Bioethanol energy balance

Notably, however, any comparison of biodiesel vs. bioethanol should be done with great caution, because analysis of an industry such as that related to biofuels is a very complex task and all conclusions are country dependent. It may be interesting, however, to compare the energy balance and environmental impact in producing biodiesel from oilseed rape and bioethanol from wheat crops [4], Table 9.3 reports this comparison. The energy balance for bioethanol is more positive than for biodiesel, in particular when straw is utilized, mainly due to the higher yield... 

I.R. Richards, Energy balances in the growth of oilseed rape for biodiesel and of wheat for bioethanol, Levington Agriculture Report, British Association for Bio Fuels and Oils (BABFO) Jan. 2000 (http //www.biodiesel.co.uk). 

Table 15.13 Summary of the mass and energy balance for the bioethanol plant.

All considerations for the use of lignocelluloses for the production of bioethanol or other platform chemicals should include the overall mass and energy balance as well as the availability through the year and the transportation needed. Regarding a study of IEA/OECD 2010 [9], there is no additional land available in the short term and only 10% of global forestry and agricultural residues are assumed to be available for biofuel or platform chemical production. Therefore, there will always be a direct competition of bioethanol or other platform chemicals production with food production even if so-called plant waste material is used as the real limitation is the arable land available. 

Recently, combined methane and ethanol reforming was tested in a two-step process with the purpose of demonstrating its applicability to bioethanol mixtures enriched with methane [84], Model studies assessed energy balances of the two-step system by verifying their effectiveness [107,108]. 

In contrast, the energy gain of ethanol fermentation from a cellulose-based crop was estimated at only 10% [31]. A fife cycle assessment of bioethanol from wood came to a similar conclusion [32]. This unsatisfactory outcome mainly results from the energy-intensive pretreatment with steam explosion, such as is used by Iogen [16]. The replacement of the latter by COz explosion [33] may redress the energetic balance. 

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