Developments for Converting Renewables to Platform Chemicals

Abstract

Terrestrial raw materials, whether petrochemical or renewable, can be converted into small families of building blocks from which other chemicals can be derived. Nonrenewable feedstocks afford a group of olefins, aromatics, CH₄ or syngas, which serve as platforms for further conversion into the thousands of products that make up the modern chemical industry.

The analogous fractionation of renewables provides a ready supply of carbohydrates, lignin or long chain hydrocarbons. However, the polymeric nature and structural complexity of the materials from this fractionation precludes their immediate assignment as platforms. As a result, the challenge becomes determining whether there are small, low molecular weight structures, derived from these biomass fractions, that can be employed in the same manner as the petrochemical industry's olefins and aromatics.

The concept of using biobased feedstocks for the production of platform chemicals is not new. As a response to the oil crises of the time, efforts were made to define renewable platforms as far back as the mid-1970s and early 1980s.^1-5 These initial studies normally focused on “picking winners”, a process of pre-identifying specific, structural targets, frequently hydrocarbon based, against which research should be directed, but sometimes regardless of whether these targets could be reasonably sourced from an initial group of renewable feedstocks.^{6, 7} It was often observed that transforming highly oxygenated carbohydrates or lignin to petrochemical-like platforms was an economic non-starter.

Thus, the importance of identifying technology, rather than structures, tailored to the unique features of biomass became critical to realizing a credible suite of biobased platforms for the chemical industry. What building blocks would be most easily and inexpensively derived from carbohydrates, lignin or plant oils? What processes were needed to make these materials? How can the structural features of biomass be accommodated by the chemical industry? Which of these materials will be true analogs to the petrochemical industry's olefins and aromatics?

Accordingly, investigations evolved to understand and develop bespoke transformations best suited to provide the interface between renewable feedstocks and the chemical industry. An early US Department of Energy evaluation appeared in 1994, which, while still describing pre-identification of targets, also began to acknowledge the need for technology development.⁸ With the DOE's release of their “Top Ten” report in 2004, the need for new technology was more strongly established.⁹ Finally, a highly cited and technology-based revisiting of the Top Ten was published in 2010, providing rationale and background for evaluating new building blocks.¹⁰ Their potential was illustrated with multiple examples of available platforms serving as starting materials for a wide array of chemical products. Since that time, many excellent reviews have continued to appear.^11-14

We felt it appropriate to provide an opportunity for examining some of the more recent developments in technology development for converting renewables to platform chemicals. A portion of this issue of Advanced Synthesis and Catalysis, builds on these foundations and provides a “mini-review” of several advances in the field. Here, the reader will find new studies describing the utility and transformation of the very well recognized renewable platforms, 1,3-propanediol and levulinic acid. Less frequently exploited renewable raw materials as sources of new platforms are also examined through the use of chitin for the production of 3-acetamidofuran and difuropyridines. Developing catalysis tailored for the structures of biomass is critical for preparing new platforms and is illustrated with the Mo-catalyzed conversion of 1,2-diols into terminal alkenes. Finally, the potential of renewables to provide novel and perhaps underexamined platforms is considered in the production of families of bioactive materials.

Interest in converting biomass to platforms and diverse families of chemicals continues to grow. We hope the reader finds these articles useful and informative, and that they are able to provide inspiration for further inclusion of renewables within the chemical industry.