Comparative Life-Cycle-Assessment of Pretreatment Processes for the Production of Biofuels From Lignocellulosic Residues

Residual and waste materials from agriculture and forestry often contain high amounts of lignocellulose, which counteracts its use to produce both bioenergy and bio-based products. These raw materials usually have to be pre-treated. Then further processing to produce chemicals for bio-based products, bioenergy or second-generation biofuels supply can take place. In this study within the framework of a life cycle assessment processes for the pretreatment of lignocellulosic materials, primarily wheat straw, are examined for their respective environmental influences. The aim of the research is to determine potential environmental impacts and to identify possible weak points in the procedures. In addition to the technical and environmental evaluation of the processes, the efficiency regarding production of biogenic substitutes, i.e. the amount of necessary derivatives for the production of fuels, was also evaluated during this trial. For this purpose, the acetone-based pretreatment process and the water-based Liquid-Hot-Water pretreatment were analyzed within a life cycle assessment. To calculate the most relevant factors the method ReCiPe 2016 v1.1 midpoint (H) and the impact factors global warming potential, eutrophic potential, human toxicity and fresh-water toxicity were chosen. Results have shown that the Liquid-Hot-Water process, which uses water as a solvent with temperatures over 200 degrees (Celsius) and a pH value of 5.6, is more environmentally friendly than the acetone-based process. Additionally, the correlation to post treatment processes like the filtration was visualized. So, vacuum filtration systems seem to be less polluting than paper-based filtration systems. Advantage of the acetone-based treatment is that the fractions have a better separation, so a better quality and especially accessibility of the lignin fractions is realized. Liquid-Hot-Water pretreatment achieves a better mass balance, especially in terms of a following biofuel production, except for its mixed cellulose and lignin fraction, which is a disadvantage.