Technology

Historical Background

The LyondellBasell PO/SM (Propylene Oxide-Styrene Monomer) process is a proprietary technology used for the co-production of Propylene Oxide (PO) and Styrene monomer (SM). 

The POSM process was originally developed by ARCO Chemical Company as part of its innovations in propylene oxide production. ARCO Chemical was a division of Atlantic Richfield Company (ARCO) and became a global leader in propylene oxide technologies by the late 20^th century^[1],[2]. In 1998, Lyondell acquired ARCO Chemical, incorporating ARCO's technologies into its portfolio^[2]. Later, Basell Polyolefins merged with Lyondell in 2007 to form LyondellBasell Industries, which now owns and licenses the PO/SM technology^[3].

The foundational patent for the PO/SM process is U.S. Patent No. 3,351,635^[4], filed by Halcon International in 1966, which describes the basic reaction sequence. Later patents, such as U.S. Patent 5,210,354^[5] (ARCO Chemical, 1992) and US20100078391A1^[6] (LyondellBasell, 2008), focus on improving residue management and product recovery. Halcon International partnered with ARCO to commercialize the technology, with ARCO eventually acquiring full ownership of the process.

Working Principles

The POSM process co-produces PO and SM through a series of chemical reactions involving ethylbenzene and propylene^[4-6]:

• Ethylbenzene Oxidation: Ethylbenzene is oxidized with oxygen to form ethylbenzene hydroperoxide (EBHP). This reaction is catalyzed by small amounts of alkali to enhance selectivity.
  
  C₆H₅CH₂CH₃ + O₂ → C₆H₅CH₂CH₂OOH
   
• Epoxidation: EBHP reacts with propylene in the presence of a molybdenum-based catalyst to produce PO and 1-phenylethanol.
  
  C₆H₅CH₂CH₂OOH + CH₃CH=CH₂ → CH₃CH(O)CH₂ + C₆H₅CH(OH)CH₃
   
• Dehydration: 1-Phenylethanol is dehydrated to form styrene monomer.
  
  C₆H₅CH(OH)CH₃  → C₆H₅CHCH₂ + H₂O
   
• The process also includes multiple distillation steps to separate unreacted materials and refine the products. 
   
• Residual heavy organic streams containing sodium compounds are treated with aqueous acid to recover valuable by-products or convert them into upgraded fuels.

Yields

• The typical production ratio of PO to SM is approximately 1:2.5.

• By-products include propane, acetophenone, and other oxygenated aryl compounds.

References

1. FUNDINGUNIVERSE, ARCO Chemical Company History. (Accessed 13^th Mar 2025)
2. Lyondellbasell, Company history 1998-1953. (Accessed 13^th Mar 2025)
3. LyondellBasell, 20^th Dec 2007, Basell and Lyondell Complete Merger Creating LyondellBasell Industries.
4. United States Patent 3,351,635, Patented 7 Nov 1967, EPOXDATION PROCESS, assignee: Halcon International, Inc.
5. United States Patent 5,210,354, Date of Patent: 11 May 1993, PROPYLENE OXIDE-STYRENE MONOMER PROCESS, assignee: ARCO Chemical Technology, L.P.
6. United States US 2010/0078391 A1, Pub. Date: 1 Apr. 2010, RESIDUAL STREAM UPGRADING IN A PROPYLENE OXDE-STYRENE MONOMER PROCESS, assignee: LyondellBasell Industries.