Oxidation of Polyvinyl chloride) Powder by Molecular Oxygen in Alkaline Solutions at High Temperatures

Oxidation of poly(vinyl chloride) (PVC) with oxygen was carried out in NaOH solutions in the range of NaOH concentration (1~25 mol/kg-H₂O), temperature (423~533 K) and the partial pressure of oxygen (1~10 MPa). The oxidation of PVC proceeded noticeably above 423 K. The major products of the oxidation were oxalic acid and CO₂. A small amount of malonic acid was also found as a minor product. The rate of formation of both oxalic acid and CO₂ increased with raising temperature and increasing the partial pressure of oxygen, but decreased with increasing NaOH concentration. However, the yield of oxalic acid increased with increasing NaOH concentration until 15 mol NaOH/kg-H₂O. The yield of CO₂ attained 50 C% in the initial stage of the oxidation, thereafter it remained almost constant. The maximum yield of oxalic acid and the yield ratio of oxalic acid/CO₂ attained 38.5 C% and 0.76, respectively, without any pretreatment prior to the oxidation. The yield of oxalic acid and CO₂ were 10.6 and 9.8 C% respectively, when 2.0 wt% CuO was added to PVC as a catalyst. The yields of oxalic acid and CO₂ were improved to 45.1 and 5.1 C%, respectively, by pretreatment of sample in air at 473 K for 1 h, prior to oxidation in NaOH solution. Under the present pretreatment conditions, 42.2% of chlorine in the original sample were eliminated as HCl. These results indicated that oxalic acid was preferentially produced to CO₂ adding the catalyst or by the pretreatment.