Synthesis and Characterization of Carbonaceous Materials from Saccharides (Glucose and Lactose) and Two Waste Biomasses by Hydrothermal Carbonization

Carbonaceous particles are synthesized under hydrothermal conditions using two waste biomasses (olive oil waste and hazel nutshell) and saccharides (glucose and lactose). A stainless steel autoclave with 75 mL of capacity was used to apply the hydrothermal carbonization (HTC) process to the starting materials stated above. In the experiments, 2.5 g of sample dispersed in 50 mL of deionized water is subjected to HTC at 180 °C for 4 h. H/C and O/C ratios for the chars were found to be more similar to the lignite than those of the starting materials. The heating values for the chars were found to be higher as compared to that of the feedstocks. FTIR investigations of the chars reveal that biochars of saccharides have different chemical structures compared with glucose and lactose, while biochars of waste biomasses are similar chemical nature with their starting materials. Hydroxymethylfurfural (HMF), phenol, acids, and aldehyde contents of aqueous phases were also determined. Solid-state ¹³C CP/MAS NMR analysis of the chars gave hints about the formation mechanism of sphere-structured biochars. Two different formation mechanisms for the biochars of waste biomasses and saccharides were proposed according to solid-state ¹³C CP/MAS NMR analysis results. The structure of biochar obtained from glucose and lactose involved furanic chains, while the biochars from olive oil waste and hazel nutshell have mainly aromatic structure.