What is Xylene, and What Does it Mean for Puget Sound?

Puget Sound sunset by Ed Suominen used under CC BY-NC 2.0

It’s a safe bet that most people have no idea what C₆H₄(CH₃)₂ refers to. It’s a chemical compound that is better known—when it is known at all—as xylene, a niche product of oil refining soon to go into development on the shores of Puget Sound. It’s a change that has potential implications for the health of the Salish Sea, for oil trains, and perhaps even for gasoline prices.

Because most people know so little about the product, we thought it would be useful to share a short course on it. So with that, welcome to “Xylene 101.”

What is xylene, exactly?

Let’s get some quick and dirty chemistry out of the way. (It won’t hurt.) Xylene refers to a group of three different isomers (molecules with the same chemical formula but different chemical structures): orthoxylene, metaxylene, and paraxylene, all of which are petrochemicals. In a process known as catalytic reforming, refiners distill petroleum naphtha (chemicals found in partly refined crude oil) and then convert it into a high octane liquid hydrocarbon called reformate. Traditionally, oil refiners blend reformate with gasoline and jet fuel to increase octane levels, but it can also serve as the “feedstock” for chemicals like xylene. (Xylenes can also be produced by coal carbonization in the manufacture of petcoke.)

Still with us? Good.

So, what do xylenes mean for Washington?

At its Anacortes Refinery, oil company Tesoro is now investing $400 million on facility upgrades that will allow it to produce mixed xylene for export to Asia at a rate of 15,000 barrels per day. That represents about 12.5 percent of the refinery’s total crude capacity and about 9 percent of total US xylene production capacity, most of which is currently in Gulf Coast states. In order to produce xylene for export at Anacortes, Tesoro will have to build a new xylene extraction unit capable of recovering xylene from petrochemical feedstock produced by refineries in Washington and California. In anticipation of what may be a large construction project, Tesoro is looking to expand its onsite infrastructure. In fact, Skagit County recently approved Tesoro’s plan to more than double the size of its existing parking lot (from 500 spaces to 1,350 spaces), expanding it 135 feet into a shoreline buffer zone.

According to Tesoro, the global xylene market is growing about 5 percent to 7 percent annually, primarily driven by demand in Asia. In addition, one industry journal notes that “because [xylene] production uses refinery-produced reformate, which is otherwise used for gasoline production, the shift could also ease what refiners consider an oversupplied US west coast gasoline market.”

In other words, Tesoro aims to produce less gasoline on the West Coast in order to free up reformate for xylene production.

Tesoro already produces 32,000 barrels of reformate per day on site at the Anacortes refinery. About half of that supply, along with additional reformate shipped by vessel from its Golden Eagle Refinery near Martinez, California, would be directed toward the production of xylene. Nowadays, both refineries are processing more light Bakken Shale crude oil than they have in the past—delivered principally by trains that have lately exhibited a nasty tendency for exploding—which yields particularly high levels of petroleum naphtha. More naphtha means more reformate, which in turn means more xylene.

The company expects to have the new xylene facility up and running by 2017, but first must seek construction permits from the State. A slow permitting process has discouraged other West Coast oil companies from pursuing similar petrochemical projects; Valero’s vice president of refining operations admitted that “It would be tough to get permits, at the end of the day.”

But what is xylene used for? And should we worry about it?

Xylenes have several primary applications. Paraxylene, often abbreviated to p-xylene, is generally considered the most valuable isomer thanks to its role as the principal precursor chemical in the production of polyethylene terephthalate (PET). PET is a plastic found in most water bottles and food containers, as well as polyester clothing. Researchers are also examining its potential to leach endocrine disrupters—chemicals that interfere with human hormones. Xylenes can also be used as a solvent in the printing, rubber, paint, and leather industries. In histology, xylenes are used in the dehydration of biological tissue to make it suitable for microscope slides.

Colorless and sweet-smelling liquids, xylenes are flammable and moderately toxic by inhalation or ingestion. They do not dissolve in—and are less dense than—water. The main effect of inhaling xylene vapor is depression of the central nervous system, resulting in symptoms such as headache, dizziness, nausea and vomiting. Long-term exposure may lead to more headaches plus irritability, depression, insomnia, agitation, extreme tiredness, tremors, impaired concentration and short-term memory loss.

Xylene poses at least some pollution risks. A xylene spill or leak into the soil or ground water could remain for months or more before it breaks down into other chemicals, while a surface water spill would be difficult to contain because it is colorless. In fact, the only method for tracking the chemical is via air tests near the spill. That said, a surface spill could potentially be less persistent because xylenes evaporate easily and are broken down by sunlight into other, less-harmful chemicals. That was the case in 2007 when a tanker carrying xylene spilled about 42,000 gallons into the Mississippi River after a collision with a grain barge; within two days, most of the chemicals either evaporated or were flushed downriver.

There is some reason to worry about Tesoro’s ability to handle xylene production appropriately. Sightline’s review of the company finds a checkered history, including persistent problems at the Golden Eagle Refinery in California (which would supply some of the reformate for xylene production), a deadly and much-criticized fire at the Anacortes Refinery, and a troubling pattern of withholding information from the public and regulators.