Sustainable Green Chemistry

Mark Anthony Benvenuto

• Publisher: De Gruyter
• Year: 2017
• ISBN:
  9783110433500
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Environmental Science

Sustainable Green Chemistry, the 1 st volume of Green Chemical Processing, covers several key aspects of modern green processing. The scope of this volume goes beyond bio- and organic chemistry, highlighting the ecological and economic benefits of enhanced sustainability in such diverse fields as petrochemistry, metal production and wastewater treatment. The authors discuss recent progresses and challenges in the implementation of green chemical processes as well as their transfer from academia to industry and teaching at all levels. Selected successes in the greening of established processes and reactions are presented, including the use of switchable polarity solvents, actinide recovery using ionic liquids, and the removal of the ubiquitous bisphenol A molecule from effluent streams by phytodegradation.

William F. Carroll, Jr.

1Upon Further Review: A Commodity Chemist on Green Chemistry

Abstract: Green chemistry is most often thought of in the context of specialty or pharmaceutical chemicals where many synthetic chemistry approaches are in play. However, principles similar to those of green chemistry and engineering were employed over the years in reducing cost and increasing volume of chemicals that became commodities. This paper considers some of those principles, their impact, and some perspectives on the potential and limits associated with green chemistry for commodity chemicals.

Keywords: Green Chemistry; Commodity Chemicals; Life Cycle Analysis

During the year I was president of the American Chemical Society (ACS), 2005, I was the head of our delegation visiting China. It was a joy to return to see the progress the Chinese people had made since my first trip on behalf of my employer, nearly 20 years before. In addition to the challenge of a week of eating two banquets a day, I had the privilege of meeting literally hundreds of bright and serious students and professors. It was a wonderful time.

One particular exchange stood out. At Tsinghua University in Beijing, we had an interesting and wide-ranging roundtable discussion with students and professors about chemistry and industry. Now, while the situation there may be different in 2015, during that discussion in 2005 one student asserted, “Of course we know that pollution is inevitable with growth and progress.”

I was stopped. In a moment, the history of the past 30 years of the chemical industry as I have known it went through my mind. I thought about the advent of voluntary chemical and safety programs like Responsible Care® and OSHA Star, and the difference they made in my company and in the industry. I thought about the progress we have made in our own universities in educating students in the principles of green chemistry. To tell the truth, when I was in that student’s place 30 years ago, I might have made the same statement. But 30 years later it seemed unimaginable.

You see, we have changed innumerable things in the practice of chemistry, but the most important thing we have changed is our minds. I couldn’t let that student’s statement pass. I said,

“Please forgive me, but I need to disagree. From the perspective of the chemical industry, pollution and progress are not synonymous. Pollution is waste and waste is cost. Progress is benefit and a better quality of life. The two things are inherently different. That understanding is fundamental to what we call Green Chemistry. Your job as a chemist is to solve problems, to be sure. However, it is not to find a solution to a technical problem, but to challenge yourself constantly to find a better solution – that is, more benefit and less cost. I suggest you visit the ACS website and learn about the Green Chemistry Institute (GCI).”

This student, before even entering the working world of chemistry, had resigned himself to defeat. It shows the depth of the misconception, the difficulty of changing minds, and the importance of the principles of green chemistry in remediating this perception problem.

To me, the message of green chemistry and engineering is whether your particular point of emphasis is environmental, as in minimizing pollution, or economic, as in minimizing cost, the principles are important tools for accomplishing your goal. And frankly, I’ve found that once made aware of them, my fellow chemists and engineers working in industry find most of them nearly intuitive.

What I’ve just described to you are the technological underpinnings of green chemistry as I see them. We in ACS have always viewed it as a process of innovation, driven by scientists in discovery mode. We have been clear: green chemistry is not a regulatory program, because regulation tends to narrow the field of thought and not expand it. On a previous incarnation of the front page of the Green Chemistry Institute (GCI) website, it said:

Green Chemistry differs from previous approaches to many environmental issues. Rather than using regulatory restrictions, it unleashes the creativity and innovation of our scientists and engineers in designing and discovering the next generation of chemicals and materials so that they provide increased performance and increased value while meeting all goals to protect and enhance human health and the environment [1].

As I write this, it is 10 years later. I am in my last week of a 36-year career with a commodity chemical manufacturer. Over that time I’ve learned that “The Chemical Industry” is not one thing: commodities are different from specialties, which are different from fine chemicals or pharmaceuticals. Each segment views its business differently because the costs and prices and products and customers are different.

I’d like to expand a bit about two of these segments, commodities, and specialties. Commodity chemicals are manufactured in large volumes. Typically, most of the cost associated with a commodity is raw material cost or the capital cost of the plant. Relatively less of the cost of a commodity is tied up in labor, advertising, or R&D.

The main thing that distinguishes a commodity from a specialty is that commodities are fungible; that means that one company’s version is indistinguishable from another company’s version. Commodities are difficult if not impossible to brand or differentiate. These things are directly the opposite of specialties, which can be custom- made, distinguished by manufacturer, branded, and sold at a premium price because of the differentiation.

So why would someone whose career was spent in the commodity chemicals industry be writing a paper about green chemistry? Perhaps I have a different and counterintuitive perspective on the benefits of green chemistry. In this paper I’d like to make three points.

First, many commodities – certain chemicals produced at low relative cost and high volumes – got that way because of chemistry and engineering operating principles that are indistinguishable from at least some of the principles of green chemistry and engineering. These principles were used to take cost out of chemical manufacturing.

The second is similar. Done correctly, the benefit of green chemistry, particularly in commodity markets, may be as much economic as it is environmental, although both are likely to occur simultaneously.

Finally, green chemistry’s greatest potential impact is on energy.

Anyone who has spent time with the principles of green chemistry and green engineering knows it is difficult if not impossible to optimize all of them simultaneously in the preparation of a chemical or product. In manipulating conditions, there is a need to simultaneously consider a number of response variables – from energy use, to greenhouse gas generation, to chemical hazard or even cost – even as the principles provide guidance on how to proceed. The principles do not always point in the same direction for all responses, which become a dilemma for those who are engaged in what is known as alternatives assessment: devising means to eliminate chemicals of concern while minimizing process impact and providing efficacy at a cost the market can afford.

I’ve always viewed the principles of green chemistry and green engineering as checkpoints in chemical and process design. For me, the principles read: “All things being equal, consider this before considering that.” Not absolute rules, but points to be taken on board. And when they send you different directions, choices must be made.

Here are some thoughts on the relationship of commodity chemicals to green chemistry.

1.1Commodity Chemicals Got That Way Through the Use of Principles Identical to Many of Those of Green Chemistry and Engineering

Perhaps the most commodity of all the commodity chemicals is ethylene. Hundreds of billions of pounds of it are made globally every year. It is the basis of most of the commodity polymers. It is also a natural product that enhances fruit ripening. And for all the volume we produce today, when the polymer industry was new, ethylene was a challenging material to make.

In the 1920s, ethylene was made by dehydrating ethanol, which was obtained from fermentation. Prior to the development of the polymer industry, most of that ethylene was reacted with bromine to make ethylene dibromide, an additive in leaded gasoline. For other industrial processes, when a two-carbon unit was needed, it could be obtained by functionalizing acetylene, which was made by adding water to calcium carbide.

As automobiles became more popular, engineers at Dow Chemical Company started working on a process to make ethylene from naphtha, a petroleum distillate [2]. Availability of ethylene increased with the more robust process and a more abundant raw material for its synthesis. Today, in many countries, naphtha is the raw material of choice for ethylene. Most of the ethylene in the United States is made by dehydrogenating ethane, harvested from natural gas.

Consider some green chemistry implications of these three processes. Calcium carbide is made from coke and limestone, heated in an electric arc furnace at 2,000°. The ovens are highly energy intensive, and the process itself (as well as coke production leading to it) can be extremely dirty. After making acetylene, two to three times the mass of acetylene is left behind as calcium hydroxide waste. Ultimately, this material can be dehydrated to make lime and used in making cement if the volume and location matches, but it is yet another process.

Dehydrating ethanol is somewhat less daunting, but was limited by the capacity to produce it, particularly in the 1930s. Then, dehydration was catalyzed by sulfuric acid. Today, it can be accomplished thermally at ca 250 °C over a zeolite catalyst. By the nature of a dehydration reaction, 100 % molecular conversion is only 61 % mass conversion.

The steam-cracking process utilizes a hydrocarbon raw material, generally ethane or other liquefiable hydrocarbons separated from natural gas. Steam is both a heating source and a diluent; the process takes place at about 850 °C, quickly, and with a fast quench, maintaining appropriate dilution and kinetic control. Steam cracking of ethane yields ethylene and hydrogen from nearly 80 % of the starting material. Minor side products include methane, propylene, butadiene, and other C4s, all useful hydrocarbons. There is virtually no waste [3].

The steam-cracking process is the dominant process in the world. It became so because of the difficulty, resource use and high cost associated with the other processes. For local reasons, calcium carbide for acetylene production is done industrially only in China; producing ethylene from ethanol is done for marketing purposes to make plastics from biologically based materials.1

From the first indication that steam cracking could produce ethylene, engineering principles congruent with many of the principles of green chemistry came into play, and at maturity this process scores fairly well on a lot of them. Nearly perfect score on preventing waste, atom economy, and avoidance of solvents and derivatization, particularly compared to the carbide process. Neither ethane nor ethylene itself is highly toxic, and the steam-cracking process uses little if any toxic ingredients.

On the other side of the coin, some of the principles are challenging. Since the target is a two-carbon hydrocarbon, there’s not much that can be done to reduce the inherent flammability or explosivity of the material. The process is done at high temperature and pressure and carries an energy cost; it is difficult to imagine the reaction occurring at ambient conditions.

Designing for degradation is a function of the downstream products, so all three processes fare the same. While the carbide process is clearly inferior on environmental (and cost) grounds, life cycle assessment is appropriate to score the other two, comparing ethanol production and taking into account atom economy of the two processes. If, however, production cost could be used as a crude surrogate for resource use, the ethane steam-cracking process is less costly.

Perhaps the principle of green chemistry that is most daunting for commodities is the preference for renewable resources, which in this case I take to mean bio-based raw materials. I see three challenges in this regard, which I will abbreviate as scale, substitution, and life cycle considerations.

1.1.1Scale

In 2014, about 14 billion gallons (92 billion pounds) of ethanol was produced in the United States, mostly from corn. At 100 % yield that would produce about 60 billion pounds of ethylene, similar to the US production. If all US ethylene were to be made from ethanol, even though the raw mate...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• List of Contributing Authors
• Where We Are and Where We Are Going with Green Chemistry
• 1 Upon Further Review: A Commodity Chemist on Green Chemistry
• 2 Green Chemistry: Progress and Barriers
• 3 Switchable Polarity Solvents: Are They Green?
• 4 Toward a Greenish Nuclear Fuel Cycle: Ionic Liquids as Solvents for Spent Nuclear Fuel Reprocessing and Other Decontamination Processes for Contaminated Metal Waste
• 5 Green Disposal of Waste Bisphenol A
• 6 Green Chemistry Pedagogy
• 7 How the Principles of Green Chemistry Changed the Way Organic Chemistry Labs Are Taught at the University of Detroit Mercy
• 8 Greening the Curriculum: Traditional and Online Offerings for Science and Nonscience Majors
• Index