Chapter 7. Conclusions and Recommendations for Future Work
7.2. Recommendations for Future Work
Based on observations and results from this study, the following areas are recommended for further study.
1) Comprehensive study of dedicated energy crops grown on marginal lands for ethanol production
Ethanol was produced from biomass grown on waterlogged, saline and saltwater lands. However, there are various types of marginal lands, including those characterized by low fertility, poor drainage and shallowness and salinity. It would be useful to gather more data about ethanol production from different plant species cultivated on various types of marginal lands. Creating a crop inventory including abiotic stress tolerance levels and actual ethanol productions would allow farmers to maximize ethanol production when using marginal lands.
2) Technoeconomic analysis of the combined pretreatment: dilute acid or hot water pretreatment followed by disk milling
In Chapter 5, hot water pretreated milled samples resulted in lower sugar yields compared to harsh dilute acid pretreated milled samples. However, combined pretreatment with hot water did not require washing or neutralization before disk milling. Also, a special corrosion resistant reactor or chemicals are not needed for hot water pretreatment. Therefore, technoeconomic
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analysis of both combined pretreatments is recommended to determine which process is more economically feasible.
In Chapters 5 and 6, pretreatment efficiency of the combined process was determined by sugar production after enzymatic hydrolysis. An advantage of combined pretreatment is that it reduces generation of inhibitors to yeast. To investigate pretreatment and overall process efficiencies, measuring fermentation yields is recommended. In addition, to perform accurate technoeconomic analysis, evaluating net process water usage is relevant.
3) Scale up disk milling process of the combined pretreatment
In Chapters 5 and 6, small diameter disks (4 in) were applied to grind corn stover. Although disk milling is used in other industries, it is necessary to scale up the disk milling process for corn stover or dedicated energy crops. Scale up could be achieved by increasing disk diameter and disk rotation speed. Disk diameter determines process flowrate and disk rotation speed is related to grinding intensity. Also, optimizing the scale up process would benefit commercialization. Characterizing the effects of milling cycles, solids loading and sample viscosity on disk milling energy consumption and sugar yields would provide valuable data for process optimization and technoeconomic analysis.
4) Optimization of combined pretreatment for industrial application
In Chapter 6, disk milling was applied to commercially dilute acid pretreated samples. However, dilute acid pretreatment conditions were not optimized for subsequent disk milling. From Chapter 6 results, pretreatment conditions were an important determinant of final sugar
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yields. Therefore, to maximize sugar yields, optimizing the commercial dilute acid pretreatment conditions for the combined pretreatment is recommended.
5) Simplify combined pretreatment by removing initial grinding before chemical pretreatment
In cellulosic ethanol process, once biomass is transferred to processing plants, biomass is ground prior to chemical pretreatment. Thus, there are two grinding steps when performing combined pretreatment: before and after chemical pretreatment. It would be beneficial to investigate whether disk milling after chemical pretreatment could replace the initial grinding without decreasing sugar yields. If disk milling was not replaceable, it would be useful to determine the optimal initial biomass size for disk milling in terms of sugar yields and energy consumption.
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