Styrene production plant
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Published: Mon, 5 Dec 2016
Project & Process
The aim of this paper was to design a styrene plant that produces 30,000 kg/h of styrene using the catalytic dehydrogenation of ethylbenzene (EB). This report determined whether the dehydrogenation of EB is an effective (both chemically and economically) and viable method of producing styrene. The paper sought to determine this by analysing the production process, cost of the building and running a styrene plant, and the chemistry involved.
Materials Hazard Data
Raw Materials, Intermediates, Products & By-Products
Ethylbenzene is harmful, a flammable liquid and is a severe eye irritant. It is the reactant used in the main process of the plant. It dehydrogenates to form styrene as the main reaction, but other side reactions form toluene and benzene. This chemical would cause problems with fires on site. ethylbenzene should be kept away from the other flammable materials in process, to avoid the risk of fire.
Styrene is a flammable liquid, mildly toxic, harmful when inhaled ( for example it may cause headache, nausea, dizziness, muscle weakness; produces central nervous system depression; irritates nose, lungs and throat.), and it moderates irritation to eyes and skin. Styrene is confirmed as a carcinogen. It should be produced by the dehydrogenation of ethylbenzene. This chemical can produce major injuries if a fire starts on site. The best condition for this chemical to be stored is on site for as short a time as possible, before being transported away by the tanker. Due styrene is flammable liquid it should be stored away from any other flammable substances such as ethylbenzene, toluene and extra care should be taken to inform the fire services of the danger, to ensure it is dealt with it promptly and properly. Pressure can build in component and they need to be checked for weakened points.
Toluene is very flammable, can cause irritation to skin and is harmful if inhaled. It is formed as one of the side reactions in the reactor, when styrene reacts with the hydrogen formed. Loss of containment would cause problems, due to the additional fire risk. The chemical should be kept away from flammable chemicals.
Benzene can cause cancer, is toxic, very flammable, irritating to eyes and skin. It is harmful for example it can cause lung damage if swallowed. Benzene is formed in the process by the reaction of ethylbenzene and hydrogen. Benzene is the most violent chemical in this process. Loss of containment could have very serious off-site effects. Cleaning up of any spills would be a problem, and extra care must be taken into account to ensure that people are trained to do so, as this chemical can destroy the environment.
Steam is used as a power in order to keep the reaction going, and thus does not participate in any chemical reaction itself. It is not toxic, however large amount are required, and care must be taken that this water is taken from a suitable source. The water is reusable in this process. The risk of loss of containment depends greatly on the pressure of the steam, excluding the temperature, it should be relatively low risk.
Emissions from other facilities
This would need to be completed when it is known what is being released by facilities near by.
KOH is corrosive and harmful if swallowed. It catalysts the dehydrogenation of ethylbenzene and reduces the energy required for this reaction.
Fe2O3 is non toxic, has no risk to it and should not be considered as a hazardous chemical. It is used as part of the catalyst for the main reaction of dehydration of ethylbenzene. Loss of containment shouldn’t cause many problems, and neither should storage or transport. There are no special handling problems with this chemical.
Tertiary butyl catchol is toxic to aquatic organisms, can cause skin sensitisation and is an irritant. It lowers the amount of tars the styrene forms from polymerisation. Disposal of this substance would be difficult, and care must be taken to dispose of it in a way that is safe for aquatic organisms. Relatively small amounts of it are needed, as it is just an addition to the styrene, and doesn’t take part in any of the main reaction.
The services required for this chemical plant are fresh water, electricity and gas. Some of the gas will be provided in the plant itself by the combustion of the light reaction products, but gas will still be provided.
Principal Materials of Construction
Materials encountered during construction/demolition
i. Important physical and chemical properties
ii. Significant chemical reactions
iii. Materials toxic, reactive or severe Environmental impact
iv. Estimates of inventory
v. Off site effects of Loss of Containment
vi. Means of handling and storage
vii. Special handling problems
Environmental Impact Statement:
As chemical engineers; it is our duty to ensure that pollution is kept to a minimum where safety of the environment and natural habitats are key priorities by safe and appropriate means of containment and disposal of all waste and effluents involved in the manufacture of styrene.
Other Environmental Considerations:
The following identifies how the product (styrene) is going to be stored, controlled and monitored:
Problem/Harm to environment: Mildly toxic, flammable, irritive to eye, inhalation may cause headache, nausea and dizziness.
Means of Containment: As table 1 indicates; styrene would be best stored in Ny – nylon, PE – polyethylene, SS – stainless steel or TF- Teflon containers. A thick container of this material would be most appropriate to store styrene as it offers “only slight changes in mass or dimensions” of styrene. Hirst (2002, p.90).
Controlling and Monitoring: when exposed to styrene, wear protective clothing such as long overalls and thick appropriate gloves to avoid direct contact with the product.
Additional safety precautions:
o All clothes which have been in contact with product should be washed and rinsed immediately.
o Air ventilates in all rooms to remove any harmful vapour.
This table identifies all by products and wastes produced during the manufacture of styrene and offers reasonable solutions as to how they can be disposed of:
Health & Toxicology
Occupational Health Statement
Statutory exposure limits
Specific Requirements for Design
Transport And Siting
Possible Modes Of Transport For Styrene Production:
Due to the hazardous nature of the materials that we are going to be handling in order to produce styrene we have to undergo various safety precautions whilst transporting the materials.
Because of the flammability hazard (in certain circumstances) and the unpleasant smell, all loading/unloading activities should preferably be carried out, having regard to the prevention of the ignition sources and styrene vapour emissions in the working area.
An inspection of the transport equipment should be carried out by the loading terminal staff before, during and after loading. The inspection list detailed inAppendix 5is recommended for use.
Previous Cargoes And Cleanliness
A tank that carries Styrene Monomer should not have carried the following substances as any of the last two cargoes:
§ Caustic soda
§ Pyrolysis gasoline
§ Fuel oils
§ Lube oils
Tanks to be loaded with Styrene Monomer should not be cleaned with materials which are reactive with Styrene Monomer or TBC, or cause increased colour, odour or a chloride problem. Salt water should never be the last wash because of possible chloride contamination.
Because of the effect of the application of heat to styrene, steam cleaning of adjacent tanks to compartments which contain styrene or styrene residues is strictly not allowed.
Facilities using styrene should have developed and implemented a comprehensive spill prevention and emergency response plan.
This plan should address:
1. Spill detection methods,
2. Emergency notification procedures,
3. Community contacts for notification and advice on evacuation needs,
4. Fire prevention and protection,
5. Provisions for spill containment/clean-up,
6. Environmental protection,
7. Compliance with applicable local regulations or laws.
Effect of Loss of Containment on Occupied Buildings
Potential Effect From Existing Plants
Iit is only slightly soluble in water (approx. 300 ppm at ambient conditions) and consequently the acute hazard of spilled styrene will be very limited for most aquatic species. However styrene may cause tainting (unpleasant taste) in food from aquatic organisms exposed to low environmental concentrations. According to the Standard European Behaviour Classification (Bonn Agreement) styrene is classified as a “floater evaporator”.
Styrene is a monocyclic alkenyl aromatic compound with a molecular weight of 104. Being rather volatile and having a flash point of 32 oC, styrene is classified as a flammable substance, which in use may form flammable/explosive vapour-air mixtures. Despite its high boiling point, styrene will eventually end up in the air.
Short-term exposure to styrene in humans results in respiratory effects, such as throat irritation and lung constriction, irritation to the eyes, and neurological effects such as dizziness (see Section 3 “Health Aspects” for more details). To date styrene is classified in the EU as harmful by inhalation, irritating to the eyes and to the skin
Very low concentrations of styrene vapour will react with bromine and with chlorine in sunlight to form an extremely potent lachrymatory agent. (causes tears to form, irritation and can even lead to blindness!!!)
Conformance With Company Policies
Company policies concerning Health, Safety and the Environment:
1. Smoking is prohibited in all areas of the premises; both indoors and outdoors and in any other enclosed spaces. Smoking is only permitted in a specified location at a safe distance from the facility and all equipment.
2. Food and drink should only be consumed in dining areas and all employees must thoroughly wash their hands prior to handling food.
3. Fire extinguishers must be present in all parts of the premises. One should be in every room/corridor or other separated enclosure. It must be clearly visible and accessible. All Employees must be fully trained in their operation.
4. Fire alarms must be present in all rooms/corridors and must be clearly signed and accessible at all times.
5. All workers should not lift any objects which they are physically uncomfortable with lifting. They must ask for assistance during any moving process and movement of chemicals/other hazardous materials should always be supervised.
6. Where necessary, workers must wear suitable physical protection. This includes hard hat, coat, gloves, goggles etc. Protection guidelines should be available in all processing areas and must be clear and visible.
7. All materials presenting potential health risks must be carefully and properly contained. This should be checked prior to and after moving, and at least once daily.
8. All equipment must be maintained properly and regularly to the manufacturers guidelines. This must be carried out by someone qualified to do so and must be supervised.
9. Equipment involving high temperatures and pressures must be located at a safe distance from all areas largely populated by employees.
10. Equipment conditions (temperature, pressure, flow rate etc) must be consistently monitored and alarms must be in place to detect loss of control.
11. Controls must be capable of complete shutdown and isolation of any and all equipment and pipes.
12. Emissions must be carefully controlled and must fall within limits set by the Environmental Health Agency.
13. All the above policies must be reviewed monthly to ensure there are being upheld consistently. This must be carried out by an external professional.
The styrene plant will adhere to all the policies set out above and all the policies will be considered and incorporated into the design of the plant to ensure they can be consistently and efficiently met.
Consent Levels And Safety, Health And Environmental Protection Criteria
Exact sizing of the plant is yet to be studied, but based on a plant in Somerville Rd Brooklyn in Melbourne owned by Huntsman Chemical Company of Australia Pty Ltd, it is likely to be approximately 40 hectares (400 km2). Depending on the proximity to civilisation, this area may increase to create a safe perimeter.
Wildlife will be affected by this development and so study needs to be done into the location of the site and habitation. Some wildlife may equally be a potential hazard to the operation of the plant itself.
The exposure limit values are a daily or weekly personal noise exposure of 87 dB; and a peak sound pressure of 140 dB. Study therefore needs to be done to investigate the level of noise produced by the machines that will operate in this plant.
As described in section 2, many of the materials involved present risks to health. All outputs in the liquid phase are irritants and some are known carcinogens. Several of the gaseous outputs are asphyxiates and flammable. The following emission controls are enforced by law (time weighted average):
Ethylbenzene: TWA: 100 STEL: 125 (ppm) [United Kingdom (UK)]
Benzene: TWA: 1.6 (mg/m3) [United Kingdom (UK)]
Styrene: Long-term exposure limit (8-hour TWA limit reference period) 430 mg.m-3
8.4 Personal Safety Criteria
Noise – workers should be provided with noise protection when noise levels exceed the noise exposure limit stated above.
Emissions – In places of the plant where there is gaseous output, workers should be provided with dust respirators or gas masks where necessary. All workers must be given training on identifying gas leaks and emergency procedures.
Machinery – Workers should be provided with personal protection when working with machinery or handling equipment. This includes gloves, hard hat, protective boots and visibility jackets. Workers should be trained not to lift any heavy or dangerous material.
Organisational, Human Factors & Emergency Requirements
Suitability and Availability of Staff
New systems of Work and Procedures
Site Emergency Facilities and Roles/Responsibilities
Facilities for peak construction staffing
The EU authorities have concluded that styrene is not bio-accumulative and meets the “ready biodegradation” criteria of the 29th Adaptation to Technical Progress of the Dangerous Substances Directive. The European Environmental Risk Assessment of styrene has concluded that no classification is needed.
Persistence of Styrene in the environment is very limited because of its volatility from soils and surface waters, its rapid destruction in air and its biodegradation in soils, and surface and ground waters.
Styrene is moderately toxic to aquatic organisms. Due to its high depletion rate from water the exposure rate may be very low.
More details on Styrene environmental effects can be found in Section 4“Environmental Aspects”.
What happens when styrene enters the environment
For the most part, inert products such as plastic parts, packaging etc. introduce styrene into the environment through the manufacture and disposal processes with evidence of styrene contamination being found in air, water and ground soils. However, in unlinked liquid form it enters the environment quickly and in larger quantities through evaporation and is also further broken down by bacteria found in water and soils allowing further rapid entry. It is not expected to enter the food chain by grazing animals.
How does it affect humans
Surprisingly, for a fairly commonly used industrial product, little is known about the effects of styrene on us, what we do know to date is that although exposure may not lead to any symptoms at all, breathing high levels of styrene for short periods can lead to possible respiratory problems and nervous system effects such as depression, tiredness, nausea, muscle weakness, ENT irritation. There is currently no test data on the effects of breathing low levels for a long time, nor is any data available on the effects of ingestion or absorption although animal studies revealed various symptoms such as damage to the brain, kidneys, liver and lung along with some reproductive effects.
The International Agency for Research on Cancer and the Environmental Protection Agency has also now determined that styrene could be a possible carcinogen to humans in airborne form and several studies of workers have shown that breathing styrene may cause leukemia. There is no current evidence to support any cancer or health risks for ﬁnal ﬁnished products containing styrene where skin contact or ingestion has occurred.
Clearly, styrene is a toxic, dangerous product in its raw form. It ﬁnds its way into the market in either solid form e.g. plastic parts, packing etc. or in liquid form. It is not harmful to humans in its inert solid form although it is harmful to the environment if not disposed of correctly. It is harmful to humans in liquid form both as a ﬁnished product and during manufacture.
The process of producing styrene on a large scale has a major benefit particularily on the local population surrounding the styrene plant as there is a great number of jobs that are created for people. The local community can therefore take advantage of this and unemployment levels in the local area should plummet. The general wealth of the community will in turn increase and so the plant is in effect responsible for the local area becoming more prosperous financially.
Further Studies would have to be conducted in the following area to assure the construction of the plant is safe and feasible:
- Wildlife in the local area – Affect any emissions/noise might have.
- Local community – whether the local community would be content with a styrene production plant in the area
- Noise produced by plant equipment
- Emissions of Benzene, Ethylbenzene, and Methylbenzene produced by the plants after reduction methods are complete. These gases are hazardous and have exposure limits which must be met.
- Emergency procedures and effects of plant layout
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