A Nitrogen-Filled Isolator?

When a process does not produce the expected results, or when a piece of equipment behaves strangely, even experienced personnel sometimes may be at a loss to understand the reason why. Equipment & Processing Report’s “Troubleshooting” column is a forum to discuss production problems. Readers submit anonymous questions, which equipment vendors and industry professionals attempt to answer. In this way, the column may help promote greater understanding of the industry's products and processes.

Q: We want to fill one of our oxygen-sensitive products inside an isolator system. Can we run an isolator with pure nitrogen and defined humidity?

A: Yes. From a technological standpoint, particularly with regard to control technology, rendering the isolator volume completely inert and preventing oxygen-sensitive products from undergoing chemical reactions within the isolator do not pose problems. These goals are achieved by implementing the pressure control inside the isolator through a nitrogen-operated control valve. In this approach, the isolator, which is designed as a closed-ventilation system, is operated with nearly 100% recirculated air. This system is different from the conventional design, which relies on the addition of fresh air to control temperature, thereby discharging internal thermal loads and using the exhaust air to control pressure. 

In a closed-ventilation system, leakage losses of the entire system have to be compensated by a controlled nitrogen supply to maintain the required pressure. But this approach, and the need to discharge internal thermal loads, requires the installation of cooling coils in the recirculation plenum. In addition, the mouse holes need a specific ventilation design (i.e., a pressure sink) to prevent excessive escape of nitrogen into the staff’s workspace.

Moreover, it is necessary to explain what is meant by defined air-humidity requirements. Running the system with nitrogen typically generates air humidity of < 10%. If, however, specific products require filling at a humidity of 45% ± 10% at 20 °C (i.e., 68° F), for example, the concept needs to have a system for controlling the nitrogen supply and simultaneously triggering nitrogen moisturization as a carrier gas. This task certainly is not easy with regard to control technology, but it can be accomplished.

—Robert Ehrhart, engineering department head for Optima Group Pharma

If you have a problem with your equipment or process, an industry expert may have the solution. Please send your question to Erik Greb, editor of Equipment and Processing Report, and we may be able to provide an answer in a future issue. All questions will remain anonymous.