Preparation of porous carbon materials from black liquor lignin and its utilization as CO2 adsorbents

Lignin-based porous carbon materials are estimated as promising CO2 capture adsorbents with thanks to their charateristics as abundant distribution, low-cost preparation and high stability. In this work, a series of porous carbon materials were synthesized from the pulping waste (black liquor lignin) through chemical activation and template method. The morphological structure, porosity and surface chemical properties of the obtained porous carbon materials identified by SEM, XRD, Raman, BET and XPS were highly influenced by the synthesis methods. The porous carbon material prepared by KOH activation (C-BLL-KOH) possessed the most disorder carbon structure, along with the largest BET surface area up to 1336.5 m2/g and the highest microporosity accounting for 93.2% of the total pore volume, which is beneficial for capturing CO2. The sulfur-contained functional groups in chemically-activated carbon materials were dominated by oxidized sulfur species and oxygen element was mainly in the form of hydroxyl groups. CO2 adsorption performance of these lignin-based porous carbon materials was carried out at different temperatures (0 °C, 25 °C and 50 °C) to investigate the effect of synthesis method. The most remarkable CO2 capture capacity was achieved for C-BLL-KOH, which was up to 5.20 mmol/g at 0 °C, 3.60 mmol/g at 25 °C and 2.23 mmol/g at 50 °C at a CO2 partial pressure of 100 kPa. This result suggested the KOH activation was an effective route to convert black liquor lignin to porous carbon materials as potential absorbents for CO2 capture.