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
Phase Transfer Catalyzed Synthesis of Organosulfur Fine Chemicals using Hydrogen Sulfide
The focus of this study is to utilize hydrogen sulfide (H2S) in the synthesis of fine chemicals, such as, thioethers and organic disulfides. Two different aqueous alkanolamines, such as, Nmethyldiethanolamine (MDEA) and monoethanolamine (MEA) were used for the absorption H2S to make H2S-rich alkanolamine solution. Dibenzyl sulfide (DBS) and dibenzyl disulfide (DBDS) were synthesized from the reaction of H2S-rich alkanolamine with organic reactant,benzyl chloride (BC). To carry out this biphasic reaction, three different phase transfer catalysts (PTCs) were used, namely, tetrabutylphosphonium bromide (TBPB), trihexyl (tetradecyl) phosphonium chloride (THTDPC) an ionic liquid (ILs) and a solid catalyst, amberlite IR-400. The main objective of the present study is to utilize H2S in synthesizing value-added chemicals such as DBS and DBDS, along with maximization of the conversion of the organic reactant, and the selectivity of desired product. Three different reaction systems have been carried out for the present work. First system dealt with the synthesis of DBS from the reaction of H2S-rich MDEA and BC using TBPB as PTC under liquid-liquid (L-L) phase transfer catalysis (PTC). Parametric study, mechanistic investigation and kinetic modeling have been performed for this system. In the second system, DBS was synthesized using THTDPC as a PTC under L-L PTC condition with around 98% BC conversion and 100% DBS selectivity. Parametric study and mechanistic investigation was performed and a detailed kinetic model was developed and validated using experimental values. In the last system, an investigation has been done on the utilization of H2S for the synthesis of DBDS under liquid-liquid-solid (L-L-S) PTC using amberlite IR-400 as a solid PTC. The effect of different parameters on the BC conversion was studied and the selectivity of desired product DBDS was found to be 100% at some level of process parameters. A suitable reaction mechanism has been proposed and a mathematical model has been developed and validated to explain the kinetics of the reaction.
A Monte Carlo treatment for reacting and coalescing dispersed phase systems
Abstract The Monte Carlo method of digital computer simulation is used to study the influence of coalescence on the progress of reactions occurring in the dispersed phase of two-phase systems in backmix reactors. Three different types of chemical reaction of both one and two reactants are studied and performance charts are prepared and discussed. It is shown that depending on the system, coalescence can either increase or decrease the extent of conversion of reactants. The Monte Carlo method, because of its simplicity, is found to be especially suited to studying discrete systems of this type since analytical solution is not yet possible and other numerical methods are very cumbersome. Possible extensions are discussed and the possibility of using the dispersed phase model for studying mixing and reaction in homogeneous systems is pointed out.