Patent Picks: New Propellant Technologies

Aerosol spray cans expel their contents with the help of volatile small molecules called propellants. Today’s cans no longer contain ozone-depleting chlorofluorocarbons and instead rely on ozone-friendly hydrofluorocarbons (HFCs). However, scientists now worry about the global warming potential of current-generation HFC propellants. Earlier this year, the Environmental Protection Agency banned three HFCs that have long atmospheric lifetimes and high global warming potentials. Additionally, the European Union has begun mandating that companies phase out environmentally harmful HFCs in their products. To help propellants firms meet these new requirements, several chemical manufacturers are developing HFC formulations that have less negative effects on the environment. Here, we highlight three advances in technologies using environmentally friendly propellants, from the databases of Chemical Abstracts Service (CAS).

Hydrofluoroolefins (HFOs) boast three environmentally friendly features: They readily degrade in the troposphere, exhibit a low global warming potential, and have near-zero impact on the ozone layer. Although HFOs are already used as propellants in aerosol cans and as heat-transfer fluids in refrigerators, they are chemically unstable relative to hydrofluorocarbons because of the presence of a C=C double bond. A recent patent from Sri R. Seshadri, Laurent Abbas, Brent L. Van Horn, and coworkers from Arkema describes using stabilizers to inhibit degradation of HFOs, such as HFO-1225ye, during storage and handling (WO 2015126662). They selected stabilizing agents, including combinations of hydroquinone, limonene, and nitromethane, that could scavenge radicals and oxygen species, as well as inhibit polymerization. Although the stabilizers protect the HFOs when in use, they don’t slow degradation of HFOs once released into the atmosphere, Arkema reports in the filing. The company states that the stabilizers were most effective at concentrations between 100 and 1,000 ppm. In a statement on their website, Arkema says it is dedicating significant resources to develop HFOs as their fourth-generation refrigerant cooling liquid because of the compounds’ overall energy efficiency and low global warming potential.

About 300 million people around the world suffer from chronic obstructive pulmonary disease, a condition that causes poor airflow in the lungs. COPD patients often rely on inhalers that deliver long-acting bronchodilators, such as tiotropium, to improve their breathing. Inhalers use hydrofluorocarbon (HFC) propellants to expel their drugs because older propellants based on chlorofluorocarbons harm the environment. Tiotropium is notoriously moisture-sensitive, but it’s usually formulated in water or alcohol solvents, so manufacturers add small amounts of mineral acid to slow the degradation process. But these mineral acids can increase the toxicity of the formulation. Researchers at Cipla found that using HFC-227 as the propellant and as the solvent for tiotropium improved the drug’s stability compared with other aqueous formulations and avoided the need for a mineral acid (US 20150250713). In India, Cipla is currently selling a metered-dose inhaler, trade name Triohale, that uses HFC-227 as a propellant to deliver a trio of COPD drugs, including tiotropium.

Aerosol dusters, also called canned air, have been around since the 1960s. These cans don’t actually contain any air. Instead, they currently use nonflammable hydrofluorocarbon propellants, such as HFC-134a. But HFC-134a has a problem: It has a high global warming potential. And other HFCs with lower global warming potentials tend to be flammable and toxic. Montfort A. Johnsen, a 90-year-old veteran of the aerosol industry, may have invented a solution by combining two nonflammable hydrofluoroolefins (HFOs). The Illinois-based entrepreneur uses a tetrafluoropropene, known as HFO-1234ze, as the propellant and a hexafluorobutene, known as HFO-1336mzz, as the solvent for his air duster (US 20140284516). In the filing, Johnsen argues that his aerosol duster formulation should provide ultimate safety when used around ignition sources, while also not harming the environment.