Since the foundation of the company in 1971, Specac has been at the forefront of developing innovative spectroscopic solutions to enable our customers to conduct quantitative measurements reliably. Specac’s involvement with Process Analytical Technology began in the 90s and has been going strong ever since.
What is an NIR Process Cell?
Process cells are the interface between a chemical process stream and its dedicated process measurement systems. They bring light to the chemistry of your process stream, literally and figuratively.
They are subject to sometimes extreme physical demands: both from the chemistry inside the process stream and the environment outside. These conditions are often more hazardous to personnel, which is why safe means to install and service the system can be as important as the in-service requirements.
On the other hand, process cells are also required to provide a path for ultraviolet, visible, or near-infrared light to probe the chemical composition of the materials inside the cell: this requires robust optics, precision fitment, and above all, physical stability over the life of the cell.
What are the benefits of on-line NIR process analysis?
Directly monitoring the chemical composition of fluids or vapours in different parts of a chemical process plant is desirable for several reasons:
- It can reveal process instabilities that would not be detected using off-line methods
- It allows your process to be run closer to its specification limits more of the time
- It replaces hazardous and time-consuming off-line sampling with continuous in-line sampling.
Process spectroscopy cells are a key component in the implementation of an on-line process analytical system, as they sit in direct contact with the chemical process itself.
Read more: Benefits of on-line NIR analysis in a continuous process
Case study 1: acetic acid production
Acetic Acid is an important intermediate chemical for the manufacturing of solvents like ethyl acetate and for key ingredients in paints like vinyl acetate monomer. It can also be used for the production of acyl chloride, which is widely used in the synthesis of pharmaceuticals and pesticides and acetic anhydride via the Ketene route.
What are the stages in specifying online NIR spectroscopy for a plant?
The first stage in specifying a new on-line NIR spectroscopy installation is to conduct feasibility studies on the chemical process. This determines whether the chosen process is even suitable for analysis by on-line NIR.
At the next stage, a pilot plant will be built. This tests the system separately from the main process plant, allowing data to be collected on how the pilot system performs in comparison to the regular process.
If all these tests are passed, the go-ahead will be given for full-scale implementation on the main plant.
The requirements for the corresponding process cells can differ at each of these stages.
Read more: Stages of online NIR installations
How do integrated process flow cells work?
Light is transmitted via an optical fiber cable from the spectrometer source to one port of the process flow cell. Collimation optics then direct this light beam through a set pathlength of process stream to a second set of optics which re-focus the beam to a return optical fiber cable attached to the second process flow cell port.
The return optical fiber cable serves to transmit the light beam back to the spectrophotometer detector. Process flow cells are typically installed as part of the process circuit either directly in the process stream or in a ‘by-pass loop’. By adopting the process flow cell in a ‘by-pass loop’ configuration, the user has the opportunity to isolate the process flow cell from the process cell for routine cleaning, servicing or calibration. Hazardous process flows should be suitably isolated before the cell can be safely removed from the installation.
There is no fixed number of NIR cells on a chemical production facility, this can range anywhere between 1 and 6. The beauty of an NIR system is the option to multiplex between different cells which can be hundreds of metres apart from each other and analyse different process streams. The process streams can have different compositions and physical states (gas and liquid cells on one spectrometer)
Read more: Integrating Process Flow Cells: Animated Guides
Case study 2: tall oil refinery
The distillation of CTO occurs in four fractional distillation columns: the first separates pitch from the CTO; the second removes the rosin soaps from the de-pitched CTO; the third distils crude fatty acids, and the final column separates these into tall oil fatty acids and distilled tall oil (DTO).
Traditional process analytics require samples to be removed from the process line for testing by chromatographic or wet chemistry techniques. The length of time between sampling and analysis, delays the taking of corrective action if the process has drifted out of specified bounds. This can cause costly production delays and result in wasted material and effort. With on-line near-infrared sampling, instantaneous feedback is possible.
Read more: AN24-01: Monitoring Tall Oil Distillation using a Vortex™ process flow cell
What kind of design considerations are there for process flow cells?
Before design of a new process cell can commence, the designer needs to know several facts about the chemical process that it will come into contact with.
This includes temperature and pressure of the process, the physical properties of the material (solid, liquid, powder, gas, particulate, etc.) and its chemical compatibility with would-be cell materials.
Once the process parameters have been specified and a solution has been chosen, the next factor will be the installation of the cell into the process. This can be a direct installation in-line with the main process pipework, or it can involve a “double block and bleed” arrangement on a bypass loop.
Read more: Design considerations for sampling of liquid process streams with NIR process cells
Case study 3: ethylene in an ethylacetate production plant
Varying amounts of Ethylene in the process stream can be monitored by NIR spectroscopy using a gas cell. The system monitors the start-up and control of the process. One of the big advantages of NIR spectroscopy for this process is the ability to monitor gas and liquid phase components with the same analyzer.
Read more: https://specac.com/process-applications/vapour-phase-process-cells-for-online-nir-spectroscopy/
Fiber optics for process flow cell integration
Specac ProCell process flow cells are compatible with a range of optical fiber cables, with core sizes of up to 600 microns diameter. These should be selected by the user to be appropriate for the application. For instance, water-free optical fiber is typically used for NIR applications, while special UV-grade optical fiber should be used if enhanced UV transmission is needed.
Optical fibers should also be appropriately coated for the temperature experienced at the point of connection to the process flow cell: polymide-coated or metal-coated fibers are recommended for higher temperature applications. Specac follows the industry standard by using the widely available and popular SMA 905 style of fiber connector to interface optical fibers with the process flow cell.
Read more: Use of Fiber Optics in NIR on-line spectroscopy
Have questions? Book a free consultation.
With state-of-the-art design and material modelling tools and over 25 years of process application experience to draw from, Specac’s range of process flow cells have a proven track record of reliability and robustness to ensure long-term operation in the most demanding industrial environments.