Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Abstract

The influence of a CO 2 or N 2 -based atmosphere on the porous structure and microstructure of the chars obtained from the nonisothermal slow devolatilization (10 °C/min), from room temperature to 900 °C, of two coals of different rank (Semi-Anthracite (SA) and High Volatile Bituminous type C (HVBC)) and different particle size distribution was studied. Physicochemical characterization (ultimate and proximate analysis), structural and morphological characterization by Raman spectroscopy, FE-SEM, BET surface area, and volume and diameter microporous by CO 2 adsorption measurements were carried out for all the chars. It was found that the kinetic parameters, the physicochemical properties, and reactivity of the chars are different, depending on the pyrolysis atmosphere. It was also determined that for the char from SA coal with particle size greater than 0.7 mm, the BET surface area increases when the atmosphere is enriched with CO 2 . This effect appears to be promoted by the interaction of different processes such as intraparticle side reactions (softening, nucleation and coalescence of bubbles, crosslinking, among others), differences in the thermal diffusivity of N 2 and CO 2 , and the reactive effects of the latter. Additionally, tests of oxidative reactivity of chars showed that the char formed in a CO 2 atmosphere is more reactive than that formed in N 2 . With the results of Raman analysis and kinetic parameters quantified, it was concluded that the reaction atmosphere determined the degree of ordering achieved by the char structure and that the thermodiffusive properties of the reaction atmosphere promoted structural differences in the char even at low heating rates.Keywords: Slow pyrolysis, Pore size distribution, large coal particles, Oxy-combustion, reactivity. RESUMENSe estudió la influencia de una atmósfera basada en CO 2 o N 2 sobre la estructura porosa y la microestructura de carbonizados de carbón obtenidos de la pirólisis lenta no isotérmica desde temperatura ambiente hasta 900 °C de dos carbones de diferente rango (Semi-Antracita (SA) y Bituminosos Alto en Volátiles tipo C (BAVC)), y de diferentes distribuciones de tamaño de partícula. Para todos los carbonizados se realizó la caracterización fisicoquímica (Análisis ultimo y próximo), la caracterización morfológica y estructural por combinación de técnicas como espectroscopia Rama, Microscopia electrónica de barrido por emisión de campo (FE-SEM), área superficial (BET -Brunauer-Emmett-Teller) y volumen y diámetro de microporos por mediciones de adsorción en CO 2 (Horvath-Kawazoe (HK) method). Se encontró que los parámetros cinéticos, las propiedades fisicoquímicas y la reactividad de los carbonizados de carbón son diferentes dependiendo de la atmósfera de pirólisis. También se determinó que para el carbonizado de carbón de SA, con un tamaño de partícula mayor de 0,7 mm, la superficie BET aumenta cuando la atmósfera se enriquece en CO 2 . Este efecto parece ser promovido por la interacción de diferentes procesos como las reacciones secund...

Kinetics and mechanisms for catalytic pyrolysis of empty fruit bunch fibre and cellulose with oxides

“…3.2). As observed, the addition of oxides caused a reduction in the frequency factor, which, by definition signifies the probability for reaction occurrence [45]. Hence, it may be hypothesized that the addition of the oxides did not affect the reaction rate of EFBF for devolatilization but rather, reduced the probability for reaction to occur.…”

Peach Pit-Activated Carbons: Effect of Row Material Form and Pyrolysis Parameters on Hydrogen Adsorption Storage

“…The main change in the synthesis procedure concerns the carbonization process. All previous synthesis methods had a carbonization process carried out in an inert environment while the activation was carried out in an oxidizing environment, but it is known from the literature that the use of CO 2 rather than N 2 during the carbonization phase can favor the formation of porosity, even at temperatures lower than the activation temperature, since CO 2 is more aggressive than N 2 . Additionally, while in the first part of this experimental work all synthesis parameters (such as activation temperature, flow, activation time, etc.)…”

Evaluation of the optimal activation parameters for almond shell bio-char production for capacitive deionization

“…Once the bubble reach the surface, it explode releasing the volatiles. The whole process is known to further increase the porosity of the material (Valdés et al, 2018).…”