Promoted Co-CNT nano-catalyst for green diesel production using Fischer-Tropsch synthesis in a fixed bed reactor
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This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.
DegreeDoctor of Philosophy (Ph.D.)
CommitteeWang, Hui; Abatzoglou, Nicolas; Niu, Catherine; Soltan, Jafar; Pereira-Almao, Pedro; Scott, Robert
Copyright DateSeptember 2010