways: transforming the inherent K into more stable borates, inhibiting the desorption of CO and CO2, and forming B2O3 as the active site blocker. Furthermore, boron doping also reduced coke deposition on the Ni particles.

Steam reforming of tar studied in bench-scale experiments and pilot-scale tests with simulations

The generation of tar is the major draw back of biomass gasification, which is a barrier on the road to clean energy. Steam reforming is a promising method to eliminate tar in the biomass gasification process, which have been shown in our pilot tests. In this paper, the steam reforming of tar is investigated in a bench-scale horizontal tube reactor with Chemkin simulation, and in a pilot-scale tar reformer with CFD simulation. A set of simplified reaction paths and kinetic data is developed from bench-scale work, which is applied in the CFD simulation to predict the detail process in pilot-scale tar reformer. The prediction of CFD simulation is in a good agreement with the data from pilot test. The results revealed that the tar in the reformer is mainly eliminated by the steam, not the oxygen injected in the reformer, and the reaction place is within the first 1 m of the length of the reformer, where the intermediates of the reaction is decomposed quickly. Our CFD simulation indicated that the design of reformer can be optimized to a much shorter length, saving investment and heat. Our work demonstrated a complete cycle from the study of mechanism in bench-scale work to the investigation in pilot scale.

Destruction of gasification tar over Ni catalysts in a modified rotating gliding arc plasma reactor: Effect of catalyst position and nickel loading

In this study, a modified rotating gliding arc (RGA) plasma reactor with fan-shaped swirl generator coupled with Ni/γ-Al2O3 catalyst was investigated for the steam reforming of gasification tar from waste materials, taking toluene as the tar surrogate. The system performance was evaluated in terms of tar conversion, energy efficiency, yield of product gas, as well as synergistic capability of plasma catalysis, with particular attention on the effects of specific energy input (SEI), positioning of the catalysts, and Ni loading of catalysts. Different characterizations of catalysts including N2 adsorption-desorption, XRD, H2-TPR, and TEM were conducted to study the properties of catalysts. Incorporation of catalyst placed sufficiently far from the anode increased toluene conversion which indicated the synergy between plasma and catalysis for tar conversion. A toluene conversion of up to 91.9% can be achieved with a distance of 62 mm between the catalyst and the anode, which was 21% higher than that in the plasma alone system. The toluene conversion can be further increased to 94.7% when the Ni loading was increased from 4% to 16%. The synergistic capability of plasma catalysis was demonstrated from an enhanced toluene conversion and the increased formation of value-added fuel gases such as H2, CO, and CH4, together with simultaneously a selective reduction in CO2 formation, especially when the Ni loading was 4% and 8%. Identification of liquid by-products also revealed the synergy between plasma and catalysis which transformed bi-radical HCCH into gaseous products, prohibiting the formation of indene and naphthalene.

Role of phosphorus (P) additive in the performance of char-supported nickel (Ni) catalyst on tar reforming

Developing high-efficiency and low-cost tar removal catalysts is immediate and critical for gasification technology. In this work, phosphorus (P) was introduced into char-supported nickel (Ni) catalysts for steam reforming of tar. P and Ni were loaded on the catalyst support precursor, Yining coal oxidized by 20% H2O2, using two kinds of loading sequence, Ni, P co-loading and stepwise loading to obtain (P + Ni)/20%O-C and P-Ni/20%O-C catalysts respectively. Sand and Ni/γ-Al2O3 were selected for blank experiment and comparison. The self-designed dual-stage quartz reactor was used as an evaluation device to test tar steam reforming activity of the catalysts. Preparation conditions for catalyst and reaction technology were also optimized. The effect of P on the structure and acidity of catalysts was investigated by XRD, N2 adsorption, SEM, TEM, XPS, and NH3-TPD. It was found that (P + Ni)/20%O-C prepared by Ni, P co-loading method exhibited superior catalytic performance due to a better dispersion of Ni, more acid sites and higher amount of Ni0. Meanwhile, it is verified that pH 11 and 600 °C is the optimal preparation condition and reaction temperature. Compared to Ni/γ-Al2O3, the (P + Ni)/20% O-C catalyst achieved the highest reforming gas yield (39.3 mmol/g) and lowest tar yield (4.9%), which could be attributed to the function of conversion heavy tar to light fraction of (P + Ni)/20%O-C catalyst. That means most polycyclic materials cracked to small molecule products.

Steam reforming of tar from raw coke oven gas over bifunctional catalysts: Reforming performance for H2 production

AbstractIn this article, the bifunctional NiO/CaO@C12A7 catalysts having reforming catalytic effect and CO2 adsorption effect were prepared with co‐precipitation method, and were used in the sorption‐enhanced steam reforming process of tar from RCOG for hydrogen production. Among six kinds of samples with different load ratios, the catalyst with the CaO:C12A7:NiO ratio of 70:15:15 showed the best catalytic performance for the steam reforming of tar to produce H2 as well as the excellent characterization. Under the action of this catalyst, the H2 yield obtained from the steam reforming process of 1‐methylnaphthalene (C11H10) as the tar model compound were higher than that from the common steam reforming process, and the best H2 yield was obtained at the reforming temperature of 750°C, the S/C ratio of 12 and the WHSV of 0.055 hr−1, with the value of 83.9%.

Resistance of Ni/perovskite catalysts to H2S in toluene steam reforming for H2 production

H2S is a kind of common impurity produced during the gasification of biomass, and it will poison the catalysts used in biomass tar steam reforming, leading to a rapid degradation on the catalytic performance. The purpose of this work is to investigate the characteristics of biomass tar steam reforming using Ni/perovskite catalysts with the presence of H2S. Results show that H2S could significantly reduce catalytic activity due to the adsorption of sulfur on Ni surface, and Ni/perovskite catalysts are less susceptible to this poisoning in comparison to the Ni-catalyst loaded on γ-Al2O3. To understand the mechanism, fresh and spent catalysts were characterized using various techniques of XRD, SEM-EDS, XPS and TPO. It is proved that the lattice oxygen in perovskite could transform into surface species, inhibit the adsorption of sulfur and thus benefit to the reactivity of catalysts during biomass tar steam reforming.

Promoting effects of Fe-Ni alloy on co-production of H2 and carbon nanotubes during steam reforming of biomass tar over Ni-Fe/α-Al2O3

Fe-modified Ni/Al2O3 catalysts with Fe/Ni molar ratios of 0, 0.5, 1 and 2 were prepared to promote the co-production of H2 and carbon nanotubes (CNTs) during steam reforming of toluene as a tar model compound. After the addition of Fe, toluene conversion increased from 55.1% of Ni/Al2O3 to 73.6% of F1N1A (Fe/Ni ratio of 1), and H2 yield over F1N1A reached the maximum of more than 2000 mmol/(g-cata). Multi-walled carbon nanotubes with average diameter of 10–30 nm were generated and follow tip-growth mechanism. Compared with Ni/Al2O3, the addition of Fe remarkably increased the amount and quality of CNTs which had longer length and less tortuosity. These dual promoting effects on H2 and CNTs after the addition of Fe were attributed to the strong interaction between Ni and Fe in Fe-Ni alloy. Fe-Ni alloy had the high activity for the decomposition performance of toluene and H2O to generate more H2 and intermediates for improving the reforming reaction. Meanwhile, the high catalytic decomposition activity supplied more carbon species and the formation of Fe-Ni alloy enhanced the generation of metal carbide for promoting CNTs growth. Besides, the deposition of amorphous carbon was suppressed and the interaction between Ni particle and catalyst support was weakened after the addition of Fe, which kept the activity of catalyst and promoted the tip-growth of CNTs.

Carbon-coated mesoporous silica-supported Ni nanocomposite catalyst for efficient hydrogen production via steam reforming of toluene

Catalytic steam reforming of biomass tars is a promising technique for H2-rich gas production. However, the undesired deactivation of nickel-based catalysts due to nanoparticle (NP) sintering and carbon deposition remains a challenge for industrial applications. In this study, we prepared a carbon-coated ordered mesoporous silica-supported Ni-based catalyst (Ni-SiO2@C) via an evaporation-induced self-assembly (EISA) and calcination process. Characterizations revealed that the Ni-SiO2@C has a regular mesostructure with graphitic carbon layers protected Ni NPs (average 5.5 nm in diameter) highly dispersed and embedded into the silica wall of mesoporous channels. Compared to the SBA-15 and activated carbon-supported catalysts (NiO/SBA-15 and Ni/AC), the Ni-SiO2@C exhibits a higher toluene (a biomass tar model compound) conversion efficiency of 99.9% at 550 °C with an excellent stability for at least 46 h during steam reforming. The good performance can be attributed to the improved Ni NP dispersion, electron transfer and hydrothermal stability by enhanced metal-support interaction (MSI) as well as carbon coating. This work provides a cost-effective and easy handling approach for the synthesis of anti-sintering and coke-resistant tar reforming catalysts.

Lab-Scale Investigation of Palm Shell Char as Tar Reforming Catalyst

This research investigated the application of palm shell char as a catalyst for the catalytic steam reforming of tar after the sorption enhanced gasification (SEG) process. The catalytic activities of palm shell char and metal-supported palm shell char were tested in a simulated SEG derived syngas with tar model compounds (i.e., toluene and naphthalene) at a concentration of 10 g m−3 NTP. The results indicated that palm shell char had an experimentally excellent catalytic activity for tar reforming with toluene and naphthalene conversions of 0.8 in a short residence time of 0.17 s at 900 °C. A theoretical residence time to reach the complete naphthalene conversion was 1.2 s at 900 °C for palm shell char, demonstrating a promising activity similar to wood char and straw char, but better than CaO. It was also found that potassium and iron-loaded palm shell chars exhibited much better catalytic activity than palm shell char, while the parallel reaction of gasification of K-loaded palm shell char influenced the conversion with its drastic mass loss. Moreover, contrary to CaO, palm shell char presented relatively low selectivity to benzene, and its spontaneous gasification generated extra syngas. In summary, the present study demonstrated that the low-cost material, palm shell char, can successfully be used as the tar-reforming catalyst after SEG process.

Highly active and stable HF acid modified HZSM-5 supported Ni catalysts for steam reforming of toluene and biomass pyrolysis tar

This paper investigated the performance of HF modified HZSM-5 supported nickel catalysts (Ni/FZ5) in steam reforming of toluene (TSR) and biomass pyrolysis tar (BSR). The mesopores volume of support increased from 0.021 to 0.061 cm3/g with decreasing acid amount from 2.27 to 0.41 mmol/g after HF treatment. Catalysts with different Ni loadings were prepared and characterized. The Ni/FZ5 with Ni loading of 9 wt% possesses relatively large specific surface area (337 m2/g) and average pore size (2.91 nm), as well as small Ni particle size (23 nm) and high dispersion. In the process of TSR, 9Ni/FZ5 was kept above 70% for 7 h. Owing to the calculated lower apparent activation energy (30.76 KJ/mol), 9Ni/FZ5 exhibited the best performance in BSR at 650 °C, achieving the largest H2 yield of 52.8 mmol/g and the highest selectivity of H2 at 72.8%. Additionally, only 1.6 mg/gcatalyst of coke deposition was detected. Moreover, its high activity was still identified with excellent hydrothermal stability even after 7 times of regeneration. All findings suggest that 9Ni/FZ5 is a promising catalyst for biomass tar cracking.

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H2) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H2 production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.

Difference in tar reforming activities between biochar catalysts activated in H2O and CO2

This study investigates the difference in the activities between biochar catalysts activated in H2O and CO2 for in situ tar reforming. The experiments were performed in a two-stage fluidized-bed/fixed-bed at 800 °C. Mallee wood biochar (106–250 μm) was activated in pure CO2 or 15 vol% H2O balanced with Ar (15 vol. %H2O/Ar) for different times (0–50 mins) before being used as a catalyst for tar reforming. Based on the analysis of tar samples, it was found that H2O-activated biochar showed higher catalytic activity than CO2-activated biochar in both steam reforming and dry reforming of tar. Moreover, under otherwise identical conditions, reforming in steam was always more rapid than that in CO2 regardless of the atmosphere in which biochar was activated. The characterisation of biochar showed that H2O activation resulted in a biochar with a higher content of O-containing functional groups and aromatic C-O structures than that from CO2 activation. In addition, the content of O-containing functional groups and aromatic C-O structures of biochar after the steam reforming were higher than those after the dry reforming of tar. The different catalytic activities between the biochars activated by H2O and CO2 could be attributed to the different amounts of O-containing functional groups and aromatic C-O structures in biochar generated by H2O or CO2 activation. An extra supply of H2O plays an important role in improving and maintaining the catalytic activity of biochar during tar reforming.

CO2 sorption-enhanced steam reforming of phenol using Ni–M/CaO–Ca12Al14O33 (M = Cu, Co, and Ce) as catalytic sorbents

Abstract In this study, two kinds of Ni/CaO–Ca12Al14O33 catalytic sorbents were synthesized by wet impregnation using different CaO–Ca12Al14O33 as supports, which were prepared via calcination hydration (CH) and sol–gel/loading (SL) methods. Sorption-enhanced steam reforming (SESR) for hydrogen production was investigated using phenol as a tar model compound in a laboratory-scale fixed bed reactor. The Ni/CaO–Ca12Al14O33(CH) exhibited a higher hydrogen production activity compared to Ni/CaO–Ca12Al14O33(SL). The optimum operation condition for SESR process was obtained as temperature of 650 °C with S/C ratio of 3.0. Under this condition, the maximum H2 concentrations of 69.75% and 67.68% were achieved for Ni/CaO–Ca12Al14O33(CH) and Ni/CaO–Ca12Al14O33(SL), respectively. The corresponding H2 yields were 1.61 L/g and 1.45 L/g. However, a rapid deactivation of the Ni/CaO–Ca12Al14O33 catalytic sorbents occurred during the cyclic tests. Thus, bimetallic catalytic sorbents, Ni–M/CaO–Ca12Al14O33 (M = Cu, Co, and Ce), were developed by introducing the guest metal oxides. Among the three bimetallic catalytic sorbents, Ni–Co/CaO–Ca12Al14O33(CH) had the greatest potential for hydrogen production due to the synergistic catalytic effect of Co and Ni. The maximum H2 concentration of 82.23% and the maximum H2 yield of 2.31 L/g at 650 °C with S/C = 3.0 were observed for Ni–Co/CaO–Ca12Al14O33(CH). During the cyclic tests, the slight decrease in the H2 yield of Ni–Co/CaO–Ca12Al14O33(CH) was attributed to the decrease in the CO2 sorption capacity. The Ni–Ce/CaO–Ca12Al14O33(CH) showed a stable CO2 sorption/desorption ability, but the H2 yield decreased sharply due to the sintering of Ni particles and carbon deposition. Although the CO2 sorption capacity of Ni–Cu/CaO–Ca12Al14O33(CH) was well below the other two, it exhibited excellent stability. The results suggest that Ni–Co/CaO–Ca12Al14O33 and Ni–Cu/CaO–Ca12Al14O33 catalytic sorbents have great potential for the steam reforming of tar.

Microwave-assisted calcined olivine catalyst steam reforming of tar for hydrogen production

ABSTRACT It is very important to study catalysts with a good microwave absorption capacity and catalytic capacity for tar catalytic reforming by microwave-assisted heating. In this paper, olivine was used as catalysts in a small fixed-bed reactor for experimental study. The experimental results show that the calcination temperature of olivine has an effect on hydrogen production from microwave-assisted catalytic reforming tar. In the range of 650–1,000°C, tar conversion and hydrogen product concentration first increase and then decrease with the increase of calcination temperature of olivine. The optimum calcination temperature was 900°C. The study also found that olivine catalyst has better tar catalytic reforming effects than charcoal catalyst.

Optimization of hydrogen production from steam reforming of biomass tar over Ni/dolomite/La2O3 catalysts

Industrially, the endothermic process of steam reforming is carried out at the lowest temperature, steam to carbon (S/C) ratio, and gas hourly space velocity (GHSV) for maximum hydrogen (H2) production. In this study, a three-level three factorial Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was applied to investigate the optimization of H2 production from steam reforming of gasified biomass tar over Ni/dolomite/La2O3 (NiDLa) catalysts. Consequently, reduced quadratic regression models were developed to fit the experimental data adequately. The effects of the independent variables (temperature, S/C ratio, and GHSV) on the responses (carbon conversion to gas and H2 yield) were examined. The results indicated that reaction temperature was the most significant factor affecting both responses. Ultimately, the optimum conditions predicted by RSM were 775 °C, S/C molar ratio of 1.02, and GHSV of 14,648 h−1, resulting in 99 mol% of carbon conversion to gas and 82 mol% of H2 yield.