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.

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Going Green on a Large Scale: The 12 Principles of Green Engineering

By Elisa Carrera, Trivia Coordinator for the GCI

As chemists, we are used to thinking about relatively small-scale reactions, and when faced with synthetic challenges we are often most concerned with improving yields of reactions. We can do this by changing reagents, solvents, temperature, and time of reaction. As green chemists, we can incorporate greener pathways into our syntheses by choosing less hazardous reagents and solvents, and designing reactions to be atom economical with low energy inputs.

If we want to translate our lab-scale syntheses to an industrial scale, however, things become more complicated. Cost and economics become the driving force in this case, so not only are yields important, but the entire process itself, including product purification (column chromatography on an industrial scale is not the purification method of choice because it is expensive and wasteful!). Of course, the environmental impacts are much higher, since huge amounts of solvents and waste could be involved in a single process.   Thus, incorporating greener processes into industry is where we can see the biggest relief in environmental impact.

This is where Green Engineering comes into play. A lot of engineering goes into developing an industrial-scale process, so it’s no surprise that if we want to make commercialization greener we need a new set of principles to follow. This led to the development of the 12 Principles of Green Engineering by Paul Anastas and Julie Zimmerman in 2003:

  1. Inherent Rather Than Circumstantialgreentreeglobe
    Designers need to strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible.
  2. Prevention Instead of Treatment
    It is better to prevent waste than to treat or clean up waste after it is formed.
  3. Design for Separation
    Separation and purification operations should be designed to minimize energy consumption and materials use.
  4. Maximize Efficiency
    Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency.
  5. Output-Pulled Versus Input-Pushed
    Products, processes, and systems should be “output-pulled” rather than “input-pushed” through the use of energy and materials.
  6. Conserve Complexity
    Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition.
  7. Durability Rather Than Immortality
    Targeted durability, not immortality, should be a design goal.
  8. Meet Need, Minimize Excess
    Design for unnecessary capacity or capability (e.g., “one size fits all”) solutions should be considered a design flaw.
  9. Minimize Material Diversity
    Material diversity in multicomponent products should be minimized to promote disassembly and value retention.
  10. Integrate Material and Energy Flows
    Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows.
  11. Design for Commercial “Afterlife”
    Products, processes, and systems should be designed for performance in a commercial “afterlife.”
  12. Renewable Rather Than Depleting
    Material and energy inputs should be renewable rather than depleting.

While some of the principles parallel some of the 12 Principles of Green Chemistry quite closely, these were created with engineering in mind rather than chemistry, so most of the principles are quite different from the way us chemists usually think. While Green Chemistry looks to reduce the use and generation of hazardous substances, Green Engineering is focused on developing processes that are economically feasible and reduce risk to the environment and human health. This is not just limited to chemical engineering either! All areas of engineering can incorporate these Green Engineering Principles to develop less harmful materials and processes.

Although this is a bit outside of our area, Green Chemistry and Green Engineering are directly linked to each other, and I think it is important for chemists to think about Green Engineering. In fact, a lot of our Green Chemistry decisions will ultimately affect Green Engineering (see this article, “Promoting Green Engineering through Green Chemistry“), and both areas ultimately have the common vision of reducing risks to human health and the environment!

What do you think about the 12 Principles of Green Engineering? Which do you think are most important? Were you surprised by any of these principles? Share your thoughts in the comments section!

References:

For more details on each of the 12 Principles of Green Engineering please see the original article by Anastas and Zimmerman:

Anastas, P.T., and Zimmerman, J.B., “Design through the Twelve Principles of Green Engineering”, Env. Sci. Tech. 200337(5), 94A-101A. http://pubs.acs.org/doi/abs/10.1021/es032373g