Sunoco is moving forward with a plan to transport by-products of Marcellus Shale natural gas to Southeastern Pennsylvania by pipeline, potentially fueling new industrial development in beleaguered Marcus Hook.

Sunoco Logistics Partners L.P. announced on Thursday a "binding open season" for Marcellus producers to commit themselves to buying capacity on the Mariner East pipeline project. Pipeline companies typically request binding bids only when they are certain that a project will get enough commitments to proceed.

The Mariner East project, which calls for repurposing an existing Sunoco pipeline that crosses Pennsylvania, was originally conceived in 2010 as a way to find markets for Marcellus ethane by sending the material to Philadelphia for shipment by sea to Gulf Coast petrochemical plants. Those plants in Texas and Louisiana convert or "crack" ethane into a key ingredient used in the manufacturing of plastics.

But the project has been reimagined in recent months to include propane, which, like ethane, is found in abundance in the rich "wet gas" produced in the Marcellus wells in southwestern Pennsylvania.

Marcellus producers have already begun trucking propane to Sunoco's Marcus Hook location for loading on ships for export to Europe, according to MarkWest Energy Partners L.P., which is working with Sunoco on the Mariner project. Propane fetches a premium price in Europe as a heating fuel and a raw material for chemical producers.

A cross-state pipeline would be able to carry far more fuel to Southeastern Pennsylvania than trucks, requiring construction of a fuel terminal and also potentially a processing plant to separate ethane and propane from natural gas liquids.

Though Sunoco itself has not identified Marcus Hook as the terminus of the pipeline, MarkWest is not so circumspect in presentations it has made to investors. The Marcus Hook site is a sensible industrial location for such activity since Sunoco shut down its oil refinery there last year and has been working to redevelop the site, which is equipped with extensive fuel storage and deepwater docking facilities.

A report released in June by the Delaware County Industrial Development Authority identified a natural-gas liquids processing facility as one potential use for the former refinery site. The report said such a plant could employ from 75 to 100 workers.

The Mariner project might export more than jobs to Philadelphia from the Marcellus region.

Shifting natural gas processing to the Delaware River would also prevent a new air pollution source from the Pittsburgh area, which faces becoming a "nonattainment area" if it fails to meet federal emissions standards.

"It also distributes more of the emissions over into the Philadelphia area away from Pittsburgh, which is becoming a bigger and bigger issue as a nonattainment area," Frank Semple, the chairman and chief executive of MarkWest, said at an investor conference in Greenwich, Conn., on May 23.

MarkWest, which is based in Colorado, is a leading processor of natural gas. Its plants purify natural gas and pull out constituents such as butane, propane and ethane that can command a higher price when sold separately.

Natural gas liquids have become a lucrative part of the Marcellus development. Since the price of natural gas has fallen, drilling operations have slowed in the "dry gas" areas in northern Pennsylvania that produce mostly methane, the main ingredient of natural gas. But many drill rigs have moved to areas that are producing wet gas or oil, which fetches a premium.

Marcellus producers in Western Pennsylvania have faced a challenge finding markets for the liquids. Sunoco and MarkWest teamed up to develop the Mariner West project, which will transport ethane through Sunoco pipelines to petrochemical producers in Sarnia, Ontario. Another pipeline project would transport ethane directly to the Gulf Coast, where the petrochemical industry is expanding production capacity.

Shell Chemical L.P. this year announced it had picked Western Pennsylvania as the site to build an ethane cracker, enticed by up to $1.65 billion in tax incentives from the Corbett administration. That plant would consume a large amount of the supply.

With sufficient outlets for ethane in the works, Marcellus producers began to campaign for markets to buy their propane. Propane, which is produced from natural gas and from oil refineries, is used for heating, drying grain and as a raw material for chemicals.

Semple, the MarkWest chief executive, told analysts on Aug. 3 to stay tuned on whether "a world-class export terminal is developed out of the Philadelphia market."

Sunoco Logistics anticipates the Mariner East project will initially transport 65,000 barrels per day of natural gas liquids and come on line in the second half of 2014.

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