The upgrading of unconventional oil using methane, the principal component of natural gas, is a promising alternative method to the conventional hydrotreating process, which consumes naturally unavailable H2 at high pressures. Methanotreating is an economically attractive process with abundant and readily available raw materials to accomplish the upgrading of bio-oil and to attain improved oil quality. The application of methane as the H donor avoids the energy consumption and CO2 rejection during the reforming of methane to produce H2. More product oil is also obtained through the incorporation of methane into the product oil. Ag/ZSM-5, Zn/ZSM-5 and Ag-Zn/ZSM-5 have been employed to upgrade bio-oil under methane environment to achieve increased oil yield and H/C molar ratio, suppressed total acid number and unsaturation degree of the product oil. Ag-Zn/ZSM-5 is used to catalyze the methanotreating of heavy oil to attain lower viscosity accompanied with good stability and compatibility, which are critical for the pipeline transportation of heavy oil to downstream refineries. Higher gasoline and diesel fractions, increased H/C molar ratio, lower total acid number are witnessed upon the upgrading in the presence of Ag-Zn/ZSM-5 under methane environment. The mechanism studies practiced in the literature using methods including solid-state NMR and FTIR have revealed at least two reaction pathways, i.e., carbenium pathway and alkyl pathway, to accomplish the activation of methane, which is crucial for the involvement of methane in the following upgrading reaction steps. The reaction thermodynamics and reaction intermediates have also been explored by computational approaches by researchers. These observations and achievements will encourage more researchers to develop more catalyst systems and attain improved catalytic performance in the unconventional oil upgrading using natural gas.
Part of the book: Advances in Natural Gas Emerging Technologies