Are you trying to remove traces of methylene chloride from the powder? If so, simply pulling a vacuum on the powder is a bad way to do it. The volitility of the solvent and high surface area of the powder will cause the powder to blow itself around and get into your vacuum pump. If you could contain the powder inside a porous container to prevent this, then it would work.
You could also do something called fluidizing. You fill a tube with some powder and gently blow something like warm, dry nitrogen through the powder from the bottom so that the powder is gently blown up (but not out) inside the tube. This is easier and doesn't take too long, but can leave traces of solvent that the vacuum might not.
For a volatile solvent like this, just heating the powder will drive off quite a bit of solvent.
