The “ozone depletion potential” is the ability of gases to degrade ozone if released into the atmosphere, and is compared against the value for CFC-11 (CCl3F), which was chosen to be 1. The “halocarbon global warming potential”, or greenhouse warming potential of a gas, is a calculation of how strongly the release of a certain quantity of that gas would contribute to global warming, via the greenhouse effect. Once again, it is compared against the value for CFC-11 (CCl3F), which has the value of 1.
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HFC-134a (1, 1, 1, 2-tetrafluroethane, CF3CH2F), a widely used refrigerant, is more environmentally suitable than many other possible refrigerants. Firstly, its ozone depletion potential (ODP) is completely nonexistent, meaning that the release of HFC-134a into the atmosphere would not damage any more of the ozone layer. This is superior to many other proposed replacements to CFC-11, which often feature greatly lowered ODP, rather than zero ODP. HFC-134a also has a reduced halocarbon global warming potential (HGWP) of 0.25, a quarter of CFC-11’s value. HFC-134a is not the lowest in this value, however.
Some other possible refrigerants, such as ammonia and iso-butane (C4H10) have incredibly low, almost non-existent HGWP values. However, both of these gases (especially ammonia) can be considered toxic to humans, and both are flammable, leaving them liable to explosion from a spark if they were to leak from a refrigeration unit. Because of this, HFC-134a is therefore a more suitable modern refrigerant for domestic use. (Website 1)
Q1ii)
CCl2=CHCl, or trichloroethylene, can be converted to HFC-134a (also called R-134a) by carrying out several reactions in sequence. In the first part of the reaction, CCl2=CHCl is reacted with hydrogen fluoride (HF) to produce CCl2F CH2Cl. In the second part of the reaction, the CCl2F CH2Cl is reacted with 2HF to form CF3 CH2Cl, and then with another HF to created the HFC-134a (CF3=CH2F). This whole reaction process is shown in full below
In order for HFC-134a’s usage to become widespread, its conversion from trichloroethene through industrial means needed not only to be feasible, but both cost and time effective as well.
Firstly, the reaction process takes place within two separate chambers. One of the chambers is where the reaction products can be separated, allowing the HFC-134a to be isolated from dangerous, or otherwise unwanted products. The other chamber deals with recycling the trichloroethylene (CCl2=CHCl) and hydrogen fluoride (HF) used within the reaction, so they can be reused within subsequent reactions. This helps to make the HFC-134a conversion process more cost effective. A fluorination catalyst is also used in the reaction process, helping to make the conversion more feasible and time efficient. The conversion process also takes place at high temperatures (up to 400oC) and at super-atmospheric pressure to further ensure that it operates both cost and time effectively. (Website 1)
Q2i)
According to the research published in the article “Regulating To Reduce Emissions Of Fluorinated Greenhouse Gases” from the Journal of fluorine chemistry, the chemical compounds which contribute the most to global warming are, in order: carbon dioxide (CO2), methane (CH4), Nitrous Oxide (N2O), the ozone depleting substances (CFCs & HCFCs), and then the fluorinated greenhouse gases, namely hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and Sulfur hexafluoride (SF6)
Carbon dioxide (CO2), the gas most contributive to global warming, is a small atmospheric molecule that is a key component of our atmosphere as it is used in the carbon cycle of plants. Of all of the contributing gases, CO2 has the lowest global warming potential (GWP). However, due to the incredibly high production and release of the gas into the atmosphere, CO2 is still the leading cause of global warming.
Methane (CH4) is another simple chemical structure, and is the main component of natural gas. Like CO2 it has a relatively low GWP, but is a major contributing factor to global warming due the large amounts of the gas released into the atmosphere.
Nitrous Oxide (N2O) is an oxide of nitrogen, more commonly called “laughing gas” that is used for both anaesthesia and for its oxidizing effects. N2O’s GWP is higher than methane and carbon dioxide, but its level of emissions is also much lower
The ozone depleting substances, namely HCFCs & CFCs, were incredibly common in the early days of domestic refrigeration, as they were non flammable, non toxic and inexpensive. They were quickly phased out from general use, however, when it was discovered that they had an extremely detrimental impact on the ozone layer. They also contribute to global warming, and though they were largely replaced by the use of other gases such as HCFs, they still contribute significantly to global warming.
Hydrofluorocarbons (HFCs) are chemically similar to CFCs, but do not share their ozone destroying effects. As a result of this similarity and due to the inert nature of HFCs (non-flammable & non-toxic in almost all cases) they are widely used as replacements for CFCs in a variety of domestic appliances and products. However, HFCs feature considerable global warming potentials (GWPs), making them a key contributor to global warming.
Compound
Compound Emissions
(million tonnes)
Global Warming Potential (100 year vs. CO2)
GWP emissions
(million tonnes CO2e)
Percentage contribution to global warming (%)
Carbon Dioxide (CO2)
30800.00
1
30800
65.4
Methane (CH4)
350.00
21
7350
15.6
Nitrous Oxide (N2O)
11.00
310
3410
7.2
Ozone Depleting Substances (CFCs &HCFCs)
0.60
8100
4860
10.3
Hydrofluorocarbons (HFCs)
0.14
2800
392
0.8
Perfluorocarbons (PFCs)
0.02
6500
130
0.3
Sulfur hexafluoride (SF6)
0.01
23900
143
0.3
Perfluorocarbons (PFCs), hydrocarbon derivatives, are another set of environmentally damaging compounds, especially when they are saturated and within the C1-C6 range. They are useful compounds in the electronics industry, though it is an aim that their usage is kept to the absolute minimum and only when no other compound would perform the desired function in their place. Like HFCs, they have a lower level of emissions, but a high GWP
Sulfur hexafluoride (SF6) is a technically diverse gas, useful for a diverse range of applications, but most commonly used as a dielectric gas in situations involving high voltages because of its dielectric strength and constant, its properties for arc (spark gap)-quenching and its suitability for use in transferring heat. Its level of emissions may be the lowest of all contributing gases, but its GWP is by far the highest. (Lindley, 2005)
Emission values for these key compounds, and their percentage contributions to global warming, are shown in the table below.
Table 1: Greenhouse gas emissions in the year 2000 [Adapted from table 1 (Lindley, 2005)]
The relative dangers of certain molecules, in regards to global warming, can also be assessed via radiative forcing. Radiative forcing is the effects of the heat energy produced by solar rays being held within the atmosphere (most crucially between the lowest part of the atmosphere [troposphere] and the stratosphere) of earth, rather than escaping out into space. This effect is made worse by the over abundance of certain gases in this section of the atmosphere. Therefore, measuring the radiative forcing effects of certain gases can, in turn, help work out how much of an effect that molecule is having on global warming. A figure, showing the extent of radiative forcing effects for different gases is shown.
Figure 1 (right): estimated radiative forcing effects of key gases from 1990-2015 [Figure 1 from (Lindley, 2005)]
It is clear from the results shown that in order for the effects of global warming to be lessened, reduction in the emissions of these key contributing compounds would need to be carried out. Most crucially, the emissions of CO2 would need to be lessened, as it has the highest percentage contribution to global warming, as well as the largest radiative forcing value. The radiative forcing values for ozone depleting substances are also very large, but as these are being phased out and replaced by the fluorinated greenhouse gases (HFCs, PFCs. & SF6), they are less of a concern. (Lindley, 2005)
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Q2ii)
F-Gas regulation is a proposal designed to keep the usage of hydrofluorocarbons and perfluorocarbons under stricter control, so that their emission levels do not contribute any more significantly to global warming. This will be achieved through a variety of means, including: improved containment of gases, reduced and restricted gas usage and putting requirements on how these gases are destroyed. In some cases, a ban may even be placed on a certain gas, preventing it from being used for specific functions. Furthermore businesses that use produce or sell f-gases are required to disclose what quantities of F-gas they are using, creating and supplying respectively. In addition to this, those involved with F-gases will be trained on how to safely handle the gases and prevent any unnecessary leaks, and any significant use of F-gases must be labelled as such. These measures all serve the purpose of limiting the amount of fluorinated greenhouse gases that are leaked into the atmosphere, keeping the percentage contribution of fluorinated greenhouse gases to global warming as low as possible. (Lindley, 2005)
In accordance with these regulations, industrial refrigeration systems are now to be inspected on a regular basis. Details on these new procedures is found in the table below
Table 2: Inspection schedules for refrigeration units of different capacities [Adapted from table 2 (Lindley, 2005)]
Quantity of F-Gas in Refrigeration System
Inspection Frequency
(With No Leak Detection)
Inspection frequency
(With Leak Detection)
Containing up to 30 kg (excluding airtight systems which contain less than 6kg)
Once every 12 months
Installation not required
Containing up to 300kg
Once every 6 months
Installation not required (Presence of install halves inspection frequency)
Containing more than 300kg
Once every 3 months
Installation mandatory (Presence of install halves inspection frequency)
[Note: In the event of a leak, the system must undergo reinspection 1 month after the leak has been fixed]
Also, the F-gas regulation stipulates that certain refrigeration applications must be banned completely. Details on those affected applications are shown in the table below.
Table 3: Banned refrigeration applicants under F-gas regulation [Adapted from table 3 (Lindley, 2005)]
Type of Gas
Prohibited Usage
Date of prohibition
Fluorinated greenhouse gases
Non-refillable containers
Start of F-Gas Regulations
Fluorinated greenhouse gases
Windows for domestic use
Start of F-Gas Regulations
Fluorinated greenhouse gases
Other windows
One year after the Start of F-Gas Regulations
Fluorinated greenhouse gases
Footwear
1 July 2006
Fluorinated greenhouse gases
Tyres
Start of F-Gas Regulations
Fluorinated greenhouse gases
One component foams
One year after the Start of F-Gas Regulations (except when required to meet national safety standards
Hydrofluorocarbons and perfluorocarbons
Refrigerants in non-confined direct-evaporation systems
Start of F-Gas Regulations
Perfluorocarbons
Fire protection systems and fire extinguishers
Start of F-Gas Regulations
Hydrofluorocarbons
Novelty aerosols
Two years after the Start of F-Gas Regulations
Q2iii)
F-Gas regulations put restrictions on the many uses of fluorinated gases. One such restriction is that of HFC-134a in mobile air-conditioning units, such as those used in cars. The popularity of air-conditioning in cars has been rising steadily since the early 1990’s, such that now over 80% of cars in Europe have this feature installed. While the HFC-134a system is much more efficient than the earlier CFC systems, using less than half of the 1.5kgs of gas that they used, and further research was being carried out in order to make more efficient systems, the EU has still decided to prohibit their future usage, having the use of the gas gradually phased out until 2017 when its usage is completely banned. This will have a considerable effect on the HFC134a industry as its usage in cars and other similar transport makes up a considerable part of their market. In turn, car manufacturers will have to develop new air-conditioning systems in cars, and this will drive up the cost of newer car models to counter development costs. (Lindley, 2005)
3)
Ever since the realisation of mankind’s negative impact on the environment, preventative measures have been put in place to try and reverse them, and several different pieces of legislation help to ensure that this is the case.
The Montreal protocol, which banned the usage of CFCs and HCFCs, was created to help protect the ozone layer from further harm. In this regard, the protocol can be considered a success. Levels of ozone damaging gases in the atmosphere have been steadily falling, and it is estimated that the ozone layer could have repaired itself as early as 2050 (WMO, 2006).
However, the replacement of CFCs and HCFCs with fluorinate gases to combat the destruction of the ozone layer lead to more environmental concerns, namely that these fluorinated greenhouse gases were making a significant impact on global warming. While the impact of these gases on global warming may be less than that of some other greenhouse gases (namely CO2) their effects are still considerable, and several pieces of legislation have been set up to try and decrease their usage. Firstly, the Kyoto protocol listed several fluorinated greenhouse gases, including HFCs, PFCs and SF6, along with CO2, CH4 and N2O, as gases that must have their levels of emissions decreased. The F-Gas regulation, making reference to the Kyoto protocol, set regulations on the usage of the HFCs and PFCs, helping to reduce their prevalence in society. Despite this, global warming problems continue to rise, thanks to increasing atmospheric levels of CO2. As long as CO2 is so prevalent in the atmosphere, reducing the effects of comparatively less harmful fluorinated gases through legislation can only do so much in helping to combat the rising problems of global warming (Lindley, 2005 & Website 2)
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