Powerful VUV radiation from low-pressure plasma for cellulose depolymerization (L2-70117)

Project Leader: Prof. Dr Miran Mozetič (Jozef Stefan Institute)

Depolymerization of cellulose is the initial step in the production of bio-ethanol. Depolymerization should enable partial decomposition of cellulose into water-soluble products. Water-soluble products are mono and some oligosaccharides. The next step is to decompose water-soluble products into sugars, which are then fermented into ethanol using standard fermentation. For the initial step, various procedures have been developed worldwide, but they have certain limitations, particularly high cost and/or ecological unsuitability. The limitations could be reduced by using gaseous plasma, which is the key task of this project.

There is little literature on the kinetics of polysaccharide degradation by gaseous plasma. All authors agree that the method is promising. Although treating cellulose with classical atmospheric plasma results in a high degree of depolymerization, the authors report a long-term treatment of approximately 1 hour. However, some authors managed to achieve good water solubility of degradation products by using low-pressure plasma, which is an abundant source of energetic particles, such as VUV photons and fast electrons. In this case, processing times of a few seconds to minutes are required, which is promising for further research on the utility of gas plasma as the first step in bio-ethanol synthesis. Energetic particles break bonds in cellulose, and their penetration depth is significantly greater than the penetration depth of plasma radicals, which are created by atmospheric plasma.

Within this proposed project, we want to elaborate on the mechanisms and determine the reaction probabilities. It seems that the treatment of cellulose with photons in the range of the photon energy from about 6 to 10 eV causes breaking bonds in the cellulose chains and water molecules, and the dangling bonds are occupied with H atoms or OH radicals to form oligo/monosaccharides, which are soluble in water at ambient conditions (room temperature, almost neutral pH).