Molecular Sieves
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Biomass carries water. Molecular sieves take it back out of your solvent so the next run starts dry.
Choosing the right bead
| Solvent | Bead | Why |
|---|---|---|
| Butane, propane and blends | 4A molecular sieve beads | Sized for hydrocarbon service. This is the bead in every N.B. Oler recovery path |
| Ethanol | 3A molecular sieve beads | 3A pores admit water but exclude ethanol |
Why not just distill ethanol?
Distillation tops out at 95.57 percent ethanol, 191 proof. At that concentration the vapor carries the same percentage of ethanol as the liquid, an azeotrope, so 200 proof is unreachable by distillation alone. Sieves finish the job.
How much bead you need
| Item | Value |
|---|---|
| Water in 100 gal of 191 proof ethanol (95.5 / 4.5 percent) | 4.5 gal of water, about 37.5 lb (17 kg) |
| Bead absorption capacity | Up to about 40 percent of bead weight in water. Efficiency drops after about 20 percent |
| 3A beads required | 100 to 190 lb (45 to 86 kg) per 100 gallons of ethanol |
A back-of-the-envelope estimate. Size generously: a bead bed working near saturation lets water through.
Regenerating spent beads
- Beads absorb water up to about 120°C (250°F) at atmospheric pressure. Regenerate by heating above that temperature, under vacuum, or both.
- Not too hot. Excessive temperature decomposes the beads.
- Results depend on temperature, pressure, bead size, bed geometry, sweep gas flow and how saturated the beads are, but reasonable regeneration is achievable in most commercial extraction labs.
Vacuum oven procedure
- Preheat the vacuum oven to 250°C (482°F).
- Spread the saturated beads in a single shallow layer on a metal tray.
- Place the tray in the oven and close the door.
- Start the vacuum pump and open the valve to the oven.
- Hold at full vacuum for 2 hours.
- Break vacuum and sweep the oven with air several times, then hold for 30 minutes.
- Shut off the pump and let the oven cool to room temperature with the door closed.
- Inspect the beads. Cracked, powdered or discolored beads are spent. Replace them.
- Return intact beads to the sieve column promptly. Dry beads start absorbing moisture from room air immediately.
Record the date, time and temperature of every regeneration. The simple check that it worked: weigh a sample of beads before and after. Regenerated beads should return close to their dry weight, and a charge that stops drying your solvent after regeneration is due for replacement.
This procedure replaces our earlier 3A Sieve Bead Regeneration post. Follow the vacuum oven maker's and bead supplier's instructions and safety precautions. Never regenerate beads that still hold hydrocarbon solvent in an oven that is not rated for it: purge them first.
Where the sieve sits
On an N.B. Oler system the molecular sieve is a 6 inch column in the passive recovery path, between the collection side and the chilled solvent tank, with a 10 µm sintered filter on both sides to keep bead dust out of your solvent. Molecular sieves are an integral part of hydrocarbon solvent recovery, and N.B. Oler builds recovery systems to fit your needs, beads and their regeneration included.
Sources. N.B. Oler Technical Brief 10e, Molecular Sieves, Rev. 2026.1 (2026 Training Binder); N.B. Oler 3A Sieve Bead Regeneration SOP (2023). Gabruś et al., Chem. Eng. J. 259 (2015); Simo et al., Ind. Eng. Chem. Res. 48 (2009); Wang, Ind. Eng. Chem. Res. 59 (2020).