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what is ethanol? All about ethanol you should know

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QuangTrungChem
05:29, հինգշաբթի, 11 օգոստոսի, 2022 թ.
what is ethanol? All about ethanol you should know

Frequency of occurrence

Ethanol is a natural product of alcoholic fermentation in ripe fruit and juice. However, ethanol also occurs naturally in all other parts of the plant, such as the roots, rhizomes, and tubers of angelica (Angelica archangelica), carrots (Daucus carota), Rheum palmatum, and onions (Angelica archangelica) . Allium cepa), flowers of Telosma cordata, buds of butterfly pea (Satureja cuneifolia), ginseng (Panax ginseng), and grape seaweed (Ephedra sinica), and resin and sheath of amber (Liquidambar styraciflua and Liquidambar orientalis) and rosemary (Rosmarinus officinalis) . Many foods naturally contain small amounts of ethanol. Even non-alcoholic beer still contains up to 0.5% ethanol by volume. According to the German Food Code, juice can have an ethanol content of about 0.38 percent by volume. For example, apple juice contains up to 0.016 and grape juice contains up to 0.059% ethanol by volume. A ripe banana can hold up to 1 percent by volume, bread up to 0.3 percent by volume. Ripe kefir can contain up to 1 percent ethanol by volume, sauerkraut up to 0.5 percent. The physiological level of ethanol in human blood is about 0.02 to 0.03 per mille. Ethanol has been detected in interstellar molecular clouds along with other organic molecules such as acetaldehyde. The formation mechanism of organic molecules is unclear.

Manufacturing

Ethanol is produced by fermentation from biomass, usually from crops containing sugar or starch, or traditionally from crop products. This process is done in a controlled manner using a variety of foods, such as the production of wine from grapes or beer from malt and hops. Wood sugar can be fermented into gaseous sulfites as a by-product of sulfites. However, this can only be used for energy purposes due to the presence of many impurities. Before actual fermentation, starch is usually first separated into disaccharides, whose glycosidic bonds are broken by hydrolases; The monosaccharide formed is then fermented by yeast or bacteria. At ethanol concentrations close to 15%, yeast and bacterial cells begin to die, so higher concentrations cannot be achieved by fermentation. The general equation of alcoholic fermentation is:

C6H12O6 2 C2H5OH + 2 CO2

Distillation

Ethanol can be concentrated by distillation for technical and consumer purposes, as it has evaporated at 78°C.

Alcohol is drinkable

Drinkable alcohol suitable for consumption is obtained by distilling a mixture of alcohol from agricultural raw materials. Depending on the distillation process, the distillate, known as spirits, contains not only ethanol but also flavorings, fusel oils, other organic compounds, and water, which determine the character and taste of the product. final product, such as brandy, whiskey or rum. On the other hand, to produce vodka, people use almost pure ethanol and only dilute it with water. Pure, undiluted ethanol, marketed as ethyl alcohol of agricultural origin, is used as a starting product for other alcoholic beverages, for example, for most liqueurs. Alcoholic beverages containing distilled ethanol are called spirits (usually also spirits or schnapps) - as opposed to wine and beer, where ethanol is produced exclusively by alcoholic fermentation.

Technical purpose

On a large scale, pure ethanol for engineering applications is produced by azeotropic rectification (entrainer rectification) . The plant consists of two rectifier columns. In the main separation column, the ethanol-water mixture is adjusted to near the azeotropic point. The bottom product here is water. The secondary cyclohexane added to the product consisted of 95.6% ethanol and 4.4% water. In the past, common absorbing agents such as benzene (Young process) or trichloroethene (Drawinol process) are no longer used today. This three-component mixture of ethanol, water and entrainer enters the secondary separation column. There it is separated into the pure alcohol generated in the storage tank and the water-cyclohexane mixture as the primary product. Cyclohexane and water are immiscible in the liquid state and separate in the decanter after condensation. The auxiliary cyclohexane is added back to the flowing, anisotropic ethanol-water mixture at the inlet of the secondary separation column. It runs in the circuit in the upper part of the sub-split column and is therefore called the "sub-runhead". Anhydrous ethanol is obtained on a laboratory scale by distillation on dehydrating chemicals such as calcium oxide, anhydrous calcium sulfate, or molecular sieve. The process of absolute alcohol production is called absolutization.

Technical synthesis

Ethanol is produced by chemical synthesis from water and ethylene in a so-called homogeneous catalyzed indirect process with the addition of sulfuric acid. Alcohol produced in this way is also known as industrial alcohol. The process is done in two steps with the format

ions of the sulfuric acid ester, which must be hydrolyzed in a second step. After hydrolysis,

sulfuric acid must be concentrated. In the direct process, phosphoric acid is applied to the silica which acts as a heterogeneous catalyst. At temperatures up to 300°C and a pressure of 70 bar, ethanol is produced directly from ethylene and water in the gas phase. However, the conversion per reactor pass is only 5% based on ethylene. Due to wastewater problems and corrosion problems caused by sulfuric acid in the indirect process, ethanol is now produced industrially by phosphoric acid catalysis. The sum equation for both processes is:

C2H4 + H2O → C2H5OH

In principle, ethanol can be obtained by catalyzing the hydrogenation of acetaldehyde. At high hydrogen pressure, acetaldehyde is thus converted at the nickel-containing contacts:

CH3CHO + H2 → C2H5OH

Furthermore, ethanol is produced in the Synol process by the reaction of carbon monoxide with hydrogen and can be separated from other alcohols produced by distillation.

Ethanol detection/analysis

Ethanol can be detected by esterification as a p-nitrobenzoic acid ester or a 3, 5-dinitrobenzoic acid ester. The reaction is carried out by reacting with the corresponding acid chloride. Nonspecifically, ethanol can be detected by the iodoform test. By chromatographic methods such as gas chromatography (GC), it is possible to determine the amount of ethanol. Wet chemical can be quantitatively detected by oxidation with excess potassium dichromate, and the amount of unreacted potassium dichromate can be determined by iodometric method. In food analysis, the difference in density between water and ethanol is exploited. The ethanol content is separated during distillation (steam) and is proportionally determined. Alternatively, density can also be measured in a bending oscillator. In both methods, the assessment is based on tabulated values. In proton resonance (HNMR) spectroscopy, ethanol exhibits a triplet structure at room temperature due to the combination of protons of the hydroxyl group with methylene protons. This indicates the fixation of the hydroxyl group to the methylene protons. With increasing temperature, the separation becomes smaller and eventually disappears completely due to the increasing rotation of the hydroxyl group. Nuclear magnetic resonance spectroscopy can be used to distinguish synthetic ethanol from fossil fuels from ethanol from renewable feedstocks based on hydrogen and carbon isotope ratios. This situation can be used to detect the adulteration of wine or spirits with industrial ethanol. In the case of ethanol produced by fermentation, the plant origin can be determined through the deuterium distribution. strip at 2900 cm-1. The infrared spectrum of ethanol has C-H, O-H and C-O vibrations, as well as different bending vibrations. The O-H stretching vibration appears as a wide band at about 3300-3500 cm-1 and the C-H stretching vibration at about 3000 cm-1.

Properties of Ethanol

Physical properties of Ethanol

Boiling point (bp) 78.37 ° C; Melting point (mp) -114.1 ° C; Flash point (fp) 12°C; Ignition temperature 400 ° C; Lower explosion limit: 3.1 mass percent; Upper flammability limit: 27.7 mass percent; maximum pressure: 8.4 bar; Speed of sound 1180 m/s (20°C), Temperature. dep: -3.6 m/s °C; Density 0.79 g/cm3 = 0.79 kg/dm3; Energy density (thermal value) 7.44 kWh/kg = 26.78 MJ/kg; 5.87 kWh/L = 21.14 MJ/L; Dynamic Viscosity 1.2 10-3 Pa/s (20°C) ; Kinematic viscosity 1.52 10-6 m2/s (20°C) ; Surface tension 0.02255 N/m (20°C) ; Refractive index 1.3638; Biodegradability 94% (OECD 301 E) ; No. 1170 of the United Nations; Danger number 30 + 33; Triple point 150 ± 20 K / 0.43 mPa; -123.15 ± 20 ° C / 0.43 mPa; Critical point 514.0 K / 6.137 MPa / 168 cm3/mol; 240.85°C / 6, 137 MPa / 168 cm3/mol; Molar mass (mw) = 46.07 g/mol

The distinguishing feature of ethanol is the presence of a hydroxyl group. Since the oxygen atom attracts electrons more strongly than hydrogen and carbon, this leads to an asymmetrical distribution of electron density along this bond: A molecular dipole is formed. This gives ethanol its typical properties. On the other hand, the dipoles attract each other at the molecular level, resulting in a relatively high boiling point of 78°C (ethane melting point = -88.6°C) . On the other hand, ethanol is miscible with liquids of similar dipole properties, for example with water and methanol. This property is called hydrophilicity. At the same time, the molecule has an organic residue that limits its miscibility with substances that are completely lipophilic. For this reason, ethanol is an important solvent in chemistry and pharmaceuticals. Plant extracts or other drugs are sold as an alcohol solution, called a "tincture".

Ethanol forms single crystals large enough at freezing point to be determined by crystal structure analysis. It crystallizes in a monoclinic crystal system with space group Pc (space group 7) and has lattice parameters a = 537.7 dimensions, b = 688.2 dimensions, c = 825.5 dimensions and β = 102, 2° at 87 K, as well as 4 formula units per unit cell. The molecules form long chains through hydrogen bonding with an oxygen-oxygen distance of 271.6

The structure around the carbon-carbon bond is offset in both molecules. While the hydroxyl group in one molecule has a gauche structure along the C-C-OH axis, the other molecule has a metabolic conformation.

Mixed with other solvents

Ethanol is miscible with water in any proportion. In this case, volume contraction occurs during mixing with the development of heat. The total volume of the water/ethanol mixture is less than the sum of the individual volumes. Therefore, mixing 50 mL of ethanol with 50 mL of water yields 97 mL of an ethanol/water mixture. The melting point of an ethanol solution in water decreases with increasing ethanol content until a eutectic melting point of -118 °C at 93.5 mass percent is achieved. At a temperature of about -20°C, ethanol (6%) is virtually non-volatile and has a rather viscous character. At -70°C it becomes even more viscous (Kühlol) . Ethanol forms azide mixtures with many other substances. In organic solvents such as tetrachloromethane, ethanol forms dimers, trimers, and tetramers through hydrogen bonding, depending on the concentration. Enthalpy of formation can be determined by infrared spectroscopy. It is 92 kJ/mol for the tetramer, 42 kJ/mol for the trimer and 21 kJ/mol for the dimer.

Chemical properties

The OH group of ethanol is very weakly acidic with a pK value of 16, making it capable of splitting protons (H+) with strong bases (such as the alkali metals sodium and potassium) . The reaction with the alkali metals quantitatively converts ethanol to its deprotonated form, the ethanolate ion (CH3CH2O-) . The reaction takes place with the evolution of hydrogen:

2 C2H5OH + 2 Na → 2 C2H5O- + 2 Na + + H2

The solubility

Ethanol is soluble in all proportions with water and many other organic solvents such as diethyl ether, chloroform, benzene.

Auto resolution

Ethanol can react as a Brønsted acid and a Brønsted base, making it an amphoteric:

2 C2H5OH → C2H5OH2 + + C2H5O-.

The self-isolation constant here is pKau = 19.5.

Nucleophilic substitution

In aprotic solvents, ethanol reacts with hydrogen halides via nucleophilic substitution to form ethyl halides. Ethanol and hydrogen chloride react to give ethyl chloride and water:

C2H5OH + HCl → C2H5Cl + H2O

Ethanol and hydrogen bromide react to give ethyl bromide and water:

C2H5OH + HBr → C2H5Br + H2O

Etyl halides can be formed more specifically with halogenated reagents such as thionyl chloride or phosphorus trigromide.

Esterification

Ethanol reacts with acids catalyzed by carboxylic acids in an equilibrated reaction to form ethyl alcohol:

R-COOH + C2H5OH → R-COOC2H5 + H2O (H+ catalyst, balanced)

However, because the water formed has a higher boiling point than ethanol, the ethyl ester is better prepared by reacting with acid anhydride. Ethyl esters are used as additives to cosmetics as well as flavoring and flavoring agents.

Dehydration

Very strong acids, such as sulfuric acid, catalyze the dehydration of ethanol. Diethyl ether or ethylene is formed: 2 C2H5OH → C2H5OC2H5 + H2O (H2SO4, ΔT) . Ethanol splits water in a elimination reaction to form a double bond:

C2H5OH → C2H4 + H2O (H2SO4, ΔT)

What products are formed depends on reaction conditions such as temperature, concentration, etc. Dehydration can form highly toxic diethyl sulfate under certain reaction conditions. Ethanol oxidation was able to be oxidized by atmospheric oxygen at room temperature via acetaldehyde to acetic acid. For example, such reactions are catalyzed by enzymes in biological systems. In the laboratory, strong inorganic oxidants such as chromic acid or potassium permanganate are used to oxidize to acetic acid. Partial oxidation to acetaldehyde is successful with a weaker oxidant, such as pyridinium chlorochromate (PCC) . The oxidation of ethanol does not have to stop at the acetic acid phase. In air, ethanol burns with a blue flame of 26.8 MJ/kg to carbon dioxide and water:

C2H5OH + 3 O2 → 2 CO2 + 3 H2O

With chlorine or bromine, ethanol reacts slowly to form acetaldehyde and other halogenated oxidation products. Acetaldehyde forms hemiacetals in excess of ethanol. However, halogen addition to the enol form of acetaldehyde prevails, leading to the (lachrymatory) formation of α-haloacetaldehyde. Oxidation continues with chlorine eventually leading to hemiacetals of chlorine.

Sterilization due to denaturation

Corresponding to denaturation by acids or alkalis, ethanol can break the hydrogen bonds required in biofilms to maintain structure by interfering with

polar solvents. This leads to regulatory changes. 50 to 70 percent ethanol denatures most proteins and nucleic acids. Since membrane proteins lose function through steric damage and the associated cells burst like air bubbles due to membrane defects, higher percentage ethanol can be used. for sterilization: Bacterial and fungal cells are irreversibly inactivated due to denaturation of their membrane proteins,

and corresponding enveloped viruses stripped of their protein coats.

Using Ethanol

Ethanol is used in three main markets:

- Acoholic drink

- Raw materials for chemical industry

- Energy carrier (gasoline additive)

Ethanol, produced by fermentation of foods containing sugar and starch, is used in all industries. Synthetic ethanol is used only as a chemical raw material and an energy carrier. The competitive use of ethanol from food production as a feedstock for chemicals and energy is controversial. Much of the ethanol produced is consumed as an alcoholic beverage for consumer purposes. It continues to be used as a solvent for both consumer products, including household (perfume, deodorant) and medical applications (solvent for drugs, disinfectants), and in itself. industry as well as a solvent and generally a fuel.

Use of Ethanol in Household and Consumer Products

Ethanol is used as an excellent solvent everywhere in the household, for example as a carrier for odorants such as perfumes, deodorants, and fragrance sprays. Ethanol is also used as a cleaning agent, e.g. for glass (window cleaner), chrome, plastic, in car windshield washer fluid and as a stain remover. As an additive to water, it acts as an antifreeze. Ethanol is widely used as a food additive. For example, ethanol is added to port wine, sherry and other southern wines, known as adders, to end fermentation at the desired time. As a result of the premature end of fermentation, these liqueurs and wines are - with a few exceptions - high in residual sugar and therefore very sweet. Ethanol can be added to preserve other foods. As the fuel for camping stoves known as methylated alcohol, ethanol is widely used in homes. By adding cellulose acetate or soap, methylated spirits can be converted into a gel known as hard alcohol. Simple capillary thermometers have a visible column of blue or red liquid filled with colored ethanol. With a sufficiently long graduated tube, the temperature can be measured from the melting point to near the boiling point, providing good coverage of outdoor temperatures.

Medical use of ethanol

Efficacy as a disinfectant or disinfectant (e.g. hand sanitizer) depends on the concentration of the ethanol-water mixture. At an optimal alcohol concentration of 50 to 80%, the bacterial envelope is destroyed and therefore ethanol has a lethal effect. All bacteria including tubercle bacilli are killed within one minute by denaturing the bacterial cell wall (bactericidal effect) . In addition, the ethanol-water mixture is effective due to the high osmotic pressure; 70% ethanol has the highest osmotic pressure of all mixtures with water at 250-106 pascals. Limited effectiveness of the mixture against viruses, not effective against bacterial endospores. Not recommended for open wounds: In addition to an unpleasant burning sensation, ethanol has a vasodilator effect (mainly in the skin), which is generally beneficial for wound cleaning, but can worsen bleeding. especially in larger wounds. Solutions containing more than 80% alcohol have an even stronger effect, but are not used often due to poor skin tolerance. Anhydrous ethanol hardens the bacterial shell, keeping the bacteria alive. Drinking ethanol or alcoholic beverages does not have a disinfecting effect. Beverages containing less than 20% ethanol are virtually germ-free. Combining it with alkali (about 1%) or peroxycarboxylic acid (0.2 to 0.5%) significantly improves effectiveness against viruses and spores, among others. Ethanol is used as a solvent for the production of iodized tincture, an iodine-in-ethanol mixture for disinfecting wounds, to which potassium iodide is added to prevent the formation of iodized hydrogen. 95% or pure ethanol can be used as PEI therapy for sclerotic "hot" thyroid nodules (percutaneous ethanol therapy) and other surrounding tumors such as hepatocellular carcinoma (also known as hepatocellular carcinoma) is percutaneous ethanol injection therapy) . Liquid drugs may contain ethanol as a solvent, solvent, or solubilizer if the drug (s) are poorly soluble or insoluble in water. Ethanol itself is freely miscible with water. It has an important function in the preservation and stabilization of liquid herbal medicines (phytotherapeutics) . Medicines must be labeled according to the German Drug Warnings Ordinance (AMWarnV) . Rub the skin with

high percentage ethanol solutions (eg rubbing alcohol) promote blood circulation. To clean wounds, "burnt wine" has been frequently used by German-speaking wound doctors since the 12th century. Folk medicine still uses diluted ethanolic solutions to treat insect bites. A cloth soaked in alcohol is placed on the new sting for some time for this purpose. Pain relief occurs due to the cooling effect of the ethanol solution; itching is prevented.

However, ethanol does not cause chemical changes or inactivation of toxic substances. Drugs containing alcohol were used in ancient times as analgesics and anesthetics to induce anesthesia. In the case of methanol poisoning, the first measure is intravenous ethanol injection, which inhibits the conversion of methanol through the enzyme alcohol dehydrogenase to toxic methanal. Ethanol binds alcohol dehydrogenase about 25 times stronger than methanol. In the case of severe alcoholism, predelir alcohol can be discontinued with ethanol to treat acute secondary disease without symptoms occurring.

Ethanol as fuel

The EU produced ethanol for the fuel industry from 2004 to 2009 Ethanol is used as fuel ethanol in the form of bio-ethanol as a fuel for gasoline engines, most commonly blended with gasoline. Both fossil bio-alcohol and bio-alcohol produced from renewable biomass can be used for this purpose, as there is no chemical difference between the two. Due to availability, production costs and political support measures, bioethanol is produced on the basis of fermentable sugars (cane and sugar beet) and starches (mainly corn and wheat starches) .) is mainly used today. Investigations are underway to determine whether wood-based cellulose ethanol can be used in the future. Ethanol is mainly used as an additive to conventional fuels, for example at concentrations of 5% ethanol (E5 as an additive in conventional gasoline) or 85% ethanol (such as E85 for fit-for-purpose vehicles) this) . In the context of the Kyoto Protocol, there is now a constant debate about the production and use of biofuels (biofuels) and the reduction of carbon dioxide emissions per kilometer of road. In the European Union, ethanol production for the fuel industry increased from 525 million liters in 2004 to 3.7 billion liters in 2009, and since 2011 ethanol production has remained the same for both fuel use and fuel use. fuel and non-fuel. Ethanol was also used as a fuel for the A1, A2, A3, A4, A4b and A5 rockets until the 1950s, as developed by Wernher von Braun. Unlike gasoline, the calorific value can be easily lowered by diluting it with water for testing purposes to prevent explosion during engine testing; on the other hand, ethanol could easily be obtained from agricultural products during the Second World War, unlike gasoline, which was in short supply. In addition to pure ethanol, its derivatives are used in the fuel sector. For example, tert-butyl ethyl ether (ETBE) is used similarly to methyl tert-butyl ether to increase the octane number of gasoline. ETBE is produced by the addition of acid-catalyzed ethanol to isobutene.

Other uses of ethanol

Ethanol is an important solvent and intermediate in the chemical industry. An important end product is ethyl chloride, which is produced from ethanol by reaction with hydrogen chloride. Oxidation produces other end products such as acetaldehyde and acetic acid. Ethanol is used in many types of esterification reactions. The resulting esters have many uses as solvents and as intermediates for downstream synthesis. An important end product is ethyl acrylate, a monomer used as a co-monomer in various polymerization processes. Ethyl acetate is used as a solvent for nail polish and adhesives and to extract antibiotics. Glycolic ethers such as 2-ethoxyethanol are widely used as solvents for oils, resins, greases, waxes, nitrocellulose and varnishes. In the process of reversing the reaction that produces petrochemicals, ethanol is converted back to ethylene, which is used, for example, by the Brazilian chemical company Braskem as a feedstock for the production of polyethylene. Braskem already produces polyethylene from sugar cane at a plant in Rio Grande, Brazil, with an annual output of 200, 000 tons. Liquid preparations from biology and medicine are usually immobilized and preserved with an ethanol-water or formalin mixture.

Market Size of Ethanol

Globally, the US and Brazil together produced more than 90% of the total annual production of 29 million tons in 2005. The largest producers in Europe are Russia and France. Germany produces almost 4 million hL annually in the form of soft drinks and alcohol for chemical-engineering purposes, which corresponds to a domestic demand of about 62%. In addition to the production of neutral alcohol for beverages, food and technical purposes, the production of fuel ethanol accounts for about 65%.

all around the world. In the United States, the construction of new ethanol plants is being particularly promoted, above all by the Energy Policy Act (EPACT) 2005, to encourage the expansion of renewable liquid energy sources.

Denaturation

Ethanol is taxed on alcohol in Germany (until 2018, spirits tax) . Customs duties are levied on the distributor (manufacturer of spirits, authorized consignee, keeper of spirits stock) at the time of depot handling. Deferred shipments can be through BVD or EVD - for example between a producer and a wholesaler with an extensive wine inventory as well as in export transactions. Ethanol may be used tax-free for technical purposes, such as in printing plants, paint manufacturing, detergent manufacturing, cosmetics and similar applications, and as methylated spirits. To prevent this ethanol from being consumed as a stimulant or added without tax, untaxed alcohol is denatured under customs supervision. Denatured means that ethanol is mixed with other chemicals, such as methyl ethyl ketone (MEK) and two other marker ingredients required by the spirits tax law, kerosene ether, cyclohexane, diethyl phthalate, Bitrex or similarly, to make it unsuitable for human consumption. This is regulated in Germany by Branntweinsteuerverordnung (BrStV) and in Austria by Verordnung des Bundesministers für Finanzen über die Vergällung von Alkohol (VO-Vergällung) . Bioethanol for blending with fuels modified with ETBE or gasoline during manufacturing. The above denaturants are normally used for mental or cosmetic purposes, for example methyl ethyl ketone (MEK), which may not be used in fuels according to EN 228. For example, in the case of ethanol used used as fuel in the form of methyl alcohol. For retraining and camping and expedition stoves, extremely bitter denatonium benzoate (1 gram per 100 liters) is added to the ethanol along with MEK. Pyridine, formerly used as a denaturant for methylated spirits, has not been used by German manufacturers since 1993 due to its health risks and has not been authorized since 1 July 2005. 2013. In contrast to pyridine, which has a boiling point of 115°C, denatonium benzoate is a solid that only melts at 163 - 170°C. It therefore evaporates during use. Therefore, it does not evaporate when methylated spirits are used, but accumulates in the wicks of spirit devices, for example, leading to performance problems in incandescent lamps and carburetor stoves. gas. The denaturants often have similar boiling points as ethanol, making them difficult to remove by distillation.

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