Sorry for the slow reply! I missed the reply apparently.
Just did a room temperature solubility test with heptane and JWH-018. 3 ml room temp heptane was added to 100 mg JWH-018 and agitated for 10-15 minutes. Then allowed to settle for a couple minutes, and 2.4 ml of clear heptane was pulled off. This was evaporated to yield 11 mg of a deep yellow and sticky (think ear wax) mass. The original product was slightly gummy and off yellow, as pure JWH-018 is reported to be -- I considered this batch to be the purest / best I have ever bought (no smell or anything, no hiding of the gumminess like some companies do by cutting with starch). So the sticky yellow impurity is not naphthalene and is fairly common to be removed with JWH washes, whatever it is.
Placed on to the end of a knife and hit with a lighter, it did not seem to burn at all. Melted and smells terrible (plastic-like) but no apparent smoke or vapor even under flame for 3-4 seconds. I'm currently evaporating off the remaining heptane on the 100 mg of JWH and I'll report back with its' final weight. Certainly no more than 15 mg was removed in 2.4 ml of room temp heptane, so solubility of JWH-018 is < 6.25 mg / ml.
edit: Chlorophyll is soluble in ethanol but JWH-018 is very poorly soluble. So I imagine that will be effective for removing at least the majority of the chlorophyll. Chlorophyll is also soluble in naphtha so should be soluble in heptane as well.
This link says both ethanol and hexane are commonly used for extracting chlorophyll. May not be able to remove 100% as a kitchen chemist but you should be able to get most of it out! Good luck. I'll edit in my final washed JWH weight shortly.
edit2: 81 mg remaining in the jar. However there is a source of some loss involved both stuck to the stirring instrument (toothpick) and a mg or two pouring out the powder to expedite the evaporation and then pouring back into the jar. I think the solubility is closer to the evaporated heptane -- 11mg/2.4ml or ~4.6 mg/ml in room temp heptane.