|Andre Fahriz Perdana Harahap||Bioprocess Engineering Program, Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Azhar Aditya Rahman||Bioprocess Engineering Program, Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Isni Nur Sadrina||Bioprocess Engineering Program, Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
Oil palm empty fruit bunch (OPEFB) is one of the prominent lignocellulosic wastes from the oil palm industry, and it has the potential for feedstock in biobased products. However, delignification must be applied. This study investigated the effect of microwave-assisted alkaline pretreatment of OPEFB by using response surface methodology with Box-Behnken design (BBD) to find the optimum pretreatment conditions. OPEFB (30-mesh) was treated with various concentrations of aqueous sodium hydroxide. The effect of three variables, microwave power (280-840 W), NaOH concentration (1-3% w/v), and reaction time (3-9 min), was evaluated to improve lignin removal. The quadratic model indicated that microwave power of 832.9 W, NaOH concentration of 2.7% (w/v), and a reaction time of 8.9 min resulted in the highest lignin removal: 88.10%. FTIR and SEM analysis was also conducted on the untreated and treated OPEFB to evaluate the effectiveness of the pretreatment. These results showed that microwave-assisted alkaline pretreatment of OPEFB could effectively remove the lignin under a relatively short time period and low alkaline concentration.
Alkaline pretreatment; Lignin; Microwave; Oil palm empty fruit bunch; Response surface methodology
The palm oil industry continues to grow in response to increased consumption and demand for palm oil. During the processing of palm oil, OPEFB is produced as solid waste. As lignocellulosic biomass, OPEFB contains 39.8% cellulose, 17.3% hemicellulose, and 28.8% lignin (Kim, 2012). OPEFB has great potential to be utilized for the production of various biochemical products. OPEFB has been specifically used as feedstock for the production of levulinic acid and furfural; the highest yields were 52.1 mol% (C6 sugar basis) and 27.94 mol% (C5 sugar basis), respectively (Gozan, 2018). OPEFB can also be used as a carbon source for the growth medium of microorganisms like Saccharomyces cerevisiae to produce bioethanol with the highest yield: 24% (glucose basis) (Hermansyah, 2015).
Due to the complex lignocellulose structure of OPEFB, pretreatment is required to remove the lignin, increase the surface area, and increase the lignocellulose’s porosity. This process will make both cellulose and hemicellulose readily available for conversion. Alkaline pretreatment is known to be an efficient method for delignification due to its capability for lignin solubilization and swelling formation of treated biomass. Alkaline pretreatment of OPEFB has been performed with either aqueous ammonia or sodium hydroxide for delignification and sugar production by means of conventional heating (Zulkiple, 2016). Microwave-assisted alkaline pretreatment is widely used because of its advantages, including high heating efficiency, rapid heating, and easy operation. Microwave-assisted alkaline pretreatment of OPEFB by using 3% NaOH could remove 74% of the lignin at a microwave power of 120 W in 12 min. This is significantly better than using conventional heating, which only removes 69% of the lignin with the same NaOH concentration at 50°C for 80 min (Nomanbhay, 2015). Although there has been some research regarding microwave-assisted alkaline pretreatment of OPEFB, the application of Response Surface Methodology (RSM) in this study was still less, thus making application more important.
This study focuses on the optimization of important variables of OPEFB microwave-assisted alkaline pretreatment: microwave power, NaOH concentration, and reaction time. The results were statistically processed using Response Surface Methodology (RSM), which had been used previously to study the effect of alkaline treatment on the physical properties of OPEFB (Fatra, 2016). The use of RSM to study the microwave-assisted alkaline pretreatment of OPEFB is appropriate because there are some external parameters affecting this process. By using RSM, effective research can be achieved through the avoidance of higher prices, longer duration, and repetition. The obtained BBD was very effective in determining the amount of research that should be carried out by using a formula that consists of a simple combination. Optimization using response surface design by BBD required random research in terms of dependent variable combinations to systematically diminish the error applied previously when studying the optimization of palm oil mill effluent electrocoagulation (Lubis, 2018).
This study showed that microwave-assisted alkaline pretreatment using sodium hydroxide was effective in removing lignin from the lignocellulose structure of OPEFB within a short period of time. The model obtained from this experiment shows that to achieve the highest lignin removal of 88.10%, the optimal conditions for the pretreatment are a combination of microwave power at 832.9 W, a NaOH concentration at 2.7% (w/v), and a reaction time of 8.9 min. The result was further confirmed by analysis of FTIR and SEM, which showed that microwave-assisted alkaline pretreatment caused chemical and morphological structure changes to OPEFB in terms of lignin removal.
This research was partially funded by BPDP Sawit Indonesia (Contract No: PRJ-20/DPKS/2018) and USAID through the SHERA program: Center for Development of Sustainable Region (CDSR). In year 2017-2021, this is led by the Center for Energy Studies-UGM.
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