High Catalyst Concentrations Research Articles

Deracemization of a Racemic Compound via Its Conglomerate-Forming Salt Using Temperature Cycling

Salts of chiral molecules, which originally crystallize as racemic compounds, could form conglomerates. The utilization of such conglomerate salts, as intermediates for the deracemization of corresponding racemic compounds, expands the theoretical application range of Viedma Ripening by roughly 10-fold. In the present study, the use of temperature cycling on conglomerate forming salts as an alternative technique for Viedma Ripening was studied. The racemic compound Phenylalanine (Phe) was successfully deracemized via its conglomerate-forming salt with 2,5-xylenesulfonic acid (XSA) by continuous heating–cooling cycles applied to its suspension in glacial acetic acid, coupled with a solution racemization reaction. In addition, the dependence of the deracemization rate on the operational parameters was studied. Enhanced racemization reaction kinetics, either by a larger amount of free amino acid or by a higher concentration of catalyst, was shown to accelerate the deracemization process. It seems to indicate...

47nm alumina–water nanofluid flow within boundary layer formed on upper horizontal surface of paraboloid of revolution in the presence of quartic autocatalysis chemical reaction

In this article, a modified version of buoyancy-induced model is considered to investigate the flow of 47nm alumina–water nanofluid along an upper surface of horizontal paraboloid of revolution in the presence of nonlinear thermal radiation, Lorentz force and quartic autocatalysis kind of homogeneous heterogeneous chemical reaction. The case of unequal diffusion coefficients of reactant A (bulk fluid) and B (high concentration of catalyst at the surface) in the presence of bioconvection is considered. Governing equation suitable to unravel the thermophoresis which takes place within the boundary layer is presented. Since chemical reactant B is of higher concentration at the surface more than the concept described as cubic autocatalytic, the suitable schemes are herein described as isothermal quartic autocatalytic reaction and first order reaction. The viscosity and thermal conductivity are assumed to vary with volume fraction (ϕ) and suitable models for the case 0%⩽ϕ⩽0.8% are adopted. The transformed governing equations are solved numerically using Runge–Kutta fourth order along with shooting technique (RK4SM). Good agreement is obtained between the solutions of RK4SM and MATLAB bvp5c for a limiting case. The influence of some pertinent parameters on velocity, temperature, diffusion of motile microorganism, concentration of bulk fluid and catalyst is illustrated graphically and discussed.

Frontal Ring-Opening Metathesis Polymerization of Exo-Dicyclopentadiene for Low Catalyst Loadings.

Polydicyclopentadiene (PDCPD) is a polymer of growing importance in industrial applications. Frontal ring-opening metathesis polymerization (FROMP) offers a means to rapidly cure PDCPD with minimal input energy owing to a propagating reaction wave sustained by the exothermic polymerization. Previous examples of FROMP have required the use of relatively high concentrations of costly ruthenium catalyst, negating many of the benefits of FROMP synthesis. In this contribution, we demonstrate that by using the highly reactive exo-dicyclopentadiene isomer for FROMP the concentration of catalyst is reduced over 3-fold, while maintaining a high frontal velocity. Reducing the amount of ruthenium required for FROMP makes this technique attractive for the production of large PDCPD structural components.

Development of an Intermittent-Flow Enantioselective Aza-Henry Reaction Using an Arylnitromethane and Homogeneous Brønsted Acid-Base Catalyst with Recycle.

A stereoselective aza-Henry reaction between an arylnitromethane and Boc-protected aryl aldimine using a homogeneous Brønsted acid-base catalyst was translated from batch format to an automated intermittent-flow process. This work demonstrates the advantages of a novel intermittent-flow setup with product crystallization and slow reagent addition which is not amenable to the standard continuous equipment: plug flow tube reactor (PFR) or continuous stirred tank reactor (CSTR). A significant benefit of this strategy was the integration of an organocatalytic enantioselective reaction with straightforward product separation, including recycle of the catalyst, resulting in increased intensity of the process by maintaining high catalyst concentration in the reactor. A continuous campaign confirmed that these conditions could effectively provide high throughput of material using an automated system while maintaining high selectivity, thereby addressing nitroalkane safety and minimizing catalyst usage.

<b>Citric waste saccharification under different chemical treatments

Second generation ethanol from lignocellulose materials has been used in applications for food processing wastes. Since Brazil has a leading position in orange juice exports, the influence of acid and alkali pretreatments on liquor saccharification, solubilization of solid fraction and mass yield was evaluated. Time and C acid or C alkaline at different concentrations of solids (low to moderate, 1 to 9%) and high catalyst concentrations were analyzed. A hydrothermal pretreatment was conducted under the same conditions of acid and alkaline treatments to investigate the relative selectivity increase in using the catalysts. The chemical analyses of wastes indicated a 70% total carbohydrate level denoting a promising raw material for bioethanol production. Pretreatment caused acid saccharifications between 25 and 65% in total reducing sugars (TRS) and mass yields (MY) between 30 and 40%. In alkaline pretreatment, these rates ranged between 2 and 22.5% and between 30 and 80, respectively. In hydrothermal pretreatment, solubilized TRS varied between 3 and 37%, whereas MY remained between 45 and 60%, respectively. C biomass strongly influenced the three variables; in the same way, time affected MY.

Cross-linking of carboxyl-terminated nitrile rubber with polyhedral oligomeric silsesquioxane

Glycidyl polyhedral oligomeric silsesquioxane (POSS) was used as a cross-linking agent to prepare a new organic–inorganic hybrid material from carboxyl-terminated poly(acrylonitrile-co-butadiene) (CTBN). The structure of the reacted material was characterized by Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) at different heating rates in the presence and absence of catalyst, triphenyl phosphine (TPP), was conducted to investigate the curing kinetics. The reaction is catalyzed by the addition of TPP, and rate is maximum at higher catalyst concentrations. Different kinetic models were used to analyze the kinetic parameters. The effect of catalyst on curing process was determined by calculating the activation energy (Ea) using Kissinger method. Dependency of Ea with extent of conversion was monitored by different isoconversional methods. The curing mechanism of POSS–CTBN system followed autocatalytic model. Moreover, the predicted curves from the kinetic models fit well with the non-isothermal DSC curve. The Ea of gelation obtained from rheological studies matched with that from DSC study, in league with the Flory’s theory of cross-linking.

Influence of Different Degradation Techniques on the Molecular Weight Distribution of κ -Carrageenan

Carrageenan as an abundant natural carbohydrate could be used as a representative material instead of synthetic polymers. In this work, the degradation of κ-Carrageenan by means of ultrasound irradiation at a frequency of 24 kHz and its combination with heterogeneous Titanium dioxide, followed by a photocatalytic process was investigated. The scission of carrageenan chains induced by a high intensity field of ultrasonic irradiation; result in various molecular weights of carrageenan. The low molecular weight species of carrageenan have biological and pharmaceutical uses that only should be obtained from the degradation method. The ultrasound power not only led to enhanced turbulence and liquid streaming, but also increased the active surface area. Therefore, TiO2 sonophotocatalysis was carried out faster than sonolysis and sonocatalysis processes. The influence of the basic operational parameters such as, ultrasound power and amount of TiO2 on the degradation rate of carrageenan was also studied. The results revealed that the extent of sonolytic degradation was increased with increasing of ultrasound power (in the range 30-80 W) and at higher catalyst concentration, the degradation rate in the solution soared. The degraded carrageenans were characterized by gel permeation chromatography (GPC).

Optimizing photo-mineralization of aqueous methyl orange by nano-ZnO catalyst under simulated natural conditions.

BackgroundPhoto-degradation of organic contaminants into non-hazardous mineral compounds is emerging as a strategy to purify water and environment. Tremendous research is being done using direct solar light for these purposes. In this paper we report on optimum conditions for complete mineralization of aqueous methyl orange using lab-prepared ZnO nanopowder catalyst under simulated solar light.ResultsNano-scale ZnO powder was prepared in the lab by standard methods, and then characterized using electronic absorption spectra, photolumenscence emission (PL) spectra, XRD, and SEM. The powder involved a wurtzite structure with ~19 nm particles living in agglomerates. Photo-degradation progressed faster under neutral or slightly acidic conditions which resemble natural waters. Increasing catalyst concentration increased photodegradation rate to a certain limit. Values of catalyst turn over number and degradation percentage increased under higher light intensity, whereas the quantum yield values decreased. The photocatalytic efficiency of nano-ZnO powders in methyl orange photodegradation in water with solar light has been affected by changing the working conditions. More importantly, the process may be used under natural water conditions with pH normally less than 7, with no need to use high concentrations of catalyst or contaminant. The results also highlight the negative impact of possible high concentrations of CO2 on water purification processes. Effects of other added gaseous flows to the reaction mixture are also discussed.ConclusionZnO nano-particles are useful catalyst for complete mineralization of organic contaminants in water. Photo-degradation of organic contaminants with ZnO nano-particles, methyl orange being an example, should be considered for future large scale water purification processes under natural conditions.

Optimization of microwave-assisted etherification of glycerol to polyglycerols by sodium carbonate as catalyst

The process optimization of etherification of glycerol to polyglycerols by sodium carbonate as a catalyst using microwaves as a heat source in solvent free conditions has been investigated in this study. The regression models describing the linear correlations between reaction parameters and reaction outcomes were developed. The three reaction parameters studied are: reaction temperature (220°C and 270°C), catalyst concentration (1wt% and 3wt%), and reaction time (0.5, 1.0, 1.5, 2.0, and 3.0h). The reaction temperature was found to have the most significant effect on the percent conversion of glycerol (X); combined yields of diglycerols, triglycerols, and tetraglycerols products (YDG+TG+TtG); selectivity toward pentaglycerols (SPG); and selectivity toward cyclic diglycerols (Sc-DG). Undesirable cyclic diglycerols formed at high temperature and the amount increased along with the longer reaction time. The higher catalyst concentration (3wt%) provides higher amounts of the desired products. Moreover, the longer reaction time also resulted in higher conversions and yields. For the optimized conditions, X, YDG+TG+TtG, and Sc-DG were predicted to be at 84%, 63%, and 9%, respectively, at the reaction temperature of 270°C, catalyst concentration of 3wt%, and reaction time of 1.0h. Experimental verification of the predicted optimum conditions gave the actual responses of 93%, 70%, and 7% for X, YDG+TG+TtG, and Sc-DG, respectively, with small deviations from the predicted responses. The results indicated that the developed models were valid and accurate in describing the actual experimental data at any conditions within the range studied. The observation suggests that the sodium carbonate catalyst with microwave heat source have the potential to be used in glycerol conversions to polyglycerols.

Divergent Mechanistic Avenues to an Aliphatic Polyesteracetal or Polyester from a Single Cyclic Esteracetal.

The cyclic esteracetal 2-methyl-1,3-dioxane-4-one (MDO) was polymerized in bulk using diethyl zinc as the catalyst and benzyl alcohol as the initiator to yield either the corresponding polyesteracetal (PMDO) or the aliphatic polyester poly(3-hydroxypropionic acid) (PHPA) at low and high catalyst concentrations, respectively. Spectral analysis gave evidence for distinct propagating species in the two catalyst concentration regimes. At low zinc concentrations ring opening by attack of the initiating species at the acetal functionality, yielding a zinc carboxylate, followed by propagation to yield pure PMDO was implicated. At high zinc concentrations we propose that ring opening via attack at the ester functionality produced a labile zinc hemiacetal, which rapidly and irreversibly expelled acetaldehyde to form a propagating zinc alkoxide and ultimately pure PHPA. Initial rate studies indicated that the rate of PHPA formation had a second-order dependence on zinc concentration; in contrast, the rate of PMDO formation was first order in zinc concentration. High molar mass PMDO exhibited only a glass transition temperature (Tg) ≈ -30 °C, whereas high molar mass PHPA had a Tg ≈ -30 °C and a melting temperature (Tm) ≈ 77 °C. When PHPA and PMDO were subjected to neutral or slightly acidic environments, PMDO exhibited expedited degradation as compared with PHPA.

Gold(I) Catalysis at Extreme Concentrations Inside Self‐Assembled Nanospheres

AbstractHomogeneous transition‐metal catalysis is a crucial technology for the sustainable preparation of valuable chemicals. The catalyst concentration is usually kept as low as possible, typically at mM or μM levels, and the effect of high catalyst concentration is hardly exploited because of solubility issues and the inherent unfavorable catalyst/substrate ratio. Herein, a self‐assembly strategy is reported which leads to local catalyst concentrations ranging from 0.05 M to 1.1 M, inside well‐defined nanospheres, whilst the overall catalyst concentration in solution remains at the conventional mM levels. We disclose that only at this high concentration, the gold(I) chloride is reactive and shows high selectivity in intramolecular CO and CC bond‐forming cyclization reactions.

Gold(I) catalysis at extreme concentrations inside self-assembled nanospheres.

Homogeneous transition-metal catalysis is a crucial technology for the sustainable preparation of valuable chemicals. The catalyst concentration is usually kept as low as possible, typically at mM or μM levels, and the effect of high catalyst concentration is hardly exploited because of solubility issues and the inherent unfavorable catalyst/substrate ratio. Herein, a self-assembly strategy is reported which leads to local catalyst concentrations ranging from 0.05 M to 1.1 M, inside well-defined nanospheres, whilst the overall catalyst concentration in solution remains at the conventional mM levels. We disclose that only at this high concentration, the gold(I) chloride is reactive and shows high selectivity in intramolecular CO and CC bond-forming cyclization reactions.

The influence of reagent concentration on the kinetics of carbon dioxide-propylene oxide copolymerization in the presence of a cobalt complex

The effect of the concentrations of propylene oxide and the catalyst (salen)CoDNP/[PPN]Cl ((salen)CoDNP: [PPN]Cl = 1: 1, mol/mol) on the kinetics of the copolymerization of CO2 and propylene oxide at 0.5 MPa and 20°C has been studied. The reaction proceeds at a constant rate after an induction period, and the value of this period varies with the reagent concentrations. The steady-state reaction rate increases linearly with the propylene oxide concentration in the range 5.0–14.3 mol/L. At high catalyst concentrations, such as (5.2–7.3) × 10−3 mol/L, the reaction rate is first order in the catalyst; at concentrations below 5 × 10−3 mol/L, the reaction rate is second order in the catalyst. Molecular mass increases in proportion to the propylene oxide conversion, that is consistent with a living polymerization process. A regioregular copolymer with 96% head-to-tail (HT) connectivity of propylene oxide has been obtained.

Recovery of algal oil from marine green macro-algae Enteromorpha intestinalis by acidic-hydrothermal process.

In this study, the recovery of algal oil from Enteromorpha intestinalis based on an acidic-hydrothermal reaction was investigated. Overall, the algal oil yield after the acidic-hydrothermal reaction was increased under the conditions of high reaction temperature, high catalyst concentration, and long reaction time within the tested ranges. Significantly, catalyst concentration, compared with reaction temperature and time, less affected algal oil recovery. The optimal acidic-hydrothermal reaction conditions for production of algal oil from E. intestinalis were as follows-200 °C reaction temperature, 2.92 % catalyst concentration, 54 min reaction time. Under these conditions, an 18.6 % algal oil yield was obtained. By increasing the combined severity factor, the algae oil recovery yield linearly increased.

Kinetics of reactive extraction/in situ transesterification of rapeseed oil

The kinetics of “reactive extraction” or “in situ transesterification” of rapeseed with methanol to produce biodiesel were investigated. It is hypothesised that in situ transesterification occurs through the reaction of triglyceride and methanol inside the seed particles followed by diffusion of mono and diglycerides, esters and glycerol into the bulk solvent. A model was developed based on this reaction/extraction mechanism and was found to be generally consistent with experimental results. The effective diffusion coefficient of esters in methanol was found to be 3.5×10−12m2/s. The model reveals that at catalyst concentrations below 0.1mol/kg-solvent, the reactive extraction rate was controlled by the reaction of triglycerides to esters. However, at higher catalyst concentrations (>0.1mol/kg-solvent), the process was controlled by the rate of diffusion of the products. The diffusion coefficient increases linearly with increasing temperature and the temperature dependence of the reaction rate constants can be described by an Arrhenius relationship. External mass transfer does not influence the extraction rate at the conditions used in these experiments.

Optimization of sulfamethoxazole degradation by TiO2/hydroxyapatite composite under ultraviolet irradiation using response surface methodology

A titanium dioxide/hydroxyapatite/ultraviolet (TiO2/HAP/UV-A) system was used to remove sulfamethoxazole (SMX) from water in a second-order response surface methodology (RSM) experiment with a three-level Box-Behnken design (BBD) for optimization. The effects of both the primary and secondary interaction effects of three photocatalytic reaction variables were examined: the concentration of SMX (X1), dose of TiO2/HAP composite (X2), and UV intensity (X3). The UV intensity and TiO2/HAP dose significantly influence the SMX and total organic carbon (TOC) removal (p<0.001). However, the SMX and TOC removal are enhanced with increasing TiO2/HAP dose up to certain levels, and further increases in the TiO2/HAP dose result in adverse effects due to hydroxyl radical scavenging at higher catalyst concentrations. Complete removal of SMX was achieved upon UV-A irradiation for 180min. Under optimal conditions, 51.2% of the TOC was removed, indicating the formation of intermediate products during SMX degradation. The optimal ratio of SMX (mg L−1) to TiO2/HAP (g L−1) to UV (W/L) was 5.4145 mg L−1 to 1.4351 g L−1 to 18W for both SMX and TOC removal. By comparison with actual applications, the experimental results were found to be in good agreement with the model’s predictions, with mean results for SMX and TOC removal of 99.89% and 51.01%, respectively.

Effect of a Lewis Acid Catalyst on the Performance of HDPE/BFR/GNPs Composites

Brominated flame-retardant high-density polyethylene (HDPE) composites containing graphene nanoplatelets (GNPs) were prepared via melt blending. A Lewis acid catalyst, aluminum chloride (AlCl3), was adopted to initiate the Friedel–Crafts reaction, which contributed to the good dispersion of GNPs and improvement of interfacial interaction. Scanning electron microscopy (SEM) showed that the size of GNPs decreased and the dispersive state of GNPs was improved with the addition of AlCl3. The maximum decomposition temperature (Tmax), modulus, and viscosity increased as the catalyst content increased, whereas the peak heat release rate (PHRR) and the total heat release (THR) decreased with increasing catalyst content. However, gel permeation chromatography (GPC) verified the degradation for HDPE at high catalyst concentration, and then thermal oxidation stability and flame retardancy worsen. The variety of performance of the composites was the result of the competition between improving the dispersion and degradation of composites.

Highly selective rearrangement of furfuryl alcohol to cyclopentanone

The aqueous phase hydrogenation of furfuryl alcohol to cyclopentanone was carried out on a series of metal supported and bulk catalysts. The effect of catalyst concentration, temperature, hydrogen pressure and reaction time has also been investigated. By changing the partial hydrogen pressure and concentration of metal catalyst it is possible to transform furfuryl alcohol with a very high selectivity either to furfuryl alcohol or cyclopentanone. High hydrogen pressure and catalyst concentration favours the formation of tetrahydrofurfuryl alcohol. At very low concentration of metal catalyst (0.25–1.0wt%) and 0.8–2.5MPa of hydrogen pressure, the product is exclusively cyclopentanone formed in yields higher than 95mol%. Very active and selective are nickel type catalysts. The differences in selectivities of products distribution are explained by the proposed reaction mechanism consisting of two parallel reactions. One reaction is catalyzed preferably by hydrogen ions produced by self-dissociation of water and other by metal catalyst.

Catalytic Conversion of Empty Fruit Bunch of Palm Oil for Producing Lactic Acid

Catalytic conversion of lignocellulosic biomass such as Empty Fruit Bunch (EFB) of Palm Oil into valuable chemicals such as lactic acid (LA) is an alternative route to currently fermentation route and it is a sustainable process for substituting petro-based chemical with biomass-based chemical. Conversion of lignocellulosic biomass (EFB) was conducted in a 100-ml batch reactor in aqueous solution using homogeneous AlCl3 catalyst at mild temperature in the range of 140-240°C, under hydrothermal condition. Some chemicals are identified in the product especialy LA and levulinic acid which are valuable chemicals produced by hydrolysis of lignocellulosic biomass and yield of LA compared with cellulosic biomass for comparison of feedstock. The sugar units in the lignocellulosic biomass (EFB) was around 48.75%, dominated by glucose (28%), xylose (16.5%), and followed with lower composistion of other sugar units such as galactose (1%), arabinose (2.5%) and mannose (0.75%). The yield of EFB conversion to lactic acid was found in the range 6-8.9% at temperature 140-240°C while for cellulosic material 19%, with reaction time 3hours and range of fixed AlCl3 concentration 50-100mM. Experimental results show that higher operating temperature and higher concentration of catalyst will produce higher percentage of LA. However, pretreatment of lignocelluloses with NaOH produced lower yield of LA 3.18 to 5.69% and probably the pretreatment leading to degradation of sugar units in the biomass.

Effect of Process Parameters of CNT Containing Friction Powder on Flexural Properties and Friction Performance of Organic Brake Friction Materials

This research is to investigate the influences of carbon nanotube (CNT) containing friction powder prepared through different process parameters on flexural properties and friction performance of organic brake friction materials. Experimental results indicate significant influence on flexural property and friction performance of organic brake friction materials when the modified CNT/friction powders are adopted. Particularly for the specimens adopted the modified CNT/friction powders prepared through 2.0 M concentration of catalyst and 30% C2H2 show the highest flexural strength, better ductility and toughness, most stable friction coefficient, and lowest weight loss. However, too many amorphous carbon clusters and CNTs aggregation derived from higher concentration of catalyst and ratio of C2H2/N2 would cause poor formation of specimens and reduction of reinforcement effectiveness.