Modeling For 1-decene Oligomerization Process Towards Molecular Weight And Distribution

High-quality synthetic lubricants,prepared from poly-alpha-olefins(PAO),exhibit good performance such as high viscosity index,low-temperature mobility and anti-shear properties,making them meet the needs of the complicated scenes in industry and real life.The relative molecular weight and distribution of PAO directly affect its macroscopic properties.In this thesis,the steady-state model based on the BF3/C2H5OH catalytic system was established to investigate the relative molecular weight and distribution of the oligomerization products.Then the process parameters of specific grades of PAO were optimized,which can provide guidance for the industrialized production of high-quality lubricants in China.A method was developed for characterizing the relative molecular weight and distribution of 1-decene oligomer,which was based on gel permeation chromatograph(GPC)equipped with differential refractive index(RI).Considering the separation effect,the conditions were optimized including the flow rate of the mobile phase and the combination mode of gel chromatographic columns.The chromatographic efflux curve was processed by universal calibration method.The weight-average molecular weight of PAO determined by the curve was coincided with that measured by gel permeation chromatography-laser light scattering(GPC-LLS)method,and the relative error was less than 3%.Compared with GPC-LLS,this method can directly determine the relative content of PAO with different degree from the efflux curve.The PC-SAFT state equation was selected to calculate the physical properties of the 1-decene oligomerization system catalyzed by BF3/C2H5OH,and the related parameters required for the calculation were determined.The unary parameters of the pure components were regressed with the saturated vapor pressure and density data from literature.The unary parameters of oligomerization were calculated based on the group contribution method.The binary interaction parameter of 1-decene and BF3 was regressed with the gas-liquid phase equilibrium data from literature.The PC-SAFT state equation with modified parameters was used to calculate the component properties and phase equilibrium,which matched well with the data from literature.This property model was used to calculate the solubility of BF3 and liquid phase volume flow rate.A steady-state of the 1-decene oligomerization catalyzed by BF3/C2H5OH in two tandem reactors was developed.The kinetic parameters of the single chain propagation model were adjusted according to the operating data and sample analysis values of grade C obtained from the plant.This model was able to accurately calculate monomer conversion rate and weight-average molecular weight of PAO,but was less effective in predicting the relative molecular weight distribution of PAO.Then the different chain propagation model was developed,in which the chain propagation kinetic parameters of monomer,dimer,trimer,tetramer and higher oligomers were different.The kinetic parameters were adjusted according to the data obtained from the first reactor of grade A,B and C in plant.The steady-state model was used to calculate the production condition of the first and the second reactor for these three grades(A,B,and C).The relative error between the calculated data and plant data was less than 5%,which demonstrated that the different chain propagation model can accurately predict the relative molecular weight and distribution of PAO.The steady-state model was used to investigate the effects of process parameters on the product composition and monomer conversion rate.The results showed that reaction temperature had a significant effect on product composition and monomer conversion,while reaction pressure,average residence time,and content of initiator mainly affected the monomer conversion.Individual and simultaneous optimization of reaction temperature and initiator dosage were performed targeting key component content,weight-average relative molecular weight and monomer conversion,respectively.The individual optimization of each process condition is more convergent,accurate,and less affected by the initial value than the simultaneous optimization of multiple process conditions.With the aim of monomer conversion over 95%and total content of trimer and tetramer near 80%,the optimum process conditions were obtained for the reaction temperature of 30℃ and the mass ratio of initiator to monomer of 0.66%using the sequential individual optimization strategy.