Hydrolyyisin ja vaalennuksen olosuhteiden vaikutus selluloosa kuitujen erottamisen tehokkuuteen käytetyistä kahvinpuruista

This literature review focuses on cellulose extraction as a method to valorize food waste, especially spent coffee grounds. Coffee is one of the most consumed beverages worldwide, and its brewing generates annually almost six million tons of spent coffee grounds (SCG). Typically, cellulose is extracted from biowaste utilizing a multi-step process, which includes acid hydrolysis, alkaline hydrolysis and bleaching. These steps are required to isolate cellulose from tightly bonded hemicellulose and lignin. In previously published studies cellulose has been extracted from various waste sources. However, little studies have been published about cellulose extraction from spent coffee grounds. Different types of biomasses contain cellulose, lignin and hemicellulose in varying proportions, which affect the reaction condition in the extraction process. For example, the concentration, time, and temperature can affect the purity and crystallinity of cellulose. In addition to the literature review, this thesis contains an experimental part where cellulose is extracted and characterized. Cellulose was extracted from the SCGs with a three-step process: first acid hydrolysis with nitric acid (HNO_3), followed by alkaline hydrolysis with sodium hydroxide (NaOH) and bleaching with sodium hypochlorite (NaClO). After the first cellulose extraction, temperatures and concentrations were modified to optimize the extraction from spent coffee grounds. Altogether, the extraction process was repeated three times. The extracted cellulose was characterized with a Fourier transform infrared (FTIR) spectra, an x-ray diffraction (XRD) and a scanning electron microscope (SEM). The results from characterization indicate that cellulose was successfully extracted from the SGCs. The extracted cellulose fibers contain both crystalline and amorphous regions and some residual lignin was present in the samples.