In Situ Synthesis of NaY Zeolite with Coal-Based Kaolin

Journal of Natural Gas Chemistry 12(2003)63-7In Situ Synthesis of NaY Zeolite with Coal-Based KaolinXinmei liu. Zifeng yan*. HIWEYantuo luooy of CatalyCNPC, Uimiversety of Petroleum, Dongying[Manuscript received December 12, 2002: revised February 21, 20031Abstract: Nay zeolites were in-situ synthesized from coal-based kaolin via the hydrot hermal methodThe effects of various factors on the structure of the samples were extensively investigated. The sampleswere characterizcd by N2 adsorpt ion XRI), IR and DTG-DTA methods, and the results show that thecryst ullization temperature and amount of added water play an important role in the formation of the zoo-lite structure. The 4A and P zeolites are the competitive phase present in the resulting product. However,Nay zeolites with a higher relative crystallinity, excluding impure crystals and the well hydrothermal stbility, can be synthesized from coal-based kaolin. These zeolites possess a larger surface arca and a Harrowpore size distribution, and this means that optirnizat ion of this process might result in a commercial routeto synthesize NaY zeolites fronI coal-based kaolinKey words: coal-based kaolin, NaY zeolite, in-situ hydrotherMal synthesis1. Introductionin an environnent ally friendly manner that has higcommercial valucCoalbased kaolin is simultaneously generatedZeolites are widely nsed in adsorption, separat iith coal, and it has become a pressing waste disposal catalysis, ion exchange and other processes. Someproblem becausc it constitutes up to 10%-20% of the groups[1 6, 11| have already st udied the preparationtotal coal yicld [1]. It is essential to develop an ef- of varions zeolites from kaolin or other Ay ashes andfective method to exploit this substance andd mitigate have Inade great progress in synthesis of 4A, morden-the cnvironmental burden on coal mining enterprises ite, X, Y zeolites. ctc. The NaY zeolite is a parent caand coal sitesalyst in catalytic cracking of hydrocarbons and petro-Of interest is that kaolin possesses the Si-Ochemical processes. InI-situ syut hesis of NaY zeolitesAl-O octahedral and tetrahedral sheets which crcatc from coal-based kaolin inight be the best way to chem-a charge imbalance in the 1: 1 layer. There is very ically utilize kaolin resources in the fiture. Althoughlittle substitution in the structural lattice. and thus coal-based kaolin is actually a type of natural clay. thehas a minimal layer charge and a low exchange ca- Si-O or Al O octahedral and tetrahedral sheets arepacity. Its surface area and absorption capacity is inactive to modification nmder moderate conditionsrelatively low, but many of the properties of kaolin The key to this process is how to activate kaolin andcan be improved by proper treatnent. The mainsubsequently hydrothermal synthesplications of kaolin are for coating paper, functionalIn our experiment. NaY zeolites were in-situ syn-illers, plastics, rubber, glass fiber and other materials thesized in a hydrothermal s stel. The effects ofed in fine chemical cngineering. Unfortunately, all various parameters on the properties of the resultingof these materials are low value-added products. It is products were systematically investigated. The re-necessary to create a suitable inethod to utilize kaolin sults prove that purc Nay zeolites with high relativeCorresponding anthor. E-mail: zfyancat @hdpu ed.中国煤化工CNMHGXinmei Liu et aL. /ournal of Natural Gas Chemistry Vol. 12 No./2003rvstallinity can bc effectively synthesizedThe crystal struct ure of coal-based kaolin is shownin Figure 1. Evidently, its dominant component is2. ExperimentalAl2(Si2O-)(OH)4, doped with a small quantity of Fcand trace aMounts of Ni. \n, Cu and Ti. In addi2.1. Synthesistion, very little quartz phase exists. Of interest is thatthis kaolin possesses the Si-O or Al O octahedral aneI'he kaolin was activated by the addition of tetrAhedral sheets. which creates a charge imbalancesodinm hydroxide at 1, 123 K for 3 h. The active san- in the 1: l layer and might be a potential raw mate-ple and a certain amount of Na2SiO which acts as a rial to synthesize zeolites. Unfortunately, the Si orein foreing silicon soure e were dispersed in deionized and Al-O structures in coal-based kaolin arc inactivewater with gentle stirring for I h. Then the mixture to Modification or activation. ' This mcans that itwas aged at rooin temperature for a desired period dilficult to directly synthesize zeolites, and the kaolinto form gel slurry. The gel slurry was transferred to llst be pre-activated to change this inert structurcthe stainless-steel autoclave with a TeHon seat to hy- 7. The most effective way to activate such naturaldrothernally crystallize. Subsequeritly, the precipi- clay is to thermally transform the inert phase intotate was filtered. repeatedlyI with deionizedthe active phase at clevated temperatures in the pres-watr and dried at 373 K overence of alkali hydroxide, which imight also be useful iusubscquent hydrothermal synthesis because the com-2.2. Characterizationmercial NaY zeolites are synthesized at the basic en-virounent. Herein, the kAolin is treated with sodiumT'he synthesized samples were characterized with hydroxide at 1.123Ka nitrogen adsorption analyzer, X-ray diffraction(XRD), infrared spectroscopy(IR), and thermal aual-ysis(TG-DTA)The nitrogen adsorption of the samples was perforined on a Micromeritics 2010nitrogen temperature(77.3 K), and the samples weredegassed at 67. K for 4 h prior to adsorption analysisThe micropore distribution and mean pore size werecaleulated from the gas adsorption using the HorvathKawazoe equation, with relative pressure (p/po) be-1∞low 0.O1. A T-plot calculation was conducted to quan-titativcly analvze the area and total volume ascribedto micropores.XRD for structural analysis of the samples wascarricd out with a Rigakn I)max-3A X-ray difrac-tometer using Cu Kt radiation with a tube voltageof 10kv, a tube current of 30 mA and scanned from539(20). The reference sample was standard NaY.Infrared spectra were recorded with an IR Spec2:(·ptrun One Inade in the US. the resolut ion was 0.2 Figure 1. XRD pattern of coal based kaolinIn,and the sample was pressed with a ccrtainamount of KBr into disks 10 inm in diameter andFurther investigat ion shows that crystal transfor-0. 1 nim thickmation of the coal-based kaolin actually occurs uponThermal analysis was carried out using a CDR- thermal activation in the presence of the sodium hythermometer. Measurements were performed in a droxide. Under the basic cnvironment, the inert skelenit rogen fow with a heating rate of 5 K/ mintal structure of coal-bascd kaolin was converted intoactivated silicate and aluminate, which might be sol-3. Results and discussionuble in acidic or basic aqueous solutions. In otherwords. this coal-based kaolin might be the optimum3. 1. The structure of coal-based kaolinfoTH中国煤化工 Y zeolitesCNMHGJournal of Natnral Gas Chemistry Vol. I2 No. I 20033.2. In-situ synthesis of NaY zeolites from 3.3. Effect of crystallization temperature orcoal-based kaolinelite formationWhen coal-based kaolin is thermally activated byCrvstallization teinperature is an important parameter in the hydrothernal synthesis of certainthe addition of sodiuIn hydroxide to form an activeAl-O structure, Nay zeolites can be in-situ syntholites. It might influence the growth velocit interface rcactions of different faces or directions and dif-sized by the hydrothermal method. The problen isthat the Si/Al ratio in coal-based kaolin is nearly nnitfusion rates of active crystal particles. Specific surand it is too low to directly synthesize Y zeolite. Soineface area was tentatively introduced to indicate thesilica source must be made up to be suitable for di. propcrtics of synthesized Y zeolites and optimize thesuitable crvstallization conditions bccause the NaYrect crvstallization. Sodium silicate was introdueas a reinforcing silicium source prior to hydrothermal zeolite with higher crystallinity and uniform struc-synthesis. As shown in Figure 2. the XRD pattern ofure usually has a higher surface area. especially innerhe synthesized zeolite is a typical crystal structure of surface area or micropore area. Various surface ana NaY zeolite, which exhibits that it is fcasible to in-eas of synthesized NaY zeolites are depicted in Figuresitu synthesize NaY using the hydrothermal method3. which shows that the crystallization temperaturefron activated coal-based kaolinplays an important role in the physical properties ofNaY zeolites. ' The specific surfaco area, microporearca and cxtcrnal arca of the samples prepared in thelow temperat ure domain increased with the crystallization temperature and all reach a maximun at 380K. Then they decreased when the temperature isH BET areaCrystallization temperature(C)Figure 2. xRD pattern of in-situ sy nthesizcd zco-· cxtcrnal arcaUpon in-situ hydrothermal synIt hesis, the activeSi and Al species dissolve in the alkali solution andform the supersaturated solution. Thcy reactcach othcr and reconstruct to form some ring.三Estructures that arc the basic units for zeolite con-struction[ 2. At crystallizing conditions, they formanother phasc. which might be thermaldynamicallnetastable. It is this reconstruction and recrystallizetion of Si and Al species that results in the formationa Y-type zeolite skeleton. To optimize the iil-situ syll-Crystallization temperaturc(C)thesis conditions of coal-based kaolin, we extensivelyTTH中国煤化工allization term-investigated many operating parametersCNMHGXinmei Liu et al. Journal of Natural Gas Chemistry Vol. 12 No. 1 200.3above :380K. This implies that the lower temperature eral crystalline phases existing in the resulting prod-realm is not only beneficial to formation of the crystal ucts during the hydrothermal synthesis, which cannucleus but also to its hydrothernal stability which be shown by the Xrd data. The diffrac tion linesresults in the ratio of formation velocity to growth of the Xrd patterns illustrate that the 4A and NaPvelocity of crystal nucleus increasing. It also sug- zeolites(Nao AlG Si1oO32-12H2O) are the competitivegests that lower temperatures are preferable for the phase present in the resulting products. From reacgrowth of crystal faces, and higher temperatures are tion kinetics, the low temperature is beneficial to thepositive for interface diffusion. This shows that crys- formation of 4A crystalline seeds, but the formationtallization at lower temperatures is feasible to syn- rate of NaY crystalline seeds is effectively acceleratedthesize metastable Y zeolite. whereas higher temper- by the increase in temperature. When the temper-tures can synthesize even condensed and thermody- ature is increased to 370 K, pure NaY zeolites withnamically stable species. It is noted that the particle higher relative crystallinity can be obtained. Whensize of the resulting product is dramatically reduced it is further increased, the zeolite P becomes the pre-and the surface area is accordingly increased at lower doninant phase, and the perfect Nap zeolite can betemperatures.prepared at 410 K( Figure 4). This means that zeoliteFromm the surface area of the samples synthe- P is the even more stable phase in thermaldynamicssized at different temperatures, there must be sev- and possesses a condensed skeletal structure30002000Figure 4. Effect of crystallization temperature on synthesia)363K,(b)373K,(c)39k,(d)413KTYH中国煤化工CNMHGJournal of Natural Gas Chemistry Vol. 12 No. I 2003The co-existence of 4A. NaY and NaP occurs due 3.4. Effect of water volume on zeoliteto the remarkable disparity between the rate of the tioninterface reaction and diffusion process at differenttemperatures resulting in the growth rate diversityThe ph value of the aqueous solution significantamong the various crystalline surfaces upon thermal influences the crystalline pattern of the zeolites. Tablesynthesis. The crystallization temperature might af- I compiles the textural characteristics of the resultingfect the sol-gel properties, especially the particlc size products and shows the cffect of added watcr voluneand electricity of the sol-gel system. With incrcasing upon NaY zeolite synthesiscrystallization temperature, particle size will be effec-The XRD analysis shows that the amount of watertively decreased and the diffusion is also accelerated. exerts a strong influence on the structure of the zeo-Hence, the thermal stable phase is forned. To synthe- lites prepared from coal-based kaolin. An increase insize metastable Y zeolite, the crystallization temper- the water volume from 20 ml to 80 ml can result in anature must be strictly controlled, and the optimum enormous change in the crystalline pattern. When thetemperature for the Nay zeolite is 370 Kwater volume is below 30 tnl the sample has an amor-The ion exchange between the solid and liq- phous pattern. However, the sharp diffusion peak ofuid phase results in the zeolite skeleton compositionthe nay zeolites can be exist when the water volumechanging over time. Therefore, the impure crystalline is as high as 40 ml, whilst there are a small number ofphase can be observed with the crystallization time. 4A zeolites accompany with it(shown in Figure 6(a)Cang et al. [8] also investigated these phenomenaPure NaY can be synthesized by increasing the waterMost importantly, the pure Nay with higher spe- volume. It can be obtained when the water volumecific area and perfect crystallinity can be synthesized is 60 ml(shown in Figure 6(b),whereas the relativeat optimum conditions. The pore distribution of Nay crystallinity is lower than 40 ml and 50 ml. The dc-synthesized from kaolin is shown in Figure 5. The crease in the relative crystallinity is ascribed to theNaY samples possess narrow micropores, which are amorphous pattern mixing in it. When the water vol-more concentrated than the commercial Nayume is above 70 ml, the sample is totally convertednto the amorphous pattern. We can see that the water volurne plays an important role in the formationof the zeolite prepared from coal-based kaoliNThe functions of water can be described as fol-lows. First, the water volume contributes to the phvalue of the colloid system and accordingly influencesthe external dielectric constant and sizes of gel par-ticles. Second, the ph value influences the sedimentation vclocity of gel particles, which results in thechange in the gel concentration and the transfer rate00.2040.60.81.01,2of gel particles. This reveals that too much or tooPore diameter(nm)little water may inhibit the fornation of perfect. NayFigure 5. Micropore distribution of NaY synthe-zeolites from kaolinsized from coal-based kaolinTable 1. Effect of water volume added upon NaY zeolites synthesisWater arnountRelative crystallinity Surface area Micropore area Pore volumeProduct compositionamorphousmainly NaY +minim 4Amainly amorphous+minim Nay中国煤化工CNMHGXinmei Lin et al. Journal of Natural Gas Chen istry Vol 12 No, I 2003000Figure 6. Efect of water volume (a)40 ml,( b)60 ml added on synthesized zeolites3. 5. Effect of crystallization time on zeolite time can accelerate the growth and agglomeration offormationgel particles so that the NaY zeolite possesses a lowerlume and surfaceThe effect of crystallization time on synthesizedNaY zeolites was also extensively investigated. Fig-ure 7 shows that the various surface areas of samplesare all low, and specific surface area ascribes to theexternal area when the crystallization temperature isbelow 363 K. This is because the crystal products syn-thesized at low temperatures are mostly amorphousmaterial. which is veritied by xrd data. with theand the surface area is accordingly inerease3.6. Effect of aging on zeolite formationAging is also an important factor for the zeoliteCrystallization time (h)synt hesis process. The effects of aging conditions onthe resulting products are listed in Table 2.Table 2 indicates that Nay zeolites wit h a highersurface area could be obtained at the prop25time. Extended aging times are negative toP the gvns820thesis of Nay zeolites becanse the micropore surfacrea and relative crystallinity of the samples markedIdecreases. The pure NaY with higher relative crys- 2tallinity shown in the Xrd diffraction patterns can bedeveloped at aging times up to 12 hours. The properging time might be favorable for the formation of theskeletal struct ure, particle size and dielectric proper-ties of the unit cell in the colloid. Furthermore, itwould optimize the composition of the reactants in thesol-gel solution. which contribute to the formation ofration time (hithe pure naY zeolite. However, prolonging the agingYH中国煤化工CNMHGJournal of Natural Gas Chemistrv Vol. 12 No. I 2003Table 2. EFfect of aging on NaY zeolites synthesisAging tinmeRelative crystallinitySurface arcamicropore areaPore volumeProduct(em ig)%856.12l6.794.33.7. Hydrothermal stabilitystretching vibration of the to I tetrahedron. externaland inner syIllnetric vibration of the 'To4 tetraheThe DTA results are shown in Figure 8. The en- dron respectively. The bands at 500 cm and 450)dotheric peak at 470 K is due to desorption of phys. cm may correspond to the bend vibration of theical adsorbtion water. The peak of the chemical des. T-O bandorption water exists bet ween 180 K and 700 K. 'Theak at 40 K is ascribed to the collapse of the Nayskeleton which is similar to the commercial NayF1Figure 8. TG-DTA diagran of coal-based NaY ze-4. Conclusion1. Coal-based kaolin with little quartz is a promis-3.8. FT-IR spectra of skeletal vibrationing material for NaY zeolite synthesis. 'The pureNay zeolites were in-situ prepared by activation treatigure 9 presents the FT-IR spectra of skeletal ment using hydroxide sodium and crystallization hybration. It shows that the Nay zeolites synthesized drotherinal synthesis under the proper synthesiswith kaolin have similar skelet al vibration spectra as ditionshose conventionally prepared. The band at 3, 402. ' The crystallization temperature and pH of thecm-i is ascribed to the tortuous vibration, and that solution play an important role in the formation ofat 1,637 cm-I is ascribed to the corresponding co- the zeolite prepared from coal-bases kaolinalent bond vibration The band at. 1. 000. 790 and3. There are apparent competition anong 4A720cm-I can be attributed to the inner asymmetric NaP at中国煤化工 hesis from coaCNMHGXinmei Liu ct al. Journal of Natural Gas Chemistry Vol. 12 No. 1 2003based kaolin. 4A and NaY zeolites are the metastablepattern and NaP is the relative stable one. Thus[4 Shigemoto N, Hayashi H, Miyaura K. J Mater Sciit is inportant to control the reaction parameters to1993.28:478lobtain the desired zeolite15) LaRosa J, Kwan S, Grutzeck M W. J Am Ceram Soc,1. Pure NaY with a high relative crystallinity can1992,75:1574e prepared from kaolin. The samples possess a larger6 Amrhein C, Haghnia G H, Kim T S et al. Environspecifie area, sharper pore distribution and good hSci Technol, 1996. 30: 7357 Liu X J, Xu M Sh, Huang T G. Guisuanyan Tongbaodrot hermal stabilitv(Silic Commun), 1998, 1:37(8 Yang W B. Cuihua Xuebao( Chin J Catan), 1998, 19References575[9] Du Y Ch. Kuangchan Baohu yu Liyong(Prot ApplI Ni Zh, Tang Y, Hua W M. Shiyou HuagongPetrochem Technol), 2000, 29: 336[10 Zhang YY Xiandai Huagong(Mod Chem Technol)2 7hao X S, Lu G Q. Zhu H Y J Porous Mater, 199798,4:911 Xu M S, Cheng M J, Tan D L et al. Cuihua Xuebao13 Singer A, BerkGaut V Environ Sci Technol, 1995Chin J Catal), 2001. 22:1中国煤化工CNMHG