The problem has been discussed here in the past. It boils down to the Philly area refineries (owned by various corporates: Sunoco, Valero, ConocoPhillips, and others in the past and changed names and hands multiple times) major new investment in a long time so the are not as complex as the ones on the Gulf Coast and elsewhere. They can only process a slate of sweeter crudes, which have become far more expensive on the international market. Add to that, Sunoco long ago gave up exploration and isn't a vertically integrated company-- exploring for crude (which is the most profitable part of the biz) and then plowing money into downstream ops.
In short: buyers at our area refiners have to shop for more expensive, sweet crude feedstocks on world markets which are benchmarked at Brent Sea Crude prices. The difference in that benchmark price and the local West Texas Intermediate keeps widening, but the end product prices are equal whether you process one type of crude or the other. So the refinery gets squeezed in their gross and operating margins. Add to that the fact that other refineries can not only switch crude slates but also produce a different ratio of products because they are more complex, thus driving out better efficiencies. So if jet fuel has better margins one day, a refinery on the Gulf Coast can produce more of that product by turning down its FCC unit and turning up some other units.
Basically, Sunoco can't make a dime on its rusted junk, it hasn't kept up with the times, and now it seems nobody wants to buy it because it would take some significant new investment before the refinery can start to be profitable.
"The only difference between the Republican and Democratic parties is the velocities with which their knees hit the floor when corporations knock on their door. That's the only difference."
- Ralph Nader