Adjusting Process Variables in Methane Tri-reforming to Achieve Suitable Syngas Quality and Low Coke Deposition

Tri-reforming of methane (TRM) combines steam reforming, dry reforming, and partial oxidation of CH4 in a single reactor. The H2/CO product ratio usually ranges from 1.5 to 2.5, which makes the TRM process highly versatile, since the synthesis gas quality can be altered by simply changing the feed composition, hence permitting a wide range of applications. A H2/CO ratio of 2 is usually desired to produce liquid fuels such as methanol and dimethyl ether (DME). In this work, operational studies of the influence of the gas hourly space velocity (GHSV) and the feed composition were carried out, with the aim of obtaining an H2/CO ratio suitable for downstream processes, as well as to achieve satisfactory CO2 conversion, which is vital for CCSU (CO2 capture, storage, and utilization) strategies. The catalyst used for these studies was nickel supported on MgAl2O4 spinels promoted with CeZrO2 (Ce/Zr molar ratio = 4). Reaction tests were performed changing the O2/CO2 and H2O/CO2 molar ratios in the reactor feed, keeping the GHSV constant at 2.95 mol·gcat –1·h–1. Each test was run for 5 h at 750 °C and atmospheric pressure. The increase of the O2/CO2 molar ratio from 0 to 1.5 in the feed reduced the amount of coke by about 30-fold, while increasing the H2O/CO2 molar ratio from 0 to 1.4 led to only an 8-fold decrease of carbon deposition, which showed that increasing the supply of oxygen was more effective for reducing the carbon deposition, compared to increasing the amount of water steam. The feed composition CH4/CO2/H2O/O2/N2 = 3:1.5:1.4:0.25:1 (O2/CO2 = 0.17) could be considered the most stable operational condition among those studied in this work, producing syngas with H2/CO ∼ 1.7 and significant CH4 and CO2 conversions (77 and 60%, respectively).