Written by PengCheng Zhu '26
Edited by Jasmine Shum '24
Petrochemical Plant in Saudi Arabia. Jan 1, 2006. Wikimedia Commons
Oil—otherwise known as petroleum—is surely running out in the foreseeable future, with most estimates projecting a date of around 2050. Yet people are more dependent on it than ever. While it is largely known that our society depends on petroleum as a fuel for cars, planes, and power plants, petroleum is perhaps more entrenched in society as the source of a vast number of chemical precursors that eventually become medicinal drugs, cosmetics, rubbers, plastics, inks, flavorings…and the list goes on. The process of extracting, separating, and processing precursors from crude fossil fuels is known as the petrochemical industry, and it is the unglamorous progenitor of materials found in nearly every consumer product.
Take the ubiquitous plastics as an example. Plastics are polymers—very, very long chains of the same base molecule (monomers). But most molecules don’t have the tendency or even the ability to join together evenly into a long polymer chain. Living organisms do produce polymers such as polysaccharides, which humans utilized to make paper a few thousand years ago. However, biological polymers tend to be very interactive with water, which is often not a desirable quality for many human applications—think about how troublesome it is when a paper bag softens and breaks when it is wet. Biological polymers also tend to have low thermal malleability—they disintegrate into monomers at higher temperatures rather than staying intact. Therefore, to satisfy societal demands, first with the USA’s need for synthetic rubber during World War II, scientists have figured out how to make artificial polymers that have high thermal malleability and do not interact with water by using crude oil.
The process to transform crude oil into plastic starts in oil refineries. What even is crude oil? It is a dark-colored substance composed of a huge variety of hydrocarbon chains, from small chains of a few carbons to long chains of up to 40 carbons. In addition to simple straight and branched chains, crude oil also contains ringed hydrocarbons, with a class of ringed hydrocarbons called aromatics being especially stable. First, crude oil is filtered into several layers based on boiling point in a process called fractional distillation. Since a higher molecular weight is associated with a higher boiling point, the longest hydrocarbons therefore make up the top layer with the highest boiling point. These long hydrocarbon chains are then subjected to cracking, where they are broken up into smaller and more useful molecules, with the most modern method referred to as fluid catalytic cracking. In this process, the long hydrocarbon chains are subjected to high temperature and moderate pressure in the presence of powdered metal catalysts; this “cracks” the long hydrocarbons into shorter chains, forming many more double bonds in the process. In particular, a small hydrocarbon with one double bond called ethylene is formed in large quantities, and it is this molecule that is then collected to form the most common type of plastic—polyethylene, which is the main component in everything from plastic bags to bulletproof vests.
Slightly shorter hydrocarbons of six to twenty carbons collected from fractional distillation are called petroleum naphtha, which is then subjected to a different process called catalytic reforming to generate stable aromatic molecules. These molecules are of the highest economic value—they can be mixed with ethylene to create plastics with different properties and serve as the precursor for dyes, drugs, and cosmetics, among many other uses. The remainder of the fractional distillation column consists of the shortest hydrocarbons with one or two carbons. These hydrocarbons are so small that they are gaseous at standard conditions, hence they are known as natural gas. The petrochemical industry reacts these molecules with either water (the steam reforming process) or oxygen (the partial oxidation process) to form synthetic gas, a mixture of carbon monoxide and hydrogen gasses. The hydrogen can then be separated to make ammonia for fertilizers, or the entire synthesis gas mixture can be supplied for other processes to make methanol to ultimately become fuels, lubricants, and many other industrial products.
From the fertilizer that makes food, to the nylon and dyes in clothes, to the drugs found in hospitals, it is dizzying to see how dependent the world is on oil-derived substances. Given the impending exhaustion of world oil supplies, some researchers and companies have begun the Herculean task to find alternative methods for producing these petrochemical precursors. The biotechnology company Genomatica has created a method to produce BDO (1,4-butanediol), a precursor to many plastics from renewable sources like sugarcane and sugar beets, and is ramping up production. Another team of researchers has created an alternative method of generating a petrochemical-derived red dye from genetically modified tomatoes. Looking at the bigger picture, a team of researchers analyzed the production and yields of many staple crops to conclude that it is possible for biomass generated from agriculture to replace petrochemical feedstocks from an energetics perspective. While most of the specific pathways to replace petrochemicals with biologically-generated alternatives remain to be discovered, the current pathways that have already been found result in excessive energy usage as well as unfavorable economic costs. Therefore, it is imperative that more funding and research are dedicated to the replacement of petrochemicals, and hopefully with the same fervor that is currently concentrated towards finding alternative fuels to gasoline.
References
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