Manufacturing ethylene glycol
Brief overview of EG manufacturing process...
A Paper On Manufacturing Of Ethylene Glycol Ethylene Glycol is nowadays one of the most industrially important chemical. Due to its demand and a vast application area lot of research is going on for improving its production statistics. In 1995 the world capacity for ethylene glycol was about 9.7 x 106 tonnes per year.
Properties of Ethylene Glycol Ethylene Glycol is specifically colorless, syrupy hygroscopic liquid with a sweet taste. Mol. Wt 62. 07 Sp. Gravity 1.116 at 200C M.P. - 15.60C B.P. 197.60C EG is soluble in water, alcohol and ether. Lowers the freezing point of water.
Uses of Ethylene Glycol 1) Antifreeze / Coolant As already noted a major use for the EG is as antifreeze for internal combustion engines, particular in the USA. There is also an increasing tendency to use glycol - water solutions as year round coolants for automobiles and as industrial heat transfer agent. Ethylene glycol based formulations are used for defrosting and de - icing aircraft and to de - ice airport runways and taxiways. Pressurized fire extinguishers and sprinkler system often contain ethylene glycol to prevent freezing. Ethylene glycol is added to asphalt emulsion paints to provide protection against freezing, which would break the emulsion. Ethylene glycol, after nitration to form dinitrate, an explosive, is mixed
with dynamite to depress its freezing point and make it safer to handle in cold weather.
2) Polyester fibers and resins : Ethylene glycol is the raw material in the manufacture of the polyester fibers ( Polyethylene terephthalate ), commonly marketed commercially as Dacron, fortrel, Kodel , terylene, Vycron etc. As noted previously , this use has become the most important market for glycol worldwide. Polyester resins which are made from ethylene glycol, vinyl tape monomers, and maleic and phthalic anhydrides have important applications in the production of laminates. These are extensively used in the manufacture of a wide range of consumer products such as furniture, automobile bodies, boat hulls, suitcases etc. Alkyd resins made from ethylene glycol and phthalic anhydride are used in the manufacture of the surface coatings. The reaction of ethylene glycol with dibasic acids ( O - ophthalmic, malefic or fumaric ) produces alkyd type resins used in adhesions, in modifying synthetic rubbers and in the other applications. Glycol based resin esters are used as politicizes in adhesives, lacquers and enamels.
3) Hydraulic fluids : Hydraulic brake and shock absorber fluids contain ethylene glycol to improve inhibitor solubility, prevent rubber swelling, and inhibit foam formulation. Ethylene glycol is mixed with polyalkylene glycols and water to produce hydro lubes , which have extensive application as nonflammable, low viscosity hydraulic fluids.
4) Capacitors : Ethylene glycol is a solvent and suspending medium for ammonium perborate , which is used in most electrolytic capacitors.
5) Other Uses : Ethylene glycol is an intermediate in the manufacture of glyoxal, which is used to treat cotton polyester fabrics to make the permanent press. It is added to water dispersions of urea formaldehyde and melamine formaldehyde to stabilize them. It is also used as a humectants for paper, textile fibers, leather, and adhesives, and in addition makes these products softer and more pliable and improves their durability.
Processes of Manufacturing of Ethylene Glycol : Ethylene Glycol has become the most important ethylene derived industrial chemical of the world. No. of processes have been studied but commercially, the hydration of the ethylene oxide is being used worldwide. Ethylene Oxide hydration route also produces small amount of the di, tri and higher glycols as co products, and these have established their own uses and markets.
First we will consider the Ethylene oxide hydration process then we will shift to other process alternatives.
* Ethylene Glycol from Hydration of the Ethylene Oxide : Material required : Consider that the ethylene oxide required is also produced In the same plant. For one ton ethylene Glycol Ethylene 1800 lb Air
Process Flow sheet :
Process chemistry The chemistry of the hydration reaction is quite simple. It consists of the reaction of the ethylene oxide with water to form Monoethylene Glycol ( MEG ).
H2C O CH2 + H2O → H2C CH2 + 91.0 kJ OH OH The above reaction is followed by the reaction of the MEG with the remaining Ethylene Oxide to form higher derivatives of the glycol.
The most Important variable affecting the glycol distribution is the water to oxide ratio. In commercial plants, the production of di and tri ethylene glycol can be effectively reduced by using a large amount of excess water. As an example, at water to oxide ratios in excess of 20 : 1 , the heavier glycols will comprise less then 10 weight percent of the total glycol produced. In the design of a
commercial glycol plant, the improvement in MEG yields that can be achieved by increasing water recycle are balanced against the increase in capital and utility costs for optimal economics. The glycol distribution from the reactor is essentially unaffected by changes in pressure and temperature over the ranges that are normally of commercially interest ( 1 to 30 bars, 90 to 2000C. ). Under neutral or acidic conditions, the product distribution is essentially unchanged. However, Basic catalysts ( or a high pH ) will substantially increase the production of higher glycols. The rate of the hydration reaction is however strongly dependent on the temperature and is catalyzed by acids, bases are only about 1 percent as effective as acids. While the use of acid catalysts permit’s the hydration reaction to proceed at lower temperatures and pressures than those required for unanalyzed conditions, the reaction solution becomes corrosive and requires acid removal.
Process Description : In a free standing glycol plant, the feeds are refined ethylene oxide and pure water. These are mixed with the cold recycle water in a feed tank to produce a dilute oxide - water solution containing 8 to 12 percent ethylene oxide. The solution is pumped through preheaters ( hot recycle water and steam ) into an adiabatic reactor where the ethylene oxide is hydrated ( non catalytically ) to produce a MEG and a small amount of higher derivatives. The glycol reactor is designed to provide sufficient residence time to react ( non catalytically ) essentially all the ethylene oxide. The reactor pressure is controlled at a level that avoids vaporization of ethylene oxide from the aqueous solution and will depend on the initial concentration of the oxide and the reaction temperature. Published information shows that commercial reactors operating at temperatures of 190 to 2000C will be at a pressure around 14 to 22 bars. The glycol water mixture from the reactor is fed to the first effect of a multiple effect evaporator. The first effect is operated at a medium pressure level and is reboiled
using high pressure steam. The following effects of the evaporator operate at progressively lower pressures, with the final stage at low pressure or even under vacuum. The evaporated water is recovered as an overhead condensate is recycled back to the glycol reaction fed tank after heat exchange with cold reactor feed. If the feed to the plant is a crude oxide water solution from an EO plant, the recycled water is sent back to the ethylene oxide recovery section. The concentrated crude glycol solution leaving the final evaporation effect is stripped of its remaining water and light impurities in the light ends column. The water free glycol mixture is then distilled in a series of vacuum towers to produce fiber grade MEG and high purity higher derivatives. The final column produces a small bottoms stream that contains heavier glycol and is usually used for fuel, but does have potential commercial value. The main problem where lot of research is going on is the selectivity of the ethylene oxide. The selectivity is low which is around 90%. The rest being the polyethylene glycol. This is a very low selectivity for a product made in such large quantities.
New synthetic paths for the glycol will make this intermediate much less important.
* From Ethylene Through Ethylene Chlorohydrin : The reaction between ethylene and hypochlorous acid yields ethylene chlorohydrin, which may be converted either directly to ethylene glycol by hydrolysis or to ethylene oxide by reaction with alkali and then to the glycol by hydrolysis. C2H4 + HOCl → CH2OHCH2Cl CH2OHCH2Cl + NaHCO3 + H2O → CH2OHCH2OH + CO2 + H2O + NaCl
Material & Utility requirement : For one ton Ethylene Glycol Ethylene 1 ton.
Sodium Hydroxide 80 lb
Chlorine 2.35 tons
Milk Of Lime 2.2 tons
24000 lb 160 kwhr.
Water 80000 gal.
Process description : To produce ethylene chlorohydrin by a continuous process, ethylene is passed under a pressure of 200 atm at 200C in to a tower. A solution of hydrated lime is then charged in to the tower, so that under the stated temperature and pressure about 28 g of ethylene per lit. of alkali results. The solution is pumped under pressure in to the mixer, where it meets a stream of chlorine at the rate of 1 mole chlorine per lit. of alkali solution. The chlorine reacted with hydrated lime to form calcium ox chloride , which is immediately decomposed to form hypochlorous acid and calcium chloride. The HOCl reacts with the ethylene in the solution to give ethylene chlorohydrin. The reaction takes place at essentially room temperature and at about 200 atm. Pressure. The solution is treated with the sodium bicarbonate solution at 70 to 800C in a closed steam jacket kettle fitted with an efficient agitator. After 4 to 6 hrs. evolution of the carbon dioxide ends, and the crude glycol solution is passed in to a vacuum still. Here under reduced , the solution is concentrated and separated from the salt by distillation.
* Direct Reaction : This procedure is at first glance the most straightforward, but really is not since practically every bond in the product molecule has to be formed. It consists of the rhodium catalyzed condensation of syngas at 3400 atm. As shown in the following equation;
2CO + 3H2 → Purified Syngas →
HOCH2CH2OH → Purified EG.
This process is reviewed by Dombek ( 1986 )
This process has the following problems, 1) Rhodium catalyst requires an extremely low sulfur syngas. 2) High pressure is needed. 3) A low rate of reaction is seen.
* Carbonization : In this process formaldehyde is reacted with more CO. This is followed by a reduction as shown. This is the oldest of the syngas EG synthesis. The process requires 2000C temperature and 700 atm of pressure. A copper oxide - magnesia catalyst is required for the reaction to carry out.
HCHO + CO + H2O → HOCH2COOH → HOCH2COOCH3 → HOCH2CH2OH
Material required : For one ton of Ethylene Glycol Formaldehyde 1300 lb
Carbon Monoxide 1250
150 lb 90 lb.
This process has the following problems : 1) The HCHO must be methanol free. 2) Syngas components have to be separated, which add to the cost of production. 3) Syngas is used as the CO source for glycolic acid formation. This separates the CO
from the hydrogen, which is used for the reduction step.
* Hydroformylation : The hydroformylation is the reaction of the formaldehyde with CO and hydrogen, followed by hydrogenation. This procedure, where HCHO is subjected to hydroformylation conditions, is discussed in a review by Dombek ( 1986 ). Normally the substrate is an olefin.
HCHO + H2 + CO → HOCH2CHO + H2 → HOCH2CH2OH
This procedure has the following problems : 1) RhCl ( CO ) [ ( C6H5 )3P ]2 catalyst is expensive and needs low sulfur content in both HCHO and syngas. 2) The form of HCHO needed is the para form or the trioxane, which are expensive. With aqueous formaldehyde , the EG yield is quite low. 3) The reaction rate is slow unless the procedure is run at high pressure ( 4000 psi )
* Reductive Hydroformylation : In this reaction, reduction and the hydroformylation are combined in one reactor. The catalyst used is Rh( CO )2 ( Acetylacetonate ) in N - Methyl pyrrolidone.
HCHO + H2 + CO → HOCH2CH2OH
This procedure has the same problems as the preceding process.
* Oxidative Coupling : As one can see from the following equation, some of the synthesis gas components have to be separated :
CO + O2 + C2H5OH → C2H5OOCCOOC2H5 + H2 → HOCH2CH2OH
The first step uses a palladium catalyst. The Pd has to be reoxidized. Copper salts are used for this , as well as alkyl nitrite.
This procedure has the following problems : 1) Syngas components must be separated, so raw material costs are high. 2) The CO has to be free of hydrogen which if present gives water, which is detrimental to oxidation. 3) Reduction of the diethyl oxalate takes extremely high pressures.
*A discussion on potential development in ethylene glycol manufacture The current basis for the manufacture of the ethylene glycol is ethylene as we have seen over. Cause up till now no alternative process can challenge the ethylene process in economic point of view and in large scale production. In future developments, the possible use of synthesis gas will have to be considered. Furthermore , in the predominant process based on ethylene, optimization of the epoxidation and following hydration and minimization of the energy requirements for the isolation of ethylene glycol from the dilute aqueous solution will be important task. However other indirect routes based on ethylene with intermediates such as ethylene glycol acetate or ethylene carbonate are also of commercial interest. The limitation in the ethylene oxide selectivity shown by the epoxidation method led to the development of processes for the oxidation in the presence of acetic acid by many firms. Ethylene is converted to glycol mono - and diacetate with up to 98%
selectivity in the first step, and hydrolyzed to ethylene glycol in the second step. Halcon, in cooperation with Arco ( Oxirane Chem ) was the first firm to use this acetoxylation of ethylene. They started up a commercial unit using TeO2 / HBr catalyst in 1978, but were forced to shut down in 1979 due to corrosion. Another area pursued by many firms is indirect hydrolysis that is ethylene oxide is reacted with carbon dioxide to form the intermediate ethylene carbonate, which is then hydrolyzed to ethylene glycol. Apart from additional process step, it has the advantages of a nearly quantitative hydrolysis of the carbonate to ethylene glycol with only a small excess of water. In a new development, Texaco has replaced the hydrolysis of ethylene carbonate with a methanol sis, leading to ethylene glycol and dimethyl carbonate. Dimethyl carbonate can then be hydrolyzed to methanol and carbon dioxide, but it is increasingly used for carbonization and methylation. Increasing interest in synthesis gas as a basis for ethylene glycol paralleled the advancement of carbon chemistry. Direct processes of CO hydrogenation to ethylene glycol as well as indirect methods based on synthesis gas dependent intermediates like methanol, methyl formate or formaldehyde have been developed. By the end of the 1940s, Du Pont had already been able to show that CO hydrogenation in aqueous cobalt salt solutions leads to ethylene glycol. In the 1970s, UCC investigated synthesis gas conversion using homogeneous rhodium carbonyl catalyst systems with numerous salt promoters and nitrogen containing Lewis bases. Ethylene glycol, 1,2 - propanediol, and glycerin can be produced in a high pressure ( 1400 - 3400 bar ) reaction at 125 - 3500C with a total selectivity of up to 70%. Both the extreme reaction conditions and the low catalyst efficiency are obstacle to practical application of this technology. Further research, including investigations by other firms of other catalyst systems ( e.g. ruthenium catalysts ), has resulted in little or no progress. In this way we can end up our discussion leading to the conclusion that there is a lot of research have to be done on the other alternative of the EG manufacturing
processes. Hence the ethylene oxide hydration process is only the best one till date on commercial level.
References : 1) Industrial Organic Chemistry By K. Weissermel, H. - J. Arpe. 2) Riegel’s Handbook Of Chemistry ( Seventh Edition ) 3) Chemical Process Analysis : Mass & Energy Balances By William Luyban & Leonard Wenzel. 4) Handbook Of Chemicals Production Processes By Robert Meyers. 5) Industrial Chemicals By W. L. Faith, Donald Keyes & Ronald Clark. 6) Industrial Organic Chemistry By Harold Wittcoff & Bryan Reuben. 7) Introduction to Industrial chemistry By Howard White. 8) Encyclopedia Of Chemical Engineering By Kirk & Othmer.