**2. Lignocellulosic biomass from weedy plants: chemical composition and potential for bioethanol production**

The major components of lignocellulosic biomass are cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are the main carbohydrates in lignocellulosic biomass. The contents of these components vary significantly depending on the type of biomass and source [6]. Cellulose is a crystalline and linear structure made up of units of glucose strongly linked together by β-1-4-glycosidic bonds. These linkages give cellulose very high crystalline structure making it resistant to degradation. It is the most abundant organic polymer on earth. Hemicellulose on the other hand, consists of linear and highly branched mixture of pentoses (xylose and arabinose) and hexoses (glucose, galactose, and mannose). Lignin is a highly branched polyphenolic polymer, which gives stability to biomass structure [12]. Cellulose and hemicellulose, the major substrates for bioethanol production, form the main components of the total dry weight of lignocellulosic biomass [7]. These fractions are linked together by covalent and hydrogen bonds, which are further strongly bonded to lignin. This gives lignocellulosic biomass a very complex structure, which is very resistant to degradation. Digestibility of lignocellulosic biomass is therefore affected by the degree of complexity and composition [11]. The structure and composition of different lignocellulosic biomass differ and this greatly affects the efficiency of their conversion to bioethanol.

Lignocellulosic biomass from weedy plants is one of the most sustainable alternative feedstock for bioethanol production [12]. Annual and perennial weedy plants are found all over the world at all seasons. They invade large areas of land and water bodies causing environmental and socioeconomic problems [2]. They grow rapidly on marginal lands under extreme conditions such as drought, low nutrient and high temperatures, hence requiring no additional economic input such as fertilizer and pesticides [7]. Weed biomass contains large amounts of chemicals and materials, which can be extracted for several industrial applications [13]. These plants have been reported to produce high dry matter yield and contain high and low percentages of cellulose and lignin contents, respectively [14]. The high dry matter

Bioethanol is currently the most widely used liquid biofuel [4]. It is an eco-friendly and renewable fuel produced from plant-based starches and sugars [5]. Global production of bioethanol is mainly from food-related crops such as corn, cassava, sugarcane, rice, and sweet potatoes [3]. However, these feedstock are directly consumed by humans as food or as animal feed. Continuous use of these crops for bioethanol production may put pressure on productive agricultural lands and result in higher food prices [6]. Concerns about sustainability of bioethanol production from food-related crops have raised attention to the potential of lignocel-

Lignocellulosic biomass is inexpensive and abundant worldwide. It includes agricultural and forestry waste, grasses, and other nonfood plants [8]. This type of biomass is a rich source of biopolymers, chemicals, and sugars [9]. Current research into bioethanol production is mainly focused on assessing the potential of nonfood crops as feedstock and improving the efficiency of their conversion [10]. Lignocellulosic biomass from invasive weeds is a good feedstock for the economic production of bioethanol [2]. These weedy cellulosic substrates do not need extra expenses as they grow on agriculturally degraded land or water bodies [11]. Large numbers of such invasive species are found all over the world. The potential of weed biomass for the production of bioethanol has been explored and discussed in this chapter.

**2. Lignocellulosic biomass from weedy plants: chemical composition** 

and this greatly affects the efficiency of their conversion to bioethanol.

The major components of lignocellulosic biomass are cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are the main carbohydrates in lignocellulosic biomass. The contents of these components vary significantly depending on the type of biomass and source [6]. Cellulose is a crystalline and linear structure made up of units of glucose strongly linked together by β-1-4-glycosidic bonds. These linkages give cellulose very high crystalline structure making it resistant to degradation. It is the most abundant organic polymer on earth. Hemicellulose on the other hand, consists of linear and highly branched mixture of pentoses (xylose and arabinose) and hexoses (glucose, galactose, and mannose). Lignin is a highly branched polyphenolic polymer, which gives stability to biomass structure [12]. Cellulose and hemicellulose, the major substrates for bioethanol production, form the main components of the total dry weight of lignocellulosic biomass [7]. These fractions are linked together by covalent and hydrogen bonds, which are further strongly bonded to lignin. This gives lignocellulosic biomass a very complex structure, which is very resistant to degradation. Digestibility of lignocellulosic biomass is therefore affected by the degree of complexity and composition [11]. The structure and composition of different lignocellulosic biomass differ

Lignocellulosic biomass from weedy plants is one of the most sustainable alternative feedstock for bioethanol production [12]. Annual and perennial weedy plants are found all over the world at all seasons. They invade large areas of land and water bodies causing environmental and socioeconomic problems [2]. They grow rapidly on marginal lands under extreme conditions such as drought, low nutrient and high temperatures, hence requiring no

lulosic biomass for bioethanol production [7].

84 Fuel Ethanol Production from Sugarcane

**and potential for bioethanol production**


**Table 1.** Chemical composition and theoretical ethanol yields of weed biomass.

yield and cellulose contents of weedy plant species make them ideal feedstock for bioethanol production. They also have an added advantage as feedstock for bioethanol production since they do not compete with food crops for productive agricultural lands [15]. Moreover, due to seasonal nature of agricultural wastes, lignocellulosic biomass from weed species is very important in ensuring continuous production of bioethanol throughout the year [16]. A wide range of weedy species are grown naturally on marginal lands all over the world that can be used as feedstock for bioethanol production. Perennial grasses and short rotation forest plants are among these weedy species growing worldwide [17]. The possibility of converting biomass from invasive weeds to fuel bioethanol is currently an area of great research interest around the world. The physical characteristics and bioethanol production potential of several weedy species have been studied.

sugars to bioethanol [26]. Unlike first generation bioethanol production where carbohydrates are easily converted to bioethanol, carbohydrate portions in weed biomass are not freely available for the conversion to bioethanol. Biological conversion of weed biomass to bioethanol involves various processes (**Figure 1**). The major steps involved in the conversion process include pretreatment of biomass to make it easily digestible in subsequent processes. The cellulose and hemicellulose contents are then hydrolyzed to monomer sugars followed by the fermentation of sugars to bioethanol. Finally, bioethanol is purified through distillation or other processes such as dehydration to conform to world bioethanol specifications [27].

Potential of Weed Biomass for Bioethanol Production http://dx.doi.org/10.5772/intechopen.77507 87

Like most lignocellulosic biomass, the recalcitrance of weed biomass is a major problem in their conversion to bioethanol. This is due to the crystalline structure of cellulose coupled with lignin and hemicellulose strongly bonded to each other and serving as a protective cover to cellulose. The pretreatment of weed biomass is thus very important in releasing fermentable sugars for bioethanol production [6]. It helps to break the bond between lignin and hemicellulose, hence destroying the protective cover of cellulose. It also helps to decrease cellulose crystallinity making it more susceptible to enzymatic hydrolysis and fermentation [12]. Different pretreatment methods can be used on various types of weed biomass for bioethanol

**Figure 1.** Schematic diagram of major steps in weed biomass conversion to bioethanol.

**3.1. Pretreatment of weed biomass**

*Parthenium hysterophorus*, a common invasive weed species was studied in India as a potential feedstock for bioethanol production. Chemical composition analysis of this weed species revealed 53.63% holocellulose and 10.44% lignin contents, making it an attractive feedstock for production of bioethanol [18]. *Cannabis sativa*, a versatile weedy plant, grows naturally in large areas in Pakistan. It produces large amount of biomass due to its rapid growth rate. *Cannabis sativa* contains 55% cellulose and only 5% lignin. It has been reported as a potential cheap and eco-friendly feedstock for bioethanol production in Pakistan [19]. *Pennisetum purpureum*, commonly known as Napier grass or elephant grass, *Vetiveria zizanioides* also known as vetiver grass, *Digitaria decumbens*, *Paspalum atratum*, *Cynodon* sp., and *Pennisetum polystachyon* are all weedy species found in Asia that have been studied and proposed as feedstock for bioethanol production [12].

In an earlier research, different types of weedy plants were identified in six provinces in lower Northern Thailand (**Table 1**). Majority of these weed biomass were found to contain high cellulose but low lignin contents. The cellulose contents of most of these weed biomass is higher or similar compared to well-known lignocellulosic materials from agricultural residues including corn stalk bagasse (43.4%) [20], corncob (31.5 ± 1.2%) [21], wheat straw (35.2 ± 0.3%) [22], paddy straw (32.6%) [23], soybean straw (34.40%) [24], and sugarcane bagasse (27.3%) [25]. High theoretical bioethanol yields were also estimated for these weed biomass based on the contents of cellulose and hemicellulose. Bioethanol yield of between 548.4 ± 1.4 and 394.0 ± 5.3 L/ton was realized from some of the weed species [14]. Majority of these weed species are potential substrate for bioethanol production.
