¦ ltrate was determined by HPLC using an Aminex BioRad-HPX-87H column and a refractive index detector. The mobile phase was 5 mM H 2 SO 4 , the § ow rate was 0.6 mL/min, and the column temperature was 55 °C. Two parallel assays were performed for each experiment. Electrochemical oxidation of PMo 12 The electrolysis cell was composed of a high-density graphite plate with a serpentine groove, a Na ¦ on 115 membrane, a silicone gasket, a platinum sheet as cathode, and graphite felt as anode. The bipolar plates of the cell were high-density graphite plates with a serpentine § ow channel 2 mm wide, 5 mm deep, and 50 mm long (the total geometry projected area of the channel was 1 cm 2 ), which is schematically illustrated in Fig. 2. The graphite felt was pretreated with concentrated HNO 3 and H 2 SO 4 in a 1:3 volumetric ratio at 50 °C for 30 min. Then, the graphite felt was washed with DI water until the pH of the wash water became neutral, dried at 80 °C, and cut into pieces with the thickness of 5 mm and width of 2 mm. These graphite felt electrodes were ¦ lled into the channel of the anode (Liu et al. 2014a). Diethyl ether was added to the dark blue waste starchâPMo 12 solution after the hydrothermal reaction. PMo 12 was extracted to the upper layer after full shaking (Okuhara 2002; Tian et al. 2010). When the diethyl ether was completely volatilized using rotary evaporator, PMo 12 was dissolved in DI water. The PMo 12 solution was then pumped into the anode, and the phosphoric acid aqueous solution (1 mol/L) was pumped into the cathode side of the cell. A potential of 1 V was applied by an electrochemical workstation for electrooxidation. From the solution, a sample was collected every 1 h and diluted to 1 mmol/L for analysis of the reduction degree of PMo 12 by spectrophotometry. Results And Discussion Analysis of the factors in § uencing the oxidative degradation of WS The factors determining the oxidative degradation of WS include reaction time, temperature, pH of the reaction system, and concentration of reactants (Girisuta et al. 2007; Mukherjee et al. 2016). We conducted single-factor experiments to select the three main factors, i.e., reaction temperature, PMo 12 dosage, and reaction time, in a targeted manner, and obtained the optimal process conditions for determination of the TRS yield. First, the standard curve of this experiment was adjusted to zero with the color reaction solution of DI water as control, and the standard working curve was drawn with the mass fraction of glucose as the abscissa and the absorbance as the ordinate (Fig. 3a). The regression equation was y = 0.0185x + 0.1074 (R 2 = 0.9980), where R 2 is the correlation coe ¨ cient and de ¦ nes the feasibility of the method and the degree of linear relationship. Generally, R 2 > 0.99 ensures an appropriate limit of error. The DNS reagent was used to determine the TRS content in the experiment.
Effect of reaction temperature on TRS and glycolic acid yield
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