Population balance modeling and simulation of liquid–liquid–liquid phase transfer catalyzed synthesis of mandelic acid from benzaldehyde
Mandelic acid has cosmetic, pharmaceutical, and antibacterial activities and is used in urinary antiseptic medicines. An attractive process for the production of mandelic acid is through reaction between benzaldehyde, sodium hydroxide, and chloroform in the presence of polyethylene glycol 4000 as a phase transfer catalyst. The liquid–liquid phase transfer catalyzed (L–L PTC) reaction can be intensified by converting it into three-liquid phases (L–L–L PTC). We address the modeling of a well-stirred reactor for the foregoing process, in which organic droplets surrounded by a thin film of catalyst-rich phase are suspended in the aqueous phase. A population balance model is formulated for the L–L–L PTC reaction and solved by Monte Carlo simulation using interval of quiescence technique. Transport processes and intrinsic reaction kinetics are extracted from the experiments. This population balance model serves to assess and interpret the relative roles of various processes in L–L–L PTC reaction, such as diffusive transport, reaction, and interaction between dispersed phase droplets. The model is expected to be an effective tool for reactor design and scale up. © 2012 American Institute of Chemical Engineers AIChE J, 2012
Novel kinetics model for third-liquid phase-transfer catalysis system of the “complex” carbanion: Competitive role between catalytic cycles
Abstract Kinetic model for Horner–Wadsworth–Emerson (HWE) reaction of the “complex” carbanion in the third-liquid phase-transfer catalysis (TLPTC) system was proposed and the factors that influenced the model parameters were investigated in details. The generation process and the composition of the third phase revealed that there were two catalytic cycles (the third phase reaction and the organic phase reaction) in this TLPTC system. Kinetic model which consisted of ion-exchange reaction rate constant, bond-forming reaction rate constant and the contribution ratio between each two catalytic cycle was deduced. Distribution of the carbanion ion-pair between the third phase and the organic phase caused the competitive relationship between these two catalytic cycles. Third phase was the preferred region for the bond-forming reaction, and which contribution was always 5–6 times higher than that of the organic phase reaction. Reaction rate of each catalytic cycle was also affected by lipophilicity of the anion in this TLPTC system. The steric hindrance, lipophilicity of the catalyst cation and polarity of the third phase were primary factors influencing catalyst activity.
KANT'S SECOND THOUGHTS ON RACE
During the 1780s, as Kant was developing his universalistic moral theory, he published texts in which he defended the superiority of whites over non-whites. Whether commentators see this as evidence of inconsistent universalism or of consistent inegalitarianism, they generally assume that Kant's position on race remained stable during the 1780s and 1790s. Against this standard view, I argue on the basis of his texts that Kant radically changed his mind. I examine his 1780s race theory and his hierarchical conception of the races, and subsequently address the question of the significance of these views, especially in the light of Kant's own ethical theory. I then show that during the 1790s Kant restricts the role of the concept of race, and drops his hierarchical account of the races in favour of a more genuinely egalitarian and cosmopolitan view.