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Hydro-processing of biomass-derived oil into straight-chain alkanes
Journal Pre-proof Hydro-processing of Biomass-derived Oil into Straight-chain Alkanes Wei-Cheng Wang, Chung-Hung Hsieh
PII:
S0263-8762(19)30500-3
DOI:
https://doi.org/10.1016/j.cherd.2019.10.030
Reference:
CHERD 3865
To appear in:
Chemical Engineering Research and Design
Received Date:
2 December 2018
Revised Date:
14 October 2019
Accepted Date:
15 October 2019
Please cite this article as: Wang W-Cheng, Hsieh C-Hung, Hydro-processing of Biomass-derived Oil into Straight-chain Alkanes, Chemical Engineering Research and Design (2019), doi: https://doi.org/10.1016/j.cherd.2019.10.030
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Hydro-processing of Biomass-derived Oil into Straight-chain Alkanes Wei-Cheng Wang1*, Chung-Hung Hsieh2
1
Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan 70101, Taiwan
2
Department of Chemistry, Tamkung University, Taipei, Taiwan.
*Corresponding author: Wei-Cheng Wang, Email: [email protected]
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Highlights Glyceride-based oil was converted into normal alkanes necessary for producing HRJ Pd/C and NiMo/γ-Al2O3 were tested with various experimental conditions Fresh and used catalysts were characterized through TGA, FTIR, XRD and SEM
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Abstract
Initially converting the glyceride-based oils derived from biomass into straight-chain alkanes are necessary for producing hydro-processed renewable jet (HRJ). In this study, palm oil was turned
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into C15-C18 alkanes over two different catalysts, Pd/C and NiMo/γ-Al2O3, with various reaction conditions such as temperature, pressure, weight hourly space velocity (WHSV) and H2-to-oil
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ratio. The fresh and used catalysts after hydro-processing reaction were then characterized through the techniques including TGA, FTIR, XRD and SEM. The liquid products were
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analysed through GC-MS/FID and the concentrations of C15-C18 were determined. The gas products, such as CO2, CO, C3H8, CH4 and H2, were analysed through GC-TCD for indirectly “visualizing” the reaction, including the performances of hydro-deoxygenation (HDO) as well
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as decarbonylation / decarboxylation, hydrogenolysis, the occurrence of methanation and the consumption of hydrogen. The suggested experimental conditions over these two catalysts were
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elaborated based on the concentration of n-alkanes and gas products.
Keyword: Hydro-processed Renewable Jet; Hydro-processing; Oil upgrading; Hydrodeoxygenation; Green Diesel; Palm oil
1. Introduction: The hydro-process which produces hydro-processed Renewable Jet (HRJ) has been viewed as one of the promising processes for converting glyceride based oils into renewable jet fuels. In 1
this process, the biomass-derived oil is first turned into straight chain alkanes and furthermore the produced alkanes are cracked and isomerized into jet fuel range products. The hydroprocessing of bio-oil is the major part of this process since the catalyst and hydrogen used in this route contribute not only economical but environmental impacts, which strongly determine the sustainability of the process.
Many oil feedstocks, such as plant oils, algae and even pyrolytic oils, are considered as the source of the process, depending on the region. In Asia, palm oil is viewed as a suitable oil feedstock for producing biofuels mainly due to its availability in southeast region. Indonesia and
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Malaysia are the two primary countries that produce crude palm oil (CPO), accounting for 19.7 million and 17.4 million metric tons, respectively [1]. In most of the regions, the oil palm yields are large than 8 ton per hectare per year [2]. Currently, the palm oil price is $573 per metric
tonne. Based on the fatty acid profile of the oil, the double bonds of the unsaturated glycerides
are first saturated through hydrogenation. Certain moles of hydrogen are consumed according to
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the number of double bonds. The propane backbone are further removed through the propane cleave route, where the free fatty acids are formed. Furthermore, the fatty acids are
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deoxygenated into straight-chain alkanes, where three routes occurred simultaneously: hydrodeoxygenation (HDO), decarboxylation and decarbonylation. The carbon chain lengths of the
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alkanes correspond to the carbons of the fatty acids in the oil. The oxygen is removed from the fatty acids through hydro-deoxygenation with the formation of water, through decarboxylation with the formation of CO2 and through decarbonylation with the formation of CO. Hydrogen is
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consumed in the hydro-deoxygenation and decarbonylation routes [3-7].
Previously, Guzman et al. [8] showed that crude palm oil can be hydro-treated into the diesel
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range products at the pressures of 40-90 bar in the hydrogen environment over NiMo/γ-Al2O3 catalyst. The cetane index decayed with the increases in time on stream (TOS), from 96.1 to
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92.5. Kovács et al. [9] has reported a process which converted triglycerides in the sunflower oil into C15 ~ C18 paraffins at the temperature of 350–370 °C, pressure of 20-40 bar, LHSV (Liquid Hourly Space Velocity) = 1.0 h−1 and H2/ oil volume ratio of 500 Nm3/m3. High yield (73.2 % ~ 75.6 %) and high paraffin content (> 99.9 %) products similar to diesel range fraction were produced. The NiMoCe/Al2O3 catalyst was also used to produce straight chain alkanes ranging from C15 to C18, with the yield of 80 %, the conversion of 89 % and selectivity of 90 %. The N2BET, SEM, XRD and TPD techniques were applied for characterizing the properties of the catalyst [10]. The catalyst Pd/C was also used for the hydro-processing of crude palm oil. 2
Compared to NiMo/γ-Al2O3, Pd/C is more suitable for fatty acid feedstocks, while NiMo/γAl2O3 fits more to the triglycerides feedstocks [11]. Other alumina-based catalysts, such as PtPd/Al2O3 and NiMoP/ Al2O3, were also investigated for the hydro-processing of nonedible jatropha oil, for the purpose of producing a high-performance additive diesel fuel [12]. It was additionally found that hydro-deoxygenation was dominated when NiMoP/Al2O3 was applied, while decarboxylation and decarbonylation were the primary reactions as PtPd/Al2O3 was used. In addition, NiMoP/Al2O3 was observed to be the catalyst for long-term process. Presulfied NiMo/γ-Al2O3 catalyst was also used for hydro-deoxygenation of microalgae oil recently [13]. The lifetime and activity of the catalyst were maintained with increases in H2-to-oil ratio,
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residence time, reaction temperature and pressure, which avoided the oxygenate contaminations on the surface of catalyst. The Ni-based (Ni/γ-Al2O3) and Co-based (Co/γ-Al2O3) catalysts were compared while conducting the hydro-deoxygenation of palm oil at 300 °C and 5 MPa [14]. The product yield decreased from 92.2 % to 76.2 % over Ni/γ-Al2O3 catalyst and 88.6 % to 56.6 % over Co/γ-Al2O3 catalyst. The decarboxylation/decarbonylation was superior over hydro-
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deoxygenation when using Ni-based catalyst, while these two routes were comparable when
using Co-based catalyst. According to the previous literatures, Pd/C and NiMo/γ-Al2O3 were the
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two popular catalysts for performing hydro-processing of glyceride-based oils. Maintaining the catalyst activity and expanding the catalyst lifetime are now the primary targets for scaling-up
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the hydro-processing process. Investigating the catalyst behaviours corresponding to the reaction kinetics becomes necessary.
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In this study, catalytic hydro-processing of palm oil over Pd/C and NiMo/γ-Al2O3 catalysts for producing straight chain alkanes was carried out in a fixed bed reactor. Different parameters such as temperature, pressure, LHSV and H2-to-oil ratio were varied for examining the reaction
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kinetics. The characteristics of catalysts were also studied through the analyses of SEM, XRD,
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TGA and FTIR.
2. Experimental method 2.1 Materials
Crude palm oil (CPO) provided by a local chemical company was chosen as the feedstock in this study. The major fatty acid compositions of CPO is 48 % saturated fatty acids (44 % Palmitic 16:0 and 4% Stearic 18:0) and 50 % unsaturated fatty acids (40 % oleic 18:1 and 10% 3
linoleic 18:2). To ensure the consistency of the palm oil, two samples taken a month apart were analyzed in GC-MS/FID and the components shown were similar. The palm oil feedstock used in this study was replaced within a month. The 5wt% Pd/C was provided by Acros organics, NiMo/γ-Al2O3 was provided by A-Plus Inc. The 5wt% Pd/C was dried overnight at 40 ˚C in the oven to remove the moisture contained in the catalyst. The experimental gases 99.99 % N2 and 99.99 % H2 were provided by the Yun-Shan Gas Company. The external standard 99.99 % C8~C20 alkanes that contains 40 mg/L each was provided by Sigma-Aldrich which was used to analyse the liquid product samples.
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2.2 Catalyst Characterizations Scanning electron microscopy (SEM) (VEGA 2 SBH, Tescan, Kohoutovice, Czech
Republic) operated at 20 kV was used to examine the morphology and crystallite of the
catalysts. The powder X-ray diffraction (XRD) patterns of the catalysts were obtained with a
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Bruker D8 ADVANCE Twin-X-ray Powder Diffractometer with LYNXEYE XE-T detector
(Bruker AXS Inc., Madison, WI, USA) using Cu Kα radiation (k = 1.54060 Å) operated at 40
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kV and 40 mA in the angular range between 10˚ and 80˚ for 2θ. The presence of functional groups of catalyst were obtained by operating NicoletTM iS5TM FT-IR spectrophotometer
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(ThermoFisher Scientific Inc., Waltham, MA, USA). The IR spectra were obtained by mixing the samples with 10 times amount of potassium bromide (KBr) and then recorded in the FT-IR spectrophotometer. The FTIR-spectra of adsorbed pyridine were collected in the region of 400-
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4000 cm-1, on the average of 16 scans at a resolution of 4 cm-1. The thermogravimetric analysis (TGA) was carried out using the Perkin Elmer STA60000 (Waltham, MA, USA). Approximately 18-25 gm of sample was prepared. The temperature in the TGA was raised from 50 °C to 105
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°C at the heating rate of 20 °C/min and held for 20 minutes under N2 atmosphere and further increased to 800 °C at the heating rate of 20 °C/min and held for 20 minutes under oxygen
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atmosphere. The change of mass was recorded with the above temperature profile. 2.3 Catalytic hydro-processing of CPO Figure 1 shows the experimental setup of hydro-processing for converting CPO into long
chain alkanes. The ball valve, needle valve, lift check valve, pressure release valves, connectors, and adapters were made up of 316 stainless steel. An industrial pressure gauge (PGI-63BPG800-LAQX) was placed in a cross union connector where the gases and the oil feedstock mixed together for the purpose of regulating the desired pressure. The reactor was surrounded 4
by a rectangular electric furnace to supply the heat and the amount of heat was controlled through a heat controller device (Ching Ying: CI-35E). Approximately 5 gm of two catalysts 5 wt % Pd/C and NiMo/γ-Al2O3 were packed separately into a tubular stainless steel fixed bed reactor (400 mm length and 30 mm inner diameter) along with cotton wool [15]. The catalyst was loaded with 0.5 gm at each layer with 10 layers in total into the reactor. The upper part of the reactor was filled with cotton wool to make sure the reactor the loaded catalyst stay stable during experiments. A space between the catalyst bed and the top of the reactor was kept for preheating the cold palm oil, for the purpose of reducing the temperature fluctuation inside the reactor. The system was kept overnight within the N2
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environment with the pressure of 50 bar controlled by back pressure relief valve to ensure no leaks throughout the system. Two mass flow controllers (Brooks 5850i) were installed individually to control the volumetric flow rates of H2 and N2 gases.
The container with CPO was first flushed with 99 % N2 to make sure no oxygen was
contained in. The CPO was stirred thoroughly via hotplate stirrer (HTS-1300) at the temperature
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of 80 ˚C throughout the experiment. Prior to the experiment, N2 was used to purge the system at a rate of 50 sccm to remove all the oxygen from the system. For both experiments, the Pd/C and
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NiMo/γ-Al2O3 were activated by flowing H2 at a rate of 50 sccm for 30 mins and 2 hours at the temperatures of 100 ˚C and 200 ˚C and the pressures of 14 bar and 20 bar, respectively. After
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catalyst activation, the temperature was further increased while maintaining the pressure in the system. As the reactor reached the desired conditions, the CPO feedstock was fed using a high pressure liquid pump (Eldex) into the reactor. A tube-in-tube heat exchanger which was
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convered with the aluminum tube was stationed to condense the product. The liquid and gas products were collected every 30 mins through liquid-gas-separated sampling system which includes a back pressure regulator (BPR, Tescom) for controlling the system pressure, a spun
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sampling cylinder (Gyrolok) with a capacity of 300 ml was used to optimize the BPR, two pressure reducing regulators used to regulating the system pressure and a metering valve to
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collect the liquid samples. In this study, the experiment was conducted under various conditions [15]: pressures of 40 ~ 80 bar, temperatures of 350 ˚C ~ 450 ˚C, weight hourly space velocities (WHSVs) of 1 h-1 ~ 4 h-1, reaction time of 2 hours and 30 mins and H2 / oil ratios of 500 ~ 1250. An experimental temperature error of ± 5 oC was taken as the tolerance for all the experiments. The liquid products were analyzed through a gas chromatography-mass spectrometer (GCMS/FID-QP2010 SHIMADZU) equipped with a DB-5MS Agilent J & W columns (length 30 m, diameter 0.250 mm, film 0.25 µm). The samples were diluted by dissolving 60 mg of product samples in 4 ml HPLC grade hexane (Fisher Scientific) and 0.2 µL of diluted sample was 5
injected into GC. The carrier gas (helium) flow rate was 0.8 ml/min. The injector temperature was set as 200 ˚C. The initial oven temperature was 40 ˚C and was held for 2 min, and then increased to 300 ˚C at 10 ˚C / min, and held for 10 min. The concentrations of the products were calculated from the GC-FID area corresponding to the concentrations of n-alkanes in the standard sample. Gas products were analyzed through two equipment: a gas chromatography-mass spectrometer (GC-MS-QP2010 SHIMADZU) and a gas chromatography- thermal conductivity detector (GC-TCD-GC2014AT SHIMADZU). The samples were purged continuously during the experiment through the auto sampler. Organic gaseous products were analyzed through the GC-MS equipped with a DB-5MS Agilent J & W columns (length 30 m, diameter 0.250 mm,
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film 0.25 µm). The injector temperature was 200 ˚C. The initial oven temperature was 35 ˚C and was held for 2 min, and then increased to 150˚C at 10 ˚C / min, and held for 5 min. Inorganic gaseous products, including CO, CO2, CH4 and H2, were analyzed through GC-TCD with a packed column (TDX-01 column, 3 m × 3 mm) using He as the carrier gas. The injector
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temperature was 200 ˚C. The initial oven temperature was 70 ˚C and was held for 2 min, and then increased to 180 ˚C at 10 ˚C / min, and held for 5 min. The gaseous products were
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quantified by the external standard method based on the TCD results. The experimental error of
3. Results and Discussion
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the GC measurements was ±5 %.
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3.1 Product distributions at various operating conditions The concentrations of C15-C18 alkanes in the product samples were measured every 30
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minutes with varying reaction temperature from 350 ˚C to 450 ˚C. The purpose of the experiments was to evaluate the start-up of the reactor. The feedstock was pumped into the
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reactor at time zero, which is the time when the temperature reached the desired one. The experiment was carried out at the reaction pressure of 40 bar, weight hourly space velocity (WHSV) of 2 h-1 and H2-to-oil ratio of 750. This time-on-stream examination is to evaluate the activity of the catalyst before the reaction reaches steady-state, which carefully considered the residence time of the feed and the liquid product within the tubes. It can be observed that the samples taken before 90 minutes have relatively low concentrations of C15C18 alkanes, which gradually increased with time. Reaction was conducted at the temperature higher than 350 ˚C due to the existence of unreacted glycerides and fatty acids 6
in the products before this temperature [16]. In addition, experiments were conducted before 450 ˚C because a high level of cracking was expected to occur at this temperature along with the reaction [16]. It can be seen in Fig. 2 (a) that over the Pd/C catalyst high temperature resulted in fast growth of C15-C18 alkane productions and the concentrations of C15-C18 alkanes reached steady-state after 120 minutes. Averagely, with the higher temperature, the productions of C15-C18 alkane were higher. As shown in Fig. 2 (b), it was interesting to see that the concentrations of C15-C18 alkane were higher with lower reaction temperatures over the catalyst of NiMo/γ-Al2O3. The reaction over NiMo/γ-Al2O3 was enhanced at lower temperatures because hydro-processing of vegetable oil is an exothermic reaction. The
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concentrations of C15-C18 alkane were decreased after 120 minutes at relatively higher temperature, which demonstrated the occurrence of a certain level of cracking. At the
temperature of 350 ˚C, the declines in C15-C18 alkanes after 120 minutes indicated the
deactivation of the catalyst. Based on the experimental results, it was recommended that the conversion of glycerides into C15-C18 alkanes can be performed well at the temperatures of
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400-425 ˚C and 375-400 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively.
The maximum concentrations of C15-C18 n-alkanes reached 227 g/L and 288 g/L over the
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catalysts of Pd/C and NiMo/γ-Al2O3, respectively. Figure 2 (c) and (d) shows the gas product distributions over the catalysts of Pd/C and NiMo/γ-Al2O3 with varying
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temperature. The relatively high amount of C3H8 productions indicated the conversions of glycerides into free fatty acids, which showed a high degree level at high temperature. The
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production of CH4 was expected to come from methanation instead of propane cracking, based on the observations of CO and CO2 and the absence of ethane [17]. The methanation happened more in the reaction over Pd/C than that over NiMo/γ-Al2O3. The productions of
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CO2 and CO indicated the degrees of decarboxylation and decarbonylation, respectively, which showed high levels at the temperature of 350 ˚C and 375 ˚C and the temperature of
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350 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3. With the NiMo/γ-Al2O3 catalyst, the decreases in DCO and DCO2 were expected at the temperatures higher than 350 °C [14], which low concentrations of CO and CO2 were presented in the product gases. Low concentration of hydrogen can be attributed to the hydrogen consumption by the reactions of hydrogenation, hydrogenolysis, DCO, hydro-deoxygenation and methanation.
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The concentrations of C15-C18 alkanes in the product samples were measured every 30 minutes with varying reaction pressure from 40 bar to 80 bar over the catalysts of Pd/C and NiMo/γAl2O3, as shown in Fig. 3, and the gas products were measured with varying reaction pressure from 40 bar to 80 bar. The reaction was carried out at the reaction temperature of 350 ˚C, WHSV of 2 and H2-to-oil ratio of 750. From the previous studies, the partial pressure of hydrogen is significant to the hydro-processing of glycerides into normal alkanes. As shown in Fig. 3 (a), increasing the hydrogen pressure enhanced the productions of C15-C18 alkanes (after 90 minutes). This was mainly due to the higher solubility of hydrogen into the oil phase, resulting in more absorbance of hydrogen onto the catalyst surface. However, too much
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hydrogen deactivated the Pd/C catalyst and decreased the level of deoxygenation. Figure 3 (b) shows the concentrations of C15-C18 alkane with various reaction pressures over NiMo/γ-
Al2O3. It can also be seen that higher pressure led to higher concentrations of C15-C18 alkane. This is because the HDO route in the deoxygenation is benefited by high hydrogen pressure.
However, same as the reactions with Pd/C catalyst, excess amount of hydrogen unfavoured the
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hydro-processing reaction and reduced the performances of the catalyst. With the NiMo/γ-Al2O3 catalyst, low pressure would change the vapor-liquid equilibrium inside the reactor, which
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resulted in a higher level of cracking happened within a longer reaction time. Besides, the cracking reaction was favored with Ni based catalyst, which caused the reduction of C15-C18
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concentrations. Based on the experimental results, to obtain high concentrations of C15-C18 alkane, it was suggested that the reaction runs at 50 bar and 70 bar for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. Figure 3 (c) and (d) shows the gas product concentrations with
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various reaction pressure. The stable values of C3H8 indicates that the pressure has little influence to the hydrogenolysis reaction. As seen in Fig. 3 (c), the slightly increase in CO2 with
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increases in pressure indicates that the level of decarboxylation increased with increases in pressure. The reactions over Pd/C catalyst have higher concentration of hydrogen in the product
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gas compared to that over NiMo/γ-Al2O3, which demonstrates that the routes of decarboxylation and decarbonylation were dominated with Pd/C. Sufficient amount of hydrogen in the reaction over Pd/C resulted in the occurrence of methanation and therefore produced more CH4.
The concentrations of C15-C18 alkanes in the product samples and gas samples were measured with various WHSV, which defines the ratio of feedstock mass flow rate to the weight of catalyst, from 1 to 4 h-1 over the catalysts of Pd/C and NiMo/γ-Al2O3, as shown in Fig. 4. The 8
reaction was carried out at the reaction temperature of 350 ˚C, pressure of 40 bar and H2-to-oil ratio of 750. Figure 4 (a) shows the production of C15-C18 alkanes over Pd/C catalyst. It can be seen that at high WHSVs the productions of alkane were higher initially compared to the ones at low WHSVs but dropped significantly after 120 minutes. On the contrary, they still increased at low WHSVs. Less feedstock flow rate or more catalyst keeps the catalyst active for a longer period. High feedstock flow rate was supposed to block the pore of the catalyst and therefore deactivated the catalyst. As seen in Fig. 4 (b), the produced C15-C18 alkanes increased with time and reached steady state after 120 minutes. High WHSV shows relatively low concentrations of produced C15-C18 alkane. For the same amount of catalyst, higher feedstock mass flow rate has
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less residence time, resulting in less productivity of C15-C18 alkanes. To maintain the activity of the catalyst, it was suggested to perform the process with WHSV of 2 for both Pd/C and NiMo/ γ-Al2O3 catalysts. As seen in Fig. 4 (c) and (d), the decrease in C3H8 with increases in WHSV indicated that high WHSV reduced the performance of catalyst and decreased the conversions
from glycerides into fatty acids. For the Pd/C catalyst, the concentration of CO2 increased with
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increases in WHSV, which demonstrated the increases in decarboxylation with higher feedstock flow rates. The increase in CH4 with increases in WHSV indicated that more methanation
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occurred as increasing in feedstock flow rate. Generally, methanation is suppressed by Pd/C catalyst. Thus, the high production of methane expresses the deactivation of the catalyst. With
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NiMo/γ-Al2O3 catalyst, the increase in CO with increases in WHSV demonstrated the increase
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in decarbonylation with high mass flow rates.
The concentrations of C15-C18 alkanes in the product samples and gas samples were measured with various H2-to-oil ratios from 500 to 1250 over the catalysts of Pd/C and NiMo/γ-Al2O3, as
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shown in Fig. 5. The reactions were carried out at the reaction temperature of 350 ˚C, pressure of 40 bar and WHSV of 2 h-1. For the Pd/C catalyst, as the H2-to-oil ratio reaches 750, the
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performance of hydro-processing increased significantly. The consumption of hydrogen is to saturate the double bond in the unsaturated glycerides during hydrogenation, to remove the propane from saturated glycerides during hydrogenolysis and to remove oxygen from fatty acids through HDO. More hydrogen is additionally for methanation, propane cracking, protection of the catalyst from coking as well as removal of water from the catalyst. Incomplete reaction might happen with insufficient hydrogen, causing the unreacted or unsaturated glycerides and fatty acids to plug the pore of the catalyst and reduce its performance. Moreover, the content of water produced from HDO would cause the reduction of activity for the Pd/C catalyst, which led 9
to the decreases in C15-C18 concentrations after a long reaction time. For the NiMo/γ-Al2O3 catalyst, as the H2-to-oil ratio reached 750, the increase in hydrogen has less effect to the productions of C15-C18 alkanes. The maximum C15-C18 n-alkanes approached to 280 g/L as H2to-oil ratio was increased to 1250. Compared to H2-to-oil ratio of 500, the alkane concentration was enhanced by approximately 22 %. Figure 5 (c) and (d) shows the distributions of the gas products with various H2-to-oil ratios over Pd/C and NiMo/γ-Al2O3 catalysts. Reactions with high H2-to-oil ratio over Pd/C catalyst produced relatively low CO2, reflecting that excess amount of hydrogen supresses decarboxylation. As seen in Fig. 5 (c), the emissions of hydrogen after reaction were similar with various H2-to-oil ratios, meaning that the H2-to-oil ratio of 500-
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750 would be sufficient for hydro-processing of palm oil. Three moles of hydrogen are necessary to saturate one double bond in the unsaturated glycerides during hydrogenation and three moles of hydrogen are needed to remove propane from the saturated glycerides during
hydrogenolysis. In addition, 2 moles of hydrogen are needed to remove the oxygen atoms in one
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mole of free fatty acid during HDO. Since no hydrogen was required for DCO2/DCO, and the
hydrogen usages for methanation and propane cracking are assumed to be excluded, the H2-tooil ratio of 500-750 is theoretically sufficient for palm oil hydro-processing. The hydrogen
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leftover is necessary for the needs of methanation and propane cracking, the protection of catalyst from coking and removed the water from the catalyst.
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The concentrations of CH4 were relatively high at high H2-to-oil ratios, indicating that methanation occurred at high hydrogen flow rates. With the catalyst of NiMo/γ-Al2O3, it can be seen from Fig. 5 (d) that hydrogenolyis has a relatively high occurrence at high H2-to-oil
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ratios, from the observation of C3H8 concentrations. More hydrogen flow is beneficial for hydrogenolysis reaction. This can also be observed from the results of hydrogen and CH4
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concentrations. The formation of CO at the H2-to-oil ratio of 750 was relatively high, showing that decarbonylation was dominated in this case. Since hydrogen is also an energy source and is
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significant for the production cost as scaling up hydro-processing, it is necessary to reduce the hydrogen consumption in the reaction.
The conversions with time over Pd/C and NiMo/γ-Al2O3 are displayed in Fig. 6, which was calculated through: Conv (%) =
Reduction of glyceride concentration from the feed to the product Glyceride concentration in the feed
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(1)
The reactions were both conducted at the reaction temperature of 350 ˚C, pressure of 40 bar, WHSV of 2 h-1 and H2-to-oil ratio of 750. The conversions were 71 % and 86 % at the time of 30 minutes for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively, and increased to nearly full conversion (98 % and 99 %) at the time of 120 minutes. It was observed that the reaction with NiMo/γ-Al2O3 has better performance compared to that with Pd/C, but started decreasing at the time of 150 minutes. The metal Ni within the catalyst of NiMo/γ-Al2O3 can be easily coked with unreacted glycerides or fatty acids and therefore the catalyst was deactivated and the performance of hydro-processing was declined. The overall performance of NiMo/γ-Al2O3 for converting glycerides into straight-chain alkanes was better than Pd/C, if its activity can be
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maintained. 3.2 Catalyst analysis
The characteristics of catalysts before and after hydro-processing through TGA are shown in Fig. 7. For NiMo/γ-Al2O3, the weight of fresh catalyst dropped initially at 60 °C and
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decreased gradually after 400 °C, as shown in Fig. 7 (a). The weight of used NiMo/γ-Al2O3
was reduced gradually before the temperature of 750 °C, indicating that the unreacted glycerides
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or fatty acids deposited onto the surface of the catalyst was desorbed and then the pyrolytic of carbon deposit happened within the temperature of 400 ~ 750 °C. At the temperature of 800 °C,
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the carrier gas was switched to oxygen, which burns the carbon coking on the surface of the catalyst, leading to a great weight loss. For the Pd/C catalyst, as shown in Fig. 7 (b), an obvious weight loss at the temperature around 300 °C was found for the fresh catalyst, mainly due to the
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bulk pyrolysis of carbon skeleton within the catalyst. The gradually reduction of weight for the spent Pd/C catalyst from the temperature of 70 °C to 790 °C was attributed to the evaporation of
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light hydrocarbons, evaporation of water and pyrolytic reaction of carbon deposit (350~450 °C).
The IR spectra of fresh and spent catalysts are shown in Fig. 8. The bands at 1637 (1630 for
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Pd/C) and 3450 cm-1 demonstrate the absorptions of water. As seen in Fig. 8 (a), the bands at 385, 1637 and 3450 cm-1 displayed for the substrate -Al2O3 remain in the fresh and spent NiMo/-Al2O3 catalysts. After reaction, three absorption bands showing at the bands of 1100, 2852 and 2923 cm-1 were found in the IR spectra, indicating the unreacted species such as alicyclic hydrocarbon and aldehyde stuck on the surface of the catalyst. Fig. 8 (b) shows the IR spectra of fresh and spent Pd/C catalysts. It can be seen that both spectra look similar, meaning that least unreacted hydrocarbons were attached on the catalyst.
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The XRD patterns of fresh and spent catalysts are shown in Fig. 9. As seen in Fig. 9 (a), The diffraction patterns of 2 values at 46˚ and 67˚ found in the fresh and spent NiMo/-Al2O3 catalysts and its substrate -Al2O3 can be assigned as the cubic -Al2O3. The peak showed at the 2 value at 22˚ for the fresh NiMo/-Al2O3 was attributed to the poor dispersion of NiMo within the Al2O3 support. After hydro-processing reaction, the disappearance of the peaks at the 2 values of 20˚ ~ 30˚ was contributed by the unreacted glycerides or fatty acids, which covered the surface of the catalyst and reduced the crystallinity of the catalyst. Figure 9 (b) shows the diffraction patterns of fresh and used Pd/C. The Pd FCC lattice planes of Pd (111), Pd (200) and
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Pd (220) found in Fig. 9 (b) agreed with the ones discussed in the previous literature [11]. After reaction, the reductions of the peaks showing at the 2 values at 40˚, 46˚ and 68˚ was attributed to the dispersion of the unreacted hydrocarbon residue onto the surface of the catalyst.
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SEM images of the fresh and spent catalysts are shown in Fig. 10, with 1500 times and 10000 times magnitudes. It can be seen from Fig. 10 (A) that the morphology of the spent NiMo/-
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Al2O3 was bigger than that of the fresh one, indicating that the hydrocarbon deposited onto the catalyst surface during hydro-processing. In Fig. 10 (B), the images of spent Pd/C show that the
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surface of the Pd/C catalyst was attached by the crystallized particles, suspected to be the
4. Conclusions
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hydrocarbon residues and coke aggregates.
In order to produce HRJ, the conversion of biomass-derived oil into straight chain C15-C18 alkanes through hydro-processing was conducted at various reaction conditions, including
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temperature, pressure, WHSV and H2-to-oil ratio. In addition, the fresh and used catalysts were also examined to study the behaviours of the catalyst before and after hydro-processing. The
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experimental results can be concluded as follows: 1. It was found that high temperature favoured the reactions over Pd/C catalyst and low temperature benefited the reactions with NiMo/γ-Al2O3. High levels of decarboxylation and decarbonylation were found at the temperatures of 350 ˚C and 375 ˚C and the temperature of 350 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. The results concluded the suggested reaction temperatures to be 400-425 ˚C and 375-400 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. 12
2. High pressure helped hydrogen to be dissolved into the oil phase and this promoted the hydro-processing reaction and led to high concentrations of C15-C18 alkane. However, excess amount of hydrogen unfavoured the hydro-processing reaction and reduced the performance of the catalyst. To obtain high concentration of C15-C18 alkane, it was suggested that the reaction runs at the pressures of 50 bar and 70 bar for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. In addition, increasing reaction pressure enhanced the level of decarboxylation. 3. Lower feedstock flow rate or higher loading of the catalyst kept the catalyst active for longer time. To maintain the activity of the catalyst, it was recommended to perform the
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process with WHSV of 2 h-1 for both Pd/C and NiMo/γ-Al2O3 catalysts. For Pd/C catalyst, high feedstock flow rate led to the increase in decarboxylation. In addition, higher level of methanation occurred with increases in WHSV. With NiMo/γ-Al2O3 catalyst, CO increased with increases in WHSV indicated the increase in decarbonylation with high mass flow rate.
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4. The H2-to-oil ratios of 500-750 were sufficient for hydro-processing of palm oil into alkanes. Hydrogen is needed for methanation, propane cracking, protection of the
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catalyst from coking as well as removal of water from the catalyst. Incomplete reaction might occur with insufficient hydrogen, resulting in the performance reduction of the
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catalyst attributed to the unreacted or unsaturated glycerides or fatty acids. 5. The relatively high C3H8 at high H2-to-oil ratios indicated that high hydrogen flow favours the hydrogenolysis reaction. Since hydrogen is also considered as an energy
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source and is significant for the process economics, reducing hydrogen consumption should be the next target to the hydroprocessing study. 6. Generally the reactions over the NiMo/γ-Al2O3 catalyst have better performances
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compared to those over the Pd/C catalyst, but the performance of the NiMo/γ-Al2O3 catalyst started declining for a longer reaction time.
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7. Through the catalyst analyses of TGA, FTIR, XRD and SEM, the unreacted glycerides or fatty acids were deposited onto the pores of the catalyst after hydro-processing. The activity of the catalyst can be re-generated via removing the deposits from the pores of the catalyst.
The hydro-processed alkanes should undergo the hydro-isomerization/cracking process to be suitable for the renewable jet fuel.
13
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Acknowledgement
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This project was supported by the Ministry of Science and Technology, Taiwan, through
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grant 107-2221-E-006 -135-.
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V. Itthibenchapong, A. Srifa, R. Kaewmeesri, P. Kidkhunthod, and K. Faungnawakij, "Deoxygenation of palm kernel oil to jet fuel-like hydrocarbons using Ni-MoS2/γ-Al2O3 catalysts," Energy Conversion and Management, vol. 134, pp. 188-196, 2017/02/15/ 2017.
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[17]
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H2
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Atmosphere
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Vapor goes upward Product
Liquid goes downward
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Fig. 1 Setup of Hydro-processing experiment (1. H2 Tank; 2. N2 Tank; 3. Filter; 4. Mass flow controller; 5. Pressure gauge; 6. Hot plate stirrer; 7. High pressure pump; 8. Safety relief valve; 9. K-Type thermocouple; 10. Reactor; 11. Electric furnace; 12. Temperature controller; 13. Condenser; 14. Circulator; 15. Liquid-gas separator; 16. Back pressure regulator; 17. Empty gas cylinder; 18. Pressure reduce regulator; 19. Metering valve; 20. Product container; 21. Multiport valve; 22. Lab view Interface system)
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240 220
180 160 140 120 100
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Fig. 2. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of temperatures: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
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Fig. 3. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of pressures: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
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Fig. 4. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of WHSV: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
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Fig. 5. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of H2-to-oil ratios: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
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(b) Fig. 7. TGA analyses of the catalysts: (a) NiMo/-Al2O3; (b) Pd/C
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Fig. 8. IR spectra of the catalysts (a): (1) fresh NiMo/-Al2O3; (2) spent NiMo/-Al2O3; (3) -Al2O3. (b): (1) fresh Pd/C; (2) spent Pd/C
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Fig. 9. XRD patterns of the catalysts. (a): (1) fresh NiMo/-Al2O3; (2) spent NiMo/-Al2O3; (3) -Al2O3. (b): (1) spent Pd/C; (2) fresh Pd/C.
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Fig. 10. SEM images of (A) NiMo/-Al2O3 catalysts: (a) fresh 1500x; (b) fresh 10000x; (c) spent 1500x; (d) spent 10000x; (B) Pd/C catalysts: (e) fresh 1500x; (f) fresh 10000x; (g) spent 1500x; (h) spent 10000x
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PII:
S0263-8762(19)30500-3
DOI:
https://doi.org/10.1016/j.cherd.2019.10.030
Reference:
CHERD 3865
To appear in:
Chemical Engineering Research and Design
Received Date:
2 December 2018
Revised Date:
14 October 2019
Accepted Date:
15 October 2019
Please cite this article as: Wang W-Cheng, Hsieh C-Hung, Hydro-processing of Biomass-derived Oil into Straight-chain Alkanes, Chemical Engineering Research and Design (2019), doi: https://doi.org/10.1016/j.cherd.2019.10.030
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Hydro-processing of Biomass-derived Oil into Straight-chain Alkanes Wei-Cheng Wang1*, Chung-Hung Hsieh2
1
Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan 70101, Taiwan
2
Department of Chemistry, Tamkung University, Taipei, Taiwan.
*Corresponding author: Wei-Cheng Wang, Email: [email protected]
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Highlights Glyceride-based oil was converted into normal alkanes necessary for producing HRJ Pd/C and NiMo/γ-Al2O3 were tested with various experimental conditions Fresh and used catalysts were characterized through TGA, FTIR, XRD and SEM
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Abstract
Initially converting the glyceride-based oils derived from biomass into straight-chain alkanes are necessary for producing hydro-processed renewable jet (HRJ). In this study, palm oil was turned
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into C15-C18 alkanes over two different catalysts, Pd/C and NiMo/γ-Al2O3, with various reaction conditions such as temperature, pressure, weight hourly space velocity (WHSV) and H2-to-oil
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ratio. The fresh and used catalysts after hydro-processing reaction were then characterized through the techniques including TGA, FTIR, XRD and SEM. The liquid products were
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analysed through GC-MS/FID and the concentrations of C15-C18 were determined. The gas products, such as CO2, CO, C3H8, CH4 and H2, were analysed through GC-TCD for indirectly “visualizing” the reaction, including the performances of hydro-deoxygenation (HDO) as well
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as decarbonylation / decarboxylation, hydrogenolysis, the occurrence of methanation and the consumption of hydrogen. The suggested experimental conditions over these two catalysts were
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elaborated based on the concentration of n-alkanes and gas products.
Keyword: Hydro-processed Renewable Jet; Hydro-processing; Oil upgrading; Hydrodeoxygenation; Green Diesel; Palm oil
1. Introduction: The hydro-process which produces hydro-processed Renewable Jet (HRJ) has been viewed as one of the promising processes for converting glyceride based oils into renewable jet fuels. In 1
this process, the biomass-derived oil is first turned into straight chain alkanes and furthermore the produced alkanes are cracked and isomerized into jet fuel range products. The hydroprocessing of bio-oil is the major part of this process since the catalyst and hydrogen used in this route contribute not only economical but environmental impacts, which strongly determine the sustainability of the process.
Many oil feedstocks, such as plant oils, algae and even pyrolytic oils, are considered as the source of the process, depending on the region. In Asia, palm oil is viewed as a suitable oil feedstock for producing biofuels mainly due to its availability in southeast region. Indonesia and
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Malaysia are the two primary countries that produce crude palm oil (CPO), accounting for 19.7 million and 17.4 million metric tons, respectively [1]. In most of the regions, the oil palm yields are large than 8 ton per hectare per year [2]. Currently, the palm oil price is $573 per metric
tonne. Based on the fatty acid profile of the oil, the double bonds of the unsaturated glycerides
are first saturated through hydrogenation. Certain moles of hydrogen are consumed according to
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the number of double bonds. The propane backbone are further removed through the propane cleave route, where the free fatty acids are formed. Furthermore, the fatty acids are
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deoxygenated into straight-chain alkanes, where three routes occurred simultaneously: hydrodeoxygenation (HDO), decarboxylation and decarbonylation. The carbon chain lengths of the
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alkanes correspond to the carbons of the fatty acids in the oil. The oxygen is removed from the fatty acids through hydro-deoxygenation with the formation of water, through decarboxylation with the formation of CO2 and through decarbonylation with the formation of CO. Hydrogen is
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consumed in the hydro-deoxygenation and decarbonylation routes [3-7].
Previously, Guzman et al. [8] showed that crude palm oil can be hydro-treated into the diesel
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range products at the pressures of 40-90 bar in the hydrogen environment over NiMo/γ-Al2O3 catalyst. The cetane index decayed with the increases in time on stream (TOS), from 96.1 to
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92.5. Kovács et al. [9] has reported a process which converted triglycerides in the sunflower oil into C15 ~ C18 paraffins at the temperature of 350–370 °C, pressure of 20-40 bar, LHSV (Liquid Hourly Space Velocity) = 1.0 h−1 and H2/ oil volume ratio of 500 Nm3/m3. High yield (73.2 % ~ 75.6 %) and high paraffin content (> 99.9 %) products similar to diesel range fraction were produced. The NiMoCe/Al2O3 catalyst was also used to produce straight chain alkanes ranging from C15 to C18, with the yield of 80 %, the conversion of 89 % and selectivity of 90 %. The N2BET, SEM, XRD and TPD techniques were applied for characterizing the properties of the catalyst [10]. The catalyst Pd/C was also used for the hydro-processing of crude palm oil. 2
Compared to NiMo/γ-Al2O3, Pd/C is more suitable for fatty acid feedstocks, while NiMo/γAl2O3 fits more to the triglycerides feedstocks [11]. Other alumina-based catalysts, such as PtPd/Al2O3 and NiMoP/ Al2O3, were also investigated for the hydro-processing of nonedible jatropha oil, for the purpose of producing a high-performance additive diesel fuel [12]. It was additionally found that hydro-deoxygenation was dominated when NiMoP/Al2O3 was applied, while decarboxylation and decarbonylation were the primary reactions as PtPd/Al2O3 was used. In addition, NiMoP/Al2O3 was observed to be the catalyst for long-term process. Presulfied NiMo/γ-Al2O3 catalyst was also used for hydro-deoxygenation of microalgae oil recently [13]. The lifetime and activity of the catalyst were maintained with increases in H2-to-oil ratio,
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residence time, reaction temperature and pressure, which avoided the oxygenate contaminations on the surface of catalyst. The Ni-based (Ni/γ-Al2O3) and Co-based (Co/γ-Al2O3) catalysts were compared while conducting the hydro-deoxygenation of palm oil at 300 °C and 5 MPa [14]. The product yield decreased from 92.2 % to 76.2 % over Ni/γ-Al2O3 catalyst and 88.6 % to 56.6 % over Co/γ-Al2O3 catalyst. The decarboxylation/decarbonylation was superior over hydro-
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deoxygenation when using Ni-based catalyst, while these two routes were comparable when
using Co-based catalyst. According to the previous literatures, Pd/C and NiMo/γ-Al2O3 were the
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two popular catalysts for performing hydro-processing of glyceride-based oils. Maintaining the catalyst activity and expanding the catalyst lifetime are now the primary targets for scaling-up
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the hydro-processing process. Investigating the catalyst behaviours corresponding to the reaction kinetics becomes necessary.
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In this study, catalytic hydro-processing of palm oil over Pd/C and NiMo/γ-Al2O3 catalysts for producing straight chain alkanes was carried out in a fixed bed reactor. Different parameters such as temperature, pressure, LHSV and H2-to-oil ratio were varied for examining the reaction
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kinetics. The characteristics of catalysts were also studied through the analyses of SEM, XRD,
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TGA and FTIR.
2. Experimental method 2.1 Materials
Crude palm oil (CPO) provided by a local chemical company was chosen as the feedstock in this study. The major fatty acid compositions of CPO is 48 % saturated fatty acids (44 % Palmitic 16:0 and 4% Stearic 18:0) and 50 % unsaturated fatty acids (40 % oleic 18:1 and 10% 3
linoleic 18:2). To ensure the consistency of the palm oil, two samples taken a month apart were analyzed in GC-MS/FID and the components shown were similar. The palm oil feedstock used in this study was replaced within a month. The 5wt% Pd/C was provided by Acros organics, NiMo/γ-Al2O3 was provided by A-Plus Inc. The 5wt% Pd/C was dried overnight at 40 ˚C in the oven to remove the moisture contained in the catalyst. The experimental gases 99.99 % N2 and 99.99 % H2 were provided by the Yun-Shan Gas Company. The external standard 99.99 % C8~C20 alkanes that contains 40 mg/L each was provided by Sigma-Aldrich which was used to analyse the liquid product samples.
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2.2 Catalyst Characterizations Scanning electron microscopy (SEM) (VEGA 2 SBH, Tescan, Kohoutovice, Czech
Republic) operated at 20 kV was used to examine the morphology and crystallite of the
catalysts. The powder X-ray diffraction (XRD) patterns of the catalysts were obtained with a
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Bruker D8 ADVANCE Twin-X-ray Powder Diffractometer with LYNXEYE XE-T detector
(Bruker AXS Inc., Madison, WI, USA) using Cu Kα radiation (k = 1.54060 Å) operated at 40
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kV and 40 mA in the angular range between 10˚ and 80˚ for 2θ. The presence of functional groups of catalyst were obtained by operating NicoletTM iS5TM FT-IR spectrophotometer
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(ThermoFisher Scientific Inc., Waltham, MA, USA). The IR spectra were obtained by mixing the samples with 10 times amount of potassium bromide (KBr) and then recorded in the FT-IR spectrophotometer. The FTIR-spectra of adsorbed pyridine were collected in the region of 400-
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4000 cm-1, on the average of 16 scans at a resolution of 4 cm-1. The thermogravimetric analysis (TGA) was carried out using the Perkin Elmer STA60000 (Waltham, MA, USA). Approximately 18-25 gm of sample was prepared. The temperature in the TGA was raised from 50 °C to 105
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°C at the heating rate of 20 °C/min and held for 20 minutes under N2 atmosphere and further increased to 800 °C at the heating rate of 20 °C/min and held for 20 minutes under oxygen
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atmosphere. The change of mass was recorded with the above temperature profile. 2.3 Catalytic hydro-processing of CPO Figure 1 shows the experimental setup of hydro-processing for converting CPO into long
chain alkanes. The ball valve, needle valve, lift check valve, pressure release valves, connectors, and adapters were made up of 316 stainless steel. An industrial pressure gauge (PGI-63BPG800-LAQX) was placed in a cross union connector where the gases and the oil feedstock mixed together for the purpose of regulating the desired pressure. The reactor was surrounded 4
by a rectangular electric furnace to supply the heat and the amount of heat was controlled through a heat controller device (Ching Ying: CI-35E). Approximately 5 gm of two catalysts 5 wt % Pd/C and NiMo/γ-Al2O3 were packed separately into a tubular stainless steel fixed bed reactor (400 mm length and 30 mm inner diameter) along with cotton wool [15]. The catalyst was loaded with 0.5 gm at each layer with 10 layers in total into the reactor. The upper part of the reactor was filled with cotton wool to make sure the reactor the loaded catalyst stay stable during experiments. A space between the catalyst bed and the top of the reactor was kept for preheating the cold palm oil, for the purpose of reducing the temperature fluctuation inside the reactor. The system was kept overnight within the N2
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environment with the pressure of 50 bar controlled by back pressure relief valve to ensure no leaks throughout the system. Two mass flow controllers (Brooks 5850i) were installed individually to control the volumetric flow rates of H2 and N2 gases.
The container with CPO was first flushed with 99 % N2 to make sure no oxygen was
contained in. The CPO was stirred thoroughly via hotplate stirrer (HTS-1300) at the temperature
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of 80 ˚C throughout the experiment. Prior to the experiment, N2 was used to purge the system at a rate of 50 sccm to remove all the oxygen from the system. For both experiments, the Pd/C and
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NiMo/γ-Al2O3 were activated by flowing H2 at a rate of 50 sccm for 30 mins and 2 hours at the temperatures of 100 ˚C and 200 ˚C and the pressures of 14 bar and 20 bar, respectively. After
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catalyst activation, the temperature was further increased while maintaining the pressure in the system. As the reactor reached the desired conditions, the CPO feedstock was fed using a high pressure liquid pump (Eldex) into the reactor. A tube-in-tube heat exchanger which was
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convered with the aluminum tube was stationed to condense the product. The liquid and gas products were collected every 30 mins through liquid-gas-separated sampling system which includes a back pressure regulator (BPR, Tescom) for controlling the system pressure, a spun
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sampling cylinder (Gyrolok) with a capacity of 300 ml was used to optimize the BPR, two pressure reducing regulators used to regulating the system pressure and a metering valve to
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collect the liquid samples. In this study, the experiment was conducted under various conditions [15]: pressures of 40 ~ 80 bar, temperatures of 350 ˚C ~ 450 ˚C, weight hourly space velocities (WHSVs) of 1 h-1 ~ 4 h-1, reaction time of 2 hours and 30 mins and H2 / oil ratios of 500 ~ 1250. An experimental temperature error of ± 5 oC was taken as the tolerance for all the experiments. The liquid products were analyzed through a gas chromatography-mass spectrometer (GCMS/FID-QP2010 SHIMADZU) equipped with a DB-5MS Agilent J & W columns (length 30 m, diameter 0.250 mm, film 0.25 µm). The samples were diluted by dissolving 60 mg of product samples in 4 ml HPLC grade hexane (Fisher Scientific) and 0.2 µL of diluted sample was 5
injected into GC. The carrier gas (helium) flow rate was 0.8 ml/min. The injector temperature was set as 200 ˚C. The initial oven temperature was 40 ˚C and was held for 2 min, and then increased to 300 ˚C at 10 ˚C / min, and held for 10 min. The concentrations of the products were calculated from the GC-FID area corresponding to the concentrations of n-alkanes in the standard sample. Gas products were analyzed through two equipment: a gas chromatography-mass spectrometer (GC-MS-QP2010 SHIMADZU) and a gas chromatography- thermal conductivity detector (GC-TCD-GC2014AT SHIMADZU). The samples were purged continuously during the experiment through the auto sampler. Organic gaseous products were analyzed through the GC-MS equipped with a DB-5MS Agilent J & W columns (length 30 m, diameter 0.250 mm,
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film 0.25 µm). The injector temperature was 200 ˚C. The initial oven temperature was 35 ˚C and was held for 2 min, and then increased to 150˚C at 10 ˚C / min, and held for 5 min. Inorganic gaseous products, including CO, CO2, CH4 and H2, were analyzed through GC-TCD with a packed column (TDX-01 column, 3 m × 3 mm) using He as the carrier gas. The injector
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temperature was 200 ˚C. The initial oven temperature was 70 ˚C and was held for 2 min, and then increased to 180 ˚C at 10 ˚C / min, and held for 5 min. The gaseous products were
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quantified by the external standard method based on the TCD results. The experimental error of
3. Results and Discussion
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the GC measurements was ±5 %.
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3.1 Product distributions at various operating conditions The concentrations of C15-C18 alkanes in the product samples were measured every 30
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minutes with varying reaction temperature from 350 ˚C to 450 ˚C. The purpose of the experiments was to evaluate the start-up of the reactor. The feedstock was pumped into the
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reactor at time zero, which is the time when the temperature reached the desired one. The experiment was carried out at the reaction pressure of 40 bar, weight hourly space velocity (WHSV) of 2 h-1 and H2-to-oil ratio of 750. This time-on-stream examination is to evaluate the activity of the catalyst before the reaction reaches steady-state, which carefully considered the residence time of the feed and the liquid product within the tubes. It can be observed that the samples taken before 90 minutes have relatively low concentrations of C15C18 alkanes, which gradually increased with time. Reaction was conducted at the temperature higher than 350 ˚C due to the existence of unreacted glycerides and fatty acids 6
in the products before this temperature [16]. In addition, experiments were conducted before 450 ˚C because a high level of cracking was expected to occur at this temperature along with the reaction [16]. It can be seen in Fig. 2 (a) that over the Pd/C catalyst high temperature resulted in fast growth of C15-C18 alkane productions and the concentrations of C15-C18 alkanes reached steady-state after 120 minutes. Averagely, with the higher temperature, the productions of C15-C18 alkane were higher. As shown in Fig. 2 (b), it was interesting to see that the concentrations of C15-C18 alkane were higher with lower reaction temperatures over the catalyst of NiMo/γ-Al2O3. The reaction over NiMo/γ-Al2O3 was enhanced at lower temperatures because hydro-processing of vegetable oil is an exothermic reaction. The
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concentrations of C15-C18 alkane were decreased after 120 minutes at relatively higher temperature, which demonstrated the occurrence of a certain level of cracking. At the
temperature of 350 ˚C, the declines in C15-C18 alkanes after 120 minutes indicated the
deactivation of the catalyst. Based on the experimental results, it was recommended that the conversion of glycerides into C15-C18 alkanes can be performed well at the temperatures of
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400-425 ˚C and 375-400 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively.
The maximum concentrations of C15-C18 n-alkanes reached 227 g/L and 288 g/L over the
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catalysts of Pd/C and NiMo/γ-Al2O3, respectively. Figure 2 (c) and (d) shows the gas product distributions over the catalysts of Pd/C and NiMo/γ-Al2O3 with varying
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temperature. The relatively high amount of C3H8 productions indicated the conversions of glycerides into free fatty acids, which showed a high degree level at high temperature. The
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production of CH4 was expected to come from methanation instead of propane cracking, based on the observations of CO and CO2 and the absence of ethane [17]. The methanation happened more in the reaction over Pd/C than that over NiMo/γ-Al2O3. The productions of
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CO2 and CO indicated the degrees of decarboxylation and decarbonylation, respectively, which showed high levels at the temperature of 350 ˚C and 375 ˚C and the temperature of
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350 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3. With the NiMo/γ-Al2O3 catalyst, the decreases in DCO and DCO2 were expected at the temperatures higher than 350 °C [14], which low concentrations of CO and CO2 were presented in the product gases. Low concentration of hydrogen can be attributed to the hydrogen consumption by the reactions of hydrogenation, hydrogenolysis, DCO, hydro-deoxygenation and methanation.
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The concentrations of C15-C18 alkanes in the product samples were measured every 30 minutes with varying reaction pressure from 40 bar to 80 bar over the catalysts of Pd/C and NiMo/γAl2O3, as shown in Fig. 3, and the gas products were measured with varying reaction pressure from 40 bar to 80 bar. The reaction was carried out at the reaction temperature of 350 ˚C, WHSV of 2 and H2-to-oil ratio of 750. From the previous studies, the partial pressure of hydrogen is significant to the hydro-processing of glycerides into normal alkanes. As shown in Fig. 3 (a), increasing the hydrogen pressure enhanced the productions of C15-C18 alkanes (after 90 minutes). This was mainly due to the higher solubility of hydrogen into the oil phase, resulting in more absorbance of hydrogen onto the catalyst surface. However, too much
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hydrogen deactivated the Pd/C catalyst and decreased the level of deoxygenation. Figure 3 (b) shows the concentrations of C15-C18 alkane with various reaction pressures over NiMo/γ-
Al2O3. It can also be seen that higher pressure led to higher concentrations of C15-C18 alkane. This is because the HDO route in the deoxygenation is benefited by high hydrogen pressure.
However, same as the reactions with Pd/C catalyst, excess amount of hydrogen unfavoured the
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hydro-processing reaction and reduced the performances of the catalyst. With the NiMo/γ-Al2O3 catalyst, low pressure would change the vapor-liquid equilibrium inside the reactor, which
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resulted in a higher level of cracking happened within a longer reaction time. Besides, the cracking reaction was favored with Ni based catalyst, which caused the reduction of C15-C18
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concentrations. Based on the experimental results, to obtain high concentrations of C15-C18 alkane, it was suggested that the reaction runs at 50 bar and 70 bar for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. Figure 3 (c) and (d) shows the gas product concentrations with
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various reaction pressure. The stable values of C3H8 indicates that the pressure has little influence to the hydrogenolysis reaction. As seen in Fig. 3 (c), the slightly increase in CO2 with
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increases in pressure indicates that the level of decarboxylation increased with increases in pressure. The reactions over Pd/C catalyst have higher concentration of hydrogen in the product
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gas compared to that over NiMo/γ-Al2O3, which demonstrates that the routes of decarboxylation and decarbonylation were dominated with Pd/C. Sufficient amount of hydrogen in the reaction over Pd/C resulted in the occurrence of methanation and therefore produced more CH4.
The concentrations of C15-C18 alkanes in the product samples and gas samples were measured with various WHSV, which defines the ratio of feedstock mass flow rate to the weight of catalyst, from 1 to 4 h-1 over the catalysts of Pd/C and NiMo/γ-Al2O3, as shown in Fig. 4. The 8
reaction was carried out at the reaction temperature of 350 ˚C, pressure of 40 bar and H2-to-oil ratio of 750. Figure 4 (a) shows the production of C15-C18 alkanes over Pd/C catalyst. It can be seen that at high WHSVs the productions of alkane were higher initially compared to the ones at low WHSVs but dropped significantly after 120 minutes. On the contrary, they still increased at low WHSVs. Less feedstock flow rate or more catalyst keeps the catalyst active for a longer period. High feedstock flow rate was supposed to block the pore of the catalyst and therefore deactivated the catalyst. As seen in Fig. 4 (b), the produced C15-C18 alkanes increased with time and reached steady state after 120 minutes. High WHSV shows relatively low concentrations of produced C15-C18 alkane. For the same amount of catalyst, higher feedstock mass flow rate has
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less residence time, resulting in less productivity of C15-C18 alkanes. To maintain the activity of the catalyst, it was suggested to perform the process with WHSV of 2 for both Pd/C and NiMo/ γ-Al2O3 catalysts. As seen in Fig. 4 (c) and (d), the decrease in C3H8 with increases in WHSV indicated that high WHSV reduced the performance of catalyst and decreased the conversions
from glycerides into fatty acids. For the Pd/C catalyst, the concentration of CO2 increased with
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increases in WHSV, which demonstrated the increases in decarboxylation with higher feedstock flow rates. The increase in CH4 with increases in WHSV indicated that more methanation
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occurred as increasing in feedstock flow rate. Generally, methanation is suppressed by Pd/C catalyst. Thus, the high production of methane expresses the deactivation of the catalyst. With
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NiMo/γ-Al2O3 catalyst, the increase in CO with increases in WHSV demonstrated the increase
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in decarbonylation with high mass flow rates.
The concentrations of C15-C18 alkanes in the product samples and gas samples were measured with various H2-to-oil ratios from 500 to 1250 over the catalysts of Pd/C and NiMo/γ-Al2O3, as
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shown in Fig. 5. The reactions were carried out at the reaction temperature of 350 ˚C, pressure of 40 bar and WHSV of 2 h-1. For the Pd/C catalyst, as the H2-to-oil ratio reaches 750, the
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performance of hydro-processing increased significantly. The consumption of hydrogen is to saturate the double bond in the unsaturated glycerides during hydrogenation, to remove the propane from saturated glycerides during hydrogenolysis and to remove oxygen from fatty acids through HDO. More hydrogen is additionally for methanation, propane cracking, protection of the catalyst from coking as well as removal of water from the catalyst. Incomplete reaction might happen with insufficient hydrogen, causing the unreacted or unsaturated glycerides and fatty acids to plug the pore of the catalyst and reduce its performance. Moreover, the content of water produced from HDO would cause the reduction of activity for the Pd/C catalyst, which led 9
to the decreases in C15-C18 concentrations after a long reaction time. For the NiMo/γ-Al2O3 catalyst, as the H2-to-oil ratio reached 750, the increase in hydrogen has less effect to the productions of C15-C18 alkanes. The maximum C15-C18 n-alkanes approached to 280 g/L as H2to-oil ratio was increased to 1250. Compared to H2-to-oil ratio of 500, the alkane concentration was enhanced by approximately 22 %. Figure 5 (c) and (d) shows the distributions of the gas products with various H2-to-oil ratios over Pd/C and NiMo/γ-Al2O3 catalysts. Reactions with high H2-to-oil ratio over Pd/C catalyst produced relatively low CO2, reflecting that excess amount of hydrogen supresses decarboxylation. As seen in Fig. 5 (c), the emissions of hydrogen after reaction were similar with various H2-to-oil ratios, meaning that the H2-to-oil ratio of 500-
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750 would be sufficient for hydro-processing of palm oil. Three moles of hydrogen are necessary to saturate one double bond in the unsaturated glycerides during hydrogenation and three moles of hydrogen are needed to remove propane from the saturated glycerides during
hydrogenolysis. In addition, 2 moles of hydrogen are needed to remove the oxygen atoms in one
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mole of free fatty acid during HDO. Since no hydrogen was required for DCO2/DCO, and the
hydrogen usages for methanation and propane cracking are assumed to be excluded, the H2-tooil ratio of 500-750 is theoretically sufficient for palm oil hydro-processing. The hydrogen
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leftover is necessary for the needs of methanation and propane cracking, the protection of catalyst from coking and removed the water from the catalyst.
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The concentrations of CH4 were relatively high at high H2-to-oil ratios, indicating that methanation occurred at high hydrogen flow rates. With the catalyst of NiMo/γ-Al2O3, it can be seen from Fig. 5 (d) that hydrogenolyis has a relatively high occurrence at high H2-to-oil
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ratios, from the observation of C3H8 concentrations. More hydrogen flow is beneficial for hydrogenolysis reaction. This can also be observed from the results of hydrogen and CH4
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concentrations. The formation of CO at the H2-to-oil ratio of 750 was relatively high, showing that decarbonylation was dominated in this case. Since hydrogen is also an energy source and is
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significant for the production cost as scaling up hydro-processing, it is necessary to reduce the hydrogen consumption in the reaction.
The conversions with time over Pd/C and NiMo/γ-Al2O3 are displayed in Fig. 6, which was calculated through: Conv (%) =
Reduction of glyceride concentration from the feed to the product Glyceride concentration in the feed
10
(1)
The reactions were both conducted at the reaction temperature of 350 ˚C, pressure of 40 bar, WHSV of 2 h-1 and H2-to-oil ratio of 750. The conversions were 71 % and 86 % at the time of 30 minutes for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively, and increased to nearly full conversion (98 % and 99 %) at the time of 120 minutes. It was observed that the reaction with NiMo/γ-Al2O3 has better performance compared to that with Pd/C, but started decreasing at the time of 150 minutes. The metal Ni within the catalyst of NiMo/γ-Al2O3 can be easily coked with unreacted glycerides or fatty acids and therefore the catalyst was deactivated and the performance of hydro-processing was declined. The overall performance of NiMo/γ-Al2O3 for converting glycerides into straight-chain alkanes was better than Pd/C, if its activity can be
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maintained. 3.2 Catalyst analysis
The characteristics of catalysts before and after hydro-processing through TGA are shown in Fig. 7. For NiMo/γ-Al2O3, the weight of fresh catalyst dropped initially at 60 °C and
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decreased gradually after 400 °C, as shown in Fig. 7 (a). The weight of used NiMo/γ-Al2O3
was reduced gradually before the temperature of 750 °C, indicating that the unreacted glycerides
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or fatty acids deposited onto the surface of the catalyst was desorbed and then the pyrolytic of carbon deposit happened within the temperature of 400 ~ 750 °C. At the temperature of 800 °C,
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the carrier gas was switched to oxygen, which burns the carbon coking on the surface of the catalyst, leading to a great weight loss. For the Pd/C catalyst, as shown in Fig. 7 (b), an obvious weight loss at the temperature around 300 °C was found for the fresh catalyst, mainly due to the
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bulk pyrolysis of carbon skeleton within the catalyst. The gradually reduction of weight for the spent Pd/C catalyst from the temperature of 70 °C to 790 °C was attributed to the evaporation of
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light hydrocarbons, evaporation of water and pyrolytic reaction of carbon deposit (350~450 °C).
The IR spectra of fresh and spent catalysts are shown in Fig. 8. The bands at 1637 (1630 for
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Pd/C) and 3450 cm-1 demonstrate the absorptions of water. As seen in Fig. 8 (a), the bands at 385, 1637 and 3450 cm-1 displayed for the substrate -Al2O3 remain in the fresh and spent NiMo/-Al2O3 catalysts. After reaction, three absorption bands showing at the bands of 1100, 2852 and 2923 cm-1 were found in the IR spectra, indicating the unreacted species such as alicyclic hydrocarbon and aldehyde stuck on the surface of the catalyst. Fig. 8 (b) shows the IR spectra of fresh and spent Pd/C catalysts. It can be seen that both spectra look similar, meaning that least unreacted hydrocarbons were attached on the catalyst.
11
The XRD patterns of fresh and spent catalysts are shown in Fig. 9. As seen in Fig. 9 (a), The diffraction patterns of 2 values at 46˚ and 67˚ found in the fresh and spent NiMo/-Al2O3 catalysts and its substrate -Al2O3 can be assigned as the cubic -Al2O3. The peak showed at the 2 value at 22˚ for the fresh NiMo/-Al2O3 was attributed to the poor dispersion of NiMo within the Al2O3 support. After hydro-processing reaction, the disappearance of the peaks at the 2 values of 20˚ ~ 30˚ was contributed by the unreacted glycerides or fatty acids, which covered the surface of the catalyst and reduced the crystallinity of the catalyst. Figure 9 (b) shows the diffraction patterns of fresh and used Pd/C. The Pd FCC lattice planes of Pd (111), Pd (200) and
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Pd (220) found in Fig. 9 (b) agreed with the ones discussed in the previous literature [11]. After reaction, the reductions of the peaks showing at the 2 values at 40˚, 46˚ and 68˚ was attributed to the dispersion of the unreacted hydrocarbon residue onto the surface of the catalyst.
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SEM images of the fresh and spent catalysts are shown in Fig. 10, with 1500 times and 10000 times magnitudes. It can be seen from Fig. 10 (A) that the morphology of the spent NiMo/-
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Al2O3 was bigger than that of the fresh one, indicating that the hydrocarbon deposited onto the catalyst surface during hydro-processing. In Fig. 10 (B), the images of spent Pd/C show that the
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surface of the Pd/C catalyst was attached by the crystallized particles, suspected to be the
4. Conclusions
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hydrocarbon residues and coke aggregates.
In order to produce HRJ, the conversion of biomass-derived oil into straight chain C15-C18 alkanes through hydro-processing was conducted at various reaction conditions, including
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temperature, pressure, WHSV and H2-to-oil ratio. In addition, the fresh and used catalysts were also examined to study the behaviours of the catalyst before and after hydro-processing. The
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experimental results can be concluded as follows: 1. It was found that high temperature favoured the reactions over Pd/C catalyst and low temperature benefited the reactions with NiMo/γ-Al2O3. High levels of decarboxylation and decarbonylation were found at the temperatures of 350 ˚C and 375 ˚C and the temperature of 350 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. The results concluded the suggested reaction temperatures to be 400-425 ˚C and 375-400 ˚C over the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. 12
2. High pressure helped hydrogen to be dissolved into the oil phase and this promoted the hydro-processing reaction and led to high concentrations of C15-C18 alkane. However, excess amount of hydrogen unfavoured the hydro-processing reaction and reduced the performance of the catalyst. To obtain high concentration of C15-C18 alkane, it was suggested that the reaction runs at the pressures of 50 bar and 70 bar for the catalysts of Pd/C and NiMo/γ-Al2O3, respectively. In addition, increasing reaction pressure enhanced the level of decarboxylation. 3. Lower feedstock flow rate or higher loading of the catalyst kept the catalyst active for longer time. To maintain the activity of the catalyst, it was recommended to perform the
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process with WHSV of 2 h-1 for both Pd/C and NiMo/γ-Al2O3 catalysts. For Pd/C catalyst, high feedstock flow rate led to the increase in decarboxylation. In addition, higher level of methanation occurred with increases in WHSV. With NiMo/γ-Al2O3 catalyst, CO increased with increases in WHSV indicated the increase in decarbonylation with high mass flow rate.
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4. The H2-to-oil ratios of 500-750 were sufficient for hydro-processing of palm oil into alkanes. Hydrogen is needed for methanation, propane cracking, protection of the
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catalyst from coking as well as removal of water from the catalyst. Incomplete reaction might occur with insufficient hydrogen, resulting in the performance reduction of the
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catalyst attributed to the unreacted or unsaturated glycerides or fatty acids. 5. The relatively high C3H8 at high H2-to-oil ratios indicated that high hydrogen flow favours the hydrogenolysis reaction. Since hydrogen is also considered as an energy
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source and is significant for the process economics, reducing hydrogen consumption should be the next target to the hydroprocessing study. 6. Generally the reactions over the NiMo/γ-Al2O3 catalyst have better performances
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compared to those over the Pd/C catalyst, but the performance of the NiMo/γ-Al2O3 catalyst started declining for a longer reaction time.
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7. Through the catalyst analyses of TGA, FTIR, XRD and SEM, the unreacted glycerides or fatty acids were deposited onto the pores of the catalyst after hydro-processing. The activity of the catalyst can be re-generated via removing the deposits from the pores of the catalyst.
The hydro-processed alkanes should undergo the hydro-isomerization/cracking process to be suitable for the renewable jet fuel.
13
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Acknowledgement
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This project was supported by the Ministry of Science and Technology, Taiwan, through
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grant 107-2221-E-006 -135-.
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na
lP
Fig. 1 Setup of Hydro-processing experiment (1. H2 Tank; 2. N2 Tank; 3. Filter; 4. Mass flow controller; 5. Pressure gauge; 6. Hot plate stirrer; 7. High pressure pump; 8. Safety relief valve; 9. K-Type thermocouple; 10. Reactor; 11. Electric furnace; 12. Temperature controller; 13. Condenser; 14. Circulator; 15. Liquid-gas separator; 16. Back pressure regulator; 17. Empty gas cylinder; 18. Pressure reduce regulator; 19. Metering valve; 20. Product container; 21. Multiport valve; 22. Lab view Interface system)
17
240 220
180 160 140 120 100
ro of
C15-C18 n-alkane Concentration (g/L)
200
80
350 °C
60
375 °C
40
400 °C
-p
20 0 60
Jo
ur
na
lP
(a)
90 Time (mins)
re
30
18
120
425 °C 450 °C
150
ro of
350 °C 375 °C 400 °C 425 °C 450 °C
60
lP
(b)
100
C3H8
90
120
150
70
CH4
CO
Jo
40
H2
ur
60 50
CO2
na
80
Gas Concentration (vol %)
90 Time (mins)
re
30
-p
C15-C18 n-alkane Concentration (g/L)
320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0
30 20 10 0
T=350
T=375
T=400 Temperature(OC)
(c) 19
T=425
T=450
100%
C3H8
CO2
H2
CH4
CO
90%
70% 60% 50% 40% 30% 20% 10% 0% T=375
T=400 Temperature(OC)
T=425
-p
T=350
ro of
Gas Concentration (vol %)
80%
(d)
T=450
Jo
ur
na
lP
re
Fig. 2. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of temperatures: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
20
240 220
C15-C18 n-alkane Concentration (g/L)
200 180 160 140 120
ro of
100 80 60 40
-p
20 0 60
90 Time (mins)
re
30
Jo
ur
na
lP
(a)
21
120
40bar 50bar 60bar 70bar 80bar 150
40bar 50bar 60bar 70bar 80bar
60
90 Time (mins)
(b)
re
100.0%
C3H8
70.0%
H2
CH4
CO
na
60.0%
30.0%
CO2
lP
80.0%
40.0%
150
ur
Gas Concentration (vol %)
90.0%
50.0%
120
-p
30
ro of
C15-C18 n-alkane Concentration (g/L)
300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0
20.0%
Jo
10.0% 0.0%
40
50
60 Pressure (bar)
(c)
22
70
80
100.0%
C3H8
CO2
H2
CH4
CO
90.0%
70.0% 60.0% 50.0% 40.0%
ro of
Gas Concentration (vol %)
80.0%
30.0% 20.0% 10.0% 40
50
60 Pressure (bar)
re
(d)
-p
0.0%
70
80
Jo
ur
na
lP
Fig. 3. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of pressures: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
23
260
240
200 180 160 140 120
ro of
C15-C18 n-alkane Concentration (g/L)
220
100 80 60
WHSV=1
-p
40
0 60
90 Time (mins)
lP
30
re
20
Jo
ur
na
(a)
24
120
WHSV=2 WHSV=3 WHSV=4 150
300 280 240 220 200 180 160 140 120 100 WHSV=1
80
60
ro of
C15-C18 n-alkane Concentration (g/L)
260
WHSV=2
40
WHSV=3
20
WHSV=4
0 90 Time (mins)
Jo
ur
na
lP
(b)
120
-p
60
re
30
25
150
100.0% C3H8
Gas Concentration (vol %)
90.0%
CO2
H2
CH4
CO
80.0% 70.0% 60.0% 50.0% 40.0% 30.0%
ro of
20.0% 10.0% 0.0% 1
2
3
re
(c)
100.0%
C3H8
80.0%
60.0%
CH4
CO
Jo
ur
50.0%
30.0%
H2
na
70.0%
40.0%
CO2
lP
90.0%
Gas Concentration (vol %)
4
-p
WHSV
(h-1)
20.0% 10.0% 0.0%
1
2
WHSV (h-1)
(d)
26
3
4
Fig. 4. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of WHSV: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
260 240 220
ro of
180 160
-p
140
re
120 100 80
lP
C15-C18 n-alkane Concentration (g/L)
200
60
ur
20 0
H2/Oil = 750
na
40
H2/Oil = 500
60
H2/Oil = 1250 90 Time (mins)
Jo
30
H2/Oil = 1000
(a)
27
120
150
H2/Oil = 500 H2/Oil = 750 H2/Oil = 1000
ro of
C15-C18 n-alkane Concentration (g/L)
300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0
H2/Oil = 1250
30
60
90 Time (mins)
150
re
-p
(b)
120
lP
100.0%
70.0%
H2
CH4
ur
60.0%
CO2
na
80.0%
C3H8
50.0% 40.0%
Jo
Gas Concentration (vol %)
90.0%
30.0% 20.0% 10.0% 0.0%
500
750
1000 H2-to-oil ratio
28
1250
CO
(c) 100.0%
C3H8
CO2
H2
CH4
CO
90.0%
70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% 750
H2-to-oil ratio
1000
-p
500
ro of
Gas Concentration (vol %)
80.0%
(d)
1250
Jo
ur
na
lP
re
Fig. 5. The concentrations of C15-C18 n-alkanes in liquid products and gas products with variation of H2-to-oil ratios: (a) liquid (Pd/C); (b) liquid (NiMo/γ-Al2O3); (c) gas (Pd/C); (d) gas (NiMo/γ-Al2O3)
29
100 95
85 80 75
ro of
Conversion (%)
90
70
NiMo/gama-Al2O3
-p
65
Pd/C
60 60
90 Time (min)
120
re
30
Jo
ur
na
lP
Fig. 6. Conversion versus time for two different catalysts
30
150
100
fresh
spent
Weight Loss (%)
95 90 85 80
ro of
75 70
re
(a) 100
spent fresh
lP
90
na
85 80
Jo
70
ur
Weight Loss (%)
95
75
-p
Temperature (°C)
Temperature (°C)
(b) Fig. 7. TGA analyses of the catalysts: (a) NiMo/-Al2O3; (b) Pd/C
31
ro of
-p
re
lP
na
ur
Jo (a)
32
ro of -p re lP
(b)
Jo
ur
na
Fig. 8. IR spectra of the catalysts (a): (1) fresh NiMo/-Al2O3; (2) spent NiMo/-Al2O3; (3) -Al2O3. (b): (1) fresh Pd/C; (2) spent Pd/C
33
ro of
-p
re
lP
na
ur
Jo
(a)
34
ro of -p re
Jo
ur
na
lP
Fig. 9. XRD patterns of the catalysts. (a): (1) fresh NiMo/-Al2O3; (2) spent NiMo/-Al2O3; (3) -Al2O3. (b): (1) spent Pd/C; (2) fresh Pd/C.
35
ro of
-p
re
lP
na
ur
Jo
(A)
36
ro of -p re lP na ur
(B)
Jo
Fig. 10. SEM images of (A) NiMo/-Al2O3 catalysts: (a) fresh 1500x; (b) fresh 10000x; (c) spent 1500x; (d) spent 10000x; (B) Pd/C catalysts: (e) fresh 1500x; (f) fresh 10000x; (g) spent 1500x; (h) spent 10000x
37