3.2.3. Effect of methanol addition

The addition of methanol at the initial pulping stage enhances chemical penetration into the woody chips by increasing the solubility of lignin, subsequently, producing a uniform (homogeneous) chemical performance in the cooking time and also suppresses the dissociation of the inorganic pulping chemicals. The trapped air from the woody cells could be removed by raising the pressure of the digester, thus accelerating the penetration of chemicals into the wood cells [44, 45].

In ASAM pulping, it is important to ensure that alkali has penetrated into the center of the chip prior to rising the temperature above 140C, since undesirable lignin condensation reactions can occur at high temperatures in the absence of alkali [46, 47]. The use of methanol is preferred over ethanol in ASAM pulping protocol because of the lower boiling point that results in lower energy consumption for recovery. In addition, compared to ethanol, methanol has less viscosity, polarity and surface tension. The low surface tension and increased pressure, together with the ability of methanol to dissolve resins, have a positive impact on the penetration of chemicals into the chips [48, 49].

Apart from enhancing chemical penetration during pulping, Sridach [50] discovered that methanol also improves the cellulose stability in the ASAM pulping, hence producing pulp with higher viscosity. This was achieved by suppressing, stopping the reaction or slowing down the transformation of the cellulose aldehydic functional groups into keto groups that initiate the peeling reaction. Due to the use of methanol in the cooking liquor, more penetration of chemicals into the chips occurs. Raising pressure of the digester and more air removal of chips are the two main ways of improving the penetration of chemical materials into wood or non-wood chips. Therefore, adding methanol while an ASAM cooking liquor is in the process of penetrating the chips leads to a higher pressure of the digester. As a result, the entrapped air of the chips is displaced, and chemical materials can penetrate into both wood and non-wood chips. Consequently, more delignification happens and fibers can be easily separated [51].

#### 3.2.4. Advantages of ASAM pulping

or sodium peroxide in the ASAM pulping process have been reported. The advantage of sodium hydroxide in ASAM pulping is that NaOH tends to accelerant delignification than sodium carbonate; furthermore, by applying NaOH as a source of alkali charge, the initial pH of the white cooking liquor enhances leading to the dissolution of more lignin and carbohy-

Apart from the substitution of sodium hydroxide with sodium carbonate in ASAM pulping, attempt has been made with the use of sodium peroxide. It was reported that sodium carbonate substitution gave better pulp products due to the fact that the sodium carbonatesubstituted ASAM mixture gave pulp with the stronger tensile index, higher pulp yield and higher brightness [39] due to greater delignification process. This results from the fact that solution of acid soluble lignin contributed to lignin dissolution. The relatively low pH of spent liquor at high temperature results in the partial cleavage of α-ether bonds in lignin [40, 41]. On the other hand, the use of alkaline sodium sulfite as an additive in the ASAM process produces a low Kappa number, high pulp yield and high brightness. In addition, the production cost is

The addition of anthraquinone (AQ) in white cooking liquor increases the delignification rate due to the rate of decrease in the lignin content of wood or non-wood as the alkali consumption during the alkaline pulping process progresses. This can be divided into three phases: (1)

In the initial reaction phase, alkali is consumed in deacetylation reaction, in neutralization of wood or non-wood acids and in dissolution of readily soluble wood or non-wood carbohydrate components (hemicellulose, tannins, etc.); hence, very little actual delignification occurs. More lignin is eliminated in the period of bulk delignification phase. This elimination occurs much more quickly than the third stage (residual delignification) [41, 42]. As a result, the proportion of lignin removal in polysaccharides happens slowly. Thus, this is only true when a sufficient amount of alkali charge is available. Thereupon, by adding AQ to the cooking liquid, more alkalinity can be stored for the bulk delignification volume and more lignin can be removed [38, 42]. On the other hand, AQ has the role of an effective stabilizer in both wood and non-wood polysaccharides. AQ is effective at extremely lower dosage levels of 0.05–0.1%

The addition of methanol at the initial pulping stage enhances chemical penetration into the woody chips by increasing the solubility of lignin, subsequently, producing a uniform (homogeneous) chemical performance in the cooking time and also suppresses the dissociation of the inorganic pulping chemicals. The trapped air from the woody cells could be removed by raising the pressure of the digester, thus accelerating the penetration of chemicals into the

also significantly reduced and the total alkalinity consumption becomes less [38].

initial reaction, (2) bulk delignification and (3) residual delignification.

on oven-dry wood, giving good results in most cases [43].

3.2.3. Effect of methanol addition

wood cells [44, 45].

drates (hemicellulose) [38].

16 Bamboo - Current and Future Prospects

3.2.2. Effect of anthraquinone (AQ) addition

In comparison with kraft pulping process, the ASAM pulping process has a higher digester pressure of 1.3–1.4 MPa and the cooking temperature of 5–10 [42]. Several studies have considered the application of ASAM in the cooking process of both hard and soft wood. Moradbak et al. [42] reported that Eucalyptus globulus had been cooked by ASAM pulping process, which results in 56.9 and 53.6% pulp yield and 14 and 10 Kappa number, respectively. Pulp yield and Kappa number of Pinus sylvestris were found to be from 52.9 to 52.5% and from 31 to 27, respectively [52].

Several reports have shown some of the unique advantages of ASAM pulping process. These include (i) prevention of air pollution, (ii) high delignification rate, (iii) high brightness of pulp, (iv) high pulp yield and (v) ease of pulp bleaching [53].
