{"id":94,"date":"2018-07-04T23:59:36","date_gmt":"2018-07-04T23:59:36","guid":{"rendered":"http:\/\/www.essentialoilmach.com\/blog\/?p=94"},"modified":"2019-12-16T09:17:09","modified_gmt":"2019-12-16T09:17:09","slug":"hydrodistillation-of-essential-oil","status":"publish","type":"post","link":"https:\/\/www.essentialoilmach.com\/blog\/hydrodistillation-of-essential-oil\/","title":{"rendered":"Hydrodistillation of essential oil"},"content":{"rendered":"

Hydrodistillation
\nIn order to isolate essential oils by hydrodistillation, the aromatic plant material is packed
\nin a still and a sufficient quantity of water is added and brought to a boil; alternatively, live steam
\nis injected into the plant charge. Due to the influence of hot water and steam, the essential oil is
\nfreed from the oil glands in the plant tissue. The vapor mixture of water and oil is condensed by
\nindirect cooling with water. From the condenser, distillate flows into a separator, where oil
\nseparates automatically from the distillate water.
\nMechanism of Distillation<\/a>
\nHydrodistillation of plant material involves the following main physicochemical processes:
\ni) Hydrodiffusion
\nii) Hydrolysis
\niii) Decomposition by heat
\nHydrodiffusion
\nDiffusion of essential oils and hot water through plant membranes is known as
\nhydrodiffusion. In steam distillation, the steam does not actually penetrate the dry cell
\nmembranes. Therefore, dry plant material can be exhausted with dry steam only when all the
\nvolatile oil has been freed from the oil-bearing cells by first thorough comminution of the plant
\nmaterial. But, when the plant material is soaked with water, exchange of vapors within the tissue
\nis based on their permeability while in swollen condition. Membranes of plant cells are almost
\nimpermeable to volatile oils. Therefore, in the actual process, at the temperature of boiling water,
\na part of volatile oil dissolves in the water present within the glands, and this oil-water solution
\npermeates, by osmosis, the swollen membranes and finally reaches the outer surface, where the
\noil is vaporized by passing steam.<\/p>\n

Another aspect of hydrodiffusion is that the speed of oil vaporization is not influenced by
\nthe volatility of the oil components, but by their degree of solubility in water. Therefore, the
\nhigh-boiling but more water-soluble constituents of oil in plant tissue distill before the lowboiling
\nbut less water-soluble constituents. Since hydrodiffusion rates are slow, distillation of
\nuncomminuted material takes longer time than comminuted material.
\nHydrolysis
\nHydrolysis in the present context is defined as a chemical reaction between water and
\ncertain constituents of essential oils. Esters are constituents of essential oils and, in the presence
\nof water, especially at high temperatures, they tend to react with water to form acids and
\nalcohols. However, the reactions are not complete in either direction and the relationship
\nbetween the molal concentrations of various constituents at equilibrium is written as:
\n(alcohol) x (acid)
\nK =
\n(ester) x (water)
\nwhere K is the equilibrium constant.
\nTherefore, if the amount of water is large, the amounts of alcohol and acid will also be
\nlarge, resulting in a decreased yield of essential oil. Furthermore, since this is a time-dependent
\nreaction, the extent to which hydrolysis proceeds depends on the time of contact between oil and
\nwater. This is one of the disadvantages of water distillation.<\/p>\n

Effect of Heat
\nAlmost all constituents of essential oils are unstable at high temperature. To obtain the
\nbest quality oil, distillation must be done at low temperatures. The temperature in steam
\ndistillation is determined entirely by the operating pressure, whereas in water distillation and in
\nwater and steam distillation the operating pressure is usually atmospheric. All the previously
\ndescribed three effects, i.e. hydrodiffusion, hydrolysis and thermal decomposition, occur
\nsimultaneously and affect one another. The rate of diffusion usually increases with temperatures
\nas does the solubility of essential oils in water. The same is true for the rate and extent of
\nhydrolysis. However, it is possible to obtain better yield and quality of oils by: (1) maintaining
\nthe temperature as low as possible, (2) using as little water as possible, in the case of steam
\ndistillation, and (3) thoroughly comminuting the plant material and packing it uniformly before
\ndistillation.
\nThree Types of Hydrodistillation
\nThree are three types of hydrodistillation for isolating essential oils<\/a> from plant materials:
\n1. Water distillation
\n2. Water and steam distillation
\n3. Direct steam distillation<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Hydrodistillation In order to isolate essential oils by hydrodistillation, the aromatic plant material is packed in a still and a sufficient quantity of water is added and brought to a boil; alternatively, live steam is injected into the plant charge. Due to…Read More »<\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[52,41,4,51,43,42],"class_list":["post-94","post","type-post","status-publish","format-standard","hentry","category-essential-oil-distillation","tag-diffusion-of-essential-oils","tag-direct-steam-distillation","tag-essential-oil","tag-hydrodistillation","tag-water-and-steam-distillation","tag-water-distillation"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t