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F-T Wax Hydrocracking Reaction Simulation and Performonce of Micro-fiber Wrapped Catalyst

Author: SunJi
Tutor: XiaoTianCun; CaoFaHai
School: East China University of Science and Technology
Course: Chemical processes
Keywords: Hydrocracking catalyst dynamic model heat transfer simulation Fischer-Tropsch wax
CLC: O643.36
Type: Master's thesis
Year: 2013
Downloads: 64
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Abstract


Utilizing low-temperature Fischer-Tropsch wax to be hydrocracked to prepare the gasoline and diesel is the good solution for the wax oil utilization. On this basis, the present work studies the hydrocracking dynamics, heat transfer and reaction simulation under the new catalysts, as well as Cu, Ni fiber package Pt or Pd-based catalysts.According to the mechanism of the F-T synthesis wax hydrocracking process, a5-lumped kinetic model is created. On the basis of the concept of the isomerization factor o, the experimental results that is combined with the isomerization reaction and the introduction of the cracking probability function, the original9-lumped kinetic model cracking assumption is improved. Two kinds of kinetic models are compared. The average relative error between the5-lumped kinetic model calculations and experimental values is3.95%.When the conversion is higher than90%, the average relative error is below0.8%. From the comparison, it is found that the product selectivity is well predicted by the5-lumped model. From this model a mathematical simulation is built for the Fischer-Tropsch waxes hydrocracking pilot. And the optimal process conditions are P=4.75MPa, inlet temperature T=593K and weight hourly space velocity2h-1The present work proposes a method of using micro-fiber wrapped fine particles in the preparation of a novel hydrocracking catalyst, and simulates the laboratory reactor by computational fluid dynamics. The calculated results show that while the wax hydrocracked, microfiber wrapped catalyst shows the better pressure drop characteristics in the trickle-bed reactor (the pressure drop of the conventional catalyst is45.1Pa/m, micro-fiber wrapped catalyst is33.4Pa/m). The microfiber wrapped catalyst caused the change on the behavior of the gas-liquid fluid flow, thereby affects the gas-liquid relative velocity. Microfiber wrapped catalyst has the good thermal conductivity characteristics to avoid the generation of the hot spots of reaction zone, and to effectively improve the reaction.The experimental results of Ni fiber package Pd catalyst show that the aperture of the catalyst becomes smaller, but the pore volume and specific surface area have increased. There is a certain degree of grain polymerization on the new catalyst and there are some larger aggregated grains on the catalyst surface. As result of the change of the crystallinity of the catalyst, the active center aggregates. The weak acidity of the new catalyst does not change too much, but the acidic sites decrease. The process conditions of the test showed that the reaction conversion reached90.23%and the selectivity of the gasoline and diesel reached48%in the conditions of H2/wax=1000, a pressure of3.5MPa, WHSV=1h-1, and T=643K.The Cu-Pt/SAB catalyst system does not exist reactivity, because the dispersion of Pt over the carriers is not well and the Pt element may expulsion galvanic interaction with the Cu element under the process of loading metallic Pt. Through the test of the Cu-Pd/SAB process conditions, the paper finds that the optimum process conditions for the weight hourly space velocity is1h-1and the temperature is380℃, under this condition, the conversion of the reactants and the selectivity of the medium-range oil are optimal.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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