Distribution of potassium during chemical activation of petroleum coke: Electron microscopy evidence and links to phase behaviour

Abstract

In this study, direct evidence for chemical penetration into petroleum coke particles during activation is presented. In addition, the porosity development was directly related to the sulphur loss and phase behaviour of the species present.Petroleum coke (petcoke, 6 wt.% sulphur) was activated with KOH and NaOH at temperatures between 400 and 800 C. The C S bonds were broken before 400 C in the presence of KOH and before 500 C in the presence of NaOH. Electron microscopy analysis of cross-sectioned and ultramicrotomed samples revealed that sulphur was still present within the particles and that the hydroxide activation agents had penetrated to the centre of the particles (90-150 μm). After heating to 800 C and washing with a weak acid aqueous solution, essentially all the sulphur was removed, as was any remaining chemical agent. The characterization results, phase diagrams, and complementary experiments with carbonate chemical agents or steam suggest that, during heating, a molten phase formed around the petcoke particles. The composition of this molten phase changed as activation proceeded and both sulphur and ash components were liberated from the petcoke. This better understanding of the activation process will improve the efficiency of preparing activated carbon.

Thermodynamic studу of ethyl alcohol sorption on activated petroleum coke

“…When the ratio of carbon material:KOH increases, the speci c surface area and pore volume increase, but the yield of porous material decreases. Thus, when the petroleum coke was activated at 800 ℃, the speci c surface area was 379, 845, 1867, 1940, 2438 m 2 /g at the mass ratio of KOH:petroleum coke of 0.5, 1, 2, 3 and 5 respectively (Liu et al, 2019;Montes et al, 2023;Zhu et al, 2013). A ratio higher than 6 reduces the surface area of the activated material.…”

“…Wu et al, 2018). Sodium and potassium carbonates poorly develop the porosity of petroleum coke at temperatures of 700-800 ℃ (Hussaro, 2014;Maulina et al, 2020;Montes et al, 2023) A speci c surface area of 1000-2000 m 2 /g was obtained by activation with zinc chloride (Caturla et al, 1991;Olivares-Marín et al, 2006). Physical activation is conducted with gases, usually steam or CO 2 at 700-900 ℃ in an inert atmosphere for 6-9 hours.…”

“…KOH develops microporosity, and the surface area varies from 1700 to 2500 m 2 /g depending on the ratio of KOH:coke (from 3:1 to 6:1) (Liu et al, 2019;Qiao et al, 2006; M. Wu et al, 2005). In comparison with KOH, sodium hydroxide gives lower porosity and speci c surface area 600-1397 m 2 /g, but larger pore diameter (Montes et al, 2023; Oguz Erdogan, 2016; J. Wu et al, 2018).…”

Issue Highlights

“…The composition of this molten phase changed as activation proceeded and both sulphur and ash components were liberated from the petcoke. [ 4 ]…”