Method to inhibit polymerization in a process water
Disclosed herein are methods for reducing fouling caused by process water present within a water recycling loop of a pyrolysis plant. Fouling is caused by phase separation and accumulation of materials from the process water on equipment surfaces. The method includes applying a total of about 5 ppm to 500 ppm total of a first polymerization inhibitor and second polymerization inhibitor to the process water to form a treated process water, wherein the first polymerization inhibitor has a pygas-water partition coefficient of about 0.0001 to 9 and the second polymerization inhibitor has a pygas-water partition coefficient of about 1000 to 50,000.
1. A method of reducing fouling in a water recycling loop, the method comprising:
selecting a first polymerization inhibitor having a a pygas-water partition coefficient of about 0.0001 to 9 and a second polymerization inhibitor having a pygas-water partition coefficient of about 1000 to 50,000, wherein the pygas-water partition coefficient is determined in water and either a pygas obtained from a process water or a simulated pygas comprising toluene, styrene, cyclohexane, n-hexane, and dicyclopentadiene;
applying the first polymerization inhibitor and the second polymerization inhibitor to a process water within the water recycling loop to form a treated process water, wherein the total concentration of the first and second polymerization inhibitors in the treated process water is about 5 ppm to 500 ppm; and
contacting the treated process water with an interior surface of the water recycling loop.
2. The method of claim 1 wherein the total concentration of the first and second polymerization inhibitors in the treated process water is about 10 ppm to 100 ppm.
3. The method of claim 1 wherein the first and second polymerization inhibitors are applied to the process water at a weight ratio of about 1:9 to 9:1.
4. The method of claim 1 wherein the first polymerization inhibitor has a pygas-water partition coefficient of about 0.001 to 1.
5. The method of claim 1 wherein the first polymerization inhibitor is selected from 2,2,6,6-tetramethylpiperidinyl-1-oxyl, 1-hydroxy-2,2,6,6-tetramethylpiperidine, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidinyl-1-oxyl, 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, and 1-hydroxy-4-oxo-2,2,6,6-tetramethylpiperidine, or a combination thereof.
6. The method of claim 1 wherein the second polymerization inhibitor has a pygas-water partition coefficient of about 5000 to 25,000.
7. The method of claim 1 wherein the second polymerization inhibitor is selected from 1,4-phenylenediamine, alkylated derivatives thereof, or a blend thereof.
8. The method of claim 1 wherein the applying is downstream from a coalescer in a pyrolysis plant.
9. The method of claim 1 wherein the process water and/or the treated process water is present at a temperature of about 60° C. to 110° C.
10. The method of claim 1 wherein the water recycling loop comprises a dilution steam system.