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.
  • Egeghy, P.P., Judson, R., Ganwal, S., Mosher, S., Smith, D., Vail, J., Cohen Hubal, E. A. Total Environ. 2012, 414, 159-166.
  • 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.

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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.

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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).

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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.

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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

Green Chemistry Principle #12: Inherently Safer Chemistry for Accident Prevention

By Brian De La Franier, Member-at-large for the GCI

  1. Inherently Safer Chemistry for Accident Prevention: Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.

In the 12th and final video of the GCI series on the 12 principles of green chemistry, Gabby and Qusai investigate the 12th principle on inherently safer chemistry and note several common issues found in many labs.

The 12th principle is frequently called the safety principle and is often overlooked when considering green chemistry principles.  However, the broad nature of the 12th principle means it both incorporates many of the other principles and is almost impossible to achieve without considering all 12 of them, given that the overall goal of green chemistry is to reduce hazards and pollution.

In the Video #11 blog post, Alex wrote about how driving a car with no windows and mirrors would lead to accidents as there would be no real-time way to analyze your surroundings. The 12th principle is akin to having that car inspected before driving it.  It is insuring that all aspects of the car, from the engine, to the brakes, to the steering are all in working order so that the car is less likely to get into an accident.  With this principle we consider the ingredients of a reaction (the parts of the car), and make sure that they don’t pose excessive hazards.

An example mentioned in the Video #12 of a hazardous chemical that can be replaced in synthesis is methyl isocyanate, a molecule used in the synthesis of the insecticide carbaryl.  In 1984, this toxic compound was released into the air from a pesticide plant in Bhopal, India, immediately killing 3,800 people, and causing premature death in thousands more.1 This disaster could have been avoided had the plant instead used methylamine to carry out the reaction.2

GCI 12th principle blog photo 1

Figure 1. The remains of the pesticide plant that led to the Bhopal disaster. [3]

Although this principle is specifically about the avoidance of using or producing hazardous compounds, the idea of avoiding hazards can be extended to other areas of the lab.  Storing chemicals that are reactive together, such as oxidizers and flammable materials, leads to a risk of release and reaction.  If these compounds leak from their containers and react, they will create a large fire. This is a hazard that could be easily avoided by storing these chemical types separately.

Another hazard in the lab is liquid spills. Anything that has been spilled should be immediately cleaned up to prevent people from slipping on it or receiving chemical burns from an unknown substance.  If someone comes across an acid spill, but does not know what it is they could easily be burned in attempting to clean it up.  Returning to the car analogy, leaving an unknown spill would be like giving someone a damaged car to drive without telling them. The unfortunate driver could be injured as a result of faulty brakes, just as another lab member could be injured by your spill in the lab.

As with our car, the lab should be kept safe and in good repair. If there are damaged parts in a car you should always repair them before driving it, just as if there are hazardous chemicals or situations in our lab they should be replaced before performing reactions.

References:

  1. Broughton, E. (2005). The Bhopal disaster and its aftermath: a review. Environmental Health, 4(1), 6.
  2. Thomas A. Unger (1996). Pesticide Synthesis Handbook (Google Books excerpt). William Andrew. pp. 67–68.
  3. https://www.dnaindia.com/analysis/column-bhopal-gas-tragedy-will-the-suffering-ever-end-2040370