Linear flow reactor

More recent process research aimed at anionic PS is that of BASF AG. Unlike the Dow Process, the BASF process utilizes continuous linear-flow reactors (LFR) with no back-mixing to make narrow polydispersity resins. This process consists of a series alternating reactors and heat exchangers (Fig. 22). Inside the reactors, the polymerization exotherm carries the temperature from 30°C at the inlet to 90°C at the outlet. The heat exchangers then take the temperature back down to 30°C. This process, which requires no solvent, results in the formation of narrow polydispersity PS. 

Chen, C.-C., Continuous production of solid polystyrene in back-mixed and linear-flow reactors, Polym. Eng. Sci., 40, 441-464 (2000). 

LFR reactor system, 23 396. See also Linear-flow reactor (LFR) polymerization process Li20-Al203-Si02 (LAS) system, glass-ceramics in, 72 637. See also Lithium entries... 

Linear combination of atomic orbitals (LCAO) method, 16 736 Linear condensation, in silanol polycondensation, 22 557-558 Linear congruential generator (LCG), 26 1002-1003 Linear copolymers, 7 610t Linear density, 19 742 of fibers, 11 166, 182 Linear dielectrics, 11 91 Linear elastic fracture mechanics (LEFM), 1 509-510 16 184 20 350 Linear ethoxylates, 23 537 Linear ethylene copolymers, 20 179-180 Linear-flow reactor (LFR) polymerization process, 23 394, 395, 396 Linear free energy relationship (LFER) methods, 16 753, 754 Linear higher a-olefins, 20 429 Linear internal olefins (LIOs), 17 724 Linear ion traps, 15 662 Linear kinetics, 9 612 Linear low density polyethylene (LLDPE), 10 596 17 724-725 20 179-211 24 267, 268. See also LLDPE entries a-olefin content in, 20 185-186 analytical and test methods for,... 

Continuous solution Free radical (linear flow reactor) Styrene monomer Recycled solvent W or W/O initiator Good range of products Good for rubber extension Good clarity and color Large number of control zones Pumping difficulties High capital Low-cost process for HIPS... 

Figure 3.13 High-impact polystyrene plant (CSTR=continuous stirred tank veactor LFR = linear flow reactor)...

In practice, the continuous mass polymerization is rather complicated. Because of the high viscosity of the copolymerizing mixture, complex machinery is required to handle mixing, heat transfer, melt transport, and devolatilization. In addition, considerable time is required to establish steady-state conditions in both a stirred-tank reactor and a linear-flow reactor. Thus, system start-up and product grade changes produce some off-grade or intermediate grade products. Copolymerization is normally carried out between 100 and 200°C. Solvents are used to reduce viscosity or the conversion is kept to 40-70%, followed by devolatilization to remove solvents and monomers. Devolatilization is carried out from 120 to 260° C... 

In continuous industrial free-radical polymerization processes, many different types of reactors are used [1]. They are continuous-flow stirred tank reactors, tower reactors, horizontal linear flow reactors, tubular reactors, and screw reactors. In some processes, different types of reactors are used together in a reactor train. In stirred tank reactors, no spatial concentration and temperature gradients exist, whereas in linear flow or tubular reactors, concentration and temperature vary in the direction of flow of the reacting fluid. Specially designed reactors such as screw reactors or extruder reactors are also used to produce specialty vinyl polymers. In this chapter, some important characteristics of continuous reactors used in industrial free-radical polymerization processes are discussed. 

Another type of linear flow reactor system for the synthesis of high-impact polystyrene is shown in Fig. 5 [1]. Here, the first-stage backmixed reactor (CSTR) is maintained just beyond the phase-inversion point (98 C, 14% solids) and the dissolved styrene reacts to form either a graft copolymer with the rubber or a homopolymer in the linear flow reactor train. Note that a portion of the effluent (130°C, 35% solids) from the second reactor is recycled to the first reactor. The temperature of the polymerizing mixture is gradually increased as it travels through the linear flow reactors and the final conversion of about 72% is achieved. 

Both batch and continuous reactors are used in industrial vinyl polymerization processes. Agitated kettles, tower reactors, and linear flow reactors are just a few examples of industrially used polymerization reactors. The choice of reactor type depends on the nature of polymerization systems, (homogeneous versus heterogeneous), the quality of product, and the amount of polymer to be produced. Sometimes, multiple reactors are used and operated at different reaction conditions. Whichever reactor system is used, it is always necessary to maximize the process productivity by reducing the reaction time (batch time or residence time) while obtaining desired polymer properties consistently. 

Styrene can be polymerized to a high conversion if a small amount, say 20%, of an unreactive solvent is present. It is often referred to as a bulk polymerization even though some solvent is present. Most atactic polystyrene is produced by free-radical polymerization in this manner. Several continuous processes have been described in some detail [9], In one process, linear-flow reactors are used in series (Figure 5.3). Each reactor contains a series of sections that are agitated and provided with heat transfer tubes. A free-radical initiator may be used. In order to lower viscosity, especially in the latter stages, a solvent, typically ethyl benzene, is present to the extent of about 20%. Polymerization to high conversion is obtained in the last reactor as the temperature is increased... 

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