Production of Materials

9.2 – Production of Materials:

Δ. Construct word and balanced formulae equations of all chemical reactions as they are encountered in this module:

• BASIC reactions to remember:

• Acid reactions:

• acid + base [pic 1] salt + water
• acid + metal [pic 2] salt + hydrogen gas
• acid + carbonate [pic 3] carbon dioxide gas + salt + water

• Complete combustion:

• hydrocarbon + oxygen [pic 4] water + carbon dioxide

• Displacement reactions:

• Y + X (anion)[pic 5] X + Y (anion); where Y > X on activity series.

• Alkene/alkane reactions:

• Cracking of pentane:

• pentane [pic 6] ethylene + propane  
• C5H12 (g)  [pic 7]  C2H4 (g) + C3H8 (g) 

• Hydrogenation of ethylene:

• ethylene + hydrogen [pic 8] ethane
• C2H4 (g) + H2 (g) [pic 9]C2H6 (g)

• Hydration of ethylene:

• ethylene + water [pic 10] ethanol
• C2H4 (g) + H2O (l) [pic 11] C2H5OH (l)

• Halogenation (more specifically, Chlorination) of ethylene:

• ethylene + chlorine [pic 12] 1,2-dichloroethane
• C2H4 (g) + Cl2 (g)  [pic 13] C2H4Cl2 (l)

• Hydrohalogenation (more specifically, Hydrofluorination) of ethylene:

• ethylene + hydrogen fluoride [pic 14] fluoroethane
• C2H4 (g) + HFl (g)  [pic 15]C2H5Fl (g)

• Reaction of cyclohexene with bromine water:

• cyclohexene + bromine + water [pic 16] 2-bromo-1-cyclohexanol + hydrogen bromide
• C6H10 (l) + Br2 (aq) + H2O (l) [pic 17] C6H10BrOH (l) + HBr (aq)

• Fermentation and other ethanol-based reactions:

• Dehydration of ethanol:

• ethanol [pic 18] ethylene + water
• C2H5OH (l) [pic 19] C2H4 (g) + H2O (l)

• Combustion of ethanol:

• ethanol + oxygen [pic 20] carbon dioxide + water
• C2H5OH (l)  + 3O2 (g)  [pic 21] 2CO2 (g) + 3H2O (g)

• Fermentation of glucose:

• glucose [pic 22] ethanol + carbon dioxide
• C6H12O6 (aq) [pic 23] 2C2H5OH (aq) + 2CO2 (g)

• Electrochemistry:

• Displacement of copper from solution due to zinc:

• zinc + copper sulfate [pic 24] zinc sulfate + copper
• Zn (s) + CuSO4 (aq)  [pic 25] ZnSO4 (aq) + Cu (s)

• Ionic equation of this reaction:

• zinc + copper(II) ion + sulfate ion [pic 26] zinc(II) ion + sulfate ion + copper
• Zn + Cu2+ + SO42- [pic 27] Zn2+ + SO42- + Cu

• Net ionic equation of this reaction:

• zinc + copper(II) ion[pic 28] zinc(II) ion + copper
• Zn (s) + Cu2+ (aq) [pic 29] Zn2+ (aq) + Cu (s)

• Half-equations of this equation:

• Zn [pic 30] Zn2+ + 2e¯
• Cu2+ + 2e¯ [pic 31] Cu

1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances:

• RECALL:

• An ALKANE is a hydrocarbon with ONLY single bonds between the carbons.
• An ALKENE is a hydrocarbon with 1 or MORE double bonds between carbons.

• Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum:

• Petroleum (crude oil) is a complex mixture of hydrocarbons consisting mainly of alkanes and smaller quantities of other hydrocarbons such as alkenes.
• Ethylene (systematic name: ethene), C2H4, is one of the most useful substances in the petrochemical industry, and is in extremely high demand.  
• Cracking is the process of ‘breaking’ large hydrocarbon molecules into smaller length chains, using heat (Δ).

• EG: the cracking of pentane into ethylene and propane:

                      [pic 32]

• Crude oil is separated into its different components using fractional distillation.
• Reason for Cracking:

• In refineries, the output of products DOES NOT match the economic demand; ETHYLENE is in very high demand, but it only makes up a very small percentage of crude oil.
• To match the demand for ethylene, low-demand, long-chain hydrocarbons are ‘cracked’ and ethylene is produced.

• There are two forms of cracking, catalytic cracking and thermal cracking.

• Catalytic Cracking:

• In this process, carried out in a ‘cat-cracker’, long alkane molecules (C15 - C25) are broken into just two molecules, an alkane and an alkene.
• This form of cracking uses a CATALYST to break the alkanes.
• The catalyst used are zeolite crystals:

• Zeolites are aluminosilicates (compounds made of aluminium, silicon and oxygen), with small amounts of metal ions attached.

• The reaction is carried out at 500°C, in the absence of air, with pressure just above atmospheric pressure.
• This process uses less heat than THERMAL cracking, but it cannot decompose large molecules completely into ethylene, so it is insufficient in meeting the demands of the industry.

• Thermal Cracking:  

• Also called ‘steam’ cracking.
• This process does not use a catalyst, only very high temperatures.
• The long-chain alkanes are passed through metal tubes at temperatures of 700°C to 1000°C, at pressure above atmospheric.
• The alkanes are decomposed completely into ethylene and other short chains.
• The use of steam is that is allows for easy flow of hydrocarbon gases, it dilutes the mixture to create smooth reactions, and it removes carbon deposits in the metal tubes.

• Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products:

• Ethylene has a highly reactive double-bond; It is a site of very HIGH ELECTRON DENSITY. One of the bonds readily breaks, creating two new bonding sites on the molecule:

                                          [pic 33]

• ADDITION reactions are a type of reaction ethylene can undergo; in these reactions, one bond in the double bond is broken, and the two atoms in a diatomic molecule are ‘added’ on.
• There are many types of addition reactions:

• Hydrogenation: Hydrogen is reacted with ethylene, using a platinum catalyst at 150°C. The product is ethane.

                         [pic 34]

• Hydration: Ethylene is reacted with water, using phosphoric acid as a catalyst, to produce ethanol. This is an industrially important reaction.

                    [pic 35]

• Halogenation: Reactive molecules from the halogen group (Fl2, Cl2 and Br2) can all react with ethylene. EG: Chlorine molecule reacting with ethylene forms 1,2-dichloroethane.  

                                [pic 36]

• Hydrohalogenation: In this reaction, a hydrohalogen (such as HCl or HFl) and ethylene react to form a halo-ethane. EG: HFl reacting with ethylene forms fluoroethane.

                          [pic 37]

• The MAIN advantage of the double bond is that ethylene can undergo polymerisation, a very important reaction that will be discussed later.

• Identify that ethylene serves as a monomer from which polymers are made:

• Polymerisation is the chemical reaction in which many identical small molecules combine to form one very large molecule.
• The small identical molecules are called MONOMERS, and the large molecule is called a POLYMER.
• Because of its reactive double bond, ethylene is able to undergo polymerisation; ethylene, a monomer, forms the polymer poly(ethylene).

• Identify polyethylene as an addition polymer and explain the meaning of this term:

• In an addition polymerisation reaction, no additional molecules (e.g. water) are produced – there is no gain or loss of atoms, the double bond simply ‘opens’ and monomers attach.
• Polyethylene is an addition polymer, as the ethylene molecules combine with each other in the following way:

                 [pic 38]

• As can be seen, no extra molecules are produced. A more realistic representation of the polyethylene polymer (with nine repeating units) is:

                 [pic 39]