SWIM is into her CSLE (Continuous Solid-Liquid Extractor) extraction using acidified water instead of IPA.

Immediately she noticed that water flows through the extractor column filled with 50 g of mhrb MUCH slower than IPA. She added a few grams of perlite as a result doubling total volume of the extracted material but the flow-through speed did not increase very much.

Same prepowdred mhrb was used.

Is this normal/expected? Is it because of greater surface tension of water?

I am guessing that as water is more dense than IPA so it should flow slightly slower...

Adding perlite helped a lot.

But still, in swim's experience, IPA extraction is 3-5 times faster than acidified water extraction. Now she is into 11-th hour and the water dripping from the extractor is still purplish. IPA would have been completely clear after the second hour.

probably has more to do with h-bonding with cellulose hydroxyl groups.
dioxane has a stronger dipole moment, propan-2-ol has van der wahls interactions because of its isopropyl moeity.