Simulation of Hydrolytic Polymerization of Nylon-6 in Industrial Reactors:  Part I. Mono-Acid-Stabilized Systems in VK Tube Reactors

Abstract

Nylon-6 polymerization in a VK tube (vertical column) reactor is largely not understood because of the complex internal structure of the reactor and the unavailability of essential industrial data on polymerization. In the present study, the hydrolytic polymerization of nylon-6 has been simulated in an industrial VK tube reactor for concentrations of various species. The model, which assumed a flat velocity profile in the radial direction, predicted the industrial results with high accuracy. The internal design of the reactor appears to be responsible for getting close to plug-flow conditions inside the VK tube. An empirical relation based on temperature and pressure was used to determine the water profile along the vertical axis of the reactor. Because the pressure increased along the axis of the reactor and the temperature first increased and then decreased, the model predicted a lowest water content (LWC) point at near the highest temperature point. The concentration of water at the LWC point was found to be critical in determining the properties of the end product. The model suggested three main zones in a VK tube reactor: a very small top turbulent zone, where most of the water was lost, followed by a large middle zone, which was a vaporizing plug-flow tubular zone, and a bottom zone, which was a nonvaporizing plug-flow tubular zone. The vaporizing zone ended and the nonvaporizing zone began where the LWC point was achieved. The small turbulent zone at the top did not appear to affect the end polymer properties of polymerization. This model was found to be useful in carrying out process optimization and suggesting improvements in VK tube designs for higher productivity.

Effect of diacid stabilizers on kinetics of hydrolytic polymerization of ϵ‐caprolactam in industrial reactors

“…The same VK Tube reactor, which was used in our previous study on monoacid catalyzed system, 20 was used for modeling the diacid system. It consisted of five different zones, in each of which the temperature is independently controlled, and thermocouple wells at six locations, where the temperature of reaction mass is measured.…”

“…The products, polymer and unreacted monomer, are removed at the bottom of the reactor. According to our previous study, 20 VK column reactor could be considered as a reactor consisting of two main zones-vaporizing and nonvaporizing as shown in Figure 1…”

“…The following data were taken as initial conditions The initial concentrations of diacid acid fed at the top of the reactor for the four cases are given in Table III. The water concentration profile from top to bottom of the reactor along with the temperature and pressure profile were determined as per the details given elsewhere. 20 Temperatures along the axis of the reactor were collected for the four different industrial polymerizations. Temperatures of the polymer melt in different zones were calculated as an average of 10-12 values measured at every 2-h interval.…”

“…5,[11][12][13][14][15][16][17][18][19] Recently, we had reported modeling of an industrial VK (Vereinfacht Konitnuierliches) tube reactor, using monocarboxylic acid (monoacid) stabilizer, where the effect of the complex internal structure (heat exchanger, internal gratings) of the reactor was considered. 20 The effect of hydrostatic pressure inside the re-actor was taken into account to predict water profile through out the reactor. Using temperature and pressure profile, lowest water content (LWC) point was predicted, which was found to be critical in determining the properties of the end product.…”

Mathematical Modeling of Nylon 6/6,6 Copolymerization: Beneficial Influence of Comonomers on Degree of Polymerization in Batch Reactor

“…Over the years, many PA6 mathematical models have been developed using Arai's kinetic parameters to simulate homopolymerization in a variety of reactors (i.e., batch and plug‐flow reactors, continuous stirred tank reactors and reactor systems involving multiple reactors in series or single reactors with multiple reaction zones; e.g., refs …”