Membranes for Air Venting and Retaining VOCs in Gasoline Storage Tanks

Fugitive emissions of volatile organic compounds (VOCs) from gasoline marketing facilities continues to be an energy, safety, and environmental issue. Beginning in model year 2000, all vehicles are required to have an onboard refueling vapor recovery (ORVR) system, which will increase fugitive emissions from refueling stations because of the interface between ORVR vehicles and gasoline station underground storage tanks (USTs). The increase of VOCs is attributed to the ingestion of fresh air into the UST and mixing with the gasoline, causing an approximate 40 percent vapor growth. This growth increases the UST pressure and vents VOCs into the atmosphere. Conventional VOC recovery membranes (silicone rubber) preferentially transport organics over air. Although this system has shown success in some gasoline/air separations, it is not appropriate for air venting in USTs. Therefore, Compact Membrane Systems, Inc. (CMS) will develop a reverse-membrane system that allows for rapid venting of air while retaining gasoline in the UST. This membrane system will represent a simple single-stage, one-unit operation versus alternative technologies that are more complex. CMS has developed a system that uses a specialty-coated membrane and pressure differential that separates clean air from the VOCs and allows the fresh air to be exhausted into the atmosphere. This system will be built and evaluated first in CMS' laboratory and then at an actual gasoline station. Specifically, in collaboration with industrial partners, CMS will be able to demonstrate performance at an actual gasoline station during Phase I. Results will be compared to alternative technologies such as flares. Also in the economical evaluation, CMS will consider specific hybrid systems if needed to meet target goals.