Modeling Of Gas Phase Polymerization Of Butadiene With Heterogeneous Catalyst

Studies on modeling of gas phase polymerization of butadiene were carried out in this thesis. Based on the kinetic experiments, a suitable intrinsic model and a molecular weight distribution were established.The catalyst developed by the Polymer Science Institute of Zhejiang University was used in this study. The main catalysts were Nd-based compounds and the cocatalysts were aluminum alkyl. Both of them were loaded on the silicon gel. The kinetic experiments were carried out in a self-cleaning stirred bed reactor with double axes and small clearances between the paddles and the wall of the reactor as well as between the paddles themselves. To this kind of catalyst, the following results were obtained: The rate of polymerization attenuates continuously with the reaction time in the gas phase polymerization of butadiene. At the same time, the decay of reaction rate becomes slow as the progress of reaction; to this kind of catalyst, higher reaction rate can be attained at lower temperature. Different catalysts will make different kinetic results. This kind of catalyst will deactivate greatly at much higher temperature; the chemical and physical properties of dispersing media will affect the kinetics performance. In the development of process, how to choose dispersing media is important. Since SiOa is often used as stuffing in production of rubbers, using SiOi as dispersing medium will be convenient to get final product by gas phase polymerization without any other processes.A new intrinsic mechanism was proposed and corresponding model was constructed. From the establishment of model and simulation, following results were obtained: the kp is increased with the increase of the temperature. But the affects of deactivation and transfer are also greatly remarkable, which makes the polymerization rate much low at high temperature.Research of average molecular weight and molecular weight distribution were carried out in Gel Permeation Chromatography (GPC) and following results were gotten: The higher temperature is, the wider molecular weight distribution and the smaller average molecular weight are. But at the medium temperature, such as 40 癈 and 50癈, the molecular weight and molecular weight distribution are similar. It is perhaps that this kind of catalyst is suitable for these conditions; At higher pressure, such as higher than 1 OOkpa, narrow molecular weight distribution and large average molecular weight are shown. Although the pressure is low, such as 65kpa, narrowerHImolecular weight distribution and larger average molecular weight than that of middle pressure, such as 1 OOkpa, can be seen.According to the three-stage phenomena of kinetics curves, a suitable criterion equation with propagation rate and deactivation of active sites were proposed. The proposed criterion equation can give an elementary theory interpretation of molecular weight and molecular weight distribution of gas phase polymerization of butadiene.Molecular weight distribution model of gas phase polymerization of butadiene was proposed and following results were shown: The deactivation of active sites of catalyst and transfer of polymer chains has great effect on the intrinsic kinetics and molecular weight distribution. At lower temperature this effect is not so great that the large molecular weight averages are gotten; as the increasing of temperature, the average molecular weight is decreased; as the increasing of reaction pressure, the molecular weight averages are increased. So at low temperature and high pressure, the butadiene rubber with high average molecular weight can be obtained; the proposed model can be used to predict the average molecular weight and the molecular weight distribution of gas phase polymerization of butadiene.