Particulate filters
A vehicular exhaust filter ( 2 ) comprising a porous substrate having an inlet face and an outlet face with the porous substrate comprising inlet channels extending from the inlet face and outlet channels extending from the outlet face is disclosed. The inlet channels and the outlet channels are separated by a plurality of filter walls having a porous structure. The vehicular exhaust filter ( 2 ) is loaded with a refractory powder having a tapped density before loading of less than 0.10 g/cm 3 and the vehicular exhaust filter has a mass loading of the refractory powder of less than 10 g/l.
1. A vehicular exhaust filter comprising a porous substrate having an inlet face and an outlet face, the porous substrate comprising inlet channels extending from the inlet face and outlet channels extending from the outlet face; the inlet channels and the outlet channels being separated by a plurality of filter walls having a porous structure;
the vehicular exhaust filter being loaded with a refractory powder having a tapped density before loading of less than 0.10 g/cm 3 ;
the vehicular exhaust filter having a mass loading of the refractory powder of less than 10 g/l; and
wherein greater than 40% of the refractory powder is located within the porous structure of the plurality of filter walls and less than 60% of the refractory powder is coated on an external surface of the plurality of filter walls.
2. The vehicular exhaust filter of claim 1 , wherein greater than 50% of the refractory powder, optionally greater than 65% of the refractory powder, optionally greater than 75% of the refractory powder, optionally up to 100% of the refractory powder is located within the porous structure of the plurality of filter walls.
3. The vehicular exhaust filter of claim 1 , wherein the percentage of the refractory powder located within the porous structure of the plurality of filter walls is calculated by the formula:
%
Powder
inwall
=
(
1
-
(
[
Envelope
volume
powdercoated
(
ml
)
-
Envelope
volume
bare
(
ml
)
]
·
Bulk
density
(
g
·
ml
-
1
)
Powder
loading
of
filter
(
g
)
)
)
·
100
%
.
4. The vehicular exhaust filter of claim 1 , wherein the refractory powder has a tapped density before loading of less than 0.08 g/cm 3 , optionally less than 0.07 g/cm 3 , optionally less than 0.06 g/cm 3 , optionally less than 0.05 g/cm 3 .
5. The vehicular exhaust filter of claim 1 , wherein the mass loading of the refractory powder is less than 7 g/l, optionally less than 5 g/l, optionally less than 3 g/l, optionally less than 1 g/l.
6. The vehicular exhaust filter of claim 1 , wherein greater than 0.5 g/l of the refractory powder is located within the porous structure of the plurality of filter walls.
7. The vehicular exhaust filter of claim 1 , having a filtration efficiency at 0.02 g/l soot loading of greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%.
8. The vehicular exhaust filter of claim 1 , having a back pressure of 20-180 mbar at a flowrate of 600 m 3 /hr.
9. The vehicular exhaust filter of claim 1 , wherein the refractory powder is an aerosol-deposited refractory powder, preferably an aerosol-deposited dry refractory powder.
10. The vehicular exhaust filter of claim 1 , wherein the refractory powder has a d50 (by volume) less than 25 microns, preferably less than 20 microns, more preferably less than 10 microns.
11. The vehicular exhaust filter of claim 1 being a wall-flow filter.
12. The wall-flow filter of claim 1 being an asymmetric wall-flow filter.
13. The vehicular exhaust filter of claim 1 , wherein the vehicular exhaust filter is a calcined filter.
14. The vehicular exhaust filter of claim 1 , wherein the porous substrate comprises one or more washcoats.
15. The vehicular exhaust filter of claim 1 , wherein the porous substrate comprises an adhesion promoter and or binder.
16. An exhaust system comprising the vehicular exhaust filter of claim 1 .
17. A plurality of vehicular exhaust filters, each vehicular exhaust filter comprising a porous substrate having an inlet face and an outlet face, the porous substrate comprising inlet channels extending from the inlet face and outlet channels extending from the outlet face; the inlet channels and the outlet channels being separated by a plurality of filter walls having a porous structure;
each vehicular exhaust filter being loaded with a refractory powder having a tapped density before loading of less than 0.10 g/cm 3 ; and
each vehicular exhaust filter having a mass loading of the refractory powder of less than 10 g/l;
wherein greater than 40% of the refractory powder is located within the porous structure of the plurality of filter walls and less than 60% of the refractory powder is coated on an external surface of the plurality of filter walls.
18. The plurality of vehicular exhaust filters as claimed in claim 17 , wherein the refractory powder is an aerosol-deposited refractory powder, preferably an aerosol-deposited dry refractory powder.