Decomposition of cellulose by plasma in salt solutions

Plasmas in salt solution are able to generate active species and can be used to decompose organic compounds. In this study, plasmas driven by AC or DC power sources in various saline-solutions are used to decompose cellulose. The solutions used include NaCl, NaNO₃, NaOH, Zn(NO₃)₂, ZnCl₂, CaCl₂, Ca(NO₃)₂, and Ca(OH)₂. The electrode at which the plasma is ignited is a platinum wire 0.5 mm in diameter covered by a glass tube while the grounding electrode is a bare platinum wire of the same diameter. The plasma voltage and current waveforms are monitored using electrical probes. Optical emission spectrometer is used to monitor the time-averaged emission spectra emanating from the plasma. The conductivity and the pH of the solution in which the plasma is ignited are monitored using commercially available meters. The decomposed products are identified and quantified using high performance liquid chromatography. It is shown that the plasma is able to effectively decompose cellulose into smaller molecules, such as glucose, fructose, glycolic acid, and several unknown products. The decomposition efficiency increases with the salt concentration. When different salt solution is used, it shows significantly different decomposition efficiencies and decomposed products. This observation strongly suggests that the decomposition process using plasmas in salt solution is chemical in nature and obtaining reaction selectivity is highly possible. Preliminary studies show that Ca(OH)₂ and ZnCl₂ solutions can most effectively decompose cellulose under optimized conditions.