Accounting for the constrained availability of land: a comparison of biobased ethanol, polyethylene, and PLA with regard to non-renewable energy use and land use

Abstract

In a bio-based economy, chemicals, materials, biofuels, and other forms of energy will be produced from biomass. Pressure on agricultural land will thus increase, calling for highly effi cient solutions in terms of land use, with minimal environmental impacts. In order to gain better insight into the available options and their trade-offs, this perspective studies the production of polylactic acid (PLA), bioethanol, and bio-based polyethylene (PE) from wheat, maize, sugarbeet, sugarcane, and Miscanthus. While in current agricultural practice some plants are harvested and used as whole crop (e.g. Miscanthus), for others only part of the plant is used, with the remainder being returned to the fi eld (e.g. wheat straw). In order to obtain an understanding of the unused potential we assume as default case that all agricultural residues and processing co-products are used for energy purposes, thereby replacing non-renewable energy. We conclude that this agricultural practice would allow to substantially reduce non-renewable energy use (NREU). We also fi nd a clear difference in ranking depending on whether we study (i) NREU per (metric) tonne of product or (ii) Avoided NREU per hectare of land. The latter seems a suitable choice in a world where land availability is limited. In this case, we identify PLA as the preferred choice, irrespective of the type of crop. The production of ethanol for the replacement of fuels scores as the worst option for all crops. For each of the products studied, sugarcane offers the highest savings per hectare followed by sugarbeet