Bamboo charcoal - LITERATURE REVIEW - PREPARATION, MODIFICATION AND CHARACTERIZATIONOF BAMBOO C

CHAPTER 2: LITERATURE REVIEW

2.2 Bamboo charcoal

2.2.1 Bamboo

Bamboo is one of the well-known plant resources of the grass family, grown in the different geographical locations in the world. The bamboo is distributed in tropical and subtropical to mild temperate regions, with the heaviest concentration and the largest number of species in the East and Southeast Asia and on islands of the Indian and Pacific oceans. There are about 22 million hectors of bamboo forest area in the worldwide.

According to the botanical taxonomy, bamboo plant is recognized as species of Bambusoideae subfamily and its family is Gramineae [25]. Bamboo is one of the rapidly growing plants and its mature time is 4 to 8 months. The optimum specific gravity and mechanical properties are obtained during its mature period. Bamboo is a sort of renewable, eco-friendly, and cheap resource for sustainable development.

The Japanese moso bamboo is known by the scientific names ‟Phyllostachys Pubescensˮ and ‟Phyllostachys Edulisˮ. Moso bamboo is mostly grown in Japan and China among the South-East Asian countries. Wide applications of bamboo are observed as household products and many industrial uses due to the increase of extensive demands for availability, price, and flexible uses. In Asian countries, the bamboo has been used for household utilities such as containers, chopsticks, woven mats, fishing poles, cricket boxes, handicrafts, chairs, etc. It is also used in building applications such as flooring, ceiling, walls, windows, doors, fences, housing roofs, trusses, rafters, and purlins.

Bamboo is one of the important raw materials in papers industries.

2.2.2 Chemical composition of bamboo

The chemical composition of bamboo is similar to that of wood. The main components of bamboo culms are cellulose, hemicellulose, and lignin, which amount to over 90% of the total mass. A minor portion of resins, tannins, waxes and inorganic salts are also contained. Moreover, the higher alkaline extractives, ash and silica contents are

19 comparable with wood. The other chemical constituents are about 2-6% starch, 2%

deoxidized saccharide, 2-4% fat, and 0.8-6% protein [26]. The presence of carbohydrate plays a key role in its high level of durability and serviceability. The durability of bamboo against mold, fungal and borers attack is strongly associated with its chemical composition. The resistance of bamboo to fungal and insect attack is poor. The natural durability of bamboo varies between 1 and 36 months depending on the species and climatic condition [27]. The presence of large amounts of starch makes bamboo highly vulnerable to attack by staining fungi and powder-post beetles. Higher benzene-ethanol extractives of some bamboo species could be an advantage for decay resistance [28].

2.2.3 Production of bamboo charcoal

Bamboo is one of the lignocellulosic plant materials. The preparation process of activated carbon from lignicelluosic materials generally involved two processes, the carbonization, and activation. The carbonization process involves pyrolysis of the precursor’s material at a certain temperature in the absence of air. The basic steps of bamboo charcoal production are shown in Figure 2.4. During the carbonization process, the fundamental porosity is developed on the carbon structure. Besides, most of the non-carbon elements such as oxygen, hydrogen and nitrogen in form of gases and tars, leaving a rigid carbon skeleton formed by aromatic structures [29].

In the activation process, generally the surface area and surface functional properties are increased by physical and chemical activation. In the physical activation process, the pyrolyzed carbon char from carbonization process is heated at temperature 400°C to 900°C in the inert gas flow [30]. Many inert gases such as nitrogen, carbon dioxide, water steam etc. are commonly used for the physical activation process. In the chemical activation process, usually carbonization and activation process is performed simultaneously [31]. The raw materials are impregnated with activation chemical as well the carbonization process is progressed at high temperature in an inert gas flow. In this case, H3PO4, H2SO4, HNO3, NaOH, KOH, and H2O2 are mostly used as activation chemicals. However, in this study bamboo charcoal prepared by carbonization process.

The activation (physical and chemical) process performed separately due to understanding the physical changes that subjected to activation or chemical modification

20 [32]. It is well established that the high carbonization temperature would result in a greater amount of volatiles being released from raw materials and eventually produce a highly porous carbon with a surface basicity. However, carbonization at lower temperature generally produces a slightly acidic surface of the charcoal materials.

Moreover, there is also a risk for less decomposition of volatiles materials and improper carbonization. Therefore, proper carbonization temperature selection is mostly important depending on the applications of the charcoal materials.

Figure 2.4: The basic steps of bamboo charcoal production.

2.2.4 Characteristics of the physical and chemical activation process

The main aim of the activation process is to increase the adsorption properties of charcoal materials by changing their physical or chemical functionalities. The major advantages and drawbacks of the physical and chemical modification process are presented in Table 2.4.

Raw bamboo

Cut into small chips Drying Carbonization at

over 350˚C

Carbonizedchips

Crushing

Bamboo charcoal

21 Table 2.4: Advantages and disadvantages of different activation processes.

Activation process Advantages Disadvantages

Physical

 Increase porosity and surface area

 The process is not corrosive

 A washing stage is not required

 Process is cheap; no chemicals are required.

 Need higher temperature for activation

 Proper control of porosity of the charcoal is difficult

Chemical

 Improved surface functionalities.

 shorter activation time

 Better control of textural properties

 Activation carbons are obtained in one step or two steps

 Corrosiveness of the process

 Required a washing stage

 Inorganic impurities

 More expensive 2.2.5 Application of bamboo charcoal for environmental remediation

Wastewater treatment has become a serious environmental issue due to the rising of the environmental consciousness all over the world. Bamboo charcoal is an eco-friendly, low-cost and renewable bioresource with the porous structure. The uses of bamboo charcoal have been increased rapidly in the recent years for the several reasons;

(1) the use of wood charcoal has been reduced rapidly and almost exhausted; (2) the harvest cycles of the bamboo is short and it grows fast. Therefore, it does not have any influence on the deforestation and environment; (3) a surface area of porous bamboo charcoal is wider than wood charcoal. Hence, it is easily replaceable with hardwood charcoal. The application of bamboo charcoal is observed a variety of fields that include food, pharmaceutical, chemical, metallurgical industries, purifying drinking water, indoor humidity control, health care, and odor adsorption etc. In the last few years, bamboo charcoal has drawn interest to the researchers as a novel adsorbent for environmental remediation due to its special microporous structure [33][34]. Some applications of bamboo charcoal as adsorbents are listed in Table 2.5.

22 Table 2.5: Applications of BC as an adsorbent.

Carbonization temperature

of bamboo charcoal Modification Applications Ref.

800˚C and 600˚C ˗ Removal of copper, lead,

chromium and cadmium [35]

Pre-carbonization 150-270°C and carbonization 270°C and 450°C

Modification with H2SO4 and NaOH

Adsorption of

chloramphenicol (CAP) [36]

600°C, 700°C, 800°C,

900°C, and 1000°C ˗

Removal of carbon