Формування поруватості буровугільних матеріалів при лужній активації з тепловим ударом

• Datum: 2019
• Hauptverfasser: Kucherenko, V. A., Таmarkina, Yu. V., Saberova, V. A.
• Format: Artikel
• Sprache: Ukrainisch
• Veröffentlicht: Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2019
• Schlagworte: буре вугілля; лужна активація; тепловий удар; нанопоруватість
• Online Zugang: https://www.cpts.com.ua/index.php/cpts/article/view/489
• Назва журналу: Chemistry, Physics and Technology of Surface

The aim of the work is to establish the effect of temperature on the porous structure characteristics of thermolysis solids (TS) prepared from brown coal (BC) during a novel process - alkaline activation with thermal shock. The BC sample is the Alexandria deposit coal, demineralized to ash content 0.5±0.1 % by treatment with HCl and HF acids. The elemental composition of the organic coal substance is as follows (%): C 70.6, H 5.9, S 3.6, N 1.9, O 18.0 (by difference). The treatment of BC with an alkaline activator (KOH) was performed by impregnation; the mass ratio of KOH/coal is 1.0. The preparation of TS was carried out in argon in three successive stages: 1) rapid introduction of the sample into the reactor, preheated to the temperature of thermal shock tTS, varied in the interval tTS = 400–800 °С; 2) isothermal holding at tTS (1 h); 3) cooling, washing from alkali compounds and drying. Based on low-temperature (77 K) nitrogen adsorption-desorption isotherms (Micromeritics ASAP 2020), there were determined pore size distributions, total volume (Vt, cm3/g) and surface (S, m2/g) of adsorbing pores, volumes of macro- (Vma) , meso- (Vmе) and micropores (Vmi), as well as micropores with a diameter of D?1 nm (V1nm). The temperature dependences of these characteristics are obtained. An increase in the tTS temperature was found to result in the forming TS with increasing specific surface areas from 14.7 (400 °C) to 1947 m2/g (800 °C): half S is formed in a narrow interval tTS=700–800 °C. The yield of TS is reduced from 67 to 25 %. The Vt value increases by a factor of 7.2 times (from 0.124 to 0.892 cm3/g), the volumes of mesopores and macropores increase equally - 2.9 times. The main growth of Vt volume is due to micropores: their volume Vmi increases from 0 to 0.547 cm3/g, the contribution of micropores with D?1 nm becomes dominant (84–98 %) at tTS=600–800 °C. Pores with D?5 nm were found to develop most dynamically under combined effect of KOH and thermal shock. Pore size distribution is characterized by three maxima: dV1 for micropores with D?1 nm, dV2 for micropores with D=1–2 nm, dV3 for mesopores with D=3–5 nm. The dependence of dV1 on temperature tTS is strictly exponential (R2=0.988), that allows us to calculate the parameter E(V1), which characterizes the effect of temperature on the increase in the volume of micropores with D?1 nm. It has the dimension of the "classical" activation energy and is 56.1 kJ/mol. As tTS values increase, the dV2 maximum value decreases by a factor of 22, and the pore diameter shifts from 1.85 to 1.39 nm. Values of dV3 are an order of magnitude lower than dV1 and approximately replicate the dependence of dV1-tTS in the interval of 400–750 °C. An increase in the thermal-shock temperature is concluded to promote the micropores formation (especially pores with D?1 nm), which is limited by the diffusion of the activator (KOH or K atoms as the products of K+ ion reduction) within the forming three-dimensional framework of carbonaceous solids.