Activated olive mill waste-based hydrochars as selective adsorbents for CO2 capture under postcombustion conditions

Abstract

Porous carbons are considered to be promising sorbents for carbon capture and sequestration. As precursors, the use of biomass materials has acquiring special interest due to its low cost and high availability. Among all the possibilities to convert low-value biomass into these interesting sorbents, hydrothermal carbonization has demonstrated several advantages such as lower energy consumption over pyrolysis. In this work, activated hydrochars using two-phase olive mill waste as precursor have been prepared through physical and chemical activation using CO2 and KOH, respectively. Additionally, with the aim to study the influence of the nitrogen on their adsorption capacity, N-doped adsorbents have been prepared through a one-step hydrothermal carbonization. The behaviour of these adsorbents has been studied in terms of CO2 uptake capacity at an absolute pressure of 15 kPa and temperatures of 0, 25 and 75 °C, apparent selectivity towards CO2 over N2, and isosteric heat of adsorption. Among all these samples, the physically activated hydrochar appears to be the best due to its higher CO2 uptakes, adsorption rates and values of selectivity at 25 °C. Therefore, considering these results, doping these materials with nitrogen does not appear to enhance their adsorption properties, contrary to what some authors have previously reported.