On-site destruction of recalcitrant perfluoroalkyl substances by molecular sieves
A two-stage treatment process for destroying per- and polyfluoroalkyl substances (PFAS) in an aqueous stream. The two-stage treatment process uses a combination of multifunctional crystalline molecular sieves, such as zeolites and zeotypes, to separate PFAS from the aqueous stream, catalytically decompose and defluorinate any PFAS molecules, and generate non-toxic waste products that are safe for disposal. The first stage includes adsorption of the PFAS within one of a pair of vessels containing porous, hydrophobic, hydrothermally stable molecular sieves, dehydration of the captured PFAS on the sieves, and catalytic ozonation of the captured PFAS molecules on the dried sieves. The second stage involves catalytic decomposition and neutralization of the ozonation results with one of a pair of vessels including a zeolite-supported CaO catalyst, catalytic oxidation of any toxic CO generated by the decomposition, and an acid wash for regeneration of the spent catalyst.
1. An apparatus for destroying recalcitrant perfluoroalkyl substances, comprising:
a first vessel having an adsorption bed formed from a porous, hydrophobic, hydrothermally stable molecular sieve;
a source of compressed air coupled to the first vessel for introducing compressed air into the first vessel;
a source of heat coupled to the first vessel that can selectively increase a temperature of the first vessel to a first temperature between 80 and 120 degrees Celsius and to a second temperature of at least 150 degrees Celsius;
a source of ozone coupled to the first vessel for introducing ozone into the first vessel;
a second vessel coupled to the first vessel to receive any off-gases from the first vessel and including a catalytic bed formed from a zeolite-supported CaO catalyst;
a catalytic oxidizer coupled to the second vessel and having a metal-oxide supported noble catalyst operating at a temperature of between 200 and 350 degrees Celsius; and
a source of a mineral acid coupled to the second vessel.
2. The apparatus of claim 1 , wherein the porous, hydrophobic, hydrothermally stable molecular sieve comprises a zeolite with a silica to metal molar ratio greater than 6 and having a *BEA topology with a higher concentration of fully-coordinated molecular binding sites than partially-hydrolyzed open sites.
3. The apparatus of claim 2 , wherein the *BEA topology includes tetravalent metal heteroatoms.
4. The apparatus of claim 3 , wherein the zeolite-supported CaO catalyst of the second vessel is impregnated with a H 2 O-soluble calcium precursor.
5. The apparatus of claim 4 , wherein the H 2 O-soluble calcium precursor comprises calcium acetate (Ca(C 2 H 3 O 2 ) 2 ).
6. The apparatus of claim 5 , wherein the metal-oxide supported noble catalyst is selected from group consisting of Pt, Pd on CeO 2 , and Al 2 O 3 .
7. The apparatus of claim 6 , wherein the mineral acid comprises HCl or HNO 3 .
8. The apparatus of claim 1 , further comprising:
a third vessel having a second adsorption bed formed from the porous, hydrophobic, hydrothermally stable molecular sieve and coupled to the source of compressed, the source of heat, and the source of ozone; and
a fourth vessel coupled to either of the first vessel or the third vessel to receive any off-gases, wherein the fourth vessel includes a second catalytic bed formed from the zeolite-supported CaO catalyst and is coupled to catalytic oxidizer and the source of a mineral acid.