Batch Reactor Design Questions and Answers

Answer: A

Correct answer: accumulation equalling generation

A batch reactor is closed, so nothing flows in or out and both flow terms vanish from the general balance. What remains is that whatever the reaction generates accumulates inside: \[ \frac{\mathrm{d}N_i}{\mathrm{d}t} = r_iV. \] The composition therefore changes with time rather than with position, which is what distinguishes a batch reactor from every flow reactor.

Answer: B

Both are true and the reason gives the advantage: concentration against time in a well mixed batch vessel is exactly what an integrated rate law predicts. No flow terms complicate the analysis. Concentration against time is what is measured.

Answer: C

Integrating the reciprocal rate from zero to the required conversion gives the reaction time. The second option is the space time of a flow reactor, which is a quite different quantity. The integral is often evaluated numerically.

Answer: D

The time is the natural logarithm of ten divided by the rate constant, and the logarithm of ten is about two point three. Ninety per cent conversion always takes about three point three half lives. The relation holds only for first order.

Answer: A

The first two are correct. The third is wrong, since a steady flow reactor has no accumulation term and its design equation takes a quite different form. Time is what the batch equation delivers. A flow reactor gives a volume instead.

Answer: B

Correct answer: charging, heating, cooling and cleaning

The reaction time is only the part of the cycle in which chemistry is happening. Around it sit charging, heating to temperature, cooling, discharging and cleaning, and the sum of all of them is the cycle time - which is what determines how many batches a vessel produces in a year and therefore what it is worth.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the arithmetic. In many batch plants the reaction occupies a smaller share of the cycle than the operations around it, so halving the reaction time might gain a fifth of the cycle while shortening the heat-up or the cleaning could gain as much for less effort. The right question is always which part of the cycle is the longest, not which part is the most interesting.

Answer: D

The cycle is five hours, so twenty-four divided by five is four point eight batches. Throughput depends on the whole cycle rather than on the reaction alone, which is the point the calculation makes. Cycle time is what fixes daily output.

Answer: A

The productive part is only one of the four, and the others are what a plant improvement programme usually attacks first. Overlapping them where possible is how throughput is raised. Only one of the four is productive.

Answer: B

Correct answer: 2 - 4 - 1 - 3

The order is fixed by the operation: charge the reactants, bring them to temperature, hold for the reaction time, then cool, discharge and clean ready for the next batch. Everything except the third step is dead time, which is precisely what the previous items are about.