Green Chemistry Principle #9: Catalysis

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

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

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


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

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

Principle 9 Figure 1 - catalysis

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

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

Principle 9 Scheme 1 - catalysis example

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

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

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

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

Green Chemistry at CSC2017 – The 100th Canadian Chemistry Conference and Exhibition

By Kevin Szkop and Alex Waked

This year, the GCI partnered with the Chemical Institute of Canada (CIC), the organizing body of the CSC2017, to be closely involved in various aspects of Canada’s largest chemistry meeting.

In collaboration with GreenCentre Canada and CIC, the GCI organized a Professional Development Workshop as part of the CSC2017 program. This event consisted of four components:

The green chemistry crash course, led by Dr. Laura Reyes. Laura is a founding member of the GCI, and is now working in marketing & communications with GreenCentre Canada.

A case study, led by Dr. Tim Clark, Technology Leader at GreenCentre Canada. The case study gave attendees a unique opportunity to learn about some projects that GreenCentre has been developing and in collaboration with peers, learn how to find applications for new intellectual property (IP) and how to make contacts within relevant companies.

Kevin CSC blog 1

Dr. Tim Clark leading the GreenCentre Canada Industry Case Study

Career panel discussion, sponsored by Gilead, featuring members of academia and industry.

A coffee mixer for an opportunity for informal networking.

 

Supplementary to the Professional Development Workshop, the GCI organized a technical session, co-hosted by the Inorganic, Environmental, and Industrial sections of the conference. This new symposium, entitled “Recent Advances in Sustainable Chemistry”, brought together students, professors, industry, and government speakers to showcase a diverse and engaging collection of new trends in green and sustainable chemistry practices across all sectors of chemistry. Highlighted talks included Dr. Martyn Poliakoff from the University of Nottingham, also a CSC2017 Plenary Lecturer, Dr. David Bergbreiter from Texas A&M University, and Dr. William Tolman from the University of Minnesota.

Kevin CSC blog 2

Dr. Martyn Poliakoff teaching the audience about NbOPO4 acid catalysts found in Brazilian mines

Dr. Bergbreiter’s lecture was an engaging one. His enthusiastic approach to the use of renewable and bio-derived polymers as green solvents was captivating to both industrial and academic chemists.

Dr. Martyn Poliakoff, a plenary speaker at the conference, gave a phenomenal talk during the first day of the symposium. His charismatic style complimented perfectly the cutting-edge research ongoing in his group at the University of Nottingham. Particularly interesting was the use of flow processes in tandem with photochemistry to yield large quantities of natural products useful in the drug industries.

Dr. Tolman’s talk was of interest to essentially anyone working in an academic environment, especially for student run groups, like the GCI, with both academic interests as well as safety awareness initiatives. In the first part of the talk, synthetic and mechanistic studies of renewable polymers were discussed. The second part shifted focus to student-led efforts to enhance the safety culture in academic labs, which stood out from most of the other talks in our symposium.

One highlight was a group of graduate students at the University of Minnesota organizing a tour of Dow Chemicals to observe the work and safety codes in an industrial setting, which they used as a lesson to bring back to their own research labs. This caught the eye of most of the GCI members, which inspired us to organize a similar day trip in the future.

In further efforts to make our symposium accessible to undergraduate and graduate students, the GCI partnered with GreenCentre Canada to award five Travel Scholarships to deserving students from across Canada to provide financial aid to participate in the conference.

We thank all of our speakers, both national and international, for their participation in the program. It was a great success!

 

Easy Peasy Lemon Squeezy – An Eco-Friendly Process for Pectin and Essential Oil Extraction From Lemon Peels

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

Industrial scale chemistry is not typically given much thought by most chemists in academia. But if the end goal is to produce our products for eventual commercial use, then why not design our syntheses and processes at the beginning to ensure that the scaling up will be smooth?

Fidalgo et. al. recently published a paper that caught my eye, in which they describe a scalable eco-friendly process for the simultaneous extraction of pectin and the essential oil d-limonene.1 Pectin is a heteropolysaccharide that has found use in a wide variety of products. It can be used as a thickening agent in jams and shampoos,2 in the medicinal field in wound-healing preparations, and has been shown to reduce blood cholesterol levels.3 In 2013, the global market for pectin reached $850 million.4 In a few words, it’s a valued, versatile product.

Pectin is contained in plant cell walls, and is extracted from citrus peel (such as lemons and oranges) traditionally by a water extraction method. This method involves heating the citrus peel for several hours under acidic conditions, filtering off the solid residue, concentrating the filtrate, and finally precipitating the pectin by addition of alcohol. A couple drawbacks include the large amount of acid waste and the excessive heating of the peel, which degrades the pectin as well as being energy intensive.

Alex_blog post figure 1

Figure 1. Microwave hydrodiffusion and gravity apparatus [5]

In this paper, the authors used two innovative methods to obtain pectin from lemon peels (the pectin obtained from both methods have slightly different properties which I won’t go into, but if you’re curious I encourage you to take a look at the paper!). The first method includes adding water to lemon peels, doing a microwave hydrodistillation (which is simply a distillation using microwave heating), separating the essential oil from the residual water, and finally freeze-drying the water to obtain pure pectin. The second method involves a technique called microwave hydrodiffusion and gravity,5 where the lemon peels and water are heated using a microwave source and the residual liquid that is expelled by the heating is passed through a filter and condenser to be collected (Figure 1). The collected aqueous solution is then freeze-dried to obtain pure pectin.

The first method was employed to test whether this process would be compatible with kilograms of material. It turns out that 20 kg of waste lemon peels produces 3 kg of pectin and 10 mL of essential oil, where 36 L of water was used (Figure 2). To put these numbers in perspective, common yields for pectin from the more conventional extraction methods are only roughly 3% of the peel weight – so 20 kg of lemon peels would produce 0.6 kg of pectin.

fig2

Figure 2. The semi-industrial scale extraction process presented in the paper [1]

So let’s take a look at some of the positive takeaways from this paper: 1) Significantly better yields of pectin were obtained compared to the current conventional processes; 2) Microwave heating (which is the only energy source in the processes) requires less time than normal heating, meaning less degradation of pectin and lower energy usage; 3) Water was the only solvent used, and; 4) This was the first reported simultaneous extraction of pectin and essential oil by an environmentally clean process.

References:

(1) Fidalgo, A.; Ciriminna, R.; Carnaroglio, D.; Tamburino, A.; Cravotto, G.; Grillo, G.; Ilharco, L. M.; Pagliaro, M. ACS Sustainable Chem. Eng. 20164, 2243–2251.

(2) Willats, W. G. T; Knox, J. P.; Mikkelsen, J. D. Trends Food Sci. Technol. 2006, 17, 97−104.

(3) Wicker, L.; Kim, Y.; Kim, M.-J.; Thirkield, B.; Lin, Z.; Jung, J. Food Hydrocolloids 2014, 42, 251−259.

(4) Bomgardner, M. M. Chem. Eng. News 2013, 91, 20.

(5) Viana, M. A.; Fernandez, X.; Visinoni, F.; Chemat, F. J. Chromatogr. A 2008, 1190, 14–17.