EXCRECIÓN FRACCIONAL DE ELECTROLITOS

Whereas in most uses of energy, oil products are in competition with other fossil fuels such as natural gas and coal, they continue to dominate in the transportation sector. Electric railways aside, this sector depends almost exclusively on oil. Yet considerable effort is being undertaken to introduce alternative fuels for transpor- tation. The motivation is not only to enhance the security of energy supply by lessening the dominance of oil but also to reduce greenhouse gas emissions. Since Table 8.6 Product portfolio of modern oil refineries

Without conversion (%) Catalytic cracking (%) Hydro cracking (%)

Refinery gas 1–3 21 7–18

Gasoline 13–22 47 28–55

Middle distillates 25–39 20 15–56

Heavy oil 38–60 7 –

Other products 5

Source: Erdmann and Zweifel (2008, p. 181)

these emissions are substantial in the conversion of gas to liquid (GtL) and coal to liquid (CtL), respectively, use of biomass as a liquid transportation fuel has been gaining attention. There are several options for biomass to liquid (BtL):

– Biodiesel (rapeseed oil methyl ester) is produced from oily plants (e.g. rape, soy, sun flower). Oil gained from conventional oil mills (e.g. rapeseed oil) contains viscous components (see Table8.7) and therefore needs to be converted into fatty acid methyl ester (FAME) in order to become a diesel substitute. Further- more, methanol is added to make up about 10% of the final product, which can be marketed as pure biodiesel or added to conventional diesel (so-called blend- ing). In the European Union biodiesel production reached a volume of 9 mn tons by 2010 but has been declining since because biodiesel offers only limited environmental advantages over diesel. Its production cost varies between 0.55 and 0.70 EUR/l diesel equivalent. Assuming equal tax treatment of diesel and biodiesel, the renewable fuel would be competitive at prices of crude in excess of 100 USD/bbl only.1

– Bioethanol (alcohol) is produced by the fermentation of plants with high sugar content. In 2014, worldwide bioethanol production has reached 90 bn liter (of which the United States accounts for 57% and Brazil for 27%). Bioethanol is mostly sold as blend (as E10 in parts of the European Union, which is 90% gasoline and 10% bioethanol) because this obviates adjustments in refueling infrastructure and gasoline engines. Production cost of bioethanol ranges from Table 8.7 Properties of liquid fuels

Density (kg/l) Lower heating value (MJ/kg) Lower heating value (MJ/l) Viscosity (mm2/s) Flame point (C) Gasoline 0.76 43.1 32.4 0.6 <20 BtL, sun fuel 0.76 43.9 33.4 4 88 Methanol (CH3OH) 0.80 19.7 15.8 11 Bioethanol (C2H5OH) 0.79 26.8 21.2 1.5 13 MTBE / ETBE 0.74 35.1 26.0 21 Diesel 0.84 42.7 35.8 4–6 >55 Rapeseed oil 0.92 37.6 34.5 74 317 Biodiesel 0.88 37.1 32.6 7–8 120

Data source: FNR (2005).MTBE Methyl-tert-butylether; ETBE Ethyl-tert-butylether

1_{These figures are based on an exchange rate of 1.30 USD/EUR and current cost structures of} refineries. With these assumptions and a crude oil price of 60 USD/bbl, the wholesale price of gasoline is about 0.35 EUR/l and that of diesel, about 0.34 EUR/l. Note that one liter of biodiesel contains the energy equivalent of 0.9 l of conventional diesel (see Table8.7).

0.20 USD/l in Brazil to 0.35 USD/l in the United States and on to 0.55 USD/l in the European Union. The energy equivalent of one liter of bioethanol corresponds to 0.65 liter of gasoline. This makes Brazilian bioethanol competi- tive at prices of crude oil of 50 USD/bbl while European ethanol becomes competitive at prices above 140 USD/bbl only.

– Biofuels of the second generation (also known as BtL, biomass to liquid) are produced using advanced technologies such as biomass gasification with a subsequent Fischer-Tropsch synthesis. Another innovation in the making is the utilization of enzymes for decomposing fibrous parts of plants designed to allow the energetic use of the entire plant mass. Unfortunately none of these technologies have been proven to be feasible outside the laboratory up to now.

With the exception of Brazilian ethanol, the supply of biofuels at present depends on political support such as (partial) exemptions from fuel tax and manda- tory blending quotas for gasoline and diesel. Additionally, there are agricultural subsidies. The subsidization of biofuels has been justified by arguments derived from the theory of innovation. By creating a market niche for the corresponding technologies and cultivation practices, an industry can benefit from learning effects which might lead to cost reductions. The hope is that in future, increasing market shares can be obtained without political support (see IEA2000; Nakicenovic2002). The risk is that this support creates a pressure group that has a strong interest in its continuation. Experience shows that subsidies in particular are very difficult to terminate.

The production of biofuels is limited by the availability of arable land and yields. It can have a potentially negative impact on food security but also on biogas production (see Sect.9.1.3). Table8.8shows the present range of yields for grains and oil plants in Central Europe. Using the example of biodiesel, 3.3 tons of rapeseed can be harvested per hectare given medium yields, resulting in 1.3 tons of rapeseed oil (given a yield of 0.4 tons rapeseed oil per ton rapeseed). Using the

Table 8.8 Yields of energy plants

(Tons/(ha a)) Very low Low Medium Good Very good

Grain

Winter barley 5.22 5.69 5-6 6.70 7.51

Oat 3.93 4.32 4.57 4.85 5.33

Winter rye 3.86 4.66 5.24 5.88 6.73

Triticale (cross of wheat and rye) 4.77 5.18 5.60 6.21 6.83

Winter wheat 5.48 6.09 6.75 7.80 8.60

Grain maize 6.04 7.10 7.41 7.96 8.85

Oil plants

Winter rapeseed 2.73 3.06 3.26 3.46 3.74

Sunflower 2.5 4.0

Source: Erdmann and Zweifel (2008)

heating value of 37.6 MJ/kg in Table8.7, the energy content of this harvest can be estimated at 49,000 GJ. About one-third of this energy is needed as an input into its transformation into biodiesel, leaving some 33,000 GJ per hectare for energy use. According to Table 8.7, this is the energy content of 1000 l biodiesel (32.6 MJ/l∙1000 l  33,000 GJ) or 900 l diesel equivalent.

These yields could be increased in the future through the use of seeds that are especially developed for the production of energy plants. Some agricultural experts believe that a 50% increase of yield is achievable.

Some years ago, the European Union aimed to increase the share of renewable energies in the transportation sector to 10% by 2020 (directive 2009/28/EG). This would require an agricultural area of more than 15 mn ha, or about 10% of the arable area in the European Union. In the meantime however, EU strategy has changed in favor of electric vehicles.