Mechanisms Involved in Cellulose Depolymerization by Treatment with Energetic Beams

Depolymerized cellulose is a precursor to bioethanol, an attractive solution for the green economy. A method for cellulose depolymerization is treatment with energetic particles that break the bonds between glucose units. The scientific literature on depolymerization by energetic electrons is reviewed and analyzed. If all electron energy is spent on complete depolymerization to fermentable sugars, the theoretical dose is estimated to be about 1000 kGy. The experimental results, however, indicate rather poor energy efficiency, which is attributable to several factors. Regardless of the cellulose source, experimental setup, and electron energy, the results reported by various teams fit a general curve. The degree of polymerization drops by an order of magnitude after receiving the dose of about 70 kGy. The general curve is explained by secondary effects, including the generation of X-rays with favorable penetration depth, which produce rather low-energy electrons and photons useful for scission of the β(1→4)-glycosidic bonds. The solubility of depolymerization products in water increases with dose and reaches 10% at a few 100 kGy. Depolymerization to simple oligosaccharides or monosaccharides is not feasible due to inadequate selectivity and is energetically too demanding.