Scholarly article on topic 'Ethanol and Methane Production from Oil Palm Frond by Two Stage SSF'

Ethanol and Methane Production from Oil Palm Frond by Two Stage SSF Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — Tussanee Srimachai, Veerasak Thonglimp, Sompong O-Thong

Abstract A two step, included process producing ethanol from oil palm fronts (OPF) by two-stage simultaneous saccharification and Saccharomyces cerevisiae fermentation followed by anaerobic digestion of its effluent to produce methane was investigated. OPF was soaked in dilute sulfuric acid, hydrogen peroxide and water consequently pretreated by microwave for preparing of cellulose and followed by simultaneous saccharification and fermentation. The result indicated OPF soaking in water gave a maximal ethanol yield was 0.32 g-ethanol/g-glucose which was 62.75% of the ethanol theoretical yield (0.51g-ethanol/g-glucose). The effluent from the ethanol production process was used to produce methane with the yield of 514 ml CH4/g VS added. Therefore, soaking in water and microwave co-pretreatment could helpful due to its low toxicity and low corrosion compare to sulfuric acid and hydrogen peroxide which improves the efficiency of enzymatic hydrolysis. The maximum energy output of the process (745 kWh/ ton of OPF) was about 72% of the energy contributed by cellulose fraction, contained in the oil palm frond.

Academic research paper on topic "Ethanol and Methane Production from Oil Palm Frond by Two Stage SSF"

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Energy Procedía 52 (2014) 352 - 361

2013 International Conference on Alternative Energy in Developing Countries and

Emerging Economies

Ethanol and Methane Production from Oil Palm Frond by

Two stage SSF

Tussanee Srimachai% Veerasak Thonglimpa, Sompong O-Thonga*'b'c

a School of Engineering and Resources, Walailak University, Nakhon si thammarat 80161, Thailand bDepartment of Biology, c Microbial Resource Management Research Unit, Faculty of Science, Thaksin University, Phatthalung

93110, Thailand (sompong.o@gmail.com)

Abstract

A two step, included process producing ethanol from oil palm fronts (OPF) by two-stage simultaneous saccharification and Saccharomyces cerevisiae fermentation followed by anaerobic digestion of its effluent to produce methane was investigated. OPF was soaked in dilute sulfuric acid, hydrogen peroxide and water consequently pretreated by microwave for preparing of cellulose and followed by simultaneous saccharification and fermentation. The result indicated OPF soaking in water gave a maximal ethanol yield was 0.32 g-ethanol/g-glucose which was 62.75% of the ethanol theoretical yield (0.51 g-ethanol/g-glucose). The effluent from the ethanol production process was used to produce methane with the yield of 514 ml CH4/g VS added. Therefore, soaking in water and microwave co-pretreatment could helpful due to its low toxicity and low corrosion compare to sulfuric acid and hydrogen peroxide which improves the efficiency of enzymatic hydrolysis. The maximum energy output of the process (745 kWh/ ton of OPF) was about 72% of the energy contributed by cellulose fraction, contained in the oil palm frond.

©2014Published by ElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the Organizing Committee of 2013 AEDCEE Keyword: Ethanol production, Methane production, Co-pretreatment , Oil palm frond ;

* Corresponding author. Tel.: +66 746 09600 ; fax: +66 746 93992. E-mail address: sompong.o@gmail.com

1876-6102 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of the Organizing Committee of 2013 AEDCEE doi:10.1016/j.egypro.2014.07.086

1. Introduction

Currently, energy demand has increased because the primary energy from oil as a fuel obtained from petroleum drilling that was expensive and running out into the future. Therefore, the need to seek the alternative energy such as ethanol which is produced from a renewable agricultural and agro-industrial wastes. Using ethanol tends to increase because it is an alternative fuel which supports a sustainable economy by reducing the use of petroleum, emitting neutral CO2, reduces particulate and NOx emissions from combustion. Additionally, the use ethanol can be increased market opportunities for the agricultural sector due to using raw materials from the agricultural sector for ethanol production. Most ethanol produced from sugar and starches from fruits and grains which was the agricultural products. Currently, ethanol is produced from renewable resources other than sugar and starches such as lignocellulosic materials [1]. Especially, agricultural wastes such as oil palm biomass, rice straw, palm trees, sugar cane, etc. were used in ethanol production. Mostly, the lignocellulosic materials contained of hexose (C-6) and pentose (C-5) which were a major past with a potential to produce ethanol [2]. Agricultural wastes interested because there a lot of several country and to use no worth. In Thailand, the biomass of palm oil is very interested because there are many in Southern Thailand. Particularly, the oil palm frond (OPF) with has approximately 7,050,000 ton/yr [3]. The OPF is cut every time (about 20 days/time) when has a harvest of palm fruits which will be left palm in palm groove as fertilizer for palms only. So, if the use of OPF produced ethanol can be increased the value of OPF and a new raw material to produce ethanol in the future.

Lignocellulosic material is a complex carbohydrate polymer of cellulose (40-50%), hemicellulose (2535%) and lignin (15-20%) [4]. The ethanol production from lignocellulosic materials consists the third main process; the first, size reduction and pretreatment for delignification are necessary to release cellulose and hemicellulose be for hydrolysis; the second, hydrolysis of cellulose and hemicellulose uses enzyme or other method to produce the glucose, xylose, arabinose, galactose, manose; the third, fermentation of reducing sugar to produce the ethanol [5]. The pretreated process could reduce a crystallinity of the cellulose and could increase the fraction of amorphous cellulose, the most suitable form for enzymatic attack [6]. There are several pretreatment such as stream explosion, wet oxidation and hydrothermal treatment have investigated; however, these methods are difficult to make and need very high pressure [7]. The pretreatment process, it should be had lower cost when compared to amount of cellulose increased after pretreatment. The microwave is the interested alternative due to high thermal efficiency and can easily test. The advantages of microwave pretreatment can be reduced of energy need in the process and can be to start and stop the process instantaneously [8]. Internal heat is generated in the biomass by microwave radiation, resulting from the vibrations of the polar bonds in the biomass and the surrounding aqueous medium [4]. The microwave/chemical pretreatment resulted in a more effective pretreatment than the conventional heating chemical pretreatment by accelerating reactions during the pretreatment process [9]. For fermentation of lignocellolosic materials, cellulose should be degraded into cellulose (saccharification) using acid or enzyme [6]. Acid and diluted acid pretreatment are required to hydrolyze the crystalline cellulose, but the degradation of glucose produced 5-Hydroxymetylfurfural and phenols (HMF). Similarly, xylose is degraded into furfural and other components which be toxic to yeast in ethanol production. Pretreatment can be done to improve the hydrolysis yield and total ethanol yield [10].

The research aimed to find the optimal conditions in the co-pretreatment of OPF by using sulfuric acid and microwave, hydrogen peroxide and microwave pretreatment to improve enzymatic hydrolysis and to study fermentation of ethanol combination with the hydrolysis by simultaneous saccharification and fermentation (SSF) in a batch. Following was to study methane production from ethanol effluent and the energy output from ethanol and methane production.

2. Methodology

2.1 Raw material

Oil palm frond (OPF) received from a local villager at Thasala district, Nakhon Si Thammarat, Thailand. It was cut into small pieces and dried at 90 0C for 24 hours to remove the moisture. Thereafter, it was grind to 0.2 - 2 mm in size and soaked in water by the ratio 1:4 for 24 hours. Then, the raw material was squeezed to collecting OPF juice and store in refrigerator at 40C. The solid fraction was dried in an oven with the temperature of 90 0C for 24 hours and to put in plastic at room temperature. The dry matter content (DM) was approximately 95%. Then, the solid fraction used for co-pretreatment method. The composition of initial OPF is shown in Table 1.

Table 1. The composition of raw OPF

Cellulose (%) Hemicellulose (%) Lignin (%) Reference

37.68 35.34 25.18 This study

30.18 24.24 12.96 [11]

31.00 19.20 14.00 [12]

47.60 34.60 15.20 [B]

2.2 Co-pretreatment of oil palm frond

Co-pretreatment method with sulfuric acid and microwave, hydrogen peroxide and microwave, water and microwave was carried out in 250 ml flask. 10% w/v of solid fraction was loaded in the flask. In experimental, different concentrations of sulfuric acid and hydrogen peroxide were studied at 0, 1, 2, 3 and 4% (v/v) and microwave (Sumsung Home Model frequency 2.45 GHz Multimode cavity and largest 800 W) set up at 500 W for 20 min were used.

2.3 Enzyme hydrolysis and ethanol production

Ethanol production from OPF cellulose by simultaneous saccharification and fermentation (SSF) was tested in a batch mode. The enzymatic hydrolysis was done in volumetric flask 250 ml by using 6% (w/w) of the treated material. Then, the 5 ml citrate buffer at a concentration of 5 M and pH 4.8 was added 88 ml of distilled water. Thereafter, the flask was sterilized at 121 0C for 15 min. The cellulosic enzyme from A. niger (Sigma) was filled at an enzymatic loading of 70 FPU for 0.5 ml and 75 IU for 0.5 ml of P-glucosidase from almonds (Sigma). Then, the mixture was incubated at 55 0C with shaking at 150 rpm for 72 hours and samples were collected for analysis at 0, 12, 24, 36, 48, 60 and 72 hours. Then, 10% (v/v) of S. cerevisiae and 1% (v/v) yeast extract was added. Finally, the samples were incubated at 37 0C with shaking at 150 rpm for 24 hours and collected for analysis at 0, 12, 24, 36 and 48 hours to analyze reducing sugar and ethanol.

2.4 Biomethane potential test

Effluents from SSF ethanol fermentation (section 2.3) were used for methane production. The methane production was evaluated by biomethane potential test (BMP) in batch reactors under mesophilic conditions (350C). The batch reactors constructed by using the serum bottle in 300 ml (working volume 100 ml) and closed with rubber stoppers and sealed with aluminum caps. The serum bottles were consisted of inoculum in 80 ml and 20 ml of substrate. Primarily, the bottles were flushed with pure nitrogen for 3-5 min to give the anaerobic condition [2]. The inoculum used from a plot-scale plant treatment POME at 350C.

2.5 Analytical methods

The total sugars were analyzed by the Somogyi - Nelson method [14]. The ethanol was analyzed by the dichromate reagent method. The chemical compositions of the residues resulted from pretreatment analyzed by the Van Soest method [15]. The pH measured by using Sartorius Docu - pH meter. The total solid (TS) or dry matter (DM) and volatile solid (VS) analyzed according to standard method for examination of water and wastewater [16]. The biogas volume and composition measured by displacement of water and analyzed by gas chromatography (GC-8A Shimadzu) equipped with thermal conductivity detector and filled with 2.0 m packed column (Shin-Carbon ST 100/120 Restex) [17]. Morphological analysis of the OPF before and after pretreatment was taken at magnification 500X using a JEOL JSM-5800 scanning electron microscope (SEM 5800). The specimens be coated, were mounted on a conductive tape and coated with gold palladium using a JEOL JFC-1200 fine coater and observed using a voltage of 10-20 kV. The enzyme hydrolysis rate was computed as the concentration of glucose released per hydrolysis time which showed in an equation 1 [1].

Glu cos e. - Glu cos e0

EHR =---0 (1)

Where, EHR (Enzyme hydrolysis rate) (g/g glucose. hours), Glucose t = concentration of glucose at time t(g/L), Glucose 0 = initial glucose concentration at time = 0 hours (g/L), t = hydrolysis time (hours) and to = time at 0 hours.

3. Result and discussion

3.1 Chemical composition of oil palm frond

Co-pretreatment method of sulfuric acid, hydrogen peroxide, water with microwave set up 500 W for 20 min was investigated. The composition of cellulose, hemicellulose of pretreated OPF was shown in Fig 1. The composition of OPF before co-pretreatment had 37.68% of cellulose, 35.34% of hemicellulose and 25.18% of lignin. The composition of cellulose in OPF was similar to the results of Goh et al. [11], Lim et al. [12] and Wanrosli et al. [13] in Table 1, which had the amount of cellulose as 30.18, 31.00 and 41.60%, respective. Co-pretreatment of OPF with sulphuric acid and microwave could increase the amount of cellulose from 35-37 to 52-66% which was higher than co-pretreatment with hydrogen peroxide and microwave, water and microwave. Cellulose increased by 9-36% in comparison with the initial cellulose from the OPF (untreated). The SUL (3%) + microwave gave the maximum amount of cellulose as 62.79% and the lowest as 41.28% of PER (4%) + microwave. The result obtained similar to the experimental value of Goh et al. [11], the largest amount of cellulose (62.50%) from OPF was achieved by hot compressed water pretreatment. Zhu et al. [18], also found that high amount of cellulose (69.3%) from rice straw was achieved with NaOH (4%) + microwave (300W) for 60 min pretreatment.

3.2 Morphological analysis

Scanning electron microscope (SEM) was used in observing the OPF fiber after pretreatment of water + microwave , 2% H2SO4 + microwave and 1% H2O2 + microwave with microwave set up 500 W for 20 min which the results showed in Fig 2. The OPF was the mesh (Fig 2A) after physical pretreatment (Fig. 2B) mesh structure was broken up to increase the surface area. Thereafter, the co-pretreatment method operated with sulfuric acid and microwave, hydrogen peroxide and microwave, water and microwave. The results indicated that co-pretreatment with 3% sulfuric acid and microwave (Fig. 2D) can be removed

external fibers resulted in a higher surface area as compared to co-pretreatment with 1% hydrogen peroxide and microwave (Fig. 2E), water and microwave (Fig. 2C). The increased surface area affected performance of the enzyme hydrolysis, but it depended on the amount of occurred inhibition after pretreatment processes.

120 100 , 80 ' 60 40 20 0

■ Cellulose(%) □Hemicellulose(%) ■Lignm(%)

50.12 52.69 58 91 62-79 57.36 51.33

42.14 43.62 41.28

*SUL = H2SO4 *PER = H2O2

Co-pretreatment

Fig. 1. Chemical composition of oil palm frond before and after the co-pretreatment

« « « « (S cS

о о о о о о о О О

Ü % ü Ü Ü Ü ü ü Ü

+ ^ SN SN SN SN Sn ÎN

1 J D m J D in p-l J D m T J D in cd M Он Cd M CL, p-l cd M Он T cd M CL,

3.3 Enzyme hydrolysis and ethanol production

The solid fraction from co-pretreated OPF with sulfuric acid and microwave, hydrogen peroxide and microwave, water and microwave was hydrolyzed by cellulase and p-glucosidase enzymes at a concentration of OPF 6% w/w for 72 hours. The results showed that co-pretreated OPF with water and microwave gave the maximum glucose concentration of 0.310 % (w/v) at 72 hours, which was higher than the co-pretreated OPF with sulfuric acid and microwave to produce glucose in range of 0.156-0.203 %(w/v) and 0.184-0.238 % (w/v) for co-pretreated OPF with hydrogen peroxide acid and microwave which the results showed in Fig 3. The results of glucose concentration in enzymatic hydrolysis indicated that increasing the concentration of the acid sulfuric acid and hydrogen peroxide during treatment that had effected to glucose concentration because high concentrations of sulfuric acid and hydrogen peroxide which caused the loss of some glucose in the co-pretreatment process. As a result, the concentration of glucose was low when compared to the co-pretreatment by using water with microwave. Furthermore, the enzyme hydrolysis rate showed that the co-pretreatment with water and microwave had the maximum value as 0.00431 g/l glucose.hr (Fig 4). The result corresponded with the experiment of EI-Zawawy et al. [1] which had the enzyme hydrolysis rate for microwave pretreatment of rice straw and banana plant waste were 0.00431 and 0.00392 g/l glucose. hours by using Trichoderma reesei. Azuma et al. [19] reported that microwave pretreatment in the presence of water could enhance the enzymatic hydrolysis of lignocellulosic materials. The high energy radiation of microwave pretreatment resulted in more change in cellulosic material which helped an increase of specific surface area and a decrease of degree of polymerization of cellulose [4]. The advantage of the co-pretreatment with water and microwave similar to the LHW pretreatment which had the low formation of inhibitory components [9]. Weil et al. [20] reported that enzymatic hydrolysis of cellulosic material increased a 2-5 fold after LHW pretreatment. Therefore, water and microwave co-pretreatment was helpful because it had low toxicity and low corrosion compared to sulfuric acid and microwave or hydrogen peroxide and microwave, efficiently increase of enzymatic hydrolysis.

Fig. 2. Morphological analysis by SEM (A) OPF fiber (Wanrosli [13]) (B) Physical pretreatment (C) Water + microwave pretreatment (D) 3% H2SO4 + microwave pretreatment (E) 1% H2O2 + microwave pretreatment

- Water+Microvave

- SUL.(2%)+Microvave

- SUL.(4%)+Microvave

- PER.(2%)+Microvave

SUL.(1%)+Microvave SUL.(3%)+Microvave PER.(1%)+Microvave PER.(3%)+Microvave

c 0.25

! 0.20

§ 0.15

g 0.10 o

3 0.05 0.00

0 10 20 30

Fig. 3. Effect of hydrolysis time on glucose concentration

6— Enzyme hydrolysis rate(g/l glucose.hr)

■s J3

Experiments

Fig. 4. Glucose concentration and rate of enzyme hydrolysis for pre-treated OPF material

* sul = h2so4 per = h2o2

Production of ethanol from cellulose hydrolysate by S. cerevisiae of the co-pretreated OPF with water and microwave for the greatest amount of ethanol was 4.313 g/l which was equal to co-pretreatment with 1% hydrogen peroxide and microwave, followed by 2.679 g/l for co-pretreatment with 2% sulfuric acid and microwave (Fig 5). Comparing the volume of ethanol produced on quantity of theoretical results showed that the co-pretreated OPF with water and microwave the volume of ethanol nearby produced of theoretical maximum was 69.59% (6.198. g/l) of the volume required by theory production. Comparison with co-pretreatment with hydrogen peroxide and microwave was 60.32% (6.848 g/l) of the theory. The co-pretreatment OPF with water and microwave for ethanol yield was 0.32 g-ethanol/g-glucose which was 62.75% of the ethanol theoretical yield (0.51g-ethanol/g-glucose) and productivity 0.09 g-ethanol/l/hours. Nearby, experiments of Kaparaju et al. [2] and Kadar et al. [21] reported that ethanol yield were 0.41 and 0.31-0.36 g-ethanol/g-glucose to produce ethanol from rice straw and industrial wastes by S. Cerevisiae. The results showed that although the co-pretreated OPF with sulfuric acid and microwave can be increased the amount of higher cellulose but it had the toxicity (Furfural, HMF etc.) generated from co-pretreatment which would affect the activity of enzymes and yeast in the SSF, the volume ethanol produced was less than when compared to co-pretreatment with water and microwave.

The co-pretreatment with water and microwave method was attractive because it could save the cost of chemicals and had the high performance.

)10 5 8

I Producted ethanol - Ethanol yield(g-ethanol/g-glucose)

Theoretical ethanol(g/L) Productivity(g-ethanol/l/hr)

Experiments

*sul = h2so4

*per = ho

Fig. 5. Effect of co-pretreatment process on experiment, theoretical ethanol and ethanol yield

3.4 Biomethane potential test (BMP)

The results of the BMP summarized in Table 2. The methane yield in this studied in the range 333-514 ml CH4/gVS-added. Tony-Smith et al. [22] reported that the methane yield of wheat stillage in the literature ranged from 380-529 ml CH4/gVS-added. The methane yield of the co-pretreated OPF with water and microwave for the greatest amount of methane yield was 514 ml CH4/gVS-added (40.66 %CH4). The methane yields of the sulfuric acid and microwave, hydrogen peroxide and microwave pretreatment had low because of toxicity such as acetovanillone and syringic acid that were noticed at high concentration in lignocellulosic material [2]. Wilkie et al. [23] suggested that high levels of potassium, metals and sulfate in addition to phenolic compounds that were produced during the ethanol production process that it could inhibit the methanogenesis. The pH digested ranges from 7.3 - 7.5 which was neutral value and optimum for methanogenic bacteria in the system.

Table 2. Biomethane potential test of OPF from ethanol effluent

Substrate Substrate concentration(g VS/l) CH4 yield (ml CH/g VS-added) pH digested

Water + Microvave 6.85 514 7.49

SUL.(1%) + Microvave 5.02 379 7.57

SUL.(2%) + Microvave 6.40 477 7.34

SUL.(3%) + Microvave 6.04 473 7.52

SUL.(4%) + Microvave 5.41 495 7.46

PER.(1%) + Microvave 6.90 333 7.45

PER.(2%) + Microvave 6.52 425 7.40

PER.(3%) + Microvave 6.08 387 7.48

PER.(4%) + Microvave 7.45 484 7.45

*SUL. = H2SO4 and PER. = H2O2

3.5 Mass balance and energy output

The mass and energy balance were used for assessing the energy output of OPF in the SSF process (Fig. 6). The energy output from 1000g of OPF can produce to total ethanol and methane were 30.31 g ethanol (SAP = 26g-ethanol, SSF = 4.31 g-ethanol) and 52 LCH4. The energy value of the ethanol was 30.31 kg-ethanol/ton of OPF or 809 MJ/ton of OPF (lower heating values of 26.7 MJ/kg-ethanol) [5]. The methane production of effluent from ethanol production was 52 m3 CH4/ton of OPF. Rabelo et al. [24] reported that the highest methane production obtained 72.1 m3 CH4/ton of bagasse when pretreated with the peroxide. The electricity production of 1 ton of OPF would be 1,872 MJ (1 m3 CH4= 36 MJ) or 518 kWh (1 m3 CH4=9.96 kWh) of electricity. Finally, The total energy output from two stage SSF was 2,681 MJ/ton of OPF or 745 kWh/ton of OPF(1 kWh= 3.6 MJ).

Fig. 6 Material and energy balance of the ethanol and methane from OPF by two stage SSF.

4. Conclusion

Co-pretreatment of OPF with water and microwave had high cellulose content and a high yield of ethanol compared with sulphuric acid and microwave, hydrogen peroxide and microwave pretreatment. The co-pretreatment with water and microwave gave maximum ethanol yield of 0.32 g-ethanol/g-glucose which was 62.75% of the ethanol theoretical yield (0.51g-ethanol/g-glucose) and maximum methane yield was 512 ml CH4/g VS added. Therefore, water and microwave co-pretreatment was helpful because it had low toxicity and low corrosion compared to sulfuric acid and microwave or hydrogen peroxide and microwave pretreatment which this process efficiently increased of enzymatic hydrolysis. The total energy output from two stage SSF and anaerobic digestion was 2,681 MJ/ton of OPF or 745 kWh/ton of OPF(1 kWh= 3.6 MJ).

Acknowledgements

I would like to thank the Office of the Higher Education Commission (OHEC) for support the funding in this research.

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