Ethylene is a prime raw material for petrochemicals and it is readily available at low cost and high purity. Ethylene reacts by addition with low cost materials such as oxygen, chlorine, hydrogen chloride and water, and the reaction take place under relatively mild condition and usually with high yields. Ethylene also reacts by substitution to producevinyl monomer. Derivatives of ethylene are used for the production of plastics, antifreeze, fibers and solvents. Ethylene and many ethylene derivatives are used for the production of polymers, like the formation of polyethylene and ethylene related polymer such as polystyrene, polyester and polyvinyl chloride. Ethylene oxides dominates the individual compounds produced fromethlene with ethylene dichloride, the precursor of vinyl chloride, next in quantity of ethylene utilized followed by ethyl benzene for styrene production. While polyethylene is the biggest individual compounds produced from ethylene and the others are ethanol, linear alcohol, vinyl acetate, alpha olefins and many others. The projected use for ethylene is mainly in low density polyethylene, high density polyethylene, vinyl chloride, styrene, ethylene oxide and others.

Tanya – Stephanus Sulaeman@upv.pertamina

8. PETROCHEMICALS FROM ETHYLENE

Ethylene is a prime raw material for petrochemicals and it is readily available at low cost and high purity. Ethylene reacts by addition with low cost materials such as oxygen, chlorine, hydrogen chloride and water, and the reaction take place under relatively mild condition and usually with high yields. Ethylene also reacts by substitution to producevinyl monomer. Derivatives of ethylene are used for the production of plastics, antifreeze, fibers and solvents. Ethylene and many ethylene derivatives are used for the production of polymers, like the formation of polyethylene and ethylene related polymer such as polystyrene, polyester and polyvinyl chloride. Ethylene oxides dominates the individual compounds produced fromethlene with ethylene dichloride, the precursor of vinyl chloride, next in quantity of ethylene utilized followed by ethyl benzene for styrene production. While polyethylene is the biggest individual compounds produced from ethylene and the others are ethanol, linear alcohol, vinyl acetate, alpha olefins and many others. The projected use for ethylene is mainly in low density polyethylene, high density polyethylene, vinyl chloride, styrene, ethylene oxide and others.

8.1. ETHYLENE OXIDE EO CH2-O-CH2

Production.

EO is produced by exothermic by air or oxygen oxidation of gas phase ethylene over a silver Ag2O catalyst in a very short time (second).

2 CH2=CH2 + O2 → 2 CH2-O-CH2

The concominant exothermic reaction is

CH2=CH2 + 3 O2 → 2 CO2 + 2 H2O

Ethylene oxide selectivity is improved when the reaction temperature lowered and the conversion of ethylene is decreased. The use of high selectivity catalyst and control of temperature are key factors in succesful production of ethylene oxide. The development of high selectivity catalyst is obtained by incorporating alkali metal cations in, on or under the silver particles on the alumina. All of Shell, Halcon and ICI patented this kind of high selectivity compound catalyst. There are many representative process for both ethylene oxide and ethylene glycol production.

With air oxidation the reaction is carried out in single stage main reactor. The oxidation reaction is controlled in a manner similar to that used for air oxidation. Most of the absorber outlet gas is recycled to the reactor and the rest is treated by potassium hydroxide solution to remove CO2 and the recycled again to the reactor. The oxygen process is approximately more economical than the air process.

Uses.

Ethylene oxide reacts exothermically, especially in the presence of catalyst, with all compounds which have a labile hydrogen atom, such as water, alcohols, amines and organic acids. This reaction introduces the hydroxyethyl group –CH2-CH2OH into various type of compounds, like

R-CH2OH + CH2-O-CH2 → R-CH2O-CH2-CH2OH

The addition of the hydroxyethyl group increases the water solubility of the resulting compounds. Further reaction with ethylene oxide produces polyethylene oxide derivatives. The number of moles of ethylene oxide determine the water solubility and the surface activity of the product.

The uses of ethylene oxide demanded mainly are ethylene glycol and surfactants. Ethylene glycol is mainly used for antifreeze and polyester, and there are two major types of surfactants, alkyl phenol ethoxylates non-biodegradable or hard surfactants and linear alcohol ethoxylates biodegradable or soft surfactants. Other compounds from EO are the higher glycols, glycol ethers and the ethanolamines, and less important product are tertiary alkyl mercaptoalcohols, glycol acetate and diacetate, beta phenyl ethyl alcohol and hydroxyethyl cellulose. Ethylene oxide is also used as a cold sterilant for bacteria, spores and viruses and with CO2 for controlling wievils in nuts. It is an effective insecticide and its also used as an intermediate for other insecticides as well as for fungicides, explosives and resins.

8.1.1. Ethylene glycol EG HOCH2-CH2OH

EG is essentially produced by the hydration of ethylene oxide. It also can be produced directly from ethylene by acetoxylation – the Oxirane process, or oxychlorination – the Teijin process. The other process to produce EG is from syn-gas by direct synthesis process.

From ethylene oxide.

The oxide ring, epoxide ring, is readily opened by water in the presence of hydrogen ions (0.5 – 1% H2SO4 catalyst).

CH2-O-CH2 + H2O H+→ HOCH2-CH2OH

This is a liquid phase process where di- and triethylene glycol ethers are formed, which is not an economics burden on the monoglycol. They have many applications with the most important being water based coatings. The tri-ethers are paramount in the brake fluid market.

From ethylene by acetoxylation.

The production of EG is carried out in two steps. The first step is the catalyzed liquid phase oxidation of ethylene in acetic acid to a mixture of mono and diacetates of ethylene glycol over TeO2 (promoted by Br compounds) catalyst.

Selengkapnya :