Figures (16)  Tables (11)

    • Figure 1. 

      Synthesis of propylene glycol monomethyl ether and side reaction equation.

    • Figure 2. 

      Schematic diagram of the reaction device.

    • Figure 3. 

      Gas phase curves of propylene glycol monomethyl ether and PO solutions: (a) propylene glycol monomethyl ether solution, (b) PO solution.

    • Figure 4. 

      (a) Standard curve of propylene glycol monomethyl ether; (b) standard curve of PO.

    • Figure 5. 

      Reaction pathways and enthalpy of reaction.

    • Figure 6. 

      The impact of various factors on yield and the maximum pressure of the system: (a) reaction temperature; (b) alcohol-to-alkane ratio; (c) catalyst concentration; (d) feeding rate.

    • Figure 7. 

      Three-dimensional response plot of PGME yield: (a) X1 and X2; (b) X1 and X3; (c) X2 and X3.

    • Figure 8. 

      Three-dimensional response diagram of the maximum pressure in the system: (a) X1 and X2; (b) X1 and X3; (c) X2 and X3.

    • Figure 9. 

      Heat release behavior under different temperature control modes: (a) isothermal mode; (b) isoperibolic mode.

    • Figure 10. 

      Exothermic characteristics at different reaction temperatures.

    • Figure 11. 

      Exothermic characteristics under different feeding rates.

    • Figure 12. 

      Exothermic characteristics under different catalyst concentrations.

    • Figure 13. 

      Exothermic characteristics under different alcohol-to-alkane ratios.

    • Figure 14. 

      Infrared spectra of samples: (a) methanol; (b) PO; (c) propylene glycol monomethyl ether.

    • Figure 15. 

      Reaction process combined with online infrared spectrum.

    • Figure 16. 

      The adiabatic calorimetric diagram of the product.

    • Chemical CAS No. Molecular formula Purity (%) Source
      MeOH 67-56-1 CH4O 99.9 Aladdin
      PO 75-56-9 C3H6O 99.5 Macklin
      KOH 1310-58-3 KOH 90 Sinopharm
      n-hexane 110-54-3 C6H14 99 Macklin
      PGME 107-98-2 C4H10O2 99 Macklin

      Table 1. 

      Chemicals used in the experiment.

    • Experimental group Reaction temperature (°C) Catalyst concentration (%) Alcohol-to-alkane ratio Feeding rate (mL/min)
      a 100 0.5 3 20
      110 0.5 3 20
      120 0.5 3 20
      130 0.5 3 20
      b 100 1 2 20
      100 1 3 20
      100 1 4 20
      100 1 5 20
      c 100 0.5 3 20
      100 1 3 20
      100 1.5 3 20
      100 2 3 20
      d 120 1 4 20
      120 1 4 30
      120 1 4 40
      The catalyst concentration is expressed as a percentage of the total mass.

      Table 2. 

      Single-factor controlled experimental group design.

    • FactorsSymbolLevels
      −101
      Tr (°C)X1100110120
      Catalyst concentration (%)X20.511.5
      Alcohol-to-alkane ratioX3234

      Table 3. 

      Box-Behnken experimental design.

    • Group Tr (°C) Catalyst concentration (%) Alcohol-to-alkane ratio Feeding rate (mL/min) Yield (%) Pmax (bar)
      a 100 0.5 3 20 85.47 3.7
      110 0.5 3 20 86.86 4.53
      120 0.5 3 20 82.27 6.02
      130 0.5 3 20 80.69 7.79
      b 100 1 2 20 81.96 3.4
      100 1 3 20 85.26 3.41
      100 1 4 20 87.57 3.43
      100 1 5 20 88.98 3.47
      c 100 0.5 3 20 85.47 3.7
      100 1 3 20 86.26 3.41
      100 1.5 3 20 82.45 3.38
      100 2 3 20 75.48 2.94
      d 120 1 4 20 79.47 5.92
      120 1 4 30 79.06 6.23
      120 1 4 40 77.6 6.5

      Table 4. 

      Results of single-factor experiment.

    • Run Independent variables Dependent variables
      X1 X2 X3 Y1 Y2
      Experimental value Predictive value Experimental value Predictive value
      1 110 1 3 86.12 86.12 4.41 4.47
      2 110 1 3 87.36 87.36 4.54 4.47
      3 120 1 2 83.72 83.72 5.88 5.84
      4 110 0.5 2 84.94 84.94 4.56 4.57
      5 110 1.5 4 84.32 84.32 4.43 4.42
      6 110 1 3 86.24 86.24 4.49 4.47
      7 100 0.5 3 85.47 85.47 3.70 3.68
      8 100 1 2 81.96 81.96 3.40 3.41
      9 120 0.5 3 82.27 82.27 6.02 6.05
      10 100 1 4 87.57 87.57 3.43 3.47
      11 110 1.5 2 83.43 83.43 4.36 4.38
      12 120 1.5 3 80.06 80.06 5.87 5.89
      13 110 0.5 4 86.95 86.95 4.68 4.66
      14 110 1 3 86.58 86.58 4.40 4.47
      15 110 1 3 86.43 86.43 4.53 4.47
      16 100 1.5 3 82.45 82.45 3.41 3.39
      17 120 1 4 79.47 79.47 5.92 5.91

      Table 5. 

      Experimental results based on Box-Behnken.

    • Factors and responses Objectives Low level High level
      X1 In range 100 120
      X2 In range 0.5 1.5
      X3 In range 2 4
      Y1 Maximize 0 100
      Y2 Minimize 0 10

      Table 6. 

      Boundary condition settings for process optimization.

    • Number Yield of PGME (%) Maximum pressure of the
      system (bar)
      1 87.84 3.62
      2 89.23 3.59
      3 88.67 3.65
      Average 88.58 3.62
      Model predicted value 88.20 3.56
      Relative error 0.43 1.69

      Table 7. 

      Results of process optimization experiments.

    • Temperature control
      mode      		 Tr
      (°C)      		 qr,max
      (W)      		 Pmax
      (bar)      		 ∆H
      (kJ/mol)      		 ∆Tmax
      (°C)      		 Total heat
      release (kJ)
      Isothermal mode 104.62 371.86 3.41 79.25 13.68 369.9
      Isoperibolic mode 112.24 371.65 3.8 71.71 12.24 334.88

      Table 8. 

      Experimental parameters under different temperature control modes.

    • Peak Wavenumber (cm–1) Functional group Affiliation
      Peak 1 1,024 C-O MeOH
      Peak 2 828 ternary monoxide ring vibration PO
      Peak 3 1,111 C-O-C PGME

      Table 9. 

      Intense absorption peaks of substances.

    • ΔTad,r (°C) Severity TMRad (h) Possibility Risk level
      158.47 marginal > 24 negligible 1

      Table 10. 

      Results of the risk matrix assessment.

    • Tp (°C) MTSRr (°C) MTT (°C) TD24 (°C) Class
      100 162.2 102.2 > 350 3

      Table 11. 

      Response risk level assessment.