Anyway, THF is miscible with water but not with saturated NaCl solution. Thus, THF, could be removed by several extractions with water. Then, the aqueous phases are saturated with NaCl, followed by removing the THF that separates at the top. The remaining mixture of hexane and heptane can easily be separated by distillation, due to the high difference of their boiling points.
But all above is theoretical and in practice, it does not seem convenient.
PS: Remember that THF mixtures must not be distilled until complete dryness, due to the possible formation of peroxides that are high explosive.