Effect of Synthesis Route on Properties of CuO as a High Temperature Oxygen Carrier

Copper oxide powders intended for use as oxygen carriers in high temperature air separation and chemical looping combustion have been synthesized by a range of ceramic synthesis techniques including citrate gel, Pechini, precipitation, alanine assisted combustion, and high temperature oxidation. The evolution of morphology and crystal structure in the synthesis of powders was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The surface chemical properties of the powders were studied using X-ray photoelectron spectroscopy (XPS). The oxygen sorptive/desorptive kinetics was studied using thermogravimetric analysis (TGA). Kinetics of the oxygen exchange reactions were analyzed and explained using empirical kinetics models with minimum error. A strong correlation was observed between the oxygen desorption parameters and oxygen to copper ratio calculated from measured XPS spectra. Copper oxide powders synthesized using the alanine assisted combustion and citrate gel methods resulted in optimum kinetic properties for use as an oxygen carrier at high temperature

Effect of Direct Coal Liquefaction Conditions on Coal Liquid Quality

Solvent extraction of coal was investigated with a focus on the quality of the coal liquids rather than coal conversion. The aim was to determine how the hydrogen/carbon ratio and other quality measures were influenced by liquefaction conditions. Liquefaction was performed using Canadian Bienfait lignite in the temperature range of 350–450 °C, 4 MPa H₂, solvent/coal ratio of 2:1, and residence times up to 30 min at liquefaction temperature. An industrial hydrotreated coal liquid was used as the solvent. The hydrogen/carbon ratio of the coal liquids decreased with an increase in coal conversion, so that coal liquid quality decreased with an increase in the maximum liquefaction temperature. Selective extraction of hydrogen-rich material during the initial stages of liquefaction could be explained in terms of the low solubility parameter of the solvent, the weaker association of less polar molecules, and the limited extent of hydrogen transfer between phases. At longer residence times, especially at higher temperature, the coal liquids became heavier (>550 °C boiling material) and more aromatic and had a higher density and refractive index. These changes were partly due to increased coal conversion and partly due to increased time for hydrogen transfer, cracking, and recombination reactions to take place. It was further found that the nitrogen content of the coal liquids increased with increasing temperature and residence time. Some industrial implications of the changes in coal liquid quality on process development for coal liquefaction were discussed

Characterization and Refining Pathways of Straight-Run Heavy Naphtha and Distillate from the Solvent Extraction of Lignite

Coal liquids were produced by solvent extraction of Bienfait lignite at 415 °C and 4 MPa H₂ for 1 h with a hydrotreated coal tar distillate in a 2:1 solvent to coal ratio. Detailed characterization was performed on four straight-run distillation fractions of the coal liquids in the 120–370 °C boiling range. It was found that the coal liquids contained very little aliphatic material. Most of the compounds were aromatics, with aromatic compounds having no alkyl substituents dominating the composition. The aromatic carbon content increased with boiling fraction from 80 wt % in the 120–250 °C fraction to 94 wt % in the 343–370 °C fraction. Major compounds identified in the coal liquids were acenaphthene, phenanthrene, fluoranthene, and pyrene, which constituted 62 wt % of the total product. The coal liquids also contained heteroatom species. Interestingly, the nitrogen content did not monotonically increase with an increase in boiling point. The maximum nitrogen content was found in the 300–343 °C boiling fraction as a result of a high concentration of carbazole. The refining pathways for transportation fuel production were evaluated. It was found that the naphtha fraction could be upgraded to a motor gasoline blending component just by hydrotreating. No subsequent catalytic reforming was necessary because of the low aliphatic content of the naphtha. The kerosene required severe hydrotreating in order to be acceptable as a jet fuel blending component, mainly because of the high dinuclear aromatic content of the straight-run kerosene. The distillate made a poor feed material for diesel fuel and required severe hydrotreating to achieve an acceptable cetane number. In general, the coal-derived distillate would benefit from ring opening to reduce its density. The prognosis for transportation fuel production from the coal liquids was not favorable. The production of aromatic chemicals was a better fit with the properties of the coal liquids

Steam Regeneration of Polyethylenimine-Impregnated Silica Sorbent for Postcombustion CO₂ Capture: A Multicyclic Study

Steam regeneration of polyethylenimine (PEI)-impregnated commercial grade silica was investigated in a packed bed reactor. Adsorption was performed at 75 °C under 10% CO₂/N₂, and desorption was carried out under steam at 110 °C for 20 consecutive cycles. CO₂ adsorption capacity was found to decrease by 9 mol % over the period of 20 cycles. No evident signs of sorbent degradation due to PEI leaching or changes in surface morphology and amine functionalities were observed upon characterization of the sorbent after the cyclic study. Most of the loss in adsorption capacity was associated with thermal degradation of the sorbent during drying under N₂ after steam stripping at 110 °C. The desorption kinetics during steam stripping was found to be much faster than during N₂ stripping. Over 80% of the total CO₂ was released within the first 3 min of steam injection into the reactor. A separate packed bed study was conducted to investigate the influence of moisture content (5.3–14.7 vol %) in flue gas on the CO₂ adsorption capacity of PEI-impregnated silica. The presence of moisture had a positive impact on CO₂ uptake of the sorbent; a 4–9 mol % increase in CO₂ uptake was observed in comparison to the adsorption under dry conditions. However, the presence of moisture increased the heat of regeneration of the sorbent significantly. It was calculated that the energy demand increased approximately 2-fold on introduction of 14.7% moisture compared to that of dry flue gas

Metal oxide nanoparticle-modified graphene oxide for removal of elemental mercury

<p>Mercury is an extremely toxic element that is primarily released by anthropogenic activities and natural sources. Controlling Hg emissions, especially from coal combustion flue gas, is of practical importance in protecting the environment and preventing human health risks. In the present work, three metal oxides (MnO₂, CuO, and ZnO) were loaded on graphene oxide (GO) sorbents (designated as MnO₂-GO, CuO-GO, and ZnO-GO). All three adsorbents were successfully synthesized and were well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the metal oxide nanoparticles (NPs) successfully decorated the GO. The elemental Hg adsorption capabilities of the three sorbents were subsequently evaluated using an in-house built setup for cold vapour atomic fluorescence spectrophotometry (CVAFS) with argon as the carrier gas for mercury detection. The testing temperature ranged from 50°C to 200°C at intervals of 50°C. MnO₂-GO showed an excel lent Hg⁰ adsorption capacity via chemisorption from 50 to 150°C and a mercury removal efficiency as high as 85% at 200°C, indicating that the MnO₂-NP-modified GO is applicable for enhancing gas-phase elemental mercury removal. However, neither CuO-GO nor ZnO-GO performed well. This work provides useful insights into the development of novel sorbent materials for the elemental mercury removal from flue gases.</p

Assessing the Depositional Environment of Cretaceous Ge-Rich Coals in the Wulantuga Mine, Shengli Coalfield, Northeastern China

To provide a new perspective on the formation of the Ge-rich coals, the depositional environment of the Wulantuga coals was studied with the incorporation of coal maceral and geochemistry-based indicators. The results show that the No.6 coal seam in the Wulantuga mine was formed in a mire with a succession of swamps, fens, and marsh. The average contents of Ge in coals formed in different mires, from high to low, are swamp (220 μg/g), marsh (205 μg/g), and fen (185 μg/g). The accumulation of the No.6 seam has been divided into four stages from bottom to top based on the identified coal facies types. The reducing condition and gelification of the ecosystem environment ranged from strong to weak, to strong, and back to weak. The variation of Ge concentrations also occurs in the same way. Strong reduction and gelification of the ecosystem environments can favor Ge enrichments in the Wulantuga coals. Sufficient sources and favorable conditions are essential for the unusual Ge enrichments in coals. This study provides a new perspective for the depositional environment of Ge-rich coals and is useful for the exploration of Ge-rich coal resources

Silica-Silver Nanocomposites as Regenerable Sorbents for Hg⁰ Removal from Flue Gases

Silica-silver nanocomposites (Ag-SBA-15) are a novel class of multifunctional materials with potential applications as sorbents, catalysts, sensors, and disinfectants. In this work, an innovative yet simple and robust method of depositing silver nanoparticles on a mesoporous silica (SBA-15) was developed. The synthesized Ag-SBA-15 was found to achieve a complete capture of Hg⁰ at temperatures up to 200 °C. Silver nanoparticles on the SBA-15 were shown to be the critical active sites for the capture of Hg⁰ by the Ag–Hg⁰ amalgamation mechanism. An Hg⁰ capture capacity as high as 13.2 mg·g^–1 was achieved by Ag(10)-SBA-15, which is much higher than that achievable by existing Ag-based sorbents and comparable with that achieved by commercial activated carbon. Even after exposure to more complex simulated flue gas flow for 1 h, the Ag(10)-SBA-15 could still achieve an Hg⁰ removal efficiency as high as 91.6% with a Hg⁰ capture capacity of 457.3 μg·g^–1. More importantly, the spent sorbent could be effectively regenerated and reused without noticeable performance degradation over five cycles. The excellent Hg⁰ removal efficiency combined with a simple synthesis procedure, strong tolerance to complex flue gas environment, great thermal stability, and outstanding regeneration capability make the Ag-SBA-15 a promising sorbent for practical applications to Hg⁰ capture from coal-fired flue gases