MANOMETRICAL STUDIES ON THE ADSORPTION OF SOME ORGANIC GASES/VAPORS ON THE SURFACE OF ACTIVATED CHARCOAL

Size: px

Start display at page:

Download "MANOMETRICAL STUDIES ON THE ADSORPTION OF SOME ORGANIC GASES/VAPORS ON THE SURFACE OF ACTIVATED CHARCOAL"

Trevor Hampton
6 years ago
Views:

1 MANOMETRICAL STUDIES ON THE ADSORPTION OF SOME ORGANIC GASES/VAPORS ON THE SURFACE OF ACTIVATED CHARCOAL Ghayasuddin Khan KCP-I, Pakistan Atomic Energy Commission P.O. Box 1114, Islamabad, Pakistan Fahim Uddin*, Nasiruddin Khan, and Hajira Tahir Department of Chemistry, University of Karachi Karachi-75270, Pakistan الخلاصة ت عنى هذه الدراسة بامتزاز الغازات والا بخرة العضوية ) تتراآلوريد الكربون ميثان والا مونيا ( مع التغير في الضغط لسطح من الفحم الم نش ط. وآشفت الدراسة عن تغييرات نمطية في الانتشار السطحي لهذه المواد وعن تلاؤم للنتاي ج مع علاقات فرونديش لانجمور. آما قمنا بحساب المميزات الثابتة في هذه العلاقات وتا ويلها ثم قمنا بحساب الحرارة الانضغاطية بالاستعانة بمعادلة آلادسيوس آلابيريون. وأشارت هذه النتاي ج إلى أن أفضل امتزاز آان للا مونيا مقارنة ببقية المواد قيد الدراسة. ABSTRACT Adsorption of organic gases/vapors: carbon tetrachloride, methane, and ammonia, on the surface of activated charcoal has been studied manometrically. Detailed examination indicates a difference in the mode of dispersion on the surface of activated charcoal. The adsorption equilibrium data were fitted to Freundlich and Langmuir isotherm equations as a function of pressure and temperature. The values of the constants were computed and interpreted. Isosteric heats of adsorption were also calculated using Clausius Clapeyron equation. From the results, we conclude that ammonia is a better adsorbate on the surface of activated charcoal as compared to carbon tetrachloride and methane. *To whom correspondence should be addressed. January 2003 The Arabian Journal for Science and Engineering, Volume 28, Number 1A. 35

2 MANOMETRICAL STUDIES ON THE ADSORPTION OF SOME ORGANIC GASES/VAPORS ON THE SURFACE OF ACTIVATED CHARCOAL INTRODUCTION Activated charcoal is a carbonaceous material which differs substantially in properties from other porous materials and so is extensively applied in the chemical industry. Activated charcoals are generally efficient adsorbents and the purification of gases represents one of their most frequent applications. The activity of charcoal depends on intrinsic properties of parent material, porosity, ash content, and the methods of activation [1 10]. Transport phenomena in porous structures consist of sorption kinetics, thermo-osmotic, isobaric, and non-isobaric flows, and isothermal transient and steady flows. The study of these processes along with sorption equilibria provide a strong foundation for determining surface properties. Activated charcoal is frequently employed for the adsorption of organic gases and liquids [11 12]. The present communication deals with the sorption of organic gases/vapors: carbon tetrachloride, methane, and ammonia on the surface of activated charcoal by manometrically. The values of Freundlich and Langmuir constants were evaluated by isotherms. Furthermore the values of heat of adsorption q isosteric were also evaluated. EXPERIMENTAL Activated charcoal (animal), carbon tetrachloride, methane, and ammonia, of E. Merck, were used without further purification. Apparatus for the adsorption of organic gases/vapors is shown in Figure 1. It consists of a Hg manometer, a Hg filled gas burette, five stopcocks, vacuum pumps, sample tube, gas cylinder, and water bath. The whole system was evacuated with a vacuum pump through stopcock A. The leak test of the apparatus was also made by manometer K, by observing any detectable change over a period of five minutes when the apparatus was evacuated. The gas was admitted through stopcock E and stopcock D was closed until the burette H was filled at atmospheric pressure (760 mm of Hg). The volume of gas in the burette was recorded by closing stopcock E and the leveling bulb G was adjusted at atmospheric pressure. Then gas from the burette was admitted into the system through stopcocks C and D at a pressure of about 50 mm Hg and the exact manometer readings, burette readings, and temperature of the bath were recorded for calculating the dead volume of the gas. Dead volume is the volume between manometer K and stopcock D in the absence of any adsorbing material in sampling tube J. At other pressures, dead volume (J) was determined in a similar manner. The burette was refilled when necessary, by closing stopcock D, opening stopcock E, and lowering the leveling bulb G. One gram of activated charcoal was taken in sampling tube J and placed in water bath at 10 C. The stopcock C was closed and the activated charcoal was degassed for 5 minutes by evacuating through stopcocks A and B. The given gas was admitted from the burette until the pressure was about 50 mm Hg. The decrease in pressure was recorded at 7.60, 15.60, 28.80, and mm Hg. When equilibrium has been reached and no more addition of gas was necessary to maintain the pressure, then volume of gas introduced from the burette was recorded. This operation was repeated at other pressures. RESULTS AND DISCUSSION The adsorption behavior of different organic gases and vapors, such as carbon tetrachloride, methane, and ammonia has been studied. Freundlich and Langmuir parameters were calculated. Figure 2 and Table 1 show the values of Freundlich constants k and n using the Freundlich isotherm expression [11]. log V = n log P + k (1) where V is corrected volume of gas (in ml) at 0 C temperature, 760 nm pressure, adsorbed per gram of activated charcoal. P is pressure in mmhg. The values of constants n and k were computed from the slope and intercept of the 36 The Arabian Journal for Science and Engineering, Volume 28, Number 1A. January 2003

3 linear plots of log (V) versus log (P). A higher fractional value of n signifies strong sorption forces. However, the higher values of K further confirm the higher affinity of adsorption on the surface of activated charcoal. The values of log (V) cannot be equal to constant k; it means that multilayer physical adsorption of gases occurs. This was also reported earlier [13]. Table 1. Freundlich and Langmuir Adsorption Isotherm Constants. Adsorbate Freundlich Langmuir n k log (k) 1/K Vu Vu K CCl CH NH Figure 1. Apparatus for the adsorption of organic gases/vapors. January 2003 The Arabian Journal for Science and Engineering, Volume 28, Number 1A. 37

4 The values of the Langmuir constants K and Vu were calculated using Langmuir isotherm expression [7]: P P 1 = + (2) V Vu K Vu where P and V are the pressure and volume of gas at 0 C temperature and 1 atmospheric pressure adsorbed per gram of activated charcoal. Vu is the volume of gas at (0 C, 1atm) adsorbed per gram of activated charcoal. K is the constant and characteristic of adsorbent pair. The values of Langmuir constants K and Vu are shown in Figure 3 and Table 1, while Tables 2 and 3 show the values of Freundlich and Langmuir parameters for plotting isotherms. The value of n log (P) at higher pressure increases and approaches to 1 in all cases. This indicates that formation of multilayers takes place and the effect of vertical interaction between adsorbate and adsorbent in the second layer is different. The values of heat of adsorption, q isosteric are tabulated in Table 4. These values were calculated by using Equation (3): ln P2 P 1 T2 T1 = qisosteric (3) R. T. T 1 2 where P 1 and P 2 are the equilibrium pressures of a given amount of adsorbed gas at temperatures T 1 and T 2 respectively. The values of heat of adsorption increases with the increase in the pressure of adsorbed gas. This might be explained on the basis of active sites present in the adsorbent. This effect is due to the change in the magnitude of the forces between adsorbent and adsorbate at higher pressures. The values of heat of adsorption also increases from J/deg.mol. at P 2 pressure with increasing Freundlich constant values n from Table 1 shows that the values of Freundlich constants n and k decrease from carbon tetrachloride to methane, while the values of Langmuir constant Vu increase. Table 2. Freundlich Adsorption Isotherm on Activated Charcoal at 10 C. Adsorbate log (P) CCl 4 NH 3 CH 4 log (V) n log (P) log (V) n log (P) log (V) n log (P) Table 3. Langmuir Adsorption Isotherm on Activated Charcoal at 10 C. Pressure mm (P) CCl 4 P/V NH 3 P/V CH 4 P/V The Arabian Journal for Science and Engineering, Volume 28, Number 1A. January 2003

5 Table 4. Heat of Adsorption q isosteric (at Different Volume of Gases Adsorbed). CCl 4 NH 3 CH 4 P 1 P q (J/deg.mol.) P q (J/deg.mol.) P q (J/deg.mol.) Temperature T 1 : 10 C Temperature T 2 : 20 C Figure 2. Freundlich Adsorption Isotherm on activated charcoal at 10 C. January 2003 The Arabian Journal for Science and Engineering, Volume 28, Number 1A. 39

6 Figure 3. Langmuir Adsorption Isotherm on activated charcoal at 10 C. REFERENCES [1] Fahimuddin, I.M. Adhami, and N. Shahid, Effect of Concentration on Adsorption of Aromatic Acids from Aqueous Solutions on Charcoal, J. Sci. Res., 17 (1988), pp [2] A. Rasheed Khan, Fahimuddin, and Ghayasuddin Khan, Titrometric Studies of the Adsorption of Some Aliphatic Organic Acids from Aqueous Solutions on the Surface of Activated Charcoal, Pak. J. Sci. Ind. Res., 32 (1989), pp [3] A. Rasheed Khan, Fahimuddin, and Ghayasuddin Khan, Adsorption of Glycolic and Lactic Acids from Aqueous Solutions on Charcoal, Pak. J. Sci. Ind. Res., 34 (1991), pp [4] A. Rasheed Khan, Fahimuddin, and S. Ali, Adsorption Studies of Tartaric Acids from Aqueous Solutions on Charcoal, Pak. J. Sci. Ind. Res., 37 (1994), pp [5] M. Afzal and A. Naseer, Adsorption of Organic Acids from Aqueous Solutions on Charcoal, Pak. J. Sci. Ind. Res., 15 (1972), pp [6] M. Saleem, M. Afzal, F. Mahmood, and A. Hameed, Thermodynamics of Adsorption of Rhodamine B and the Nile Blue Sulphate on Alumina from Aqueous Solutions, J. Chem. Soc. Pak., 16 (1994), pp [7] I. Langmuir, The Adsorption of Gases on Plane Surfaces of Glass, J. Am. Chem. Soc., 40 (1918), pp The Arabian Journal for Science and Engineering, Volume 28, Number 1A. January 2003

7 [8] Fahimuddin, Ghayasuddin Khan, and Zafaruddin Khan, Thermodynamics of Adsorption of Acrylic Acid from Aqueous Solution on the Surface of Activated Charcoal, J. Sci. Res., 27 (1998), pp [9] Fahimuddin, Ghayasuddin Khan, and Zafaruddin Khan, Thermodynamics of Adsorption of Tartaric Acid from Aqueous Solution on the Surface of Activated Charcoal, J. Pure. Appl. Sci., 20 (2001), pp [10] A. Malek and S. Farooq, Kinetics of Hydrocarbon Adsorption on Activated Carbon and Silica Gel, AICHE Journal, 43 (1997), pp [11] T.G. Brunko, I.N. Ermolenko, and G.A. Lazerko, Study of Ammonia Sorption by Fibrous Carbon Sorbents, Vestsi Akad. Navuk BSSR7, Ser. Khim. Navuk, 6 (1979), pp [12] J. Hajduk, Adsorption of Ammonia on Activated Carbon. Thermodynamic Equations, Przem. Chem., 58 (1979), pp [13] A.W. Adamson, Physical Chemistry of Surfaces, 5 th edn. New York: John Wiley and Sons, 1990, 636 pp. Paper Received 3 April 2000; Revised 4 December 2000; Accepted 11 October January 2003 The Arabian Journal for Science and Engineering, Volume 28, Number 1A. 41

EQUILIBRIUM ADSORPTION OF METHANE AND CARBON DIOXIDE ON 5A MOLECULAR SIEVE

Volume3 December 2007 EQUILIBRIUM ADSORPTION OF METHANE AND CARBON DIOXIDE ON 5A MOLECULAR SIEVE Dr. Abbas Khalaf Mohammed Shua'ab Chemical Engineering Department, Baghdad University, P. O. Box 47024,