Abstract
Purpose In converting lignocellulosic biomass into biofuel, a pretreatment stage is required in order to make the biomass more readily available for the transformation. There are numerous pretreatment techniques that can be chosen, which are broken down into four categories: chemical, physical, physicochemical, and biological. The aim of this work is to provide a new assessment for some of the emerging technologies using life cycle assessment (LCA) combined with an analysis of the overall product yield. Methods Using literature data, an LCA of four different pretreatment methods was carried out. Liquid hot water (LHW), steam explosion (SE), dilute acid (DA), and organosolv (OS) were chosen as the most common techniques with high scalability potential. Models were constructed using GaBi software. A cradle-to-gate analysis was selected with a common model of the corn stover growth and harvesting cycle being combined with the individual models for each pretreatment. Four impact categories were analyzed, and a selection has been discussed based on relevance to the biofuel production process. Results and discussion In nearly all of the impact categories, DA performs the worst due to the length of the process (12 h) and the amount of electricity required to elevate the temperature to 60 °C for that time period. In many of the other categories, the remaining three pretreatments perform comparably to each other with the exception of LHW which has significantly reduced CO2 emissions. LHW has slightly higher water depletion rates than both SE and OS, which is to be expected given the nature of the process. In terms of product yield, LHW produced twice as much total sugar than any of the other processes. Conclusions The project concluded that while LHW and SE are viable options for the pretreatment of biomass,LHWis the most suitable technique for the pretreatment of corn stover. Thispretreatmentwas environmentally friendly as it produced the lowest CO2 emissions, aligning with the main objective behind developing biofuels from agricultural residues. The process was also technically the most effective as it resulted in the highest sugar yields.
Highlights
Social responsibility coupled with concerns about carbon emissions and fossil fuel supplies have led researchers to investigate alternative sources of energy
First generation biofuels derived predominantly from plant matter such as grains, sugar beet, and oil seeds do not present a sustainable option as a substitute to fossil fuel production mainly because the majority of them are being shown to provide little or no net life cycle benefit in terms of carbon dioxide and other greenhouse gas (GHG) emission reductions, especially when land use changes are taken into account (Eisentraut 2010) (Timilsina and Shrestha 2010)
It has been reported that cellulosic ethanol has the potential to reduce greenhouse gas emissions of a vehicle by 86 % (Wang et al 2007), whereas first generation biofuels only reduce the emissions by approximately 12–13 % (Stephen et al 2013) when compared with conventional petrol
Summary
Social responsibility coupled with concerns about carbon emissions and fossil fuel supplies have led researchers to investigate alternative sources of energy. The US Energy Information Administration (EIA) has established that fossil fuels currently supply nearly 80 % of the world energy use and are projecting the global energy consumption to increase by 56 % by 2040 owing to an increase in the world population and global industrialization (Energy Information Administration 2013). This massive escalation in the demand for energy coupled with ever increasing depletion rates of fossil fuel reserves and the desire to reduce greenhouse gas emissions have. It has been reported that cellulosic ethanol has the potential to reduce greenhouse gas emissions of a vehicle by 86 % (Wang et al 2007), whereas first generation biofuels only reduce the emissions by approximately 12–13 % (Stephen et al 2013) when compared with conventional petrol
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