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.
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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.
2.2 Effluents
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.
2.3 Emissions from other facilities
This would need to be completed when it is known what is being released by facilities near by.
2.4 Support Materials
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.
2.5 Services
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.
2.6 Principal Materials of Construction
2.7 Materials encountered during construction/demolition
i. Important physical and chemical properties
ii. Significant chemical reactions
iii. Materials toxic, reactive or severe Environmental impact
Estimates of inventory
Off site effects of Loss of Containment
vi. Means of handling and storage
vii. Special handling problems
3. ENVIRONMENTAL ASPECTS
3.1 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.
3.2 Other Environmental Considerations:
The following identifies how the product (styrene) is going to be stored, controlled and monitored:
Product: Styrene
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:
All clothes which have been in contact with product should be washed and rinsed immediately.
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:
Waste/By-product
Harm to Environment/ Hazard
Means of Containment
Disposal
Other
Carbon dioxide
Greenhouse gas which contributes to global warming
Compress carbon dioxide into liquid and inject into porous rock.
Ethyl Benzene
Methyl Benzene
Water
Additional water re-used back into stream 2
4. HEALTH & TOXICOLOGY
4.1 Occupational Health Statement
4.2 Statutory exposure limits
4.4 Specific Requirements for Design
5. TRANSPORT AND SITING
5.1 Transport Stages
There are three main methods for transportation – rail, road and ferry. In order to determine the method by which we are going to transport the raw materials and the product (styrene) we would need to compare the costs and effectiveness of the different modes of transport.
We must first look at the basic hazards and safety guidelines that must be adhered to at all times in order for a successful transport system to be set up. If we take a closer look at the SDS for styrene, we can clearly see that there are two areas of the safety data sheet that are very important: http://www.styreneforum.org/regulatory_index.html
Handling and Storage:
Table 1
Handling
Avoid contact with skin, eyes and clothing. Do not breathe vapour. Only use in well ventilated areas. Use local exhaust extraction. Extinguish any naked flames. Remove ignition sources. Avoid sparks. Do not smoke. Take precautionary measures against static discharges. Earth all equipment. Do not empty into drains.
Handling Temperatures
Ambient
Storage
Keep away from direct sunlight and other sources of heat or ignition. Do not smoke in storage areas.
Storage Temperatures
25 °C maximum
Product Transfer
Take precautionary measures against static discharge. Earth all equipment. Avoid splash filling. Do not use compressed air for filling, discharging or handling. If positive displacement pumps are used, these must be fitted with a non-integral pressure relief valve. Restrict line velocity during pumping in order to avoid generation of electrostatic discharge.
The table above highlights the relevant dangers and precautions needed in order to handle and store styrene in the most comprehensively safe manner. These guidelines are crucial in the protection of the workers special care should be taken in order to ensure that everyone adheres to these rules in the strictest manner at all times. For example, there should be heavy repercussions for those who transgress these boundaries, this would act as an effective deterrent and would ensure that everyone complies.
Stability/Reactivity:
Table 2
Stability
Reacts violently with strong oxidising agents. Oxidises on contact with air. Polymerises exothermically on exposure to light, heat and most halides. In case of contact with water the inhibitor concentration might decrease and cause polymerisation.
Conditions to avoid
Heat, flames and sparks. Exposure to air. Exposure to sunlight
Materials to avoid
Strong oxidising agents. Halides.
Hazardous decomposition products
Decomposition products are not expected to form during normal storage.
When transporting styrene we have to consider the potential dangers of how it can react with other materials. The table above is critical information that needs to be taken into account. We can see that it is very important for styrene to be kept away from any oxidising agents, heat, flames and sparks. Because of the immense danger of fire we must look at the correct fire fighting measures required. All of the staff who are involved with styrene will need to be made aware of the steps that should be taken.
Effect of Loss of Containment on Occupied Buildings
It is extremely important that workers are equipped with the relevant protective equipment, and also the general public needs to be protected from any of the vapour entering the environment. According to the MSDS for ethyl benzene ethyl benzene enters your body when you breathe air containing ethyl benzene. It enters your body rapidly almost completely via your lungs. If ethyl benzene is ingested through food or water then it will enter through the digestive tract. It can also enter your skin when it comes into contact with liquid containing ethyl benzene.
Styrene can affect people by eating, drinking, breathing and skin contact (similar to ethyl benzene). According to HPA Compendium of Chemical Hazards Styrene (2008), “Breathing air contaminated with styrene vapours can cause irritation of the nose and throat, coughing, wheezing and build-up of fluid in the lungs. Severe exposures can lead to “styrene sickness”, which relates to a series of health effects due to depression of the central nervous system (CNS). These symptoms include headache, nausea, vomiting, weakness, tiredness, dizziness and unsteady and clumsy motion of the limbs. Styrene is an irritant and contact with the skin can cause mild irritation, itching and dermatitis. Getting splashes of styrene or vapours in the eyes is likely to cause moderate to severe irritation”.
Fire Fighting measures:
According to the MSDS by Ashland Chemical Co. (1999) you should:
“Wear a self-contained breathing apparatus with a full face piece operated in the positive pressure demand mode with appropriate turn-out gear and chemical resistant personal protective equipment” using “regular foam, water fog, carbon dioxide, dry chemical” as the extinguishing media. The respiratory protection is essential because of the hazardous emissions like “carbon dioxide and carbon monoxide, various hydrocarbons”.
The raw materials that are being used are ethyl benzene and water. If we look at occupational exposure limits list EH40/2005 which has been approved by the health and safety commission ethyl benzene has the following exposure limits properties:
Substance
CAS Number
Work Place Exposure Limit
Comments
Long-term exposure
limit (8-hour TWA
reference period)
ppm mg.m-3
Short-term exposure limit (15-minute reference period)
ppm mg.m-3
Ethyl benzene
100-41-4
100 441 125 552
Sk
R11.20
Table 3
King (1990) states that “OELs are the maximum concentrations in air of the substances which should not be exceeded in the breathing zone of workers”. We can see that the long term exposure limit is 100ppm and the short term limit is 125ppm. It is critical that these limits are not exceeded and the limits are followed rigorously.
According to Wentz (1998) chapter 13 personal protective equipment, the relevant safety precautions would be to provide:
Respiratory Protection – which is compressed air line breathing apparatus for use with a full face mask, half mask or a mouthpiece assembly.
Eye Protection – Style B chemical splash goggles are recommended.
Protective Clothing – Boots and apron are recommended. If there is a risk of ethyl benzene splashing or in an ethyl benzene spillage, a chemical resistant one-piece overall with integral hood and chemical resistant gloves should be worn.
5.3 – Potential Effects from Existing Plants:
There are many effects from existing plants. I have highlighted many of these in the previous sections. For example, the effects of breathing air contaminated with styrene. However, we have to look very seriously at the effect it may have on the ecosystem. The relevant EU authorities have stated that styrene meets the criteria for ready biodegradation and is therefore a substance that will break down very quickly and won’t stay in the ecosystem for very long (in a state in which it can be harmful).
Another point that supports the view that styrene isn’t very harmful to the environment is the fact that the European Environmental Risk Assessment of styrene concluded that no classification is needed. Therefore, they don’t see styrene as being a significant danger.
6. 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.
7. CONSULTATION WITH EXTERNAL AUTHORITIES
Authorities to be contacted
Reason to Contact
8. CONSENT LEVELS AND SAFETY, HEALTH AND ENVIRONMENTAL PROTECTION CRITERIA
8.1 Environment
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.
8.2 Noise
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.
8.3 Health Effects
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.
DESIGN GUIDELINES & CODES
We have already made the size estimations for the main components of our process. However, there are various guidelines concerning designing the process that we must follow closely. These are immensely important particularly in inhibiting any hazards that may occur.
The storage tanks for styrene will need to be kept apart from other substances such as strong acids and oxidising agents because of the way in which styrene may react with these substances if there were any unfortunate accidents (see 5.1). Also, pumps should be used for discharge. According to appendix 5 (design and construction of storage tanks), “Pumps should be located outside tank bunds, on an impervious base, in an open space, and not in walled or confined spaces.” They should also be constructed “of either cast steel or stainless steel. Copper, bronze or plastic should not be used”.
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Also, “valves should be fitted directly on all bottom outlets of a tank, unless these branches are blanked off”. Furthermore, the size of the various tanks should be reasonable when thinking about the method of transportation. For example, if the size of the tanks does not comply with the requirements for shipping then that would be a major problem when exporting the styrene produced. Another important rule of thumb is that styrene should not be stored for too long. This is because extended storage times will inevitably lead to the deterioration of styrene quality.
The materials that are suitable for use with styrene are carbon steel or stainless steel. This is also an essential rule. If an incorrect material is in contact with styrene then salts can be formed. For example, if carbon or alloys of carbon are used then soluble carbon salts can be formed.
A manhole (of minimum 500mm diameter) is an essential criterion for each tank to allow for cleaning and inspection. The tanks should also have a natural gradient that is sloped towards the outlet, there should be no blockages.
Also, tanks that contain flammable liquids should have a PVRV valve (pressure/vacuum relief valve). This is essential in conditions in which the pressure exceeds too high or vacuum conditions.
Key Design Standards & codes
Responsibility
10. ORGANISATIONAL, HUMAN FACTORS & EMERGENCY REQUIREMENTS
10.1 Suitability and Availability of Staff
10.2 New systems of Work and Procedures
10.4 Site Emergency Facilities and Roles/Responsibilities
10.5 Facilities for peak construction staffing
11. SUSTAINABILITY
11.1 – Environmental Responsibility:
As I have already explained styrene doesn’t really pose much of a threat to the environment when compared to other substances. Furthermore there are no links to styrene being a carcinogenic. However, we still have a responsibility in protecting the ecosystem. This is because (as explained before) high levels of styrene can be potentially lethal and certainly immensely harmful.
A major characteristic of styrene that enables it to be relatively acceptable in the environment is its volatility. If styrene is spilled or contaminates water it will slowly turn into vapour and little will actually dissolve or remain in the ground. The rate at which this process occurs depends on the temperature and turbulence. As the temperature and the turbulence increases the volatility increases.
11.2 – Wealth Creation:
The process of producing styrene on a large scale has a major benefit particularly on the local population surrounding the styrene plant. There are a colossal number of jobs created in the community which range from transportation of raw materials to general operatives. 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.
11.3 – Social Development:
James Midgley (1995, p. 25) states,” process of planned social change designed to promote the well-being of the population as a whole in conjunction with a dynamic process of economic development”. Therefore, the very aim of social development is to better a community. The increase in wealth achieves this goal and so will propel them on their road to social development. Social development is linked very strongly with financial background. As the community’s wealth will increase (see 11.2), the community will, in turn, develop socially and only grow in status.
11.1 Environmental Responsibility
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 ¬nal ¬nished products containing styrene where skin contact or ingestion has occurred.
Clearly, styrene is a toxic, dangerous product in its raw form. It ¬nds 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 ¬nished product and during manufacture.
11.2 Wealth Creation:
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.
11.3 Social Development
12. FURTHER STUDIES
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
Appendix c
Hazard Study 1 – Chemical Hazard Form
Project No.
Page of
Description Date:
Chemical or Group of Chemicals
Physical State
Quantity (Inventory or throughput)
A
B
C
D
E
F
G
H
I
J
Hazard Potential Key: – – Insignificant Hazard
K – Hazards Known and Understood
â- – Significant Hazard
No. – See Numbered Notes
A
B
C
D
E
F
G
H
I
J
K
L
Explosion and Flammability Hazards
Fire
Deflagration/Detonation
Electrical Static
Reactivity/Stability Hazards
Immediate Health Hazards
Inhalation Toxicity
Other Toxicity
Irritant/Corrosive
Sensitiser
Chronic Health Hazards
Other Health Hazards
Odour
Radiation
Environmental Hazards
Aqueous
Gaseous
Ground
Hazardous Breakdown Products
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