Green Chemistry

Green chemistry is one of the hottest topics in the market today, and for a variety of reasons: environmentalism, “greener” methods using less solvent to combat the ACN shortage and price spike, and more. Whatever the inspiration, green methods are sweeping the industry like never before, and here, LCGC invites some of the industry’s best known experts to discuss this topic.

Joining us for this discussion are Jeremy Bierman of Phenomenex; Larry Taylor of Virginia Tech; Linda Lopez of Dionex Corporation; and Tom Hall of FMS.

What techniques seem to be favorable for green chemistry and why?

Bierman:One of the most valuable benefits of UHPLC is decreased solvent consumption. The ultra-high efficiencies that are attained with UHPLC technology allow for greater resolution between eluting peaks, giving chromatographers the ability to achieve the same resolution they would get on a traditional 3 µm or 5 µm fully porous particle column on a significantly shorter length UHPLC column. Shorter UHPLC columns result in decreased run times and thus, decreased solvent consumption.

SFC can probably be credited with bringing about the term “green chemistry” to the chromatography community. This chromatography technique allows analysts to perform separations with as little as 1 percent organic modifier. In addition to the obvious benefits to the environment, chromatographers benefit from significant cost and time savings due to decreased organic solvent consumption, decreased waste disposal, faster cycle times, and rapid sample blow down. In recent years, the popularity of SFC has grown significantly, leading to the creation of many SFC-certified phases and different selectivities – both chiral and achiral.

Taylor: (1) Preparative supercritical fluid chromatography with inexpensive and readily available carbon dioxide-based mobile phases can replace toxic, flammable, and water immiscible petrochemical hydrocarbons that are difficult to dispose. (2) Ultra high pressure LC (UHPLC) with sub-2-micron particle-size columns can demonstrate a multifold improvement in throughput and a greater than 80% reduction of mobile phase solvent with excellent resolution, thereby achieving a greener, more productive operation. (3) The use of high temperature to perform subcritical water chromatography that requires no organic co-solvent is another possibility. (4) Microscale HPLC (or chip HPLC) will result in reduced consumption of both mobile and stationary phases as well as enhanced mass sensitivity on concentration-sensitive detectors relative to conventional analytical instruments. The savings in solvent is impressive considering that these instruments operate day-after-day in around-the-clock fashion for the analysis of a complete 96-well plate.

Lopez:Automated sample preparation techniques such as solid- and liquid-phase extraction can significantly reduce solvent consumption, minimizing environmental and laboratory costs while increasing sample throughput. Such methods include accelerated solvent extraction (ASE) technology that uses minimal solvent volumes to automatically extract samples in minutes while reducing solvent consumption by up to 90%.

Modern HPLC and UHPLC methods offer nano- and microflow rates that can provide significant savings in mobile phase waste generation. Typical HPLC solvents consist of methanol, acetonitrile, IPA, hexanes, and/or water combined with target analytes and modifiers. Many of these compounds are not only toxic and harmful to the environment, they require special handling and disposal procedures that are energy intensive and contribute to greenhouse gas emissions.

Hall:Systems that automate and scale down the entire sample preparation process (TRP), ultraperformance HPLC (UPLC), and supercritical fluid chromatography (SFC) fit well when looking to green-up or create a new laboratory implementing green technologies. These techniques have the potential to eliminate or dramatically reduce chemical usage, human exposure, power consumption, HVAC costs, hood space, as well as the footprint traditional techniques require versus these new technologies.

What is the future of green chemistry?

Bierman:Beyond the challenges of the current global economy, efforts to reduce operating costs and environmental pollution will always be needed. For this reason, labs will constantly be looking to new and “greener” technologies. Companies like mine will continue to focus R&D efforts on new technologies, like core-shell technology, that allow all chromatographers to participate in reduced solvent consumption. SFC will also likely play a more prominent role, especially in preparative chromatography labs.

Taylor:The commitment to “green chemistry” today seems more serious than ever in terms of synthetic reactions and separation science. Green separation techniques have been going in and out of fashion since the early 1980s when it was realized that analytical sample preparation with methylene chloride for environmental monitoring purposes was a major source of environmental pollution. It is not green chemistry when in order to make one thing clean we make lots of something else dirty. The goal of greening separation science is to find ways to bring about separation with a net reduction in the amount of waste generated. This situation brought about the great interest in supercritical fluid extraction (SFE) with carbon dioxide that existed in the late 1980s. By the mid-1990s, interest in green chemistry insofar as sample preparation via SFE appeared to wane and was replaced by a host of micro-extraction technologies that used less organic solvent. The greening of separation science during this time was not a factor. Today, the use of supercritical fluid chromatography (SFC) is growing significantly due both to the solvent savings that can be delivered by this technology and the superiority separation-wise of the technology that it replaces (i.e., normal phase HPLC). The SFC advantage is best seen in the area of preparative chromatography, where hundreds of liters of solvent are employed for every kilogram of product that is purified. The pharmaceutical industry to date has most actively embraced this technology for drug discovery and drug development.

Lopez: I believe in the future, process analytical technology (PAT) will have a greater role in green chemistry. Industrial processes will rely more on real-time analytical techniques to minimize the formation of toxic byproducts, improve reaction yields, increase energy efficiency, and minimize waste and the potential for accidents. Process analytical technologies (PAT) will likely play a greater role in the discovery and development of pharmaceuticals, chemicals, and other products. The use of in-line and on-line analytical instruments such as HPLC, IC, NIR, etc. enables more precise control of the addition of reagents during a reaction to minimize the formation of impurities produced via side reactions that can take place if reactants are added in excess.

I also think that the chemical industry will look to use more biomass feedstocks for the production of not only fuels, but chemicals and other high-value products. Most fuels and chemicals are made from fossil-derived petroleum feedstocks that are produced using relatively energy-intensive and inefficient processes run at high temperatures and pressures. By contrast, biochemical conversion pathways exist to produce hydrocarbons and alcohols from sugars, and there are emerging technologies currently in development to do this efficiently and cost-effectively. The technology holds the promise of running at ambient temperatures and pressures and there’s currently a tremendous amount of basic research going into the development of catalysts to breakdown lignocellulosic material into fermentable sugars, as well as engineering microbial organisms capable of fermenting the sugars to produce fuel alcohols and other chemicals and products.

Hall: Green Chemistry is the way forward. Consumers are increasingly interested in more environmentally friendly companies and products. The concept is to reduce waste and make materials safer, which will positively affect the safety and quality of our global food and water supply, climate, etc. Many companies implementing greener chemistries view it as not only a way to reduce hazardous waste and make regulatory compliance easier, but also a way to increase laboratory throughput, productivity, produce better analysis results, and lower the cost-per-sample. There are many universities engaged in incorporating green techniques into their curriculum and I can only see that becoming a key piece of education moving forward. Government agencies throughout the world have programs in place to implement greener technology now and in the future. Other markets are also starting to embrace green chemistries and this will only grow. In the area of sample preparation, we see many people looking to reap the benefits of one-step sample prep. Manual sample prep techniques require large amounts of solvent, hood space, and, in many cases, are the largest consumer of energy in the laboratory. Techniques that couple the entire sample prep process where the sample goes in and the compounds of interest come out ready to inject without intervention significantly reduces solvent usage, glassware, operator time, errors, energy consumption, and cost-per-sample in the lab.

Have you noticed a trend in conferences, e.g., Pittcon, promoting a green chemistry movement?

Bierman:Yes. One cannot attend a conference or read an industry-focused periodical without seeing multiple advertisements, technical presentations, or marketing pieces that are focusing on the “green” benefits of particular technologies. This exciting trend has helped to push for innovation within the industry and lead to “game-changing” advancements in chromatography. Not only are you seeing a greater presence of green chemistry technologies at tradeshows like Pittcon, but you are now starting to see new tradeshows being established that focus solely on green technologies like SFC.

Taylor:SFC 2009, PREP 2009, and HPLC 2009 had short courses and/or presentations that promoted green separation science. The reaction side of green chemistry appears to have had a longer sustained national emphasis in, for example, the American Chemical Society and the Environmental Protection Agency in the chemistry community.

Lopez:I’ve noticed more conferences are either having green chemistry themes or are including green sessions in their programs. For example, the conference theme for the upcoming spring 2010 ACS National Meeting in San Francisco, CA is “Chemistry for a Sustainable World” and there are expected to be numerous green chemistry and engineering topics there. This year’s Pittcon Expo also featured a new area called the “Green Corner,” which featured 13 companies displaying products and services for green chemistry solutions, resource conservation, and laboratory pollution prevention techniques. My company is currently running a free seminar series in North America focused on leaner and greener liquid chromatography techniques designed to increase productivity, reduce costs, and minimize the environmental footprint of the analytical laboratory.

Hall:Most of the conferences we attend are promoting the green chemistry movement. The conferences usually have roundtables, presentations on how to identify conservation opportunities, and best practices for implementing green techniques in the laboratory. The roundtables and presentations are an excellent forum to find out what other laboratories and vendors are doing in green chemistry. We find the roundtables to be a productive communication vehicle between end users from many market segments to explain what obstacles they are trying to overcome and how vendors can provide solutions to these obstacles.

What limitations are involved with green chemistry?

Bierman:Until recently, the “green” benefits offered by UHPLC technologies were only available to those labs that had the capital budgets to purchase costly UHPLC systems. Today, those benefits are available to any chromatographer, regardless of their system, with core-shell technology.

In the application of SFC, the primary limitation is a lack of application knowledge and experience. But as we move forward, greater resources will be created that make it easier for new users to adopt these technologies. Strong relationships between manufacturers and chromatographers will be a key contributor to this knowledge base expansion.

Taylor:For supercritical fluid chromatography, multiple-charged or highly water-soluble analytes, such as nucleotides and oligosaccharides, have limited solubility in carbon dioxide-based mobile phases. SFC systems typically operate at a higher pressure than HPLC systems in order to keep the carbon dioxide in the liquid phase for delivery to the column. High temperature liquid phase separations run the risk of sample thermal degradation. The shift to small particle column technology has been accompanied by a shift to greater operating pressures for analytical instrumentation with backpressure limits in excess of 10,000 psi. Finally, significant changes within separation science always face a certain amount of inertia. New fundamentals must be learned. Adoption of greener chromatographies will be costly in terms of both acquired instrumentation and user training. Green separations will require state-of-the-art analytical sensitivity, robustness, and validation before they can be accepted.

Lopez:Capital equipment purchases will likely be necessary in order to fully equip a green analytical laboratory and this could be an obstacle to complete implementation. The quality function may also be resistant to adopting green analytical methods because they’re new and lack a proven track record of adequately identifying quality issues.

Hall:No matter what industry or market segment a company is in they can implement some green chemistries. Limitations come with how much, when, and how fast you can transition to green chemistries. Not all current techniques in the lab can be replaced with greener techniques. Many laboratories have the perception that is difficult and expensive to implement. It can be difficult and expensive if you try to implement many green techniques at one time. It is best to identify techniques that you can transfer and understand the ROI of the new techniques before creating an implementation plan. It is not uncommon for labs to take two or three years to execute and implement their green technology plan. Recently, we have seen clients as they expand and grow into new facilities go green from the ground up.

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