The Development of a Novel Cu-Mn Oxygen Carrier for the Chemical Looping Gasification of Biomass

Circulating fluidized bed technology applied to combustion processes in which oxygen and fuel are fed into separate reactors is referred to as Chemical Looping Combustion. Typically, oxygen reacts with a reduced metal (-oxide), then it is transferred to a second vessel where the metal oxide is reduced by a hydrocarbon. In chemical looping gasification, a fuel is contacted indirectly by oxygen and/or steam again with a metal oxide shuttling between two vessels reducing the contact between fuel and air. In this case, a concentrated stream of syngas exits the fuel reactor undiluted by nitrogen. The objective of this study is to develop a solids substrate capable of releasing oxygen in the fuel reactor. A bimetallic Cu-Mn oxygen carrier was synthesized by incipient wetness impregnation at ambient conditions over Al2O3. Copper-based oxygen carriers have superior oxygen transfer capacity and environmental and economical characteristics compared to nickel, iron and cobalt, but the operating temperatures are limited due to the low melting point of the metallic copper. Adding manganese to copper minimizes the formation of copper aluminate. Moreover, it inhibits copper agglomeration and carbon deposition. The developed oxygen carriers were characterized by BET, XRD and SEM analyzers. Also, oxygen transfer capacities of particles were tested using thermo gravimetric analysis (TGA). Results indicate that Cu-Mn is a superior carrier, which is suitable for the separation of oxygen in a chemical looping process. Also, adding manganese to copper allows working at high temperatures and improves the reactivity of copper

FIBRE-OPTIC PROBE FOR THE SIMULTANEOUS MEASUREMENT OF GASEOUS SPECIES COMPOSITION AND SOLIDS VOLUME FRACTION

A novel infrared fibre-optic probe was developed to measure quantitatively and simultaneously solids volume fraction (1-E) and gaseous species composition (Yi) in a gas/solid fluidized bed. The fibre-optic probe was used with a FT-IR spectrometer to perform real-time and in-situ measurements of absorbance in the fluidized bed. The effect of (1-E) and Yi on the absorbance spectra were additive and could be independently calibrated. To calibrate the probe, fuel mole fractions and (1-E) were varied between 1.8 - 10.1 mol% and 0 - 0.45, respectively. A proof of concept for a novel application in fluidized beds was completed: the fibre-optic probe was used to measure the molar fraction of a tracer gas inside the emulsion and bubble phases during gas tracer experiments

FLUIDIZED BED COMBUSTION OF C1-C4 N-ALKANES

The non-premixed combustion of C1 to C4 n-alkanes was investigated inside a bubbling fluidized bed of inert sand particles at intermediate temperatures: 923 K (650oC) ≤ TB ≤ 1123 K (850oC). Lower (T1) and upper (T2) critical transition bed temperatures were measured for ethane, propane and n-butane as 923 K (650oC) and 1073 K (800oC), respectively. The values for methane were significantly higher with T1 = 1023 K (750oC) and T2 \u3e 1123 K (850oC). Alkane conversion was accurately modeled with first-order kinetics and C2 to C4 n-alkanes combustion rates were characterized by a uniform Arrhenius expression: (. The reaction rate of methane was significantly slower with : (

Gas-solid conversion of lignin to carboxylic acids

Lignin is the only source of aromatics from lignocellulosic biomass and is a potential alternative to petroleum as a sustainable source of chemicals . Lignin constitutes 15% to 40% of the dry weight of lignocellulose, but because its a complex heterogeneous molecule. Thermo-chemical processes break lignin down to light gases (CO, H2, CH4) and pyrolysis oils characterized by a wide range of compounds, which requires further processing. The challenge is to activate lignin at lower temperatures to reduce the yield of light gases and to target a narrow class of compounds. Catalysts can improve selectivity towards the target molecules at lower temperature but carbonaceous species coke the active sites within seconds and minutes. Here we describe a two stage reactor in which we oxidize and steam crack lignin in the first stage (at heating rate of 5°Cmin−1 up to 550°C) of lignin and catalytically oxidize the effluent in the second stage. We targeted carboxylic acids that have a higher market than biofuel. With a gas feed composition of 10% oxygen and 50% steam all the lignin reacted. In the second stage, vanadium catalyst cleaved the remaining lignin bonds and opened up aromatic rings to make carboxylic acids — mostly C4 acids. In the presence of vanadium pyrophosphate 24% of the lignin formed a condensable product of which 48% was maleic acid 31% C5-C8 aromatics and fumaric ,malonic and gallic acid. Only ∼ 5% of the lignin formed coke

Citation analysis of scientific categories

Databases catalogue the corpus of research literature into scientific categories and report classes of bibliometric data such as the number of citations to articles, the number of authors, journals, funding agencies, institutes, references, etc. The number of articles and citations in a category are gauges of productivity and scientific impact but a quantitative basis to compare researchers between categories is limited. Here, we compile a list of bibliometric indicators for 236 science categories and citation rates of the 500 most cited articles of each category. The number of citations per paper vary by several orders of magnitude and are highest in multidisciplinary sciences, general internal medicine, and biochemistry and lowest in literature, poetry, and dance. A regression model demonstrates that citation rates to the top articles in each category increase with the square root of the number of articles in a category and decrease proportionately with the age of the references: articles in categories that cite recent research are also cited more frequently. The citation rate correlates positively with the number of funding agencies that finance the research. The category h-index correlates with the average number of cites to the top 500 ranked articles of each category (R² = 0.997). Furthermore, only a few journals publish the top 500 cited articles in each category: four journals publish 60% (σ = ±20%) of these and ten publish 81% (σ = ±15%)

Catalyst preparation for fluidized bed reactors by spray drying

Spray dried fluidized bed catalysts belong to the Geldart Group A classification and vary between 22 m to 200 m in diameter (1). Binder is either distributed throughout the particle with the active phase or surrounds the active phase as in a core-shell structure (2, 3). We slurried WO3/TiO2 micronized powder (0.2 m to 2 m) with colloidal silica (LUDOX® HS-40) to form a slurry with a mass fraction of 5 % to 20 % solids. The solution entered the top of GB-22 Yamato fluidized bed spray dryer chamber (0.12 m ID) through a two-fluid nozzle and the drying air entered the bottom counter-currently. We varied the feed slurry concentration, binder concentration, slurry and drying air flow rates, two-phase nozzle pressure drop and inlet temperature. Most conditions only produced a very fine powder (Group C, dpm) (Fig. 1a). (Ideally, the particle size should exceed 80 m for laboratory experimental equipment). The small particles were often fully spherical but we also produced large clusters that reached 150 m (Fig. 1b). The high pressure drop through the nozzle and low slurry concentration produced the fine powder. Particles agglomerated in the fluidized bed when we increased the slurry flow rate to the chamber such that the powder had not yet dried sufficiently. Please click Additional Files below to see the full abstract

Photo initiated chemical vapour deposition to increase polymer hydrophobicity

Apple growers face new challenges to produce organic apples and now many cover orchards with high-density polyethylene (HDPE) nets to exclude insects, rather than spraying insecticides. However, rainwater- associated wetness favours the development of apple scabs, Venturia inaequalis, whose lesions accumulate on the leaves and fruit causing unsightly spots. Treating the nets with a superhydrophobic coating should reduce the amount of water that passes through the net. Here we treat HDPE and polyethylene terephthalate using photo-initiated chemical vapour deposition (PICVD). We placed polymer samples in a quartz tube and passed a mixture of H2 and CO through it while a UVC lamp (254 nm) illuminated the surface. After the treatment, the contact angle between water droplets and the surface increased by an average of 20°. The contact angle of samples placed 70 cm from the entrance of the tube was higher than those at 45 cm and 20 cm. The PICVD-treated HDPE achieved a contact angle of 124°. Nets spray coated with a solvent-based commercial product achieved 180° but water ingress was, surprisingly, higher than that for nets with a lower contact angle

Experimental methods in chemical engineering: X ‐ray absorption spectroscopy— XAS , XANES , EXAFS

Although X-ray absorption spectroscopy (XAS) was conceived in the early 20th century, it took 60 years after the advent of synchrotrons for researchers to exploit its tremendous potential. Counterintuitively, researchers are now developing bench type polychromatic X-ray sources that are less brilliant to measure catalyst stability and work with toxic substances. XAS measures the absorption spectra of electrons that X-rays eject from the tightly bound core electrons to the continuum. The spectrum from 10 to 150 eV (kinetic energy of the photoelectrons) above the chemical potential—binding energy of core electrons—identifies oxidation state and band occupancy (X-ray absorption near edge structure, XANES), while higher energies in the spectrum relate to local atomic structure like coordination number and distance, Debye-Waller factor, and inner potential correction (extended X-ray absorption fine structure, EXAFS). Combining XAS with complementary spectroscopic techniques like Raman, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) elucidates the nature of the chemical bonds at the catalyst surface to better understand reaction mechanisms and intermediates. Because synchrotrons continue to be the light source of choice for most researchers, the number of articles Web of Science indexes per year has grown from 1000 in 1991 to 1700 in 2020. Material scientists and physical chemists publish an order of magnitude articles more than chemical engineers. Based on a bibliometric analysis, the research comprises five clusters centred around: electronic and optical properties, oxidation and hydrogenation catalysis, complementary analytical techniques like FTIR, nanoparticles and electrocatalysis, and iron, metals, and complexes

Catalytic glycerol hydrogenolysis to 1,3-propanediol in a gas–solid fluidized bed

Glycerol is a potential feedstock to produce 1,3-propanediol (1,3-PDO), which is a valuable commercial polyester monomer. Here, we report the gas-phase glycerol hydrogenolysis to 1,3-propanediol over Pt/WO3/Al2O3 in a fluidized bed operating above 240 degrees C and at ambient pressure. Fluidized beds are ideal contactors for this reaction because the heat transfer rates are sufficiently high to vaporize glycerol thereby minimizing its combustion and thermal degradation. The yield of 1,3-PDO approached 14% after 2 h at 260 degrees C. The major co-products were 1,2-PDO (18%), 1-propanol (28%) and 2-propanol (15%). In the first step, glycerol may dehydrate to acrolein, followed by rehydration to 3-hydroxypropanal and then hydrogenation to 1,3-PDO. The concentrations of the by-products including acrolein, ethylene glycol, propane, and acetone increased with increasing temperature

Shedding light on iron pentacarbonyl photochemistry through a CVD case study

During our studies on surface engineering, we photopolymerize syngas onto silicon surfaces. XPS and TOF-SIMS analyses show that the syngas-derived oligomer covalently bonds to free silanol sites. Iron atoms appear in the coating, despite the fact that no iron was (intentionally) added to the system. GC–MS analysis reveals low concentrations of iron pentacarbonyl (IPC) are generated within the carbon monoxide cylinder. Its presence plays a determinant photocatalytic role in the reaction