Life cycle environmental sustainability of lignocellulosic ethanol produced in integrated thermo-chemical biorefineries.

There is a growing interest in producing biofuels and bio-chemicals from lignocellulosicfeedstocks in integrated biorefi neries. However, the sustainability implications of integratedbiorefi neries are still poorly understood. Using a life cycle approach, this paper examines environmentalimpacts of second-generation ethanol produced in thermo-chemical refi neries together withchemicals and energy. Four feedstocks are considered: wheat straw, poplar, Miscanthus and forestresidue. The results suggest that the production of ethanol from these feedstocks offers signifi cantsavings in eight out of 12 environmental impacts when the system is credited for the avoided impactsfrom producing the co-products from fossil resources. Ethanol from forest residue is the best andwheat straw the worst option for most impacts. Land use change has a signifi cant effect on theglobal warming potential (GWP) of ethanol. For example, conversion of forest to grow Miscanthusincreases the GWP from –234 to 6685 g CO2 eq./l of ethanol. The effect is opposite when grasslandis converted to grow poplar: the GWP is reduced by two times because of carbon sequestrationby poplar. The thermo-chemical route for producing ethanol from poplar and forest residue is moresustainable for most impacts than the bio-chemical conversion with the same feedstocks. Althoughethanol saves up to 83% of GHG emissions per MJ of fuel compared to petrol, the savings are muchsmaller (~3%) for current ethanol blends of 5%. Therefore, unless a much higher proportion of ethanolwas used, the contribution of second-generation ethanol to climate change mitigation would be small.© 2015 The Authors. Biofuels, Bioproducts, Biorefi ning published by Society of Chemical Industry