Topic 3 – Chemical Monitoring and Management /
Topic 3 – Chemical Monitoring and Management
By: Raymond Chen

11 – The Industrial Chemist

11.1 – The Work of an Industrial Chemist

The Role of a Working Chemist
  • Chemists employed in the industrial sector have many roles including:
  • Development Chemist - Designing chemical processes for the manufacture of a chemical product to ensure the rate of the reaction and yield product are optimised.
  • Production Chemist - Working with chemical engineers to designing the equipment to carry out the industrial process
  • Research Chemist - Undertaking ongoing research to improve the product or process or to develop new products.
  • Teamwork, collaboration and communication skills are important for chemists.
  • A company has many chemists that are skilled in different areas.
  • There are a variety of chemists, including:
  • Environmental chemist:
  • Employed by a wide variety of organisations, including mining.
  • Developed expertise in analytical chemistry.
  • They collect, analyse and assess environmental data from the air, water and soil.
  • Metallurgical chemist:
  • They have a high understanding of metals, alloys and ores and their reactions.
  • They specialise in all aspects of the use and development of metals and alloys in society.
  • They design and monitor methods of extracting metals from ores.
  • Biochemists:
  • They help determine the chemical structure and functions of molecules in living things.
  • They study organic chemistry and biochemistry
  • They can be employed in areas including pharmaceutical laboratories, hospitals and in the food and agricultural industries.
Monitoring Combustion Reactions
  • The combustion of alkanes obtained from petroleum is a major source of heat and power.
  • Though they are stable in oxygen, they are combustible when ignited - the products from this are carbon dioxide and water.
  • In a space where is a plentiful supply of oxygen the reaction is:
  • However when there is a lack of oxygen - like in a car engine - then incomplete combustion may occur:
Catalytic Converters and Emission Control
  • Industrial chemists have developed catalysts that help to reduce carbon monoxide, nitrogen oxide and unburnt hydrocarbon emissions from vehicle exhausts.
  • Catalytic converters are made from alloys of rhodium and platinum - they speed up reactions that convert pollutant gases to materials which are present in the air naturally.
  • The aim of this is to convert otherwise dangers NO and CO to N2 and CO2 respectively and also unburnt hydrocarbons into water.

11.2 – The Haber Process

The Uses and Importance of Ammonia
  • Ammonia is a gas that produces an alkaline solution when dissolved in water.
  • Solutions of ammonia in water are used domestically are cleaning agents and also as refrigerant gas.
  • Ammonia is the feedstock for a large variety of industrial chemicals.
  • Fertilisers account for over 80% of worldwide use of ammonia.

Industrial Product Derived from Ammonia / Use of Product
  • Urea
  • Ammonium Sulfate
  • Ammonium Nitrate
  • Ammonium Hydrogen Phosphate
/
  • Fertilisers

  • Nitric Acid
/
  • Production of explosives
  • Nitrate salts
  • Strong laboratory acids

  • Acrylonitrile
/
  • Acrylic plastics

  • Diaminoalkanes
/
  • Nylon plastics

  • Cyanides
/
  • Extraction of gold from gold veins

  • Hydrazine
/
  • Rocket propellant

  • Sulfonamides
/
  • Antibiotic drugs

  • Aniline Derivatives
/
  • Dyes

  • Alkylammonium Hydrocarbons
/
  • Cationic detergents

Industrial Manufacture of Ammonia
  • The production involves balancing the conditions of the reaction so that the products are produced at a fast rate and the quantity is of the product is maximised.
  • Ammonia is manufactured by a process developed by Fritz Haber in early 20th century.
  • It was manufactured from its component gas elements - the reaction is exothermic.
  • At the standard conditions of temperature and pressure lies to the left - Haber process changes this.
  • Conditions in the Haber process make the manufacturing of ammonia viable.
Feedstocks for the Haber Process
  • The ammonia industry requires nitrogen and hydrogen.
  • They are derived from air, water and natural gas.
  • The ammonia produced is not only used to make solid fertiliser, but is also directly applied to the soil in anhydrous gaseous form.

Nitrogen

  • Filtered air is the source of nitrogen for the Haber process.
  • Air contains ~78% nitrogen by volume.
  • An expensive method for nitrogen extraction is to fractionally distil liquefied air.
  • Nitrogen is more commonly extracted from air using chemical reactions involving natural gas or methane.
Hydrogen
  • Hydrogen can be obtained via the electrolysis of salt water - but it is too expensive.
  • Hydrogen is derived from the steam reforming of natural gas - CH4.
  • Extraction of hydrogen is as follows:
  • Natural gas is purified to remove sulfur compounds through a cobalt/nickel/alumina catalyst.
  • Hydrogen is extracted by reacting natural gas with steam at about 750°C with nickel catalyst - primary steam reforming - 90% of methane is consumed.
  • The introduction of air produces steam with nitrogen remaining unreacted - high temperatures ~1000°C ensures combustion of almost all methane.
  • Carbon monoxide is removed by passing it over two different catalysts - iron oxide (~400°C) and cooper (~200°C)
  • CO must be removed as it is poisonous - 0.2% remaining
  • Reaction is exothermic - heat is recovered for further use.
  • CO2 is removed by neutralisation with potassium carbonate under pressure - the decomposed potassium hydrogen carbonate is stored for further use.
  • There must not be any oxygen as it is explosive with hydrogen under high pressure and temperature.
  • The final gaseous mixture contains nitrogen and hydrogen in a ratio of 1:3 - very small amounts of methane and argon are present.
Haber Process
  • The Haber Process is as follows:
  • Reactants pass through the catalytic reactors
  • The mixture is cooled to condense out the ammonia formed
  • The ammonia is drained out as required with the unreacted gas fed back into the catalyst chamber with incoming reactants
  • None of the reactant mixture is wasted.
Haber Process
  • The conditions present in the Haber process is a compromise between temperature and pressure and also kinetic factors.

Equilibrium Factors

  • Temperature:
  • The Haber process is an exothermic reaction - high temperature, low yield.
  • According to L.C.P. - Lower the temperature the higher the yield.
  • Pressure:
  • Stoichiometric equation shows that there are 4 moles of reactants for 2 moles of products - increased pressure, high yield.
  • According to L.C.P. - Higher the pressure, the higher the yield.

Kinetic Factors

  • Kinetic factors relate the speed at which reactions occur and how rapidly the ammonia is formed.
  • High temperatures increase kinetic energies of molecules therefore increased productivity.
  • High pressures increase frequency of collisions therefore increased productivity.
  • The presence of a catalyst increases the reaction rate.

Economic Factors

  • Constructing strong pipes and maintaining a high-pressure reactor vessel is very expensive - therefore selected pressure should not be too high.
  • Ammonia plants should be located locally with natural gas.
  • Heat is not wasted as they are recycled in heat exchangers.
  • Carbon dioxide is not wasted as it is used to manufacture urea and sold to brewers and soft drink manufacturers.

Compromise Conditions

  • The conditions in the manufacturing of ammonia vary but these are some of the typical ranges:
  • Reactants: N2 and H2 (ratio 1:3) can be shifted to the left by increased concentration - stoichiometric ratio must be maintained.
  • Pressure: 15-35MPa - although it should be as high as possible, but economic and safety concerns require the pressure to be lower.
  • Temperature: 400°C-550°C - equilibrium and kinetic factors are a problem; a compromise has to be struck so that the activation energy level can be reached.
  • Catalyst: Magnetite (Fe3O4) - fused with K2O, Al2O3, and CaO - it is then reduced to porous iron. By grinding the iron catalyst to produce maximum surface area - this allows low temperatures and low pressures to be used.
Monitoring and Management
  • The Haber process must be monitored and managed for productivity maximisation and safety concerns.
  • Reasons include:
  • Feedstock must be pure and free contaminants - they interfere with yield and can damage the catalyst.
  • Oxygen must not be present as it is explosive.
  • Ratio of nitrogen and hydrogen must be kept at 1:3 for optimum production.
  • Temperature and pressure should be maintained - temperature too high can damage the catalyst, pressure too high may cause the vessels to rupture.
  • Overtime, minor gases in the atmosphere such as argon and inert gases accumulate - they need to be removed when it reaches 5%.
  • Remove ammonia at regular intervals to ensure no impurity contamination
  • Structural integrity of reaction vessel must be maintained.
  • Monitoring devices are connected to critical parts of the containment vessels.
  • Electronic devices sound alarms when values fall outside acceptable limits.

12 – The Analytical Chemist

12.1 – Identification of Ions

Anion Analyses
  • Chemists analyse materials for the presence of specific cations and anions.
  • Anions can be identified and distinguished using a variety of simple qualitative tests involving the formation of gasses or precipitates.
  • There is a series of elimination tests conducted in strict order.
  • Then there are additional confirmation tests.
  • Solubility rules include:
  • Nitrate salts are soluble - no precipitation of cations
  • Group 1 salts are soluble - no precipitation

Anion / Soluble / Slightly Soluble / Insoluble
/ / - / Most
/ Most / /
/ / / Most
/ / - / Most
/ Most / /

Anion Elimination Tests

  • To test for unknown solutions, there is a listed sequence.
  • It is known as the elimination sequence - must be done in order to prevent invalid conclusions.

Anion / Procedure / Observation/Conclusion
/ Add 2mol/L nitric acid / Effervescence of colourless gas (CO2) indicates a carbonate
Use limewater to confirm

Confirmation Test: Test the original solution with pH paper / If solution is alkaline then the results are true.
+
/ Acidify the unknown solution with nitric acid and add drops of dilute barium nitrate / A white precipitate of barium sulfate indicates sulfate ions are present

Confirmation Test: Add drops of lead nitrate solution / A white lead (II) sulfate precipitate forms

/ Acidify the unknown solution with nitric acid and add silver nitrate solution / A white precipitate of silver chloride

Confirmation Test: Add ammonia solution then heat in water bath / White precipitate should dissolved

/ Add drops of ammonia solution then solution of barium nitrate / White precipitates forms

Confirmation Tests:
Add ammonium molybdate and warm the mixture
Acidify the solution with sulfuric acid, then add ammonium molybdate and ascorbic acid / A yellow precipitate of ammonium phosphomolybdate forms
A blue complex forms
Cation Analysis

Colour of Solution

  • In aqueous solution many cations are colourless - but some are distinctive in colour

Hydrated Cation / Solution Colour
/ Yellow-orange to pale yellow
/ Pale green to colourless
/ Blue to green-blue

Flame Tests

  • Many metal ions produce characteristic colours when their salts are heated - flame test
  • Some metal ions produce characteristic flame colours.
  • Chloride salts of various cations work best.
  • As an atom is heated the electrons in the atom moves to a higher energy level but it is unstable hence they fall back.
  • According to the Law of Conservation of Energy the energy in the electron is emitted in the form of a frequency in the electromagnetic spectrum - coloured photons.
  • There are two ways to perform the flame test:
  • Dip a platinum wire into concentrated HCl to clean it.
  • Heat the wire to remove impurities
  • Dip the wire into acid and then into powdered salt so that the salt sticks
  • Heat using Bunsen burner and colour is displayed in the flame
  • Dissolve the chloride salt in water and spray the resulting solution into the blue Bunsen flame using an atomiser.
  • Sodium may sometimes mask the colour of the unknown metal – it has a strong yellow colour.

Cation / Flame Colour
Calcium / Brick red
Barium / Yellow-green
Copper / Green
Sodium / Yellow
Strontium / Scarlet-Red

Cation Elimination Tests

  • Like with anions, a series of elimination tests are carried out.
  • These elimination tests are based on the formation of precipitates in solutions of varying pH.
  • The cation solutions should have a minimum concentration of 0.1 molar.

Cations / Procedure / Observation/Conclusion
Pb2+ / Add hydrochloric acid / White precipitate indicates lead ions

Lead chloride is soluble in hot water
Confirmation Test: Add drops of sodium iodide to original solution / Yellow precipitate forms

Ba2+, Ca2+ / Add sulfuric acid / White precipitate indicates either barium or calcium ions


Confirmation Test:
Add solution of sodium fluoride
Conduct flame test / White precipitate confirms calcium - no precipitate confirms barium
Brick red - calcium

Yellow-green - barium
Cu2+ / Add sodium hydroxide then add ammonia solution / Blue precipitate forms from an original blue-green solution - precipitate dissolves in ammonia to form deep blue solution


Confirmation Test: Conduct flame test / Green flame
Fe2+, Fe3+ / Add same of sodium hydroxide / Brown precipitate indicates Fe3+

Greenish precipitate indicates Fe2+ - rapidly turns brown

Confirmation Test: Add HCl
Add potassium hexacyanferrate reagent
Add potassium thiocyanate reagent / Dark blue indicates Fe2+

Deep blood red indicates Fe3+

Quantitative Analysis
  • There are a variety of techniques to determine the amount or concentration of an element, ion or compound in the sample.
  • These techniques include:
  • Gravimetric Analysis - involves weighing materials and determining the percentage composition of elements
  • Volumetric analysis - involves measuring the volume of solutions that react with other solutions
  • Instrumental analysis - involves the use of special instruments that can determine the concentration or amount of material by measuring a property of the material.

12.2 – Instrumental Analysis

Atomic Absorption Spectroscopy (AAS)
  • Atomic vapours selectively absorb and emit various frequencies of light.
  • When a sample of an element is vapourised in a hot flame, electrons are promoted from the ground state into unstable or excited energy levels.
  • As the electrons fall back to more stable levels they emit light through characteristic frequencies.
  • If white light is passed through an atomic vapour at a suitable low temperature, some wavelengths are selectively absorbed and dark lines appear the in the spectrum produced.
  • The dark lines correspond to the exact bright line wavelengths in atomic emission spectra.
  • The AAS was developed by CSIRO scientist Alan Walsh - AAS uses the exact principles as above.
  • This technique is very sensitive - it can detect concentrations in part per million and parts per billion.

Hollow-Cathode Lamp Selection

  • The light source in the AAS is usually a hollow-cathode lamp of the element.
  • Specific wavelengths of light characteristic of the elements being analysed are generated from this lamp.

Standard Solution Preparation

  • A standard solution of the metal being analysed is prepared using standard volumetric techniques.

Aspirating the Solutions

  • The dilution standards and the unknown solution are sprayed or aspirated into the flame or graphite furnace.
  • The flame in the AAS is about 1000C to increase absorbance of light.
  • The graphite furnace is about 3000C - it is more efficient.

Measuring Light Absorption

  • As the light beam passes through the vapourised sample, some of the light is absorbed.
  • A second reference beam passes through a monochromator which contains a diffraction grating and focussing mirrors.
  • The light then passes through a narrow slight to select only one of the wavelength bands - the light is now monochromatic.
  • Photomultiplier tubes are used the measure the light intensity and convert it into an electrical signal.

Calibration

  • Concentration measurements are determined from a calibration curve created with the standard solutions.
  • A control blank is also run - it should indicate zero.
Monitoring Trace Elements and Pollutants in the Environment

Essential Trace Elements

  • There are many elements that are needed in small quantities by plants and animals for the proper function or their physiological processes.
  • There trace elements include copper, zinc, cobalt and molybdenum.
  • The advent of AAS has allowed for a deeper understanding of trace elements and its composition in organisms and the environment.

Metal / Function
Copper / Haemoglobin formation and enzyme action
Zinc / Enzyme action, metabolism of amino acids and insulin synthesis
Selenium / Enzyme action
Manganese / Enzyme action, blood clotting, carbohydrate and fat metabolism
Cobalt / Red blood cell formation
Chromium / Required for carbohydrate, fat and nucleic acid metabolism
Iodine / Proper functioning of the thyroid gland

Uses of AAS

  • AAS is capable of detecting the presence of well over sixty metals in minute concentrations.
  • It can be used for:
  • To test the purity of metallic samples in the mining industry
  • Monitor pollution levels in waste waters - especially heavy metals
  • Detect harmful levels of metals in organisms
  • Monitor dangerous air-borne metallic particles
  • Quality control of alloys
  • Detect minute contaminants in food

Why Monitor Cations and Anions

  • Phosphate occurs in waterways at low concentrations and essential for normal aquatic plant growth.
  • At high concentrations can lead to:
  • Algal bloom
  • Covers surface of lake
  • Prevents penetration of light - hence plants and fish die
  • Algae dies when phosphate is used up
  • Decay uses oxygen in water
  • Zinc and copper:
  • Desirable in small concentrations in water bodies
  • High concentrations are harmful to humans and cause poisoning
  • Lead is poisonous - intellectually retards young children and causes brain damage.
  • Was widely used in petrol
  • Was a constituent of house paint

Chapter 13 – Atmospheric Chemistry

13.1 – Chemistry of Atmospheric Pollution and Ozone Depletion

Composition and Structure of the Atmosphere
  • The atmosphere is a thin gaseous layer that extends to a distance of about 600 km above the Earth's surface.

Troposphere

  • The troposphere is the layer closest to the ground.
  • 75% of mass in concentrated in the troposphere.
  • The air pressure is also the highest - 100kPa on the ground.
  • At 15km altitude the air pressure drops to 10kPa.
  • Temperature decreases with increase altitude.
  • 15C at the bottom and -50C to -60C at the tropopause.
  • The transfer of gases of pollutants across the tropopause is slow.
  • Water vapours freezes before reaching the stratosphere as to prevent water loss
  • The tropopause is at a higher altitude above the equator than at the poles due the expansion of air.

Stratosphere