Refining chemical cause of concern

Citgo plant fire spurs new look at hydrogen fluoride

By Denise Malan
Originally published 10:13 p.m., August 15, 2009
Updated 10:37 p.m., August 15, 2009

CORPUS CHRISTI — A fire last month at a local Citgo refinery has focused attention on what is likely the most dangerous chemical used in the refining process.

Hydrogen fluoride, an acid, is used as a catalyst for chemical reactions in the alkylation unit, which produces a high-octane component for gasoline. The Citgo alkylation unit was the site of the July fire and another in 1997.

Environmental groups, worried about the risk of a hydrogen fluoride vapor cloud, are pushing for safer alternatives. But each method has its drawbacks.

The only other proven chemical for alkylation is sulfuric acid, which like hydrogen fluoride can burn skin, tissue and lungs, though sulfuric acid is generally considered less toxic and less lethal. The third choice, a solid mineral that can be handled safely, hasn’t been tested in commercial-scale refineries.

Industry and academic experts say a switch is expensive and difficult. But the fire, which severely burned a Citgo worker, is an opportunity to open debate, environmentalists say.

“This is a very important learning experience for Corpus Christi,” said homeland security consultant Fred Millar, who would choose sulfuric acid over hydrogen fluoride. “Somebody should make sure there’s a very thorough investigation of continued use of hydrogen fluoride in a populated area.”

The United Steel Workers also is considering taking a stance on the chemical, said Mike Wright, director of health, safety and the environment for the union.

“The union is very concerned about HF,” Wright said. “First because of risks to our members in refineries. Second because of risks to the surrounding communities. We’re looking carefully at alternatives, and you can expect to hear something from us on that later in the year.”

Preliminary reports from Citgo to the state show at least 101 pounds of hydrogen fluoride were released in the incident. The Texas Commission on Environmental Quality has said hydrogen fluoride was detected in the air at a concentration of 5 parts per million at the Citgo fence line facing a nonresidential area.

About one hour exposure to that level could cause respiratory irritation. There is no evidence that residents were exposed, according to the TCEQ. The chemical becomes dangerous and potentially deadly at around 30 parts per million, according to federal agencies. The Occupational Safety and Health Administration allows exposures of up to 3 parts per million averaged over an eight-hour work shift.

Hydrogen fluoride burns skin, tissue and eyes and if inhaled can cause respiratory hemorrhage. The Citgo employee who was burned in the explosion remains in intensive care at Brooke Army Medical Center in San Antonio.

The fire, which burned for two days, is under investigation internally and by the TCEQ, OSHA and the U.S. Chemical Safety Board, which looks into the top 10 to 15 most serious chemical incidents in the country.

Groups urge change

Environmentalists are worried that hydrogen fluoride vapors may have harmed nearby residents. After a similar incident in 1997, people living near the refinery reported health effects and damage to vehicles.

The local Citizens for Environmental Justice and the statewide Sierra Club asked the state and federal governments to push the company to switch catalysts. They also have asked the Chemical Safety Board to hold a public meeting soon to provide preliminary investigation results.

In a complaint July 30 to the TCEQ, the groups say residents complained about sore throats, headaches and dizziness.

“Since Citgo cannot be a good neighbor to the local community, it must end all use of HF as soon as possible,” the letter read. “We believe that safer catalysts exist and Citgo has an obligation to switch.”

Company spokesman Larry Elizondo did not return calls for comment last week.

New method

Though the groups first pushed for sulfuric acid, they backed off that because of worker safety concerns. They are now asking for another method that has not been used commercially for alkylation, solid-acid catalysts, which essentially are rocks that act chemically as acids. New Jersey company Exelus Inc. promotes a technology called ExSact made of the mineral zeolite and other metals.

The material is commonly used as a catalyst in other refinery processes, such as fluid catalytic cracking, but not in alkylation because it wears out after a short time. After years of research, Exelus has designed a product that lasts long enough to be practical, said James Nehlsen, process development manager with the company. Though it performed well in a pilot test, ExSact has yet to be tested on a commercial scale.

Nehlsen said the company has seen the most interest from overseas refiners. Many U.S. refineries are reluctant to try something unproven.

“People have expected it to replace acid technology for a long time,” he said. “For technical reasons it hasn’t happened yet. Now it’s just a matter of getting someone to be willing to be the first one to try it.”

Ron Chittim, a senior policy adviser with the American Petroleum Institute, said among the two-thirds of U.S. refineries that use alkylation, half use hydrogen fluoride and half use sulfuric acid. The remaining ones use processes other than alkylation.

Besides Citgo’s east plant, three other local refineries list hydrogen fluoride in their risk management plans with the EPA. The four refineries use a total of 895,000 pounds of the acid in their alkylation units.

Millar said a few U.S. refineries use modified hydrogen fluoride, which is mixed with other hydrocarbons to reduce danger to neighborhoods but can still form vapor clouds.

The decision depends on several factors, such as which chemical is more readily available, Chittim said.

“It is somewhat shortsighted to say hydrogen fluoride is dangerous and replace all the hydrogen fluoride with sulfuric acid,” Chittim said. “That’s not the answer either. You need people who are highly trained to decide what makes the most sense for their facility.”

Cost concerns

Chittum said he is unaware of any company that retrofitted a plant to switch, but he has seen cost estimates of $50 million to $150 million depending on size. A refiner would have to essentially build a whole new unit. Building a unit for a solid catalyst would cost around $43 million, according to a 2003 study by the U.S. Public Interest Research Groups.

Hydrogen fluoride is more toxic than sulfuric acid, said Sam Mannan, professor of chemical engineering at Texas A&M University and director of the Mary Kay O’Connor Process Safety Center. But the alkylation process can use 40 to 140 times as much sulfuric acid as hydrogen fluoride.

The larger quantities mean there’s a bigger chance the chemical could be released or more vulnerable to attack while it is being transported, Chittim and Mannan said. Both chemicals also need to be regenerated — or prepared to be reused — creating an even bigger transportation issue, unless companies build a regeneration plant on location.

“The problem boils down to, on one hand you have a relatively small quantity of hydrogen fluoride, with pound-for-pound high toxicity,” Mannan said. “But on the other hand, we have much larger quantities of sulfuric acid, which pound for pound has a lower toxicity. I don’t know that the answer to that question is as simple as some people would think it would be.”

Chemical reactions

The chemicals also behave somewhat differently in the case of a leak, Chittim and Mannan said. Hydrogen fluoride tends to form a vapor cloud, while sulfuric acid tends to pool on the ground near the leak.

It seems, then, that sulfuric acid would be safer for nearby neighborhoods. But if there is a fire, which is common in such incidents, water from firefighting efforts will react violently with sulfuric acid, causing a vapor cloud as well. Sulfuric acid is heavier than air, though, reducing the risk of a cloud moving out of the refinery.

Millar believes sulfuric acid presents a smaller risk to the community, especially if local refineries combined to build a joint regeneration facility to eliminate the need to transport so much of it.

“These are the things that some independent environmental impact assessment needs to look at,” he said. “You need to have somebody you can trust to do that.”