Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev
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Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

capacity4dev.ec.europa.eu
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30.10.2014 Views

7 DISTILLATION TECHNOLOGY FOR ESSENTIAL OILS a) As the plant material near the bottom of the still comes in direct contact with the fi re from the furnace, it may char and thus impart an objectionable odor to the essential oil. b) The prolonged action of hot water can cause hydrolysis of some constituents of the essential oil, such as esters. c) Heat control is diffi cult, which may lead to variable rates of distillation. d) The process is slow and distillation times are much longer than those of steam distillation. 7.3.2 Water and Steam Distillation To eliminate some of the drawbacks of water distillation, some modifi cations were made to the distillation units. A perforated grid was introduced in the still, to support the plant material and to avoid its direct contact with the hot furnace bottom. When the water level is kept below the grid, the essential oil is distilled by the rising steam from the boiling water. This mode of distillation is generally termed water and steam distillation. The fi eld distillation unit (FDU), also known as a directly fi redtype distillation unit, is designed according to the principle of water and steam distillation. The FDU consists of a still or tank made of mild stainless steel with a perforated grid and is fi tted directly to a brick furnace. A chimney is connected to the furnace to minimize the pollution at the workplace and also to induce proper fi ring and draft. The plant material is loaded on the perforated grid of the tank and water is fi lled below it. The tank is connected to the condenser through a vapor line. The water is boiled and the steam vapors pass through the herb, vaporize the oil and get condensed, mostly in a coil condenser by cooling water. The condensate (oil-vapor mixture) is then separated in the oil separator. These units are simple to fabricate and can be installed in the farmer’s fi eld. Due to their simple construction, low cost and easy operation, FDUs are extremely popular with essential oil producers in developing countries. The furnace is always fueled by locally available fi rewood or straw. This makes the unit suited for use in remote areas where the raw material is available. This also helps in reducing transportation costs in the production of essential oils. FDUs are currently fi nding application in distillation of patchouli oil in Indonesia, aromatic grass and mint oil in India, citronella oil in Taiwan and many more all over the world. A local FDU currently being used by rural farmers in India for the distillation of mint oils is shown in Figure 2. Such fi eld units generally can hold 100-2000 kg plant material. Total time for distillation with these units is about 6-8 h. 118

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS Figure 2: Local type fi eld distillation unit in India 7.3.2.1 Improved Field Distillation Units Due to the limited heating surface available, the rate of steam production in the FDU is always insuffi cient. This results in prolonged distillation periods and sometimes lower oil yields. Refl uxing of oil back into the still due to inadequate steam rate may lead to decomposition reactions and poorer oil quality. Experimental measurements made at the Central Institute of Medicinal and Aromatic Plants (CIMAP), India, have shown that fi rewood consumption in a conventional fi eld still may be up to 2.5-times greater than that of a modern steam distillation unit operated by an external boiler. This factor may not be critical where fuel supplies are cheap and abundant but, in many developing countries, fuel supplies are getting scarce and costly and low thermal effi ciency can directly affect the cost of production. Figure 3: CIMAP’s improved fi eld distillation unit 119

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS<br />

Figure 2: Local type fi eld distillation unit in India<br />

7.3.2.1 Improved Field Distillation Units<br />

Due to the limited heating surface available, the rate of steam<br />

production in the FDU is always insuffi cient. This results in prolonged distillation<br />

periods <strong>and</strong> sometimes lower oil yields. Refl uxing of oil back into the<br />

still due to inadequate steam rate may lead to decomposition reactions <strong>and</strong><br />

poorer oil quality. Experimental measurements made at the Central Institute<br />

of <strong>Medicinal</strong> <strong>and</strong> <strong>Aromatic</strong> Plants (CIMAP), India, have shown that fi rewood<br />

consumption in a conventional fi eld still may be up to 2.5-times greater than<br />

that of a modern steam distillation unit operated by an external boiler. This<br />

factor may not be critical where fuel supplies are cheap <strong>and</strong> abundant but, in<br />

many developing countries, fuel supplies are getting scarce <strong>and</strong> costly <strong>and</strong><br />

low thermal effi ciency can directly affect the cost of production.<br />

Figure 3: CIMAP’s improved fi eld distillation unit<br />

119

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