[Al Ezzi, 2(12): December, 2013] ISSN: Impact Factor: 1.852

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1 IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Effect of Addin Alcohols, Superficial Gas Velocity and Solid-Suspended on Desin Parameters in Circulation Loop Bubble Columns Ali Abdul Rahman Al Ezzi 1,2, * Ghazi Faisal Najmuldeen 1 1 Faculty of Chemical & Natural Resources Enineerin/ Universiti Malaysia Pahan 2 Department of Chemical Enineerin, University of Technoloy/ Bahdad, Iraq ali_alezy65@yahoo.com Abstract The influence of superficial as velocity and the addition of alcohols with respect to oxyen mass transfer (K La ), and as hold-up (ɛ ) in circulation loop bubble column usin three aqueous solutions of 10% concentration methanol, ethanol and isopropanol as liquids were investiated. The column was constructed usin a plexilass tube of inner diameter of 0.9m and 1.3m in heiht with drauht tube. The ratio of drauht tube diameter to the column diameter equals 0.5 and the air dispersion into the base of the drauht tubeusin a porous as distributor. The various as velocities ( ) m/sec are used and the results were compared in the case of usin water only without the addition of alcohols.the solid particles (polyethylene 3.4mm particle diameter and the density K/m 3 ) were added to the liquid in the column. The concentration of solid particles was (50) k/m 3. From experimental observations, (ɛ ) and (K La ) increase with increasin as velocity and with the coalescence inhibition of liquid. Keywords: Internal Loop Bubble Column Reactor; Three-Phase; Alcohols; Desin Parameters. Introduction Three phase internal air lift loop reactors are increasinly used in the fields of chemical and biotechnoloy as simple and effective contactors for processes involvin ases, liquids and solids. The internal loop reactor has found many applications in many industrial processes such as hydroenation, desulfurization, coal liquefaction, Fisher Tropsch synthesis etc. The simplicity of their desin and construction, hih heat and mass transfer capacity, and excellent mixin properties with low power requirements are makin them very attractive [1,2]. Several investiators have studied the hydrodynamics of three-phase internal-loop airlift reactors. Miyahara and Kawate,[3] measured the as holdup in the riser and the down comer, and the pressure drop at the upper and lower ends of the riser due to flow reversal for a solid-suspended air-lift reactor containin low-density particles Karamanev et al.,[4], used 3 mm soft polyurethane foam particles in their experiments. They found that the as holdup decreased sinificantly with increasin solids loadin and the as holdup was 1. proportional to v 2. However, most works in the literature that study the hydrodynamics in slurry reactors have been performed under conditions of low solid concentrations. These works showed that particles with typical particle sizes smaller than 100µm are uniformly suspended in both the axial and radial directions in a slurry system [5,6]. In the concentric-tube airlift bioreactor, some eometrical parameters affect as holdup, liquid circulation, mixin time and the volumetric oxyen transfer coefficient. Extensive study of reactor hydrodynamics and reactor eometry enhances the importance of the eometrical parameters in the desin and scale-up of concentrictube airlift bioreactors [7-9]. The volumetric as-liquid mass transfer coefficient, (K la ), plays an important role in the characterization of the performance of bioreactors [10-12]. A lare number of researchers, Koide et al., [13]; Chisti and Moo, [14]; Choi and Lee, [15]; Merchuk et al., [16]; Shimizu et al., [17], Zhan et al., [18]; Tonwan et al., [19] have investiated the mass transfer performance in the air lift loop reactors toether with their hydrodynamic behavior. Airlift reactors are aitated pneumatically and circulation takes place in a defined cyclic pattern throuh a loop, which divides the reactor into two zones: a flow-upward and a flow-downward zone. The as-spared zone or the riser has hiher as holdup than the relatively as-free zone, the down comer, where the flow is downward [2]. However, few studies have addressed three-phase airlift reactors with low density solids [20,21]. However, little attention has been

2 focused on the effect of alcohols additive in the hydrodynamic desin parameters in internal air lift loop reactors. The main objective of the present study is to establish whether chanes in liquid coalescin properties caused by alcohols additive can reatly affect the hydrodynamic properties of a three-phase internal loop column and to investiate the influence of the superficial as velocity and fluid properties on as holdup and mass transfer coefficient. Experimental Section A schematic diaram of the experimental setup in this work is shown in Fiures 1, 1a and 1b. A Plexilass column of 9 cm inside diameter and about 130cm total heiht with drauht tube dimensions of 4.5cm inside diameter and 90 cm total heiht was used. The top and bottom clearances were maintained constant at 5 cm. The drauht tube was fitted with three support les in the upper and the lower end of the column so as to locate it in a central position at any distance above the base. The column consists of two main sections namely, the as inlet section and the liquid recyclin testin section. The as inlet section consists of a as distributor. At the bottom of this section, two lines are connected toether before enterin the distributor section each line has a value to be opened or closed as required. One of these lines is the air inlet flow. Air compressor supplied the line with the desired amount of air needed; the amount of air was measured usin a as meter. The other line is the nitroen as inlet flow. The nitroen as was supplied from a cylinder. A ate valve was used in the nitroen flow, which must be shut off when the air was spared to the column, and must be opened durin the desorption process. The liquid testin section contains two openins, one for liquid out-flow and the other for liquid in flow. The circulation of liquid in the column was achieved usin a dosin pump placed in the recyclin line. A ball valve placed in the middle of the recyclin line was used to take various samples at various times to measure the concentration of the dissolved oxyen durin the operation. The column was filled with water and alcohols to the desired heiht above the distributor 0.7 m. Then the solid particles (polyethylene 3.4mm particle diameter and the density K/m 3 ) were added to the liquid in the column. The concentration of solid particles was 50 k/m 3.Compressed air at ( ) psi was supplied usin a reciprocatin compressor. The desired air flow rate was set-up usin ate valve and the amount measured with a as meter. The dissolved oxyen concentration in the liquid phase was measured usinoxyen meter device type a (YSI-5100), which consists of a probe metal electrode. The liquid phase (batch) consists of the followin systems (water and solid, water, alcohols and solids) the chemicals used in the present study were procured from Permula Chemicals SDN.BHD., Malaysia. The as distributor Fiure 1.c was constructed from a ceramic material and the type is multi holes tyere. Results on Gas Hold Up (ε ) and Solid Hold Up (ε s ) The averae as hold up ε was calculated from the equation (1) usinthe data of the clear - liquid heiht (H l ) and the heiht of the aerated liquid (H f ) which was determined by visual observation: ( V / S ) H f H H ε (1) F i L o ( V i / S o ) In Eq. (1) is a correction term for the volume of the draft tube [22] The solid-hold-up was calculated from the equation(2).usin the date of static liquid heiht (HF) and the heiht of slurry after addin solid particles (HF / ): H H F L ε s (2) H F The experimental as hold up was found by measurin the difference between initial liquid heiht and final liquid heiht. Since it was rather difficult to read directly the level of the aerated liquid the values of as hold up thus obtained probably involves an error of about 5%, established via repeated measurements. Fiure 3 shows the effect of as velocity for water system with and without solid particles. The variation of a as holdup in the riser (ε ) with superficial as velocity for air-alcohol-solid systems are shown in Fiure 2. The experiments were carried out with constant solids (polyethylene 3.4mm particle diameter and the density K/m 3 ) loadin of 50K/m 3 and the desired liquid heiht above the distributor (0.7) m. It was observed that the as hold-upincreased linearly with increase in as throuhput (as velocity), but interact mutually, dependin on liquid phase properties. The as hold-up of isopropanol with solid is rouhly twice that of water with solid.in the presence of alcohols, the bubbles become more riid and hence have low rise velocities resultin in a bubbly flow reime up to surprisinly hih as velocities (0.1 m/sec).this was mainly due to the suppression of bubble coalescence i.e. number of small bubbles produced in the riser had an insufficient bubble rise velocity to escape from the liquid,for aqueous solutions of aliphatic alcohols, a considerable increase in

3 the as hold-upin alcohol chain lenth was observed. The as hold up decreased in the followin order isopropanol > ethanol > methanol. The decrease in surface tension in the presence of alcohols was not sufficient to explain this phenomenon. Bubble dynamics and bubble swarm structure in the presence of surfactant solutions can explain this behavior qualitatively. A similar trend was observed by Koide et al.,[23], Nicol and Davidson [24] and Al-Masry and Dukkan[25].The solid particles retard the bubble rise velocity and prevent increases in bubble size. Mass Transfer Coefficient Results The physical absorption of oxyen in the air by the liquid was employed to determine themass transfer coefficient. A material balance of oxyen in the liquid ives: ( 1 ε ε s ) CSa Ci K La. Lo (3) t C C Rearranin equation (3) ives C Lo C Sa Sa Ci C i K ε Sa La. ( ε ) t S o (4) dispersion into the base of drauht tube usin porous distributor. Nomenclature a Specific as-liquid interfacial area based on aerated liquid volume m -1 C i Concentration of dissolved oxyen at any time p.p.m C 0 Initial Concentration of dissolved oxyen p.p.m C Sa Saturated concentration of dissolved oxyen p.p.m C S Solid particle concentration K /m 3 D C Column diameter D d Draft tube diameter D i Diffusivity of oxyen in solution m 2 /sec D L Axial dispersion coefficient (liquid) m 2 /sec Acceleration of ravity m/sec 2 H L Static slurry heiht (m) H F Level of aerated slurry (m) Level of liquid phase+ solids (m) H F K L Liquid phase mass transfer coefficient (m.s -1 ) K La Overall mass transfer coefficient, based on aerated slurry volume. (Sec-1) t Time (min) Gas velocity (m/sec) V Plottin the left hand side of equation (4) with (t), the averae slope of the plot will ive the term K ε ε the values of (ε ) and (ε s ) were La ( ) s determined as mentioned in (1) and (2) respectively, then (k La ) can be calculated. Fiure 3 shows that the mass transfer coefficients increase with increasin as velocity. The axial dispersion coefficients (D L ) increase with increasin as velocity and therefore increase (K La ). On account of the stron coalescence inhibition the volumetric mass transfer coefficient in (waterisopropanol+ solid) system reach double the values as in (water- solid). For aqueous solutions of aliphatic alcohols with solid, (Ethanol, Methanol), the presence of solid particles retards the bubble rise velocity and prevent increases in bubble size, so that the mass transfer coefficients are larer than that in (water-solid). Conclusions For the present study the followin conclusions were made: The as hold-up and mass transfer coefficient increase with increasin as velocityforv 0.1 m/sec and decrease with increasin liquid surface tension in an air lift loop reactor in the presence of alcohol and suspended solid particles(polyethylene)and the ratio of drauht tube diameter to the column diameter equals 0.5 and the air Greek symbol ε Gas hold up ε s Solid hold up ρ L Liquid phase density k/m 3 ρ S Solid phase density k/m 3 µ L Liquid phase viscosity(c p ) ν L Kinematic viscosity of liquid phase (cm 2 /sec) Liquid phase surface tension dyn/cm σ L Subscripts G as L liquid Reference [1] Wei, Yu.W.,Malin, T.L. and Zhanwen, W. (2008). Bubble circulation reimes in a multi-stae internalloop airlift reactor. Chemical Enineerin Journal.142: [2] Chisti, M.Y. (1989). Airlift Bioreactors. Elsevier, New York. [3] Miyahara, T. and Kawate, O. (1993).Chem. En. Sci. 48: [4] Karamanev, D. G., Naamune, T. and Endo, I. (1992).Chemical Enineerin Science. 47 :

4 [5] Wilhelm, R.H. and Kwauk, M. (1948). Fluidization of solid particles.chemical Enineerin Proress.44: [6] Yan, G.Q., Du, B., Fan, L.S., (2007). Bubble formation and dynamics in as liquid solid fluidization: a review. Chemical Enineerin Science.62: [7] Gavrilescu, M. and Tudose, R.Z. (1998a). Concentric-tube Airlift Bioreactors. Part I: Effects of eometry on Gas Holdup. Bioprocess Enineerin.19: [8] Gavrilescu, M. and Tudose, R.Z. (1998b). Concentric-tube Airlift Bioreactors. Part II: Effects of eometry on Liquid Circulation. Bioprocess Enineerin.19: [9] Gavrilescu, M. and Tudose, R.Z. (1998c). Concentric-tube Airlift Bioreactors. Part III: Effects of eometry on Mass Transfer. Bioprocess Enineerin.19: [10] Blenke, H., Loop Reactors. (1979).In: Ghose T.K., Fiechte A. and BlackebrouhN., Advances inbiochemical Enineerin, vol. 13, Spriner Berlin Heidelber New York, pp , [11] Blenke, H. Biochemical Loop Reactors. (1985). Biotechnoloy.2: [12] Youn, M. M. and Blanch, H.W. (1981). Advances in Biochemical Enineerin.19:1 69. [13] Koide, K., Hiroyuki, S. and Shinji, I. (1983a). Gas holdup and volumetric liquid phase mass transfer coefficient in bubble column with drauht tube and with as dispersion into annulus.journal of Chemical Enineerin of Japan.16(5): [14]Chisti, M. Y., and Moo-Youn, M.(1988). Hydrodynamics and oxyen transfer in pneumatic devices. Biotechnoloy & Bioenineerin.31: [15] Choi, K.H., and W.K. Lee, (1993). Circulation liquid velocity, as holdup and volumetric oxyen transfer coefficient in external-loop airlift reactors. Journal of Chemical Technoloy and Biotechnoloy.56: [16] Merchuk, J.C., Ladwa N., Cameron A., Bulmer M., and Pickett A. (1994). Concentric-Tube Airlift Reactors: Effects of Geometrical Desin on Performance. AIChE Journal. 40(7): [17] Shimizu, K., Takada, S., Takahashi, T., and Kawase, Y. (2001). Phenomenoloical simulation model for as holdups andvolumetric mass transfer coefficients in external-loop airlift reactors. Chemical Enineerin Journal.84: [18] Zhan, T., Wan, T., and Wan, J. (2006). Analysis and measurement of mass transfer in airlift loop reactors. Chinese Journal of Chemical Enineerin.14.(5): [19] Tonwan, Z., Zhao, B. and Wan, J. (2006). Mathematical models for macro-scale mass transfer in airlift loop reactors. Chemical Enineerin Journal.119: [20] Kawase, Y., Hashimoto, N. (1996). Gas holdup and oxyen transfer in three-phase external-loop airlift bioreactors: non-newtonian fermentation broths. Journal of Chemical Technoloy and Biotechnoloy.65 : [21] Tun, H. L., Chan, Y. Y., Hwan, T.-K. and Wu, W. T. (1998). liquid mixin and mass transfer in a modified bubble column with suspended particles. Journal of the Chinese Institute of Chemical Enineers.29 : [22] Koide, K., Katsumi, K., Shinji, I., Yutaka, I. and Kazuyoshi, H. (1983b). Gas holdup and volumetric liquid-phase mass transfer coefficient in bubble column with drauht tube and with as dispersion into tube.journal of Chemical Enineerin of Japan.16(5): [23] Koide, K., Horibe, K., Kawabata, H., and Ito, S. (1985). Journal of Chemical Enineerin of Japan.18 (3): [24] Nicol, R.S. and Davidson J.F. (1988). Chemical Enineerin Research and Desin.66: [25] Al-Masry, W.A., and Dukkan A.R. (1997). Chemical Enineerin Journal. 65: Galindez-Mayer, J., Sanchez-Teja, O., Christiani- Urbina, E. and Ruiz-Ordaz, N A Novel Splitcylinder Airlift Reactor for Fed-batch Cultures. Bioprocess and Biosystems Enineerin. 24:

5 Table1. physical-properties for pure liquids at T20 o c ρ density K/m µ CP σ dyn/cm ν Lcm 2 /sec Water Methanol Ethanol Iso-propanol Table 2. physical properties for mixtures used with various concentration at T20 o C ρ ensityk/m µ CP σ dyn/cm ν Lcm 2 /sec Water-Methanol 10% Water-Ethanol 10% Water-isopropanol 10%

6 [Al Ezzi, 2(12): December, 2013] ISSN: (a) (b) (c) Fi.1. (a) Experimental-Apparatus; (b) Column and (c) Gas distributor.

7 [Al Ezzi, 2(12): December, 2013] ISSN: Fi.2.Gas hold-up versus as velocities for various systems. Fi.3.Mass Transfer Coefficient vs. Gas Velocity for Various Systems.