Production of Hydrotreated Jatropha Oil Using Co–Mo and Ni–Mo

Article Cite This: Energy Fuels 2018, 32, 1812−1821

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Production of Hydrotreated Jatropha Oil Using Co−Mo and Ni−Mo Catalysts and Its Blending with Petroleum Diesel Shailesh J. Patil and Prakash D. Vaidya* Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai 400019, India ABSTRACT: Jatropha oil is a prospective non-edible resource for green diesel manufacturing. In this work, diesel-range hydrocarbons (mostly C15−C18 n-paraffins) were produced from the hydrotreatment of jatropha oil over traditional CoMo/Al2O3 and NiMo/Al2O3 catalysts in a fixed-bed reactor. The reaction variables were varied as follows: temperature, 563−653 K; pressure, 1.5−3 MPa; H2/oil ratio, 200−800 (v/v); and weight hourly space velocity, 1−4 h−1. Oil conversion was maximized (Co−Mo, 97%; Ni−Mo, 88.6%) at T = 653 K and P = 3 MPa. The hydrocarbon yield at these conditions was 62.6% (Co−Mo) and 63% (Ni−Mo). These findings were juxtaposed with our latest results on the hydrotreatment of the non-edible karanja oil. From the first-order plots of conversion of triglycerides in jatropha oil, rate constants and energy of activation were found. To improve the cold flow properties of the hydrotreated jatropha oil without isomerization, it was blended with usual diesel in varying proportions. As the concentration of usual diesel in such mixtures increased, the viscosity, cetane number, and pour point decreased. Employing tailored blends of hydrotreated vegetable oil and petroleum diesel thus appeared preferential. Finally, the performance of Co−Mo and Ni−Mo catalysts prepared by wet impregnation was tested, but the activity of the commercial catalysts was superior.

1. INTRODUCTION Thus far, the production of green diesel from hydrotreatment of vegetable oils has been extensively studied. In this secondgeneration biofuel, also renowned as hydrotreated vegetable oil (HVO), straight-chain paraffins with 15−18 carbon atoms are prevalent. It can be made by reacting oil with hydrogen (H2) at high temperature and high pressure over traditional CoMo/Al2O3 and NiMo/Al2O3 catalysts. After the triglycerides are hydrolyzed to produce fatty acids and glycerol, hydrogenolysis follows. Fatty acids are converted into n-paraffins, whereas glycerol is transformed into lighter products, such as propane. As soon as n-paraffins in HVO are isomerized, they act like the liquid hydrocarbons of usual diesel, and such post-treated HVO acquires better cold flow properties. HVO has several benefits, e.g., integration of sustainable liquids in refineries, high process adaptability, low production cost, and small ecological trail. Besides, it goes well together with usual diesel, and its properties are superior to those of biodiesel. In this work, non-edible jatropha oil (Jatropha curcas) was chosen as feed for producing HVO. Jatropha is a crucial feedstock for producing biofuels in India. It easily grows with little or no care in many parts of tropical countries, such as India. It is robust, perpetual, drought-resistant, and adaptable to infertile soil.1 It has a low gestation period (2−3 years) and high potential yield (seeds, 3−5; oil, 1−1.5 tons/hectare).2 Typical hydrotreating catalysts (sulfided Co−Mo and Ni−Mo on highsurface-area Al2O3), whose high efficacy for hydroprocessing of biofeeds is renowned,3 were selected for this study. In a fixed-bed reactor, we compared the performance of commercial Co−Mo and Ni−Mo catalysts over wide ranges of temperature (563−653 K), pressure (1.5−3 MPa), H2/oil ratio (200−800, v/v), and weight hourly space velocity (WHSV, 1−4 h−1). Also, the hydrotreatment processing of two non-edible oils, jatropha and karanja, was contrasted. © 2017 American Chemical Society

The performance of Co−Mo and Ni−Mo catalysts for hydrotreating vegetable oils of sunflower,4 rapeseed,5−7 and palm8 and model compounds, such as fatty acids9 and ester,10 is promising. Besides, Mo and Ni/Co are also effective for the jatropha application.11−18 In these works, the influence of catalyst modifiers (P, Si, Ce, La, W, and Ti) and feed composition on the process and product was emphasized. For example, Gong et al.11 reported that sulfided NiMoP/Al2O3 is promising for the hydrotreatment process. Liu et al.12,13 found that hydrotreated jatropha oil obtained using the Ni−Mo/SiO2−Al2O3 catalyst was akin to normal diesel. Liu et al.14,15 reported superior performance of non-sulfided NiMo catalysts doped with Ce and La. Kumar et al.16 developed Ni−W, Ni−Mo, and Co−Mo for producing green diesel from jatropha oil−gas oil mixtures. Using Ni−Mo and Co−Mo catalysts, Sharma et al.17 compared the performance of a traditional Al2O3 support with mesoporous titanosilicate. Recently, Satyarthi et al.18 investigated co-processing of jatropha oil with a diesel fraction using Co−Mo and Ni−Mo catalysts. Although there are many reported works on jatropha oil, knowledge on hydrotreating kinetics is scarce. Here, we used first-order plots of triglyceride conversion to determine the reaction rate constant. Notwithstanding their high cetane number in the 70−100 range,11 high-melting n-paraffins in HVO are unsuitable for diesel engines as a result of their higher viscosity than usual diesel and poor cold-flow properties.7 Thus, isomerization to the low-melting isoparaffins is crucial. To avoid the energy-demanding isomerization of the hydrotreated jatropha oil, we mixed it with usual diesel in varying proportions, and the viscosity, cetane number, and pour point of such mixtures were measured. Cold-flow Received: October 26, 2017 Revised: December 20, 2017 Published: December 21, 2017 1812

DOI: 10.1021/acs.energyfuels.7b03305 Energy Fuels 2018, 32, 1812−1821

Article

Energy & Fuels properties and viscosity of such blends were superior to those of the HVO product. To the best of our knowledge, there exists no systematic study on the properties of HVO−diesel blends made from jatropha oil. Past works on jatropha oil hydrotreating led to key insights into improved catalysts and reaction conditions. In this work, we provided new details on diesel blends, substitute feeds, and reaction kinetics. These features are not quite reported hitherto, and we wish to fill this gap. Additionally, we synthesized Co−Mo and Ni−Mo catalysts by the successive wet impregnation method and assessed their performance for HVO production from jatropha oil.

Table 1. Key Properties of Jatropha Oil property

method

value

saponification value (mg of KOH/g) iodine value (g of I2/100 g of oil) acid value (mg of KOH/g) density (g/cm3) flash point (K) pour point (K) cloud point (K)

AOCS Tl 1a-64 AOCS Tg 1-64 AOCS Te 2a-64 specific gravity bottle ASTM D93 ASTM D97

201 ± 3 100 ± 2 7.5 ± 3 0.94 ± 0.19 495 ± 2 275 280

Table 2. Fatty Acid Composition of Jatropha Oil

2. EXPERIMENTAL SECTION

fatty acid

2.1. Materials. Jatropha oil was purchased from SVM Agro Processor, Nagpur, India. H2 (purity of 99.9%) and nitrogen (purity of 99.9%) cylinders were purchased from Rakhangi Gas Suppliers, Mumbai, India. To identify the reaction products in the gas phase, mixtures of H2, methane, ethane, propane, and carbon oxides were purchased from Chemtron Science Laboratory Pvt. Ltd., Mumbai, India. CoMo/γ-Al2O3 (CoO, 4%; MoO3, 14%) and NiMo/γ-Al2O3 (NiO, 3.6%; MoO3, 14.8%) catalysts were purchased from Strem Chemicals, Newburyport, MA, U.S.A. and Sud-Chemie India Pvt. Ltd., New Delhi, India, correspondingly. For lab-made catalysts, precursor salts of Mo, Co, and Ni were purchased from Merck, Ltd. The Brunauer−Emmett−Teller (BET) surface area (245 and 255 m2/g) of the unused CoMo and NiMo catalysts was determined by nitrogen adsorption−desorption measurements (accuracy of ±1 m2/g) using a Micromeritics ASAP2010 instrument. The respective pore volumes were 0.5 and 0.6 cm3/g. Reagents for degumming jatropha oil and preparation and analysis of methyl esters were purchased from S. D. Fine Chemicals Pvt. Ltd., Mumbai, India. Standards for fatty acids, methyl esters, and liquid hydrocarbons in diesel were purchased from Aldrich. Usual diesel was obtained from a local petrol filling station in Mumbai, India. 2.2. Oil Characterization. The oil was pretreated by water degumming, acid degumming, and TOP degumming processes according to procedures described in a previous work.19 Key oil properties, such as saponification value, iodine value, acid value, density, and free fatty acid content, were measured (see Table 1). Using a Thermo Finnegan analyzer (Flash EA1112 series, Italy), the elemental composition (N, 1.72%; C, 77.03%; H, 9.8%; and O, 10.54%) was found. After transesterification of jatropha oil with methanol and sodium hydroxide,20 the fatty acid composition was found using gas chromatography (GC) analysis of the methyl esters (BPX-70 column, 50 m × 0.22 mm × 0.25 μm). The results are represented in Table 2. Jatropha oil comprises

palmitic acid palmitoleic acid stearic acid oleic acid linoleic acid

C16:0 C16:1 C18:0 C18:1 C18:2

formula

percentage in jatropha oil (%)

C16H32O2 C16H30O2 C18H36O2 C18H34O2 C18H32O2

13.49 1.09 5.23 43.57 36.62

free fatty acids with an even number of carbon atoms (16, palmitic and palmitoleic acids; 18, stearic, oleic, and linoleic acids); the detailed composition was as follows: 14.58% C16 and 85.42% C18. The saturated fatty acid content (palmitic and stearic acids) was 18.72%, whereas the unsaturated acid content (palmitoleic, oleic, and linoleic acids) was 81.28%. The iodine value was high (100 g of I2/100 g of oil) as a result of the high degree of unsaturation. 2.3. Experimental Setup and Procedure. Trials were made in an apparatus provided by Chemito Technologies Pvt. Ltd., Mumbai, India. The entire setup is shown in Figure 1. It consisted of a SS316 fixed-bed reactor (length, 49 cm; diameter, 2.54 cm), two electric furnaces, two preheaters (PH1 and PH2), two mass flow controllers (MFCs) for N2 and H2, high-pressure pump, back-pressure regulator (BPR), condenser, and gas−liquid separator. To control the process parameters, a proportional−integral−derivative (PID) controller and Proficy HMI/SCADA-iFIX software were used. Catalysts were diluted with quartz powder. This mixture was sandwiched between ceramic wool and placed inside the reactor. The remaining portion of the reactor was filled with glass beads. By this way, complete wetting of the catalyst was ensured; besides, channeling of the liquid feed was avoided. During each trial, the catalyst was pretreated at 573 K for 2 h under flowing H2 (340 mL/min). Afterward, it was activated by in situ sulfidation (T, 633 K; P, 3 MPa; t, 3 h) by adding dimethyl disulfide

Figure 1. Schematic diagram of the experimental setup. 1813

DOI: 10.1021/acs.energyfuels.7b03305 Energy Fuels 2018, 32, 1812−1821

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Energy & Fuels

Figure 2. (a) GC data for the liquid product (T, 623 K; P, 3 MPa; WHSV, 2 h−1; catalyst, Co−Mo; and H2/oil ratio, 600, v/v) and (b) GC data for petroleum diesel. are shown in panels a and b of Figure 2. The products n-C16H34 and n-C18H38 were formed via hydrodeoxygenation, whereas the other products n-C15H32 and n-C17H36 were formed via decarboxylation and decarbonylation. Cracking reactions favored at a high temperature resulted in the formation of C8−C14 hydrocarbons. Product constituents were identified using standard samples of the individual paraffins. When gas chromatography−mass spectroscopy (GC−MS, Clarus 500, PerkinElmer) was used together with a capillary column (Flite-1, 30 m × 0.25 mm × 0.25 μm), the spectrum showed molecular ion peaks at m/z 121, 226, 240, and 254, thereby confirming the presence of C15−C18 hydrocarbons. No paraffins were formed in the absence of the catalyst. 2.5. Reaction Metrics. Conversion of jatropha oil was found using the relation

(3 wt %) to the feed. Thus, the oxidation state of the catalysts was sustained. Jatropha oil was pumped and preheated to 373 K using PH1. Then, it was mixed with H2 and heated to 498 K using PH2. This mixture was sent to the catalytic reactor. Subsequently, the hydrotreatment processing was performed for 3 h in the 563−653 K range. On the whole, heating to the desired temperature was achieved within 45 min. The reaction products were condensed and separated in the gas−liquid separator. The gaseous product was collected separately. After water separation, the liquid product was filtered and distilled. 2.4. Product Analysis. Both gaseous and liquid products were analyzed by the GC technique (GC-8610, Thermo Fisher). To analyze the product gas, a thermal conductivity detector was used along with a HAYESEP-DB packed GC column. Besides, unreacted H2, CO, CO2, CH4, and C3H8 were present. For analysis of the liquid product, a flame ionization detector (FID) and BPX-5 capillary column (30 m × 0.25 mm × 0.25 μm) were used. 1-Methylnaphthalene was used as the internal standard. GC data for the liquid product and usual diesel

percent conversion (%) saponification value of feed − saponification value of product = × 100 saponification value of feed

(1) 1814

DOI: 10.1021/acs.energyfuels.7b03305 Energy Fuels 2018, 32, 1812−1821

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Energy & Fuels

Figure 3. XRD patterns for Co−Mo and Ni−Mo catalysts. Saponification values of the feed and product were determined using the AOCS Tl 1a-64 method. The product yield was calculated according to the relation

percent yield (%) =

mass of C15−C18 hydrocarbons × 100 mass of feed

(2)

2.6. Blending of Hydrotreated Jatropha Oil with Usual Diesel. Because hydrotreated jatropha oil and usual diesel contain similar hydrocarbons (see panels a and b of Figure 2), it is possible to use this hydrotreated product as a diesel additive. HVO, usual diesel, and their mixture have a similar calorific heating value.21 In this work, the distilled liquid product was blended with usual diesel in varying proportions (20−80, 40−60, 50−50, 60−40, and 80−20%). The cetane number and pour point of the HVO product, diesel, and blends were measured. Using the method by Nelson,22 the diesel index was determined from the aniline point and American Petroleum Institute (API) gravity. Knowing the diesel index, the cetane number was found. Earlier, McCoy23 reported the cetane number for mixtures of biodiesel with ethanol and usual diesel. A dynamic viscosity measurement of HVO, usual diesel, and blends was performed using an AntonPaar rheometer (MCR 301, Germany) in the 300−373 K range. 2.7. Catalyst Characterization. Both Co−Mo and Ni−Mo catalysts were characterized by the X-ray diffraction (XRD) technique using a Rigaku Miniflex D500 diffractometer and monochromic Cu Kα radiation. Catalyst crystallinity and metal dispersion on the Al2O3 support were examined. Samples were scanned from 10° to 90° with the step of 2θ = 0.01°. In Figure 3, XRD patterns for fresh and spent catalysts showed peaks at 2θ = 37.3°, 46°, and 66.5°, which are characteristic of alumina.24 No significant peak was observed for CoO and NiO, thereby suggesting complete dispersion of CoO and NiO throughout the surface of alumina. These results were in good agreement with a previous work.7 XRD patterns for spent catalysts showed peaks at 33°, which were not seen in those for the fresh catalysts. These peaks were due to MoS2, which is formed by sulfidation of molybdenum.25 Other peak patterns for the fresh and spent catalysts were identical. Thus, we concluded that no major changes in the catalyst surface occurred during reaction. Surface morphology of the catalysts was investigated by the scanning electron microscopy (SEM) technique using a JEOL-JSM 6653 LA instrument. SEM images for fresh CoMo and NiMo catalysts exhibited irregular shapes (see panels a and b of Figure 4).

Figure 4. (a) SEM image for the fresh Co−Mo catalyst and (b) SEM image for the fresh Ni−Mo catalyst. 2.8. Catalyst Synthesis. We synthesized CoMo/Al2O3 and NiMo/Al2O3 catalysts using the successive wet impregnation technique. Commercial-grade γ-Al2O3 powder (Degussa) was screened 1815

DOI: 10.1021/acs.energyfuels.7b03305 Energy Fuels 2018, 32, 1812−1821

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Energy & Fuels (20−80 mesh), calcined at 773 K, and impregnated with an aqueous solution of (NH4)6Mo7O24·4H2O. After overnight drying at 373 K, resulting Mo/Al2O3 was calcined at 773 K for 5 h. Cobalt nitrate hexahydrate was then deposited on calcined Mo/Al2O3 to yield the Co−Mo catalyst (nickel nitrate hexahydrate was used for the Ni−Mo catalyst). Again, the catalysts were dried overnight at 373 K and calcined at 773 K for 5 h. These Co−Mo and Ni−Mo catalysts exhibited 214 and 231 m2/g BET surface area and 0.4 and 0.5 cm3/g pore volume. Their XRD patterns are shown in panels a and b of Figure 5.

Figure 6. (a) Effect of the temperature on the conversion and yield for the Co−Mo catalyst (P, 3 MPa; WHSV, 2 h−1; and H2/oil ratio, 600, v/v) and (b) effect of the temperature on the conversion and yield for the Ni−Mo catalyst (P, 3 MPa; WHSV, 2 h−1; and H2/oil ratio, 600, v/v).

reactions and transformation into smaller hydrocarbons (>C15).7 With the rise in the temperature, the product thus becomes richer in smaller hydrocarbons (