The Polystyrene Problem

By Victor Lotocki, Ph.D. Student in the Seferos Research Group at the University of Toronto

It isn’t a surprise that the world has a plastic problem that impacts human and environmental health, yet we continue to over-rely on the material. In Canada, for example, plastic is found in 95% of manufactured goods, most of which are single-use.¹  Recognizing the issue, in October 2020, Canada’s Minister of Environment and Climate Change announced the government’s plan to achieve zero plastic waste by 2030.² Since only 9% of plastics are recycled in the country, Canada’s Zero Plastic Waste Agenda emphasizes ramping up recycling regulation and technology, and critically, many common single-use plastics including plastic checkout bags, straws, stir sticks, six-pack rings, and cutlery were also promised to be banned. Unfortunately, a recent report from Environmental Defense revealed that the Government of Canada will need to institute new substantial measures to increase the prevention, reuse, and recycling of plastics, as a million tonnes of waste will continue to be generated even in the best-case scenario.³ Due to current difficulties in managing its recycling as well as the dangers it poses to human and environmental health, polystyrene is a particularly relevant target for new recycling strategies and regulatory action.

Polystyrene is the most common waste item found in the South Atlantic, Indian, as well as Pacific oceans, where it accumulates in the Great Pacific Garbage Patch.⁴ More concerning is that of the major plastic pollutants, which also include polyethylene and polyethylene terephthalate, polystyrene is the fastest to degrade into microplastics,⁵ which have been linked to oxidative stress, inflammation, and metabolic disorders in humans.⁶ Styrene monomers and oligomers, which are anticipated carcinogens, in particular, have been found to leech out of polystyrene microplastics.⁷ This issue is also found closer to home. For example, in Lake Ontario, researchers have found an alarming 760 particles per kilogram of sediment sampled, with each of these particles being larger than 2 mm.⁸

Most polystyrene comes in the form of expanded polystyrene foam, which includes Styrofoam, and is notoriously difficult to recycle, with about 10% of it being recycled overall in Canada. What’s more, only 35% of communities within Canada even collect polystyrene, to begin with.⁹ Currently, the only province or territory in Canada in which every locality collects Styrofoam products is British Columbia, while most others vary by region.³ Manitoba and Prince Edward Island don’t collect polystyrene, while Nunavut has no plastic collection program in place at all. One of the challenges in collecting Styrofoam relates to its low density. Since most of its volume is air, it would take up a lot of space that could more efficiently be filled using denser plastics, and it could break apart in transit, contaminating other recyclables. As a result, many regions cannot justify the cost required for collection. Here in Toronto, we even have to pay companies such as to collect our polystyrene waste.⁹

Another issue with polystyrene, along with other common plastics, is in its starting material sourcing. The production of polystyrene is strongly tied to the petroleum industry, as the two key starting reagents, benzene, and ethylene, are generated from it through methods including steam cracking and catalytic reformation.¹⁰ Benzene is alkylated with ethylene in an acid-catalyzed reaction to form ethylbenzene, typically in the liquid phase with AlCl3 or zeolitic catalysts. Then, styrene is produced from ethylbenzene through catalytic dehydrogenation, before finally being polymerized into polystyrene. As over 99% of global ethylbenzene is used in this process, the production of the two is strongly linked.¹¹ Overall, the manufacture of polystyrene is unsustainable from the very beginning of the process as it involves the emission of greenhouse gases and other pollutants (Figure 1). However, polystyrene production will be difficult to ramp down as it’s very cheap and will continue to be economical as long as crude oil and natural gas are in demand.

Figure 1. Synthesis of polystyrene from petroleum industry-sourced benzene and ethylene.

The other major issue associated with expanded polystyrene foam recycling stems from the fact that its lightweight cellular structure cannot be easily reproduced following the more common mechanical recycling methods; therefore, we need to turn to other methods for recycling. Pyrolysis, or thermal degradation, is the most widely studied form of degradation for plastics, and its advantages include being able to handle more contamination than mechanical recycling.¹² Polystyrene pyrolysis is typically conducted at 350–700 °C, and more than 90% of the material by weight is consistently retained.¹⁰ Most of the material yielded by pyrolysis consists of styrene monomers and oligomers, allowing for reuse after repolymerization (Figure 2). The rate-determining step for the degradation of polystyrene through pyrolysis is β-scission on the polymer chain. However, this is mostly true for polystyrene containing many branching points, typically produced through radical polymerization. For higher-grade linear polystyrene synthesized using methods such as anionic polymerization or controlled radical polymerization, decomposition begins with scission at the chain end, generating the necessary radicals for further decomposition. Unfortunately, polymers with fewer branching points are also more thermally resistant, so they require higher temperatures, and therefore more energy-intensive conditions, for chains to begin breaking down.  

Figure 2. Thermal degradation of polystyrene. Reproduced from reference [10].

Although public facilities may be lagging behind, a few Canadian start-ups have fortunately stepped forward to try and tackle the polystyrene recycling problem. GreenMantra is a Brantford, Ontario-based start-up which has patented a method for the catalytic depolymerization of polystyrene using pyrolysis. Their recovered styrene monomers and other styrenic by-products have found commercial applications after repolymerization.¹³ In 2019, GreenMantra reached a joint development agreement with INEOS Styrolution and has begun providing their degraded polystyrene to replace a portion of INEOS Styrolution’s feedstock in manufacturing plastic goods, thereby creating a closed polystyrene cycle.¹⁴ More recently, INEOS Styrolution has also collaborated with Agilyx, based in Oregon, to open up a polystyrene recycling plant in Illinois that will be capable of recycling polystyrene contaminated with food back into food-grade plastics.¹⁵ In Montreal, Pyrowave is a company that uses a similar catalytic decomposition process but heated with microwave reactors that effectively decontaminate polystyrene from food and other organics, in forming styrene monomers for further use.¹⁶

Polystyvert is another Montreal-based company that has developed a rather different, yet arguably more effective way of recycling polystyrene. Instead of degrading it, Polystyvert uses cymene, an essential oil, which dissolves polystyrene, but not other contaminants that can then be filtered out.¹⁷ After separating the polystyrene from cymene using a patent-pending technology, the cymene can itself be recycled for later dissolution. Since dissolution only affects the state and not the chemical structure of polystyrene, the recycled material has virtually identical properties to the original product, and it can be re-foamed with a blowing agent. Crucially, this technology could address one of the largest current issues with expanded polystyrene foam recycling – the size and low density of the material. Immersing the material at the point of collection, or more realistically at the sorting facility, could give the economical impetus for polystyrene waste management needs.

All in all, green chemists are making decent progress in tackling the issues of polystyrene recycling. What’s left is for Canadian regulation to catch up. Right now, only British Columbia, Ontario, and Quebec have plans for systems that can reliably measure the amount of plastic waste that is collected, sorted, and sent to processing facilities, yet only Quebec has set targets for the amount of recycled material that should be used in new products.³ More importantly, the industrial sector, which is responsible for most plastic packaging waste, is not currently subject to legislation making it responsible for its own plastic products.

References

(1)         The Role of Chemistry in a Circular Economy; Chemistry Industry Association of Canada, 2020. https://canadianchemistry.ca/wp-content/uploads/2020/07/The-Role-of-Chemistry_ENG_Web-FINAL.pdf.

(2)         Canada One-Step Closer to Zero Plastic Waste by 2030; Environment and Climate Change Canada, 2020. https://www.canada.ca/en/environment-climate-change/news/2020/10/canada-one-step-closer-to-zero-plastic-waste-by-2030.html.

(3)         Canada’s Zero Plastics Packaging Waste Report Card; Environmental Defence, 2022. https://environmentaldefence.ca/wp-content/uploads/2022/10/Environmental-Defence-Zero-Plastics-Waste-Report-Card_September-9-2022-October-7-2022.pdf.

(4)         Eriksen, M.; Lebreton, L. C. M.; Carson, H. S.; Thiel, M.; Moore, C. J.; Borerro, J. C.; Galgani, F.; Ryan, P. G.; Reisser, J. Plastic Pollution in the World’s Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLOS ONE 2014, 9 (12), e111913. https://doi.org/10.1371/journal.pone.0111913.

(5)         Biber, N. F. A.; Foggo, A.; Thompson, R. C. Characterising the Deterioration of Different Plastics in Air and Seawater. Mar. Pollut. Bull. 2019, 141, 595–602. https://doi.org/10.1016/j.marpolbul.2019.02.068.

(6)         Yee, M. S.-L.; Hii, L.-W.; Looi, C. K.; Lim, W.-M.; Wong, S.-F.; Kok, Y.-Y.; Tan, B.-K.; Wong, C.-Y.; Leong, C.-O. Impact of Microplastics and Nanoplastics on Human Health. Nanomaterials 2021, 11 (2), 496.

(7)         Kwon, B. G.; Koizumi, K.; Chung, S.-Y.; Kodera, Y.; Kim, J.-O.; Saido, K. Global Styrene Oligomers Monitoring as New Chemical Contamination from Polystyrene Plastic Marine Pollution. J. Hazard. Mater. 2015, 300, 359–367. https://doi.org/10.1016/j.jhazmat.2015.07.039.

(8)         Ballent, A.; Corcoran, P. L.; Madden, O.; Helm, P. A.; Longstaffe, F. J. Sources and Sinks of Microplastics in Canadian Lake Ontario Nearshore, Tributary and Beach Sediments. Mar. Pollut. Bull. 2016, 110 (1), 383–395. https://doi.org/10.1016/j.marpolbul.2016.06.037.

(9)         Chung, Emily. Most Styrofoam Isn’t Recycled. Here’s How 3 Startups Aim to Fix That. CBC News. 2019. https://www.cbc.ca/news/science/styrofoam-chemical-recycling-polystyrene-1.5067879.

(10)       Li, H.; Aguirre-Villegas, H. A.; Allen, R. D.; Bai, X.; Benson, C. H.; Beckham, G. T.; Bradshaw, S. L.; Brown, J. L.; Brown, R. C.; Cecon, V. S.; Curley, J. B.; Curtzwiler, G. W.; Dong, S.; Gaddameedi, S.; García, J. E.; Hermans, I.; Kim, M. S.; Ma, J.; Mark, L. O.; Mavrikakis, M.; Olafasakin, O. O.; Osswald, T. A.; Papanikolaou, K. G.; Radhakrishnan, H.; Sanchez Castillo, M. A.; Sánchez-Rivera, K. L.; Tumu, K. N.; Van Lehn, R. C.; Vorst, K. L.; Wright, M. M.; Wu, J.; Zavala, V. M.; Zhou, P.; Huber, G. W. Expanding Plastics Recycling Technologies: Chemical Aspects, Technology Status and Challenges. Green Chem. 2022, 24 (23), 8899–9002. https://doi.org/10.1039/D2GC02588D.

(11)       Ullmann ́s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley-VCH: 1999, 1999.

(12)       Davidson, M. G.; Furlong, R. A.; McManus, M. C. Developments in the Life Cycle Assessment of Chemical Recycling of Plastic Waste–A Review. J. Clean. Prod. 2021, 293, 126163.

(13)       Di Mondo, D.; Scott, B. Reactor for Treating Polystyrene Material. U.S. Patent 11,072,676.

(14)       INEOS Styrolution and GreenMantra Sign JDA to Advance Polystyrene Chemical Recycling. INEOS Styrolution. Brantford, Ontario 2019. https://www.ineos-styrolution.com/news/ineos-styrolution-and-greenmantra-sign-jda-to-advance-polystyrene-chemical-recycling.

(15)       INEOS Styrolution and Agilyx Advance Polystyrene Chemical Recycling Plant in Channahon, Illinois. INEOS Styrolution. Aurora, Illinois 2019. https://www.ineos-styrolution.com/news/ineos-styrolution-and-agilyx-advance-polystyrene-chemical-recycling-plant-in-channahon-illinois.

(16)       Doucet, J.; Laviolette, J.-P. Catalytic Microwave Depolymerisation of Plastic for Production of Monomer and Waxes. U.S. Patent 11,518,864.

(17)       Roland, C. Ô. T. É. Processes for Recycling Polystyrene Waste. U.S. Patent 11,407,878.

Accessible Chemical Recycling Catalysts for the Ever-Growing Challenge of Plastic Waste

By Jack Lin, a graduate student in the Song Group at the University of Toronto and Member-at-large for the GCI

Plastics are ubiquitous in industry and consumer markets, providing countless goods with unparalleled cost, convenience, and utility. However, these benefits come at a severe cost to the environment where millions of tons of plastic produced annually accumulate in the biosphere.¹ Recent emphasis has been placed on the impact of microplastics stemming from degradation of larger plastic waste. This phenomenon has been coined a “plastic time bomb” by Dr. Albert Koelmans, a professor in Aquatic Ecology and Water Quality at Wageningen University.² Microplastics can be of similar size to biological organisms leading to the risk of particles entering cells or crossing the blood-brain barrier, a major human health concern. Given that plastic consumption and waste has emerged as a global health and sustainability challenge at an unprecedented scale, chemists are now spending enormous effort towards remediation of this issue.³

Amongst the numerous types of consumer plastics, polyethylene terephthalate (PET) is one of the most common due to its durability, chemical resistance, and low price.However, mechanical recycling of PET poses challenges such as the low quality of recycled PET due to residual contaminants. Moreover, sorting costs are high as the recycling feedstock for PET demands high quality. Recycled PET is also undesirable due to diminished thermal stability as well as the presence of trace metals which affect consistency of each recycled batch of PET. Mechanical recycling is also dependent on consumer compliance where the recovery rate of plastic waste in the US was 8.8 % in 2012.⁴ An alternative is chemical recycling, which recycles PET into useful monomer molecules.

An elegant example of chemical PET recycling is shown by Zhao and coworkers, where a low-cost process was developed to recycle PET into p-xylene, a valuable component in gasoline, and ethylene glycol, a commodity chemical with applications as an anti-freeze agent.⁵ PET is designed to be chemically resistant and its durability is a prominent feature, making chemical recycling of PET particularly challenging. As such, this work represents a breakthrough in depolymerization strategies towards PET recycling. The authors employed a copper catalyst supported on silica (SiO₂) with methanol serving as the reaction solvent as well as the hydrogen source. PET first undergoes a methanolysis reaction to make ethylene glycol and dimethylterephthalate (DMT). The latter product then produces p-xylene using the developed catalyst. (Figure 1)

Figure 1. One-pot strategy for chemical recycling of PET into ethylene glycol (EG) and p-xylene (PX).⁵

A secondary advantage of this process is the lack of hydrogen gas that is typically required for p-xylene formation from DMT. This is particularly advantageous in communities that lack large industrial sites to provide cheap sources of hydrogen gas. In these cases, the ideal economic choice for plastic disposal is energy recoupment by incineration. To combat this, cost-effective methods for PET recycling is needed. The authors conducted a preliminary test on Phuket Island, a tourism-driven community riddled with plastic contamination. From 1000 kg of beach sediments collected from the island, 33.1 % was found to be PET plastic by weight. This waste was subjected to the copper-based catalyst to generate 181 kg of p-xylene and 105 kg of ethylene glycol at quantitative yields (Figure 2). This demonstrates a viable and scalable option for PET waste recycling into value-added chemicals. Perhaps more valuable is the design of this work to be effective across the globe regardless of socioeconomic status of any given community.

Figure 2. Application of the developed catalyst towards PET recycling using beach sediments from Phuket Island.⁵

Ultimately, the hope is that green chemists around the world will be able to push the boundaries of sustainability, a topic that is paramount in the context of plastic waste recycling.

References

1. George, N.; Kurian, T. Ind. Eng. Chem. Res. 2014, 53, 14185. DOI: 10.1021/ie501995m.
2. Lim, X. Nature 2021, 593, 22. DOI: 10.1038/d41586-021-01143-3.
3. Rochman, C. M. Science 2018, 360, 28. DOI: 10.1126/science.aar7734.
4. Environmental Protection Agency. Plastics. EPA. 2015. https://www3.epa.gov/epawaste/conserve/tools/warm/pdfs/Plastics.pdf.
5. Gao, Z.; Ma, B.; Chen, S.; Tian, J.; Zhao, C. Nat. Commun. 2022, 13, 3343. DOI: 10.1038/s41467-022-31078-w.

Green Chemistry Principle #9: Catalysis

By Alex Waked, Member-At-Large for the GCI

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

In Video #9, Lilin and Jamy discuss the advantages of catalytic reagents over stoichiometric reagents.

In stoichiometric reactions, the reaction can often be very slow, may require significant energy input in the form of heat, or may produce unwanted byproducts that could be harmful to the environment or cost lots of money to dispose of. Most chemical processes employing catalysts are able to bypass these drawbacks.

A catalyst is a reagent that participates in a chemical reaction, yet remains unchanged after the reaction is complete. The way they typically work is by lowering the energy barrier of a given reaction by interacting with specific locations on the reactants, as demonstrated in Figure 1 below. The reactants are represented by the red and blue objects, and the catalyst by the green one. Without catalyst, the reactants cannot react with each other to form the desired product. However, once the catalyst interacts with them, the reactants become compatible and can subsequently react together. The desired product is released and the catalyst is regenerated to continue interacting with the remaining reactants to produce more product.

Figure 1. Graphic of a catalyst’s function in a catalytic reaction. The catalyst is green, and the reactants are red and blue.

In other words, a catalyst can be thought of as a key that can unlock specific keyholes, where a keyhole represents a particular chemical reaction. One common example of a catalytic reaction that is taught in introductory organic chemistry is the hydrogenation of ketones (Scheme 1, also discussed in the video). The stoichiometric reaction involves the addition of sodium borohydride, followed by addition of water. In this reaction, borane (BH3) and sodium hydroxide are (formally) generated as waste. By simply employing palladium on carbon as catalyst, the ketone can react directly with H2 to generate the same desired product without producing any waste.

Scheme 1. Stoichiometric vs. catalytic reduction of a ketone.

While catalytic reagents appear to play an impactful role in the development of greener processes, there are always a couple points on the flip side of the coin to consider. For instance, a reaction employing a catalyst may not necessarily be “green”, since the “greenness” of the catalyst itself should be considered as well (ie. Is the catalyst itself toxic? Is it environmentally benign?). In addition, the lifetime of a catalyst matters; a catalyst can in theory perform a reaction an infinite number of times, but in practice it loses its effectiveness after a certain period of time.

Nevertheless, when these points are considered and addressed, the impact of catalytic reagents on green processes cannot be ignored. The production of fine chemicals and the pharmaceutical industries are just a couple areas where this impact is seen.[1] By focusing innovative research around the principle of catalysis, together with the other principles of Green Chemistry, we are moving in the right direction by paving the way to new sustainable processes.

Reference:
[1] Delidovich, I.; Palkovits, R. Green Chem. 2016, 18, 590-593.

Proper Chemical Waste Disposal: Posters & Memes

By Cookie Cho, Member-at-Large for the GCI

One of the unfortunately inevitable aspects of doing research is creating chemical waste. Previously, we have launched a Waste Awareness Campaign to try to reduce the amount of waste produced, and hosted a lecture on Chemical Waste FAQs to encourage proper waste disposal.

In the chemistry building at the University of Toronto, two general types of groups produce chemical waste: the research chemists, and undergraduate students.

Recently, the GCI partnered with UofT’s Environmental Health and Safety (EHS) office to develop and distribute an easy-to-follow waste disposal poster. This guide was designed to answer common questions about proper sorting of waste classes, and to make it easier for the research chemists to dispose of their chemical waste. These were then posted in all research labs throughout the chemistry building. We have received great feedback from many department members so far, including the researchers themselves and administrative staff!

Fig. 1: Waste Disposal Poster, produced in partnership with EHS and GCI.

In order to guide the undergraduates, many of whom have never worked in a chemistry lab before, we developed a series of meme-themed posters to point out proper chemical disposal in undergraduate laboratories. Through the use of humour and easily recognized images, our goal was to help the undergraduates remember that proper disposal of chemical waste is the right thing to do. Here are some of the memes we developed.

Fig. 2: Archer meme – Chemical waste goes in waste containers, not down the drain!

Fig. 3: Lumbergh meme – Lumbergh insists that chemical wastes be disposed of properly.

Fig. 4: World’s Most Interesting Man disposes acid waste properly.

Currently, we are also collaborating with course instructors to develop more formal diagrams and materials, in order to better train new undergraduates on proper chemical waste disposal. We welcome any ideas that our readers may have! How is chemical waste disposal taught and encouraged at your institution?

Chemical Waste FAQs

By Peter Mirtchev, Member-at-Large for the GCI and Laura Reyes, Co-Chair for the GCI

All chemists create chemical waste, it’s simply part of our job. Recently, we started a Waste Awareness Campaign to track the amount of waste being generated by our chemistry department. Aside from this, the chemical waste disposal process was a bit of a mystery. Learning how to properly sort, label, and dispose of chemical waste should be part of every chemists’ early training, but typically gets overlooked. In academic research labs, waste disposal habits tend to get passed down from one person to the next, and often stem from tradition rather than regulation. With this post, we hope to clarify some of the confusion surrounding proper disposal of different types of chemical waste.

We recently co-hosted a seminar about waste disposal with the Chemistry Students’ Union. Our speakers were Ken Greaves (Chemistry Department Supplies & Services Supervisor) and Rob Provost (Environmental Protection Manager at the UofT EH&S Office). We found that many members of the department had important questions regarding proper disposal practices and what happens to chemical waste after it is picked up. We have summarized the crucial points of the talk in Q&A format below. There’s also very useful information at this EH&S website on chemical waste. If you have other unanswered questions regarding chemical waste, leave them in the comments and we’ll get them answered for you!

Disclaimer: the information below is specific to the Department of Chemistry at the University of Toronto, and may change according to institution. Check with your own institution regarding the rules of chemical waste disposal.

Q: What are the most common types of chemical waste produced in a research laboratory?

A: Solvents. At the University of Toronto, the three most common chemicals are 1) acetone, 2) hexanes, and 3) dichloromethane. The Department of Chemistry purchases over 10,000L of acetone per year alone.

Q: What is considered ‘flammable’ waste?

A: A flammable liquid is one that has a flashpoint of 23.8°C or lower.

Q: Is a mixture of water and organic solvents considered aqueous or flammable waste?

A: If the mixture is more than 50% water, it is considered aqueous waste. If it is less than 50% water, it is considered flammable waste. If the amounts are uncertain, treat as aqueous (see below for more about the treatment of waste types).

Q: What mixtures are treated as chlorinated waste?

Waste Awareness Campaign

By Karl Demmans, Workshop Coordinator for the GCI

Welcome back to the GCI’s monthly updates about our recent endeavors and findings in green research! Today I’d like to discuss the efforts put forth by various faculty and graduate students over the past eight months to collect and distribute data about the amount of waste produced in the Lash Miller Chemical Laboratories, the main building for the Department of Chemistry at UofT. Our hope is that once students are presented with this information, they will be more conscious about their chemical procedures and consider alternate green methods to help reduce waste. For an example of the types of data we have collected, take a look at the poster found below.

Waste data for Lash Miller Chemical Laboratories (Department of Chemistry, University of Toronto).

In Lash Miller, waste collection occurs every Friday. Each research group gathers their labelled waste containers and brings them to  our waste department for sorting and temporary storage, before eventual disposal.  The rather colourful chart in the poster displays the amount of solid or solvent waste, broken down for each chemistry discipline, concluding with the percent of total waste each discipline produces, as well as the type of waste that is made.

The colour gradient of the five waste categories denotes the combined environmental and economic concerns ranging from solid decontaminated waste (‘best’) to acidic waste (worst). Overall, the waste picture for Lash Miller looks pretty good, with only 9% of the total waste produced in the building coming from the two red categories (acidic and chlorinated). By specifically targeting these types of waste for reduction, we can continue to improve and make the waste profile of our department even better.

For Lash Miller graduate students, if you’d like to know specifically how much waste your group is producing, send an inquiry e-mail to green [at] chem.utoronto.ca!

Lastly, the final part of the poster describes what each type of waste is, and explains the disposal process. The topic of how chemical waste is disposed of was recently discussed during our last GCI seminar. Click here to read our Chemical Waste FAQs!

In the upcoming months there will be another poster displaying the percent reductions in waste produced per discipline, to see how graduate students react to the current information. Thanks for stopping by to learn about our Waste Awareness Campaign and how we are helping to reduce our environmental footprint.

Green Chemistry Principle #3: Less Hazardous Synthesis

By Kenny Chen, Member-at-Large for the GCI and Laura Reyes, Co-Chair for the GCI

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

The idea of practicing safe chemistry sounds intuitive, but contemporary technology, policy, and knowledge of long-term health and environmental impacts are often limiting factors in determining how safe a process is. In other words, scientists are always working with what they have in terms of technology and knowledge of hazards, and that story may change as we learn more.

In our video, we briefly described the recent history of technologies used to generate chlorine gas, focusing on the transition from mercury cell processes to membrane cell processes.

Chlorine has been produced industrially since the 19^th century, when it was widely used in textiles and paper industries. Nowadays, it is essential in many plastics and chemical industries, for example to make the plastic polyvinyl chloride or PVC.

In the past, the mercury cell process was widely used to make chlorine. We now know that resulting contamination from mercury waste has tragic health and environmental effects, but that was not always the case due to previous limitations in technology, knowledge of heavy metal accumulation, and resulting policies. For example, as we talk about in the video, the mercury cell-based chloralkali process caused the infamous case of Minamata disease that struck Ontario in 1970, severely affecting two native communities.

Now, the membrane cell is the preferred choice for the chloralkali process. The increased use of this cellulose-based technology has resulted in decreased use of the mercury cell, which in turn has reduced mercury emissions into the environment.

Despite large improvements, even in 2013 more than 5 tonnes of mercury were released into the environment due to the chloralkali process, which leaves significant room for improvement as we move forward, whether by improved technology or stricter regulation.

Sometimes, we can’t help but learn new information over time about the long-term safety of technologies and chemical processes. Even so, we must use the knowledge that is available at all times so that we can create and modify processes that are less hazardous by design. In this way, we will have inherently safer chemistry by keeping green chemistry principle #3 in mind.

References

Handbook of Chlor-Alkali Technology – History of the Chlor-Alkali Industry (http://link.springer.com/book/10.1007%2Fb113786)

Best Available Techniques (BAT) Reference Document for the Production of Chlor-alkali (http://www.eurochlor.org/chlorine-industry-issues/chlor-alkali-bref.aspx)

Chlorine Industry Review 2013-2014 (http://www.chlorinethings.eu/files/downloads/annual-report-2014-full-final.pdf)