Plant Compounds & Absorbents

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Chlorophyll

Is the green color found in most plant based extracts. High molecular weight and high boiling point makes chlorophyll easily removed by distillation, but the polar nature of the molecule also makes it easy to separate with other techniques that take advantage of differences in polarity such as liquid to liquid separation. Exposure to light can turn the extract from green to red because the chlorophyll acts as a photosensitizer and initiates the oxidation of oils. It is thus good practice to take measures to reduce exposure of light to oils that contain chlorophyll. It is worth noting that chlorophyll is locked away in the plant cells. To reduce the extraction of chlorophyll agitation that would rupture the plant cells should be reduce, yet if extraction of chlorophyll is wanted then heavy agitation such as ultra-sonication should be used.

 

Carotenoids

Easily the largest source of yellow/red pigment in the fats of plant and animals. The long hydrocarbon chain makes the molecule very non-polar and give it a high molecular weight and boiling point. With our target molecules being non-polar in nature distillation tends to be the best method of removing these compounds, but it is possible there are other methods that could be used that take advantage of differences in molecular weight. Carotenoids oppose the initiation of photooxidation. Acid activated clays and carbon remove carotenoids but not silicas. Absorption occurs in the range of 420-475nm. Hydrogenation attacks the double bond and thus removes the associated color.

 

Flavonoids

These compounds tend to have similar boiling points, viscosity, and color as the cannabinoids fraction. It is suspected that the yellow color found in the cannabinoid fraction is caused by flavonoids that have been carried over with the cannabinoid fraction. Some flavonoid compounds have a higher boiling point than cannabinoids and thus would not be able to be removed through distillation techniques and is best removed by clay adsorption. The phenolic groups possibly lend to its antioxidant effects.

 

Anthocyanidins

Classified as a type of tannin anthocyanidins are compounds that are found in the tissues of plants. As changes in pH occur the color associated with these compounds shift (alkali blue, or acidic red). Absorption 480-550nm. Some are water soluble and easily removed through liquid to liquid separation with water and a non-polar solvent. Absorbed in clay bleaching.

 

Cannabinoids

Like many other phenolic compounds cannabinoids exhibit antioxidant properties. Pure cannabinoids are colorless or light yellow. Molecular weight of roughly 315g/mol. Oxidation will eventually break them down to a red byproduct that stubbornly resists removal. The avoidance of oxidative conditions wherever feasible, from harvesting to processing, is good practice.

 

Phosphatides/gums

Severely interfere with further processing steps if allowed to remain. It diminishes the absorptive properties of clay and carbon by adhering to the surfaces. Darkens the color of oil if they become broken down by heat, and lead to impaired smell, taste, and shelf stability. It is best to remove them with silica before bleaching, hydrogenation, distillation, or other steps.

 

Clays

There are many different types of clay used for bleaching or absorption. Many have been processed by acid activation and other techniques to improve absorptive properties or for specific uses. A thorough search and experimentation of different clays is advisable. The optimal proportion of oil to clay, temperature, and duration of contact are all variable which must also be optimized as an excess of either will reduce performance and encourage undesirable side effects. A small amount of water in the clay helps the effect of adsorption. Good for removal of chlorophyll, oxidized by-products, and many other pigments. If an excess of heat is applied activated clays are pro-oxidant catalysts which will lead to migration of double bonds (isomerization), side reactions, and degradation in general.

 

Carbon

Has an average internal surface ranges from 500-1500 m2/g while the outer surface area is 10-200 m2/g which emphasizes the huge surface area within the particle. Carbon tends to work better for deeply colored pigments whereas clays work better for lighter pigments, but this is a general rule of thumb and obviously not true of all compounds. Carbon retains up to 150% or more its weight in oils, activated earth up to 70%, and neutral up to 30%. The use of activated carbon comes at a high cost and the total amount and proportion to clay should be carefully considered. Activated carbon in conjunction with clay has been found to be the most effective and economical.

Up to 40% carbon to clay has yield the best results but in practice 8-12% would be used as the loss to carbon can become quite high as the level rises. Activated carbon comes from many different sources, each of which has different surface properties based on its particle size and macro/micro pores. Carbon derived from coconut shell for example has roughly 95% of its internal surface as micropores which is great for the adsorption of smaller molecules such as volatile organic compounds and terpenes, but not good for the adsorption of larger ones like pigments. Wood and peat based carbons have mainly meso/macropore structures which are particularly well adapted for adsorbing larger molecules like pigments.

   

Silica

The large surface area provided by silica makes it useful as a generation filtration aid which can not only increase filtration speed if applied correctly, it can also increase the filtration abilities. The silica is also somewhat polar. Using a polar solvent like alcohols diminishes its absorptive abilities. Using a non-polar solvent like pentane, hexane, or heptane will aid the remove of the more polar compounds. Some pesticides that are carried over during distillation can be removed as such.

Activated magnesium silicate also known as florisil is especially suited for removal of pesticides. The use of silica to remove soaps, phospholipids, and iron greatly enhances the performance of activated bleaching clays which can decompose peroxides and absorb products of secondary oxidation. Molecules which reduce surface tension at an interface between a solid and a solution will tend to be adsorbed on the solid. Solvents with high surface tension like water will cause most solutes to be adsorbed whereas alcohol has much less surface tension and thus exerts less of a force.

 

Chemisorption

Greater than 10x the power as physical adsorption and is most evident at moderate temperatures. Chemical type attraction quickly loses its force as the sites for this attraction are filled whereas Van der Waal forces have a stacking effect that continually maintains its attractive force and build layers.

 

Temperature

For physical adsorption temperatures lower than 130°C will encourage more pigment to be retained. At temps above 100°C Van der Waal forces are disrupted. When temperatures are raised to 160°C in the presence of activated clays or carbon isomerization tends to occur. Neutral clays work best at 118-132°C, and activated 100-106°C. Some adsorbents that contain a high proportion of silicas tend to have their best effect at around the 200°C range.

 

Duration

Time of duration between the oil and the adsorbent should be considered. One half of the color is likely to be adsorbed within the first 5 mins. After 15 mins, the reduction is slight and after 30 mins the color is likely reversing.

 

Dosage

If clay or carbon dosages are increased well above the range needed for color removal, the oxidative stability will begin to fall. The losses of oil to the absorbent will also be heavy.

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