Nonionic surfactants have been utilized to improve the enzymatic hydrolysis of lignocellulosic materials. However, the role of surfactant adsorption affecting enzymatic hydrolysis has not been elaborated well. In this work, nonionic surfactants differing in their molecular structures, namely the polyoxyethylene sorbitan monooleate (Tween 80), the secondary alcohol ethoxylate (Tergitol 15-S-9), and the branched alcohol ethoxylate (Tergitol TMN-6), were studied for their effects on the enzymatic hydrolysis of palm fruit bunch (PFB). The PFB was pretreated with a 10% w/v sodium hydroxide solution and then hydrolyzed using the cellulase enzyme from Trichoderma reesei (ATCC 26921) at 50 °C and pH 5. The optimal conditions providing similar yields of reducing sugar required Tween 80 and Tergitol TMN-6 at 0.25% w/v, while Tergitol 15-S-9 was required at 0.1% w/v. All the surfactants improved the enzymatic conversion efficiency and reduced unproductive binding of the enzyme to lignin. In addition, the adsorption isotherm of cellulase was fit well by the Freundlich isotherm, while adsorption of the three nonionic surfactants agreed well with the Langmuir isotherm. Adsorption capacities of the three nonionic surfactants were consistent with their enhancement efficiencies in hydrolysis. The critical micelle concentration was observed as a key property of nonionic surfactant for adsorption capacity.
Palm fruit bunch (PFB) and palm fruit residue (PFR) are considered as potential raw materials for ethanol production due to their large availability from palm oil industry. However, the presence of lignin can retard the rate of enzymatic hydrolysis. Both PFB and PFR were pretreated with a 10% w/v sodium hydroxide solution. The amounts of their hemicellulose were substantially decreased whereas their lignin contents were slightly reduced. After that, they were hydrolyzed using cellulase from Trichoderma reesei (ATCC 26921) at 50 °C and pH 5. An addition of Tween 80, nonionic surfactant, with 0.25% w/v concentration provided an increase in reducing sugar production about 50.5% at 10 FPU/g PFB cellulase loading, while the addition of Tween 80 with 0.5% w/v concentration increased reducing sugar production by 38.8% at 20 FPU/g PFR cellulase loading. The greater the amount of lignin in the lignocellulosic materials, the higher the dosages of enzyme and surfactant required for the enzymatic hydrolysis. The adsorption of added nonionic surfactant onto the hydrophobic surface of lignin resulted in an increase in the availability of added enzyme to both cellulose and hemicellulose, leading to the enhancement of enzymatic hydrolysis. Additionally, the adsorption of cellulase on PFB and PFR were well fitted with the Freundlich isotherm.
Abstract-Palm fiber is a lignocellulosic material, which is available in large quantity from oil palm industry. Due to its cellulosic structure, it is considered as a highly potential alternative material for ethanol production. Thus, the palm fiber is utilized as a raw material in this study. The palm fiber is obtained from local industry and mechanically ground to reduce the size in the range of 0.417-1 mm. Then, it is pretreated with 10% sodium hydroxide. Then, it is further utilized in the enzymatic hydrolysis. The commercial cellulase enzyme (Trichoderma reesei) is employed in this study. The nonionic surfactant (Tween80) is applied to enhance the conversion of cellulose to sugar. In the experiment, the effects of enzyme loading, surfactant concentration, and hydrolysis time on sugar yield are investigated at 50 C and pH 5. By employing the response surface methodology, optimum sugar yield was obtained at as high as 67.65 % from palm fiber at 107 h hydrolysis time, 20 FPU/g substrate enzyme loading, and 7.39 g/L surfactant concentration.Index Terms-Palm fiber, ethanol, enzymatic hydrolysis, nonionic surfactant, response surface method.
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