Vanadium Phosphate Catalyst

Methane, CH₄, in natural gas can be used as a raw material to produce bromomethane, CH₃Br. Bromomethane (methyl bromide) can then be used in the chemical industry to produce fuels, chemicals, polymers and pharmaceuticals. When  bromomethane is converted into fuels and other chemicals, bromine is released in the form of hydrogen bromide, HBr. Using oxygen and a suitable catalyst, bromine from the hydrogen bromide by-product is embedded back into bromomethane so that no bromine is lost from the system.
Researchers at ETH, Zurich, have identified vanadium phosphate as an ideal catalyst for this reaction.
Vanadium(III) phosphate (vanadium(3+) phosphate), has the structure shown below:

It is a relatively mild oxidising catalyst.
It is a strong enough oxidising catalyst to allow hydrogen bromide to react with oxygen at the surface of the catalyst, but, it is not strong enough to oxidise the methane and brominated reaction products.
It is therefore possible to brominate methane in a single step at atmospheric pressure and at a temperature below 500°C.  The catalyst is also stable, able to resist the corrosive reaction environment.
This makes it an attractive catalyst for this important, industrial, chemical reaction.

Reference:
Vladimir Paunović, Guido Zichittella, Maximilian Moser, Amol P. Amrute, Javier Pérez-Ramírez. Catalyst design for natural-gas upgrading through oxybromination chemistry. Nature Chemistry, 2016; DOI:10.1038/nchem.2522

Further Reading:
Lewis Structures (electron dot diagrams): http://www.ausetute.com.au/lewisstr.html
2-Dimensional Structural Formula: http://www.ausetute.com.au/structural2D.html
Molecular Formula: http://www.ausetute.com.au/molecularformula.html
Halogenation of Hydrocarbons: http://www.ausetute.com.au/halogalk.html
Energy Profiles: http://www.ausetute.com.au/enerprof.html
Reaction Rates: http://www.ausetute.com.au/reactrate.html
Redox Reaction Concepts: http://www.ausetute.com.au/redoxreactions.html

Suggested Study Questions:

1. Draw the Lewis Structures (electron dot diagrams) for each of the following molecules:
   • methane
   • bromomethane
   • hydrogen bromide
2. Draw the 2-dimensional structural formula for each of the following molecules:
   • methane
   • bromomethane
   • hydrogen bromide
3. Give the molecular formula for each of the following molecules:
   • methane
   • bromomethane
   • hydrogen bromide
4. Write a chemical equation to represent the reaction between methane and bromine to produce bromomethane
5. Name the type of reaction given in question 4.
6. Give the reaction conditions necessary for this reaction in question 5 to occur at room temperature and pressure in your laboratory.
7. Why do you think a catalyst is required for this reaction above in order to produce commercial quantities of bromomethane?
8. Which organic compound, methane or bromomethane, do you expect to be the most chemically reactive? Explain your answer.
9. What is meant by the term "oxidising agent"?
10. Is the bromination of methane using bromine a redox reaction? Explain your answer.
11. Refer to the structure of vanadium(III) phosphate given in the article. Give the oxidation state (oxidation number) for each of the following:
    • vanadium
    • oxygen
    • phosphorus
12. Why do you think vanadium phosphate is talked about as being an "oxidising catalyst" rather than as an "oxidising agent"? Explain your answer.

Sulfuric Acid Train Derailed

A locomotive and all 26 carriages containing sulfuric acid derailed in north Queensland on Sunday 27^th December 2015.
The 800,000 L of sulfuric acid was bought by Incitec Pivot Limited (IPL) to be used in the production of ammonium phosphate fertiliser at its plant at Phosphate Hill (south of Mount Isa).

Glencore Plc has an agreement with Incitec Pivot Ltd to provide sulfur dioxide from the copper smelter to the Mount Isa acid plant. Sulfuric acid is produced by collecting and cleaning sulfur dioxide before converting it, first to sulfur trioxide, and then to sulfuric acid. The acid plant has the capacity to take up to 80% of the sulfur dioxide emissions from the copper smelter, significantly reducing the emissions of sulfur dioxide into the atmosphere. The sulfuric acid is then taken by train to Phosphate Hill, more than 100 km away.

Phosphate Hill combines a large open-cut phosphate mine with a plant for the production of fertiliser. The proved reserve is 29 Mt at 24.6% P₂O₅. The phosphate ore is first crushed and washed before being dissolved in sulfuric acid to produce phosphoric acid. Gypsum, CaSO₄.2H₂O, a by-product of the process, is stockpiled. The phosphoric acid is converted into ammonium phosphate fertiliser using ammonia gas:
 NH₃ + H₃PO₄ → NH₄H₂PO₄ (known as MAP)
2NH₃ + H₃PO₄ → (NH₄)₂HPO₄ (known as DAP)
The ammonium phosphate is then sent by train to the port at Townsville about 900 km away for shipment.

Wet weather hampered access to the disaster site for several days, but testing of the waters 8 km downstream in Horse Creek revealed changes in acidity. Locally sourced limestone is being used to treat the water.

References:
http://statements.qld.gov.au/Statement/2015/12/31/environmental-testing-continues-around-train-derailment-near-julia-creek
 http://www.abc.net.au/news/2015-12-30/fear-sulphuric-acid-leaked-train-derailed-waterway-julia-creek/7060070

Further Reading
 Copper Smelting
 Electrorefining
 Sulfuric Acid Production
Density Calculations
Percentage Composition 
 Intermolecular Forces
pH Scale 
pH Calculations for Acids  
Neutralisation

Suggested Study Questions:

1. Convert 800 000 L of sulfuric to a volume in:
   • megalitires (ML)
   • kilolitres (KL)
   • millilitres (mL)
2.  Assume the density of this sulfuric acid is 1.84 g mL^-1. What is the mass of 800,000 L of sulfuric acid?
3. Assuming all the sulfuric acid was distributed equally between the 26 carriages, what volume of sulfuric acid was contained in each carriage?
4. Write the chemical formula for each of the following:
• sulfur dioxide
• sulfur trioxide
• sulfuric acid
• sulfurous acid
5.  Convert 29 Mt of phosphate ore to a mass in
   • tonnes (t)
   • kilotonnes (kt)
   • kilograms (kg)
   • grams (g)
6.   A phosphate ore contains 24.6% P₂O₅
   • What mass of P₂O₅ is present in 1 tonne of the ore?
   • What mass of the element phosphorus is present?
   • What mass of the element oxygen is present?
7.  Give the systematic IUPAC name for each of the following:
   • NH₄H₂PO₄
   • (NH₄)₂HPO₄
8. Calculate the percentage by mass of nitrogen in
   • NH₄H₂PO₄
   • (NH₄)₂HPO₄
9. In situations in which too much nitrogen in the fertiliser can adversely affect germination, which phosphate, MAP or DAP, should be used? Explain your answer. 
10. Hygroscopy is the ability of a substance to  attract and hold water molcules from the surrounding environment. Which phosphate, MAP or DAP, would you expect to be more hygroscopic? Explain your answer.
11. Sulfuric acid from the derailed carriages is believed to be leaking into the water of Horse Creek. Do you expect the pH of the creek to be rising or falling? Explain your answer.
12. If the pH of the creek water was 3.0, calculate the concentration of hydrogen ions in the creek water.
13. Explain what the term neutralisation means.
14. Assuming limestone is composed of calcium carbonate only, write a balanced chemical equation for the reaction between sulfuric acid and limestone.
15. Would you describe the chemical reaction described by the equation in question 14 as a neutralisation reaction? Explain your answer.
16. In the laboratory you could use sodium hydroxide to neutralise sulfuric acid. Why isn't sodium hydroxide used to neutralise the sulfuric acid at the train derailment site?

 

Replacing Phosphates in Detergents

From the Sydney Morning Herald (Australia) July 17, 2011, "IN THE latest round of supermarket ''me-too-ism'', Coles and Woolworths have backed a plan to rid shelves of environmentally damaging detergents.

The supermarkets have pledged to make their home brand laundry detergents phosphate-free by next year, a year ahead of a pledge this month by discount supermarket chain Aldi to ban the chemicals, which have been linked with damage to waterways and marine life."

Sodium phosphates have often been added to detergents as a builder, or water softener. Builders are chemical compounds that remove calcium ions from solution by complexation or precipitation.

The sodium phosphates that have been used as builders include orthophosphates and complex phosphates:

1. Orthophosphates which precipitate out metallic ions such as calcium:
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
2. Complex phosphates which produce metallic complexes with metallic ions that do not necessarily precipitate out of solution:
   
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆

Sodium tripolyphosphate (STPP), the main detergent phosphate, is something of a wonder ingredient for detergents, helping to maintain pH, remove food and grease, inhibit corrosion, and suspend insoluble dirt. For the consumer, its main visible benefit was to reduce spotting and filming by sequestering calcium and magnesium ions in the wash water.

Sodium phosphates, which can make up to 50% of the weight of a detergent, can lead to problems with eutrophication of lakes and streams, resulting in the growth of algal blooms, killing fish and plants.

On July 1, 2010, major cleaning product manufacturers finished removing phosphates from all home automatic dishwasher detergents sold in the U.S. a result of new laws in 16 states, but consumers living in areas with hard water were not happy with many of the new phosphate-free products. Phosphate alternatives such as zeolites leave residue on dishware while citrates are expensive and don’t work as well.

In order to replace the effectiveness of phosphates, a long list of additives is used which can include:

• sodium citrate which helps maintain the proper pH level of the detergent helps immobilize soils that have been removed during the wash
  
• polyacrylates which are polymers designed to bind with calcium and magnesium ions, allowing the detergent to better perform
  
• tetrasodium etidronate which is also used as a water softening agent
  
• phosphonates which are also a water softening agents, but, although they contain phosphorus, the toxicity of phosphonates to aquatic organisms is low.
  

Reference:

http://www.smh.com.au/environment/conservation/phosphates-are-all-washed-up-20110416-1dijs.html#ixzz1JkEcsejm

Further Reading

Detergents

Naming Ionic Compounds

Writing Ionic Formula

Molecular Mass Calculations

Percentage Composition

Concentration (molarity)

Concentration (ppm)

Study Questions

1. Calculate the molecular mass (formula weight) of each of the following compounds:
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆
2. Calculate the percent by mass of phosphorus present _{in each of the following compounds:}
   
• trisodium phosphate, Na₃PO₄
• disodium phosphate, Na₂PO₄
• tetrasodium pyrophosphate Na₄P₂O₇
• sodium tripolyphosphate (STPP) Na₅P₃O₁₀
• sodium tetraphosphate Na₆P₄O₁₃
• sodium hexametaphosphate (NaPO₃)₆
3. Write the formula for each of the following
   
• tripotassium phosphate
• dipotassium phosphate
• tetrapotassium pyrophosphate
• potassium tripolyphosphate
• potassium tetraphosphate
• potassium hexametaphosphate
  
4. What do each of the following prefixes mean?
   • di
   • tri
   • tetra
   • hexa
   • poly
   
   
5. Assuming a particular brand of detergent, ABC, contains 35% by mass of sodium tripolyphosphate (STPP) Na₅P₃O_{10, how much phosphorus would be present in 10 grams?}
6. _{If 10g of ABC were placed in a dishwasher which used 60L of water to wash the dishwashers, what would be the concentration of ABC detergent in mol/L?}
7. _{Using the information in question 4, calculate the concentration of phosphorus in the wash water, in parts per million.}