Study On Ethylene Oligomerization Process With Late Transition Iron Catalyst

Linear α-olefins are multicomponent and multipurpose organic raw materials and they are all widely used in all areas of petrochemical based on carbon numbers, of which C8～C12 are the most rapidly increased product. Due to the advantage of product made of even carbon number, high degree of linearity and low separation cost, a-olefins produced by ethylene oligomerization has been the most common method of production for α-olefins. And moreover the late transition iron catalysts for oligomerization have become quite important research filed, because they have rarely high activity, gentle reaction conditions and adjustable product distribution just through changing the structure of ligands. The iron catalyst for oligomerization has characteristics of rapid deactivation rate, rapid heat release and broad product distribution. The high molecular weight a-olefins increase the viscosity of product which may easily lead to sticking on the wall or blocking the pipeline, thus impeding the industrialization of process. Therefore, study on ethylene oligomerization process with late transition iron catalyst, overcoming the two typical engineering problems with heat removal and wall sticking, and accelerating the industrialization of process become the primary task of domestic research.Based on the oligomerization properties of homogeneous catalytic system with acetylacetone iron/bis(imino)pyridine ligand/MAO, we investigated the kinetics behavior of the catalytic system’s ethylene oligomerization, focusing on establishment of the kinetic model. In order to master the amplification effect of oligomerization reaction, we conducted the small scale evaluation of the catalyst and pilot test at 10 L and 300 L polymerization reactor respectively using progressively larger way. We mainly focused on the catalytic activity, kinetics and oligomerization product composition, to provide effective guidance to development of the ethylene oligomerization process with this iron-based catalyst system. Finally, we established the simulation of the whole ethylene oligomerization process by use of chemical process simulation software. Moreover, we proposed the conceptual design of core oligomerization reactor structure to provide guidance for the designment and development of industrial reactor.1. The kinetics of the catalytic system’s ethylene oligomerization was studied in 1L Buchi clave. The kinetic behavior of acetylacetone iron/bis(imino)pyridine ligand/ MAO was analyzed to find similar with the results found by Brookhart and Gibson et al. It presented a typical "speed up decay-type" feature, which meaned the oligomerization process had no induction period, the activity reached the maximum quickly from the beginning of the reaction, then decayed at a rapid rate with increasing reaction time. The reaction rate equation of ethylene oligomerization was derivated and the kinetic model parameters were solved by fitting experimental results. The kinetic model parameters included the reaction orders of catalyst concentration and ethylene pressure on the apparent reaction rate of ethylene oligomerization, the apparent activation energy Ea and pre-exponential factor A about catalytic of ethylene oligomerization. Finally the apparent reaction rate equation for Fe(acac)3/L3 catalytic ethylene oligomerization was obtained Within the scope of 0℃～60℃ and the 0.1MPa-0.8MPa.2. The amplification rule of reactor scale-up on the catalyst system’s oligomerization reaction characteristics and product properties was studied by pilot trail. The characteristics of dynamic behavior of the catalyst system for ethylene oligomerization were analyzed in 10 L and 300 L stirred tanks respectivelyand found to exhibite consistent with previous finding, which was called the "speed up decay-type" feature. At the same time as the amplification reaction device size, reaction control was found to become more difficult. It was shown that the oligomerization catalyst activity increased and the products distribution had the trend of moving to low-carbon direction as the pressure increased in both scale stirred tanks. The influence of the catalyst amount was studied to exhibite different situations while compared to the laboratory study results in 10 L reactor:when the amount of catalyst increased from 10μmol to 20 μmol, the catalytic activity of ethylene oligomerization remained essentially the same, but the trend of activity decay slowed down; when the amount of catalyst increased from 20 μmol to 30 μmol, the catalytic activity was decreased, but the activity decay trend remained essentially the same; the catalyst amount had little effect on the product distribution.3. The whole process simulation of ethylene oligomerization with iron-based catalyst system was established by using the chemical process simulation software Polymers Plus. The oligomerization process with ethylene capacity of 10,000 tons/year was designed including the units as oligomerization reaction, product isolation and solvent recycling. The characteristics of this process were that the core reaction was carried out in a stirred tank reactor, the wax by oligomerization was separated by a centrifuge, the liquid component was cleavaged to products in distillation column system, and the solvent was recycled and reused after distillation. The Process Flow Diagram was proposed by summing up the above features.4. A detailed conceptual design for the core reactor of ethylene oligomerization process was carried out by bonding process design objective. The design of the oligomerization reactor with conventional process criteria and full kettle criteria was proposed with reference of mature technology of related polyethylene industries, which included the major structural size and mixing, intake and other ancillary items. The heat of ethylene oligomerization was calculated by thermodynamic theory. The heat withdrawal calculation of oligomerization tank was carried out with four kinds of ways such as feed endothermic, jacket, slurry outer loop and top tank condensation. It was found that the operation of jacket insulation to maintain the temperature difference between 5～10℃ could effectively reduce the wall sticking phenomenon, and the additional heat load introduced by jacket insulation were set off against the heat load carried away by feed endothermic. At the same time, the designed slurry outer loop system and top circulati on gas condensation system could effectively remove the reaction heat. Finally, we detailed designed the heat exchange system scale to accomplish the objectives of heat load, including the specific structure selection of heat exchanger.