Continuous polymerization process

The polymerization of monomers to form hydrocarbon resins is typically carried out by either the direct addition of catalyst to a hydrocarbon fraction or by the addition of feed to a solvent—catalyst slurry or solution. Most commercial manufacturers use a continuous polymerization process as opposed to a batch process. Reactor temperatures are typically in the range of 0—120°C. 

As the polymer molecular weight increases, so does the melt viscosity, and the power to the stirrer drive is monitored so that an end point can be determined for each batch. When the desired melt viscosity is reached, the molten polymer is discharged through a bottom valve, often under positive pressure of the blanketing gas, and extmded as a ribbon or as thick strands which are water-quenched and chopped continuously by a set of mechanical knives. Large amounts of PET are also made by continuous polymerization processes. PBT is made both by batch and continuous polymerization processes (79—81). 

PA-6,6 is made from the relatively expensive materials hexamethylene diamine and adipic acid. An alternative synthesis of PA-6,6 from adiponitrile and hexamethylene diamine utilizing water is under investigation.16 PA-6 can be synthesized in a continuous process at atmospheric pressure, but reaction times are very long as the ring-opening initiation step is particularly slow. The reaction time can be shortened considerably by carrying out prepolymerization in the presence of excess water at pressure however, this makes the continuous polymerization process more complex. Copolymers with amide units of uniform length (diamides) are relatively new the diamide units are able to crystallize easily and have a thermally stable crystalline structure. 

Continuous polymerization processes for PA-6,6 have been reported for over 30 years.5,6,28 Prepolymerization in tubular (Fig. 3.21) or baffled reactors is particularly well suited to continuous polymerization. The polymerization of prepolymers to high-molecular-weight materials in a continuous process is more difficult to control as small differences is molecular weights result in large differences in viscosities. Viscosity differences result in different hold-up times in die reactor and thus nonhomogeneous products. 

Continuous polymerization processes, 167 Convergent method, 8 COOH-terminated poly(ethylene adipate), 95-96... 

The polymerization temperature is in the range of 50-80°C. The ethene pressure is 2-8 M Pa. In the case of a continuous polymerization process, the average residence time should be in the range of 3-4 h (1). 

Polymer Production. Three processes are used to produce nylon-6,6. Two of these start with nylon-6,6 salt, a combination of adipic acid and hexamethylenediamine in water they are the batch or autoclave process and the continuous polymerization process. The third, the solid-phase polymerization process, starts with low molecular weight pellets usually made via the autoclave process, and continues to build the molecular weight of the polymer in a heated inert gas, the temperature of which never reaches the melting point of the polymer. 

As in any type of polymerization, a batch reaction is not as commercially attractive as a continuous polymerization process that can produce larger quantities of polymer in the same amount of time. The first continuous polymerizations in C02 were reported (Charpentier et al., 1999) with the monomers acrylic acid and vinylidene fluoride. The vinylidene fluoride polymerization was extensively studied at 75 °C, 275 bar. The polymerizations were run with residence times that varied between 15 and 40 min in a continuous-stirred-tank reactor before collection in a filter. The maximum rate of polymerization was determined to be 19 x 10 5 mol L-1s-1. Future research will move toward continuous removal of polymer, recycling of unreacted monomer and C02, and expansion to other monomers. 

A continuous polymerization process has been developed by Hercules Co. using triethylaluminum catalyst at elevated temperatures [135]. 

Figure 1.7 Schematic of Dow s tube tank process which represents the first commercial continuous polymerization process for polystyrene in the USA. The figure shows a cross-section through the centre of three longitudinal unagitated tanks. Styrene was thermally polymerized in tube tanks 1 and 2 and then devolatilized in the bottom receiving tank, which was always about half full and under vacuum [adapted from Boyer, R. F., J. Macromol. Sci. Chem., A15, 1411 (1981)]...

Winyl polymerization as a rule is sensitive to a number of reaction variables, notably temperature, initiator concentration, monomer concentration, and concentration of additives or impurities of high activity in chain transfer or inhibition. In detailed studies of a vinyl polymerization reaction, especially in the case of development of a practical process suitable for production, it is often desirable to isolate the several variables involved and ascertain the effect of each. This is difficult with the conventional batch polymerization technique, because the temperature variations due to the highly exothermic nature of vinyl polymerization frequently overshadow the effect of other variables. In a continuous polymerization process, on the other hand, the reaction can be carried out under very closely controlled conditions. The effect of an individual variable can be established accurately. In addition, compared to a batch process, a continuous process normally gives a much greater throughput per unit volume of reactor capacity and usually requires less labor. 

During the authors investigation of acrylamide polymerization in aqueous solutions, a laboratory scale continuous process, with reactors of 2- or 3-liter capacity, was developed. It offered simple and flexible operation, and close control of conditions. This article describes the technique adopted and some experimental results showing the effect of individual variables on the molecular weight of the polymer formed. A theoretical treatment of the continuous polymerization process has been made recently by Jenkins (4). The empirical data obtained in the present work are examined with the aid of theoretical relationships. 

The ring-opening polymerization of PLA is traditionally realized during a discontinuous batch-process, but recently continuous processes have been developed. As another alternative to continuous polymerization processes the reactive extrusion of PLA was realized. By combining Lewis-acid catalysts with cocatalysts it is possible to increase the catalytic activity and to reduce the polymerization time [18]. 

Uhde Inventa-FIscher Polyamide 6 Caprolactam Two-stage or single-stage continuous polymerization process to produce PA-6 chips for textiles, film, engineering plastics 79 2009... 

To overcome fhe challenges described above, associated wifh fhe production of low molecular weigh acrylic polymers by solution processes, a high temperature continuous polymerization processes was developed in the early 1980s by the S.C. Johnson Co. Several US patents disclose... 

Figure 13.11 Schematic of bulk continuous polymerization process for high molecular weight PBT [67].

It may be concluded from what has been observed that the sensitometric evaluation based on the color density detects both transitions - from liquid to gel and from soft gel to vitrified solid - most precisely, while other techniques reveal information on the continuous polymerization process. 

ABS resins are produced primarily by grafting styrene and acrylonitrile onto polybutadiene latex in a batch or continuous polymerization process. They may also be made by blending emulsion latexes of styrene-acrylonitrile (SAN) and nitrile rubber (NBR). 

Since the 1940s continuous polymerization processes have been developed for a variety of products and with different reactor configurations. Latex products manufactured in continuous systems include polychloroprene and other synthetic elastomers, ethylene-vinyl acetate copolymers, components for engineering plastics and coating formulations. 

The compositions of EPDM elastomers are controlled by using the appropriate monomer feed ratio (see Eq. (2.38)) to obtain the desired composition in a continuous polymerization process. In general the excess propylene required is recycled. The molecular weights of EPDM polymers are controlled primarily by chain transfer reactions with added molecular hydrogen (Eqs. (2.86) and (2.87)), as is common with other Ziegler-Natta polymerizations (Boor, 1979). 

Here m, is the manipulation to be made at time t, g is the process gain, Yj is the deviation of the measurement from setpoint at time j, and jS is a tuning parameter. Many continuous polymerization processes fit the assumptions used to derive the above controller (the process is fast with respect to the sampling interval, but the samples are still autocorrelated, and an integrated white noise model is appropriate). Other noise models may be used. If the process is not fast with respect to the sampling time, the process model must capture the dynamics of the process. Similar controllers can be derived for these situations. If the process is slow with respect to the sampling time, then conventional process control is appropriate. 

Courtaulds initially made a PAN fiber (RL Polymer) by a batch process, to be replaced by Courtelle, made by a continuous polymerization process. The author can remember the day when WG Schmidt found a suitable solvent for the RL acrylic polymer and went running round the laboratory holding a test tube aloft containing a solution of PAN in NaSCN. The process was developed and following two pilot plants at Coventry, a continuous production plant was built at Grimsby in 1959, based on a terpolymer, acrylonitrile/methyl acrylate/itaconic acid (AN/MA/ITA) system using NaSCN as a solvent [4]. An important parallel development was a plant to recover and purify the spent NaSCN, which was fed back into the system. 

Most acrylic fibers are produced by this method, utilizing a batch or continuous polymerization process, where de-ionized water is the continuous phase and the initiators and... 

Continuous polymerization is a second process practiced on a large commercial scale (88). An illustrative example taken from the patent literature illustrates the continuous polymerization process. Thus a mixture of chloroprene, 2,3-dichloro-l,3-butadiene, dodecyl mercaptan, and phenothiazine (15 ppm) was fed to the first of a cascade of seven reactors. Water solution containing dispropor-tionated potassium abietate, potassium hydroxide, and formamidine sulfonic acid catalyst were fed with the monomer solution to the first reactor. Polymerization initiated immediately. The emulsion was then cascaded to the second reactor and the process continued. The residence time in each reactor was 25 min at 45°C. The emulsion exited the reaction train at 66% monomer conversion. In a second similar process, the catalyst was fed to each reactor along the reaction train. 

PEN and copolyesters are readily prepared from NDC and ethylene glycol using either batch or continnous polymerization (12). Solubility data for NDC in ethylene glycol is snmmarized in Table 10. An example of a typical continuous polymerization process is shown in Figure 8. 

---