Deuterium Tracer Study: Effect Of Operation Condition On The Product Distribution In The Cobalt-catalyzed Fischer-Tropsch Synthesis

Fischer-Tropsch (FT) synthesis gas is a promising catalysis process for synthesis gas conversion to environmentally clean fuels. Supported cobalt is the preferred catalyst for the FT synthesis due to its reasonable price and high selectivity for heavy hydrocarbons. It is well known that the product distribution of FT synthesis follows the so called Anderson-Schulz-Flory (ASF) rules, the high selective formation of specific hydrocarbons is difficult. Thus, one of the most important tasks in the field of mechanism and process control is the investigation of reaction condition effect on product distribution of FT synthesis.As to make a summary of the literatures about cobalt-catalyzed FT synthesis, the results towards the effect of total pressure and synthesis gas space velocity on the product distribution remains unclear even contrary. Such conflicting results could be partially ascribed to the existence of the product accumulation in FT reaction system, which may affect the veracity of results obtained previously. New experiment methods are required as to obtain more reliable data for the investigation of the effect of pressure and synthesis gas space velocity on the product distribution.In this thesis, the accumulation factor is eliminated using deuterium/hydrogen switching method and correct product distribution under different reaction condition is obtained, in-depth discuss has been made as refer to the effect of reaction condition on the product distribution and the secondary reaction of olefin in FT synthesis. The main results are as following:1. Reverse-isotopic effect is observed when deuterium is introduced into the reaction system, synthesis gas conversion increased during switching period and the retention time of deuterium-containing compound is shorter than that of hydrogen-containing compound.2. Synthesis gas conversion increases with an increase in operating pressure or a decrease in synthesis gas space velocity, while the selectivity of parrafin and branched products is increased with a decrease in operating pressure or synthesis gas space velocity.3. The obtained correct product distribution follows ASF distribution. Only one the chain growth probability is observed, which is independent of chain length and synthesis gas space velocity. It is indicated that the effect of 1-olefins readsorption for secondary chain growth is quite small and negligible.4. Different composition of liquid phase at catalyst surface caused by different operating pressure could affect the ratio of rate coefficient for chain propagation and termination, which lead to the increased chain growth probability at elevated pressure. 5. The obtained Pr/O ratio increases with increasing chain length, which could be associated with the concentration enrichment of long-chain hydrocarbons phsisorpted at the catalyst surface. However, the secondary reaction probability for olefin which is desorbed from phsisorption state into gas or liquid phase is negligible.6. The Pr/O ratio of hydrocarbons with same carbon number decreases remarkably by increasing the operating pressure or synthesis gas space velocity. The tune over frequency (TOF) of active metal atom on catalyst surface and the partial pressure of CO have remarkable effect on the secondary reaction of olefin, because the higher of these values the weaker intensity of the olefin competition for secondary reaction.