Styrene monomer

Styrene monomer is one of the derivatives of benzene. Styrene monomer is an oily, colorless liquid with a sweet smell, which may turn yellow over time. Figure (1) shows the molecular structure of styrene monomer.

Fig (1): Molecular structure of styrene monomer

Styrene is present in small amounts in some foods, including some plants such as cinnamon, coffee beans, henna trees, and peanuts. Styrene monomer is usually converted or polymerized into other materials, the following is an example of the key derivatives of this compound:

• Expandable polystyrene (EPS)
• Acrylonitrile Butadiene Styrene (ABS)
• Styrene Butadiene Rubber (SBR)
• Unsaturated polyester resins
• Styrene Butadiene Latex (SBL)
• High-impact polystyrene (HIPS)
• General-purpose polystyrene (GPPS)

Industrial methods of styrene monomer production

During the Second World War, the use of styrene monomer was developed at the same time as the use of chemicals that can be obtained from oil grew and it was able to open its place among industries.

The production of styrene through dehydrogenation began in 1930 and was first commercially produced on an industrial scale in 1934 by the Dow Company. This action attracted attention as one of the most important industrial processes in the world for the preparation of synthetic rubber by the producers of polymer materials.

Styrene production plant in Iran was designed in 2008 in Pars Petrochemical with the technical knowledge of Polimeri Europa company and by snampro getti companies and its business partner (Sazeh Consulting Engineers).

According to the explanatory report of Petrochemical Management in 2016, the annual nominal production capacity reaches 600 thousand tons.
Styrene monomer is produced in industrial methods using the following processes:

• Ethylbenzene process

A significant amount of styrene monomer is produced from ethylbenzene, so that it can be said that all the ethylbenzene produced in the world is used as a feedstock for styrene production. In this process, styrene monomer is produced through the reaction between benzene and ethylene in the presence of aluminum chloride catalyst. It is worth mentioning that nowadays in the production of this material, this catalyst has been replaced with zeolite.

• Dehydrogenation process

About 80% of styrene is produced from the dehydrogenation of ethylbenzene. This reaction is achieved by using superheated steam (up to 600°C) on iron (III) oxide catalyst. The reaction is very exothermic and reversible and its efficiency is 88-94%.

• The reaction of benzene and ethane

Another way to produce styrene involves the reaction of benzene and ethane. Ethane together with ethylbenzene enters a dehydrogenation reactor with a catalyst capable of simultaneously producing styrene and ethylene. The dehydrogenation effluent is recycled in the alkylation unit after cooling and separation.

• Styrene Monomer Market Review

In terms of demand, Northeast Asia is a major consumer of styrene monomer, accounting for 55% of global consumption. In 2019, about 34% of styrene in Northeast Asia was consumed in China. In 2013, the global demand for this compound was reported to be more than 27 million tons.

According to these reports, the global market of this material in 2019 was equal to 41,690 million dollars and it is expected to grow at a rate of 1.25% by 2025 and reach 45,280 million dollars. According to Styrene Monomer Marketing Strategy Analysis Report 2020, Top Manufacturers are announced as follows:

• Shell
• SADAF
• FCFC
• Total
• Lyondell Basell
• Styrolution
• Pars Petrochemical
• LG Chemical
• Asahi Kasei
• Jubail Chevron
• Trinseo
• Americas Styrenics

Application of styrene monomer

• Plastic industry: Light, flexible plastics are prepared from polystyrene obtained from styrene monomers, which are used in the production of disposable containers.
• Automotive industry: By combining styrene and butadiene, it is possible to produce styrene butadiene rubber, which is used to make car tires.
• Pesticide: Styrene is used as an emulsifier in the production of various insecticides.
• Perfume Industry: Very small amounts of styrene are used as an intermediate compound in the perfume industry.
• Pharmaceuticals: Chloromethylation of styrene is used to produce cinnamyl chloride, which acts as a painkiller and is also used in anesthesia.
• Polymer industry: Styrene with materials such as acrylonitrile and butadiene forms copolymers such as acrylonitrile butadiene styrene, which is a plastic with high endurance and is used in engineering.
• Construction industry: In construction, styrene butadiene latex is used to produce floor coverings and sound and thermal insulation.

Investigating the safety issues of styrene monomer

Extensive health and safety studies have been conducted by manufacturers and researchers regarding the safety of styrene monomer, and the results of these studies show that this material is highly safe, and for this reason, this material is used in styrene-based plastics.

Styrene should be stored in closed containers and in a place with proper ventilation. Because the accumulation of its vapors will cause ignition. Its storage container can be glass, metal or plastic. After every month of storage, the degree of polymerization should be checked and if necessary, polymer inhibitor should be added.

The use of safety gates is installed at the top of the stairs and any other openings to ensure the safety of the operator at all times. Figure (2) shows an example of a safety gate related to a styrene unit.

Fig (2): Safety gate related to a styrene unit

ANSI guidelines state that in industrial units where styrene is used, eyewash showers must be within 10 seconds (16.8 meters) of contaminants or hazardous materials. Eye wash stations should be placed on a horizontal surface without any obstructions. Therefore, in our safety references, it is recommended to install a standard combined shower/eyewash unit that can be easily placed in any work environment. Figure (3) shows a shower equipped with an eyewash near a styrene unit.

Fig (3): A shower equipped with an eye wash near a styrene unit

Styrene monomer storage conditions

Styrene monomer should be stored in well-ventilated places away from direct sunlight, ignition sources and other heat sources. The temperature of the styrene monomer must be monitored and controlled to prevent the product temperature from exceeding 30 degrees Celsius. Due to its various sources, styrene is considered a “hazardous chemical”, especially if it comes into contact with the eyes, skin, ingestion, and inhalation.

Some regulatory bodies have assigned hazard classifications to styrene monomer, but it is important to note that these categories and lists are related to the monomer and not to the products produced from it. These monomer hazard classifications do not reflect the hazards of using styrene-based polymers or end-use products. Figure (4) shows the safety label of styrene monomer.

Fig (4): Styrene monomer safety label

Effect of styrene monomer on the environment

This valuable monomer is flammable and toxic. It has low vapor pressure and high refractive index. It is chemically reactive and readily undergoes polymerization (by heat, light, or peroxide catalysts). Polymerization leads to exothermic heat (17.8 kcal/mol). Therefore, it can have many effects on the environment contaminated with this substance.

Pure styrene monomer is a colorless and flammable transparent liquid that boils at a temperature of 145 degrees Celsius and freezes at a temperature of -30.6 degrees Celsius. Also, the vapor of this flammable liquid can explode in the air. This material is highly flammable. Hearing loss has been observed in animals exposed to very high concentrations of styrene. It also causes liver problems.

In order to prevent styrene monomer from infiltrating the ground and causing risks due to its infiltration into underground water pools, leak containment pans are used at the operation and loading site, and this is an essential issue of the equipment in the overall safety of the production site and environmental protection. Figure (5) shows an example of these pans in a styrene monomer loading area.

Figure (5): Safety space to prevent styrene from leaking to the ground in a loading area

Dangers of styrene monomer for humans

In fact, the evidence shows that styrene is not harmful to people and its low presence does not cause major problems in the workplace and in daily life. This conclusion has been supported by many prestigious international groups and regulatory organizations, including the European Union, the Harvard Center for Risk Analysis, the US FDA and Health/Environment Canada.

Small amounts of styrene are naturally present in a variety of foods such as fruits, vegetables, nuts, beverages, and meats. Small amounts of styrene can be transferred from styrene-based packaging to food. Evidence shows that styrene is not harmful in the amounts that people are exposed to either at work, as consumers, or in everyday life.

A large number of workers in the plastics industry are exposed to air contaminated with styrene, and skin contact with styrene when working with liquid styrene leads to problems. The most common health problems in workers exposed to styrene include nervous system disorders. These health effects include changes in vision, fatigue, feeling drunk, concentration and balance problems.

Harms that this substance may have for any person exposed to this substance include skin, eye and upper respiratory tract irritation. Acute exposure may cause adverse effects in the gastrointestinal tract.

Chronic exposure affects the central nervous system, leading to the following symptoms:

• Depression
• Headache
• Fatigue
• Weakness

This substance is slightly toxic to the nervous system if ingested or inhaled. In direct contact with the skin and eyes, it causes irritation in that position. It has been mentioned in some studies that it can be fatal if inhaled or swallowed.

According to several sources, styrene is known as a “carcinogenic” substance and causes problems if it comes into contact with the eyes, skin, swallowing and inhalation. Styrene is largely metabolized to styrene oxide in the human body. Styrene oxide is toxic, mutagenic and possibly carcinogenic.

Styrene oxide is subsequently hydrolyzed to styrene glycol by the enzyme epoxide hydrolase in vivo. But as noted earlier, the US Environmental Protection Agency does not have a carcinogenic classification for styrene, while the National Toxicology Program of the US Department of Health and Human Services has determined that styrene is considered to be carcinogenic to humans.

Styrene monomer and global warming

Pure styrene turns into polystyrene by itself without the need for external initiators. This is known as autopolymerization. It autopolymerizes at a rate of 2% per hour at 100 degrees Celsius and faster at higher temperatures. The polymerization reaction is exothermic. Hence, there is a real risk of thermal runaway and explosion.

The autopolymerization reaction can only be controlled by the continuous addition of polymerization inhibitors. The polymerization reaction is exothermic, so there is a real risk of fire and explosion. The autopolymerization reaction can only be controlled by the continuous addition of polymerization inhibitors. Because the polymerization reaction is a reaction with heat, there is a risk of explosion and fire.

The autopolymerization reaction can only be controlled by the continuous addition of polymerization inhibitors.

Styrene monomer is typically loaded into railcars or tank trucks via stainless steel loading arms or chemical hoses with flanged end connections. The arm or hose has a top inlet with a check valve to ensure it is self-draining after use and is supported along the length of the mechanical loading arm to improve handling. This arm is known as the bypass arm. A liquid arm and a vapor arm can be installed for draining, or both liquid and vapor hoses can be installed on a bypass arm.
For unloading, a rigid stainless steel loading arm with the following seals is usually used:

• Fluorocarbon
• PTFE
• Viton