Smart Monitoring & Optimization Solutions for SMB Processes: In-Line and Off-Line Tools for SMB Systems

Smart Monitoring & Optimization Solutions for SMB Processes — Expert Summary

Significance of the topic

Simulated Moving Bed (SMB) chromatography is a high-efficiency continuous separation technology widely used to purify binary or pseudo-binary mixtures in industries from pharmaceuticals to food and petrochemicals. Reliable monitoring and rapid optimization of SMB processes are essential because SMB runs are continuous and can last hours to days; small deviations in flow or pressure propagate throughout the cycle and can compromise product purity and yield. Implementing robust in-line and off-line analytical tools accelerates development, supports reproducible scale-up, and reduces solvent and material consumption compared with batch approaches.

Objectives and scope of the study

This work presents a practical overview of in-line and off-line monitoring and optimization tools for SMB systems, demonstrates their roles on KNAUER AZURA Lab and Pilot SMB platforms, and illustrates how combinations of sensors, detectors, sampling valves and software visualization improve process control during method development and production.

Methodology and monitoring strategy

The study describes a typical SMB hardware configuration: a 2:2:2:2 column zone arrangement using seven 8‑port multiposition valves, four pumps (three integrated in the SMB loop for zones and one feed pump), and optional in-line sensors. Monitoring strategies are grouped into two classes:

• In-line tools — continuous signals recorded during runs: pump/zone pressure sensors, mass flowmeters (one to four, placed after pumps or at a column position), refractive-index (RI) and UV detectors at raffinate/extract outlets, and inline sampling valves to trap loop samples at defined switch times.
• Off-line tools — discrete sample analysis by analytical HPLC: collection of raffinate, extract and waste samples over one switch or a full cycle to evaluate separation performance and steady state purity profiles.

Key measurement practices highlighted include collecting samples over entire switches (not just point samples) to capture concentration profile dynamics, locating flowmeters strategically (e.g., one flowmeter placed before a particular column to monitor all zones as it cycles), and using software visualization (PurityChrom®MCC) to display pressures, theoretical and measured zone flows, detector traces, and real‑time column positions.

Instrumentation (used or recommended)

The article lists specific KNAUER equipment and accessories used for demonstration and as recommended options:

• AZURA SMB Lab systems — PEEK (biocompatible) and stainless steel variants (typical zone1 flows ~30 mL/min, feed flows ~4 mL/min, pressure ranges 10–130 bar).
• AZURA Pilot SMB systems — standard and high flow variants (zone1 flows 250–400 mL/min, feed flows 40–100 mL/min, pressure ranges 2–100 bar).
• Mass flowmeters — mini CORI-FLOW™ M13/M14 (available in single or four-unit configurations, including Hastelloy option for compatibility).
• Sampling hardware — outlet collection (raffinate/extract) valves, inline sampling valve upgrade kits for lab and stainless systems.
• Detectors — AZURA RID2.1L high-flow refractive index detector (100 mL/min) and AZURA UVD 2.1S UV detectors (standard and fiber-optic variants).

Main results and discussion

Pressure monitoring

Pressure sensors on each pump provide zone‑specific backpressure traces. Overlaying the four pump pressures reveals predictable cyclic patterns: insertion of a flowmeter or a high‑backpressure element with a column into a zone elevates that zone’s pressure during the switches when that column occupies the zone. Analogous pressure signatures also indicate blocked columns or constricted capillaries. Therefore, continuous pressure traces are an effective diagnostic for mechanical issues and flow anomalies.

Flow monitoring and control

Stable and accurate zone flow rates are fundamental for achieving the intended SMB separation. Installing flowmeters after pumps (ideally one per pump) yields the best control and immediate detection of interruptions or pump misbehavior. When cost constrains full instrumentation, a single flowmeter installed before a moving column can still monitor all zones over a cycle because the flowmeter cycles through zones with the column; a second flowmeter dedicated to the feed stream is recommended to check the feed/pump balance. Measured outlet volumes during a switch or cycle offer a pragmatic and lower‑cost alternative to continuous outlet flowmeters when assessing extract and raffinate flow balance.

Detector usage and interpretation

Placed at raffinate and extract outlets, UV or RI detectors serve three principal roles: (1) showing the initial rise in component concentrations at process start-up, (2) monitoring steady-state maintenance and detecting concentration deviations during runs, and (3) confirming column washout/cleaning by observing declining signals. Because SMB is continuous, detector signals reflect aggregated concentration profiles over switches rather than classical chromatographic peaks; interpretation therefore focuses on trends and steady-state stability rather than discrete peak shapes.

Off-line sampling and concentration profiling

Collecting outlet samples over an entire switch or full cycle and analyzing them by HPLC provides definitive evidence of separation performance (i.e., raffinate dominated by fast-eluting components and extract dominated by late-eluting components). Inline sampling loops used at fixed time points during each switch enable construction of intracycle concentration profiles, which help to visualize component band positions across zones and to guide flow adjustments for optimization.

Practical implementation and software support

Integration of the sensors and sampling hardware into the PurityChrom®MCC control interface supports live visualization of pump pressures, measured and theoretical flows, detector traces, and dynamic column positions. The software also permits adjustment of flow setpoints during a run, with changes applied at the next cycle — enabling iterative, in‑run optimization and compensation for pump performance deviations.

Benefits and practical applications

• Faster method development: in-line diagnostics and inline sampling significantly reduce the number of trial runs needed to reach steady state and target purity.
• Improved troubleshooting: pressure and flow signatures allow early detection of blocked lines, squeezed capillaries, pump faults, or misdirected flow paths.
• Reliable scale-up: reproducible monitoring facilitates translation from lab to pilot and production scale while conserving solvents and product material.
• Operational flexibility: software-controlled flow adjustments and sampling valves enable rapid process tuning and quality control during long continuous runs.

Future trends and potential applications

Opportunities to advance SMB monitoring and control include:

• Broader deployment of process analytical technology (PAT) — e.g., inline mass spectrometry or real-time spectroscopy — to augment UV/RI signals for component-specific quantification.
• Data-driven control — application of multivariate models and machine learning to correlate multidimensional sensor data (pressure, flow, detector traces) with purity and yield and to automate process adjustments.
• Improved sensor robustness and miniaturization — more compact, chemically resistant flow and pressure sensors supporting higher pressures and harsher solvents.
• Enhanced sample handling — automated high-throughput inline sampling and fraction routing for rapid off-line analysis or direct coupling to analytical instruments.
• Wider adoption in bioprocessing and green chemistry contexts via biocompatible materials and reduced solvent footprints.

Conclusion

Combining in-line monitoring (pressure, flow, detectors, inline sampling) with off-line analytical verification (HPLC of switch/cycle samples) yields a pragmatic, reliable strategy for developing and operating SMB separations. Strategic placement of flowmeters and detectors, supported by software visualization, enables rapid detection of mechanical issues, controlled optimization of zone flows, and confident assessment of steady-state product quality. These capabilities accelerate development, support robust scale-up, and reduce operational risk in continuous preparative separations.

References

1. Stephan S., et al. Simultaneous sampling of two product streams. KNAUER Application Note VTN0012.
2. Stephan S., et al. Simulated Moving Bed (SMB) inline sampling. KNAUER Application Note VTN0011.