삼상 역유동층에서 표면 개질한 폴리에틸렌 입자에 대한 수력학적 특성 연구

한 희동, 노 창현, 최 호석, 강 용

충남대학교 화학공학과

Hydrodynamics Study on the Surface-Modified-Polyethylene Particles in a Three-Phase Inverse Fluidized Bed

Hee-Dong Han, Chang-Hyun Rho, Ho-Suk Choi, Yong Kang

Dept. of Chemical Engineering, Chungnam National University,

Taejon 305-764, Korea

Introduction

Biotechnology has been greatly imporoved in the field of the immobilization of microbes on the solid substrate[1-2]. This technique is better than the immobilization of enzymes because it is stable as well as economic [3]. The immobilization of microbes allows us to constantly provide enzymes from immobilized microbes. In order to effectively apply this technique to industry, the development of suitable biocarriers is very import. The biocarriers for the immobilization of microbes are divided into two kinds: organic and inorganic material. In this study, we choose polyethylene beads as biocarriers since the polyethylene is used in various applications due to its low cost, ready availability and resistance to chemical and harsh environments. Also, the high specific modulus and strength of polyethylene make it a good candidate for acting as a reinforcing component in laminates/composites. One of the major markets for polyethylene is the packging industry where it is used directly or in the form of laminates with aluminum foil, paper, etc. [4]. However, polyethylene has a hydrophobic surface property which is not good for the immobilization of microbes. Thus, we modified the surface property of the polymer substrate from hydrophobic to hydrophilic by treating the polyethylene surface with chlorosulfonic acid. This chemical modification not only changes the hydrodynamic characteristics of particles in fluid phase but also increases the retention capacity of microbes on the solid biocarriers [5]. To effectively use the biocarriers with density lower than that of liquid for the application of wastewater treatment, the concept of inverse fluidized is needed [6-10]. Such a system can be operated with downward flow of the liquid counter to the net upward buoyancy force on the particles. The gas flow is upward, counter to the liquid flow and bed expansion can be supported by either the(downward) liquid phase, the (upward) gas bubbles, or both. In this study, we investigated the hydrodynamic characteristics of two different inverse fluidization: one is using usual polyethylene beads and the other surface-modified polyethylene beads.

Experimental

We studied the inverse fluidized reactor using aeration. In Fig. 1, the air from the bottom air distributor makes water recirculate in the bed and biocarriers fall down. In this apparatus with a transparent acrylic column of 12cm diameter and 200cm height, hydrodynamic experiments were mainly performed. Equally spaced pressure taps were mounted on the column wall from the sparger up and connected to water manometers. To prevent solid particles from entering into the pressure measurement lines, a polymeric screen was attached to the tip of each pressure tap.

We used chemically treated low density polyethylene(LDPE) beads as biocarriers. The shape of biocarriers is oblate and the average diameter is 4.4mm, thickness of 1.6mm, average density 0.920g/□; sphericity 0.45; void fraction 0.357. We used three steps for modifying the surface of polyethylene beads. First, polyethylene beads were mixed with 10mM-ferric chloride solution at 30℃ for 3hours. The pretreated beads were water washed and vacuum dried for 30min. Then, we etched polyethylene beads in chlorosulfonic acid solution [ClSO3H: CCl4=2:1(w/w)] with stirring for 4hours at room temperature. After etching, polyethylene beads were water-washed for at least 15min and vacuum-dried over 1hour.

Fig.1. Schematic diagram of the inverse fluidized reactor using aeration

(1) Column	(2) Gas-Liquid distributor
(3) Flow meter	(4) Compressor
(5) Pump	(6) Liquid Reservoir
(7) Pressure taps	(8) Weir

Results and discussion

We obtained the gas holdups of the bubble column(without solid particle) in the reactor(Fig. 1) to check the performance of the apparatus and compared the values obtained from the observation of liquid level rise with the values calculated from the pressure drop measurements (Fig. 2). Fig.3 shows good agreement between the measured and calculated values and confirms the accuracy of the manometer. The observed result was obtained from the height of bed expansion due to aeration.

The critical fluidization velocity was determined in the apparatus of Fig.1. Fig.4. shows the variations of the pressure profiles versus the superficial gas velocity and the average phase holdups in the reactor in the reactor with 20% particle loading.

Fig.2. Pressure variations with respect to position in a bubble column

Fig.3. Gas holdups at different [eqn: {U}_{G}] in a bubble column.

Fig.4. Variations of the pressure profiles versus the superficial gas velocity

References

1. Yoon, H. H., Ghim, Y. S., Chang, H. N., Kim, Y. J. and Rhee, J. S.,          "Wastewater Treatment Using a Dual Biological Reactor System,"              HWAKHAK KONGHAK, 20, 293 (1982).

2. Koh, J. S. and Chang, H. N., "Anaerobic Treatment of MSG Waste with       CSTR and Filter," HWAHAK KONGHAK, 17, 281 (1979).

3. Frieda, Dr. and Kolot, B., "Microbial Carriers Strategy for Selection,"          Process Biochemistry, Aug/Sept., 2 (1981).

4. Dibyendu, S., Bag, V., Pradeep, K. and Sukamar, M., "Etching of a            Low-density Polyethylene Film by Fuming Nitric Acid." Die Aangewandte     Makromorekulate Chemic, 249 (1997)

5. Yang, D. C., Kim, J. H. and Yoo, Y. J., "Development of Support by          Chemical Modification for the Immobilization of Activated Sludge,"            HWAHAK KONGHAK, 35, 129 (1997)

6. Bastoul, D., Roustan, M., Capdeville, B. and Audic, J. M., "Multiphase          Reactors for Biological Treatment of Urban Wastewaters," In                 Environmental Technologies and Trends, Produserv Verlagservice, Berlin,      183 (1996)

7. Lee, S. L. P. and De Lasa, H. I., "Phase Holdups in Three Phase Fluidized     Beads," AIChE., 33, 1359 (1987)

8. Nikolov, L. and Karamanev, D., "Experimental Study of the Inverse            Fluidized Bed Biofilm Reactor," Can. J. of Chem, Eng., 65, 214 (1987)

9. Roustan, M., Bastoul, D. and Capdeville, B., "Influence of the Hydrodynamic     Behavirour of a Three Phase Fluidized Bed for Effluent Treatment. 3rd,"       Int. Conf. on Bioreactor and Bioprocess Fluid Dynamics, Cambridge, UK       (1993)

10. Wild, G., Saberian, M., Schwartz, J. L. and Charpentier, J. C., "Les           racteurs lits fluidises gas-liquide-solide. Etat de l'art et perpectives           industrielles," Enrtopoe, 106, 3 (1982)