Catalytic Reforming Of Tar Research Articles

Mechanism of in-situ dynamic catalysis and selective deactivation of H2O-activated biochar for biomass tar reforming

Biochar, produced during gasification, is effective for tar catalytic reforming, finally with carbon deposition for deactivation. It explores the mechanism of in-situ dynamic catalysis and selective deactivation of H2O-activated biochar for tar reforming. The results indicate that ensuring the syngas quality, the gasification time can be extended for the high catalytic reactivity of biochar. The carbon deposit from tar on biochar surface causes the complete deactivation of H2O-activated biochar after 75 min-tar-reforming. In early stage (<45 min), the O-containing tars are selectively reformed on biochar surface with the formation of O-containing coke, while latter stage (45–75 min) is mainly dominated by coke carbonization. The surface functional groups could react directly with hydrocarbons, and metal species would act as active sites for tar reforming with their transformation. The coke leads to permanent deactivation of the active sites inside micropores of biochar, while meso/macropores become viable options to reform tars. The coke initially exists in dispersed single-layer ones, and then begins to grow, superimpose, and agglomerate to connecting into pieces, finally covering the entire surface of biochar. The amount/structure-difference of nascent tar ultimately determines the difference in the catalytic tar-reform ability of biochar. The tar containing heteroatoms such as oxygen has a high ability of addition and polymerization during coke formation. The higher porosity and hierarchical pore structure, more defects in graphene-like carbon structure and oxygen containing groups on the surface contribute to the better catalytic reactivity of biochar for tar reforming.

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.

Role of O-containing functional groups in biochar during the catalytic steam reforming of tar using the biochar as a catalyst

Tar formation is practically unavoidable during gasification. Catalytic tar forming is one of the most promising techniques for producing high-quality syngas at a commercial scale. Biochar has great potential to be used as a catalyst for the removal of tar from the syngas produced from the pyrolysis/gasification of biomass. The structure of biochar is a critical factor affecting its catalytic performance. This study investigates the role of O-containing functional groups in biochar during steam reforming of tar using biochar as a catalyst. Mallee wood biochar (106–250 μm) was activated in H2O for different times (0–50 min) and then used as a catalyst for the steam reforming of tar at 800 °C. The chemical structural features of biochars were characterized with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that H2O activation increased the concentration of O-containing functional groups, mainly the aromatic CO structures in biochar, which enhanced the catalytic destruction of tar. During the catalytic reforming of tar, the content of aromatic CO groups decreased while the catalyst activity decreased. It is believed that the aromatic CO functional groups in biochar play a vital role in the steam reforming of tar.

Hydrogen and methane mixture from biomass gasification coupled with catalytic tar reforming, methanation and adsorption enhanced reforming

In order to obtain fuel gas rich of hydrogen and methane from biomass gasification, an integrated process of catalytic tar steam reforming, methanation and adsorption enhanced reforming (AER) was established. A free-fall gasifier followed by a moving bed upgrading reactor loaded with bed materials was applied as the reaction device. The bed materials consisted of Ni/hematite, calcined limestone and quartz sand. The Ni/hematite was used for catalyzing both tar reforming and methanation, and the calcined limestone as CO2 capturer and the quartz sand as diluting agent. In the free fall reactor, white pine sawdust was gasified with steam to produce syngas containing tar. Then the syngas with tar was introduced upwardly into the moving bed reactor and passed through the downwardly moving bed materials. The tar in the syngas was catalytically reformed to produce a H2-rich gas, and thereafter the gas underwent WGS reaction, CO2 adsorption and methanation at the upper part of the reactor. The reactions were optimized through a decreased temperature gradient along with the up flow of reaction gas in the moving bed reactor. The influences of the mass ratio of steam to biomass (S/B) in the gasifier and the amounts of Ni/hematite and calcined limestone in the bed materials on the reactions were investigated. Under the condition of the temperature gradient from 500 to 600 °C, S/B 0.4, and bed materials composed of 20% Ni/hematite, 60% calcined limestone and 20% quartz sand, a fuel gas with H2 and CH4 mixture concentration over 97 vol% was obtained.

Assessment of char property on tar catalytic reforming in a fluidized bed reactor for adopting a two-stage gasification process

To well understand the effect of char property on tar catalytic reforming and support the development of two-stage gasification technology for the clean fuel gas production, the roles of pore structure and metal oxide in tar removal behavior were examined and compared on a fluidized bed two-stage reactor. The results show that although both of micro pore and meso pore had a remarkable influence on tar removal efficiency, fuel gas component and distilling fractions in tar, perhaps micro pore played a much more important role. Moreover, the tar removal efficiency did not have a good proportional relationship with the specific surface area of char. For the spent char, the activation treatment in steam was very beneficial to renew the catalytic reforming on tar by increasing the surface area of micro pore and maintain its high gasification activity. Compared to the demineralized char, the char samples that loaded metal oxide by impregnation approach largely promoted the tar removal efficiency, following the rank of Na2O > Fe2O3 > CaO > MgO. For Na2O, it not only had the best catalytic activity on tar, but also greatly promoted the generations of light tar and effective fuel gas, such as H2 and CO. Finally, considering the different effect of pore structure and metal oxide on tar catalytic reforming, a brief mechanism of tar catalytic reforming by char was proposed.

A hot syngas purification system integrated with downdraft gasification of municipal solid waste

Gasification of municipal solid waste (MSW) with subsequent utilization of syngas in gas engines/turbines and solid oxide fuel cells can substantially increase the power generation of waste-to-energy facilities and optimize the utilization of wastes as a sustainable energy resources. However, purification of syngas to remove multiple impurities such as particulates, tar, HCl, alkali chlorides and sulfur species is required. This study investigates the feasibility of high temperature purification of syngas from MSW gasification with the focus on catalytic tar reforming and desulfurization. Syngas produced from a downdraft fixed-bed gasifier is purified by a multi-stage system. The system comprises of a fluidized-bed catalytic tar reformer, a filter for particulates and a fixed-bed reactor for dechlorination and then desulfurization with overall downward cascading of the operating temperatures throughout the system. Novel nano-structured nickel catalyst supported on alumina and regenerable Ni-Zn desulfurization sorbent loaded on honeycomb are synthesized. Complementary sampling and analysis methods are applied to quantify the impurities and determine their distribution at different stages. Experimental and thermodynamic modeling results are compared to determine the kinetic constraints in the integrated system. The hot purification system demonstrates up to 90% of tar and sulfur removal efficiency, increased total syngas yield (14%) and improved cold gas efficiency (12%). The treated syngas is potentially applicable in gas engines/turbines and solid oxide fuel cells based on the dew points and concentration limits of the remaining tar compounds. Reforming of raw syngas by nickel catalyst for over 20 h on stream shows strong resistance to deactivation. Desulfurization of syngas from MSW gasification containing significantly higher proportion of carbonyl sulfide than hydrogen sulfide, traces of tar and hydrogen chloride demonstrates high performance of Ni-Zn sorbents.

Assessing tar removal in biomass gasification by steam reforming over a commercial automotive catalyst

Biomass gasification is a primary thermochemical conversion technology for transforming woody biomass feedstocks into a range of renewable fuels and chemicals. However in practice during biomass gasification, tar formation is practically unavoidable and tar removal during downstream synthesis gas cleaning is crucial to achieving high-quality synthesis gas at commercial scale. A category of catalytic tar reforming (tar cracking) catalysts typically utilizes precious metals including rhodium, which shows high reactivity toward gasification tar, resists coking and is more tolerant to sulphur compared to nickel. As such, they are similar to automotive exhaust after-treatment catalysts. In this study we evaluated how a commercial automotive catalyst performed as a gasification tar reforming catalyst. We tested the catalyst at bench scale for methanol reforming and tar reforming at 700 °C using 80/20 mixtures of methanol/water, and 79.5/20/0.5 mixtures of methanol/water/tar and methanol/water/guaiacol in flowing nitrogen.Methanol was 95% converted to synthesis gas at 700 °C and the catalyst did not deactivate during 48 h on stream. Methanol/water mixtures containing 4925 ppm gasification tar also reacted readily over the catalyst to produce syngas, but catalyst deactivation occurred over tens of hours of continuous operation, indicated by decreased conversion of the methanol/tar feed. The catalyst was regenerated by calcining in air at 500 °C, which allowed catalyst to operate for 120 h. Methanol/water/guaiacol mixtures also reacted readily to produce syngas, but as with tar, the catalyst deactivated over tens of hours continuous operation with methanol/guaiacol feed. SEM data confirmed that coking of the catalyst was the likely cause of deactivation. At relatively high reaction temperature and contact times of seconds used in this study, guaiacol was completely deoxygenated, but a fraction of the guaiacol was methylated over the catalyst to form methyl-substituted benzenes, toluenes and xylenes (BTX).

Characteristics of tar abatement by thermal cracking and char catalytic reforming in a fluidized bed two-stage reactor

With respect to the newly proposed fluidized bed two-stage (FBTS) gasification process, the researches on tar thermal cracking and catalytic removal by char bed layer were conducted on a FB two-stage reaction apparatus. It shows that the effect of char on tar removal was much related to the reaction temperature and residence time of tar-containing fuel gas in the tar reformer. Under the tested experimental conditions, increasing reaction temperature and residence time can effectively promote tar abatement and generate more H2, CO and CH4. For catalytic reforming by char, the higher reaction temperature and the longer residence time, the lower tar content in fuel gas. Compared to thermal cracking, catalytic reforming of tar by char was more effective in tar removal efficiency and inhibition of carbon deposition, upgrading the quality of fuel gas. The researches indicated that the suitable operational conditions for tar removal by char in the FB two-stage gasification process were at reforming temperature of 1000 °C, and residence time above 0.9 s.

Catalytic cracking of biomass pyrolysis tar over char-supported catalysts

The work aims to investigate an effective method of catalytic reforming of tar during biomass high-temperature pyrolysis using rice husk char (RHC) and metal impregnated (Fe, Cu and K) char in a dual-stage reactor. The char and char-supported catalysts exhibited high catalytic performance, in terms of the high tar conversion efficiencies of 77.1% for RHC, 82.7% for K-RHC, 92.6% for Fe-RHC and 90.6% for Cu-RHC at 800 °C. Moreover, K-RHC and Cu-RHC catalysts after three cycles still exhibited high activity for tar removal. The catalytic tar conversion by char or char-supported catalysts contributes to improving the yield of syngas, particularly the combustible gases of H2, CO and CH4, corresponding to the syngas yield increasing from 196.6 mL/g for thermal reforming to 269.6 mL/g for K-RHC, 274.9 mL/g for Cu-RHC and 342.7 mL/g for Fe-RHC at 800 °C, respectively. The results from GC–MS analysis illustrated that the addition of char and char-supported catalysts promoted the transformation of larger polycyclic aromatic hydrocarbons into lighter tar compounds, leading to an increase in the proportion of single-ring tars. XRD results indicated that the most active phases of the fresh K-RHC, Cu-RHC and Fe-RHC for tar cracking and reforming were KCl, Cu and Fe, respectively. Textural characterization showed the addition of Fe and Cu was in favor of producing highly porous carbon materials and led to the increase in specific surface area and total pore volume.

The catalytic reforming of tar from pyrolysis and gasification of brown coal: Effects of parental carbon materials on the performance of char catalysts

The carbon structure of char as catalysts is very crucial as it greatly governs the catalytic activity of char for tar reforming reactions. More importantly, the char structure also plays an important role in affecting the interactions between the inherent metal species and carbon atoms, thus affecting the catalytic performances. This study aims to investigate the effects of char structure on the reforming of tar derived from the gasification and pyrolysis of Shengli brown coal. Chars prepared from five kinds of acid-washed carbonaceous materials, including biomass, brown coal, bituminous coal, anthracite and graphite, were used as tar reforming catalysts in this work. The different effectiveness of H-form char catalysts from the different ranking carbon materials have clearly shed light on the effects of char structure on tar reforming. Results show that the chars from biomass and low rank coals featured obviously higher catalytic activity than those from high rank fuels. The variation in char structure that was revealed by FT-Raman has greatly exerted impacts on tar yields as well as tar compositions. Interestingly, the supply of steam (in the gasification condition) did not always see the reduction in tar yields, very much depending on the type of char catalysts used in the experiments.

Catalytic Tar Reforming during Brown Coal Pyrolysis: Effects of Heating Rate and Activation Time on Char Catalysts

Chars from low rank fuels (i.e., brown coal and biomass) have attracted increasing attention as a promising candidate for catalytically reforming tarry material into light hydrocarbons and gases. The effects of heating rate and activation time on the preparation of char catalysts were examined. The catalytic activity of the char catalysts was tested for tar reforming during the pyrolysis of brown coal at different temperatures. The experiments of char preparation and tar reforming were conducted in a bench-scale quartz reactor. Results indicate that the char derived from a fast heating rate showed a much better activity on tar reforming than the one from a slow heating rate. The char with 3–5 min activation time gave the best catalytic performance, achieving a very low tar yield of 1.18 wt %. The increase in the surface area of char catalysts due to the char–steam reaction did not always increase the catalytic activity of char catalysts. Raman spectra of chars revealed that the char properties (i.e., O-co...

Utilization of MSW-Derived Char for Catalytic Reforming of Tars and Light Hydrocarbons in the Primary Syngas Produced During Wood Chips and MSW-RDF Air Gasification

The present work aimed at optimising the design and operation of char utilization as a low cost catalyst for tars reforming. The effect of temperature, tars composition, light hydrocarbons composition, steam content and type of reformer on the conversion of tars and light hydrocarbons into additional syngas using sorted municipal solid waste (MSW)—derived char was systematically monitored. Reforming tests were carried out using industrial primary syngas produced by air gasification of wood chips and MSW-RDF in a commercial fluidized bed gasifier. Up to 85% of tars present in the primary syngas have been converted to permanent gases at 871 °C, while passing through the catalytic fixed bed of char, for 1.4 s, at atmospheric pressure and syngas space velocities in the 3500–4000/h relative to the char in the bed (0.82 NL/g h). Content of multi-ring aromatics decreased following the passage of the syngas through the char bed leaving naphthalene and xylene as the predominant residuals. Propane, propylene and ethylene were completely converted. Up to 30% methane conversion was reached at 925 °C while ethane conversion was only occurring under high steam content of 65 vol%.

Catalytic reforming of tar using corncob char and char-supported potassium catalysts

This work aims to investigate the importance of biomass char and the metal oxides in the ash in tar cracking during the volatile–char interactions. Experiments were carried out in a two-stage fixed reactor, and corncob, one typical agricultural biomass rich in potassium, was chosen as raw material. Results showed that char and char-supported potassium catalysts have good activity for tar elimination due to the good absorbability of char and catalytic property of potassium. In particular, tar conversion efficiency can reach 95.8% by using 1.5 K-char catalyst at 700 °C. The reforming reactions can be significantly enhanced during the volatile–char interactions in the presence of char and char-supported potassium catalysts. As a result, the syngas yield increased significantly with increasing temperature and supported K+, particularly the combustible gases including H2, CO and CH4. Physical and chemical structure of char changed due to reforming reactions related to the carbon, while the content of potassium was almost unchanged.

An advanced biomass gasification technology with integrated catalytic hot gas cleaning. Part III: Effects of inorganic species in char on the reforming of tars from wood and agricultural wastes

Char is used directly as a catalyst for the catalytic reforming of tar during gasification. Experiments have been carried out to examine the effects of inorganics in char as a catalyst for the catalytic reforming of tar during the gasification of mallee wood, corn stalk and wheat straw in a pilot plant. The char catalyst was prepared from the pyrolysis of mallee wood at a fast heating rate. The catalytic activities of char and acid-washed char for tar reforming were compared under otherwise identical gasification conditions. For all biomass feedstocks tested for gasification, the tar contents in product gas could be drastically reduced by the catalyst, reaching a tar concentration level well below 100mg/Nm3. The acid-washed char also showed profound activity for tar reforming although its catalytic activity was definitely lower than the raw char. Both catalysts could effectively reform the aromatic ring systems (especially large aromatic ring systems with three or more fused benzene rings) in tars as is revealed using UV-fluorescence spectroscopy. The char itself was also partially gasified. After being used as a catalyst, the condensation of the aromatic rings and the accumulation of inorganic species led to drastic changes in char reactivity with O2 at 400°C. The inorganic species in char tended to enhance the formation of H2 and CO during the reforming reactions in the catalytic reactor.

Use of alkali-feldspar as bed material for upgrading a biomass-derived producer gas from a gasifier

Gasification of biomass has strong potential for biofuels production. However, one challenge to its competitiveness is the efficient elimination of the tars present in the raw gas. The use of active bed materials in tar reforming is an appealing approach and can be employed as part of primary and/or secondary measures. Here, the activity of an alkali-feldspar [(K, Na)AlSi3O8] ore was assessed in relation to upgrading the producer gas from the Chalmers 2–4 MW indirect biomass gasifier. This material was tested in a single bubbling bed reactor previously developed for studies involving catalytic tar reforming. The bed of feldspar was fluidized with raw gas. The material was tested at three temperatures: 700°C, 800°C, and 900°C. The results indicate that alkali-feldspar shows: (1) a high potential for the Water–Gas Shift reaction even at low temperature (H2/CO∼3); (2) no reduction of the methane content in the cleaned gas and net formation of methane at 900°C; (3) the elimination of most C2H2 and C3H6 already at 800°C; and (4) a striking tar selectivity, which resulted in the reformed gas having exclusively pure ring-compounds. In the same reactor set-up at 800°C, fresh olivine was comparatively less efficient than feldspar in reducing tar levels. At 900°C, the feldspar decomposed 47% excepting benzene. Moreover, it retained its mechanical integrity, withstood longer reducing periods (3h), and displayed neither signs of agglomeration nor loss of activity, despite the formation of a carbon deposit. The deposits were readily removed by introducing an oxidizing atmosphere. Furthermore, the raw feldspar showed a low capacity for oxygen transport, advantageous in this application. Taken together, our results indicate that this material is clearly promising and warrants further investigations.

Catalytic reforming of pyrolysis tar over metallic nickel nanoparticles embedded in pyrochar

Metallic nickel (Ni0) nanoparticles could be in situ generated in the carbon matrix of rice husk char (RHC) via a facile one-step pyrolysis. The synthesized RHC Ni has a considerable performance on tar reforming. Tar reforming efficiency is increased with the increases of the used catalyst weight and reforming temperature. In particular, tar reforming efficiency can reach up to 90.5% and 99.8% by using 5g and 10g of RHC Ni, respectively. Tar reforming efficiency can also keep stable after 5 cycles. Besides, RHC Ni showed high tar conversion efficiency, increasing from 92.3% to 100%, when the reforming temperature was increased from 500°C to 900°C. RHC Ni showed a high catalytic activity even at the relatively lower temperatures. Furthermore, the yield of liquid products was decreased from 30.2% to 10.7%, corresponding to tar reforming. Accordingly, the gas yield was increased from 37.5% to 58.0%, in which the main components of syngas are CO and H2. It is noted that the PAHs compounds in tar could be significantly reduced by using the RHC Ni. The surface areas of the used RHC Ni were increased due to the char gasification rate higher than deposition rate. The RHC Ni has a high potential to be used for tar catalytic reforming.

Tar Elimination from Producer Gas by Using &lt;i&gt;In Situ&lt;/i&gt; Catalytic Reforming of Tar

Tar removal from producer gas was investigated using activated carbon supported iron catalyst. Activated carbon was derived from jute stick biomass. The catalyst surface areas and pore volume were characterized by using iodiometric titration which shows that as the iron loading percentage increased, the adsorption capability was also increased which represents the increment of pore volume of the catalyst. Based on XRD pattern, the iron species formed on the activated carbon surface is mostly amorphous magnetite (Fe3O4) species coexisted with the reduced irons (α-Fe and γ-Fe). The reduced iron on catalyst surface justify the active phase which enhances the tar reforming during biomass gasification.

Steam–oxygen gasification of forest residues and bark followed by hot gas filtration and catalytic reforming of tars: Results of an extended time test

Steam–oxygen gasification in a Circulating Fluidized-bed (CFB) reactor was developed for producing transportation fuels from different wood residues. This article presents the results of a two week test campaign, in which crushed forest residues and industrial bark mixture were used as the feedstocks. The aim of the work was to carry out extended time testing of the developed gasification and hot gas cleaning process and to determine the fate of different gas contaminants and trace components of wood. In the test runs, wood fuels were gasified in the CFB reactor at a 0.2–0.25MPa pressure using a mixture of steam and oxygen as the gasification agent. A mixture of sand and dolomite was used as the bed material in order to maintain stable fluidization and to catalyse in-situ tar decomposition before hot filtration. Raw gas was filtered at ca. 550°C and the filtered gas was then led into a two-stage catalytic tar reformer. The gasifier performance and the concentrations of different gas contaminants were determined at four different operating variable set points during a total of 215h of operation. The results for carbon conversion efficiency, raw gas composition and the fate of fuel nitrogen, chlorine and trace metals are presented in this paper. The concentrations of gas contaminants were determined after the ceramic filter unit and after the catalytic reformer. The conversion efficiencies for hydrocarbon gases, tars and ammonia in the reformer are also presented. The test run was carried out as a continuous operation without any interruptions or operational problems.

Olive oil residue gasification and syngas integrated clean up system

Gasification is one of the most promising technologies to convert low quality fuels into more valuable ones. The main problem in the use of biomass in gasification processes is the high amount of tar released in the pyrolysis step. It is thus necessary to recover the tar and to transform it in lighter combustible gas species such as CH4, CO and H2 by means of catalytic processes. In this work the gasification of olive husk is performed in order to produce a high quality syngas, composed mainly of carbon monoxide and hydrogen, using an innovative laboratory scale plant composed of a unique reactor divided into three sections. The first section is dedicated to the pyrolysis, the second to the gasification of char produced during pyrolysis and the third to the catalytic reforming of tar. In the reformer two catalysts were tested: a CeO2 promoted bimetallic Ni–Co catalyst and a Ni catalyst, both supported on γ-Al2O3. This plant design allows one to minimize the heat dispersion enhancing the energy efficiency of the unit.

Metal catalysts for steam reforming of tar derived from the gasification of lignocellulosic biomass

Biomass gasification is one of the most important technologies for the conversion of biomass to electricity, fuels, and chemicals. The main obstacle preventing the commercial application of this technology is the presence of tar in the product gas. Catalytic reforming of tar appears a promising approach to remove tar and supported metal catalysts are among the most effective catalysts. Nevertheless, improvement of catalytic performances including activity, stability, resistance to coke deposition and aggregation of metal particles, as well as catalyst regenerability is greatly needed. This review focuses on the design and catalysis of supported metal catalysts for the removal of tar in the gasification of biomass. The recent development of metal catalysts including Rh, Ni, Co, and their alloys for steam reforming of biomass tar and tar model compounds is introduced. The role of metal species, support materials, promoters, and their interfaces is described.