Reaction parameters effect on hydrothermal liquefaction of castor (Ricinus Communis) residue for energy and valuable hydrocarbons recovery

Renewable Energy 141 (2019) 1026e1041

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Reaction parameters effect on hydrothermal liquefaction of castor (Ricinus Communis) residue for energy and valuable hydrocarbons recovery Ravneet Kaur a, b, Poonam Gera a, Mithilesh Kumar Jha a, Thallada Bhaskar b, c, * a b c

Dr B R Ambedkar National Institute of Technology, Jalandhar, India Materials Resource Efficiency Division (MRED), CSIR-Indian Institute of Petroleum, Dehradun, India Academy of Scientific and Innovative Research (AcSIR), New Delhi, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 20 August 2018 Received in revised form 2 March 2019 Accepted 13 April 2019 Available online 15 April 2019

Castor plant (Ricinus communis) is a fast growing, perennial shrub also known as wonder tree from Euphorbiaceae family. India ranks globally first with production of 87% of the castor seed, while second and third largest producer countries, China and Brazil produced 5% and 1%, respectively. Hydrothermal liquefaction (HTL) is one of the most promising thermochemical conversion process used to convert wet/ high moisture biomass to biofuels and value-added hydrocarbons. HTL of castor residue (stem and leaves) was performed at 260, 280, 300
C and 15, 30, 60, 90 min. Investigations on the effect of temperature and residence time on distribution of products (bio-oil, bio-char) indicated the maximum Total Bio-oil (TBO) yield of c.a. 15.8 wt% was obtained at 300
C at 60 min. The major compounds observed by GC-MS were phenols and their derivatives, aromatic hydrocarbons, N-containing compounds, acids. In addition, the recovery of carbon and corresponding energy recovery with respect to castor residue indicated that the carbon and energy recovery for bio-oil 1 were 24.23% and 31.08% respectively. An increase in the carbon and decrease of oxygen content in bio-oil (BO) demonstrates that the castor residue can be used as a potential feedstock for bioenergy applications. © 2019 Elsevier Ltd. All rights reserved.

Keywords: Ricinus communis Hydrothermal liquefaction Bio-oil Carbon recovery Energy recovery

1. Introduction The increase in petroleum price and sustainability towards the environment are the movers for the use of biomass as a renewable energy source. Second generation biofuels are considered as a potential candidate as they reduce greenhouse gas emissions, limits the food vs. fuel competition and reduce disposal problems [1]. Lignocellulosic biomass is an abundant and cheap energy source used for the production of thermal/electrical energy, raw material for chemicals, as fuel for transportation. Ricinus Communis (Castor plant) belongs to Euphorbiaceae family and genus Ricinus. It is an evergreen plant which grows up to 10 m height. Castor plant includes seeds, stems and leaves and the residue generated by per ton of castor plant are seeds: 468 Kg, stems: 388 Kg and leaves:144 Kg [2]. It is native to the India and Eastern Africa but is widespread throughout tropical and

* Corresponding author. CSIR-Indian Institute of Petroleum, Dehradun, India. E-mail addresses: [email protected], [email protected] (T. Bhaskar). https://doi.org/10.1016/j.renene.2019.04.064 0960-1481/© 2019 Elsevier Ltd. All rights reserved.

subtropical regions. The growth of castor plant is rich along stream banks, distributed areas, river beds, bottomlands. Production of castor plant in India increases drastically as India ranks first in the world trade followed by China and Brazil [3]. Around 14 hybrids and 18 varieties of castor are cultivated in India to obtain good quality and high yield of castor oil. In 2016, India produces 22, 36, 000 MT of castor seed with an oil content of around 10, 28, 560 MT [4]. Castor oil from seeds can be extracted using different processes like Mechanical Extraction, Chemical Extraction using solvent, Reactive Extraction, and Biochemical Extraction. The applications of castor oil in ancient India was for lighting, as an ointment, a motor lubricant in internal combustion engines, racing cars and airplanes. Castor bean was used as bomb because it contains toxic compound Ricin. Castor oil and its derivatives are used for many purposes like manufacturing of soaps, lubricants, carbon paper, inks, paints, waxes, polishes, nylon fiber, pharmaceuticals, perfumes, dyes, electronics, and telecommunication etc. [5,6]. Castor oil is an important ingredient of medicines like anticancer, antidote, antioxidant, antimicrobial, antidiabetic, boils, dog bite, dermatitis, antiasthmatic, tuberculosis, cold tumours, urethritis, venereal diseases,

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

wound healing etc. [7]. Castor oil is also used as feedstock for the production of biodiesel by different researchers [8e11]. Catalysts were used to reduce the viscosity, improve the quality and performance of the biodiesel produced from castor oil [2,12e14]. The kinetic study on castor cake were also reported by different researchers [15,16]. The pyrolysis of castor bean cake was done by Aldobouni et al. [17] where highest bio-oil yield of 63% w/w was obtained at 400
C for 60 min. The pyrolysis kinetics and thermodynamic parameters of castor residue using thermogravimetric analysis was reported by Kaur et al. [18]. Castor oil has many applications for both in industrial scale and medicinal purposes. India ranks first in the world for the production of castor seed and the cultivation of the castor plant is done to obtain oil from its seeds. The remaining part of the plant consists of stems and leaves which generates approximately 50% of residue. The applications of the castor stems and leaves are limited and are therefore considered as waste. For the effective utilization of castor plant, we use castor residue (stem and leaves) as a potential feedstock. Different thermochemical conversion techniques used for the conversion of biomass to biofuels are gasification, combustion, pyrolysis, and liquefaction. Hydrothermal liquefaction (HTL) gained more attraction as compared to other processes due to its advantages like feedstock flexibility, high energy and resource efficiency of the process, and high output product quality [19,20]. Hydrothermal liquefaction process involves conversion of biomass to biofuels and value-added products at temperature of 250e374
C and pressure 4e22 MPa, in the presence of water [21]. Water is non-flammable, non-toxic, readily available and considered as greener solvent. The key property of water to be used as a solvent is stabilization of structures and affecting the reaction routes by hydrogen bonding. At standard conditions (20
C, 101,325 KPa) water will not react with organic compounds. As temperature increases, properties of water like solubility, density, dielectric constant and reactivity changes. Increase in temperature, decreases the dielectric constant (Er). For example, increase in temperature from 25
C to 300
C, value of Er becomes 78.85 to 19.66. Electronegativity of the oxygen molecule is reduced as temperature increases and shared electron by oxygen and hydrogen tends to circulate more evenly. As per Arrhenius theory reaction rate, the dissociation constant Kw at 300
C is about 500 times higher than that of 25
C. Increasing the temperature, dissociation constant also increases which leads to increase the rate of both acid and base catalyzed reactions in water. Due to the above properties of water, it is considered as an excellent solvent for the hydrothermal liquefaction of biomass. The various conditions that affects the hydrothermal liquefaction process are: temperature, pressure, residence time and biomass to solvent ratio. Temperature is the one of the main parameters that effects the bio-oil yield and conversion [21]. The effect of sub- and supercritical conditions of jack pine powder was investigated by Xu and Etcheverry. An increase in liquid yield was observed at the temperature range of 250e300
C. In liquefaction process, an endothermic reaction will take place at low temperature, and becomes exothermic at higher temperatures [22]. Increase in bio-oil yield was observed with increase in temperature while further increase in temperature suppresses liquefaction. A temperature range of 300e374
C is recommended as final temperature which depends upon the biomass type and specifications for composition of bio-oil. The optimum temperature for cellulose, hemicellulose, grasses, softwood and algae are 300e330
C [21]. Pressure is crucial factor in the HTL process as it helps water in the liquid state and incur saving by avoiding the high energy costs of a two-phase system [23]. However, pressure imparts little effect on bio-oil yield near or at supercritical liquefaction conditions. In subcritical system, the role of the pressure becomes insignificant

1027

[24]. Residence time is considered as secondary parameter that effects the bio-oil yield and conversion. Under supercritical conditions usually short residence time is desirable. At very high residence time secondary reactions occurs, which further reduces the bio-oil yield [25]. Hydrothermal liquefaction of rice straw was done in the presence and absence of catalyst and the optimum conditions for bio-oil yield was obtained at 300
C and 120 min [26]. High solvent to biomass ratios is generally unfavorable due to the large amounts of solvent cost, higher energy inputs and wastewater treatment problems. At high biomass to water ratios, the relative interactions among molecules of biomass and that of water become less influential which can suppress dissolution of biomass component. Even at very high biomass to solvent ratios the hydrothermal liquefaction tends to behave like pyrolysis. At very low Biomass/solvent ratios, the amount of liquid oils decreased comprehensively. The effect of the biomass to solvent ratios were reported in literature [27e30] and concludes that 1:6 ratio is best for maximum production of liquid fuels. Considering the extensive literature support and our own studies [29,31e34], we have chosen temperature (260, 280, 300
C) and residence time (15, 30, 60,90 min) as main parameters to know the effect of bio-oil yield and conversion. This is the first report in the literature where castor residue used as a feedstock to produce biocrude using HTL process along with carbon and energy recovery of castor residue bio-products. The effect of operating temperature (260e300
C) and residence time (15, 30, 60, 90 min) on product yields was investigated. The major compounds of the liquid product were identified by Gas Chromatography-Mass Spectrometry (GC-MS). Products were characterized by Fourier transform infrared spectroscopy (FT-IR), Elemental (CHNS), Proton Nuclear magnetic resonance spectroscopy (1H NMR), Scanning electron microscope (SEM), and X-ray diffraction (XRD) analysis. Further, this work includes the carbon and energy distribution of the bio-products based on elemental analysis data in order to know the characteristics, end -uses and potentials of HTL based on the concept of bio-refinery. 2. Materials and methods 2.1. Raw material and characterization Castor residue (leaves and stems) was collected from boundary of Dr B R Ambedkar National Institute of Technology, Jalandhar campus (31.3962
N, 75.5354
E) Jalandhar, Punjab. The sample was milled to about 60e70 mesh size using crusher and sieve shaker. The powder form of the sample was used for further analysis. Deionized water prepared in lab and used for experiments. Proximate analysis of biomass i.e., moisture content, ash content, volatile matter was done using ASTM D-3173, D-3174, and D-3175 standards respectively. Fixed Carbon (FC) (wt.%) present in castor residue was calculated by using formula:

FC; wt:% ¼ 100  ðMoisture content; wt:% þ Ash content; wt:% þ Volatile matter; wt:%Þ

(1)

The process involved to determine components present in castor residue was reported in our previous study [18]. The Elemental analysis, Thermogravimetric analysis (TGA), FT-IR, XRD, SEM of castor residue was also reported in this study. The Higher heating value (HHV) is the total energy content released when the material is burnt under air, and obtained from elemental analysis with Dulong’s formula. Dulong’s formula is used for the calculation of HHV as: the heat value of waste is directly proportional to the carbon content of the residue [35], the residue and products has oxygen content of more than 15% [36], dulong formula is more

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better than modified dulong formula [37]. The main elements C, H, O was calculated and HHV of castor residue and all products were calculated using Dulong’s formula: Heating value, MJ/kg ¼ 0.338 C þ 1.428 (H- O/8) þ 0.095 S

(2)

All the experiments were carried out in a high-pressure batch autoclave (Parr reactor, Model no. 4598) made up of Hastelloy. In a typical run, 5 gm of castor residue and 30 gm of distilled water were loaded. Then the reactor was sealed and purged with nitrogen for five times to remove the inside air. The reactants were agitated at z 200 rpm using vertical magnetic stirrer. The reactor was then heated up to the desired temperature (260, 280, 300
C) and kept for desired residence time (15, 30, 60,90 min). After the reaction was completed the reactor was cooled to room temperature. Gaseous products were vented out, while the liquid and solid products were separated out using vacuum filtration. Phase separation of liquid product was done using separating funnel. The aqueous phase is a mixture of water-soluble hydrocarbons (WSH), designated as Others. The organic phase was extracted with an equal quantity of diethyl ether. The ethereal solution was then dried using anhydrous sodium sulfate filtrated and evaporated using rotary vacuum evaporator under reduced pressure. The final product after evaporation was designated as bio-oil 1 or BO1. The solid products were extracted using acetone in soxhlet apparatus until the solvent in thimble become colorless. The liquid fraction obtained after evaporating the solvent under reduced pressure was weighed and termed as bio-oil 2 or BO2. Total bio-oil (TBO) is the sum of bio-oil 1 and bio-oil 2. The insoluble acetone fraction was then dried at 105
C and designated as bio-char or BC. The mass balance equations used in this procedure are:

W feed  W biochar  100 W feed

(3)

Bio  oil 1 or BO1 yield; wt:% ¼

W ethersoluble  100 W feed

(4)

Bio  oil 2 or BO2 yield; wt:% ¼

W acetonesoluble  100 W feed

(5)

Bio  char yield; wt:% ¼

Gas yield; wt:% ¼

is the weight of ether soluble bio-oil 1 or BO1; W acetoneis the weight of acetone soluble bio-oil 2 or BO2. Other yields represent the water-soluble oxygenated hydrocarbons and some loses. The carbon recovery and energy recovery of bio-oil 1 and bio-oil 2 and bio-char were calculated using the following equations:

Carbon recovery ¼

2.2. Experimental procedure

Conversion; % ¼

ether-soluble: soluble:

W biochar  100 W feed

(6)

Carbon content in bio  oil = bio  char Carbon content in castor residue  bio  oil = char yield (9)

Energy recovery ¼

HHV of bio  oil= bio  char  bio HHV of castor residue  oil = char yield

Energy Densification factor ¼

HHV of biochar HHV of castor residue

(10)

(11)

2.3. Characterization methods Liquid products were characterized using Elemental analysis (CHNS), HHV, GC-MS, FT-IR, 1H NMR. Bio-char obtained after reaction were characterized by Elemental analysis (CHNS), HHV, SEM, FT-IR, and XRD. Elemental analysis (CHNS) was done using Thermo Finnigan, Italy elemental analyzer. The oxygen content present in biomass was calculated by difference. Thermogravimetric analysis (TGA) was carried out in Shimadzu DTG-60 instrument. GC-MS analyses of organic fraction were conducted on a GC/MS, Agilent 7890 B equipped with HP-1 column (25 m  0.32 mm  0.17 mm). The injected volume was 0.4 mL in a splitless mode. Helium was used as carrier gas with flow rate of 1 ml min1. The temperature program of GC used in this study was: 50
C (hold for 2 min) / heating till 280
C (5
C/min, hold 5 min). Compounds were identified by comparing the major peaks in the total ion chromatograms with NIST library. Functional group analysis of all samples was carried out using Perkin Elmer Spectrum Two spectrometer. 1H NMR spectra of organic phase were recorded in the Bruker Avance III 500 MHz instrument using CDCl3 (Merck 99.5%) as a solvent. Xray powder diffraction (XRD) analysis of solid samples was carried out using X’PERT -PRO Model: PW 3064, Philips, Japan with Cu Ka radiation. Surface topography and composition of all solid samples were analyzed by using Digital Scanning Electron Microscope -JSM 6100 (JEOL).

Wðvessel þ feed þ waterÞ before HTL  Wðvessel þ feed þ waterÞ after HTL  100 Amount of feed taken ðgÞ þ amount of water added ðgÞ

(7)

3. Results and discussions 3.1. Characterization of castor residue

Other yield; wt:% ¼ 100  ðbio  oil 1 þ bio  oil 2 þ bio  char þ gasÞ (8) Wfeed: is the weight of feed; W bio-char: is the weight of bio-char; W

3.1.1. Elemental, proximate, component and ICP analysis of castor residue Table 1 represents the elemental, proximate, component and ICP analysis of castor residue. Castor residue has 43.59 wt% C,

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

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Table 1 Elemental, proximate, component, ICP analysis of castor residue. Element Analysis

wt.%

Proximate Analysis

wt.%

Component Analysis

wt.%

Carbon Hydrogen Nitrogen Oxygen* HHV, MJ/kg

43.59 5.56 4.69 46.16 14.43

Moisture Ash Volatile Matter Fixed Carbon * by difference

11.14 5.40 74.30 9.16

Extractives Cellulose Hemicellulose Lignin

16.40 38.42 22.40 20.20

Mg, ppm 3078

Ca, ppm 17,500

Cr, ppm 32

Na, ppm 104

K, ppm 16,653

Fe, ppm 341

100 0.000

TGA DTG

-0.001

60 -0.002

40

DTG, mg/sec

Weight loss, %

80

-0.003

20

-0.004

0

200

400

600

-0.005

800

Temperature, C

1183 1491 1240 1413

Transmittance, %

P, ppm 3325

1317

3404

1051 2926 1634 500

1000

1500

2000

2500

3000

3500

4000

-1

Wavenumber, cm

Fig. 1. (a) Thermogravimetric analysis of castor residue at 10
C/min (b) FT-IR analysis of castor residue.

Cu, ppm 10

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R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

5.56 wt% H, 4.69 wt% N, and 46.16 wt% O. The HHV of castor residue calculated using Dulong formula was 14.43 MJ/kg. The moisture content and ash content in castor residue were 11.14 and 5.4 wt% respectively. It is observed that the castor residue has less ash content as compared to other biomass present in literature [38]. The problems associated with high ash content are; it affects the burning rate, slagging, corrosion, fouling and aggregation. Biomass ash can be used for the production of adsorbents and construction material, recovery of valuable components and their utilization, for soil amendment and fertilisation. Castor residue has cellulose and lignin content of 38.42 and 20.20 wt % respectively. The major elements present in castor residue were Ca, K, and P around 17,500, 16,653, and 3325 ppm respectively. 3.1.2. Thermogravimetric analysis of castor residue Fig. 1(a) shows the TG/DTG curves of castor residue at 10
C/min. The thermal decomposition of castor residue was done in three stages: (i) Moisture removal, (ii) Active pyrolysis, and (iii) Passive pyrolysis. In the first stage, the weight loss up to 128
C is due to the evaporation of water and extractives present in biomass [39]. The thermal decomposition of castor residue was started at 150
C, followed by major loss in the temperature range of 150e530
C, where decomposition of hemicellulose, cellulose and small amount of lignin takes place. This stage is known as active pyrolysis. Decomposition of biomass components at distinct temperatures were clearly shown in DTG curve. The first shoulder at lower temperature represents the decomposition of hemicellulose while the second shoulder corresponds to the decomposition of cellulose. The tailing section also known as passive pyrolysis is done at broader temperature range (150e900
C) represents the decomposition of lignin. The final product as char is obtained after passive pyrolysis. 3.1.3. FT-IR analysis of castor residue The FT-IR spectrum of castor residue was shown in Fig. 1(b). The broad peak at frequency range from 3200 to 3600 cm1 were due to N-H and O-H stretching vibrations represents the presence of secondary amines and phenols & alcohols respectively. The presence of N-H vibrations is ascribed to proteins while O-H is ascribed to cellulose and lignin in biomass [40]. The absorption at wavenumber 2926 cm1 represents the ¼ C-H and C-H vibrations. These vibrations are mainly due to presence of cellulose. The stretching band at 1634 cm1 were assigned to aromatic groups shows the presence of lignin. The absorption peak at 1413 cm1 shows the presence of saturated aliphatic hydrocarbons (C-H bending). The CN stretching vibrations are due to presence of nitrogen was observed in the range 1240e1350 cm1. The absorption peak at

1051 cm1 shows the presence of C-O due to the presence of cellulose and hemicellulose in it. In general, characteristic peaks shows the presence of all the three components i.e., cellulose, hemicellulose, and lignin in it. 3.2. Effect of reaction parameters on products yield Table 2 depicts the product distribution of castor residue obtained after hydrothermal liquefaction. The reactions were conducted at 260
C, 280
C, 300
C for different residence time (15, 30, 60, 90 min). It was observed that the temperature is the most influential parameter affecting the yields of products. The maximum conversion of 83.80 wt% was observed at 280
C for 15 min while the lowest conversion of 75.25 wt % was observed at 260
C for 15 min. The increase in conversion was observed with increase in temperature from 260
C to 280
C. Further increase in temperature from 280
C to 300
C leads to decrease in conversion. The maximum Total Bio-oil (TBO) yield ca. 15.8 wt % was obtained at 300
C for 60 min. The highest total bio-oil yield at different temperature were 9.4 wt % at 260, 10.2 wt % at 280 and 15.8 wt % at 300
C. The same effect on bio-oil yield was observed when domestic sewage waste was used as feedstock at different reaction parameters [41]. Similar effect on biooil yield were obtained when HTL of rice straw was done at 300
C [26]. The optimized range (200e300
C) may prevent the secondary decomposition of liquefied products to gaseous products. At higher temperature, phase change of water to gaseous ultimately favors Boudouard gas reactions. The major fraction obtained was water-soluble hydrocarbons (WSH) or others ranging from 57.8 to 68.8 wt % depending upon the reaction conditions. The aqueous fraction or WSH may be derived from hydrolysis of carbohydrates present in castor residue. At lower temperature hydrolysis reaction is predominant leads to increase the WSH products [42,43]. As the temperature increases, the amount of WSH decreases forms oily and gaseous products by dehydration, decarboxylation and deoxygenation reactions. The gas and total bio-oil yield ranges from 1.1 to 11.4 wt % and 3.2e15.8 wt % respectively. The bio-char ranging from 16.2 to 24.5 wt % was the second largest fraction. It was observed that the bio-char yield was first decreases with temperature from 260 to 280
C and then increases at 300
C. The liquefaction process will done based on two competitive reactions: (i) the solid products were formed due to condensation, cyclization, and repolymerization of liquid products, (ii) Decomposition of solids and condensation of gases could enhance the bio-oil yield [44]. It was observed that the increasing the temperature increases the total bio-oil yield and decreases the water-soluble hydrocarbons (WSH). The influence of residence time (RT) on products yield were

Table 2 Product distributions, wt.% of castor residue from hydrothermal liquefaction at different reaction conditions. Sample Code

C260-15 C260-30 C260-60 C260-90 C280-15 C280-30 C280-60 C280-90 C300-15 C300-30 C300-60 C300-90

Bio-oils Bio-oil 1

Bio-oil 2

5.8 6.4 6.6 2.2 5.4 5.0 5.4 2.0 7.0 7.4 9.0 4.6

2.0 2.8 2.8 1.0 2.8 3.4 4.8 1.8 5.0 5.6 6.8 3.0

Total Bio-oil

Gases

Bio-char

Other yield

Conversion

7.8 9.2 9.4 3.2 8.2 8.4 10.2 3.8 12.0 13.0 15.8 7.6

9.1 8.6 7.4 11.4 6.9 4.6 4.3 7.4 1.7 2.6 1.1 2.0

24.5 24.4 23.6 22.0 16.2 22.4 21.8 20.0 21.0 23.6 23.0 24.0

58.6 57.8 59.6 63.4 68.7 64.6 63.7 68.8 65.3 60.8 60.1 66.40

75.25 75.56 76.43 78.00 83.80 77.60 78.19 80.00 79.00 76.40 77.00 76.00

where, C defines castor residue, 260,280,300 are Temperature (
C) and 15,30,60,90 are Residence time (in mins).

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

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Table 3 Major compounds identified in BO1 (Area, %) of castor residue from hydrothermal liquefaction at different reaction conditions detected using GC-MS. Retention Time

Compound Identified

Chemical Formula

7.81

Phenol

8.04

Chemical Structure

Molecular weight

BO1 26060

BO1 28060

BO1 30060

C6H6O

94.111

0.66

1.34

11.42

Pyrazine, 2-ethyl-6-methyl-

C7H10N2

122.168

e

e

1.51

8.74

2-Cyclopenten-1-one, 2,3-dimethyl-

C7H10O

110.154

e

e

1.21

9.62

Phenol, 2-methyl-

C7H8O

108.138

e

e

0.78

10.05

2(1H)-Pyridinethione, 3-hydroxy-

C5H5NOS

127.161

e

e

0.61

10.12

2-Cyclopenten-1-one, 3,4,4-trimethyl-

C8H12O

124.180

e

e

0.45

10.25

p-Cresol

C7H8O

108.138

e

0.65

5.54

10.84

Phenylethyl Alcohol

C8H10O

122.164

e

e

1.31

11.25

Bicyclo[2.2.1]heptane-2-carboxaldehyde, exo-

C8H12O

124.180

e

e

2.19

11.35

3-Pyridinol

C5H5NO

95.099

e

17.62

e

11.54

4-Pyridinol

C5H5NO

95.099

12.90

e

e

12.59

Phenol, 4-ethyl-

C8H10O

122.164

e

e

4.21

(continued on next page)

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R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

Table 3 (continued ) Retention Time

Compound Identified

Chemical Formula

12.61

Phenol, 4-amino-

12.68

Chemical Structure

Molecular weight

BO1 26060

BO1 28060

BO1 30060

C6H7NO

109.126

2.72

e

e

3-Pyridinol, 6-methyl-

C6H7NO

109.126

e

4.73

e

13.46

3-Formyl-4,5-dimethyl-pyrrole

C7H9NO

123.152

e

1.21

e

13.94

2-Propenenitrile, 3-phenyl-, (E)-

C9H7N

129.159

e

e

1.10

14.58

Phenol, 3-(dimethylamino)-

C8H11NO

137.179

e

e

1.70

15.42

Hydroquinone

C6H6O2

110.111

7.96

14.07

14.45

17.67

1H-Indole, 4-methyl-

C9H9N

131.174

e

e

1.21

17.67

1H-Indole, 6-methyl-

C9H9N

131.174

e

0.88

e

18.20

5 Ethylcyclopent-1-ene-1-carboxylic acid

C8H12O

140.180

e

1.53

e

19.93

Benzonitrile, 2,4,6-trimethyl-

C10H11N

145.201

e

e

1.17

20.11

1H-Indole, 2,3-dimethyl-

C10H11N

145.201

1.05

e

1.04

20.11

2-Methyl-5-(1-butyn-1-yl) pyridine

C10H11N

145.201

e

0.90

e

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

1033

Table 3 (continued ) Retention Time

Compound Identified

Chemical Formula

29.68

Benzene, 1,3,5-trimethoxy-

33.77

Molecular weight

BO1 26060

BO1 28060

BO1 30060

C9H12O3

168.190

e

e

2.43

2,5-Piperazinedione, 3-benzyl-6-isopropyl-

C14H18N2O2

246.305

3.83

3.56

e

33.92

Hexadecanamide

C16H33NO

255.439

2.42

1.57

e

33.90

Octadecanamide

C18H37NO

283.492

e

e

2.56

34.55

N-Methyldodecanamide

C13H27NO

213.360

1.26

2.36

4.19

39.18

Cyclohexanecarboxylic acid, 3-(1,1-dimethylethyl)-, C11H20O2 cis-

184.275

e

2.03

e

40.07

Pyrrolidine, 1-(1-oxopentadecyl)-

C19H37NO

295.503

1.28

e

1.75

43.92

Squalene

C30H50

410.718

1.07

e

e

47.44

Vitamin E

C29H50O2

430.706

6.70

6.03

6.90

48.75

Stigmasterol

C29H48O

412.691

9.34

5.52

3.28

49.44

g-Sitosterol

C29H50O

414.707

16.80

10.41

6.54

Total

67.99

74.41

77.55

shown in Table 2. The effect of residence time is necessary to know the optimum time for effective decomposition of biomass. It was observed that the TBO yields increases with time and decreases with further increase in time. At temperature 280
C, the yield of bio-char increases at RT ¼ 30 and then decreases at RT ¼ 60 and 90 min, while for 300
C the bio-char yield increases at 90 min. The gas yield and water soluble hydrocarbons (WSH) yield decreases at higher RT (60 min) results to generate more BO or gas [45]. As the reaction time increases from 15 min to 60 min, WSH yield decreases from 65.3 wt% to 60.1 wt%. The decrease in water soluble hydrocarbons (WSH) yield, increases the total bio-oil yield. The increase in RT from 60 to 90 min results the further decrease in TBO yield, and increase in gas and WSH yield.

Chemical Structure

3.3. Analysis of liquid products 3.3.1. Molecular characterization of bio-oil 1 The chemical composition of bio-oils obtained at different temperature (260, 280, 300
C) were qualitatively characterized by GC-MS. Table 3 lists the information about compound and area (%) of compounds present in BO1 at different reaction conditions. The identification of compounds was performed with the help of NIST mass spectral database. The various chemical compounds of bio-oil 1 were identified as phenolics, aromatic hydrocarbons, N-contained compounds, aldehydes, ketones. amides, alcohols, and acids. The major compounds formed in bio-oil 1 were Phenol, p-cresol, Hydroquinone, Vitamin E, Stigmasterol, and gamma-Sitosterol. The

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compound name of Vitamin E is Tocopherols and tocotrienols. It was observed that the content of compounds was greatly affected by temperature. An increase in area percentage of Hydroquinone was observed with increase in temperature. At 260
C, it was 7.96 while for 280 and 300
C it was 14.07 and 14.46 respectively. Similar to hydroquinone, the area percentage of vitamin E also increases from 6.70 to 6.90 for 260e300
C respectively. A decrease in area percentage (6.03) of vitamin E was observed at 280
C. The area percentage of phenol was increased with increase in temperature. At 260
C it was 0.66, at 280
C it was 1.35 while at 300
C it was 11.42. Major phenolic compounds may be formed by (i) from degradation of lignin, (ii) Degradation of cellulose via hydrolysis to sugars by dehydration and ring closure reactions [46]. The opposite trend in the area percentage was observed for stigmasterol and gamma sitosterol. At 260
C, the area percentage of stigmasterol is 9.34, while at 280 and 300
C it was 5.53 and 3.29 respectively. The area percentage of gamma sitosterol at 260
C was 16.79, 10.42 at 280
C and 6.54 at 300
C. Nitrogen-containing compounds pyridinol, pyrazine, pyridine was formed, may be due to presence of nitrogen in bio-oil 1 or by decomposition of protein. N -containing organic compounds were formed from Maillard Reaction [47]. Nitrile compounds categorized as others were originated from dehydration of acid amines. These acid amines were formed from the reactions of fatty acids and amines. Amides such as Hexadecanamide, Octadecanamide, and N-Methyldodecanamide were formed which are generally used for medicinal purposes. Fig. 2 represents the compounds distribution of BO1 obtained at different temperature based on key groups. It was observed that BO produced at 300
C had higher phenolic compounds and lower N contained compounds than 260 and 280
C. Similar results were observed when rice husk was used as feedstock [48]. Acids were not observed in BO obtained at 300 and 260
C while it was only observed at 280
C. Similar to this, aldehydes and ketones were observed at 300
C. Some compounds have its medicinal applications while high amount of phenolic compounds make castor residue a promising material to be used as biofuel or as a phenol substitute in bio - phenolic resins [49]. 3.3.2. FT-IR analysis of bio-oil 1 The FT-IR spectra of bio-oil 1 or BO1 obtained at different temperature was shown in Fig. 3. The absorption peak in the range

of 3200e3600 cm1 is due to N-H and O-H stretching indicate the presence of amides/amines and alcohols and phenols in the BO. The C-H stretching vibrations at 2863 and 2935 cm1 may indicate the presence of alkanes [50]. The carbonyl group (C]O) stretching vibrations between 1665 and 1760 cm1 indicate the presence of ketones, carboxylic acids, and aldehydes. The absorption peak at 1518 cm1 may be attributed to N-O stretching indicate the presence of nitro compounds, while the peak at 1611 cm1 is ascribed to N-H bending vibrations from amines. The absorption peak between 1400 and 1500 cm1 suggests the presence of aromatics (C-C stretch). The C-H bending vibrations at 1381 cm1 indicate the presence of alkanes in BO. The bands in the region 1020 1360 cm1 were assigned to C-N stretching vibrations which are possibly due to aliphatic amines. The C-N stretching vibrations at 1040 cm1 shows the presence of aliphatic amines. The band between 675 and 900 cm1 are attributed to the C-H vibrations indicate the presence of aromatics in BO. Comparing the FT-IR analysis obtained at different temperature, it was noticed that the almost same functional groups are present in all BO samples but at different relative intensity. It was observed that increases the temperature, diminishes the absorption peak at 1040 cm1 and 816 cm1. 3.3.3. 1H NMR analysis of bio-oil 1 NMR is used to determine the structure of all the complex organic compound present in BO [51]. The organic fraction or BO1 obtained after HTL at different temperature (260, 280, 300
C) has been analyzed using 1H NMR as shown in Fig. 4. The spectra from 0.5 to 1.5 ppm represent the aliphatic proton attached to carbon atoms or heteroatom (O or N) i.e., alkane group protons [52]. The aliphatic protons were observed 59.07% at 260
C, 51.28% at 280
C, 52.69% at 300
C. The next region 1.5e3.0 ppm represents the protons on aliphatic carbon atoms that may be bonded to a C]C double bond or heteroatom. It is observed that increasing the temperature from 260 to 300
C decrease these protons. In 1.5e3.0 ppm protons obtained at 300
C was 31.25%, while at 280
C it was 28.72% and for 260
C it was 27.78%. The next portion of spectrum 3.0e4.7 ppm represents proton on carbon atom next to an aliphatic alcohol/ether or a methylene group that joins two aromatic rings. The amount of proton percentage in this region was 0.43, 3.37 and 0.9 at 300, 280, 260
C respectively. The region

Aromatic compounds

BO1 300-60 BO1 280-60 BO1 260-60

Amides Acids Others Aldehydes Ketones N-contained compounds Phenolic compounds Tocopherols and tocotrienols 0

5

10

15

20

25

30

35

Area, % Fig. 2. Distribution of BO1 compounds based on key groups obtained at different reaction conditions.

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1381

735 1040

1668 1611

Transmittance, %

1280

816

1115 735

1040

1381

1280

816 735

1115 1040

500

1115

1000

1712

3318

BO1 280-60

1611

1712

1518

2935

2863

1474 1381

2935

2863

1668

1668

3318

BO1 300-60

1280 1611

816

3318

BO1 260-60

1518

1474

1035

1712 1518

1474

1500

2863

2000

2500

2935

3000

3500

4000

-1

Wavenumber, cm

Fig. 3. FT-IR analysis of BO1 obtained at different reaction conditions.

between 4.7 and 6.0 represents the presence of phenolic OH or olefinic protons. The lignin-derived methoxyl phenols and hydrogen atoms of carbohydrate like molecules were formed. The maximum proton percentage was 4.39 at 280
C. The next region 6.0e8.5 ppm corresponds to aromatic region. The maximum percentage of 14.89 was observed at 300
C while for 280 and 260
C the proton percentage decreases i.e., 12.24 and 9.79 respectively. The downfield region 8.5e10.0 ppm was not shown as no major protons were observed in this region. Similar to GC-MS and FT-IR results, 1H NMR also revealed that the maximum amount of phenolic compounds were observed at 300
C. The presence of Ne containing compounds, aromatic compounds were also observed in all analysis. This shows that the results obtained from BO analysis through GC-MS, 1H NMR, and FT-IR were in accordance.

60

BO1 300-60 BO1 280-60 BO1 260-60

50

Protons, %

40

30

20

10

0

0.5-1.5

1.5-3.0

3.0-4.7

4.7-6.0

6.0-7.2

7.3-8.5

Chemical shift, ppm Fig. 4. 1H NMR analysis of BO1 obtained at different reaction conditions.

3.3.4. Elemental composition of BO1, wt.% and BO2, wt.% The elemental composition of BO1 and BO2 obtained after HTL of castor residue at 260, 280 and 300
C with residence time 15, 30, 60 min were shown in Fig. 5 (a) and (b). The BO1 and BO2 contains more carbon and less oxygen compared to the raw material. The decrease in oxygen content is may be due to dehydrogenation (-H2), decarbonylation (eCO) and decarboxylation (eCOO) reaction during the HTL of biomass [53]. Like castor residue, the sulphur is not detected in the BO1 and BO2 which is the advantage of the process concerning to clean environment. The nitrogen content present in BO1 varies from 3.88 to 4.94 wt% and for BO2 it was 1.42e4.25 wt%. Although the N content of the BO is still high which may be due to the degradation of other organic molecules except proteins during HTL. The reduction of nitrogen content in bio-oil as compared to raw material was may be due to decomposition of proteins during HTL. The undesirable nitrogen content in BO 1 and BO 2 may leads to formation of NOx, which may be reduced by post treatments through denitrogenation, hydro-treating and hydro-cracking. H/C ratio of castor residue is 1.53 and for BO1 and BO2 it was varying between 0.80 and 1.56. Low H/C ratio produces more aromatic contents in BO [54]. The O/C ratio of castor residue was 0.79 which is more than that of all BO1 and BO2. Reduction of O/C in all BO shows that deoxygenation reaction takes places during HTL of biomass. N/C content of BO2 was minimum at temperature 280
C and RT ¼ 60 min as compared to raw material shows the nitrogencontaining compounds are more reactive. To make biofuel as effective transport fuel, further deoxygenation and denitrogenation of BO is required. 3.3.5. Carbon and energy recovery of BO1 and BO2 The heating value of BO1 and BO2 were shown in Fig. 5 (c) and (d) and higher as compared to the raw material. The maximum heating value of BO1 was 28.36 MJ/kg and for BO2 it was 32.69 MJ/ kg at temperature 300
C and 60 min. The heating value of bio-oil were in the range of 21.90e32.69 MJ/kg. Carbon and Energy recovery (ER) of BO1 and BO2 was calculated using equations (9) and

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Fig. 5. (a). Elemental analysis of BO1, wt.% obtained at different reaction conditions. (b). Elemental analysis of BO2, wt.% obtained at different reaction conditions. (c). Carbon and Energy recovery of BO1 obtained at different reaction conditions. (d). Carbon and Energy recovery of BO2 obtained at different reaction conditions. (e). Elemental analysis of biochar, wt.% obtained at different reaction conditions. (f). Carbon and Energy recovery of bio-char obtained at different reaction conditions.

(10) and represented in Fig. 5 (c) and (d). The main advantage of calculating carbon and energy recovery is to understand the product efficiency in the liquefaction process, so that the product could be an alternative to fossil fuel and valuable product. The carbon and energy recovery of BO1 and BO2 are in the range of 11.12e24.23%, 11.10e24.91% and 11.84e31.05%, 13.35e35.79% respectively. The maximum carbon recovery of BO1 ¼ 24.23% and BO2 ¼ 24.91% was obtained at 300
C for 60 min. The energy recovery of BO1 and BO2 is maximum at 300
C for 60 min. Comparing with the literature, the carbon recovery of castor residue obtained at 300
C is less than from barley straw [55], and Cunninghamia lanceolata [56] in the absence of catalyst. The possible reason of decrease in carbon recovery may be due to less

total bio-oil yield from castor residue. The carbon recovery of castor residue at 300
C is higher than from wheat straw [57,58] at temperature of 350 and 400
C where no catalyst is used. Similar to carbon recovery, the energy recovery of castor residue is less than barley straw [55], and Cunninghamia lanceolata [56] while more than wheat straw [57,58]. The variation in ER % of G. gracilis and C. glomerate [59] with castor residue was observed due to variation in biomass composition, reaction parameters, products yield, and HHV of the product. The G. gracilis and C. glomerate have more biocrude yield, more ER%. The change in carbon recovery and energy recovery of non-catalyzed and catalyzed HTL of rice straw was observed. The carbon recovery of non-catalyzed light bio-oil produced from rice straw was 22.5% while for heavy bio-oil was 29.9%.

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

1037

Fig. 5. (continued).

Energy recovery for light bio-oil was 15.1% and for heavy bio-oil was 27.4%. The use of catalysts may help to increase the total bio-oil yield which further boosts the carbon and energy recovery [26]. 3.4. Analysis of bio-char 3.4.1. Elemental analysis, carbon and energy recovery of bio-char (BC) Elemental Analysis of bio-char obtained after HTL using different reaction conditions is represent in Fig. 5 (e) and (f) represents the HHV, carbon recovery, energy recovery and energy densification factor of bio-char obtained at different reaction conditions. Bio-char has high carbon content and lower in oxygen content as compared to the castor residue. The HHV of bio-char is more as compared to castor residue may be due to dehydration, deoxygenation reactions which take place during HTL. The carbon recovery and energy recovery of bio-char of castor residue is in the range of 19.25e31.04% and 20.87e36.47% respectively. The castor residue has more ER% as compared to G. gracilis and C. glomerate [59] due to more yield and HHV of the bio-char. The energy densification factor for optimum condition (300
C and 60 min) is 1.58. During HTL, dehydration and decarboxylation reactions are responsible for energy densification. Comparing with castor residue, the H/C and O/C ratio of bio-char decreases, thus producing a carbonaceous bio-char or hydro char which has similar applications as pyrolysis char [60]. Bio-char contains various organic and inorganic materials so can be directly used as for fertilizer, soil conditioner, and soil nutrient. Concerning the environmental and energy prospective, the various potential applications of bio-char are: used as an adsorbent for harmful pollutants, feedstock for carbon fuel cells.

3.4.2. FT-IR, XRD and SEM analysis of bio-char The FT-IR spectra of bio-char after hydrothermal liquefaction at different reaction conditions were shown in Fig. 6 (a). The stretching vibrations at 3395 cm1 is due to O-H and N-H groups indicates the presence of alcoholic and phenolic compounds and amines due to cellulose, lignin, and nitrogen present in castor residue. The bands between 2800 and 3000 cm1 confirm the presence of alkanes (C-H) which may be due to presence of cellulose in biomass [61]. The peak at 1581 cm1 may be due to the amines (N-H) while peak at 1407 cm1 shows the presence of aromatics (C-C). The absorption peak at 1273 cm1 may be due to aromatic amines (C-N). The band in the range of 1120e1030 cm1 shows the presence of C-O group and the peak at 734 and 545 cm1 represents the presence of alkenes due to the presence of cellulose and hemicellulose in it. Increasing the temperature from 260 to 300
C, the disappearance of peaks at 1581, 1407, 1273, 1047, 734, 545 cm1 were observed which shows the decomposition of cellulose, hemicellulose, and lignin in castor residue during HTL. The crystallinity of raw material and bio-char obtained after HTL was examined using powder X-ray diffraction. X-ray diffraction patterns of raw material and bio-char are shown in Fig. 6 (b). Using thermochemical processes (pyrolysis, liquefaction), the change in cellulose crystalline structures was observed by interrupting hydrogen bonding of cellulose chains [62]. The X-ray diffraction pattern of raw material showed two distinct peaks at 2q ¼ 15
and 22
of cellulose. Increasing the temperature shifts the cellulose peak by which may crystallinity may losses and bio-char is produced [63,64]. The peaks obtained at 2q ¼ 24
and 26
in all SRs shows the presence of amorphous and turbostratic carbon [65]. The presence of these carbon peaks shows the formation of hydrochar due to the decomposition of the cellulose and lignin during HTL.

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545

BC 260-60

1273 1407

3395 734

Transmittance, %

1047

2832

1581

2935

BC 280-60

1273 1407 545

3395

734 2832

1047 1273

2935

1581

1407

BC 300-60 3395

2935

545 734 1047

500

2832

1581

1000

1500

2000

2500

3000

3500

4000

-1

Wavenumber, cm 5000 4500 4000

BC300-60

Intensity, counts

3500 3000 2500

BC280-60

2000 1500

BC260-60

1000 500

Castor residue

0 5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

2 theta, degrees Fig. 6. (a): FT-IR analysis of bio-char obtained at different reaction conditions. (b): XRD patterns of bio-char obtained at different reaction conditions. (c): SEM images of castor residue and bio-char obtained at different reaction conditions.

The surface morphology of the raw material and bio-char has been studied by scanning electron microscopy. Fig. 6 (c) represents the micrographs of raw material and bio-char obtained at different reaction parameters T ¼ 260
C, 280
C, 300
C at 60 min. Change in structure of raw material was shown in Fig. 6 (c) (i). The lumpy solid, dense matrix having strongly bounded stripes was observed in Fig. 6 (c) (i) of raw material. After Hydrothermal liquefaction, the change in surface were observed in Fig. 6 (c) (ii) - (iv) of bio-char at 300, 280, 260
C respectively. As the cell structure was broken, small size particles which are porous in nature were formed due to the decomposition of cellulose and hemicellulose in it. In bio-char, more agglomerates appeared on the surface may be due to crosslinking caused by dehydration between molecules of cellulose and hemicellulose [66]. The other small particles deposits on the surface are mineral residues left after the HTL of biomass [67].

4. Conclusions The optimum reaction conditions to obtain maximum total biooil yield was at 300
C and at 60 min. The highest conversion of 83.80 wt % was obtained at 280
C with the residence time of 15 min. Major identified compounds from GC-MS were: Hydroquinone, Phenol, p-cresol and categorized as phenolic compounds, which makes it promising material to be used as either bio-fuel or as a phenol substitute in bio-phenolic resins. The carbon recovery and energy recovery of bio-oils lies within 11.12e24.23% BO1, 11.10e24.91% BO2 and 11.84e31.05% BO1, 13.35e35.79% BO2 respectively. The obtained results conclude that the castor residue can be utilized as feedstock for thermochemical conversion processes and obtained products may be used as potential feedstock in various biorefinery applications. Further hydrogenation of bio-oil 1 is required to be used as a transportation fuel.

R. Kaur et al. / Renewable Energy 141 (2019) 1026e1041

1039

Fig. 6. (continued).

Acknowledgement The authors gratefully acknowledge the Director, CSIR-Indian Institute of Petroleum (IIP) and Director, National Institute of Technology, Jalandhar for constant support and encouragement. RK would like to thank the CSIR-IIP Analytical Sciences Division (ASD) at CSIR-Indian Institute of Petroleum (IIP) for providing analytical support. RK would like to acknowledge the Elemental analysis group of IITB and testing facilities provided by SAIF and CIL labs at PU, Chandigarh. RK acknowledges MHRD, Govt of India for rendering fellowship and NIT Jalandhar for their financial support for carrying out this work. The authors are highly thankful to the unknown reviewers for their valuable suggestions for the improvement of the research work. References [1] S.N. Naik, V.V. Goud, P.K. Rout, A.K. Dalai, Production of first and second generation biofuels: a comprehensive review, Renew. Sustain. Energy Rev. 14 (2010) 578e597, https://doi.org/10.1016/j.rser.2009.10.003. [2] H. Bateni, K. Karimi, Biodiesel production from castor plant integrating ethanol production via a biorefinery approach, Chem. Eng. Res. Des. 107 (2016) 4e12, https://doi.org/10.1016/j.cherd.2015.08.014. [3] online, FAO, 2006. Online Available at:http://faostat.fao.org.

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