Physicochemical Properties Of Chars Research Articles

Synergistic and Antagonistic Effects of the Co-Pyrolysis of Plastics and Corn Stover to Produce Char and Activated Carbon.

The physicochemical properties of char and activated carbon produced from the co-pyrolysis of corn stover (CS) and plastics, polystyrene (PS) and polyethylene terephthalate (PET), were studied. Non-isothermal gas analysis of the volatiles was conducted using an online mass spectrometer to correlate the thermal degradation of gaseous byproducts to the formation of pores in the char materials. The findings determined that the addition of PS or PET promotes the formation of the solid char product with either higher than average pore sizes or surface areas compared to control samples. The addition of PET to corn stover increases the surface area of the char formed. The char formed from a CS:PET mass ratio of 1:1 produced char with a surface area of 423.8 ± 24.8 m2/g at 500 °C and a duration of 2 h. The surface area of the chars formed from CS and PET decreased as the amount of PET decreased, showing a tendency for PET to increase the surface area of the char materials synergistically. The addition of PS to corn stover promoted the formation of chars with, on average, larger pore sizes than the control char samples. The chars were chemically activated with potassium hydroxide, and the activated carbon that formed had lower surface areas but comparable surface functional groups to the control samples. Vanillin adsorption testing showed that activated carbon from corn stover performed the best at removing 95% of the vanillin after 2 h. In contrast, the activated carbon from the chars produced from the co-pyrolysis of corn stover and polystyrene or corn stover and polyethylene terephthalate removed 45% and 46% of vanillin after 2 h, respectively. The findings suggest that plastics have a synergistic relationship in producing char precursors with improved porosity but antagonistically affect the activated carbon adsorbent properties.

The competition/inhibition effect of H2O/CO2-char gasification in typical in situ gasification-chemical looping combustion (iG-CLC) conditions via particle-resolved simulation

In the fuel reactor of in-situ gasification chemical looping combustion (iG-CLC), the solid fuel (e.g., coal, biomass) goes through two typical processes: devolatilization and char gasification. Then the pyrolysis and gasification products react with oxygen carrier to produce CO2 and H2O ideally. The slow char gasification rate during iG-CLC is responsible for combustion efficiency. Therefore, a deeper understanding of char conversion characteristics is required to optimize iG-CLC conditions. In this paper, a particle-resolved simulation with detailed heterogeneous reactions is conducted, in which the effects of char particle size and reaction temperature on char conversion characteristics are carefully studied. To understand the competition between CO2 gasification and H2O gasification, single-particle simulations are carried out under mixed and separate atmospheres. The char gasification rate in CO2/H2O mixtures (rmix) is lower than the sum of the char-H2O gasification rate (rH2O) and the char-CO2 gasification rate (rCO2). We find that the competition for active sites between char-H2O gasification and char-CO2 gasification is not significant, while the inhibition of gasification products play an important role in char-CO2 gasification, particularly the inhibition of CO (from char-H2O or char-CO2 gasification), due to the accumulation of H2 and CO inside the char particle. The inhibition effect is quantified via particle-resolved simulations and then a quantitative formula is attained to describe the complex relationship between H2O gasification and CO2 gasification. Then the point-source model for H2O/CO2-char gasification is developed for computational fluid dynamics simulations. Straightforward cloud diagrams are presented to explore the relationship between conversion rate characteristics and physicochemical properties of char, providing useful information for the optimization of iG-CLC conditions.

Influence of active alkali and alkaline earth metals on physicochemical structures of co-pyrolysis-gasification coupling char

ABSTRACT The influences of active alkali and alkaline earth metals (Ac-AAEMs) on the physicochemical properties of chars during co-pyrolysis-gasification coupling were studied in this paper. The mixed samples were obtained according to four mixing ways: original coal and original corn stovers (OSM+OCS), pickling coal and original corn stovers (PSM+OCS), original coal and pickling corn stovers (OSM+PCS), and pickling coal and pickling corn stovers (PSM+PCS). The influences of Ac-AAEMs in OSM (Ac-AAEMs-OSM), Ac-AAEMs in OCS (Ac-AAEMs-OCS), and Ac-AAEMs in OSM+OCS (Ac-AAEMs-blends) on the pore structures of gasification chars were characterized by IOSM, IOCS, and IOSM+OCS, respectively. The results showed that Ac-AAEMs-OCS and Ac-AAEMs-blends, especially Ac-AAEMs-OCS, significantly promoted the development of mesopores. Furthermore, Ac-AAEMs-OCS and Ac-AAEMs-blends have good catalytic effects on the specific surface area of chars, especially at 20 minutes of gasification. Compared with PSM+PCS char, the specific surface areas of PSM+OCS char, OSM+OCS char, and OSM+PCS char obtained at 20 minutes of gasification increased by 203%, 157%, and 7%, respectively. Besides, the Ac-AAEMs are conducive to destroying the carbon structure with a high graphitization degree and promoting the formation of disordered amorphous carbon. The magnitude of their catalytic ability is Ac-AAEMs-blends >Ac-AAEMs-OCS>Ac-AAEMs-OSM.

Influence and action mechanism of pressure on pyrolysis process of a low rank Naomaohu coal at different temperatures

In this study, the effect of pressure on the pyrolysis characteristics of Naomaohu coal and the physicochemical properties of char during slow pyrolysis is evaluated, and the mechanism of pressure is explored. The results show that the influences of pressure on char yield and physical properties are reflected in both promoting and inhibiting effect, and the latter is more obvious with the increasing temperature. As the pressure increases, the char yield first reduces and then improves, and at 600 °C and 800 °C the minimum yields are in 1.0 MPa and 0.1 MPa, which are 57.48% and 54.04%, respectively. The SBET of char increases first and then decreases. At 800 °C, the SBET of char increases from 7.86 m2/g at 0.1 MPa to 19.81 m2/g at 0.5 MPa and then decreases. The effect of pressure on the chemical properties of char is relatively simple. As the pressure rises, the content of functional groups in char reduces and the degree of graphitization enhances. The TG-DTG curve, XPS, BET, SEM test, experiments on the pressurized micro-fluidized bed reaction analyzer and pressurized pyrolysis-gas chromatography/mass spectrometry show that the pressure mainly affects the pyrolysis process by affecting the secondary reaction of the primary volatiles in the particle and is related to temperature.

Comparative evaluation of bone chars derived from bovine parts: Physicochemical properties and copper sorption behavior

With the increasing demand for beef worldwide, a considerable amount of bovine bone is discharged as solid waste. Therefore, in this study, the physicochemical properties of chars from bovine bones (ribs, scapulae, vertebrae, and legs) and their copper sorption behavior in aqueous solutions were investigated. The bone chars were pyrolyzed at 500 °C and the ash contents were approximately 85.08%, although the leg bone char had significantly higher values. The rib bone char showed a larger specific surface area (172 m2/g), smaller average pore diameter (7.7 nm), and more basic functional groups than the other char types. The maximum sorption capacity varied from 72.53 to 83.71 g/kg, with the rib bone char exhibiting the best adsorption characteristics, followed by the scapulae, vertebrae, and legs. A correlation analysis demonstrated that the adsorption capacity of Cu(II) on bone char is closely related to surface pore characteristics. An adsorption kinetic analysis and physicochemical characterization of the chars indicate that the Cu(II) adsorption mechanism in bovine bone char is primarily surface chemisorption. Based on the different of physicochemical properties and sorption behavior, bone chars pyrolyzed from bovine ribs are most suitable for adsorption-related applications. The results of this study demonstrate the potential for classified utilization of animal bones, including the use of graded bone chars as low-cost adsorbents requiring no chemical pre-treatment.

Coal pyrolysis: Comparative evaluation of the technical performance of two Southern Hemisphere demineralized bituminous coals

Differences in the physico-chemical properties of char can fundamentally affect the reactivity of the char during conversion processes and even the reaction pathway. Transformations from coal to char using a high heating rate have been thoroughly assessed; however, there is less information on the reactivity of this transition to chars. Two South African bituminous coals of ≤75μm were acid washed, and subjected to a slow heating rate of 25°C/min from 450 to 700°C at atmospheric atmosphere. The chars were characterized by physical, chemical and petrographic evaluations. The effect of the heat treatment conditions on the reactivity of the chars towards oxygen under chemical kinetic controlled regime was assessed. The oxygen content of the resultant chars was also measured directly by scanning electron microscope (SEM) attached with element detector sensor (EDS) technique. The coals are medium rank C bituminous (Rov=0.73 for high volatile and Rov=0.78 for low volatile). Char properties determined revealed correlations of the chemical structural changes during the coal to char transition. The findings of this study would suggest that the loss of carbon combustion reactivity cannot be assessed on the basis of its time-temperature history only, but the extent of carbon interaction with oxygen also come into play. The synergy of reactions induced by modifications of the carbon structure, oxygen uptake and the reaction between oxygen and the resultant chars is presented and discussed.