A chemical reaction due to leftover butadiene residue in a storage tank probably was the cause of the March 27 explosion at Phillips Petroleum Co.'s K-Resin plant in Pasadena, Texas, company officials said. The blast killed one and injured 69. The firm previously reported 74 were hurt but realized last week some people had been counted twice, spokesman Fred Ramos said by telephone April 17.
The tank in question had been shut down for routine maintenance. Workers had thought the tank was empty, he said.
Phillips' own investigative team now believes "popcorn polymer," which is formed when resin reacts with itself and bonds together to make shapes resembling popcorn, clogged some of the purge lines of the tank, Ramos said.
Nitrogen had been pumped through the tank to clear it of resin, he said, but apparently enough residue was left to react with itself when temperatures in the tank got too high.
When a tank is in use it continuously is cooled to prevent a chemical reaction. "The longer it sits, the longer it has the opportunity to react," Ramos said. He was unsure how long the tank had been shut down.
Workers had taken all the precautions to make sure the tank was empty, even looking inside it, he said, but he added that there was no way to make sure the purge lines were empty.
Phillips' investigation team has not formally determined the cause of the blast and the Occupational Safety and Health Administration is continuing its own investigation.
As of now, Phillips has closed the K-Resin plant indefinitely, Ramos said.
In the meantime, K-Resin users have had to look elsewhere to source their material or find alternatives. Diamond Polymers, an ABS producer and compounder in Akron, Ohio, has fielded 20 calls from K-Resin processors since the most recent outage, according to President Bruce Petersen.
Diamond's transparent ABS and acrylic-stryrene-acrylonitrile products can replace K-Resin in many applications, Petersen said, while the firm's styrene methyl methacrylate and styrene-acrylonitrile resins can be used as an additive to extend K-Resin supplies.
Although Diamond recently added 10 million to 20 million more pounds of ABS and ASA capacity, its new total of 60 million pounds is well short of being able to match K-Resin's 300-million-pound market.
Diamond's ABS and ASA resins sell for $1.65-$2 per pound — well above K-Resin's list price of 95 cents to $1 per pound — but they offer excellent transparency and ductile impact, Petersen said.
"We're looking to develop these applications long term. Continuity of supply is something [processors] have to have," he said.
While some have speculated that the K-Resin shortage will create a sizable opportunity for the crystal polystyrene market, Petersen said he doesn't see that happening, because crystal PS would be too brittle for many K-Resin applications.
Applications where the K-Resin-to-ABS/ASA switch could take place include pump parts for food and beverage dispensers, medical items, toys, appliances and small hand-held tools, he added.
Officials at Deltech Polymers Corp., a resin maker in Troy, Ohio, said they've received at least 10 calls from K-Resin users.
The firm, which produces about 145 million pounds of crystal PS each year, entered into SMMA production earlier this year. Its SMMA can be effectively blended with K-Resin, Deltech sales and marketing manager Brent Reedstrom said.
"The question processors need to be asking themselves right now is whether or not their current use of K-Resin, 100 percent or as a component of a blend, is optimal, based on the requirements of the application," Reedstrom said.
