Study of thermochemical transformation of fir bark under conditions of its activation by potassium compounds

The effect of modifying additives of chemical compounds on the pyrolysis of organic biomass of the fir bark, on the efficiency of the process and its selectivity, on the properties of the obtained carbon materials has been investigated. Thermogravimetry (TG / DTG) and differential scanning calorimetry (DSC) have been used to study the effect of KCl and K₃PO₄ compounds on the thermal decomposition of the original and modified fir bark and determine the main thermal effects accompanying this process. As a result of the studies carried out, it was found that KCl additives practically do not affect the decomposition of hemicelluloses, but they shift the maximum decomposition of the cellulose peak in the direction of decreasing temperature to 340.9 °C compared to untreated bark (357.5 °C). K₃PO₄ promotes the simultaneous decomposition of hemicelluloses and cellulose in the temperature range with a maximum at 277.8 ° C. In both cases, the additions of KCl and K₃PO₄ reduce the maximum rate of weight loss, that leads to a higher yield of carbon residues: the yield of coal from the original fir bark is 26.6%, in the presence of K₃PO₄ and KCl it is 52.6 and 65%, respectively. The comparative effect of potassium compounds KCl and K₃PO₄ on the formation of the porous structure of carbon materials during carbonization at 800 ° C was studied. Obtained on the basis of the analysis of adsorption isotherms (BET method), data on the porous structure of carbon materials indicate that under the influence ofpotassium compounds, a better development of porosity occurs in comparison with untreated bark. Carbon samples modified with K₃PO₄ and KCl have, respectively, a larger specific surface area (S_BET 284.6 and 499.3 m² / g) than those obtained from the original bark (239 m² / g). The treatment of the bark with KCl promotes the formation of microporosity in the carbon sample with an average pore size of about 2.05 nm. Under the influence of K₃PO₄, a predominantly micro- / mesoporous structure is formed in the sample, where the average pore width is 4.31 nm. The results obtained in this work show that the use of KCl and K₃PO₄ compounds is promising for the production of carbon materials and adsorbents with different porous structures from an available and inexpensive natural source - fir bark.

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