Thermogravimetric Apparatus Research Articles

Enhancement of direct sulfation of limestone by Na 2CO 3 addition

For an oxy-fuel circulating fluidized bed combustion system, the limestone calcination is normally prevented due to excessive CO 2 partial pressures and the limestone is subject to a direct sulfation reaction. The enhancement of the direct sulfation of limestone by Na 2CO 3 was investigated under high CO 2 partial pressure in a thermogravimetric apparatus (TGA) and scanning electron microscope (SEM) analysis method. A commercial limestone with a mean size of 18.8 μm was used. Experimental results indicate that the incorporation of Na + ions in solid product CaSO 4 lattice structures results in formation of more extrinsic point defects in the crystal lattices of CaSO 4 and a significantly increased solid-state diffusivity/mobility in the solid product. So the direct sulfation of Na 2CO 3-doped limestone shows higher rate and higher degree of conversion in the later stage of sulfation, in comparison with the direct sulfation of original limestone. The reaction changes from diffusional control to chemical reaction control in the presence of Na 2CO 3 because of the effect of foreign ions on accelerating the solid-state diffusion.

High-Temperature CaO Hydration/Ca(OH)2 Decomposition over a Multitude of Cycles

CaO hydration and Ca(OH)2 decomposition cycles can be used to supply or transport energy (heat). The reaction rates and properties of these materials are important parameters for the design of a reactor. In this work, the rates of CaO hydration and Ca(OH)2 decomposition were measured continuously over 20 hydration/decomposition cycles by means of a high-pressure thermogravimetric apparatus. CaO was completely converted to Ca(OH)2 in all cycles, but the CaO hydration rate decreased with increasing number of cycles. Ca(OH)2 was decomposed to CaO completely in all cycles. The extent and rate of conversion for Ca(OH)2 decomposition were not influenced by increasing cycle number. Eutectic melting of CaO and Ca(OH)2 was not observed on the particles after CaO hydration or after Ca(OH)2 decomposition. The compressive strength of CaO particles decreased with increasing cycle number, and the average compressive strength of CaO particles after 20 cycles was about 16.5 kg/cm2.

Carbonation and Hydration Characteristics of Dry Potassium-Based Sorbents for CO2 Capture

Thermogravimetric apparatus (TGA) and X-ray diffraction (XRD) have been used to study the characteristics of potassium-based sorbents for CO2 capture. The carbonation reactivity of K2CO3·1.5H2O and K2CO3 dehydrated from K2CO3·1.5H2O was weak. However, K2CO3 calcined from KHCO3 showed excellent carbonation capacity and no deactivation of sorbents during multiple cycles. The XRD results showed that the sample dehydrated from K2CO3·1.5H2O was K2CO3 with structure of monoclinic crystal (PC#1). The carbonation products of PC#1 included K2CO3·1.5H2O and KHCO3, and K2CO3·1.5H2O was the main product. Correspondingly, K2CO3 with structure of hexagonal crystal (PC#2) was the product calcined from KHCO3, and the main carbonation product of PC#2 was KHCO3. The byproduct of K4H2(CO3)3·1.5H2O for PC#2 would affect the carbonation processes. Hydration tests confirmed the two hypotheses: the hydration reaction will first occur for K2CO3 with structure of monoclinic crystal, and the carbonation reaction will first occur for K2CO3 with structure of hexagonal crystal. The reaction principles were analyzed by product and the relevant reactions. This investigation can be used as basic data for dry potassium-based sorbents capturing CO2 from flue gas.

Effects of Surface Oxide Film on Massive Hydriding of Zr Alloy

Oxide effects experiments on massive hydriding reactions of Zr alloy with hydrogen gas were carried out at <TEX>$400^{\circ}C$</TEX> under 1 atm in a <TEX>$H_2$</TEX> environment with a thermo-gravimetric apparatus (TGA). Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness. The results also show that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and that the hydriding rates are similar to that of oxide-free Zr alloys once massive hydriding is initiated. Unlikely microstructure of the oxide during incubation time, physical defects such as micro-cracks and pores were observed in the oxide after incubation time. Therefore, it seems that the massive hydriding of Zr alloys can be ascribed to short circuit paths and mechanical or physical defects, such as micro-cracks and pores in the oxide, rather than to hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypo-stoichiometric oxide.

Investigation of the Vaporization of Boric Acid by Transpiration Thermogravimetry and Knudsen Effusion Mass Spectrometry

The vaporization of H3BO3(s) was studied by using a commercial thermogravimetric apparatus and a Knudsen effusion mass spectrometer. The thermogravimetric measurements involved use of argon as the carrier gas for vapor transport and derivation of vapor pressures of H3BO3(g) in the temperature range 315-352 K through many flow dependence and temperature dependence runs. The vapor pressures as well as the enthalpy of sublimation obtained in this study represent the first results from measurements at low temperatures that are in accord with the previously reported near-classical transpiration measurements (by Stackelberg et al. 70 years ago) at higher temperatures (382-413 K with steam as the carrier gas). The KEMS measurements performed for the first time on boric acid showed H3BO3(g) as the principal vapor species with no meaningful information discernible on H2O(g) though. The thermodynamic parameters, both p(H3BO3) and Delta sub H degrees m(H3BO3,g), deduced from KEMS results in the temperature range 295-342 K are in excellent agreement with the transpiration results lending further credibility to the latter. All this information points toward congruent vaporization at the H3BO3 composition in the H2O-B2O3 binary system. The vapor pressures obtained from transpiration (this study and that of Stackelberg et al.) as well as from KEMS measurements are combined to recommend the following: log [p(H3BO3)/Pa]=-(5199+/-74)/(T/K)+(15.65+/-0.23), valid for T=295-413 K; and Delta sub H degrees m=98.3+/-9.5 kJ mol (-1) at T=298 K for H3BO3(s)=H3BO3(g).

Pyrolysis characteristics of organic components of municipal solid waste at high heating rates

The pyrolysis characteristics of six representative organic components of municipal solid waste (MSW) and their mixtures were studied in a specially designed thermogravimetric analysis apparatus with a maximum recorded heating rate of 864.8 degrees Cmin(-1). The pyrolysis behavior of individual components was described by the Avrami-Erofeev equation. The influence of final temperature on individual components was studied, and it was concluded that final temperature was a factor in reaction speed and intensity, but that it played only a limited role in determining the reaction mechanism. The interactions between different components were evaluated, and it was concluded that the interaction between homogeneous materials was minimal, whereas the interaction between polyethylene and biomass was significant.

Effect of magnetic field on property and structure of polyaniline doped with multiple sulfonic acids

Polyaniline(PAn) doped with multiple sulfonic acid system of dodecylbenzenesulfonic acid(DBSA) and sulfosalicylic acid(SSA) was synthesized by emulsion polymerization using ammonium persulfate(APS) as an oxidizing agent in the presence and the absence of a constant magnetic field(MF)of 0.8 T. The structure and properties of the PAn were characterized by X-ray diffractometer(XRD), thermogravimetric apparatus(TGA), FT-IR spectroscope(FT-IR) and four probe digital multimeter. The results indicate that, when the molar ratio of DBSA to SSA is 1/3, that of dopant to An is 3/2, that of APS to An is 4/5 in the synthesizing media, and the doping time is 3 h, the conductivity of the PAn synthesized in the presence of the MF of 0.8 T reaches 5.88 S/cm, which is higher than that of the PAn synthesized in the absence of the MF. The thermal stability, the crystallinity and the doping degree of the PAn synthesized in the presence of the MF are also improved. MF not only enhances the conductivity, but also reduces the doping time, the dosage of the dopant and the oxidizing agent when the conductivity reaches the maximum.

Catalytic combustion of soot. Effects of added alkali metals on CaO–MgO physical mixtures

The effect of adding alkali metals (Li, Na, K) to a CaO–MgO mixture, on the catalytic combustion of carbon black (CB), a model compound for soot, was studied. Catalysts were prepared by the Sol–Gel method and characterized by surface (BET surface area, XPS, DRIFTS) and bulk (AAS, XRD and TPR) techniques. Samples with a 4:1 catalyst-CB ratio were subjected to catalytic oxidation in a thermo-gravimetric apparatus and the temperature T m, at which combustion occurs at its maximum rate, was recorded for comparison of catalytic activity. The addition of alkali metals (Li, Na, K) over the CaO–MgO mixture significantly increased the catalytic activity, due to the formation of surface oxygenated species that enhanced the oxidizing properties of the catalyst surface. That activity for CB combustion increases with the atomic number of the alkali metal contained in the catalyst. The presence of alkali metals also diminished the amount and stability of carbonates formed on the catalyst. The K-containing catalyst showed the largest activity for the catalytic CB combustion, because it shows the largest capacity to enrich its surface with α-oxygen type and promotes best the surface dissociation of that oxygen. Furthermore, surface-adsorbed OH and carbonate groups that disable the active sites and prevent the oxygen adsorption and dissociation, were less abundant and desorbed at lower temperatures, showing to be less stable on this K-containing catalyst.

Styrene–butadiene rubber pyrolysis: Products, kinetics, modelling

The pyrolysis of SBR (styrene–butadiene rubber) was investigated by a dynamic thermogravimetric apparatus, where it is possible to treat samples in form of cylinders with a weight of about 30 g. Various heating rates between 0.1 and 1 °C/s were investigated. A distributed parameter model able to describe heating inside the sample and its kinetics of decomposition was built. The pyrolysis enthalpy seems to be a very important parameter; its best fitting value was identified equal to 200 kJ/kg. Light gases produced by pyrolysis were analyzed and the influence of heating rate and sample size on the pyrolysis products (gases, tar, and char) was studied. This investigation showed that for big samples (some tenths of grams) the influence of heating rate on the pyrolysis products is often less important than for few mg samples, as often reported in the literature. Different pyrolysis conditions lead to strong variation of light gas yield, but the molar fraction of most of the light gases is almost constant.

Steam Catalysis in CaO Carbonation under Low Steam Partial Pressure

CaO was widely used to capture CO2 in direct hydrogen production process, where steam always existed simultaneously. The effect of steam on CaO carbonation performance under low steam partial pressure was investigated using a pressurized thermogravimetric apparatus. The experimental results revealed that steam improved CaO carbonation performance significantly no matter whether Ca(OH)2 was produced or not. At 823 K and 0.5 MPa of steam partial pressure, effect of steam on CaO carbonation performance could not be attributed mainly to production of Ca(OH)2 because the hydration rate of CaO was very slow. The main reason was steam catalysis in CaO carbonation. Enhancement of steam on CaO carbonation performance without Ca(OH)2 production could not be attributed to improvement of steam on the physical property, but to catalytic effect of steam. Effects of CaO precursors, CO2 partial pressure, steam partial pressure, and temperature with steam addition on CaO carbonation performance were also investigated.

Materials Performance of Modified 430 Stainless Steel in Simulated SOFC Stack Environments for Integrated Gasification Fuel Cell System Applications

The corrosion behaviors of a low silicon and aluminum 430 stainless steel with and without ceria surface treatment were investigated in a simulated coal syngas at 800 {degree sign}C and in air. Thermodynamic calculations were made to predict carbon activities for the coal syngas as a function of temperature. At 800 {degree sign}C, carbon activity is ~1.1, which indicates that carbon that forms could diffuse into the steel and induce carbon corrosion, e.g. carburization and metal dusting. The surface morphology was investigated with X-ray diffraction and scanning electron microscopy. In coal gas, the scale formed on bare steel consisted of Mn1.5Cr1.5O4 and Cr2O3 and on ceria treated steel (Fe, Mn)O, FeCr2O4, Cr2O3, and CeCrO3. Both materials underwent carburization, but not metal dusting. The results of oxidation in air using a thermogravimetric apparatus confirmed that the 430 sample was less resistant to oxidation than the 430 treated with ceria.

Activation of Mg–Al hydrotalcite catalysts for transesterification of rape oil

Mg–Al hydrotalcites with different Mg/Al molar ratios were prepared and characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), thermogravimetric apparatus and differential thermal analysis (TGA-DTA) and scanning electron micrograph (SEM). It was confirmed by XRD that the materials had hydrotalcite structure. The hydrotalcite catalyst calcined at 773 K with Mg/Al molar ratio of 3.0 exhibited the highest catalytic activity in the transesterification. In addition, a study for optimizing the transesterification reaction conditions such as molar ratio of the methanol to oil, the reaction temperature, the reaction time, the stirring speed and the amount of catalyst, was performed. The optimized parameters, 6:1 methanol/oil molar ratio with 1.5% catalyst (w/w of oil) reacted under stirring speed 300 rpm at 65 °C for 4 h reaction, gave a maximum ester conversion of 90.5%. Moreover, the solid catalyst could be easily separated and possibly reused.

Formation of multi-walled carbon nanotubes by Ni-catalyzed decomposition of methane at 600–750 °C

Ni-catalyzed decomposition of methane at high temperatures was examined by using a thermogravimetric apparatus. The catalyst (10 wt.% Ni supported on spherical alumina) gave quite a high carbon nanotube (CNT) yield at the temperatures below 680 °C. At > 700 °C, however, carbon formation rate decreased with increasing the reaction temperature. Temperature-programmed reaction also showed the maximum CNT growth rate at ~ 690 °C. This result ruled out the possibility that the apparent negative activation energy is caused by sintering of Ni particles. Detailed examination on the kinetic expression led us to a conclusion that the dissolution of carbon atoms formed by dissociation of methane into bulk of the nickel particles is the rate-determining step at high temperatures, while methane adsorption is the rate-determining step at lower temperatures. This idea also explains the fact that the carbon yield drastically decreased at high temperatures. The CNTs formed at these temperatures had thinner walls than those formed at lower temperatures. The latter fact also supports the idea that the solubility of carbon in the nickel particles decreases at high temperatures.

Mechanisms of Methane Decomposition over Ni Catalysts at High Temperatures

Decomposition of methane over nickel catalyst supported on spherical alumina was investigated using a thermogravimetric apparatus. The reaction products were hydrogen and multi-walled carbon nanotubes. Initial rate of carbon formation increased with reaction temperature up to 680°C. However, the initial rate decreased at higher reaction temperatures, implying that the reaction had an apparent negative activation energy, although thermodynamic considerations suggest that higher temperatures should favor the decomposition of methane. The reaction order with respect to methane was ca. 1.4, irrespective of the reaction temperature, whereas the reaction order with respect to hydrogen changed from −1/2 to zero by increasing the reaction temperature from <700°C to >720°C. The kinetic expression based on the Langmuir-Hinshelwood mechanism suggested that the rate- determining step changed from the adsorption of methane, which is disturbed by surface hydrogen atoms at below 700°C, to the dissolution of carbon species into the bulk of nickel particles at above 720°C. The apparent negative activation energy is interpreted by the decrease of solubility of carbon species into the bulk of nickel particles.

SYNTHESIS OF POLYURETHANE MODIFIED BISMALEIMIDE (UBMI) AND POLYURETHANE-IMIDE ELASTOMER

Urethane modified bismaleimide (UBMI) was synthesized by the reaction of maleic anhydride (MA) with NCO group terminated polyurethane prepolymer (PUP) in presence of acetone. The product was determined by infrared analysis. Then ultrasonic assistant process was introduced into the solvent removal of the prepolymer mixture of UBMI and PUP. Polyurethane-imide (PUI) elastomer was synthesized from the above PUP-UBMI prepolymer mixture by the infusion technology with 2,5-dimethyl-2,5-bis(tert-butylperoxy)-hexane (B25) as liquid initiator at 120°C. The thermal properties and stress-strain behavior of PUI elastomer was characterised by thermogravimetric (TG) analysis and tensile testing apparatus, respectively. Compared with pure polyurethane elastomer, the PUI elastomer composite showed the better thermal stability.

CO 2 decomposition over freshly reduced nano-crystallite Cu 0.5Zn 0.5Fe 2O 4 at 400–600 °C

The decomposition of CO 2 was investigated as a process of both industrial and environmental importance. The decomposition of CO 2 over nano-crystalline oxygen-deficient Cu 0.5Zn 0.5Fe 2O 4 was tested through simultaneously reduction–reoxidation technique. The experiments were carried out isothermally using thermo-gravimetric apparatus. The prepared, completely reduced and reoxidized Cu 0.5Zn 0.5Fe 2O 4 compacts were characterized by XRD, SEM, TEM, carbon content analysis and reflected light microscope. The influence of the experimental conditions on the structural characteristics of the products was extensively studied to get clear comprehension of re-oxidation process. The experimental measurements were used to elucidate the re-oxidation mechanism under isothermal conditions. For the re-oxidation process, it was found that at the initial stages, the reaction is controlled by the interfacial chemical reaction mechanism with some contribution to the gaseous diffusion mechanism. On the other hand, the mechanism of reaction was found to be solid-state diffusion at the final stages. Carbon nanotubes were extensively formed on the surface of the reduced samples as a result of the decomposition of CO 2.

Effect of CaO content on hydration rates of Ca-based sorbents at high temperature

The CaO hydration behavior of four Ca-based sorbents (Deyang, Yangguan, Dawa, and Kuzuu) with different CaO contents was examined. A high-pressure thermogravimetric apparatus was used to measure the hydration rates at high temperatures (773–923 K) and high steam pressures (1.3–2.3 MPa). CaO hydration occurred at high temperatures up to 923 K at high steam pressure. The hydration rates and the final CaO conversion values varied substantially among the different sorbents. Hydration rate and CaO conversion decreased with increasing CaO content. The order of CaO hydration rate with respect to the difference between the reactant steam pressure and the equilibrium steam pressure (PH2O−P⁎H2O) varied with CaO content. The apparent activation energy for rate constant k also varied with CaO content.

Synthesis and gas phase nitridation of nanocrystalline TiO2

Gas phase nitridation of nc-TiO2 was carried out for obtaining nc-TiN. The nc-TiO2 precursor itself was derived from a Ti(OH)x precipitate formed through hydrolysis of titanium nitrate solution by aqueous ammonia reagent. Calcination of titanium hydroxide at 1000 °C yielded nc-TiO2 powder with an average particle size of ∼5 nm. Both nc-Ti(OH)x as well as nc-TiO2 were separately nitrided in an environment of argon and ammonia for synthesizing nc-TiN. A home-built thermogravimetric analysis-mass spectrometer apparatus was used for the nitridation experiment. The nanocrystalline phases of Ti(OH)x, TiO2 and TiN were characterized by XRD, TEM, IR and XPS techniques. The powders' XRD patterns indicated the formation of nanocrystalline TiN by ammonia bases nitridation of nc-TiO2. These studies also revealed sequential crystallo-chemical transformation of the intermediate precursor. FTIR studies revealed the existence of IR active modes in nc-TiO2 and the formation of a chemically pure TiN phase. The TEM image of TiN powder depicted the formation of nanocrystalline phase. Ti(2p3/2) photoelectron spectra indicated complete conversion of nc-TiO2 to nc-TiN.

Studies on the Reaction Engineering of Combustion and Carbonization of Indian Coals, Depolymerized Coals and Residual Coal Obtained After Organo-Refining

Kinetics of the combustion of original and depolymerized Assam, Raniganj and Talcher coals and Neyveli lignite has been studied under non-isothermal conditions in a thermogravimetric analysis apparatus by employing Coats and Redfern kinetic modeling. Depolymerization of coals through acidic phenoation was found to improve the reactivity of the coals for combustion. Similarly, depolymerization reaction also led to the improvement in the pyrolysis behavior of coals. The order and activation energy of the reactions have been reported. The kinetics studies of the residual coal obtained after the successive solvent extraction of coal has also been studied. The present studies on the reaction engineering of coal conversion and utilization technologies may help in the reactor design and in the process development engineering.

Low Temperature Formation of Iron Carbide from Iron Oxide with CO‐H2 Gas Mixtures

Commercially pure iron oxide in the form of fine particles were reacted with CO‐H2 gas mixtures at ambient pressure (≍ 0.8 atm) in the temperature range 573 to 1073K. Reduction to metallic iron was carried out with pure hydrogen. The rate of formation of iron carbide was measured by recording the weight change with a thermogravimetric apparatus. The results obtained indicate that for each gas phase composition a maximum rate was observed, at apparently the same temperature. These maxima in the rate occur at a lower temperature than those reported in previous investigations. A dissociative adsorption model, based on the reduction of CO with hydrogen was developed which qualitatively describes the observed results.