2. Product Information and Characteristics
2.3. Manufacturing and Use
The conventional method for producing styrene involves two steps: the alkylation of benzene with ethylene to produce ethyl benzene followed by dehydrogenation of the ethyl benzene to produce styrene (refer to Figure 2). Over the almost fifty years of practicing the conventional two step process refinements have constantly been made to improve conversion and selectivity to ethyl benzene and finally to styrene along with design changes to conserve and utilize the energy in particular from the exothermic alkylation step. The traditional aluminum chloride catalyst used in this alkylation is slowly being replaced by zeolite catalyst technology. Currently the predominant route for the commercial production of styrene is by dehydrogenation of ethyl benzene in the presence of steam over a catalyst (iron oxide) in either fixed bed adiabatic or tubular isothermal reactors. Another route involves co-production of styrene and propylene oxide via hydroperoxidation of ethyl benzene. Limited scale extraction from steam cracker pyrolysis gasoline is also practised.
For more details on production technologies and the latest technology trends, please refer to Reference 1 and 2 of the bibliography
For more information on ethyl benzene (CAS RN: 100-41-4; EC No.: 202-849-4; Annex I Index No.: 601-023-00-4) please refer to CEFIC’s Environmental, Health and Safety Guidelines
Figure 2: Dehydrogenation of Ethyl benzene to Styrene
The specification and analytical methods for styrene have changed through the years. The majority of the manufacturers have defined their sales specifications according to the standard D2827 “Standard Specification for Styrene Monomer” of the American Society for Testing and Materials (ASTM). Key parameters of a typical sales specification are: a minimum purity of 99.7 wt. % and a maximum colour of 10 on the Platinum-Cobalt (Pt-Co) scale, while the specified impurities and their concentrations depend upon the manufacturing route employed, along with plant performance characteristics. The typical inhibitor content of the standard grade is 10-15 ppm TBC (4-tert-butylcatechol), while a higher dose may be defined in the customer specification depending on the expected storage period and use conditions at the customer site.
Styrene is widely used in the manufacture of resins, plastics, and latices/emulsion polymers by both batch and continuous mass polymerisation; by solution, suspension, and emulsion processes; and by various modifications and combinations of these techniques. Styrene responds to many different initiators, including peroxides and other free radical initiators, redox initiator systems, and ionic initiators. Styrene can be reacted with acrylates, methacrylates, acrylonitrile, butadiene, divinyl benzene and maleic anhydride, to form copolymers.
In 2004 the global styrene demand was reported to be over 24,000 Kt (data calculated from Reference 1
). Figure 3 presents the global styrene polymer derivatives demand based on 2004 data. Although declining in proportion polystyrene is by far the largest segment (46%) primarily used in packaging, disposables, electronics and appliances, followed by expandable polystyrene (16%) and acrylonitrile-butadiene-styrene (ABS) resins (14%). The heat-resistant, tough ABS resins are widely used for appliances and telephone casings, luggage, sporting helmets, pipe fittings and automotive parts. Styrene-Butadiene (SB) latex and SB rubber account for 10% of the global demand. SB latex finds its use as paper coating for glossy magazines, as component of carpet and upholstery backing, for the adhesive production and for latex paints. The majority of SB rubber is consumed in the manufacture of tires, automobile parts and electronic components. Unsaturated polyester resins (UPR) are used over a broad spread of industries, mainly the construction, boat building, automotive and electrical industries (5% of the global styrene polymer derivative demand, see Figure 6). Details on these and other applications can be found in Reference 2
or consult the following website: www.styreneforum.org
Figure 3: Global Demand for Styrene Polymer Derivatives in 2004