Fig. 1. Schematic diagram of Raman spectrum analysis system

Fig. 2. An image of a sample (5 Wt% glycine solution) sealed in fused silica capillary reactor

Fig. 3. Raman spectrum of 5 Wt% glycine aqueous solution at room temperature

Fig. 4. The characteristic Raman peak of glycine, ν (C—C), changes with time at different temperatures
(a): 270 ℃; (b): 280 ℃; (c): 290 ℃

Fig. 5. The characteristic Raman peak of glycine, ν(C—N), changes with time at different temperatures
(a): 270 ℃; (b): 280 ℃; (c): 290 ℃

Fig. 6. The characteristic Raman peak of glycine, ν_as(COO^-), changes with time at different temperatures
(a): 270 ℃; (b): 280 ℃; (c): 290 ℃

Fig. 7. The intensity of characteristic Raman peaks of glycine change with time
(a): ν(C—C); (b): ν(C—N); (c): ν_as(COO^-)

Fig. 8. Raman spectra of 5 Wt% glycine aqueous solution before and after reaction
a: The spectrum of glycine solution at room temperature before reaction; b—d: The spectra of reactant after reaction at different temperatures: b: 270 ℃, c: 280 ℃, d: 290 ℃

Fig. 9. ln(I₀/I_t)~t fitting curve of C—C stretching Raman peak at different temperatures. The quadratic coefficient is denoted the rate for its hydrothermal liquefaction

Fig. 10. lnk-1/RT fitting curve of C—C stretching Raman peak. The slope of the curve is the activation energy for its hydrothermal liquefaction