Figure 1: Schematic diagram of device used in the experiment. 1. Low pressure gradient mixer; 2. High-pressure metering pump; 3. Electric stove; 4. Spiral tubular reactor; 5. PID controller; 6. Cooling device; 7. Back pressure valve; 8. Pressure gage; 9. Gas-liquid separator; 10. Mass flowmeter; 11. Nitrogen cylinder; 12. Electronic dehumidifier; 13. NDIR detector; 14. Computer.