ETHYLENE GLYCOL Introduction [1]: Glycols are dihydric alcohols having an aliphatic carbon chain. They have the general chemical formula C n H 2n (OH) 2. is the simplest and the most important of the glycols. It is a colorless, nearly odorless, sweet-tasting, hygroscopic liquid. The chemical formula of ethylene glycol is: C 2 H 6 O 2. was first produced in 1859 by Wurtz. He saponified ethylene glycol diacetate with potassium hydroxide. Three years later he made ethylene glycol by hydration of ethylene oxide. This glycol encounted a commercial importance in 1925 when it was first manufactured in large scale quantities from ethylene oxide through the intermediate ethylene chlorohydrin. Some of the physical properties of the ethylene glycol are shown in Table 1.1. Molecular weight, g/gmol 62.07 Freezing point, 0 C -13 Boiling point, 0 C 197.2 Solubility at 20 0 C., wt.% In water Complete Water in Complete Table 1.1 Physical properties of is relatively nonvolatile and viscous. It is also soluble in common alcohols and phenol.
Manufacture [1]: I. Most of the ethylene glycol produced today is obtained by hydration of ethylene oxide. The reaction is: CH 2 -O-CH 2 + H 2 O CH 2 -OH-CH 2 -OH Ethylene oxide is readily converted to ethylene glycol by either of the following methods: - by the action of a dilute aqueous solution of a strong acid - by reaction with water at elevated temperature and pressure The ethylene glycol which results from these methods is concentrated by evaporations and further purified by vacuum distillations. II. A second commercial method of producing ethylene glycol is based on the reaction of formaldehyde and a mixture of carbon monoxide and water at high pressure and temperature to produce glycolic acid. CH 2 + CO + H 2 O CH 2 -OH-CH 2 -OH The latter is esterified with methanol or n-propanol to form the corresponding alkyl glycolates. These are then hydrogenated to glycol in the presence of a catalyst containing copper and magnesium oxides at temperatures of 125-325 0 C and pressure above 100 atm. is recovered from the reaction mixture by fractional distillation. III. has been produced in Germany from ethyl alcohol via ethylene and ethylene dichloride. The latter is saponified by heating with aqueous solution of sodium bicarbonate, ferric oxide or some similar agent. This process was used for manufacturing glycol in small quantities for explosives during the World War. IV. Other methods have been tried for the production of ethylene glycol but they were not proved commercially attractive. These methods are: direct hydroxylation of ethylene, decomposition and hydrogenation of sugars and polyhydroxy compounds and direct hydrolysis of ethylene chlorohydrin to ethylene glycol. V. On a laboratory scale, ethylene glycol is readily formed by the hydrolysis of ethylene dihalides or ethylene diacetate.
1.2 Uses (Applications) [1]: is one of the most important of all synthetic organic chemicals. It has widespread applications in many branches of industry : - Its most important use are as an nonvolatile, permanent-type antifreeze. - The antifreeze grade of ethylene glycol is used in sprinkler systems for unheated buildings and in place of salt solutions in heat exchange systems where corrosion is a factor. - It is incorporated into water-containing products such as asphalt-emulsion paints to prevent breaking of the emulsion by freezing of the water. - is as an intermediate in the production of ethylene glycol dinitrate for use in low-freezing dynamites. - It is also used as a high-temperature coolant in aircraft engines, x-rays tubes, machine guns and army tanks. - It permits operations at considerably high temperature than water when it is used as the coolant. - Solutions of boric acid or its salts in ethylene glycol are widely used to form the electrolyte in electrolytic condensers employed in midget radio sets, induction motors, radar equipment and other electronic devices. - is the diluent in many types of hydraulic-brake and shock-absorber fluids. - It is also a component of the aqueous-base, nonflammable hydraulic fluids known as hydrolubes. - It acts as a softening agent for cellophane and as a stabilizer in the soybean liquidbase airfoam used in extinguishing oil and chemical fires. - It is the starting material in the commercial production of glyoxal and in the production of the unsaturated ester type of alkyd resins. - It is a component of carbon-removal formulations for cleaning aluminum pistons, of non-grain-raising wood strains and of electropolishing solutions for steel and aluminum. - It is a raw material for the preparations of a large variety of synthetic resins, plasticizers and elastomers.
1.3 Production of ethylene glycol 1.3.1 Minimal process requirements One process alternative is to produce ethylene glycol from ethylene oxide. The minimal requirements for such an alternative process include one reactor, two separators and one distillation column. The schematic representation of this process is shown in Figure 1.3. Ethylene glycol H 2 O (CH 2 ) 2 O Reactor Ethylene oxide separation Water separation D i s t i l l a t i o n Di-and triglycols Figure 1.3 Schematic diagram of a process to manufacture ethylene glycol [2]. Ethylene oxide and water are introduced in the reactor, the product of the reaction is ethylene glycol. The product stream will contain, besides ethylene glycol, other materials (unreacted water and/or ethylene oxide, di- and triethylene glycol). (The di-and triethylene glycols are formed because the hydroxyl group is very reactive). For this reason in the process are included other units: a unit that removes water (water separations), one that removes unreacted ethylene oxide (ethylene oxide separation). The distillation column unit permits the separation of the ethylene glycol from di- and triglycol.
1.3.2 Additional requirements A more complete process is shown in Figure 1.4. Vacuum Vacuum H 2 O Ethylene oxide C D H2O H 2 O M R S1 S2 H2O Diethylene glycol Triethylene glycol Diethylene glycol Triethylene glycol Diethylene glycol Triethylene glycol Figure 1.4 Schematic representation of a process to manufacture ethylene glycol [3]. The process includes a mixer, M, where the ethylene oxide and the water, stored in a unit, are mixed. The amount of ethylene oxide and water that are going into the mixer are controlled by valves. From the mixer, the mixed product is going into the rector, R, where the glycols are formed. A controller, C, is used to manipulate the ratio of water to ethylene oxide. From reactor, the product stream is going into the distillation column, D, which in this process is steam heated. The condensers are collected at the top of the column and recycled in the water unit. At the bottom of the column are collected the unreacted materials: water, ethylene glycol, di- and triethylene glycol. The process includes two separators. The first one, S1, separates the unreacted water from the rest of
the products. The second separator, S2, separates the ethylene glycol from the rest of the products. The separators are provided with boilers and condensers. To separate the di-and triethylene glycols two more separators will be needed. 1.4 Benefits of Modeling: A mathematical representation of the process (a model) can be useful for many different purposes. For example, the daily operation of the plant can be both planned and scheduled. The performance of the units can be assessed. Studies related to productivity, cost, and safety can be performed using the data from the process but without disturbing the plant. If a dynamic model is available, transient and control studies can be easily conducted to investigate the behavior of the process during start-ups and shut-down operations. Another important use of the models is for troubleshooting the process. References: [1] Jacqueline I. Kroschwitz (executive editor); Mary Howe-Grant (editor), Encyclopedia of Chemical Technology, 4 th Edition, New York : Wiley, c1991, At head of title: Kirk- Othmer [2] T.W.Fraser Russell and Morton M. Denn, Introduction to Chemical Engineering Analysis, John Wiley & Sons, Inc., New York 1972 [3] Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Germany; New York: VCH, c1994-c1996.