Ethylene Glycol Represented by the Empirical Formula CHO Is a Common

Warm-up project on Ethylene Glycol for ECH 6412

Introduction and Uses3,4

Ethylene glycol (EG) represented by the empirical formula C2H6O2 is a high volume chemical, with a production capacity of over million pounds annually in the US alone. It is a clear, colourless and odourless liquid at room temperature. It is hygroscopic in nature & has a sweet taste. It dissolves in water and is miscible in alcohol. Its molecular formula can be represented as

Other names for ethylene glycol are 1,2-dihydroxyethane, 1,2-ethanediol, 2- hydroxyethanol, ethylene alcohol, glycol, and ethylene dihydrate. The CAS registry # for EG is 107-21-1

It has a wide range of applications some of which are:  As anti-freeze for automotive coolants  As de-icing agents for aircrafts, runways and taxiways.  As a heat transfer medium due to its ability to hold large amount of heat before boiling.  As an industrial drying agent due to its hygroscopic nature.  As semiconductor developers  As rubber manufacturing softeners  As intermediates in polymers – for resinous products, polyester fibres like Dacron and terylene, esters and ethers  As printing solvents in lithography  In the paint & plastics industries where it is used as a solvent for preparing printers’ inks, stamp pad inks, and inks for ball point pens, and as a softening agent in cellophane  As an ingredient in hydraulic brake fluids of automobiles  In fire extinguishers as a stabiliser to the foam  In pharmaceuticals preparations like skin lotions and powders as a substitute for glycerine.

According to a report from the Agency For Toxic Substances & Disease Registry (ATSDR) approximately 39% of all ethylene glycol produced in the United States, is used to make antifreeze, 29% is used to make polyester fibres, 26% is exported, and 23% is used to make polyethylene terephthalate (PET) bottles, films, resin products, and in other miscellaneous industrial applications.

Process alternatives

There have been a number of routes taken by the industry to manufacture EG. Some of them are:

 Direct production from synthesis gas2  Carbonylation of formaldehyde2  Hydroformylation of formaldehyde2  Reductive hydroformylation of formaldehyde2  Condensation of formaldehyde2  Redox process2  Hydration of ethylene oxide1

Direct production from synthesis gas

45g THF 3400atm CO/H2 9.8g EG

o 0.52g Rh(CO)12Acac 4.5h @ 230 C 1.5g Propylene glycol 1.5g Glycerine

According to Kollar processing costs of the syngas are high due to the slow rate of reaction and material costs.

Carbonylation of formaldehyde 1M H2CO 900atm CO 98% Glycolic acid

1M H2CO + 0.1M HCl 2M HOAc 1h @ 170oC

This is one of the oldest processes adopted by Du Pont , which produces glycolic acid which was then converted to methyl glycolate, which was then hydrogenated to EG at high pressures.

Hydroformylation of formaldehyde

1g Paraformaldehyde 1230psi 1:1 CO/H2 0.26g Glycoaldehyde 10ml N-methyl pyrrolidone 0.016 EG

o 0.06g Rh(CO)12Acac 3.5h @ 150 C 0.08 MeOH

Reductive hydroformylation of formaldehyde

0.5g Paraformaldehyde 4350psi 2.2:1 H2/CO 0.43g EG 5g N-methyl pyrrolidone 0.3g MeOH

o 0.019g Rh(CO)12Acac 5h @ 150 C

Condensation of formaldehyde

16% H2CO (aq) NaOH – zeolite 12% glycoaldehyde 0.33-0.8 hr 94oC

Redox process

2-10 % Methanolic Formaldehyde ROOR 300psi 6 – 8 % EG 0.16 - 0.33 h 140 – 160 oC

The redox reactions can be carried out in either vapour or liquid phase. The vapour phase reactions do proceed rapidly, thus offering kinetic advantages. Hydration of ethylene oxide (EO)

This process is by far the latest process, which is carried out using a reactive distillation setup with a typical reboiler and condenser. The main reaction is non- isomolar, exothermic and irreversible and is as follows

C2H4O + H2O  C2H6O EO water EG

The conventional unit of a reactor inline with a series of separation units has its own advantages but the reactive distillation setup definitely scores well over the reactor- separator system by cutting down in the number of equipments involved and also helps the chemistry by separating the EG produced from the EO so as to minimize the formation of di- and tri- glycol. Okasinski et al1 have modelled and simulated a reactive distillation setup and have shown that such a system can be run effectively and can be made a viable processing alternative.

The top of the column could operate at total reflux. Thus allowing direct vaporisation of the liquid through the heat of reaction, which is generally removed from the condenser unit at the top of the column. The condensed vapours from the top of the column are refluxed totally to the reactive stage, below which is the stripping section of the column is responsible for separating the EG from the EO. Although the feed ratio of water/EO is pretty much stoichiometric, the large relative volatility difference ensures the excess of water/EO in the reactive stage.

Thus with the help of simulation techniques Okasinski et al have been able to find the optimal reflux ratios, operating conditions in terms of temperature, pressure, feed flows and also carried out energy balance calculations. They did find that the conventional system used half as much power as the reactive distillation unit but the equipment costs more than made up for the balance. Thus process modelling and simulation is an extremely important tool for any researcher because it does save a lot of time, money and effort by actually running the pilot plants. It also gives us a good idea of the system under study and can help out in addressing our concerns namely in terms of the environment, safety, economic viability, quality of product that is part of the processes.

References and links 1. Okasinski, M.J.; Doherty M.F.; Ind. Eng. Chem. Res., Vol. 37, No. 7, 1998 2. Kollar J.; Chemtech, Aug.1984, 504 -511 3. http://www-personal.engin.umich.edu/~gordonk/module3.html 4. http://www.atsdr.cdc.gov/toxprofiles/tp96-c4.pdf