From how I think they work it should be possible to put them all in one location. It will remove the pollution from that chunk and the way regular factorio handles pollution should have the surrounding chunks start spreading their pollution into the now empty one. It should reduce overall pollution level but might not result in a totally clean base. It would probably be quicker to spread them out as well unless you have a very dense factory.
If you are removing more pollution than you are creating then eventually you should eliminate most of the pollution but if you have lots being generated far away then it will spread out in all directions until it meets the chunk that has the purifiers in it.
