DEOXYGENATION OF PALM OIL TO BIO-HYDROGENATED DIESEL OVER Pd/Al 2 O 3 CATALYST USING MICROSCALE-BASED REACTOR

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1 DEOXYGENATION OF PALM OIL TO BIO-HYDROGENATED DIESEL OVER Pd/Al 2 O 3 CATALYST USING MICROSCALE-BASED REACTOR Raviporn Nernrimnong a, Siriporn Jongpatiwut *,a,b, Yuttanant Boonyongmaneerat c, Thana Sornchamni d, Nichaporn Sirimungkalakul d a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Center of Excellence on Petrochemical and Materials Technology, Bangkok, Thailand c Metallurgy and Materials Science Research Institute, Chulalongkorn University, Bangkok, Thailand d PTT Research and Technology Institute, Wangnoi, Ayutthaya, Thailand Keywords : Deoxygenation, Bio-hydrogenated diesel, Microscale-based reactor ABSTRACT Bio-hydrogenated diesel (BHD) is one of the alternative fuels which derived from renewable resources becomes attractive because of the compatibility with petroleum-based diesel due to its similar structure. BHD can be produced from triglyceride feedstocks by deoxygenation reaction in the presence of hydrotreating catalyst. Normally, the BHD production is carried out in a conventional fixed-bed reactor having limitation of mass and heat transfer. Thus, microscale-based reactor turns to be more interesting due to the higher heat and mass transfer, high surface to volume ratio, lower pressure drop and lower quantity of catalyst comparing with the conventional fixed-bed reactor. In terms of catalysts, Al 2 O 3 support which is the conventional support for hydrotreating catalysts has high surface area, high thermal stability, and inexpensive cost. In this work, Pd/Al 2 O 3 will be prepared and tested for BHD production from palm oil in microscale-based reactor. In addition, the appropriate catalyst coating on stainless steel plates of microscale-based reactor i.e. dip-coating by suspension solution (SUS/DC), dip coating by sol-gel solution (SG/DC), and electrophoretic deposition by sol solution (SOL/EPD) will be investigated. Moreover, the catalysts will be characterized by XRD, BET, SEM-EDX, XPS, and 3D Optical Microscope. The results showed that Pd/Al 2 O 3 (SUS/DC) exhibited the highest BHD yield due to the highest catalyst weight resulting in Pd active site available on that. However, the Pd/Al 2 O 3 (SOL/EPD) gave the strongest adherence but it obtained the lowest amount of catalyst on the plate and low Pd dispersion leading to the lowest BHD yield. *Siriporn.j@chula.ac.th INTRODUCTION Bio-hydrogenated diesel (BHD) is one of the alternative fuels produced from renewable resources which are a triglyceride-based feedstock by deoxygenation reaction in the presence of hydrotreating catalyst at elevated temperature and pressure. The biohydrogenated diesel product gives the favorable specifications such as low greenhouse gas emission, high heating value and high cetane number. Moreover, it is compatible with petroleum-based diesel due to its similar structure. Generally, the deoxygenation of triglyceride-based feedstock is carried out by a conventional fixed-bed reactor which gives a limitation of mass and heat transfer, high pressure drop and using a large quantity of catalyst. Thus, microscale-based reactor turns to be more interesting because it gives higher Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

2 heat and mass transfer coefficient, smaller process volume, shorter residence time, lower pressure drop, lower quantity of catalyst, smaller equipment size comparing with conventional fixed-bed reactor. However, the coating of the catalyst on the stainless steel plate for microscale-based reactor was still a challenging task. In terms of catalysts, the advantages of Al 2 O 3 supports are high surface area and high thermal stability leading to high catalyst activity and good long term stability. Moreover, Al 2 O 3 supports are inexpensive and commercially used in microscale-based reactor. In this work, Pd/Al 2 O 3 catalyst coated on stainless steel plate were prepared by different coating methods i.e. dipcoating by suspension solution (SUS/DC), dip coating by sol-gel solution (SG/DC), and electrophoretic deposition by sol solution (SOL/EPD). The coated catalysts were tested for BHD production from palm oil using microscale-based reactor. Moreover, the catalysts will be characterized by various techniques. EXPERIMENTAL A. Material Aluminum oxide powder (Al 2 O 3 ) was purchased from SASOL. Polyvinyl alcohol (PVA) was purchased from Polysciences. Aluminum isopropoxide (AIP), Aluminum acetyl acetonate (AlAcAc), and Palladium nitrate dihydrate (Pd(NO 3 ) 2.2H 2 O) were purchased from Sigma-Aldrich. Stainless steel plates (SS316) were obtained from PTT RTI. B. Catalyst Preparation and Coating Before dip-coating, the stainless steel plate was treated by rinsing with DI water and ethanol. Then, the plate was sonicated in 20 wt.% citric acid for 30 min and rinsed with DI water again then dried 110 ºC for 3 h and calcination at 800 ºC for 2 h by 1.7 ºC /min. For preparation of Al 2 O 3 (SUS/DC), the Al 2 O 3 solution was synthesized by suspension method by using the mass ratio of the components, Al 2 O 3 : CH 3 COOH: H 2 O: PVA, equals to 10: 1: 100: 5. Firstly, PVA was slowly added into the DI water at 85 ºC and stirred for 3 h. Afterwards, acetic acid and Al 2 O 3 powder was added into the solution and stirred for 3 h at 85 ºC followed by stirring for 3 days at room temperature. Then, the solution was coated on the plate by dip coating method for 1 min and dried at 110 ºC for 12 h then calcined at 500 ºC for 4 h. For preparation of Al 2 O 3 (SG/DC), the Al 2 O 3 solution was synthesized by using the molar ratio of the components, AIP:H 2 O:EtOH:AlAcAc, equals to 1:100:10:0.5 and using 3 wt.% PVA as binder. Firstly, DI water and ethanol were mixed and stirred at 45 ºC for 15 min. Afterwards, AIP was added and stirred for 45 min at 80 ºC. Then, AlAcAc and PVA were added and stirred for 15 min at 80 ºC. After that, HNO 3 was added dropwise until ph equalled to 4 and stirred at 80 ºC for 24 h. Then, the solution was coated on the plate by dip coating method for 1 min and dried at room temperature for 5 h followed by drying in an oven at 100 ºC for overnight and calcination at 600 ºC, for 2 h. For the pretreatment step of EPD process, the stainless steel plate was cleaned by 2 steps. Firstly, the stainless steel plate was cleaned by the electrochemical method in the solution containing 40 g/l NaOH, 40 g/l Na 2 CO 3, and 40 g/l Na 3 PO 4 at 80 ºC and 5V for 5 min. Secondly, the stainless steel plate was etched by soaking in the solution containing 100 g/l H 2 SO 4 and 200 g/l NaCl at 80 ºC for 1 min. For preparation of Al 2 O 3 (SOL/EPD), AIP was added to the distilled water at the molar ratio of AIP: H 2 O equaling to 1:100 then stirred for 20 min at ºC. Afterwards, HNO 3 was added into the solution at the molar Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

3 ratio of HNO 3 : AIP equaling to 0.1: 1 then the solution was stirred for 6 h at ºC. Then, the stainless steel plate was placed into the prepared Al 2 O 3 sol solution and a direct current was passed at 5V for 1.5 min. Then, the coated plate was dried at room temperature for 24 h and followed by calcination at 550 ºC for 2 h. After obtaining the Al 2 O 3 supports coated on the stainless steel plate from each method, the next step is to impregnate Pd metal on the coated Al 2 O 3 supports by using palladium nitrate dihydrate solution for the Pd loading of 1 wt.% then dried at 110 ºC overnight followed by calcination at 500 ºC, for 4 h by 10 ºC /min. C. Catalyst Characterization X-ray diffraction (XRD) was used to identify the unknown crystalline material. The XRD patterns were obtained by a Rigaku X-ray diffractometer system (RINT-2200). The catalysts were measured in the 2θ range of 5 80º. The surface area, pore volume, and pore size of the catalysts was measured by Brunauer-Emmett-Tellet (BET) surface area analyzer (BEL, Belsorp Mini-II). Scanning electron microscope (SEM-EDS), (JEOL JSM-6610LV), was used at a voltage of 12 kv to determine chemical composition and morphology of catalyst. X-ray photoelectron spectroscopy (XPS, AXIS ULTRA DLD) was employed to determine the chemical element composition on the surface of catalysts. 3D optical profiler was analyzed by the ZeGage machine. It was utilized to identify the surface texture, thickness, and roughness of catalysts coated on stainless steel plates. D. Catalystic Activity Testing Microscale-based reactor was used to perform the deoxygenation reaction of refined palm oil in the presence of hydrotreating catalyst at high pressure and temperature. Prior to the reaction, the coated Pd/Al 2 O 3 catalysts were reduced at 200 ºC, 500 psig for 3.5 h under H 2 flow (150 ml/min). After reduction, the conditions were set to 325 ºC and 500 psig under H 2 flow (232 ml/min). Then, the 50 wt.% of refined palm oil in dodecane feedstock was fed into the reactor with the flowrate 0.2 ml/min. The liquid product was trapped in a separator and collected in a small glass bottle and then analyzed by a gas chromatograph (Agilent 7890) equipped with a DB-5HT column and FID detector. RESULTS AND DISCUSSION A. Catalyst Characterization The XRD results shown in Figure 1 showed that all Pd/Al 2 O 3 catalysts contained a pure gamma phase as support and Pd as active metal but the metal was shown in the XRD pattern as PdO phase due to the calcination step. The crystalline structure of Al 2 O 3 supports were exhibited a main diffraction peak at 2θ value of 37.56º, 39.68º, 46.02º, 60.75º, and 67.12º which represent gamma alumina phase. Moreover, the peaks of gamma alumina phase from Pd/Al 2 O 3 (SUS/DC) catalyst were sharper than from Pd/Al 2 O 3 (SG/DC) and Pd/Al 2 O 3 (SOL/EPD) catalysts. It can be indicated that the Pd/Al 2 O 3 (SUS/DC) catalyst had more crystallinity than the Pd/Al 2 O 3 (SG/DC) and Pd/Al 2 O 3 (SOL/EPD) catalysts. (Gil et al., 2015) For the XRD patterns corresponding to PdO in these catalysts, it can be noticed that the main diffraction peaks of PdO in Pd/Al 2 O 3 (SOL/EPD) catalysts at a 2θ value of 33.9º were relatively high due to low Pd dispersion. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

4 Figure 1 XRD pattern of 1 wt.% Pd/Al 2 O 3 catalysts synthesized by (a) commercial gamma alumina from SASOL, (b) SUS/DC, (c) SG/DC, and (d) SOL/EPD. As shown in Figure 2, it can be seen that Pd/Al 2 O 3 (SUS/DC) gave homogeneous layer because SUS/DC method used commercial Al 2 O 3 powder which has constantly particle size. While Pd/Al 2 O 3 (SG/DC) gave the rough layer of Pd/Al 2 O 3 and Pd/Al 2 O 3 (SOL/EPD) gave the separated layer between Al 2 O 3 layer in dark grey zone and Pd active metal in light grey zone. The layer of PdO and Al 2 O 3 Pd/Al 2 O 3 (SOL/EPD) catalyst was separated because Al 2 O 3 layer from EPD method used voltage to the force the sol solution of boehmite to stick with the plate that gave strong adherent and high dense of Al 2 O 3 on the plate and it also stick with the plate by hydrogen bonding which was very strong bond. Thus, when Pd was impregnated on the Al 2 O 3 layer it was hard to go into the Al 2 O 3 layer. In Table 1, it could confirm that Pd/Al 2 O 3 (SUS/DC) and Pd/Al 2 O 3 (SG/DC) had well dispersed of Pd on the Al 2 O 3 layer because the actual Pd percentages were closed to the theoretical value which are 1wt.% but Pd/Al 2 O 3 (SOL/EPD) gave unexpected high percentage of Pd (13.42%). This indicates that most of PdO stayed on the Al 2 O 3 layer. Thus, it could confirm that Pd had low dispersion on Al 2 O 3 support layer coated by EPD. Moreover, the high percentages of Cr and Fe from Pd/Al 2 O 3 (SUS/DC) and Pd/Al 2 O 3 (SG/DC) came from the oxide layer of stainless steel that dissolved with the catalysts. Table 1 The average atomic percentages of Pd/Al 2 O 3 catalysts from SEM-EDX Catalyst Average Atomic Percentage (%) O Al Pd Cr Fe Pd/Al 2 O 3 (SUS/DC) Pd/Al 2 O 3 (SG/DC) Pd/Al 2 O 3 (SOL/EPD) Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

5 (a) SUS/DC (b) SG/DC (c) SOL/EPD Figure 2 SEM images of the Pd/Al 2 O 3 catalysts synthesized and coated by (a) SUS/DC, (b) SG/DC, and (c) SOL/EPD methods. As shown in Figure 3, the 2D optical profile images and the thickness values of all Pd/Al 2 O 3 catalysts coated on the stainless steel are shown in the Figure 3. The results showed that the thickness of Pd/Al 2 O 3 catalysts coated on the stainless steel plate were decreased as following order; Pd/Al 2 O 3 SG/DC > Pd/Al 2 O 3 SUS/DC > Pd/Al 2 O 3 SOL/EPD. The Pd/Al 2 O 3 (SG/DC) gave highest thickness and also showed the roughness layer of catalyst on the plate because this method could not control the size of particle. For Pd/Al 2 O 3 (SUS/DC), it gave homogeneous layer on the plate, it may cause by using PVA which help on the adherence and Al 2 O 3 powder which has consistently particle. For Pd/Al 2 O 3 (SOL/EPD), it gave the lowest thickness resulting in its strongest adherence. (a) Thickness = μm. (b) Thickness = μm. (c) Thickness = 9-11 μm. Figure 3 2D optical profile images of Pd/Al 2 O 3 catalysts coated on the stainless steel by (a) SUS/DC, (b) SG/DC, and (c) SOL/EPD methods. B. Catalytic Activity Testing The Pd/Al 2 O 3 catalysts were tested for the BHD production by deoxygenation of palm oil using microscale-based reactor at 325 ºC, 500 psig, H 2 /feed molar ratio of 96. The coated Pd/Al 2 O 3 catalysts had to be reduced at 200 ºC and 500 psig under H 2 of 150 NmL/min for 3.5 h to convert metal oxide to active metal form. The results showed that the BHD yield over Pd/Al 2 O 3 catalysts were decreased with the following order; Pd/Al 2 O 3 (SUS/DC) > Pd/Al 2 O 3 (SG/DC) > Pd/Al 2 O 3 (SOL/EPD) catalysts as shown in Figure 4(a). The Pd/Al 2 O 3 (SUS/DC) catalyst exhibited the highest BHD yield because the Pd/Al 2 O 3 (SUS/DC) catalyst gave the highest catalyst weight as 1.03 g led to more Pd active metal available on that resulting in the highest BHD yield. Moreover, it could be due to high dispersion of Pd on Al 2 O 3 support layer. In contrary, Pd/Al 2 O 3 (SOL/EPD) exhibited the lowest BHD yield because this method gave the lowest weight of catalyst. Thus, it would have the lowest amount of Pd active metal resulting in the lowest BHD yield. Moreover, it could be seen that the Pd/Al 2 O 3 (SOL/EPD) had the lowest Pd metal dispersion which leads to the lowest BHD yield. From the images of liquid products obtained over all Pd/Al 2 O 3 catalysts as shown in Figure 4(b), it was noticed that the liquid products were clear or light yellow with low viscosity at the first few hours of reaction for all Pd/Al 2 O 3 catalysts. However, the Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

6 liquid product from Pd/Al 2 O 3 (SUS/DC) and (SG/DC) catalysts in the last few hours of reaction turned to be dark yellow and brown due to the intermediates oxygenated compounds and some precipitates which come from catalyst detachment and stainless steel corrosion caused by the oxide layer from thermal treatment. In contrast, the liquid product from Pd/Al 2 O 3 (SOL/EPD) catalyst in the last few hours of reaction exhibited only brown clear color without any precipitates from catalyst detachment and corroded stainless steel plate. Thus, it could confirm that Pd/Al 2 O 3 (SOL/EPD) gave the strongest adherence among the other methods due to the lowest thickness, strong H-bonding with stainless steel and pretreatment method which was not generated the oxide layer like thermal treatment. Pd/Al 2O 3 (SUS/DC) (1.03 g) Pd/Al 2O 3 (SG/DC) (0.49 g) Pd/Al 2O 3 (SOL/EPD) (0.34 g) Pd/Al 2O 3 (SUS/DC) (1.03 g) Pd/Al 2O 3 (SG/DC) (0.49 g) Pd/Al 2O 3 (SOL/EPD) (0.34 g) Figure 4 (a) The BHD yield over Pd/Al 2 O 3 catalysts synthesized by SUS/DC, SG/DC, and SOL/EPD methods using microscale-based reactor and (b) the liquid product appearances. CONCLUSIONS The deoxygenation of palm oil feedstock to BHD was carried out in microscale-based reactor at 325 ºC, 500 psig, H 2 /feed molar ratio of 96. The results showed that the BHD yield over Pd/Al 2 O 3 catalysts was decreased with the following order; Pd/Al 2 O 3 (SUS/DC) > Pd/Al 2 O 3 (SG/DC) > Pd/Al 2 O 3 (SOL/EPD). The Pd/Al 2 O 3 (SUS/DC) catalyst exhibited the highest BHD yield which could be due to its highest catalyst weight which gave more active site available on that and also its high Pd dispersion. However, Pd/Al 2 O 3 (SOL/EPD) exhibited the lowest BHD yield due to the lowest PD dispersion and the lowest catalyst weight. In terms of the adherent ability, even Pd/Al 2 O 3 (SUS/DC) and Pd/Al 2 O 3 (SG/DC) exhibited high BHD yield but it still had catalyst detachment and corrosion of stainless steel problems. In contrary, Pd/Al 2 O 3 (SOL/EPD) catalyst gave the strongest adherence because of the strong H-bonding with stainless steel and optimized thickness which can be controlled by EPD voltage and time respectively. In addition, the pretreatment method did not generate the oxide layer like thermal treatment. ACKNOWLEDGEMENTS The authors would like to gratefully acknowledge on The Petroleum and Petrochemical College, Chulalongkorn University, Center of Excellence on Petrochemical and Materials Technology, Metallurgy and Materials Science Research Institute, and PTT Research and Technology Institute for the funding and invaluable discussion. (a) 1h 8h (b) Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6

7 REFERENCES Gil, S., Garcia-Vargas, J.M., Liotta, L.F., Pantaleo, G., Ousmane, M., Retailleau, L. and Giroir-Fendler, A. (2015). Catalysts, 2015 (5), Lin, Z. and Adeniyi, L. (2015). Energy & Fuels, 29 (1), Kiwi-Minsker, L. and Renken, A. (2005). Catalysis Today, 110 (1 2), Vorob eva, M.P., Greish, A.A., Ivanov, A.V. and Kustov, L.M. (1999). Applied Catalysis A: General, 199 (2000), Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7