Solid-Liquid Equilibrium for the System Activated Carbon and Aqueous Solution of both Phenol and Dinitro-o-Cresol.

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1 Sold-Lqud Equlbrum for the System Actvated Carbon and Aqueous Soluton of both Phenol and Dntro-o-Cresol. G. Sambenedetto, L. Spera, L. Tagler and G. D Gacomo* Dpartmento d Chmca Ingegnera Chmca e Materal, Unverstà degl Stud dell'aqula, I Monteluco d Roo, L'Aqula, ITALY * Tel , Fax Emal:dgacomo@ng.unvaq.t Water purfcaton processes, based on rather severe chemcal condtons, partcularly oxdaton, have a tendency to produce dangerous by-products. Among chemcals that undergo ths transformaton there are phenolc compounds whch are qute usual contamnants n ndustral wastewaters. Adsorpton of phenolc compounds dssolved n aqueous soluton by usng ndustral actvated carbon s an nterestng alternatve snce t makes possble to acheve a practcally complete removal of the pollutng compounds wthout any negatve consequence. To ths purpose, new equlbrum data for two pseudo bnary systems: a) actvated carbon - aqueous solutons of phenol; b) actvated carbon - aqueous solutons of dntro-o-cresol, along wth new ermental data for the pseudo ternary system: c) actvated carbon - aqueous solutons of both phenol and dntro-o-cresol, were measured at K and K, after a proper characterzaton of the adsorpton materal as receved by SICAV (Italy). All the pseudo bnary SLE data are n good agreement wth correspondng lterature data, whle for the pseudo ternary SLE s not possble any comparson. SLE data were satsfactorly correlated by a Freundlch based compettv model. 1. Expermental secton 1.1 Materals The man characterstcs of the actvated carbon, as measured by us, are: total Surface Area: 37 m /g (N BET method); Sngle Pont Total Pore Volume of pores less than 17 Å at P/Po = : 0.14 cm 3 /g; Average Pore Dameter (4V/A by Langmur): 0.0 Å; Mosture Content: 3.10 %; Iodne Number: 800 mg/g; Apparent Densty: 400 kg/m 3. The as-receved powdered actvated carbon was seved and the m fracton was used to perform the equlbrum ermental tests. Phenol (component A; MW=94.1) and 4,6-dntro-o-cresol (DNOC; component B; MW=198.1) were bought from Aldrch. De-onzed water was obtaned from a reverse osmoss laboratory devce (ROS-50T).

2 1. Apparatus and Expermental Procedures Adsorpton quantfcaton of phenol and/or DNOC dssolved n lqud phase was carred out n specally desgned acketed glass-stoppered flasks havng a volume capacty of 50 ml. A known quantty (typcally, 1 g) of actvated carbon, havng predetermned mosture content, was placed n several of these cells. Accordng to ermental procedure followed by other Authors (e.g.: Edgehll and Lu, 1998) a constant quantty of organc aqueous soluton (typcally, 100 ml) wth a predetermned composton was poured nto the flasks. The cells content was kept at constant temperature by crculatng n the acket a stream of water comng from a controlled water bath (Heto Brkerød thermostat). The ermental equlbrum measurements were carred out at 98 ± 0.1 K and at 308 ± 0.1 K. Strrng of the solutons nsde the flasks was obtaned by magnetc strrng at controlled speed. To prevent photodecomposton of organc compounds, flasks were covered wth alumnum fols. Prelmnarly, t was verfed that practcal equlbrum s always reached n a tme much lower than 30 hours. At the end of equlbraton, strrng was stopped, actvated carbon was allowed to settle and, to remove the fnest sold partcles, the recovered soluton was fltered by Supelco flter (0.45m pore dameter). The resdual concentraton of organc compound/s n the equlbrated aqueous solutons, C e, (g/l) were determned by means of a UV-VIS spectrophotometer (Perkn Elmer Lambda S), prevously calbrated. The measured quantty was the typcal assorbance of each organc compound, whch s lnearly related to the concentraton. The concentraton of each phenolc compound n the sold phase was calculated usng the materal balance equatons: ( C Ce ) V qe = A, B (1) m where: C A and C B are the ntal lqud phase concentratons (g/l) of A and B respectvely; C ea and C eb are the equlbrum lqud phase concentratons (g/l) of A and B respectvely; q ea and q eb are the equlbrum sold phase concentratons n grams of A for each gram of actvated carbon (g/g); m s the mass of actvated carbon (g), V s the volume of the soluton n lters.. Results and Dscusson.1 Pseudo Bnary Systems All the measured SLE data (q e, C e ) are reported n Table 1. Freundlch equaton n ( q K C ) was used to ft the ermental data where K F has been ressed as a e F e lnear functon of temperature n the range between K and K. q n C e, K1 K T e = A, B () The followng Obectve Functon (OF) was mnmzed n order to fnd the numercal values of the model parameters: K 1, K, and n for each component. N cal q e qe OFK 1, K, n = A, B (3) 1 qe

3 Table 1. Expermental SLE Data for the Pseudo Bnary Systems. Actvated carbon aqueous Actvated carbon-aqueous Test T (K) solutons of Phenol solutons of DNOC N. C ea (g/l) q ea (g/g) C eb (g/l) q eb (g/g) The results are summarzed n Table along wth the per cent Absolute Average Devaton (AAD) defned as: AAD N cal 100 qe qe N 1 qe = A, B (4)

4 Table. Results obtaned by fttng Pseudo Bnary SLE ermental data. Organc Component OF K 1 K n AAD Phenol (A) 1, DNOC (B) Where N s the number of ermental measurements for each component. When comparable, our SLE data are n good agreement wth lterature data (Edgehll and Lu, 1998; Khan, et al. 1999; Rav, et al. 1998). Fgure 1 shows the comparson between ermental and calculated SLE data as functon of phenol (a) and DNOC (b) composton n the aqueous soluton, at K and K. As can be seen, n both cases, the agreement s satsfactory and, consequently, the Freundlch model can be confdently used, n combnaton wth the parameters reported n Table, to predct SLE for the pseudo bnary systems. Fgure 1. Comparson between measured and calculated SLE compostons for the Pseudo Bnary Systems: a) actvated carbon - aqueous solutons of Phenol and, b) actvated carbon - aqueous solutons of DNOC. Calculated at K; Measured at K; Calculated at K; Measured at K.. Pseudo Ternary System All the measured SLE data (qe, Ce) are reported n Table 3. The values of the actvtes n the aqueous solutons of phenol and DNOC, a A and a B, respectvely, were calculated usng equatons (5) and were compared wth the values of the fractons on water free bases, X A and X B, respectvely. qej a J = A, B (5) n K K T C 1J J J ej a A dffers sgnfcantly from X A and a B dffers sgnfcantly from X B, as a consequence of the non neglgble nteractons exstng between molecules of phenol and molecules of DNOC when both these compounds are dssolved n the aqueous solutons. For ths

5 reason t s not possble to predct SLE related to the pseudo ternary systems by only usng pseudo bnary model parameters. Table 3. Expermental SLE Data for the Pseudo Ternary System: actvated carbon aqueous solutons of Phenol and 4,6 Dntro-o-Cresol at K and K. Test N. C ea (g/l) q ea (g/g) C eb (g/l) q eb (g/g) X A a A a B T (K) , , To account for the above mentoned molecular nteractons, t s used the Wlson Equaton (Wlson, 1964) prevously parametrzed by fttng all the SLE ermental data reported on Table 3. To ths purpose, t was mnmzed the followng OF: N cal N cal N cal q ea qea qeb qeb qet qet OF AB, (6) BA 1 qea 1 qeb 1 qet Where: q ea and q eb are the ermental data, q et = q ea + q eb, whlle q cal cal ea and q eb are the correspondng quanttes calculated by usng the actvty of phenol and the actvty of DNOC obtaned wth the Wlson model (a Amod and a Bmod ). The rato between molar volumes of A and B whch appears nsde AB and BA s Table 4 shows the results obtaned by fttng pseudo ternary SLE ermental data. A comparson between ermental and calculated values of q ea and q eb are reported on Fgure. Comparson of the values of AAD reported on Table wth the correspondng values reported on Table 4 show that, n any case, smulaton of pseudo

6 ternary SLE behavour s more dffcult than smulaton of pseudo bnary SLE behavour. In fact, the values of AAD reported on Table are about 50% of the correspondng values reported n Table 4. However, Fgures 1 and shows that devaton between calculated and ermental equlbrum adsorbate concentraton n the sold phase are always well dstrbuted. Ths result s the drect consequence of the ntroducton of the Wlson model for smulatng pseudo ternary SLE snce, the smple predcton, gves rse to completely undstrbuted devatons for the calculated equlbrum adsorbate concentraton n the sold phase along wth hgher values (up to almost 400%) for the two AAD. Table 4. Results obtaned by fttng Pseudo Ternary SLE ermental data. Organc AB OF AA BA (K) BB (K) AAD Component R R Phenol (A) DNOC (B) 16.8 Fgure. Per cent Relatve Devaton between. and calc. q e,a and q e,b for the Pseudo Ternary System at K and K. Phenol; DNOC. 3. References Edgehll, R.U., Lu, G.Q., Adsorpton Characterstcs of Carbonzed Bark for Phenol and Pentachlorophenol. J. Chem. Technol. Botechnol. 71, Khan, A.R., Al-Bahr, T.A., Al-Habbab, A Adsorpton of phenol Based Organc Pollutans on Actvated Carbon From multcomponent Dlute Aqueous solutons. Water Research; 31 (8), Rav, V.P., Jashra, R.V., Bhat, T.S.G., Adsorpton of Phenol, Cresol Isomers and Benzyl Alcohol from Aqueous Soluton on Actvated Carbon at 78, 98 and 33 K J. Chem. Tech. Bochem. 71, Wlson, G. M., Vapo-lqud equlbrum XI: A new resson for the excess free energy of mxng. J. Am. Chem. Soc. 86,

Assignment 4. Adsorption Isotherms

Assignment 4. Adsorption Isotherms Insttute of Process Engneerng Assgnment 4. Adsorpton Isotherms Part A: Compettve adsorpton of methane and ethane In large scale adsorpton processes, more than one compound from a mxture of gases get adsorbed,