The Costs Of The Co Catalysts Modified Montmorillonite Load - Tropsch Synthesis Behavior

Fischer-Tropsch Synthesis (FTS) is an effective technology to make clean fuels and chemicals from syngas originated from natural gas, coal, and biomass (GTL, CTL, BTL). Recently, the FT synthesis has received increasingly worldwide attention in both industrial and academic domains due to the increased concern over energy security and the implementation of more and more stringent environmental legislations on liquid fuels. However, because the reaction is limited by Anderson-Schulz-Flory (ASF) polymerization kinetics, the product of FT synthesis is a very complicated mixture, composed mainly of normal paraffins with varied carbon numbers (C1～C100+) and nonselective to any specific product. Thus, breaking the ASF distribution of the FT synthesis via catalyst design for selectively synthesizing desired products such as diesel or gasoline is theoretically and industrially targeted. However, this is also a challenge.Because of the abundance, cheapness, environmental compatibility, adjustable acidity and structural properties of the MMT, in this thesis, Co-loaded on acid activated MMTs and ion-exchanged MMTs were investigated for controlling the product distribution of FT synthesis. The structure, texture, acidity and reduction behaviors of the catalysts were characterized by XRD, SEM, N2 adsorption-desorption at low temperature, FT-IR, NH3- TPD, pyridine-FTIR, and H2-TPR. The FT catalytic activity and product selectivity were correlated with the characterization results of the catalysts, i.e., the textural, structural, and acidic properties of MMT. The main works and conclusions of this thesis are as follows:(1) The Na-MMT was modified by ion-exchanging the interlayer Na+ with the purposefully selected cations of NH4+, Co2+, and Al3+, respectively. The degree of the interlayer Na+ replaced by the selected cations was regulated by changing the ion-exchange conditions. The 20 wt.% Co/MMT catalyst was prepared by the incipient impregnation method. Results indicate that the MMT interlayer structure was well reserved for all the ion-exchanged MMTs. Moreover, acidic sites, rich micropores and open mesopores were created after exchanging the Na-MMT with NH4+, Co2+, or Al3+. The Co-supported catalysts were comparatively investigated for the FT synthesis in a fixed-bed reactor under the conditions of 1.0 MPa,235℃, H2/CO=2, and W/F=5.02 g·h·mol-1. Results indicate that Co/Na-MMT was a bad catalyst for the FT synthesis. On the contrary, the Co/ion-exchanged MMT showed sharply increased CO conversion, which strongly depends on the ion-exchange conditions. Moreover, the product selectivity over Co/ion-MMT was significantly deviated from the ASF distribution of the FT synthesis. Based on the characterization data, the difference of the FT activity over Co/MMT catalysts was mainly induced from the interlayer cations, especially Na+, in which the reduction behavior of the catalyst is significantly changed. The narrowed product distribution of the FT synthesis over Co/MMT catalysts caused mainly from the cracking of the long-chain FT hydrocarbons was well correlated with the NH3-TPD results.(2) The Na-MMT activated with HNO3 at elevated temperatures for different times was investigated for the selective synthesis of liquid fuels via the FT synthesis over 20 wt.% Co-supported catalysts under the conditions of 1.0 MPa,235℃, H2/CO=2, and W/F=5.02 g·h·mol-1 Depending on the activation conditions, the activated MMT showed different acidity and textural properties, due to the following events occurred in different degrees:the leaching of the substituted cations, H+ exchanged with the interlayer Na+,and the destruction of the MMT interlayer structure. The MMT laminar structure was completely destructed after activation of Na-MMT at 100℃for 24 h. However, high CO conversion over Co/activated MMT catalysts similar to that of Co/SiO2 was obtained. Moreover, the product selectivity over Co/activated MMT, i.e., clearly higher selectivity of C4-C12 hydrocarbons and obviously lower selectivity of C21+hydrocarbons than those over Co/SiO2, was significantly deviated from the ASF distribution of the FT synthesis. Co/Acid-MMT-12/80 was the best catalyst to control the product distribution of the FT synthesis. The reaction results were well explained based on the characterization data. The content of Na+ was revealed the main factor to control the FT activity, and the acidity of the activated MMT was responsible for the narrowed product distribution.