A REPORT ON ETHYLE OXIDE AND MONO ETHYLENE GLYCOL (MEG)
DEPARTMENT OF CHEMICAL ENGINEERING E NGINEERING INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
SUBMITTED TO:
SUBMITTED BY:
Dr. ID Mall Professor IIT Roorkee
Kushagra Varshney (10112022) rd B.Tech 3 Yr. CH &
K. Vijayalakshmi (10112017) rd
B.Tech 3 Yr. CH
1
CONTENTS
Ethylene oxide 1.1
Introduction ………………………………………………………………………...3
1.2
History……………………………………………………………………………….…4
1.3
Structure………………………………………………………………….…………..5
1.4
Physical Properties…………………………………...……………………….…6
1.5
Production……………………………………………………………………………6
1.6
Direct Oxidation Process……………………………………………………...7
1.7
Uses…………………………………………………………………………………....10
Mono Ethylene Glycol 2.1
Introduction…………………………………………......................................11
2.2
Structure…..............................................................................................11
2.3
Production……………………………………….…………………………………12
2.4
Uses…………………………………………………………………………………….13
References ……………….………………………………………………………………………….17
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ETHYLENE OXIDE
1.1
INTRODUCTION Ethylene oxide , also called oxirane, is the organic compound with the
formula C2H4O. It is a cyclic ether. (A cyclic ether consists of an alkane with an oxygen atom bonded to two carbon atoms of the alkane, forming a ring.) Ethylene oxide is a colorless flammable gas at room temperature, with a faintly sweet odor; it is the simplest epoxide: a three-membered ring consisting of one oxygen atom and two carbon atoms. Because of its special molecular structure, ethylene oxide easily participates in addition reactions; e.g., opening its ring and thus easily polymerizing. Ethylene oxide is isomeric with acetaldehyde. Although it is a vital raw material with diverse applications, including the manufacture of products like polysorbate 20 and polyethylene glycol that are often more effective and less toxic than alternative materials, ethylene oxide itself is a very hazardous substance: at room temperature it is a flammable, carcinogenic, mutagenic, irritating, and anaesthetic gas with a misleadingly pleasant aroma. The chemical reactivity that is responsible for many of ethylene oxide's hazards has also made it a key industrial chemical. Although too dangerous for direct household use and generally unfamiliar to consumers, ethylene oxide is used industrially for making many consumer products as well as non-consumer chemicals and intermediates. Ethylene oxide is important or critical to the production of detergents, thickeners, solvents, plastics, and various organic chemicals such as ethylene glycol, ethanolamines, simple and complex glycols, polyglycol ethers and other compounds. As a poison gas that leaves no residue on items it contacts, pure ethylene oxide is a disinfectant that is widely used in hospitals and the medical equipment industry to replace steam in the sterilization of heat-sensitive tools and equipment, such as disposable plastic syringes.
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Ethylene oxide is industrially produced by direct oxidation of ethylene in the presence of silver catalyst. It is extremely flammable and explosive and is used as a main component of thermobaric weapons; therefore, it is commonly handled and shipped as a refrigerated liquid.
1.2
HISTORY Ethylene oxide was first reported in 1859 by the French chemist Charles-
Adolphe Wurtz, who prepared it by treating 2-chloroethanol with potassium hydroxide: Cl –CH2CH2 –OH + KOH
→
(CH2CH2)O + KCl + H 2O
Wurtz measured the boiling point of ethylene oxide as 13.5 °C, slightly higher than the present value, and discovered the ability of ethylene oxide to react with acids and salts of metals. Wurtz mistakenly assumed that ethylene oxide has the properties of an organic base. This misconception persisted until 1896 when Georg Bredig found that ethylene oxide is not an electrolyte. That it differed from other ethers — particularly by its propensity to engage in addition reactions, which are typical of unsaturated compounds — had long been a matter of debate. The heterocyclic triangular structure of ethylene oxide was proposed at least as early as 1868. Wurtz's 1859 synthesis long remained the only method of preparing ethylene oxide, despite numerous attempts by scientists, including Wurtz himself, to produce ethylene oxide directly fromethylene. Only in 1931 did French chemist Theodore Lefort develop a method of direct oxidation of ethylene in the presence of silver catalyst. Since 1940, almost all industrial production of ethylene oxide has used this process. Sterilization by ethylene oxide for the preservation of spices was patented in 1938 by the American chemist Lloyd Hall. Ethylene oxide achieved industrial importance during World War I as a precursor to both the coolant ethylene glycol and the chemical weapon mustard gas.
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1.3
STRUCTURE The epoxy cycle of ethylene oxide is an almost regular triangle with bond
angles of about 60° and a significant angular stress corresponding to the energy of 105 kJ/mol.
The relative instability of the carbon-oxygen bonds in the molecule is revealed by the comparison in the table of the energy required to break two C –O bonds in the ethylene oxide or one C –O bond in ethanol and dimethyl ether:
Reaction
ΔH°298, kJ/mol
(C2H4)O → C2H4 + O (cleavage of two bonds)
354.38
C2H5OH → C2H5 + OH (breaking one bond)
405.85
CH3OCH3 → CH3O + CH3 (breaking one bond)
334.72
This instability determines the chemical activity of ethylene oxide and explains the ease of opening its cycle in addition reactions.
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1.4
PHYSICAL PROPERTIES Ethylene oxide is a colorless gas at 25 °C and is a mobile liquid at 0 °C –
viscosity of liquid ethylene oxide at 0 °C is about 5.5 times lower than that of water. The gas has a characteristic sweet odor of ether, noticeable when its concentration in air exceeds 500 ppm. Ethylene oxide is readily soluble in water, ethanol, diethyl ether and many organic solvents. 1.5
PRODUCTION Ethylene oxide has been produced commercially by two basic routes:
1. From ethylene chlorohydrin. 2. Direct oxidation process. The chlorohydrin process was first introduced during World War I in Germany by Badische Anilin-und Soda-Fabrik (BASF). The process involves the reaction of ethylene with hypochlorous acid followed by dehydrochlorination of the chlorohydrin with lime to produce ethylene oxide and calcium chloride. Union Carbide Corp. was the first to commercialize this process in United States. The chlorohydrin process is not economically competitive, and was quickly replaced by the direct oxidation process as the dominant technology. At present time, all the ethylene oxide production in the world is achieved by the direct oxidation process. The direct oxidation technology, as the name implies, utilizes the catalytic oxidation of ethylene with oxygen over a silver based catalyst to yield ethylene oxide. The process can be divided into two categories depending on the source of the oxidizing agent. The air-based process and the oxygen based process. In the first , air or air enriched with oxygen is fed directly to the system. In the second high purity oxygen stream (>98 mol%) from an air separation unit is employed as the source of the oxidizing agent. Union Carbide Corp. was the first to commercialize an air-based direct oxidation process in 1937. The first oxygen-based system was commercialized by 6
Shell Oil Co. in 1958. All the ethylene oxide plants that have been built during the last 15 years were oxygen-based processes and a number of plants were converted from the air to the oxygen-based process during the same period. The total world production capacity of ethylene oxide in 1992 was about 9.6X 106 metric tons. Most of the ethylene oxide produced is consumed by its producers in making derivatives. The chosen process for this design thesis is the oxygen-based oxidation process, because this is the latest process for the production of ethylene oxide production.
1.6
DIRECT OXIDATION PROCESS The phenomenal growth in United States and world ethylene oxide
production capacity since 1940 and the market trend toward larger single train plant is chiefly due to the commercial success of the direct oxidation process. Compared to the chlorohydrin process, direct oxidation eliminates the need for large volumes of chlorine. Also there are no chlorinated hydrocarbons by products to be sold, processing facilities can be made simpler, and operating costs are lower. The main disadvantage of the direct oxidation process is the lower yield or selectivity of ethylene oxide per unit of feed ethylene consumed. The main inefficiency in the process results from the loss of 20-25 mol% of the ethylene to carbon dioxide and water. Consequently the operating conditions must be carefully controlled to maximize selectivity. All the ethylene oxide palnts are based on the original process chemistry discovered by Lefort in 1931. C2H4 + ½ O2
C2H4O
The only significant by-products are carbon dioxide and water, which are formed either by complete combustion of ethylene: 7
C2H4 + 3O2
2CO2 + 2H2O
Or by further oxidation of ethylene oxide: C2H4O +2½ O2
2CO2 + 2 H2O
To prevent the further oxidation of ethylene oxide, the ethylene conversion is typically between 20-30% for ethylene oxide. In addition to ethylene oxide, carbon dioxide, water, small quantities of acetaldehyde and traces of formaldehyde are also produced. In this calculation this is neglected and assumed to go with the bottom products. The total percentage of production of these compounds is 0.2% of the total ethylene oxide produced. A large amount of heat is released by the ethylene oxide reactions. At 600 K, each Kg of ethylene converted to ethylene oxide releases 3.756 MJ; each Kg of ethylene converted to carbon dioxide and water releases 50.68 MJ. Energy recovery and integration is a prime concern in process design. 1.6.1 PROCESS DESCRIPTION Ethylene (95-98% purity) and oxygen (air with 95 mole % of oxygen) are mixed in a ratio of 1:10 by weight and passed over a catalyst consisting of silver oxide deposited on an inert carrier such as corundum. Generally an anti catalyst such as ethylene dichloride (about 2% based on the weight of ethylene) is added to the ethylene feed to suppress the formation of carbon dioxide. As an alternative vent gases form the absorber may be recycled to the reactor in such quantity as to keep the ethylene concentration in the feed at 3-5%. At a pressure of 4-5 atmosphere and temperature of 270-
when a contact time of 1 sec is
used, about 50 % of ethylene is converted. 25% of the ethylene is converted to ethylene oxide. The effluent gases from the reactor are washed with water under pressure in an absorber. The ethylene is absorbed and sent to a desorber to desorb the water, which is used for the absorption. This water is recycled. 8
The overhead product from the desorber is sent to a steam stripper to remove the dissolved gases. The water- ethylene oxide mixture with small amount of ethylene and other impurities are fed to a fractionating column to purify the ethylene oxide to 99 mole%. Commercial processes operate under recycle conditions in a packed bed multi-tubular reactor. The reactor is of shell and tube type comprised of several thousand mild steel or stainless steel tubes, 20-50 mm inside diameter. The reactor can be either oil or boiling water-cooled. These tubes are filled with a silver based catalyst ca 3-10 mm diameter supported on a carrier material with surface area usually < 1m2/g. The yield (moles of product formed per moles of ethylene consumed in the process) is normally 70-80% depending on catalyst type, per pass conversion, reactor design and normally a large number of other process variables. 1.6.2 OXYGEN BASED DIRECT OXIDATION Even though the fundamental reaction and the ultimate results are the same there are substantial differences in air and oxygen based processes. Virtually all the differences arise from the change in the oxidizing agent from air to pure oxygen (95 mole% O2). Due to the low per pass conversion, the need for complete removal for ethylene oxide by absorption, and the accumulation of nitrogen in the cycle, the air process requires a substantial purge stream. As a direct consequence of this air process requires the staged reaction- absorption system. The oxygen-based process uses substantially pure oxygen reduces the quantities of inert gases introduced into the cycle, and thereby results in almost complete recycle of the unreacted ethylene. This eliminates the need for purge reactor in the oxygen-based process. However the volume of the carbon dioxide formed is about 2 times the volume of the ethylene reacted at a catalyst selectivity of 70-80%. This CO2 must be eliminated on a continuous basis in order to control its concentration at an acceptable level in the cycle. Concentrations of CO2 much in excess of 15-mole% adversely affect the catalyst selectivity. Therefore in oxygenbased process the 9
recycled gas is treated in a CO2 removing tower before it is send back to the reactor. The operation of the main reactor can be at much higher ethylene concentration than that possible in air-based process is much smaller than an airbased unit. The high ethylene concentration improves the catalyst selectivity because the per pass conversions are lower for a given ethylene oxide production. In the flow sheet of the shown the process is an oxygen-based process. Ethylene, oxygen, and the recycle gas stream are combined before entering the tubular rectors. The basic equipment used in this process is same as that used in air-based process. The purge reactor is not used in this process.
1.7
USES Ethylene oxide is an excellent fumigant and sterilizing agent. Ethylene oxide
is used as an antimicrobial pesticide to fumigate species and to sterilize medical devices, such as sutures, bandages, endoscopes and cardiac pacemakers. Most medical devices in the USA are sterilized using EO. Ethylene oxide sterilization process requires relatively low temperatures and pressures, and does not damage the materials or packaging being sterilized. Ethylene oxide sterilant gases are supplied as liquefied compressed gases, either pure or as a mixture with a flame retardant. When supplied as a pure gas, the ethylene oxide is shipped in special insulated containers. For safety reasons, nitrogen gas is added to the vapour phase up to a total pressure of a345 Kpa (50 the flammability of ethylene oxide is usually controlled by purging the sterilization chamber with nitrogen gas at the beginning and the end of the sterilization process. In some cases, the effects of a potential deflagration are moderated by operating under great vacuum or, in the case of small hospital sterilizers, by using very small quantities of ethylene oxide. Ethylene oxide has been studied for use as a rocket fuel and as a component in munitions. It has been reported, ethylene oxide to be used as a fuel in FAE (fuel air explosive) bombs.
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MONO ETHYLENE GLYCOL
2.1
INTRODUCTION Mono ethylene glycol also known as Ethylene glycol (IUPAC name: ethane-
1,2-diol) is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweettasting liquid. Ethylene glycol is toxic, and ingestion can result in death.
2.2
STRUCTURE
2.3
PHYSICAL PROPERTIES
Molecular formula
C2H6O2
Molar mass
62.07 g mol−1
Density
1.1132 g/cm³
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Melting point
−12.9 °C, 260 K, 9 °F
Boiling point
197.3 °C, 470 K, 387 °F
Solubility in water
Miscible with water in all proportions.
Viscosity
1.61 × 10−2 N*s / m2
2.4
PRODUCTION Although almost all sources state that French chemist Charles-Adolphe
Wurtz (1817-1884) first prepared ethylene glycol in 1859, he actually first prepared it in 1856.
[2]
He first treated "ethylene iodide" (C2H4I2) with silver acetate
and then hydrolyzed the resultant "ethylene diacetate" with potassium hydroxide. Wurtz named his new compound "glycol" because it was intermediate to ethyl alcohol (with one hydroxyl group) and glycerin (with three hydroxyl groups). In 1860, Wurtz prepared ethylene glycol from the hydration of ethylene oxide. There appears to have been no commercial manufacture or application of ethylene glycol prior to World War I, when it was synthesized from ethylene dichloride in
Germany
and
used
as
a
substitute
for glycerol in
the explosives industry. In the United States, semicommercial production of ethylene glycol via ethylene chlorohydrin started in 1917. The first large-scale commercial glycol plant was erected in 1925 at South Charleston, West Virginia, by Carbide and Carbon Chemicals Co. (now Union Carbide Corp.). By 1929, ethylene glycol was being used by almost all dynamite manufacturers. In 1937, Carbide started up the first plant based on Lefort's process for vapor-phase oxidation of ethylene to ethylene oxide. Carbide maintained a monopoly on the direct oxidation process until 1953, when the Scientific Design process was commercialized and offered for licenses.This molecule has been observed in outer space. 12
2.4.1 CURRENT METHODS Ethylene
glycol
is
produced
from ethylene (ethene),
via
the
intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol according to the chemical equation: C2H4O + H2O → HO–CH2CH2 –OH This reaction can be catalyzed by either acids or bases, or can occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH with a large excess of water. Under these conditions, ethylene glycol yields of 90% can be achieved. The major byproducts are the ethylene glycol oligomers diethylene glycol, triethylene glycol, and tetraethylene glycol. About 6.7 billion kilograms are produced annually. A higher selectivity is achieved by use of the Shell's OMEGA process. In the OMEGA process, the ethylene oxide is first converted with carbon dioxide (CO2) to ethylene carbonate to then react with water in a second step to selectively produce mono-ethylene glycol. The carbon dioxide is released in this step again and can be fed back into the process circuit. The carbon dioxide comes in part from the ethylene oxide production, where a part of the ethylene is completely oxidized.
2.5
USES The major end uses of ethylene glycol are as antifreeze, which accounts for
over 50% of ethylene glycol's commercial uses, and as raw material in the production of polyester fibers, mainly PET, which accounts for 40% of total ethylene glycol consumption. Because this material is cheaply available, it finds many niche applications.
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2.5.1 COOLANT AND HEAT TRANSFER AGENT The major use of ethylene glycol is as a medium for convective heat transfer in, for example, automobiles and liquid cooled computers. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside or systems that must cool below the freezing temperature of water. In geothermal heating/cooling systems, ethylene glycol is the fluid that transports heat through the use of ageothermal heat pump. The ethylene glycol either gains energy from the source (lake, ocean, water well) or dissipates heat to the source, depending if the system is being used for heating or cooling. Pure ethylene glycol has a specific heat capacity about one half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 50/50 mix by mass has a specific heat capacity of about 3140 J/Kg C (0.75 BTU/lb F) three quarters that of pure water, thus requiring increased flow rates in same system comparisons with water. Additionally, the increase in boiling point over pure water inhibits nucleate boiling on heat transfer surfaces thus reducing heat transfer efficiency in some cases, such as gasoline engine cylinder walls. Therefore, pure ethylene glycol should not be used as an engine coolant in most cases.
2.5.2 ANTIFREEZE Due to its low freezing point ethylene glycol resists freezing. A mixture of 60% ethylene glycol and 40% water freezes at −45 °C (−49 °F). Diethylene glycol
behaves similarly. It is used as a de-icing fluid for windshields and aircraft. The antifreeze capabilities of ethylene glycol have made it an important component of vitrification (anti-crystallization) mixtures for low-temperature preservation of biological tissues and organs.
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Ethylene glycol disrupts hydrogen bonding when dissolved in water. Pure ethylene glycol freezes at about −12 °C (10.4 °F), but when mixed with water
molecules, neither can readily form a solid crystal structure, and therefore the freezing point of the mixture is depressed significantly. The minimum freezing point is observed when the ethylene glycol percent in water is about 70%, as shown below. This is the reason pure ethylene glycol is not used as an antifreeze—water is a necessary component as well.
2.5.3 PRECURSOR TO POLYMERS In
the plastics industry,
ethylene
glycol
is
important
precursor
to polyester fibers and resins. Polyethylene terephthalate, used to make plastic bottles for soft drinks, is prepared from ethylene glycol.
2.5.4 HYDRATE INHIBITION Because of its high boiling point and affinity for water, ethylene glycol is a useful desiccant. Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to an onshore processing facility. Ethylene glycol can be recovered from the natural gas and reused as an inhibitor after purification treatment that removes water and inorganic salts. Natural gas is dehydrated by ethylene glycol. In this application, ethylene glycol flows down from the top of a tower and meets a rising mixture of water vapor and hydrocarbon gases. Dry gas exits from the top of the tower. The glycol and water are separated, and the glycol recycled. Instead of removing water, ethylene glycol can also be used to depress the temperature at which hydrates are formed. The purity of glycol used for hydrate suppression (monoethylene glycol) is typically around 80%, whereas the purity of glycol used for dehydration (triethylene glycol) is typically 95 to more than 99%. Moreover, the injection rate 15
for hydrate suppression is much lower than the circulation rate in a glycol dehydration tower. 2.5.5 NICHE APPLICATIONS Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of 1,4-dioxane, and as an additive to prevent corrosion in liquid cooling systems for personal computers. Ethylene glycol is also used in the manufacture of some vaccines, but it is not itself present in these injections. It is used as a minor (1 –2%) ingredient in shoe polish and also in some inks and dyes. Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after the fact. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats, and is relatively cheap. Ethylene glycol may also be one of the minor ingredients in screen cleaning solutions, along with the main ingredient isopropyl a preservative for
alcohol.
biological
Ethylene specimens,
glycol
is
especially
commonly in
used
secondary
as
schools
during dissection as a safer alternative to formaldehyde. It can also be used in killing jars. It is also used as part of the water-based fluid used to control subsea oil and gas production equipment.
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REFRENCES
Petrochemical Process Technology- by Dr. ID Mall
http://en.wikipedia.org/wiki/Ethylene_glycol
https://www.google.co.in/
http://www.epa.gov/ttnatw01/hlthef/ethy-gly.html
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