130 Figure A.5: Left – calibration plot of a precision rotameter for hexafluoropropene gas used for the falling film microreactor experimental setup. 131 Figure A.6: Left – calibration plot of a precision rotameter for hexafluoropropene oxide gas used for the falling film microreactor experimental setup.
Previous work
Background and importance of topic
By structuring the fluid flow in microchannels, high specific interface areas of up to 20,000 m2/m3 can be achieved in FFMRs (Al-Rawashdeh et al., 2008). This has been found to be remarkably greater than currently used gas-liquid contactors (Zhang et al., 2009).
Aims and objectives
Outline of thesis
The model development includes the generation of a reaction model based on fundamental equations in chapter 2 as well as an overview of the function of the kinetic models. The appendices provide additional information such as instrument and analytical calibrations, raw data, sample calculations, MATLAB script files, and chemical toxicology data sheets.
Organofluorine chemistry
Organofluorine synthesis techniques
Hydrofluorocarbons are another important organofluorine that gained great importance when the Montreal Protocol imposed restrictions on the use of CFCs. Tetrafluoroethylene is synthesized by pyrolysis of chlorodifluoromethane in the reaction steps shown in Figure 2.3.
Partially fluorinated dialkyl ethers
The reaction products II and III then form the alkyl tetrafluoropropionate IV in the presence of water. 2004) found, however, that the selectivity towards II was high with a yield of the reaction products III and IV not exceeding more than 5% in all experiments (Il'in et al., 2004). Defluorination of I leads to an alkenyl ether III and in the presence of water II and III forms an alkyltetrafluoropropionate IV (Il'in et al., 2004).
Trifluorovinyl ethers
Fritz et al., (1963) proposed an alternative way to synthesize perfluorinated vinyl ethers by reacting an acid fluoride with hexafluoropropene oxide to produce an etherified acid fluoride according to the reaction scheme shown in Figure 2.6. Lousenberg and Shoichet (1997) adopted the reaction procedure proposed by Fritz et al., (1963) to produce partially fluorinated trifluorovinyl ethers.
Experimental equipment
Conversely, the simplicity of the batch reactor is at the same time its greatest disadvantage (Froment et al., 1990, Nauman, 2008). This involves the immediate mixing of the contents of the reactor with the new liquid entering the vessel (Bird et al., 2007).
Experimental design
The central design points can then be described as a set of experimental conditions at level 0 of the design variable. From Equation 2.9, the experimental conditions of the axial design points can be calculated by substituting - and + into Equation 2.10.
Kinetic modelling
The next step in the kinetic model formulation is a description of the reaction chemistry of the system. Where, 𝑟𝑖 is the reaction rate of species 𝑖, 𝐶𝑖 represents the concentration of species 𝑖 and 𝑘 is the kinetic rate constant of the reaction (Nauman, 2008).
Response surface methodology
Minimization of the objective function occurs when the magnitudes of the kinetic parameters are varied. The response function indicated in Equation 2.54 can be visually interpreted as the response surface of the k-th dimension (a hypersurface).
Preliminary investigations
All samples were prepared with an average percentage uncertainty of 0.33% on the concentration of the potassium methoxide raw material. To guarantee this, the temperature in the two baths was set 1 hour before running an experiment. The first step in each experiment was to ensure that the liquid content in the reactor was at the desired reaction temperature.
Falling film microreactor equipment validation
The authors of these studies chose to observe the absorption and subsequent reaction of carbon dioxide in sodium hydroxide solution to produce sodium carbonate. The resulting liquid containing absorbed carbon dioxide is transferred to a beaker containing 0.1 mol∙L-1 sodium hydroxide solution. The absorbed carbon dioxide then reacts with the available sodium hydroxide to produce sodium carbonate.
Present work: falling film microreactor experiments
Gases were fed to the base of the reactor to operate it in countercurrent mode, i.e. flooding of the reactor guaranteed that the reaction plate had a completely wetted surface maximizing the interfacial contact area between the gas and liquid phases. Once the flow rates of the gas were set, valve D was opened, thereby directing the reactant gas to the reactor.
Quantitative analysis using gas chromatography
The selected standard can also be one of the peaks already in the injected sample (McNair and Miller, 2011). Once determined The proportionality constants 𝑘𝐴 and 𝑘𝐼𝑆 indicate the sensitivity of the analyte and the internal standard to the detector respectively.
Calibrations
Analytical techniques
I is the 50 ml final volume of the bubble flowmeter while II indicates the position of the bubble front. As with most standardization techniques; the accuracy of the technique is only as good as the calibration used so an accurate calibration increases the reliability of the results (Raal and Mühlbauer, 1998). This procedure was repeated three times to improve the accuracy and consistency of the calibration.
Model overview
The constrained optimizer then passed the kinetic parameter guesses to a reactor model, which was responsible for calculating the hydrodynamic and thermophysical properties of the system. The grid size is an input to the momentum balance, which calculates the steady-state velocity profile in the reactor's microchannel. Surface response methodology allowed the visual triangulation of the set of input parameters resulting in the global minimum of the summed relative squared error.
Reaction model
Therefore, the concentration of the mediator is very low, but limited, and the net rate of change of concentration is zero. To navigate this problem, a commonly accepted approach is to use the quasi-steady-state approximation to express the concentration of an active site, in this case, the reaction intermediate (Roberts, 2009). Thus, there is a limited concentration of intermediate at any time to allow the formation of HME and methyl 1,2,3,3,3-pentafluoro-1-methoxyprop-1-ene (according to reactions 2 and 3).
Initial and Boundary conditions
Finally, in the z-direction all species except potassium methoxide were assumed to have zero concentration at the top of the microchannel. Potassium methoxide concentration at the top of the microchannel is equal to that of the raw material. Potassium methoxide concentration at the top of the microchannel is equal to that of the raw material as with the HME system.
Variables of interest
At time zero, the only species present in the fully wetted microchannel were potassium methoxide ions equal to the catalyst concentration in the feedstock, all other species were defined as zero. Similarly, a no-slip condition was imposed for the y direction at the boundary at the bottom of the reactor channel. Due to the use of the quasi-steady state approximation, the rate of reaction 2 was equivalent to that of reaction 1 (Figure 4.4, Section 4.3.2).
Preliminary investigations: Semi-batch gas-liquid stirred tank reactor
The yields of the by-products were also quantified and the yields of alkenyl ethers were found to vary between 0.07 and 1.03%, while alkyl tetrafluoropropionate varied from 2.42 to 5.10%. When analyzing the effect of the reaction conditions on the yield of HME, it was found that the yield was favored at higher reaction temperatures, high hexafluoropropene concentrations, and low to moderate potassium hydroxide concentrations. Higher concentrations of hexafluoropropene allowed more of the limiting reactant to be available for conversion to the desired product.
Falling film microreactor equipment validation
From Figure 5.1 it can be seen that the experimentally determined mass transfer coefficient is up to three times greater than that predicted by the penetration model as well as the experimental and model results presented by Zhang et al., (2009). The increased mass transfer observed may be due to an increase in the specific interfacial areas of the installed apparatus resulting from the formation of ripples on the surface of each microchannel. The larger mass transfer coefficients observed in the experimental setup do not hinder mass transfer and in fact improve the yield of reactions.
Falling film microreactor experiments
The solid would then accumulate on the reaction plate and in the fluid flow lines, causing blockages and reducing the efficiency of the microstructured reaction plate (Photo 5.1). 30 experiments were performed on FFMR for the synthesis of MTFMP, where the yield of the target compound was found to vary from zero to 23.62%. In order to improve the yield and concentration of MTFMP in the product stream, the residence time of the liquid in the reactor can be increased.
Kinetic models
The reaction mechanism shown in Figure 4.3 (Section 4.3.1) was developed to incorporate the presence of side products into the model. Plots of corresponding parity, residual deviation, and absolute relative deviation are shown for each species in the system. The average percent absolute relative deviation of the model was found to be 34.12%, which is slightly worse than the simplified HME kinetic model presented in Section 5.4.1 B .
Conclusions
There were 4 reaction variables of interest in the FFMR experiments and these were the mole fraction of hexafluoropropene in the feed, the concentration of potassium hydroxide, the reaction temperature and the liquid flow rate. The range investigated for these parameters was between 0.17 and 0.61 mol∙L-1, 2.0 to 22.0 0C and 0.50 to 5.50 mL∙min-1 for the hexafluoropropene mole fraction in the gas feed, the concentration of potassium hydroxide and the liquid flow temperature, the reaction temperature respectively. There were 4 reaction variables of interest in the MTFMP system and these were the mole fraction of hexafluoropropene oxide in the feed, the concentration of potassium hydroxide, the reaction temperature and the liquid flow rate.
Recommendations
Where 𝑢𝑖 is the standard uncertainty, σ is the standard deviation of replicate data points and 𝑁𝑟𝑝 is the number of replicate data points. The uncertainty of the overall calibration was then calculated by finding the square root of the sum of squares, i.e. we know that the mass balance used to measure these masses has a standard uncertainty of ± 0.001 g, a partial uncertainty of 𝑚𝑎 and 𝑚𝑏 is obtained by dividing the standard uncertainty by the measurement value.
HME system
Henry’s law constants regression
Kinetic model files
Methoxide - the initial condition is that the concentration at the inlet is the concentration everywhere u0(:,[(ny+1):(2*ny)],:) = cMeth0;. B - initial condition is zero everywhere (Alkenyl Ether) %KF - initial condition is zero everywhere. Inlet conditions determining the concentration of all 7 species at all points in the reactor channel.
MTFMP system
Henry’s law constants regression
Kinetic model files
Response surface methodology files
Momentum Balance
Main file
Function file
