Showing papers on "Coke published in 2013"

Nanosize-Enhanced Lifetime of SAPO-34 Catalysts in Methanol-to-Olefin Reactions

Abstract: In this work, we systematically investigated the size effect of silicoaluminophosphate molecular sieve catalysts SAPO-34 on the catalytic performance of methanol-to-olefin (MTO) reactions. Four highly crystalline SAPO-34 molecular sieves with different crystallite sizes were synthesized under hydrothermal conditions carried out in conventional or microwave ovens with the same starting gel composition using TEAOH as the structure-directing agent. The as-prepared SAPO-34s have similar composition, and their average crystal size can be controlled between 20 nm and 8 μm. Textural properties and chemical environments of framework atoms as well as acid concentration were characterized by N2 adsorption and NMR measurements. The MTO reactions were carried out over these four SAPO-34 catalysts to study their catalytic performances dependent on the crystal size. The occurrence of catalyst deactivation varied considerably with the crystal size of SAPO-34s. Significantly, the nanosized catalysts, especially the sheetlike SAPO-34 catalyst with 20 nm thickness, exhibited the longest catalyst lifetime and lowest coking rate in MTO reactions. On the basis of the measurement of coke formation and the determination of retained coke species, a scheme is proposed to elucidate the reduction in coke deposition and consequently the remarkably enhanced lifetime on the nanosized SAPO-34 catalysts in methanol conversion.

Co-gasification of Biomass and Non-biomass Feedstocks: Synergistic and Inhibition Effects of Switchgrass Mixed with Sub-bituminous Coal and Fluid Coke During CO2 Gasification

Abstract: Co-gasification of biomass, namely, switchgrass, with coal and fluid coke was performed to investigate the availability of the gasification catalysts to the mixed feedstock, especially alkali and alkaline earth elements, naturally present on switchgrass. Rates of CO2 gasification of the single and mixed materials were measured at temperatures between 750 and 950 °C and atmospheric pressure by thermogravimetry. High interparticle mobility of the catalysts is indicated by a prompt and lasting effect on the mixed feed gasification rate when compared with the separate rates. The switchgrass–coal mixtures show a deactivation (antagonism), attributed to sequestration of the mobile alkali elements by reaction with aluminosilicate minerals in coal to form inactive alkali aluminosilicates, such as KAlSi3O8 and KAlSiO4. Remaining catalytic activity is evident when excess alkali is present in the feed mixture to satisfy the stoichiometric requirements of these deactivation reactions. In co-gasification of switchgras...

Biochar affected by composting with farmyard manure.

Abstract: Biochar applications to soils can improve soil fertility by increasing the soil's cation exchange capacity (CEC) and nutrient retention. Because biochar amendment may occur with the applications of organic fertilizers, we tested to which extent composting with farmyard manure increases CEC and nutrient content of charcoal and gasification coke. Both types of biochar absorbed leachate generated during the composting process. As a result, the moisture content of gasification coke increased from 0.02 to 0.94 g g, and that of charcoal increased from 0.03 to 0.52 g g. With the leachate, the chars absorbed organic matter and nutrients, increasing contents of water-extractable organic carbon (gasification coke: from 0.09 to 7.00 g kg; charcoal: from 0.03 to 3.52 g kg), total soluble nitrogen (gasification coke: from not detected to 705.5 mg kg; charcoal: from 3.2 to 377.2 mg kg), plant-available phosphorus (gasification coke: from 351 to 635 mg kg; charcoal: from 44 to 190 mg kg), and plant-available potassium (gasification coke: from 6.0 to 15.3 g kg; charcoal: from 0.6 to 8.5 g kg). The potential CEC increased from 22.4 to 88.6 mmol kg for the gasification coke and from 20.8 to 39.0 mmol kg for the charcoal. There were little if any changes in the contents and patterns of benzene polycarboxylic acids of the biochars, suggesting that degradation of black carbon during the composting process was negligible. The surface area of the biochars declined during the composting process due to the clogging of micropores by sorbed compost-derived materials. Interactions with composting substrate thus enhance the nutrient loads but alter the surface properties of biochars.

Catalytic upgrading of biomass pyrolysis vapours using faujasite zeolite catalysts

Abstract: Bio-oil produced via fast pyrolysis of biomass has the potential to be processed in a FCC (fluid catalytic cracking) unit to generate liquid fuel. However, this oil requires a significant upgrade to become an acceptable feedstock for refinery plants due to its high oxygen content. One promising route to improve the quality of bio-oil is to pyrolyse the parent biomass in the presence of a catalyst. This work investigates the influence of faujasite catalysts on the pyrolysis of pinewood. Pyrolysis process with Na-faujasite, Na0.2H0.8-faujasite, and H-faujasite (Na-FAU, Na0.2H0.8-FAU, and H-FAU) were carried out in a fixed-bed reactor at 500 °C. It is shown that, in the same condition, catalytic upgrading of pyrolysis vapour is superior to in-situ catalytic pyrolysis of biomass when it comes to quality of bio-oil. The yields of coke, gas and water increase while that of organic phase decreases proportional with the concentration of protons in catalysts. Compared to the other two catalysts, Na0.2H0.8-FAU removes the most oxygen from bio-oil, reduces amount of acids and aldehydes/ketones which result in a higher energy-contained and more stable oil with less corrosive property. However, the biggest contribution to the oxygen removal is via the formation of reaction water, which is not an optimum path. This leaves space for future development.

Coke- and sintering-resistant monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires for dry reforming of methane

Abstract: Monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires display high resistance to coke formation and sintering in the dry reforming of methane due to their hierarchical porous structure, well dispersed metallic nickel species, more basic sites and strong metal–support interaction effect.

Facile Fabrication of ZSM-5 Zeolite Catalyst with High Durability to Coke Formation during Catalytic Cracking of Paraffins

Abstract: Post-synthetic HNO3 treatment of ZSM-5 zeolite synthesized in the absence of organic structure-directing agent removes framework Al selectively from the external surface, producing a unique ZSM-5 zeolite catalyst that has very few acid sites on its external surfaces. The resulting external acid sites can be readily deactivated at the early stage of the reaction, giving a potentially long-life catalyst as a result of a high durability to coke formation during the cracking of hexane or other paraffin molecules.

Aromatic Chemicals by Iron-Catalyzed Hydrotreatment of Lignin Pyrolysis Vapor

Abstract: Lignin is a potential renewable material for the production of bio-sourced aromatic chemicals. We present the first hydrotreatment of lignin pyrolysis vapors, before any condensation, using inexpensive and sustainable iron-silica (Fe/SiO2) and iron-activated carbon (Fe/AC) catalysts. Lignin pyrolysis was conducted in a tubular reactor and vapors were injected in a fixed bed of catalysts (673 K, 1 bar) with stacks to investigate the profile of coke deposit. More than 170 GC-analyzable compounds were identified by GCxGC (heart cutting)/flame ionization detector mass spectrometry. Lignin oligomers were analyzed by very high resolution mass spectrometry, called the "petroleomic" method. They are trapped by the catalytic fixed bed and, in particular, by the AC. The catalysts showed a good selectivity for the hydrodeoxygenation of real lignin vapors to benzene, toluene, xylenes, phenol, cresols, and alkyl phenols. The spent catalysts were characterized by temperature-programmed oxidation, transmission electron microscopy (TEM), and N2 sorption. Micropores in the Fe/AC catalyst are completely plugged by coke deposits, whereas the mesoporous structure of Fe/SiO2 is unaffected. TEM images reveal two different types of coke deposit: 1) catalytic coke deposited in the vicinity of iron particles and 2) thermal coke (carbonaceous particles ≈1 μm in diameter) formed from the gas-phase growth of lignin oligomers. Lignin is fond of iron: Lignin is a promising source for renewable aromatics. Inexpensive iron-based catalysts are very selective for the direct hydrodeoxygenation of lignin pyrolysis vapors. Two types of coke deposit are revealed. Lignin oligomers are analyzed by very high resolution mass spectrometry.

Steam treatment on Ni/γ-Al2O3 for enhanced carbon resistance in combined steam and carbon dioxide reforming of methane

Abstract: Coke deposition on reforming reaction catalysts, typically Ni particles deposited on alumina supports, has been a major obstacle barring their practical industrial application. In this work, a Ni/γ-Al2O3 catalyst was stabilized by a pretreatment with steam at high temperature of 850 °C. The steam-treated Ni/γ-Al2O3 catalyst showed thermodynamically possible highest conversion (98.3% for methane and 82.4% for carbon dioxide) and H2/CO ratio of 2.01 for combined steam and carbon dioxide reforming of methane, and operated stably for 200 h. The amount of deposited carbon coke was 3.6% for steam-treated catalysts whereas conventional catalysts had 15.4% of coke after 200 h of the reaction. The steam pretreatment removed unstable aluminum that can otherwise leach out, which causes severe carbon deposition at the early stage of the reaction. This novel steam pretreatment enhanced the carbon resistance of the catalysts significantly, resulting in improved activity and long-term stability.

Activated Semi-coke in SO2 Removal from Flue Gas: Selection of Activation Methodology and Desulfurization Mechanism Study

Abstract: Activated semi-coke, an economical carbonaceous material, is employed in the removal of SO2 from simulated flue gas of an industrial power plant. Activation by four commonly used agents, including CO2, KOH, ZnCl2, and H3PO4, is studied in detail, which demonstrates that the sample treated with KOH at high temperature presents the best performance on removal of SO2. Further investigation on the physical and chemical properties reveals that both optimized pore structure and increased amount of active sites of activated semi-coke could contribute to the high desulfurization capacity. The semi-coke activated with KOH is selected to discuss possible mechanisms of the adsorption and desorption processes. Performances with variation of desulfurization temperatures evidence that physically adsorbed SO2 can transform into chemically adsorbed SO2, which is significantly affected by temperature. Desulfurization behaviors under different flue gas compositions show that oxidation of SO2 to SO3 plays a key role in SO2 ...

Methane Dry Reforming at High Temperature and Elevated Pressure: Impact of Gas-Phase Reactions

Abstract: Catalytic dry reforming over a platinum-based catalyst is described experimentally and numerically in a laboratory pilot-plant flow reactor. The results reveal that coking in the upper part of the catalyst bed and at the entrance of the reactor occurs, depending on the composition of the reaction mixture and the respective temperature. To a significant extent, gas-phase reactions play a role as being the cause for the observed coking behavior in the reforming of methane in the presence of carbon dioxide at high temperatures of 1123–1273 K and at 20 bar. Hydrogen addition can inhibit coke formation better than water addition. The reactor is modeled by a one-dimensional description of the reacting field using elementary-step reaction mechanisms of up to 4238 gas-phase reactions among 1034 species and 58 heterogeneous reactions among 8 gas-phase species and 14 surface-adsorbed species. The study leads an optimized positioning of the catalyst in a technical reformer tube.

Ilmenite and Nickel as Catalysts for Upgrading of Raw Gas Derived from Biomass Gasification

Abstract: Two metal oxides, naturally occurring ilmenite (iron titanium oxide) and manufactured nickel oxide supported on an α-Al2O3 matrix (NiO/AL2O3), were compared as catalysts for secondary biomass gas upgrading. The experiments were conducted in a Chemical-Looping Reforming (CLR) reactor, which combines biomass gas upgrading with continuous regeneration of coke deposits. The CLR system was fed with a tar-rich producer gas from the Chalmers 2–4 MW biomass gasifier, and the possibilities to reduce the tar fraction and to increase the yield of hydrogen were evaluated for temperatures between 700°C and 880°C. A system-wide molar balance was established, to enable calculations of tar removal efficiency on a mass basis; these results were further compared with those for the more widely used tar-to-reformed gas ratio, yielding tar concentrations in units of gtar/Nm3gas. Both materials exhibited activity with respect to tar decomposition and increased the yield of hydrogen. In addition, both tar removal and hydrogen production were increased with increases in temperature. All the phenolic compounds and a large proportion of the one-ring branched tars were decomposed at 800oC by the two catalysts, despite the fact that the tar load in the raw gas was as high as 30 gtar/Nm3gas. Results from the mole balance showed that it is important to specify on what basis the tar removal efficiency is calculated. The tar removal efficiency was calculated to 95% for the Ni/Al2O3 catalyst at 880°C and to 60% for the ilmenite catalyst at 850°C on tar-to-reformed gas basis. When the produced permanent gases were removed from the reformed gas the same calculations yielded the tar removal efficiency of 86% and 42% respectively. The testing of serial samples of the effluent stream from the regeneration reactor for carbon oxides showed that coke was removed from the catalyst, and no deactivation by coke deposits was detected during the 8 hours of operation of the CLR reactor.