Sharing high standards in styrene storage

The conditions under which styrene is kept have to be carefully controlled.

The ability of styrene to mix easily with other molecules and form new polymers makes it one of the most versatile materials in the chemical industry. This reactivity, however, also means that the conditions under which it is kept have to be carefully controlled.

Due to its chemical structure, styrene may start to polymerise (form solid polystyrene polymer) under certain storage conditions. A small amount of polymer build-up is normal, and has no negative impact on product quality or safety, but if the process is not recognised and controlled it can ‘snowball’.

“If the polymerisation is allowed to become rapid and self-sustaining, it can develop into a runaway exothermic reaction,” explains Susanne Trebert-Haeberlin, Shell Chemicals Senior Product Steward. “Ultimately, if not checked, this could result in the release of large quantities of heat and volumetric expansion which may cause a storage tank to rupture.”

She says that although incidents involving runaway reactions had been rare, Shell decided to investigate the issue further, particularly in light of the industry’s increasing use of third party terminals and storage facilities.

“As a key player in the industry it was important for us to gain a better understanding of this issue and the potential implications for quality and safety,” she says.

Drawing on experience

Shell’s findings on styrene storage have been shared with customers and co-producers.

Technical and HSSE (Health Safety, Security and Environment) teams drew on Shell’s 40 years of experience in producing and handling styrene monomer. Their work highlighted the fact that if sufficient attention is not paid to the equipment and methods used to store the product, as well as to monitoring procedures, situations can arise where product quality degenerates or, in worst cases, may pose a serious safety concern.

As a result, new storage guidelines were developed, covering the critical areas that, alone or in combination, can be contributing factors to polymerisation. These included:

• the correct use of polymerisation inhibitor; 
• tank cooling, circulation and cleaning processes; 
• the use of tanks made from appropriate materials; 
• and procedures for monitoring oxygen, contaminant and polymer levels.

“We used these new guidelines to review all our storage facilities and those we contract from third parties around the world,” says Trebert-Haeberlin. “We also prepared and implemented training for operators at these facilities, as well as making a number of small changes to equipment or procedures.”

But because this was an industry-wide issue, efforts did not stop there. “As a producer committed to the principles of Responsible Care® it was important we used this knowledge to contribute to raising standards of styrene monomer product stewardship across the industry,” she says.

Shell’s findings were shared with customers and co-producers through the Styrene Producers Association (SPA), a sector group of Cefic, the European chemical industry body. As a result, Shell’s input has been incorporated into the latest official guidelines promoted by SPA for styrene transport, handling and storage, which are now generally accepted as a global standard.

“Our input was well received and we believe it has made a positive impact on awareness of issues around polymerisation of styrene during storage and the measures needed to manage them safely and effectively.”

Did you know?

- Styrene is one of the most versatile chemicals and is used to produce polymers such as polystyrene, unsaturated polyester resins and thermoplastic elastomers.

- Shell companies have been producing and supplying styrene monomer around the globe for more than 40 years.

- The Shell Group is the second largest producer of styrene, with a global manufacturing base and supply network, and a leading position in the merchant market.

This feature was added to the Innovations section in October 2009

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