Developing Novel Heterogeneous Catalysts for the Selective Hydrogenation of Olefins in Light Petroleum Distillates
Abstract
Olefins produced in light petroleum distillates during thermal and catalytic steam cracking processes of bitumen have raised serious concerns regarding the transportation of diluted bitumen. In addition to the problematic issues caused by olefins in refineries, such as fouling, coke formation and catalyst deactivation, Canadian pipeline companies have put stringent specifications for the transportation of diluted bitumen to avoid plugging of pipelines. These specifications set by the Canadian Association of Petroleum Producers (CAPP) require a final olefins content which is less than 1 wt. % in the transported diluted bitumen (dilbit) and a final viscosity less than 350 cP at the desired operating temperature (7.5 o C). This generally requires the use of expensive noble metal catalysts for the selective hydrogenation of olefins and their elimination from light hydrocarbon fractions.
This work aims on testing new inexpensive catalysts for the selective hydrogenation of olefins, which can compete with noble metals. Three novel catalysts: carbides (molybdenum carbide), zeolites (Ni-MFI) and pyroxenes (Ni-AEG) have been tested with model molecules (1-octene and toluene) at low pressure (70 psig = 4.82 x 105 Pascals) and moderate temperatures (140-200 o C). All catalysts showed promising results for olefins hydrogenation at low pressure. However, when the catalysts were tested with a cracked naphtha feedstock, molybdenum carbide showed the highest reduction in olefins content at moderate temperatures (200-280 o C) and pressure (500 psig = 3.44 x 106 Pascals). The hydrogenated naphtha was added to Athabasca bitumen as a diluent to reduce its viscosity. The dilbit had a final viscosity of 220 cP at 7.5 o C and a final olefins content lower than 1 wt. %, thus meeting pipeline specifications for transportation. Furthermore, the carbide catalyst also proved to be active and selective for olefins hydrogenation in the presence of steam, proving to be a potential hydrogenating catalyst for naphtha streams produced from the hot separator. On the other hand, 7.5Ni-AEG-12 extrudates showed a better selectivity to olefins hydrogenation with minimal aromatics hydrogenation. Moreover, Ni-MFI catalysts showed the lowest reduction in olefins content with the naphtha feedstock.
Description
Keywords
Engineering--Chemical
Citation
Sebakhy, K. O. (2017). Developing Novel Heterogeneous Catalysts for the Selective Hydrogenation of Olefins in Light Petroleum Distillates (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25626