Wei-Ping Pan

Thermal characterization of organically modified montmorillonite

Abstract Polymer/organically modified layered silicate (PLS) nanocomposites are a new class of filled polymers with ultrafine phase dimensions. They offer an outstanding combination of stiffness, strength and weight that is difficult to attain separately from the individual components. Additionally, the nanoscopic phase distribution as well as synergism between polymer and the layered silicate result in additional properties, such as flame retardency, enhanced barrier properties and ablation resistance, which are not observed in either component. These nanocomposites are synthesized by blending the organically modified layered silicate (OLS) into the polymer melt. Thus, understanding the relationship between the molecular structure and the thermal stability (decomposition temperature, rate, and the degradation products) of the organic modification of the layered silicate is critical. During this study, modern thermal analysis techniques combined with infrared spectroscopy and mass spectrometry (TGA–FTIR–MS) were used to obtain information on the thermal stability and degradation products. The effect of chemical variation (alkyl chain length, number of alkyls, and unsaturation) of organic modifiers on the thermal stability of the organically exchanged montmorillonite are discussed. A range of interesting results is observed, however, not all are currently understandable.

Studying the mechanisms of ignition of coal particles by TG-DTA

The mechanisms of ignition of coal of different quality, such as anthracite, bituminous coal and lignite, were studied by thermogravimetry (TG) and differential thermal analysis (DTA). Experiments on coal ignition were carried out at a low heating rate (10 K min−1) with particle sizes ranging from 37 to 4000 μm. It is concluded from this experimental work that 1. (1) ignition measurement by TG-DTA is an excellent method for accurate determination of the ignition temperature of coal particles; 2. (2) with increasing coal quality from lignite through bituminous coal to anthracite, the type of ignition changes from homogeneous ignition through hetero-homogeneous ignition to heterogeneous ignition, and the ignition temperatures also increase; 3. (3) with increasing coal particle size, the type of ignition of Kaipin bituminous coal changes from hetero-homogeneous to homogeneous ignition, and ignition of the char separates from that of the volatile matter and shifts to a higher temperature, whereas both types of ignition of Loy Yang lignite coal and Hongay anthracite coal are not effected by particle size.

Influence of metal ions on volatile products of pyrolysis of wood

Abstract Volatile products from the pyrolysis of wood have been determined by gas-phase Fourier transform infrared spectrometry, coupled to a thermal balance. Progressive yields of water, carbon dioxide, carbon monoxide, acetic and formic acids and methanol have been determined isothermally at 523 K and at 373–823 K. The influence of the removal of inorganic salts and of ion-exchanged cations on these yields has been studied, as also has the effect of adding back potassium ions and calcium ions by ion exchange. Potassium, but not calcium, acts as a catalyst in pyrolytic reactions resulting in formation of carbon dioxide and carbon monoxide (especially from polysaccharides), acetic acid (from hemicelluloses), formic acid (from polysaccharides) and methanol (from lignin).

Polycyclic aromatic hydrocarbon (PAH) emissions from a coal-fired pilot FBC system

Due to the extensive amount of data suggesting the hazards of these compounds, 16 polycyclic aromatic hydrocarbons (PAHs) are on the Environmental Protection Agency (EPA) Priority Pollutant List. Emissions of these PAHs in the flue gas from the combustion of four coals were measured during four 1000h combustion runs using the 0.1MW heat-input (MWth) bench-scale fluidized bed combustor (FBC). An on-line sampling system was designed for the 16 PAHs, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and a Tenax trap. The filters and Tenax were extracted by methylene chloride and hexane, respectively, followed by GC/MS analysis using the selective ion monitoring (SIM) mode. In this project, the effects of operating parameters, limestone addition, chlorine content in the coal, and Ca/S molar ratio on the emissions of PAHs were studied. The results indicated that the emissions of PAHs in an FBC system are primarily dependent on the combustion temperature and excess air ratio. The injection of secondary air with high velocity in the freeboard effectively reduces PAH emissions. The addition of extra limestone can promote the formation of PAHs in the FBC system. Chlorine in the coal can possibly lead to large benzene ring PAH formation during combustion. The total PAH emission increases with an increase in the sulfur content of coal. Incomplete combustion results in PAHs with four or more benzene rings. High efficiency combustion results in PAHs with two or three benzene rings.

First chemical events in pyrolysis of wood

Wood has been heated at 250°C on a thermal balance and the evolved gases have been analyzed by Fourier transform infrared spectroscopy (FTIR). The heated wood has been analyzed for glycoses, uronic acids and by nitrobenzene oxidation to vanillin and syringaldehyde. About 60% of the weight loss is accounted for by five compounds, which are the only products detected in the gases by FTIR. These products are water, carbon dioxide, methanol, acetic acid and formic acid. By relating the rates of formation of these compounds to weight loss, the following major conclusions are reached regarding the first chemical events in pyrolysis of wood. Uronic acids in the hemicelluloses and pectic substances decompose very readily to yield carbon dioxide, water, char (or char precursors) and perhaps some methanol. This decomposition may lead to further pyrolysis of the xylose units to which the uronic acids are attached in the hemicelluloses. Acetyl ester groups in the hemicelluloses are much more resistant to pyrolysis, but are released slowly as acetic acid. A small proportion of the potential methanol product is released very readily and at least part of this product is derived from lignin. Formic acid is released at a slow and continuing rate at 250°C by unknown mechanisms and is probably derived from degradation of hemicelluloses.

Thermal Characterization of Materials Using Evolved Gas Analysis

Thermal analysis combined with evolved gas analysis has been used for some time. Thermogravimetry (TG) coupled with Fourier transform infrared (FTIR) spectroscopy(TG/FTIR), Thermogravimetry (TG) coupled with mass spectrometry (TG/MS), and Thermogravimetry (TG) coupled with GC/MS offers structural identification of compounds evolving during thermal processes. These evolved gas analysis (EGA) techniques allow to evaluate the chemical pathway of the degradation reaction by determining the decomposition products. In this paper the TG/FTIR, TG/MS, and Pyrolysis/GC-MS systems will be described and their applications in the study of several materials will be discussed, including the analysis of the degradation mechanisms of organically modified clays, polymers, and coal blends.

A study of chlorine behavior in a simulated fluidized bed combustion system

Fluidized bed combustion techniques have been widely used throughout the world in an effort to reduce sulfur oxide emissions, especially from burning high-sulfur coal. However, in the utilization of FBC systems for co-firing high chlorine coals with municipal solid waste (MSW) there are some concerns about the possible emission of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). PCDD/Fs may be produced from the reaction of volatile organic compounds (VOCs) and molecular chlorine under relatively low combustion temperature conditions. In oxygen-rich conditions during combustion molecular chlorine can be formed through the Deacon Reaction when the temperature is around 600°C. It is also likely that chloride might affect the detailed chemistry of desulfurization in FBC processes. In order to better understand the behavior of chlorine in an FBC system during combustion processes, a comprehensive study was carried out in a simulated FBC system with an on-line feeder at Western Kentucky University. Conditions used simulated the flue gas and operating conditions of an FBC system. Optimum operating conditions to suppress HCl, Cl2 and SOx emissions from FBC systems were determined. A better understanding of the chlorine behavior during combustion will help in controlling possible PCDD and PCDF formation and reducing corrosion in FBC systems. The test results indicated that the formation of molecular chlorine is favored at temperatures above 600°C, in oxygen-rich atmospheres, and in relatively high HCl concentrations. The reaction temperature plays a key role in the capture of HCl. The optimum combustion conditions for controlling PCDD/Fs formation in FBC systems is to maintain combustion temperature around 850°C in the bed area, 600°C in the freeboard area, low oxygen concentrations in the flue gas and enough residence time for fine particles in the freeboard.

The Characterization of Organic Modified Montmorillonite and Its Filled PMMA Nanocomposite

Thermogravimetric analysis (TG) and Fourier transform infrared (FTIR)results of commercial montmorillonite were compared to that exchanged with trimethyloctadecyl quaternary ammonium chloride (SCPX2048), both were treated up to500°C. The time-of-flight mass spectrometer (TOF/MS) results of SCPX2048 trapped under300 and 500°C were compared with that of N,N,Ntrimethyl-1-dodecanammonium chloride(A 18-50) trapped under 200 and 300°C. The degradation mechanism of organic modified montmorillonite was proposed. PMMA-clay nanocomposite was synthesized through intercalation method and its properties were examined by both TG and DSC techniques. The thermal stability and glass transition temperature of montmorillonite filled PMMA increase comparing with that of the pure PMMA.

Studies of the Fate of Sulfur Trioxide in Coal-Fired Utility Boilers Based on Modified Selected Condensation Methods

The formation of sulfur trioxide (SO(3)) in coal-fired utility boilers can have negative effects on boiler performance and operation, such as fouling and corrosion of equipment, efficiency loss in the air preheater (APH), increase in stack opacity, and the formation of PM(2.5). Sulfur trioxide can also compete with mercury when bonding with injected activated carbons. Tests in a lab-scale reactor confirmed there are major interferences between fly ash and SO(3) during SO(3) sampling. A modified SO(3) procedure to maximize the elimination of measurement biases, based on the inertial-filter-sampling and the selective-condensation-collecting of SO(3), was applied in SO(3) tests in three full-scale utility boilers. For the two units burning bituminous coal, SO(3) levels starting at 20 to 25 ppmv at the inlet to the selective catalytic reduction (SCR), increased slightly across the SCR, owing to catalytic conversion of SO(2) to SO(3,) and then declined in other air pollutant control device (APCD) modules downstream to approximately 5 ppmv and 15 ppmv at the two sites, respectively. In the unit burning sub-bituminous coal, the much lower initial concentration of SO(3) estimated to be approximately 1.5 ppmv at the inlet to the SCR was reduced to about 0.8 ppmv across the SCR and to about 0.3 ppmv at the exit of the wet flue gas desulfurization (WFGD). The SO(3) removal efficiency across the WFGD scrubbers at the three sites was generally 35% or less. Reductions in SO(3) across either the APH or the dry electrostatic precipitator (ESP) in units burning high-sulfur bituminous coal were attributed to operating temperatures being below the dew point of SO(3).

Oxidation of a La2O3-modified aluminide coating

acad sinica, inst met res, state key lab corros & protect, shenyang 110015, peoples r china. western kentucky univ, ctr mat characterizat, bowling green, ky 42101 usa.;peng, x (reprint author), acad sinica, inst met res, state key lab corros & protect, shenyang 110015, peoples r china