Model building in complex catalytic reaction systems. A case study: p-xylene manufacture

Abstract

Ind. Eng. Chem. process Des. Dev, lg83, 22, 135-143 135 liquid-liquid dispersion. Since equal power per unit mass results in equal drop size, this implies that a bigger impeller can be employed to produce the same final drop size faster using the same amount of energy. Conclusion 1. Unsteady-state drop size, ita distribution, and the minimum transition time required to reach steady state during the initial period of liquid-liquid dispersion have been measured by using a microphotographic technique and a light transmittance method.2. The average drop size was found to follow the exponential decay rule.3. The drop size distribution changes from a very wide (multi-modal) distribution to a narrower (normal) distribution to, finally, a very narrow (skewed or log-normal) distribution as drop size becomes smaller and smaller.4. The minimum time required to reach a steady state is very strongly dependent on impeller size and speed and on tank size. At the same power input per unit mass, a larger impeller is more efficient. Nomenclature a = interfacial area per unit volume, m-l DI = impeller diameter, m DT = tank diameter, m d = particle or droplet diameter, m ds2 = Sauter mean droplet diameter defined by eq 2, m dS2* = Sauter mean droplet diameter at steady state, m I = emergent light intensity Io = incident light intensity ml, m2 = constants used in eq 1 n = number of drops N = impeller stirring speed, rpm T = fractional light transmittance = I/&,, dimensionless AT = fluctuation in T readings, dimensionless t = time, min t, = minimum transition time required to reach steady-stateGreek Letters a, 6 = constants used in eq 4 y = constant defined in eq 5 t = rate of energy dissipation per unit mass of fluid, W/kg p = viscosity, N.s/m2 p = density, kg/m3 9 = Kolmogoroffs length scale, m u = standard deviation based on dS2, m ' $d = volume fraction of dispersed phase, dimensionless Literature Cited Coulakglou, C. A.; Tavlarides, L. L. AIChE J . 1976, 22, 289. Lee, J. M. Ph.D. Dlssertatlon, University of Kentucky, Lextngtm, KY, 1978. McCoy, B. J.; Madden, A. J. Chem. Eng. Sci. 1969, 24, 416. Narslmhan, G.; Ramkrishna, D.; Gupta, J. P. A I C M J . 1980. 2 6 , 991. Roger. W. A.; Trlce. V. G., Jr.; Rushton, J. H. Chem. Eng. Prog. 1956, 52, Ross, S. L.; V e h f f , F. H.; Curl, R. L. Ind. Eng. Chem. Fundam. 1878, 77, Ramkrishna, D. Chem. Eng. Scl. 1974, 2 9 , 987. Skelland. A. H. P.; Lee, J. M. Ind. Eng. Chem. Process Des. Dev. 1978, Skelland, A. H. P.; Lee, J. M. AIChE J . 1981, 27, 99. Sprow. F. B. A I C M J . 1967, 73, 995. Vermeulen, T.; Williams, G. M.; Langlols, 0. E. Chem. Eng. Prog. 1955, 57, drop size, min 515. 101. 77, 473. 85-F.A strategy of model building In complex catalytic reaction systems is described based on the deployment of different types of laboratory reactors and independent measurement of pore diffusion within a single-pellet diffusion cell. The approach is applied to the kinetic modeling of simultaneous isomerlzation and disproportionation of a mixture of xylenes over a commercial silica-alumina catalys...