Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the Department of Energy’s Joint BioEnergy Institute (JBEI), which is managed by Berkeley Lab, have quantified how bioproduct accumulation in planta—i.e., engineering plants to produce valuable chemical compounds, or bioproducts, as they grow—affects biofuel selling prices.

Their open-access study, jointly led by Corinne Scown and Patrick Shih, was published recently in the Proceedings of the National Academy of Sciences. In the study, they present the range of bioproduct selling prices and accumulation rates needed to compensate for additional extraction steps and reach a target $2.50/gallon minimum biofuel selling price.

Minimum required selling price ranges for bioproducts ($/kg) under different in planta accumulation amount (dry basis) in order to reach the MESP parity ($3.61/gal) and targeted selling price of ethanol ($2.50/gal). The Inset shows the estimated bioproduct selling price of less than $100/kg. Yang et al.

The researchers first gathered information on a group of well-studied bioproducts that plants can already effectively produce—ranging from flavors and fragrances to biodegradable plastic. Making a valuable bioproduct would help offset the cost of making biofuels and make the whole process cheaper.

They then designed and simulated what it would take to extract these bioproducts from plant material in the context of an ethanol biorefinery. In this setting, valuable bioproducts would be extracted from the plant, while the remaining plant material would be converted into ethanol.

A schematic of bioethanol production process with the value-added bioproduct and the integrated one-pot high gravity ionic liquid-based pretreatment process. Biomass sorghum is used as a representative bioenergy crop. In this study, the selected value-added bioproducts are limonene, artemisinin, PHB, latex, and cannabidiol. Yang et al.

The results showed that the amount plants need to make is actually quite feasible. For example, they calculated that when accumulated at 0.6% of the biomass dry weight, a compound such as limonene would offer net economic benefits to biorefineries. In other words, for 10 dry metric tons of sorghum biomass from an acre of land, they need to recover only around 130 pounds of limonene from that biomass.

The researchers in our Feedstocks Division were surprised by how modest the target levels were. The levels we need to accumulate in plants to offset the cost of bioproduct recovery and drive down the price of biofuels are well within reach.

—Corinne Scown

The results show that this strategy for reducing the cost of biofuels is feasible; but also that the market for each high-value product is limited in size. The analysis suggests that just five commercial-scale biorefineries could support the entire projected 2025 market demand for limonene. Scown said crops need to be engineered to produce a broad range of products to make sure the industry is diversified and the market is not flooded for any one product.

This research was supported by the DOE Office of Science.

Resources

• Minliang Yang, Nawa Raj Baral, Blake A. Simmons, Jenny C. Mortimer, Patrick M. Shih, Corinne D. Scown (2020) “Accumulation of high-value bioproducts in planta can improve the economics of advanced biofuels” Proceedings of the National Academy of Sciences doi: 10.1073/pnas.2000053117