Summary: Acrylic monomers are important intermediates for the chemical industry. Especially acrylic acid (AA) is the basis for various reactions, such as polymerizations and esterifications and is, therefore, responsible for high product diversity. Spontaneous polymerization is a safety problem during the transportation and storage of acrylic monomers. In the production process, polymerization leads to blockages in the apparatus. For the prevention of these issues, special stabilizer systems are used such as hydroquinone monomethyl ether (MeHQ)/oxygen and phenothiazine (PTZ). The reactions of these stabilizer systems are not well understood at the moment. Therefore a lot of expertise and experience are necessary to guarantee safe handling. In this paper some methods for the investigation of stability related reaction kinetics are presented. A better comprehension of the mechanism of the polymerization inhibition is generated by the kinetic simulation with these data.
Die hydrothermale Carbonisierung (HTC) ist in Hinblick auf die energetische Verwertung von Biomasse eine vielversprechende Methode. Trotz der langen Historie dieses Verfahrens sind Mechanismus und Kinetik nur unzureichend verstanden. In den hier vorgestellten Experimenten wurde mithilfe der Kombination von Analysenmethoden die Umsetzung von Kohlenhydraten mit sauren und basischen Zusätzen untersucht. Dabei konnte vor allem der Einfluss von Säure auf die Hydrolyse von Cellulose beobachtet werden. Die HTC von Glucose hingegen bleibt weitestgehend von den Zusätzen wie Säure oder Base unbeeinflusst. Durch Veränderung der Reaktionsbedingungen wie der Heizrate können die Biokohle‐Eigenschaften wie z. B. die Acidität der Kohle variiert werden.
During acrylic acid (AA) storage, a quality loss occurs due to the formation of by-products such as diacrylic acid (DiAA), triacrylic acid (TriAA), and higher oligomers. This problem intensifies in the presence of water since the formation rate of oligomers increases and further by-products such as 3-hydroxypropionic acid (3-HPA) and 3-hydroxydiacrylic acid (3-HDiAA) are formed. However, water is often essential during storage and transport to raise the flash point or reduce the melting point. In this work, the formation kinetics are investigated for all mentioned components in pure and aqueous AA. The formation mechanisms of 3-HPA and 3-HDiAA are assumed as acid-catalyzed ester hydrolyses of DiAA or TriAA. The introduced reactions are modeled with the measured kinetic data in order to confirm the proposed reactions.
For a safe storage and handling of acrylic acid (AA), a lot of knowledge is necessary. In the present work, investigations were made in order to describe the stabilization processes during the inhibition period (IP) of AA more exactly. The oxygen and p‐methoxyphenol consumption was determined for AA at 70 and 80 °C in an enhanced parameter range and simulated with a kinetic model, using the software Presto Kinetics (R). In the simulation accelerated stabilizer consumptions at 80 °C could be confirmed. The known stabilization mechanism must be enhanced with autocatalytic steps, which lead to an accelerated stabilizer consumption. Furthermore, the stability of AA was examined as a function of the dissolved oxygen mass fraction and the temperature in isoperibolic reactors. The IP follows an Arrhenius behavior; therefore, an extrapolation from higher reaction temperatures to storage conditions is possible. These measurements also confirm the nonlinear stabilizer consumption during the IP at temperatures over 75 °C.
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