It was hypothesized that activated carbons (ACs) prepared from hydrochar could be dispersed in solvents under certain conditions. The crude hydrochar formed by the hydrothermal carbonization (HTC) of glucose and was purified by dialysis. Dried dispersions of hydrochar were chemically activated with potassium bicarbonate (KHCO₃) at temperatures of 750–800 ​°C in N₂. The AC prepared from a freeze-dried dispersion of hydrochar could be dispersed in ethanol as 500 nm-sized colloids. It was noted that on regular drying of the hydrochar dispersions, macroscopically large, long, curved, and thin rods of hydrochar formed in the vials. The rods comprised colloidally-packed spherical particles. The rods may have formed from cracked and fractured colloidal coatings and detached from the wall of the vials. This conclusion was supported by analysing the structural features of the rods. The macroscopic shapes were retained on the chemical activation when the hydrochar precursor had been pyrolyzed in N₂ before activation. The ACs had specific surface areas of up to 1800 ​m²/g, and CO₂ uptake levels of up to 7.1 ​mmol/g at 0 ​°C and 101 ​kPa.

The CO₂ and N₂ adsorption on small-pore zeolite |Na_12-xK_x|-A was hypothesized to be affected by the ion exchange sequence used for the zeolite preparation. Zeolites were prepared by ion exchange of a commercially available zeolite |Na₁₂|-A (4A) and a zeolite |K₁₂|-A (3A) composition prepared from zeolite 4A. The CO₂ and N₂ adsorption properties were studied experimentally, and the binary CO₂-over-N₂ selectivity was estimated from single-component adsorption data using the apparent Henry's law coefficients. It was observed that the level of CO₂ adsorption was reduced by increasing the K content for both series of zeolite NaKA. Zeolite |Na_12-xK_x|-A-from-4A had the highest CO₂ adsorption capacity (at 1 atm and 273 K) for a given K content. At low K content, zeolite |Na_12-xK_x|-A-from-3A had the highest CO₂-over-N₂ selectivity. At an intermediate K content, the zeolites prepared from 4A had the highest selectivity. These differences show that non-equilibrium processes during the ion exchange are important for the CO₂ and N₂ adsorption properties of the derived zeolites. As of now, we refrain from speculating whether they relate to the detailed positioning of K⁺ and Na⁺ cations in the local structure of the zeolite or to mass-transport-related concentration gradients of the cations in the structure. Irrespectively, it was observed that the ion-exchange sequence affects the CO₂ and N₂ adsorption properties of the zeolites, which could be of general importance when it comes to the tuning of the properties of cation-rich zeolites.

The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.

Lignin is naturally abundant and a renewable [GRAPHICS] precursor with the potential to be used in the production of both chemicals and materials. As many lignin conversion processes suffer from a significant production of solid wastes in the form of hydrochars, this study focused on transforming hydrochars into magnetic activated carbons (MAC). The hydrochars were produced via hydrothermal treatment of lignins together with formic acid. The activation of the hydrochars was performed chemically with KOH with a focus on the optimization of the MACs as adsorbents for CO2. MACs are potentially relevant to carbon capture and storage (CCS) and gas purification processes. In general, the MACs had high specific surface areas (up to 2875 m(2)/g), high specific pore volumes, and CO2 adsorption capacities of up to 6.0 mmol/g (I atm, 0 degrees C). The textual properties of the MACs depended on the temperature of the activation. MACs activated at a temperature of 700 degrees C had very high ultramicropore volumes, which are relevant for potential adsorption-driven separation of CO2 from N-2. Activation at 800 degrees C led to MACs with larger pores and very high specific surface areas. This temperature-dependent optimization option, combined with the magnetic properties, provided numerous potential applications of the MACs besides those of CCS. The hydrochar was derived from eucalyptus lignin, and the corresponding MACs displayed soft magnetic behavior with coercivities of <100 Oe and saturation magnetization values of 1-10 emu/g.

Activated carbons were produced by chemical activation of hydrothermally carbonized (HTC) beer waste, withphosphoric acid as the activation agent. The activation was optimized within a full factorial design, using the outcome of 19different experiments. Four different parameters (concentration of the acid, activation time, activation temperature, flow rate)were analyzed with respect to their influence on the median pore size. The concentration of H3PO4 had a strong positive effecton the median pore size. The specific surface areas of these activated carbons were ∼1000 m2/g, which compared wellcommercially available activated carbons. The activated carbons had mostly large pores with a size of ∼4 nm, and a significantamount of acid surface groups. Scanning electron microscopy (SEM) revealed that the morphology of the HTC beer wastechanged significantly after the chemical activation. The capacity to adsorb methylene blue from aqueous solutions was 341 mg/g,for one of the activated carbons at pH 7. A Langmuir model described the uptake of the dye quite well, which suggested ahomogeneous adsorption of Methylene Blue (MB).

Particles of iron oxide (Fe3O4; 20-40nm) were embedded within activated carbons during the activation of hydrothermally carbonized (HTC) biomasses in a flow of CO2. Four different HTC biomass samples (horse manure, grass cuttings, beer production waste, and biosludge) were used as precursors for the activated carbons. Nanoparticles of iron oxide formed from iron catalyst included in the HTC biomasses. After systematic optimization, the activated carbons had specific surface areas of about 800m(2)g(-1). The pore size distributions of the activated carbons depended strongly on the degree of carbonization of the precursors. Activated carbons prepared from highly carbonized precursors had mainly micropores, whereas those prepared from less carbonized precursors contained mainly mesopores. Given the strong magnetism of the activated carbon-nano-Fe3O4 composites, they could be particularly useful for water purification.

Hydrothermally treated biomass could not only be used as a fuel or a fertilizer but it can also be refined into high-value products. Activated carbons are one of those. In the studies of this thesis, four different hydrothermally carbonized (HTC) biomasses, including horse manure, grass cuttings, beer waste and biosludge, have been successfully made into activated carbons. The activated carbon materials were in the forms of powdered activated carbons, powdered composites of activated carbon and iron oxide nano-crystals, and activated carbon discs.

The HTC biomasses and the activated carbons were characterized and analyzed using several methods. The biomasses were carbonized to different extent during the hydrothermal treatment, which depended on the different natures of the biomasses. The HTC biomasses were activated into powdered activated carbons by both physical activation, using CO₂, and by chemical activation, using H₃PO₄. Full factorial design matrices were applied to design experiments and study the influence of different parameters used during both physical and chemical activation. Activated carbons with embedded iron oxide nanoparticles were synthesized through hydrothermal carbonization followed by CO₂ activation. These composites had high surface areas and showed a strong magnetism, and the powders could be separated from liquid phase by applying a magnetic field. Strong and dense activated carbon discs were also prepared from powdered HTC beer waste by pulsed current processing (PCP) and a subsequent CO₂ activation procedure. The potential for carbon dioxide separation from nitrogen, and methylene blue adsorption in aqueous solution, were assessed for the powdered activated carbons produced from HTC biomasses. They showed good performance in both applications. 

Strong and dense activated carbon discs (ACDs) were synthesized and studied. The discs were produced in a multistep manner from a precursor based on hydrothermally treated beer waste (HTC-BW). The precursor was processed by pulsed current processing (PCP) into ACDs. These discs were activated by physical activation in CO₂ at an elevated temperature. The ACDs had surface areas of ∼500 m²/g and contained significant amounts of micro-, meso-, and macropores. The effect on the temperature during the PCP and the presence of tar in the precursor were studied with respect to the properties of the discs. The ACDs had strengths up to 7.2 MPa with densities up to 1.4 g/cm³. The density is the highest reported for discs of activated carbon.

Activated carbons prepared from hydrothermally carbonized (HTC) waste biomass were studied with respect to the adsorption of carbon dioxide. The physically activated carbons (PAC) exhibited a large adsorption of CO2 of 1.45 mmol/g at a small partial pressure of CO2 (10 kPa and a temperature of 0 degrees C). These PACs were prepared by activation in a stream of CO2 and had significant amounts of ultramicropores, which were established by analyzing the adsorption of CO2 with a density functional theory. The uptake at such low pressures of CO2 is of most importance for an adsorption-driven CO2 capture from flue gas at large power stations, as it is difficult to imagine a pressurization of the flue gas. The capacities to adsorb CO2 of the different activated carbons were compared with both the micropore volumes as established by N-2 adsorption, and the ultramicropore volumes as established by CO2 adsorption. The ultramicropore volume is of crucial importance for the capture of CO2 from flue gas. PAC from HTC grass cuttings and from horse manure had the largest ultramicropore volumes. In general, the PAC showed excellent cyclability of adsorption/desorption of CO2 and a minimal capacity loss after subsequent cycles. In addition, the PAC showed a rapid adsorption of CO2. Both characteristics are essential for the eventual use of such PACs in the adsorption driven separation of CO2 from flue gas. A chemically activated carbon (CAC) was prepared by treating hydrothermally carbonized beer waste with H3PO4 and a heat treatment in a flow of N-2. This CAC showed a significant amount of mesopores in the range of 5 nm, in addition to micropores. The apparent selectivity for the activated carbons for CO2-over-N-2 adsorption was determined at 0 degrees C and 10 kPa.