Solving Environmental Problems through Engineering

Content Background

Electricity has revolutionized the quality of human life since the end of the nineteenth century, allowing more accessible energy sources. New devices and applications such as dynamo and electric lighting motivated direct current. Later the alternator and alternating permitted current electrical energy to be transformed and transmitted on a large scale.

Currently, the oscillation of energy demand is covered by the on/off generators. However, electricity is difficult to store for later use. The best system in terms of efficiency and cost is also more widespread for the storage of energy from a large-scale grid is pump storage, which consists of pumping water to a higher dam and generating the electricity demanded by hydroelectricity. However, this method does not work for mobile energy storage applications. There are smaller storage alternatives such as capacitors, but they have the problem of low energy density. Batteries also have low energy density and take time to charge and discharge.

Around the same time that electricity began to run, a portable power source was discovered. These are naturally internal combustion engines, which burn hydrocarbons. Internal combustion engines devastated their competitors, such as compressed air or steam engines. They provided greater possibilities under the efficiency of the internal combustion engine and the high energy density of fuel, even though they contributed to climate change and exploited people in emerging countries.

What is energy?

Energy, in physics, is the capacity for doing work. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms. Moreover, there are heat and work—i.e., energy in the transfer from one body to another. After it has been transferred, energy is always designated according to its nature. Hence, heat transferred may become thermal energy, while work is done may manifest itself in the form of mechanical energy.⁴

What are the renewable resources that produce energy?

Renewable energy, also called alternative energy, usable energy derived from replenishable sources such as the Sun (solar energy), wind (wind power), rivers (hydroelectric power), hot springs (geothermal energy), tides (tidal power), and biomass (biofuels).⁵

Non-renewable energy

A non-renewable resource (also called a finite resource) is a natural resource that cannot be readily replaced by natural means at a quick enough pace to keep up with consumption. An example is a carbon-based fossil fuel. With the aid of heat and pressure, the original organic matter becomes a fuel such as oil or natural gas. Earth minerals and metal ores, fossil fuels (coal, petroleum, natural gas), and groundwater in certain aquifers are all considered non-renewable resources. However, individual elements are always conserved (except in nuclear reactions).⁶ Non-renewable resources can eventually become unavailable because there is no way to replenish the ones already used; for instance, by burning oil, the composition of matter produces a chemical reaction producing water, carbon dioxide, and many other sup products. It is not easy to make this reaction reversible even thermodynamically, but the economic point of view will be too expensive.

Fossil fuels

Fossil fuel⁷ that comes from the biomass produced in past eras, which has suffered burial and behind it, transformation processes, by increasing pressure and temperature, until the formation of substances of high energy content, such as coal, oil, or natural gas. Since it is not renewable energy, it is not considered as biomass energy.

Most of the energy currently used in the world comes from fossil fuels. They are used for engine fuel, electricity generation, air conditioning environments, and cooking. Most countries in the world are trying hard to reduce or eliminate fossil fuels' use due to climate change. They may be the most common now, but chemists and engineers who want to have a future in energy, are working on renewable fuels.

Examples of fossil fuels⁸

Coal is a dark black sedimentary rock, rich in carbon and other chemical elements such as hydrogen, sulfur, oxygen, and nitrogen. The extraction of this mineral can be done in two ways: through open-pit mining (when coal is less than 60 meters deep) or through underground mining. Between the nineteenth and mid-20th century, trains, ships, and industrial machinery operated thanks to this fuel's energy. Despite being overtaken by oil in terms of its energy capacity, coal is used to produce plastics and lubricants, among other uses.

Oil is a liquid more or less viscous composed of carbon and hydrogen (conjunction called "hydrocarbon") extracted from a well, between 600 and 5000 meters deep. Drilling towers are installed that can be located on the Earth's surface or platforms at sea. From petroleum can be produced plastic, printing inks, rubber for the manufacture of tires, gasoline, among the main ones of a long list.

Natural gas is a mixture of hydrocarbons in the gaseous state, mostly methane and smaller quantities, nitrogen, carbon dioxide, butane, among others. Most natural gas can be found a few thousands of meters under the Earth's surface, but some locations can be at least 4500 m deep. It is extracted from subsurface formations with drill towers and, by pipes designed to transport gases on a large scale, is directed to the plants for further transport by sea. Drilling for deep natural gas is not always economically feasible. Methane has no odor and is colorless; that is, we cannot perceive it with the senses. Therefore, an odor product is added to detect it in cases of leakage.

Liquefied petroleum gas is composed mainly of butane and propane gases that are compressed into liquids. It is obtained as a by-product of the oil or natural gas refining process and primarily used as an alternative fuel for gasoline-powered cars. These are adapted to work with both gasoline and liquefied petroleum gas. Despite generating a lower power than gasoline, its differential advantages are the economical price and the lower emission of carbon dioxide, as seen in Table 1.

Table 1. Energy Content of Fossil Fuels.⁹

Chemical reactions related to the burning of fossil fuels and the products considered as pollutants produced are carbon monoxide (CO), carbon dioxide (CO₂), sulfur dioxide (SO₂), a mixture of nitrogen oxide (like NO₂, N₂O),  Volatile Organic Compounds (VOCs), hydrocarbons and many other solid products. Some of these gases released by the combustion of fossil fuel like SO₂ and NO_x, react with water falling to the ground as acid rain (mainly H₂SO₄ and HNO₃.¹⁰

The hydrocarbons have combustion reactions, in which they combine with oxygen to give rise to carbon dioxide and water:

Hydrocarbons + O₂ ➔ CO₂ + H₂O

The fundamental feature of combustion reactions is that they release much energy in the form of heat; that is, they are highly exothermic, so historically they have been used as fuel. Examples include methane, propane, or butane.

Nuclear power

Nuclear or atomic energy¹¹ is the one that is released spontaneously or artificially in nuclear reactions. Controlled nuclear reactions can be used for obtaining electrical energy, thermal energy, and mechanical energy. Thus, it is common to refer to nuclear energy not only as of the result of a reaction but as a broader concept that includes the knowledge and techniques that allow the use of this energy by the human being.

These reactions occur in the atomic nuclei of some isotopes of certain chemical elements (radioisotopes), the most well-known being the fission of uranium-235 (235U), with which nuclear reactors operate, and the most common in nature, inside the stars, the fusion of deuterium-tritium (2H-3H). However, to produce this type of energy, nuclear reactions can be based on other isotopes, such as thorium-232, plutonium-239, strontium-90, or polonium-210 (232Th, 239Pu, 90Sr, 210Po; respectively).

Solar energy

Solar energy¹² is renewable energy, obtained from the use of electromagnetic radiation from the Sun. Since ancient times, the solar radiation that reaches Earth has been harnessed by humans by different technologies that have evolved. Today, heat and sunlight can be harnessed through various collectors such as photoelectric cells, heliostats, or solar collectors, and can be transformed into electrical or thermal energy. It is one of the so-called renewable energy or clean energy, which could help solve some of the most urgent current problems facing living beings.

Different solar technologies can be classified as passive or active as they capture, convert, and distribute solar energy. Active technologies include the use of photovoltaic panels and solar thermal collectors to collect energy. Passive techniques include different techniques framed in bioclimatic architecture: the orientation of buildings to the Sun, the selection of materials with a favorable thermal mass, or that have properties for the scattering of light, and the design of spaces by natural ventilation.

Hydrogen

Hydrogen¹³ is the most abundant element in the universe because 90% of matter is made up of hydrogen. It is often combined with other elements in its composition, such as water (H₂O) and other organic elements. It is odorless, colorless, and tasteless in its non-gaseous natural form. It is non-toxic and can be breathed safely. It is extremely light and rises rapidly from the Earth's surface to the atmosphere. From this, we can point out the possibility of using hydrogen as energy, although it is not a force that produces energy on its own. Hydrogen is a vector as it does not exist isolated in nature and cannot be extracted from anywhere at a low cost. This means that if we want to use hydrogen for any purpose, we must generate it first, a process in which more energy is always consumed than you get later when using it. The combustion reaction of hydrogen can be represented by the following balanced equation:¹⁴

2H₂ (g) + O₂ (g) ➔ 2H₂O (l)

This reaction is exothermic. During the combustion of hydrogen -482 KJ is being released from the reaction; this energy can be used for producing electricity; the most important thing is that there is no carbon dioxide being released, which is one the gases causing the greenhouse effect.

Hydrogen energy is an alternative energy source that can be used instead of coal or oil. How to transform this energy element? Hydrogen can be transformed thanks to technology like that used for the manufacture of batteries. This releases electricity, heat, and water (H₂O).

In the Table 2, a summary of some advantages and disadvantages of using some of the sources energy.

Table 2. Advantages and disadvantages of different sources of energy.

Principles of Green Chemistry

One of the most critical aspects of the production and consumption of energy is the environmental impact. That is why we need to take into account the principles of Green Chemistry to minimize the side effects of this part of our lives.

Green Chemistry is the design of products and chemical processes that diminish the production of toxic substances like the emission of CO₂ or other gases that can negatively impact the environment.

By following those principles¹⁵ we can produce and consume energy without impacting negatively or with minimum impact on the environment, the principles listed below apply to any form of producing energy. They are explicit instructions on how to deal with the negative impacts explained before, like the greenhouse effect, which is the process by which the planet's surface is warmed by the presence of some gases released by the combustion of hydrocarbons.

Prevention: It is better to prevent waste than treat or clean up waste after it has been created.

Atom Economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

Less Hazardous Chemical Syntheses: Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

Designing Safer Chemicals: Chemical products should be designed to preserve the efficacy of function while reducing toxicity.

Safer Solvents and Auxiliaries: The use of auxiliary substances (e.g., solvents, separation agents) should be made unnecessary wherever possible and innocuous.

Design for Energy Efficiency: Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.

Use of Renewable Feedstocks: A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.

Reduce Derivatives: Unnecessary derivatization (use of blocking groups, protection/ deprotection, and temporary modification of physical/chemical processes) should be minimized or avoided if possible because such steps require additional reagents and can generate waste.

Catalysis: Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

Design for Degradation: Chemical products should be designed to break down into innocuous degradation products at the end of their function and do not persist in the environment.

Real-time analysis for Pollution Prevention: Analytical methodologies need to be further developed to allow real-time, in-process monitoring, and control before the formation of hazardous substances.

Inherently Safer Chemistry for Accident Prevention: Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.