Petroleum (or oil) and natural gas are widely used sources of fuel. Around the world many transportation, energy, and heating infrastructures depend in large part on one or both of these hydrocarbon-rich fuels.
What is a Hydrocarbon?
What is a hydrocarbon? Put simply, it is a compound made up of only hydrogen and carbon atoms. When petroleum is extracted from the ground as crude oil it is not a hydrocarbon in and of itself. Rather it contains hydrocarbons and several other chemical elements. When people refer to things like oil and natural gas as hydrocarbons it is a figure of speech known as metonymy, that is calling a thing by a name that it is highly associated with. Another example of metonymy is referring to the executive branch of a government by its executive official’s residence, such as with the White House in the United States.
Figures of speech aside, hydrocarbons are prized as fuel sources due to their combustible properties. Because of this they can be used to power internal combustion engines or to generate electricity. In 2019 the United States used 68% of its petroleum for transportation and less than one percent was converted to electricity. While it should shock no one that the majority of a country’s oil usage would be as fuel, the second largest usage category might surprise some. In the same year, 26% of the United State’s petroleum went toward its industrial sector for processing into petrochemicals. From plastics to shampoos, roads, and fertilizers, petrochemicals are a part of most people’s everyday lives. To understand how this came to be, we first need to get a sense of what petrochemicals are.
Petrochemicals are chemicals and compounds that can found inside petroleum and natural gas. Often this term is also extended to chemicals and compounds that can be synthesized using the components of oil and natural gas. An example of the former is helium, which is mostly acquired as a byproduct when extracting natural gas, and an example of the latter is ammonia, which is synthesized using hydrogen pulled from hydrocarbons that is then combined with nitrogen. Many petrochemicals can also be extracted from other sources, like coal, and thus the word is not a scientific label but more of a commercial term.
Petrochemicals: Crude Oil and Cracking
When it comes to crude oil, petrochemicals are separated via a process known as cracking. Various methods of cracking exist, such as steam cracking and hydrocracking, but the most pivotal was the first method developed at the turn of the twentieth century: thermal cracking. Thermal cracking involves subjecting crude oil to massive amounts of heat and pressure so that the longer chains of hydrocarbons break apart (or crack) into shorter chains. These shorter chains are simpler and thus more chemically versatile.
Initially, thermal cracking was only used to extract gases that were mainly for fueling gas lamps, but by the 1920s it was discovered that these materials had other potential uses. When discussing the raw materials that are to be made into petrochemicals, those in the industry usually refer to them as feedstock. In modern industrial terms, petrochemicals are generally grouped into one of three categories: olefins, aromatics, and synthesized gases.
Olefins and Ethylene
Olefins are compounds composed of strait chains and unsaturated molecules. Unsaturated in this context means a chemical compound where the carbon molecules have multiple bonds. This makes the compound more open to further bonding with other chemicals, a property known as reactivity. The opposite of an unsaturated compound is a saturated one, and this means that its carbon bonds are limited to single bonds, which in turn leads them to be uncreative. Saturated compounds are more stable and less liable to change into different compounds when encountering other chemicals, and for this reason unsaturated compounds are preferred when synthesizing petrochemicals as they can more readily be changed into other compounds.
One of the main olefins is ethylene. Ethylene can be used to make ethylene glycol, a component of polyester fibers and antifreeze, ethyl alcohol (ethanol), polyethylene, which is used in film and resins, and propylene, which is used to make acrylics, epoxies, and rubbing alcohol.
Aromatics, Ammonia, Methanol
Aromatics are another petrochemical category. Aromatics are also unsaturated, though their compounds are ring-shaped. Some of these include benzene, a component of polystyrene, paints, and glues, toluene, which is used to make fuel additives and explosives, and naphthalene, an ingredient in many insecticides.
Ammonia and methanol are the major products in the synthesis gas category. These are used to produce fertilizer, in the case of ammonia, and formaldehyde, synthetic fibers, and other plastics rely on methanol.
Petrochemicals and Plastics
For both consumer and industrial markets, plastic is the largest breakthrough in petrochemical products. Plastics are so ubiquitous it is hard to image society today without them. Despite this monumental impact, plastics are barely over a century and a half old. The first plastic, what we now know as celluloid, was debuted at London’s Great International Exhibition in 1862 by Alexander Parkes. However, what is likely the most consequential discovery of an early plastic came in 1907 when Leo Hendrik Baekland developed a synthetic polymer he dubbed Bakelite (though he was attempting to synthesize a varnish). Bakelite’s tough, heat-resistant nature made it ideal for emerging technologies like telephones and cameras. Baekland was also the one who went on to coin the term plastic for the up-and-coming class of substances. The commercial and industrial success of Bakelite and other soon-to-follow plastics like polyvinyl chloride (PVC) was made possible due to the experimentation of chemists like Baekland, but outside circumstances propelled them to worldwide mainstays as commercial and industrial products.
Material shortages brought on by World War I, and latter World War II, forced manufacturers to look beyond supply lines of wood and metal that were tied up in various war efforts. Plastics began as specialty products, sometimes even used as novelty materials to replace things like jade, but as more plastics were discovered their versatility and wide availability made them prime targets as replacements for unavailable materials.
Beyond these reasons and historical exigencies, plastics can be durable with respect to weathering and chemicals, work well at insulating heat and electricity, are relatively strong and lightweight, and can be manufactured into a vast array of shapes and forms from large structures to small fibers to liquid components in things like detergent.
In manufacturing, plastics can be put into one of two categories, these being thermoplastics and thermosets. Most plastics fall into the former group. Thermoplastics are those that can be reformed via heating after they have set into a specific shape. Thermosets on the other hand cannot be melted down again and cast into another form, which makes them unrecyclable as they break down in a way that degrades their base compounds.
Environmental Impacts of Petrochemical Products: Recycling, Landfills, and Pollution
Recycling is one of the main ways that industries involved in or related to plastic production reduce their environmental footprint. In some ways plastic is better for the environment than certain competitor products, such as paper bags. In this instance, plastic bag production releases less carbon emissions and being lighter than paper bag allows their shipment to be more fuel efficient. Plastics are also central to the manufacturing of building insulation, so in this way they can also be used to cut down on carbon emissions. However, plastics are a significant pollutant, whether they remain on land or end up in the ocean.
Returning to the comparison between paper and plastic bags, paper bags are biodegradable, and thus once exposed to the elements they break down relatively quickly, leaving few if any harmful byproducts in this process. The same cannot be said for plastics. Of course some plastics are recycled, but in the United States only about 60% of the population has immediate access to a recycling program. Even then, not all plastics are recyclable, and most people are not always perfect about recycling. Sometimes when the recycling bin is full, recyclables go into the trash. But ecological ruin is not a path paved by individual consumer choices. As previously mentioned, plastic production and shipping contribute to climate change, but what happens to the plastic that does not get recycled?
Plastics are often sent to and grown the size of landfills. Landfills are breeding grounds for bacteria that produce greenhouse gases like methane and carbon dioxide. Some landfills have gas capture systems to partially counter this, though these systems can be prohibitively expensive to install. Landfills also take up space that could otherwise be left undeveloped so as to provide ecosystem services.
Of course, not all unrecycled plastic ends up in landfills. As plastics have become ubiquitous the ocean has turned into dumping ground for them as well. Water and sunlight break down several different types of maritime litter, but plastic are not really biodegradable. Photodegradation can partially break apart things like plastic bottles and shoes, though this renders them into microplastics, which are often more dangerous to various forms of life. Fish and sea birds mistakenly fill their stomachs with indigestible plastic, and when microplastics converge on the water’s surface they can block the sunlight that photosynthesizers like plankton require. Given that other animals depend on these creatures to survive, deaths caused by microplastics can have cascading effects. And then there are other plastic objects that do not break down as readily, such as abandoned fishing nets, which can fatally entrap fish, seals, sea turtles, and other sea creatures.
While individual littering contributes to this ongoing problem, consumer recycling alone is not a solution to plastic pollution of the ocean. Commercial fishing operations illegal discard their nets at sea and companies and governments illegally dump trash into the ocean as well. Curtailing each of these activities would alleviate some of the strain on oceanic ecosystems, but more cleanups and different products are also needed. Some petrochemicals could instead be obtained from renewable resources like corn and cotton linters. If done efficiently, this could cut down on some of the pollution associated with the extraction of petrochemicals, though in the end it would still produce plastic products.
While in the past it may have seemed inconceivable that people would have to step away from fossil fuels, climate change increasingly necessitates greener alternatives. It is also hard to imagine life without plastics. For many applications, such as in healthcare, there may be no better materials. A future with zero plastic is neither warranted nor desirable, but the threats to various ecosystems are likely to force the development of greener and more sustainable materials.
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