Polymer Applications - End of Reaction

Determining end-of-reaction in resin reactors is critical to achieve desired product properties, such as molecular weight. Knowing exactly when the reaction is over saves cook time and batch conversion time, and hence, lowers the overall manufacturing cost. Having real-time chemical information often leads to significant improvements in process control because you will see activity with continuous readout that less frequent grab sampling may miss. Go from in-spec to on-target with continuous monitoring.

Polyester resins
Alkyd resins
Phenol/Formaldehyde resins

NIR provides one of the key parameters – acid value – used to determine molecular weight. Another key parameter is viscosity, also measured in the reactor. Both parameters are used together to monitor the path of the reaction. They are used to accurately determine the end-of-reaction. Different products can be distinguished by these paths, as shown for hypothetical Products A and B here.

No need to grab samples near the end of the reaction. No need to put pressure on your analytical lab for rapid turnaround of titration results. Get used to real-time monitoring of:

NIR

Acid Value
Hydroxyl Number
ppm Water
Isocyanate

VISIBLE

Yellowness

Isocyanate is commonly added near the end of the reaction to modify the final viscosity and as an end-blocker to achieve certain physical properties, such a wear resistance and electrical properties.

Color is a good indicator of oxidation where air might be brought into the reactor under vacuum from a leaky seal, or just from "cooking the batch too hard". Guided Wave's Optical Solutions brand photometers are unique in that they simultaneously analyze NIR chemical properties and VISIBLE color.

Notice that the fiber optic sample probe shown in the above picture is directly inserted into a 250 °C reactor and is secured with welded ANSI flange. Think of this “probe” as a glass cuvette placed in a rugged container INSIDE your reactor being refreshed continuously. This is where light interacts with your sample. This insertion probe, and similar probes that we offer, are designed to withstand the frequent heating/cooling cycles in batch reactors at temperatures up to 300 °C. The insertion probes can be placed in transfer pipes in continuous processes, as well.

After the reactor is drained, the probe can be removed and placed securely on the tray shown above for rapid cleaning and re-zeroing, as needed. We provide you with the diagnostic tools to know if you have to re-zero the probe.

Insertion probes are not the only means to make continuous measurements. If your resins or polyols are routed through a bypass loop (side stream) at temperatures < 150 °C, you can use one of our flow cells, as shown here.

Here, it is important that your material does not freeze up and block sample flow. The sample can be valved off from the cell and drained. The flow cell has a clean port that provides you with access to the optics for cleaning without moving anything.

Our probes and flow cells can be connected to our analyzer 50 meters away using optical fibers in reinforced cables. You can see the dark-colored flexible conduits coming out of the flow probe (left and right) in this picture.

Fiber optic cables are routed to the analyzer in the control room or to a suitable enclosure that meets your local safety requirements, such as Z-Purged for Class 1, Division 2, Groups B-D in North America, or ATEX (II G EEx d IIC T6, for example) in Europe.

Guided Wave offers two types of analyzer technologies for these measurements:

Optical Solutions’ Brand SMART Photometers for one or several sample points
Guided Wave’s Model 412 Spectrophotometer for multiple sample points

How do you decide between these technologies?

Choose Photometers:
- Smaller number of property measurements at each sample point
- Relatively fixed chemistry that does not require frequent model development
- STEP-UP Technology
  - Buy a single-point NEMA 4X ChemView and probe. Develop your calibrations and monitor your process. Return the ChemView to us and we will return it to you as a 4-6-8 point ChemViewMx for the difference in price + conversion fee. You don't lose your calibrations since we are using the same optics, but just adding multiplexing.
Choose Spectrophotometers
- Larger number of sample property measurements at each point (e.g., end-blockers, other chemistry, such as isocyanates, etc.)
- Larger mix of products
- Changing chemistry requiring frequent model development

There are several points to consider:

Many of your resin products are likely closely related and possibly can be grouped together in one predictive model. The same wavelength regions contain the vital information. Thus, model management may not be as complicated as you first think.
You may not want the analyzer to perform the analysis and store the calibrations. The analyzer, such as one of our photometers, can simply provide the spectral absorbance data, and you maintain your own models in your process control computer system. This has worked well for a number of our top customers.