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NuPro Technologies, Inc.
1531-B Westbrook Plaza Dr. Winston-Salem, NC 27103
Phone: 336-768-6070
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DISTILLATION of FPXTM

F.A.Q's
Background
Terpene-based solvents used to develop flexographic printing plates are relatively expensive. This makes it desirable to re-use the solvent as many times a possible. After being used in a developer machine, the solvent will contain uncured polymer that was dissolved from the plates. Because the solvent is volatile and the polymer is not, the solvent can be recovered for re-use by distillation. Because of the low volatility of most terpene-based developer solvents, vacuum distillation is required.

Safety
All terpene-based flexographic solvents are combustible, and have flash points below their boiling points (even at very low pressure). As a result, distillation should be performed in an apparatus that is designed and certified for flammable materials. At no time should solvent vapors be exposed to temperatures above their flash points outside a sealed still that are completely purged of air. The combination of air and vapors at temperatures above the flash point can lead to an explosion.
In addition, hot still bottoms at temperatures above the autoignition temperature must be allowed to cool before being drained from the still. Always cool still-bottoms before dumping.

Procedure
1. Charge spent solvent to a cold still per the manufacturers instructions. Charging flammable solvents into a hot still can cause a fire or explosion.
2. Set the pressure (vacuum) controls to the maximum vacuum practical. A minimum vacuum of 27 inches mercury (approx. 75 torr) is required. Failure to achieve high vacuum will cause valuable solvent components to be left in the still bottoms.
3. Verify that the condenser water flow and temperature are appropriate to condense the entire vapor.
4. Set the heating fluid temperature control to 380oF (or at least 50o above the final boiling point).
5. Remove condensed distillate as it comes off. Take off product until all the volatile materials are removed. Failure to recover all the volatile components in the spent solvent will result in poor performance of the recovered product. The following vapor temperatures should be achieved as a function of system pressure when all of the volatile solvent has been recovered:

System Vacuum
(inches fig.)
25
26
27
28
29
Maximum Vapor Temperature
(Degrees F)
319 (159 C)
307 (153 C)
293 (145 C)
274 (134 C)
242 (117 C)
At the end of the distillation cycle the apparent vapor temperature may fall because there is little vapor being generated in the stillpot. When this happens the takeoff rate will slow and eventually stop.
6. Blend all recovered product together to insure that the batch is homogenous and consistent.
7. Cool the still bottoms to 200 degrees F or below and remove. Do not allow the still bottoms to over-cool as the pour is often well above room temperature (150-160 F). Dropping hot still bottoms in air can cause a fire.
8. Determine the % solvent recovered from the starting spent solvent. Typical recovery rates are in the 90% range. Failure to recover all the volatile solvent can impact performance.

F.A.Q's
Q: - What will happen if I distill at a lower temperature (or vacuum) than is recommended above?
A: - You may fail to recover all of the terpene component that dissolves the unexposed areas of the plate, resulting in longer wash times in the developer solution. In addition, the resulting solvent may not be homogenous and may appear cloudy or separate into two layers.

Q: - If I distill more than one drum at a time of solvent, can I take the distilled product directly into drums?
A: - No. The "solvent" is actually a mixture of solvents, each with a slightly different boiling point. The first 10% of the distillate will have a slightly different composition than the last 10% that comes over. All of the distillate must be blended together to insure consistency.

Q: - What thermal oil temperature is required to reach the correct vapor temperature?
A: - This is dependent on the system pressure and equipment design. The boiling point of the solvent will drop as the system pressure decreases (vacuum increases). At any boiling point vaporization will only occur when the thermal fluid temperature is sufficiently above the temperature of the solvent that heat is transferred into the solvent. A still with efficient heat transfer and insulation may only require that the heating fluid be slightly above the boiling point. In other stills it might need to run as high as 100oF above the boiling point of the solvent in order to transfer enough heal for distillation. Most successful installations report normal thermal fluid temperatures in the range of 380oF.

Q: - How important is vacuum?
A: - As discussed above, the higher the vacuum, the lower the temperature that is required to cause the solvent to boil (distill). In the absence of vacuum, the boiling point of the solvent would be prohibitively high for distillation.

Q: - How much solvent is typically recovered?
A: - This depends on soil loading, since none of the polymer is volatile. In most installations we see soil loading in the 5% to 7% range and recovery rates in the 90% to 95% range (9drums of recovered solvent is produced form 10 drums of dirty solvent). If soil loading increases to 10%, recovery will likely be reduced to 80-85%.

Q: - Why does my recovered solvent appear cloudy?
A: - Water can enter the system if solvent is exposed to open air for an extended period of time or if containers are stored outside without being tightly sealed. Redistill the batch drying off the water as it will come across the solvent.

Q: - I have recovered all the solvent at the correct temperature and pressure and the resulting product is still cloudy. What could be the reason?
A: - Possibly there is water contamination in the starting solvent or finished product. If it is suspected that the water is coming from a leak in the distillation unit, consider adding a colorant (e.g. food coloring) into the cooling water supply to assist in finding the leak.

Q: - Can I check my distilled product to determine if it is on spec?
A: - Yes. All distilled product should be clear and light in color, have no suspended matter, and appear to he homogenous (in a single phase). In addition. Specific gravity is often an excellent indicator. Compare the SG of the distillate to that of virgin solvent to determine if all the components in the solvent have been recovered.

Q: - Can I store distilled solvents in plastic tote tanks or drums?
A: - No. Firstly, terpenes and many other solvents can attack some plastics. This could result in a spill or leak, or even dissolve some of the additives out of the plastic. In addition, there is the possibility that the distillate may be hot from distillation. Hot solvents can often melt plastic tanks, resulting in accidents or impurities in the product.

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