2.4. Effect of biomass pelleting on enzymatic digestibility

Densification of biomass is primarily achieved by pelletizing which is the application of mechanical force to compact biomass into uniformly sized solid particles [80, 81]. Densification increases the density of biomass into a pellet product having a density of 600–1200 kg/m3 [82] for efficient transportation and low moisture for safe storage [83]. Particle size and preconditioning of biomass prior to pelletization can facilitate the binding characteristics and chemical composition of biomass, thereby improving the overall pellet quality [84]. In addition, moisture content as a factor during preheating of biomass before pelleting assists in loosening the natural binders to produce durable pellets [85].

The pretreatment process helps to complete biomass conversion into valuable bioproducts. Therefore, the pretreatment of lignocellulosic biomass is important in enhancing enzymatic cellulosic digestibility to increase glucose yields [86]. There is only one cited paper on the effects of MW-assisted alkali pretreatment and densification on improving enzymatic saccharification of biomass conversion into ethanol. Sugar yields were reported to increase after MWassisted alkali pretreatments of canola straw and oat hull pellets. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) at various concentrations were used in the study. The authors highlighted that samples selected for cellulosic substrate analysis were based on parameters that describe pellet quality such as tensile strength, dimensional stability, and pellet density [3].

Table 2 shows MW-assisted alkali canola straw and oat hull pellet data and corresponding glucose yield results. The tensile strength, dimensional stability, and pellet density showed little or no significant effect on the sugar yields on canola straw and oat hull pellets. It is evident that samples ground in a 1.6-mm hammer mill screen size had a significant effect on the cellulosic enzymatic digestibility. Table 2 shows data and results from Hoover et al. [85] and Shi et al. [87] which were compared. Hoover et al. [85] indicated that preheating AFEXpretreated biomass pellets had no effect on sugar yield while the non-preheated pellet had a


holistic view of the emissions and resource requirements of a product system. Also, the importance of LCA study is to analyze the impact on the environment, energy consumption, and economic viability [94, 99]. Azapagic and Stichnothe [100] reported that LCA can be translated into quantitative measures of sustainability such as environmental, social, and economic. Different types of International Standard Organization (ISO) documents have been developed for LCA standards in providing flexible methodology and enabling modification of analysis by meeting up the goal and scope of the study [94, 97]. In the setting of innovation targets, the major impacts of LCA can be identified using these intensive products: raw material, manufacturing, distribution, the use of intensive product such as automobiles and laser printers, and disposal-intensive product [94, 100]. Many software, tools, and databases have been developed to assist in data processing and calculation of LCAs. These include Athena, BEES 4.0, CMLCA, Ecolnvent, EMIS, GaBi, GEMIS, IdeMAT, REGIS, SimaPro, and Umberto [101]. Many software are in market and many more are disappearing each year due to the dynamic nature and availability of the software [94]. Patel et al. [102] studied the technoeconomic and life cycle assessment of lignocellulosic biomass thermochemical conversion technologies. The study stated that a lot of research works are only focusing attention on calculating the cost of one specific production chain product. It suggested more technoeconomic investigation on multiple processes of product co-generation. Mupondwa et al. [103] reported that bioenergy research investigations and developments in Canada for biomass pretreatments and conversions into bioproducts using different technologies have recently shown significant growth. However, the study highlighted that there are challenges in designing business models and commercial bioconversion pathways based on various biomass feedstocks available. Despite the varieties of research that have been conducted on microwave pretreatment technique, the growth of industrial application of microwave heating is limited globally. Xu [31] reported that most pretreatment experiments still take place in domestic MW ovens except for few modified MW reactors which are used by less than 30 companies globally on the pretreatment of various feedstocks. The study on the TEA of MW-assisted alkali pretreatment is not available except for TEA on MW torrefaction and pyrolysis of biomass. Even with TEA on MW torrefaction or pyrolysis published papers displayed, an extensive literature search still showed limited information on the economic evaluation on the processes. Therefore, the technoeconomics of MW-assisted alkali pretreatment of biomass needs to be evaluated using available data to determine economic viability of the process, and this will be

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

http://dx.doi.org/10.5772/intechopen.79103

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one of the topics of research that our group will undertake.

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.

3. Summary

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

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

#### 2.5. Economic evaluation of microwave pretreatment process

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, and CHEMCAD [93].

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 holistic view of the emissions and resource requirements of a product system. Also, the importance of LCA study is to analyze the impact on the environment, energy consumption, and economic viability [94, 99]. Azapagic and Stichnothe [100] reported that LCA can be translated into quantitative measures of sustainability such as environmental, social, and economic. Different types of International Standard Organization (ISO) documents have been developed for LCA standards in providing flexible methodology and enabling modification of analysis by meeting up the goal and scope of the study [94, 97]. In the setting of innovation targets, the major impacts of LCA can be identified using these intensive products: raw material, manufacturing, distribution, the use of intensive product such as automobiles and laser printers, and disposal-intensive product [94, 100]. Many software, tools, and databases have been developed to assist in data processing and calculation of LCAs. These include Athena, BEES 4.0, CMLCA, Ecolnvent, EMIS, GaBi, GEMIS, IdeMAT, REGIS, SimaPro, and Umberto [101]. Many software are in market and many more are disappearing each year due to the dynamic nature and availability of the software [94]. Patel et al. [102] studied the technoeconomic and life cycle assessment of lignocellulosic biomass thermochemical conversion technologies. The study stated that a lot of research works are only focusing attention on calculating the cost of one specific production chain product. It suggested more technoeconomic investigation on multiple processes of product co-generation. Mupondwa et al. [103] reported that bioenergy research investigations and developments in Canada for biomass pretreatments and conversions into bioproducts using different technologies have recently shown significant growth. However, the study highlighted that there are challenges in designing business models and commercial bioconversion pathways based on various biomass feedstocks available. Despite the varieties of research that have been conducted on microwave pretreatment technique, the growth of industrial application of microwave heating is limited globally. Xu [31] reported that most pretreatment experiments still take place in domestic MW ovens except for few modified MW reactors which are used by less than 30 companies globally on the pretreatment of various feedstocks. The study on the TEA of MW-assisted alkali pretreatment is not available except for TEA on MW torrefaction and pyrolysis of biomass. Even with TEA on MW torrefaction or pyrolysis published papers displayed, an extensive literature search still showed limited information on the economic evaluation on the processes. Therefore, the technoeconomics of MW-assisted alkali pretreatment of biomass needs to be evaluated using available data to determine economic viability of the process, and this will be one of the topics of research that our group will undertake.
