Biofuel yield

Figure 9.1 reports the prospective average biofuel yield from different crops in EU-15 over 2005-2010 (GJ ha-1) [3]. Bioethanol yield in EU-15 normally is higher than the biodiesel yield, e.g., a smaller land area will be needed to produce... 

Fig. 9.1 Prospective average biofuel yield from different crops in EU-15 over 2005—2010 (GJ/ha). (Adapted from [5]).

The biofuel yield of different crops is differs, but a more correct analysis also requires consideration of the (fossil) energy inputs needed to seed, harvest, and process the crops, etc. Clearly, the results depend significantly on regional and technology details, but an overall comparison of net energy yield factors is given in Fig. 1. 

J., Xu, J., Tang, Y.J., Wiegel, J., Phelps, T.J., and Zhou, J. (2011) Correlation of genomic and physiological traits of Thermoanaerobacter species with biofuel yields. Appl Environ. Microbiol, 77, 7998-8008. 

Research is being done in the United States and worldwide to lower some ot the barriers to biofuels. Researchers hope to develop high-yield, fast-growing feedstocks for reliable biomass fuel supplies. Research is also being done to improve the efficiency of energy conversion technologies so that more of the biomass is utilized. 

The assessment of the sustainability of the cultivation of energy crops includes the input and recycling of nutrients, the application of pesticides, the water-use efficiency, the consumption of fossil fuels and the balance of soil carbon. The aim is to recycle the nutrients, which is simple in the case of anaerobic digestion by applying the digestate to the field. If crops are combusted many of the minerals can be returned via the ash. In the case of liquid biofuels, exported nutrients are lost and have to be replaced. The application of pesticides, mainly herbicides, can often be reduced in comparison to food production, but the energy yield per hectare might be reduced if the share of weeds exceeds certain thresholds. Water use efficiency,... 

The potential of biomass to make a large contribution towards replacing conventional fuels is constrained by land availability and competition with other end-use sectors. In particular, the potential for oil seeds to generate FAME is limited. Generally, yields of biofuels from purpose-grown crops depend on the species, soil type and climate.22 At a global level, it is estimated that biofuels could substitute up... 

Cereals can yield around 1500-3000 litres of gasoline equivalent (lge)/ha sugarcane, 3000-6000 lge/ha sugarheet, 2000-4000 lge/ha vegetable oil crops, 700-1300 litres of diesel equivalent (lde)/ha and palm oil, 2500-3000 lde/ha (IEA, 2007). In addition, there are novel biofuel production processes under development, for example biodiesel from marine algae, which are claimed to have a 15 times higher yield per ha than rapeseed. 

The same holds true for hydrogen however, biomass yields more kilometres when used via hydrogen in fuel-cell cars than liquid biofuels in ICE cars (see Fig. 7.5). Moreover, as hydrogen is produced via gasification, it is equivalent to second-generation biofuels, as it can use feedstock that does not interfere with the food chain. 

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... 

Palm oil has been cracked at atmospheric pressure and a reaction temperature of 723 K to produce biofuel in a fixed-bed microreactor. The reaction was carried out over microporous HZSM-5 zeolite, mesoporous MCM-41, and composite micromesoporous zeolite as catalysts. The products obtained were gas, organic liquid product, water, and coke. The organic liquid product was composed of hydrocarbons corresponding to gasoline, kerosene, and diesel boiling point range. The maximiun conversion of palm oil, 99 wt.%, and gasoUne yield of 48 wt.% was... 

Potatoes yield more calories per acre than any other major crop, a criterion that becomes even more important in light of the planet s ever-increasing population, food shortages, price spikes, and the recent competition for farmland by biofuel crops. Collectively, these facts emphasize the impact potatoes can have on global nutrition. 

Chen F, Dixon RA. 2007. Lignin modification improves fermentable sugar yields for biofuel production. Nature Biotech 25 759-761. 

However, to demonstrate that SSPs deserve their place in the mix of energy crops, one comparison with other biofuel crops should be made. Table 1 gives the physical characteristics of the nine plants in the SSP set. Of particular importance in Table 1 is the last column, which represents the projected yield of each (in t/acre). 

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