2.4.1. Biomass Conversion Technologies

Different conversion technologies are available to convert forest and wood residues into a variety of biofuels and chemicals [40]. Conversion technologies of biomass to biofuels fall into two principal categories: thermo-chemical and bio-chemical technologies [41], which closely investigated several thermochemical and biological conversion processes employing three important metrics: mass ratio, energy ratio, and energy efficiency. The calculated metrics of ethanol from hardwood and softwood through different conversion processes are presented in Tables 2 and 3.

**Table 2.** Mass ratio of ethanol from hardwood and softwood through different conversion processes (Based on study of [41]).



**Table 3.** Energy ratio of ethanol from hardwood and softwood through different conversion processes (Based on study of [41]).

Since there was no mass and energy ratio information provided for woody residue, the two metrics for the residues were assumed to be the same as timber. For Michigan's case, this assumption stands because residue volume accounts only 3.3% (obtained from Equation (4)) of timber volume.
