Overview Of Fractional Distillation Environmental Sciences Essay

Overview Of Fractional Distillation Environmental Sciences Essay Definition: A process by which components in a chemical mixture are separated according to their different boiling points. Vapours from a boiling solution are passed along a column. The temperature of the column gradually decreases along its length. Components with a higher boiling points condense on the column and return to the solutions; components with a lower boiling points pass through the column and are collected. Fractional distillation is used to separate mixtures of miscible liquids, such as ethanol and water. The process depends on the components of the mixture having different boiling points. The liquid is heated so that it turns into a gas. The vapours pass up a fractionating column where they are gradually cooled. As each of the components of the mixture cools to its boiling point, it turns back into a liquid. The different components of the mixture condense at different levels in the fractionating column and thus may be separated. Laboratory setup Fractional distillation in a laboratory makes use of common laboratory glassware and apparatuses, typically including a Bunsen burner a round-bottomed flask and a condenser as well as the single-purpose fractionating column. Apparatus Fractional distillation apparatus using a Liebig condenser. A conical flask is used as a receiving flask. Here the distillation head and fractionating column are combined in one piece. heat source, such as a hot plate with a bath, and ideally with a magnetic stirrer. distilling flask, typically a round-bottom flask receiving flask, often also a round-bottom flask fractionating column distillation head thermometer and adapter if needed condenser, such as a Liebig condenser, Graham condenser . vacuum adapter . Standard laboratory glassware with ground glass joints, e.g. quickfit apparatus. Discussion , Consider the distillation of a mixture of water and ethanol. Ethanol boils at 78.4  Ã‚ °C while water boils at 100  Ã‚ °C. So, by gently heating the mixture, the most volatile component will concentrate to a greater degree in the vapor leaving the liquid. Some mixtures form azeotropes, where the mixture boils at a lower temperature than either component. In this example, a mixture of 96% ethanol and 4% water boils at 78.2  °C, being more volatile than pure ethanol. For this reason, ethanol cannot be completely purified by direct fractional distillation of ethanol-water mixtures. The apparatus is assembled as in the diagram. (The diagram represents a batch apparatus, as opposed to a continuous apparatus.) The mixture is put into the round bottomed flask along with a few anti-bumping granules (or a Teflon coated magnetic stirrer bar if using magnetic stirring), and the fractionating column is fitted into the top. As the mixture boils, vapor rises up the column. The vapor condenses on the glass platforms, known as trays, inside the column, and runs back down into the liquid below, refluxing distillate. The column is heated from the bottom. The efficiency in terms of the amount of heating and time required to get fractionation can be improved by insulating the outside of the column in an insulator such as wool, aluminium foil or preferably a vacuum jacket. The hottest tray is at the bottom and the coolest is at the top. At steady state conditions, the vapor and liquid on each tray are at equilibrium. Only the most volatile of the vapors stays in gaseous form all the way to the top. The vapor at the top of the column, then passes into the condenser, which cools it down until it liquefies. The separation is more pure with the addition of more trays (to a practical limitation of heat, flow, etc.) The condensate that was initially very close to the azeotrope composition becomes gradually richer in water. The process continues until all the ethanol boils out of the mixture. This point can be recognized by the sharp rise in temperature shown on the thermometer. Typically the example above now only reflects the theoretical way fractionation works. Normal laboratory fractionation columns will be simple glass tubes (often vacuum jacketed, and sometimes internally silvered) filled with a packing, often small glass helices of 4 to 7 mm diameter. Such a column can be calibrated by the distillation of a known mixture system to quantify the column in terms of number of theoretical plates. To improve fractionation the apparatus is set up to return condensate to the column by the use of some sort of reflux splitter (reflux wire, gago, Magnetic swinging bucket, etc.) a typical careful fractionation would employ a reflux ratio of around 10:1 (10 parts returned condensate to 1 part condensate take off). In laboratory distillation, several types of condensers are commonly found. The Liebigcondenser is simply a straight tube within a water jacket , and is the simplest (and relatively least expensive) form of condenser. Industrial distillation Image 2: Typical industrial fractional distillation columns Distillation is the most common form of separation technology used in petroleum refineries, petrochemical and chemical plants , natural gas processing and cryogenic air separation plants. In most cases, the distillation is operated at a continuous steady state .New feed is always being added to the distillation column and products are always being removed. Unless the process is disturbed due to changes in feed, heat, ambient temperature, or condensing, the amount of feed being added and the amount of product being removed are normally equal. This is known as continuous, steady-state fractional distillation. Industrial distillation is typically performed in large, vertical cylindrical columns known as distillation or fractionation towers or distillation columns with diameters ranging from about 65 centimetres to 6 metres and heights ranging from about 6 metres to 60 metres or more. The distillation towers have liquid outlets at intervals up the column which allow for the withdrawal of different fractions or products having different boiling points or boiling ranges. By increasing the temperature of the product inside the columns, the different hydrocarbons are separated. The lightest products (those with the lowest boiling point) exit from the top of the columns and the heaviest products (those with the highest boiling point) exit from the bottom of the column. For example, fractional distillation is used in oil refineries to separate crude oil into useful substances (or fractions) having different hydrocarbons of different boiling points. The crude oil fractions with higher boiling points: have more carbon atoms have higher molecular weights are more branched chain alkanes are darker in color are more viscous are more difficult to ignite and to burn Figure 1: Diagram of a typical industrial distillation tower Large-scale industrial towers use reflux to achieve a more complete separation of products. Reflux refers to the portion of the condensed overhead liquid product from a distillation or fractionation tower that is returned to the upper part of the tower as shown in the schematic diagram of a typical, large-scale industrial distillation tower. Inside the tower, the reflux liquid flowing downwards provides the cooling needed to condense the vapors flowing upwards, thereby increasing the effectiveness of the distillation tower. The more reflux is provided for a given number of theoretical plates, the better the towers separation of lower boiling materials from higher boiling materials. Alternatively, the more reflux provided for a given desired separation, the fewer theoretical plates are required. Figure 2. Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units. Fractional distillation is also used in air separation, producing liquid oxygen, liquid nitrogen, and highly concentrated argon. Distillation of chlorosilanes also enable the production of high-purity silicon for use as a semiconductor. In industrial uses, sometimes a packing material is used in the column instead of trays, especially when low pressure drops across the column are required, as when operating under vacuum. This packing material can either be random dumped packing (1-3 wide) such as Raschig rings or structured sheet metal. Typical manufacturers are Koch, Sulzer and other companies. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where mass transfer takes place. Unlike conventional tray distillation in which every tray represents a separate point of vapor liquid equilibrium the vapor liquid equilibrium curve in a packed column is continuous. However, when modeling packed columns it is useful to compute a number of theroticalplates to denote the separation efficiency of the packed column with respect to more traditional trays. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing perfor mance. Design of industrial distillation columns . Figure 3: Chemical engineering schematic of typical bubble-cap trays in a distillation tower Moreover, the efficiencies of the vapor-liquid contact devices (referred to as plates or trays) used in distillation columns, as seen in Figure 3, are typically lower than that of a theoretical 100% efficient equilibrium stage. Hence, a distillation column needs more plates than the number of theoretical vapor-liquid equilibrium stages. An indication of numbers: the separation of two compounds with relative volatility of 1.1 requires a minimum of 130 theoretical plates with a minimum reflux ratio of 20.. With a relative volatility of 4, the required number of theoretical plates decreased to 9 with a reflux ratio of 0.66. In another source, a boiling point difference of 30  °C requires 12 theoretical plates and, for a difference of 3  °C, the number of plates increased to 1000. The reflux ratio is the ratio of the amount of moles returned as refluxed liquid to the fractionating column and the amount of moles of final product, both per unit time. OTHER USES OF FRACTIONAL DISTILLATION: An essential oil is a concentrated, hydrophobic liquid containing volatile aromatic compounds extracted from plants. It may be produced by distillation, expression, or solvent extraction. Essential oils are used in perfumery, aromatherapy, cosmetics, incense,medicine, household cleaning products, and for flavoring food and drink. They are valuable commodities in the fragrance and food industries. Essential oil is also known as volatile oil and ethereal oil. It may also be referred to as oil ofthe raw plant mat 1 White spirit White spirit, also known as Stoddard solvent is a paraffin-derived clear, transparent liquid which is a common organic solvent used in painting and decorating. It is a mixture of saturated aliphatic and alicyclic C7 to C12 hydrocarbons with a maximum content of 25% of C7 to C12 alkyl aromatic hydrocarbons. White spirit is used as an extraction solvent, as a cleaning solvent, as a degreasing solvent and as a solvent in aersonal. paints, wood preservatives, lacquers, varnishes, and asphalt products. In western Europe :2-Propan-1-ol Propan-1-ol is a primary alcohol with the formula CH3CH2CH2OH. It is also known as 1-propanol, 1-propyl alcohol n-propyl alcohol, or simply propanol. It is used as a solvent in the pharmaceutical industry, and for resins and cellulose esters. It is formed naturally in small amounts during many fermentation processes. Propan-1-ol Chemical properties. 1-Propanol shows the normal reactions of a primary alcohol. Thus it can be converted to alkyl halide. 3-Acetone: In chemistry acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and beta-ketopropane) is the simplest representative of the ketones. Acetone is a colorless mobile flammable liquid with melting point at -95.4  Ãƒâ€šÃ‚ °C and boiling point at 56.53  Ãƒâ€šÃ‚ °C. It has a relative density of 0.819 (at 0  Ãƒâ€šÃ‚ °C). It is readily soluble in water, ethanol, ether, etc., and itself serves as an important solvent. The most familiar household use of acetone is as the active ingredient 4-Cashew The Cashew (Anacardium occidentale) is a tree in the flowering plant family Anacardiaceae. The plant is native to northeastern Brazil, where it is called by its Portuguese name Caju (the fruit) or Cajueiro (the tree). It is now widely grown in tropical climates for its cashew nuts and cashew apples. Originally spread from Brazil by the Portuguese, the cashew tree today can be found in all regions with a sufficiently warm and humid climate. What appears on the tree to be the fruit of the cashew tree is an ov 5- Cracking chemistry In petroleum qeology and chemistry, cracking is the process whereby complex organic molecules (e.g. kerogens or heavy hydrocarbons) are converted to simpler molecules (e.g. light hydrocarbons) by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of any catalysts. Cracking chemistry Applications. In an oil refinery cracking processes allow the production of lightproducts (such as LPG and gasoline) from 6 Perfume Perfume is a mixture of fragrant essential oils and aroma compounds, fixatives, and solvents used to give the human body, objects, and living spaces a lasting and pleasant smell. The amount and type of solvent mix with the fragrance oil dictates whether a perfume is considered a perfume extract, Eau de parfum, Eau de toilette, or Eau de Cologne. Perfume Obtaining odorants. Before perfumes can be composed, the odorants used in various perfume compositions must first be obtained. Synthetic odorants are produce 7- Chemical oxygen demand In environmental chemistry, the chmical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers), making COD a useful measure of water quality. It is expressed in millgrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution. Older references may express the units as parts per million (ppm). Chemical oxygen demand Over 8- Nitrogen Nitrogen is the chemical element in the periodic table that has the symbol N and atomic number 7. Commonly a colorless, odorless, tasteless and mostly inert diatomic non-metal gas, nitrogen constitutes 78 percent of Earths atmosphere and is a constituent of all living tissues. Nitrogen forms many important compounds such as amino acids ammonia nitric acid, and cyanides. Nitrogen Notable characteristics. Nitrogen is a non-metal, with an electronegativity of 3.0. It has five electron 9- Alkane Purification and use Alkanes are both important raw materials of the chemical industry and the most important fuels of the world economy. The starting materials for the processing are always natural gas and crude oil. The latter is separated in an oil refinery by fractional distillation and processed into many different products, for example gasoline. The different fractionsof crude oil have different boiling points and can be isolated and separated quite easily: within the individual fra , 10-Essential oil Production Main high-volume products turpentine; orange, lemon, mint and citronella are essential oils. Prior to the discovery of distillation, essential oils were extracted by pressing, and this is still the case in cultures such as Egypt. Traditional Egyptian practice involves pressing the plant material, and then burying it in unglazed ceramic vessels in the desert for a period of months to drive out water, the water having a smaller molecular size diffuses through the ceramic vessels while the larger essential oils do not. The lotus oil in Tutankhamuns tomb, which retained its scent after 3000 years sealed in al 11-Kerosene Distillation Kerosene is obtained from the fractional distillation of petroleum at 150 °C and 275 °C [carbon chains from the C12 to C15 range). Typically, kerosene directly distilled from crude oil requires some treatment, either in a Merox unit or a hydrotreater, to reduce its sulfur content and its corrosiveness. Kerosene can also be produced by a hydrocracker, which is used to upgrade the parts of crude oil that w