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We present an experiment offered as a course for undergraduate students at our Faculty. During the laboratory classes, students synthesized 20% MnO /Al O catalyst, which is then used in the catalytic reaction—the propionic acid ketonization leading to wt 2 2 3 3-pentanone. The reaction is carried out in a flow system, in the presence of a solid catalyst bed, in the range of temperatures from 573 to 673 K. Students also perform thermodynamic calculations regarding the reaction. They estimate Gibbs free energy, then calculate equilibrium constant and the conversion of substrate—propionic acid. . . . . Keywords Chemical education Laboratory experiment Fixed-bed flow reactor Ketonization reaction Catalysis Introduction the presence of catalyst was introduced later and its first in- dustrial application was the preparation of acetone . For the Presented laboratory experiment consists of three main parts: last two decades it has aroused great interest due to biomass catalyst synthesis (MnO /Al O —solid oxide catalyst), cata- processing . 2 2 3 lytic reaction (ketonization of propionic acid) and thermody- Depending on the substrate different ketones are obtained: namic calculations (estimation of propionic acid conversion). The experiment complements the lecture and calculation ex- & symmetrical ketones (if only one acid is used as sub- ercises in chemical technology. strate—Eg. 1), Ketonization reaction is a classical method of ketones syn- & unsymmetrical ketones (if two various carboxylic acids thesis (Eq. 1)—carboxylic acids undergo transformation into are used—cross ketonization—Eq. 2)[6, 7], ketone, carbon dioxide and water . This method of ketones’ & cyclic ketones (dicarboxylic acids as substrates— synthesis raises a legitimate interest as it is a one step reaction, cycloketonization—Eq. 3). no solvents are needed, and solid catalyst is used. It is an example of green chemistry process. The preparation of cyclopentanone in this way does not present any particular difficulties, unlike the preparation of other cyclic ketones. One must be aware that dicarboxylic acids are solids, which posses high melting points (> 373 K). It makes difficult to introduce them to the flow reac- ð1Þ tor. Hence, their esters can be used instead of the dicarboxylic acids—Eq. 4 [9, 10]. The ketonization reaction has been known since the mid- nineteenth century [2, 3]—at that time, it was a pyrolysis of metallic salts of carboxylic acids (no catalyst). Ketonization in ð2Þ * Urszula Ulkowska email@example.com Chair of Chemical Technology, Faculty of Chemistry, Warsaw University of Technology (WUT), Noakowskiego 3, ð3Þ 00-664 Warsaw, Poland 88 J Flow Chem (2021) 11:87–90 Reagents. Al O (Degussa C, S =103 m /g, grain di- 2 3 BET ameter 0.5–1.0 mm), Mn(NO ) ·4H O(Fluka, >97%), 3 2 2 propionic acid (BDH, b.p. 141 °C, purified by distillation). ð4Þ Catalyst preparation (20% MnO /Al O ). Aluminium ox- wt 2 2 3 ide was calcined at 873 K in a muffle furnance during 5 h. After cooling down, 1 g of Al O was impregnated with a water 2 3 Ketonization is catalyzed by metal oxides and zeo- solution of manganese (II) nitrate (0.722 g Mn(NO ) ·4H O, 3 2 2 lites . Among metal oxides, ones the most active 1.6 cm H O). As prepared pre-catalyst was dried at 353 K are: CeO ,MnO ,La O . 2 2 2 3 during 1 h. Then it was poured into the flow reactor (the same Thermodynamics is an immanent feature of catalysis; in order in which the reaction would be performed; internal diameter: to make students aware of this, we introduced elements of ther- 10 mm, height: 265 mm), where it was calcined in stream of air modynamics to the exercise. In this part of the exercise, the at 723Kduring3h. students’ goal is to perform thermodynamic calculations and Catalytic reaction was performed in the flow reactor (men- check if the reaction they are dealing with is thermodynamically tioned above) at temperatures between 573 and 673 K. The favored. To achieve this goal, students use the group contribution substrate stream was fed continuously, LHSV = 3 cm /(g·h). method—the van Krevelen and Chermin method. This method is The reaction mixture was cooled in a condenser and collected. used for estimating Gibbs free energy values of formation of the Three samples were taken at three temperatures: 573, 623, and compounds . Knowledge (even superficial) of such methods 673 K. Before each sample was taken, the foreruns were col- seems to be important mainly due to the fact that not all thermo- lected (first—during 45 min, the last two—10 min). dynamic data (for all chemical reactions) are available in the Collection time for analytical samples—10 min. literature. Details concerning the method can be found in the Analytics. Samples were titrated with 0.0100 M KOH in supplementary materials (Student handout). the presence of phenolphthalein as indicator. This allowed to The presented experiment is a part of a technological block determine the amount of propionic acid which did not undergo carried out in the same semester - lecture, exercises and labora- ketonization reaction. At the lowest reaction temperature tory (all these are obligatory for all students at our Faculty). Most (573 K), propionic anhydride can be formed (Eq. 5). During often it is the first meeting of students with a flow reactor in a the titration it hydrolyzes. It is possible to measure the amount laboratory (at earlier stages, students work rather with batch or of the anhydride—the titration should be conducted not till the semibatch reactors). Students are already substantively (also first color of the solution, but till the constant color of solution computationally) prepared to work with the flow reactor. (1 min without the discoloration). During the experiment, the basic issues related to the het- erogeneous catalysis and the use of flow reactors are discussed. Pedagogical goals are as follows: ð5Þ & Students will be able to prepare a solid catalyst using dry impregnation method. & Students will be able to conduct the catalytic reaction in flow conditions in a laboratory scale (in a flow reactor Results and discussion with catalyst fixed bed). & Students will be able to determine the effect of reaction Students carried out a ketonization reaction of propionic acid. temperature on substrate conversion. The products of this reaction are 3-pentanone, carbon dioxide, & Students will be able to apply van Krevelen and Chermin and water: procedure for thermodynamic calculations. & Students will be able to compare the results of thermody- namic calculations with the values obtained in a real experiment. ð6Þ In Table 1 you can find: Experimental & the Gibbs free energy values estimated using the van Krevelen and Chermin method, The experiment is planned for 3 students. It takes & and the reaction equilibrium constant, and 2 days, 6 h each. Details are given in Instructor notes & conversion rates of propionic acid calculated on their basis. and Students Handout. J Flow Chem (2021) 11:87–90 89 Table 1 Estimated Gibbs free energy (ΔG ), equilibrium constant (K) In Table 2 we present the conversion of propionic acid and propionic acid conversion (α) in the function of temperature. P = values obtained by students. The experiment was planned in 0.1 MPa such a way that the students measured only the degree of T[K] ΔG [kJ/mol] K α [%] substrate conversion (substrate loss). They did not check the yield of 3-pentanone. At the lowest temperature (573 K), they 573 −16.576 32.44 95.3 found the conversion of propionic acid far away from 623 −24.237 107.7 97.3 estimated—even around 20%, in comparison to theoretical 673 −31.625 284.9 98.3 value—95.3% (Table 1). The results obtained by students vary (especially at 573 K). This is most likely due to lack of labolatory skills (setting and maintaing the right temperature seem particularly tricky). The reaction rate is strongly dependent on the temperature. Slight The values of Gibbs free energy are negative in the range of variations at lower temperatures result in large differences in temperatures taken into the account in calculations. As the substrate conversion. Therefore, at higher temperatures, such reaction temperature increases, ΔG decreases and the conver- a difference is not so visible—the reaction rate is so high that sion of the substrate increases. Estimated conversion values small temperature differences do not have such an impact on are all above 95%. The maximum estimated conversion value the substrate conversion. is 98.3% in 673 K. At the highest temperature, the experimental values of con- vection are close to the calculated values. The calculated values are only estimates, and are therefore in some cases lower than the experimental values. Table 2 Sample results obtained by students (years 2016–2019). Catalytic ketonization of propionic acid over 20% MnO /Al O , gas 2 2 3 phase reaction, flow reactor with solid catalyst bed. LHSV = 3 cm / (g·h). The influence of temperature on substrate conversion Conclusions Students group no. T [K] α [%] Students T[K] α [%] group no. The described laboratory experiment allows students to famil- 1 573 64.0 9 573 19.6 iarize themselves with the methods of organic synthesis under 623 89.3 623 98.4 flowing conditions and compliant with the principles of green 673 97.3 673 99.2 chemistry. Students also perform thermodynamic calculations 2 573 37.5 10 573 40.6 related to the studied reaction. The reaction is thermodynam- 623 97.7 623 79.7 ically favored. The calculation results are confirmed by the results obtained in the laboratory. 673 99.4 673 98.6 3 573 60.3 11 573 42.1 623 94.5 623 78.9 673 99.3 673 98.0 Supplementary Information The online version contains supplementary 4 573 57.5 12 573 75.0 material available at https://doi.org/10.1007/s41981-021-00149-2. 623 95.0 623 80.8 Acknowledgements This work was financially supported by the Warsaw 673 99.4 673 99.0 University of Technology. 5 573 37.8 13 573 45.3 623 83.8 623 83.1 Declarations 673 98.6 673 98.0 6 573 56.3 14 573 92.6 Conflict of interest On behalf of all authors, the corresponding author 623 79.9 623 97.7 states that there is no conflict of interest. 673 97.2 673 99.2 7 573 64.3 15 573 27.5 Open Access This article is licensed under a Creative Commons 623 88.1 623 98.4 Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long as 673 97.9 673 99.2 you give appropriate credit to the original author(s) and the source, pro- 8 573 48.9 16 573 26.8 vide a link to the Creative Commons licence, and indicate if changes were 623 75.5 623 98.6 made. The images or other third party material in this article are included 673 98.6 673 99.3 in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by propionic acid conversion 90 J Flow Chem (2021) 11:87–90 statutory regulation or exceeds the permitted use, you will need to obtain 7. Back O, Marion P (2018) Process for the catalytic decarboxylative permission directly from the copyright holder. To view a copy of this cross-ketonization of aryl and aliphatic carboxylic acids. Chem licence, visit http://creativecommons.org/licenses/by/4.0/. Abstr 170:123749 8. Renz M, Corma A (2004) Ketonic decarboxylation catalysed by weak bases and its application to an optically pure substrate. Eur J Org Chem 9:2036–2039 References 9. Gliński M, Kaszubski M (2004) Catalytic ketonisation over oxide catalysts, part VIII. 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Journal of Flow Chemistry – Springer Journals
Published: Mar 4, 2021
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