Fouling in a low-density polyethylene (LDPE) tubular polymerization reactor is caused by the polyethylene/ethylene mixture forming two phases inside the reactor. Some of the polymer-rich phase is deposited on the reactor's inside wall, which considerably reduces heat-transfer rates. At a given reactor pressure, the reactor inside wall temperature is the critical parameter in determining when fouling occurs and this is controlled by the coolant stream temperatures. In this work, plant data and a heat-transfer model were used to determine the fouling thickness in a LDPE industrial reactor and the speed at which the foulant material is deposited.

In this work, we investigated various approaches for the modeling of the high-and low-pressure separator units downstream from a low-density polyethylene tubular reactor using the Polymers Plus software package. First, we examined the performance of thermodynamic equilibrium by using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state. Experimental data taken from the open literature were used to obtain the model parameters.Comparison with data from an Equistar plant showed that the PC-SAFT simulations agreed very well with the low-pressure separator residual-ethylene solubility measurements. There were, however, significant discrepancies between the model and the plant data for the highpressure separator, indicating that the high-pressure separator is not operating at equilibrium conditions. A further investigation was performed where a physical mechanism based on a bubble formation model was evaluated and a mathematical correlation using dimensionless numbers developed. The resulting model yielded high-pressure separator predictions that agreed adequately with plant data.

We present a formalism for accurate estimation of dipole moments using quantum mechanics for complex molecules having conformational degrees of freedom. Dipole moments of complex molecules are often needed for use in correlations for estimating viscosities and other thermophysical properties. However, experimentally measured dipole moments are not available for many molecules, especially those used in proprietary industrial processes and products. Many complex molecules have dipole moments that change significantly in response to the conformation of the molecules. We show that proper accounting of the conformation-dependent dipole moment may be required to achieve an acceptably accurate estimate of the experimental dipole moment and provide recommendations on efficient estimation techniques. We also demonstrate that for molecules with dipole moments above about 1.3 D reasonably accurate estimation of the dipole moment is required for reliable prediction of vapor phase viscosity, whereas estimation of thermal conductivity is less sensitive to the dipole moment.

Fouling in a low-density polyethylene (LDPE) tubular polymerization reactor is caused by the polyethylene/ethylene mixture forming two phases inside the reactor. Some of the polymer-rich phase is deposited on the reactor's inside wall, which considerably reduces heat-transfer rates. Phase equilibria calculations show a high degree of sensitivity of the single-phase/two-phase process fluid boundary to temperature. Almost all of the process stream is single phase and the fluid mixture is only two phase in the boundary layer close to the reactor wall where the temperature is low enough to cause phase separation. At a given reactor pressure, the reactor inside wall temperature is the critical parameter in determining when fouling occurs, and this is controlled by the coolant stream temperatures.

A method of micromixing parameter estimation is proposed which is convenient and applicable to a wide variety of models. One conducts a typical tracer response test, except that in addition to the (timeaveraged) mean tracer response, the variance of the tracer response is also recorded as a function of time. Micromixing parameters for a given model are determined by equating the predicted and measured values of the time response of the tracer concentration variance. The predicted tracer concentration fluctuation response has been determined for both step and pulse tracer tests, for the IEM model, the coalescenceredispersion model, and the two-, three-and four-environment models. Parameter estimates were calculated by minimizing the mismatch between predicted and measured concentration fluctuation responses.Preliminary numerical results indicate that the method provides satisfactory parameter estimates, even from moderately noisy measurements. These results also show that statistical analysis of the fit to measured response data can provide discrimination between competing mixing models.