Sustainable Energy: Towards a Zero-Carbon Economy using Chemistry, Electrochemistry and Catalysis

By Julian R.H. Ross

Sustainable Energy, Towards a Zero-Carbon Economy Using Chemistry, Electrochemistry and Catalysis provides the reader with a clear outline of some of the strategies, particularly those based on various chemical approaches, that have been put forward with the aim of reducing greenhouse gas emissions in order to achieve “zero carbon" by 2050. The author describes the chemistry of some of the processes involved, paying particular attention to those that involve heterogeneous catalytic steps and electrolysis methods. In cases in which the technology is already established, details are given of the reactor systems used. He discusses novel developments in the areas of transport, the production of essential products using renewable energy and the uses of sustainable biomass.

• Outlines international approaches to cutting or reducing greenhouse gas emissions
• Describes current production and uses of energy
• Outlines new approaches to energy supply and usage
• Discusses the hydrogen economy and the uses of renewable energy
• Outlines the importance of fuel-cell and electrolysis systems
• Discusses biomass as a resource of energy and fuels

• Language: English
• Publisher: Elsevier Science
• Release date: Feb 23, 2022
• ISBN: 9780128236307

Julian R.H. Ross

Julian Ross is a Physical Chemist with wide experience in the field of heterogeneous catalysis applied particularly to the conversion of hydrocarbons and to environmental protection. He was the founding editor of Catalysis Today and acted as Senior Editor of that journal for almost 30 years. He holds two Honorary Visiting Professorships in China where he has lectured frequently. Julian Ross has had wide experience assessing projects associated with energy and the environment, for example, for EU programmes. He was a member of the Council of Scientists of INTAS (funding projects in the former Soviet Union) and was its Chairman for three years during its final three years of operation. He was also for a number of years a member of the European Research Council panel assessing Advanced Grant proposals on engineering topics. He is a Member of the Royal Irish Academy (MRIA) and a Fellow of the Royal Society of Chemistry (FRSC).

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Chapter 1: Introduction

Abstract

This chapter introduces the problem of the increasing emissions of greenhouse gases from all regions of the earth and the effects of these emissions on the health of the planet, giving details of some of the most significant contributing molecules. It then discusses the aims relating to reductions of these gases established by the United Nations Framework Convention on Climate Change (UNFCCC) as shown in the sustainable development goals outlined in the Kyoto Protocol and the Paris Agreement. This is followed by a summary of some of the statistics on the emissions resulting from different sectors of the economy in European countries, this being largely based on a comprehensive report from the European Environment Agency. The data included, which are representative of values in other countries, show clearly the steadily increasing effects arising from the use of energy in categories such as industry, transport and agriculture.

Keywords

Greenhouse gases; Carbon dioxide; Water vapour; Methane; Nitrous oxide; Ozone; Chlorohydrocarbons; Kyoto protocol; Paris agreement; European emission statistics

Energy production and the greenhouse effect

Solar activity and global warming

For centuries, we have relied on our natural resources for the provision of energy. Early man relied on the combustion of biomass (predominantly wood) to provide heat and fuel for cooking. Very much later, roughly at the time of the Industrial Revolution, he discovered coal, oil and natural gas and these discoveries led to our current almost total dependence on fossil fuels for the provision of energy.a Until the Industrial Revolution, the earth’s population was predominantly agrarian and any fluctuations in climate that occurred were related only to variations in solar activity. Since then, however, there has been a steady increase in the average global temperature and it is now generally recognised that this change of temperature is related to increased emissions of the so-called greenhouse gases.

Fig. 1.1 shows the values of the solar irradiance and also the global temperature that have been measured over the period since 1880; although there have been some significant changes in the solar activity (and there was a marked maximum value around 1960), the measured values have remained relatively steady over the last 50 years. However, there has been a very significant increase in global temperature during the same period. It is now generally accepted (see Fig. 1.2) that human activities have been responsible for this increase in temperature.b

Fig. 1.1

Fig. 1.1 Global temperature and solar activity since 1880. The yearly variations of both these parameters are shown by lighter curves and these have been averaged to give the more distinct curves. (Source: https://climate.nasa.gov/.)

Fig. 1.2

Fig. 1.2 IPPC key findings. Predicted major changes due to global warming. (Source: https://climate.nasa.gov/.)

The greenhouse effect

Much life on earth as we know it depends on the light radiation from the sun that penetrates through the atmosphere to warm the earth’s surface. Without the atmosphere, much of the incident radiation would be re-emitted from the surface and would be totally lost in space. Fortunately however, the atmosphere acts in the same way as does the glass in a greenhouse,c absorbing and reflecting back much of the re-emitted radiation and ensuring that the temperature of the atmosphere is increased. This process is shown schematically in Fig. 1.3. The resultant temperature on earth is a delicate balance of the levels of incoming and reflected radiation and is thus very susceptible to changes in the composition of the atmosphere; if too much of the reflected radiation is retained by the atmosphere, the temperature of the earth will rise.

Fig. 1.3

Fig. 1.3 Schematic representation of the greenhouse effect. (Source: From Wikipedia (https://en.wikipedia.org/wiki/Greenhouse_effect/).)

Greenhouse gases

Table 1.1 lists the main greenhouse gases associated with global warming, giving for each the chemical formula, the global warming potential relative to that for CO2 over a 100-year lifespan and the atmospheric lifetime in years.

Table 1.1

Reproduced from the Fourth Assessment Report (Intergovernmental Panel on Climate Change, IPCC, 2007).

Table 1.2 shows the main sources of these greenhouse gases and also gives the pre-industrial atmospheric concentrations and the current atmospheric concentrations. The first three gases all existed in the pre-industrial era, although the concentrations have all increased since, while the last entries all refer to man-made gases introduced over the last century. We obtain an approximation to the relative contributions of the relevant gases to global warming if we multiply the current concentrations of each gas by the global warming potential from Table 1.1. The resultant figures show that the main culprits are CO2, methane and nitrous oxide: not taking into account the small contributions of the fluorine-containing molecules, CO2 contributes 73.3% of the total global warming potential of these gases while methane contributes 8.5% and N2O contributes 18.2%. Although the contributions of the various fluorinated molecules are relatively low, it needs to be recognised that the lifetimes of these species are significantly above those of the other greenhouse gases and it is for this reason that they are no longer manufactured. As we will see below, there are a number of other greenhouse gases, some of which contribute to global warming while others do not. Water vapour is one example of a gas which does not contribute directly to global warming and ozone is another. We will now consider each greenhouse gas in turn, starting with water vapour.

Table 1.2

Water vapour

The most important greenhouse gases are water vapour and carbon dioxide. Both of these result from the combustion of fossil fuels but may also arise from other sources. Water-vapour, which results predominantly from the evaporation of surface water, has a feedback effect: it forms clouds in the atmosphere and these lead to precipitation, this having the consequence that the level of water-vapour in the atmosphere is well controlled. The clouds also reflect some of the radiation (UV, visible and infra-red) reaching the atmosphere from the sun, this also restricting the temperature rise. One consequence of the presence of increased partial pressures of carbon dioxide in the atmosphere (see below) is that the resulting temperature rise also causes an increase in the partial pressure of the water in the atmosphere, thus giving rise to a further increase in the temperature. Hence, water vapour has an indirect effect on global warming.

Carbon dioxide

Even though the concentration of carbon dioxide in the atmosphere is much lower than that of water, its effect is much greater since there is no equivalent feedback mechanism to that with water: once the carbon dioxide reaches the atmosphere, its residence time there is very much greater than that of water. The double bonds of the C glyph_dbnd O linkages of the CO2 absorb much of the infrared radiation emitted from the earth and prevent this radiation from leaving the atmosphere. The result is an increase in atmospheric temperature. It should be recognised that the CO2 reaching the atmosphere can come from many sources apart from combustion, for example, respiration and volcanic eruptions. It can also arise from deforestation and changes in land use. As discussed above, the increase in atmospheric temperature caused by the CO2 also has an effect on the level of water vapour in the atmosphere since the saturation vapour pressure of the water increases with increasing temperature and hence this magnifies the effect of the increase in CO2 concentration. Atmospheric CO2 is essential for the growth of plants and all types of vegetation. Hence, we rely on a steady partial pressure of CO2 to enable agricultural activities. We will return to the subject of CO2 utilisation in subsequent chapters. As shown in Fig. 1.4 of Box 1.1, there has been a dramatic increase in the concentration of CO2 in the atmosphere over the last 70 years.

Fig. 1.4

Fig. 1.4 The variation in carbon dioxide concentration as a function of time. It is clear that there has been a dramatic increase in the level of carbon dioxide since 1950 that is well outside the normal temporal variations. (Source: https://climate.nasa.gov/resources/)

Box 1.1

Variation of global CO2 concentrations as a function of time

Fig. 1.4 shows the concentration of CO2 in the atmosphere as a function of time over many centuries. These data have been compiled from the analysis of air bubbles trapped in ice over the last 400,000 years. During ice ages, the levels were about 200 ppm (ppm) and they rose to around 280 ppm in the warmer interglacial periods. The rise after about 1950 is attributable to a rapid increase in the use of fossil fuels as will be discussed further in later sections.

Methane

Methane (CH4), the simplest hydrocarbon molecule, may arise from a number of sources, both natural and man-made. It is produced by the decomposition of wastes in landfills, from agricultural sources such as rice paddies, from digestive processes of ruminants (e.g. cattle and sheep) and manure management from domestic livestock. It was also commonly emitted as waste from oil well operations and as leakages from chemical processing; however, both of these sources are now much more carefully controlled. (See Box 1.2 for an example of methane emission.) Methane is a much more active greenhouse gas than is CO2, its ‘global warming potential’ being much higher (see Table 1.1). The atmosphere also contains yet lower concentrations of other hydrocarbons such as the vapours of petroleum and diesel components and these too are greenhouse gases. Methane and the other hydrocarbons have much longer lifetimes than does CO2 in the atmosphere; while CO2 is removed by natural processes, the hydrocarbons are relatively stable. As a result, they all have higher global warming potentials (Table