Originally By Tony Ackland
Stainless Steel Wool Scrubbers/ScourersFrom the above analysis, I figure that Stainless Steel Wool Scrubbers (pot scourers) are 2-3 times better than rachig rings with the typical small diameter columns we use in this hobby.
Using these as the best type of packing will allow you to use a smaller column or a lower reflux ratio to get the same purity. Or keep the same height & reflux ratio, and have improved purity. Are you happy with the existing purity, or do you want cleaner alcohol ?
The stainless steel scrubbers are probably only good however up to about 2-3 inch diameter columns. Beyond this, they will be difficult to keep in place & have even liquid flow over them (e.g. don't want areas where they are really packed tight or spread too thin - it has to be uniform). It is at the larger diameters that the more regular packings like rachig rings come into their own (as they won't compact up or seperate to leave holes), and for even larger diameters, that you'd consider structured packings (i.e. carefully stacked into a regular pattern). One rule of thumb I've heard of for raching rings is to size them 1/10th the diameter of the column; e.g. the small 6mm rachig rings are really only suitable down to about 60mm (2.4") diameter columns (and they're expensive!).
So for columns up to 2-3 inches in diameter (50-75mm), you might as well go for the better performing, cheaper option of scrubbers. Bigger than this though, and you might need to start using what commercial units do.
David comments ...
Do not unravel but tease them out by hand a bit so they fill the whole column diameter rather than just a part of it. Most of the ones I have seen in NZ do not have rubber bands around them. Place them into the column from the bottom one at a time using some sort of restriction at the top and bottom to prevent them going further or dropping out back into the boiler.. I use a 2" pall ring which works well.
On a slightly longer column (1m = 39.37" ) I use 19 off memory so 17 is probably around the right number. You dont want them too loose or too tight. If too tight they will compact more. The main thing is to have an even constant heat so you dont get surging. Surging causes compaction.