Hall of Fame: Norwood honored for his invention of the loop reactor

BARTLESVILLE, OKLA. — Donald Norwood's invention in 1957 of the loop reactor to produce polyethylene slashed production costs by 70 to 80 percent, and the material spread through nearly every conceivable type of package.

Milk jugs. Detergent bottles. Trash bags. Pipe. A flood of consumer products that continues today.

In 1951, Phillips Petroleum Co. scientists discovered the first transition metal catalyst capable of polymerizing olefins — polyethylene and polypropylene — at low pressure. By the time Norwood came to the Bartlesville-based company in 1957, excitement was in the air.

“People working on the development had a great attitude. They were gung-ho, because it was a new event for them,” he said. “For a little town, they were paying good wages. We had great management support here in Bartlesville.”

The U.S. economy was booming after World War II. At Phillips, scientists regularly talked with executives, pilot-plant technicians and marketing people. “They were high-spirited in those days. The lab people were interested in what was going on,” Norwood said.

Now Norwood, 88, is going into the Plastics Hall of Fame. He spent his entire career at Phillips, now Chevron Phillips Chemical Co.

Simple invention changes process

The loop reactor was “new and daringly simple,” wrote Max McDaniel, catalysis scientist at Chevron Phillips. Norwood was nominated for the Plastics Hall of Fame by McDaniel and Don Peters, retired principal engineer at Phillips, and himself a hall of famer. Both men worked with Norwood in Bartlesville.

Norwood, a Missouri native, was an infantryman in World War II. He was in the invasion of the Philippines and the occupation of Japan. After the war, he earned a chemical engineering degree from the University of Missouri-Rolla.

For four years, he worked on the separation of uranium isotopes in Oak Ridge, Tenn.  He joined Phillips in 1956. They put him on a team assigned to PE development.

“It was well organized, and they had what they called group leaders,” he said.

Phillips was using the solution-form process in conventional, pot-type vessels. Norwood worked at a solution-form Marlex pilot plant for his first few months. Pressures had been greatly reduced, but the new technology had some weaknesses. The solution process still required that the polymer be dissolved in a heavy hydrocarbon liquid, and removing the solvent afterwards was costly, by centrifuge and filtration. And removing heat caused by the ethylene conversion required longer residence time in the reactor. It all added up to low production rates and higher costs.

And the pot vessels had quiescent zones — areas of inactive flow and turbulence, where polymers could build up. In extreme cases, they had to shut the reactor down and burn it out.

Norwood came up with the idea of a reactor in an unusual shape of a vertical loop.

“There was a lot of development work that went on leading up that,” Norwood recalled. “I sketched up what I wanted to try, based on what I learned from the trials and tribulations that we'd run.”

The material did not have to go into a solution — and so the loop method was called slurry “particle-form” process, or PF. Particle instead of solution.

Another advantage: By moving the materials through the loop at a high velocity, driven by pumps, the material could not build up. And the team decided the temperature of the reaction would be relatively low, to prevent melting of the polymer.

Norwood realized that, to accomplish this, what was needed was not a good solvent, but rather a bad one. He found that in pentane, a light-branched alkane. He also chose a hydrocarbon non-solvent, or diluent, for its heat transfer capability.

The diluent also had a desirable vapor pressure, so the hot diluent would vaporize, or “flash,” and be carried away as a gas to be recycled. That is one reason the loop reactor particle-form process reduced costs sharply over the solution-phase.

“We didn't want the polymer to go in solution. So we used a real light hydrocarbon,” Norwood said.

The scientists and engineers worked as a team.

“Of course this was a group effort, you know,” Norwood said. “In those days there were a lot of other people working, either in solution, and they were just getting started in particle form. But they ran the solution pilot plant around the clock.”

In the history section of the nomination, McDaniel wrote: “The polymer fell into a silo as a dry clean powder. Given the high productivity, the catalyst did not need to be removed from the polymer, yielding an incredibly simple and clean process, compared to the complicated and expensive solution-form process.”

Phillips authorized Norwood to build a pilot plant, a 100-gallon loop, which started up in 1958.

“The cumulative design was audacious in its simplicity,” McDaniel wrote.

Phillips scaled up the loop commercially, first to make PE and then PP. The first commercial loop polyethylene reactor came on stream in Houston in 1961. A “bulk” polypropylene loop reactor soon followed.

The company quickly licensed the loop technology to major PE and PP producers around the world. Today about 250 loop reactors are in operation, using many kinds of catalysts, such as chromium, Ziegler Natta and metallocene.

Phillips patented Norwood's loop reactor in 1966.

By the time the loop reactors were in full force, Norwood had already moved on to other duties within the company. From 1962 to 1970, he did process development research at Phillips' synthetic rubber and elastomers operation. Then he returned to polyolefins, as supervisor of PE and PP pilot plants, where he continued to develop the loop reactor.

He worked full-time as an engineering consultant from 1986 to 1996. Chevron Phillips presented Norwood with a Lifetime Achievement Award in 2006. And Norwood is capping it off by entering the Plastics Hall of Fame.

Norwood has kept returning to his groundbreaking innovation.

Life is like a loop.

Check out a video profile of Norwood: