Ethanol and activated carbon in the CBD/Hemp Industry

By Jillian Jastrzembski

Ethanol and activated carbon are two of the most important materials in the CBD and hemp industry. In this article, we’ll discuss how both of these materials play a key role in the processing of CBD and hemp.

What is activated carbon?

Activated carbon is a common and versatile adsorbent material. It is prepared from a carbon-rich source such as wood, bamboo, olive stones, rice residues, nut shells, or fossils. In fact, the list of cheap, recyclable carbon sources that can be used as precursors for activated carbon is ever-expanding.

The porous carbon precursor material must be “activated” to create activated carbon. This can be a physical and/or chemical process that alters the internal surface area, porosity, and other physicochemical properties like surface chemistry.

These modified properties allow activated carbon to interact with a broad range of different toxins, pollutants, or impurities.

Activated carbon offers many advantages over alternative adsorbents. Some advantages are:

• Prepared from recycled organic waste materials
• Source materials are low cost
• Materials are “tunable” – meaning they can be physically and chemically optimized for different molecules
• Adsorption on activated carbon can be reversible, which means that it is regenerative material

How is activated carbon used?

We see activated carbon used across many industries and applications – not just the CBD/hemp industry. In fact, activated carbon is incredibly versatile because it can be used to adsorb a wide range of different molecules.

Often activated carbon is used as a purification or separation technique for herbal extracts. For example, in the hemp industry, activated carbon can be used to remove chlorophyll from ethanol hemp extracts.

That said, activated carbon is not one-size-fits-all. Different parameters such as porosity and surface chemistry can be optimized to adsorb specific molecules, depending on the application.

The interaction between activated carbon and ethanol is of particular importance for certain applications. Among these, ethanol adsorption is important for pollution control as well as bioethanol production. Specifically, during fermentation of biomass to produce bioethanol, the increasing ethanol concentration inhibits microbial activity which could slow or eventually stop the fermentation.

The interaction of activated carbon with ethanol is particularly relevant in the hemp industry, since hemp and CBD extracts are commonly ethanol-based. Ethanol is an ideal solvent for CBD extraction thanks to its polarity, size, and consumer safety profile.

Let’s discuss how ethanol does (and doesn’t) interact with activated carbon.

How does activated carbon interact with ethanol?

First, let’s review the general physical and chemical principles involved with adsorption. Remember that the process of adsorption is different from absorption. During adsorption, molecules are being held on the outside of the solid adsorbent material. During absorption, on the other hand, molecules are “taken inside” the solid material. (You can use the imagery of a sponge absorbing water to help conceptualize absorption.)

In the case of activated carbon, we’re dealing with adsorption, which can be physical or chemical, or both.

Physical adsorption involves intermolecular forces, such as van der waals forces or hydrogen bonding. Even though there is an attractive interaction between the adsorbent material and the adsorbed molecules, no chemical bonds are broken or formed. The chemical structure of the molecules does not change.

Chemical adsorption is a more powerful and more permanent interaction, because it involves breaking bonds and forming new ones. Much more energy is required to break bonds and form new ones, especially compared to the relatively weak intermolecular forces involved in physical adsorption.

These same basic principles apply when we talk specifically about ethanol molecules. Remember that ethanol is a polar molecule, particularly since it has such a short carbon chain of only two units. In other words, the polar hydroxyl group contributes significantly to the overall polarity of the molecule. This is important because it will only interact with other materials that have a similar chemical nature.

With that in mind, the affinity of ethanol for activated carbon is largely dependent on two things:

1. The nature of the interaction
2. The total number of interactions

Effect of surface chemistry

Let’s start by talking about the nature of the interaction.

Activated carbon without chemical modifications is a relatively hydrophobic material. That means that, unless it is chemically modified, it will have somewhat minimal affinity for ethanol. In fact, activated carbon will have better affinity for ethanol (as well as other polar molecules) when the surface chemistry is modified to incorporate oxygen functionalities. The presence of oxygen-containing functional groups greatly increases the hydrophilicity. That makes the activated carbon more willing to interact with polar molecules like ethanol.

The only issue with this is that some applications of activated carbon require that the adsorption process be reversible. In other words, sometimes it is useful to be able to temporarily adsorb ethanol on activated carbon, and later release it again. We already mentioned above that reversibility is one of the advantages of adsorption.

The stronger the physicochemical reaction between ethanol and activated carbon, the harder it is to make the activated carbon “let go” of the ethanol to regenerate. The regeneration process is mostly affected by the nature of the oxygen functionalities, as opposed to the number of functionalities. Depending on the surface chemistry, up to 98% of ethanol can be recovered even at room temperature.

Effect of porosity

The other important parameter is the number of interactions. Part of the “activation” process for activated carbon involves modifying the porosity, because it increases the surface area. This increases the availability of adsorption sites.

For a polar molecule such as ethanol, there is thought to be a “critical pore size” that allows for maximum adsorption of ethanol molecules. Up until that critical point, adsorption of ethanol increases. However, if we continue to increase the porosity beyond that critical point, adsorption starts to decrease. This is probably related to the packing formation of ethanol molecules on the adsorbent.

Summary

Activated carbon is a useful adsorbent material, especially because it can be tuned depending on the application.

Within the CBD/Hemp industry, activated carbon is a popular adsorbent and purification material. Depending on the goal of the processing step, it may be desirable to have an adsorbent that interacts very little with ethanol, favoring the filtration of other compounds. In other cases, it may be advantageous to have an adsorbent that is optimized to filter ethanol molecules. Luckily, activated carbon is a tunable material which can be used for many different purposes.

Activated carbon and food grade ethanol are key materials in the CBD/hemp industry, as well as many others. Lab Alley is proud to provide you with the highest quality food grade ethanol and activated carbon for your industry needs.

References

Mohammad-Khah, A., and R. Ansari. “Activated charcoal: preparation, characterization and applications: a review article.” Int J Chem Tech Res 1.4 (2009): 859-864.

Saleem, J., Shahid, U. B., Hijab, M., Mackey, H., & McKay, G. (2019). Production and applications of activated carbons as adsorbents from olive stones. Biomass Conversion and Biorefinery, 9, 775-802.

Silvestre-Albero, A., Silvestre-Albero, J., Sepúlveda-Escribano, A., & Rodríguez-Reinoso, F. (2009). Ethanol removal using activated carbon: Effect of porous structure and surface chemistry. Microporous and Mesoporous Materials, 120(1-2), 62-68.

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