I claim the ornamental design for a portable material separator, as shown and described.
FIG. 1 is a perspective view of the portable material separator.
FIG. 2 is a side view of the portable material separator.
FIG. 3 is an opposite side view of the portable material separator.
FIG. 4 is another side view of the portable material separator.
FIG. 5 is a top view of the portable material separator.
FIG. 6 is a bottom view of the portable material separator; and,
FIG. 7 is a perspective view of the portable material separator with a bucket (illustrated by broken lines).
The broken lines shown in FIG. 7 depict a container (such as a bucket) utilized with the portable material separator and represent unclaimed subject matter and form no part of the claimed design.