Reaction kinetics for the heterogeneously resin-catalyzed and homogeneously self-catalyzed esterification of thioglycolic acid with 2-ethyl-1-hexanol

Producing 2-ethyl-1-hexyl thioglycolate(ETE)via esterification reaction with thioglycolic acid(TGA)aqueous solution as raw material by reactive-separation coupling technology is a promising process intensification method.To choose suitable reactive-separation coupling strategy,the kinetic studies of the esterification of TGA with 2-ethyl-1-hexanol(EHL)were carried out in a batch system.The commercial ion exchange resin was employed as an eco-friendly catalyst.The effects of temperature,catalyst concentration and molar ratio were determined.It was interesting to observe that the equilibrium conversion of TGA increased with the increase of catalyst mass fraction due to the adsorption of product water onto resin surface.The activity-based pseudo-homogeneous(PH),Eley-Rideal(ER)and Langmuir-Hinshelwood-Ho ugen-Watson(LHHW)models were used to fit the kinetics data of the resin-catalyzed reaction.The models of ER and LHHW performed better than the PH model.The kinetics of the TGA-self-catalyzed reaction was also determined.An activity-based homogeneous kinetics model could well describe this self-catalyzed reaction.These results would be meaningful to the selection and design of an appropriate reactionseparation strategy for the production of ETE,to realize the process intensification.

Chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism and kinetics

The chitosan was found to possess an excellent catalytic performance in n-butyraldehyde selfcondensation to 2 E2 H.Under suitable conditions,the conversion of n-butyraldehyde,the yield and selectivity of 2 E2 H separately attained 96.0%,86.0%and 89.6%.The chitosan catalyst could be recovered and used for 5 times without a significant deactivation after being treated with ammonium hydroxide.In order to elucidate the reaction mechanism,the adsorption and desorption of n-butyraldehyde on the surface of chitosan were studied using in situ FT-IR spectroscopy analysis.The result showed that n-butyraldehyde interacts with\\NH2 group of chitosan to form an intermediate species with an enamine structure.Then the reaction process of n-butyraldehyde self-condensation was monitored by React-IR technique and it was found that n-butyraldehyde self-condensation to 2-ethyl-3-hydroxyhexanal followed by a dehydration reaction to 2-ethyl-2-hexenal.On this basis,chitosan-catalyzed n-butyraldehyde self-condensation reaction mechanism was speculated and its reaction kinetics was investigated.The self-condensation reaction follows auto-catalytic reaction characteristics and then the corresponding kinetic model was established.

Bioconvection Mangnetohydrodynamic Tangent Hyperbolic Nanofluid Flow with Quartic Chemical Reaction Past a Paraboloid Surface

In this numerical study,the effect of quartic autocatalysis type of chemical reaction,buoyancy force and thermal radiation phenomenon and magnetic effect on tangent hyperbolic nanofluid past an upper horizontal surface of a paraboloid has been studied.By considering the Buongiorno model approach,a diffusion of unequal coefficients in the presence of gyrotactic microorganism is discussed.Implementation of microorganism’s idea is used to stabilize the nanoparticles through bioconvection.The modeled PDEs of the problems are converted into nonlinear ODEs with the assistant of the similarity transformations.To tackle nonlinear ODEs,MATLAB package bvp4c is used.In addition,a hallmark of the Matlab code with the reported results in the literature is achieved by benchmarking.The variations in motion,concentration,temperature,and motile density due to sundry parameters have been analyzed in-depth via graphs.Our analysis shows that the density profile of motile of microorganism is hiked with an increment in the bioconvection Rayleigh number but decreases for higher thermal Grashof number.

Kinetic Modelling of the Influence of H₂S on Dibenzothiophene Hydrodesulfurization in a Batch System over Nano-MoS₂

In this work, the possibility of enhanced activity during the hydrodesulfurization of dibenzothiophene over certain nano-MoS2 catalyst due to the presence of H2S was examined by focusing on the reaction kinetics. With H2S generated in situ, the overall reaction followed the autocatalytic rate law;while in the absence of H2S the kinetics indicated a pseudo-first-order reaction. H2S appears to modify the relative contributions of parallel hydrogenation and desulfurization reactions by drastically increasing the hydrogenation rate. Kinetic models were developed that describe the hydrodesulfurization reaction at various H2S concentrations, and the kinetic parameters and adsorption equilibrium constants associated with this process were estimated by fitting the experimental data. The results suggest that the promotion and/or inhibition of hydrodesulfurization by H2S likely result from the same overall reaction mechanism.

Autocatalytic strategy for tuning drug release from peptide-drug supramolecular hydrogel

Peptide-drug conjugates(PDCs) composed of peptide, spacer and drug have gained extensive attention in the field of drug delivery owing to its precise control over the drug payload and architecture. However,the achievement of controllable and rapid drug release at targeted site by PDCs is still a great challenge for pharmaceutist. Herein, we introduced the histidine residue into PDCs to generate a supramolecular hydrogel via a p H-trigger strategy, which exhibited an autocatalytic effect to precisely tune drug release from PDCs hydrogel. Using indomethacin(Idm) as model drug, various PDCs(Y(Idm)EEH, Y(Idm)EEK and Y(Idm)EER) were synthesized and their self-assembling properties were investigated in terms of critical aggregation concentration(CAC), transmission electron microscopy(TEM) and rheometer. Introduction of histidine residue into PDCs presented a robust catalytic activity on the ester hydrolysis of p-nitrophenyl acetate in aqueous solution, as well conferred the autocatalytic capacity to hydrolyze the PDCs into active parent drug(Idm). Overall, we reported an autocatalytic activity of histidine residue to precisely tune drug release from PDCs hydrogels.

Cubic Auto-Catalysis Reactions in Three-Dimensional Nanofluid Flow Considering Viscous and Joule Dissipations Under Thermal Jump

In this problem,simultaneous effects of Joule and viscous dissipation in three-dimensional flow of nanoliquid have been addressed in slip flow regime under time dependent rotational oscillations.Silver nanoparticles are submerged in the base fluid(water)due to their chemical and biological features.To increment the novelty,effects of cubic autocatalysis chemical reactions and radiative heat transfer have been incorporated in the related boundary layer equations.Dimensionless partial differential system is solved by employing the proposed implicit finite difference approach.Convergence conditions and stability criteria are obtained to ensure the convergence and accuracy of solutions.A comparative analysis is proposed for no-slip nanofluid flow(NSNF)and slip nanofluid flow(SNF).Variations in skin-friction coefficients,Sherwood and Nusselt numbers against physical parameters are tabulated.It is investigated that velocity slip and temperature jump significantly control drag forces and rate of heat transfer.

Construction of a Homogeneous Enzyme-Free Autocatalytic Nucleic Acid Machinery for High-Performance Intracellular Imaging of MicroRNA

Enzyme-free autocatalytic nucleic acidmachinery has been widely used to engineer various self-assembled nanostructures as well as high-performance bioanalysis,yet has rarely been realized in live cells for complicated design,low robustness,and limited reliability.Herein,we constructed simple yet versatile enthalpy-driven autocatalytic hybridization chain reaction(AHCR)machinery with high reliability and robustness for in situ microRNA analysis in live cells.The homogeneous AHCR machine was composed of two differently designed HCR modules,the lead-in HCR-1 amplification module,and the reverse HCR-2 feedback module.After the AHCR amplification system was delivered into live cells,target microRNA stimulated the autonomous cross-invasion of the HCR-1 module and the HCR-2 module for assembling hyperbranched dsDNA nanostructures with synergistically amplified Förster resonance energy transfer readout,thus enabling accurate intracellular micro-RNA imaging.The synergistic AHCR execution was systematically investigated by a series of experimental studies and computer-aided theoretical simulations.The multiple recognition capacity of HCR constituents and the successive signal amplification of the AHCR machine enabled the accurate intracellular microRNA imaging with precise signal localization inside living cells.Based on its intriguing and modular design,the AHCR machinery can be extended for analyzing diverse biomarkers,thus supplementing a powerful toolbox for clinical diagnosis and therapeutic assessment.