Pyrolysis-temperature-dependent pore evolution and reactivity of CaO–carbon composite pellets with a pitch/polyvinyl alcohol hybrid binder for calcium carbide production

Calcium carbide (CaC 2 ) production is highly energy- and carbon-intensive, creating an urgent need for feedstock upgrading to enable low-carbon operation. Herein, CaO–carbon composite pellets (CCCPs) were prepared by granulating fine CaO and semi-coke powders with a hybrid binder (coal tar pitch + polyvinyl alcohol), which balances ambient green strength and high-temperature structural integrity. The effects of pyrolysis temperature (600–1000 °C) on devolatilization behavior, Ca-bearing phase transitions, pore structure evolution, and intrinsic reactivity were systematically investigated. Thermogravimetric analysis revealed two dominant mass-loss stages: 20–600 °C, dominated by binder decomposition and Ca(OH) 2 dehydroxylation (total mass loss ∼24.67%), and 600–1000 °C, governed by CaCO 3 decomposition (mass loss ∼11.11%). With increasing temperature, pore coalescence was promoted: submicron pore volume decreased, while macropores (10–100 μm) first increased and peaked at 800 °C (highest volume fraction). Raman analysis showed that the carbon disorder degree ( A D1 / A G ) reached a maximum of 2.05 at 800 °C, indicating optimal carbon reactivity. CaO underwent progressive carbonation at 600–800 °C, and CaCO 3 decomposition initiated near 800 °C and was completed by 1000 °C. Notably, CCCPs pyrolyzed at 800 °C exhibited the highest thermal strength (13.20 MPa at 800 °C, 7.69 MPa at 1200 °C) and optimal reactivity, attributed to the synergistic effect of favorable pore structure and enhanced CaO-carbon interfacial contact. This work provides a mechanistic basis for the design of high-performance CCCPs, offering a promising waste-derived feed strategy to reduce energy consumption in CaC 2 synthesis. Download: Download high-res image (177KB) Download: Download full-size image