**8. LCA on GHG emissions and techno-economic evaluation of lignocellulosic ethanol production**

Numerous life cycle analyses (LCAs) of lignocellulosic ethanol have been published over the last 15 years and several reviews of these LCA studies have been completed and are cited in a more recent review [67]. These studies show a clear reduction in GHG emissions for lignocellulosic ethanol compared to gasoline. However, accurate quantification of GHG emission reduction is hard to obtain as gaps remain in understanding life cycle performance due to insufficient data, and model and methodological issues. Critical unresolved issues that are expected to impact its energy/GHG emissions performance include feedstock-related emissions, consequential versus attributional life cycle aspects, choice of system boundaries, and allocation methods.

Decisions regarding feedstock, process technology and co-products can significantly impact GHG emissions calculations. Predicted life cycle GHG emissions vary widely depending on how the following key parameters are considered: nitrogenrelated emissions due to supplemental fertilizer requirements and the N content of feedstock, cellulase requirements, farming energy, ethanol yield, and how the value of co-products such as lignin are realized, among others.

Government support (i.e., Ethanol mandate, tax credit, etc.) is not expected to last forever. To be sustainable, lignocellulosic biofuels production must meet or exceed the economic performance of their first-generation counterparts.

### *Lignocellulosic Ethanol: Technology and Economics DOI: http://dx.doi.org/10.5772/intechopen.86701*

The growth in the capacity of commercial lignocellulosic ethanol production has been slow in the past decade, despite significantly better predicted performance on various environmental and energy security criteria than corn-based ethanol in the various techno-economic evaluations published before 2010 [68]. The slow growth has been due to both large technological risk, large capital cost, and the poor predicted economic performance of biorefineries in the short term.

An LCA of US softwood cellulosic ethanol was reported in 2012 by Stephen et al. [68]. In the paper, the base case (capacity: 50 mL ethanol year<sup>−</sup><sup>1</sup> ) softwood ethanol production cost was compared with costs of ethanol produced from corn and sugarcane found in the literature. Softwood lignocellulosic ethanol was predicted to have a production cost of \$0.90 L<sup>−</sup><sup>1</sup> , 250–300% higher than US corn and Brazilian sugarcane ethanol production costs, which were in the range of \$0.30–\$0.40 L<sup>−</sup><sup>1</sup> . The lignocellulosic base case scale of 50 mL year<sup>−</sup><sup>1</sup> , compared to 150 mL year<sup>−</sup><sup>1</sup> of US corn and 365 mL year<sup>−</sup><sup>1</sup> of and Brazilian sugarcane, is much smaller as it was chosen based both on the projects funded under the US Department of Energy's commercial biorefinery program and those operating in other places such as Denmark. Production costs of sugar- or starch-based ethanol are expected to continue to decline to \$0.22–\$0.25 L<sup>−</sup><sup>1</sup> by 2020. Thus, second-generation ethanol is not going to catch up with first-generation ethanol on production cost soon.

Another very recent techno-economic evaluation was performed on production cost of ethanol produced from corn stover using either biochemical or thermochemical methods. For heat integrated biochemical route, the predicted bioethanol product costs at \$2.00 for a production capacity of 43,300,000 gallon year<sup>−</sup><sup>1</sup> [69]. This result was clearly an underestimation of lignocellulosic ethanol as a major cost item, capital investment cost, was not included. Furthermore, the corn stover price of 46.8 \$/ton was an underestimation, and feedstock transportation cost was not included in LCA. Feedstock cost can impact total cost by 40 percent according to a Lux Research report of 2016 [70]. The Brazilian birefinery company Raizen has the lowest projected minimum ethanol selling price of \$2.17 per gallon while Abengoa's capital-intensive \$500 million Hugoton facility has the highest price of \$4.55 with feedstock cost emerging as the most critical variable. The low cost of Raizen's cellulosic ethanol is largely attributed to its access to low cost sugarcane straw and sugarcane bagasse (\$40 and \$38 per dry metric ton), respectively, compared with corn stover (\$90) used by Abengoa and POET-DSM and wheat straw (\$75) used by Beta Renewables [71].
