Procedia Engineering 148 ( 2016 ) 275 – 281

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1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of ICPEAM 2016doi: 10.1016/j.proeng.2016.06.565

ScienceDirect

4th International Conference on Process Engineering and Advanced Materials

Hydroprocessing of Crude Jatropha Oil Using Hierarchical Structured TiO2 Nanocatalysts

Madiha Yasira, M. Tazli Azizana,*, Anita Ramlib, Mariam Ameena aChemical Engineering Department, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia

bDepartment of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, 32610, Bandar Seri Iskandar, Perak, Malaysia

Abstract

Hydroprocessing of crude jatropha oil (CJO) has been studied over different hierarchical structured titania (TiO2) nanomaterial supports doped with Ni and Ce metals. Three different hierarchical structured TiO2 suport material were used including commercial TiO2 nanopowder, titania nanotubes (TNT) and titania nanosheets (TNS). The TNT and TNS support nanomaterials were synthesized using hydrothermal chemical route. However, the catalyst loading was performed using wet impregnation method. All the catalysts were characterized using Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopic (TEM) and Accelerated Surface Area and Porosimetry (ASAP) analysis. NiCe/TNT catalysts exhibited highest conversion of triglycerides to hydrocarbon products as compared to NiCe/TiO2 and NiCe/TNS. The main products involved in the HC reaction are straight chain hydrocarbons ranging n-C15 to n-C18. However, the reaction pathways observed are: hydrodeoxygenation (HDO) and decarboxylation/decarbonylation (DCO/DCN). DCO/DCN was found to be the major reaction route under the studied conditions. © 2016 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of ICPEAM 2016.

Keywords: Hydroprocessing; TiO2 nanotubes; TiO2 nanosheets; Crude Jatropha oil; Hierarchical structured nanomaterials

1. Introduction

Depleting world’s energy resources and increasing greenhouse gasses are emphasizing towards the search of

* Corresponding author. Tel.: +605-3687611; fax: +605-3656176.

E-mail address: tazliazizan@petronas.com.my

© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of ICPEAM 2016

276 Madiha Yasir et al. / Procedia Engineering 148 ( 2016 ) 275 – 281

renewable energy sources. Biofuels obtained from vegetable oils are considered as sustainable and environmental friendly alternate for fossil fuels due to sulfur and nitrogen free emissions [1, 2]. Hydroconversion (HC) of triglycerides from vegetable oils have attracted immense focus of researchers as the hydrocarbon products obtained from the reaction are similar to fossil diesel fuels, therefore commonly known as ‘green diesel’ [3, 4].

Hydroprocessing of triglyceride yields straight chain hydrocarbons of 15-20 carbon range. The process involves reaction of triglyceride molecules with H2 gas at high pressure usually above 30 bar and temperature in the range 250-350 0C in the presence of suitable active catalyst [5]. The reaction of triglycerides follows three main reaction routes: hydrodeoxygenation (HDO), decarboxylation (DCO) and decarbonylation reactions (DCN). HDO reaction pathway yields the hydrocarbon products with the same carbon number as in the parent glyceride molecule but DCO/DCN gives the product with 1 carbon less than the parent molecule. Therefore, various research works have been done tailoring the selectivity towards a specific route of reaction to get desired product. It has been proved that the catalyst is the key factor not only for controlling reaction but also for selectivity towards a certain route of reaction [1, 6].

For HC reactions, the most extensively used catalysts are sulfided metal catalysts and noble metal catalysts [7, 8]. Transition metal catalysts requires sulfiding the catalyst with sulfur containing compounds such as CS2 or H2S, in order to activate the catalyst [8, 9]. However, prolonged reactions using these catalysts can cause sulfur contamination of the products which in turn effects the quality of the biofuel obtained. On the other hand, noble metals are also not suitable for large scale usage because of their high costs. Commonly used metal oxide supports include zeolites, carbon, mesoporous silica, TiO2, Al2O3, SiO2, MCM-41 and SAPO-11, while active metals include the combination of NiCo, NiMo, CoMo and NiW etc. [10]. Though, very less research work has been done using rare earth metals like Lanthanides and Actinides. It has been reported that rare earth metals when combined with transition metals proved to be very active catalysts due to their tremendous properties like, thermal stability, less carbon deposition, high catalytic activity and good dispersion capability [11-13]. It has been stated that cerium metal greatly enhance the activity of Ni/Al2O3 catalyst for hydrogenation reaction [14]. Thus, the main objective of this work is to synthesize the hierarchical structured TiO2 nanomaterials doped with Ni and Ce metals in order to utilize for the hydroprocessing of crude jatropha oil.

Nomenclature

HC Hydroconversion TNT Titania nanotubes TNS Titania nanosheets CJO Crude jatropha oil

2. Methodology

2.1. Catalyst synthesis

2.1.1. Synthesis of TiO2 nanosheets (TNS)

Titania nanosheets (TNS) were prepared using the following procedure. Initially, hydrofluoric acid (HF) (37% solution), and ethanol were added to commercially available titania nanopowder (Degussa P25) with 99.7% purity (Sigma-Aldrich), in a Teflon-lined stainless steel autoclave. The autoclave was kept at a temperature of 150 0C for 24 h and then allowed to cool until room temperature. The white precipitates obtained after the hydrothermal treatment were vacuum-filtered and washed with ethanol and deionized water alternately. The sample was then dried at 90 0C overnight to obtain titania nanosheets denoted as TNS.

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2.1.2. Synthesis of TiO2 nanotubes (TNT)

In a typical procedure, TNTs were prepared using a hydrothermal process by mixing commercial TiO2 nanopowder with ethanol and NaOH solution (10 M), followed by hydrothermal treatment of the mixture at 180 0C in a Teflon-lined autoclave for 24 h. After the hydrothermal reaction, the products of the reaction were washed and dried properly and denoted as TNT.

2.1.3. Metal loading

All the catalysts support materials including commercial TiO2 nanopowder, TNT’s and TNS’s were loaded with Ni and Ce metals using wet co-impregnation method with percentage loading of Ni = 10 wt% and Ce = 20 wt%. The Ni and Ce loaded catalysts has been prepared by adding aq. solution of Ni(NO3)2 (Merck) and Ce(NO3)3 (Merck) on the support solutions separately, followed by stirring at room temperature for 1h. The impregnated samples were dried overnight at 90 0C then calcined at 300 0C for 6h.

2.2. Catalyst characterization

The synthesized catalysts were further characterized in order to understand their morphology and textural properties. High resolution transmission electron microscope (HR-TEM) images were recorded using Zeiss LIBRA 200 FE, operated at 200 kV with the magnification of 80,000 and 200,000. Electron microscopy images of samples were taken with Variable Pressure Field Emission Scanning Electron Microscope (VPFESEM, Zeiss Supra55 VP) equipped with X-ray energy-dispersive (EDX) microanalyzer. The pore volume and surface area of the samples were obtained by N2 adsorption-desorption isotherm at 73 K on Micromeritics, ASAP 2020 apparatus. The sample was degassed at 300 0C for 240 min prior to N2 adsorption.

2.3. Catalytic activity measurements

Crude jatropha oil (CJO) purchased from Bionas Sendirian Berhad, was used as the feedstock. Purified H2 gas (>99% purity) was utilized for HC experiments. The experiment was performed in a 100 ml high pressure stainless steel batch reactor. All the catalysts were activated prior to the reaction in the presence of H2 at ambient pressure and 400 0C temperature for 1 hour. The HC reaction was carried out at 50 bar H2 pressure and 300 0C with 5wt% of catalyst.

Liquid samples were tested using gas chromatograph HP 5890 equipped with flame ionization detector (GC-FID). The method uses derivatization with N-methyl-N-trimethylsilylfluoracetamide (MSTFA) in the presence of pyridine. After silylation, the sample was dissolved in n-heptane and analyzed using gas chromatography equipped with non-polar column type DB-5: L = 30 m; d = 0.25 mm; film thickness 0.25 μm. Nitrogen was used as the carrier gas (2.5 cm3 min-1). The following analysis conditions were used: 1 min at 50 0C, followed by a linear increase at 15 0C min-1 to 180 0C, next linear increase at 7 0C min-1 to 230 0C; last ramp at 10 0C min-1 (5 min).

The conversion (C) of CJO was calculated as follows:

C = 100% ‒ CTG (1)

Where CTG is the percentage concentration of unreacted triglycerides present in the final product.

3. Results and Discussion

3.1. Catalyst characterization results

The TEM images (figure 1) and FESEM images (figure 2) of all the catalysts i.e. NiCe/TiO2, NiCe/TNS and NiCe/TNT revealed that Ni and Ce metals are very well dispersed throughout the catalyst surface. The size of doped Ni and Ce metals were in the range of 1-3 nm and 5-10 nm, respectively, while the size of commercial TiO2, TNT’s and TNS’s was recorded in the range of 15-30 nm, 20-50 nm and 100-200 nm (width 8-10 nm), respectively.

278 Madiha Yasir et al. / Procedia Engineering 148 ( 2016 ) 275 – 281

Figure 1: TEM images of (a) NiCe/TiO2, (b) NiCe/TNS and (c) NiCe/TNT

Figure 2: FESEM images of (a) NiCe/TiO2, (b) NiCe/TNS and (c) NiCe/TNT

The physicochemical properties of all the catalysts has been shown in table 1. The specific surface area of NiCe/TiO2, NiCe/TNS and NiCe/TNT was found to be 44, 16 and 157 m2/g, respectively. Doping of Ni or Ce on titania supports cause decrease in specific surface area of actual catalyst support material. However, the decrease in the surface area is even higher after doping of both Ni and Ce metals (17%). This happened as the size of Ni and Ce metals are small enough to fit inside the pores of titania support material. Therefore, adding Ni and Ce as active metals seems to be responsible for the decrease in surface area and pore volume of the titania supports due to blockage of some pores by adding active metals [1, 15].

(a) (b) (c)

(a)

(b)

(c)

Table 1: Physicochemical properties of NiCe/TiO2, NiCe/TNS and NiCe/TNT catalysts

279 Madiha Yasir et al. / Procedia Engineering 148 ( 2016 ) 275 – 281

Figure 3: Gas chromatograms of the hydroprocessed CJO using (a) NiCe/TiO2, (b) NiCe/TNS and (c) NiCe/TNT

catalysts at 300 0C and 50 bar H2 pressure for 1 h of reaction time

Catalysts Specific surface area (m2/g)

Total pore volume (cm3/g)

Average pore diameter (nm)

Ni.Ce/TiO2 44 0.373 29.7

NiCe/TNS 16 0.076 17.0

NiCe/TNT 157 0.441 11.1

(a)

(b)

(c)

280 Madiha Yasir et al. / Procedia Engineering 148 ( 2016 ) 275 – 281

3.1. Hydroconversion of crude jatropha oil

Hydroconversion of CJO using NiCe/TiO2, NiCe/TNS and NiCe/TNT catalysts produced two types of products: gaseous products and liquid products. The liquid products were analyzed with gas chromatography (GC). The major products obtained include C15–C18 range hydrocarbons, triglycerides, fatty acids, waxes and esters of fatty acids. However, the products did not contain short chain hydrocarbons. Considerable amounts of esters especially stearyl stearate were identified by GC-MS (figure 3) which were formed by the esterification of fatty acids. The triglycerides obtained in the product were actually formed by the hydrogenation of double bonds of the original triglycerides, but still they were considered as raw materials as the key goal was the deoxygenation of triglycerides. During hydrodeoxygenation of triglycerides, the triglyceride molecules first undergo hydrogenation of double bonds as the C=C double bonds can be dissociated already at low temperatures (100-180 0C) over hydrogenation or hydrotreating catalysts, i.e. at temperatures too low for deoxygenation to take place [16, 17].

All the investigated catalysts were found to be active for the triglycerides conversion into hydrocarbon products, with higher selectivity towards n-C17. As the major component in the CJO is triolein, which is triglyceride of oleic acid consisting of C18 back bone, presence of n-C18 represents the extent of HDO reaction route while presence of n-C17 represents the DCO/DCN route of reaction. The higher concentration of n-C17 represents that the preferred route of reaction is DCO/DCN with all three different catalysts supports. Highest conversion (85%) of triglycerides was achieved by NiCe/TNT catalyst at 300 0C and 50 bar H2 pressure for 1 h of reaction time. During the whole range of reaction conditions, almost all the triglycerides were found to be hydrogenated to their saturated counterparts. However, it was observed that different hierarchical structured catalyst supports showed different degrees of conversions towards hydrocarbon products. Whereas, a significant difference was found between NiCe/TiO2, NiCe/TNS and NiCe/TNT as shown in figure 4. The catalyst supported on TNS showed the lowest conversion (54%), while NiCe catalyst supported on commercial TiO2 showed better performance than NiCe/TNS (71%).

Figure 4: Percentage conversion of CJO using NiCe/TiO2 NiCe/TNS and NiCe/TNT catalysts at 300 0C and 50

bar H2 pressure for 1 h of reaction time.

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4. Conclusion

In conclusion, green diesel (diesel range hydrocarbon n-C15 to n-C18) can be produced by hydroconversion reaction of CJO over NiCe loaded on hierarchical structured titania catalysts. DCO/DCN was found to be the preferred route of reaction over HDO route under the tested reaction conditions (300 0C temperature, 30 bar pressure and 1 h reaction time). Among all the tested catalysts (NiCe/TiO2, NiCe/TNS and NiCe/TNT), highest triglyceride conversion of 85 % has been achieved with NiCe/TNT catalyst at 300 0C temperature, 30 bar pressure and 1 h reaction time. However, the major reaction product was heptadecane (n-C17). It has been found that structural hierarchy of catalysts have a pronounced effect on the reaction output.

Acknowledgement

The authors highly appreciate and regard the technical and financial support from Universiti Teknologi PETRONAS.

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