Chapter -II Physico-chemical Characterization of
2.1 Introductionand review of literature
Chapter -II
Depending on the geographical regions and environments or food habit of the local people the sources of biomasses are diverse; it may be agricultural waste products, forest residues, dedicated energy crops or combinations of thereof. The major advantage of energy production from agricultural waste or forest residues is negligible raw material cost. It is a win -win situation for both the energy producer and raw material harvesters.
Therefore, research is going on to search for suitable agricultural wastes or forest residues, which can be utilized as renewable energy sources. The major lignocellulosic biomass species available in North -East region of India are bamboo, sugarcane, rice husk. All these biomass materials are the proven source of bio energy. Though these materials are plenty in nature, but to put more stress on these materials to generate energy is not beneficial for the dwellers in North East India, as all those crops require a systematic cultivation process which demands a huge dedicated cultivation lands apart from sound agricultural knowledge to cultivate. The present economic, social and geographical scenario of the North-east India may not cope up with such systematic cultivation system. The North-East India is well known throughout the world for its biological diversity, several forests and agricultural waste products exists here, fuel woods hold a consequential function in the societies abode at higher reaches of North East India, not only for cooking but also for heating and other day to day activities. There is a conspicuous lack of knowledge with regard to the biomass characteristics of indigenous tree and shrub species present in the forests and several provinces of North- East India, which retards to set up biomass based energy plants. In order to exploit the biomasses harvested from North-East India for its fermentable sugar and other valuable chemicals the chemistry of lignocellulose must be understood.
Cellulose consists of long chains of hydro-D-glucopyranose units (AGU) with each cellulose molecule having three hydroxyl groups per AGU, with the exception of the terminal ends[1]. The polymer contains three reactive hydroxyl groups at the C-2, C-3, and C-6 atoms, which are, in general, accessible to the typical conversions of primary and secondary alcoholic OH groups [2]. The un-branched β1-4 linkage results in linear chains that are stabilized by hydrogen bonds within the chain and between neighboring chains.
A cellulose molecule may contain more than 104 glucose residues (mass 1–2 ×106 Da) and can reach lengths of 6–8 μM.
Hemicelluloses are heterogeneous branched chain polymers of pentoses (xylose, arabinose), hexoses (mannose, glucose, galactose), and sugar acids, located beside cellulose as an amorphous mass. In contrast with cellulose, hemi-cellulose differs, in consisting primarily of xylose and other five-carbon monosaccharides. Hardwood hemicelluloses contain mostly xylans, whereas softwood hemicelluloses contain mostly glucomannans. The degree of polymerization and concentration of building block such as monosaccharide varies from plant to plant. The xylan of hemicellulose could be extracted quite well in an acid or alkaline environment, while glucomannan can hardly be extracted in an acid environment and needs a stronger alkaline environment than xylan for extraction[3]
Fig. 2.1Picture of selected lignocellulosic biomass (a) Areca nut (b) Bonbogori (c) Moj
Lignin is a complex high molecular weight polymer of coumaryl, conferyl and sinapyl alcohol. The concentration of these alcohols varies with plant to plant. This polymer intimately associated with cellulose and hemicellulose and imparts physical strength to the plant. The solubility of the lignin in acid, neutral or alkaline environments depends however on the precursor (p-coumaryl, coniferyl, sinapyl alcohol or combinations of them) of the lignin [4].
The present study focused on three biomass samples namely Arecanut husk,bon bogori and Moj. The Arecanut husk is well known as an agricultural waste residue in North-East India.Betel nut (Arecan Catechu), also known as Areca nut (Fig.2.1 (B)), has applications in human and animal medicine and is used in the paint and leather industries [5].Areca is a genus of about 50 species of single-stemmed palms in the family Arecaceae, found in humid tropical forests.The well-known member of the genus is A. catechu, the Areca nut palm. Several species of Areca nuts, known for their bitter and tangy taste, raw or dried are routinely used for chewing. These nuts are widely used as a popular masticator in India and Pakistan. India is the largest producer of Areca nut in the world. Karnataka tops the list of Areca nut producing states with 40 per cent of the country’s total output. India is also the largest consumer of it in the world at 3.2 lakh tones a year. The total area under the crop is estimated at 2.7 lakh hectares and the annual production is estimated at around 3.3 lakh tones, with Karnataka and Kerala accounting for nearly 72 per cent of total output. Over six million people are engaged in Areca nut cultivation, processing and trade. More than 85 percent of the area under cultivation is made up of small and marginal holdings [6]. The Areca nut husk is considered as an agricultural waste product. The nut has commercial importance and is processed by boiling the whole nut. The husk of the fruit is removed and it has no other traditional use. Husks are left in piles to dry; it is often a nuisance to the processor. The large amount of solid husk, formed during separation of kernel from the fruit, disposed without any treatment, though this lingocellulosic material contains a good amount of fermentable sugar (21%) [7]. Therefore, a number of wide opportunities exist to use this so-called agricultural waste material as a feedstock for bio-energy production.
Bon bogori and Mojare the rapid growing trees found in subtropical and tropical regions of world. Both these plants are common flora in Assam and other states of North- East India. Local tribal people and villagers traditionally preferred it as fuel wood.The major advantage of using such kind of biomass is its availability and there will be no upheaval for collection and formation of bio-refinery.
The present study deals with few important characteristics of lignocellulosic biomasses which are significant for biofuel production, e.g. crystalinity, thermogravimetric analysis (TGA) and Fourier transformation infrared (FTIR) study etc.