PDFill PDF Editor Tools allow you to do that and its free.
(it's for windows only but if you have a mac you can always use a virtualization software to run it)
First it's better to remove all pages (cover, etc.) that are not formatted in double column (you can reinsert them later).
You need then to make two copy of the resulting PDF.
Then using the crop command, in the first copy you crop the right side of all the pages, keeping only the first column.
In the second copy you keep the second column only.
After that you merge the two files, and then reorder the pages using the reorder function like this :
For a 100 pages PDF : pages 1,51,2,52, etc.
(you can use Excel & word to generate and copy/paste the list quickly)
After that you can reinsert the cover and other normally formatted pages you removed first.
Making the first conversion is a bit tedious but once you know your way around the software it's very fast as all the steps are automated.
It's also works for every double column pdf, while with some bad pdf relying on the reflow function will mess up the text.
(The reflow displays first the first paragraph of the first column, then the first paragraph of the second column, then goes back to the first, etc.