Jatropha waste meal as an alternative energy source via pressurized pyrolysis: A study on temperature effects

Energy 113 (2016) 631e642

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Jatropha waste meal as an alternative energy source via pressurized pyrolysis: A study on temperature effects Jinjuta Kongkasawan*, Hyungseok Nam, Sergio C. Capareda Bio-Energy Testing and Analysis Laboratory (BETA Lab), Biological and Agricultural Engineering Department, Texas A&M University, College Station, TX 77843, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 November 2015 Received in revised form 23 March 2016 Accepted 6 July 2016

As an alternative energy source, Jatropha is a promising biomass resource due to its high content of oil contained in the seed. However, after the oil extraction process, more than 50% of initial weight remained as residue. This Jatropha de-oiled cake was considered a valuable feedstock for thermochemical conversion process due to its high volatile matter (73%) and energy content (20.5 MJ/kg). Pyrolysis turned biomass into solid product of biochar, liquid product (bio-oil and aqueous phase), and pyrolysis gas. The effects of pyrolysis temperature under the pressure of 0.69 MPa on the product yields and characteristics were investigated using a bench-scale batch reactor. The gross calorific value of pyrolytic oil was measured to be 35 MJ/kg with high carbon content (71%) and low oxygen content (10%). Phenols and hydrocarbons were the main compounds present in the pyrolytic oil. The heating value of the biochar was also high (28 MJ/kg), which was comparable to the fuel coke. More combustible gases were released at high pyrolysis temperature with methane as a main constituent. Pyrolysis temperature of 500
C, was determined to be an optimum condition for the mass and energy conversions with 89% of the mass and 77% of the energy recovered. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Pressurized pyrolysis Jatropha waste Biomass Renewable energy

1. Introduction Energy is a crucial factor for the development of human civilization. It is the main input to almost all production and consumption activities [1]. With the rapid population and economic growth, the energy demand has been dramatically increasing year by year but not the energy resources [2]. Fossil fuels (i.e., oil, coal, natural gas) act as the main source to meet the world energy consumption over other energy sources for many decades [3]. The replenishment rate of fossil source is significantly slower than the extraction rate, so it is predicted to be completely exhausted in the near future [4]. Due to the limited fossil fuel resources, the development of renewable energy is essential, as it is an alternative way for a fossil fuel substitution. Furthermore, renewable energy not only helps to fulfill the deficiency of fossil fuel but it is also environmental friendly and cost-effective [5,6]. As of 2015, biomass meets around 10e14% of the global energy supply. Both purposely-grown biomass and waste-biomass can be

* Corresponding author. E-mail addresses: [email protected] (J. Kongkasawan), [email protected] (H. Nam), [email protected] (S.C. Capareda). http://dx.doi.org/10.1016/j.energy.2016.07.030 0360-5442/© 2016 Elsevier Ltd. All rights reserved.

considered for energy production [7]. Nevertheless, the growth in agricultural production has been associated with many environmental problems. There are a lot of residues left behind after crop harvesting and processing, and this can pollute the environment if the waste is not managed properly. Utilization of by-products is substantially required because it reduces waste products that may be harmful to the environment, increases the economic profit from the use of whole product chain, and is appropriate for the development of bio-based economies [8]. Agricultural and industrial residues such as husk, rice bran, rice straw, corn straw, corncob, bagasse, and de-oiled seed cakes can be utilized by the biomass-toenergy conversion processes [9e11]. Pyrolysis is a thermal cracking process that decomposes the organic feedstock in the absence of oxygen. Pyrolysis turns biomass into the liquid product composing of bio-oil and aqueous phase, solid product of biochar, and pyrolysis gas [12]. This thermal conversion process is considered a potential option for waste management. The products obtained from pyrolysis can be used as feedstock to produce hydrocarbons, which are the primary energy source for petroleum refineries or biorefineries [13]. Moreover, pyrolysis has become an innovative option among the thermochemical methods due to its simple operation, its suitability as fuel

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for energy production and its uncomplicated reproduction [8,14e16]. The pyrolysis of oilseed by-product has been investigated by many researchers. Oilseeds such as hazelnut, groundnut, olive, sunflower, rapeseed and Jatropha were first extracted by a mechanic press. The de-oiled cakes were then used to perform a pyrolysis process at a pyrolysis temperature in the range of 450e550
C with the liquid product yield of about 40e60 wt%. The properties of produced bio-oil were within the acceptable range of quality fuels. Furthermore, the bio-oil generated from pyrolysis had a very high gross calorific value, which enabled it to be used as a fuel after proper treatment [9,17e19]. However, there is no study on the pressurized pyrolysis of Jatropha wastes. Few studies on the pyrolysis under elevated pressures using different biomass had been performed such as corn stover [20], Nannochloropsis oculata [21], wheat straw [22], and rice husk [23]. Jatropha curcas L. is a drought-resistant tree and can be grown easily under various soil conditions. Previous studies showed that Jatropha seed has a potential to serve as a fossil fuel substitute. In comparison to other fruit seeds, Jatropha seed has a very high oil content, which can be around 35e55%. The major fatty acids in Jatropha oil such as oleic and linoleic acids make it suitable for biodiesel production [24e28]. However, after the Jatropha oil was extracted, more than 50% of input biomass was left as a residue. It was found that Jatropha residue from a press machine still has a high composition of volatile matter and reasonable gross energy value. The press-cake contains high protein and carbohydrates, but it cannot be used to feed animals because of its toxicity [13,29,30]. Therefore, the Jatropha de-oiled cake is considered to be an interesting feedstock for an energy conversion via pyrolysis. In previous work, the Jatropha oil was extracted, performed a refining process and successfully converted into biodiesel [28]. In this paper, the residue from oil extraction process was then used as a feedstock to conduct pyrolysis runs at different operating temperatures. The properties of pyrolysis products at each operating temperature were investigated to determine the possibility of serving as an alternative energy source.

as (1) Preparation of samples for compositional analysis, (2) Determination of extractives in biomass, (3) Determination of structural carbohydrates and lignin in biomass, and (4) Determination of acid soluble lignin concentration curve by UVeVis spectroscopy. The prepared biomass and extractives free biomass samples were sent to Soil, Water and Forage Testing Laboratory, Texas A&M University, for a protein content analysis.

2.2. Pyrolysis set-up Pyrolysis runs were carried out using a bench-scale batch pressure reactor (Series 4580 HP/HT Reactors, Parr Instrument Company, Moline, IL) with automatic temperature controller (Series 4848, Parr Instrument Company, Moline, IL) as illustrated in Fig. 1, which was previously used in the pyrolysis of rice straw study [31]. The batch reactor was equipped with a condenser connected directly to the head of the reactor. The condensed liquid products were collected in a cylinder, which was attached to the condenser. The condenser was equipped with an indirect heat exchange cooling jacket connected to a chiller containing 4
C glycol water as a working fluid. The volume of the gas produced was measured using a gas flow meter (METRIS 250, Itron, Oweenton, KY) connected at the gas outlet of the reactor. Approximately 200 g of the sample was placed in the reactor. Before starting each run, the reactor was purged with nitrogen for 15 min to make sure that the process would operate in an absence of oxygen. The reactor controller and heater were then turned on. The operating temperatures of pyrolysis for this study were chosen to be 400, 500, and 600
C. The reactor was heated until it reached the desired temperature. While the operating temperature was increasing, the outlet valve of the reactor was fully closed until the reactor pressure approached 0.69 MPa. As the pressure increased above 0.69 MPa due to the gas production and expansion, the outlet valve was gently opened to maintain the pressure. When the desired temperature was achieved, the process continued to run for 20 min, and the gas produced was collected in a sampling bag for the gas composition analysis. After that, the reactor was allowed to

2. Materials and methods 2.1. Jatropha press-cake preparation and characterization The oil extraction of Jatropha seeds was carried out using a screw press machine (HFG 505 WN) with 7 mm discharge nozzle diameter. The extracted oil was recovered at 44%, and the de-oiled cake was obtained at 54% of the input raw seed. The produced oil was converted into biodiesel as it was reported in a previous study [28]. The de-oiled cake remained after the oil extraction process was used in the current study. The Jatropha de-oiled cake was ground through a Wiley mill (Arthur A. Thomas Co., Philadelphia, PA) using 1.0 mm screen filter and dried in 105
C oven for 24 h. Moisture content of ground press-cake were brought to less than 10 wt% before proceeding with pyrolysis runs. The ASTM E 1756 Standard Test Method for Determination of Total Solids in Biomass was selected to determine the moisture content. Jatropha de-oiled cake was also analyzed for its properties including heating value, proximate analysis and ultimate analysis. Gross heating value was determined according to ASTM D 2015 using PARR Isoperibol Bomb Calorimeter Model 6200, made by Parr Instrument Company, Moline, IL. Proximate analysis was done in accordance with ASTM D 3172 and ASTM E 1755. The ultimate analysis of the sample was also determined based on ASTM D 3176 using Vario MICRO Elemental Analyzer manufactured by Elementar Analysemsysteme GmbH, Germany. The compositional analysis of Jatropha raw seed, de-oiled cake, and biochar was also done according to NREL procedures such

Fig. 1. Batch pyrolysis set-up [31].

J. Kongkasawan et al. / Energy 113 (2016) 631e642

cool down and the products were collected and weighed. The liquid product was collected from the cylinder below the condenser and the biochar was collected from the reactor for further analysis. Each pyrolysis temperature was conducted in triplicate. 2.3. Pyrolysis products characterization Pyrolysis products obtained at all operating temperatures were analyzed for their properties as described in the following sections: 2.3.1. Gross calorific value The gross calorific values of bio-oil and biochar products were determined using PARR isoperibol bomb calorimeter in reference to ASTM D 2015. Solid products were ground with a Wiley mill using a 2 mm screen prior to the bomb calorimeter operation. 2.3.2. Proximate analysis and ash content Proximate analysis is the measurement of moisture content (MC), volatile combustible matter (VCM), fixed carbon (FC), and ash content containing in biomass. Proximate analysis of the biochar was completed by following the ASTM standards (D 3172 and E 1755). The biochar obtained from pyrolysis experiment were hammer ground before conducting an analysis. The ash content of bio-oil was also determined according to ASTM D 0482-07. 2.3.3. Ultimate analysis The ASTM standard (D 3176) was used to determine for the elemental composition of bio-oil and biochar using Vario MICRO Elemental Analyzer (Elementar Analysemsysteme GmbH, Germany). Then, the empirical formulas of bio-oil and biochar were calculated. 2.3.4. FTIR A Shimadzu IRAffinity-1 FTIR (Fourier Transform Infrared) Spectrophotometer (Shimadzu, Inc.) was used to identify the existence of functional groups in the bio-oils at different operating temperature. 2.3.5. Chemical composition (GC-MS) The GC-MS analysis was used to identify the chemical composition of bio-oil. Dichloromethane (10%vol) was used to dilute the concentration of crude bio-oil before performing an analysis. The GC-MS system was performed on Shimadzu QP2010 with DB-5 ms column (25 m  0.25 mm (i.d.), 0.25 mm film thickness). The injection temperature was 295
C. Helium was used as a carrier gas with flow rate of 0.83 ml/min. The column temperature was held at 45
C for 4 min, then heated up to 250
C at rate of 5
C/min and maintained at this temperature for 10 min. The ion source temperature was set at 250
C with m/z ranging from 40 to 500. 2.3.6. Gas composition The pyrolysis gas collected at different pyrolysis temperatures was then analyzed for its composition by SRI Multiple Gas Analyzer #1 (MG#1) gas chromatograph (SRI GC, Torrance, CA). The detectors used in the analyzer were helium ionization detector (HID) and thermal conductivity detector (TCD). The columns for the syngas analysis were 60 Molecular Sieve 13X and 60 Silica Gel, with helium as the carrier gas. The calibration gas standard mixture consisted of H2, N2, O2, CO, CH4, CO2 and C2H6 (Praxair Specialty Gases, Austin, TX) with an analytical accuracy of ±5%. The column temperature was initially set at 65
C for 10 min before rising at a rate of 16
C/min to 250
C as a final temperature.

633

2.4. Mass and energy balance The product yields (wt%) from pyrolysis process were calculated using Eq. (1). The amount of gas produced was measured in the form of gas volume; therefore, the mass of gas was calculated after the gas composition was determined. Eq. (2) was used for mass of gas calculation under the assumption that the gas was collected at normal temperature and pressure (25
C and 1 atm). The densities of each gas were obtained from the Handbook of Natural Gas Engineering [32]. Energy distribution of pyrolysis products were also determined using Eq. (3). Product yield (%wt) ¼ (Product weight/Initial biomass weight)  100

(1)

Mass of gas ¼ (Gas density  Volume  Gas fraction from GC)/ 100 (2) %Energy recovery ¼ Product yield (%wt)  (HHV of product/HHV of biomass) (3) The statistical tests including Analysis of Variance (ANOVA) and Fisher's Least Significant Difference (LSD) were used to analyze the data at 95% confidence level. The standard deviations were represented in the results as the indication of experimental errors.

3. Results and discussion 3.1. Characteristics of Jatropha seed and de-oiled cake The chemical properties of Jatropha seed and de-oiled cake are presented in Table 1 along with other non-edible de-oiled cakes. The HHV (higher heating value) of Jatropha de-oiled cake was lower than the raw seed, and higher than other non-edible seed cakes such as Pongamia and Neem. Moreover, the HHV was even higher compared to other waste biomass that can be used for energy conversion such as rapeseed oil cake (19.49) [19], corn stover (18.45) [33], sugarcane bagasse (15.08) [34], rice husk (16.8) [35], and cotton stalk (16.9) [36]. The results from proximate analysis showed an increase in FC, and decrease in VCM and ash from raw seed to de-oiled cake due to the extracted Jatropha crude oil of 37.6 MJ/kg HHV [28]. The ultimate analysis also revealed the significant decrease in carbon content and increase in oxygen content, which resulted in lowering the heating value of the de-oiled cake. The heating value can also be calculated from elemental mass fractions in biomass (i.e., C, H, O, N, S) using Eq. (4) (Boie's formula) [37]. The theoretical values were not much different from the values obtained from the experiment. HHV (MJ/kg) ¼ 0.3515 C þ 1.1617 H þ 0.06276 N þ 0.1046 S  0.1109 O (4) The results from compositional analysis showed that the raw seed had high extractives (44.6%) due to a large amount of oil contained in the seed. The extractives of de-oiled cake reduced to 20.4% after the oil extraction process. The inorganic compounds, nonstructural sugars, and nitrogen containing substances were present in water extractives whereas ethanol extractives contained chlorophyll, waxes, oils and fats [12]. The sugar content was obtained by difference. The protein contents of the Jatropha seed and de-oiled cake were also high, which was related to the nitrogen content that existed in the biomass. The percent protein contents did not changed much even after the oil extraction process.

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Table 1 Characteristics of Jatropha raw seed and de-oiled cake, and other non-edible oil cakes. Jatropha seeda

Characteristics

De-oiled cake

Calorific value (MJ/kg) ASTM D 2015 24.0 ± 0.24 Boie's equation 25.3 ± 0.78 Proximate analysis (wt%) Moisture 7.5 ± 0.12 VCM 77.1 ± 0.95 Fixed carbon 9.4 ± 0.53 Ash 5.9 ± 0.55 Ultimate analysis (wt%) C 53.7 ± 0.79 H 8.0 ± 0.02 N 4.5 ± 0.23 S e O (by difference) 27.9 ± 0.69 Chemical Formula CH1.79O0.39N0.07 Compositional analysis (wt%) Extractives 44.6 Water 15.5 Ethanol 29.1 Lignin 26.1 Acid insolubles 14.8 Acid solubles 11.3 Sugars 3.7 Protein 25.6 a b

Jatrophaa

Pongamia [38]

Mahua [39]

Neem [40]

20.5 ± 0.40 18.2 ± 0.42

17.65 18.5b

21 19.8b

18.2 14.8b

6.5 ± 0.01 73.0 ± 1.29 11.3 ± 1.01 9.2 ± 0.76

12.00 71.21 11.71 5.08

4.18 88.38 3.07 4.36

6.13 79.26 4.61 10.00

43.3 ± 0.56 5.8 ± 0.04 5.0 ± 0.46 e 36.7 ± 0.48 CH1.61O0.63N0.10

47.11 5.63 0.27 e 41.91 CH1.43N0.005Ob0.67

49.65 5.71 3.34 0.61 40.69 CH1.379N0.0576 S0.004O0.614

42.5 4.5 1.9 1.3 49.8 CH1.275N0.0375S0.011O0.878

20.4 13.5 6.9 39.2 20.7 18.5 16.1 24.3

e e e e e e e e

e e e e e e e e

e e e e e e e e

From experiment. Calculated from original work.

3.2. Effect of operating temperature on pyrolysis products yields and mass distribution The pyrolysis product yields at different operating temperatures were calculated using the initial weight of input biomass and the weights of final products as shown in Fig. 2. According to the graph, the amount of biochar decreased with an increase of temperature. Pyrolysis gas increased from 400
C to 500
C then decreased from 500
C to 600
C. However, it appeared that the pyrolysis temperature did not affect the liquid product yield. The statistical analysis by ANOVA verified that the operating temperature significantly affected the yield of biochar (p-value ¼ 0.001) and pyrolysis gas (pvalue ¼ 0.004) but not the liquid product at 95% confidence level. Among all products at different operating temperatures, biochar yielded the highest amount at 37e44%, followed by liquid product (24e27%) and pyrolysis gas (13e21%). A possible reason for a higher biochar yield than other products could be explained by the pressure used and the lower temperature. As the pressure was maintained at 0.69 MPa during the

50.0

44.5

45.0

400 40.3

40.0

500

36.6

600

Yield (%wt)

35.0 30.0 25.0

26.6 27.1

24.3

21.8 17.4

20.0 13.1

15.0

heating process of pyrolysis, the gas produced from biomass remained in the reactor, resulting in the secondary cracking reaction of pyrolytic gas. Consequently, this came out with the production of biochar like carbonaceous substances left in the reactor [20]. Also, a lower temperature led to the low amount of liquid and gaseous products with high amount of biochar as a result of incomplete pyrolysis reaction. On the other hand, when the temperature was increased, more volatiles of lignin and hemicellulose released because of the primary thermal decomposition and secondary reaction of biomass, leading to the reduction of biochar yield [13]. Many researchers also obtained similar trends for the pyrolysis yields of different feedstock, including corn stover [20], microalgae (Nannochloropsis oculata) [21], rice straw [31], and cherry seed [41]. Raja et al. [42] explained that a decrease in liquid yield and an increase in bio-char and gas were caused by the secondary reaction of volatile liquids and degeneration of the char particles at a higher temperature. Aquino [43] also clarified that the secondary thermal cracking of volatiles that decomposed the biomass into noncondensable compounds led to the increase in gaseous products when the operating temperature was increased. However, the reduction in liquid product and pyrolysis gas with the temperature increased from 500 to 600
C could be explained by the rapid devolatilization of cellulosic and hemicellulosic biomass at higher temperatures [44]. Park et al. [45] also observed a decreased yield of bio-oil at a higher temperature as results of the cracking or secondary tar reactions at an elevated temperature of reactor and char surface. In addition, maximum loss occurred at 600
C was because of the reduction in gas yields that discussed later in gas composition section.

10.0 5.0 0.0 Liquid product

Biochar Pyrolysis products

Syngas

Fig. 2. Pyrolysis product yields at different operating temperatures.

3.3. Effect of operating temperature on pyrolysis products properties Bio-oil, biochar and pyrolysis gas were obtained from the pyrolysis experiment. All products were analyzed for their chemical

J. Kongkasawan et al. / Energy 113 (2016) 631e642

properties such as energy content, moisture content, and component elements.

635

Biochar

40.0

Bio-oil

90.0

50.0

MJ/kg

20.5

10.0 5.0 De-oiled cake

analysis of biochar from different feedstock such as corn stover [20], cotton gin trash [43], and safflower seed press cake [49]. Fig. 4 shows the heating values of the Jatropha de-oiled cake and the pyrolysis products. The gross calorific value of the biochar was significantly improved from the de-oiled cake (20.5 MJ/kg). This could be described by the carbonization during pyrolysis process that converted biomass into a solid residue abundant in carbon content (i.e., biochar). The maximum heating value of the biochar was achieved at 400
C (28.2 MJ/kg). According to the graph, the heating value of the biochar slightly decreased with an increase in operating temperature as more VCM released at a higher temperature, which lowered the HHV value of the biochar. However, the statistical analysis by ANOVA indicated that pyrolysis temperature did not have an effect on the gross heating value of the biochar at 95% confidence level (p-value ¼ 0.394). The slight difference of HHV of biochar and bio-oil at different temperatures can be supported by the chemical analysis discussed in the following sections. The elemental composition of the biochar at different operating temperatures was also completed in comparison with the de-oiled cake as demonstrated in Fig. 5. The graph shows that the major differences between the de-oiled cake and biochar were carbon and oxygen contents, while the minor differences were hydrogen content. The oxygen and hydrogen content of the de-oiled cake diminished with the rise in carbon content as temperature increased. The carbon content of the de-oiled cake increased from 43% to 67% with the oxygen content reduced from 37% to 5%. The hydrogen content decreased from 6% at 400
C to 2% at 600
C. The results proved that the deoxygenation occurred during thermal

80 De-oiled cake 70

600

50

20

10.0

10

Compositions Fig. 3. Proximate analysis of de-oiled cake and Jatropha biochar at different pyrolysis temperatures.

biochar 400 biochar 500 biochar 600

40

20.0

Ash

600

Fig. 4. Heating value of de-oiled cake and pyrolysis products at different temperatures.

30

FC

500

Temperature (oC)

30.0

VCM

400

4.2

2.1

0.1

0.0

60

0.0

27.3

20.0

500

40.0

27.5

15.0

%wt

%wt

60.0

34.6

25.0

400

70.0

28.2

30.0

De-oiled cake

80.0

35.1

34.3

35.0

3.3.1. Biochar After the pyrolysis process was completed, the solid product or biochar was collected from the reactor where the initial biomass was placed. The biochar was first analyzed for the proximate analysis (VCM, FC, and ash). VCM is strongly related to the thermal conversion process since it creates more combustible gases during the process while FC is the remaining solid combustible residues after the volatile matter is released. The proximate analysis of Jatropha de-oiled cake and biochar obtained at different temperatures were compared as shown in Fig. 3. The VCM of the seedcake significantly dropped from 78% to around 30% with a substantial increase of FC from 12% to approximately 54% after the pyrolysis process. The ash content increased from 10% to the maximum of 20% at 600
C. Biomass rather released more volatiles at higher temperature, which led to the reduction in VCM from the de-oiled cake. Meanwhile, the FC was the remaining solid combustible residue after VCM was discharged. Therefore, FC content in the biochar had a significant rise compared to the de-oiled cake. It was reported that the decomposition of lignin started at relatively low temperature of 200e275
C and the significant decomposition occurred at around 400e500
C. This led to the release of volatile components, which left behind the solid rich in carbon referred as biochar [46]. The reduction of VCM at higher temperatures, which contributed to the increase of FC, resulted in the reduction of biochar yields. A small percent change in the FC composition was observed compared to a decrease of VCM when the temperature was increased from 500 to 600
C owing to the lignin contents that were barely degraded at temperatures above 500
C. Thus, the change of VCM and FC contents can be used to predict the biochar yield over temperature conditions as the absolute amount of compositional components (hemicellulose, cellulose, lignin, and sugars) degrades also based on mainly temperature condition [47]. The ash content was observed to increase with an increase of temperature, which can be explained by the reduction of the elements such as nitrogen, carbon, hydrogen, and oxygen. Moreover, the volatilization of sulphur during heating but not the inorganic compounds contributed to the increase of ash content [48]. Statistical analysis by ANOVA also confirmed that the operating temperature had an effect on VCM, FC and ash contents of biochar (p-value < 0.001). However, the LSD test supported that the FC content of biochar obtained at 500 and 600
C was not significantly different at 95% confidence level. Many studies on pyrolysis temperature also had a similar trend of proximate

Gaseous product

0 C

H

Component

N

O*

Fig. 5. Ultimate analysis of de-oiled cake and biochar at different temperatures (*O by difference).

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J. Kongkasawan et al. / Energy 113 (2016) 631e642

decomposition of biomass, which relates to an increase in carbon content. The trend in the increase in carbon content also corresponded to an increase in FC from the proximate analysis as described earlier. The empirical formulas of the biochar at 400, 500, and 600
C were calculated to be CH0.90O0.20N0.08, CH0.57O0.13N0.08, and CH0.43O0.06N0.07, respectively. The empirical formulas of biochar at different temperatures showed the reduction of H, O, and N components with an increase of temperatures. This could be explained by the secondary reactions and thermal decomposition at high temperatures, which led to the release of nitrogen components into the gases of HCN, NH3, and HNCO [50,51]. The similar HHV of biochar and bio-oil at different temperatures can also be explained by the elemental compositions according to the Boie's formula (Eq. (4)). A large increase in carbon and a large decrease in oxygen, which increased the HHV, were balanced out by a small decrease in hydrogen with a high coefficient of 1.1617. The different coefficients on each element made HHV almost constant even though they were produced at different conditions. The Van Krevelen diagram can be constructed by calculating the H:C and O:C ratios of each sample as demonstrated in Fig. 6. Jatropha de-oiled cake fell into the region where most biomass was found while the biochar obtained at different operating temperatures located in the coal area. The H:C ratios of the biochar were found to be between 0.4 and 0.9 and O:C ratio ranging from 0.06 to 0.2. The values reported for the biochar obtained at 600
C and 400
C were comparable to anthracite and lignite, respectively [52]. Similar results of the biochar characteristics were also found with pyrolysis of different feedstock such as corn stover [20], wheat straw [22], and Pongamia pinnata de-oiled cake [53]. Nam et al. [31] also reported the similar ranges of O:C and H:C ratios of rice straw pyrolysis from a batch reactor. The bio-oil and biochar regions indicated in Fig. 6 were based on different feedstocks of rice straw, sorghum, switchgrass, algae, and corncob. They also reported the O:C ratios varied depending on reactor types of a batch, an auger, and a fluidized bed. The carbon to carbon bonds had greater energy than carbon-oxygen and carbon-hydrogen bonds. The lower O:C ratio was preferable to obtain higher energy value [7]. Therefore, the reduction in O:C ratio of the biochar led to the increase in heating values. The properties of biochar such as high carbon content and reasonable heating value made it appropriate for making an activated carbon or using as fuel substitute. 3.3.2. Liquid product The produced heavy volatiles were condensed and formed into the liquid product, which comprised of two phases in separated

layers (bio-oil and aqueous phase). The bio-oil obtained at all operating temperatures was a black viscous smoky oil with a very strong irritable smell, while the aqueous phase was a slightly cloudy yellow-brown solution. The amount of aqueous phase presented in liquid product affected its energy content. Thus, the separation of bio-oil from liquid product resulted in a greater heating value. The gross heating values of the bio-oil obtained at different temperatures are illustrated in Fig. 4. The maximum heating value of the bio-oil was achieved at 500
C (35.1 MJ/kg). However, the statistical analysis by ANOVA revealed that there was no significant difference among heating values of the bio-oil at different operating temperatures (p-value ¼ 0.564). The heating value of the biooil was considerably greater than the Jatropha de-oiled cake and the highest among all pyrolysis products. The gross heating values of bio-oil obtained from the current experiment (slow pyrolysis) were much higher than the reported heating values of pyrolysis from Jatropha residue using fluidized bed [13,42]. These experimental values were also higher than the pyrolytic oil from other biomass residues such as sunflower cake [18], sesame cake, mustard cake [40], and olive waste [55]. The ash content of the biooil was found to be about 0.1% for 400 and 500
C and 0.5% for 600
C. Fig. 7 shows the elemental composition of the bio-oil at different pyrolysis temperatures. Carbon was the major composition found in the bio-oil obtained at all conditions. The carbon content of the bio-oil was found to be 71% while the oxygen content was around 10%. A significant increase in carbon and a decrease in oxygen content of bio-oil from the de-oiled cake (carbon 43% and oxygen 37%) resulted in a substantial improvement in the gross heating value. High oxygen content in the bio-oil was undesirable since it will lower the energy content and will lead to the instability of the bio-oil. The chemical formulas of the bio-oil were found to be CH1.37O0.11N0.12 for 400
C, CH1.39O0.10N0.12 for 500
C, and CH1.28O0.13N0.10 for 600
C. The elemental compositions (C, H, N, and O) of bio-oil at different temperatures were not significantly different resulting in the similar heating values in accordance with the Boie's formula. According to the Van Krevelen diagram (Fig. 6), the bio-oil at different operating temperatures had an O:C ratio of around 0.1. The H:C ratio of the bio-oil obtained at 600
C was found to be 1.28 while the bio-oil at 400 and 500
C had better H:C ratio (1.38). The ranges of H:C and O:C ratios in the current study were located in the same area where a bio-oil region produced from a batch type reactor as reported by Nam et al. [31]. It can be seen that the H:C and O:C ratios of bio-oil pyrolyzed at 400 and 500
C close to the area of crude oil. However, it may need further upgrading

80 bio-oil 400

70

bio-oil 500

60

bio-oil 600

%wt

50 40 30 20 10 0 C Fig. 6. Van Krevelen diagram of Jatropha de-oiled cake and its pyrolysis products at different temperatures (petroleum crude oil adapted from Ref. [54]) and the bio-oil and biochar region from a batch reactor adapted from Ref. [31].

H

Component

N

O*

Fig. 7. Ultimate analysis of bio-oil at different temperatures (*O by difference).

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637

0.4 400B 400Aq

0.35

500B 500Aq

600B 600Aq

Absorbance

0.3 0.25 0.2 0.15 0.1 0.05 0 4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 8. FTIR spectra of aqueous (Aq) and bio-oil (B) fractions in liquid product at different pyrolysis temperatures.

process to make it suitable to use as fuel replacement by reducing the oxygen content. The functional groups presented in liquid product was analyzed using FTIR spectroscopy as demonstrated in Fig. 8. According to the diagram, the FTIR spectra of the aqueous and bio-oil phases at different operating temperatures appear to be similar. The dominant peaks of the aqueous fraction at 3640e3200 cm1 referred to the OeH stretching vibrations, which suggested the presence of phenols, alcohols, or water. In the bio-oil phase, it can be observed that the peak identified at 3600e3500 cm1 can relate to the presence of alcohol or phenol group. Furthermore, the absorbance peak at 3000e2850 cm1 indicated alkanes group for CeH stretching vibrations. CeH stretch off C]O vibrations at 2850e2800 cm1 also suggested the existence of aldehydes. The peak observed in the 2300e2200 cm1 range suggested the presence of nitrile compounds. C]O stretching vibrations found in the range of 1760e1665 cm1 can be due to carbonyls, carboxylic acids, esters, aldehydes and ketones. The CeC stretching vibrations at 1600e1400 cm1 designated the presence of aromatics. The peak at 1000e900 cm1 for ¼ CeH bending indicated the alkene group and the peak observed at 725e720 cm1 specified the alkane group existed in bio-oil. Bio-oil obtained at different operating temperatures were then analyzed for the chemical compositions using GC-MS. Fig. 9

demonstrates the percent relative content of chemical compounds present in the bio-oil at each temperature. The compounds were classified into each chemical groups. Phenols seem to be the major component for the bio-oil obtained at 400 and 600
C follows by aromatics. On the other hand, the highest component found in the bio-oil at 500
C was aromatics and phenols. The amounts of phenolic compounds in the bio-oil was a result of high lignin content of the de-oiled cake. Murata et al. [56] also reported phenols as the main compounds found in the Jatropha bio-oil. Bio-oil containing high amounts of phenolic compounds had become an interest because of the introduction of petroleum-based phenol after the segregation of phenols from bio-oil [57]. On the other hand, high oxygen content in the bio-oil would reduce the energy density, increase the acidity, and lower the miscibility with hydrocarbon fuel [58]. Other major components found in the bio-oil including alkanes, alkenes and aromatics with some small portions of ketones, alcohols, amides, amines, and aldehydes. The presence of nitrile group in bio-oil was due to high amount of protein contained in Jatropha de-oiled cake (24.3%). The high amount of oxygenated compounds (phenols, ketones, carboxylic acids, and aldehydes) and some nitrogenous substances indicated bio-oil required further upgrading process to remove these unwanted compounds and make it suitable to use as transport fuel. Table 2 shows the relative percentages of chemical composition

45

400

500

40

Relative content (%)

35 30 25 20 15 10 5 0

Compounds Fig. 9. Functional groups present in bio-oil at different operating temperatures.

600

638

J. Kongkasawan et al. / Energy 113 (2016) 631e642

Table 2 Chemical compositions of bio-oil at 500
C with relative content. Compound

Relative content (%)

Compound

Relative content (%)

Alkane Nonane, 4-ethyl-5-methylCyclopropane, 1-hexyl-2-propyl-, cisPentadecane, 7-methylPropane, 2-bromo-2-methylCyclotetradecane Octadecane Heneicosane Tridecane Pentadecane Hexadecane

11.6 0.36 0.2 0.3 1.04 0.33 0.33 0.19 3.87 1.66 3.32

Alkene 1-Decene 6-Cyano-1-hexene 1-Undecene 7-Tetradecene, (E)Indene Naphthalene Naphthalene, 1-methyl3-Tetradecene, (Z)5-Tetradecene, (E)Naphthalene, 2-methyl9-Octadecene, (E)7-Hexadecene, (Z)8-Heptadecene 9-Eicosene, (E)3-Hexadecene, (Z)5-Octadecene, (E)1-Octadecene

10.45 1.24 0.29 1.45 0.53 0.32 0.75 0.62 1.04 0.36 0.74 0.47 0.44 0.75 0.32 0.56 0.2 0.37

Ketone 3-Hexanone 2-Hexanone, 4-methyl2-Hexanone, 5-methylCyclopentanone, 2,3-dimethylEthanone, 1-(2-furanyl)Ethanone, 1-(1H-pyrrol-2-yl)2-Hexanone 2-Cyclopenten-1-one, 2-methylCycloheptanone 2-Cyclopenten-1-one, 2,3-dimethyl-

2.85 0.21 0.14 0.39 0.11 0.35 0.22 0.64 0.28 0.21 0.3

Aromatics Pyridine, 2,6-dimethylBenzenamine, 3-methylPyridine, 2-(1-methylethyl)Pyridine, 3-ethylBenzene, 1-ethyl-3-methylBenzonitrile Benzene, 1,2,3-trimethylBenzene, 1-propenylPyrazine, ethyl1H-Pyrrole, 2,4-dimethylBenzene, (1-methylethyl)Pyridine, 2,4-dimethylAniline, N-methyl1H-Pyrrole, 2-ethyl-4-methylPyrazine, 2-(n-propyl)Pyridine, 2-ethyl-6-methyl1H-Indole, 2,3-dimethylBenzene, propylBenzene, 1-ethyl-2-methylBenzene, 1,2,4-trimethylPyrazine, 2-ethyl-6-methylBenzene, pentylBenzofuran, 4,7-dimethyl1H-Pyrrole, 1-methylPyridine Pyrrole Toluene 1H-Pyrrole, 1-ethylPyridine, 2-methylPyrazine, methylEthylbenzene Benzene, 1,3-dimethyl-

32.31 1.79 0.68 0.16 0.4 0.3 0.29 0.43 0.25 1.7 0.66 0.11 0.82 0.36 0.93 0.4 1.39 0.25 0.72 0.46 0.5 1.12 0.66 0.39 1.27 1.37 3.19 3.51 0.52 2.11 1.09 3.43 1.05

Carboxylic acid Pentanoic acid, 3-methyl-, methyl ester Hexanoic acid, methyl ester Hexadecanoic acid, methyl ester n-Hexadecanoic acid 9-Octadecenoic acid (Z)-, methyl ester Octadecanoic acid, methyl ester

2.47 0.79 0.22 0.52 0.27 0.43 0.24

Alcohol 2-Furanmethanol 1-Hexanol, 2-ethyl1-Dodecanol, 3,7,11-trimethylPhenol Phenol Phenol, 2-methylPhenol, 3-methylPhenol, 2-methoxyPhenol, 2,4-dimethylPhenol, 2-ethylPhenol, 4-ethylPhenol, 2,5-dimethylPhenol, 2,6-dimethoxyPhenol, 3,4-dimethylPhenol, 2-methoxy-4-methylPhenol, 4-(1-methylethyl)Phenol, 2,3,6-trimethylPhenol, 2-ethyl-5-methylPhenol, 2-ethyl-4-methylPhenol, 2,3,5-trimethylPhenol, 4-ethyl-2-methoxyPhenol, 3-ethyl-5-methylPhenol, 2,4,6-trimethyl-

2.61 0.68 1.64 0.29 29.21 3.94 3.21 3.82 3.92 2.06 1.22 1.99 0.85 0.72 1.33 0.59 0.86 0.58 1.12 0.69 0.32 0.92 0.41 0.66

Amide N-Methyldodecanamide 9-Octadecenamide, (Z)Octadecanamide

0.62 0.21 0.17 0.24

Nitrile Butanenitrile, 2-methylButanenitrile, 3-methylPentanenitrile, 4-methylHexanenitrile Octanenitrile Hexadecanenitrile Oleanitrile

6.17 0.3 1.27 1.67 0.57 0.61 1.2 0.55

Amines Silanediamine, 1,1-dimethyl-N,N0 -diphenyl-

1.71 1.71

for the bio-oil obtained at 500
C. Around 100 chemical compounds were detected from the GC-MS. The highest component came from aromatics (32%) followed by phenol (29%). Phenol and 2-methoxy phenol were the main compounds found in this bio-oil. Most

lignocellulosic biomass produced phenol as a major composition [20,41]. Moreover, this bio-oil contained high portions of paraffinic hydrocarbons such as tridecane, pentadecane, and hexadecane of C13-C16 range. Some other minor portions of parraffinic and olefinic

J. Kongkasawan et al. / Energy 113 (2016) 631e642

639

hydrocarbons were observed with carbon range from C10 to C21. The results from the GC-MS was in agreement with the FTIR results. 3.3.3. Pyrolysis gas The pyrolysis gas produced from pyrolysis at different temperatures was analyzed for its composition using a GC. Combustible gases such as hydrogen, carbon monoxide, and hydrocarbons (methane, ethylene, ethane, propene, and propane) were generated from the pyrolysis process as demonstrated in Fig. 10. Hydrogen and hydrocarbons increased while carbon dioxide decreased with an increase in pyrolysis temperature. The secondary thermal cracking of volatiles resulted in the release of hydrogen and hydrocarbon gases at a higher temperature [20]. Therefore, more hydrogen and combustible gases were observed when the temperatures increased from 400 to 600
C. The amount of carbon dioxide produced also decreased with an increase of pyrolysis temperature because carbon dioxide was rather unleashed at low temperature. In addition, the discharge of COx gases was a result of oxygenated compounds contained in biomass through decarboxylation [19,59]. However, a significant increase in hydrogen production at 600
C could lead to the gas losses during the run due to a very low density of hydrogen gas compared to other gases. Fig. 11 shows the gross heating value of each gas component at different operating temperatures. The total energy content significantly increases with an increase of pyrolysis temperature because more of hydrogen and hydrocarbon gases were likely produced at high temperatures. The total gross heating value of the gas rose from 0.1 MJ/kg at 400
C to 4.2 MJ/kg at 600
C. The lower amount of combustible gases was released at a low pyrolysis temperature, which led to low energy content. At 500 and 600
C, almost 50% of the total energy in the pyrolysis gas came from methane, ethane and propane. 3.3.4. Further discussions on characteristics of pyrolysis products Pyrolysis can be classified into fast and slow pyrolysis based on the heating rate and residence time. Slow pyrolysis refers to the process with long residence time at a slow heating rate, which produces mainly biochar at low temperatures and pyrolysis gas at high temperatures. On the other hand, fast pyrolysis is conducted at a fast heating rate and short residence time, which generates high yield of bio-oil. Also, a broad and abrasive contact of the fluidizing

Fig. 11. Gross heating values of gas product at different pyrolysis temperatures.

medium to feedstocks produce more of bio-oil [31]. Moreover, the yields and properties of pyrolysis products are strongly influenced by pyrolysis reactor design, operating conditions, and biomass type [20,41,60]. Most of pyrolysis studies on Jatropha de-oiled cake were conducted via fast pyrolysis. The bio-oil as a main product from fast pyrolysis had a low HHV of 19.7 MJ/kg [42], which is much lower than the one obtained from this study. Jourabchi et al. [61] performed the slow pyrolysis of Jatropha de-oiled cake with temperatures ranging between 300 and 800
C under atmospheric pressure using the lab-scale reactor. They reported the heating value of 15.12 MJ/kg for bio-oil at an optimum condition. Only few studies on the analysis of biochar from pyrolysis of Jatropha wastes have been reported. Sricharoenchaikul and Atong [62] reported that the carbon content (39.41%) and FC (40.31%) of biochar from fast pyrolysis of Jatropha de-oiled cake were significantly lower than the biochar (carbon 61e67% and FC 49e57%) obtained from this study. High carbon content and FC in biochar are beneficial to use as a catalyst support and electrode material due to low-cost renewable carbon source. The commercial activated carbons are produced mostly from petroleum and coal, which are more expensive and not environmentally friendly. Therefore, the activated carbon from biochar seems to be a promising option, which is cheap, renewable and environmentally friendly [63].

60 55 50

Concentration (%v/v)

45 40 35 30 25 20 15 10 5 0 400 500 600

H2 0 2.52 17.08

CO 9.32 10.7 4.54

CH4 0.18 12.0 32.5

C2H4 0.03 1.14 1.39

C2H6 0.11 5.54 8.61

C3H6 0 1.10 1.50

C3H8 0.01 2.76 2.81

Gas component Fig. 10. Gas product components at different operating temperatures.

CO2 59.9 52.4 23.3

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J. Kongkasawan et al. / Energy 113 (2016) 631e642

formation of noncombustible substances such as water or carbon dioxide could lead to the losses in mass and energy distributions as well as some uncollectible products stuck in the reactor [21]. The bench-scale reactor used in the current study made some bio-oil and biochar adhered to the wall and some condensed bio-oil remained in the gas line leading to the percent loss. According to the previous studies, similar mass losses were observed using the same reactor [20,21,31]. Based on the overall mass and energy distributions, the pyrolysis temperature at 500
C appeared to be the most effective for Jatropha residues utilization due to its high values for both mass and energy conversion efficiencies. Gunaseelan [29] reported the annual Jatropha seed production was around 4  105 kg/km2. According to the de-oiled cake yield (54% of input biomass) as mentioned in section 2.1, approximately 2.16  105 kg/km2/yr of Jatropha residue can be produced after the oil extraction process. Fig. 14 shows the annual production of pyrolysis products from Jatropha waste if the optimum condition of pyrolysis is applied. The biochar can be produced from the residues at around 8.7  104 kg/km2/yr with approximately 65.6 m3/km2/yr of liquid product and 4.4  104 m3/km2/yr of gas products. It can be seen the total energy value of 3.4  106 MJ/km2/yr recovered from the Jatropha de-oiled cake, which can be divided into 2.4  106 MJ from biochar, 5.5  105 MJ from bio-oil, and 4.4  105 MJ from gas products.

There were also some pressurized pyrolysis studies using other biomass. The pyrolysis of rice husk showed that the bio-oil obtained under elevated pressures had significantly less oxygen and a higher heating value than that from atmospheric pressure [23]. Maguyon and Capareda [21] also found that the bio-oil produced from pressurized pyrolysis of microalgae (Nannochloropsis oculata) had a better quality than the one from atmospheric pressure. Therefore, pressurized pyrolysis could be an interesting option to generate better quality products.

3.4. Mass and energy balance Mass and energy distribution for pyrolysis processes at different operating temperatures were determined based on product yields and their heating values as provided in Figs. 12 and 13. The highest mass conversion efficiency was obtained at 500
C (89%) followed by 400
C (84%) and 600
C (79%). The optimum total energy recovery was found at 600
C (78%) but was not significantly different from 500
C (77%). Biochar yielded the highest amount for both mass and energy distributions at all pyrolysis temperatures. Low energy distribution of the bio-oil was caused by large mass portion of aqueous fraction contained in liquid product. In addition, only 0.5% of energy recovery from the gas product at 400
C was achieved due to the fact that low combustible gases were generated at low temperature. The energy conversion of the biochar decreased when a pyrolysis temperature was increased because of the reduction in biochar mass yield at higher operating temperatures. The thermal degradation of lignin and hemicellulose could lead to a significant mass loss in a form of volatiles [47]. In addition, the

Liquid product

4. Conclusion Pyrolysis studies of Jatropha de-oiled cake using a pressurized batch reactor indicated that the operating temperatures affected

Bio-char

Syngas

Mass loss

100% 90%

Mass distribution

80% 70% 60% 50% 40% 30% 20% 10% 0% 400

500

600

Pyrolysis temperature (oC) Fig. 12. Mass conversions of pyrolysis process at different temperatures.

Bio-oil

Bio-char

Syngas

Energy loss

100% 90%

Energy distribution

80% 70% 60% 50% 40% 30% 20% 10% 0% 400

500

600

Pyrolysis temperature (oC) Fig. 13. Energy recoveries from pyrolysis process at different temperatures.

J. Kongkasawan et al. / Energy 113 (2016) 631e642

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References

2.3×104 kg

(a)

5.9×104 kg or 65.6 m3

4.7×104

kg or 4.4×104 m3

8.7×104 kg

liquid product

biochar

(b)

gas product

losses

5.5×105 MJ 1.0×106 MJ

4.4×105 MJ 2.4×106 MJ

bio-oil

biochar

gas product

losses

Fig. 14. Annual Jatropha residues conversion into other energy products via pyrolysis (a) mass distribution and (b) energy distribution.

the product yields as well as their chemical properties. The HHVs of biochar and bio-oil significantly improved from the Jatropha residues. In addition, the chemical compositions of pyrolysis products showed the possibility of using this as fuel replacement. High carbon content present in the biochar showed a high potential applications for activated carbon or fuel substitute. Bio-oil also contained high phenol and hydrocarbon compounds, which needed further upgrading process to make it acceptable to use as transportation fuel. The maximum pyrolysis gas yield was obtained at 600
C with the energy content of 4.2 MJ/kg. According to the mass and energy distribution, pyrolysis at 500
C was the optimum condition with 89% of mass conversion and 77% of energy recovery.

Nomenclature ANOVA FC GC HHV LSD MC VCM

analysis of variance fixed carbon gas chromatograph high heating value (MJ/kg) Fisher's least significant difference moisture content volatile combustible matter

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