Hydrogen Production from Ethanol Reforming by a Microwave Discharge Using Air as a Working Gas

Hydrogen production from ethanol reforming using microwave plasmas has great potential. In this study, a microwave plasma torch is used as a plasma source. Air is used as a discharge gas to generate the plasma. Ethanol and air are mixed and injected directly into the plasma reaction zone in a vortex flow. The effects of the oxygen-to-ethanol molar ratio (O₂/Et), ethanol flow rate, and absorbed microwave power on the reforming results are investigated. When the O₂/Et exceeds 0.9, ethanol is completely converted. The hydrogen selectivity is the largest when the O₂/Et is 1.1, which is about 66.5%. The maximum hydrogen production rate is 2.19 mol(H₂)/mol(C₂H₅OH). The best carrier gas residence time is 0.64-0.81 s. An appropriate increase in the ethanol flow rate can improve the ethanol conversion rate and energy efficiency while reducing the hydrogen selectivity and hydrogen yield, so the ethanol flow rate should not exceed 42.1 mL/min. The cost of hydrogen production is minimum [$3.66/kg(H₂)] when the ethanol flow rate is 42.1 mL/min. The positive effect of the absorbed microwave power on the reforming reaction is significant, but too much microwave power also reduces energy efficiency. The optimum experimental conditions are an O₂/Et of 0.9, an ethanol flow rate of 42.1 mL/min, and an absorbed microwave power of 700 W. The maximum energy yield is 861.91 NL(H₂)/kWh at an absorbed microwave power of 700 W. The main reforming products are H₂, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₁₀n, and C₄H₁₀i. The content of C2 or higher hydrocarbons is considerably low. Almost no deposited carbon is generated in the experiment, which means that the design of the reforming system is effective in suppressing carbon deposition.