Energy Procedia 32 ( 2013 ) 183 – 189

1876-6102 © 2013 The Authors. Published by Elsevier Ltd.Selection and peer-review under responsibility of the Research Centre for Electrical Power and Mechatronics, Indonesian Institute of Sciences.doi: 10.1016/j.egypro.2013.05.024

International Conference on Sustainable Energy Engineering and Application

[ICSEEA 2012]

Effect of pretreatment process by using diluted acid to characteristic of oil palm’s frond

Anis Kristiani*, Haznan Abimanyu, A. H Setiawan, Sudiyarmanto, Fauzan Aulia

Research Centre for Chemistry, Indonesian Institute of Sciences, Kawasan PUSPIPTEK Serpong, Tangerang 15314, Indonesia

Abstract

One of lignocellulosic biomass feedstock, oil palm’s frond is the raw material for a potential second-generation bio-ethanol production. Pretreatment process is an important process in series of process to produce bio-ethanol. This research aims to study the effect of pretreatment process by using diluted acid to oil palm’s frond characterization as raw materials in the hydrolysis reaction producing monomer sugars which will be fermented into ethanol. The raw materials are characterized in term of specific surface area and surface morphology. Analysis results of the specific surface area by BET (Brunauer Emmett Teller) method showed that after pretreatment by using diluted acid, their specific surface area increasing from 2.23 m2/g to 5.57 m2/g, while the surface morphology of the images shown by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) showed that there is changing the morphology of surface followed by the increasing of amorphous part. © 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Research Centre for Electrical Power and Mechatronics, Indonesian Institute of Sciences Keywords: Bioethanol; diluted acid; oil palm’s frond; pretreatment; spesific surface and surface morphology.

1. Introduction

Lignocellulosic biomass as a renewable energy resource has big potency for ethanol production because it is less expensive than starch (corn) dan sucrose (mollase) producing ethanol in high yield and abundance [1]. Lignocellulose is composed by cellulose, hemicellulose, lignin, extractive, and some

* Corresponding author. Tel.: +62-21-7560090; fax: +62-21-7560549. E-mail address: anis.kristiani87@gmail.com.

Available online at www.sciencedirect.com

© 2013 The Authors. Published by Elsevier Ltd.Selection and peer-review under responsibility of the Research Centre for Electrical Power and Mechatronics, Indonesian Institute of Sciences.

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inorganic materials [2]. Cellulose or -1-4-glukan is polysaccharide linear polymer from glucose composed by celobiose units [3,4]. Cellulose chain is wrapped by hydrogen bonding named elementer and microfibril [5]. These fibrils are attached one to another by hemicellulose, amorphous polymer from different sugar like other polymers, such as pectin and closed by lignin [3].

Microfibril is connected to macrofibril. This special and complicated structure caused cellulose being resistant to biology and chemistry treatments. Cellulose is available in lignocellulose or purified into paper or pure cellulose, such as cotton or blended by other materials [6].

Lignin is a complex molecule composed by fenilpropan units and connected to three dimentional structure which is difficult to be biodegradabled. Lignin is hard to be degradabled both of chemically and enzymatically. Soft wood contains more lignin than hard wood and mostly agriculture residue. Since there is chemical bonding between lignin and hemicellulose in fermentation so it makes lignocellulose to be resistant for chemical and biological degradation [7,8].

Ethanol production from lignocellulose biomass includes three main processes, which are pretreatment, hydrolysis and fermentation. Pretreatment process by physical, chemical and biological is one of the main processes in ethanol production process from lignocelluloses [9]. This pretreatment is needed to produce macroscopic and microscopic biomass structure for fast and efficient hydrolysis to fermentable sugar [10]. Pretreatment can effect bio-digestibility of waste for ethanol production and increase enzyme accessibility into material [11]. Pretreatment process also aims to break lignin and hemicellulose bonding and cystal structure to be simple sugar compound [12].

According to Nathan et.al [10] and Zheng et.al [23], pretreatment process by using diluted acid can dissolve almost all hemicellulose and break lignin and cellulose bonding so it can increase digestibility of enzyme/catalyst in hydrolysis process. Yang et.al use diluted sulfur acid in the chemical pretreatment process and this chemical pretreatment process can dissolve almost all hemicellulose component (80-90 %), increase suspectibility of cellulose, but little break lignin component [22]. Pretreatment process by using diluted acid can dissolve almost all hemicellulose, but not for lignin component [23].

The size of raw material will affect porosity so it will maximize contact between material and acid to increase hemicellulose hydrolysis rate. Since the smaller size of raw materials size will produce a large surface area, this will make the degradation process easier. Sun [12] has done pretreatment process for bagasse by 80 mesh. In this research, we will use lignocellulose from oil palm’s frond about 30-40 mesh.

Acid pretreatment can operate in high temperature and low acid concentration or in low temperature and high acid concentration. Sulfuric acid is commonly used, while other acids such as chloride acid and nitric acid have been reported. The pretreatment of lignocellulose in high temperature can increase enzymatic hydrolysis efficiently [13]. But, high acid concentration (30-70 %) makes the process to be more corrosive and dangerous. Therefore, this process needs a special non metal construction or expensive alloy [14-16].

Diluted acid hydrolysis perhaps is common method used in pretreatment method. It can be used well in lignocellulose pretreatment for enzymatic hydrolysis, or as actual sugar hydrolysis method. These processes and different aspects from diluted acid hydrolysis have been reviewed [13,17]. In a limit temperature (140-190 °C) and low acid concentration (0.1-1 % sulfuric acid), the pretreatment can reach high reaction rate and increase cellulose hydrolysis significantly. Almost 100 % removing hemicellulose is done by diluted acid pretreatment. Pretreatment is not effective to dissolve lignin but it can interfere lignin and increase cellulose suspectibility for enzymatic hydrolysis [14,18].

Diluted acid pretreatment can take place in short resistence time (5 minutes) at temperature of 180 °C or relative long resistence time (30-90 minutes) at temperature of 120 °C. Sun and Cheng [19] have done pretreatment of rye straw and grass to produce ethanol by using enzymatic hydrolysis at 121 °C with different concentration of sulfuric acid (0.6; 0.9; 1.2 and 1.5%, w/w) and residence time (30; 60; and 90 minutes). Emmel et al. [20] have done pretreatment Eucalyptus grandis impregnated by 0.087 and 0.175

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% (w/w) H2SO4 at 200–210 °C for 2 to 5 minutes. The best condition for recovering hemicellulose is at 210 °C for 2 minutes, while the optimum pretreatment temperature is at 200 °C.

The aim of pretreatment process is to change these properties for preparing materials of enzymatic degradation. Because of lignocelullose is so complex, pretreatment process needed is not simple. The best pretreatment method and condition depend on the type of lignocellulose. This research aims to study the effect of pretreatment process by using diluted acid to the characteristic of oil palm’s frond as a raw material in term of specific surface area and surface morphology.

2. Materials and experimental

2.1. Materials

Raw material of oil palm’s frond used in this research is oil palm’s frond from PT. Perkebunan Nusantara VIII (PTPN VIII) in Malimping, Lebak-Banten. While, chemical used pretreatment process is NaOH and H2SO4.

2.2. Instrumentation

Equipments used in this pretreatment process are milling-grinding machine, autoclave, glass equipments, Sorptomatic 1800 CARLO ERBA Instruments, XRD Phillip PW 1710 and SEM JEOL.

2.3. Procedure

A simplified process diagram is shown in Fig.1. Raw material used is oil palm’s frond will be pretreated physically by milling then chemically by using diluted acid, H2SO4. After neutralized by using NaOH, solid sample will be analyzed its chemical component and physical properties.

2.3.1. Milling (physical/mechanic pretreatment process)

Oil palm’s frond is cut into 2-3 cm then dried at 50oC for 24 hours and then milled by using milling-grinding machine and sifted to 30-40 mesh. Water content from oil palm’s frond resulted from milling process is measured and characterized.

Raw material

Physical/Mechanic Pretreatment Process

Chemical Pretreatment Process

Solid Part Liquid Part

Characterization

Fig. 1. Experimental process diagram

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Table 1. Chemical compound content of oil palm’s frond raw material

Characteristic Content (% w/w)

Lignin 29.50

Cellulose 40.01

Hemicellulose 30.78

2.3.2. Chemical pretreatment

In this research, we use pretreatment technology of oil palm’s frond by using diluted acid. Comparison between solid with liquid (S/L) ratio of 1:15 (w/v) use sulfuric acid concentration, H2SO4 of 0.25 until 2 % (v/v). The sample was put into autoclave at 121 oC for 30, 60, and 90 minutes. A slurry mixture with pH between 1 to 2 was neutralized to pH 7 by adding NaOH solution then the liquid and its solid was separated.

2.3.3. Characterization

Solid samples are analyzed their lignin, cellulose and hemicellulose content by using TAPPI T 13m-45 and ASTM 1104-56 method, specific surface area by using BET, surface morphology by using SEM, and crystalinity by using XRD methods.

3. Result and discussion

Lignocellulose biomass is composed by cellulose, hemicellulose and lignin connected each other because of amorphous structure and 1,4’- bonding in cellulose and also the existence of lignin between cellulose chain [10]. Analysis result of oil palm’s frond is shown in Table 1. Table 1 showed that cellulose content in oil palm’s frond raw material is higher than lignin and hemicelluloses [21]. Higher cellulose content in the sample can produce higher glucose, however hemicellulose content can also hydrolyze to xylose, while lignin can produce derivative compound of phenol. This research used a chemical pretreatment process using diluted sulfuric acid. The use of dilute sulfuric acid is dissolving most of the hemicellulose, increasing the susceptibility of cellulose, but breaking little of the lignin [22].

Figure 2 shows the influence of acid pretreatment to the composition of oil palm’s frond. As can be seen from the figure, a smaller percentage of hemicelluloses were at pretreatment condition of 2 % sulfuric acid at 30 minutes than at any other conditions. In fact, this condition accounted for 10 % of the hemicelluloses. On the other hand, the process condition of less than 2 % sulfuric acid accounted for 30 % of the hemicelluloses. In addition, the percentage of lignin was more or less same at any conditions. It is also show that percentage of cellulose changed with the hemicellulose content. It is caused by the addition of acid concentration broke the microfibril bonding of lignin and hemicellulose bonded in cellulose component so cellulose content will increase. Oil palm’s frond pretreated by using 2 % sulfuric acid has the highest cellulose and the lower lignin will be characterized their physical properties to observe the effect of pretreatment process.

Oil palm’s frond sample before and after pretreatment process are analyzed on their specific surface area by using BET method. Oil palm’s frond material has two type of specific surface area, which is external and internal. External specific surface area is related to particle size and shape; while internal specific surface area is depend on capiler structure of celullosic fiber. Specifically, dry cellulosic fiber has small size about 15 until 40 μm, and so it has external specific surface area which can be considered,

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about 0.6 to 1.6 m2/g. But, internal specific surface area of this dry celullosic fiber is smaller than external specific surface area [24].

Table 2 showed that pretreatment of oil palm’s frond by using 2 % H2SO4 for 30 minutes increase specific surface area of raw material. Specific surface area measured by this BET method is external specific surface area. Higher specific surface area will make contact between raw material and solvent to be effective so hydrolysis reaction will be more optimal. Figure 3 and 4 showed the SEM micrograph and XRD profile of oil palm’s frond before and after 2% H2SO4 pretreatment. The goal of the pretreatment process is to break down the lignin structure and disrupt the crystalline structure of cellulose, so that the acids or enzymes can easily access and hydrolyze the cellulose [10].

Fig. 2. Chemical content in oil palm’s frond after H2SO4 pretreatment at 121°C for 30 minutes [21]

Table 2. Specific surface area of oil palm’s frond before and after H2SO4 pretreatment

Sample Specific Surface Area (m2/g)

Raw material oil palm’s frond 2,2334

Pretreated oil palm’s frond 5,5670

Fig. 3. SEM micrograph and XRD profile of oil palm’s frond before H2SO4 pretreatment

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The effect of the pretreatment is to change their morphology and crystalinity. As can be seen from the SEM micrograph at 100 micrometer scale, it is clear the change of their morphology before and after pretreatment process. The peaks at 2 = 15° is the amorphous peak and the peak of 2 = 23o is the crystal peak. From the figures, it may be calculated that the ratio between amorphous peak and crystal peak before pretreatment more than their ratio after pretreatment process. On this basis, it may be concluded that the pretreatment process could increase the amorphous part and consequently decrease the crystal part of oil palm’s frond morphology. The amorphous part will make cellulose more accessible to the enzyme that converts the carbohydrate polymers into fermentable sugars.

4. Conclusion

Pretreatment process of oil palm’s frond by using diluted acid, H2SO4 2 % at 121 0C for 30 minutes increase the specific surface area, from 2.23 to 5.57 m2/g, and changing the morphology surface, which is probably decreasing crystalinity of cellulose molecule.

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