Effects of Parent Coal Properties on the Pyrolytic Char Chemical Structure: Insights from Micro-Raman Spectroscopy Based on 32 Kinds of Chinese Coals

The chemical structures of pyrolytic chars prepared from 32 kinds of Chinese coals were investigated with micro-Raman spectroscopy in this study. Both first-order and second-order Raman spectra of the chars were curve-fitted and analyzed. The effects of the parent coal properties, including coal rank, volatile, fixed carbon, and ash content, on the pyrolytic char structures were detailed discussed and the correlations between these coal properties and pyrolytic char chemical structures were set up. Multiple-factor analysis was done to propose a comprehensive coal property index that relates well to the pyrolytic char chemical structure. The results indicate that the aromatization degree is the key distinguishable structure of pyrolytic chars prepared from coals with various rank, and the alkyl C−H and aryl C−H structures have no significant difference. The aromatization degree of pyrolytic char decreases with the increase of coal rank, while it increases with the increase of the fixed carbon content in parent coals. The high content of moisture in parent coal can induce condensation of the pyrolytic char, but the inorganic composition probably prevents the condensation of the char. Limited correlations between the coal rank, fixed carbon, moisture and ash content, and the aromatization degree of pyrolytic chars were found. A comprehensive coal property index: (fixed carbon content + moisture content)/(volatile content + ash content) (in air dry basis) combining the coal properties together relates well to the aromatization degree of pyrolytic char and can act as a good indicator for the pyrolytic char chemical structure. This study reveals the effects of the parent coal properties, including coal rank, fixed carbon, moisture, and ash content, on the pyrolytic char chemical structure, and provides a new comprehensive coal property index to predict the pyrolytic char chemical structure.

Aging characteristics of asphalt binders modified with waste tire and plastic pyrolytic chars

Globally, the growing volume of waste tires and plastics has posed significant concerns about their sustainable and economical disposal. Pyrolysis provides a way for effective treatment and management of these wastes, enabling recovery of energy and produces solid pyrolytic char as a by-product. The use of pyrolytic chars in asphalt binder modification has recently gained significant interest among researchers. As asphalt binder aging influences the cracking, rutting, and moisture damage performance of asphalt binder and the mixtures, evaluation of aging characteristics of char modified asphalt binders is quite important. The main objective of this study is the investigation of the aging characteristics of asphalt binders modified with waste tire pyrolytic char (TPC) and waste plastic pyrolytic char (PPC) through rheological and spectroscopic evaluations. To imitate short-term and long-term aging conditions, the asphalt binders were first treated in a rolling thin film oven (RTFO) and then in a pressure aging vessel (PAV). The aging characteristics were determined using four rheological aging indices based on complex modulus (G*), phase angle (δ), zero shear viscosity (ZSV), and non-recoverable creep compliance (Jnr) from multiple stress creep and recovery (MSCR) test. The fatigue cracking potential was then measured through binder yield energy test (BYET). These parameters were measured through a dynamic shear rheometer. Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H-NMR) spectroscopy analyses were then used to investigate changes in chemical composition due to aging in the char modified binders. Both TPC and PPC improved the high-temperature deformation resistance properties of asphalt binder. The TPC-modified binder showed better aging resistance than the control and PPC-modified binders, based on the different rheological and spectroscopic indices. The pyrolytic char modified binders also demonstrated good fatigue performance.

Characterization of thermal storage stability of waste plastic pyrolytic char modified asphalt binders with sulfur

Pyrolysis has gained a strong interest in recent times for sustainable treatment and recovery of energy-rich products from different wastes including plastic. Waste plastic pyrolytic char (PPC) generated as a carbonaceous by-product in the pyrolysis process, is gaining attention as an asphalt binder modifier. Adequate thermal storage stability is an essential requirement for a modified asphalt binder to ensure that the composite offers integrity and homogeneous properties during its storage, handling and transportation in the field. The objective of this study was to evaluate and characterize the thermal storage stability properties of PPC modified binders. PPC modified asphalt binders were fabricated and evaluated at multiple dosages of sulfur as a cross-linking agent. In addition to the conventionally used softening point difference (SPD), characterization of thermal storage stability was attempted using rheology-based separation indices (SIs) derived through temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) tests. These rheological SIs were based on complex modulus (G*), Superpave rutting parameter (G*/sin δ), Shenoy rutting parameter (SRP), zero shear viscosity (ZSV), and MSCR Jnr (at three stress levels 0.1, 3.2 and 10 kPa). Two formulations of each rheology-based separation index were studied: (1) ratio, and (2) maximum-average difference formulations. The temperature and frequency dependencies of rheological SIs were also evaluated. Further, the Fourier transform infrared spectroscopy (FTIR) was used to characterize storage stability by comparing the chemical functionalities of the PPC modified binders. A 0.3% dosage of sulfur was found to produce the best results considering all SPD, rheology-based SIs and FTIR. Principal component analysis showed that the ratio and maximum-average formulations had similar contributions to the first principal component accounting for more than 99% of the variability.

Thermal and Catalytic Cracking of Toluene Using Char from Commercial Gasification Systems

Tar formation hinders the development of biomass gasification technologies. The use of pyrolytic char as a catalyst for removing tar has been widely investigated; its large specific surface area and pores distribution make it a good candidate for the cracking of heavy hydrocarbons. The present work assesses the catalytic activity of char from a commercial gasifier. Thermal degradation tests in N2 and in CO2 proved that the char is suitable for high-temperature applications (catalytic cracking) and showed release of CO and H2, which might affect the catalytic performance of the char when used for tar removal applications. For inspecting the potential of the char for tar removal, toluene was chosen as model tar. Through GC-FID, toluene removal efficiency and the amount of benzene produced from its decomposition were evaluated. Tests up to 1273 K resulted in tar removal efficiencies as high as 99.0%, and empty reactor tests allowed for discerning the effects of thermal and catalytic cracking. The catalytic activity of the char was more pronounced at 1173 K, as char increased the toluene removal efficiency from 39.9% (empty reactor) to 60.3%. The results confirmed that gasification char, like pyrolytic char, has a high potential for catalytic tar removal applications.