Page 255 - Advances in Eco-Fuels for a Sustainable Environment

218 Advances in Eco-Fuels for a Sustainable Environment

the commercial ethanol production plants are using dry milling as wet milling requires
a high capital cost because of the complex and extensive equipment [39]. Addition-
ally, wet milling is appropriate for larger scales of production while dry milling is suit-
able for small-scale ethanol plants that require less equipment and investment.
The lignocellulosic biomass lignin along with cellulose and hemicellulose forms a
rigid structure that exhibits recalcitrance against enzymatic attack during enzymatic
hydrolysis [40, 41]. Therefore, various pretreatment techniques such as chemical and
physicochemical have been adopted to deconstruct the structure. Pretreatment
removes lignin and hemicellulose from the lignocellulosic structure while also
decreasing crystallinity and increasing the porous surface area, which is favorable
for hydrolysis [42]. In contrast to the other process, the conversion of lignocellulosic
biomass into ethanol requires two extra process steps such as pretreatment and detox-
ification prior to the hydrolysis and fermentation steps, which are the major techno-
logical hurdles for lignocellulosic conversion.
Over the last 15years, a number of significant modifications for technological
improvements have been made in order to increase the efficiency of the ethanol pro-
duction process as well as the profitability. In the field of corn and starchy feedstock
fermentation, mechanical fractionation has been developed for reducing non-
fermentable material in the hydrolysate [43]. The POET biorefining company
established a low-temperature fermentation process. In addition to these, researchers
and industries are trying to explore an energy-efficient separation process such as
membrane technology in replacement of the distillation/dehydration process. Integra-
tion of reactor systems in the ligocellulosic ethanol production process can make the
process cost-effective with a minimum enzyme requirement. Fig. 8.5 illustrates the
integrated application of a membrane bioreactor with a separation unit. The

CO 2

Nutrient
Ethanol

Sugar
Salt
Sugar
Yeast

Bioreactor MD
Fig. 8.5 Membrane bioreactor integrated with membrane distillation process [44].