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Synthesis of composite material MCM-41/Beta and its catalytic performance in waste used palm oil cracking

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Synthesis of composite material MCM-41/Beta and its catalytic performance in waste used palm oil cracking
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  Applied Catalysis A: General 274 (2004) 15–23 Synthesis of composite material MCM-41/Beta and its catalyticperformance in waste used palm oil cracking Yean-Sang Ooi, Ridzuan Zakaria, Abdul Rahman Mohamed, Subhash Bhatia ∗ School of Chemical Engineering, University Science of Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, SPS Penang, Malaysia Received in revised form 14 April 2004; accepted 7 May 2004Available online 20 June 2004 Abstract CompositematerialscomposedofMCM-41/Betaweresynthesizedusingtwomethods:(1)seedingmethod,and(2)two-stepcrystallizationprocess. Powder XRD showed the existence of well-structured microphase zeolite Beta and mesophase MCM-41 in the composite materials.The performance of the composite material as a catalyst was investigated in the cracking of waste used palm oil for the production of liquidhydrocarbons and its activity was compared with the catalytic activity of a physical mixture of zeolite Beta and MCM-41. The compositematerial synthesized via seeding method gave a better performance in terms of conversion and yield of liquid fuel gasoline fraction comparedto composite material obtained from two-step crystallization process and physical mixing. The composite material was found to be moreselective for liquid fuel gasoline fraction enriched with more olefins compared to zeolite Beta or MCM-41 catalyst alone.© 2004 Elsevier B.V. All rights reserved. Keywords:  Composite MCM-41/Beta; Catalytic cracking; Waste used palm oil; Biofuel 1. Introduction Since the discovery of the well-structured mesoporousmaterial MCM-41 during the 1990s, the catalytic prop-erties of this material have been intensively studied [1].Due to the higher accessibility of reactants in mesoporousMCM-41 as compared to zeolite (microporous material),it is suitable for catalytic reactions dealing with large sizemolecules such as heavy gas oil cracking. Nevertheless, thelack of acidity and poor hydrothermal stability of MCM-41have restricted its applications in commercially relevantoperating conditions. Extensive efforts have been directedtowards improving the thermal and hydrothermal stabilityof MCM-41 besides improving its acidity. There are severalimportant paths related to this improvement, such as pHadjustment [2–4] and incorporation of crystalline material(zeolite) into the amorphous mesoporous material [5–9].Zeolite Beta with an interconnected 12-ring pore systemand pore size of 0 . 56nm × 0 . 74nm is one of the potentialcatalysts in fluid catalytic cracking [8]. Due to the highcrystalline structure, high acidity and shape-selective prop- ∗ Corresponding author. Tel.:  + 60-4-593-7788x6409;fax:  + 60-4-594-1013.  E-mail address:  chbhatia@eng.usm.my (S. Bhatia). erties, it has been studied in the cracking of palm oil [10].Since the composite materials with two-fold pore structurecombined the advantages of both the microporous and themesoporous material, they have drawn a lot of attentionfrom the researchers who study their performance.Liquid biofuel offers an alternative fuel option in termsof environmental benefits (less green house effect and localair pollution) since it is free of nitrogen and sulfur com-pounds. The production of sulfur-free fuels and chemicalsfrom cracking of palm oil over various types of crackingcatalysts has been investigated [10,11]. However, palm oil has been utilized not only as cooking oil but also as theraw material for oleochemical industries in Malaysia. Thehigh cost of the raw material was one of the main drawback for the growth of biorefinery for production of fuels andchemicals from renewable resources. Hence, the abundantwaste used palm oil from restaurants can be utilized insteadof crude palm oil. Several papers reported that compositecatalyst showed a better performance compared to physi-cal mixture of individual materials as catalyst in a numberof chemical reactions [6–8]. Kloestra et al. [7] reported that composite MCM-41/FAU showed a higher conversionin the cracking of vacuum gas oil. The same observationwas also reported by Guo et al. [8] in  n -heptane crack-ing using composite MCM-41/Beta. In the present study, 0926-860X/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.apcata.2004.05.011  16  Y.-S. Ooi et al./Applied Catalysis A: General 274 (2004) 15–23 two preparation methods: (a) seeding method; (b) two-stepcrystallization, are employed for the synthesis of com-posite MCM-41/Beta. The two methods of synthesis arecompared. The pH adjustment is also included in yieldinglong-ranged order micro-mesoporous composite materials,thereby improving catalytic activity. The performance of the composite material is tested as cracking catalyst inbiofuel production from waste used palm oil. The aim of the research is to maximize the yield of gasoline fractionin the organic liquid product (OLP) obtained from the cat-alytic cracking of waste used palm oil over MCM-41/Betacomposite. 2. Experimental 2.1. Synthesis of MCM-41 The MCM-41 was synthesized following the methodreported by Lindlar et al. [2] with the Si/Al ratio of thesynthesis gel of 39. About 12.0g of sodium silicate solu-tion (27% SiO 2 , 10% NaOH, Riedel-deHaen) and 0.36gof Cab-osil M5 (Fluka) were mixed with 14ml of deion-ized water in beaker I. Then, 15.4g of hexadecyltrimethy-lammonium chloride solution (25%, Fluka) and 0.08g of ammonia solution (25%, Merck) were mixed in beaker II.The contents of beaker I were slowly added to beaker IIwith vigorous stirring at room temperature. Subsequently,0.14g of sodium aluminate (56% Al 2 O 3 , 45% Na 2 O,Riedel-deHaen) in 3ml of deionized water were added withvigorous stirring. The mixture was stirred for 1h at roomtemperature before being heated at 100 ◦ C for 24h withoutstirring. The mixture was then cooled to room temperatureand the pH was adjusted to about 11 by dropwise additionof acetic acid under vigorous stirring. The reaction mixturewas heated again to 100 ◦ C for 24h; this procedure forpH adjustment and heating was repeated twice. The prod-uct was filtered, washed with deionized water and dried atroom temperature overnight before being calcined at 550 ◦ Cfor 6h. 2.2. Synthesis of composite catalyst via seeding method  The composite material was prepared by coating zeoliteBeta with mesoporous material (MCM-41) using hexade-cyltrimethylammonium chloride (C 16 TMACl) as templatefollowing the procedure reported by Kloestra et al. [7] withsome modifications. Zeolite Beta with Si/Al ratio of 12.5was obtained from Sud-Chemie AG, Munich, Germany.The procedures of pH adjustment and subsequent heatingfor three times were followed the same as those reported inthe synthesis of MCM-41. The composite of pure siliceousMCM-41 with zeolite Beta is coded as CMB  X   where Crefers to composite, M to mesoporous,  B  to Beta and  X   refersto the weight percent (20, 30 and 40) of mesophase in thecomposite synthesis gel. The Si/Al ratio in the mesophasewas varied from 10 to 40, for 40wt.% mesophase in thecoating of the composite material. This was coded as CM-BAY, where A refers to aluminum and Y to the Si/Alratio. 2.3. In situ synthesis of composite catalyst  The preparation of composite MCM-41/Beta was con-ducted in situ following the procedure reported in the litera-ture [8]. About 0.50g of sodium aluminate was dissolved in16.5g of tetraethylammonium hydroxide (20%, Merck) un-der mild stirring before 4.81g of Cab-osil M5 silica (Fluka)was added. The mixture was stirred for another 30min andthen heated to 140 ◦ C in autoclave Parr reactor for 48h(coded as CMBI48 where I refers to in situ), 96h (codedas CMBI96) and 144h (coded as CMBI144), respectively.After cooling to room temperature, the product was addeddropwise into a cetyltrimethylammonium bromide solution(4.66g of CTAB and 25.7g of water) with stirring. The pHof the mixture was adjusted to 9.6 with 50wt.% acetic acidunder vigorous stirring. The mixture was again heated to100 ◦ C for 48h in the reactor before filtered and washedthoroughly with deionized water. The resultant solid wasdried overnight at room temperature and calcined at 550 ◦ Cfor 7h. 2.4. Characterization The catalyst was characterized by XRD to determine thestructure and composition of crystalline material using aPhilips diffractometer with Cu K   radiation at 2 θ   valuesof 1.5–90 ◦ with a step of 0.04 ◦  /10s. The BET surfacearea and pore volume were measured by nitrogen adsorp-tion using an Autosorb I (Quantachrome Automated GasSorption System). The samples were degassed for 5h un-der vacuum at 300 ◦ C prior to the analysis. The acidity of the catalyst was measured using temperature programmeddesorption (TPD) of ammonia. The TPD was carried out us-ing a Chembet 3000 instrument (Quantachrome) equippedwith TPRWin, Version 1 software to calculate the acidity.About 0.05g of sample was activated at 500 ◦ C for 1hwith helium flowing at 60ml/min, followed by adsorp-tion of 1% ammonia in helium at room temperature for1h. The sample was then heated to 100 ◦ C for 1h to re-move physisorbed ammonia before performing the TPDrun with a heating rate of 10K/min. The nature of the acidsites present in the MCM-41 was determined using FTIRtechnique. The sample was exposed to excess pyridinefor 1h after degasing at 200 ◦ C, followed by desorptionof physically adsorbed pyridine at 150 ◦ C under vacuum.The IR spectra were scanned using a Perkin-Elmer FTIR(Model 2000). Transmission electron microscopy (TEM)was performed with a Philips CM12 transmission elec-tron microscope operated at 80kV. SEM photographs weretaken using a Leica Cambridge S-360 scanning electronmicroscope.  Y.-S. Ooi et al./Applied Catalysis A: General 274 (2004) 15–23  17 2.5. Activity measurements The catalytic cracking activity of composite materialswas measured at reaction temperature of 450 ◦ C and a feedrate of waste used palm oil (weight hourly space velocity,WHSV) of 2.5h − 1 at atmospheric pressure in a fixed-bedmicro-reactor rig reported elsewhere [10]. Then, 1.0g of composite catalyst was loaded over 0.2g of quartz woolsupported by a stainless steel mesh in the micro-reactor(185mm × 10mm ID) placed in the vertical tube furnace(Model No. MTF 10/25/130, Carbolite). The reactor tem-perature was monitored by a thermocouple positioned at thecenter of the catalyst bed. Nitrogen gas was passed throughthe reactor for 1h before the waste used palm oil was fed us-ing a syringe pump (Model No. E-74900-05, Cole-Parmer).The liquid product was collected in a glass liquid sampler,while the gaseous products were collected in a gas-samplingbulb once the steady state was reached in the reactor. Theresidue oil was separated from the liquid product by dis-tillation in a micro-distillation unit (Buchi B850, GKR) at200 ◦ C for 30min under vacuum (5Pa) with the pitch as theresidual oil. The gaseous products were analyzed over a gaschromatograph (Hewlett Packard, Model 5890 series II) us-ing a HP Plot Q capillary column (divinyl benzene/styrene Table 1Physicochemical properties of the catalystsCatalyst Surface area(m 2  /g)Pore volume at  P  /  P 0 = 0.5 (cm 3  /g)Mesophase APS,BJH method (nm)Lattice parameter, a 0  (nm)Acidity, mmolH +  /g catH-Beta 454 0.2640 – – 0.31CMB20 602 0.4201 2.90 4.63 0.23CMB30 659 0.4814 2.89 4.69 0.16CMB40 737 0.5626 2.88 4.73 0.14CMBA40 732 0.5315 2.88 4.56 0.16CMBA20 751 0.5207 2.90 4.85 0.18CMBA10 696 0.4475 2.91 3.98 0.22MCM-41 964 0.8064 2.90 4.61 0.09CMBI48 547 0.3274 2.90 4.71 0.42CMBI96 491 0.2799 – – 0.41CMBI144 529 0.3033 – – 0.38Fig. 1. (a) Nitrogen adsorption–desorption isotherms, and (b) pore size distribution for the pure H-beta, MCM-41 and their composite with differentcompositions. porouspolymer,30mlong × 0 . 53mmID × 40  mfilmthick-ness) equipped with a thermal conductivity detector (TCD)and nitrogen as a carrier gas. The OLP was analyzed usinga capillary glass column (Petrocol DH 50.2, film thickness0.5  m, 50m long × 0 . 2mm ID) at a split ratio of 1:100,using a FID detector. The composition of OLP was definedaccording to the boiling range of petroleum products in threecategories, i.e. gasoline fraction (333–393K), kerosene frac-tion (393–453K) and diesel fraction (453–473K). The spentcatalyst was washed with acetone prior to the coke analy-sis. The amount of coke was determined by the differencein weight before and after calcination in muffle furnace. 3. Results and discussion 3.1. Catalysts characterization The BET surface area and the average pore size of thecomposite materials are presented in Table 1. The table shows that when the siliceous mesophase coating was in-creased from 20 to 40wt.%, the BET surface area of thecomposite material was increased from 602 to 737m 2  /g.Fig. 1 shows the adsorption–desorption isotherms of the  18  Y.-S. Ooi et al./Applied Catalysis A: General 274 (2004) 15–23 Fig. 2. Isotherms of composite MCM-41 with zeolite Beta with different Si/Al ratios in the reaction gel of MCM-41. composite catalyst and its pore size distribution. A sharp in-creaseintheisothermat P/P  0  = 0 . 3–0 . 4wasobserved.Thiscorresponds to the mesoporous molecular sieve with a poresize of about 3.0nm as can be seen from the pore size distri-bution curves. The rapid uptakes of nitrogen become morepronounced once the amount of coating layer was increased.This shows the presence of a new crystalline mesophase andindicates the gradual increase of siliceous mesoporous ma-terial in the composite. When the aluminum was included inthe synthesis gel, the isotherm showed a drop in the nitrogenuptake as compared to pure siliceous mesophase, especiallyfor CMBA10 (Fig. 2). The isotherm showed hysteresis of  type B, confirming the non-uniform pore system whereslit-shaped pores were present inside the mesopores [12].ThecompositeMCM-41/Betasynthesizedviatwo-stepcrys-tallization showed less pronounced mesopore size of 2.9nm(Fig. 3). On further increase in the aging time from 48 to Fig. 3. Nitrogen adsorption–desorption isotherms and pore size distribution for the composite MCM-41/Beta in situ synthesized. 144h, the mesophase diminished, but a broad distribution of secondary mesophase centered around 15.0nm was formed.This attributed to the filling of interparticle spaces [8].Fig. 4 displays the XRD pattern of composite mate-rial prepared via seeding method. The figure shows threepeaks at 2 θ   lower than 5 ◦ which are characteristic of long-range ordered hexagonal MCM-41 mesophases. Thepeak intensity increased as the coating percentage was in-creased. This was consistent with the isotherm of nitrogenadsorption–desorption result showing the increase in nitro-gen uptake. This confirmed that pH adjustment during theaging process shifted the reaction equilibrium towards theformation of MCM-41. This resulted in improved struc-ture as compared to the composite synthesized by Kloestraet al. [7] which did not show any peaks corresponding toMCM-41 in the XRD pattern. Besides, the XRD patternsshow diffraction peaks at higher 2 θ  , which belong to zeolite  Y.-S. Ooi et al./Applied Catalysis A: General 274 (2004) 15–23  19Fig. 4. XRD patterns of samples synthesized via seeding method for (a) pure silica coating, and (b) different Si/Al ratios in coating layer. Beta. Hence, the preadded zeolite Beta retained the structureafter hydrothermal treatment. The composite containingaluminum and the increase of aluminum content did notsignificantly change the BET surface area, except for Si/Alratio of 10. However, the lattice parameter,  a 0  decreasedfrom 4.56 to 3.98nm. This was in line with the fact thatcrystallinity of the mesoporous material decreased with anincrease of aluminum in the aluminosilicate materials [2].As can be observed in Fig. 4(b), the intensity of the first peak decreased when more aluminum was added. The 2 θ  value of this peak also shifted to a higher value and sub-sequently decreased the  d  100  spacing. As a consequence,the pore size of the mesophase was reduced. The higherangle peaks vanished indicating a disordered structure of mesophase for CMBA10. Fig. 5 shows the XRD profilesof composite MCM-41/Beta obtained from two-step crys-tallization process; only the CMBI48 sample shows thepresence of mesoporous MCM-41. This was due to a longeraging time that allowed the synthesis gel to convert to crys- Fig. 5. XRD patterns of samples synthesized in situ at different agingtimes. talline zeolite Beta. Thus, the addition of surfactant CTABwas unable to promote the formation of mesophase.The TEM image shows the morphology of the compos-ite of CMBA40 (Fig. 6). The image clearly shows the exis- tence of long-range uni-dimensional mesophase. The SEMimages in Fig. 7 show the change of the appearance of the zeolite Beta before and after the coating with mesophaseAl-MCM-41. Zeolite Beta exhibited agglomerate ball-likecrystals. With the coating of mesophase, the composite ma-terial displayed loose aggregate particles with flat surfaces.This shows that zeolite Beta crystals were covered with asmooth layer of mesophase.The acidity values of the samples are presented inTable 1. The acidity of the composite material decreasedupon addition of coating layer. This was due to the presenceof purely siliceous MCM-41 which did not contribute anyacidity to the composite material. Fig. 8 shows the infraredspectra of pyridine absorbed on the composites materials. Fig. 6. TEM image of CMBA40 which shows the presence of hexagonaluni-dimensional pore structure of MCM-41.
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