**4. Manufacturing processes**

Ethanol can be produced in various ways: syngas from coal and biomass, synthesized from petroleum-based ethylene, or by fermentation of sugary contents. Bio-ethanol is produced through the procedures of fermentation of regenerative biomass, distillation, and purification.

Sugar canes and corns are mainly used to produce bio-ethanol in Brazil and the United States, respectively. Overall manufacturing process for bio-ethanol composes the following key parts: pretreatment, saccharification (hydrolysis), fermentation, and purification as shown in **Figures 6** and **7**.

Ethanol is mainly made by fermenting the sugars found in grains, such as corn and wheat, as well as potato wastes, cheese whey, corn fiber, rice straw, urban wastes, and yard clippings. There are several processes that can produce alcohol (ethanol) from biomass. The most commonly used processes today use yeast to

**Figure 6.**

*Steps involved in biochemical conversion of biomass to alcohol fuels (modified from Ref. [8]).*

**Figure 7.** *Schematic flow diagram of bio-ethanol production process [15].*

ferment the sugars and starch in the feedstock to produce ethanol. Another process uses enzymes to break down the cellulose in woody fibers, making it possible to produce ethanol from trees, grasses, and crop residues [8].

Synthesis of ethanol as a sustainable source of energy, especially related to more high-end product form of alcohol with high carbon contents, requires the accumulation of technical know-how in preparation for future depletion of petroleum oil resources. The bio-alcohol production process is shown in schematic flow diagram for bio-butanol manufacturing in **Figure 8**.
