A Mechanistic Proposal on Puffing of Coke and Its Inhibition

Abstract

The phenomenon of puffing is related to the rates of gas evolution and graphitization, molecular size of evolved gas, and porosity, texture and graphitizability of coke. Evolution of gases containing sulfur, nitrogen or metals (in the secondary puffing) causes the problem at the graphitization process by pressing the pore wall of the carbon which exhibits some local plastisity. The pressure induced is a function of the pore size relative to the rate of gas evolution and its molecular size. Thus, the timing of the gas evolution and graphitization is a key factor. The rapid heating for the graphitization allows more overlap-ping of these phenomena and increases the gas evolution at a time to produce higher pres-sure, enhancing the extent of puffing.
Cokes of low GTE often with large-sized optical texture of flow orientation are most susceptible to puffing because of its smallest resistivity against pressure for expansion.The macroscopic shrinkage of the coke due to the graphitization is known small with the coke of flow texture. Since such shrinkage can compensate the puffing to some extent, the needle coke suffers more puffing than the regular coke.Based on such understandings, the preferable structure of coke is proposed for the smaller puffing trend. Additives can also reduce the extent of puffing through the acceleration of graphitization, trapping the evolved gas molecules, and gasification. The former two roles changes the timing of graphitization and gas evolution and the last increases the porosity in the coke to allow the free gas evolution.
The puffing of carbon artifact is briefly discussed from the view of its composite natures.