Natural Gas

Nota:

•  A mixture of gases, whose main components are saturated hydrocarbons characterised into wet and dry gas

1. Liquefied Natural Gas

   Nota:

   • Liquefied by cooling to -162C and increasing the pressure rapid phase transmission occurs when LNG meets liquid water   
   1. Transportation & Marketing
   2. Treatment
      1. Condensate removal,
      2. CO2 removal
      3. Dehydration
      4. Mercury & H2S removal
   3. Refrigeration
   4. Liquefaction
   5. Storage & Loading

      Nota:

      • Aluminium is used as a material for containment, requires Hg to be below detection limit, as it causes the metal to be brittle
2. Uses
   1. Domestic heating and cooking
   2. Electric generation
   3. industrial production of higher value chemicals
   4. Commercial heating, transport fuel
3. Combustion of Methane

   Nota:

   • The highly exothermic overall equation is:CH4 + 2O2  → CO2 + 2H2O  collision theory best explains the combustion
   1. Calorific Value

      Nota:

      • Measure of the heat released when burnt measured in british thermal units per cubic ft
      1. 1000 British Thermal Unit
   2. Specific Gravity

      Nota:

      • Determines how much gas will pass through the orifice in a set of time at a given pressure air has a value of 1 while lighter gases have lower values
   3. Burning Velocity
   4. Wobbe number

      Nota:

      • gases with the same Wobbe number delivers the same amount of heat Wobbe number combines the calorific and specific gravity, it is calculated by:Wobbe number = (Calorific Value)/√(Specific Gravity)
      1. Wobbe No =(cal value/√(specifc grav)
      2. wobbe no of NG 1357
   5. Burning velocity of a Gas

      Nota:

      • •Measures the speed at which a flame is propagated in a gas. •Often expressed as the flame speed factor, S. S = 100 for Hydrogen.
4. Industrial reactions
   1. water gas shift (WGS)

      Nota:

      • Reaction of the produced CO with water to increase H2 from SR and CO2 hydrogen is purified by the removal of CO which ooisons catalysts  uses FeO and CrO as catalyst
      1. High temperature shift

         Nota:

         • at 370-420C over an Fe catalyst that is reduced to magnetite. large amount of steam is are added to prevent methanation caused by metallic Fe, it raises the production cost
         1. Fe catalyst
         2. 370-420C
      2. Low temperature shift

         Nota:

         • at about 230C over a CuO/ ZnO/ Al2O3. the temperature should be too high because of sintering problems
         1. T= 230C
         2. Catalyst: Zno/CuO
         3. Sintering
      3. CO2, H2O
   2. Methanol synthesis

      Nota:

      • high pressure 50-100 bar and low temperature (500-550K). selective catalysts such as Cu/ ZnO/Al2O3. low yield, recycling built into the system
      1. acetic acid
      2. Methyl formate
      3. formaldehyde
      4. acetaldehyde
      5. Esters
      6. fuel cells
   3. Catalyst

      Nota:

      • •A substance that promotes the rate of reaction by providing an alternative reaction pathway, and is regenerated at the end
      1. Homogenous Catalyst

         Nota:

         • •Catalysts that are in the same phase as the reactants.Normally gas or liquid. Not common in industrial chemistry, as separation problemsExamples are use of KOH in production of Biodiesel in small scale batch process.
      2. Heterogeneous Catalyst

         Nota:

         • catalysts that are in a different phase as the reactants, normally a solid (transitional metal or an oxide of a transmission metal)common in industrial chemistry as separation is normally straight forward
      3. Catalyst components
         1. Active species
         2. Support

            Nota:

            • often catalyst are mounted on support materials, they must be inert, have high surface area, high strength and stability and be attrition resistant.
         3. Solvent sytem
         4. Promoters and Poisons

            Nota:

            • substances that when added to the catalyst in small mount, improve one or more of its properties. promoters are usually electropositive while poisons are usually electro negative species.
            1. Activity enhancement

               Nota:

               • alkali metals are often added to increase activity.
            2. selectivity improvment

               Nota:

               • This can occur by changing the reaction pathway on the surface, even poisoning the surface 
            3. Increased catalytic lifetime

               Nota:

               • improves the lifetime by preventing sintering or slowing the build up of irrevesible poisons on the surface
      4. Catalyst Decay
         1. Sintering

            Nota:

            • when metal on support undergoes heating, the individual particles can migrate and fuse together.
         2. Attrition

            Nota:

            • Powdering of the catalyst, blocking the reactor and reducing gas flow
            • powdering of the catalyst blocking the reactor and reducing gas flow
         3. Poisoning
      5. Catalyst descriptors
         1. % Conversion

            Nota:

            • the % of reactants which are reacted to form products.
         2. % Selectivity

            Nota:

            • the % of desired product expressed as a percentage of the total reaction products.
         3. % Yield

            Nota:

            • conversion x selectivity.
         4. Turnover number

            Nota:

            • Specifies the maximum use that can be made of a catalyst for a particular reaction under defined conditions by the number of molecular reactions or cycles occurring at the reactive centre up to the decay of activity.
   4. Auto thermal reforming

      Nota:

      • exothermic process that uses oxygen and carbon dioxide or steam with methane to produce syngas. outlet temperature and pressure is 1000C and 100 atm   
      1. Syn gas
         1. CO, H2
      2. T: 1000C, P: 100atm
   5. Steam reforming
      1. Ammonia synthesis

         Nota:

         • reaction between N and H base cheicals for fertilizers, explosives and domestic cleaning agents 
         1. Fe catalyst
            1. Nitric acid

               Nota:

               • catalytic oxidation of ammonia, known as the Oswald process
         2. P:100-250 bar
         3. T: 675-770K
      2. Process

         Nota:

         • highly Endothermic reaction with Ni catalyst between CH4 and water to produce a mixture of CO and H2 from heating coal in an air free environment at 900 C
         1. feedstock purification

            Nota:

            • removes poisons including S and Cl to increase life of the downstream steam reforming and other catalyst
         2. Reforming and steam generation
         3. High temperature conversion
         4. Heat exchanger
         5. Product purification

            Nota:

            • Liquid absorption for CO2 removal e.g amine process PSA unit is used to purify gases by changing pressures, materials used include zeolite and acticated charcoal
      3. CO, H20
   6. stranded gas
      1. Fischer – Tropsch chemistry

         Nota:

         • used an alternative in converting the gas to LNG. main reaction for gas to liquid technology the products includes olefins, paraffins, oxygenates, branched compounds, aromatics modern plants use Co and Fe based catalyst  
         1. Catalyst:
         2. LNG
         3. Co, Fe,Rh catalyst
            1. Products
               1. Oleffins
               2. Parraffins
               3. Aromatics
               4. oxygenate
               5. Branched compounds
5. components
   1. Aliphatic Hydrcarbons
      1. Methane

         Nota:

         • Colourless/ odourless alkane Melting point – 182.5 °C Boiling point – 161.6 °C
      2. Ethane
      3. Propane
      4. Butane
   2. CO2
   3. Oxygen
   4. Nitrogen
   5. Hydrogen Sulphide

      Nota:

      • Used in the production of other Chemicals Sulphuric acid, cellophane, vulcanised rubber, etc
      1. Sulphuric acid
      2. cellophane
      3. vulcanised rubber
   6. Rare Gases: Ar, He, Ne, Xe

      Nota:

      • Used in Hospitals for MRI scanners
   7. Water
   8. Mercaptans
6. treatment
   1. Condensate separation
   2. Dehydration
   3. Contaminant removal
   4. Nitrogen Extraction
   5. fractionator
   6. Demethanizing
   7. Gas -oil separation
7. Advantages of burning
   1. Reduced sludge from scrubbing SO2
   2. Fewer emissions
8. Town gas
   1. cal value: 500btu
   2. wobbe no of 730
   3. Flame speed: 41