Primary Model Validation

To validate the reactive distillation model without experimental data, Smith's MTBE column was simulated for the case described in his patent application (Smith, 1980) using both Pro/II and SpeedUp. The numbers of rectification, reaction and stripping stages were based on previous estimates (Abufares and Douglas, 1995). The model described by equations (3.12)-(3.27) and (3.29-3.52) has three degrees of freedom (excluding the feed definition and the mass of catalyst on each reactive stage): the column pressure and two product specifications. Where uncertainty exists in the system inputs, the choice of product specifications can significantly affect the results but an appropriate combination of specifications (e.g. one external flow rate and one internal flow rate) can minimise the effect of the uncertainty. In this case, the bottoms flow rate (determined implicitly from the patent results) and the reflux ratio (given explicitly in the patent application) were specified. Table 3.3 compares the simulation results, obtained with both Pro/II and SpeedUp using the equation structure and physical property routines described above, with the limited experimental data from the patent application.

Table 3.3 - Simulation Results and Experimental Data for Smith's MTBE Column

Property

Pro/II

SpeedUp

Experimental

Condenser Temperature (°C)

61.0

64.6

n/a

Reaction Zone Temperature (°C)

69.0

70 1

71

Reboiler Temperature (°C)

128.0

125 7

127

Isobutene Conversion (mol%)

91.6

91.6

91

Bottoms MTBE Purity (mol%)

92.2

92.6

91.9

DIB Bottoms Concentration (mol%)

1.2

0.9

6.1

Condenser Duty (kW)

2.14

1.99

n/a

Reboiler Duty (kW)

2.32

2.16

n/a

The agreement between Pro/II, SpeedUp and the experimental results is generally excellent, especially for the key indicators of bottoms temperature, isobutene conversion and MTBE purity. The most significant discrepancy between the experimental data and the simulation models is the estimate of DIB concentration in the bottoms product. However, both sets of simulation results presented here predict DIB concentrations of around 1% which is also in agreement with previously published simulation results (Abufares and Douglas, 1995), suggesting an alternative explanation for the values reported for the experimental system.

The acceptable accuracy of the MTBE simulations demonstrates the adequacy of the modeling process and validates its extension to ETBE reactive distillation columns where the column configuration, operating conditions and phase behaviour are similar. Subsequently, there is a high degree of confidence in the ETBE simulation results presented here.

Was this article helpful?

0 0

Post a comment