Operational studies related to gas hourly space velocity (GHSV) and feed compositions were carried out in this work aiming to search adequate H2/CO ratio destined to GTL processes as well as high CO2 conversion, considering that it competes for the same active sites for water adsorption.
In these studies, Ni (10% wt) supported on MgAl2O4 spinel promoted with CeZrO2 (Ce/Zr molar ratio= 4) was employed and the catalyst was activated in situ under H2 flow at 750oC. The catalytic tests were carried out at 750oC and atmospheric pressure, for 300 minutes. The ratio (nCO2+nH2O+ 2.nO2)/nCH4 was kept at 1 for any feed composition, where ni represents the reactant molar flow rate. The CH4 volumetric flow rate was 73.4 NmL.min-1 for any feed composition. Water was pre-heated before reaching the reactor. The gases effluent composition was analyzed in a gas chromatograph, which was equipped with two Porapak-N® and a 13X molecular sieve columns. Four space velocities were evaluated: 3.0, 4.0, 5.3 and 10.5 mol.gcat-1.h-1.
This study showed that below 4 mol.gcat-1.h-1 and under stoichiometric feed (3 CH4:1 CO2: 1H2O: 0.5 O2), the reactants conversion (CH4= 77% and CO2=54%) did not change, while CH4 and CO2 conversions decreased up to 58% and 33%, respectively, as GHSV increased up to 10.5 mol.gcat-1.h-1. Thus, the feed composition studies were made using a GHSV of 4 mol.gcat‑1.h‑1 and varying the O2/CO2 and H2O/CO2 molar ratios (0, 0.17 and 1.5).
Increasing either O2/CO2 or H2O/CO2 from 0 to 1.5, the CO2 conversion decreases from 73% to 30%, despite increasing H2/CO ratio, once the partial oxidation and steam reforming of methane increase the H2 production under higher O2 and H2O contents, respectively. O2 consumption was always complete at any reaction condition, due to O2 affinity to active sites. The O2/CO2 ratio of 0.17 in the feed was considered appropriate for operation, once the achieved conversions were 79% for CH4 and 60% for CO2, while the H2/CO ratio was 1.75.
See more of this Group/Topical: General Submissions