'Outline the chemical and physical processes involved in the production of ONE of the following from a natural raw material'
(I chose polyethylene bottle):
Include relevant chemical equations in your answer. (6 marks)
My answer:
Harvesting sugar canes:
Sugar canes are solid raw materials from where glucose can be extracted, through crushing which increases the surface area for the process of fermentation.
Fermentation of glucose:
Fermentation is an exothermic process in which glucose is broken down to ethanol and carbon dioxide by the action of enzymes present in yeast. The yeast secretes enzymes, each of which catalyses a specific step in the fermentation reaction sequence. Sucrase enzymes in yeast catalyses the break down of sucrose into glucose and/or fructose, then zymase enzymes catalyses the breakdown of glucose into ethanol and carbon dioxide:
•*(chemical reaction)
• (chemical reaction)
Yeast can produce ethanol concentrations of up to 15% ethanol. At these concentrations, yeast cells die and fermentation stops. Fractional distillation is then used to obtain 95% ethanol. In order to obtain 100% ethanol, more complex distillation is required due to the strong hydrogen bonding between ethanol and water.
Dehydration of Ethanol:
Ethanol can be dehydrated to give ethene by heating it with an excess of concentrated H2SO4 at about 170˚. A strong catalyst is required as the hydroxyl functional group (-OH) is bonded relatively strongly to the CH3CH2 chain. As such, a catalyst provides an alternative pathway which lowers activation energy for the reaction to occur.
(structural equation)
Production of polyethylene
Initiation:
An organic peroxide is heated to produce free radicals. The free radicals open out a double bond in an ethylene monomer and forms an ethene radical.
(structural equations)
Propagation:
The ethene radical opens out the double bond in a neighbouring ethene to create a dimer radical. The opening out of bonds and joining continues to produce an ever-increasing chain length
(structural equation)
Termination:
Long radicals meet and bond to form a non-activated polymer (polyethylene). Since these process relies on random molecular collisions, chain lengths and thus molecular weights vary. An inhibitor is added to halt the formation of free radicals so that size/molecular weight of polymer chains can be regulated.
(structural equation)
LDPE:
If these polymer chains are regulated where there is an extensive chain-branching, then LDPE can be produced, because of this property as well as the lack of chain-stiffening side groups and cross-linking. Due to the dispersion forces between the long chains of polymers of the C and H atoms, it is relatively soft and very flexible with a fairly low melting point. These properties thus make it suited for making squeeze bottles in both the laboratory and the home.
Any feedback?
Much thanks
(I chose polyethylene bottle):
Include relevant chemical equations in your answer. (6 marks)
My answer:
Harvesting sugar canes:
Sugar canes are solid raw materials from where glucose can be extracted, through crushing which increases the surface area for the process of fermentation.
Fermentation of glucose:
Fermentation is an exothermic process in which glucose is broken down to ethanol and carbon dioxide by the action of enzymes present in yeast. The yeast secretes enzymes, each of which catalyses a specific step in the fermentation reaction sequence. Sucrase enzymes in yeast catalyses the break down of sucrose into glucose and/or fructose, then zymase enzymes catalyses the breakdown of glucose into ethanol and carbon dioxide:
•*(chemical reaction)
• (chemical reaction)
Yeast can produce ethanol concentrations of up to 15% ethanol. At these concentrations, yeast cells die and fermentation stops. Fractional distillation is then used to obtain 95% ethanol. In order to obtain 100% ethanol, more complex distillation is required due to the strong hydrogen bonding between ethanol and water.
Dehydration of Ethanol:
Ethanol can be dehydrated to give ethene by heating it with an excess of concentrated H2SO4 at about 170˚. A strong catalyst is required as the hydroxyl functional group (-OH) is bonded relatively strongly to the CH3CH2 chain. As such, a catalyst provides an alternative pathway which lowers activation energy for the reaction to occur.
(structural equation)
Production of polyethylene
Initiation:
An organic peroxide is heated to produce free radicals. The free radicals open out a double bond in an ethylene monomer and forms an ethene radical.
(structural equations)
Propagation:
The ethene radical opens out the double bond in a neighbouring ethene to create a dimer radical. The opening out of bonds and joining continues to produce an ever-increasing chain length
(structural equation)
Termination:
Long radicals meet and bond to form a non-activated polymer (polyethylene). Since these process relies on random molecular collisions, chain lengths and thus molecular weights vary. An inhibitor is added to halt the formation of free radicals so that size/molecular weight of polymer chains can be regulated.
(structural equation)
LDPE:
If these polymer chains are regulated where there is an extensive chain-branching, then LDPE can be produced, because of this property as well as the lack of chain-stiffening side groups and cross-linking. Due to the dispersion forces between the long chains of polymers of the C and H atoms, it is relatively soft and very flexible with a fairly low melting point. These properties thus make it suited for making squeeze bottles in both the laboratory and the home.
Any feedback?
Much thanks
