I really appreciate @bird being the necromancer for this thread, and he brings up a most sublime advantage of solid phase chemistry with his question about “BHO and pH”. These applications for media are either not well known or they have largely gone unspoken until now! Here’s what I know:
Running the carboxylic acid forms of cannabinoids* over a solid pH-medium**, regardless of the solvent***, will have an effect on the cannbinoid-acid’s ability to crystallize.****
*which make up the majority of what we extract directly from the Cannabis plant, especially from younger and/or fresher biomass
**any media which have some sort of pH effect when measured in contact with water
***whether the cannabinoid acids are dissolved in a non-polar solvent like butane or dissolved and partially disassociated in a more polar solvent like ethanol
****via the hydrogen bonding (-H-O-H-) mechanism of inter-molecular lattice formation
This is because of that solid-state reaction mechanism I mentioned before, as I was explaining the nuances of pH to Kotk, wherein the acidic solid (e.g. THCa) can be deprotonated by a solid base (e.g. mineral-hydroxide)… which CREATES water! I.e… [H+] + [OH-] —> [H2O]
(I believe this type of solid-state neutralization is what had you so adamantly believing in non-aqueous/non-polar pH, @Kingofthekush420… Right? I admit it can be confusing, and it is almost an argument of semantics, but does this automatic generation of water by the Brönstead acid-base reaction perhaps help “solidify” my point?)
The various media have 3 different means by which they can affect the pH of water. In my work with Carbon Chemistry, I have identified these as Mobile, Immobile & Buffered in the context of media pH values and their relationships with our solvents and solutes. And, yes, for the sake of simplicity we can just say they “have solid-state pH.” 
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Mobile = media contains some free acid/alkali that may leach into filtrates.
This is strictly mechanical mobility, as in “rinsing” acids/bases from the solid surfaces, although the effect may be greater or smaller under different solvents and conditions.
Water and polarity of the fluid solution (aka: mobile phase or MP) enhance mobility of acids/bases via solvation effects, while, by the same token, a minimum of water hydrating the medium may reduce mechanical mobility of a/b by non-polar mobile phase.
Mobility of a/b in any MP is directly proportional to temperature & fluid velocity.
Mobility of a/b in any MP is inversely proportional to molecular weight & fluid viscosity. -
Immobile = no free acid/alkali, but media may change pH of acidic/alkaline filtrates (may adsorb H+ or OH-)
This is always the case for chemically inert media, but some of these can have pH-modified surfaces that will attract and even strip opposing labile protons or hydroxyl groups from passing solutes. The most common cases are those of silica and alumina. Silica is mostly inert and pH neutral, although it may be mildly “activated” with strong acid (strong alkali etches/dissolves silica), especially when in forms with high surface area. Alumina, however, is easily, powerfully and cleanly activated with alkali or acid (albeit less commonly, since strong acid etches alumina) . Activated alumina surfaces strongly attract their electrochemical opposites, and can even cleave the H+ or OH- ions from solutes with sufficiently weak conjugates (i.e. stronger acids & bases have weaker conjugate bases & acids, respectively). The activated alumina usually only attracts and holds onto (for statistically longer time) the “weak” acids and bases, due to their stronger conjugates. That said, all of these strengths are juxtaposed with the conjugates’ affinities (relative to their labile ions) for the mobile phase that carries them… So even some “stronger” conjugates may lose their labile groups to the activated alumina surface if they are enveloped in even stronger solvating power. -
Buffered = ions in media may exchange with those in filtrates (adsorbs cations+ and/or anions-, mainly via water)
This is the most complex “pH effect” of media, but also the least concerning for those working with Cannabis, since it requires water. This is actually known as “cation exchange capacity” or CEC in clays. The most important things to understand about it are
A. Its need for water to move ions around… so it works best in alcohol solutions or other wetted circumstances.
B. Cations are positively charged, so they attract to negative charge surfaces like hydroxyl groups at clay edges.
C. This is the best way to adsorb heavy metals in cationic form, so utilize the above two points, A. & B.
Here is a formal document I helped Carbon Chemistry put together for our various products, which includes each product’s particle size range, standard pH range, and our lots’ pH averages along with their pH effect values:
MaterialPropertiesQRG (005).pdf (1.0 MB)
The practical upshot of all this is…
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Mobile pH media is best for changing crystallization effects of acidic (and potentially non-acidic) cannabinoids, but beware that leftover acid or base in your resin can cause unwanted reactions, especially when heated (with or without air present).
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Immobile pH media is most likely to attract species with opposing solid-phase pH or charge… although it can strip labile protons or hydroxyl ions if they are “loose” enough and the ion’s conjugate dissolution in the mobile solvent is strongly favored, even without the ion (E.g. CBDcarboxylate- ion in ethanol).
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Buffered pH media can behave like immobile pH media, but it also has the ability to adsorb larger cations or anions, depending on charge… though this is very nearly always mediated by water, and most often refers to cation exchange capacity (negative charge surfaces) in clays.
Finally, here is the most direct way I can explain it, using the Products of Carbon Chemistry, through which I discerned most of these concepts by empirical observation…
Carbon Chemistry’s MagSil-PR® or, with enough solvent strength, Alumicel B, can outright deprotonate the acidic cannabinoids like THCa and CBDa. This removal of the H+ leaves the carbonyl group (COO-) attached to the cannabinoid molecule.
This can:
- Inhibit crystallization of THCa (by eliminating the carbonyl OH group)
- Enhance crystallization of CBDa (by limiting lattice-forming to the alcohol hydroxyl pairs)
Carbon Chemistry’s granular Activated Alumina, while certainly alkaline, given the same temperature and rate of fluid flow, will do more attracting than stripping of acids.
The same goes for the Molecular Sieves, except they also exclude species by size, and they are buffered negative, so cation adsorption tends to be strong with them, assuming the cation fits!
Carbon chemistry’s bentonite clays like Pure-Flo® B80 can adsorb cations when moisture is present in alkanes… T-5® has the best heavy metal cation capacity, especially for typically hydrated alcohol:resin solutions.
Carbon chemistry’s attapulgite clay products, the granular ZeoClear™ Y, and ZeoClear™ L are also effective adsorbers of heavy metals in solutions with a little moisture in alkanes.
Last but not least, anything buffered or immobile can have its surface charge changed by adsorption of oppositely charged species. Buffered media most often just neutralize (and can dissolve) in strong A/B, while immobile pH media flip in pH. Remember that when it comes to contact with your cannabinoids and their acids!