Figures (9)  Tables (5)

    • Figure 1. 

      Product separation procedure of HTL process.

    • Figure 2. 

      Product distributions under different HTL processes.

    • Figure 3. 

      Van Krevelen diagrams for (a) MS and (b) bio-oil.

    • Figure 4. 

      Compounds contained in bio-oil obtained by different HTL processes. (a) Distribution of main compounds. (b) Content of nitrogen-containing compounds.

    • Figure 5. 

      XPS spectra of N1s in the solid product from (a) MS, (b) D1, (c) D2, (d) C, (e) S2-I, and (f) S2-II.

    • Figure 6. 

      Distribution of main compounds in aqueous phase products from different HTL processes.

    • Figure 7. 

      TN and TOC concentrations of aqueous phase products from different HTL processes.

    • Figure 8. 

      Nitrogen distribution of HTL products.

    • Figure 9. 

      Nitrogen migration and evolution pathways of ST-HTL (black arrows indicate the reaction pathway of the first stage, yellow arrows indicate the reaction pathway of the second stage, and dashed lines indicate the weakening of the reaction).

    • Feedstock MS
      Elemental analysisa (wt.%) C 45.84
      H 7.51
      N 7.22
      S 0.81
      Ob 38.62
      Proximate analysis (wt.%) Ash 51.79
      VM 45.10
      FCc 3.11
      Moisture (wt.%) 82.70
      Higher heating value (MJ/kg) 19.40
      a Dry ash-free basis; b O% = 100% − C% − H% − N% − S%; c FC% = 100% − Ash% − VM%.

      Table 1. 

      Basic properties of MS

    • HTL process Label Temperature
      (°C)      		 Pressure
      (MPa)      		 Residence
      time (min)
      D-HTL D1 200 12 50
      D2 325 12 50
      CT-HTL C 200/325 12 20/30
      ST-HTL S1 200(I)/325(II) 12 10(I)/40(II)
      S2 200(I)/325(II) 12 20(I)/30(II)

      Table 2. 

      The experimental parameters for HTL of MS used in this work

    • HTL process Elemental composition (wt.%) Atomic ratio Higher heating
      value (MJ/kg)      		 Energy recovery
      rate (%)
      C H N S Oa H/C O/C N/C
      D1 70.24 9.61 4.10 1.17 14.88 1.642 0.159 0.050 34.92 9.68
      D2 74.99 8.60 5.33 1.19 9.89 1.376 0.099 0.061 35.98 32.20
      C1 74.93 8.95 5.50 1.26 9.36 1.433 0.094 0.063 36.56 28.90
      S1-I 69.48 10.08 3.71 0.78 15.95 1.741 0.172 0.046 35.11 5.10
      S1-II 72.60 9.52 3.36 0.98 13.54 1.574 0.140 0.040 35.81 15.27
      S2-I 69.58 9.55 4.18 0.99 15.70 1.647 0.169 0.052 34.45 7.80
      S2-II 75.51 9.45 3.42 0.88 10.74 1.502 0.107 0.039 37.18 15.15
      a Calculated by difference method: O% = 100% – C% – H% – N% – S%.

      Table 3. 

      Elemental compositions, atomic ratios, higher heating values and energy recovery rates of bio-oil obtained via different HTL processes

    • HTL process Elemental composition (wt.%) Atomic ratio Proximate analysis (wt.%)
      C H N S Oa H/C O/C N/C Ash VM FCb
      D1 15.27 2.08 1.72 0.21 7.90 1.6346 0.3880 0.0965 72.82 26.19 0.99
      D2 10.6 1.91 0.95 0.23 1.53 2.1623 0.1083 0.0768 84.78 14.63 0.59
      C 9.94 1.14 0.9 0.28 3.02 1.3763 0.2279 0.0776 84.72 14.80 0.48
      S1-I 15.03 2.17 1.78 0.23 9.72 1.7325 0.4850 0.1015 71.07 28.28 0.65
      S1-II 7.88 1.05 0.71 0.08 3.94 1.5990 0.3750 0.0772 86.34 13.34 0.32
      S2-I 13.92 1.93 1.44 0.28 10.58 1.6638 0.5700 0.0887 71.85 28.05 0.10
      S2-II 8.47 1.16 0.65 0.23 3.74 1.6434 0.3312 0.0658 85.75 14.20 0.05
      a O% = 100% – C% – H% – N% – S% – Ash%; b FC% = 100% – Ash% – VM%.

      Table 4. 

      Elemental compositions, atomic ratios and proximate analysis results of solid products from different HTL processes

    • N species MS D1 D2 C S2-I S2-II
      Inorganic-N 6.3% − − − − −
      Ammonia-N 93.7% 25.2% 13.6% 25.7% 41.1% 23.6%
      Quaternary-N − 21.0% 27.1% 30.1% 26.0% 26.4%
      Pyrrole-N − 48.8% 41.8% 38.0% 27.6% 44.3%
      Pyridine-N − 5.0% 17.5% 6.2% 5.2% 5.7%

      Table 5. 

      Relative contents of nitrogen-containing functional groups in ms and solid products under different conditions