The key to understanding the acid thing probably lies in the fact that almost everything is a little soluble in everything else, @Sapper502! However, there is a major difference between dissolved and dissociated.
Any acid (or base, or salt, or anything, really) may be dissolved (i.e. homogeneously dispersed in a solvent at the molecular level, becoming “solute”) to some degree in a non-polar solvent like heptane or in a polar solvent like water.
The acid in water will also dissociate (i.e. “ionize” or break apart to form charged particles: cations (+), usually the naked hydrogen “proton” & anions (-), the rest of the molecule, known as the “conjugate base”) to some degree, based on its pKa (the dissociation constant). Only ionic bonds, like those in acids, bases and salts, can dissociate in water or other polar solvents.
Acid dissolved in heptane does NOT dissociate at all; it remains whole molecules of the acid compound. The acidic hydrogens in the molecules are still relatively positively charged, while the conjugate base is or contains relative negative charge. In other words, the acid molecules are still polar, and they float around like tiny electronic “magnets”, which gather near any polar regions on other dissolved molecules. This statistically slows down the rotation, vibration, and translation (movement) of these other compounds (e.g. THCa), effectively shielding their polar regions and exposing their non-polar regions to other non-polar regions in the solution… or, in this case, to the non-polar “backsides” of THC molecules that are stuck to the mol-sieve by their hydroxyl group sides.
As you can imagine, dissolved bases in the non-polar solvent would grab onto the carboxyl groups of THCa molecules even “harder” than acid does. So why don’t we use alkaline solutes in heptane?
Well, the bases grab too hard! Strong enough base, like sodium hydroxide, could even react with the THCa, especially when the water is later introduced to wash the base out of the heptane, before solvent recovery! This could even cause the THCa to stay in solution, since the net effect of the associated base molecule is neutralization, or zero charge, aka: non-polarity! Just as easily, the base molecules could remain stuck to the THCa while it is stuck to the THC, which is stuck to the zeolite. Worse still, the hydroxide groups on the base molecules could very rapidly (especially when base molecules are small) adhere/adsorb to all those OH sites on the zeolite, blocking the bulkier THC-OH from adsorbing in the first place!
An acid, especially a bulky (bigger than the 3Å pores), weak, multi-protic organic acid like citric acid, is perfect. It will weakly associate with the carboxylic acid groups and make the non-polar regions of the THCa more readily available to adsorb to the non-polar “bums” of THC sticking out from the zeolite… and because it has 2 extra weak protons sticking out, it could ostensibly hold up another 1 or 2 more THCa molecules passing by! Note: Because the triprotic citric acid does not dissociate in heptane, all 3 of its O=COH groups will retain equal affinity for other carboxylic acid groups… unlike dissociation, where the 1st, 2nd, and 3rd protons have progressively weaker dissociation constants (pKa), thereby weaker ability to generate acidity (pH).
Just think about all this stuff as little static electrical magnets made of + & - regions on otherwise neutral (non-polar) “non-magnetic” blobs. The carboxylic groups (negative O=C-O region & positive H) on two different organic acid molecules (e.g. citric acid & THCa) can weakly stick together, like so:
(HOC:O)…citric… (O:COH)×2
(+ - * : - ) •••~~••• (- : * - + )×2
(- : * - +) ~ ~ ~ ~ ( HOC:O…thc )×2
(O:COH)…thc
