Transcript
DEPARTMENT OF CHEMICAL ENGINEERING
FACULTY OF ENGINEERING, ARCHITECTURE AND SCIENCE
Course Number
CHE 415
Course Title
Unit Operation Laboratory II
Semester/Year
Fall 2012
Instructor
Dr. Ginette Turcotte
Teaching Assistants
Nicholas Jones
Lab Report for
Experiment No.
1
Report Title
Fluidization
Section No.
02
Group No.
02
Submission Date
October 23, 2011
Due Date
October 23, 2011
Students’ Name
Student ID
Signature*
Leader:
Data Recorder:
Safety Officer:
(Note: remove the first 4 digits from your student ID)
*By signing above you attest that you have contributed to this submission and confirm that all work you have contributed to this submission is your own work. Any suspicion of copying or plagiarism in this work will result in an investigation of Academic Misconduct and may result in a “0” on the work, an “F” in the course, or possibly more severe penalties, as well as a Disciplinary Notice on your academic record under the Student Code of Academic Conduct, which can be found online at: www.ryerson.ca/senate/current/pol60.pdf.
CHE 415 Lab Report Marking Scheme – Fall 2011
Marking Scheme
Formatting General Appearance; Grammar and Spelling / 5
Complete and Informative Tables and Graphs / 15
Contents Calculation of Accuracy and of Precision of Results / 20
Comparison with Literature Data (expected results) / 10
Discussion on Influence of Procedural Design on Results / 10
Analysis and Conclusion / 30
Sample Calculations / 10
_____ Total: / 100
Note 1: The original (raw) data sheets must be included as an appendix in the laboratory report. If a report does not contain the signed raw data sheet, it results in the automatic deduction of 20 marks from the total mark for that report.
Note 2: The original Information Gathering form must be included as an appendix in the laboratory report. If a report does not contain the signed and filled Information Gathering form, it results in the automatic deduction of 10 marks from the total mark for that report.
Note 3: Any report that does not contain sample calculations will result in the automatic deduction of 20 marks of the total marks for that report.
Contents
Objective 4
Theory 4
Procedure 8
Result and Discussion 10
Error Analysis 12
Conclusion and Recommendation 13
Reference 14
Appendix 15
Figure 1: Armfield CEM MkII Continuous Stirred Tank Reactor 7
Figure 2: Conductivity Reading of CSTR solution vs. Time of Experiment 11
Table 1: Experimental Data 18
Objective:
The objective of this experiment is to determine the rate constant and conversion of the saponification reaction between 0.1M Sodium Hydroxide (NaOH) and 0.1M Ethyl Acetate (C4H8O2) in the Armfield CEM MkII Continuous Stirred Tank Reactor (CSTR).
Theory:
The experiment requires finding the rate constant value and conversion values of the reaction in the CSTR with the help of the conductivity probe. The reaction in this experiment will be as follows:
NaOH + C4H8O2 ? C2H3NaO2 (Sodium Acetate) + C2H5OH (Ethyl alcohol) (1)
The conductivity is read from the solution’s charged molecules. In this experiment, only NaOH and C2H3NaO2 will be capable of creating a conductive reading. NaOH has a much higher degree of conductivity than C2H3NaO2. As a result, the consumption of NaOH will be the reference used to determine the reaction variables according to the conductivity readings. This relationship with the conductivity readings will be modeled as seen below:
(2)
Where,
al = concentration of NaOH at time t,
a? = concentration of NaOH at end of reaction,
ao = initial concentration of NaOH in reactor vessel,
?o = initial conductivity of solution, and
?? = solution conductivity at the end of reaction.
Since the conductivity contribution due to NaOH is different from the contribution due to C2H3NaO2, ?? must be determined for each experiment.
From the Armfield CEM MkII Continuous Stirred Tank Reactor Instructions Manual, the equations shown below to transform conductivity values into concentrations:
(3) (4)
(5) (6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
Where, Fa = feed flow rate of NaOH,
Fb = feed flow rate of ethyl acetate, C4H8O2,
aµ = concentration of NaOH in feed vessel,
bo = initial concentration of C4H8O2 in reactor vessel,
bµ = concentration of C4H8O2 in feed vessel,
c? = concentration of C2H3NaO2 at end of reaction,
?c ? = conductivity of C2H3NaO2 at end of reaction,
?a o = conductivity of NaOH in reactor vessel at time zero,
Xa = conversion of NaOH, and
Xc = conversion of C2H3NaO2.
It must be verified that the concentration of NaOH at any instant “t” in the CSTR reactor is:
(18)
Or:
(19)
Where, k = rate of reaction,
F = total feed flow rate of all reactants, and
V = volume of reaction solution.
Schematic diagram:
Figure 1: Armfield CEM MkII Continuous Stirred Tank Reactor
Procedure:
The Pump was calibrated with distilled water.
Sodium Hydroxide reactant solution was prepared by placing 20g sodium hydroxide pellets into 5L and H2O
CSTR power was turned on.
The cooling water circulation pump was prepared and the temperature was set to 30C.
Reactant pumps was set to 40mL/mi and mixing motor to 7.
Feed pump and mixer was switched for mixture to react.
Conductivity was recorded every minute as for data recording purposes.
When the volume in reactor became 1L, the pumps and mixer were stopped.
Then mixture and the un-reacted solutions were disposed in container which is for chemical disposals.
Safety Concerns:
Ethyl acetate spillage:
Let everyone know about the area that leak happen.
Remove anything which could ignite fire.
Protective equipment should be worn.
Collect the liquid in a container that can withstand which has inert material and dispose it in chemical disposal container.
Stay away from flushing any of the chemicals.
Sodium hydroxide spillage:
Let everyone know about the area that leak happen.
Remove anything which could ignite fire.
Protective equipment should be worn.
Collect the liquid in a container that can withstand which will not generate dust.
Stay away from flushing any of the chemicals.
If these solutions come in contact with skin, some measures need to be taken care of. For inhalation, get fresh air right away. In case of ingestion, vomiting should not be encouraged. Nothing should be fed and calling a physician would be the best solution. In case of skin contact, the exposed skin should be watered for at least 15 minutes. Any contaminated clothes and shoes should be removed. In case of eye contact, eyes should be watered for at least 15 minutes. All these steps should be done till medical help arrives.
Results and Discussion:
As mentioned earlier, the objective of this experiment was to determine the rate constant and conversion of the saponification reaction between 0.1M Sodium Hydroxide (NaOH) and 0.1M Ethyl Acetate (C4H8O2). The conversion of the saponification reaction was calculated to be about 1.536. The data obtained from the experiment gave the reaction rate constant “k” a value of 0.3744 L/mol-min. Both these values may have been inaccurate, especially the conversion value, due to several factors which will be discussed later in the error analysis section. The reactants involved were first order. As mentioned earlier, the overall reaction was also first order.
As seen in the figure below, the conductivity started rising after approximately 7 minutes. At this point, the temperatures were rising as well. At the beginning time span of 0-7 minutes, there was no change in the conductivity reading because the CTSR drainage valve was left open. This affected the conductivity readings. This shall also be discussed later in the error analysis. Prior to the increase in conductivity, the temperature reading was about 34.7oC. Once the CSTR drainage valve was closed, the conductivity readings went through a fluctuating period until about 15 minutes. The temperature readings went through a similar phase as well. From the time span of 15-25 minutes, the conductivity reading increased until the 18 minutes and after, the conductivity readings stabilized. It was the same case for the temperature readings as well. The time span of the conductivity stability was important for the calculations that were required to achieve the objectives.
Figure 2: Conductivity Reading of CSTR solution vs. Time of Experiment
Error Analysis:
There were many errors that were carried out during the experiment. The temperature was fluctuating because it was set to 30 oC but because the auto button was not pressed, the temperature kept rising. Therefore, initial temperatures were not constant which resulted in acquiring inaccurate data for this experiment. The temperatures fluctuated between 25 oC and 40 oC. As a result, the reactor was stopped, so that the temperature could reach the desired set temperature of 30 oC. However, the desired temperature was changed to 35 oC because there was not enough time to wait for the temperature to return to 30 oC.
The drain valve of the CSTR was open at the beginning which resulted in unchanged conductivity. Due to the previous errors, there was also loss of reactants. So, a new batch of reactants was prepared and poured in to the reactor. As a result, this addition may have led to obtaining inaccurate data.
The water pump had a leak. It was flooding the station. So, the reactor was stopped. However, the reaction could not be stopped. Also, no data was recorded during this time. So, there were lapses during the experiment where no values were recorded.
The readings taken during this experiment were not accurate. Since, it was not possible to write down all values at the same time, the accuracy of the data was definitely off. Height was difficult to measure because of the reactor design and lack of time. Since there was rapid change in conductivity, the values were hard to record.
Conclusion and Recommendations:
As indicated earlier, the objective of this experiment was to determine the rate constant and conversion of the saponification reaction between 0.1M Sodium Hydroxide (NaOH) and 0.1M Ethyl Acetate (C4H8O2). The calculated reaction rate constant value of 0.3744 L/mol-min was not an accurate value due to several factors. Therefore, it was not a successful experiment. Also, due to the temperature fluctuation, the graphical trend was not accurate. The graph was inconsistant for the entire experiment, except the last 10 minutes.
Therefore, in order to have better and more accurate results, the error factors discussed in the previous section need to be avoided. These errors can be avoided by taking precautions. For example, checking if there are any leakages or not, making sure that the reactor drain valve is closed, before beginning the experiment. If a mistake occurs, the experiment should be started again with another 1 L batch of the reactants. Therefore, if the reactants run out during the experiment, there won’t be a lapse in conductivity measurements and a stop in the supply of reactants. Finally, the temperature should be kept at a constant temperature throughout the entire experiment.
If all these factors of recommendations are kept in mind, then the CSTR experiment will have a higher chance of resulting in a more accurate reaction rate constant value.
References:
CEX Chemical Reactors Teaching Equipment. Hampshire: Armfield Limited, 2006.
Turcotte, G. CHE425 Unit Operations II Laboratory Manual. Toronto: Ryerson University, 2012.
Appendix:
Sample Calculations
Mass of reactants needed:
For a 0.1 M solution of NaOH and a volume of 5 L
Mass required =
Mass of NaOH used =20.757 g
For a 0.1M solution of Ethyl Acetate and a volume of 5L:
Mass required =
Mass of Ethyl Acetate used = 45.797 g
Experimental rate constant:
This experiment was attempted to be maintained at 30 oC, but due to experimental errors, it fluctuated in the range of 26-44 degrees Celsius, using an average range of 35 oC.
a represents NaOH and b represents Ethyl Acetate
Flow rates of the reactants:
Concentration of reactants in the feed vessel:
The initial concentrations of the reactants are:
c? = =
Note: only charged molecules affect conductivity, for this experiment it will only be sodium hydroxide and sodium acetate.
The conductivity of Sodium acetate at the end of reaction is and conductivity of the solution at the beginning of reaction is.
At 308 K
c?= 5.451*10-3 S
= 0.01226 S
? = (-) = 0
??=c?+=5.451*10-3 + 0.01226=0.01771 S
The concentration of NaOH at a time t can be found using this formula
assuming at time =9 minutes the conductivity is 1.80 mS= 0.0018
M
Diameter of the column is 15 cm and height of the solution is 130 mm = 13 cm
= 2.296 L
Raw data
Table 1: Experimental Data
Time (minutes)
Conductivity (mS)
Height of solution (mm)
Temperature (oC)
0
0.09
0
26.7
1
0.09
0
27.3
2
0.09
10.0
27.7
3
0.09
15
28.7
4
0.09
15
29.4
5
0.09
60
30.4
6
0.09
65
29.8
7
0.09
75
31.1
8
0.69
100
34.7
9
1.80
130
40.3
10
3.16
300
44.0
11
2.54
200
39.8
12
2.64
210
41.2
13
2.72
220
40.5
14
2.42
300
39.7
15
2.36
310
39.5
16
2.47
330
38.6
17
2.50
340
37.7
18
2.64
340
37.5
19
2.64
340
39.2
20
2.65
340
38.5
21
2.63
330
37.5
22
2.68
340
37.6
23
2.65
340
37.8
24
2.65
330
37.7
25
2.63
330
37.3
