Just Keep Flowing

Just Keep Flowing

By Nour Tanbouza (twitter @Nour_Tanbouza), PhD student, Laval University

Flow chemistry is a synthetic technique that enables chemical reactions to take place in a continuously flowing manner as opposed to running a reaction in a flask, sometimes termed batch chemistry. It has become incredibly mainstream and has been adopted by many chemical industries as a means to increase efficiency of large-scale reactions in highly controlled setups.1 What is flow chemistry, and why is it important? Furthermore, the main question, how does it contribute to sustainability?

Let us start by putting on a lab coat and safety goggles and strolling through a modern synthetic chemistry lab. Now, have a look around. What you will absolutely recognize and remember is a vast space of fume hoods and benches with different apparatus lying around like round bottom flasks, chromatography columns, stirrers, hot plates, etc. After that, take a browse through images of those same types of laboratories from the 1900s or even from the 1700s. Surely you will notice some improved safety features but what will strike you the most is how similar they are in terms of the equipment used then and now. We indeed currently have better stirring and heating equipment etc., but we still do reactions in round bottom flasks as batches.

Figure 1. on the left: 18th century laboratory used by Antoine Lavoisier (credits Sandstein / CC BY (https://creativecommons.org/licenses/by/3.0)); on the right: Modern synthetic chemistry laboratory ( credits Elrond / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

In 2005, the catastrophic T2 laboratories explosion occurred after a thermal runaway and high-pressure build-up of their 2,500-gallon batch reactor producing MMT (methylcyclopentadienyl manganese tricarbonyl).2 These types of accidents pose a huge risk to human life and the environment in addition to the legal and financial troubles that the company could face. Thus, there is an exigent need for safe and practical technologies that enable an efficient scale up of chemical reactions. These pursuits explain the recent uptake of flow chemistry by many manufacturing companies, especially those in the pharmaceutical industry.

Picture3

Figure 2. Aerial view of T2 Laboratories explosion

Flow chemistry can be thought of as a bench chemist’s very own cherry tree. The raw material is fed into the roots (pumps). Roots are the heart of the tree, and the same holds for the pumps of a flow system, so it is pivotal that they are well taken care of and are in perfect shape. Those nice healthy roots then flow the raw material over a large surface area up into the stems and leaves where reaction conditions are highly controlled and in perfect balance to elute the desired product continuously. Thus, whether targeting a few milligrams or multi-kilograms of product, it is dependent on how much feed material is flowed into the reactor. A flow reactor can be as small as a chip and still produce the needed amount of product. In 2019, flow chemistry was announced by the IUPAC (International Union of Pure and Applied Chemistry) as one of the ten chemical innovations that will change our world.3 There has been a significant paradigm shift by many industries, especially the pharmaceutical industry, to adopt flow chemistry. It is a technology that promises on-demand drug production, which is vital primarily for developing countries to access drugs in a decentralized manner.1

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Figure 3. An academic flow system (equipped with a photoreactor)

Green chemistry principles and a chemical industry’s agenda align when it comes to large scale reactions. Thus, it is not so surprising to see a significant uptake of flow chemistry by many companies. This kind of endorsement has helped spark research in continuous flow which is beginning to become a dominating area of study. Among the UN Sustainability Goals is responsibility for consumption and production, which is achieved in flow because it minimizes the amount of material needed for screening and allows reactions to take place in highly concentrated media. Reaction conditions being highly controlled (such as temperatures, pressure, mixing, etc.), allow reactions to be more selective and thus decreases any by-products and increases productivity.4 Also, hazardous chemicals can be safely manipulated in flow because there is no significant build-up at any given time. It is very versatile and modular where multiple reactions can be installed in sequence to consume any reactive intermediates in situ, and purification systems can be added directly as well. A reaction can be run at extremely high temperatures that go above boiling points which can enable reactions to proceed faster while being inherently safer and consuming significantly less energy when compared to a batch reactor.

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Figure 4. Illustration of a flow chemistry setup

This type of “thinking outside the flask” means stepping outside of a long-standing comfort zone which is not always trivial. However, this type of venture and side-by-side work of engineers and chemists is what made flow chemistry possible, and it is changing our world. Flow chemistry is still in its early stages, yet so much innovation has already been introduced. Give it a few years, and when you walk back into that synthetic chemistry lab, prepare to be flabbergasted by a space that resembles nothing of the past.

 

References:

  1. Malet-Sanz, L.; Susanne, F., Continuous flow synthesis. A pharma perspective. J. Med. Chem. 2012, 55, 4062-4098.
  2. http://www.csb.gov/UserFiles/file/T2%20Final%20Report.pdf
  3. Gomollón-Bel, F., Ten Chemical Innovations That Will Change Our World. Chemistry International 2019.
  4. Jensen, K. F.; Rogers, L., Continuous manufacturing – the Green Chemistry promise? Green Chemistry 2019, 21, 3481-3498.

Electrosynthesis: A Green Methodology for Organic Chemistry

By Dr. Matthew Leech, post-doctoral fellow, University of Greenwich

According to the International Energy Agency (IEA), global energy-related carbon dioxide emissions were estimated to be approximately 33 gigatonnes (Gt).1 It is perhaps unsurprising that the two largest sources of carbon dioxide emissions arise from transportation and the generation of electricity (Figure 1).  However, what is surprising is that the aggregate global emissions of the pharmaceutical sector far outweigh those of the automotive industry – 52 million tonnes vs 46.4 million tonnes in the year 2018.1

Figure 1

Figure 1: World carbon dioxide emissions by sector between 1990 and 2010. Source – https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions

 

This is because a large proportion of chemical syntheses in an industrial setting are conducted under thermochemical conditions, meaning that they must be heated to high temperatures for prolonged periods of time.  These conditions are very energy intensive, and the reagents used are often hazardous and difficult to remove from the final product.  The latter is particularly problematic for redox reactions (reactions involving the addition or removal of electrons), where toxic metal complexes are often used.

In contrast, the electrochemical synthesis of organic molecules, also known as Organic Electrosynthesis, uses the cheapest and most versatile redox agent available on the market, electricity, to perform chemical transformations at room temperature.  Organic electrosynthesis has experienced a resurgence in interest in recent years, owing to the increasing availability of affordable and standardised equipment,2 which has improved experiment reproducibility, and the growing desire by the chemistry community to find milder and greener reaction conditions. A typical modern academic electrosynthesis setup can be seen in Figure 2.

 

Figure 2

Figure 2: Modern organic electrosynthesis equipment, comprising of a combined stirrer/potentiostat, cell lid, 10 mL glass cell, and two carbon graphite electrodes.

 

Aside from saving energy by switching from thermochemical to electrochemical synthesis, electrosynthesis is often safer than traditional methods, as it reduces or eliminates the need for toxic solvents and catalysts.  In 2019 it was reported that substituted lactones, which are known for their fungicidal, antibiotic, and anticancer properties, can be synthesised using photochemistry (Scheme 1).3 However, the reported procedure necessitates the use of a potentially toxic nickel catalyst, in addition to a solvent mixture comprising of benzene and 1,4-dioxane, both of which are suspected carcinogens.  Fortunately, a complimentary electrochemical method was reported in the same year which not only removed the need for the nickel catalyst, but also uses methanol as a solvent, which is less toxic and is considered to be greener by comparison (Scheme 1).4

Scheme 1

Scheme 1: Synthesis of substituted γ-butyrolactones via photochemical (top) and electrochemical (bottom) methods.

 

Photochemistry also necessitates the use of a photocatalyst, a compound which can convert absorbed light into useable electrons.  These are normally based upon third-row transition metals such as iridium, which makes them very expensive (a typical photocatalyst costs between £40 – 60 for 0.1 g), which usually limits the uptake of photochemical methods within industry.  In contrast, electricity is cheap, with 1 mole of electrons (6.02×1023 electrons) costing around £0.83.4

 

Furthermore, through electrosynthesis, it is possible to avoid the use of reactive and often highly toxic reagents by generating them in-situ.  For example, methoxymethyl (MOM) ethers, which are used as protecting groups in organic chemistry, are normally synthesised using chloromethyl methyl ether (CMME) which, aside from being flammable and toxic, is known to cause cancer.  However, it is now possible to synthesise these ethers using electrosynthesis at room temperature, using a very low current, inexpensive graphite electrodes,  and greener solvents (Scheme 2).5,6

Scheme 2

Scheme 2: Electrochemical synthesis of methoxymethyl ethers from carboxylic acid derivatives in methanol at room temperature using graphite electrodes.

 

But organic electrosynthesis is not limited to university laboratories, as electrosynthetic methodologies can often be scaled-up to be used in industrial laboratories with relative ease.  Perhaps the most well-known example of industrial scale electrosynthesis is the electrohydrodimerisation of acrylonitrile into adiponitrile by Monsanto, which is a key intermediate in the manufacturing of nylon (Scheme 3).7–9  Under aqueous conditions, it has been possible to synthesise approximately 300 000 tons of adiponitrile worldwide, with the sole by-product being oxygen, arising from the oxidation of water.

Scheme 3

Scheme 3: Industrial electrochemical synthesis of adiponitrile from two acrylonitrile molecules using cadmium and stainless-steel electrodes under aqueous conditions.

 

In summary, organic electrosynthesis represents a modern, greener, more economical, and safer alternative to traditional chemical syntheses.  With the advent of new and more user-friendly equipment, the field has experienced a resurgence in interest, with many new methodologies being developed in recent years.  Through the use of electrosynthesis, the challenge of making the pharmaceutical sector greener is starting to look much more achievable.

References

 

1            L. Belkhir and A. Elmeligi, Carbon footprint of the global pharmaceutical industry and relative impact of its major players, J. Clean. Prod., 2019, 214, 185–194.

2            M. Yan, Y. Kawamata and P. S. Baran, Synthetic Organic Electrochemistry: Calling All Engineers, Angew. Chem. Int. Ed., 2018, 57, 4149–4155.

3            L. E. Overman, N. A. Weires and Y. Slutskyy, Facile Preparation of Spirolactones by an Alkoxycarbonyl Radical Cyclization Cross-Coupling Cascade, Angew. Chem. Int. Ed., 2019, 58, 8561–8565.

4            A. Petti, M. C. Leech, A. D. Garcia, I. C. A. Goodall, A. P. Dobbs and K. Lam, Economical, Green and Safe Route Towards Substituted Lactones via the Anodic Generation of Oxycarbonyl Radicals, Angew. Chem. Int. Ed., 2019, 58, 16115–16118.

5            X. Luo, X. Ma, F. Lebreux, I. E. Markó and K. Lam, Electrochemical methoxymethylation of alcohols – A new, green and safe approach for the preparation of MOM ethers and other acetals, Chem. Commun., 2018, 54, 9969–9972.

6            C. G. W. van Melis, M. R. Penny, A. D. Garcia, A. Petti, A. P. Dobbs, S. T. Hilton and K. Lam, Supporting-Electrolyte-Free Electrochemical Methoxymethylation of Alcohols Using a 3D-Printed Electrosynthesis Continuous Flow Cell System, ChemElectroChem, 2019, 6, 4144–4148.

7            D. E. Danly, Development and Commercialization of the Monsanto Electrochemical Adiponitrile Process, J. Electrochem. Soc., 1984, 131, 435C.

8            M. M. Baizer, Electrolytic Reductive Coupling, J. Electrochem. Soc., 1964, 111, 215.

9            M. C. Leech, A. D. Garcia, A. Petti, A. P. Dobbs and K. Lam, Organic electrosynthesis: from academia to industry, React. Chem. Eng., 2020, Advanced Article, DOI: 10.1039/D0RE00064G

 

 

A Quirky Chemistry Break: Solvent-less Polymerization with Ball Milling

By Hyungjun Cho, member-at-large for the GCI

In April of 2019, the International Union of Pure and Applied Chemistry (IUPAC) named reactive extrusion as part of the 10 chemical innovations that could have high impact in society [1]. One of the reactive extrusion technique that is of interest is the use of ball mills instead of solvents to mix reagents. An exciting example of such a reaction is solvent-less polymerization. This method of making polymers in a ball mill has been blossoming in recent years but has not attracted much mainstream attention in the chemical community. This article will present the pivotal publication that re-invigorated interest the field of solvent-less polymerization.

There is the typical list of ingredients required for making polymers: 1) monomer, 2) an initiator and/or catalyst, 3) a constant input of energy, and 4) a solvent. Like in organic chemistry, the solvent is almost always critical to the success of the process. Although some solvent-less polymerization techniques are have known for (such as bulk [2] and solid-state polymerization [3]), these methods are not widely applicable and often requires elevated temperatures, which needs a lot of energy. In contrast, ball milling polymerization is a solvent-free technique that is at its early stages of development, but may avoid these issues.

 

Figure 1

Figure 1. A cartoon diagram of the vibrational ball milling process.

 

Ball milling is a mechanochemical process, where solid chemical samples are added to a grinding jar with solid metal balls (Figure 1). The grinding jar is shaken or spun which results in collisions between the balls and the chemical material. This generates high instant pressure and heat through impact and friction [4].

Although ball mills are conventionally used to break down polymers [5], a handful of reports demonstrated the synthesis of polymers using ball mills [6-10]. In 2014, Ravnsbaek et al. synthesized the polymer poly(p-phenylene vinylene) using a ball mill [5]. This work seems to have reinvigorated the field of ball mill polymerization, and is briefly presented here.

Figure 2

Figure 2. Solvent-less synthesis of poly(2-methoxy- 5-2′-ethylhexyloxy phenylene vinylene) in a ball mill. ACS Macro Lett. 2014, 3 (4), 305–309 [5]. Copyright 2014 American Chemical Society.

Briefly, the solid chemicals bis(chloromethyl)-methoxy-ethylhexyloxy-benzene and potassium tert­-butoxide were added to a zirconium oxide grinding jar, along with a zirconium oxide ball (diameter = 10 mm) (Figure 2). The reaction mixture was shaken horizontally at a frequency of 30 Hz at room temperature to synthesize poly(2-methoxy- 5-2′-ethylhexyloxy phenylene vinylene) (MEH-PPV). The authors found that after ca. 10 minutes of shaking, the polymers grew to its maximum average molecular weight (Mn = 35 kDa) (Figure 3). The size dispersity of the polymer was broad (Đ ~ 4) which is typical of stepwise growth polymerizations. The yield was ca. 60% after 10 minutes of shaking and did not improve with longer shaking time. This was especially remarkable because similar polymerization in solution typically requires several hours and elevated temperature [11-13].

Figure 3

Figure 3. The synthesis and degradation of MEH-PPV with respect to ball milling time Reprinted with permission from Ravnsbæk J. B. and Swager, T. M. ACS Macro Lett. 2014, 3 (4), 305–309 [5]. Copyright 2014 American Chemical Society.

In another set of experiments, Ravnsbaek et al. obtained a pre-made sample of MEH-PPV with a larger Mn (Mn =150 kDa) and exposed it to the same grinding conditions used for their synthesis of MEH-PPV. The authors found that the Mn of the larger polymer sample decreased over time to 35 kDa (Figure 3), which suggested that there exists a maximum size of polymer that can be synthesized using a ball mill.

Since this report by Ravnsbaek et al., other research groups have been using ball mills for solvent-less polymerizations. The Borchardt group [14-16], the Kim group [17-18], and the Song group [19] published their findings within the last 4 years. These reports collectively demonstrate many novel ball mill polymerizations, including co-polymerization (more than one monomer) [15-16,19], metal catalyzed polymerization (palladium-catalyzed polymerization) [15-16], and the synthesis of non-conjugated polymers (i.e. poly(lactic acid) and polyurethanes) [17-19].

In 2019, Christensen et al. published an article in Nature Chemistry showing their work regarding a new type of polymer called the vitrimer [20], which was synthesized as the product of the reaction of ketones and amines in a ball mill. While the focus of this article was on the chemistry of the polymer, it is noteworthy that the ball mill polymerization has been highlighted in a high impact journal. This will likely encourage more polymer research groups to look into this unconventional technique as it has a lot of room for growth and improvement, and even more potential to reduce the use of solvent in polymer production.

References

  1. Gomollón-Bel, F. Ten Chemical Innovations That Will Change Our World: IUPAC Identifies Emerging Technologies in Chemistry with Potential to Make Our Planet More Sustainable. Chemistry International 2019, 41 (2), 12–17.
  2. Han, X.; Fan, J.; He, J.; Xu, J.; Fan, D.; Yang, Y. Direct Observation of the RAFT Polymerization Process by Chromatography. Macromolecules 2007, 40 (15), 5618–5624.
  3. Duh, B. Effects of Crystallinity on Solid-State Polymerization of Poly(Ethylene Terephthalate). Journal of Applied Polymer Science 2006, 102 (1), 623–632.
  4. Janot, R.; Guérard, D. Ball-Milling in Liquid Media: Applications to the Preparation of Anodic Materials for Lithium-Ion Batteries. Progress in Materials Science 2005, 50 (1), 1–92.
  5. Ravnsbæk, J. B.; Swager, T. M. Mechanochemical Synthesis of Poly(Phenylene Vinylenes). ACS Macro Lett. 2014, 3 (4), 305–309.
  6. Huang, J.; Moore, J. A.; Acquaye, J. H.; Kaner, R. B. Mechanochemical Route to the Conducting Polymer Polyaniline. Macromolecules 2005, 38 (2), 317–321.
  7. Murakami, S.; Tabata, M.; Sohma, J.; Hatano, M. Mechanochemical Polymerization of Acetylene. Journal of Applied Polymer Science 1984, 29 (11), 3445–3455.
  8. Posudievsky, O. Yu.; Goncharuk, O. A.; Barillé, R.; Pokhodenko, V. D. Structure–Property Relationship in Mechanochemically Prepared Polyaniline. Synthetic Metals 2010, 160 (5), 462–467.
  9. Posudievsky, O. Yu.; Goncharuk, O. A.; Pokhodenko, V. D. Mechanochemical Preparation of Conducting Polymers and Oligomers. Synthetic Metals 2010, 160 (1), 47–51.
  10. Thorwirth, R.; Stolle, A.; Ondruschka, B.; Wild, A.; Schubert, U. S. Fast, Ligand- and Solvent-Free Copper-Catalyzed Click Reactions in a Ball Mill. Commun. 2011, 47 (15), 4370–4372.
  11. Jin, S.-H.; Kang, S.-Y.; Yeom, I.-S.; Kim, J. Y.; Park, S. H.; Lee, K.; Gal, Y.-S.; Cho, H.-N. Color-Tunable Electroluminescent Polymers by Substitutents on the Poly(p-Phenylenevinylene) Derivatives for Light-Emitting Diodes. Mater. 2002, 14 (12), 5090–5097.
  12. Liu, B.; Lü, X.; Wang, C.; Tong, C.; He, Y.; Lü, C. White Light Emission Transparent Polymer Nanocomposites with Novel Poly(p-Phenylene Vinylene) Derivatives and Surface Functionalized CdSe/ZnS NCs. Dyes and Pigments 2013, 99 (1), 192–200.
  13. Schwalm, T.; Wiesecke, J.; Immel, S.; Rehahn, M. The Gilch Synthesis of Poly(p-Phenylene Vinylenes): Mechanistic Knowledge in the Service of Advanced Materials. Macromolecular Rapid Communications 2009, 30 (15), 1295–1322.
  14. Grätz, S.; Borchardt, L. Mechanochemical Polymerization – Controlling a Polycondensation Reaction between a Diamine and a Dialdehyde in a Ball Mill. RSC Adv. 2016, 6 (69), 64799–64802.
  15. Grätz, S.; Wolfrum, B.; Borchardt, L. Mechanochemical Suzuki Polycondensation – from Linear to Hyperbranched Polyphenylenes. Green Chem. 2017, 19 (13), 2973–2979.
  16. Vogt, C. G.; Grätz, S.; Lukin, S.; Halasz, I.; Etter, M.; Evans, J. D.; Borchardt, L. Direct Mechanocatalysis: Palladium as Milling Media and Catalyst in the Mechanochemical Suzuki Polymerization. Angewandte Chemie International Edition 2019, 58 (52), 18942–18947.
  17. Lee, G. S.; Moon, B. R.; Jeong, H.; Shin, J.; Kim, J. G. Mechanochemical Synthesis of Poly(Lactic Acid) Block Copolymers: Overcoming the Miscibility of the Macroinitiator, Monomer and Catalyst under Solvent-Free Conditions. Chem. 2019, 10 (4), 539–545.
  18. Ohn, N.; Shin, J.; Kim, S. S.; Kim, J. G. Mechanochemical Ring-Opening Polymerization of Lactide: Liquid-Assisted Grinding for the Green Synthesis of Poly(Lactic Acid) with High Molecular Weight. ChemSusChem 2017, 10 (18), 3529–3533.
  19. Oh, C.; Choi, E. H.; Choi, E. J.; Premkumar, T.; Song, C. Facile Solid-State Mechanochemical Synthesis of Eco-Friendly Thermoplastic Polyurethanes and Copolymers Using a Biomass-Derived Furan Diol. ACS Sustainable Chem. Eng. 2020, 8 (11), 4400–4406.
  20. Christensen, P. R.; Scheuermann, A. M.; Loeffler, K. E.; Helms, B. A. Closed-Loop Recycling of Plastics Enabled by Dynamic Covalent Diketoenamine Bonds. Chem. 2019, 11 (5), 442–448.

Textiles True Colours: How Sustainable are they?

By Brian Tsui, Website Coordinator for the GCI

The rise of fast-fashion trends in our global economy has led to a booming textiles manufacturing industry. According to the Ellen MacArthur Foundation, globally the industry consumes over 98 million tonnes of non-renewable resources per year.1 The majority of these items have seen less utilization compared with early 2000s. With an increasing consumer awareness of eco-friendly and sustainable practices in manufacturing, pressures at the consumer level have led to changes to these labour-intensive processes. Of note is the dyeing process, which historically has been a wet process. The dyeing, printing, and washing steps consume large amounts of energy and generate large volumes of wastewater, which contain the excess dyes, surfactants, and salts. In 2014 alone, coloration of textiles generated over 1.5 billion tons of wastewater.1 Much of this wastewater is neither environmentally benign nor biodegradable and requires further energy investment during the remediation step. Smaller eco-conscious manufacturers such as Ikeuchi Organic, a company located in Japan, have been tackling these issues by utilizing 100% wind power for their operations.2 The smaller scale allows for easier implementation of wastewater treatment and a final product which passes Class 1 certification as set by OEKO-TEX STANDARD 100, a global leader in textiles regulations.3 The underutilization of sustainable textiles dyeing processes on a large scale, however, continues to be a problem. The search for highly competitive, as well as energy and cost-efficient processes along with bridging the gap between laboratory and industrial scales to deliver the benefits of eco-friendly manufacturing is an ongoing goal in the textile research community.

Figure 1

Figure 1. Growth of clothing sales and decline in clothing utilization since 2000.1

Traditionally, the dyeing process involves an interaction between a dye molecule and a fibre (adsorption). This is accompanied by the movement of the dye to the interior of the fibre (diffusion). Consider cotton, which comprises an estimated 21% of global fibre usage.4 Cellulose is the primary component of cotton fibers, totalling up to 95% by mass. The most common method for dyeing cotton involves reactive dyes. As their name suggests, a reactive dye is a high energy molecule which can react with natural cellulose and form a covalent bond. The reactive molecule is low cost, easily tuned to a variety of vibrant colors, and simple to apply.

Figure 2

Figure 2. Types of reactions involving reactive dye and cellulose. Top is substitution, bottom is addition.

At each step of the process, there are several factors that determine the quality of the final product.5 Temperature has a pronounced effect on increasing dye penetration and more rapid diffusion, but at the cost of increased dye hydrolysis. Tight cotton fibres require higher temperature for effective permeation of the dye into the fibre, while loose cotton fibres require lower temperatures for the same effect. The alkalinity of the solution also plays an important role, as the concentration of the cellulose anion is proportional to the pH of the solution. During the dyeing process, some alkali is consumed, and therefore the pH of the final dye solution is lower than the initial pH. Electrolytes are also important to the dyeing solution, acting to overcome the electrostatic repulsions between anionic cellulose and the anionic dye linkers. Finally, the concentration of these additives also impacts the dyeing process. There is a fine line between rate of dyeing and negative impacts on production costs and the environment. These are just some examples of challenges textiles research scientists face when developing a new dye process.

Kim et al highlighted the use of nanofibrillated cellulose (NFC) as a supplement to normal cotton cellulose.6 The large surface area of NFC resulted in an abundance of surface cellulose hydroxyls. Consequently, the salt, alkali, and water amounts could be reduced by an order of magnitude, generating significantly less wastewater. Most importantly, the dyeing process was not significantly impacted by these changes and the resulting fabric is largely indistinguishable from traditional dyeing methods. A life-cycle assessment based on the experimental data suggested that the NFC-based process would result in a significant reduction on wastewater load.

Figure 3

Figure 3. Comparison of various dyeing methods. a) conventional dyeing method; b) conventional dyeing method with decreased salt and alkali concentration; c) NFC-based dyeing with decreased salt and alkali concentration.

Xia et al demonstrated the use of a co-solvent, ethanol, effective for eliminating the need for electrolytes.7 The ethanol was found to impact the dyeing process in four main ways: improving the solubility of the reactive dyes, decreasing the dielectric constant and electrostatic repulsion of the solution, increased aggregation of dyes leading to enhanced dyeing kinetics, and decreasing the surface tension improving dyeing efficiency. These efforts, too, improved the clarity of the resulting waste solution compared to commercial wastewater without loss of fabric colour.

Figure 4

Figure 4. Comparison of fabric wastewater with ethanol-water salt-free method and traditional electrolyte-added dyeing method.

Ding et al developed a method for dyeing without the use of reactive organic dyes, instead opting for base metal nanoparticles.8 Carbon black nanoparticles are first functionalized onto cotton fibres via radiation grafting. Subsequent immobilization of iron oxide red, cobalt green, or cobalt blue for red, green, and blue colors respectively, give rise to colorized cotton fabric. Various approximate colors can be created by varying the concentration of each nanoparticle, and the colour is retained even after 20 wash cycles. Most importantly, the lack of reactive dyes results in pronounced clarity of the resulting dye solution compared to real wastewater.

Figure 5

Figure 5. Images of wastewater samples. W0 is real wastewater from a dyeing factory. WCB1–WCB5, WCoG1–WCoG5, WCoG1–WCoG5, WFeR1–WFeR5 are samples from various concentrations of nanoparticle dyes.

Textiles and clothing play an important part of everyday life. The current clothing manufacture system is wasteful and polluting to the environment. With material and process scientists at the forefront, a new textiles economy built from sustainable methodologies will be vital as we continue to deplete our non-renewable resources.

 

References

  1. Ellen MacArthur Foundation, A new textiles economy: Redesigning fashion’s future, (2017, http://www.ellenmacarthurfoundation.org/publications).
  2. Ikeuchi Organic – Our Philosophy. https://www.ikeuchi.org/about-us/en/concept/ (accessed Mar 15, 2020)
  3. STANDARD 100 by OEKO-TEX. https://www.oeko-tex.com/en/our-standards/standard-100-by-oeko-tex (accessed Mar 15, 2020)
  4. Yang, Q. M. Global Fibres Overview, Synthetic Fibres Raw Materials Committee Meeting at APIC, Pattaya, 16 May 2014.
  5. Shang, S. M. Process control in dyeing of textiles. Process Control in Textile Manufacturing, 300–338. (2013) doi:10.1533/9780857095633.3.300
  6. Kim, Y.; McCoy, L. T.; Lee, E.; Lee, H.; Saremi, R.; Feit, C.; Hardin, I. R.; Sharma, S.; Mani, S.; Minko, S. Green Chem. 2017, 19, 4031.
  7. Xia, L.; Wang, A.; Zhang, C.; Liu, Y.; Guo, H.; Ding, C.; Wang, Y.; Xu, W. Green Chem. 2018, 20, 4473.
  8. Ding, X.; Yu, M.; Wang, Z.; Zhang, B.; Li, L.; Li, J. Green Chem. 2019, 21, 6611

A Greener Future for Chemicals

By Jose Jimenez Santiago, member-at-large for the GCI

Over the last four decades, the development of the chemical industry has transformed the global economy and provided a better quality of life for societies worldwide. However, the mass production and disposal of persistent chemicals has been a threat for the environment and the human health. Understanding the effect of chemicals in the environment is necessary in order to replace current harmful molecules with more benign ones1. Fortunately, chemist have learned from negative past experiences and the next generation of chemicals are expected to cause less toxicity and be less environmentally persistent.

Some chemicals have had a negative impact on wildlife populations, some of those effects appear after several years of exposure and bioaccumulation of the toxic molecules in the environment (Figure 1). The first step to prevent further tragedies in wildlife populations is to know the environmental impact of every chemical that is released into the market. However, in places where this data is available, like the United States and Europe, the percentage of chemicals with known environmental information is relatively small. There are around 75, 000 to140, 000 chemicals on the market, out of those, empirical data on persistence is available for only 0.2%, bioconcentration data for only 1% and aquatic toxicity for 11%2,3. Without this information, how can we make an accurate risk assessment of those chemicals? Moreover, molecules with high persistence in the environment may show a negative impact after many years of accumulation. It is important to keep in mind that that for most molecules on the market, we do not know the extent of their negative effects on the environment in the short term and long term2,4.

Jose blog picture

Figure 1. Examples of wildlife scenarios where chemicals have had or are having population effects 1,6,7,8.

 

 

It is hard to shift to a greener chemical industry that prioritizes the environment due to the cost involved in testing the toxicity of molecules. However, there have been advances from the government and chemistry community towards that goal:

  1. More regulation of chemicals in the environment.

Previously, chemical regulations were targeting the emission of a limited number of pollutants into the environment. New regulations, such as Registration, Evaluation, Authorization and Restriction of Chemicals (REACH2006) in the European Union, are looking to ensure that new chemicals entering the market will conform to minimum human safety and environmental standards5. Thus, manufacturers are responsible for evaluating the impact of new compounds being introduced into the market.

  1. Analytical development and computer models

Many analytical methods have achieved low limits of detection (LOD). It is now possible to identify all the molecules present in a sample. For example, these methods have been used to analyze urban runoff water and identify unusual pollutants4. With the help of these new, sensitive methods approach it is possible to investigate pollution incidents and identify the industrial location responsible for those incidents.

One major ethical concern when running toxicity tests is the large number of animals needed2. In addition, the many thousands of chemicals yet to be tested make this approach unreasonable. Recently, computer models were used to predict which chemicals will be of greatest concern; namely chemicals which are persistent, bioaccumulative and toxic (PBT). In this survey, out of 95,000 chemicals, only 3-5% were likely to be PBT4. These tolls can make feasible the lab test of the most hazardous chemicals and will reduce the ethical concerns.

  1. Better wastewater treatment

The incorporation of a secondary biological treatment into wastewater has considerable benefits for the water quality and chemicals reduction. The Activated Sludge Process is the most common method and has been applied in cities all around the world. For example, in China, 81% of the water distributed to the urban population undergoes the Activated Sludge Process9. This shows how we can find cost effective ways to remove chemicals that have accumulated in the environment for many years.

The amount of chemicals used worldwide, their production, diversity, and incorporation has never been greater1. As chemists, it is important to understand the environmental challenges that we face. In addition, chemists should be aware that chemical problems require chemical solutions. We can be pessimistic about the current status of pollutants, but there are tangible reasons to be optimistic about solutions and methods to reduce the negative impact of our current chemical production. Learning from the past is the starting point to ensure that the next generation of chemicals will have less negative impact on the environment.

 

  • Johnson, A.C., Jin, X., Nakada, N., Sumpter, J. P. Science, 2020, 367, 384-387.
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  • Judson et al., Environ. Health Perspect. 2009, 117, 685–695.
  • Strempel, M. Scheringer, C. A. Ng, K. Hungerbühler, Environ.Sci. Technol. 2012, 46, 5680–5687.
  • European Commission, Introduction to REACH regulation, 2019; https://ec.europa.eu/environment/chemicals/reach/reach_en.htm
  • P. Desforges et al., Science, 2018, 361, 1373–1376.
  • L. Oaks et al., Nature, 2004, 427, 630–633.
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  • H. Zhang et al., Environ. Int. 2016, 92–93, 11–22.

 

The Great Step Backwards: Polymer to Monomer

By Hyungjun Cho, member-at-large for the GCI

There is a movement to develop a new type of product life system called ‘the circular economy’ [3]. Part of this movement aims to manufacture products from recycled or raw materials, and after its useful lifetime, re-introduce the product (now considered waste) as recycled material. The motivation for the introduction of the circular economy is to minimize the need for virgin raw material, especially when it originates from non-renewable resources. This effort is being spearheaded by the Ellen MacArthur Foundation with major industry partners like Google, Unilever, Solvay, and Philips, among others [3]. A critical component to the function of the circular economy is developing the capability to turn waste into a desirable product.

There are several methods of recycling all the different types of materials we use in every day life. This blog will discuss a niche in the ‘plastic to monomer’ field. Evidently, in April of 2019, IUPAC named ‘plastic to monomer’ as part of the 10 chemical innovations that could have high impact in society [6]. Before discussing ‘plastic to monomer’, I must clarify the term ‘plastic’. Generally, plastic is made up of many polymer chains that are physically entangled with one another. A macroscopic analogy is when many electrical wires (think of Christmas tree lights) become entangled: the wires are stuck to each other and the rigidity of the ball of wire is greater than the rigidity of a single wire.

Much like the type of wire influences the tangled ball it forms, the chemical structure of the polymer influences the material properties of the plastic. Examples of properties of plastics include rigidity, elasticity, malleability, gas permeability, friction to skin, transparency, and many others. The polymers that are used for commercial plastic products have been studied and developed for decades to be able perform a specific function. For example, polyvinyl chloride and polystyrene were initially discovered in the 1800s [2,8]. Thus, it would be ideal if the currently used polymers can be de-polymerized back into monomers for recycling purposes. This would be a major move by the plastics industry to become environmentally friendly.

The conventional method to turn polymers into monomer is thermal decomposition. Samples of polymer can be heated to high temperature (typically 220-500 °C) to break some of the bonds that hold the monomers together [10]. When this occurs, radicals can form at the site of the broken bond, which can lead to de-polymerization [10]. The required temperature and how much monomer is formed is dependent on the chemical structure of the monomers that are formed. Thermal decomposition to recover monomer is suitable only for a few types of polymers, such as poly(α-methylstyrene), which has ceiling temperature of 66 °C to propagate depolymerization; the monomer recovery after thermal decomposition of poly(α-methylstyrene) is excellent at 95% [11]. However, for polymers like polyethylene (PE, the most produced polymer) and polypropylene (PP, 2nd most produced polymer), the monomer recovery yield is poor (0.025-2%) [11]. In some cases such as polyvinylchloride (PVC, 3rd most produced polymer), thermal decomposition is even more problematic because PVC will release harmful hydrochloric acid and vinylenes upon heating [11]. Thus, the monomer recovery is poor (1 %) and the process is highly corrosive.

Therefore, one of the key challenges to address for ‘polymer to monomer’ is to perform de-polymerization at a low temperature. There are 4 recent publications that explore this challenge [5,7,9,12]. In general, the authors synthesized polymers using reversible-deactivation radical polymerization (RDRP) techniques and explored the de-polymerization reactions they encountered. Below is a brief highlight from the publications from the Haddleton group [9] and the Gramlich group [5].

Picture1

Scheme 1: De-polymerization of RAFT polymers with trithioester end-group [5]. Reproduced from ref. [5] with permission from The Royal Society of Chemistry.

Flanders et al. polymerized methacrylate monomers, including methylmethacrylate (MMA), using reversible addition-fragmentation chain-transfer (RAFT) polymerization with a trithioester chain-transfer agent (CTA) [5]. This type of polymerization places trithioester end-group at end of the polymer chain (Scheme 1). Typically, this end-group is used to re-start the polymerization at the trithioester end of the polymer. However, as we will see, it may have another function. The authors isolated the polymer, then re-dissolved the polymer in 1,4-dioxane at 70 °C (Scheme 1). This caused monomers to be released from the polymer chains at a temperature much less than the ceiling temperature of MMA, which is 227 °C [13]. Analysis of the polymer after partial de-polymerization demonstrated that the trithioester end-group was still attached to the polymer and the size dispersity (range of polymer ‘molecular weight’) was low, which suggested that the de-polymerization was moderated by the trithioester end-group. The authors observed 10-35% de-polymerization after heating at 70 °C for 12-60 hrs.

Picture2

Scheme 2: ATRP of NIPAM in carbonated water, followed by de-polymerization [9]. Reproduced from ref. [9] with permission from The Royal Society of Chemistry.

Lloyd et al. used an alkylbromide initiator, Cu-based catalyst system to polymerize N-isopropylacrylamide (NIPAM) in Highland Spring carbonated water at 0 °C (Scheme 2) [9]. This type of polymerization places a halide at the end of the polymer chain. The authors monitored the monomer conversion into polymer using 1H-NMR spectroscopy. They measured that ca. 99% of the monomer was converted into polymer chains within 10 min. Unexpectedly, in the next 50 min. the authors observed 50% de-polymerization. The authors attempted to optimize de-polymerization conditions by changing the pH, using dry ice in HPLC grade water instead of Highland Spring carbonated water, etc. which led to 34-71% de-polymerization after 0.5-24 hrs. Years later, the same group used a very similar polymerization condition to polymerize NIPAM [1]. This time, non-carbonated water was used as the solvent and they did not report any de-polymerization.

The reports on RDRP followed by de-polymerization highlighted here are not yet ready to make an impact to ‘plastic to monomer’. The authors admit that the mechanism of de-polymerization is unknown. However, these seem to be the first set of reports on de-polymerization occurring at low temperatures. Perhaps these publications could be the birth of the reversible-deactivation radical de-polymerization (RDRDe-P) field. This is especially intriguing because RDRP have already been studied for decades in academia and are being adopted by the polymer industry [4]. Companies like BASF, Solvay, DuPont, L’Oréal, Unilever, 3 M, Arkema, PPG Industries, etc. already claimed patents for technology and products based on RDRP [4]. Somewhat ironically, RDRP was also part of the IUPAC’s 10 chemical innovations for impact on society but not for its potential to recycle polymer [6].

The polymers of the future may not be made from monomers abundantly used today, but the polymers of the future may be degradable through a low energy process.

References

  1.  Alsubaie, F.; Liarou, E.; Nikolaou, V.; Wilson, P.; Haddleton, D. M. Thermoresponsive Viscosity of Polyacrylamide Block Copolymers Synthesised via Aqueous Cu-RDRP. European Polymer Journal 2019, 114, 326–331.
  2. Baumann, E. Ueber Einige Vinylverbindungen. Justus Liebigs Annalen der Chemie 1872, 163 (3), 308–322.
  3. Circular Economy – UK, USA, Europe, Asia & South America – The Ellen MacArthur Foundation https://www.ellenmacarthurfoundation.org/ (accessed Jan 5, 2020).
  4. Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over? Chem. 2018, 9 (40), 4947–4967.
  5. Flanders, M. J.; Gramlich, W. M. Reversible-Addition Fragmentation Chain Transfer (RAFT) Mediated Depolymerization of Brush Polymers. Chem. 2018, 9 (17), 2328–2335.
  6. Gomollón-Bel, F. Ten Chemical Innovations That Will Change Our World: IUPAC Identifies Emerging Technologies in Chemistry with Potential to Make Our Planet More Sustainable. Chemistry International 2019, 41 (2), 12–17.
  7. Li, L.; Shu, X.; Zhu, J. Low Temperature Depolymerization from a Copper-Based Aqueous Vinyl Polymerization System. Polymer 2012, 53 (22), 5010–5015.
  8. Liebig, J. Justus Liebig’s Annalen Der Chemie. Annalen der Chemie 1832, 1874-1978.
  9. Lloyd, D. J.; Nikolaou, V.; Collins, J.; Waldron, C.; Anastasaki, A.; Bassett, S. P.; Howdle, S. M.; Blanazs, A.; Wilson, P.; Kempe, K.; et al. Controlled Aqueous Polymerization of Acrylamides and Acrylates and “in Situ” Depolymerization in the Presence of Dissolved CO2. Commun. 2016, 52 (39), 6533–6536.
  10. Microwave-Assisted Polymer Synthesis. Springer eBooks 2016
  11. Moldoveanu, Șerban. Analytical Pyrolysis of Synthetic Organic Polymers; Techniques and instrumentation in analytical chemistry; Elsevier: Amsterdam ; Oxford, 2005.
  12. Sano, Y.; Konishi, T.; Sawamoto, M.; Ouchi, M. Controlled Radical Depolymerization of Chlorine-Capped PMMA via Reversible Activation of the Terminal Group by Ruthenium Catalyst. European Polymer Journal 2019, 120, 109181.
  13. SFPE Handbook of Fire Protection Engineering, 5th ed.; Hurley, M. J., Gottuk, D. T., Jr, J. R. H., Harada, K., Kuligowski, E. D., Puchovsky, M., Torero, J. L., Jr, J. M. W., Wieczorek, C. J., Eds.; Springer-Verlag: New York, 2016.

Green Marketing in the Plastic Era: Honesty or Hype?

By Nina-Francesca Farac, Member-at-Large for the GCI

The impact of human activity on climate and the environment has moved beyond a mainstream headline. It has come to the point where we are considered the dominant influence on our ecosystems and geology, so much so that there is a buzzword for it: ‘Anthropocene’. Within the Anthropocene, our greatest challenge is lessening the effects of our immense footprint on Earth, mainly caused by consumption of fossil fuels and our obsession with plastics. Consequently, there has been a considerable spike in eco-friendly or ‘green’ marketing of numerous products labeled as ‘organic’, ‘biodegradable’, or ‘sustainable’ ranging from fuels, cars, skincare, all the way to clothing1. One common advertising theme for several everyday products is post-consumer recycled materials and their incorporation into the design and production of such commodities.  But to what extent are the advertised claims legitimate and whether they allow for a circular economy (e.g. make, use, recover)? Here, we will cover the chemistry of popular sustainable alternatives to plastics and compare them to their non-sustainable counterparts to assess whether the ‘green’ hype is valid.

Recycling Plastics: Single-Use vs. Biodegradable vs. Compostable

Let’s start with why commonly used plastics, including single-use plastics, pose such an environmental liability. The reality of plastic recycling is that it is far less efficient in practice than one would hope. The types of plastics that can be recycled, the number of times they can be recycled and reused starts with the ubiquitous recycling symbols found on the bottom of plastic products2. A common misconception is to equate the presence of this symbol to the ability of recycling a given type of plastic; however, this is not the case. The truth is just because there is a recycling sign doesn’t necessarily mean it gets recycled3. According to Resin Identification Codes (RICs), plastics are organized into 7 categories according to the temperature at which the material has been heated, and this numerical categorization is only indicative of the kind of plastic it is, and not necessarily its recyclability (Fig. 1).

Image 1

Figure 1. Resin Identification Codes (RICs) designating the seven categories of plastics, the corresponding chemical structure of each polymer, and graphical illustrations of common plastic products of each type.

In other words, just because we place it in a blue bin doesn’t mean it gets recycled. In fact, an astonishing 91% of plastics are not recycled2. You may be wondering, “how are recycling rates that low?” As with any commodity, recycling is ultimately determined by the market.  If there is a demand, recyclers and companies will pay for post-consumer recyclables; but, without market demand, recycling bares no profit and placing them in a blue bin doesn’t make a difference3. For example, out of the seven categories of plastics depicted in Figure 1, only PET has a high recycling value (i.e. the price of PET scrap is high) while other plastics are projected to see a drop in recycling rates (at least in North America)4–6. In addition, certain types of everyday plastics are simply not recyclable, such as plastic bags, straws, and coffee cups (the latter is not possible unless the paper exterior is separated from the plastic interior)3; in effect, these items are tossed together in the “everything else” category #7 (Other) as non-recyclables and mainly contribute to plastic waste generation. Other limiting factors include the inability to recycle dirty plastic and how the quality of plastic is downgraded each time plastic is recycled7.

Since many everyday items are plastic-based and plastics are a staple of modern life, the most common sustainable alternative to single-use plastics are bioplastics, a.ka biodegradable plastics (Figure 2).

Image 2

Figure 2. Types of biodegradable plastics in use today, their chemical structures, and their applications.

Consumer confusion often arises when the terms “biodegradable” and “compostable” are used interchangeably, although they do not convey the same concept. Biodegradable plastics are a class of polymers that can break down by the action of living organisms into natural byproducts such as water, biomass, gases (e.g. N2, CO2, H2, CH4), and inorganic salts within a reasonable amount of time8. The issue with this definition is that many plastic products eventually degrade; for instance, low density polyethylene (LDPE, category #4 – Fig. 1) has been shown to biodegrade slowly to carbon dioxide (0.35% in 2.5 years) and thus can be considered a biodegradable polymer according to the above description9. Because certain definitions of biodegradability do not state a time limit or timeframe within which degradation should occur, consumers can be easily misled, and companies can hide behind this ambiguity. It is assumed, however, that a biodegradable product has a degradation rate that is comparable to that of its application rate, i.e. the break down process is fast such that product accumulation in the environment does not occur.

To understand why certain polymers biodegrade and others do not, one has to consider the chemical structure of biodegradable polymers along with the mechanisms through which polymeric material are biodegraded. Structurally, many biodegradable polymers, both natural and synthetic, often contain amide, ester, or ether bonds10. Those deriving from biomass (i.e. agro-polymers) include polysaccharides (glycosidic bonds via condensation of a saccharide hemiacetal bond and an alcohol) and proteins (chains of amino acids linked via amide groups). The other major category is biopolyesters, which are typically derived from microorganisms or are synthetically made (Figure 3).

Image 3

Figure 3. Categories of biodegradable polymers.

Mechanistically, biodegradation is defined as a process caused by biological activity, especially driven by enzymes, but it can occur simultaneously with – and sometimes even initiated by – abiotic process such as photodegradation and hydrolysis9. From the chemical perspective, biodegradation can occur in the presence of oxygen (aerobic, Equation 1.1) or in the absence of oxygen (anaeriobic, Equation 1.2), where Cpolymer represents either a polymer or a fragment from an earlier degradation process9.

Cpolymer + O2→CO2 + H2O + Cresidue + Cbiomass (Aerobic biodegradation,1.1)

Cpolymer→ CO2 + CH4 + H2O + Cresidue + Cbiomass (Anaeriobic biodegradation,1.2)

Complete biodegradation is said to occur when no Cresidue remains, and no oligomers or polymers are left to be further broken down9. As polymers represent major constituents in living cells that have a high turnover rate, i.e. they are constantly degraded in response to environmental changes and metabolic requirements, numerous microorganisms are capable of breaking down naturally occurring polymers as a result of millions of years of adaption. However, for many new synthetic polymers invented in the last 100 years (categories 1-6, Fig. 1) which find their way into the environment, such biodegradation mechanisms have yet to be developed. Other key factors affecting polymer biodegradation include copolymer composition and environmental factors such as pH, temperature, and water content9. This suggests that even if a product is made from bioplastics, it doesn’t necessarily mean it will fully decompose. If such products end up in landfills, for instance, the low oxygen content of such an environment impedes complete degradation. Furthermore, although bioplastics fall within category 7 (Fig.1), these plastics aren’t suitable for recycling and can even degrade the quality of plastic if added to a recycled mixture.

In contrast, compostable materials can break down into water, carbon dioxide, inorganic salts and biomass at the same rate as cellulose, or roughly 90 days11,12. In addition, compostable plastics must disintegrate fully and be indistinguishable in the compost while leaving no toxic material behind. Although compostable plastics appear to have more environmental benefits, this material is equally limited by an inability to biodegrade in a landfill and being incompatible with mixed recycled plastics11. When it comes to biodegradable and compostable plastics, these products make for sustainable alternatives only if they are destined for the appropriate composting facilities whereby the specific conditions for their complete biodegradation are met.

In short, today’s environmental pressures have urged the mainstream production of sustainable alternatives to an ever-growing plastic problem. Although socially responsible plastic products exist with the intention of lessening their environmental footprints, their legitimacy as sustainable alternatives lies in their proper disposal and complete integration into a given environment without any adverse or toxic effects. For a more concrete circular economy, products made of glass and metal can be recycled infinitely without losing product quality, have no need for additional virgin material in the recycling process, and do not generate waste during the process3. Ultimately, a future with a reduced plastic impact depends not only on closed-loop recycling habits, but also on consumer education and awareness about how these products are made and disposed of.

References

(1)        Schmuck, D.; Matthes, J.; Naderer, B. Misleading Consumers with Green Advertising? An Affect–Reason–Involvement Account of Greenwashing Effects in Environmental Advertising. J. Advert. 2018, 47 (2), 127–145.

(2)        Lu, C. The Truth about Recycling Plastics. Mitte. 2018. https://mitte.co/2018/07/18/truth-recycling-plastic/

(3)        Sedaghat, L. 7 Things You Didn’t Know About Plastic (and Recycling). https://blog.nationalgeographic.org/2018/04/04/7-things-you-didnt-know-about-plastic-and-recycling/

(4)        Toto, D. The Value of Plastics. https://www.recyclingtoday.com/article/recyclingtoday-1011-plastics-value/

(5)        Dell, J. U.S. Plastic Recycling Rate Projected to Drop to 4.4% in 2018 https://www.waste360.com/plastics/us-plastic-recycling-rate-projected-drop-44-2018.

(6)        A Circular Economy For Plastics In Canada: A bold vision for less waste and more value. http://circulareconomyleaders.ca/downloads/A_Circular_Economy_for_Plastics_in_Canada.pdf

(7)        Hopewell, J.; Dvorak, R.; Kosior, E. Plastics Recycling: Challenges and Opportunities. Philos. Trans. R. Soc. B Biol. Sci. 2009, 364 (1526), 2115–2126.

(8)        Gross, R. A.; Kalra, B. Biodegradable Polymers for the Environment. Science (80-. ). 2002, 297 (5582), 803–807.

(9)        Bastiolo, C. Handbook of Biodegradable Polymers; 2005. Rapra Technology Limited.

(10)      Vroman, I.; Tighzert, L. Biodegradable Polymers. Materials (Basel). 2009, 2 (2), 307–344.

(11)      https://pelacase.com/blogs/news/5-things-you-probably-didnt-know-about-compostable-plastics

(12)     https://www.food.ee/blog/compostable-vs-recyclable-vs-biodegradable/

Boat Antifouling Technology: the problems and the green chemistry solutions!

Boat Antifouling Technology: the problems and the green chemistry solutions!

By Alana Rangaswamy (Vice-President, Dalhousie University Green Chemistry Initiative)

Picture1

The iconic Halifax Ferry is one of many boats to traverse the Harbour every day.

One great part of attending Dalhousie University is living steps away from the ocean. Much of Halifax’s history and development is due to its access to water, both as a naval base and port of call. With the massive amount of boat traffic seen daily by the harbour, marine industries strive to maximize the efficiency of travel. And one major way to do that is preventing small creatures from hitching a ride on your boat, causing drag and lowering the efficiency of your vessel. Enter antifoulants: coatings that kill organisms or otherwise block their ability to stick onto your ship. Antifouling is a necessary technology, but introducing biocidal agents into a marine environment, unsurprisingly, poses many environmental challenges. Let’s take a look at two commonly used antifoulants, their issues, and how scientists have tried to fix them:

Tributyltin 

You may have heard of tributyltin (TBT) as a biocidal agent. TBT is an excellent poison – effectively nonpolar due to its alkyl groups, it’s able to accumulate in organisms, rapidly killing them due to the high toxicity of SnIII. This property makes TBT an extremely effective antifouling agent, however, it easily leaches from boat hull paint into the ocean where it persists due to its high stability. Fortunately, the dangers TBT have been recognized worldwide and use as a biocidal agent has been banned as of 20081. Canada jumped on the bandwagon slightly earlier, with the last TBT-containing paint product registered in 1999.2 With this restriction, the industry is searching for alternatives that are as effective as TBT, without the environmental drawbacks.

Copper

Copper as a bulk metal is naturally antiseptic, promoting the formation of reactive hydroxyl radical species which lead to cell death in living systems.3 Copper has been used on boat hulls since the 1700s, and now usually shows up in paints as its metal oxide4 or as a suspension of copper powder.5 Although copper is less bioavailable than TBT, it persists and continually forms unstable radical species (and can, therefore. wreak ecological havoc) in a marine environment. Since copper is widely considered the new “gold” standard in antifouling, the sheer amount of it present on (and leaching off of) boat hulls today points to a long-term impact.

New Antifouling Tech

Green chemistry and engineering are all about designing cleaner systems that work as well as, or better than, the existing standard. TBT and copper are high bars to clear, but scientists are up to the challenge. As early as 1996, the environmentally benign Sea-Nine antifouling compound had received the Designing Greener Chemistry Award as part of the US EPA’s Presidential Green Chemistry Challenge.6 Sea-Nine is a derivative of isothiazolinone, a 5-membered heterocycle containing nitrogen and sulfur atoms. The compound is acutely toxic to marine organisms at the surface of boats, but biodegrades rapidly in marine environments through a ring-opening mechanism to form non-toxic by-products. Sea-Nine (and its derivatives) is currently present in commercial boat hull paints,7 however, degradation times may vary based on geographical location and local environment8 so our job isn’t done yet.

There are many newer studies in the works. For instance, investigation has been done into using natural products as antifouling agents. Natural products are secondary metabolites produced by microorganisms as a defence mechanism in response to stress. As such, they often have antimicrobial properties, while being naturally biodegradable. For example, 1-hydroxymyristic acid, a simple alpha-hydroxy fatty acid, was isolated from the marine bacterium Shwanella oneidensis. When panels were coated with paint containing the fatty acid, and subsequently immersed in a marine environment, no growth of foulants was observed even after 1.5 years.9 Other studies have added hydrophobic coatings which disrupt the binding interactions between the microorganism and the vessel’s hull, and promote detachment due to the natural flow of the water over the hull.10 Some research has diverted away from chemical modifiers altogether, using microtextures, which remove the flat surfaces required for spores to settle,10 to deter growth. UV-LEDs11 which are mutagenic and cytotoxic at a small scale, have also been used to reduce growth of foulants.

The long history and many methods developed to prevent boat hull fouling demonstrates that this is an important and challenging problem. But many results are promising, and green chemists and engineers are well on their way to solving it.

References:

  1. http://wwf.panda.org/?145704/tributyltin-canned
  2. Health Canada – Consumer Product Safety Registrar

http://pr-rp.hc-sc.gc.ca/ls-re/result-eng.php?p_search_label=antifouling+paint&searchfield1=ACT&operator1=CONTAIN&criteria1=tin&logicfield1=AND&searchfield2=NONE&operator2=CONTAIN&criteria2=&logicfield2=AND&searchfield3=NONE&operator3=CONTAIN&criteria3=&logicfield3=AND&searchfield4=NONE&operator4=CONTAIN&criteria4=&logicfield4=AND&p_operatordate=%3D&p_criteriadate=&p_status_reg=REGISTERED&p_status_hist=HISTORICAL&p_searchexpdate=EXP

  1. Grass, G., Rensing, C., and Solioz, M. Metallic copper as an antimicrobial surface. Environ. Microbiol. 2011, 77, 1541-1547. DOI: 10.1128/AEM.02766-10.
  2. https://www.chemistryworld.com/news/antifouling-coatings-cling-to-copper/3010011.article
  3. http://coppercoat.com/coppercoat-info/antifoul-how-it-works/
  4. https://www.epa.gov/greenchemistry/presidential-green-chemistry-challenge-1996-designing-greener-chemicals-award
  5. https://www.epaint.com/product/sn-1-antifouling-paint/
  6. Chen, L. and Lam, J. C. W. SeaNine 211 as an antifouling biocide: a coastal pollutant of emerging concern. Environ. Sci., 2017, 61, 68-79. DOI: 10.1016/j.jes.2017.03.040.
  7. Qian, P-Y., Xu, Y. and Fusetani, N. Natural products as antifouling compounds: recent progress and future perspectives. Biofouling, 2009, 26, 223-234. DOI: 10.1080/08927010903470815.
  8. Salta, M. et al. Designing biomimetic antifouling surfaces. Trans. R. Soc. A, 2010, 368, 4729-4757. DOI:10.1098/rsta.2010.0195
  9. https://www.pcimag.com/articles/104484-marine-fouling-prevention-solution-to-use-uv-led-technology

 

 

 

Canada Becomes a Leader in Carbon Capture

Canada Becomes a Leader in Carbon Capture

By Karlee Bamford, Treasurer for the GCI

The attention of international media has been captured by the remarkable success in CO2 sequestration achieved by the Canadian company Carbon Engineering, located in Squamish, British Columbia. Sustainability-related, world-saving initiatives often have an easier sell in the media than, say, incremental advances reported by researchers on equally sustainable academic pursuits (rough, eh?). In this instance the craze over Carbon Engineering’s advances has been amplified by the news of their recent partnerships with household-name energy and oil giants, such as Chevron, BHP, and Occidental Petroleum, in the form of a CAD $68 million investment.  So, what is this incredible advance?

From the success of their pilot plant and the data they’ve accumulated thus far, Carbon Engineering implementation of their technology has achieved capture of The technology in question can be split into two major advances. Referred to as direct air capture, or DAC, the first process developed by Carbon Engineering involves the transfer of gaseous CO2 from ambient air to an absorber fluid, a strongly basic solution of sodium or potassium hydroxide. The transfer process is achieved using an air-liquid contactor, designed and described by the company in 2012,4 that involves an array of fans, pumps, cheap PVC piping and structure, and fluid distributors. These components are fundamentally no different than those commonly found in cooling towers used as heat exchangers for water cooling. However, the orthogonal geometry (Figure 1) of air (atmospheric, ~ 400 ppm CO2) and fluid (the absorber) flow differs significantly, making repurposing of existing cooling tower designs for DAC an inefficient and expensive strategy for CO2 capture.

Picture

Figure 1. Commercial realization of air-fluid contactor designed by Carbon Engineering. M = Na or K. Image obtained from CanTech Letter and modified.5

The CO2 taken up by the alkaline absorber fluid is converted to carbonate (CO32-) salts and can be precipitated from the aqueous solution by treatment with calcium hydroxide to give calcium carbonate pellets. The captured CO2 can thus be stored as calcium carbonate or can be cleanly regenerated as pure CO2 gas, with elimination of a CaO , at high temperatures (650 °C) for commercial resale. The byproduct CaO may even repurposed by conversion back to Ca(OH)2 in a lime slaker, using water.1 Carbon Engineering has been piloting this process at their facility in Squamish since 2015, according to their website, after having tested a smaller prototype from 2010 and published the performance results in 2013.6 At the time of Carbon Engineering’s founding and until as recently as 2018, no commercial-scale air capture systems had been developed, which was a direct result of the anticipated inefficiency of CO2 capture using conventional cooling tower designs.4 Undeterred, Carbon Engineering has proven otherwise with their innovative use of cross-flow geometry.

The second break-through technology from Carbon Engineering is their patented Air To FuelsTM process, which they’ve been piloting since 2017. Taking the stored CO2 from their DAC process, Carbon Engineering has successfully produced a clean, sulfur-free, source of hydrocarbon fuel that requires no further modification for consumer consumption. The process involves passing the regenerated CO2 gas through a reactor containing hydrogen (H2) gas to generate synthesis gas (syn-gas), a mixture of CO and . The syn-gas is then passed through a Fischer-Tropsch reactor where the synthetic hydrocarbon fuel is thermally generated over a heterogenous base-metal catalyst (e.g. iron, cobalt, nickel).7

The technologies have been developed by the research groups of founder and U of T alumnus Prof. David Keith. Prof. Keith is currently faculty at Harvard University in the School of Engineering and Applied Sciences. To date, the company has filed 13 patents and produced numerous publications describing their innovations. According to media reports,8 recent multimillion-dollar investments will allow their and the company has already signed a memorandum of understanding with Squamish First Nations about their intentions.9

One of the most attractive aspects of the DAC and Air to FuelsTM technology is location. Plants could, hypothetically, be built anywhere, as CO2 is well mixed in the atmosphere and Carbon Engineering’s technology does not require that CO2 capture occur at the point of CO2 generation as in, for example, CO2-scrubbers used in exhaust systems.

However, with the excitement surrounding Carbon Engineering’s projected ability to capture CO2 at low cost and high volume, controversy has inevitably been close to follow. The interest from large oil corporations in this technology may not be as principled in sustainability as it appears but driven in part by their need for large volumes of CO2 for so-called green fracking (hydraulic fracturing). Supporting further oil extraction in this way goes completely counter to the need for elimination of emissions that the 2018 Intergovernmental Panel on Climate Change (IPCC) report clearly indicates must accompany advances in carbon capture and storage.10 Still, perhaps the positives outweigh the negatives in this instance. This very week, Environment and Climate Change Canada reported that Canada is warming at twice the rate of the rest of the globe.11 The need for efficient technologies to address climate change has never been more immediate. Fortunately, Carbon Engineering is not alone: at least two other companies with commercial plans for CO2 capture have started in Switzerland (Climeworks)12 and the USA (Global Thermostat).13 Whether the Canadian solution is adapted worldwide will depend not only upon Carbon Engineering, but also upon how these alternative approaches evolve.  For once, it is probably best not to pick a team to cheer for but, instead, hope that each country’s company develop a complimentary capture strategy to address the international dilemma that is climate change.

References:

  1. Keith, D. W.; Holmes, G.; St. Angelo, D.; Heidel, K., Joule 2018, 2, 1573-1594.
  2. American Physical Society. Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs. June 1, 2011 https://www.aps.org/policy/reports/assessments/upload/dac2011.pdf ; accessed April 24, 2019.
  3. Carbon Engineering, https://carbonengineering.com/ .
  4. Holmes, G.; Keith, D. W., Trans. R. Soc. A 2012, 370, 4380-403.
  5. Artist’s rendition of a commercial scale Carbon Engineering contactor, CanTech Letter. https://www.cantechletter.com/2016/10/squamish-b-c-s-carbon-engineering-begins-scale-co2-capture-new-deal/ ; accessed April 4, 2019.
  6. Holmes, K. Nold, T. Walsh, K. Heidel, M. A. Henderson, J. Ritchie, P. Klavins, A. Singh and D. W. Keith, Energy Procedia, 2013, 37, 6079-6095.
  7. Heidel, Keton et al. Method and system for synthesizing fuel from dilute carbon dioxide source. WO2018112654A1, 2017.
  8. BBC News, Matt McGrath. Climate change: ‘Magic bullet’ carbon solution takes big step. April 3, 2019 https://www.bbc.com/news/science-environment-47638586 ; accesed April 3, 2019.
  9. CBC News, Angela Sterritt. In fight to combat climate change, Squamish Nation joins forces to capture carbon. November 29, 2018. https://www.cbc.ca/news/canada/british-columbia/in-fight-to-combat-climate-change-squamish-nation-joins-forces-to-capture-carbon-1.4924017 ; accesesd April 4, 2019.
  10. Intergovernmental Panel on Climate Change 2018 Summary for Policy Makers, Global Warming of 1.5 °C. https://www.ipcc.ch/site/assets/uploads/sites/2/2018/07/SR15_SPM_version_stand_alone_LR.pdf ; accessed April 4, 2019.
  11. Environment and Climate Change Canada, Canada’s Changing Climate Report, April 1, 2019. https://www.nrcan.gc.ca/environment/impacts-adaptation/21177 ; accesed April 4, 2019.
  12. Climeworks, http://www.climeworks.com/
  13. Global Thermostat, https://globalthermostat.com/
How green is your bromination reaction?

How green is your bromination reaction?

By Diya Zhu: Symposium Coordinator for the GCI

Electrophilic bromination is a common type of reaction in undergraduate organic laboratories. In these experiments, we rarely use Br2 as a bromine source. Why? This dense brownish-red liquid is a pain in the butt for a few reasons. First of all, it fumes. Once you open the bottle, orange fumes start migrating everywhere. Without efficient ventilation, soon you will smell an offensive and suffocating odor. Second, bromine is corrosive to human tissue as a liquid and its vapours irritate the eyes and throat. Moreover, with inhalation, bromine vapours are very toxic. Third, bromine is very dense, with a density of 3.1 g/cm3, which makes it very difficult to measure and transfer.

Picture1

Figure 1. A bottle containing bromine.1

Instead, N-bromosuccinimide (NBS) is often used as a brominating and oxidizing agent in various electrophilic addition, radical addition, and electrophilic substitution reactions. Pure NBS is a white crystalline solid with a melting point of 175-180 oC. Even though it’s a solid and easier to handle, you still need to be careful when working with NBS. Due to the higher electronegativity of nitrogen, the Br atom is partially positively charged and thus electrophilic, ready to be attacked by a nucleophile (eg. an alkene).

Picture2

Figure 2. N-bromosuccinimide (NBS)

NBS will form bromonium ions with alkenes, and when an alcohol or water is added, it will attack the bromonium ion, which will generate bromohydrins. Importantly, the nucleophilic attack only happens on the face opposite the bromonium ion.

Picture3

Figure 3. Alkene reaction with NBS showing the bromonium ion and attack of water to form a racemic mixture.

Usually, when undergraduate students preform this experiment, we also emphasized the importance of Green Chemistry. Green chemistry and its 12 principles help to improve conventional reactions. For example, increasing the efficiency of synthetic methods, reducing the steps of synthesis, and minimizing toxic reagents and solvents. In the formation of bromohydrins, compared to using Br2, NBS is less hazardous.  Also, water or alcohol can be used as the solvent which eliminates the use of organic solvents, especially chlorinated solvents.

However, the use of NBS also creates by-products. For example, succinimide and the very strong hydrobromic acid. It also has a reduced atom economy, since only one Br atom of 8 atoms in a NBS molecule is used in bromination.

With all of this taken into consideration, can it be concluded that NBS is a greener alternative to Br2? What do you think, and which reagent will you be reaching for in your next bromination experiment?

References:

  1. https://en.wikipedia.org/wiki/Bromine