A study was made of the rate of decomposition of diacetone alcohol by anion exchange resins in a packed bed under adiabatic and isothermal conditions. Two different resins were compared: a conventional type gel structure resin, Amberlite IRA-400, and a newly marketed maorore-ticular resin, Amberlyst A-26.
In a substrate with low water content, the rate of decomposition of diacetone alcohol by Amberlite IRA-400 vas controlled by intraparticle diffusion. This vas due to shrinkage of the polymer chain matrix of the resin. When dry diacetone alcohol feed was introduced the amount of decomposition was not measurable.
It was found that the macroreticular type resin, Amberlyst A-26 was considerably more effective as a catalyst due to its porous structure. Decreasing the water content of the feed actually increased the rate of decomposition. Amberlyst A-26 effectively catalyzed the decomposition of dry diacetone alcohol. Intraparticle diffusion does not control the rate of decomposition over the range of variables studied.
The equilibrium concentration at 25°C for this reaction,using the Amberlyst resin, was determined by extrapolating to zero space velocity the concentration of acetone in the effluent. The value obtained was 88.95 weight per cent acetone. This is in reasonable agreement with the value reported by Davis and Burrows (6) of 88.27%, who conducted the decomposition reaction at 25°C in an agitated batch system using barium hydroxide as a catalytic agent. A value of the equilibrium constant of K = 18.65 was calculated from the Amberlyst equilibrium concentration data at 25°C.
An attempt was made to develop a mathematical model for the flow reaction in a packed bed, using the simplifying assumption that a single step controlled the overall rate. Equations have been derived for the following cases:
- First order kinetic control unidirectional.
- Bidirectional first order kinetic control.
- Bidirectional reaction, first order for the decomposition and second order for the formation of diacetone alcohol.
- Film diffusion control.
- Intraparticle diffusion control.
It was found that none of the above reaction mechanisms involving diffusion and reaction kinetics could be reduced to a linear or non linear form and solved with the data obtained using Amberlyst A-26 at 25°C over the entire range of variable studied. Therefore, the simplifying assumption that a single step controls the overall rate does not seem to apply for the system studied.
The effect of film diffusion vas studied by varying the superficial velocity while maintaining all other variables constant. The differences in superficial velocity did not affect the conversions obtained using Amberlyst A-26. It was concluded that film diffusion to and from the bulk of the fluid did not influence the rate of decomposition of diacetone alcohol for superficial velocities in the range of 0.001 to 0.014 feet per second. This study, as veil as the entire investigation, was conducted in the laminar flow region of low Reynolds Numbers.
The first order kinetic equation for the unidirection reaction will fit the experimental data for conversions below 85W. Above 85% conversion, the effect of the reverse reaction becomes apparent. The rate constant for the decomposition of diacetone alcohol by Amberlyst A-26 resin at 25°C was calculated and found to be k = 0.0194 sec.-1 which compares favorably with a value of k = 0.0205 sec.-1 reported by Akerlof (1) using 0.1N KOH for first order kinetics at the same temperature of 25°C. Basinski and Narebeka (2) reported a value of k a 0.000535 sec.-1 for the decomposition reaction at 25°C using Amberlite IRA-400 in a batch system with an ethanol-water substrate.
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