د اميل ومحمد عطية ومها Al-Khwarizmi Engineering Journal Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) Enhancement of Iraqi Light Naphtha Octane Number Using Pt Supported HMOR Zeolite Catalyst Mohammed A. Atiya* Ameel Mohammed Rahman** Maha H. Al-Hassani*** * Research and Development Directorate / Ministry of Higher Education and Scientific Research **Department of Biochemical Engineering / Al-Khawarizmi College of Engineering / University of Baghdad ***Department of Chemical Engineering / College of Engineering / University of Baghdad *Email:mohatiya1955@gmail.com **Email:explorerxp50@yahoo.com ***Email:alhassani_maha@yahoo.com (Received 5 September 2013; accepted 3 December 2013) Abstract The hydroconversion of Iraqi light straight run naphtha was studied on zeolite catalyst. 0.3wt.%Pt/HMOR catalyst was prepared locally and used in the present work. The hydroconversion performed on a continuous fixed-bed laboratory reaction unit. Experiments were performed in the temperature range of 200 to 350°C, pressure range of 3 to 15 bars, LHSV range of 0.5-2.5h-1, and the hydrogen to naphtha ratio of 300. The results show that the hydroconversion of Iraqi light straight naphtha increases with increase in reaction temperature and decreases with increase in LHSV. High octane number isomers were formed at low temperature of 240°C. The selectivity of hydroisomerization improved by increasing reaction pressure up to 15 bars. Catalyst activity almost stable and independent of time on stream at 15 bar up to 20 h. Keywords: Hydroisomerization, Light naphtha, Zeolite, Octane number, Mordenite. 1. Introduction With the continuously increasing environmental concerns and stringent regulations on the utilization of gasoline as an automotive fuel, there is a great need to search for alternative gasoline octane number enhancers. Currently, various additives are available for gasoline octane number enhancement e.g. oxygenate and aromatic compounds (Alexander et al., 2013; Sandeep et al., 2013; Liu et al., 2011; Nikolaou et al., 2004; Chao et al., 1996). These compounds are considered as environment harmful compounds. Finding a harmless substituent to the high-octane oxygenates and aromatics is not a straightforward task, since main octane enhancers have either been completely phased out due to their toxicity in many countries worldwide, such as in the case of lead-containing additives, or seen their use decline due to their environmental problems, like oxygenates such as MTBE (Methyl t-butyl ether). In addition, using octane-rich reformates fails to do the trick since aromatics are a major constituent of them (Busto et al., 2012; Chiang et al., 2011; Chao et al., 2000). However, the utilization of an upgraded low-value refinery stream to the gasoline pool might present a solution to the problem, as it can considerably lower the cost of gasoline production, while losing only some of its original quality, but still remain environmentally friendly. It is a promising objective to produce high octane number gasoline from petroleum sources. The requirements to reduce these additives in Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 2 gasoline present a need to find an alternative way to maintain its research octane number (RON). An alternative way is to increase the RON for the paraffinic content of gasoline, which can be accomplished through hydroisomerization. Light paraffin hydroisomerization has been used provide a cost-effective solution to manage benzene in motor fuels (Stanislav et al., 2012, Raed et al., 2010; Liu et al., 2009; Theo et al., 2008). The process of light naphtha hydroisomerization involves the transformation of normal paraffins (i.e. normal C5-C7 fraction which is the main constituent) into their isomers, which have higher octane numbers than the normal paraffins over acidic catalysts (Sege et al., 2003; Gauw et al., 2002; Lee et al., 1997; Guisnet et al., 1991). Mechanically, hydroisomerization occurs in three elementary steps. First, the alkane is dehydrogenated. Then generated alkene adsorbs on a Brønsted acid site, forming an alkoxy group (a carbenium ion in the transition state), which isomerizes and eventually desorbs. Finally, the iso-olefin is hydrogenated to iso-alkane. Therefore, catalysts are bifunctional, with a metal (Pt, Pd) catalyzing the hydrogenation/ dehydrogenation step and an acidic function for the formation and isomerization of the alkoxy group/ carbenium ion. The metal component also helps reduce catalyst deactivation by hydrogenation coke precursors (Gauw et al., 2002; Hollo et al., 2002; Aboul-Gheit et al., 1998; Allian et al., 1997). As the reaction proceeds via carbenium ions, other Brønsted acid catalyzed reactions, as oligomerization and cracking compete with isomerization (Gauw et al., 2002; Hollo et al., 2002). In addition, side reactions on the metal, as hydrogenolysis of the alkane to smaller alkanes, may reduce the selectivity of the overall hydroisomerization reaction (Gauw et al., 2002; Hollo et al., 2002). In the present study, Pt supported HMOR zeolite catalyst is prepared locally and used to hydroisomerize Iraqi light straight run naphtha (LSRN). The main objective in this work is to develop a useful catalyst and optimize the limited ranges of operating conditions (temperature, LHSV, and operating pressure) on the naphtha transformation and octane number in a fixed bed continuous laboratory reaction unit. Catalyst stability is also highlighted. 2. Experimental Work 2.1. Materials 2.1.1. Feedstock Light straight run naphtha (LSRN) supplied from Al-Dura Refinery was used as a feedstock in hydroisomerization experiments. The properties of LSRN are listed in Table. 1 Table 1, Properties of straight run light naphtha. API @ 60°/60°F 78.6 Octane Number 61.4 Sulfur Content < 2ppm Kinematic Viscosity at 25℃ 7.2×10 -7 m2/s Composition Wt.% Propane 0.01 i-butane 3.19 n-butane 4.27 i-pentane 33.46 n-pentane 21.57 cyclo-pentane 0.94 i-hexane 6 n-hexane 15.27 cyclo-hexane 4.1 i-heptane 2.5 n-heptane 4.58 i- and n-octane 1.37 Benzene 0.76 Toluene 0.95 Xylene 0.16 Naphthalene C8 0.2 Naphthene C8 0.39 Naphthene C9 0.28 Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 3 2.1.2. Hydrogen and Nitrogen Gases High purity (99.999 vol. %) of hydrogen and nitrogen gases supplied from the local market were used in the present work. 2.1.3. Ammonium Mordenite Zeolite Ammonium mordenite zeolite (CBV-21A) supplied as a powder from Zeolyst International Company. It was used in the preparation of the proposed catalyst. The properties of this zeolite are listed in Table 2. Table 2, Properties of ammonium mordenite zeolite powder (CBV-21A). SiO2/Al2O3 Mole Ratio Nominal Cation Form Na2O Weight % Surface Area, m2/g 20 Ammonium 0.08 500 2.1.4. Hexachloroplatinic Acid Hexachloroplatinic acid (H2PtClO6.6H2O) of an analytical grad (40 wt.% Pt) was supplied by Fluka Chemi AG. 2.2. Catalyst Preparation 100 g of Ammonium mordenite (CBV-21A) powder was shaped as a pelletes with 3mm×5mm using a laboratory scale pelleting machine (model TDP-1.5 from MINHUA PHARMACEUTICAL MACHINERY CO., LIMITED). The final form was dried at 110°C and stored in an evacuated place. 2.3. 0.3 wt.%Pt/ HMOR Zeolite Preparation 0.3wt%Pt on HMOR zeolite was prepared by impregnation method. HMOR pellets were dried over night at 110°C and impregnated with 0.3 g of H2PtClO6.6H2O in 10 ml deionized water. The final impregnated pellets were dried at 110°C over night and calcinated at 300°C for 3 hrs in a furnace with dry air. The calcinated catalyst pellets were then reduced with hydrogen at 350°C for 3 hrs (Al-Hassani, 2007). The properties of the prepared catalyst are listed in Table 3. Table 3, Properties of the 0.3wt%Pt/HMOR zeolite. Surface Area m2/g 662 Bulk density g/cm3 0.592 Pore volume, cm3/g 0.143 2.4. Hydroisomerization Reaction Unit Hydroisomerization experiments were conducted in a continuous fixed bed reactor laboratory scale unit. Figure 1 shows the schematic diagram of this unit. It consist of feed tank (T-301), gas flow meter and controller (FCV), feed pump (P-301), evaporator (M-301), fixed bed reactor (R-301), high pressure separator (E-301), low pressure separator (S-301), and an appropriate heating system (H-301). The reactor was heated and controlled automatically with computer control software and by four steel- jacket heaters using chromal alumel thermocouple (type k). 2.5. Hydroisomerization Experiments 30 cm3 of fresh catalyst was charged to the reactor and between two layers of inert material (glass balls). In the beginning of each experiment, the reactor was flashed with nitrogen 2 l/h for 1 h to purge the air from the system, then the reactor is heated to the desired temperature. When reactor temperature is reached, the nitrogen valve is closed. A pre-specified flow rate of light naphtha was set on, vaporized in the evaporator and the vapor was mixed with the hydrogen in the mixing unit at a specified flow rates. The mixture entered the reactor from the top, distributed uniformly and reacted on the catalyst. The gaseous products passed through the high pressure separator and the final condensates were collected in the low pressure separator only after steady state operation was established and the initial products were discarded. The hydroisomerization reaction conditions employed are temperature range 200- 350°C, liquid hourly space velocity (LHVS) range 0.5-2.5h-1, hydrogen to light naphtha volumetric ratio 300 and the pressure was ranging from 3- 15bar. Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 4 R-301 Tubular Reactor P-301 Feed Pump FCV-301 FCV-302 FCV-303 FCV-304 Mass flow controller T-301 Feed Tank E-301 Condenser S-301 Separator M-301 Mixer H-301 Heater PRV-301 Pressure Relief Valve Piping and Instrument Flow Diagram Laboratory Reaction Unit University of Baghdad Al-Khawarizmi College of Engineering Department of Biochemical Engineering Fig. 1. Schematic Diagram of Laboratory Continuous Fixed Bed Reaction Unit. Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 5 2.6. Analysis 2.6.1. Atomic Absorption Analysis The analysis of platinum, in the prepared catalyst, was achieved using atomic absorption spectrophotometer (model PYE-UNICAM SP9) in IBN Sina State Company. 2.6.2. Gas Chromatographic Analysis The collected products (liquid and gas) were analysis into their components by gas chromatographic (GC) analysis using SHIMADZU GC model 2014A with FID detector. 2.6.3. Octane Number Test This test was achieved in DURA refinery using RON method (ASTM -D 2699). 3. Results and Discussion The results of hydroconversion runs of Iraqi LSRN are discussed in this section in order to evaluate the catalyst performance. The purpose of the present work is to choose the optimal experimental conditions that most satisfy high catalyst stability and product octane number. The hydroconversion involve three main reactions hydroisomerization, hydrocracking, and hydrocycalization and aromatization. In this section, discussions were built upon the results of these reactions. 3.1. Effect of Temperature The effect of temperature on LSRN transformation is shown in Figs. 2-4. It is clearly temperature dependent; in fact, in the temperature range of 473 to 513K the hydroconversion shifted towards the hydroisomerization conversion and as shown in Fig. 3, while above 513 the isomers formation decreases and the reaction is shifted towards the hydrocracking, hydrocycalization aromatization reactions and as shown in Figs. 2 to 4. This means that the formation of isomers is favored at lower temperature and this phenomenon is further explained by Fig. 5. The octane number of n-hexane is around 25, n- pentane is around 62, the MP isomer is around 75 and DMB is around 95, furthermore, the lower reaction temperature, the greater the percentage of branched alkane at thermodynamic equilibrium, hence the higher the octane number (Sege, 2003; Gauw et al., 2002; Grillo et al., 1997). 40 50 60 70 80 90 100 110 440 490 540 590 640 Temperature, K w t. % Fig. 2. Isomers Formation Percent vs. Temperature at LHSV of 0.5h-1 and Pressure of 15bar. 0 1 2 3 4 5 6 7 8 9 440 490 540 590 640 Temperature, K w t. % Fig. 3. Hydrocracking Products Formation Percent vs. Temperature at LHSV of 0.5h-1 and Pressure of 15bar. 0 0.5 1 1.5 2 2.5 3 3.5 440 490 540 590 640 Temperature, K w t. % Fig. 4. Percent of Hydrocyclization and Aromatization Products vs. Temperature at LHSV of 0.5h-1 and Pressure of 15bar. Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 6 70 75 80 85 90 95 450 470 490 510 530 550 570 590 610 630 650 Temperature, K R O N Fig. 5. Effect of Temperature on the RON at LHSV of 0.5 h-1 and Pressure of 15bar. 3.2. Effect of Contact Time Figures 6 to 8 show the change in LSRN transformation as a function of contact time. The contact time is expressed as the reverse of LHSV, the liquid hourly space velocity taken as the ratio between the volumetric flow rate of LSRN and catalyst volume. It can be observed from these figures that as the contact time increases the hydroconversion increases so the rates of hydroisomerization, cracking and hydrocycalization and aromatization increases. Also isomers are formed at low contact times (i.e. low conversion), a small amount of cracking products appearing at higher contact times. A high increase in RON number was observed with the increase in contact time and as shown in Fig. 9. This increases many be attributed to the formation of high octane number isomers and as explained above. The same observations were reported in other works (Busto et al., 2012; Jiménez et al., 2003; Partylak et al., 1998; Allian et al., 1997). 0 10 20 30 40 50 60 70 80 90 0 0.5 1 1.5 2 2.5 3 1/LHSV, h w t. % Fig. 6. Isomers Formation Percent vs. LHSV at Temperature of 553K and Pressure of 15bar. 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 3 1/LHSV, h w t. % Fig. 7. Hydrocracking Products Formation Percent vs. LHSV at Temperature of 553K and Pressure of 15bar. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 0.5 1 1.5 2 2.5 3 1/LHSV, h w t. % Fig. 8. Percent of Hydrocyclization and Aromatization Products vs. LHSV at Temperature of 553K and Pressure of 15bar. Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 7 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 1/LHSV, h R O N Fig. 9. Effect of Contact Time on RON at Temperature of 553K and Pressure of 15bar. 3.3. Effect of Pressure The effect of pressure on the Iraqi LSRN reaction selectivities and RON are shown in Figs. 10, 11, and 12. As the operating pressure increases the selectivity of hydroisomerization increases and the selectivity of hydrocracking decreases rapidly while the selectivity of hydrocyclization and aromatization slightly increases. The increase in operating pressure is probably leads to a decrease in alkenes formation, in turn, diminish the probability to proceeds the dimerization cracking and provide higher isomerization selectivity as shown in Fig. 10. As a results RON increases rapidly with the increases in the operating pressure and up to 15bar, after this value RON unaffected by the change in operating pressure. The reaction of alkane transformation proceeds with the skeletal hydroisomerization via bimolecular mechanism. Abuda Wood et al.; 2010, showed that the hydrogenation activity increased at a higher hydrogen pressure that results in the hydrogenation of more intermediate olefins, which can be due to a shorter intermediate olefin residence time inside the catalyst, and thus minimizing the cracking activity. These observations are agree well with the results reported by Gauw et al., (2002), Liu et al., (1997), Chao et al., (1996) and Guisnet et al., (1991); Chao et al., 2000. 86 88 90 92 94 96 98 100 0 5 10 15 20 25 Pressure, (bar) S e le c ti v it y , (w t. % ) Fig. 10. Hydroisomerization Selectivity vs. Operating Pressure at LHSV of 1h-1 and Temperature of 553K. 0 2 4 6 8 10 12 14 0 5 10 15 20 Pressure, (bar) S e le c ti v it y , (w t. % ) Hydrocracking Hydrocycalization and aromatization Fig. 11. Hydrocracking, Hydrocycalization and Aromatization Selectivities vs. Operating Pressure at LHSV of 1h-1 and Temperature of 553K. 40 50 60 70 80 90 100 0 5 10 15 20 25 Pressure, (bar) R O N Fig. 12. Effect of Operating Pressure on RON at LHSV of 1h-1 and Temperature of 553K. Mohammed Abd Atiya Al-Khwarizmi Engineering Journal, Vol. 9, No. 4, P.P. 1- 11 (2013) 8 3.4. Catalyst Stability and Time on Stream The stability during the reaction of zeolite catalysts is measured by Time on stream. It can be observed from Fig. 13 that the present 0.3wt.%Pt/HMOR catalyst is very stable with almost no (i.e. very slight change) change in activity when tested for 20 hours. Unfortunately, this stability is in the expense of hydroisomerization activity towards high octane numbers isomers. This is partly due to a very slow coking that may have poisoned the acid sites on the catalyst and changed the effective amount of acid sites density on the catalyst needed. These results are agree well with other observation reported by Stanislav et al., 2012; Theo et al., 2008; Nikolaou et al., 2004; Gauw et al., 2002; Burckle et al., 2000; Chao et al. 2000. 85 86 87 88 89 90 91 92 93 0 5 10 15 20 25 Time on Stream, (h) R O N Fig. 13. Effect of Time on Stream on RON at LHSV of 1h-1 and Temperature of 553K. 4. Conclusions The hydro transformation of Iraqi LSRN was evaluated in a laboratory fixed bed reaction unit using 0.3wt.%Pt/HMOR zeolite catalyst. The following conclusions were drawn from the experimental results: 1. The prepared catalyst exhibits a high hydroisomerization activity within the studied range of operating conditions. 2. The hydroisomerization reaction is temperature dependent, and the lower temperature the greater hydrosiomerization selectivity and in turn high RON value. The optimum reaction temperature ranging between 240-280 for producing high octane number is omers. 3. The selectivity of LSRN hydroisomerization on 0.3wt.%Pt/HMOR catalyst could be significantly improved by increasing reaction pressure and reducing the reaction temperature. The increase of reaction pressure also causes decrease in the cracking selectivity on the catalyst. 4. The activity of 0.3wt.%Pt/HMOR catalyst almost independent of time on stream at 15 bar up to 20h. Acknowledgement This study was supported by a grand provided by the Ministry of Higher Education and Scientific Research/ Research and Development Department. Authors gratefully acknowledge this contribution and supporting. Nomenclature HMOR H-Mordenite LHSV Liquid hourly space velocity LSRN Light straight run naphtha RON Research octane number MP Methyl Pentane isomer DMB Dimethyl butane isomer 5. References [1] Aboul-Gheit A. K., Ghoneim S. 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