Destruction of PFAS via an oxidation process and apparatus suitable for transportation to contaminated sites
Per- and polyfluoroalkyl substances (PFAS) are destroyed by oxidation in supercritical conditions. PFAS in water can be concentrated and prepared for destruction in a pretreatment phase. Following annihilation of the PFAS in supercritical conditions to levels below 5 parts per trillion (ppt), the water effluent can be used to recover heat, returned to sub-critical conditions, and then released back into the environment.
1. A method of destroying PFAS in a PFAS-containing mixture, comprising: subjecting the PFAS-containing mixture to a separation procedure comprising separating the PFAS-containing mixture into a PFAS-enriched fraction and a PFAS-depleted fraction;
heating at least a portion of the PFAS-depleted fraction to a temperature of at least 300° C. to form a heated PFAS-depleted fraction and wherein the PFAS-enriched fraction not being subjected to this heating step; and
prior to a supercritical destruction phase, combining the heated PFAS-depleted fraction with the PFAS-enriched fraction having a lower temperature than the heated PFAS-depleted fraction to form a hot PFAS-containing mixture; and
reacting the hot PFAS-containing mixture with an oxidant under supercritical conditions in the supercritical destruction phase.
2. The method of claim 1 wherein the PFAS-containing mixture comprises at least 100 ppm PFOA and wherein the PFOA is destroyed by the method of claim 1 to decrease the PFOA concentration by at least 10 6 .
3. The method of claim 1 wherein the oxidant comprises hydrogen peroxide.
4. The method of claim 1 comprising, prior to the step of reacting the PFAS with an oxidant, super-saturating the PFAS-containing mixture with air and passing the PFAS-containing mixture into a tank and reducing pressure in the tank such that bubbles are generated in the mixture to create a foamed mixture.
5. The method of claim 4 wherein a vacuum pump is used to suck out the foamed mixture.
6. The method of claim 1 further comprising treating an effluent from the step of reacting with an oxidant comprising NaOH, LiOH, or KOH.
7. The method of claim 6 wherein the PFAS-containing mixture comprises at least 100 ppm PFOA and the effluent comprises 1 ppm to 5 ppt PFOA.
8. The method of claim 1 wherein the PFAS-containing mixture comprises at least 100 ppm PFOS and the effluent comprises 1 ppm to 5 ppt PFOS.
9. The method of claim 1 wherein the PFAS-containing mixture comprises at least 100 ppt of at least one compound selected from the group consisting of PFBA, PFHxA, PFHpA, PFOA, 6:2 FTS, and 8:2 FTS and the method reduces the concentration of the at least one compound by at least 3 orders of magnitude.
10. The method of claim 1 wherein an organic fuel is added to the PFAS-containing mixture such that, during the step of reacting PFAS with an oxidant under supercritical conditions, the PFAS-containing mixture comprises 0.5 to 5 wt % of the organic fuel.
11. The method claim 10 wherein the organic fuel comprises an alcohol or acetone.
12. The method of claim 1 wherein the step of reacting with an oxidant occurs in a reactor that comprises a pipe having interior walls coated with a coating that resists corrosion by HF.
13. The method of claim 1 wherein flow during the supercritical oxidation step is consistently downward with respect to gravity.
14. The method of claim 1 wherein the PFAS-containing mixture is subjected to a pretreatment selected from: ion exchange with an ion exchange resin; lime softening; and contacting with a chelating agent.
15. The method of claim 14 wherein the PFAS-containing mixture is pre-concentrated using microbubbles to cause the PFAS to rise to the top of a tank.
16. The method of claim 1 where the step of reacting under supercritical conditions occurs in a reactor, and where heat from the step of reacting under supercritical conditions is transferred to heat the PFAS-depleted fraction that enters the reactor and where the step of transferring occurs in a tube-in-tube heat exchanger.
17. The method of claim 1 wherein effluent from the step of reacting is treated with an alkali or alkaline earth element after the effluent is no longer supercritical.
18. The method of claim 1 where the step of reacting under supercritical conditions occurs in a reactor, and wherein an alkali or alkaline earth element is added to the PFAS-containing mixture or heated PFAS-containing mixture prior to the hot PFAS-containing mixture entering the reactor.
19. The method of claim 1 wherein the step of reacting the hot PFAS-containing mixture with an oxidant forms an effluent and further comprising a quench step following the step of reacting the hot PFAS-containing mixture with an oxidant; and removing CaF 2 from the effluent.
20. The method of claim 1 where the step of reacting at supercritical conditions occurs in a reactor, and wherein effluent from the step of reacting the hot PFAS-containing mixture with an oxidant under supercritical conditions flows into a salt separator under supercritical conditions.