Closed-loop multi-stage chilled filter system
A series of vertically oriented filters of decreasing pore size is sealed from the atmosphere. Pressurized gas is used to force the liquid to be filtered through the filters. The filter stages are thermally insulated from ambient temperatures in order to maintain the liquid passing through at a reduced temperature. Each filter stage has a removable lid, which provides convenient access for replacing the filter cartridge, allowing it to be changed without disturbing the thermally insulated sidewalls of the filter stage.
1. A filtration system comprising a solvent vessel, a plurality of filter stages and the same plurality of transfer tubes wherein:
each filter stage has:
a thermally insulated cylindrical side wall;
a lid that is removable from said wall;
a replaceable, elongated filter cartridge;
a support having a beveled edge that positions a base of said filter cartridge centrally in the filter stage;
an inlet port in the lid located to introduce liquid into the filter cartridge;
an inlet port located to introduce pressurized gas into the filter stage outside of the filter cartridge; and
a base with an outlet port that drains fluid from outside the filter cartridge;
the solvent vessel has:
a thermally insulated side wall;
an inlet port for introducing pressurized gas; and
an outlet tube having a first end located at a bottom region of the solvent vessel and a second end located outside the solvent vessel;
and the transfer tubes are each removably connected:
at an outlet end thereof to one of the inlet ports in one of the lids of the filter stages; and
at an inlet end thereof to either the second end of the outlet tube of the solvent vessel or the outlet port of another of said filter stages such that the solvent vessel and the filter stages are connected in series.
2. The filtration system of claim 1 further comprising a guide positioned to locate an upper portion of the filter cartridge centrally in the filter stage.
3. The filtration system of claim 1 further comprising a seal between each filter cartridge and the lid of the corresponding filter stage.
4. The filtration system of claim 1 , wherein each support defines a fluid communication path from a volume above the support to a volume adjacent the outlet port.
5. The filtration system of claim 1 , wherein each guide defines a fluid communication path from a volume above the guide to a volume below the guide.
6. The filtration system of claim 1 , wherein there are three filter stages and:
a first of the filter stages is connected to the solvent vessel and its filter cartridge has a pore size of 10-15 μm;
a second of the filter stages is connected to the first filter stage and its filter cartridge has a pore size of 3-10 μm; and
the third of the filter stages is connected to the second filter stage and its filter cartridge has a pore size of ≤1 μm.
7. The filtration system of claim 1 , wherein each filter cartridge is made from polypropylene.
8. The filtration system of claim 1 , wherein the solvent vessel has chilled liquid carbon dioxide in its side wall.
9. The filtration system of claim 8 , wherein the side wall of the solvent vessel is at a temperature between −20° C. and −40° C.
10. The filtration system of claim 1 , wherein each filter stage has chilled liquid carbon dioxide in its side wall.
11. The filtration system of claim 10 , wherein the side walls of the filter stages are at a temperature of ≤−10° C.
12. The filtration system of claim 1 , wherein the pressurized gas is nitrogen that is pressurized to 70-210 kPa.
13. The filtration system of claim 1 , wherein the filtration system is sealed from an external atmosphere everywhere except at the outlet port of the filter stage that is at an end of the series.
14. The filtration system of claim 13 , wherein the outlet port of the filter stage that is at an end of the series discharges into a collection vessel.
15. The filtration system of claim 14 , wherein the outlet port of the filter stage that is at the end of the series discharges via a collection tube into the collection vessel.
16. The filtration system of claim 1 , wherein:
the outlet port of the filter stage that is at the end of the series discharges via a collection tube into a collection vessel; and
the collection vessel is sealed from an external atmosphere via a pressure relief valve.
17. The filtration system of claim 1 , wherein the transfer tubes are thermally insulated.
18. The filtration system of claim 1 , wherein the bases of the filter stages and a base of the solvent vessel are thermally insulated from an external atmosphere.
19. The filtration system of claim 1 , wherein the side walls of one or both of the filter stages and the solvent vessel are evacuated.
20. The filtration system of claim 1 , wherein the bases of the filter stages and a base of the solvent vessel are double walled and are either evacuated or filled with liquid carbon dioxide.
21. The filtration system of claim 1 , wherein each filter stage comprises a further inlet located to introduce solvent into the filter cartridge.