Dec 17, 2001 - ALEX TULLO ... In addition, the company is closing benzene, cyclohexane, and ... The company is also idling, but not closing, a 650 mil...
0 downloads 0 Views 545KB Size



CHEVRON PHILLIPS SHUTTERS PLANTS Commodity petrochemical units are latest victims of economic downturn UNWANTED Too little demand has led Chevron Phillips to close this ethylene cracker in Sweeny, Texas.



cal is making a rare move: It is shutting down an ethylene cracker. In addition, the company is closing benzene, cyclohexane, and polyethylene capacity The cracker is a small, 400 million-lb-per-year unit at the firm's Sweeny Texas, petrochemicals complex that has been idleforayear because of the weak ethylene market. The company is also idling, but not closing, a 650 million-lb


ethylene cracker at the complex. Chevron Phillips isn't alone in slating ethylene closures. Dow Chemical recently told investors that it may close older ethylene units in Seadrift and Texas City Texas, and replace them with a new cracker in Seadrift (C&EN, Nov. 19, page 17). In addition, Equistar has had an 850 millionlb cracker in Lake Charles, La., idle since February Earl H. Armstrong, director of olefins and derivatives for consultancy De Witt & Co., says crackers like the Chevron Phillips

unit that were built in the 1960s and 70s are not competitive with newer units. "Producers would just as soon put the cost of upgrading into a new plant," he adds. In addition, Armstrong says profitability and demand in the industry have been particularly poor this year. Operating rates, he says, are barely more than 80%. "Those are the lowest Fve seen in the last 15 or 16 years." Chevron Phillips is also shutting indefinitely benzene and cyclohexane plants in Guayama, PR., that have been idle since March. And it is delaying the restart of 0-xylene and ^-xylene units at the site that were due back on-line early next year. The company is also closing two loop polyethylene reactors at its Orange, Texas, complex over the next couple of months. This will reduce polyethylene capacity at the site by 25%, to 900 million lb per year.—ALEX TULL0

processes to be fully visualized by a simulation," Grubmuller says. In nature, aquaporin rapidly filters water through membranes. Larger molecules are kept from passing through the protein pore by the pore's small size. But tiny protons would be expected to skim through easily by hopping along the network of hydrogen bonds that inevitably forms when bined the atomic resolution water molecules are near one structure of the protein aqua- another. porin with a virtual bilayer memThe simulation reveals a delibrane surrounded by a large num- cately choreographed dance ofthe ber of water molecules to create water molecules, directed by careone of the largest and most com- fully positioned amino acid resplex computer simulations of the idues throughout the channel inmovement of molecules ever terior. "The water molecules are generated [Science, 294, 2353 handed off from one residue to (2001)}. The researchers were the next," Grubmuller explains. able to accurately calculate the "Each time you break a hydrogen movements of some 100,000 bond between two water moleatoms for a period of 10 nanosec- cules, you form another between onds. That's long enough to water and the protein." The re"watch" 16 water molecules pass sult is an energy-efficient process through the channel of the that allows the water molecules protein. to move rapidly through the "This is one of a very few, if not membrane and leaves the protons the first, complete biological behind-REBECCA RAWLS


WATCHING WATER LINE DANCE SAFE PASSAGE Water molecules (red and gray) are guided one by one through protein pores (blue) to cross bilayer membrane.



To pass through a membrane pore quickly, H 2 0 must 'change partners'



Planck Institute for Biophysical Chemistry in Gottingen, Germany, have used molecular dynamics simulations to solve a biological mystery: how water molecules can pass through a protein pore in a cell membrane as rapidly as they do without ferrying extra protons across with them. Theoretical biophysicist Helmut Grubmuller and chemist Bert L. de Groot com-

17. 2001