STUDY OF THE ADSORPTION OF ACETIC ACID ON SILICA GEL IN AQUEOUS SOLUTION

Transcription

1 ACADEMIA ROMÂNĂ Rvu Roumain d Chimi Rv. Roum. Chim., 2013, 58(1), STUDY OF THE ADSORPTION OF ACETIC ACID ON SILICA GEL IN AQUEOUS SOLUTION Samadani Langroodi NARGES * Scinc Faculty, Chmistry Dpartmnt, Golstan Univrsity, Gorgan, Iran Rcivd Octobr 15, 2012 Adsorption of organic molculs on silica gl surfacs is widly usd in a numbr of tchnological applications such as htrognous catalysis. A ky stp is th undrstanding of th natur of th adsorption on such surfacs, which is th spcific aim of our study of th adsorption of actic acid on silica gl. Th adsorption of actic acid on silica gl was studid undr various conditions such as tmpratur, contact tim, adsorbant dos and concntration of adsorbat. Batch adsorption xprimnts wr conductd and th rsult showd that th adsorption was dpndnt on all ths paramtrs. Th adsorption procss obys th Langmuir and Frundlich adsorption isothrms. By ths adsorption isothrms, thrmodynamics adsorption paramtrs such as chang in Gibb s fr nrgy, nthalpy, ntropy and kintics adsorption paramtrs such as rat constant of adsorption wr calculatd. INTRODUCTION * Th chmical and adsorption proprtis of silica surfacs hav bn xtnsivly studid for many dcads bcaus of thir us as adsorbnts and carrirs in gas and liquid chromatography and as support for catalysts. 1-4 Thr ar hydroxyl groups on a silica gl surfac thrfor along with th hydrogn bonding with surfac hydroxyl groups or oxygn ions, organic acids can intract with surfac. 5,6 Rmoval mthods of organic compounds in industrial dischargs may b traditionally dividd into thr main catgoris: physical, chmical, and biological procsss. Among thm, physical adsorption is gnrally considrd to b th most fficint mthod for quickly lowring th concntration of dissolvd organic componds in th solution. Actic acid is an organic acid which is an important compound in biochmistry, natur and industry. In many cass is ncssary to isolat it from th nvironmnt. Intrst in th surfac chmistry of carboxylic acids on transition mtal surfacs and transition mtal oxid surfacs partly stms from th fact that th associat spcis ar important ithr as raction intrmdiats or as product in catalytic oxidation ractions. S for xampl Svral workrs hav rportd on th potntial us of TiO 2, 11,12 silicas, 13 ion-xchang rsins in nonaquous conditions, 14 Au/Pd(1 1 1) alloy surfacs 15 and smooth Pt lctrods, 16 as good substrats for th rmoval of actic acid from aquous solutions. In this rsarch work, is studid th adsorption of actic acid in aquous solution on silica gl as a modl systm. Th purpos of this work was to study th adsorption proprtis of commrcial * Corrsponding author: nsamadani@yahoo.com

2 44 Samadani Langroodi Nargs silica gl with rspct to actic acid from aquous solution. Batch xprimnts wr conductd to invstigat th ffcts of adsorbnt dos, contact tim, absorbat concntration and tmpratur on th adsorption of actic acid on th Silica gl. Langmuir and Frundlich isothrm modls wr usd to illustrat th xprimntal isothrms modls and isothrms constants. C 0 C V q W whr C 0 and C (mg/l) ar th liquid-phas concntrations of actic acid at initial and quilibrium, rspctivly. V (l) is th volum of th solution and W (g) is th mass of dry adsorbnt usd. 17 MATERIALS AND METHODS Commrcial KSKG Silica gl with a particl siz mm was usd as adsorbnt. Its spcific surfac ara, s, dtrmind by th thrmal dsorption of nitrogn quald 340 m 2 /g. Th adsorbnt tratd prliminary at 400 C for 6 h. All xprimnts wr carrid out by th sampls containing 50 cc of diffrnt initial concntration ( M) of actic acid in th rang of C tmpratur. 3.5 g of th adsorbnt was transfrrd into various 250 ml Erlnmyr flask and actic acid solution by fixd concntration was addd and mixd using a stirrr- magnt for 20 min. Thn th solution was filtrd its concntration was dtrmind by titration with 0.1 M solution of NaOH. Th amount of quilibrium adsorption, q (mg/g), was calculatd by: EFFECT OF ADSORBATE CONCENTRATION Svral stock solutions with concntration ( M) wr prpard. Each solution was addd to 3.5 g of th adsorbnt in diffrnt 250 ml flasks and agitatd using a mchanical agitator for 20 min ach. At th nd of th tim, th contnts of th flasks wr filtrd and analyzd. Th rsults ar shown in Fig. 1. EFFECT OF ADSORBENT DOSE 50 ml ach of th actic acid solutions wr addd to various amount of th adsorbnt ( g) in diffrnt 250 ml flasks, flasks wr agitatd for 1hr on a mchanical stirrr. Th contnt of th flask was filtrd and analyzd. Th rsults ar prsntd in Fig. 2. Fig. 1 Influnc of initial actic acid concntration on adsorption of actic acid on silica gl.

3 Adsorption of actic acid on silica gl 45 Fig. 2 Influnc of adsorbnt dos on adsorption of actic acid on silica gl. EFFECT OF CONTACT TIME 50 ml ach of stock solution of actic acid was transfrrd into diffrnt 250 cm 3 Erlnmyr flask, corkd and labld. 3.5 g ach of th adsorbnt was wighd into th diffrnt labld flasks and agitatd in a shakr for diffrnt contact tims (0.5, 1, 1.5, 3, 5 and 10 minuts). Aftr th mntiond tim, th contnt of ach flask was filtrd. Th quilibrium concntration of th actic acid in ach of th filtrat was dtrmind. Th rsults obtaind ar shown in Fig. 3. EFFECT OF TEMPERATURE 50 ml ach of stock solution was transfrrd into various 250 cm 3 flask containing 3.5 g ach of th adsorbnt, corkd and labld for diffrnt tmpraturs 22, 35, 55, 70 C rspctivly. Th mixtur was hatd and shakn to th appropriat tmpratur in a watr bath. At th right tmpratur, th contnt of th ach of th flask was rmovd, filtrd and analyzd. Th rsults obtaind ar shown in Fig. 4. % actic acid adsorbd t, min Fig. 3 Influnc of contact tim on adsorption of actic acid acid on silica gl.

4 46 Samadani Langroodi Nargs % actic acid adsorbd Fig. 4 Influnc of tmpratur on adsorption of actic acid on silica gl. T, K RESULTS AND DISCUSSION Th concntration-dpndnt data for th adsorption of actic acid is prsntd in Fig. 1. This dcras in % adsorption of actic acid is du to lssr availability of th adsorption sit. Morovr, this can b xplaind by th fact that mor adsorption sits wr bing covrd as th actic acid concntration incrass. Th ffct of th adsorbnt dos on th rmoval of actic acid from aquous solution was invstigatd by varying th dos of th adsorbnt from g. It is xpctd that an incras in th dos of adsorbnt should yild a corrsponding incras in th amount of actic acid adsorbd on th surfac of th adsorbnt sinc thr will b mor sits for th adsorbat to b adsorbd. Thrfor comptition for bonding sits btwn molculs of th adsorbat should dcras with incras in dos of th adsorbnt. 18,19 From Fig. 2 this trnd was inconsistnt and thrfor suggsts that th us of silica gl as adsorbnt partly dpnds on its dos in aquous solution. Furthr incras of adsorbnt dos did not caus any significant chang bcaus quilibrium was achivd btwn solution and solid phas. Th rsult obtaind from tim-dpndnt xprimnts for th adsorption of actic acid on silica gl was prsntd in Fig. 3. As th contact tim was incrasd, th amount of actic acid rmovd also incrasd. Th data showd actic acid rmoval from aquous solution incrass initially until quilibrium was attaind and thn was constant. In according to Fig. 3, th obsrvabl tim for maximum adsorption is btwn 7-10 minuts. Th ffct of tmpratur on th rmoval of actic acid from aquous solution was invstigatd by varying th tmpratur of adsorption btwn 22 C and 70 C (Fig. 4). Th data showd that with incrasing tmpratur th amount of actic acid adsorbd on th surfac of th adsorbnt dcrass. Th attractiv forcs btwn th adsorbnt and th adsorbat ion may hav bn waknd making th adsorption to dcras. At high tmpratur, th thicknss of th boundary layr is xpctd to dcras du to th incrasd tndncy of th ions to scap from th surfac of th adsorbnt to th solution phas hnc thr is bound to b wak adsorption intractions btwn th adsorbnt and th adsorbat. ADSORPTION ISOTHERMS Th quilibrium adsorption isothrm is on of th most important data to undrstand th mchanism of th adsorption systms. In this mannr, th Langmuir, th Frundlich isothrm quations wr usd to intrprt th xprimntal data. Langmuir isothrm thory is basd on th assumption that adsorption on a homognous surfac, i.., th surfac consists of idntical sits, qually availabl for adsorption and with qual nrgis of adsorption and that th adsorbnt is saturatd aftr on layr of adsorbat molculs forms onto surfac. 20 Th linarizd form of th Langmuir adsorption isothrm quation is C C = + 1 q q K q m L m

5 Adsorption of actic acid on silica gl 47 Th Langmuir constants, which ar q m and K L valus, can b calculatd from th plot C/q vrsus C. Isothrm modls constants and corrlation cofficints for actic acid adsorption on silica gl listd in Tabl 1. Th linarizd Frundlich isothrm quation that corrsponds to th adsorption on htrognous surfac is givn as: 1 log q = log KF + logc n whr C is th quilibrium concntration of th solut (mg/l) and q is th quilibrium adsorption capacity (mg/g). Th Frundlich isothrm constants KF and 1/n can b calculatd from th plot of ln q vrsus ln C. Th slop (1/n) masurs th surfac htrognity. Htrognity bcoms mor prvalnt as 1/n gts closr to zro.th Langmuir and Frundlich adsorption constants calculatd from th corrsponding isothrms with th corrlation cofficints ar prsntd in Tabl 1. Th corrlation cofficint shows that th adsorption procss could b dscribd by th both Langmuir and Frundlich modl quation. Th Langmuir constants (q m and K L ) valus wr fit th xprimntal data. THERMODYNAMIC STUDIES Thrmodynamic paramtrs such as chang in Gibb s fr nrgy ( G ), nthalpy ( H ), and ntropy ( S ) wr dtrminatd using th following quations: 21,22 q m ln = S C G = H H R T S RT whr m is th adsorbnt dos (mg/l), C is th quilibrium concntration (mg/l) of th malonic acid in solution, R is th gas constant (8.314 J/mol/K) and T is th tmpratur (K). G, H and S ar changs in Gibb s fr nrgy (J/mol), nthalpy (J/mol), ntropy (J/mol/K), rspctivly. Th valus of H and S wr dtrmind H / R and th intrcpts from th slops ( ) ( S / R) of th plots of qm ln vs.1/t. C Th valus of thrmodynamic paramtrs ar prsntd in Tabl 2. Th ngativ valus of G indicat that th adsorption procss is fasibl and spontanous in natur. Th dcras in th valus of G, with th incras of tmpratur, dmonstratd that th adsorption was bnfitd by th high tmpratur. Th ngativ valu of H suggst th xothrmic natur of adsorption and th positiv valu of S dscribd th randomnss at th adsorbnt-solution intrfac incrasd during th adsorption. SORPTION KINETICS Sorption kintics was studid for adsorption of actic acid on silica gl of initial concntration 0.15 mol/l. Th rat constant of adsorption was dtrmind from th psudo-scond ordr rat xprssion: 23 t 2 2 q + t / q = 1/ k t / q whr k 2 is th rat constant of adsorption (g/mg/min), q and q t ar th amount of malonic acid adsorbd at quilibrium and at tim t (mg/g) cal rspctivly. Th valus of k 2 and q wr calculatd from th intrcpts (1/k 2 q 2 ) and th slops (1/q ) of th plots of t/q vs. t. rspctivly, rportd in Tabl 3. Th rsults show that th valus cal of q and q xp ar almost qual and rgrssion corrlation cofficint (R 2 ) is clos to unity which confirm that adsorption of actic acid on silica gl follows psudo-scond ordr kintic modl. Tabl 1 Isothrm modls constants and corrlation cofficints for actic acid adsorption on silica gl Frundlich Langmuir T, K K f, mg/g n, mg/l R 2 K L, l/mg q m, mg/g R Tabl 2 Thrmodynamic paramtrs for actic acid adsorption on silica gl G, kj/mol S, kj/mol.k -1 H, kj/mol

6 48 Samadani Langroodi Nargs Tabl 3 Kintic paramtrs for actic acid adsorption on silica gl Psudo scond ordr q xp, mg/g q cal, mg/g K 2, g/mg.min R CONCLUSIONS Th adsorption of actic acid on silica gl (5.66 mg/g) occurs bcaus of donor-accptor intractions. In this rsarch work, Silica gl to compr othrs adsorbnts such as silicas, Au/Pd (1 1 1) alloy surfacs and smooth Pt lctrods has advantags such as radily availabl, good adsorption capacity and high adsorption rat. Th study indicats that rmoval of actic acid from aquous solutions dpnds on th solution adsorbnt dos, contact tim, initial actic acid concntration and tmpratur. Th adsorption procss obys both Langmuir and Frundlich adsorption isothrms. Th thrmodynamic study shows that th adsorption procss was xothrmic and spontanous in natur. Th adsorption of actic acid on th silica gl followd rvrsibl scondordr rat kintics. Th adsorption is rlativly quick and th procss is vry fficint spcially for watr containing low concntrations of actic acid. REFRENCES 1. A. A. Issirkyan and A. V. Kislv, Zh. Fiz. Khim., 1957, 31, V. Ya. Davydov, A. V. Kislv and B. V. Kuzntsov, Fiz. Khim., 1965, 39, R. Blinski, J. Colloid Intrfac Sci., 2000, 225, B. L. Nwalkar, N. V. Choudary and U. T. Turaga, Micropor. Msopor. Mat., 2003, 65, G. V. Lisichkin, G. V. Kudryavtsv and A. A. Srdan, Catalysis and Chromatography, Khimiya, Moscow, A. V. Kislv and V. I. Lygin, Infrard Spctra of Surfac Compounds, Nauka, Moscow, J. J. Vajo, Y. K. Sun and W. H. Wnbrg, Appl. Surf. Sci., 1987, 29, C. M. Frind and X. Xu. Ann. Rv. Phys. Chm., 1991, 42, J. Ushio, I. Papai, A. St-Amant and D. R. Salahub, Surf. Sci., 1992, 262, L M. A. Szymanski and M. J. Gilan, Surf. Sci., 1996, 367, G. Capcchi, M. Giulia Faga, G. Martra, S. Coluccia, M. Francsca Iozzi and M. Cossi, Rs. Chm. Intrmd., 2007, 33, I. D. Cocks, Q. Guo, R. Patl, E. M. Williams, E. Roman and J. L. d Sgovia, Surfac Scinc., 1997, , S. David Jackson, G. J. Klly and D. Lnnon, Ract. Kint. Catal. Ltt., 2000, 70, H. M Anasthas and V.G. Gaikar, Ractiv and Functional Polymrs., 2001, 47, Z. Li, F. Calaza, F. Gao and W.T. Tyso, Surfac Scinc, 2007, 601, E.K. Krauskop and A. Wickowski, Journ. Elctroanal. Chm. Intrfacial Elctrochm., 1989, 271, P. Brown and I. A. Jfcoat, Adv. Environ. Rs., 2000, 4, W. S. Wan Ngah, M. Hanafiah, Biochm. Eng. J., 2008, 39, Y. Bulut, H. A. Aydin, Dsalination., 2006, 194, R. S. Araujo, D. C. S. Azvdo, Jr. Cavalcant, C. L. Jimnz-Lopz, and A. Rodriguz-Castllon, Micropor. Msopor. Mat., 2008, 108, J. Romro-Gonzalz, J. R. Pralta-Vida, E. Rodriguz, M. Dlgado and J. L. Garda-Torrsdy, Biorsour. Tchnol., 2006, 97, B. K. Nandi, A. Goswami and M. K. Purkait. J. Hazard. Matr., 2009, 161, M. Dogan, M. Alkan, A. Turkyilmaz and Y. Ozdmir. J. Hazard. Matr., 2004, B109, 141.