CHAPTER 4: EXPERIMENTAL
4.1.2. Batch absorber for the R-22-methanol kinetic study
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Figure 4-12. The valve panel: front view and back view
4.1.2.2. Reactor vessel
The reactor apparatus is shown in Figure 4-13. The reactor vessel consisted of a long cylindrical unit surrounded by a glass jacket. A drainage valve at the bottom of the reactor allowed for ease of cleaning. Water was pumped through the jacket at reaction temperature. The reactor unit was mounted on a tripod stand, thereby supplying the operator access to the drainage valve. Support was supplemented by situating the reactor within a confinement structure. A thick slab of board was screwed onto one side of a wire mesh cage. The reactor was placed within a square hole cut into the structure.
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Figure 4-13. Reactor apparatus
The reactor top flange was manufactured with four necks, although the original design specified five necks. By attaching a forked neck to a single neck on the reactor top flange, both the temperature probe and the reflux condenser were accommodated for. The three other necks were utilized for the gas sparger, a liquid sample point and an overhead stirrer. The cooling coil, fabricated from ¼” glass tubing, was permanently attached through the reactor top flange for ease of assembly. The purpose of the cooling coil was to maintain the reactor temperature because of the highly exothermic nature of the reaction. The double-jacketed reflux condenser was manufactured from glass. The double jacket provided a greater surface area for increased cooling. The condenser
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refluxed methanol carried out with the product gas. Loss of methanol would alter the conditions within the reactor because methanol is the sole source of the methoxide anion, CH3O- (Hine and Porter, 1957). The flanges were greased with silicone gel to maintain an airtight vessel. A metal clamp sealed the flanges of the reactor and the reactor top tight.
An overhead mechanical stirrer was used to provide more efficient mixing of the reactor contents.
The stirrer comprised a glass rod attached to an overhead stirrer motor, with a Teflon paddle of length 50 mm. To achieve the appropriate height above the reactor, the stirrer motor was mounted onto a thick metal rod supported by angled leg stands. The gas sparger was a glass rod with a sintered disc at the lower end.
4.1.2.3. Reactor temperature control system
Both reactions considered in this work are exothermic resulting in a combined reactor heat duty of 545 W, as determined by the summaric product of the reaction rate and the heat of reaction for each reaction, respectively. The details of this calculation are explained in Appendix A. Continuous cooling was therefore required to maintain the correct reaction temperature. The glass reactor was equipped with an internal glass cooling coil for this purpose. A portion of the study required experiments to be carried out at above ambient temperatures. The glass reactor was therefore also equipped with a heating jacket. Input from a 200 mm long Pt 100 temperature detector was passed to an RKC microprocessor based digital temperature controller with a supply voltage of 100-240 V AC. The Pt 100 had a probe diameter of 8 mm and was attached to a 3 m 3-core Teflon insulated cable. The two outputs of the temperature controller were equipped with two control actions:
heating and cooling. Output 1 and Output 2 provided a heating and cooling action respectively.
Both outputs were contact relays. The PID parameters were tuned for ideal temperature control (Section 4.2.). Two solenoid valves were placed on the cooling line (as demonstrated in Figure 4- 14) such that flow would be alternated between the cooling coil and the bypass line returning to the source. ½” normally closed stainless steel solenoid valves were used with pressure limitations ranging between 0-9 bar. During actual experiments, the heating and cooling media passing through the jacket and coil, respectively, were used in conjunction to maintain the set point temperature. The heating medium passed continuously through the jacket. When cooling was required the solenoid valve on the cooling line leading to the coil was opened allowing cooling of the reaction mixture.
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When the cooling cycle was over, the solenoid valve on the bypass line was opened. Hot water was used as the heating medium. Ethanol was used as the cooling medium.
To cooling coil
Bypass line returning to cold fluid source
Line leaving cold fluid source V-001
V-002 Temperature controller
Figure 4-14. Schematic of temperature control system
Figure 4-15. Solenoid valves and vacuum degassing manifold
Solenoid valves Vacuum
degassing manifold
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4.1.2.4. Vacuum degassing rig
Vacuum degassing is a process that preceded the analysis of samples withdrawn from the reactor vessel. The reactions occurring in the reactor vessel do not cease once the withdrawn samples are decanted into the volumetric flasks for storage (prior to analysis). To stop the reactions, the reactant gas (R-22) was removed from the samples by means of vacuum degassing. The degassing rig was constructed in the ethanol bath that fed cold fluid to the cooling coils (Figure 4-16). A metal rod was secured across the width of the bath. Four clamps were attached to the rod using boss heads. A Polyflow tubing line connected the vacuum pump to the central connection point on the manifold in Figure 4-15. The manifold had four other connection points: at the top, bottom, top right and bottom right. All five connection points on the manifold had push-in fittings at the ends. Four ¼” round handle Swagelok needle valves were attached to the manifold at the connection points. In this way, each connection point could be opened or closed independent of the other points. The Polyflow lines leaving the push-in fittings were fitted into rubber bungs on the opposite end. An annular space was created in the rubber bung for this purpose. The rubber bungs were sized to fit the necks of the 50 cm3 volumetric flasks used to store the samples.
Figure 4-16. Ethanol bath used for the degassing process
Figure 4-17 shows the process and instrumentation diagram for the experimental setup using the batch absorber.
s
V-001
V-002
V-003 V-004
V-005
Figure 4-17. Process and instrumentation diagram of the kinetic study for the selective production of
Author: Rasmika Prithipal Drawing no. 003
V-006
V-007
To vent
To vent
T-001 T-002
Cold fluid in
Cold fluid out
Cold fluid inlet from ethanol bath
Cold fluid bypass to ethanol bath
Cold fluid outlet to ethanol bath
Hot fluid inlet from water bath
Hot fluid outlet to water bath
R-001
HX-001
CT-001 CT-002
V-008
difluorodimethyl ether from R-22 in a jacketed glass reactor
Date: 21 November 2012
CT-001-002
R-001 Semi-batch reactor
T-001 Cylinder bottles
V-001-004 Two-way valves
V-005, V-008 Three-way valves V-006, V-007 Solenoid valves
Cold traps
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