ABSTRACT/SUMMARYFor tubular reactor model BP 101-B, we carried out two experiments. In the first experiment, we have examined the effect of pulse input in a tubular flow reactor and we have constructed a residence time distribution (RTD) function for the tubular flow reactor. In this experiment the deionised water are let to continue flowing through the reactor until the inlet and outlet conductivity values are stable at low levels. We need to maintain flow rate of deionized water at approximately 700mL/min. Then, the salt solution is let to flow for 1 minute. Both the inlet and outlet conductivity values at the regular intervals of 30 seconds are recorded. In the second experiment, our aims are to examine the effect of step change in tubular flow reactor and we have constructed a residence time distribution (RTD) function for the tubular flow reactor. Only the deionized water is allowed to continue flowing until the inlet and outlet conductivity values are stable at low levels. We continued record the conductivity values until all readings are almost constant. Graphs of conductivity versus time and RTD function versus time were plotted and analyse for both pulse input and step change input. From the RTD function calculated, the mean residence time (tm), variance (2) and skewness (s3) values were calculated using appropriate numerical method for both experiment which gives the value of 1.9713min, 0.3662min2 and 0.2123min3 respectively for pulse input and 1.7788min, 1.236785min2 and 1.7371min3 respectively for step change input.

INTRODUCTIONTubular reactors of BP101-B are often used when continuous operation is required but without back mixing of products and reactants. It is one of three reactor types which are interchangeable on the Reactor Service Unit. Reactions are monitored by conductivity probe as the conductivity of the solution changes with conversion of the reactants to products. The unit is small in scale for ease of operation but capable of demonstrating the principles of industrial reactor behaviour. The unit includes a 10 litres reactor vessel as a water jacket, and is equipped with a variable speed stirrer, inlet and outlet ports for the feed and product streams, sampling, conductivity measurements and temperature measurements and control. A cooling coil and immersion heater are provided inside the vessel to provide constant reaction temperature. The desired reaction temperature is achieved by controlling the heating using a digital temperature controller located on the front panel.Two non-corroding feed storage vessels are supplied, together with chemically resistant pumps and flow meters. A product collection vessel is also provided and if necessary, the products are neutralised before discharging to the laboratory drains. The tubular reactor is a coil of long tubing wound around a cylinder inside the vessel to give a total reactor volume of approximately 0.4 litres. The spiral design is practically the best approximation to plug flow conditions, as the secondary flow ensures good radial mixing while minimising longitudinal dispersion. Two reactants are pre-heated prior to mixing and entering the reactorIn the tubular reactor, the reactants are continually consumed as they flow down the length of the reactor. Flow in tubular reactor can be laminar, as with viscous fluids in small-diameter tubes, and greatly deviate from ideal plug-flow behaviour, or turbulent, as with gases. Turbulent flow generally is preferred to laminar flow, because mixing and heat transfer are improved. For slow reactions and especially in small laboratory and pilot-plant reactors, establishing turbulent flow can result in conveniently long reactors or may require unacceptable high feed rates.However, many tubular reactors that are used to carry out a reaction do not fully conform to this idealized flow concept. In an ideal plug flow reactor, a pulse of tracer injected at the inlet would not undergo any dispersion as it passed through the reactor and would appear as a pulse at the outlet. The degree of dispersion that occurs in a real reactor can be assessed by following the concentration of tracer versus time at the exit. This procedure is called the stimulus-response technique. The nature of the tracer peak gives an indication of the non-ideal that would be characteristic of the reactor.For most chemical reactions, it is impossible for the reaction to proceed to 100% completion. The rate of reaction decreases as the percent completion increases until the point where the system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs). The equilibrium point for most systems is less than 100% complete. For this reason a separation process, such asdistillation, often follows a chemical reactor in order to separate any remaining reagents or by products from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in theHaber process.Tubular flow reactors are usually used for this application which are:1. Large scale reactions1. Fast reactions1. Homogeneous or heterogeneous reactions1. Continuous production1. High temperature reactions

Residence Time Distribution (RTD) analysis is a very efficient diagnosis tool that can be used to inspect the malfunction of chemical reactors. It can also be very useful in modelling reactor behaviour and in the estimation of effluent properties. This technique is, thus, also extremely important in teaching reaction engineering, in particular when the non-ideal reactors become the issue. The work involves determining RTDs, both by impulse and step tracer injection techniques, and applying them to the modelling of the reactor flow and to the estimation of the behaviour of a nonlinear chemical transformation. The RTD technique has also been used for the experimental characterization of flow pattern of a packed bed and a tubular reactor that exhibit, respectively, axially dispersed plug flow and laminar flow patterns (FEUP).The concept of using a tracer species to measure the mixing characteristics is not limited to chemical reactors. In the area of pharmacokinetics, the time course of renal excretion of species originating from intravenous injections in many ways resembles the input of a pulse of tracer into a chemical reactor. Normally, a radioactive labelled (2H, 14C, 32P, etc.) version of a drug is used to follow the pharmacokinetics of the drug in animals and human. Another important field of RTD applications lies in the prediction of the real reactor performance, since the known project equations for ideal reactor are no longer valid. Now the concepts of macro and micro mixing are fundamental. For each macro mixing level, expressed in the form of a specific RTD, there is a given micro mixing level, which lies between two limiting cases, complete segregation and perfect micro mixing.

Residence time distribution factorThe Residence time distribution factor (RTD) of a reactor is a characteristic of the mixing that occurs in the chemical reactor. In a plug flow reactor, there is no axial mixing. Thus the omission is reflected in the RTD exhibited by the reactors. OBJECTIVESEXPERIMENT 1:To examine the effects of a pulse input in a tubular flow reactorTo construct a residence time distribution (RTD) function for the tubular flow reactor. EXPERIMENT 2:To examine the effects of a step change input in a tubular flow reactorTo construct a residence time distribution (RTD) function for the tubular flow reactor.

THEORY

In a pulse input, for a short time as possible, an amount of tracer, No is suddenly injected in one shot into the feed stream entering the reactor. The euent concentration-time curve is referred to as the C curve in the RTD analysis. If we select an increment of time t suciently small that the concentration of tracer, C(t), exiting between time t and t + t is essentially constant, then the amount of tracer material, N, leaving the reactor between time t and t + t is where, v is the euent volumetric ow rate.

= C (t) t

And now divide it by the actual amount of material that was injected into the reactor, N, we obtain new equation for a pulse injection,

E(t) = Rewriting the above equation in the differential form,dN= C(t)vdtAfter integrating, we obtain:No = = constant, soE(t) = The integral in the denominator is the area under the C(t) curve.However, for a step input, it consider a constant rate at tracer addition to a fed that is initiated at time, t = 0. Thus,C (t) = 0t < 0C (t) = Ct 0If input [ ] from a vessel is related to the input concentration by the convolution integral.Cout (t) = This is because, the C is constant with time. Thus,

Dividing by yields, = For a laminar flow reactor, by using a similar analysis as shown above, we obtain the complete RTD function for a laminar flow reactor as:

The variance is defined as,2 = 2 =

APPARATUS SOLTEQ Tubular Reactor (Model: BP 101-B), Conical flask, Stopwatch, Calibration meter, Sodium hydroxide, NaOH (0.1M) Sodium Acetate, Na(Ac) (0.1M) Deionised water, H2O

PROCEDURE EXPERIMENT 1:Pulse Input in a Tubular Flow Reactor1. The general start-up procedures were performed.2. Valve V9 was opened and pump P1 was switched on.3. Pump P1 flow controller was adjusted to give a constant flow rate of deionised water into the reactor R1 at approximately 700 ml/min at F1-01.4. The deionized water was let to continue flowing through the reactor until the inlet (Q1-01) and outlet (Q1-02) conductivity values were stable at low levels. Both conductivity values were recorded. 5. Valve V9 was closed and the pump P1 was switched off.6. Valve V11 was opened and the pump P2 was switched on. The timer was started simultaneously.7. Pump P2 flow controller was adjusted to give a constant flow rate of salt solution into the reactor R1 at 700 ml/min at F1-02.8. The salt solution was let to flow for 1 minutes, the timer is reset and restarted. The time was started at the average pulse input.9. Valve V11 was closed and pump P2 was switched off. Then, valve V9 was opened quickly and the pump P1 was switched on. 10. The deionised water flow rate was maintained at 700 ml/min by adjusting the P1 flow controller.11. Both the inlet (Q1-01) and outlet (Q1-02) conductivity values were recorded at regular intervals of 30 seconds.12. The conductivity values were recorded continuously until all readings were almost constant and stable low level values approached.

EXPERIMENT 2:Step Change Input in a Tubular Flow Reactor1. The general start-up procedures were performed.2. Valve V9 was opened and pump P1 was switched on.3. Pump P1 flow controller was adjusted to give a constant flow rate of deionised water into the reactor R1 at approximately 700 ml/min at F1-01.4. The deionized water was let to continue flowing through the reactor until the inlet (Q1-01) and outlet (Q1-02) conductivity values were stable at low levels. Both conductivity values were recorded. 5. Valve V9 was closed and the pump P1 was switched off.6. Valve V11 was opened and the pump P2 was switched on. The timer was started simultaneously.7. Both the inlet (Q1-01) and outlet (Q1-02) conductivity values were recorded at regular intervals of 30 seconds.8. The conductivity values were recorded continuously until all readings were almost constant and stable low level values approached

RESULTSExperiment 1:Pulse Input in a Tubular Flow ReactorFlow rate:700 ml/minInput type:Salt solutionTime (min)Conductivity (mS/cm)

InletOutlet

0.00.00.0

0.50.40.1

1.00.20.1

1.50.11.3

2.00.11.9

2.50.10.8

3.00.10.3

3.50.10.1

4.00.10.1

Time (min)Conductivity (mS/cm)E(t)t E(t)(t - tm)2 E(t)(t - tm)3 E(t)

InletOutlet

0.00.00.00.00000.00000.00000.0000

0.50.40.10.04320.02160.0935-0.1376

1.00.20.10.04320.04320.0408-0.0396

1.50.11.30.56110.84170.1246-0.0587

2.00.11.90.82011.64026.76 x 10-41.94 x 10-5

2.50.10.80.34530.86330.09650.0510

3.00.10.30.12950.38850.13700.1410

3.50.10.10.04320.15120.10100.1543

4.00.10.10.04320.17280.17780.3606

Summation, 2.02884.12250.7718760.4710194

Graph of Outlet Graph of Conductivity Vs Time for Pulse Input

Graph of E(t) Vs Time (min) for Pulse Input

Experiment 2:Step Change Input in a Tubular Flow ReactorFlow rate:700 ml/minInput type:Salt solutionTime (min)Conductivity (mS/cm)

InletOutlet

0.02.00.0

0.52.60.1

1.02.70.1

1.52.70.0

2.02.70.1

2.52.61.2

3.02.51.7

3.52.51.7

4.02.41.7

Time(min)Conductivity(mS/cm)E(t)t E(t)(t - tm)2 E(t)(t - tm)3 E(t)

InletOutlet

0.00.00.00.00000.00000.00000.0000

0.52.60.10.01920.00960.0314-0.0402

1.02.70.10.01850.01850.0112-0.00874

1.52.70.00.00000.00000.00000.0000

2.02.70.10.01850.03649.05 10-40.0002

2.52.61.20.23080.57700.12000.0866

3.02.51.70.34001.02000.50710.6192

3.52.51.70.34001.19001.00731.7337

4.02.41.70.35421.41681.74753.8816

Summation, 1.32124.26833.42456.27236

Graph of Conductivity (mS/cm) Vs Time (min) for Step Change Input

Graph of E(t) Vs Time (min) for Step Change Input

SAMPLE CALCULATIONSPulse Input

mSmin/cm

At time = 0.5, C (t) = 0.1; min-1

Mean residence time, At t = 0.5, = 0.5 0.0432 = 0.0216

Second moment, Variance, 2= At t = 0.5min,(t - tm)2 E(t) = (0.5-1.9713)2 (0.0432) = 0.0935 min

= 0.2464

2 = 0.2464 + 0.1198 = 0.3662 min2

Third moment, Skewness, s3 = At t = 0.5min,(t - tm)3 E(t) = (0.5-1.9713)3 (0.0432) = -0.1376

0.18647S3 = ( 0.2123 min3

Step Change Input

At t = 0.5min;

min-1

Mean residence time, At t = 0.5, = 0.5 0.0192 = 0.0096

Second moment, Variance, 2= At t = 0.5min,(t - tm)2 E(t) = (0.5-1.7788)2 (0.0432) = 0.0935 min0.0248175

2 = 0.0248175 + 1.2119675 = 1.236785 min2

Third moment, Skewness, s3 = At t = 0.5min,(t - tm)3 E(t) = (0.5-1.7788)3 (0.0185) = -0.0402

S3 = (min3

DISCUSSIONSBy doing this experiment, we are able to examine the effect of pulse input in a tubular flow reactor. At the end of the experiment, we are also able to construct a residence time distribution (RTD) function for the tubular flow reactor. The experiment was run at flow rate of 700 mL/min. The conductivity for the inlet and outlet was recorded from time equal to t0=0 until them both reaching a constant value for itself. In the end, the conductivity we get for the inlet is 0.1 mS/cm and meanwhile for the outlet conductivity is also 0.1 mS/cm.For the pulse input experiment, the highest outlet conductivity was recorded at 2 minutes with 1.9 mS/cm. The conductivity started at zero at continues to increase until the second minute before it started to decrease and finally become constant of 0.1 mS/cm at time of 4 minutes. However, for step change experiment, the conductivity increases without decreasing its value until its finally constant at the time of 3 minutes with the value of 1.7 mS/cm. This explains the above theory of pulse input being a batch reactor and step change as continuous reactor. The residence time distribution we get in the end is 1.3212 minutes.From the result obtain, there are 2 graphs that needed to be plot. There are graph of conductivity against time and graph of distribution of exit times, E(t) against time. Variance is defined as the average value of the quantity (distance from mean)2. Based on the RTD values calculated for both pulse input and step change experiment, mean residence time, tm, can be calculate by integration. The value of tm for pulse input is 1.9713 min while for step change is 1.7788 min. Variance, 2, is defined as the average value of the quantity while skewness, s3, is a measure of the asymmetry of the probability distribution of a real-valued random variable. The value of 2 in the pulse input and step change experiment are 0.3662 and 1.236785 min2 respectively. The reason for the square is to avoid the value is negative. However, the s3 for both experiment are 0.2123 and 1.7371 min3 respectively. The value could be positive or negative or even undefined. Qualitatively, a negative skew indicates that the tail on the left side of the probability density function is longer than the right side and the bulk of the value lie to the right of the mean. A positive skew indicates that the tail on the right side is longer than the left side and the bulk of the values lie to the left of the mean. A zero value indicates that the values are relatively even distributed on both sides of the mean, typically but not necessarily implying a symmetric distribution.

Figure of Graph of negative skewness and positive skewness

CONCLUSIONSAs the conclusion, the objective to examine the effect of pulse input in the tubular reactor is achieved. It also can be conclude that the E(t) is depends on the vessel outlet conductivity. The time that we get when its reaching the zero value which is at 4 minutes show that our experiment is succeed as its seem similar to the theoretical and lastly we also managed to construct a residence time distribution (RTD). Where for pulse input, the value for tm, 2 and s3 are 1.9713, 0.3662 and 0.2123 respectively. The outlet conductivity at 2 mins is 1.9. However, for step change input, the value for tm, 2 and s3 are 1.7788, 1.236785 and 1.7371 respectively. The conductivity value at 4 minute is 1.7 mS/cm. Compared with the theoretical graph, the pattern of graph is same.

RECOMMENDATIONSAfter we have finished this experiment, we find that there are several factors in this experiment that can be fixed to make sure that the experiments runs better. Below is some of the recommendation for this experiment runs better. 1. Open valve fully to ensure constant value.2. Conduct values for three times to get accurate value.3. Always check and rectify any leak at the reactor.4. Make sure the conductivity of the inlet and outlet stable before start the experiment.5. The flow rate must be kept constant.

REFERENCES1. Tubular Flow Reactor Model: BP101, SOLTEQ.2. Nabil, Abdullah et. al, Isothermal Laminar-Flow Reactor, 1999.3. H. Scott Fogler, Elements of Chemical Reaction Engineering, 4th Edition, Pearson Education International, 2006.4. Marie Curie, Fogler_ECRE_CDROM.book, Distributions of Residence Times for Chemical Reactors5. Robert H.Perry, Don W.Green, Perrys Chemical Engineers Handbook, McGraw Hill, 1998.

APPENDICES