Centrifugal Extractors and Contactors for the reaction, purification, and isolation of valuable chemical products
Liquid-Liquid Extraction Equipment: Centrifugal Extractors and Mixer-Settlers for Counter-Current Separation
Rousselet Robatel designs and manufactures a full range of liquid-liquid extraction (LLE) equipment — multistage centrifugal extractors (Model LX), monostage centrifugal extractors (Model BXP), and mixer-settlers (Models SX/RX/UX) — built to solve counter-current and cross-current extraction challenges across pharmaceutical, fine chemical, food, hydrometallurgy, and nuclear applications.
Conventional single-stage extraction often can’t hit the separation efficiency a process demands, and not every LLE technology fits every process. Reaction kinetics, required flow rate, footprint constraints, and flow-pattern needs (counter-current vs. cross-current) all determine which platform is the right fit — and getting that match wrong means paying for stages you don’t need, or under-delivering on extraction efficiency. Rousselet Robatel’s LLE portfolio covers this entire decision space under one engineering team: from laboratory mixer-settlers used to establish a solvent system, to BXP batteries handling large flow rates and mixed flow patterns, to LX units delivering maximum stage count in a minimal footprint.
Extraction efficiencies of >85% theoretical per stage (mixer-settlers) and >95% theoretical per stage (BXP) are achievable depending on platform and chemistry, with all three lines available from laboratory through industrial scale, cart or skid-mounted, and available for rental.
Liquid-Liquid Extraction Systems
Model LX — Multistage Centrifugal Extractors
Multistage centrifugal extractors deliver up to 7 extraction stages within a single rotor — the entire counter-current cascade happens inside one compact piece of hardware.
- Counter-current continuous extraction for maximum efficiency
- Up to 7 stages in a single rotor — no interstage piping or pumps between stages
- Single-rotor design minimizes spare parts and maintenance costs
- Very low residence time with rapid chemical and hydraulic equilibrium
- No mechanical seals required; vapor-tight construction with inert gas blanketing available
- Interphase position independent of total and relative flow rates of the two phases
- Unattended operation, laboratory through industrial scale
- Cart or skid-mounted configurations; rental available
Best fit: processes where footprint is the primary constraint and a strict counter-current flow pattern meets the process need. Because all stages reside in one rotor, LX is the most compact way to achieve a multistage counter-current cascade.
Applications: pharmaceutical, agricultural/food products, hydrometallurgy, chemical processing
Model BXP — Monostage Centrifugal Extractors
Monostage centrifugal extractors are single-stage units, connected in series to build the stage count a process requires — giving you the flexibility to configure your process in any way your chemistry requires.
- Continuous counter-current extraction with direct motor coupling
- Short retention time and low liquid holdup
- Extraction efficiency typically greater than 95% theoretical per stage
- No bottom bearing in the process area; cGMP-ready designs for multi-product pharmaceutical processing
- Kynar (PVDF) construction available for corrosive applications
- No interstage pumps required when connected in series
- Optional CIP (clean-in-place) systems
Best fit: processes requiring high flow rates beyond what typical extractors can accommodate — a battery of larger units (e.g., BXP 800) can be scaled to handle throughput up to 70,000 lph. At bench scale, our annular contactor BXPs can use flow rates as low 1 lph. At any scale, each stage is a discrete unit, batteries can be arranged for counter-current, cross-current, or a mix of both flow patterns.
Applications: pharmaceutical, agricultural/food products, hydrometallurgy, chemical processing
Mixer-Settlers (Models SX / RX / UX)
Mixer-settlers use a “pump-mix” design that eliminates the need for interstage feed pumps, and remain the preferred technology for processes that centrifugal extraction isn’t suited for due to increased kinetic transfer time or emulsion formation.
- Counter-current continuous extraction, connected in series for the required stage count
- “Pump-mix” design — no interstage feed pumps needed
- Extraction efficiency typically greater than 85% theoretical per stage
- Kynar or PTFE construction for corrosive applications
- Internal recycling systems available
- Three configurations: standard (SX), recycling (RX), universal (UX)
- Well adapted to batch or continuous operation
Best fit: processes with slow mass-transfer kinetics — common in hydrometallurgy and other metallurgical extraction processes — where the longer residence time a mixer-settler provides is necessary to reach equilibrium. Mixer-settlers are also the standard platform for early-stage solvent-system evaluation and R&D.
Applications: pharmaceutical, fine chemical, food products, hydrometallurgy, nuclear
Which LLE Platform Fits Your Process?
Rather than a simple lab-to-production ladder, platform selection depends on process characteristics — not just scale. Use this table as a starting point, then talk to our applications team to confirm fit for your specific chemistry.
Recommended platform: Mixer-settler
Longer residence time allows the system to reach equilibrium; centrifugal extractors are optimized for fast-equilibrium chemistries
Recommended platform: Mixer-settler or lab-scale BXP
Stage-by-stage visibility and operational simplicity make it easiest to evaluate a new chemistry before scale-up in a mixer-settler. Centrifugal extractors test if the density ratio and emulsibility of the solvent system will work for high throughput, large scale operations.
Recommended platform: LX multistage liquid-liquid extractor
Delivers up to 7 stages in a single rotor — the most compact way to achieve a multistage counter-current cascade
Recommended platform: BXP monostage liquid-liquid extractor
BXP extractors can scale up to 70,000 liters per hour throughput, and customizable configurations allow your process to have as many or few separation stages are required simply by changing the number of BXPs in series.
Recommended platform: Mixer-settler or BXP monostage liquid-liquid extractor
Scale and kinetics will determine if mixer-settlers or BXP extractors are the right candidate for any given separation. Both mixer-settlers and BXP extractors can be configured for any combination of cross-current or counter-current extraction, as well as combinations of both cross and counter-current, i.e. wash steps.
Not sure which one fits?
Talk to an LLE specialist about your kinetics, flow rate, footprint, and flow-pattern requirements.
How Liquid-Liquid Extraction Works
Liquid-Liquid Partitioning
Two immiscible liquid phases contact one another; target solutes distribute between the phases according to their partition behavior. Repeating this contact across multiple stages — with fresh solvent introduced counter-current or cross-current to the feed — drives the separation closer to completion with each stage.
Mixing and Settling
Every LLE stage requires two steps: mixing the two phases to promote mass transfer, then settling them back into distinct layers for separation. How a platform performs these two steps — and how quickly it reaches equilibrium — is what differentiates mixer-settlers from centrifugal extractors.
Centrifugal vs. Gravity-Driven Settling
Mixer-settlers rely on gravity settling, which takes longer but accommodates slower-kinetics chemistries well. Centrifugal extractors (LX, BXP) use centrifugal force to separate the phases rapidly, dramatically shortening residence time — ideal for fast-equilibrium systems, less advantageous for chemistries that need time to reach equilibrium regardless of how fast the phases are separated afterward.
Building Stage Count — Rotor vs. Battery
LX achieves its stage count within a single rotor. BXP and mixer-settlers achieve stage count by connecting individual units in series — which is what gives BXP its flow-pattern flexibility (counter-current, cross-current, or mixed) that a single fixed-cascade LX rotor cannot offer.
Why Choose Rousselet Robatel for Liquid-Liquid Extraction
- Engineering experience: decades of LLE-specific design across LX, BXP, and mixer-settler platforms — not a single-technology vendor forcing one solution on every process
- System-level expertise: turnkey skid-mounted systems, process integration, custom engineering, pilot testing and scale-up support
- Technical depth: single-rotor multistage design (LX), cGMP/corrosion-resistant battery design (BXP), and pump-mix simplicity (mixer-settlers) — genuine platform breadth, not badge-engineering
- Customization: Kynar/PTFE corrosive-service construction, cart or skid-mounted formats, CIP and internal recycling options
- Manufacturing & QC: in-house fabrication, factory acceptance testing
- Industry-specific expertise: pharmaceutical, fine chemical, food products, hydrometallurgy, nuclear
- Flexible rental & pilot testing programs: rent LX, BXP, or mixer-settler units to validate process fit before capital investment, or work with Robatel Engineers to have your materials tested in their laboratory
- Lifecycle support: spare parts, field service, commissioning, preventative maintenance, training
Process Development Support
We understand that every process is different, and scaling up from another technology can be challenging. Our team members are experts in liquid-liquid extraction, and we offer:
- Solvent system and method development support, typically starting on bench-scale to establish Kd and kinetics behavior
- Guidance matching flow rate, kinetics, footprint, and flow-pattern requirements to the right platform (mixer-settler, BXP, or LX)
- Scale-up support from laboratory through pilot and industrial production
- Wet lab test center available for on-site process evaluation, or rent a pilot unit for testing at your own facility
- Application review and feasibility discussions before capital investment
Frequently Asked Questions About Liquid-Liquid Extraction
LLE is a separation technique that uses two immiscible liquid phases to extract, wash, or purify target compounds based on their distribution between the phases, typically across multiple stages to reach the required separation efficiency.
Mixer-settlers separate phases by gravity settling, which takes longer but suits slower reaction kinetics. Centrifugal extractors (LX, BXP) use centrifugal force to separate phases rapidly, which is better suited to fast-equilibrium chemistries.
When your process has slow mass-transfer kinetics — common in hydrometallurgical and other metallurgical extractions — a mixer-settler’s longer residence time allows the system to actually reach equilibrium, which a fast centrifugal separation may not achieve for that chemistry.
LX delivers up to 7 stages within a single rotor — the most compact option, but with a throughput ceiling and fixed counter-current flow pattern. BXP is a single-stage unit connected into batteries; larger BXP models can handle higher flow rates than LX, and BXP batteries can be arranged for counter-current, cross-current, or mixed flow patterns.
BXP extractor batteries can be configured for cross-current, counter-current, or a mix of both, offering more flow-pattern flexibility. The LX’s single-rotor design is built for counter-current operation.
A battery of larger BXP units (e.g., BXP 800) is typically better suited to high flow rate requirements than a single LX rotor, which is optimized for footprint rather than maximum throughput.
No. While mixer-settlers are one of the standard tools for early-stage solvent-system evaluation, they are also used at production scale for processes with slow extraction kinetics, where their longer residence time is a process requirement, not a limitation.
LX extractors are available in several metals, ranging from 316L stainless steel to Alloy C22, and even more exotic metals such as Monel or Inconel if the process requires it.
BXP extractors are available in the same metals as the LX extractors, and are also available in PVDF for highly corrosive applications such as high concentration hydrofluoric acid.
Mixer-settlers are available in polypropylene, polyethylene, PVDF, PTFE, PEEK, and many other application dependent materials of construction.
Yes — LX, BXP, and mixer-settler platforms are all available from laboratory through industrial scale, and rental units are available to validate a process before committing to capital equipment.
Platform choice depends on reaction kinetics, required flow rate, footprint constraints, and whether your process needs counter-current, cross-current, or mixed flow patterns. Our applications team can help match these factors to the right system.
Request a Technical Discussion or Application Review
We would be happy to have a discussion with you regarding:
- Your chemistry kinetics, target purification, and required final process scale
- Footprint requirements for full-scall processing
- Equipment selection based on processing requirements
- Rental equipment options and wet-lab process evaluation and development