Scaling up a rotary evaporator process can be very straightforward in many applications. However, there are some factors you need to bear in mind. It’s not always as simple as just using a bigger flask. For larger scale-ups, you may need to purchase entirely new equipment.
In this post, we look at what factors you need to consider when scaling up your process.
Factors to Consider When Purchasing New Equipment
If your existing setup doesn’t have the capacity for your desired scale, then it’s time to consider purchasing a new unit. Here are some of the main things to bear in mind.
Of course, one of the most important factors will be capacity. Traditional large-scale rotovaps such as models by Across International and BEING generally come in 10 L, 20 L, and 50 L models. Just bear in mind that your maximum working volume will be around half the maximum flask size: due to the flask being held at an angle, you cannot fill your flask more than half full or else you will experience bumping and foaming which will force you to restart your distillation.
There is a newer style of evaporator that doesn’t use flask rotation, allowing for larger volumes. One of the primary reasons for rotation is to speed up evaporation. However, with a large enough vessel, you can use an overhead stirrer to agitate the contents of the flask. Some models in Ecodyst’s EcoChyll series of high-capacity rotovaps use this method and come in sizes with up to 200 L true capacity (eight times the capacity of 50 L rotary evaporators).
The EcoChyll® X9 High-Capacity Evaporation System (200 L true capacity).
Of course, before deciding on a model, you also need to check other specifications such as temperature range (most go up to 99°C but some up to 250°C), rotation speed (if applicable), and maximum evaporation rate.
When considering how much space your setup will take, you need to consider the footprint. And it’s not just the rotovap itself you need to worry about. You also have to factor in the pump and chiller, both of which can take up a considerable amount of space.
When costing your rotovap, its energy consumption is a key concern. Any process that uses heat can be a considerable drain on energy. Plus you have to factor in the energy consumed and heat generated by the chiller, as well as the energy consumption of the pump.
The EcoChyll units mentioned above are designed to be exceptionally energy efficient. They represent a large up-front investment, but could be worth it in terms of efficiency and energy savings in the long run.
Aside from choosing the right rotovap, you also need to select the ideal vacuum pump. You’ll want a pump that offers sufficient vacuum pressure and flow rate for an efficient evaporation process. The right pump can also help you avoid problems such as safety issues, pump damage, and solvent loss. When scaling up, you should be able to use the same vacuum pressure, but will need a pump with a higher evacuation rate.
Using an oversized pump can lead to significant issues, however, both in terms of process and safety. Using an oversized pump could result in vapor clearing out of the condenser too quickly without condensing. The solvent will enter the pump, where it will recondense once exposed to atmospheric pressure, and could cause it to flood. You could even end up with solvent spurting out of the pump. This is of particular concern when using a flammable solvent such as ethanol. Ensuring the pump you use is neither too slow nor too fast is important to your process.
Selecting the right chiller is also very important, the key concern being that the chiller must have enough cooling capacity to effectively cool the solvent. Knowing what your desired setpoint temperature will be is important when selecting a chiller as cooling capacity decreases as you lower the setpoint temperature. You should aim to have a chiller that can provide roughly as much cooling capacity at the needed coolant temperature as the rotary evaporator bath has heating power.
Scaling Up Using the Same Equipment
Many rotovaps are capable of handling a broad range of volumes. For example, the LabTech EV400 Rotary Evaporator can handle a maximum flask size of 3L.
If you’re able to use the same rotovap setup for your scaled up process, then the main things you need to consider are the speed, temperature, and vacuum settings. Thankfully, however, you shouldn’t need to adjust parameters as you switch to a larger flask size and higher volume. Rotation speed, bath temperature, and vacuum level can all remain the same.