4. Results & discussion
Mass and energy flows are broken down into unit operations in Table 2A,B and C, corresponding to the three cases modelled. Inputs and outputs for the whole process are summarized in Table 3. Before discussing the results it is of interest to set the context by reviewing some key points of the bioethanol debate (for reviews of the debate see Refs.  and ). The two main issues of contention are the Vildagliptin for arable land between food and fuel, and whether or not the manufacture of ethanol leads to a net production of energy. Cellulose ethanol holds promise in both of these areas because the residue of a food producing plant (wheat, corn, rice, sugarcane) can be utilised after the food has been harvested so no additional land or energy inputs are required to produce the feedstock.
One frequently used measure of the energy efficiency of ethanol (or any fuel) is the ratio of the energy contained in the fuel to the non-renewable energy invested in producing it. This ratio has been called the energy yield ratio or energy returned on energy invested. Typically the energy invested includes agricultural inputs (fertilizer, pesticide, fuel), transport and the conversion process itself. It is reasonable to conclude that if a process has an energy yield ratio less than one, it is hardly worth carrying out, and certainly not sustainable.