Macromolecular Reaction Engineering最新文献

This work uses sol–gel and sonochemical methods to prepare bimetallic PdCu catalysts supported on modified ZrO₂ with Ti and Al. The catalysts are tested for vinyl acetate synthesis from ethylene, acetic acid, and oxygen, varying the reaction temperature for two catalysts prepared, which show higher activity. Catalysts characterization results show bimetallic species and distort alloys with a dispersed distribution of active metal onto the support. The in situ reaction by DRIFT-MS identifies the surface formation of main intermediates like palladium acetate monomers and mono and bidentate intermediates, associated to vinyl acetate formation, like vinyl hydrogenated species over PdCu. Finally, this behavior will be attributed to the bimetallic distortions of PdCu samples, provided by interaction effects between PdCu and supports, indicating a more exposition of PdCu species suitable for the reaction, according to high-resolution transmission microscopy electron microscopy results for PdCu/ZrTi sample. Thus, this sample exhibits a minimal formation of sub-products and catalytic stability for 18 hh. These results evidence the participation of hydroxyls and oxygen vacancies of the catalyst in the catalytic reaction measured in situ, monitoring the products formed at the reactor outlet. Finally, it is proposed a reaction pathway as a function of reaction conditions.

In this paper, a detailed description of particle adsorption/diffusion model in batch systems is presented. The phenomenological equations are based on a mechanism combining mass transfer by convection from bulk phase to particle surface, intraparticle mass diffusion and equilibrium adsorption processes. The change of bulk and particle concentration is modeled through differential mass balance equations, leading to a system of one ordinary differential equation and one partial differential equation. When adsorption equilibrium follows a linear relationship, this system of equations can be solved by the Laplace transform method. The purpose of this paper is the development of a generalized analytical solution, that is rewritten specifically for each of the traditional particle shapes: slab, cylinder, and sphere. Finally, this analytical solution is evaluated through several simulations in different batch conditions and compared to simulated experimental data, showing the capability of this analytical solution to predict batch adsorption processes when adsorbate concentration is low. This result clearly indicates the feasibility of applying the analytical solution presented in this paper, which is based on phenomenological concepts, to describe the adsorption kinetics of processes, when the linear isotherm can be considered adequate to represent the adsorption equilibrium.

ω-Alkenyltrimethylsilanes of different alkenyl moieties, i.e., 3-butenyltrimethylsilane, 5-hexenyltrimethylsilane, and 7-octenyltrimethylsilane, are used as model compounds to study the alkenyl length effect in copolymerization of ethylene with steric-hindered tri-substituted silane-functionalized α-olefins over MgCl₂/TiCl₄ catalysts. The experimental results reveal that 3-butenyltrimethylsilane tops the three α-olefins in incorporation rate into PE while 7-octenyltrimethylsilane is slightly better than 5-hexenyltrimethylsilane. The coordination-insertion events for different ω-alkenyltrimethylsilanes are investigated by DFT simulation. The results suggest that the three ω-alkenyltrimethylsilanes encounter similar energy barriers during insertion, with similar repulsive interactions between the bulky trimethylsilane substituent and growing PE chain found in the energy decomposition of transition state configuration. However, complexation abilities at the Ti active site for the three ω-alkenyltrimethylsilanes follow the order of 3-butenyltrimethylsilane > 5-hexenyltrimethylsilane > 7-octenyltrimethylsilane, in line with their molecular compactness, which are deemed to be where the alkenyl length effect originates in the ω-alkenyltrimethylsilane/ethylene copolymerization.

This work addresses a comparative study focused on the synthesis of alkyd resins from different renewable resources such as chia, castor and palm vegetable oils through the alcoholysis–polycondensation process. The formed alkyd resins are analyzed by Fourier transform infrared (FTIR), ¹H NMR, and ¹³C NMR. Besides, intrinsic viscosity and gel permeation chromatography (GPC) assays are conducted to evaluate the differences between the obtained resins focusing on their molecular weight and physicochemical properties. FTIR shows a satisfactory conversion from vegetable oils to alkyd resins. Both ¹H NMR and ¹³C NMR indicate that alkyd resins are successfully synthesized. The values for molecular-weight dispersity (Ð_M) obtained for the resins are 2.3, 1.3, and 1.7 from chia, palm, and crude castor, along with the weight-average molecular weight (M_w) of 4516, 1025, and 2451 g mol⁻¹, respectively. The chia alkyd resin shows a 571.92 cP and is the highest viscosity obtained. It is also observed that an increase in phthalic anhydride can increase the molecular weight of the alkyd resin. This comparative study indicates that chia oil alkyd resin has enormous potential to be employed as a surface coating agent.

The oil well drilling process is a nonlinear system with transient nature. Conventional drilling is unable to assure safe and cost-effective operation for fractured, cavernous, and highly permeable carbonate reservoirs, which contain the largest oil reserves worldwide. Concerning drilling technologies, Pressurized Mud Cap Drilling (PMCD) is suitable for the challenging scenario previously mentioned. According to PMCD technique, a sacrificial fluid is injected through the drill string and a light annular mud is pumped in countercurrent through the annulus region (bullheading), without surface return, forcing gas and drilled cuttings back to formation. A two-phase flow distributed model (Drift Flux Model – DFM) is developed to properly describe the complex nature of the system. Also, an experimental facility, presenting field similarity, is employed to validate the open – closed loop schemes. The main objective of the controller (control reconfiguration with gain scheduling) is to regulate annulus pressure, handling gas kick, drilling fluid losses and inverse response dynamics. Besides, gas injection, migration and bullheading are studied. The simulations, validated through experimental data, highlight the methodology usefulness for field applications.

A mathematical model is proposed that couples the decomposition kinetics of persulfate (S₂O₈²⁻) and the free radical polymerization kinetics of itaconic acid (IA); the results are compared with experimental data reported in the literature. It is found that the former is highly affected by the acidification of the aqueous medium which is caused by the equilibrium dissociation of IA but mainly by HSO₄⁻ produced by side reactions of the S₂O₈²⁻ decomposition. This qualitatively explains the dependence of d[S₂O₈²⁻]/dt with [IA] and the initial concentration of persulfate ([S₂O₈²⁻]₀), reported in the literature. According to the model results, temperature overshoots are very likely to occur in the experiments so there is doubt whether the reaction order >1 with respect to [IA] that is sometimes reported in the literature for the rate of polymerization (Rp) is an artifact related to an imprecise temperature (T) control or is due to a more complex mechanism. Due to the higher activation energy of the persulfate decomposition compared to the propagation reaction, small variations of T can lead to significant variations of d[S₂O₈²⁻]/dt but to an almost imperceptible effect on Rp. Recommendations for future experimental work and refinement of the kinetic model are provided.

Front Cover: This study deals with the development of a reaction kinetic model describing the inhibition mechanism of RAFT dispersion polymerization by oxygen and its application to investigate the effect of re-initiation on the synthesized polymer quality. The experimental validation of the kinetic model creates a functional digital twin, establishing a valid method for diblock copolymer synthesis from a non-successful polymerization attempt. This is reported by Emil Pashayev, Felix Kandelhard, and Prokopios Georgopanos in article number 2200068.

The mechanical properties and blocking resistance of films cast from latex particles can be improved by addition of a reinforcing polymer of high modulus that acts as a “hard” phase. This work demonstrates that blocking resistance, a key performance parameter for use in coatings, of such films can be understood in terms of the relative contribution of the “hard” and “soft” components to the rheological properties of the material. In order to do so, representative latexes that contain a semicrystalline core of poly(stearyl acrylate) as a reinforcing phase and a shell of amorphous poly(styrene-co-butyl acrylate) are synthesized. By varying the composition of the amorphous phase (glass transition temperature, molar mass) and the relative amorphous/semicrystalline fraction, it is demonstrated that the improvement in blocking resistance is strongly correlated with the increase in the modulus of the material but is also affected by the dynamics of polymer diffusion of chains in the soft phase. This work allows to establish design rules for polymer and colloidal structures that can be targeted to maximize blocking resistance.