Building a bigger and better solvent still

Most labs have a small still for quickly purifying solvents. But for Stefan Böhmdorfer and his colleagues at the University of Natural Resources & Life Sciences in Austria, that wasn’t enough. The researchers carry out a lot of chromatography and realized they had much to gain by purifying and reusing their solvents, rather than paying someone to cart them away for recycling. The team had a hard time finding a commercially available still that could do everything they wanted, including handling between 2-L bench-scale and 30-L pilot-scale amounts, having fully solvent-resistant components, and offering precise control over separating solvent fractions. So the researchers decided to build their own system. That’s not a new idea, but the team spared no detail in designing its system to handle solvents of all polarities and a wide range of boiling points and to collect fractions automatically (Org. Process Res. Dev. 2017, DOI: 10.1021/acs.oprd.7b00007). The researchers built two stills for 6-L batches inside a walk-in fume hood. The basic setup includes a 10-L round-bottom flask, a 100-cm-long/30-mm-diameter packed column, a condenser, drying tubes, and collection vessels. Temperature sensors and electronically controlled valves enable the automated fraction collection and also serve as a safety feature to shut the system down if something starts to go wrong. The distilled solvents are typically of higher purity than the analytical-grade solvents the group was buying. “I am convinced that a lot of research groups are facing the same situation of having larger amounts of easily redistillable solvents and can decide to build their own device,” Böhmdorfer says.