History Commercial production of ethylene oxide dates back to 1914 when
BASF built the first factory which used the chlorohydrin process (reaction of ethylene chlorohydrin with calcium hydroxide). The chlorohydrin process was unattractive for several reasons, including low efficiency and loss of valuable chlorine into
calcium chloride. More efficient direct oxidation of ethylene by air was invented by Lefort in 1931 and in 1937
Union Carbide opened the first plant using this process. It was further improved in 1958 by Shell Oil Co. by replacing air with oxygen and using elevated temperature of and pressure ().
Chlorohydrin process of production of ethylene oxide Although the chlorohydrin process is almost entirely superseded in the industry by the direct oxidation of ethylene, the knowledge of this method is still important for educational reasons and because it is still used in the production of
propylene oxide. A similar production method was developed by Scientific Design Co., but it received wider use because of the licensing system – it accounts for 25% of the world's production and for 75% of world's licensed production of ethylene oxide. A proprietary variation of this method is used by Japan Catalytic Chemical Co., which adapted synthesis of both ethylene oxide and ethylene glycol in a single industrial complex. A different modification was developed Shell International Chemicals BV. Their method is rather flexible with regard to the specific requirements of specific industries; it is characterized by high selectivity with respect to the ethylene oxide product and long lifetime of the catalyst (3 years). It accounts for about 40% of global production. : O2 + Ag → Ag+O2− This species reacts with ethylene : Ag+O2− + H2C=CH2 → (CH2CH2)O + AgO The resulting silver oxide then oxidizes ethylene or ethylene oxide to CO2 and water. This reaction replenishes the silver catalyst. Thus the overall reaction is expressed as : 7 CH2=CH2 + 6 O2 → 6 (CH2CH2)O + 2 CO2 + 2 H2O and the maximum degree of conversion of ethylene to ethylene oxide is theoretically predicted to be 6/7 or 85.7%, The catalyst for the reaction is metallic silver deposited on various matrixes, including
pumice,
silica gel, various
silicates and
aluminosilicates,
alumina, and
silicon carbide, and activated by certain additives (
antimony,
bismuth,
barium peroxide, etc.). The process temperature was optimized as . Lower temperatures reduce the activity of the catalyst, and higher temperatures promote the complete oxidation of ethylene thereby reducing the yield of ethylene oxide. Elevated pressure of increases the productivity of the catalyst and facilitates absorption of ethylene oxide from the reacting gases.
Process overview The production of ethylene oxide on a commercial scale is attained with the unification of the following
unit processes: • Main reactor • Ethylene oxide
scrubber • Ethylene oxide de-sorber •
Stripping and
distillation column • CO2 scrubber and CO2 de-scrubber
Main Reactor: The main reactor consists of thousands of catalyst tubes in bundles. These tubes are generally long with an inner diameter of . The catalyst packed in these tubes is in the form of spheres or rings of diameter . The operating conditions of with a pressure of prevail in the reactor. To maintain this temperature, the cooling system of the reactor plays a vital role. With the aging of the catalyst, its selectivity decreases and it produces more exothermic side products of CO2.
Ethylene oxide scrubber: After the gaseous stream from the main reactor, containing ethylene oxide (1–2%) and CO2 (5%), is cooled, it is then passed to the ethylene oxide scrubber. Here, water is used as the scrubbing media which scrubs away majority of ethylene oxide along with some amounts of CO2, N2, CH2=CH2, CH4 and
aldehydes (introduced by the recycle stream). Also, a small proportion of the gas leaving the ethylene oxide scrubber (0.1–0.2%) is removed continuously (combusted) to prevent the buildup of inert compounds (N2, Ar, and C2H6), which are introduced as impurities with the reactants.
Ethylene oxide de-sorber: The aqueous stream resulting from the above scrubbing process is then sent to the ethylene oxide de-sorber. Here, ethylene oxide is obtained as the overhead product, whereas the bottom product obtained is known as the
glycol bleed. When ethylene oxide is scrubbed from the recycle gas with an aqueous solution, ethylene glycols (viz. mono-ethylene glycol, di-ethylene glycol and other poly-ethylene glycols) get unavoidably produced. Thus, in-order to prevent them from building up in the system, they are continuously bled off.
Stripping and distillation column: Here, the ethylene oxide stream is stripped off its low boiling components and then distilled in-order to separate it into water and ethylene oxide.
CO2 scrubber: The recycle stream obtained from the ethylene oxide scrubber is compressed and a side-stream is fed to the CO2 scrubber. Here, CO2 gets dissolved into the hot aqueous solution of potassium carbonate (i.e., the scrubbing media). The dissolution of CO2 is not only a physical phenomenon, but a chemical phenomenon as well, for, the CO2 reacts with potassium carbonate to produce potassium hydrogen carbonate. : K2CO3 + CO2 + H2O → 2 KHCO3
CO2 de-scrubber: The above potassium carbonate solution (enriched with CO2) is then sent to the CO2 de-scrubber where CO2 is de-scrubbed by stepwise (usually two steps)
flashing. The first step is done to remove the hydrocarbon gases, and the second step is employed to strip off CO2.
World production of ethylene oxide The world production of ethylene oxide was in 2009, SRI Consulting forecasted the growth of consumption of ethylene oxide of 4.4% per year during 2008–2013 and 3% from 2013 to 2018.),
Saudi Basic Industries ( in 2006),
BASF ( in 2008–2009),
China Petrochemical Corporation (~ in 2006 ==Applications==