Choosing a glass reactor by nominal capacity alone is not enough.
If your process requires a 20L batch, a 20L reactor is not automatically the correct choice. The important question is whether 20L means total vessel volume or actual working volume.
For equipment selection, HJCHEM normally recommends starting with the real batch volume and process steps rather than simply specifying a reactor size.
What Is the Difference Between Total Volume and Working Volume?
Total volume is the internal capacity of the vessel.
Working volume is the amount of material that can practically be processed while leaving enough space for mixing, feeding, boiling, foaming, or other process requirements.
Therefore: 20L total volume does not mean 20L usable working volume.
The required working volume depends on what happens during the reaction.
Why Does a Glass Reactor Need Headspace?
The unused space above the liquid is not wasted volume.
Headspace is required for:
- agitation
- later liquid addition
- powder charging
- foaming
- gas generation
- reflux
- boiling
- vacuum evaporation
A simple liquid reaction requires less headspace than a foaming reaction or vacuum concentration process.
For this reason, HJCHEM don’t suggest to use one fixed filling percentage for every process.
What Size Reactor Do You Need for a 10L Batch?
It depends on whether 10L is the initial charge or the maximum volume during the process.
For example:
Case 1: Simple Liquid Reaction
Initial charge: 10L
No major additional feeding
No serious foaming or boiling
A reactor moderately larger than the batch volume is suitable.
Case 2: 10L Initial Charge + 5L Dosing
The final liquid volume becomes approximately 15L.
In this case, selecting the reactor based only on the initial 10L charge would underestimate the required capacity.
Case 3: 10L Vacuum Evaporation Process
Even though the liquid charge is only 10L, additional headspace is needed because boiling and foaming can occur under vacuum.
For vacuum applications, see our guide on choosing a glass reactor for vacuum reactions.
Can You Use a Large Reactor for a Small Batch?
Sometimes yes, but a larger reactor is not always better.
For example: Can I process 5L of material in a 20L glass reactor?
The answer depends on the equipment configuration.
Check whether:
- the agitator is sufficiently immersed
- the temperature probe reaches the material
- mixing is still effective at the low liquid level
- the jacket covers the useful heat-transfer area
- sampling and discharge remain practical
If the liquid level is too low, increasing reactor size can actually reduce mixing and temperature-control performance.
This is particularly important for small laboratory systems. Our bench-scale glass reactor guide covers additional considerations for smaller reactors.
Does the Required Working Volume Change with the Process?
Yes, the same batch volume can require different reactor sizes depending on the operation.
| Process | Main Capacity Consideration |
|---|---|
| Simple liquid reaction | Mixing and normal headspace |
| Controlled dosing | Final volume after all additions |
| Powder addition | Space for solids and mixing |
| Foaming reaction | Additional headspace |
| Gas-generating reaction | Gas disengagement space |
| Reflux | Boiling and vapor space |
| Vacuum concentration | Foaming and boiling behavior |
| Crystallization | Solids suspension and slurry volume |
This is why reactor capacity should be selected from the complete process, not only the starting liquid volume.
Should You Specify Working Volume or Reactor Volume in an RFQ?
If your process requires a specific usable capacity, specify the required working volume.
For example:
Required working volume: 20L
is clearer than:
Required reactor capacity: 20L
You can also provide:
Normal batch volume: 15L
Maximum process volume: 20L
The manufacturer can then determine the appropriate total vessel volume.
For customized projects, HJCHEM evaluates vessel capacity together with agitation, feeding, temperature control, vacuum, and other process requirements as part of the custom glass reactor configuration.
FAQ
1. Is a 20L glass reactor designed to hold exactly 20L of material?
Not necessarily. You need to confirm whether 20L refers to total vessel volume or recommended working volume.
2. How full should a glass reactor be?
There is no single filling percentage suitable for every process. The required headspace depends on feeding, foaming, boiling, gas generation, agitation, and vacuum operation. Recommend is 70~80% of the full volume.
3. Can I use a 20L reactor for a 5L batch?
Possibly, but the agitator, temperature probe, heat-transfer area, and minimum operating liquid level should be checked first.
4. Should I select the reactor according to initial charge volume?
Not always. If additional material is added later, the maximum process volume is usually more important.
Conclusion
The correct glass reactor size is not determined by batch volume alone.
Before selecting a reactor, confirm:
Initial Volume → Additional Feeding → Maximum Process Volume → Required Headspace → Minimum Operating Level
For an RFQ, telling HJCHEM your actual batch volume and process sequence is more useful than simply requesting a “20L” or “50L” reactor.
This helps avoid both undersizing and unnecessarily oversized equipment.
Not Sure What Glass Reactor Size You Need?
Send HJCHEM your initial batch volume, maximum process volume, feeding steps, material properties, and operating conditions.
We can help determine a suitable working volume and total reactor capacity for your process.