Biodiesel vs. ethanol

The primary feedstocks for classic biodiesel are vegetable oils such as rape seed, soybean and palm oil, as well as jatropha. Unfortunately, none of these sources have high enough yields per acre. Plus, food grains are well-optimized crops and should therefore, unlike cellulosic biomass, not see their oil yields increase significantly over time.

The two biodiesel feedstocks that might have more potential are jatropha and algae. Jatropha has the benefit of growing on non-food crop lands, limiting the food vs. fuel conflicts. Algae, which has not been optimised, could offer high yields. Enclosed bioreactors and synthetic biology could be used to improve yields but:
• raising capital and operating costs could undermine profitability,
• using genetically engineered organisms in oceans is controversial.

Other disadvantages of biodiesel are the following:
• Biodiesel from different feedstocks has different properties.
• Biodiesel cannot be customized to meet needs, where as it is possible to dictate the structure of hydrocarbons and thus control the properties of the fuel.

In contrast, ethanol is compatible and complementary to other petroleum use reduction technologies like hybrids and plug-in electric hybrid cars.

The high cost of hybrids and plug-in hybrids will limit their penetration in the coming two decades. In contrast, flex-fuel vehicles (FFV’s) capable of running on either gasoline or ethanol for a marginal cost of only $35 per car could see their penetration greatly increase.

Moreover, as biofuel penetration grows, engines should be optimized for biofuels. Engines designed for ethanol first will operate at much higher compression ratios and thus get far more mileage per gallon of ethanol.


Source: V. Khosla