Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

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1 AN OVERVIEW OF EXTRACTION TECHNIQUES FOR MEDICINAL AND AROMATIC PLANTS rate can be enhanced if some sort of movement is created between the particles and the solvent. This can be achieved either by providing inside agitation with a mechanical stirrer or by repeated circulation of the extract back to the percolator. The fi rst method is cumbersome and power intensive whereas the latter has been successful. A circulation pump that continuously circulates the miscella back to the top of the percolator gives a better mass transfer rate and reduces the equilibrium time considerably. Still, this type of percolation is energy-consuming as large amounts of miscella from multiple washes must be concentrated to remove the solvent. To overcome this problem, a battery of percolators can be connected in series. If three washes are required for completion of the extraction, four percolators are connected in series with their respective miscella storage tanks. At a particular time, one percolator is out of circuit, for charging and discharging the material and also for stripping solvent from the marc, whereas the other three percolators are in operation. Material is fed into all the percolators and the solvent is fed into the fi rst percolator. When the equilibrium in the fi rst percolator is reached, the extract from the fi rst percolator is sent to the second percolator. The fi rst percolator is again fi lled with fresh solvent. The extract of second percolator is transferred to the third, the extract of fi rst is transferred to second, and fresh solvent is added to the fi rst. The extract of the third percolator is transfered to the fourth percolator. After attaining equilibrium, the extract from the fourth percolator is drained off. The extract of the third percolator goes to fourth, the extract of second goes to third, and the extract of fi rst goes to second percolator. The material of the fi rst percolator, which has received three washes, is completely exhausted. This percolator is taken out of the system for stripping the solvent and discharging the extracted marc. This is again fi lled with fresh plant material and the sequence is repeated with other percolators. In this way, solvent of each percolator comes in contact three times with solid material and gets fully enriched with active principle. The enriched extract is sent for solvent recovery and concentration. Thus, instead of concentrating three volumes of solvent, only one volume has to be concentrated; this saves energy and the process is effi cient. 1.2.2.3.2 Hot Percolation Increasing the temperature of the solvent increases the solubility of the active principle, which increases the concentration gradient and therefore enhances the mass transfer of active principle from solid material to the solvent, provided the active principle is not heat sensitive. This is achieved by incorporating a heat exchanger between the circulation pump and the feed inlet of the percolator. The extract is continuously pumped into 32
EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS a tubular heat exchanger which is heated by steam. The temperature of the extract in the percolator is controlled by a steam solenoid valve through a temperature indicator controller. This sort of arrangement can be incorporated in single percolators or in a battery of percolators as needed. The percolators that are tall cylindrical towers must be housed in sheds of relatively great height. Tall towers are diffi cult to operate, especially when charging material and discharging the marc from the top and bottom manholes, which are time-consuming and labor-intensive procedures. Tall towers have been replaced by extractors of smaller height for which the H/D ratio is not more than 1.5. These extractors have perforated baskets in which the material to be extracted is charged. These perforated baskets, when loaded outside, can be inserted into the extractor with a chain pulley block and, after the extraction, they can be lifted out from the extractor for discharging the marc. Some extractors have an electrical hoist for the charging the material and discharging the marc, which makes the operation less labor-intensive, quick and efficient. The other type of instrument for extraction of medicinal ingredients from plant material is the Soxhlet apparatus, which consists of an extractor, a distillation still, a tubular condenser for the distillation still, a tubular condenser for the recovery of solvent from the marc, a receiver for collecting the condensate from the condenser, and a solvent storage tank. The plant material is fed into the extractor, and solvent is added until it reaches the siphon point of the extractor. Then, the extract is siphoned out into the distillation still, which is heated with steam. The solvent vapors go to the distillation condenser, get condensed and return to the extractor. The level of the solvent in the extractor again rises to the siphon point and the extract is siphoned out into the distillation still. In this way, fresh solvent comes in contact with the plant material a number of times, until the plant material is completely extracted. The fi nal extract in the distillation still, which is rich in active principle, is concentrated and the solvent is recovered. 1.2.2.3.3 Concentration The enriched extract from percolators or extractors, known as miscella, is fed into a wiped fi lm evaporator where it is concentrated under vacuum to produce a thick concentrated extract. The concentrated extract is further fed into a vacuum chamber dryer to produce a solid mass free from solvent. The solvent recovered from the wiped fi lm evaporator and vacuum chamber dryer is recycled back to the percolator or extractor for the next batch of plant material. The solid mass thus obtained is pulverized and used directly for the desired pharmaceutical formulations or further processed for isolation of its phytoconstituents. 33
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9 SOLID PHASE MICRO-EXTRACTION AND
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12 FLASH CHROMATOGRAPHY AND LOW PRE
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13 COUNTER-CURRENT CHROMATOGRAPHY C
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13 COUNTER-CURRENT CHROMATOGRAPHY 1
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13 COUNTER-CURRENT CHROMATOGRAPHY a
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13 COUNTER-CURRENT CHROMATOGRAPHY H
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