Characterization of Powder River Basin coal pyrolysis with cost-effective and environmentally-friendly composite NaFe catalysts in a thermogravimetric analyzer and a fixed-bed reactor
Graphical abstract
Introduction
The rising interest in clean coal conversion and utilization technology is expanding research efforts in coal science and engineering worldwide. As a key step in coal thermochemical conversion technology, gasification and combustion processes, pyrolysis and its applications is a point of focus for such researches. By means of pyrolysis, coal can be converted into useful energy holder (bio-oil), adsorbent bio-char and various useful-chemicals such as benzene, toluene, naphthalene, phenol, creosote oil, and so on [1], [2]. However, conventional coal pyrolysis techniques are often plagued with problems, such as low efficiency of coal conversion, high contents of oxygen and heavy component (boiling point higher than 360 °C) in the coal oil product, difficulties in separating coal particle and coal oil. Thus, coal catalytic pyrolysis has become exceedingly desirable technology to improve coal pyrolysis conversion and orientation of pyrolysis products, especially developing a cost-effective and environmentally-friendly catalyst.
Previously, catalysts used in the pyrolysis of coal mainly include alkali and alkaline earth metallic compounds, transition metallic compounds, natural minerals, or mineral matters in coal [3], [4], [5], [6]. It has been demonstrated that alkali metal carbonates, such as Na2CO3 and K2CO3, can improve the gas yield and reduce tar and char yields during coal pyrolysis. Moreover, some results indicate that the addition of Na2CO3 can improve the quality of pyrolysis oil produced by oil sludge and biomass. Also, the oxygen content of the bio-oil from biomass pyrolysis is decreased from 47.5 wt.% to 16.4 wt.% with Na2CO3 [4], [7], [8]. These results suggest that Na2CO3 is a potentially superior catalyst for producing chemicals by coal pyrolysis and gasification. Meanwhile, iron-based catalysts are also widely used in coal pyrolysis and gasification due to its low price, favorable environmental attributes, and its better catalytic activity for hydrogenation reactions. Studies have shown that Fe2CO3 catalyst can be decomposed into iron oxides and then be reduced to iron and iron carbide above 719 °C during coal pyrolysis [9], [10]. Fe2CO3 could help decompose most of the hydrocarbons at 900 °C, producing only a small amount of CH4 [11], which is beneficial to coal-to-liquid utilization processes.
Proper use of composite catalysts has the potential to improve reaction rates and production rates of desirable products when compared with the use of individual catalysts. By using the composite Na2CO3FeCO3 catalysts, one may expect some advantages such as changes in the selectivity of H2/CO and tar yields, increased conversion rate or general improvements of the overall efficiency of pyrolysis and gasification. With these aims, the knowledge of pyrolysis kinetics of coal with the use of composite Na2CO3FeCO3 catalysts deserves a careful study. This will be critical to the goal of developing new coal conversion technologies and to the design of proper and efficient reactors.
Thermogravimetric analysis (TGA) is one of the most common techniques used to investigate the characteristics of decomposition and kinetic parameters during pyrolysis of solid samples such as coal, biomass, plastic, and so on [12], [13]. Historically, various methods were applied in evaluating devolatilization kinetic process of solid fuels using non-isothermal TG analysis, especially some popular model-free methods developed by Friedman (FR) [14], Flynn-Wall-Ozawa (FWO) [15], [16], Kissinger-Akahira-Sunose (KAS) [17], [18] and Vyazovkin (V) [19], [20]. These methods are based on the assumption that the reaction rate at a constant extent of conversion only depends on the temperature. Hence, the activation energy can be evaluated without the need of a reaction model. Moreover, many methods including master plot methods, Popescu and Satave [21], [22], [23] methods have been developed to establish the kinetic model of thermal decomposition of solid fuels without assuming of kinetic model. All methods were adopted in this study to calculate kinetic parameters of coal pyrolysis with and without catalysts.
In our present work, Powder River Basin (PRB) coal has been analyzed by proximate analysis, ultimate analysis, FTIR analysis, X-ray diffraction analysis, and solid state 13C NMR analysis to obtain its physical and chemical characteristics. In addition, the pyrolysis behavior of coal with and without composite Na2CO3FeCO3 catalysts were studied using a thermogravimetric analyzer and a fixed-bed reactor. The aim is to investigate effects of catalysts and heating rate on the pyrolysis process of coal and to study pyrolysis kinetic characteristics of coal with and without catalysts. The activation energies were estimated by model-free methods, which includes KAS, FWO, FR, and VA. In addition, From the pyrolysis in the fixed bed reactor, XRD and FTIR tests for coal chars produced by PRB coal pyrolysis with use of catalysts were conducted. The catalytic mechanism of PRB coal pyrolysis with Na2CO3FeCO3 composite catalysts was proposed.
Section snippets
Sample preparation
Raw coal used in this work is from the Wyoming Powder River Basin and is provided by Wyodak Resources Development Corp. The proximate analysis was measured according to ASTM D5142 and D5016 [24]. The ultimate analysis (C, H, N, and S) of raw coal was performed using the elemental analyzer (Vario EL cube, Germany) and the oxygen (O) content was calculated by difference. The results of proximate and ultimate analysis of the coal are shown in Table 1. The ash of raw coal was prepared by air
Physical and chemical characteristics of raw coal with and without catalysts
13C NMR was used to analyze the different carbon types in the raw coal structure. Generally, the solid-state 13C NMR spectrum of coal can be divided into two main chemical regions: aromatic carbon (90–220 ppm) and aliphatic carbon (0–90 ppm) functional groups, respectively [39]. Different carbon functional groups can be represented by different chemical shifts, which are assigned into different carbon types, while the relative size of different peak areas indicates the relative contents of
Conclusions
Four model-free methods were applied to study the pyrolysis kinetics of a Powder River Basin coal with a NaFe composite catalyst. The results show that the nonlinear VA method appears to have the most reasonable E values in the range of α considered. Further, the An (random-nucleation and nuclei growth model) appears to be the appropriate reaction model for the raw coal pyrolysis with and without the use of Na2CO3FeCO3 composite catalyst. As an effective catalyst for coal gasification, Na2CO3
Acknowledgements
The authors gratefully acknowledge the Department of Energy (DE-FE0023999) and the Idaho National Laboratory Directed Research and Development Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517 for supporting this work.
References (58)
- et al.
Chemicals and materials from coal in the 21st century
Fuel
(2002) Mild conversion of coal for producing valuable chemicals
Fuel Process Technol
(2000)- et al.
Effect of inorganic matter on reactivity and kinetics of coal pyrolysis
Fuel
(2004) - et al.
Fates and roles of alkali and alkaline earth metals during the pyrolysis of a Victorian brown coal
Fuel
(2000) - et al.
Effects of mineral matter on products and sulfur distributions in hydropyrolysis
Fuel
(1999) - et al.
High quality bio-oil from catalytic flash pyrolysis of lignocellulosic biomass over alumina-supported sodium carbonate
Fuel Process Technol
(2014) - et al.
Pyrolysis of oil sludge with additives of sodium and potassium compounds
Resour Conserv Recy
(2003) - et al.
H2 and COx generation from coal gasification catalyzed by a cost-effective iron catalyst
Appl Catal A Gen
(2013) - et al.
Pyrolysis of coal and iron oxides mixtures. 2. Reduction of iron oxides
Fuel
(1981) - et al.
Effect of metal oxides on the secondary reactions of volatiles from coal
Fuel
(1989)
Thermogravimetric analysis and kinetics of co-pyrolysis of raw/torrefied wood and coal blends
Appl Energy
Co-pyrolysis characteristics of microalgae Chlorella vulgaris and coal through TGA.
Bioresour Technol
Applicability of the master plots in kinetic analysis of non-isothermal data
Thermochim Acta
The kinetic analysis of non-isothermal data
Thermochim Acta
Catalytic gasification of a powder river basin coal
Fuel
Characterization of the mechanism of gasification of a powder river basin coal with a composite catalyst for producing desired syngases and liquids
Appl Catal A Gen
High-quality oil and gas from pyrolysis of powder river basin coal catalyzed by an environmentally-friendly, inexpensive composite iron-sodium catalysts
Fuel Process Technol
The ‘temperature integral’—its use and abuse
Thermochim Acta
Thermogravimetric study on the pressurized hydropyrolysis kinetics of a lignite coal
Int J Hydrogy Energy
Hydrogen production from polystyrene pyrolysis and gasification: characteristics and kinetics
Int J Hydrogy Energy
Non-isothermal pyrolysis of de-oiled microalgal biomass: kinetics and evolved gas analysis
Bioresour Technol
Model-free kinetic analysis of melamine–formaldehyde resin cure
Chem Eng J
Kinetic study on the pyrolysis behavior of Huadian oil shale via non-isothermal thermogravimetric data
Fuel
The kinetic study of temperature-programmed reduction of nickel oxide in hydrogen atmosphere
Chem Eng Sci
Insight into the structural features of Zhaotong lignite using multiple techniques
Fuel
Pyrolysis characteristics and kinetics of low rank coals by distributed activation energy model
Energy Convers Manag
Primary tar of different coking coal ranks
Int J Coal Geol
Flash pyrolysis of coals. 1. Devolatilization of a Victorian brown coal in a small fluidized-bed reactor
Fuel
Chemical structural models for coalified wood (vitrinite) in low rank coal
Org Geochem
Cited by (11)
Role of novel additives (reservoir rock and activated carbon) in bio-oil synthesis from LRC microwave pyrolysis
2024, International Journal of Hydrogen EnergyEffect of precipitating agents for the preparation of Fe-based catalysts on coal pyrolysis: Effect of Ba and Mg additives
2022, FuelCitation Excerpt :The empty d orbitals of Fe have adsorption effect on oxygen-containing functional groups in coal, and promote the side chain breaking and dehydrogenation reactions in aliphatic hydrocarbons in coal, thus increasing the gas yield, among which H2, CO and CO2 gas yields are significantly increased [13]. Moreover, Fe can inhibit the emission of N and S gases, so it has a wide range of research [14–17]. However, Fe is prone to sintering or combining with S elements in coal during coal pyrolysis resulting in Fe catalyst deactivation [18–20].
Effect of natural carbon filler on thermo-oxidative degradation of thermoplastic-based composites
2022, Thermochimica ActaCitation Excerpt :Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to study the different carbon types in the coal structure. Coal NMR spectra (Fig. 1a) can be categorized into three regions based on their chemical shift: aliphatic carbon (0–90 ppm), aromatic (90–165 ppm), and carbonyl groups (165–220 ppm) [36,37]. The relative abundance of each carbon type can be estimated by integrating the NMR spectra over the associated interval.
Study on the co-pyrolysis characteristics of oil-based drill cuttings and lees
2022, Biomass and BioenergyCitation Excerpt :This indicates that co-pyrolysis has a favorable effect. It was inferred that the mechanism of the mutual pyrolysis interaction is as follows: the hydrogen atoms in the lees were higher, in accordance with the theory of coal pyrolysis chemistry, and if hydrogen atoms could be allocated to carbon atoms during coal pyrolysis, it could promote the full volatilization of all available hydrogen [31,32]. In addition, owing to hydrogen depletion and structural limitations of coal, aromatic compounds are difficult to crack in a hydrogen-deficient state, although at higher temperatures heavy coal tar and a mixture of semi-coke and coke are produced [33].