Process Summary

Lummus Technology and UOP's “Classic” SM process is a deep vacuum/adiabatic ethylbenzene dehydrogenation technology with demonstrated high mechanical integrity. The unique dehydrogenation reactor system is designed to operate at the most cost effective, minimal operating pressure for achieving the highest Styrene Monomer selectivities at high conversions. An off-line optimizer (SM GAIN™) can also be provided to allow personnel to closely monitor the important process variables and operate the plant at optimum conditions. More than 30 commercial plants are in operation worldwide^[1].

Process Description

The major reactions in the manufacture of SM are the dehydrogenation of EB to SM and hydrogen:

• The feedstock, ethylbenzene, is catalytically dehydrogenated to styrene in the presence of steam in a fixed-bed, radial flow reactor system. The dehydrogenation
  reaction is favored by low pressures and is generally conducted under deep vacuum.
  • Toluene, benzene, and some light compounds are formed as by-products.
  • The overall reaction is endothermic with heat supplied by steam generated by a superheater in the adiabatic reactors.
• Reactor effluent waste heat is recovered through heat exchange with combined feed and by generating steam which is utilized in the process.
• The offgas stream is compressed, processed through the off gas recovery section, and used as fuel in the steam superheater.
• The condensates from the condenser and off gas recovery section flow into the separator where hydrocarbon and water phases separate.
• The dehydrogenated mixture is fractionated to recover the styrene monomer product and recycle ethylbenzene, as well as benzene and toluene by-products.
  • Unreacted EB is recycled to the reactors.
  • Benzene and toluene are produced as by-products. Proprietary treaters allow recycle of by-product benzene to the EB Unit.
• Inhibitors are added to prevent styrene polymerization in the process equipment^[1],[2].

Process Features

• Styrene monomer purity of 99.85 wt-% minimum;
• High per pass EB conversion (up to 69%) for lower operating costs due to less EB recycle;
• Overall EB selectivity to styrene of more than 97 mol-% for lower EB feed consumption;
• Low equipment pressure drop, which permits the reactor operation to operate at high vacuum, for higher product quality and lower EB feed consumption;
• Minimum pressure drop radial bed reactors for lower operating pressure, resulting in lower EB feed consumption and reduced by-product formation;
• Energy savings from patented heat recovery that does not require compression equipment^[2].

References

1. LUMMUS Technology, 23^rd Sep 2020, Ethylbenzene / Styrene Monomer Tech Sheet.
2. UOP LLC, 2006, UOP Process Technology and Equipment, Lummus/UOP Classic SM^TM Process.