Hydroflouric acid (HF) is one of the most dangerous acids in the world, and it’s commonly used as a catalyst to produce alkylate, a gasoline blending component for clean-burning fuels. But using HF comes with risks to people and the environment. Only automatic representative sampling can perform safe, reliable and efficient sampling of HF in a hydrocarbon plant.

In the early morning hours of June 21, 2019, three loud booms woke up the residents of South Philadelphia, Pennsylvania. An explosion at the Philadelphia Energy Solutions refinery had shaken houses and sent fireballs into the sky above the area’s 168,000 residents.

The explosion destroyed the refinery's hydrofluoric alkylation unit, where crude oil is converted to high-octane gas, and led to the plant’s permanent closure. It also revived safety concerns over the alkylation process in hydrocarbon plants like this one and the hydroflouric acid (HF) used as the catalyst in the process.

Hydrofluoric Acid and alkylation

Alkylation technologies are commonly used in the refining industry to produce the high-octane gasoline blending components needed to make clean-burning fuels. Alkylate is a premium gasoline blending component that has a high-octane number and low vapor pressure, which makes it less volatile and helps gas burn more cleanly.

In the 1980s, new regulations drove a surge in alkylation capacity at hydrocarbon plants around the world. According to the federal Energy Information Administration, in January 2018 there were 135 petroleum refineries operating in the United States. And about 50 of them use alkylation units with HF as a catalyst in the alkylation process.

The dangers of hydrofluoric acid (HF)

HF is an inorganic, corrosive compound that is one of the most dangerous inorganic acids in the world. It’s severely toxic through ingestion, inhalation or contact with skin. Any exposure to HF can be devastating, and burns as small as the size of the palm of your hand can be fatal.

Transporting and working with HF also pose safety risks. Hydrofluoric acid tends to form a vapor cloud that’s difficult to disperse. Under intense pressure, HF could form an airborne aerosol cloud that can travel for miles. One study estimated that 26 million Americans could be at risk from a worst-case release of HF.

In addition, approximately 70 accident reports involving HF were made around the country from 2012 to 2016, according to the U.S. Coast Guard’s National Response Center database.

Limitations of Grab Sampling

The alkylation process generates a significant amount of heat, which requires regular cooling. HF alkylation units are also particularly vulnerable to HF corrosion, making sampling a critical process in alkylation to protect people, assets and the environment. While grab sampling is often considered for sampling HF, it’s simply insufficient to properly sample HF to maintain safety and accuracy in the alkylation process.

Danger to personnel – Grab samples must be taken in sealed containers or sample cylinders (also previously called sample “bombs”) by specially trained personnel wearing full protective gear and respiratory apparatus. Lab analysis must be conducted in a designated, segregated laboratory area with safety showers both in the lab and along the transportation route.

Analytical challenges – HF is a reactive mixture and removing the grab sample from the process doesn’t stop the reaction. In other words, the clock is ticking on how representative the grab sample is of the process. Removal of the sample from the cylinder, and all subsequent handling, must be carried out anaerobically using materials and instruments that can withstand exposure to HF. Most laboratory glassware, metals and plastics can’t be used. No matter how efficient the analyst or accurate the results, uncertainty grows as time elapses between sampling and the return of the results.

Automatic representative sampling can perform safe, reliable and efficient sampling of HF in a hydrocarbon plant. No matter what alkylation process you use in your plant, it’s more important than ever to work with an experienced partner to ensure your sampling program meets the expanding needs of your hydrocarbon plant.