Huntsman Chemicals Styrene Plant, West Footscray, Australia


Huntsman Chemical Company Australia's (HCAA) styrene plant in West Footscray, Australia, produces industrial chemicals such as styrene monomer, polystyrene and expandable polystyrene (EPS).

"Known as Monsanto Australia, the plant was purchased by Consolidated Press Holdings in 1988 and renamed Chemplex. In 1993, 50% of the plant was sold to Huntsman Chemical."

These chemicals are used for producing paints, latex, car seats, building materials and packaging materials. HCAA is part of the Huntsman Base Chemicals and Polymers division.

The West Footscray site has an area of 100 acres. In September 2009, Huntsman announced closure of the styrene plant after finishing an internal review.

The decision was taken as the products manufactured at the plant represented less than 2% of the company's global sales in 2008. The plant incurred a loss of $24m in 2008.

Operations at the styrene plant were ceased in the first quarter of 2010. About 325 jobs (200 Huntsman employees and 125 contractors) were lost because of the closure. Huntsman incurred closure costs amounting to $63m. Demolition of the facility commenced in May 2010.

The plant has undergone several modifications and closures since its establishment in 1941. Since the 1980s, many of the operating units had been shut down for reasons including economic recession.

The most significant of the closures was the phenol plant in 2005, which began its operations in 1968.

Background

The West Footscray plant was originally owned by Monsanto to produce pharmaceutical chemicals. It later started manufacturing phenol chemicals and benzene chemicals, before shifting to styrene-based chemicals.

Known as Monsanto Australia, the plant was purchased by Consolidated Press Holdings in 1988 and was renamed Chemplex. In 1993, 50% of the plant was sold to Huntsman Chemical.

Plant design

In 2006, the site had several individual manufacturing plants including the styrene plant, polystyrene plant, EPS plant, phenol formaldehyde resins plant, ground resins plant, polyester resins plant and gelcoat resins plant.

The styrene plant and polystyrene plant operate continuously and the rest manufacture products in batch processes.

The styrene plant consists of several units - a storage tank farm, ethylene plant, litol (benzene) plant, alkylation (ethylene benzene) plant, alkylation distillation plant, dehydrogenation (styrene monomer) plant and dehydrogenation distillation plant. The plant also has cooling towers, fire water tanks, pumps, a sprinkler system, boiler house, laboratories, maintenance workshops, warehouses, effluent treatment plant and offices.

The tank farm consists of large steel tanks bordered by concrete bunds used to store liquid raw materials - benzene and BTX. Vapours ejected during unloading of raw materials from road tankers are collected by two carbon beds in the tank farms. The other tanks are also part of the tank farm. They are used to store styrene monomer and other intermediate liquids.

Water from the cooling tower is used for distillation processes in various plants. The water is cooled in a large conventional air-cooling tower and treated to arrest the build up of algae. The boiler house supplies steams at different temperatures to heat the re-boilers in the distillation columns of the distillation plants. It also contains a condensate header to gather condensed steam.

Process technology

The ethylene plant produces ethylene in a thermal cracker through a steam cracking process. Gaseous ethane is transported to the plant through a pipeline from Esso Long Island Point.

The gaseous ethane flows inside the thermal cracker where it is heated for a short period at a temperature of 750-950°C. On heating, ethane gets partially converted into ethylene and hydrogen. The reaction is controlled by the addition of hydrogen sulphide.

The ethylene produced is purified in a compression plant. After being cleaned with water and caustic to remove acid gas and sulphides, ethylene is produced by cryogenic separation.

The ethylene produced is directly sent to the alkylation plant. Any excess ethylene that cannot be used in the alkylation plant is sent to the flare. The cryogenic separation also produces hydrogen which is used in the litol plant.

Dealkylation

The main chemical process in the styrene plant is dealkylation which is carried out in the litol plant. The raw material used is BTX purified into animation-grade benzene. Toluene and xylene in BTX are transformed into benzene and methane using hydrogen supplied by the ethylene plant.

The conversion is carried out through a reaction in two reactors at high temperature and pressure. Methane produced from the reaction is separated from benzene which is distilled in two distillation columns. The benzene produced is then transferred to the alkylation plant for alkylation process.

Alkylation and dehydrogenation

The alkylation process, a variation of the Friedel-Crafts reaction, is carried out in a chemical reactor. The process involves addition of an alkyl group to another molecule.

"Huntsman Chemical Company Australia's (HCAA) styrene plant in West Footscray, Australia, produces industrial chemicals such as styrene monomer, polystyrene and expandable polystyrene (EPS)."

Gaseous ethylene from the ethylene plant and liquid benzene from litol plant are combined to form ethylbenzene. Aluminium chloride is added to form a complex with poly ethyl benzene which is circulated as the catalyst for the reaction.

The alkylation process produces a mixture of benzene, ethylbenzene and small amounts of poly ethylbenzene. This mixture is transported to the alkylation distillation plant which contains four distillation columns.

Three columns of the plant contain direct fired re-boilers and the benzene drying column contains a steam-heated re-boiler. The final product from the plant is a pure ethylbenzene which is sent to the dehydrogenation plant.

The final process in the styrene plant is the conversion of ethylbenzene to styrene using the dehydrogenation process in the dehydrogenation plant.

The process involves an endothermic dehydrogenation reaction which is carried out in a large single fixed bed catalytic reactor.

Following the reaction, distillation is carried out in the distillation plant. In the distillation plant, styrene is isolated from ethylbenzene in a tall, continuously packed distillation tower.

Two other columns are also part of the distillation tower. They operate in a vacuum. The separation process is difficult due to close boiling points of ethylbenzene (136°C) and styrene (145°C).

To stop self polymerisation of styrene during the distillation process an inhibitor is added to the mixture of ethylbenzene and styrene before it enters the column.

The pure styrene produced from the distillation process is sent to the tank farm. The ethylbenzene resulting from the distillation process is recycled to the alkylation plant.

Feedstock used

The primary raw materials used in the styrene plant are benzene and BTX (benzene, toluene and xylene). HCCA imports about 80% of these raw materials and exports one-third of the styrene manufactured.