Heterogeneous Reaction Systems Research Articles

Chemical Grafting of Polystyrene Sodium Sulfonate (PSS) onto Polyethersulfone (PES) Powder and Effect on the Characteristics of the Resultant Ultrafiltration Membranes

The quest to introduce better performing and more resilience polymeric filtration membranes is currently a topical issue. In pursuance of this, polyethersulfone-based (PES) membrane functionalized with polystyrene sodium sulfonate (PSS) were produced and assessed. In the first instance, PES powder was grafted with PSS using the benzoyl peroxide (BPO) as the radical initiator. The polymerization was carried out in a heterogeneous polymer-polymer reaction system using water as the reaction medium under inert conditions using varying amounts of PSS. The PSS grafted PES powder was characterized using a combination of FTIR and 1H-NMR spectroscopy to confirm grafting. The grafting was also confirmed through gravimetric analysis of the powder before and after the grafting reaction. The pristine PES and the series of grafted PES polymer were cast into ultrafiltration (UF) membranes via phase inversion process under similar conditions. The influence of PSSconcentration on the morphological changes, contact angle, graft yield and permeation studies was studied. The grafted PES revealed a significant change in morphology upon an increase in the PSSconcentration. An increasein hydrophilicity and pure water flux was observed to increase with the amount of PSS added to the reaction mixture.

Quantum Tunneling Hydrogenation of Solid Benzene and Its Control via Surface Structure.

Despite the rapid accumulation of structural information about organic materials, the correlation between the surface structure of these materials and their chemical properties, a potentially important aspect of their chemistry, is not fully understood. Here, we show that the amorphous or crystalline structure of a solid benzene surface controls its chemical reactivity toward hydrogen. In situ infrared spectroscopy revealed that cold hydrogen atoms can add to an amorphous benzene surface at 20 K to form cyclohexane by tunneling. However, hydrogenation is greatly reduced on crystalline benzene. We suggest that the origin of the high selectivity of this reaction is the large difference in geometric constraints between the amorphous and the crystalline surfaces. The present findings can lead us to a more complete understanding of heterogeneous reaction systems, especially those involving tunneling, as well as to the possibility of nonenergetic surface chemical modification without undesired side reactions or physical processes.

Aerobic oxidation of benzene to phenol over polyoxometalate-paired PdII-coordinated hybrid: Reductant-free heterogeneous catalysis

Aerobic oxidation of benzene was carried out over the organic–inorganic hybrid catalyst of [(C3CNpy)2Pd(OAc)2]2HPMoV2, a solid catalyst containing the Keggin polyoxometalate PMoV2 and noble metal Pd(OAc)2 in its ionic structure. The features of this heterogeneous reaction system were studied by tuning various reaction parameters including solvent selection, function of buffer agent, and effects of reaction time, reaction temperature and catalyst amount. The results show the high phenol yield of 9.8% without aided by any sacrificial reducing reagents. The conjugation of Pd(OAc)2 and PMoV2 within the ionic structure of [(C3CNpy)2Pd(OAc)2]2HPMoV2 that accounts for its high activity is preliminarily discussed.

Surface Enhanced Raman Spectroscopy-Based Method for Leukemia Biomarker Detection Using Magnetic Core @ Gold Shell Nanoparticles

We present here the surface-enhanced Raman spectroscopic (SERS)-based detection of the Wilm’s tumor gene (WT1) sequence using dye-labeled reporter oligonucleotide and magnetic core @ gold shell nanoparticles. Thiolated single-stranded DNA (ssDNA) complementers of the WT1 sequence were used to functionalize the gold shell with capture oligonucleotides in a facile and fast two-step method. The signal amplification performance of the core @ shell colloidal SERS substrate was tested using malachite green as label dye. The Raman signal enhancing efficacy of the magnetic core @ gold shell nanomaterial was compared with the efficacy of spherical gold particles produced using the conventional citrate reduction method. The core @ shell particles were found to be superior both regarding robustness in SERS and facile separation in a heterogeneous reaction system. The core @ shell particles functionalized with target specific oligonucleotide were able to capture the WT1 target and worked as Raman signal amplifiers in our assay system. The good physicochemical characteristics of these particles and the sensitivity observed in SERS experiments allow us to expect good performance in the further development steps of a novel, fast and reliable spectroscopic method for WT1 detection in minimal residual disease patients.

High Temperature TEMPO Oxidation in a Heterogeneous Reaction System: An Investigation of Reaction Kinetics, Pulp Properties, and Disintegration Behavior

TEMPO oxidation was performed on never-dried bleached softwood kraft pulp fibres to study the influence of reaction temperature and the dosage of sodium hypochlorite in the oxidation treatment. It was found that oxidation at a high temperature shortened oxidation time, but it also resulted in more extensive degradation of the pulp. Harsh reaction conditions (high temperature and high dosage of sodium hypochlorite) enabled the rapid disintegration of pulp fibres with a low energy demand. The freeze-dried disintegrated pulp fibres had a high absorption capacity of saline liquid, 40 to 80 g/g, and retained 9 to 14 g saline liquid/g material in a standard centrifuge retention test. Four different models were investigated to describe the kinetics of TEMPO oxidation of pulp fibres. However, none of the models could adequately describe all the mechanisms involved in this reaction system. The results showed that the diffusion of hypochlorite ions was sufficiently fast compared to the chemical reactions. In contrast, the concentration of the catalytic compounds, NaBr and TEMPO, both had a strong influence on the reaction rate. Results show that the reactions have different phases, possibly with different rate-determining steps. It remains to be determined which reaction steps correspond to the different phases.

Heterogeneous Nucleophilic Transformation of Metolachlor by Bisulfide on Alumina Surface

AbstractThe present research elucidates the accelerating effect of alumina minerals on metolachlor transformation using sulfur nucleophiles and also determines the metolachlor transformation mechanisms in the heterogeneous reaction systems. Metolachlor transformation was first systematically investigated under different conditions. Then, the Fourier transform infrared (FTIR) spectra were used to characterize the changes in the surface bonds of the aluminas. The transformation products were qualitatively identified using LC/MS. The results showed that bisulfide can produce efficient metolachlor transformation rates, and the presence of the aluminas can further accelerate the transformation by achieving complete transformation in <21 days. In addition, a higher pH and higher bisulfide concentration are more favorable for metolachlor transformation. When normalized to the surface area, the metolachlor transformation rates were found to follow the order of α‐Al2O3>γ‐AlOOH>γ‐Al2O3 in the presence of different aluminas. FTIR results indicated that the enhancement of metolachlor transformation rates by bisulfide with aluminas can be attributed to the surface active nucleophiles on alumina surfaces formed through AlS and AlO bonds. The substitution of chlorine on the metolachlor followed the SN2 mechanism by bisulfide with accelerated rate through mediating the heterogeneous reactions with aluminas.

Triglyceride transesterification in heterogeneous reaction system with calcium oxide as catalyst

In this work, the behavior of the CaO as a potential catalyst for the transesterification of triglyceride towards biodiesel production was studied. The effect of the alcohol type, the ratio of alcohol/triacetin, the amount of catalyst, and the chain length of triglyceride on the catalytic behavior of CaO was analyzed. Total conversion was obtained at room temperature with a 6:1 molar ratio of methanol to triacetin over 1% of CaO, after 1 h. It was demonstrated that the whole reaction occurs in heterogeneous phase. During five reaction cycles the CaO maintained a high catalytic activity, showing its good stability. Additionally, it was established that the length of the triglyceride used influenced the transesterification reaction yield due to the steric hindrances and diffusional limitations in the fluid phase.

Iron removal from extremely fine quartz and its kinetics

The iron impurity removal from extremely fine quartz and its kinetics have been explored. The investigation reveals that the product layer diffusion in heterogeneous reaction system is the rate-control step and the activation energy was found to be 45.37kJ/mol. But the mechanism seems to have a trend towards homogeneous reaction system with the second order rate model from the heterogeneous system. Because the homogeneous reaction system’s average linear correlation coefficient is up to 0.978, which is very close to 0.995 of its counterpart in heterogeneous system. This result was confirmed through examination of the homogeneous system models with the first and the second order rates, as well as the heterogeneous system models with interface film, product layer diffusion and chemical reaction models. Additionally, other interesting results revealed that the leaching efficiency for such extremely fine silica sand decreased with increasing stirring speed – this observation was opposite to that for coarse particles. Usually, leaching efficiency of coarse particles increases with increasing stirring speed or higher ultrasonic power.

Synthesis of branched cores by poly-O-alkylation reaction under phase transfer conditions. A systematic study

In the present paper is described a systematic study of poly-O-alkylation reactions of pentaerythritol (PE) and 1,1,1-tris(hydroxymethyl)ethane (TME) by 1,4 Michael addition, under phase transfer catalysis (PTC), considering the effect of: (1) the organophilicity of PTC (three different catalysts were tested), (2) PTC concentration (from catalytic to equimolar conditions), and (3) the regime of addition of reactants coexisting in the aqueous phase of the heterogeneous reaction system. The less organophilic transfer agent showed the best performance on these reactions. In our case, benzyltriethylammonium chloride (TEBAC) gathers the best features. The presence of NaOH as base, promotes the interfacial mechanism and not the bulk one. Out of the optimal range of concentration of NaOH (35–40%), competition between nucleophiles can occur, due to the saturation of the medium. Regarding the regime of addition of reactants, the scenario where NaOH and TEBAC are less time in contact, favors the formation of the desired products. Finally, the deprotection of tert-butyl groups of the poly-O-alkylated compounds is described, to get branched cores with terminal carboxylic acid groups in good yields (90–94%). Spectroscopic properties, such as IR, 1H and 13C NMR, of the synthesized compounds are also described.

숙신산 추출반응이 일어나는 단일 액적계에서의 비정상상태 물질 전달

단일 액적 시스템에서의 비정상상태 물질 전달에 대한 연구를 진행하였다. 단일 액적계를 위한 이성분계로는 옥탄올(연속상)-물(분산상) 시스템이 이용되었으며 동반되는 불균일 반응으로는 아민추출제(tri-n-octylamine,TOA)를 이용한 숙신산 추출 반응을 모델 시스템으로 선정하였다. 점도, 밀도, 용질의 분배계수, 연속상에서 하강하는 액적의 종말 속도, 용질과 추출제의 확산계수 등과 같은 시스템의 기본 특성을 파악하기 위한 실험과 이론적 계산들이 수행되었다. 액적의 종말 속도는 숙신산 농도에는 크게 영향을 받지 않는 것으로 보이나 TOA가 없을 때는 숙신산 농도에 따라 약간 증가하는 경향을 보였고, TOA 농도 증가와 함께 감소하였다. 액적의 낙하는 수직 낙하 경로를 기준으로 좌우로 진동하면서 움직이는 경향을 보였다. 낙하하는 액적에서의 물질 전달 관찰을 위해 물질 전달 셀을 제작하여 시간에 따른 액적 내의 평균 농도 변화를 관찰하였고, 그 결과를 무차원 변수를 이용하여 해석하였다. 50 g/L의 숙신산 농도 조건하에서 TOA 농도를 0.1과 0.5 mol/kg 으로 조절하였을 때, 전자의 경우에는 관찰 시간 범위 내에서 일정한 Sh 값을 유지하여 용질의 이동 방향으로의 농도 기울기가 감소함에 따라 훌럭스도 그에 비례하여 감소함을 알 수 있었지만, 후자의 경우에는 시간의 경과와 함께 Sh가 급격히 증가하는 현상을 보여 계면에서의 숙신산 훌럭스 감소에 비해 농도기울기 감소가 상대적으로 빠르게 일어남을 알 수 있다. The transient mass transfer in a single droplet system consisting of 1-octanol (continuous phase)/aqueous succinic acid solution (dispersed phase) was investigated in the presence of chemical reaction, which is acid/anion exchange reaction of succinic acid and tri-n-octylamine (TOA). This succinic acid extraction by TOA can be considered to occur at the interface between organic and aqueous phase, that is, heterogeneous reaction system. The basic properties of the system such as viscosity, density, distribution coefficient, terminal velocity of droplet, and diffusion coefficient were measured experimentally or calculated theoretically, and used for theoretical calculation of characteristic parameters of mass transfer later. The effects of succinic acid concentration on the terminal velocity was negligible in the existence of TOA, although the terminal velocity increases with succinic acid concentration in the absence of TOA. On the contrary, the terminal velocity decreases with TOA concentration. While droplets falls through organic phase, the trajectory of droplets is observed to oscillate around its vertical path. A mass trnasfer cell was prepared to monitor the mass transfer behavior in a single droplet and used to measure the mean concentration of succinic acid inside droplet. The results are expressed with dimensionless parameters. Under 50 g/L succinic acid condition, the system with 0.1 mol/kg TOA showed that the molar flux decreases in proportion to the decrease of concentration gradient, while in the case of 0.5 mol/kg TOA Sh increases rapidly with time indicating the molar flux of succinic acid decreases relatively slowly compared to the decrease in concentration gradient.

Perspectives of heterogeneous process intensification in microreactors

Recent developments in microreactor technology basing on different types of heterogeneous reaction systems: phase transfer catalysis, biocatalysis, and synthesis of nanoparticles are reviewed. Special attention is focused on the intensification of processes in microreactors compared with traditional approaches, which makes microtechnique of great interest for industry.

Carbonation Behavior and the Reaction Kinetic of a New Dry Potassium-Based Sorbent for CO2 Capture

The carbonation behaviors of K2CO3 generated by calcination of KHCO3 were investigated with a pressurized thermo gravimetric apparatus, and the shrinking-core model in the noncatalytic heterogeneous reaction systems was used to explain the kinetics of the reaction between K2CO3, CO2, and H2O using analysis of the experimental breakthrough data. The carbonation reaction process can be divided into two stage-controlled regions, one is the surface chemical reaction-controlled region at the initial stage and another is the internal diffusion-controlled region at the last stage. The total amount of carbonation conversion is mainly dependent on the first stage. The reaction rate of this stage decreases as the reaction temperature increases. It increases in the same temperature when the CO2 and H2O concentrations increase. The total carbonation conversion decreases as the pressure increases. On the basis of the Arrhenius equation, the apparent activation energy and pre-exponential factor for these two stages are calculated, when the temperature is in the range of 55–80 °C and the pressure is 0.1 MPa. They are 33.4 kJ/mol and 3.56 cm/min for the surface chemical reaction-controlled region and 99.1 kJ/mol and 4.01 × 10–22 cm2/min for the internal diffusion-controlled region. This paper provides theoretical basis for the further study on the capture of CO2 from flue gas using dry potassium-based sorbents.

Esterification of acetic acid with n-Butanol using vanadium oxides supported on γ-alumina

Abstract Esterification of acetic acid with n -Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N 2 adsorption, EDX analysis and NH 3 -TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V 2 O 5 (10V-Al 2 O 3 sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n -Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH 3 increased in the following order: Al 2 O 3 2 O 3 (5 wt % V 2 O 5 /Al 2 O 3 ) 2 O 3 . In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V 2 O 5 –Al 2 O 3 catalyst was observed.

Nonclassical Chemical Kinetics for Description of Chemical Fluctuation in a Dynamically Heterogeneous Biological System

We review novel chemical kinetics proposed for quantitative description of fluctuations in reaction times and in the number of product molecules in a heterogeneous biological system, and discuss quantitative interpretation of randomness parameter data in enzymatic turnover times of -galactosidase. We discuss generalization of renewal theory for description of chemical fluctuation in product level in a multistep biopolymer reaction occurring in a dynamically heterogeneous environment. New stochastic simulation results are presented for the chemical fluctuation of a dynamically heterogeneous reaction system, which clearly show the effects of the initial state distribution on the chemical fluctuation. Our stochastic simulation results are found to be in good agreement with predictions of the analytic results obtained from the generalized master equation.

ChemInform Abstract: Recent Progress in the Preparation of Organoboron Reagents via Direct Borylations

AbstractReview: ca. 50 refs.

Modelo Matemático para Estimación de Eficiencias Fotónicas No-Intrínsecas en Reacciones Fotocatalíticas Heterogéneas

A semi-empirical model was formulated to estimate the photonic efficiency of photocatalytic reactions in heterogeneous systems. This is a function of a pre-exponential factor called intrinsic photonic-efficiency and an exponential factor that quantified the effect of catalyst loading, geometry, and initial concentration of substrate. The assumptions and the model were validated on the photodegradation of dichloroacetic acid in three lab-scale heterogeneous photocatalytic reactors, using TiO2-P25 and low energy monochromatic radiation. It was found that the model is highly predictive for photonic efficiencies with relative errors below 1.8%.

Modeling of a Liquid–Liquid–Solid Heterogeneous Reaction System: Model System and Peroxyvaleric Acid

A mathematical model was developed to interpret a liquid–liquid–solid heterogeneous reaction system using valeric acid (pentanoic acid) perhydrolysis as model. Kinetic, thermodynamic, and mass transfer parameters were included in this model. Perhydrolysis of valeric acid (pentanoic acid) on Amberlite IR-120 catalyst experiments were carried out in the temperature range of 40–60 °C and with an initial valeric acid concentration of 50 wt %. The influence of water and the acid catalyst was taken into account to develop a suitable kinetic model. The thermodynamic parameters, such as the reaction enthalpy (ΔHR0) and the molar equilibrium ratio (m) were determined experimentally. The kinetic parameters were determined by nonlinear regression analysis and they were statistically well-identified. The standard reaction enthalpy was estimated to −13.84 kJ·mol–1 and the activation energy of the reaction was estimated to 64.5 kJ·mol–1.

ChemInform Abstract: Biomass Pyrolysis Kinetics: A Comparative Critical Review with Relevant Agricultural Residue Case Studies

AbstractReview: 412 refs.

Microreactors as the new way of intensification of heterogeneous processes

Microstructure reactors (microreactors) in recent decades became one of the most actively studied subjects of the reaction equipment aimed at intensification of chemical processes and increase in their safety. It is not surprising because due to miniature dimensions of microstructures which do not exceed 2 mm microreactors contribute to minimization of the material at their production as well as raw material and energy in the process of exploitation. Moreover, due to acceleration of heat and mass transfer the productivity of equipment with microreactors in a range of cases is significantly higher than classical batch reactors applied in industry. The brief overview of the modern development and achievements of microreactor technology is given in this article by an example of heterogeneous reaction systems which are different by their nature and occur in different types of microreactors: phase-transfer catalysis, biocatalysis, and synthesis of nanoparticles. A special attention in the article is paid to the aspects of intensification of the considered processes because exactly the possibility of intensification makes microreactor technology attractive for the industry.

Polyoxometalate Nanocone Nanoreactors: Magnetic Manipulation and Enhanced Catalytic Performance

Rationally designed assembly structures are of high scientific and technological importance for the development of multifunctional materials and devices. Among various types of nanobuilding blocks, polyoxometalates (POMs) are a class of metal oxide nanoclusters that offer rich structural versatility and enormous applications. The recent progresses in the synthesis of POM-based amphiphilic units have revolutionized POM chemistry, and consequently a variety of robust and well-defined assembly architectures with tunable properties have been developed, including one-dimensional wires and fibers, two-dimensional thin-films and disks, and threedimensional vesicles, spheres, tubes, and flowers. Although, these assembly structures hold great promise for the design of new functional materials, in reality they have been less explored for their potential use in various scientific fields. POMs have been extensively applied as catalysts for the oxidation of a variety of compounds such as alkenes, alcohols, and sulfides. Particularly, the oxidation of sulfides to sulfones, which is environmentally highly important, yet brings up a key challenge. To meet this challenge, many strategies in both homogeneous and heterogeneous catalytic reaction systems have been developed. The homogeneous approaches utilize the POM catalyst in bare form or in combination with a phase-transfer reagent, which generally have drawbacks associated with difficult catalyst separation and recovery. The heterogeneous approaches involve encapsulation with specific cations, immobilization of POM into silica or polymer matrices, or microemulsion formation. Although, heterogeneous systems provide easier catalyst recovery, generally it is based on filtration, which may be highly cumbersome on an industrial scale. In addition, the immobilization of POMs in supporting matrices involves complicated and lengthy catalyst preparation processes. Therefore, alternative multifunctional and superior approaches are needed. Recently, we reported well-defined, robust Keggin ion based nanocones, obtained by a simple and fast synthesis technique at room temperature. Herein, we report the functionalization of nanocones with magnetite nanocrystals and their controlled manipulation in the reaction system. For example, we applied these nanocones for the catalytic oxidation of sulfides in which they act as nanoreactors to provide enhanced efficiency, selectivity, and easier recovery under an external magnetic field. Figure 1 illustrates the concept of the nanocone nanoreactors. According to the accepted mechanism for the increased efficiency of the POM hybrid building block (DODA)3PW12O40 (DODA= dimethyldioctadecylammo-