Hydrolysis of fatty acid esters in subcritical waterHydrolysis of esters of higher fatty acids by subcritical water, performed in a flowthrough tubular reactor, was investigated at temperatures from 280 up to 340 7C and pressures exceeding 12 MPa, using an ester/water ratio of 1 : 2 or 1 : 4 (vol/vol). The kinetics of the hydrolysis of both the triacylglycerols and the methyl esters obeyed the rate equation valid for first-order reactions. Conversion of the esters to free fatty acids exceeding 95% was reached at the temperature of 340 7C during 12 min. IR spectroscopy revealed structural changes in the chains of the unsaturated fatty acids and their partial polymerization during the hydrolysis.
High-temperature esterification of fatty acids with methanol at ambient pressureThe article presents the results of the kinetic study of the acid-catalyzed esterification of free fatty acids (FFA) with methanol (MeOH) at elevated temperatures above the boiling point of MeOH, at ambient pressure, and at continual flow of liquid MeOH into the reaction mixture. Under these conditions, the reaction follows the rate equation valid for reactions of the first order. Beside temperature, the pseudo rate constant depends also on the flow rate of MeOH and on the concentration of a catalyst. At temperatures 50-60 7C higher than the boiling point of MeOH, the reaction rate is two to three times higher than at the temperatures close to the boiling point of MeOH. Apart from the temperature, the increase of the rate is facilitated also by a high local molar excess of MeOH in the input site with respect to FFA and by effective removal of water from the reaction mixture. The composition of the reaction mixture is then farther from the equilibrium composition. High conversion of FFA to methyl esters (above 99%) with low residual acidity of the product (acid value around 2-3 mg KOH/g) is achieved at short times of several tens of minutes and at a low total molar ratio of MeOH/FFA of around 3-4.
Miniemulsion polymerization of butyl acrylate initiated by 2,2¢-azobisisobutyronitrile in the presence of carbon nanotubes (CNTs) has been investigated. The miniemulsions were stabilized by non-ionic, cationic and anionic emulsifiers. The maximal rate of polymerization (R pmax ) increases with the type of emulsifier in the following order: Triton X-405 (Tr)oTween 60 (Tw)Bdioctyl sodium sulfosuccinate (AOT)oDowfax 2A1 (DW)Bcetylpyridinium bromide (CPB)ocetyl trimethylammonium bromide (CTAB). R pmax increases on addition of CNTs in the runs with Tw and Tr, slightly increases in the runs with CTAB, AOT and DW, and decreases in the run with CPB. Particle evolution is discussed in terms of two 'apparent' limiting cases: zero-one and pseudo-bulk kinetics. In the former case (polymer nanoparticles (PNP) approach), monomer droplets are nucleated by simple entry of radicals and transformed into polymer particles by growth events. Pseudo-bulk kinetics govern the polymerization process by the formation of radicals in the monomer phase (monomer/polymer nanoparticles (MPNP) approach).
The kinetics of aqueous phase radical polymerization of acrylamide initiated by ammonium peroxodisulfate (APS) and 2,2 -azobisizobutyronitrile (AIBN) were studied in the presence of the non-ionic hydrophilic Tween-20 and hydrophobic Tween-85. The polymerization rate vs. conversion curve is described by a curve with two or three rate intervals and the maximal rate is located at medium conversion. This behavior strongly deviates from the kinetic model of the ideal solution polymerization with the steady-state kinetics at low and medium conversions. On the contrary, the present data indicate the kinetics typical for the transparent heterogeneous-micellar or microemulsion polymerization. The associates of polyacrylamide and acrylamide play the role of active particles. Indeed, the light scattering measurements confirmed the presence of polyacrylamide nanoparticles in both polymerization systems with and without emulsifier. The intra-and intermolecular association of polyacrylamide with its monomer is suggested to be the dominant process which induces the formation of particles responsible for the kinetics typical for the micellar or microemulsion polymerization. The experimental data show that the dependence of the maximal rate of polymerization (R p,max ) vs. conversion is the result of polymerization within the nanoscaled polymer aggregates and not by the gel effect. R p,max decreases with increasing emulsifier concentration and the decrease is much more pronounced with hydrophilic emulsifier. Polymerization is faster for the APS-initiated system than for the AIBN-initiated one. The radical polymerization of AAm polymerization with and without emulsifier was discussed in terms of the formation of polymer chain aggregation (nanoparticle) into polymer chains as a main reaction locus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.