Green Chemistry – Saving Us From Petroleum Plastics

Ask a typical American where he thinks rising oil prices will have the most impact on his life, and he’ll probably answer “at the gas pump” (that is, if he owns a car). He may be right – as of 2006, gasoline accounts for roughly 45% pump of total American oil consumption^[1]. But far from the minds of many consumers is the prevalence of goods that are manufactured from petroleum derivatives: polyethylene terephthalate (“polyester”) in plastic bottles and synthetic textiles, polystyrene (“styrofoam”) used in packaging, low- and high-density polyethylene used in a variety of products. As the price of petroleum continues to climb, the prices of products containing petroleum-derived plastics will rise accordingly.

Just last week, Dow Chemical Company announced a price increase of up to 20% for all of its products, citing rising energy costs. Most of Dow’s sales come from plastics and chemicals (mostly derived from petroleum) used in industrial processes, and not in finished goods, so the impact on consumers isn’t so direct. However, the reality is that plastic goods will continue to rise as petroleum prices skyrocket. But must we begin our parting with inexpensive and ubiquitous petroleum goods not only at the gas pumps, but in our latex condoms, grocery bags, cell phones, water bottles, and medical supplies? 

Developments in green chemistry may stave these tearful goodbyes. Green chemistry is a philosophy which emphasizes research into the development of environmentally friendly, energy efficient, and sustainable chemical processes. Green chemists are working on exciting and innovative ways to avoid the use of toxic solvents and reagents and to replace wasteful and expensive chemical reagents with catalysts, which can be reused over and over again. Of particular interest to us is the development of alternative polymers that combine useful material properties with sustainable production.

Adipic acid, the monomer used to produce the ubiquitous polymer nylon and some polyurethanes, has traditionally been produced from petroleum. In 2001, a team of chemists at Michigan State University published their two-step synthesis of adipic acid^[2] from D-glucose – a naturally occurring sugar produced by cellular respiration in all living things – using genetically modified E. coli bacteria. The process was completely free of petroleum feedstock. The total yield of adipic acid from glucose was 21%, considered poor, but genetically engineered improvements to the biochemical pathways responsible for the metabolic production of cis-cis-muconic acid, the intermediate in the synthesis, may offer more economically feasible yields^[3].

A significant problem faced by any plastic good comes long after its production, whether from sustainable or petroleum feedstock: disposal. Only two of the “Big Six” synthetic polymers, which account for 76% of all United States production, are readily recyclable^[4]. Nearly all plastics which are not recycled do not degrade readily, and comprise an estimated 11% of solid municipal waste^[4]. Another class of biologically produced plastic, polyhydroxyalkanoates, are not only readily synthesized by metabolic bacterial pathways, but are also readily degraded to water and carbon dioxide by bacteria naturally present in oxygen-rich soil. PHAs have a variety of applications, from thin films to packing materials to biomedical grafts.

Green chemistry is still a young and burgeoning field. As the price of petroleum, and products derived from petroleum, continues to climb, green chemistry will receive greater attention in both academic and industrial circles, and its potential offers hope for the use of sustainable plastics in the post-petroleum world. Of course, the solution to our plastic problem must not only come from scientific research, but also from changes that we make to our consumption of plastic goods.

References:

1. “U.S. Product Supplied for Crude Oil and Petroleum Products”, Department of Energy
2. “Benzene-Free Synthesis of Adipic Acid”, Niu, W., Draths, K.M., Frost, J.W.
3. “Altered Glucose Transport and Shikimate Pathway Product Yields in E. coli”, Yi, J., Draths, K.M., Li, K., Frost, J.W.
4. “Organic Chemistry”, Smith, J.G. pp 1167-1168