Styrene Plant Operation

The dehydrogenation of ethyl benzene is endothermic so that heat must be sup-pUed during operation. The two commercial styrene processes either incorporate several adiabatic beds with interbed heat exchange/steam addition or isothermal tubular reactors with a siritable heating mediirm in order to maintain operating 

Carbon deposition and dealkylation reactions are both inhibited by the addition of potash to the catalyst. The equilibrium of the forward reaction is favored 

Some catalysts can catalyze the dealkylation of the ethyl benzene to ethylene and benzene, as well as the required dehydrogenation reaction to give styrene and hydrogen. This undesirable reaction can be suppressed by allowing a 

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In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

Personal 8-h TWA measurements taken in 1978 and 1979 in companies where acrylonitrile-butadiene-styrene moulding operations were conducted showed levels of < 0.05-1.9 mg/nr (Burroughs, 1979 Belanger Elesh, 1980 Ruhe Jannerfeldt, 1980). In a polybutadiene rubber warehouse, levels of 0.003 ppm [0.007 mg/m ] were found in area samples area and personal samples taken in tyre plants found 0.007-0.05 ppm [0.016-0.11 mg/m ] (Rubber Manufacturers Association, 1984). In a tyre and tube manufacturing plant in the United States in 1975, a cutter man/Banbmy operator was reported to have been exposed to butadiene at 2.1 ppm [4.6 mg/m ] (personal 6-h sample) (Ropert, 1976). 

Several other archery bow manufacturers have installed catalyst-heat systems for making wood-plastics but little is known about their production. A number of pilot plant operations have been installed in the United States but little of this proprietory information is available. Pilot plant quantities of cutlery handles have been produced for market studies, a laminated type of flooring was produced using a styrene-polyester composite cured in a hot press, parquet flooring using the catalyst-heat system is presently being produced for market studies. Many other small volume items, such as, jewelry, bird calls, transformer cores, etc. are finding their way into the market place. 

Ethane cracking is conducted across the world. The scales of operation range from the smallest, less than 50,000 t/y, when small amounts of ethylene is required, for example for a stand-alone styrene plant, to the largest ethylene production operations of over 1 million tonnes of ethylene. The block flow layout for a small stand-alone ethane cracking operation is illustrated in Figure 7.1. 

In the ethylbenzene process the 1-methylbenzyl alcohol (MBA) co-product is dehydrated to monomeric styrene (SM). The theoretical SM/PO ratio is 1.8 1 and commercial plants operate in the range 2.2-2.7 l, indicating that the selectivity of ethylbenzene hydroperoxide (EBHP) formation is much higher than that of... 

The commercialization of liquid phase processes, which operate at substantially lower temperatures, decreased the side reactions dramatically, resulting in ultra-high-purity EB product. This improvement alleviated problems previously encountered in the downstream styrene plant. The first liquid phase commercial plant based on the Lummus/UOP process was commissioned in 1990. Since then, more than 25 projects have been licensed with more than 17 plants in commercial operation as of 2004. The liquid phase plants typically achieve high onstream efficiency, often greater than 99%, which results in low turnaround and maintenance costs. This technology is now licensed by UOP LLC and ABB Lummus Global. 

Ethylene is of course a basic building block from which chemical synthesis may branch out in many directions. The move towards large units to shave fractions of cents from unit manufacturing costs, however, is extending to derivatives such as styrene and vinyl chloride. Until relatively recently a styrene plant could operate profitably at the rate of 100 to 200 million pounds per year. New engineering and risk capital have now raised this competitive threshold to around 300 million pounds, and units capable of one-half a billion are coming on stream. 

Figure 5.9 Part of the styrene distillation plant operated by Dow, Temeuzen/Netherlands...

The result is that the driving force at the wall must increase by a factor of about 10 when scaling with S = 512 and constant power per unit volume. This may be acceptable when the pilot unit operates with a AT of 2°C but becomes problematic when the pilot plant operates with a 20°C AT. There are many solutions. In a CSTR, use cold feed. Some processes for PMMA use a 40°C feed to control the reaction exotherm. Diluents and low per-pass conversions can also be used this approach is typical of solution polyolefin processes. Reflux boiling can be used it is common in styrenic polymerizations where the reflux solvent is normally returned as a liquid. In some polypropylene processes, the returning propylene is flashed into the first reaction vessel. Finally, the external loop shown in Figure... 

Ethylbenzene Separation. Ethylbenzene [100-41-4] which is primarily used in the production of styrene, is difficult to separate from mixed Cg aromatics by fractionation. A column of about 350 trays operated at a refluxTeed ratio of 20 is required. No commercial adsorptive unit to accomplish this separation has yet been installed, but the operation has been performed successhiUy in pilot plants (see Table 5). About 99% of the ethylbenzene in the feed was recovered at a purity of 99.7%. This operation, the UOP Ebex process, requires about 40% of the energy that is required by fractional distillation. 

The hydroperoxide process involves oxidation of propjiene (qv) to propylene oxide by an organic hydroperoxide. An alcohol is produced as a coproduct. Two different hydroperoxides are used commercially that result in / fZ-butanol or 1-phenylethanol as the coproduct. The / fZ-butanol (TBA) has been used as a gasoline additive, dehydrated to isobutjiene, and used as feedstock to produce methyl tert-huty ether (MTBE), a gasoline additive. The 1-phenyl ethanol is dehydrated to styrene. ARCO Chemical has plants producing the TBA coproduct in the United States, Erance, and the Netherlands. Texaco has a TBA coproduct plant in the United States. Styrene coproduct plants are operated by ARCO Chemical in the United States and Japan, Shell in the Netherlands, Repsol in Spain, and Yukong in South Korea. 

Viable operating eonditions were identified experimentally for maximising the produetion of ethylene, propylene, styrene and benzene from the pyrolysis of waste produets. Data are given for pyrolysis temperature, produet reaetion time, and quench time using a batch microreactor and a pilot-plant-sized reactor. 26 refs. CANADA... 

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