Hydrogen production optimization from methanol partial oxidation via ultrasonic sprays using response surface methodology and analysis of variance

Hydrogen production via partial oxidation of methanol (POM) in an ultrasonic spray system was studied experimentally, using an h-BN-Pt/Al2O3 catalyst with ultra-low Pt contents (0.2 wt%). The effects of oxygen-to-methanol (O2/C) ratio, methanol flow rate, and gas hourly space velocity (GHSV) of air and carrier gas on H2 yield were examined. Compared to conventional spray systems, the ultrasonic spray system could produce more uniformly dispersed methanol and thus further enhance the POM reaction. The results showed a higher O2/C ratio (0.8) enhanced the POM, which poses higher CH3OH conversion, higher reaction temperature, and lower CO and CH4 productions. The CO2 concentration was mainly affected by GHSV and CH3OH flow rate. A higher GHSV led to a quicker retention time for the reactants in the catalyst bed, and a lower CH3OH flow rate deteriorates the CO2 concentration. Based on the Box Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA), the optimal operating conditions are found to be O2/C ratio = 0.8, CH3OH flow rate = 0.7 mL min−1, and GHSV = 10 000 h−1. Combining these conditions, the predicted maximum H2 yield is 1.635 mol‧(mol CH3OH)−1 which is close to the experimental value of 1.646 mol‧(mol CH3OH)−1. The RSM and ANOVA not only resulted in a quadratic response surface regression model and significant regression coefficients but also indicated CH3OH flow rate being the primary factor.