Industrial Chem Dotpoints (1 Viewer)

[dan964]

If you need a formatted document rather than this let me know.

5.1 Replacements for Natural Products
1. Issues Associated with Limited Natural Resources

• Some of the general issues associated with all natural resources:
• Increasing demand for the resource, even if only for a short period of time
• The inability of resources to meet currents demands for the resource, even if only for a short period of time.
• The depletion (non-replenishment) of these resources
• More uses for the natural resource as well competition between current uses.
• Increasing prices for the natural products, usually due to limited supply and high demand
• Easier to produce synthetic forms of the resource due to increased availability or decreasing cost of production.

The need to replace natural resources with synthetically made resources will continue due to the following factors:

• Human population is increasing
• Human consumption levels are increasing
• Natural resources being depleted and unable to meet current demands and uses for the resource

Properties and Uses of Rubber
The addition of sulfur to rubber in the process of vulcanisation, gives rubber the following favourable properties:

• Good elasticity and able to retain its shape when deformed (rigid)
• Insoluble in water
• Relatively low chemical reactivity with some chemicals and resistance to weathering
• Good electrical insulator

It is used in the following applications:

• Raincoats because of rubber’s insolubility in water and low chemical reactivity
• Hoses because of rubber’s elasticity and insolubility in water
• Balls and toys because of rubber’s elasticity
• Tyres because of rubber’s rigidity and elasticity.
• Electrical insulation because of its extremely poor conduction of electricity.

Changes in the Use of Rubber over Time
Originally rubber had limited uses, such as balloon cloth (fabric coated with rubber dissolved in turpentine) and raincoats. Rubber when heated would melt, and became brittle when cooled. The discovery of vulcanisation by Charles Goodyear in 1839, allowed rubber to become more resistant to changes in temperature and allowed for more uses of rubber.
Problems associated with the use of rubber
Some of the current problems associated with the use of natural rubber include:

• Natural rubber is not very resistant to chemical attack from certain chemicals, in particular oils and other petroleum-based chemicals.
• Natural rubber is also not suitable for long periods of exposure to ozone, sunlight, oxygen and heat.

Sources of Rubber

• Originally native to South America, rubber occurs naturally as latex in the sap of the rubber tree. Native South Americans have used it for footwear and bottles.
• Until 1940, large rubber plantations in South-East Asia, particular Malaysia, Thailand and Indonesia provided the majority of the world’s rubber supplies and demands.
• As demand for rubber increased, the need for an alternative increased.
• Cause of Shortages of Rubber
• Natural rubber became very useful especially in its application of tyres. The growing demand for automobiles meant a greater demand for rubber.
• In particular in World War II, the USA needs for rubber for its military vehicles required half of the world’s supply of rubber at that time.

Alternate Sources of Rubber

• Synthetic rubbers had been developed from 1920, but it wasn’t until 1940 when the rising need for rubber increased to the extent, where existing resources could not supply this demand. This lower the production costs for synthetic rubber.
• American, English and German scientists independently developed different synthetic rubbers.
• These new rubbers were more chemically resistant than natural rubber and were also cheaper to produce, making a more desirable alternative to the natural resource.
• Common synthetic rubbers now make up 80% of the world’s rubber production. Some of those that have been developed include ethylene-propylene-diene rubber and styrene-butadiene rubber (SBR).

Some of the properties of synthetic rubber that make a favourable alternative:

• Some synthetic rubbers are resistant to chemical attack from ozone, sunlight and long exposure to heat.
• Other synthetic rubbers are resistant to chemical attack from petroleum-based chemicals

Current research is being undertaken to create synthetic rubbers that have better resistant to temperature and chemical attack from different chemicals. Research is being undertaken to also develop rubbers from biomass.

Practicals and Research
1. Problems and Solutions Associated with Rubber
The Development of Non-Petroleum-Based Synthetic Rubbers

• These synthetic rubbers are derived from petroleum-based compounds, a non-renewable resource which will be unsustainable in the long term. Research is currently been undertaken to implement synthetic rubbers that have been derived from biomass.
• One such synthetic rubber that has been developed from biomass is high-cis polyisoprene, developed by Bridgestone Corporation, as part of an initiative to create 100% sustainable resources by 2050.
• It is expected that these new synthetic rubbers will supplement current demands which continue to rise.
• Environmental Concerns with Natural Rubber Plantations
• There are also environmental concerns with current natural rubber plantations in South-East Asia, especially on the biodiversity and ecosystem, as the amount of rubber plantations increase in South-East Asia.
• One particular concern is the groundwater supply during the dry season is shortage due to rubber drawing on the deep groundwater reserves.
• Other concerns include the loss of tree cover and possible land erosion. 

5.3 Industrial Production of Sulfuric Acid
1. Uses of Sulfuric Acid in Industry
Sulfuric acid is used in many processes in industry including:

• The production of fertilizers including superphosphate fertilizers and ammonium sulfate.
• The extraction of metals from their ores including copper and titanium dioxide from their ores (the latter is a key ingredient in paints, plastics, paper and sunscreen).
• A dehydrating agent and catalyst in reactions requiring the removal of water, include the esterification process, and the conversion of ethylene to ethanol.
• Electrolytes, in particular the lead acid battery.
• Cleaning of metals prior to electroplating or galvanisation; in particular the ‘pickling’ of iron and steel.
• The production of phosphoric acid, which is then converted into sodium phosphate (a key ingredient in many detergents)

2. Extraction of Sulfur from Mineral Deposits
Natural Sources of Sulfur
Sulfur exists in the spheres of the Earth naturally as:

• deposits of the free element, especially in areas of high volcanic and seismic activity.
• metal sulfide ores
• hydrogen sulfide, which is present in natural gas and petroleum
• sulfates present in ocean water

The Frasch Process

• The Frasch Process is the process used to extract elemental sulfur from sulfide mineral deposits which then then be used in production of sulfuric acid.
• It involves three concentric pipes being placed into the sulfur deposit. The outermost pipe carries superheated water, while compressed hot air is blown down the central pipe.
• The water is superheated to a temperature of 165°C which is above the melting point of sulfur (115°C), but under pressure to prevent the water from boiling
• The compressed air then drives the melted sulfur through the second pipe, into bins where it solidifies, forming 99.5% pure sulfur.

Properties of Sulfur used in the extraction process

• The relatively low melting point of sulfur at 113-115°C allows the sulfur to be melted.
• The insolubility of sulfur in water allows it to be easily recovered at the surface
• Its low density of 2.07 g cm–3 produces a sulfur-water emulsion that can be easily transported to the surface using compressed air.

Environmental Concerns

• Sulfur easily oxidises to form SO2 which can then result in the production of acid rain. Sulfur also can be reduced to H2S. Both SO2 and H2S rare serious air pollutants and also cause irritations to the respiratory tract.
• The water which is used in the extraction process may still contain impurities of sulfur. This water needs to be recycled or purified before being released back into the environment.
• The superheated water if not deposed properly can cause thermal pollution. If the water is not recycled (which is more preferable), it needs to be returned at a more suitable temperature. Some of the effects of thermal pollution on the ecosystem include stress for fish due to lower dissolved oxygen in the water, changing breeding or migration times, or death of fish and fish eggs. 

3. The Production of Sulfuric Acid
The Nitration Process

• In the nitration process, developed in 1746, nitrogen compounds, particular oxides of nitrogen acts as catalysts in the oxidation reduction of sulfur dioxide to sulfur trioxide.
• The process involves the formation of nitrosylsufuric acid (HOSO2ONO) which then decomposes to sulfur trioxide which dissolves in the water present in the chamber to form sulfuric acid.
• Nitric oxide is also produced which then can be converted back into nitrogen dioxide, which along with the nitric oxide can be recycled again.
• Large lead chambers were typically used to facilitate the removal of the heat generated during the reaction, and hence the process was also called the lead-chamber process (or the chamber process).
• The sulfuric acid produced has a lower concentration than the newer contact process, but is suitable for sulfuric acid which is then used to produce fertilizers.

The Contact Process
The contact process is a newer process, developed in 1831 (commercial production became viable from 1927), which is the method used to produce most of the current demands for sulfuric acid.

• The contact process first involves the production of sulfur dioxide which is then catalytically oxidised, in the presence of oxygen.
• Traditionally, the catalyst used was heated platinum, which proved very expensive and required extensive gas cleaning systems to prevent “poisoning” by impurities.
• Since 1927, a more efficient catalyst has been used – vanadium pentoxide (V2O5) often combined with potassium sulfate or potassium oxide dissipated on a silica base. It provides a porous surface for the reaction to take place.
• The vanadium oxide catalyst increases the rate of the overall reaction by lowering the activation energy.
• Its surface also absorbs the SO2 and O2 molecules, resulting in the weakening of bonds, allowing a more efficient process. Vanadium oxide oxidises the SO2 to SO3, and then is re-oxidised itself by the oxygen:
  2SO2 (g) + O2 (g) ⇌ 2SO3 (g) (requires a porous V2O5 catalyst to drive reaction to the right).
• This step is conducted typically at 450°C and moderately high pressures (200 kPa) to ensure a 99.5-99.7% conversion of sulfur dioxide into sulfur trioxide.
  The pure sulfuric trioxide produced is then absorbed into 98% sulfuric acid:
• This forms oleum (H2SO7) which then forms pure sulfuric acid when dissolved in water:
  SO3 (g) + H2SO4 (l) → H2SO7 (l)
  H2SO7 (l) + H2O (l) → 2H2SO4 (aq)
• In this process temperature and concentration needs to be monitored to maximise the efficiency of this section of the reaction. The temperature is maintained at 70°C and the sulfuric acid maintained at 98% concentration. 

4. Reaction Conditions in the Production of Sulfur Dioxide and Sulfur Trioxide
Reaction Conditions for Sulfur Dioxide

• Sulfur is easily converted into sulfur dioxide, by combustion of sulfur in the excess of clean, dry air:
  S(s) + O2 (g) → SO2 (g) (ΔH = – 300kJ mol–1)
• This reaction is very exothermic resulting in the sulfur dioxide gas reaching a temperature of around 1000°C, which needs to be lowered if it is going to be converted into sulfur trioxide.

Reaction Conditions for Sulfur Trioxide
The ideal conditions for the production of sulfur trioxide in the industrial production of sulfuric acid are:

• Low Temperatures – ideally a temperature around 450°C (400-500°C)
• Catalyst – a porous V2O5 catalyst allows the reaction to proceed faster, especially at lower temperatures
• Pressure – pressures slightly above atmospheric pressure are used (around 200 kPa)
• A small excess oxygen – to ensure all SO2 is reacted and to increase yield

5. Equilibrium Considerations for Sulfur Trioxide

• The reaction between sulfur dioxide and oxygen to form sulfur trioxide is an equilibrium reaction:
  2SO2 (g) + O2 (g) ⇌ 2SO3 (g) (ΔH = – 100 kJ mol–1)
• In order to maximise yield, chemists monitor the conditions of the reaction to maximise conversion of sulfur dioxide to sulfur trioxide.

Temperature

• The reaction is exothermic producing heat and thus according to Le Chatelier’s Principle, a decrease in temperature would shift the equilibrium to the right producing more sulfur trioxide.
• However, as the temperature decreases, the rate of the reaction also decreases.
• A moderate temperature is required, to ensure that the rate of reaction isn’t too slow, and also to maximise yield. Typically a temperature between 400-500°C is used as a compromise.

Pressure

• There are more moles of gas on the left-hand side of the equation and thus according to Le Chatelier’s Principle, as pressure increases, the equilibrium will shift to the right to produce more sulfur trioxide.
• Higher pressures are more expensive and have more risks associated with them.
• A gas pressure between 100-200 kPa increases the collision frequency between the gas molecules.

Concentration

• In order to increase yield, an excess of oxygen is supplied and thus according to Le Chatelier’s Principle, as the concentration of the products increases, the equilibrium will shift to use up more sulfur dioxide to produce more sulfur trioxide.
• The small excess of oxygen ensures that most sulfur dioxide is reacted, to reduce the emissions to a safe level that can be released into the atmosphere

Catalyst

• The catalyst used (typically V2O5) are used to increase the rate of reaction by lowering the activation energy.
• The high surface area of the catalyst ensures a rapid reaction.
• A catalyst is needed, because the decrease in temperature lowers the rate of the reaction.

Practicals and Research
1. Analysing the Sulfuric Acid Production Process
Conversion of Sulfur to Sulfur Dioxide
Overall reaction: S(s) + O2 (g) → SO2 (g) (ΔH = – 300kJ mol–1)

• The starting material for the production of sulfuric acid is either sulfur that has been extracted using the Frasch process, or sulfur that is a by-product in the refining of petroleum and other hydrocarbons.
• Elemental sulfur is melted by steam coils at 140°C in brick-lined tanks, and then is filtered to remove any impurities.
• The molten sulfur is then transported to the burner, where it combusts in the presence of an excess of dry air to form sulfur dioxide. The heat generated in the reaction is used to heat up further reactants and hence is recycled.
• The gas produced has a temperature of 830-1000°C and is then passed through a hot gas filter to remove any ash contamination. The mixture of gases are cleaned using electrostatic precipitators, dried, heated to 450°C

Conversion of Sulfur Dioxide to Sulfur Trioxide
Overall reaction: 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) (ΔH = – 100 kJ mol–1)

• The reaction between sulfur dioxide and oxygen to form sulfur trioxide occurs in a four-stage reaction vessel.
• Each stage contains the vanadium-oxide catalyst which provides a porous surface for the chemical reaction to take place.
• The reaction is exothermic and so the equilibrium constant decreases with increasing temperature. But if the temperature is too low, the equilibrium point will not be reached.
• The output of sulfur trioxide can be maximised by maintaining the temperature between 400-500°C and a pressure of around 200kPa.
• Heat is generated at each stage, which needs to be removed to ensure temperature is maintained.

Conversion of Sulfur Trioxide to Sulfuric Acid
Overall reaction: SO3 (g) + H2O(l) → H2SO4 (g) (ΔH = – 200 kJ mol–1)

• The gas is then transported to the absorption tower, where the sulfur trioxide is absorbed into 98% concentrated sulfuric acid.
• The sulfuric acid is maintained at about 98% concentration to ensure that the vapour pressure is kept at a minimum. If the water vapour pressure is too high (i.e. if the concentration is any higher or lower) then the gases formed in the process are easily absorbed, and are released into the atmosphere.
• The sulfuric acid is circulated at a rate to ensure that there is a minimal increase in concentration.

Production of Superphosphate from Sulfuric Acid
Overall reaction: 2Ca5 (PO4)3F + 7H2SO4 + 3H2O → 7CaSO4 + 3Ca(H2PO4)2.H2O + 2HF

• In this particular case, the main use for the sulfuric acid produced is the production of superphosphate fertilizer.
• Phosphate rock which is rich in fluorapatite (Ca5(PO4)3F) is reacted with 98% concentrated sulfuric acid and water to form superphosphate.
• Additives such as limestone, potassium chloride (potash) and ammonium sulfate are sometimes added to the superphosphate mix.
• Superphosphate is then ground to particles up to 6 mm in diameter, which then can be used for fertilizer.
• Superphosphate is used to supplement the soil with phosphate required in order maintaining high usage of the land for animal or plant cultivation. It ensures the soil has a sufficiently high phosphorous content.

In order to maximise yield of sulfuric acid, the temperature, pressure and concentration required for each stage needs to be monitored.

 

[Vizsla]

No yes or folder?