Continuous tower process

Figure 1. Ohlinger s continuous tower process of 1936 (Ludwigshafen, Germanv)...

Polystyrene using the continuous tower process Maximization of the monomer conversion and minimization of the polydispersity index of the product. NSGA-II A unique solution was obtained instead of a Pareto-optimal set. Bhat et al. (2004)... 

The continuous mass process is divided into 4 steps rubber solution in styrene monomer, polymerization, devolatilization and compounding. In 1970 N. Platzer (40) drew up a survey of the state of the art. Polymerization is divided into prepolymerization and main polymerization for both steps reactor designs other than the tower reactors shown in Figure 2 have been proposed. Main polymerization is taken to a conversion of 75 to 85% residual monomer and any solvent are separated under vacuum. The copolymer then passes to granulating equipment, frequently through one or more intermediate extruders in which colorant and other auxiliaries are added. 

Figure 1.5 Schematic of BASF s early tower process for the continuous polymerization of styrene. This configuration was designed by C. Wulff and E. Dorrer in the early 1930s. Polymerization was thermally initiated and the exotherm controlled by heat transfer tubes (courtesy of BASF, Ludwigshafen)...

The alternative path of evolution was to the continuous solution process, first demonstrated with the tower process by I. G. Farben and implemented by Dow and others as either towers or tanks filled with heat transfer tubes. These... 

Because of the rate limitations of the tower and tube-tank processes that were primarily heat transfer constraints, further developments in the continuous solution process for crystal polystyrene (GP) were aimed at improving heat transfer. One obvious solution was to incorporate agitation of some type in the reactor. Although at Dow the incorporation of agitation in the reactors came about with the development of rubber-modified polystyrene [11], and this aspect will be discussed in a later section, agitation also significantly raises the heat transfer... 

Reppe was also working on the preparation of ethylene oxide. The first step was the reaction of ethylene with chlorine and water to form ethylene chlorohydrin (2-chloroethanol). He was able to convert the unsatisfactory batch process, which had been used for indigo manufacture, into a continuous process. This was called the tower process (Turm-Verfahren), because a mixture of ethylene and a carefully controlled amount of chlorine was driven up a tower filled with water. The dilute solution of ethylene chlorohydrin was drawn off at the top and then heated, without being isolated, with lime water to form ethylene oxide. Ethylene oxide was chiefly converted into the glycol by adding water, but it could also be used to make diethylene glycoF (diglycol). 

The planar reinforcement was coated and cured in a continuous production process as depicted in Fig. 5. The fabric was driven through a mold filled with epoxy resin. Excessive resin was squeezed out between rollers, so that a uniform application of the resin as well as a nearly saturated roving was achieved. Immediately after coating, the textile was cured in a heating tower at a maximum temperature of 160°C and coiled up to a roll. 

Thermal polymerization (see also Section 20.2.6) is carried out by the tower process. In this case, a prepolymerizate of about 30% poly(styrene) in styrene is passed down a tower of upper temperature lOO C and lower temperature of about 220 C over a period of about one day. The processes continuous, with polymer being drawn off at the bottom. Large quantities of poly(styrene) are also produced discontinuously by the suspension polymerization process. 

Vinyl acetate is polymerized free radically in bulk, emulsion, or suspension. Bulk polymerization occurs at the boiling temperature of the monomer (72.5 C at 1 bar), and yields highly branched polymer because of chain transfer via the ester groups (see also Section 20.4.3). Commercially, the polymerization is taken to a specific yield and the residual monomer is removed by thin-layer evaporation. Alternatively, continuous polymerization can be carried out in a tower. But this method only produces moderate degrees of polymerization since the tower process requires that the polymer should flow and the flow temperature should lie below the decomposition tempera-... 

A batch separation will require an amount of time inversely proportional to the rate at which heat is introduced. Consequently, if processing time is to be minimized, heat input must be maintained at the maximum permissible level throughout distillation. This feature then fixes one of the variables which was subject to manipulation on a continuous tower. With vapor rate fixed, a material balance can be readily constructed for the batch still shown In Fig. 11.26. 

German vinyl ether plants were described in detail at the end of World War II and variations of these processes are stiU in use. Vinylation of alcohols from methyl to butyl was carried out under pressure typically 2—2.3 MPa (20—22 atm) and 160—165°C for methyl, and 0.4—0.5 MPa (4—5 atm) and 150—155°C for isobutyl. An unpacked tower, operating continuously, produced about 300 t/month, with yields of 90—95% (247). 

Later it was synthesized in a batch process from dimethyl ether and sulfur thoxide (93) and this combination was adapted for continuous operation. Gaseous dimethyl ether was bubbled at 15.4 kg/h into the bottom of a tower 20 cm in diameter and 365 cm high and filled with the reaction product dimethyl sulfate. Liquid sulfur thoxide was introduced at 26.5 kg/h at the top of the tower. The mildly exothermic reaction was controlled at 45—47°C, and the reaction product (96—97 wt % dimethyl sulfate, sulfuhc acid, and methyl hydrogen sulfate) was continuously withdrawn and purified by vacuum distillation over sodium sulfate. The yield was almost quantitative, and the product was a clear, colorless, mobile Hquid. A modified process is deschbed in Reference 94. Properties are Hsted in Table 3. 

If a waste contains a mixture of volatile components that have similar vapor pressures, it is more difficult to separate these components and continuous fractional distillation is required. In this type of distillation unit (Fig. 4), a packed tower or tray column is used. Steam is introduced at the bottom of the column while the waste stream is introduced above and flows downward, countercurrent to the steam. As the steam vaporizes the volatile components and rises, it passes through a rectification section above the waste feed. In this section, vapors that have been condensed from the process are refluxed to the column, contacting the rising vapors and enriching them with the more volatile components. The vapors are then collected and condensed. Organics in the condensate may be separated from the aqueous stream after which the aqueous stream can be recycled to the stripper. 

Continuous chlorination of a cooling water system often seems most pmdent for microbial slime control. However, it is economically difficult to maintain a continuous free residual in some systems, especially those with process leaks. In some high demand systems it is often impossible to achieve a free residual, and a combined residual must be accepted. In addition, high chlorine feed rates, with or without high residuals, can increase system metal corrosion and tower wood decay. Supplementing with nonoxidizing antimicrobials is preferable to high chlorination rates. 

---