At the start of the modern petroleum industry in the 1850s, we devised ways to distill useful products from the otherwise largely worthless oily tar we now go to great lengths to extract, process and sell. With kerosene replacing whale oil lights and similar innovations, adoption of these products helped save precious natural resources.
More than 150 years later, we so thoroughly rely on oil for heat, transportation and materials yet understand the reserves are finite, so we find ourselves needing to transition back to biomass. While few would suggest a return to whale oil lights the path to our future, most understand we need renewable alternatives to the limited petroleum resources that so thoroughly support modern society.
Each stop at the gas station serves as a reminder of how fossil fuels fulfill the lion’s share of our energy demands. A more subtle reminder of oil’s ubiquity can be found in all the synthetic materials we rely on: fabrics, plastics, insulation, packaging, etc. More subtle still but equally pervasive is our reliance on petroleum products for fine chemicals and pharmaceuticals.
The transition away from petroleum and back to renewable resources will include solar, wind, geothermal, hydro and biofuels to meet our energy demands, bioplastics for materials and biomass feedstocks for the production of fine chemicals.
With exponential population growth since the last time our society met its demands solely with renewable resources — hundreds of years ago — food security concerns today stand in the way of diverting annually renewable crops or even just the arable land to grow them for the high volume production of fuels and materials.
To understand why we rely on petrochemicals, it is useful to compare and contrast the chemical composition of petroleum and biomass. Thousands of years ago, petroleum was biomass, composed predominantly of carbon, hydrogen and oxygen and possessing a high degree of chemical complexity.
The long process of biomass conversion to petroleum includes a loss of chemical complexity, breakdown into smaller constituent components and a loss of most of the oxygen content from the original biomass.
From a fuel standpoint, the reduction in oxygen content allows for a more complete burn. From a materials and fine chemicals standpoint, the utility of petroleum lies in its simplicity and predictability. Biochemistry relies heavily on the reactivity that oxygen imparts to organic compounds, and the loss of much of the oxygen content in petroleum provides us with less reactive, simpler building blocks we can piece together in predictable ways.
Ironically, many of the fine chemicals our society relies on have a high oxygen content, so we end up re-installing the oxygen at the end of the synthesis after building our molecular architecture with the less reactive petroleum-derived precursors.
This similarity in oxygen content, structure and reactivity between many desirable fine chemicals and our available pool of biomass-derived chemical precursors provides an opportunity and a challenge to wean ourselves from petrochemical-based precursors. The opportunity is the direct use of highly oxygenated biomass, which could result in quicker and less wasteful routes to desirable target molecules. The challenge is reining in the reactivity so we can predictably manipulate and piece together the precursors, just as we have learned to do with simpler, less reactive petroleum products.
The synthesis of vanillin exemplifies this direct-from-biomass approach. Worldwide demand for flavoring agent vanillin far exceeds our capacity to extract it from vanilla beans, so we make it synthetically to meet the demand.
If you’ve ever found yourself enjoying the smell of a used book store or library, it likely is because of the release of vanillin from the slow breakdown of lignin, the structural component of wood still present in the pages. It would seem straightforward, then, to derive synthetic vanillin from wood, which we used to do in the ’80s. But since we’ve found them easier to manipulate, we instead use petrochemical feedstocks. However, with the re-emergence and clean-up of that 1980s technology, this wood-to-vanillin route once again seems viable.
With Maine’s forestry industry in need of a way to produce value-added products from wood and without the concern we’re diverting a potential food source for fine chemical production, this is exactly the type of process that could help wean us from oil. Of course, to make a more significant dent in the oil drum, the higher-volume industries of energy and bulk materials also will need to continue their transition back to biomass as well.
Reuben Hudson is a postdoctoral fellow in chemistry at Colby College in Waterville.