Thermogravimetric Evidence for Better Thermal Stability in Char Produced Under Unconfined Conditions

Thermogravimetric degradation of two kinds of char obtained from two different types of systems, confined and unconfined, was studied. In a confined system, charring was accomplished in a closed chamber in which vapors produced during the charring process were captured within the system and were forced to condense on the char being produced. In the unconfined charring system, a passage was available for the escape of gaseous substances evolved during the charring process; the presence of condensed volatiles in produced char was low. Using thermogravimetric analysis, differences between chars produced in these two systems were studied and it was proved that the char from the unconfined system showed a superior profile of apparent activation energy as compared with the char from the confined system due to higher presence of condensed vapors of volatiles in the char produced in confined conditions. A first-order derivative of thermogram of the char generated in the unconfined system showed a broad peak, at higher temperature segments, ascribed to the thermal decomposition of heavier volatiles and lignin. Activation energies for both types of char were determined and compared using the Coats-Redfern method. Char obtained from the unconfined system had higher thermal stability. This article recommends that for generation of more thermally stable char, unconfined charring chambers should be preferred. A new direct and simple method was used in this article to define the accelerating or retarding nature of thermal decomposition process using segmental analysis of conversion fraction.