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
0.06g Rh(CO)12Acac 3.5h @ 150oC 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
0.019g Rh(CO)12Acac 5h @ 150oC
Condensation of formaldehyde
16% H2CO (aq) NaOH – zeolite 12% glycoaldehyde
o
0.33-0.8 hr 94 C
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