Life cycle greenhouse gas emissions were estimated for two pathways of sugarcane ethanol production. This project was done as a case-study for an environmental agency in February 2020.

1. 1
LIFE CYCLE ANALYSIS OF SUGARCANE ETHANOL
Kalaivanan Murthy
February 6, 2020
[1] INTRODUCTION
In this project, carbon intensities of two pathways of ethanol production from sugarcane are estimated. First, the system
boundary was established. Second, the carbon intensities of each component of the system were calculated using the
activity and emission factors given in CA-GREET3.0. Finally, the individual carbon intensities were added to obtain the
total carbon intensity.
[2] PATHWAYS
Ethanol (EtOH) is produced from sugarcane via two pathways: the first generation (1G) or conventional pathway, and
the second generation (2G) pathway. The difference between them is that bagasse, the cellulosic byproduct remaining
after sugarcane juice extraction, is combusted in 1G pathway, thus recovering electricity, whereas, in 2G pathway, it is
converted into cellulosic ethanol, thus recovering biofuel.
[3] SYSTEM BOUNDARY
For 1G pathway, the following components make up the system boundary: (1) Agriculture, (2) Land Use Change (LUC),
(3) Transportation (sugarcane from field to biorefinery and filter cake from biorefinery to field), (4) Biorefining
(conversion of sugarcane to ethanol), (5) Co-products (bagasse combustion for electricity recovery), (6) Transportation
(ethanol from biorefinery to consumers), (7) Vehicles (tailpipe emissions).
For 2G pathway, the components are the same as the above, except that instead of electricity, ethanol is recovered from
the fifth component, “co-products.”
[4] EMISSIONS ESTIMATION
[4.1] For 1G pathway:
From USDA’s economic feasibility report[1]
, it is assumed that 1 metric tonne of wet sugarcane yields 21.5 gallons of
ethanol. This is close to CA-GREET3.0’s value, 21.4. The activity and emission factors are taken from CA-GREET3.0 and
“Tier 1 Sugarcane-derived Ethanol Pathway (release 08/13/2018).”
(1) Agriculture = 30.03 gCO2e/MJ (This includes farming, fertilizers, insecticide, herbicide, straw field burning,
mechanized harvesting, filter-cake transportation)
(2) Indirect Land Use Change (iLUC) = 11.8 gCO2e/MJ[2]
(3) Transportation (sugarcane from field to biorefinery and filter cake from biorefinery to field) = 4.5 gCO2e/MJ
(4) Biorefining (sugarcane to ethanol) = 9.89 gCO2e/MJ
(5) Co-Products (bagasse combustion for electricity recovery) = –12.67 gCO2e/MJ
(6) Transportation (biorefinery to consumers + denaturant) = 0.45 + 3.33 gCO2e/MJ
(7) Vehicles (biogenic tailpipe + other tailpipe) = 0 + 1 = 1 gCO2e/MJ (Biogenic tailpipe emissions are nullified because it
was originally absorbed from the atmosphere.)
Total (CI Score) = 48.3 gCO2e/MJ
Ethanol Yield = 21.5 gal/tonne sugarcane
[4.2] For 2G pathway:

2. 2
Since ethanol is produced from bagasse as well (besides sugarcane juice), the assumption 21.5 gal EtOH/tonne of wet
sugarcane will be an underestimation. But to start with, we will use that value, and once we estimate the ethanol yield
from bagasse, we will scale all other values, including the carbon intensities of the system components.
(5) Co-Products (bagasse delignification for ethanol recovery)
2G ethanol recovery = 205 kg/tonne dry bagasse[3]
= 9.6 gal/tonne sugarcane = 79.72 MJ / tonne sugarcane
Increase in ethanol yield = 2G ethanol yield/ 1G ethanol yield = 0.45
CI due to ethanol recovery = 0.28*9.89 gCO2e/MJ = 2.77 gCO2e/MJ (It is assumed that recovering 2G ethanol
from bagasse generates same amount of emissions as recovering 1G ethanol from sugarcane.)
CI due to 2G electricity recovery (using 2G ethanol byproducts) = –12.67 * 2100/6900[3]
= –3.86 gCO2e/MJ
The above numbers indicate that by recovering ethanol from bagasse, we gain 79.72 MJ per tonne sugarcane
(besides 178.47 MJ from 1G), and by recovering electricity from the byproducts of 2G ethanol recovery, we gain
3.86 gCO2e/MJ carbon emissions (instead of 12.67 gCO2e/MJ from 1G).
Therefore, (5) Co-Products = 2.77 + (–3.86) = –1.09 gCO2e/MJ
In addition, the carbon intensities of the system components preceding “Co-Products” need to be scaled down, and
hence factored by 1/1.45 to account for the excess 2G ethanol production. This results the following: (1) Agriculture +
(2) iLUC + (3) Transportation + (4) Biorefining = 56.22/1.45 = 38.77 gCO2e/MJ.
However, the carbon intensities of system components succeeding the “Co-Products” will remain the same, and they do
not need to be scaled-up since the values are based on unit energy (per MJ). Hence, (6) Transportation + (7) Vehicles =
4.78 gCO2e/MJ.
Total (CI Score) = 42.46 gCO2e/MJ
Ethanol Yield = 21.5 + 9.6 = 31.1 gal/tonne sugarcane
[5] RESULTS AND CONCLUSION
Above analysis shows: (1) ethanol yield of 2G pathway is 31.1 gal/tonne sugarcane, which is 44.65% higher than that of
1G pathway; (2) CI Score of 2G pathway is 42.46 gCO2e/MJ, which is 12.09% lower than that of 1G pathway, and hence
2G pathway has a better CI Score.
[6] REFERENCES
[1] USDA Feasibility Report, Page-iii, https://www.usda.gov/oce/reports/energy/EthanolSugarFeasibilityReport3.pdf
(Date Referred: February 6, 2020).
[2] Detailed Analysis for Indirect Land Use Change, Page-1-25,
https://ww3.arb.ca.gov/fuels/lcfs/iluc_assessment/iluc_analysis.pdf (Date Referred: February 6, 2020).
[3] Botha, T., & Von Blottnitz, H. (2006). A comparison of the environmental benefits of bagasse-derived electricity and
fuel ethanol on a life-cycle basis. Energy Policy, 34(17), 2654-2661.