CO2 gas-adsorption calorimetry applied to the study of chemically activated carbons

SOARES MAIA, DÉBORA ALINE; ALEXANDRE DE OLIVEIRA, JOSÉ CARLOS; NAZZARRO, MARCELO SANDRO; SAPAG, KARIM MANUEL; LÓPEZ, RAUL HORÁCIO; LUCENA, SEBASTIÃO MARDÔNIO PEREIRA DE; DE AZEVEDO, DIANA CRISTINA SILVA

CHEMICAL ENGINEERING RESEARCH & DESIGN

INST CHEMICAL ENGINEERS

Año: 2018 vol. 136 p. 753 - 760

0263-8762

tIn this work, the microporous structure of a series of H3PO4chemically activated carbonsfrom peach stones with increased activation degree were investigated. CO2Adsorption equi-librium isotherms and differential enthalpy curves were simultaneously measured at 300 Kusing a Tian-Calvet microcalorimeter coupled to an adsorption manometric setup. Tem-perature programmed decomposition experiments were used to assess density of oxygenfunctional groups and determine the impact of surface chemistry on CO2adsorption capac-ity. Computer based theoretical calculations were also performed to attempt to predict theadsorption enthalpy profiles. The most activated sample (Xp = 0.90) has an average adsorp-tion enthalpy which is approximately 8 kJ/mol lower than that of the non-activated samplescarbonized under the same conditions. The combination of techniques enabled a betterunderstanding of the pore filling regimes with increasing coverage, since the use of CO2asa probe gas allows accessing small pores, which otherwise would not be identified from N2isotherms at 77 K. The oxygen content on the carbon surface decreased almost 80% with theincreasing degree of activation and did not influence in the CO2adsorption. Besides provid-ing information about carbon chemistry, CO2adsorption calorimetry can also be successfullyapplied to the screening of carbons intended for CO2capture.