3. Summary

greater effect on the sugar yield. Also, Shi et al. [87] reported that efficiency in the mixed feedstocks pretreatments and densification demonstrated significant effect on sugar yields. Many studies without MW-assisted alkali pretreatment method using pelletization on different biomass have reported similar sugar yield, considering the biomass used in the conversion. Furthermore, conclusions made from these studies focused more on the effects of pelletization parameters on improving enzymatic hydrolysis process for biomass sugar conversion [85, 87–91]. The advantages of densifying biomass using different technologies to produce pellets are to

Technoeconomic analysis (TEA) involves technologies, system, and production processes evaluation. Different technoeconomic studies have classified the analysis into two major groups such as technical (maintenance requirement and service life, operation and maintenance skill requirement, the ease of transportation and installation, processing capacities available, material, esthetic and inherent risk for a system or product process) and economic (capital and operating costs, biomass cost, and profit revenues) depending on the process technology used [93, 94]. The TEA report also assists in understanding and providing additional information to the economic viability via production cost and market price [94], and the profitability and sensitivity analysis of a product or a process [95, 96]. To perform technical and economic evaluation, various software with in-built analysis tool to estimate capital and operational costs have been developed by different software developers, and the choice of software is dependent on the project evaluation. The available commercial TEA software includes Super-Pro designer, PRO/II and DYNSIM, Aspen Plus HYSYS, DESIGN II,

Life cycle assessment (LCA) involves the collection and evaluation of relevant input and output data of a product system including potential environment impacts within the process period [97]. Adams et al. [98] indicated that the main reason for using the LCA tool is to give a

improve handling, storage, and transportation efficiencies [92].

2.5. Economic evaluation of microwave pretreatment process

and CHEMCAD [93].

Feedstock Screen size (mm)

56 Renewable Resources and Biorefineries

Canola straw

Alkali Alkali

concentration (%)

MW time (min) Tensile strength (MPa)

1.6 NaOH 1.5 18 2.31 0.79 1370.27 110.05

3.2 NaOH 0.75 6 4.85 2.60 1324.75 55.78

3.2 NaOH 0.75 6 1.23 1.68 1205.73 72.22

Oat hull 1.6 NaOH 0.75 18 1.33 5.28 1221.99 99.10

Table 2. MW-assisted alkali pretreated canola straw and oat hull pellets and glucose yields results [3].

KOH 1.5 6 3.78 0.83 1392.21 53.42

KOH 1.5 6 5.19 0.83 1382.62 96.77

KOH 1.5 6 0.63 1.04 1185.69 97.53

KOH 1.5 18 1.17 5.95 1210.94 84.87

Dimensional stability (%)

Pellet density (kg/m<sup>3</sup> ) Average glucose yield (mg/g)

> MW pretreatment technique has gained research attention and its future is growing. In spite of this, it is still under bench-scale development. Sufficient data generated from previous and recent studies can be used to quantify the dielectric properties of input biomass and to design and develop a continuous MW-assisted pretreatment and enzymatic saccharification process unit for commercial scale-up. Feedstock properties and reaction conditions are the two factors influencing microwave pretreatment characterization and yield of the final product.

The cost of MW pretreatment process is the main determinant associated with the adoption of this technology. Emphasis on the capital and operating cost investment will improve the pretreatment technique and hydrolysis process, thereby reducing the cost of the final product (bioethanol). Future research studies in MW-assisted biological pretreatment in improving lignocellulosic biomass digestibility, and techno-economic analysis and life cycle impact assessment of the process need to be considered. The concept is to develop a more economic pretreatment and hydrolysis techniques that can be environmentally sustainable and accepted by the bioenergy industry.

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Pretreatment of Crop Residues by Application of Microwave Heating and Alkaline Solution for Biofuel…

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