Preparation And Catalytic Performance Of Cobalt Based Catalysts For FT Synthesis

The synthesis of liquid fuel based on FT synthesis through syngas (CO and H2) has significant meaning in resolving the problems of shortage of oil resource and environmental pollution. The catalyst development is the key techonology of FT synthesis. Cobalt based catalysts are considered to be the most promising catalysts for FT synthesis due to its high conversion per pass and low activity for water-gas shift reaction. In order to obtain the ideal product distribution of FT synthesis, one of the common methods is to modify the catalyst.In this paper, cobalt catalysts for FT synthesis were prepared by using excessive impregnation. The optimal catalysts were used to the preparae the structured catalysts. Their catalytic performances for FT synthesis were evaluated in a fixed bed reactor. And the properties of the catalysts were characterized by BET, XRD, TPR, and so on.This paper includes the following aspects:(1) The influences of the molecular sieve carrier, solution pH, ultrasound treatment time, the pre-treatment process and the promoters were investigated. The results showed that Co/HB catalyst had higher catalytic activity than Co/MCM-22catalyst; the CO conversion improved with the increasing of solution pH, but the selectivity of C5+hydrocarbons was decreased; the suitable ultrasound time could improve the catalytic activity of FT synthesis; during the pre-treat process, the ammonia concentration for12.5%was favorable to the catalytic activity of FT reaction; the order of the addition of promoter had a impact on the performance of catalyst significantly.(2) In order to further improve the catalytic performance of FT synthesis, a series of cobalt-iron based catalysts were prepared. Firstly, the influences of different iron contents on the reaction performance of the catalysts were tested. Then, by the addition of different promoters to the4%Fe-10%Co/Hβ catalyst, the influences of the promoters were investigated. The results showed that suitable amount of Fe can improve the CO conversion and C5+hydrocarbon selectivity; the addition of La, Mn, and Ce would reduce the activity of catalyst.(3) Based on the previous study, the optimal catalysts were used to prepare structured catalysts. When the catakyst usage was enlarged, the biomass gasfication was used as feed gas, the influences of reduction temperature, reaction temperature, feed gas space velocity and reaction pressure on the activity were studied and optimized. It found that the best reaction conditions were reduction temperature of400℃, reaction temperature of230℃, feed gas space velocity of1.5SL/(h·g-cat), and reaction pressure of3.0MPa.(4) According to above best, the60hours stability test of Co-Fe/Hβ structured catalyst for FT synthesis was also measured. The results showed that CO average conversion and the average yield of C5+hydrocarbon, respectively, were maintained at87.11%and67.93%during60hours. Then, the structured reactor was designed, when the catalyst usage was enlarged further to5times, the results showed that CO conversion were maintained at78.60%, the yield of methane and C5+hydrocarbon, maintained at9.94%and82.09%for13hours, respectively. Thus, the structured catalysts and structured reactor developmented in this project could remove the reaction heat effectively to avoid the decline of catalysts activeness.