Thermogravimetric Analysis Unit Research Articles

Impact of particle size and catalyst dispersion on gasification rates measured in a thermogravimetric analysis unit: Case study of carbon black catalyzed by potassium or calcium

Gasification is often studied in the laboratory using a thermogravimetric analysis (TGA) unit with less than 1 g of sample in order to obtain intrinsic rates. Many studies, however, neglect to consider the impact of particle size, of both the gasification feed and the catalyst, and catalyst dispersion on the measured rates. The impact of these factors was demonstrated using catalytic gasification of carbon black, an ash-free feed, as a case study, with K2CO3 or CaCO3 as catalysts at 850 °C in a CO2 atmosphere. Hand-mixing and ball-milling were used to alter the initial parameters. Ball-milling reduced both the particle size of both species and increased the catalyst dispersion, resulting in higher interfacial areas and gasification rates than hand-mixing. The changes in gasification kinetics were estimated by modeling the rates using the random pore and extended random pore models (RPM and eRPM, respectively). The impact of the interfacial contact area between carbon and catalysts (varied by particle size and mixing method) was dependent on the activity of the catalyst with the more active (potassium) catalyst being less affected. CaCO3 was found to sinter at 850 °C, reducing available catalytic surface area and blocking CO2 access to the carbon feed. It is recommended to consider these factors in future studies and to always report the particle sizes used.

On the use of an in situ magnetometer to study redox and sintering properties of NiO based oxygen carrier materials for chemical looping steam methane reforming

Two NiO based oxygen carrier materials (OCMs) were synthesized and tested for use as potential materials in chemical looping reforming applications. Redox properties of these materials were evaluated in successive methane reduction – air oxidation (redox) cycles in a thermogravimetric analyzer unit (TGA) and an in situ magnetometer. Zirconia supported (Ni–Zr) OCM exhibited excellent redox activity (high degree of reduction and oxidation) and stability during ten CH4 reduction-air oxidation cycles. The degree of reduction of the alumina supported (Ni–Al) OCM increased gradually during cycling experiments, due to the formation of easily reducible NiO from nickel aluminate species with successive reduction/re-oxidation. The Ni–Al OCM exhibited excellent stability with respect to oxidation resulting in nearly complete oxidation of reduced Ni in all cycles. Results from measurements in the magnetometer were in good agreement with those in the TGA for the Ni–Zr OCM (both with regards to the degree of reduction and oxidation) and the degree of oxidation of the Ni–Al OCM. A moderate crystallite growth with cycling was observed for Ni–Al, whereas a decrease in nickel crystallite size was observed for Ni–Zr.

Interaction of Potassium and Calcium in the Catalytic Gasification of Biosolids and Switchgrass

Catalytic gasification is a method of converting biosolids, the solids created during wastewater treatment, into a valuable gaseous stream. One of the challenges with this process is that the components in the ash of the biosolids can interact with the gasification catalyst(s)—in particular, calcium and potassium. In this study, the behaviors of different combinations of switchgrass (the source of potassium), biosolids, ash-free carbon black, and mixtures of each feed with added calcium and/or potassium were observed with a thermogravimetric analysis unit. The results were consistent with calcium preferentially reacting with components in the ash, preventing the deactivation of potassium. Any additional calcium available may form bimetallic compounds with the potassium, but this interaction did not increase the rate of reaction. Modeling was performed using the random pore model and extended random pore model, with the appropriate model chosen for each mixture. The extended random pore model was better su...

Formation and Evaluation of Protective Layer over Magnesium Melt Under CO2/Air Mixtures

Molten magnesium oxidizes rapidly when exposed to air causing melt loss and handling difficulties. The use of certain additive gases to form a protective MgO layer over a magnesium melt has been proposed. The oxidation behavior of molten magnesium in air that contains various concentrations of CO2 was investigated, including the kinetics of the oxide layer growth. Experiments were performed using a thermogravimetric analysis unit in the temperature range of 943 K to 1043 K (670 °C to 770 °C). Results showed that a thin, coherent, and protective MgO-C layer was formed under the test conditions. The thicknesses of this layer formed under CO2/air ranged from 500 nm to 12 μm. Rate parameters were calculated and a model for the process was developed. The morphology and composition of the surface films were studied using SEM and EDS.

Formation and Evaluation of Protective Layer Over Magnesium Melt Under SF6/Air Atmospheres

Molten magnesium oxidizes rapidly when exposed to air causing melt loss and handling difficulties. The use of certain additive gases such as SF6, SO2, and CO2 to form a protective MgO layer over a magnesium melt has been proposed. The oxidation behavior of molten magnesium in air containing various concentrations of SF6 was investigated. Measurements of the kinetics of the oxide layer growth at various SF6 concentrations in air and temperatures were made. Experiments were performed using a thermogravimetric analysis unit in the temperature range of 943 K to 1043 K (670 °C to 770 °C). Results showed that a thin, coherent, and protective MgF2 layer was formed under SF6/Air mixtures, with a thickness ranging from 300 nm to 3 μm depending on SF6 concentration, temperature, and exposure time. Rate parameters were calculated and a model for the process was developed. The morphology and composition of the surface films were studied using scanning electron microscope and energy-dispersive spectroscope.

Surface modification of a low cost bentonite for post-combustion CO2 capture

A low cost bentonite was modified with PEI (polyethylenimine) through a physical impregnation method. Bentonite in its natural state and after amine modification were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, N2 adsorption–desorption isotherms, and investigated for CO2 capture using a thermogravimetric analysis unit connected to a flow panel. The effect of adsorption temperature, PEI loading and CO2 partial pressure on the CO2 capture performance of the PEI-modified bentonite was examined. A cyclic CO2 adsorption–desorption test was also carried out to assess the stability of PEI-modified bentonite as a CO2 adsorbent. Bentonite in its natural state showed negligible CO2 uptake. After amine modification, the CO2 uptake increased significantly due to CO2 capture by amine species introduced via chemisorption. The PEI-modified bentonites showed high CO2 capture selectivity over N2, and exhibited excellent stability in cyclic CO2 adsorption–desorption runs.

Effect of Pyrolysis and CO2 Gasification Pressure on the Surface Area and Pore Size Distribution of Petroleum Coke

During pyrolysis and gasification, the pore structure of the feed material will change, and these changes affect the reaction rates. In this study, the surface area and reactivity of petroleum coke char prepared at different pyrolysis pressures were studied. In addition, the surface area and pore size distribution of petroleum coke have been monitored during gasification at various pressures. The change in these properties has been related to reactivity to determine how the physical structure of the petroleum coke influences the gasification rate. The samples were characterized using nitrogen and carbon dioxide physisorption and X-ray diffraction, while the reactivity was measured in a thermogravimetric analysis unit at 1173 K and total pressures of CO2 between 0.1 and 2.1 MPa. The surface area of char, prepared at higher pressures, is slightly higher than that prepared at 0.1 MPa. The corresponding increase in reactivity with an increasing surface area suggested that the different reactivities of chars prepared at different pressures were a result of the effect of the pressure on the surface area. In contrast to the minor effect of the pyrolysis pressure on the char surface area, an increase in pressure during gasification significantly increased pore development and, hence, surface area. Normalization of the reaction rate by the surface area indicated that the effect of the pressure on the physical characteristics of the petcoke was the main but not sole factor in the change of the reaction rate with the gasification pressure.

Kinetic Analysis of CO2 Gasification of Petroleum Coke at High Pressures

Determining the intrinsic gasification rates at high pressures is essential for designing and modeling high-pressure technologies. In this study, the intrinsic kinetics of CO2 gasification of petroleum coke was investigated. The kinetic experiments were performed in a high-pressure thermogravimetric analysis unit at different temperatures (1173–1248 K) and pressures (0.1–2.4 MPa). Grain, volume, and random-pore models were applied to the experimental results to determine the kinetic parameters. The random-pore model provided the best fit to the data and was used to determine the kinetic parameters such that the activation energies and reaction orders could be determined. The reaction rates were described by a power law model that was half-order (0.49 ± 0.02) in CO2 pressure. Similar activation energies, 260 ± 24 and 254 ± 12 kJ/mol, were determined for pressures of 0.1 and 1.4 MPa, respectively, indicating similar reaction mechanisms for these pressures.

Coke removal from deactivated Co–Ni steam reforming catalyst using different gasifying agents: An analysis of the gas–solid reaction kinetics

Abstract The reactivity of various gases, namely; O 2 , air, CO 2 , H 2 and N 2 , with carbon deposited on alumina-supported Co–Ni catalyst during propane reforming in a fluidized bed reactor at 773–973 K using relatively low feed steam:carbon ratio (0.8–1.5) has been investigated in a thermogravimetric analysis unit. Analysis of the transient solid weight loss revealed that carbon removal mechanism is dependent on the type of gasifying agent. Carbon gasification kinetics using O 2 and air followed the Avrami-Erofeev (A2) model while data for both CO 2 and H 2 were captured by the geometrical (contracting area, R2) model. However, carbon gasification with inert N 2 proceeded at much slower rate (about 10 times lower than air) and was adequately fitted by the one-dimensional diffusion (D1) model. Specific reaction rates from these phenomenological models were also linearly correlated with the catalyst carbon content with reactivity coefficient of the gasifying agent decreasing in the order, O 2 > air > CO 2 > H 2 > N 2 . In order to minimize energy consumption during catalyst regeneration, reduce greenhouse gas emissions and reduce catalyst sintering, it would be desirable to employ a mixture of air and CO 2 as the carbon gasifying agent to take advantage of the coupled exothermic (air oxidation) and endothermic (reverse Boudouard reaction involving CO 2 and carbon) nature taking place during the carbon removal operation.

The oxidation of molybdenum sulphide concentrate with water vapour Part 2 – Macrokinetics and mechanism

The oxidation of molybdenum sulphide concentrate by water vapour at high temperatures has been investigated experimentally. The progress of the reaction was followed by a thermogravimetric analysis unit and the exit gas was analysed to determine its composition. The conditions under which the water vapour oxidation process takes place without forming volatile molybdenum oxides have been determined.

Thermal Stability of Direct Dental Esthetic Restorative Materials at Elevated Temperatures

With increasing use of direct esthetic restorative materials, the identity of a body may rely upon knowledge of temperature effects on this class of dental restorations. This research examined the effect of atmospheric gas on thermal decomposition and color change of a wide variety of direct esthetic restorative materials. Cured discs (4 x 1 and 8 x 1 mm) were made using manufacturer's directions: traditional glass ionomer (Fuji II), light-curable resonomer (Fuji II LC), compomer (Geristore), and three types of resin composites--highly filled, urethane-based (Occlusin), and two Bis-GMA/TEGDMA resins: hybrid (Herculite XRV) and microfill (Silux Plus). Three replications of each material were heated at 5 degrees C/min in a thermogravimetric analysis unit using either room air or nitrogen purge to simulate different thermal environments. First derivative values of percent weight loss with respect to temperature were obtained to determine temperatures associated with increased decomposition rates. Room-air heating showed greater numbers of decomposition events than did nitrogen-heated discs. The only material decomposing less than 200 degrees C in either atmosphere was traditional glass ionomer. The majority of decomposition occurred between 200 degrees and 500 degrees C for all materials. Only products containing glass ionomer components decomposed between 600 degrees and 800 degrees C. Room-air heating resulted in ash white discs at 800 degrees C and higher. Specimens heated in nitrogen were gray to black at 600 degrees C and higher. Heating atmosphere greatly affected color, and some products demonstrated distinguishing color changes: glass ionomers, in particular, showed characteristic color features. An atlas was constructed from color change of specimens recovered after 200 degrees, 400 degrees, 600 degrees, 800 degrees, and 1000 degrees C compared with non-heated controls.

Selectivity and Yield of Components of a Composite Cracking Catalyst: Effect of Interactions between Composite Components

Coking, activity, and product distribution of a composite catalyst and its components, an REY zeolite and a silica-alumina matrix, are studied in the cracking of n-hexadecane at 500°C in a pulse microreactor equipped with a thermogravimetric analysis unit (TGA), an integral sample collector, and a GC. The matrix component alone does not show significant activity beyond thermal cracking. The zeolite component has high activity and high coking rate. The composite catalyst shows much higher conversion, much higher yield to C 5-C 10, and much lower coking rate than the values predicted from its components. The activity and the product distribution are affected by coke deposition, and this effect depends on coke level of the catalysts. Product yields for the three catalysts as functions of coke levels allow us to determine yield enhancement factors and selectivity enhancement factors (referring to the zeolite component in the composite catalyst relative to the pure zeolite catalyst at the same zeolite coke level) for four product groups. Examination of the selectivity enhancement factors indicates how the heaviest products (C 17+) from the matrix component of the composite catalyst convert to kerosene, gasoline, and lightest (C 4−) product groups over the zeolite component of the composite catalyst, and how these interconversions change with the coke level on the zeolite.

Activity, selectivity, and deactivation of high-sodium HY zeolite

The effect of deactivation on the activity and selectivity of (very high) Na + content HY zeolite catalysts was studied in a pulse microreactor equipped with a thermogravimetric analysis unit (TGA). Cumene was used as the reactant. The Na + level studied was from 3.2 to 11.8% of Na 2O. As the Na + content decreases, the acidity of the zeolite increases and deactivation decreases. The effect of coke level on selectivity to benzene, toluene, ethylbenzene, dimethylbenzene, ethyltoluene, cymene, and diisopropylbenzene depends on the Na + content. For example, the selectivity to benzene, the major aromatic formed by the fresh catalyst, decreases with increasing coke level and Na + level, while the selectivity to ethyltoluene increases under the same conditions. A maximum in selectivity with coke level is obtained for most other products. At intermediate Na + levels (around 7% Na 2O), ethylbenzene shows a maximum in selectivity while cymene passes through a minimum. The maximum coke deposition and the coke level for the maximum incremental coke deposition are two important parameters that distinguish conversion and selectivity patterns.