Based on the law of similarity and intermiscibility like dissolves like , solvents with a polarity value near to the polarity of the solute are likely to perform better and vice versa. Generally, the finer the particle size is, the better result the extraction achieves.
The extraction efficiency will be enhanced by the small particle size due to the enhanced penetration of solvents and diffusion of solutes. Too fine particle size, however, will cost the excessive absorption of solute in solid and difficulty in subsequent filtration.
High temperatures increase the solubility and diffusion. Temperatures that too high, however, may cause solvents to be lost, leading to extracts of undesirable impurities and the decomposition of thermolabile components. The extraction efficiency increases with the increase in extraction duration in a certain time range.
Increasing time will not affect the extraction after the equilibrium of the solute is reached inside and outside the solid material. The greater the solvent-to-solid ratio is, the higher the extraction yield is; however, a solvent-to-solid ratio that is too high will cause excessive extraction solvent and requires a long time for concentration. The conventional extraction methods, including maceration, percolation and reflux extraction, usually use organic solvents and require a large volume of solvents and long extraction time.
Some modern or greener extraction methods such as super critical fluid extraction SFC , pressurized liquid extraction PLE and microwave assisted extraction MAE , have also been applied in natural products extraction, and they offer some advantages such as lower organic solvent consumption, shorter extraction time and higher selectivity.
Some extraction methods, however, such as sublimation, expeller pressing and enfleurage are rarely used in current phytochemical investigation and will not discussed in this review. A brief summary of the various extraction methods used for natural products is shown in Table 1. This is a very simple extraction method with the disadvantage of long extraction time and low extraction efficiency. It could be used for the extraction of thermolabile components.
A study on the extraction of catechin 1 , Fig. Based on the content of total polyphenols, ultrasonic-assisted extraction produced the highest total flavonoids yield and no statistically significant difference were found between maceration and heat assisted extraction [ 13 ].
Cajanus cajan leaves are used in Chinese folk medicine for the treatment of hepatitis, chickenpox and diabetes. Flavonoids are the bioactive compounds. Jin et al. The extraction efficiency of orientoside, luteolin, and total flavonoids was found to be the lowest in the extract from maceration method [ 14 ]. Percolation is more efficient than maceration because it is a continuous process in which the saturated solvent is constantly being replaced by fresh solvent.
Zhang et al. They found that the contents of the major component, fucoxanthin 4 , Fig. Goupi patch is a compound Chinese medicine preparation consisting of 29 Chinese medicines. Fu et al. The transfer rates of sinomenine and ephedrine hydrochloride were The extract from decoction contains a large amount of water-soluble impurities.
Decoction cannot be used for the extraction of thermolabile or volatile components. The ginsenosides 7 — 31 in ginseng encounter hydrolysis, dehydration, decarboxylation and addition reactions during decocting Fig. The hydrolysis efficiency was strongly affected by pH, temperature, and the amount of herbs [ 19 ]. The decoction process might enhance the dissolution of some bioactive compounds compared with the maceration process.
The contents of 11 constituents [benzoylaconine 36 , benzoylhypaconine 37 , benzoylmesaconine 38 , berberine 39 , coptisine 40 , palmatine 41 , jatrorrhizine 42 , aloe-emodin 43 and emodin 44 , baicalin 45 , wogonoside 46 ] in decoctions of SXT and FXT were significantly higher than those in macerations of SXT and FXT. The interaction between chemicals from different herbs was also observed.
The diester-diterpenoid alkaloids were not detected in the decoction and maceration of FXT, but diester-diterpenoid alkaloid hypaconitine 49 was found in the decoction of the single herb Aconiti Lateralis Radix Preparata. The constituents of the other three herbs in FXT might promote the transformation from diester-diterpenoid alkaloids in Aconiti Lateralis Radix Preparata to other less toxic monoester-diterpenoid alkaloids, which might explain the mechanism of toxicity reduction and efficacy enhancement of TCM by formulation [ 20 ].
Reflux extraction is more efficient than percolation or maceration and requires less extraction time and solvent. It cannot be used for the extraction of thermolabile natural products.
Zhang compared the extraction efficiency of active ingredients baicalin 45 , Fig. The Soxhlet extraction method integrates the advantages of the reflux extraction and percolation, which utilizes the principle of reflux and siphoning to continuously extract the herb with fresh solvent. The Soxhlet extraction is an automatic continuous extraction method with high extraction efficiency that requires less time and solvent consumption than maceration or percolation.
The high temperature and long extraction time in the Soxhlet extraction will increase the possibilities of thermal degradation. Wei et al.
The degradation of catechins in tea was also observed in Soxhlet extraction due to the high extraction temperature applied. Pressurized liquid extraction PLE has also been described as accelerated solvent extraction, enhanced solvent extraction, pressurized fluid extraction, accelerated fluid extraction, and high pressure solvent extraction by different research groups.
PLE applies high pressure in extraction. High pressure keeps solvents in a liquid state above their boiling point resulting in a high solubility and high diffusion rate of lipid solutes in the solvent, and a high penetration of the solvent in the matrix. PLE dramatically decreased the consumption of extraction time and solvent and had better repeatability compared to other methods.
Pressurized liquid extraction has been successfully applied by the researchers at the University of Macau and other institutes in extracting many types of natural products including saponins, flavonoids and essential oil from TCM [ 8 , 25 , 26 , 27 ]. Some researchers believed PLE could not be used to extract thermolabile compounds due to the high extraction temperature, while others believed it could be used for the extraction of thermolabile compounds because of the shorter extraction time used in PLE.
Anthocyanins are thermolabile. Gizir et al. SF has similar solubility to liquid and similar diffusivity to gas, and can dissolve a wide variety of natural products. Their solvating properties dramatically changed near their critical points due to small pressure and temperature changes.
The low polarity of S-CO 2 makes it ideal for the extraction of non-polar natural products such as lipid and volatile oil. A modifier may be added to S-CO 2 to enhance its solvating properties significantly. He found that both yields of essential oil and antioxidant activity of SFC extract were higher than those from other two methods [ 30 ]. Ultrasonic-assisted extraction UAE , also called ultrasonic extraction or sonication, uses ultrasonic wave energy in the extraction.
Ultrasound in the solvent producing cavitation accelerates the dissolution and diffusion of the solute as well as the heat transfer, which improves the extraction efficiency. The other advantage of UAE includes low solvent and energy consumption, and the reduction of extraction temperature and time.
UAE is applicable for the extraction of thermolabile and unstable compounds. UAE is commonly employed in the extraction of many types of natural products [ 32 , 33 ]. Wu et al. Guo et al. Microwaves generate heat by interacting with polar compounds such as water and some organic components in the plant matrix following the ionic conduction and dipole rotation mechanisms.
The transfers of heat and mass are in the same direction in MAE, which generates a synergistic effect to accelerate extraction and improve extraction yield. The application of MAE provides many advantages, such as increasing the extract yield, decreasing the thermal degradation and selective heating of vegetal material. MAE is also regraded as a green technology because it reduces the usage of organic solvent. There are two types of MAE methods: solvent-free extraction usually for volatile compounds and solvent extraction usually for non-volatile compounds [ 36 , 37 ].
Chen optimized the conditions for MAE to extract resveratrol 60 , Fig. An extraction yield of 1. Benmoussa et al.
The yield and aromatic profile in the enhanced solvent-free MAE extract was similar to those extracted by hydro distillation and cost only one-sixth of the time of hydro distillation [ 39 ]. Xiong et al. Pulsed electric field extraction significantly increases the extraction yield and decreased the extraction time because it can increase mass transfer during extraction by destroying membrane structures. The effectiveness of PEF treatment depends on several parameters including field strength, specific energy input, pulse number and treatment temperature.
PEF extraction is a non-thermal method and minimizes the degradation of the thermolabile compounds. Hou et al. The entire PEF extraction process took less than 1 s and much less than the other tested methods [ 41 ].
In a study of antioxidants extracted from Norway spruce bark, Bouras found that much higher phenolic content eight times and antioxidant activity 30 times were achieved after the PEF treatment compared to untreated samples [ 42 ].
The structure of the cell membrane and cell wall, micelles formed by macromolecules such polysaccharides and protein, and the coagulation and denaturation of proteins at high temperatures during extraction are the main barriers to the extraction of natural products.
The extraction efficiency will be enhanced by EAE due to the hydrolytic action of the enzymes on the components of the cell wall and membrane and the macromolecules inside the cell which facilitate the release of the natural product.
Chen et al. The extraction yield of chlorogenic acid 66 , Fig. Strati el al. Compared to the non-enzyme treated solvent extraction method, sixfold and tenfold higher yields of the two target compounds were obtained in samples treated with cellulase and pectinase, respectively [ 45 ].
Hydro distillation HD and steam distillation SD are commonly used methods for the extraction of volatile oil. Some natural compounds encounter decomposition in HD and SD. The chemical composition and antibacterial activity of the primary essential oil and secondary essential oil from Mentha citrata were significantly affected by distillation methods.
Both primary essential oil and secondary essential oil yields by HD were higher than those by SD [ 46 , 50 ]. Yahya and Yunus found that the extraction time did affect the quality of the essential patchouli oil extracted.
When the extraction time increased, the contents of some components decreased or increased [ 47 ]. The components in the extract from above methods are complex and contain a variety of natural products that require further separation and purification to obtain the active fraction or pure natural products.
The separation depends on the physical or chemical difference of the individual natural product. Chromatography, especially column chromatography, is the main method used to obtain pure natural products from a complex mixture.
Adsorption column chromatography is widely used for the separation of natural products, especially in the initial separation stage, due to its simplicity, high capacity and low cost of adsorbents such as silica gel and macroporous resins. The separation is based on the differences between the adsorption affinities of the natural products for the surface of the adsorbents. The selection of adsorbents stationary phase as well as the mobile phase is crucial to achieve good separation of natural products, maximize the recovery of target compounds and avoid the irreversible adsorption of target compounds onto the adsorbents.
Silica gel is the most widely used adsorbent in phytochemical investigation. Silica gel is a polar absorbent with silanol groups. Molecules are retained by the silica gel through hydrogen bonds and dipole—dipole interactions. Thus, polar natural products are retained longer in silica gel columns than nonpolar ones.
Sometimes, certain polar natural products might undergo irreversible chemisorption. The deactivation of silica gel by adding water before use or using a water-containing mobile phase will weaken the adsorption. Severe tailing may occur when separating alkaloids on silica gel, and the addition of a small amount of ammonia or organic amines such as triethylamine may reduce the tailing. Twelve alkaloids belonging to the methyl chanofruticosinate group including six new alkaloids, prunifolines A—F 68 — 73 , Fig.
Alumina aluminum oxide is a strong polar adsorbent used in the separation of natural products especially in the separation of alkaloids. The application of alumina in the separation of natural products has decreased significantly in recent years because it can catalyze dehydration, decomposition or isomerization during separation. Zhang and Su reported a chromatographic protocol using basic alumina to separate taxol 74 , Fig.
They found that the increase of taxol came from the isomerization of 7- epi -taxol 75 catalyzed by alumina. It was also found that a small amount of taxol could be decomposed to baccatin III 76 and deacetylbaccatin III 77 in the alumina column [ 49 ].
Further investigation into the separation of taxol on acidic, neutral and basic alumina indicated that the Lewis souci and the basic activity cores on the surface of alumina induced the isomerization of 7- epi -taxol to taxol [ 50 ].
The structures of polyamides used in chromatography contain both acryl and amide groups. When polar solvents such as aqueous solvents are used as the mobile phase, the polyamides act as the non-polar stationary phase and the chromatography behavior is similar to reversed-phase chromatography. In the contrast, the polyamides act as the polar stationary phase and the chromatography behavior is similar to normal phase chromatography. Polyamide column chromatography is a conventional tool for the separation of natural polyphenols including anthraquinones, phenolic acids and flavonoids, whose mechanisms are ascribed to hydrogen bond formation between polyamide absorbents, mobile phase and target compounds.
Gao et al. It was found that the polyamide functioned as a hydrogen bond acceptor, and the numbers of phenolic hydroxyls and their positions in the molecule affected the strength of adsorption [ 51 ]. In addition to polyphenols, the separation of other types of natural products by polyamide column chromatography were also reported. The total saponins of Kuqingcha can be enriched by polyamide column chromatography, which significantly reduced the systolic pressure of SHR rat [ 52 ].
Using a mixture of dichloromethane and methanol in a gradient as the eluent, the seven major isoquinoline alkaloids in Coptidis Rhizoma including berberine 39 , coptisine 40 , palmatine 41 , jatrorrhizine 42 , columbamine 78 , groenlandicine 79 Fig. Adsorptive macroporous resins are polymer adsorbents with macroporous structures but without ion exchange groups that can selectively adsorb almost any type of natural products.
They have been widely used either as a standalone system, or as part of a pretreatment process for removing impurities or enriching target compounds due to their advantages, which include high adsorptive capacity, relatively low cost, easy regeneration and easy scale-up. The adsorptive mechanisms of adsorptive macroporous resins include electrostatic forces, hydrogen bonding, complex formation and size-sieving actions between the resins and the natural products in solution.
Surface area, pore diameter and polarity are the key factors affecting the capacity of the resins [ 54 ]. Recently, Meng et al. Some researchers assumed that the principal adsorptive mechanism between macroporous resins and polyphenols was associated with the hydrogen bonding formation between the oxygen atom of the ether bond of the resin and the hydrogen atom of phenolic hydroxyl group of the phenol. The hydrogen bonding interaction force was significantly affected by the pH value of the solution [ 57 , 58 ].
Silver nitrate is another useful solid support in the separation of natural products. The greater the number of double bonds or aromaticity of the natural product, the stronger the complexation forms. Silver nitrate is typically impregnated on silica gel SNIS or alumina for separation. Several research groups reported the separation of fatty acids on SNIS [ 59 , 60 , 61 ].
Wang et al. A pair of isomers, brasiliensic acid 83 , Fig. Some research groups also applied silver nitrate in the two-phase system in high-speed counter-current chromatography HSCCC to improve the separation.
Partition chromatography PC follows the liquid—liquid extraction principle based on the relative solubility in two different immiscible liquids.
In the early stage, one liquid phase was coated to a solid matrix silica gel, carbon, cellulose, etc. The disadvantage of an easily removed stationary phase and unrepeatable results has led to this kind of PC being rarely used today.
The bonded-phase, in which the liquid stationary phase is chemically bound to the inert support, which is used as the stationary phase overcomes those drawbacks. Commercially available alkyl such as C8 and C18, aryl, cyano and amino substituted silanes are often used as bonded phases, which are widely used to separate a variety of natural products, especially in the final purification step.
A novel polyacrylamide-based silica stationary phase was synthesized by Cai et al. Counter-current chromatography CCC is kind of PC that holds the liquid stationary phase by gravity or centrifugal force.
CCC has rarely been used in early stages due to its poor stationary retention, long separation time and labor intensive process. The hydrodynamic CCC systems such as HSCCC have a planetary rotation movement around two rotating axes with no rotating seals, which offers a low pressure drop process. Hydrostatic CCC, e. The high system pressure in CPC prevents the improvement of the resolution by increasing the length of the column.
Compared to the conventional column separation method using a solid stationary phase, both hydrostatic and hydrodynamic CCC systems offer some advantages including the elimination of irreversible adsorption and peak tailing, high loading capacity, high sample recovery, minimal risk of sample denaturation and low solvent consumption. The limitation of CCC is that it only separates the compounds in a relatively narrow polarity window.
Tang et al. Li et al. Few reports could be obtained due to commercial confidentiality. It is difficult to judge whether hydrostatic or hydrodynamic CCC is better for industrial applications. Users might select different types of CCC instrument for different purposes. When the stationary phase is poorly retained in hydrodynamic CCC due to high viscosity and small density differences between the mobile and stationary phases, the hydrostatic CCC is more practical than hydrodynamic CCC because the retention of the stationary phase of hydrostatic CCC is less sensitive to the physical properties of liquid systems and will have a higher retention of the stationary phase.
When the stationary phase is well retained in hydrodynamic CCC, higher separation efficiency will be obtained from hydrodynamic CCC than from hydrostatic CCC with the same liquid system and similar column volumes because hydrostatic CCC has relatively low partition efficiency due to a limited degree of mixing, and the hydrodynamic system provides efficient mixing to yield a high partition efficiency.
The separation of natural products by membrane filtration MF or gel filtration chromatography GFC is based on their molecular sizes.
In MF, the semipermeable membrane allows smaller molecules to pass through and retains the larger molecules. MF of natural products could be characterized as microfiltration, ultrafiltration, and nanofiltration based on the pore size of the membrane applied.
Membrane filtration has been a powerful tool for the concentration, clarification and removal of impurities in the lab, as well as in the food and pharmaceutical industries. Coupling membrane filtration is applied when a single membrane filtration step is not satisfactory.
A sequence of microfiltration, ultrafiltration and nanofiltration was applied in the isolation of bioactive components from olive leaf extract.
Microfiltration followed by ultrafiltration removed the impurities larger than 5 kDa. Nanofiltration recovered the antioxidative and antibacterial polyphenols and flavonoids, and the content of the major component, oleuropein , in the nanofiltration retentate was concentrated approximately ten times [ 74 ].
Gel filtration chromatography is also known as gel permeation chromatography or size exclusion chromatography. These include acetones, ketones, aliphatic hydrocarbons and alcohols. When vapor is cooled and condensed, the liquid condensate becomes a valuable product that can be sold back into industry. The higher boiling point portion of the original mixture that does not vaporize remains in the bottom of the recovery still used on site for the distillation process.
One benefit of using this type of distillation process is that the portion remaining in the recovery still is valuable as an alternative fuel source for facilities such as cement kilns.
Solvent recycling offers a more environmentally-friendly way to dispose of hazardous substances, and distillation is the most common method of solvent recycling. Environmentally friendly solvents can be used in the extraction process. Water is the classic example. In recent years, there has been a higher emphasis as well on developing and using more green solvents.
Through the processing of agricultural crops, these green solvents - also known as biosolvents - are derived. Solvent extraction also has the advantage of low energy consumption, compared to solvent distillation. However, solvent distillation can provide many environmentally-friendly benefits as well, especially when used as part of a Closed Loop Recycling and Recovery system. At Temarry Recycling, solvent distillation is part of the circular economy because nothing is wasted and a marriage is created between solvent distillation and waste to energy treatments.
This closed-loop system allows received waste to be treated and turned back into a reusable product. For this to occur, solid wastes received are thermally treated at degrees F to generate steam. This steam is then used to power our solvent recovery systems.
Larry Burton November 21, What Is A Solvent? What Is Solvent Extraction? Is Extraction Environmentally Friendly? Larry Burton Larry Burton has over 25 years of experience in the hazardous waste and chemical industries. However, the main difference in these types is the way compounds are separated from one another.
The most commonly used form of distillation is simple distillation and fractional distillation. The simple distillation process is used when two liquids have different boiling points whereas fractional distillation is used when two liquids have equivalent boiling points. It is extremely crucial for business and industries nowadays to use and adopt environmentally friendly practices in their manufacturing and processing journey.
If businesses can adopt environmentally friendly initiatives even in one step of the manufacturing process, that alone can bring immense positive impact to the environment.
The simple answer is using environmentally friendly solvents will make the extraction process eco-friendly. For instance, water is the preferred liquid for environmentally friendly extractions. As more and more businesses look for green solvent initiatives where water is not the best solution, bio solvents have come to the rescue. Bio solvents are derived from the processing of agricultural crops. That said, solvent distillation when used as a part of the closed loop recycling and recovery system, has its environmental benefits as well.
The closed loop recycling and recovery system allows businesses to collect waste to be treated and repurposed into a reusable product again and again. Some businesses also look for ways to reduce waste produced by the solvent distillation process. For instance, solid wastes can be treated at a degree thermal magnitude to generate steam. This steam can be repurposed to power up solvent recovery system.
CleanPlanet partners with its customers to ensure they are maximizing their onsite chemical recycling. Our advanced solvent distillation technology allows our customers to recover more chemical than any other distillation unit. Skip to content. Solvent Extraction vs. Solvent Distillation.
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