110th Anniversary: Nonideal Mixing Phenomena in High-Pressure Low-Density Polyethylene Autoclaves: Prediction of Variable Initiator Efficiency and Ethylene Decomposition

Abstract

A segregation–backmixing model is developed to simulate the dynamic operation of multifeed high-pressure low-density polyethylene (LDPE) autoclaves, calculate the specific initiator consumption (grams of initiator per kilogram of LDPE), and assess the risk of ethylene decomposition under different nonideal mixing and operating scenarios. To describe the nonideal macro- and micromixing phenomena in a LDPE autoclave, a user-specified multizone model representation of the actual reactor is established. One of the key features of the present model is that the continuously fed initiator into a reaction zone can exhibit two distinct states, namely, a “segregated” or a “molecular” one. Simulation results are presented, showing the effects of macro- and micromixing model parameters on the spatial temperature distribution and specific initiator consumption with respect to the initiator feed concentration to a two-compartment reaction zone. Finally, the operational conditions and process faults that can lead to ethylene decomposition in a reaction zone are investigated.

On the Elucidation of Polymer Fouling Mechanisms and Ethylene Decomposition in High‐Pressure LDPE Tubular Reactors

“…In dealing with nonideal mixing phenomena in high-pressure LDPE reactors two quantities are of interest. [71] The first is the blob size of the injected initiator feed stream. The second is the rate of erosion of the added initiator fluid blobs or the inverse local mixing time.…”

“…It should be pointed that for the calculation of the characteristic mixing time, t m , the Corrsin Equation ( 5) was used. [71] Note that the numerical value of the kinematic viscosity (𝜈 = viscosity/density) will depend on the solution viscosity (i.e., a complex function of temperature, polymer concentration and, MWD of LDPE) and density of the polymerization mixture (i.e., as well a function of temperature, pressure, and polymer content).…”

A graph theory assisted Monte Carlo algorithm for simulating the topology structure of LDPE and connection with molecular dynamics simulation

“…Low‐density polyethylene (LDPE) is one of the most popular polyethylene products, and the commodity made of it can be seen nearly every day 1 . Currently, two reactor technologies (autoclave and tubular) are employed in industry to produce the LDPE, 2,3 and both obey the high‐pressure radical polymerization reaction scheme. Under high pressure (120–320 MPa) and high temperature (160–320°C), 3 polymerization reactions start with initiator decomposition, followed by propagation and/or chain transfer reactions, and end with termination by combination or disproportionation.…”

“…Currently, two reactor technologies (autoclave and tubular) are employed in industry to produce the LDPE, 2,3 and both obey the high‐pressure radical polymerization reaction scheme. Under high pressure (120–320 MPa) and high temperature (160–320°C), 3 polymerization reactions start with initiator decomposition, followed by propagation and/or chain transfer reactions, and end with termination by combination or disproportionation. Due to the chain transfer reactions, LDPE products show highly branched topology structures together with wide molecular weight distribution (MWD), copolymer composition distribution (CCD), long chain branching distribution (LCBD), and short chain branching distribution (SCBD).…”

DFT Investigation of Polyethylene-co-vinyl Acetate: Kinetics of Initiation and Propagation, Copolymer Composition, and Unit Sequence Distribution

“…The industrial design and development of the copolymerization reactor remains difficult due to the complexity of the reactions. Some research studies on the reactor of EVA have been published; − however, their kinetic data are based on simplification and combination from various sources. Obviously, obtaining reliable elemental kinetics is of great significance for the reactor-scale academic study and industrial design.…”