Green chemistry, which is similar to sustainable chemistry and circular chemistry, is a field of chemistry and chemical engineering that works to create products and processes that reduce or stop the use and creation of harmful materials. While environmental chemistry studies how polluting chemicals affect the natural world, green chemistry focuses on how chemical processes affect the environment. This includes using fewer resources that cannot be replaced and finding ways to stop pollution before it happens.

The main goals of green chemistry—such as using resources more efficiently and creating safer designs for molecules, materials, products, and processes—can be applied in many different situations.

Definition

Green chemistry, also known as sustainable chemistry, is about creating chemical products and methods that help reduce or stop the use of harmful materials. Green chemistry combines ways to prevent pollution and make processes more efficient in both labs and factories. This helps use resources better, create less waste, and lower risks from chemicals throughout their entire life, from creation to disposal.

History

Green chemistry developed from earlier ideas and research, such as pollution prevention, atom economy, and catalysis, during the years before the 1990s. This happened as more attention was given to problems like chemical pollution and the loss of natural resources. In Europe and the United States, there was a change in how environmental issues were addressed. People moved away from strict rules that required industries to reduce pollution at the end of their processes and instead focused on preventing pollution by designing better production technologies. These ideas, which were later called green chemistry, became more clearly defined in the mid- to late-1990s. The term "green chemistry" became widely used in academic writing, replacing earlier terms like "clean" and "sustainable" chemistry.

In the United States, the Environmental Protection Agency helped develop green chemistry by supporting pollution prevention programs, providing funding, and working with industry. Around the same time, in the United Kingdom, researchers at the University of York used the term "clean technology" in the early 1990s. They helped create the Green Chemistry Network within the Royal Society of Chemistry and started the journal Green Chemistry. In 1991, in the Netherlands, a special issue titled "green chemistry" (groene chemie) was published in Chemisch Magazine. In the Netherlands, the term "green chemistry" was linked to using biomass as a renewable resource.

Principles

In 1998, Paul Anastas (then leading the Green Chemistry Program at the US EPA) and John C. Warner (then working at Polaroid Corporation) introduced a set of guidelines to help people practice green chemistry. These twelve principles explain ways to reduce the harm chemicals can cause to the environment and human health. They also show what areas of research are most important for creating better green chemistry technologies.

The principles include ideas such as:

• Creating processes that use as much of the raw materials as possible in the final product.
• Using materials and energy sources that can be naturally replaced, like plants or sunlight.
• Choosing safe, harmless substances, such as solvents, whenever possible.
• Designing processes that use as little energy as possible.
• Avoiding waste creation, which is considered the best way to manage waste.

The twelve principles of green chemistry are:

• Prevention: It is better to stop waste from being made than to clean it up later.
• Atom Economy: Methods should use as much of the starting materials as possible to make the final product, reducing waste.
• Less Hazardous Chemical Syntheses: Methods should avoid using or creating harmful substances for people or the environment.
• Designing Safer Chemicals: Chemicals should be made to do their job without being harmful to people or the environment.
• Safer Solvents and Auxiliaries: Extra substances should be avoided if possible, and when used, they should be as harmless as possible.
• Design for Energy Efficiency: Energy use should be kept to a minimum, and processes should be done at normal temperature and pressure when possible.
• Use of Renewable Feedstocks: Renewable materials, such as those from plants, are better than non-renewable ones when practical.
• Reduce Derivatives: Steps that create unnecessary chemical changes, like using extra reagents, should be avoided to reduce waste.
• Catalysis: Using small amounts of catalysts (substances that help reactions happen) is better than using large amounts of substances that are used up in the reaction.
• Design for Degradation: Chemicals should be made to break down into harmless substances after they are used.
• Real-Time Analysis for Pollution Prevention: Better tools should be developed to monitor and control harmful substances before they form during a process.
• Inherently Safer Chemistry for Accident Prevention: Chemicals and their forms should be chosen to reduce risks like explosions, fires, or leaks.

Trends

Scientists are trying to measure how green a chemical process is, while also considering other factors like how much product is made, the cost of materials used, safety when handling chemicals, the equipment needed, the energy used, and how easy it is to separate and clean the final product. In one study, a process that changes nitrobenzene into aniline scores 64 out of 100, which is considered a good method. However, a method using HMDS to make an amide scores 32 out of 100, which is considered average.

Green-chemistry methods are used when creating and making nanomaterials. Scientists pay attention to how these materials affect the environment over their lifetime and whether they could be harmful to living things.

Examples

The most common use of solvents in human activities is in paints and coatings, which account for about 46% of all solvent use. Other uses include cleaning, removing grease, making adhesives, and creating chemicals. Traditional solvents are often harmful to health and the environment, and some contain chlorine. Green solvents, however, are usually less harmful and more sustainable. Ideally, green solvents should come from natural sources and break down into harmless substances. However, making solvents from plant materials can sometimes harm the environment more than using fossil fuels. Therefore, when choosing a solvent, the environmental impact of its production must be considered. Another important factor is what happens to the solvent after it is used. If a solvent is used in a closed system where it can be collected and reused, the energy and environmental costs of recycling should be considered. In such cases, water might not be the best choice because purifying it requires a lot of energy. On the other hand, if a solvent is used in a product that is released into the environment, the solvent's own environmental impact is more important than the cost of recycling. In this case, water is often a good choice. In short, the environmental impact of a solvent throughout its entire life—from creation to disposal or reuse—must be considered. The most complete definition of a green solvent is: "A green solvent is the one that causes the least harm to the environment over its entire life cycle."

By this definition, a solvent might be green for one use but not for another. For example, water is a good green solvent for products like toilet bowl cleaners but is not suitable for making a chemical called polytetrafluoroethylene. This is because using water in that process requires adding harmful chemicals called perfluorinated surfactants. Instead, supercritical carbon dioxide is a better choice for this application because it works well without needing surfactants. In conclusion, no solvent can be called "green" unless it is specifically tied to a certain use.

New or improved chemical methods can help reduce environmental harm and follow green chemistry principles. For example, the 2005 Nobel Prize in Chemistry was given to scientists for developing a method called metathesis, which helps make chemicals more efficiently and with less waste. A 2005 review highlighted three important green chemistry advances: using supercritical carbon dioxide as a solvent, using water-based hydrogen peroxide for chemical reactions, and using hydrogen in chemical processes that create specific products. Other examples include supercritical water oxidation, reactions that happen in water, and reactions that occur without liquid solvents.

Bioengineering is also a promising way to achieve green chemistry goals. Some chemicals can be made by genetically modified organisms, such as shikimate, which is used in making a medicine called Tamiflu. Click chemistry is a type of chemical process that aligns with green chemistry goals. The idea of "green pharmacy" has been introduced based on these same principles.

In 1996, Dow Chemical won an award for using carbon dioxide as a blowing agent in making polystyrene foam. Polystyrene foam is used for packaging and shipping food. In the past, harmful chemicals called CFCs were used, which damaged the ozone layer. Later, other chemicals were used instead, but they also had problems. Dow discovered that carbon dioxide under high pressure and temperature works just as well as a blowing agent without needing harmful substances. This makes the polystyrene easier to recycle. The carbon dioxide used in the process is reused from other industries, so no new carbon is released into the environment.

To address principle #2, a greener way to make hydrazine (a chemical used in various industries) is by using hydrogen peroxide instead of traditional methods. Traditional production creates salt as a byproduct, but the new method produces water instead. This avoids the need to handle salt waste.

To address principle #4, this process does not require extra solvents to separate the product. A solvent called methyl ethyl ketone is used to carry the hydrazine, and the intermediate product separates naturally, making the process easier.

To address principle #7, a green way to make 1,3-propanediol (a chemical used in making carpets) is by using a genetically modified strain of bacteria. This avoids using petroleum-based materials. The chemical is used to create new types of polyester for carpets.

In 2002, Cargill Dow (now NatureWorks) won an award for improving the way polylactic acid is made. Lactic acid, used to make this polymer, is made by fermenting corn. The process avoids using harmful solvents and produces a recyclable and compostable material. However, the project was later stopped because the final product did not perform well enough.

In 2003, Shaw Industries chose a type of plastic called polyolefin as the main material for a product called EcoWorx. This choice was made because the plastic is less toxic, works well with other materials, and can be recycled. The product was designed to be compatible with nylon carpet fibers, which are easier to recycle than other materials. Research showed that separating the carpet fibers and backing through specific methods was the best way to recover materials. Postconsumer EcoWorx carpet tiles were found to have economic value after their useful life. EcoWorx is recognized for meeting performance, health, and environmental standards.

Legislation

In 2007, the European Union (EU) created the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) program. This program requires companies to share information proving their products are safe. The regulation (1907/2006) checks the dangers and risks of chemicals during their use. It also includes rules to ban or limit the use of certain harmful substances. The EU Chemicals Agency (ECHA) in Helsinki manages the program, while EU member states are responsible for enforcing the rules.

In 1970, the United States formed the Environmental Protection Agency (EPA) to protect people and the environment by creating and enforcing environmental rules. Green chemistry supports the EPA’s goals by helping scientists and engineers create chemicals, products, and processes that avoid making harmful substances or waste.

The main U.S. law that controls most industrial chemicals (except pesticides, food, and medicines) is the Toxic Substances Control Act (TSCA) from 1976. Studies have shown that TSCA has weaknesses. For example, a 2006 report to the California Legislature said TSCA has led to a market that focuses more on the cost and performance of chemicals than their safety. Experts say these issues make it harder for green chemistry to succeed in the U.S. They believe major changes to the law are needed to fix these problems.

In 1990, the Pollution Prevention Act was passed. This law encouraged new ways to reduce pollution by preventing problems before they occur. After this law was passed, green chemistry became more popular in the U.S. The law said pollution should be reduced by improving product designs instead of treating or getting rid of waste. These rules inspired scientists to find better ways to reduce harmful chemicals in the air. In 1991, the EPA Office of Pollution Prevention and Toxics started a grant program to support research on safer chemical products and processes. The EPA also holds an annual event called The Green Chemistry Challenge to encourage the use of green chemistry for environmental and economic benefits.

In 2008, California passed two laws to support green chemistry, starting the California Green Chemistry Initiative. One law required California’s Department of Toxic Substances Control (DTSC) to create new rules to identify "chemicals of concern" and replace harmful chemicals with safer options. These rules began in 2013, leading to the Safer Consumer Products Program managed by DTSC.

Scientific journals specialized in green chemistry

• Green Chemistry (RSC)
• Green Chemistry Letters and Reviews (Open Access) (Taylor & Francis)
• ChemSusChem (Wiley)
• ACS Sustainable Chemistry & Engineering (ACS)

Contested definition

There are unclear parts in how green chemistry is defined and understood by scientists, policymakers, and business leaders. Even among chemists, the term "green chemistry" has been used to describe many different types of work, not always following the 12 principles created by Anastas and Warner. While some uses of the term are not accurate (such as greenwashing), others are valid. No single definition of green chemistry is considered the most authoritative. Additionally, the idea of green chemistry can be linked to or confused with similar ideas like green engineering, environmental design, or general sustainability. Because green chemistry involves many different aspects, it is hard to create simple and clear ways to measure it. As a result, people often disagree about what truly qualifies as "green."

Awards

Several scientific groups have established awards to support research in green chemistry.

• In Australia, the Green Chemistry Challenge Awards are managed by The Royal Australian Chemical Institute (RACI).
• Canada has the Green Chemistry Medal.
• In Italy, green chemistry efforts are led by a group of universities called INCA.
• In Japan, the Green & Sustainable Chemistry Network manages the GSC awards program.
• In the United Kingdom, the Green Chemical Technology Awards are given by Crystal Faraday.
• In the United States, the Presidential Green Chemistry Challenge Awards honor individuals and businesses.