Research Of A New Kind Of Catalyst For FT Synthesis

FT synthesis is an important constituent of the coal indirect liquefaction engineering, which has more than 70 years history and has recalled much attention of various countries because of the recent petroleum energy crisis. FT synthesis is usually carried on the iron or cobalt base catalyst, which is composed by a series of parallel reaction and consecutive reaction. The product is complex, the product distribution observes the traditional SF distribution, which means that only the selectivity of methyl alcohol,methane and hydrocarbon C35 polymer carbon chain or above may achieve the very high level, the gasoline fraction and the diesel oil fraction selectivity can't surpass 50%. In the actual operation, the deep processing is carried on in order to obtain the bunker oil C9～C25 hydrocarbon, which will increase the cost of FT synthesis with no doubt.This topic mainly researches a new kind of iron clay catalyst, the main characteristic of which is that: the carrier has layered structure as the montmorillonite clay type in which each layer is composed of one octahedral sheet sandwiched by two tetrahedral sheets, the passageway is even, iron distributes in the catalyst skeleton and the level, the iron in the level becomes the active component after reduction. The level spacing can provide the appropriate space in which the gasoline, the diesel oil chain grows. This catalyst can be used in the FT synthesis to obtain the bunker oils. The bubbling slurry bed reactor becomes the development direction because of its ability of removing heat well, the ease of operation, on-line catalyst replacement. In this experiment, FT synthesis was done in a continuous stirred bed reactor to simulate the slurry bed reactor.In this research, nine kinds of iron clay catalyst was prepared at first in order to optimize the preparation condition, which based on the different active constituent raw material, the different precipitating agent, the different order that the precipitating agent and the active ingredient join, the different pH value of the precipitation, and the different hydro-thermal synthesis method. The catalysts were characterized by XRD, SEM and BET. Carbon distributions of the nine catalysts' liquid product that was got under the same FT synthesis condition were compared. Optimal of catalyst II and III was carried on to got the best FT synthesis condition. The inspection of production rate was carried on for catalyst III in 30 hours to exploration catalyst life.The XRD determination result indicated that nine kinds of catalyst all had the laminated structure, characteristic peak of catalyst I, II, III, IV, V and IX was more remarkable, while characteristic peak of catalyst VI, VII and VIII was weaker. SEM paragraph of catalyst II indicated that the particle size of this catalyst was approximately 1μm, the superficial appearance assumed the level laminated shape. The BET examination indicated the iron clay catalyst had big specific area, the highest specific area might achieve 376.67m²/g.The optimal catalyst preparation conditions is that: The Fe³⁺ ferric salt as the raw material of active constituent, NaOH and KOH as the precipitating agent, addition and counter-addition preparation, pH value between 6.6～8.7, dynamic hydro-thermal synthesis. The catalyst selectivity to the C9～C25 hydrocarbon compound may achieve 80% which was prepared under this condition, and the distribution has positive displacement compared with the SF distribution.The FT synthesis condition optimization to catalyst II and III indicates two kinds of catalysts have approximately the same influence factors: temperature and pressure influence factor more remarkable, the H₂/CO influence factor is smaller. Catalyst II has a higher liquid yield at the reaction condition of 270℃, 0.5MPa, H₂/CO=1, while catalyst III has a higher liquid yield at the reaction condition of 280℃, 0.9MPa, H₂/CO=1. Lifespan experiment of catalyst III shows that, the activity of the catalyst done in the experiment has not reduced within 30 hours.It's discovered in the experiment that the carrier structure played an important part in the liquid product selectivity. In order to inspect the carrier structure to the FT synthesis selective influence, the iron loaded KL zeolite catalyst, the iron loaded HL zeolite catalyst, and the iron loaded silica gel catalyst were prepared. Liquid product carbon distribution of ferric radical catalyst with different carrier was compared: iron clay catalyst II and the iron loaded silica gel catalyst have a higher selectivity to the diesel oil component, but the former liquid product carbon distribution is more centralized; the iron loaded KL zeolite catalyst and the iron loaded HL zeolite catalyst have a higher selectivity to the gasoline component, the former has a higher selectivity to C5～C12 and the C13～C18 hydrocarbon compound, but the latter has a higher selectivity to C2～C4 and theC19～C40 hydrocarbon compound. This phenomenon may due to the catalyst configuration selectivity.The iron clay catalyst prepared in this experiment can be used in bubbling slurry bed reactor of FT synthesis to obtain the C9～C25 the gasoline and diesel oil sloppy cut; the research of the carrier influence to the FT synthesis product can provide some references for the synthetic liquid fuel selectively.