High-pressure Thermogravimetric Analyzer Research Articles

Effect of pressure on thermo-oxidative reactions of saturates, aromatics, and resins (S-Ar-R) from extra-heavy crude oil

This work investigates the thermo-oxidative behaviour of saturates, aromatics, and resins, at different pressures of 0.084, 3.0, and 6.0 MPa. Saturates (S), aromatics (Ar), and resins (R) were characterized by elemental analysis, vapor pressure osmometry, 1H- and 13C-nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The atmospheric evaporation of S, Ar, and R was evaluated by simulated distillation, whereas high-pressure distillation curves were created by calculation using the Clapeyron equation with the Redlich Kwong equation of state. The mass change and rate of mass change profiles were assessed in a high-pressure thermogravimetric analyzer (HP-TGA) by injecting nitrogen and air to obtain the pyrolysis and oxidation responses. Kinetic analysis was performed using a first-order kinetic model discretizing thermal oxidation profiles in four different regions, namely, oxygen chemisorption (OC), decomposition of chemisorbed oxygen-based compounds (DCO), first combustion (FC), and second combustion (SC). As main results, it was obtained that the saturates were just described by FC and SC regions at all pressures, while aromatics and resins by the four stages (OC, DCO, FC, and SC) for pressures higher than 3.0 MPa. At 6.0 MPa, aromatics exhibit a rapid consumption in the FC region, while resins present a more controlled consumption, distributed in the three decomposition regions. This implies that as pressure increases, aromatics have a greater influence on oxidation reactions at high temperatures. From pyrolysis curves, it was noted that the amount of coke generated follows the increasing order saturates < aromatics < resins for all pressures used. The kinetic parameters corroborated the results obtained. For the higher chemisorption systems, the effective activation energy values ​​were higher, and therefore the DCO values. At the same time, the pre-exponential factor showed opposite results given slower reaction kinetics in these stages.

Determination of the Intrinsic Gasification Kinetics of a Bituminous Coal Including Product Gas Inhibition and Char Deactivation Under Entrained Flow Conditions

Abstract This work provides experimentally obtained data concerning the gasification of bituminous coal under entrained-flow conditions. The main focus lies on the determination of reaction kinetics with and without product gas inhibition as well as on thermal deactivation behavior. For this reason, experiments were carried out in a pressurized high-temperature entrained-flow reactor. The reactor is designed for temperatures of up to 1800 °C and pressures of up to 50 bar. In this study, char samples with different residence times at temperatures between 1200 °C and 1600 °C and a pressure of 10 bar were obtained. Pyrolysis experiments were performed in pure nitrogen, while an O/C ratio of one was selected for the gasification. In addition to ultimate, proximate, and structural analyses of the char samples, e.g., to calculate conversion according to the ash tracer method, intrinsic reaction kinetics of the pyrolysis chars with carbon dioxide and steam were determined in a high-pressure thermogravimetric analyzer. The influence of carbon monoxide inhibition on carbon dioxide gasification and of hydrogen on steam gasification was quantified using the Langmuir–Hinshelwood equation. Further, the deactivation behavior of the pyrolysis chars was analyzed by measuring their reactivities under constant reaction conditions and plotting them as a function of residence time. The presented results give an overview about factors like temperature, pressure, gas composition, and residence time affecting fuel conversion. Furthermore, constants describing the reaction behavior of the fuel were determined, which can be used for future simulation of gasification processes.

Intrinsic gasification kinetics of coal chars generated in a high-pressure, high-temperature flow reactor

An understanding of the intrinsic gasification rates of chars generated at high temperatures and elevated pressures is crucial for the design and optimization of gasifiers. Therefore, a widely used Pittsburgh No. 8 coal was partially gasified in a CO2/N2 atmosphere at 1300 °C at a range of pressures (3.4, 6.2, 11.3, 15.5, and 21.7 bar) in a high-pressure, high-temperature flow reactor to generate char. The intrinsic reaction rate of those chars with CO2 was obtained using a high-pressure thermogravimetric analyzer. The kinetic parameters were obtained using an nth-order model. The results show that the intrinsic reaction rate was less affected by the char generation pressure, while the apparent reaction rate was primarily dependent on the surface area evolution during the gasification process. The apparent reactivity reached a maximum for the char generated at 6.2 bar and decreased with further increases in pressure. Among the kinetic parameters, the activation energies were not affected over the range of char generation pressures (3.4–21.7 bar), while the pre-exponential factors were within similar orders of magnitude. The order of reaction was determined by varying the CO2 partial pressure. The order of reaction decreased with increasing char generation pressure and closely followed the surface area at that conversion in most cases.

Porous Structure Properties of Andropogon gerardi Derived Carbon Materials.

Various carbonaceous materials are valuable resources for thermochemical conversion processes and for production of materials of proven sorption properties, useful in environmental applications for gaseous and liquid media treatment. In both cases, the parameters of the porous structure of carbon materials are decisive in terms of their physical and mechanical properties, having direct effects on heat and mass transport as well as on sorption capacity and selectivity. The physical activation of carbon materials produced from various precursors is widely discussed in literature. In this respect, the effects of temperature and partial oxidation of carbonaceous materials with steam or carbon dioxide are mostly considered. The reports on the effects of pressure on the development of porous structures of carbon materials are, however, extremely limited, especially when biomass as a precursor is concerned. In this paper, the results of an experimental study on the effects of pressure in the range of 1–4 MPa on the specific surface area, the total pore volume, average pore diameter, and microporosity of carbon materials prepared with the use of Andropogon gerardi biomass as a precursor are presented. The tested samples were prepared at the temperature of 1000 °C under an inert gas atmosphere in the high-pressure thermogravimetric analyzer. The most developed porous structure was reported for carbon materials produced under 3 MPa. The highest volume of narrow micropores was characteristic for materials carbonized under 2 MPa.

Experimental study on kinetics of coal char\u2013CO2 reaction by means of pressurized thermogravimetric analysis

Comprehensive kinetic studies were performed to establish the validity of many kinetic expressions that describe the behavior of char samples during pressurized gasification toward CO2. The gasification experiments were carried out isothermally in a high-pressure thermogravimetric analyzer (TG-HPs, TA Instruments, USA). Two char samples derived from Turów lignite B and Janina sub-bituminous C were used for the studies. The models that were employed are regarded as the most popular: the volumetric (VM); the modified volumetric (MVM); the grain (GM); the random pore (RPM); and the Langmuir–Hinshelwood model. The models were validated at 850, 950, and 1050 °C, and at CO2 pressures of 0.4, 1, 11, and 21 bar. The effects of temperature and pressure were significant and increased the reaction rate. The calculated values of activation energy were similar for the various models employed and ranged from 169 to 212 kJ mol−1 for the Turów sample and 182 to 238 kJ mol−1 for the Janina coal char sample. The GM, RPM, and MVM fit the experimental data well, in contrast to the VM and LH models.

CO2 gasification process performance for energetic valorization of microalgae

In this study, CO2 gasification process of a marine biomass (Nannochloropsis gaditana microalgae char) has been evaluated. The experiments have been carried out according to a central composite design (CCD), by using a high-pressure thermogravimetric analyzer (HP-TGA). The effect of temperature, total pressure and gasifying agent volume concentration on the CO2 gasification process was studied. Within the CCD studied range, the process performance, expressed as reactivity and gasification rate at 50% conversion, was positively influenced by the increase of temperature and pressure, while CO2 concentration effect was negligible. Empirical models describing the gasification performance as a function of temperature and pressure are presented and discussed. The proposed models allow a more realistic approach of the microalgae gasification process, in comparison with other models where the catalytic effect is often neglected. This study reveals useful process aspects for the development and implementation of microalgae CO2 gasification at industrial scale.

Novel method for investigation of a K–Mg-based CO2 sorbent for sorption-enhanced water–gas shift reaction

CO2 sorption reactions at 20 bar and two different temperatures (i.e., 180 and 220 °C) using a K–Mg-based CO2 sorbent were carried out in a custom-designed high-pressure thermogravimetric analyzer (pressurized bubbling fluidized bed reactor on a scale) coupled with a gas chromatograph. The experimental apparatus, including the thermogravimetric analyzer, was custom-designed to measure weight changes caused by either CO2 sorption or water sorption or both. Analysis of the CO2 sorption reaction revealed that water sorption takes place rapidly with a moderate CO2 sorption rate at the early stage of the reaction. Then, the reaction migrates to CO2 sorption with simultaneous water desorption. Therefore, the mechanism of the CO2 sorption reaction is assumed to consist of fast hydration of K2CO3 and MgO, formation and decomposition of KHCO3, and finally carbonation of Mg(OH)2 resulting in MgCO3 as the main product. K2CO3 is assumed to provide an efficient pathway for CO2 and water to travel into the core region of the sorbent via a reversible reaction between K2CO3 and KHCO3.

High-pressure thermogravimetric adsorption of CO2 for BET surface area calculations

This work presents the implementation of a methodology for the characterization of surface area of porous materials using adsorption data of CO2 at high pressure. The adsorption data were obtained in a high-pressure thermogravimetric analyzer at 298 K and 1.0 MPa. The adsorption methodology is based on a modification of the classic gravimetric adsorption method where the total pressure is maintained constant while changing the adsorbate partial pressure. The test sample was a synthetic carbonaceous material known as Unicarb®. The BET surface area was accurate and reproducible with an experimental error of 3 %. The methodology was also successful reproducing the surface area of commercial materials of different porous structure: molecular sieve 13×, silica–alumina and a sucrose char.

The isothermal studies of char-CO2 gasification using the high-pressure thermo-gravimetric method

The char-CO2 gasification reactions in isothermal and pressurized conditions were studied kinetically by high-pressure thermo-gravimetric analyzer, and the primary objective of this paper was to study the effects of pressure, temperature and char rank on the intrinsic reaction kinetics of the char-CO2 gasification by the Langmuir–Hinshelwood model. The results indicated that the order of reactivity sequence at the same temperature and pressure was Char A > Char B > Char C (Char A from subbituminous coal, and Char B and C from bituminous coals). With the increase in the pressure and temperature, both the intrinsic reaction rate at the same carbon conversion and the carbon conversion efficiency at the same reaction time increased. The results also showed that the gasification rate experienced an initially slow increase, followed by a rapid increase, and finally a decrease corresponding to the increase in the carbon conversion efficiency. It implied that the Langmuir–Hinshelwood model was incompatible to thorough presentation of the complete conversion of the char-CO2 gasification, but was well agreeable to the intrinsic reaction kinetics of char-CO2 gasification when the carbon conversion efficiency was low at the initial stage of the carbon conversion (0–0.6). Based on this, the intrinsic reaction kinetic models of the selected char samples were built.

Kinetics studies and structure characteristics of coal char under pressurized CO2 gasification conditions

The combined effects of surface area, pore structure, degrees of graphitization and graphite crystallites on the char gasification kinetics were studied under elevated pressure and temperature conditions using a High-Pressure Thermo-Gravimetric Analyzer (HP-TGA) and characterization methods, such as BET, XRD, Raman spectroscopy, FTIR and SEM. The BET and SEM results indicated that the porous structures of the chars developed quickly until the carbon conversion reached 0.9, and then rapidly collapsed to the end of the whole carbon conversion. The changes in char structures were in good agreement with the gasification rate. XRD, Raman and FTIR analysis provided evidence demonstrating an increased ratio of graphite to amorphous carbon in bone-structure of chars, which was attributed to the consumption of the amorphous carbon and the retention of the graphite carbon during the gasification process. The collected data implied that the contributions of surface area and pore volume of the char on its kinetics were much greater than its graphite crystallites during the char CO2 gasification.

Soot oxidation kinetics under pressurized conditions

The oxidation kinetics, under different pressures, of soot samples obtained from different liquid fuels and two standards (a commercial black carbon sample and a reference diesel soot) was studied. Soot samples were generated in a flat-flame, premixed burner under heavily-sooting conditions and captured on a water-cooled stabilization plate located above the burner surface. The collected soot was oxidized using a high-pressure thermogravimetric analyzer (HTGA). TGA operation was optimized to reduce mass transfer effects by adjusting the oxidizer flow rate and initial sample mass. Further corrections for mass transfer were accomplished by computing the effectiveness factors for intraparticle, interparticle, and external mass transfer. Two pressures were evaluated (1 and 10atm) and O2 concentration was varied between 10 and 21%.There was not a significant difference in the activation energies of the soot samples for either pure components or as a mixture, with exception of soot from oxygen-containing fuels, and activation energies for both standards were within the range reported by others.Pressure did not change the activation energies when mass transfer corrections were applied.Soot nanostructure for the soot collected from the flat flame “nascent”, and partially oxidized at 1, 10 and 40atm was studied by High-Resolution Transmission Electron Microscopy (HRTEM). The lattice fringe length and fringe tortuosity were estimated to correlate the nanostructure and the soot reactivity, and the nascent soot nanostructure was similar across the five fuels. n-butanol/n-dodecane soot showed a significant change in nanostructure with increasing pressure; however, there was no apparent change in the nanostructure (length or tortuosity) for the other fuels. Corroborating the HRTEM data, surface carbon oxidation studies by X-ray photoelectron spectroscopy (XPS) revealed that the sp2/sp3 content for the oxygenated fuel blend was six times lower than the other fuels leading to lower activation energy and external surface lamellae break-up.

Potassium catalyzed CO2 gasification of petroleum coke at elevated pressures

The rate of gasification can be increased by the addition of an alkali metal catalyst such as potassium. The effectiveness of potassium, however, depends on the characteristics of the feed material and the operating conditions. In this study, the effect of total pressure and partial CO2 pressure on the gasification rate of K-impregnated petroleum coke was studied. Both raw petroleum coke and the produced char were impregnated with potassium carbonate at different loadings (0.03, 0.06, 0.10, 0.16K/C molar ratio). The CO2 gasification experiments were performed in a high-pressure thermogravimetric analyzer at different temperatures (998 to 1098K) and pressures (0.1 to 2.1MPa), while the samples were characterized with Fourier transform infrared spectroscopy and inductively coupled plasma analysis. The rate increased with increasing pressure because of decreased catalyst volatilization and increased catalyst distribution. The determined activation energies at 0.1MPa were 254±21kJ/mol and 133±17kJ/mol, for K-impregnated char and petroleum coke, respectively. The impregnation of potassium was more effective on raw petroleum coke because petroleum coke had more surface functional groups and a less ordered crystal structure than char.

Effect of temperature and pressure on the mineralogical and fusion characteristics of Jincheng coal ash in simulated combustion and gasification environments

The effects of the pressure and temperature on the fusibility of coal ash during combustion and gasification were investigated. Experimentation was conducted using a high pressure thermogravimetric analyzer (HPTGA) apparatus. In order to observe the conversion of minerals with changing temperature and pressure in different atmospheres, the resulting ash samples were analyzed using an X-ray diffractometry (XRD) analyzer. In addition, the quantitative XRD analyses of ash samples and a field emission scanning electron microscope (FSEM), together with X-ray energy dispersive spectroscopy (EDS) were employed to verify the detailed mechanisms of ash fusion. The results indicated that temperature and type of atmosphere had a dominant effect on the ash fusion characteristics while the effect of pressure was somewhat more complicated, depending on the temperature and atmosphere being experienced by the ash. The high-temperature minerals such as mullite were formed with increasing temperature under both combustion and gasification atmospheres. However, in gasification atmosphere, there were more fluxing minerals and feldspar minerals present, such as muscovite, anhydrite and K-feldspar, decreasing the fusion temperature. The effect of pressure on the ash fusibility showed different behavior at different temperatures. At 900°C, the decompositions of low-temperature minerals, such as muscovite, anhydrite and oldhamite, were suppressed with increasing pressure, resulting in a decrease in the fusion temperatures. On the other hand, at 1000°C, the low-temperature minerals transformed into high-temperature minerals such as mullite and sanidine with rising pressure. However, the presence of fluxing minerals and the melting of iron-containing minerals resulted in the lowering of the fusion temperatures.

Preparation of platinum impregnated activated carbon via vacuum treatment and effect on hydrogen storage rate

Hydrogen uptake was effectively enhanced by platinum impregnated activated carbon (Pt/AC) prepared in an improved vacuum treatment process. Under high vacuum condition, the precursor of Pt could be infused into deep pores of AC. The fine Pt nanoparticles (<2nm) were well dispersed in mesopores and micropores of AC after heating reduction. The characterization results indicate the modified vacuum treatment in this research effectively decreased the size and improved the dispersion of Pt catalysts. The impregnating condition of Pt nanocrystals obviously influenced specific surface area and pore structure, and also evidently resulted in dissimilar hydrogen adsorption behavior. Depending on the measurement of high pressure thermo-gravimetric analyzer under hydrogen atmosphere, the hydrogen adsorption rate could be accurately analyzed. Notably, the exceptional result was found in this investigation. Even with much lower surface area and pore volume, tiny Pt nanoparticles uniformly distributed in pores effectively assisted in hydrogen diffusing in deeper sites of AC via spillover phenomenon, and then substantially enhanced twice higher hydrogen uptake rate as comparing to the original process without vacuum treatment. It means the size and distribution of Pt catalysts in the pores of AC should be important key factors for hydrogen spillover behavior.

Hydrogen storage measurement, synthesis and characterization of metal–organic frameworks via bridged spillover

The present study established a time-saving technique for hydrogen uptake measurements using a high-pressure thermo-gravimetric analyzer (HPTGA). The critical buoyancy effects were considered in the analysis model. The HPTGA technique developed here for metal–organic frameworks (MOFs) was validated through independent experiments. The room temperature (RT) hydrogen uptake of MOFs via spillover was significantly enhanced by use of a bridge-building treatment. MOF samples with different structural parameters and RT hydrogen uptake performance can be prepared and manipulated through various factors affecting their synthesis. The structural evolution of MOFs within various steps during the synthesis and bridge-building processes were investigated by electron microscopy, nitrogen sorption isotherm analysis, and powder X-ray diffraction.

Adsorption Properties of Activated Carbon Fibers Characterized by Electric Decomposition

Pitch based activated carbon fibers(ACFs) were characterized by electric decomposition method in the various kinds of acid electrolyte. The felt-type commercialized ACFs were used as raw material and the acids such as HCl, H2SO4, HNO3 and HF were used as electrolytes for electric decomposition. ACFs were treated with 0.7 ~ 2.0A/g-ACF of DC as an anode material for few hours in the acid electrolyte bath and voltage was varied 10~50V according to the condition of current and electrolyte. The pore properties of surface characterized ACFs were measured by adsorption analyzer and changes of surface morphology were also observed by scanning electron microscope and transmitting electron microscope. In order to estimate possibility of use as hydrogen storage material, hydrogen adsorption amount was measured with high pressure thermogravimetric analyzer. In the result the pore size distribution of surface characterized ACFs were changed with respect to electric decomposition condition, especially species and concentration of electrolytes and hydrogen adsorption amount also changed according to pore properties of ACFs.

Effects of pressure in coal pyrolysis observed by high pressure TGA

High-pressure thermogravimetric analyzer was employed to investigate the effects of pressure on the thermal decomposition process, which is the very first step in most coal utilizing processes, and pyrolyzates from TGA were analyzed by on-line GC/MS. Results showed that pyrolysis of coal with steam under high-pressure conditions exhibited a slower reaction rate compared to the lower pressure conditions, and the effect is more evident at the high temperature region. Coal rank also exhibited a distinct effect on the pyrolysis rate such that a subbituminous coal showed a bigger effect by steam-addition and pressure than bituminous coals. Weathered coal sample illustrated a slower reaction rate compared to the unoxidized coal. In addition, the implication of pressure effects on pyrolysis has been described.

Combustion of Spanish coals under simulated pressurized-fluidized-bed-combustion conditions

Coal reactivity is an important parameter related to efficiency of boilers, and learning how to predict it can reduce costs when screening for new fuels. We have measured the reactivity of Spanish coals in a high pressure thermogravimetric analyzer, under operational conditions similar to those found in Pressurized-Fluidized-Bed-Combustion (PFBC). The results obtained from non-isothermal tests were used to look for correlations between the reactivity and the physical and chemical properties of the coals. Reactivity increased with increasing rank, but no relationship was found with the initial pore or surface characteristics of either the coals or the chars. We found a correlation between the true density of the chars and their reactivity. We also observed a decrease in the reactivity, calculated from isothermal tests, as the pressure was increased, while there was a slight increase in reactivity with increasing temperature.