Biorefinery for the Production of Lowand HighGrade Activated Carbon from forestry wastes, maize residues and biogas digestate

Publishable summary: 

Waste management of biomass has become a critical issue in terms of global warming and contamination of Earth resources. The slash and burn of maize wastes or the uncontrolled burning of forestry wastes cause wildfires, smog and greenhouse gases. Another problem is the proper digestate handling from biogas plants. This biomass has a very high water content, which reduces dramatically the energetic efficiency of incineration plants when burned. Also, the amount produced is too high to use it as organic fertilizer. A biorefinery is proposed in this project that will take advantage of these lowcost materials to produce high quality activated carbon (AC). AC is used in a many applications that require high surface areas. Lowgrade activated carbon (LGAC) is used as adsorbent of impurities in liquid or gaseous media and as carbon molecular sieve to recover methane (CH4) from biogas. Highgrade activated carbons (HGAC) can replace expensive nanomaterials in energy storage systems like supercapacitors. This project will concentrate on these three applications. The AC production will occur in two stages: carbonization and activation. For the first one, maize and forest residues will be pyrolyzed and the biogas digestate will be pretreated with hydrothermal carbonization (HTC). The activation process will depend on the preferred type of AC: physical activation for LGAC and chemical activation for HGAC. The energy demand of the biorefinery will be partially covered from electricity produced from burning the pyrolysis gases and the methane from the biogas process. The production of LGACs and HGACs from biomass residues in a selfsustainable biorefinery is an ecological way to produce high-quality and technologically relevant material without impairing the food production or polluting the environment.