Applied Mechanics and Materials Vol 575 (2014) pp 628-634

Applied Mechanics and Materials Vol 575 (2014) pp 628-634 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.575.628

Submitted: 2014-04-25 Accepted: 2014-04-28 Online: 2014-06-25

Biofuels Produced from Hydrothermal Liquefaction of Rice Husk SYAMSUL Hadi1, a, SUYITNO1, b, KINASTRYAN Jita Kroda1, c, ZAINAL Arifin1, 2, d and HERY Kusbandriyo1, e 1

Mechanical Engineering Department, Sebelas Maret University, Jl. Ir. Sutami 36 A, Surakarta, Central Java, Indonesia

2

Graduate Program of Mechanical Engineering, Brawijaya University, Jl. Veteran, Malang, East Java, Indonesia a

[email protected], [email protected], [email protected], d [email protected], [email protected]

Keywords: Hydrothermal liquefaction, heavy fuel, light fuel, bio-fuel, rice husk.

Abstract. This research is conducted for getting and examining bio-fuel from the process of hydrothermal liquefaction (HTL) using rice husk as raw material. The HTL process used ethanol as a solvent with concentration of 96%. Properties of the produced light fuels were examined on parameter such as water content, viscosity, calorific value, density, flash point, and gas chromatography-mass spectroscopy (GC-MS). The optimum yield 36.3 wt% of light fuel from HTL process of rice husk occurred at reactor temperature of 325°C and holding time of 45 minutes. Meanwhile, the optimum production of bio-fuel (light fuel + heavy fuel) was 69.3 wt% at reactor temperature of 325 °C and holding time of 30 minutes. The resulted light fuel has the calorivic value from 12.1 to 20.2 MJ/kg, viscosity from 1.11 to 1.6 cSt, and flash point from 14 to 29 °C. For the yield of bio-fuel from HTL process, the effect of reactor temperature was more pronounced than the effect of holding time. Further, the light fuels from HTL process with low water content are interesting objects as a fuel in internal combustion engines. Introduction Developments of renewable liquid fuels (bio-fuels) particularly from biomass have received much attention because of the limiting resources of fossil fuel nowadays. Main methods to produce biofuel from biomass are Fischer Tropsch [1,2], hydrothermal liquefaction [3-7], and pyrolysis [8-14]. Comparing to two other methods, hydrothermal liquefaction (HTL) has several advantages. Biofuel from the HTL process [16,17] has low water content comparing to the biofuel from the pyrolysis process which has water content within 25% [15,16].. Beside this fact, in the HTL temperature process are only in between 250 to 400 °C [17] while in the pyrolysis temperature process usually reach 500°C [18-20]. Furthermore, HTL process has capability to proceed raw materials which have high water content until 80–90 wt% [3], although in the process the solvent is needed but the results of biofuel is not influenced significantly by this solvent existences.. The raw material of HTL process were rice husk [21], microalgae [4], soybean stalk [22], and swine manure [17]. The products of HTL process can be influenced by several factors, i.e.: temperature, particle size, heating rate, ratio of the solvent and the biomass, pressure, holding time, inert gas in the reactor [3], solvent acidity [4], and type of the solvent [6]. Study on HTL process usually concerned to the effect of previous parameters to the biofuel yield. The yield of the bio-fuel up to 29% was obtained by the process of HTL using biomass from microalgae and cyanobacteria [4]. Furthermore, the bio-fuel yield produced via HTL process with ethanol solvent reached 26.5 wt%, higher than aceton solvent 20.0 wt% and water 18.6 wt% [6]. To best of our knowledge, the study of biofuels produced by HTL process as the effect of reactor temperatures and holding times for rice husks with ethanol solvent is still limited. Whereas, the technology to produce bio-fuels from rice husk for the agricultural countries which have a big amount of rice husks is very promising.

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Methods The local rice husks that used in the HTL process were dried firstly to attain a moisture content of 8% to 12%. The elemental analysis of rice husk is shown in Table 1. Liquefaction was carried out by introducing rice husks (700 g) and 96% ethanol (2690 g) into the reactor. The HTL process of rice husks was conducted in a closed stainless steel reactor (1200 mm length × 100 mm diameter) which was designed to withstand pressure up to 350 bars. A schematic illustration of the HTL reactor is shown in Fig. 1. The heater was installed in the center of the reactor, so that the heater contacted to the biomass and the solvent directly to eliminate energy losses. Reactor temperatures were set in 250 °C, 275 °C, 300 °C, dan 325 °C and the holding time in 15, 30, and 45 minutes. Table 1. Analysis of rice husk Carbon 38.02

Ultimate [%] Hydrogen Nitrogen 5.28 0.74

Sulphur 0.07

HV [MJ/kg] 14.03

Pressure Gauge

Proximate [%] MC AC VM FC 7.62 18.75 59.4 14.23

Fig. 1. Schematic of HTL reactor. The results of the HTL process were in the liquid and solid phase. For the liquid phase, the results could be proceed to next steps, but for the solid phase the results had to pass through the cleaning process using ethanol and screening process. Using last two steps, left biofuel was obtained. For the next steps, the results of the screening process for the solid phase was blend with the liquid phase to carry out the destilation process in the vacuum condition in order to separate biofuel and the ethanol. After HTL process was complete, the crude biofuels were separated from the ethanol solvent using a rotary evaporator which operated at temperature of 75 °C and pressure of 55 mmHg. Then, the biofuels were separated into heavy and light fuel fractions using a vacuum evaporator at 90°C and 55 mmHg. The physical properties (calorific value, flash point, water content, density, and viscosity) of the light fuels were examined. Furthermore, the compositions of light fuels were examined by gas chromatography-mass spectroscopy (GC-MS, QP2010S SHIMADZU). The column was Rastek stabilwak R–DA with dimension 30.0 m x 0.25 mm. The oven temperature was initially held at 60 °C for 5 min, then temperature was increased to 215 °C at 4 °C/min, for 26.25 minutes. The injector temperature was 215 °C. Carrier gas was helium, and total scan time was 70 minutes. EI mode of ionization was applied and mass scan was from 28 to 600 m/z. For identification of the produced light fuels, library search was carried out using NIST, NBS and Wiley GC-MS library. Results and Discussion Products from HTL Process. The product compositions of the HTL process for the rice husk are shown in the Table 1. A higher reactor temperature caused a higher amount of bio-fuel. Meanwhile, char was another result from the HTL process. The HTL process with a higher temperature produced fewer chars because some parts of the solid of biomass were converted into bio-fuel. The higher temperature and longer holding time mean higher the yields of bio-fuels and lower the yield of gas, because there was no secondary reaction and Boudouard reaction. Both reactions implied to the increase content of char [3]. The maximum results of biofuel from the HTL process was obtained in

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the range of temperature of 300-350 °C [23]. IThe maximum yield of bio-fuel was 69.3% when the HTL process was performed at a temperature of 325 °C and a holding time of 30 minutes as shown in Table 2 and Fig. 2 (a). Table 2. Products of bio-fuels. Temperature [°C] / Hoding Time [min]

No

Solid [wt%]

Total bio-fuel [wt%]

Gas [wt%]

40

80 60

15

30

45

(a)

40 20 0 250

Light Fuel [wt %]

Total bio-fuel [wt%]

1 250 /15 62.2 17.8 20.0 2 250 / 30 64.4 15.1 20.4 3 250 / 45 44.8 14.4 40.8 4 275 / 15 47.8 16.3 35.9 5 275 / 30 50.7 12.9 36.4 6 275 / 45 40.0 18.5 41.6 7 300 / 15 46.1 11.5 42.4 8 300 / 30 37.3 15.3 47.4 9 300 / 45 34.6 5.4 60.0 10 325 / 15 24.1 5.1 67.0 11 325 / 30 25.6 8.9 69.3 12 325 / 45 30.0 6.3 63.6 When the reactor temperature increased, increasing results of the biofuel was not accompanied by increasing results of gas. The yields of gas tend to decrease when the reactor temperature of HTL increased.The yield of gas decreased from 17.8% to 5.1% when temperature rise from 250 °C to 325 °C. The effect of the reactor temperature from 250 °C to 325 °C to the yield of biofuel was more dominant compared to the holding time effect from 15 to 45 minutes. Finally the results of the bio-fuel increased until 60–70% at a temperature 325°C if compared until 20–30 wt% at a temperature 250 °C.

15

30

45

(b)

30 20 10 0

275 300 325 Temperature [ºC]

250

275 300 325 Temperature [ºC]

Fig. 2. Yield of bio-fuels for different temperatures at various holding times: (a) total bio-fuels, (b) light fuels Light Fuel. The bio-fuels as results of HTL process in this research consisted of heavy fuel and light fuel. The reactor temperature had a significant influence to yields of the light fuel comparing to the holding time. The HTL process at the temperature of 250 °C obtained light fuels within 0–10 wt%, then the results increased along with the temperature rising until 30–40 wt% at temperatur of 325°C. The holding time had big influence to the yields of light fuel in the HTL process in low reactor temperature 250–280°C [3]. The effect of the holding time to the results was shown in Fig. 2 (b), which it shows that holding time has no big influence to the yields of light fuel at temperature of 250– 300 °C. The holding time starts to give an effect to the yield of light fuel at temperatur of 300–325 °C.


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The highest yield of light fuel of 36.3% was obtained at the temperature 325 ºC and holding time 45 minutes while the lowest yield of 3.0% was produced at a temperature of 250 °C and a holding time of 15 minutes. Properties of Light Fuels. The properties of light fuel from the HTL process was shown in Table 3 based on the tests of calorific value, flash point, water content, specific density, and viscosity. Table 3 shows the specific density of light fuels has almost the same value within 0.870g.cm-3, lower than that of biodiesel approximately 0.852–0.899 g.cm-3 and that of bio-fuels from microalgae produced by HTL process 1.18 g.cm-3 [24]. Table 3 shows also the mean viscosity of the light fuels is 1.478 cSt in which the lowest viscosity of the light fuels is 1.11 cSt at 250 °C/30 min and the highest viscosity is 1.6 cSt at 325 ºC/15 min. This value is lower than the viscosity of biodiesel ranging from 1.9 to 6 cSt at 40°C [25]. The viscosity of light fuel is affected by several aspects for examples the length of carbon chain and the existence of the ester groups [25]. Table 4 shows that the compounds of the light fuels have a relatively low chain. It means the formed carbon chain in the compounds of the light fuel are almost in the identical form, furthermore the viscosity of light fuel has same phenomenon. The fuel with high viscosity may cause problems to the machine such as need a higher pumping power and a sedimentation on the machine [26]. The mean value of flash point of the light fuels was 18.6 °C, while the lowest flash point of 14 ºC was obtained at 325 ºC/15 min. This value is lower than that of biodiesel in which its flash point is higher than 130 ºC and lower than pyrolysis oil of 40-65 ºC [27]. Based on this fact, the flash point of light fuels is lower than atmospheric temperature causing the light fuel is able to be burned without preheating process. Moreover, the flash point also is influenced by the compounds contained in the light fuel. At the holding time 45 minutes, when temperature of the reactor rise from 250 ºC to 275 ºC, the flash point decrease from 19 ºC to 14 ºC. Increasing content of the butane and propane in light fuel is one of the reasons for this phenomenon. At temperature 325 ºC, flash point rise again to 29 ºC because neither at this temperature the propane and butane were nor be produced but the compounds of phenol increase. Meanwhile, the phenol has value of flash point of 79 ºC. Table 3. Properties of light fuels Temperature [ºC]/ Holding Time [min] 250 /15 250 / 30 250 / 45 275 / 15 275 / 30 275 / 45 300 / 15 300 / 30 300 / 45 325 / 15 325 / 30 325 / 45

Specific Density [g.cm-3] 0.852 0.878 0.881 0.886 0.853 0.899 0.890 0.877 0.854 0.873 0.875 0.886

Viscosity [cSt]

Flash Point [ºC]

Water Content [% ]

1.56 1.11 1.48 1.58 1.44 1.51 1.56 1.45 1.52 1.60 1.41 1.52

20 18 19 15 29 15 14 18 16 14 17 29

17.43 28.58 24.77 23.94 20.95 14.58 14.11 13.65 19.18 16.07 17.55 22.51

Calorific Value [MJ/kg] 16.4 13.6 14.7 18.1 11.3 20.8 13.8 19.4 20.0 14.9 14.9 12.1

The results of GC-MS analysis from the light fuels produced by HTL process with holding time of 45 minutes are shown in Table 4. At the 250 °C, short chain compounds such as butanoic acid, acetic acid, and propanoic acid exist more than 50%. Existence of the acid in high content in the light fuel has a bad effect to the engine because the fuels have a higher acidity. The higher the temperatures of HTL reactor, the lower acidic compounds were detected. At temperature 325 ºC, the acidic compounds which less than 23% means that almost 50 % of the acidic compounds changed to the other compounds. Next, water content of the light fuels from HTL process has mean value of 19.4%. The highest water content of 28.58% was obtained at 250 ºC/30 min. Water content has negative effect to the light

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fuel because higher water content in fuel means lower calorific value. The lowest calorific value of the light fuels was produced at 275 ºC/30 min, 325 ºC/45 min, and 250 ºC/30 min by which the bio fuels have water content more than 20%. The water content of this light fuels from HTL process was slightly lower than that of the pyrolysis oil ranging from 20 to 30% [27]. The highest calorific value of the light fuels produce by the HTL process was 20.7 MJ/kg at 275 ºC/45 min. This value is lower than the calorific value of biodiesel (41.21 MJ/kg) [25], but it is almost same with the calorific value of pyrolysis oil ranging from 13 to 19 MJ/kg [27]. The component of the rice husk which has low calorific value and high ash content is the reasonable argument for this phenomenon. Table 4. Compounds in light fuels detected by GC-MS 250 °C / 45 min

275 °C / 45 min

300 °C / 45 min

325 °C / 45 min

2-Furanmethanol Phenol

8.86 2.45

Propane Butana

10.02 4.68

Propane 1-Butanol

9.60 1-Propanol 5.60 Phenol

2.10 13.40

3-Pentanol 2-Propanone 1-Hydroxy-2butanone Butanoic acid

1.84 3.75

Butanol Furanmethanol

3.15 1.79

1-Propanol 1.3-Butanediol

7.80 4.00

3.42

Pentanol

1.67

Phenol

19.30 Phenol

1.29

Acetic acid

18.41 Propanol

1.15

Propanoic acid Pentanoic acid Butanedioic acid Oxirane-2carboxylic acid Furfuryl formate Propanamide

15.81 Cyclopentane 2.79 Pentanone 2.73 Propanone

2.65 1.34 1.12

1.42

Butanone

2.67

2.84 0.87

Propanoic acid Butanoic acid Acetic acid Butanedioic acid Pentanoic acid

28.70 13.17 11.21 3.41 1.72

2-Propanol 2.3-Dimethyl-2cyclopenten Cyclopentanone 2-Cyclopenten 2-Butenal Ethane-1.1-diol dibutanoate Acetic acid Butanoic acid Pentanoic acid

2.60 1-Butanol 2.20 Cyclopentanone 2.3-Dimethyl-23.70 cyclopenten 1.50 2-Cyclopenten Tetrahydrofurfuryl 3.60 acetate 8.80 Acetic acid 5.60 Propanoic acid 1.60 Furfuryl formate

3.50 6.30 17.20 15.60 7.70 4.10

10.4 4.10 2.50 13.7

Conclusions The bio-fuels were succesfully produced by HTL process for rice husks. The largest production of bio-fuels of 69.3% was obtained at a reactor temperature of 325 °C and holding time of 30 min. While the largest yield of light fules of 36.3% was obtained at a reactor temperature of 325 °C and holding time 45 min. The ligh fuel which has optimum properties was produced at a reactor temperature of 275 °C and holding time 45 min. The light fuel has calorific value of 20.8 MJ/kg, viscosity of 1.51 cSt, and flash point of 15°C. The holding time has capabilities to increase bio-fuel productivity. However, the calorific value of light fuels from HTL process was categorized as low calorific value caused by a significant amount of water content. Therefore, the light fuels from HTL process with low water content are interesting to further study as a fuel in internal combustion engines. Acknowledgement The authors thank the Rector of Sebelas Maret University for financial support through the UNS Research Grant 2014.


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Biofuels Produced from Hydrothermal Liquefaction of Rice Husk 10.4028/www.scientific.net/AMM.575.628 DOI References [21] C. Wang, Z. Du, J. Pan, J. Li, Z. Yang, Direct conversion of biomass to bio-petroleum at low temperature, Pyrolysis. 78 (2007) 438-444. http://dx.doi.org/10.1016/j.jaap.2006.10.016 [22] J. Li, L. Wu, Z. Yang, Analysis and upgrading of bio-petroleum from biomass by direct deoxyliquefaction, J. Anal. Appl. Pyrolysis. 81 (2008) 199-204. http://dx.doi.org/10.1016/j.jaap.2007.11.004 [23] C.S. Theegala, J.S. Midgett, Hydrothermal liquefaction of separated dairy manure for production of biooils with simultaneous waste treatment, Bioresour. Technol. 107 (2012) 456-463. http://dx.doi.org/10.1016/j.biortech.2011.12.061 [24] Z. Shuping, W. Yulong, Y. Mingde, I. Kaleem, L. Chun, J. Tong, Production and characterization of biooil from hydrothermal liquefaction of microalgae dunaliella tertiolecta cake, Energy. 35 (2010) 5406-5411. http://dx.doi.org/10.1016/j.energy.2010.07.013 [26] G. Knothe, K.R. Steidley, Kinematic viscosity of biodiesel fuel components and related compounds. Influence of compound structure and comparison to petrodiesel fuel components, Fuel. 84 (2005) 1059-1065. http://dx.doi.org/10.1016/j.fuel.2005.01.016