Introduction
Climate change is on the agenda – “they even talk about it on Gogglebox”. So ran a conversation in a discussion group in 2021. “I think they’re planning a huge wind farm on an island in the North Sea” Jean ventured. “And isn’t China beginning to close coal pits?” added Wendy hopefully. But it’s not straightforward, she continued: “even veganism would consume large amounts of land and energy, if it went to scale”.
Sally added to the difficulties by thinking of “unexpected effects, like the rise of cryptocurrency, based on computers that consume vast amounts of energy”. Reflecting on the sheer number and diversity of factors, Helen commented that “ideas will just have to coalesce from many different sources”. Her colleague Wendy added: “yes we need to look at the system as a whole – as we do with the weather or the human body”.
In grappling with the endless list of climate change issues, the group soon reached an all too familiar impasse: what is there to discuss that might give us some hope? The idea they settled on was to look at some of the ideas and initiatives aimed at mitigating its effects.
Recycling plastics
First thoughts were about cutting down greenhouse gas emissions in manufacturing and construction, by rethinking “waste” – re-using cast-off materials. A Government-funded initiative in New Zealand – the Learning Hub – is addressing recycling in one particular area of manufacturing: plastics. A national plan aims to phase out all plastics that cannot be recycled by 2025, including food packaging made of PVC and polystyrene and single-use plastic bags. One of the many projects in the scheme is based on the concept of the “circular economy”. A type of plastic called PET is reused repeatedly in an endless loop. The PET plastic in soft drink bottles is collected, processed into flakes and reconstituted as new PET for new packaging … and so on, over and over repeatedly. It doesn’t eliminate the problem but reduces the cost to the climate of continuously manufacturing new plastic.
The possibility of cutting back on the production of plastics, raised a set of fundamental questions in the discussion group: what is plastic? How is it made? What goes into making it? Why doesn’t it degrade naturally?
All plastics are made of molecules called hydrocarbons, which are themselves composed of hydrogen and carbon atoms in long chains, called polymers. Oil and natural gas are common sources of these molecules. Various kinds of plastic with different properties are made by introducing specific additives into the process.
Figure 1a shows a model of a short section of a long polypropylene molecule. This type of polymer is used for stronger objects like baskets and containers (figure 1b)
Figure 1a short section of a polypropylene molecule
Figure 1b polypropylene baskets
More flexible things, such as plastic bags or sandwich wrappers are made of polyethylene (known as polythene) as shown in figures 2a and 2b.
Figure 2a polythene sheet (aka polyethylene)
Figure 2b Short section of a polyethylene molecule
These models of molecules of plastic offer a clue as to how plastics are made. As the polymers are just long chains of simple repeating units (called monomers) they are produced by joining one monomer to another repeatedly in a chemical reaction. The source of most monomers is petroleum. Plastics are doubly damaging for the environment: not only do they not degrade, but they also contribute significantly to greenhouse gas emissions in the production process. 3.4% of global emissions were due to plastics in 2019, mainly from the fossil fuels used in their production.
Initiatives that recycle existing plastic to make new plastic objects obviously help reduce overall emissions by reducing demand for new production. Other initiatives seek to avoid the use of oil at all, as the source of the vital monomers. Biological sources, including starch, cellulose, lignin (from wood) and sugar, are being used to produce the polymers used for plastics, in areas such as packaging and crockery and cutlery for the catering industry. Welcome though such bioplastics are, new challenges will have to be met as their use increases, to ensure they don’t compete unfavourably for land and to minimise the release greenhouse gases as they decompose.
Electrical energy
Whatever the fate of oil and gas in the coming decades, we will continue to need energy to cook our food, manufacture goods and get around; where will it come from? The energy to which we have become accustomed is locked up in the molecules of which coal, oil and gas are composed. These fuels originally came from the decay of ancient plants that had captured energy directly from the Sun through photosynthesis. What alternative ways are available to us for tapping into the Sun’s energy, without the release of carbon dioxide?
One obvious way is to set up solar panels on rooves to heat up water directly. Another is to capture the energy of movement in wind or the waves it causes on the oceans. Rainfall captured in high-level mountain reservoirs is another potential source. These all result indirectly from the Sun, through the weather systems it creates in the atmosphere. The Moon also offers an alternative, through the rhythmic movement of the tides it energises thanks to the gravitational attraction between it and the Earth. A completely different source is the energy locked up, not in molecules but in the miniscule nuclei lying at the core of atoms. This source of energy can be tapped into when unstable nuclei of radioactive elements such as uranium and plutonium break up (“fission”) in nuclear reactors. Inordinate quantities of energy are released in this process because extraordinarily strong forces are involved in holding together the components of the nucleus in an atom. In this sense, a nucleus is rather like a jack-in-a-box, with an exceptionally strong spring inside, locked down with an incredibly strong latch.
The question of how to source energy renewably is a key issue for the near future. Equally important, however, is the issue of getting it to where it’s needed, when it’s needed. Some sources, such as rooftop solar panels, can be tapped into directly and used locally as needed; most, however, need to be linked to a system capable of storing and distributing energy according to demand.
Electrical energy is especially well suited for distribution over large areas. It can be transmitted readily and rapidly through wires and cables, in contrast to the time and cost of shipping oil and gas. Storage, on the other hand, is more of a problem; electrical energy from a generator is available only at the instant that it is produced. It is generated in huge turbines, driven by high pressure steam in a power station, by wind in a wind-turbine or the flow of water in a hydroelectric system. These are switched on and off during the day and night, in response to overall demand across the network (the National Grid in the case of the UK).
The common factor, in all these examples of electrical generation, is rotation. The basic physical principle is that electrical energy is produced whenever a metal wire passes through a magnetic field. Inside giant generators are copper wires coiled round and round on a spinning rotor which is itself immersed in a strong magnetic field.
Figure 3 Wire rotating through a magnetic field
Figure 4 Cutaway model of a generator
When connected to an outside circuit – leading to homes and factories – this makes electrical energy instantly available at every socket, in every location connected at that moment.
Fossil fuels have traditionally been used to create the steam to drive the turbines. Today’s challenge is to install alternative systems for turning the turbines – at scale. The energy in the movement of wind is one way, the ebb and flow of the tides another; the nuclei of atoms, yet another. A combination of many alternative sources will be required to supply the energy required around the world in the future.
Demand for this instant energy fluctuates dramatically, however, with the cycle of day and night and passing of the seasons. We need it at home, in the workplace, on the road, in the air and on the seas. To distribute energy for consumption when and where it’s needed, rather than when it’s generated, some system of storage is needed. A major question for the future is how to hold onto energy for later use and get it to where there are no sockets in the wall – vehicles, mobile phones and aircraft, for example. This is the role of batteries.
Redesigning batteries
Batteries are devices in which energy that is locked up in the structure of specific chemicals gets transformed into electrical energy, ready for use wherever and whenever it is needed. This transformation is made possible because the atoms in the materials of a battery, like all atoms, are made of electrically charged particles. Matter is fundamentally electrical, although we aren’t usually aware of this because the positive and negative parts balance out exactly, rendering most everyday materials electrically neutral.
The positive components of atoms (called protons) are concentrated in the centre in the nucleus. The negative parts (called electrons) are in a kind of spherical cloud around the nucleus, but far from it. In most everyday materials these components remain in position permanently, giving us the steady, electrically neutral world of objects and surroundings to which we are generally accustomed. A battery however is designed to upset this condition. It has two “ends” (known as electrodes) which are made of dissimilar materials and separated by a gel or liquid (called an “electrolyte”). Chemical reactions take place at each end where the gel or liquid meets the electrodes. In these reactions, negatively charged electrons are released at one electrode and are taken up at the other. The electrode at which the electrons accumulate becomes negatively charged and is denoted by a – sign on the outside of the battery. If wires (or other metal links) are connected to this terminal, then to a light bulb – or mobile phone, radio or any other device – and then back to the battery at its positive end, a circuit is formed. This enables the electrons to flow along the wire from the negative terminal towards the positive one.
In a simple “lemon battery (figure 5), two everyday metals form the electrodes (a copper coin and zinc nail) and the lemon juice provides the electrolyte. Demonstrations of this wonderful effect are given to many schoolchildren.
Figure 5 Lemon battery
Energy is released during the chemical reactions at the electrodes of the battery, which is transferred to the passing electrons. This is released in the device(s) in the circuit – mobile phone, torch bulb or radio, for example. The voltage of the battery reflects the amount of energy each electron carries, and this depends on the choice of materials of which it is made.
The main materials that make up a battery are the two electrodes and the paste or gel of the electrolyte between them. The type commonly found in torches and other domestic devices have one electrode made of carbon in the shape of a rod running down the centre and the other, forming the outer case, made of zinc. Between the two is a paste which acts as the electrolyte.
Figure 6 Carbon-zinc torch battery
The kind of battery being increasingly used in portable devices and electric vehicles, however, has an electrode made from a derivative of lithium.
The batteries traditionally used in motor vehicles use lead in their electrodes and other types of battery use other metals – nickel and cadmium, for example.
Figure 7 Lithium ion battery
As electrification rapidly develops, in order to phase out fossil fuels, a new environmental concern arises: environmental damage due to mining and disposal of the metals needed for batteries. The lithium extraction process uses large quantities of water – 65% of the region’s water in the case of Salar de Atacama in Chile, where it impacts on local farming. There is also the danger of leakage of toxic chemicals during the processing of lithium which can impact on wildlife. An alternative type of battery, using sodium in place of lithium, is currently the subject of intensive research. It causes far less environmental damage, and the main component, sodium, is plentiful, not least in the salt (sodium chloride) of the briny seas.
Part one of this blog has looked at plastics, electrical energy and batteries. If you have the appetite, a second part continues with descriptions of innovations in building design and construction.
© Andrew Morris 5th December 2022
Getting to Grips with Science 