TGA Reactor Research Articles

Effect of pretreatment and activation conditions on pore development of coal-based activated carbon

Abundant pore volume and appropriate pore configuration are two crucial characteristics of high-performance carbonaceous adsorbents and catalysts. In this study, influences of pre-treatments (e.g., breaking, sieving and ash removal by acid) and activation conditions (e.g., activation time) on pore parameters (including BET surface area, pore diameter and pore hierarchy degree) of resultant activated carbon were systematically investigated. In addition, the difference between conventional carbonization-activation (i.e., the two-step preparation method) and one-step activation in pore development of activated carbons was revealed. The sample prepared by a 120-minute one-step activation exhibited a BET surface area high to 1038.1 m2/g and a pore hierarchy at 50.7 %. Based on the kinetics analysis using TGA reactor, reaction between the activator (i.e., CO2) and carbon matrix was found enhanced in one-step activation, contributing to the generation of mesopores. Remarkably, a new indicator, Effective Activation Rate (EAR) was proposed to accurately describe the activation rate in one-step synthesis after decoupling the release of moisture and volatile compounds. The above conclusions provide guidance for flexibly regulating the pore configurations of activated carbons derived from natural precursors.

Pyrolysis reaction mechanism of typical Chinese agriculture and forest waste pellets at high heating rates based on the photo-thermal TGA

To investigate gas generation characteristics and the kinetics mechanism of biomass pyrolysis process at fast heating rates, a concentrated Photo-thermal TGA reactor (Pt-TGA) was set up. The reactor was reliable for the study of thermochemical kinetics because the average difference between the commercial TGA and Pt-TGA curves for the cellulose pyrolysis process was only 2.1%. Four kinds of typical Chinese forest and agriculture wastes were selected to study the pyrolysis process in Pt-TGA. At higher heating rates, the volatiles from pyrolysis eventually formed more non-condensable gases because of inner-particle secondary reactions. In the range of 450–850 °C, with the temperature rising, the production of H2 increased, and the highest H2 yield reached 279 mL/g. Combined with kinetic analysis, with the increase of heating rate, heat and mass transfer had a more prominent effect on the pyrolysis of biomass particles, and the reactions were controlled by three-dimensional diffusion model.

Study of pyrolysis kinetics of coal fines using model free method

The study is focussed on the experimental investigation of fine coal pyrolysis in TGA reactor. The non-isothermal pyrolysis experiment is conducted at three different heating rates (20,30 and 40 °C/min) in Nitrogen ambience. The highest experimental temperature was maintained at 950 °C. The mass loss profile shows that higher heating rate favours the higher conversion as compared to low heating rate but the final conversion on the given time span is lower in the case of higher heating rate. The reaction kinetics is estimated using Iso-conversional method. activation energy varies from the range of 31.41 kJ/mol to 50.42 kJ/mol. Also, the pre-exponential factor value varies in the range of 1.05 × 106 to 1.4 × 107 min−1. The average pre-exponential factor was calculated from the average energy of activation found by model-free method. The value of pre-exponential factor is found to be A0 = 5.52 × 1010 min−1.

High-Solids, Solvent-Free Modification of Engineered Polysaccharides.

The nature-identical engineered polysaccharide α-(1,3) glucan, produced by the enzymatic polymerization of sucrose, was chemically modified by acylation with succinic anhydride. This modification reaction was initially performed at the micro scale in a TGA reactor to access a range of reaction conditions and to study the mechanism of the reaction. Subsequently, the best performing conditions were reproduced at the larger laboratory scale. The reaction products were characterized via coupled TGA/DSC analysis, FT-IR spectroscopy, solution viscosity and pH determination. The acylation path resulted in partially modifying the polysaccharide by altering its behavior in terms of thermal properties and solubility. The acylation in a solvent-free approach was found promising for the development of novel, potentially melt-processable and fully bio-based and biodegradable ester compounds.

Experimental analysis and evaluation on the CO2 adsorption performance of modified CaO-based adsorbents doped with high aluminum cement in different reactors

CaO-based carbon capture system is a very promising technology to reduce carbon emissions. In this work, modified CaO-based adsorbents doped with high aluminum cement were prepared by hydration method. The effect of operating variables on the performance of modified CaO-based adsorbents in different reactors was studied, including different proportions of high aluminum cement, carbonation temperature and time. The results showed the adsorbent doped with 5 wt.% high aluminum cement had best CO2 capture capability in all reactors. After 20 carbonation-calcination cycles, the adsorption efficiency of modified CaO-based adsorbent doped with 5 wt.% high alumina cement was around 50.8% at 700 °C in the bubbling fluidized bed reactor, 34.5% at 700 °C in the fixed bed, 23.2% at 750 °C in the TGA reactor, respectively. It was found that the adsorption efficiency of modified adsorbent had obvious advantages in the bubbling fluidized bed. In addition, the effect of carbonation temperature and CO2 concentration on reaction kinetic for adsorbent was investigated. The results showed that the activation energy of modified CaO-based adsorbent doped with 5 wt.% high alumina cement in the rapid reaction stage and reaction diffusion stage was 40.3 KJ/mol and 120 KJ/mol, respectively. The time required to complete the carbonation reaction was shortened from 25 min to 6 min from fixed bed reactor to small bubbling fluidized bed reactor. This work provides a comprehensive study for the adsorption performance of low-cost CaO-based adsorbents in different reactors.

Biomass chemical-looping gasification coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier

Bio-syngas generation with flexible H2 to CO ratios via biomass chemical-looping gasification (CLG) coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier (OC) was proposed in the present work. The presence of NiFe2O4 OC promotes biomass conversion, especially bio-char conversion at elevated temperature stage. Addition steam and/or CO2 into the carrying gas increased the weight loss rates of biomass. Up to 5.88 wt%/min and 4.97 wt%/min of the maximum weight loss rates were achieved during biomass conversion with NiFe2O4 OC in CO2 and steam flows in a TGA reactor, respectively. With NiFe2O4 as an oxygen carrier, an optimal lattice oxygen/biomass mass ratio is 0.51 giving the highest syngas yield of 0.77 m3/kgbiomass in the absence of steam or CO2 at 850 °C. Steam/biomass mass ratio of 2.25 gave the maximum carbon conversion of 92.53% and syngas yield of 1.38 m3/kgbiomass suggesting that steam addition significantly improves the biomass conversion and the syngas yield. Introducing a fraction of CO2 into steam could reduce the steam consumption as well as enhance the carbon conversion in biomass gasification step. NiFe2O4 OC serves as an effective catalyst for tars cracking in biomass-CLG. The tars content in the syngas generated in biomass-CLG with NiFe2O4 is 2.83 g/m3, which is much lower than that (14.25 g/m3) in biomass gasification with inert ZrO2. The productivities of H2 and CO are 211 ml/gOC and 101 ml/gOC in water- and CO2-splitting steps. The proposed approach can potentially be applied for providing bio-syngas with flexible H2 to CO ratios from 1:1 to 2.2:1 for purpose of various synthesis processes such as Fischer-Tropsch, acetic acid, and oxo-synthesis.

Emission of volatile organic compounds (VOCs) during coal combustion at different heating rates

The emission of volatile organic compounds (VOCs) during coal combustion at different heating rates in a power plant boiler, a drop tube furnace and a TGA reactor was studied. TD-GC/MS and online FTIR were used to measure VOCs during coal combustion. This study shows that the combustion temperature has a distinct effect on VOC composition. Larger VOC concentrations were detected in the flue gas collected at higher furnace temperatures in a drop tube furnace. Higher furnace temperatures led to a faster heating rate and a shorter residence time for the flue gas in the furnace, resulting in increased VOC generation. In the power plant boiler study, passing the flue gas through the SCR system increased the oxidation of hydrocarbons and reduced VOC emissions by 61%. Moisture effects in the WFGD and WESP systems reduced the VOCs by 10–15%. The ESP might release a small amount of the condensed VOCs on the surface of the fly ash. Overall, the APCD systems in a power plant can reduce VOC emissions. This study used measurements obtained during coal combustion at three different heating rates to generate a complete VOC emission profile. In addition, this study demonstrates the ability of air pollution control devices to reduce VOC emissions.

Isoconversional Methods for Kinetic Modeling of Kerogen Pyrolysis Using TG Data

The pyrolysis kinetics of the Jordanian Lajjun oil shale kerogen was investigated inside a TGA reactor. Kerogen samples (extracted by mineral digestion) were non-isothermally heated at rates varying from 1 to 50°C/min under 350-550C in N2 atmosphere. Friedman, Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) models were employed to estimate the kinetic parameters at isoconversional points ranging from 0.1 to 0.9. The value of the calculated apparent activation energy (E) was found to vary with both the employed model and the conversion (x). Using the three models, the calculated increased with from 10 to 30% (low level), and then decreased with from 30 to 60% (medium level). At high level (60 to 90%), however, increased with increase using both KAS and FWO models, while it continuously dropped with increase using Friedman model. The frequency factor (k0) calculated form each model was found to linearly correlate with E. Compared to KAS and FWO models, Friedman' provided a more accurate fit to the experimental data.

Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical Looping Hydrogen Production

The objective of this paper is to systematically investigate the influences of different preparation methods on the properties of NiFe2O4 nanoparticles as oxygen carrier in chemical looping hydrogen production (CLH). The solid state (SS), coprecipitation (CP), hydrothermal (HT), and sol–gel (SG) methods were used to prepare NiFe2O4 oxygen carriers. Samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, as well as Barrett–Joyner–Halenda (BJH) porosity test. The performance of the prepared materials was first evaluated in a TGA reactor through a CO reduction and subsequent steam oxidation process. Then a complete redox process was conducted in a fixed-bed reactor, where the NiFe2O4 oxygen carrier was first reduced by simulated biomass pyrolysis gas (24% H2 + 24% CO + 12% CO2 + N2 balance), then reacted with steam to produce H2, and finally fully oxidized by a...

Effect of Oxide Devitrification on Oxidation Kinetics of SiC

The effect of oxide crystallinity on the oxidation rate of silicon carbide was investigated. CVD SiC coupons were oxidized in a clean TGA reactor system at 1300°C initially in flowing oxygen, immediately annealed in argon, and then reoxidized, all in situ and without cooling (so as to preserve oxide integrity). The parabolic rate constants determined for the preoxidation regime (of mainly amorphous oxide film) and reoxidation regime (of devitrified oxide) were compared. The oxidation rate decreased by a factor of }30 following full oxide crystallization induced by the anneal.

Useful experimental technique for the study of heterogeneous reactions

The heterogeneous CaO/SO2 reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO2removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO2-partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction period.