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Q1         A reactor train of a 6 m3 CSTR followed by a 4 m3 CSTR is used to convert 3600L/hr of reactant A as a
1.8 mol/L solution in toluene. The solid catalyst (1000 GBP/kg) is continuously fed by a screw feeder into the reactor. The reaction rate is given by:

The kinetics are not temperature dependent, and the reaction is operated at 40℃. The physical system properties of the solution are the same as those of toluene.

• (a) Determine the minimal catalyst feed rate in kg/hr for a 95% conversion of A.

10 marks

• (b) A new, more stable catalyst has been discovered, priced at 3000 GBP/kg.

Is there a catalyst cost saving if a single plug flow reactor is used instead of the two CSTR’s?

10 marks

Remember.

• Provide your rationale, not just equations.
Look at the MCQ answer documents for inspiration

for instance:

• The question number & letter that you are answering (e.g. Q2a)
• Summarise the situation, and your approach
• Draw a picture that captures your understanding of the process
• list assumptions, derivation steps,
• supporting figures, tables
• Explain variables, if not commonly used in Levenspiel/the handout/the question

• Press ‘Alt+=’ to insert a formula, and within the equation field, Q_p^2 gives :

 A, B solution           Cat dispersion 5g/L
 Outlet

Q2         The RTR reactor (https://www.amt.uk/coflore-rtr), consists of a rotating tube, with internal baffles and agitation. Each compartment between two baffles has a 1/2-inch inlet. The flow in the reactor traverses from the inlet (left) through each of the compartments (the space between two baffles). The agitation ensures good mixing in between two baffles, so the 140L reactor may be treated as 10 equal-sized CSTR in series.

A pharma company wants to use this equipment for a homogeneously catalysed coupling reaction. The raw material solution is fed to the first (most left) compartment at 11 L/min containing [A]=0.85 mole/L and [B]=4 mole/. The catalysed reaction follows the reaction equation below:

Here,  represents the free sites on the catalyst, and  are catalytic intermediates and the concentrations of the catalytic species are in gr/L. The concentrations [A] and [B] are in mol/L. To allow temperature equilibration of the reactant feed, the 12.5 g/L catalyst feed solution is charged to the second compartment with a flowrate of 200 mL/min.

1. Develop the rate equation for A and B in and work out the parameters for the observed reaction rate  at initial conditions:

Note: the molecular weight of Cat, CatA and CatAB are considered to be the same
[10 marks]

1. Calculate the conversion of A, assuming
[10 marks]

Q3         Residence time experiments in the 140 L RTR reactor described in Q2 have been conducted and demonstrate that the system does not quite behave as 10 CSTRs in series (see table Q3).
In the experiment, a small volume of tracer was added quickly via the catalyst feed in compartment 2. The main feed flowrate of clean solvent into compartment 1 was set at 11 L/min. The outlet concentration of the reactor was measured and is given in the table below.

1. Assuming each compartment has the same fill level evaluate the overall fill-ratio of the reactor
Note: fill-ratio is defined as the total liquid volume/empty reactor volume
[5 marks]
2. Calculate the dispersion, expressed as the equivalent number of tanks, for the whole reactor
(all 10 compartments combined)
[5 marks]
3. Calculate the conversion of A, assuming  and the process
(i.e. flowrates, concentrations) as described in Q2 (note  is the Heaviside function)
[10 marks]

Table Q3: measured tracer concentration at the outlet.

 t (min) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 C (g/L) 0 0 0 0 0.02 0.07 0.2 0.4 0.8 1.6 1.5 1.1 0.8 0.3 0.11 0.04 0

Q4         The chemistry department proposes a liquid phase batch hydrogenation reaction of Chloronitrobenzene to aniline at 6 bar absolute and 50 °C using a 50/50 mixture of Hydrogen and  and a micro porous spherical catalyst:

The reaction is irreversible with the rate equation given by:

The only available vessel on the plant is a tall vessel of 1 m diameter and is equipped with a 0.8 m diameter fixed speed agitator (100 rpm, Agitator Power Number Po=5). The proposed gas flow is
24 m3/min. You observed that the bubbles tend to rise up in the vessel, without much recirculation, and mixing experiments show that the recirculation time in the vessel is about 11 s.

Using the data provided in table 4.1:

• (a) Starting with the process scheme for this system, evaluate the overall mass transfer resistance and use it to predict the volume fraction of Hydrogen in the outlet (at initial conditions)

10 marks

• (a) How long do you estimate it will take to convert 95% of the Nitrobenzene at plant scale?

10 marks

 Table 4.1: process data for Q4 Mw density Content gr/mole Solvent 5 60 900 ChloroNitroBenzene 1200 kg 158 900 ChloroAniline 0 kg 128 900 Catalyst 60 kg – 1800 Catalyst Particle Diameter 50 200 2.00E-9 L-S Mass transfer: = 12 Hydrogen Hydrogen/CO2 Flow rate 24 Henry Coefficient: 86000 G-L Mass transfer with  the reaction mass volume and  the agitator power input and  is the superficial gas velocity

Q5         Lab trials show catalytic wet air oxidation of bisphenol A (BPA) in water follows a zero-order reaction rate with respect to BPA:

With the liquid oxygen concentration at the catalyst surface, ,  in .

This process is typically operated in a trickle bed reactor, where the BPA solution and a stream of air flow down over cylindrical, non-porous, catalyst pellets. The liquid film over the solid area is thin, and the oxygen essentially diffuses through the film from the gas liquid interface to the solid surface where it reacts. The Oxygen Flux through the film is then based on Fickian diffusion:

With the  concentrations at the two interfaces of the film given in .

Your boss hopes to reach 95% conversion in a 1  trickle bed reactor of a 12.5 L/min feed containing  solution of BPA in water. The trickle bed operates at 200  and 1.5 Bar (absolute). The air is sparged in to the reactor at 75 L/min (at reactor P,T, 21% oxygen). Assume the reactor’s gas phase oxygen concentration to be constant and the same as in the feed

1. Identify the mass transfer resistances and evaluate the
overall oxygen mass transfer resistance in seconds
[10 marks]
2. Work out the weight of the catalyst for a 75% conversion of BPA assuming the mass transfer resistance 100 s.
[10 marks]

The Henry coefficient:
The bulk density of the catalyst is 1250  and the interfacial solid area is .

The gas side MT coefficient (multiplied by the Henry coefficient) .
The diffusion constant  for oxygen is

The liquid film thickness on the catalyst is

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